MANUAL RELÉ 751

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20200603
*PM751-01-NB*
SEL-751
Feeder Protection Relay
Instruction Manual
SEL-751 Relay Instruction Manual Date Code 20200603
© 2011–2020 by Schweitzer Engineering Laboratories, Inc. All rights reserved.
SEL products appearing in this document may be covered by U.S. and Foreign patents. Schweitzer Engineering Laboratories, Inc. reserves all rights 
and benefits afforded under federal and international copyright and patent laws in its products, including without limitation software, firmware, and 
documentation.
The information in this document is provided for informational use only and is subject to change without notice. Schweitzer Engineering 
Laboratories, Inc. has approved only the English language document.
This product is covered by the standard SEL 10-year warranty. For warranty details, visit selinc.com or contact your customer service
representative. PM751-01
https://selinc.com
Date Code 20200603 Instruction Manual SEL-751 Relay
Table of Contents
R.Instruction Manual
List of Tables ........................................................................................................................................................ v
List of Figures .................................................................................................................................................... xv
Preface................................................................................................................................................................ xxv
Manual Overview ........................................................................................................................................... xxv
Safety Information......................................................................................................................................... xxvi
General Information ...................................................................................................................................... xxxi
Section 1: Introduction and Specifications
Overview ......................................................................................................................................................... 1.1
Features............................................................................................................................................................ 1.1
Models, Options, and Accessories................................................................................................................... 1.5
Applications..................................................................................................................................................... 1.7
Getting Started................................................................................................................................................. 1.9
Specifications ................................................................................................................................................ 1.13
Section 2: Installation
Overview ......................................................................................................................................................... 2.1
Relay Placement .............................................................................................................................................. 2.1
I/O Configuration ............................................................................................................................................ 2.2
Relay Connections......................................................................................................................................... 2.20
AC/DC Control Connection Diagrams.......................................................................................................... 2.27
Arc-Flash Protection...................................................................................................................................... 2.43
Field Serviceability........................................................................................................................................ 2.53
Section 3: PC Interface
Overview ......................................................................................................................................................... 3.1
Web Server ...................................................................................................................................................... 3.1
QuickSet Software......................................................................................................................................... 3.11
Section 4: Protection and Logic Functions
Overview ......................................................................................................................................................... 4.1
Application Data.............................................................................................................................................. 4.4
Group Settings (SET Command)..................................................................................................................... 4.4
Logic Settings (SET L Command) .............................................................................................................. 4.161
Global Settings (SET G Command) ............................................................................................................ 4.172
Port Settings (SET P Command)................................................................................................................. 4.194
Front-Panel Settings (SET F Command)..................................................................................................... 4.200
Report Settings (SET R Command) ............................................................................................................ 4.212
DNP Map Settings (Set D Command) .......................................................................................................... 4.215
Modbus Map Settings (SET M Command)................................................................................................. 4.215
EtherNet/IP Assembly Map Settings (SET E Command).............................................................................. 4.216
Touchscreen Settings ................................................................................................................................... 4.217
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SEL-751 Relay Instruction Manual Date Code 20200603
Table of Contents
Section 5: Metering and Monitoring
Overview ......................................................................................................................................................... 5.1
Power Measurement Conventions ................................................................................................................... 5.2
Metering .......................................................................................................................................................... 5.2
Load Profiling................................................................................................................................................ 5.14
Station DC Battery Monitor .......................................................................................................................... 5.15
Breaker Monitor ............................................................................................................................................ 5.18
Section 6: Settings
Overview ......................................................................................................................................................... 6.1
View/Change Settings...................................................................................................................................... 6.2
Setting Entry Error Messages..........................................................................................................................6.7
SEL-751 Settings Sheets
Section 7: Communications
Overview ......................................................................................................................................................... 7.1
Communications Interfaces ............................................................................................................................. 7.1
Communications Protocols............................................................................................................................ 7.12
SEL ASCII Protocol and Commands ........................................................................................................... 7.21
Virtual File Interface...................................................................................................................................... 7.72
Section 8: Front-Panel Operations
Overview ......................................................................................................................................................... 8.1
Two-Line Display Front Panel......................................................................................................................... 8.2
Touchscreen Display Front Panel .................................................................................................................. 8.18
Section 9: Bay Control
Overview ......................................................................................................................................................... 9.1
Bay Control Application Example ................................................................................................................ 9.18
Section 10: Analyzing Events
Overview ....................................................................................................................................................... 10.1
Event Reporting............................................................................................................................................. 10.2
Section 11: Testing and Troubleshooting
Overview ....................................................................................................................................................... 11.1
Testing Tools.................................................................................................................................................. 11.1
Commissioning Tests..................................................................................................................................... 11.3
Periodic Tests (Routine Maintenance)......................................................................................................... 11.12
Self-Test....................................................................................................................................................... 11.13
Troubleshooting........................................................................................................................................... 11.16
Technical Support ........................................................................................................................................ 11.17
Appendix A: Firmware, ICD, and Manual Versions
Firmware......................................................................................................................................................... A.1
ICD File ........................................................................................................................................................ A.13
Instruction Manual........................................................................................................................................ A.19
Appendix B: Firmware Upgrade Instructions
Overview .........................................................................................................................................................B.1
Special Instructions for Upgrading to R300 Series Firmware......................................................................................B.3
Upgrade the Firmware Using a Terminal Emulator ........................................................................................B.5
Upgrade the Firmware Using QuickSet ..........................................................................................................B.7
Upgrade the Firmware Using the Web Server...............................................................................................B.11
Upgrade the Firmware Using File Transfer Protocol ....................................................................................B.15
Upgrade the Firmware Via Terminal Emulator Using the FILE Command Over Telnet..............................B.16
Protocol Verification for Relays With IEC 61850 Option...............................................................................................B.17
Technical Support ..........................................................................................................................................B.17
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Table of Contents
Appendix C: SEL Communications Processors
SEL Communications Protocols......................................................................................................................C.1
SEL Communications Processor .....................................................................................................................C.3
SEL Communications Processor and Relay Architecture.....................................................................................C.5
SEL Communications Processor Example......................................................................................................C.7
Appendix D: DNP3 Communications
Overview ........................................................................................................................................................ D.1
Introduction to DNP3 ..................................................................................................................................... D.1
DNP3 in the SEL-751..................................................................................................................................... D.6
DNP3 Documentation .................................................................................................................................. D.14
Appendix E: Modbus Communications
Overview .........................................................................................................................................................E.1
Communications Protocol ...............................................................................................................................E.2
Modbus Register Map ...................................................................................................................................E.26
Appendix F: EtherNet/IP Communications
Overview ......................................................................................................................................................... F.1
Specifications .................................................................................................................................................. F.1
CIP Data Model ............................................................................................................................................... F.2
CIP Connections and Corresponding Assembly Map ................................................................................... F.12
EtherNet/IP Settings ...................................................................................................................................... F.13
Electronic Data Sheet File ............................................................................................................................. F.14
Appendix G: IEC 61850 Communications
Features...........................................................................................................................................................G.1
IEC 61850 Introduction.................................................................................................................................. G.2
IEC 61850 Operation...................................................................................................................................... G.3
Simulation Mode .......................................................................................................................................... G.15
IEC 61850 Mode/Behavior........................................................................................................................... G.16
IEC 61850 Configuration ............................................................................................................................. G.22
Logical Nodes............................................................................................................................................... G.23
Protocol Implementation Conformance Statement ...................................................................................... G.58
ACSI Conformance Statements.................................................................................................................... G.64
Potential Client and Automation Application Issues With Edition 2 Upgrades........................................... G.68
Appendix H: IEC 60870-5-103 Communications
Overview ........................................................................................................................................................ H.1
Introduction to IEC 60870-5-103 ................................................................................................................... H.1
IEC 60870-5-103 in the SEL-751................................................................................................................... H.9
IEC 60870-5-103 Documentation ................................................................................................................ H.12
Appendix I: DeviceNet Communications
Overview .......................................................................................................................................................... I.1
DeviceNet Card ................................................................................................................................................ I.1
Features............................................................................................................................................................. I.2
Electronic Data Sheet ....................................................................................................................................... I.3
Appendix J: MIRRORED BITS Communications
Overview ..........................................................................................................................................................J.1
Operation ..........................................................................................................................................................J.1
MIRRORED BITS Protocol for the Pulsar 9600 Modem ....................................................................................J.5
Settings .............................................................................................................................................................J.5
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Table of Contents
Appendix K: Synchrophasors
Overview ........................................................................................................................................................ K.1
Synchrophasor Measurement ......................................................................................................................... K.2
Settings for Synchrophasors ........................................................................................................................... K.4
Serial Port Settings for IEEE C37.118 Synchrophasors .................................................................................... K.8
Ethernet Port Settings for IEEE C37.118 Synchrophasors .................................................................................. K.9
Synchrophasor Relay Word Bits................................................................................................................... K.12
View Synchrophasors Using the MET PM Command................................................................................. K.14
IEEE C37.118 Synchrophasor Protocol ....................................................................................................... K.15
Appendix L: Relay Word Bits
Overview .........................................................................................................................................................L.1
Definitions .......................................................................................................................................................L.7
Appendix M: Analog Quantities
Appendix N: Cybersecurity Features
Access Control................................................................................................................................................ N.1
Configuration Management............................................................................................................................ N.3
Malware Protection ........................................................................................................................................ N.3
Physical Access Security................................................................................................................................ N.3
Vulnerability Notification Process.................................................................................................................. N.4
Settings Erasure .............................................................................................................................................. N.4
Glossary
Index
SEL-751 Relay Command Summary
Date Code 20200603 Instruction Manual SEL-751 Relay
List of Tables
R.Instruction Manual Table 1.1 Phase and Neutral Current Ratings Selection for the SEL-751 Models ................................ 1.1
Table 1.2 Current (ACI) and Voltage (AVI) Card Selection for SEL-751 Models ................................ 1.2
Table 1.3 SEL-751 Protection Elements ................................................................................................ 1.2
Table 1.4 SEL-751 Front-Panel Options ................................................................................................ 1.4
Table 1.5 SEL-751 Serial Port Settings................................................................................................ 1.10
Table 2.1 Power Supply Inputs (PSIO/2 DI/3 DO) Card Terminal Designations.................................. 2.4
Table 2.2 Communications Ports ........................................................................................................... 2.5
Table 2.3 Communications Card Interfaces and Connectors ................................................................. 2.6
Table 2.4 Current Inputs (4 ACI) Card Terminal Designations ............................................................. 2.7
Table 2.5 Current/Voltage Inputs (4 ACI/3 AVI) Card Terminal Designations ..................................... 2.8
Table 2.6 Voltage/Arc-Flash Detection Inputs (2 AVI/4 AFDI) Card Terminal Designations .............. 2.8
Table 2.7 Eight Arc-Flash Detection Inputs (8 AFDI) Card Terminal Designations............................. 2.9
Table 2.8 Eight Analog Inputs (8 AI) Card Terminal Designations ...................................................... 2.9
Table 2.9 Four Analog Inputs/Four Analog Outputs (4 AI/4 AO) Card Terminal Designations ......... 2.10
Table 2.10 I/O (3 DI/4 DO/1 AO) Card Terminal Designations ............................................................ 2.10Table 2.11 RTD (10 RTD) Card Terminal Designations........................................................................ 2.11
Table 2.12 Four Digital Inputs/Three Digital Outputs (4 DI/3 DO) Card Terminal Designations ........ 2.11
Table 2.13 Four Digital Inputs/Four Digital Outputs (4 DI/4 DO) Card Terminal Designations .......... 2.12
Table 2.14 Eight Digital Inputs (8 DI) Card Terminal Designations ..................................................... 2.12
Table 2.15 Eight Digital Outputs (8 DO) Card Terminal Designations ................................................. 2.13
Table 2.16 Fourteen Digital Inputs (14 DI) Card Terminal Designations.............................................. 2.13
Table 2.17 Jumper Functions and Default Positions.............................................................................. 2.19
Table 2.18 Typical Maximum RTD Lead Length .................................................................................. 2.26
Table 2.19 Optical Budget Calculations................................................................................................. 2.50
Table 2.20 SEL-C804 and SEL-C814 Arc-Flash Detection Cable Specifications ................................ 2.50
Table 3.1 SEL Software Solutions ....................................................................................................... 3.11
Table 3.2 QuickSet Applications.......................................................................................................... 3.11
Table 3.3 File/Tools Menus.................................................................................................................. 3.16
Table 3.4 QuickSet Help ...................................................................................................................... 3.26
Table 4.1 Identifier Settings ................................................................................................................... 4.4
Table 4.2 CT Configuration Settings ..................................................................................................... 4.5
Table 4.3 Voltage Configuration Settings .............................................................................................. 4.5
Table 4.4 Effect on Group Settings When SINGLEV := Y ................................................................... 4.6
Table 4.5 Main Relay Functions That Change With VNOM := OFF .................................................... 4.8
Table 4.6 Line Parameter Settings ....................................................................................................... 4.11
Table 4.7 Fault Locator Setting ............................................................................................................ 4.12
Table 4.8 Maximum Phase Overcurrent Settings................................................................................. 4.12
Table 4.9 Neutral Overcurrent Settings................................................................................................ 4.14
Table 4.10 Residual Overcurrent Settings.............................................................................................. 4.16
Table 4.11 Negative-Sequence Overcurrent Settings............................................................................. 4.16
Table 4.12 Incipient Cable Fault Settings .............................................................................................. 4.18
Table 4.13 A-, B-, and C-Phase Time-Overcurrent Settings.................................................................. 4.19
Table 4.14 Maximum Phase Time-Overcurrent ..................................................................................... 4.20
Table 4.15 Negative-Sequence Time-Overcurrent Settings ................................................................... 4.21
Table 4.16 Neutral Time-Overcurrent Settings ...................................................................................... 4.22
Table 4.17 Residual Time-Overcurrent Settings .................................................................................... 4.23
Table 4.18 Equations Associated With U.S. Curves .............................................................................. 4.25
Table 4.19 Equations Associated With IEC Curves............................................................................... 4.25
Table 4.20 Available Ground Directional Elements............................................................................... 4.30
Table 4.21 Best Choice Ground Directional Element Logic.................................................................. 4.31
Table 4.22 Ground Directional Element Availability by Voltage Connection Settings ......................... 4.32
Table 4.23 Directional Control Settings................................................................................................. 4.56
Table 4.24 Wattmetric Settings .............................................................................................................. 4.57
Table 4.25 Directional Control Settings Not Made for Particular Conditions ....................................... 4.59
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Tables
Table 4.26 Overcurrent Elements Controlled by Level Direction Settings DIR1 Through DIR4 
(Corresponding Overcurrent Element Figure Numbers in Parentheses) .......................... 4.59
Table 4.27 Effect of Settings VSCONN and DELTA_Y on Petersen Coil Directional Elements ......... 4.79
Table 4.28 Load-Encroachment Settings ............................................................................................... 4.81
Table 4.29 HIF Detection Settings ......................................................................................................... 4.87
Table 4.30 HIF Relay Word Bits............................................................................................................ 4.88
Table 4.31 Harmonic Blocking Settings ................................................................................................ 4.90
Table 4.32 RTD Settings ........................................................................................................................ 4.92
Table 4.33 RTD Resistance Versus Temperature ................................................................................... 4.93
Table 4.34 IEC Thermal Element Settings............................................................................................. 4.99
Table 4.35 Undervoltage Function ....................................................................................................... 4.100
Table 4.36 Overvoltage Function ......................................................................................................... 4.101
Table 4.37 Operating Quantities for the 27I Element .......................................................................... 4.104
Table 4.38 Inverse-Time Undervoltage Settings .................................................................................. 4.105
Table 4.39 Specification Of Inverse-Time Undervoltage Protection Element ..................................... 4.105
Table 4.40 Operating Quantities for the 59I Element .......................................................................... 4.106
Table 4.41 Inverse-Time Overvoltage Settings .................................................................................... 4.107
Table 4.42 Specification of Inverse-Time Overvoltage Protection Element ........................................ 4.108
Table 4.43 Synchronism-Check Settings ............................................................................................. 4.111
Table 4.44 Voltages When Setting SINGLEV := Y............................................................................. 4.118
Table 4.45 Power Element Settings...................................................................................................... 4.118
Table 4.46 Power Factor Settings.........................................................................................................4.120
Table 4.47 Loss-of-Potential (LOP) Setting......................................................................................... 4.122
Table 4.48 Vector Shift Element Settings ............................................................................................ 4.126
Table 4.49 Frequency Settings ............................................................................................................. 4.126
Table 4.50 Rate-of-Change-of-Frequency Settings.............................................................................. 4.127
Table 4.51 Time Window Versus 81RnTP Setting............................................................................... 4.128
Table 4.52 Fast Rate-of-Change-of-Frequency Settings ...................................................................... 4.130
Table 4.53 Trip/Close Logic Settings................................................................................................... 4.132
Table 4.54 Relay Word Bit and Front-Panel Correspondence to Reclosing Relay States ................... 4.142
Table 4.55 Reclosing Control Settings................................................................................................. 4.144
Table 4.56 Shot Counter Correspondence to Relay Word Bits and Open Interval Times ................... 4.146
Table 4.57 Open Interval Time Example Settings ............................................................................... 4.151
Table 4.58 Demand Meter Settings...................................................................................................... 4.157
Table 4.59 Enable Settings................................................................................................................... 4.161
Table 4.60 Latch Bits Equation Settings .............................................................................................. 4.162
Table 4.61 Math Variable Fractional Multiplication Results ............................................................... 4.164
Table 4.62 SELOGIC Control Equation Operators (Listed in Operator Precedence) ........................... 4.165
Table 4.63 Other SELOGIC Control Equation Operators/Values.......................................................... 4.168
Table 4.64 SELOGIC Variable Settings................................................................................................. 4.168
Table 4.65 Counter Input/Output Description...................................................................................... 4.169
Table 4.66 Order of Precedence of the Control Inputs......................................................................... 4.170
Table 4.67 Control Output Equations and Contact Behavior Settings................................................. 4.171
Table 4.68 General Global Settings ..................................................................................................... 4.172
Table 4.69 Event Messenger Settings .................................................................................................. 4.173
Table 4.70 Settings Group Selection.................................................................................................... 4.175
Table 4.71 LEA Ratio and Phase Correction Settings for Phase Voltages........................................... 4.176
Table 4.72 LEA Ratio and Phase Correction Settings for Synchronism-Check Voltage..................... 4.176
Table 4.73 Time and Date Management Settings ................................................................................ 4.176
Table 4.74 Breaker Failure Settings ..................................................................................................... 4.179
Table 4.75 Arc-Flash Overcurrent Settings.......................................................................................... 4.182
Table 4.76 Arc-Flash Time-Overlight Settings .................................................................................... 4.183
Table 4.77 Typical Ambient Illumination Light Levels ....................................................................... 4.185
Table 4.78 Summary of Steps .............................................................................................................. 4.187
Table 4.79 Analog Input Card Settings in Slot C................................................................................. 4.189
Table 4.80 Analog Output Card Settings in Slot C .............................................................................. 4.190
Table 4.81 Slot C Input Debounce Settings ......................................................................................... 4.193
Table 4.82 Data Reset Settings............................................................................................................. 4.193
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List of Tables
Table 4.83 Setting Change Disable Setting.......................................................................................... 4.193
Table 4.84 Time Synchronization Source Setting................................................................................ 4.194
Table 4.85 Front-Panel Serial Port Settings ......................................................................................... 4.194
Table 4.86 Ethernet Port Settings......................................................................................................... 4.195
Table 4.87 Port Number Settings That Must be Unique ...................................................................... 4.197
Table 4.88 Fiber-Optic Serial Port Settings ......................................................................................... 4.197
Table 4.89 Rear-Panel Serial Port (EIA-232) Settings......................................................................... 4.198
Table 4.90 Rear-Panel Serial Port (EIA-232/EIA-485) Settings.......................................................... 4.198
Table 4.91 Rear-Panel DeviceNet Port Settings................................................................................... 4.199
Table 4.92 Display Point and Local Bit Default Settings .................................................................... 4.200
Table 4.93 LCD Settings ...................................................................................................................... 4.201
Table 4.94 Front-Panel Display Point Settings .................................................................................... 4.201
Table 4.95 Settings That Always, Never, or Conditionally Hide a Display Point ............................... 4.202
Table 4.96 Entries for the Four Strings ................................................................................................ 4.203
Table 4.97 Binary Entry in the Name String Only............................................................................... 4.204
Table 4.98 Analog Entry in the Name String Only.............................................................................. 4.205
Table 4.99 Entry in the Name String and the Alias Strings ................................................................. 4.206
Table 4.100 Example Settings and Displays .......................................................................................... 4.206
Table 4.101 Target LED Settings ........................................................................................................... 4.210
Table 4.102 Pushbutton LED Settings ................................................................................................... 4.211
Table 4.103 Auto-Removal Settings ...................................................................................................... 4.212
Table 4.104 SER Trigger Settings.......................................................................................................... 4.213
Table 4.105 Enable Alias Settings ......................................................................................................... 4.213
Table 4.106SET R SER Alias Settings ................................................................................................. 4.214
Table 4.107 Event Report Settings......................................................................................................... 4.214
Table 4.108 HIF Event Report Settings ................................................................................................. 4.214
Table 4.109 Load Profile Settings .......................................................................................................... 4.214
Table 4.110 DNP Map Settings.............................................................................................................. 4.215
Table 4.111 User Map Register Settings ............................................................................................... 4.216
Table 4.112 EtherNet/IP Assembly Map ............................................................................................... 4.216
Table 5.1 Measured Fundamental Meter Values .................................................................................... 5.3
Table 5.2 Thermal Meter Values ............................................................................................................ 5.5
Table 5.3 RTD Input Status Messages ................................................................................................... 5.6
Table 5.4 Maximum/Minimum Meter Values........................................................................................ 5.7
Table 5.5 RMS Meter Values ................................................................................................................. 5.9
Table 5.6 Demand Values..................................................................................................................... 5.11
Table 5.7 Synchrophasor Measured Values ......................................................................................... 5.12
Table 5.8 HIF Metering Measured Values ........................................................................................... 5.13
Table 5.9 Station DC Battery Monitor Settings ................................................................................... 5.15
Table 5.10 Breaker Maintenance Information for a 25 kV Circuit Breaker .......................................... 5.19
Table 5.11 Breaker Monitor Settings ..................................................................................................... 5.19
Table 6.1 Methods of Accessing Settings .............................................................................................. 6.1
Table 6.2 SHOW Command Options..................................................................................................... 6.4
Table 6.3 SET Command Options ......................................................................................................... 6.4
Table 6.4 SET Command Editing Keystrokes........................................................................................ 6.5
Table 6.5 SET Command Format........................................................................................................... 6.6
Table SET.1 Range Dependencies for the EDIR Setting ....................................................................... SET.6
Table SET.2 Range Dependencies for the ORDER Setting ................................................................... SET.7
Table SET.3 Range Dependencies for 27I Operating Quantities ......................................................... SET.14
Table SET.4 Range Dependencies for 59I Operating Quantities ......................................................... SET.15
Table SET.5 Port Number Settings That Must be Unique ................................................................... SET.57
Table 7.1 SEL-751 Communications Port Interfaces............................................................................. 7.1
Table 7.2 PRP Settings........................................................................................................................... 7.6
Table 7.3 EIA-232/EIA-485 Serial Port Pin Functions ....................................................................... 7.10
Table 7.4 Protocols Supported on the Various Ports ............................................................................ 7.12
Table 7.5 Settings Associated With SNTP........................................................................................... 7.16
Table 7.6 HTTP Server Configuration ................................................................................................. 7.18
Table 7.7 Settings Associated With PTP.............................................................................................. 7.18
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Tables
Table 7.8 Serial Port Automatic Messages .......................................................................................... 7.22
Table 7.9 Command Response Header Definitions ............................................................................. 7.24
Table 7.10 Access Commands ............................................................................................................... 7.25
Table 7.11 89CLOSE Command............................................................................................................ 7.27
Table 7.12 89OPEN Command.............................................................................................................. 7.28
Table 7.13 ANALOG Command ........................................................................................................... 7.30
Table 7.14 COM PTP Command ........................................................................................................... 7.35
Table 7.15 PTP Data Set Descriptions ................................................................................................... 7.37
Table 7.16 COM Command ................................................................................................................... 7.41
Table 7.17 CONTROL Command ......................................................................................................... 7.42
Table 7.18 COPY Command.................................................................................................................. 7.43
Table 7.19 COUNTER Command ......................................................................................................... 7.43
Table 7.20 Date Command..................................................................................................................... 7.43
Table 7.21 EVENT Command (Event Reports)..................................................................................... 7.46
Table 7.22 FILE Command.................................................................................................................... 7.46
Table 7.23 GOOSE Command Variants................................................................................................. 7.46
Table 7.24 GOOSE IED Description ..................................................................................................... 7.47
Table 7.25 GROUP Command............................................................................................................... 7.49
Table 7.26 HELP Command .................................................................................................................. 7.50
Table 7.27 HISTORY Command ........................................................................................................... 7.50
Table 7.28 HIS HIF Command .............................................................................................................. 7.51
Table 7.29 HSG Command .................................................................................................................... 7.51
Table 7.30 ID Command ........................................................................................................................7.52
Table 7.31 INI HIF Command ............................................................................................................... 7.52
Table 7.32 IRI Command....................................................................................................................... 7.53
Table 7.33 L_D Command (Load Firmware) ........................................................................................ 7.53
Table 7.34 LDP Commands ................................................................................................................... 7.54
Table 7.35 LOG HIF Command............................................................................................................. 7.54
Table 7.36 LOO Command .................................................................................................................... 7.55
Table 7.37 MET Command.................................................................................................................... 7.56
Table 7.38 Meter Class........................................................................................................................... 7.56
Table 7.39 PASSWORD Command....................................................................................................... 7.58
Table 7.40 Factory-Default Passwords for Access Levels 1, 2, and C................................................... 7.58
Table 7.41 Valid Password Characters ................................................................................................... 7.58
Table 7.42 PUL OUTnnn Command ..................................................................................................... 7.59
Table 7.43 QUIT Command................................................................................................................... 7.60
Table 7.44 R_S Command (Restore Factory-Defaults) ......................................................................... 7.60
Table 7.45 SER Command (Sequential Events Recorder Report) ......................................................... 7.60
Table 7.46 SER D Command ................................................................................................................. 7.61
Table 7.47 SET Command (Change Settings) ....................................................................................... 7.61
Table 7.48 SET Command Editing Keystrokes...................................................................................... 7.62
Table 7.49 SHOW Command (Show/View Settings)............................................................................. 7.62
Table 7.50 STATUS Command (Relay Self-Test Status)....................................................................... 7.65
Table 7.51 STATUS Command Report and Definitions ........................................................................ 7.65
Table 7.52 SUMMARY Command........................................................................................................ 7.66
Table 7.53 SUM HIF Command ............................................................................................................ 7.67
Table 7.54 TARGET Command (Display Relay Word Bit Status) ........................................................ 7.67
Table 7.55 Front-Panel LEDs and the TAR 0 Command....................................................................... 7.67
Table 7.56 TEST DB Commands........................................................................................................... 7.68
Table 7.57 THE Command (Preload or Reset Thermal Capacity)......................................................... 7.70
Table 7.58 TIME Command (View/Change Time)................................................................................ 7.70
Table 7.59 TRIGGER Command (Trigger Event Report) ..................................................................... 7.71
Table 7.60 TRIGGER HIF Command ................................................................................................... 7.71
Table 7.61 VEC Command .................................................................................................................... 7.71
Table 7.62 FTP and MMS Virtual File Structure................................................................................... 7.72
Table 7.63 Settings Directory Files........................................................................................................ 7.74
Table 7.64 Reports Directory Files ........................................................................................................ 7.74
Table 7.65 Event Directory Files ........................................................................................................... 7.75
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Date Code 20200603 Instruction Manual SEL-751 Relay
List of Tables
Table 7.66 Files Available for Ymodem Protocol.................................................................................. 7.76
Table 7.67 FTP and MMS Wildcard Usage Examples .......................................................................... 7.78
Table 7.68 Ymodem Wildcard Usage Examples ................................................................................... 7.78
Table 8.1 Front-Panel Automatic Messages (FP_AUTO := OVERRIDE) ............................................ 8.3
Table 8.2 Front-Panel Pushbutton Functions ......................................................................................... 8.5
Table 8.3 Possible Warning Conditions (Flashing TRIP LED) ........................................................... 8.14
Table 8.4 SEL-751 Front-Panel Operator Control Functions .............................................................. 8.16
Table 8.5 Touchscreen Display Component and Indicator Descriptions ............................................. 8.19
Table 8.6 Front-Panel Automatic Messages......................................................................................... 8.20
Table 8.7 Sidebar Buttons .................................................................................................................... 8.21
Table 8.8 Home Folders and Applications ........................................................................................... 8.22
Table 8.9 Meter Application Availability............................................................................................. 8.23
Table 8.10 Monitor Application Availability ......................................................................................... 8.25
Table 8.11 Reports Application Availability.......................................................................................... 8.26
Table 8.12 Control Application Availability .......................................................................................... 8.28
Table 8.13 Device Info Application Availability ................................................................................... 8.30
Table 8.14 Access Level Application Availability ................................................................................. 8.32
Table 8.15 Settings Folder and Application Availability ....................................................................... 8.33
Table 8.16 Settings Folders Port, Group, and Date and Time Application Availability ........................ 8.33
Table 8.17 Screens Available for the Rotating Display, HOME Pushbutton, and Programmable 
Pushbuttons....................................................................................................................... 8.36
Table 9.1 Circuit Breaker Symbols ........................................................................................................ 9.2
Table 9.2 Two-Position Disconnect Settings.......................................................................................... 9.3
Table 9.3 Three-Position Disconnect Settings ....................................................................................... 9.3
Table 9.4 Disconnect Control Setting Guidelines ..................................................................................9.6
Table 9.5 Two- and Three-Position Disconnect Symbols ...................................................................... 9.7
Table 9.6 Local/Remote Control Settings .............................................................................................. 9.7
Table 9.7 Touchscreen Settings............................................................................................................ 9.11
Table 9.8 Symbols Required for the Single-Line Diagram Schematic in Figure 9.12......................... 9.21
Table 10.1 Event Types .......................................................................................................................... 10.4
Table 10.2 Phase Involvement Event Type ............................................................................................ 10.5
Table 10.3 Event Report Current and Voltage Columns ...................................................................... 10.10
Table 10.4 Output, Input, Protection, and Control Element Event Report Columns ........................... 10.10
Table 10.5 CEV HIF Commands ......................................................................................................... 10.30
Table 10.6 HIF Event Types................................................................................................................. 10.31
Table 10.7 HIF Event Phases ............................................................................................................... 10.32
Table 10.8 HIF Downed Conductor ..................................................................................................... 10.32
Table 10.9 SUM HIF Command .......................................................................................................... 10.33
Table 10.10 HIS HIF Command ............................................................................................................ 10.35
Table 11.1 Resultant Scale Factors for Inputs........................................................................................ 11.2
Table 11.2 Serial Port Commands That Clear Relay Data Buffers........................................................ 11.6
Table 11.3 Phase Current Measuring Accuracy ..................................................................................... 11.7
Table 11.4 Current Unbalance Measuring Accuracy ............................................................................. 11.8
Table 11.5 Power Quantity Accuracy—Wye Voltages........................................................................... 11.9
Table 11.6 Power Quantity Accuracy—Delta Voltages ....................................................................... 11.10
Table 11.7 Periodic Relay Checks ....................................................................................................... 11.13
Table 11.8 Relay Self-Tests.................................................................................................................. 11.14
Table 11.9 Troubleshooting.................................................................................................................. 11.16
Table A.1 R300 Series Firmware Revision History............................................................................... A.1
Table A.2 R200 Series Firmware Revision History............................................................................... A.3
Table A.3 R100 Series Firmware Revision History............................................................................... A.6
Table A.4 SELBOOT Firmware Revision History ................................................................................ A.11
Table A.5 SEL Display Package Revision History .............................................................................. A.11
Table A.6 SEL Display Package Compatibility With Relay Firmware ............................................... A.12
Table A.7 DeviceNet Card Version...................................................................................................... A.12
Table A.8 EDS File Compatibility....................................................................................................... A.12
Table A.9 SEL-751 ICD File Revision History ................................................................................... A.13
Table A.10 Instruction Manual Revision History .................................................................................. A.19
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Tables
Table B.1 Firmware Upgrade Methods...................................................................................................B.2
Table B.2 Ethernet Firmware Upgrade User Messages ........................................................................B.14
Table C.1 Supported Serial Command Sets............................................................................................C.1
Table C.2 Compressed ASCII Commands .............................................................................................C.2
Table C.3 SEL Communications Processors Protocol Interfaces ...........................................................C.4
Table C.4 SEL Communications Processor Port 1 Settings ...................................................................C.7
Table C.5 SEL Communications Processor Data Collection Automessages..........................................C.7
Table C.6 SEL Communications Processor Port 1 Automatic Messaging Settings ...............................C.8
Table C.7 SEL Communications Processor Port 1 Region Map ............................................................C.8
Table C.8 Communications Processor METER Region Map With the 2 AVI/4 AFD Card Installed....C.9
Table C.9 Communications Processor TARGET Region .......................................................................C.9
Table C.10 Communications Processor DEMAND Region Map...........................................................C.11
Table D.1 DNP3 Implementation Levels ............................................................................................... D.1
Table D.2 Selected DNP3 Function Codes ............................................................................................ D.3
Table D.3 DNP3 Access Methods.......................................................................................................... D.4
Table D.4 TCP/UDP Selection Guidelines ............................................................................................ D.6
Table D.5 DNP3 Access Methods.......................................................................................................... D.6
Table D.6 SEL-751 Event Buffer Capacity............................................................................................ D.9
Table D.7 Port DNP3 Protocol Settings............................................................................................... D.11
Table D.8 Serial Port DNP3 Modem Settings...................................................................................... D.13
Table D.9 SEL-751 DNP Object List................................................................................................... D.14
Table D.10 DNP3 Reference Data Map................................................................................................. D.19
Table D.11 DNP3 Default Data Map ..................................................................................................... D.21
Table D.12 SEL-751 Object 12 Control Operations .............................................................................. D.24
Table D.13 Sample Custom DNP3 AI Map........................................................................................... D.29
Table E.1 Modbus Query Fields .............................................................................................................E.2
Table E.2 SEL-751 Modbus Function Codes .........................................................................................E.2
TableE.3 SEL-751 Modbus Exception Codes .......................................................................................E.3
Table E.4 01h Read Discrete Output Coil Status Command..................................................................E.4
Table E.5 Responses to 01h Read Discrete Output Coil Query Errors ..................................................E.4
Table E.6 02h Read Input Status Command...........................................................................................E.4
Table E.7 02h SEL-751 Inputs ...............................................................................................................E.5
Table E.8 Responses to 02h Read Input Query Errors ...........................................................................E.6
Table E.9 03h Read Holding Register Command...................................................................................E.6
Table E.10 Responses to 03h Read Holding Register Query Errors ........................................................E.6
Table E.11 04h Read Input Register Command .......................................................................................E.7
Table E.12 Responses to 04h Read Input Register Query Errors .............................................................E.7
Table E.13 05h Force Single Coil Command ...........................................................................................E.7
Table E.14 01h, 05h SEL-751 Output ......................................................................................................E.8
Table E.15 Responses to 05h Force Single Coil Query Errors...............................................................E.10
Table E.16 06h Preset Single Register Command..................................................................................E.10
Table E.17 Responses to 06h Preset Single Register Query Errors........................................................E.11
Table E.18 08h Loopback Diagnostic Command...................................................................................E.11
Table E.19 Responses to 08h Loopback Diagnostic Query Errors.........................................................E.11
Table E.20 10h Preset Multiple Registers Command.............................................................................E.12
Table E.21 10h Preset Multiple Registers Query Error Messages .........................................................E.12
Table E.22 60h Read Parameter Information Command........................................................................E.12
Table E.23 60h Read Parameter Descriptor Field Definition .................................................................E.13
Table E.24 60h Read Parameter Conversion Field Definition................................................................E.13
Table E.25 Responses to 60h Read Parameter Information Query Errors .............................................E.14
Table E.26 61h Read Parameter Text Command....................................................................................E.14
Table E.27 61h Read Parameter Text Query Error Messages.................................................................E.15
Table E.28 62h Read Enumeration Text Command ...............................................................................E.15
Table E.29 61h Read Parameter Enumeration Text Query Error Messages...........................................E.15
Table E.30 7Dh Encapsulated Packet With Control Command .............................................................E.15
Table E.31 7Dh Encapsulated Packet Query Errors ...............................................................................E.16
Table E.32 7Eh NOP Command.............................................................................................................E.16
Table E.33 Modbus Register Labels for Use With SET M Command...................................................E.18
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List of Tables
Table E.34 Modbus Register Map ..........................................................................................................E.26
Table E.35 Trigger Conditions for the Trip/Warn Status Register Bits ..................................................E.64
Table F.1 EtherNet/IP Specifications ..................................................................................................... F.1
Table F.2 CIP Data Model Profile.......................................................................................................... F.2
Table F.3 Identity Object List of Attributes ........................................................................................... F.2
Table F.4 Status WORD Bits Descriptions ............................................................................................ F.3
Table F.5 Identity Object Supported Services........................................................................................ F.4
Table F.6 Message Router Object List of Attributes.............................................................................. F.4
Table F.7 Message Router Supported Services ...................................................................................... F.4
Table F.8 Assembly Object List of Attributes........................................................................................ F.5
Table F.9 Assembly Object Supported Services .................................................................................... F.5
Table F.10 Connection Manager Object List of Attributes ...................................................................... F.6
Table F.11 Connection Manager Object Supported Services................................................................... F.6
Table F.12 File Object List of Attributes.................................................................................................. F.7
Table F.13 File Object Supported Services .............................................................................................. F.8
Table F.14 TCP/IP Interface Object List of Attributes............................................................................. F.8
Table F.15 TCP/IP Interface Object Supported Services ....................................................................... F.10
Table F.16 Ethernet Link Object List of Attributes................................................................................ F.10
Table F.18 Ethernet Link Object Supported Services ............................................................................ F.11
Table F.17 Interface Flags Bits Descriptions ......................................................................................... F.11
Table F.19 Vendor Specific Object List of Attributes ............................................................................ F.11
Table F.20 Vendor Specific Object Supported Services......................................................................... F.11
Table F.21 Class 1 Connection Support ................................................................................................. F.13
Table F.22 Port 1 EtherNet/IP Protocol Settings.................................................................................... F.13
Table F.23 File Description Section Entries........................................................................................... F.14
Table F.24 Device Description Section Entries...................................................................................... F.14
Table F.25 Device Classification Section Entry..................................................................................... F.15
Table F.26 Parameters of the EDS File .................................................................................................. F.15
Table F.27 RPI Parameter Structure....................................................................................................... F.16
Table F.28 Assembly Section Entries.....................................................................................................F.17
Table F.29 Input Only Connection Entries............................................................................................. F.17
Table F.30 Listen Only Connection Entries ........................................................................................... F.18
Table F.31 Exclusive Owner Connection Entries................................................................................... F.18
Table F.32 Vendor Specific Object Section Entries ............................................................................... F.19
Table F.33 Capacity Section Entries ...................................................................................................... F.19
Table F.34 Ethernet Link Class .............................................................................................................. F.19
Table G.1 IEC 61850 Document Set...................................................................................................... G.2
Table G.2 Example IEC 61850 Descriptor Components ....................................................................... G.4
Table G.3 SEL-751 Logical Devices ..................................................................................................... G.4
Table G.4 Buffered Report Control Block Client Access ...................................................................... G.7
Table G.5 Unbuffered Report Control Block Client Access.................................................................. G.8
Table G.6 AddCause Descriptions ....................................................................................................... G.12
Table G.7 IEC 61850 Services Based on Mode/Behavior ................................................................... G.16
Table G.8 Analog Quantity I850MOD Status Based on the Selected IEC 61850 Mode/Behavior ..... G.16
Table G.9 IEC 61850 Mode/Behavior List of Writable Values ........................................................... G.17
Table G.10 IEC 61850 Mode/Behavior Evaluated States of SC850TM and SC850BM....................... G.18
Table G.11 IEC 61850 Incoming Message Handling in On Mode........................................................ G.19
Table G.12 IEC 61850 Outgoing Message Handling in On Mode ........................................................ G.19
Table G.13 IEC 61850 Incoming Message Handling in Test Mode ...................................................... G.20
Table G.14 IEC 61850 Outgoing Message Handling in Test Mode ...................................................... G.20
Table G.15 IEC 61850 Incoming Message Handling in Off Mode ....................................................... G.21
Table G.16 IEC 61850 Outgoing Message Handling in Off Mode........................................................ G.21
Table G.17 IEC 61850 Settings.............................................................................................................. G.22
Table G.18 New Logical Node Extensions ............................................................................................ G.25
Table G.19 Arc-Flash Detection Logical Node Class Definition .......................................................... G.25
Table G.20 Thermal Metering Data Logical Node Class Definition ..................................................... G.25
Table G.21 Thermal Element Metering Data Logical Node Class Definition....................................... G.26
Table G.22 Metering Statistics Logical Node Class Definition............................................................. G.27
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Table G.23 Demand Metering Statistics Logical Node Class Definition .............................................. G.28
Table G.24 Compatible Logical Nodes With Extensions ...................................................................... G.29
Table G.25 Fault Locator Logical Node Class Definition ..................................................................... G.29
Table G.26 Circuit Breaker Logical Node Class Definition .................................................................. G.30
Table G.27 Measurement Logical Node Class Definition ..................................................................... G.30
Table G.28 Measurement Logical Node Class Definition ..................................................................... G.31
Table G.29 Generic Process I/O Logical Node Class Definition........................................................... G.31
Table G.30 Circuit Breaker Supervision (Per-Phase) Logical Node Class Definition........................... G.32
Table G.31 Logical Device: PRO (Protection)....................................................................................... G.32
Table G.32 Logical Device: MET (Metering)........................................................................................ G.48
Table G.33 Logical Device: CON (Remote Control)............................................................................. G.52
Table G.34 Logical Device: ANN (Annunciation) ................................................................................ G.52
Table G.35 Logical Device: CFG (Configuration) ................................................................................ G.57
Table G.36 SEL Nameplate Data........................................................................................................... G.58
Table G.37 PICS for A-Profile Support ................................................................................................. G.58
Table G.38 PICS for T-Profile Support .................................................................................................. G.58
Table G.39 MMS Service Supported Conformance .............................................................................. G.59
Table G.40 MMS Parameter CBB ......................................................................................................... G.61
Table G.41 AlternateAccessSelection Conformance Statement ............................................................ G.61
Table G.42 VariableAccessSpecification Conformance Statement ....................................................... G.62
Table G.43 VariableSpecification Conformance Statement................................................................... G.62
Table G.44 Read Conformance Statement............................................................................................. G.62
Table G.45 GetVariableAccessAttributes Conformance Statement....................................................... G.62
Table G.46 DefineNamedVariableList Conformance Statement ........................................................... G.62
Table G.47 GetNamedVariableListAttributes Conformance Statement ................................................ G.63
Table G.48 DeleteNamedVariableList ................................................................................................... G.63
Table G.49 GOOSE Conformance......................................................................................................... G.63
Table G.50 ACSI Basic Conformance Statement .................................................................................. G.64
Table G.51 ACSI Models Conformance Statement ............................................................................... G.64
Table G.52 ACSI Services Conformance Statement.............................................................................. G.65
Table H.1 IEC 60870-5 Standard Documents........................................................................................ H.1
Table H.2 IEC 60870-5 Enhanced Performance Architecture Model ................................................... H.2
Table H.3 History of IEC 60870-5......................................................................................................... H.2
Table H.4 SEL-751 ASDU Types ..........................................................................................................H.3
Table H.5 IEC 60870-5-103 Category Map Settings ............................................................................. H.4
Table H.6 IEC 60870-5-103 Cause Of Transmission ............................................................................ H.5
Table H.7 IEC 60870-5-103 Information Numbers ............................................................................... H.5
Table H.8 IEC 60870-5-103 Standard Function Types.......................................................................... H.6
Table H.9 IEC 60870-5-103 Data Map.................................................................................................. H.6
Table H.10 SEL-751 IEC 60870-5-103 Port Settings.............................................................................. H.9
Table H.11 SEL-751 Analog Fault Quantities ....................................................................................... H.10
Table J.1 Number of MIRRORED BITS Messages for Different Data Rates ............................................J.2
Table J.2 Positions of the MIRRORED BITS.............................................................................................J.3
Table J.3 MIRRORED BITS Values for a RXDFLT Setting of 10100111.................................................J.3
Table J.4 MIRRORED BITS Communications Message Transmission Period..........................................J.5
Table J.5 MIRRORED BITS Protocol Settings ..........................................................................................J.5
Table K.1 PMU Settings in the SEL-751 for C37.118 Protocol in Global Settings .............................. K.4
Table K.2 Synchrophasor Order in Data Stream (Voltages and Currents)............................................. K.6
Table K.3 User-Defined Analog Values Selected by the NUMANA Setting ........................................ K.7
Table K.4 User-Defined Digital Status Words Selected by the NUMDSW Setting .............................. K.8
Table K.5 SEL-751 Serial Port Settings for Synchrophasors ................................................................ K.8
Table K.6 SEL-751 Ethernet Port Settings for Synchrophasors ............................................................ K.9
Table K.7 Synchrophasor Trigger Relay Word Bits ............................................................................ K.12
Table K.8 Time Synchronization Relay Word Bits.............................................................................. K.12
Table K.9 TQUAL Bits Translation to Time Quality........................................................................... K.13
Table K.10 Size of a C37.118 Synchrophasor Message ........................................................................ K.16
Table K.11 Serial Port Bandwidth for Synchrophasors (in Bytes) ........................................................ K.16
Table K.12 Example Synchrophasor Global Settings............................................................................ K.18
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Table K.13 Example Synchrophasor Logic Settings ............................................................................. K.18
Table K.14 Example Synchrophasor SELOGIC Settings........................................................................ K.19
Table K.15 Example Synchrophasor Port Settings ................................................................................ K.19
Table L.1 SELOGIC Relay Word Bits .....................................................................................................L.1
Table L.2 Relay Word Bit Definitions for the SEL-751 .........................................................................L.7
Table M.1 Analog Quantities..................................................................................................................M.1
Table N.1 IP Port Numbers .................................................................................................................... N.1
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Date Code 20200603 Instruction Manual SEL-751 Relay
List of Figures
R.Instruction Manual Figure 1.1 SEL-751 Feeder Protection Relay Applied Throughout the Power System .......................... 1.8
Figure 1.2 Typical Current Connections.................................................................................................. 1.9
Figure 1.3 Response Header .................................................................................................................. 1.10
Figure 1.4 STA Command Response—No Communications Card or EIA-232/EIA-485 
Communications Card ...................................................................................................... 1.11
Figure 1.5 STA Command Response—Communications Card/DeviceNet Protocol ............................ 1.11
Figure 2.1 Relay Panel-Mount Dimensions............................................................................................. 2.2
Figure 2.2 Slot Allocations for Different Cards ...................................................................................... 2.4
Figure 2.3 Circuit Board of Analog I/O Board, Showing Jumper Selection ......................................... 2.17
Figure 2.4 JMP1 Through JMP4 Locations on 4 AI/4 AO Board ......................................................... 2.18
Figure 2.5 Current Output Jumpers ....................................................................................................... 2.18
Figure 2.6 Voltage Output Jumpers ....................................................................................................... 2.18
Figure 2.7 Pins for Password, Breaker Control, and SELBOOT Jumper................................................ 2.19
Figure 2.8 Dual Fiber Ethernet With 2 AVI/4 AFDI Voltage Option With Arc-Flash 
Detector Inputs, DeviceNet Card, and Fast Hybrid 4 DI/4 DO Card 
(Relay MOT 751501AA3CA70850830) .......................................................................... 2.20
Figure 2.9 Single Copper Ethernet, EIA-485 Communication, 8 DO (Form A) Card, 
4 AI/4 AO Card, and 2 AVI/4 AFDI Voltage Option With Arc-Flash Detector Inputs 
(Relay MOT 751201A2A6X70810320)........................................................................... 2.21
Figure 2.10 Single Copper Ethernet With EIA-232 Communication, 10 RTD Card, 4 DI/4 DO Card
and 2 AVI/4 AFDI Voltage Option Card With Arc-Flash Detector Inputs 
(Relay MOT 751501A1A9X70850230)........................................................................... 2.21
Figure 2.11 No Ethernet, EIA-232 Serial Communications, EIA-232/EIA-485 Communications 
Card, 8 DI Card, and 8 DO Card (Form A) (Relay MOT 751401AA03A2A850000)..... 2.22
Figure 2.12 Dual Copper Ethernet, 4 DI/4 DO Card, 14 DI Card, 8 AFDI With Arc-Flash Detector 
Inputs, 4 ACI/3 AVI Card With 5 A Phase, 200 mA Neutral, and Three-Phase 
AC Voltage Inputs (300 Vac) (Relay MOT 7515S1A1A4A77870671) ........................... 2.22
Figure 2.13 Dual Copper Ethernet, 14 DI Card, 8 DO (Form B) Card, 2 AVI/4 AFDI Card 
With LEA Vsync, Vbat Inputs, and 4 Arc-Flash Detection Inputs, 4 ACI/3 AVI Card 
With 5 A Phase, 200 mA Neutral, and Three-Phase LEA Voltage Inputs (8 Vac) 
(Relay MOT 751501A4A2BL0L70671) .......................................................................... 2.23
Figure 2.14 Dual 10/100 Base-T Ethernet, EIA-232 Rear Port, Without Single Multimode ST 
Fiber-Optic Serial Port Rear, With DeviceNet Card, Fast Hybrid 4 DI/4 DO Card, 
8 DI Card and 4 ACI Card (No Voltage Inputs) 
(Relay MOT 751001AA3CA3AA50F30) ........................................................................ 2.23
Figure 2.15 Control I/O Connections—4 AI/4 AO Option in Slot D and Fiber-Optic Port in Slot B..... 2.25
Figure 2.16 Control I/O Connections—Internal RTD Option in Slot D.................................................. 2.26
Figure 2.17 Analog Output Wiring Example...........................................................................................2.27
Figure 2.18 Output OUT103 Relay Output Contact Configuration ........................................................ 2.27
Figure 2.19 Breaker Trip Coil Connections With OUT103FS := Y and OUT103FS := N ..................... 2.28
Figure 2.20 Single-Phase Voltage Connections....................................................................................... 2.29
Figure 2.21 Voltage Connections............................................................................................................. 2.30
Figure 2.22 Typical Current Connections................................................................................................ 2.32
Figure 2.23 SEL-751 Provides Overcurrent Protection and Reclosing for a Distribution Feeder 
(Includes Fast Bus Trip Scheme) (Delta-Connected PTs)................................................ 2.33
Figure 2.24 SEL-751 Provides Overcurrent Protection for a Distribution Bus 
(Includes Fast Bus Trip Scheme) (Wye-Connected PTs) ................................................. 2.34
Figure 2.25 Transmission Line Directional Overcurrent Protection and Reclosing With Current-
Polarization Source Connected to Channel IN (Wye-Connected PTs) ............................ 2.35
Figure 2.26 SEL-751 Provides Overcurrent Protection for a Delta-Wye Transformer Bank 
(Wye-Connected PTs)....................................................................................................... 2.36
Figure 2.27 SEL-751 Provides Overcurrent Protection for a Transformer Bank With a Tertiary 
Winding (Wye-Connected PTs)........................................................................................ 2.37
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Figures
Figure 2.28 SEL-751 Provides Overcurrent Protection for an Industrial Distribution Feeder 
(Core-Balance Current Transformer Connected to Channel IN)...................................... 2.38
Figure 2.29 SEL-751 Provides Overcurrent Protection for a High-Impedance or Low-Impedance 
Grounded System (Wye-Connected PTs) ......................................................................... 2.39
Figure 2.30 SEL-751 Provides Overcurrent Protection for a Petersen Coil-Grounded System 
(Wye-Connected PTs)....................................................................................................... 2.40
Figure 2.31 SEL-751 Provides Overcurrent Protection for an Ungrounded System 
(Wye-Connected PTs)....................................................................................................... 2.41
Figure 2.32 SEL-751 Provides Overcurrent Protection for an Ungrounded System 
(Open-Delta Connected PTs, Broken-Delta 3V0 Connection)......................................... 2.42
Figure 2.33 SEL-751 With an Arc-Flash Option Card and Fiber-Optic Based Point Sensor ................. 2.43
Figure 2.34 Black-Jacketed Fiber installation Example .......................................................................... 2.44
Figure 2.35 Point-Sensor Assembly ........................................................................................................ 2.44
Figure 2.36 Point-Sensor Dimensions ..................................................................................................... 2.45
Figure 2.37 Point-Sensor Installation ...................................................................................................... 2.45
Figure 2.38 Point-Sensor Directivity (0–360° Around the Mounting Plane) .......................................... 2.46
Figure 2.39 Point-Sensor Directivity (Front to Back, Above the Mounting Plane) ................................ 2.46
Figure 2.40 Point-Sensor Directivity (Left to Right, Above the Mounting Plane).................................. 2.47
Figure 2.41 Clear-Jacketed Fiber Sensor Assembly................................................................................ 2.47
Figure 2.42 Clear-Jacketed Fiber Sensor Mounting Example................................................................. 2.48
Figure 2.43 Clear-Jacketed Fiber Sensor Components (V-Pin Style)...................................................... 2.48
Figure 2.44 Clear-Jacketed Fiber Sensor Showing Transition From Clear- to Black-Jacketed
Fiber Section..................................................................................................................... 2.48
Figure 2.45 Switchgear Application Example......................................................................................... 2.49
Figure 2.46 Bare-Fiber Sensor Assembly With Two Splices .................................................................. 2.51
Figure 2.47 Point Sensor Assembly......................................................................................................... 2.51
Figure 2.48 Bare-Fiber Sensor Assembly With Two Additional ST Splice Connectors......................... 2.52
Figure 2.49 Point Sensor Assembly With Two V-Pin Splice Connectors ............................................... 2.52
Figure 3.1 Direct Connection of an SEL-751 to a Computer .................................................................. 3.2
Figure 3.2 Login Page of Web Server for an SEL-751............................................................................ 3.2
Figure 3.3 Select Access Level 2 From the Web Server Login ............................................................... 3.3
Figure 3.4 Fundamental Meter Report Webpage..................................................................................... 3.3
Figure 3.5 Event Report Webpage ........................................................................................................... 3.4
Figure 3.6 HIF Event Report Webpage ................................................................................................... 3.5
Figure 3.7 Sequential Events Recorder Report Webpage........................................................................ 3.5
Figure 3.8 Load Profile Webpage ............................................................................................................ 3.6
Figure 3.9 Breaker Wear Monitor Webpage ............................................................................................ 3.6
Figure 3.10 MAC Address......................................................................................................................... 3.7
Figure 3.11 Self-Tests Webpage ................................................................................................................ 3.7
Figure 3.12 Relay Word Bits Webpage...................................................................................................... 3.8
Figure 3.13 SELOGIC Counters Webpage.................................................................................................. 3.9
Figure 3.14 Group 1 Settings Webpage ..................................................................................................... 3.9
Figure 3.15 Upgrade Relay Firmware From the File Management Webpage......................................... 3.10
Figure 3.16 Communications Parameter Menu Selection ....................................................................... 3.12
Figure 3.17 Serial Port Communication Parameters Dialog Box............................................................ 3.13
Figure 3.18 Network Communication Parameters Dialog Box............................................................... 3.13
Figure 3.19 Communications Terminal Menu Selection ......................................................................... 3.13
Figure 3.20 Device Response to the ID Command ................................................................................. 3.14
Figure 3.21 Driver Selection.................................................................................................................... 3.17
Figure 3.22 Update Part Number............................................................................................................. 3.17
Figure 3.23 New Settings Screen.............................................................................................................3.18
Figure 3.24 Expression Created With Expression Builder ...................................................................... 3.19
Figure 3.25 Retrieve Events Screen......................................................................................................... 3.20
Figure 3.26 Save the Retrieved Event...................................................................................................... 3.21
Figure 3.27 Device Overview Screen ...................................................................................................... 3.22
Figure 3.28 Control Screen...................................................................................................................... 3.23
Figure 3.29 Remote Operation Selection................................................................................................. 3.23
Figure 3.30 Language Support Options................................................................................................... 3.24
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Date Code 20200603 Instruction Manual SEL-751 Relay
List of Figures
Figure 3.31 Spanish Settings QuickSet Display ...................................................................................... 3.25
Figure 3.32 Spanish Control Window (Ventana de Control) Display ..................................................... 3.26
Figure 4.1 Low-Energy Analog Voltage Sensor (Capacitive Voltage Divider) ....................................... 4.8
Figure 4.2 Instantaneous Overcurrent Element Logic ........................................................................... 4.15
Figure 4.3 Instantaneous Overcurrent Element Pickup Time Curve ..................................................... 4.17
Figure 4.4 Instantaneous Overcurrent Element Reset Time Curve ....................................................... 4.17
Figure 4.5 HIS 50INC Report Response ............................................................................................... 4.18
Figure 4.6 Incipient Cable Fault Logic.................................................................................................. 4.18
Figure 4.7 Phase Time-Overcurrent Elements 51AT, 51BT, and 51CT ................................................ 4.20
Figure 4.8 Maximum Phase Time-Overcurrent Elements 51P1T and 51P2T ....................................... 4.21
Figure 4.9 Negative-Sequence Time-Overcurrent Element 51QT ........................................................ 4.22
Figure 4.10 Neutral Time-Overcurrent Elements 51N1T and 51N2T..................................................... 4.23
Figure 4.11 Residual Time-Overcurrent Elements 51G1T and 51G2T................................................... 4.24
Figure 4.12 U.S. Moderately Inverse Curve: U1 ..................................................................................... 4.26
Figure 4.13 U.S. Inverse Curve: U2 ........................................................................................................ 4.26
Figure 4.14 U.S. Very Inverse Curve: U3 ................................................................................................ 4.26
Figure 4.15 U.S. Extremely Inverse Curve: U4....................................................................................... 4.26
Figure 4.16 U.S. Short-Time Inverse Curve: U5 ..................................................................................... 4.27
Figure 4.17 IEC Class A Curve (Standard Inverse): C1.......................................................................... 4.27
Figure 4.18 IEC Class B Curve (Very Inverse): C2................................................................................. 4.27
Figure 4.19 IEC Class C Curve (Extremely Inverse): C3........................................................................ 4.27
Figure 4.20 IEC Long-Time Inverse Curve: C4 ...................................................................................... 4.28
Figure 4.21 IEC Short-Time Inverse Curve: C5 ...................................................................................... 4.28
Figure 4.22 General Logic Flow of Directional Control for Neutral Ground and Residual 
Ground Overcurrent Elements (Excluding Ungrounded/High-Impedance 
Grounded Systems)........................................................................................................... 4.29
Figure 4.23 General Logic Flow of Directional Control for Neutral Ground and Residual 
Ground Overcurrent Elements (Ungrounded/High-Impedance Grounded Systems; 
ORDER := U) ................................................................................................................... 4.30
Figure 4.24 Logic for Relay Word Bit GNDSW ..................................................................................... 4.33
Figure 4.25 Internal Enables (DIRQE and DIRQGE) Logic for Negative-Sequence 
Voltage-Polarized Directional Elements........................................................................... 4.38
Figure 4.26 Internal Enables (DIRVE and DIRIE) Logic for Zero-Sequence Voltage-Polarized 
and Channel IN Current-Polarized Directional Elements ................................................ 4.39
Figure 4.27 Internal Enable (DIRNE) Logic for Zero-Sequence Voltage-Polarized Directional 
Elements (Low-Impedance Grounded, Petersen Coil-Grounded, and 
Ungrounded/High-Impedance Grounded Systems).......................................................... 4.40
Figure 4.28 Negative-Sequence Voltage-Polarized Directional Element for Neutral Ground 
and Residual Ground Overcurrent Elements .................................................................... 4.41
Figure 4.29 Zero-Sequence Voltage-Polarized Directional Element....................................................... 4.42
Figure 4.30 Channel IN Current-Polarized Directional Element ............................................................ 4.43
Figure 4.31 Zero-Sequence Voltage-Polarized Directional Element 
(Low-Impedance Grounded Systems) .............................................................................. 4.44
Figure 4.32 Wattmetric and Incremental Conductance Directional Elements 
(Petersen Coil-Grounded Systems) .................................................................................. 4.45
Figure 4.33 Zero-Sequence Voltage-Polarized Directional Element 
(Ungrounded/High-Impedance Grounded Systems) ........................................................ 4.46
Figure 4.34 Routing of Directional Elements to Residual Ground Overcurrent Elements ..................... 4.47
Figure 4.35 Routing of Directional Elements to Neutral Ground Overcurrent Elements ....................... 4.47
Figure 4.36 Direction Forward/Reverse Logic for Residual Ground Overcurrent Elements .................. 4.48
Figure 4.37 Direction Forward/Reverse Logic for Neutral Ground Overcurrent Elements .................... 4.49
Figure 4.38 General Logic Flow of Directional Control for Negative-Sequence and Phase 
Overcurrent Elements ....................................................................................................... 4.50
Figure 4.39 Negative-Sequence Voltage-Polarized Directional Element for Negative-Sequence 
and Phase Overcurrent Elements ...................................................................................... 4.52
Figure 4.40 Positive-Sequence Voltage-Polarized Directional Element for Phase Overcurrent 
Elements ........................................................................................................................... 4.53
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Figures
Figure 4.41 Routing of Directional Elements to Negative-Sequence and Phase Overcurrent 
Elements ........................................................................................................................... 4.54
Figure 4.42 Direction Forward/Reverse Logic for Negative-Sequence Overcurrent Elements .............. 4.55
Figure 4.43 Direction Forward/Reverse Logic for Phase Overcurrent Elements ....................................4.56
Figure 4.44 Traditional Channel IN Current-Polarized Directional Element.......................................... 4.64
Figure 4.45 Current-Polarized Directional Element Characteristic When INMTA  0.00 ..................... 4.65
Figure 4.46 Zero-Sequence Impedance Network and Relay Polarity ..................................................... 4.67
Figure 4.47 Zero-Sequence Impedance Plot for Solidly-Grounded, Mostly Inductive System .............. 4.67
Figure 4.48 Low-Impedance Grounded Distribution System With a Ground Fault on Feeder 1............ 4.68
Figure 4.49 Zero-Sequence Impedance Network for Low-Impedance Grounded Distribution 
System With a Ground Fault on Feeder 1......................................................................... 4.69
Figure 4.50 Decreasing Neutral Resistance RG Results in Increasing Zero-Sequence Current IOG....... 4.70
Figure 4.51 Decreasing Neutral Resistance RG Results in Increasing Zero-Sequence Current I0(1) 
(Seen by Relay 1) ............................................................................................................. 4.70
Figure 4.52 Zero-Sequence Impedance Plots for Ground Fault on Low-Impedance Grounded 
Distribution System .......................................................................................................... 4.71
Figure 4.53 Z0MTA Setting Provides Forward/Reverse Ground Fault Discrimination 
in a Low-Impedance Grounded Distribution System ....................................................... 4.72
Figure 4.54 Zero-Sequence Impedance Network for Ground Fault on Feeder 1 .................................... 4.75
Figure 4.55 Wattmetric Element Operation for Ground Fault on Feeder 1 ............................................. 4.76
Figure 4.56 Load-Encroachment Logic................................................................................................... 4.82
Figure 4.57 HIF Current Levels Depend on Ground Surface Type ......................................................... 4.84
Figure 4.58 HIF Detection Block Diagram ............................................................................................. 4.86
Figure 4.59 A-Phase Second-Harmonic Blocking................................................................................... 4.90
Figure 4.60 Three-Phase Second- and Fifth-Harmonic Blocking Logic................................................. 4.90
Figure 4.61 Thermal Alarm and Trip Logic ............................................................................................ 4.97
Figure 4.62 Thermal Element Current Overload Logic........................................................................... 4.97
Figure 4.63 Undervoltage Element Logic.............................................................................................. 4.102
Figure 4.64 Overvoltage Element Logic................................................................................................ 4.103
Figure 4.65 Logic Diagram of the Inverse-Time Undervoltage Element .............................................. 4.104
Figure 4.66 Inverse Time-Undervoltage Element Curves ..................................................................... 4.106
Figure 4.67 Logic Diagram of the Inverse-Time Overvoltage Element ................................................ 4.107
Figure 4.68 Inverse Time-Overvoltage Element Curves ....................................................................... 4.108
Figure 4.69 Synchronism-Check Voltage Window and Slip Frequency Elements................................ 4.109
Figure 4.70 Synchronism-Check Elements ........................................................................................... 4.110
Figure 4.71 Angle Difference Between VP and VS Compensated by Breaker Close Time 
(fP < fS and VP Shown as Reference in This Example) ................................................ 4.115
Figure 4.72 Three-Phase Power Elements Logic................................................................................... 4.119
Figure 4.73 Power Elements Operation in the Real/Reactive Power Plane........................................... 4.120
Figure 4.74 Power Factor Elements Logic ............................................................................................ 4.121
Figure 4.75 Loss-of-Potential (LOP) Logic........................................................................................... 4.123
Figure 4.76 Logic Diagram of the Vector Shift Element....................................................................... 4.124
Figure 4.77 Over- and Underfrequency Element Logic ........................................................................ 4.127
Figure 4.78 81R Frequency Rate-of-Change Scheme Logic................................................................. 4.128
Figure 4.79 81RF Characteristics .......................................................................................................... 4.129
Figure 4.80 81RF Fast Rate-of-Change-of-Frequency Logic................................................................ 4.131
Figure 4.81 Trip Logic........................................................................................................................... 4.132
Figure 4.82 Close Logic ........................................................................................................................ 4.135
Figure 4.83 Reclose Supervision Logic (Following Open Interval Time-Out) ..................................... 4.135
Figure 4.84 Reclose Supervision Limit Timer Operation...................................................................... 4.136
Figure 4.85 SEL-751 Relays Installed at Both Ends of a Transmission Line in a 
High-Speed Reclose Scheme.......................................................................................... 4.139
Figure 4.86 Reclosing Relay States and General Operation.................................................................. 4.141
Figure 4.87 Reclosing Sequence From Reset to Lockout With Example Settings................................ 4.145
Figure 4.88 Reclose Blocking for Islanded Generator .......................................................................... 4.151
Figure 4.89 Sequence Coordination Between the SEL-751 and a Line Recloser ................................. 4.154
Figure 4.90 Operation of SEL-751 Shot Counter for Sequence Coordination With Line Recloser 
(Additional Settings Example 1) .................................................................................... 4.154
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Date Code 20200603 Instruction Manual SEL-751 Relay
List of Figures
Figure 4.91 Operation of SEL-751 Shot Counter for Sequence Coordination With Line Recloser 
(Additional Settings Example 2) .................................................................................... 4.156
Figure 4.92 Demand Current Logic Outputs ......................................................................................... 4.157
Figure 4.93 Response of Thermal and Rolling Demand Meters to a Step Input 
(Setting DMTC = 15 minutes)........................................................................................ 4.158
Figure 4.94 Voltage VS Applied to Series RC Circuit .......................................................................... 4.159
Figure 4.95 Schematic Diagram of a Traditional Latching Device ....................................................... 4.162
Figure 4.96 Logic Diagram of a Latch Switch ...................................................................................... 4.162
Figure 4.97 SELOGIC Control Equation Variable/Timers SV01/SV01T–SV32T ................................. 4.163
Figure 4.98 Result of Falling-Edge Operator on a Deasserting Input ................................................... 4.167
Figure 4.99 Example Use of SELOGIC Variables/Timers ...................................................................... 4.168
Figure 4.100 Counter 01 ..........................................................................................................................4.169
Figure 4.101 Example of the Effects of the Input Precedence ................................................................ 4.170
Figure 4.102 Phase Rotation Setting ....................................................................................................... 4.172
Figure 4.103 Breaker Failure Logic......................................................................................................... 4.180
Figure 4.104 Breaker Failure Trip Logic ................................................................................................. 4.181
Figure 4.105 Arc-Flash Instantaneous Overcurrent Element Logic ........................................................ 4.182
Figure 4.106 Inverse Time-Overlight Element Logic.............................................................................. 4.184
Figure 4.107 TOL Element Inverse Curve Characteristic ....................................................................... 4.184
Figure 4.108 Analog Input Card Adaptive Name.................................................................................... 4.186
Figure 4.109 Settings to Configure Input 1 as a 4–20 mA Transducer Measuring Temperatures 
Between –50°C and 150°C............................................................................................. 4.189
Figure 4.110 Analog Output Number Allocation .................................................................................... 4.190
Figure 4.111 Analog Output Settings ...................................................................................................... 4.191
Figure 4.112 DC Mode Processing.......................................................................................................... 4.191
Figure 4.113 AC Mode Processing.......................................................................................................... 4.192
Figure 4.114 Timing Diagram for Debounce Timer Operation When Operating in AC Mode .............. 4.192
Figure 4.115 Display Point Settings ........................................................................................................ 4.203
Figure 4.116 Front-Panel Display—Both HV and LV Breakers Open ................................................... 4.203
Figure 4.117 Front-Panel Display—HV Breaker Closed, LV Breaker Open.......................................... 4.203
Figure 4.118 Front-Panel Display—Both HV and LV Breakers Closed ................................................. 4.204
Figure 4.119 Front-Panel Display—HV Breaker Open, LV Breaker Closed.......................................... 4.204
Figure 4.120 Front-Panel Display—HV Breaker Open, LV Breaker Closed.......................................... 4.204
Figure 4.121 Front-Panel Display for a Binary Entry in the Name String Only ..................................... 4.205
Figure 4.122 Front-Panel Display for an Analog Entry in the Name String Only .................................. 4.205
Figure 4.123 Front-Panel Display for an Entry in (a) Boolean Name and Alias Strings and 
(b) Analog Name and User Text and Formatting Strings ............................................... 4.206
Figure 4.124 Front-Panel Display for an Entry in (a) Boolean Name and Alias Strings and 
(b) Analog Name, User Text and Formatting Strings, and Engineering Units ............... 4.206
Figure 4.125 Adding Temperature Measurement Display Points ........................................................... 4.207
Figure 4.126 Rotating Display................................................................................................................. 4.207
Figure 4.127 Adding Two Local Bits ...................................................................................................... 4.208
Figure 5.1 Complex Power Measurement Conventions .......................................................................... 5.2
Figure 5.2 METER Command Report With Voltage/Arc-Flash Detection 2 AVI/4 AFDI Card 
in Slot E and 4 ACI/3 AVI Card in Slot Z .......................................................................... 5.5
Figure 5.3 METER T Command Report With RTDs .............................................................................. 5.6
Figure 5.4 METER E Command Response............................................................................................. 5.7
Figure 5.5 METER RE Command Response .......................................................................................... 5.7
Figure 5.6 METER M Command Response............................................................................................ 5.8
Figure 5.7 METER RM Command Response ......................................................................................... 5.8
Figure 5.8 METER MV Command Response......................................................................................... 5.9
Figure 5.9 METER RMS Command Response....................................................................................... 5.9
Figure 5.10 METER AI Command Response ......................................................................................... 5.10
Figure 5.11 METER L (Light) Command Response............................................................................... 5.10
Figure 5.12 MET DE Command Response ............................................................................................. 5.11
Figure 5.13 MET PE Command Response.............................................................................................. 5.11
Figure 5.14 MET RA Command Response............................................................................................. 5.13
Figure 5.15 MET H (HIF) Command Response ..................................................................................... 5.13
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Figures
Figure 5.16 LDP Command Response .................................................................................................... 5.14
Figure 5.17 DC Under- and Overvoltage Elements................................................................................. 5.15
Figure 5.18 Create DC Voltage Elements With SELOGIC Control Equations......................................... 5.16
Figure 5.19 Plotted Breaker Maintenance Points for a 25 kV Circuit Breaker ....................................... 5.20
Figure 5.20 SEL-751 Breaker Maintenance Curve for a 25 kV Circuit Breaker .................................... 5.21
Figure 5.21 Operation of SELOGIC Control Equation Breaker Monitor Initiation Setting ..................... 5.22
Figure 5.22 Breaker Monitor Accumulates 10 Percent Wear .................................................................. 5.23
Figure 5.23 Breaker Monitor Accumulates 25 Percent Wear .................................................................. 5.24
Figure 5.24 Breaker Monitor Accumulates 50 Percent Wear .................................................................. 5.25
Figure 5.25 Breaker Monitor Accumulates 100 Percent Wear ................................................................ 5.26
Figure 5.26 Input INxxx Connected to Trip Bus for Breaker Monitor Initiation .................................... 5.29
Figure 6.1 Front-Panel Setting Entry Example........................................................................................ 6.3
Figure 6.2 Logic 1 Settings Webpage...................................................................................................... 6.6
Figure 7.1 Simple Ethernet Network Configuration................................................................................ 7.4
Figure 7.2 Ethernet Network Configuration With Dual Redundant Connections (Failover Mode) ........ 7.4
Figure 7.3 Ethernet Network Configuration With Ring Structure (Switched Mode).............................. 7.5
Figure 7.4 IRIG-B Input (Relay Terminals B01–B02) ............................................................................ 7.8
Figure 7.5 IRIG-B Input Via EIA-232 Port3 (SEL Communications Processor as Source) .................. 7.8
Figure 7.6 IRIG-B Input Via EIA-232 Port 3 (SEL-2401/2404/2407 Time Source) .............................. 7.8
Figure 7.7 IRIG-B Input Via Fiber-Optic EIA-232 Port 2 (SEL-2030/2032 Time Source).................... 7.9
Figure 7.8 IRIG-B Input Via Fiber-Optic EIA-232 Port 2 (SEL-2401/2404/2407 Time Source)........... 7.9
Figure 7.9 EIA-232 DB-9 Connector Pin Numbers ................................................................................ 7.9
Figure 7.10 SEL-C234A Cable—SEL-751 to DTE Device ................................................................... 7.10
Figure 7.11 SEL-C227A Cable—SEL-751 to DTE Device ................................................................... 7.10
Figure 7.12 SEL-C222 Cable—SEL-751 to Modem.............................................................................. 7.11
Figure 7.13 SEL-C272A Cable—SEL-751 to SEL Communications Processor
(Without IRIG-B Signal) .................................................................................................. 7.11
Figure 7.14 SEL-C273A Cable—SEL-751 to SEL Communications Processor
(With IRIG-B Signal) ....................................................................................................... 7.11
Figure 7.15 SEL-C387 Cable—SEL-751 to SEL-3010 .......................................................................... 7.11
Figure 7.16 AFT Command Response .................................................................................................... 7.29
Figure 7.17 Breaker Monitor Report ....................................................................................................... 7.31
Figure 7.18 Breaker Wear Report ............................................................................................................ 7.32
Figure 7.19 Breaker Reset Response ....................................................................................................... 7.32
Figure 7.20 CEV HIF Command Response ............................................................................................ 7.33
Figure 7.21 COM PTP Command Response When PTP is Available..................................................... 7.36
Figure 7.22 Ethernet Port (PORT 1) Status Report When NETMODE := PRP...................................... 7.44
Figure 7.23 Ethernet Port (PORT 1) Status Report When NETMODE := FIXED ................................. 7.44
Figure 7.24 Ethernet Port (PORT 1) Status Report When NETMODE := FAILOVER, E61850 := Y, 
and EGSE := Y ................................................................................................................. 7.44
Figure 7.25 Ethernet Port (PORT 1) Status Report When NETMODE := SWITCHED ........................ 7.45
Figure 7.26 Ethernet Port (PORT 1) Status Report for the Single Ethernet Port Option ........................ 7.45
Figure 7.27 GOOSE Command Response............................................................................................... 7.48
Figure 7.28 HSG Command Response.................................................................................................... 7.52
Figure 7.29 LOG H (HIF) Command Response...................................................................................... 7.55
Figure 7.30 PING Command Response................................................................................................... 7.59
Figure 7.31 SHOW Command Example ................................................................................................. 7.63
Figure 7.32 Typical Relay Output for STATUS S Command.................................................................. 7.66
Figure 7.33 THE Command Example ..................................................................................................... 7.70
Figure 7.34 CFG.TXT File ...................................................................................................................... 7.72
Figure 8.1 SEL-751 Front-Panel Options ................................................................................................ 8.1
Figure 8.2 Front-Panel Overview ............................................................................................................ 8.2
Figure 8.3 Access Level Security Padlock Symbol ................................................................................. 8.4
Figure 8.4 Password Entry Screen........................................................................................................... 8.4
Figure 8.5 Front-Panel Pushbuttons......................................................................................................... 8.5
Figure 8.6 Main Menu ............................................................................................................................. 8.6
Figure 8.7 MAIN Menu and METER Submenu ..................................................................................... 8.6
Figure 8.8 METER Menu and ENERGY Submenu................................................................................ 8.6
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Date Code 20200603 Instruction Manual SEL-751 Relay
List of Figures
Figure 8.9 Relay Response When Energy (or Max/Min, Demand, Peak Demand) Metering Is Reset... 8.7
Figure 8.10 Relay Response When No Analog Cards Are Installed......................................................... 8.7
Figure 8.11 Relay Response When No Math Variables Enabled .............................................................. 8.7
Figure 8.12 MAIN Menu and EVENTS Submenu.................................................................................... 8.7
Figure 8.13 EVENTS Menu and DISPLAY Submenu.............................................................................. 8.8
Figure 8.14 Relay Response When No Event Data Available................................................................... 8.8
Figure 8.15 Relay Response When Events Are Cleared ........................................................................... 8.8
Figure 8.16 MAIN Menu and TARGETS Submenu ................................................................................. 8.8
Figure 8.17 TARGETS Menu Navigation ................................................................................................. 8.9
Figure 8.18 MAIN Menu and CONTROL Submenu ................................................................................ 8.9
Figure 8.19 CONTROL Menu and OUTPUTS Submenu....................................................................... 8.10
Figure 8.20 CONTROL Menu and LOCAL BITS Submenu.................................................................. 8.10
Figure 8.21 MAIN Menu and SET/SHOW Submenu ............................................................................. 8.11
Figure 8.22 SET/SHOW Menu................................................................................................................ 8.12
Figure 8.23 MAIN Menu and Status Submenu ....................................................................................... 8.12
Figure 8.24 MAIN Menu and Breaker Submenu .................................................................................... 8.13
Figure 8.25 Factory Default Front-Panel LEDs....................................................................................... 8.13
Figure 8.26 Target Reset Pushbutton ....................................................................................................... 8.15
Figure 8.27 Operator Control Pushbuttons and LEDs............................................................................. 8.15
Figure 8.28 Touchscreen Display Components and Indicators ............................................................... 8.18
Figure 8.29 Home (Default FPHOME Setting) ....................................................................................... 8.21
Figure 8.30 Bay Screens Application ...................................................................................................... 8.22
Figure 8.31 MeterApplications............................................................................................................... 8.23
Figure 8.32 Meter Phasors....................................................................................................................... 8.24
Figure 8.33 Meter Fundamental .............................................................................................................. 8.24
Figure 8.34 Meter Energy........................................................................................................................ 8.24
Figure 8.35 Meter Energy Reset .............................................................................................................. 8.24
Figure 8.36 Monitor Applications ........................................................................................................... 8.25
Figure 8.37 Breaker Wear Trips............................................................................................................... 8.25
Figure 8.38 Breaker Wear A, B, C, and Last Reset ................................................................................. 8.25
Figure 8.39 Monitor Relay Word Bits ..................................................................................................... 8.26
Figure 8.40 Search Relay Word Bits ....................................................................................................... 8.26
Figure 8.41 Reports Applications ............................................................................................................ 8.26
Figure 8.42 Event History........................................................................................................................ 8.27
Figure 8.43 Event Summary .................................................................................................................... 8.27
Figure 8.44 Sequential Events Recorder ................................................................................................. 8.27
Figure 8.45 Control Applications ............................................................................................................ 8.27
Figure 8.46 Local Bits Confirmation....................................................................................................... 8.28
Figure 8.47 Digital Output Pulsing—Slot A ........................................................................................... 8.29
Figure 8.48 Digital Output Pulsing Confirmation ................................................................................... 8.29
Figure 8.49 Local Bits ............................................................................................................................. 8.29
Figure 8.50 Local Bits Notification ......................................................................................................... 8.29
Figure 8.51 Local Bits Confirmation....................................................................................................... 8.29
Figure 8.52 Device Info Applications...................................................................................................... 8.30
Figure 8.53 Device Status........................................................................................................................ 8.30
Figure 8.54 Device Configuration ........................................................................................................... 8.30
Figure 8.55 Model Number Confirmation............................................................................................... 8.31
Figure 8.56 Trip and Diagnostic Messages ............................................................................................. 8.31
Figure 8.57 Arc-Flash Diagnostics .......................................................................................................... 8.31
Figure 8.58 Arc-Flash Diagnostics Confirmation.................................................................................... 8.31
Figure 8.59 Access Level Applications ................................................................................................... 8.32
Figure 8.60 Authentication ...................................................................................................................... 8.32
Figure 8.61 Login Confirmation.............................................................................................................. 8.32
Figure 8.62 Settings Folders and Applications........................................................................................ 8.33
Figure 8.63 Port Settings ......................................................................................................................... 8.34
Figure 8.64 Group Settings...................................................................................................................... 8.34
Figure 8.65 Global Settings ..................................................................................................................... 8.34
Figure 8.66 General Settings ................................................................................................................... 8.34
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SEL-751 Relay Instruction Manual Date Code 20200603
List of Figures
Figure 8.67 Set/Show Settings Edit ......................................................................................................... 8.34
Figure 8.68 Touchscreen Settings............................................................................................................ 8.35
Figure 8.69 Touchscreen Settings Edit .................................................................................................... 8.35
Figure 8.70 Rotating Display................................................................................................................... 8.35
Figure 9.1 Dual-Point Disconnect Status Logic ...................................................................................... 9.5
Figure 9.2 Disconnect Close Logic ......................................................................................................... 9.5
Figure 9.3 Disconnect Open Logic.......................................................................................................... 9.6
Figure 9.4 Local/Remote Control Mode Indication ................................................................................ 9.8
Figure 9.5 Bay Screens Application Display With a Single-Line Diagram ............................................ 9.9
Figure 9.6 Breaker Control Application .................................................................................................. 9.9
Figure 9.7 QuickSet Front-Panel Options ............................................................................................. 9.10
Figure 9.8 QuickSet Touchscreen Settings ............................................................................................ 9.11
Figure 9.9 Layout of Bay Screen Builder.............................................................................................. 9.15
Figure 9.10 Project Analysis Pane: Analysis Results Tab ....................................................................... 9.17
Figure 9.11 Project Analysis Pane: Constraints Summary Tab ............................................................... 9.17
Figure 9.12 Bay Control Single-Line Diagram Schematic...................................................................... 9.18
Figure 9.13 Device Part Number Touchscreen Configuration Option..................................................... 9.19
Figure 9.14 QuickSet Bay Control Project Management and Project Preview Display.......................... 9.19
Figure 9.15 Open Single-Line Diagram in Bay Screen Builder.............................................................. 9.20
Figure 9.16 Drag-and-Drop Symbols ...................................................................................................... 9.20
Figure 9.17 Selected Breaker SymbolSettings Displayed in the Properties Pane .................................. 9.22
Figure 9.18 Close/Open/Alarm Color Property Drop Down Menu......................................................... 9.22
Figure 9.19 Publish Bay Screen Builder Project to QuickSet ................................................................. 9.23
Figure 9.20 QuickSet Updated Single-Line Diagram and Corresponding Settings ................................ 9.23
Figure 9.21 Final Bay Screen Builder Rendering.................................................................................... 9.28
Figure 9.22 Import/Export of the Bay Control Screen in QuickSet ........................................................ 9.28
Figure 9.23 ANSI Main Bus and Transfer Bus ....................................................................................... 9.29
Figure 9.24 IEC Main Bus and Transfer Bus .......................................................................................... 9.29
Figure 10.1 Example Event Summary..................................................................................................... 10.3
Figure 10.2 Sample Event History........................................................................................................... 10.8
Figure 10.3 Example Standard 15-Cycle Event Report 1/4-Cycle Resolution ..................................... 10.12
Figure 10.4 Derivation of Event Report Current Values and RMS Current Values From 
Sampled Current Waveform ........................................................................................... 10.18
Figure 10.5 Derivation of Phasor RMS Current Values From Event Report Current Values................ 10.19
Figure 10.6 Sample Compressed ASCII Event Report ......................................................................... 10.20
Figure 10.7 Sample CEV Report Viewed With SYNCHROWAVE Event ................................................ 10.24
Figure 10.8 Sample COMTRADE .HDR Header File .......................................................................... 10.25
Figure 10.9 Sample COMTRADE .CFG Configuration File Data........................................................ 10.29
Figure 10.10 Sample HIF Event Summary Report.................................................................................. 10.31
Figure 10.11 Sample Compressed ASCII HIF Summary........................................................................ 10.33
Figure 10.12 Sample HIF Event History ................................................................................................. 10.34
Figure 10.13 Sample Compressed HIF History Report........................................................................... 10.35
Figure 10.14 Sample HIF COMTRADE .HDR Header File................................................................... 10.36
Figure 10.15 Sample HIF COMTRADE .CFG Configuration File Data ................................................ 10.36
Figure 10.16 Example Sequential Events Recorder (SER) Event Report ............................................... 10.39
Figure 11.1 Low-Level Test Interface (J2 and J4) ................................................................................... 11.2
Figure 11.2 Three-Phase Wye AC Connections ...................................................................................... 11.5
Figure 11.3 Three-Phase Open-Delta AC Connections........................................................................... 11.5
Figure 11.4 Current Source Connections................................................................................................. 11.7
Figure 11.5 Wye Voltage Source Connections ........................................................................................ 11.8
Figure 11.6 Delta Voltage Source Connections ....................................................................................... 11.9
Figure 11.7 CEV R Light Event Capture Example ............................................................................... 11.12
Figure B.1 Special SELBOOT Upgrade Process .......................................................................................B.4
Figure B.2 Firmware File Transfer Process..............................................................................................B.6
Figure B.3 Firmware Upgrade Via FTP .................................................................................................B.16
Figure C.1 SEL Communications Processor Star Integration Network ...................................................C.3
Figure C.2 Multitiered SEL Communications Processor Architecture....................................................C.4
Figure C.3 Enhancing Multidrop Networks With SEL Communications Processors..............................C.6
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Date Code 20200603 Instruction Manual SEL-751 Relay
List of Figures
Figure C.4 Example of SEL Relay and SEL Communications Processor Configuration........................C.7
Figure C.5 Unsolicited Write Settings ...................................................................................................C.12
Figure C.6 Setting Remote Analogs RA01 Through RA13...................................................................C.14
Figure D.1 Application Confirmation Timing With URETRY n = 2 ...................................................... D.7
Figure D.2 Message Transmission Timing.............................................................................................. D.8
Figure D.3 Sample Response to SHO DNP Command......................................................................... D.26
Figure D.4 Port MAP Command........................................................................................................... D.27
Figure D.5 Sample Custom DNP3 AI Map Settings ............................................................................. D.29
Figure D.6 Analog Input Map Entry in QuickSet Software .................................................................. D.30
Figure D.7 AI Point Scaling and Deadband in QuickSet Software....................................................... D.30
Figure D.8 Sample Custom DNP3 AO Map Settings............................................................................ D.30
Figure D.9 Analog Output Map Entry in QuickSet Software ............................................................... D.31
Figure D.10 Sample Custom DNP3 BO Map Settings............................................................................ D.31
Figure D.11 Binary Output Map Entry in QuickSet Software ................................................................ D.32
Figure G.1 SEL-751 Datasets.................................................................................................................. G.6
Figure G.2 SEL-751 Predefined Reports................................................................................................. G.7
Figure G.3 GOOSE Quality..................................................................................................................... G.9
Figure G.4 MMS Client View of the CON Logical Device .................................................................. G.12
Figure G.5 Set controllableModeSupported = True .............................................................................. G.17
Figure G.6 Default Quality Check on GOOSE Subscription if Quality is Present ............................... G.19
Figure G.7 Relay Operations in On Mode............................................................................................. G.19
Figure G.8 Relay Operations in Blocked Mode .................................................................................... G.20
Figure G.9 Relay Operations in Test Mode........................................................................................... G.20
Figure G.10 Relay Operations in Test/Blocked Mode............................................................................. G.21
Figure G.11 Relay Operations in Off Mode ............................................................................................G.22
Figure I.1 DeviceNet Card Component Overview................................................................................... I.1
Figure K.1 Phase Reference .................................................................................................................... K.2
Figure K.2 Waveform at Relay Terminals May Have a Phase Shift........................................................ K.3
Figure K.3 Correction of Measured Phase Angle.................................................................................... K.3
Figure K.4 TCP Connection .................................................................................................................. K.10
Figure K.5 UDP_T and UDP_U Connections....................................................................................... K.11
Figure K.6 UDP_S Connection ............................................................................................................. K.11
Figure K.7 Sample MET PM Command Response............................................................................... K.14
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Date Code 20200603 Instruction Manual SEL-751 Relay
Preface
Manual Overview
The SEL-751 Feeder Protection Relay Instruction Manual describes common 
aspects of feeder relay application and use. It includes the necessary 
information to install, set, test, and operate the relay.
An overview of each manual section and topics follows:
Preface. Describes the manual organization, safety information, and 
conventions used to present information.
Section 1: Introduction and Specifications. Describes the basic features 
and functions of the SEL-751; lists the relay specifications.
Section 2: Installation. Describes how to mount and wire the SEL-751; 
illustrates wiring connections for various applications.
Section 3: PC Interface. Describes the built-in web server and its features, 
including settings, metering and monitoring, reports, and firmware 
upgrade. Also describes the features, installation methods, and types of 
help available with the ACSELERATOR QuickSet SEL-5030 Software.
Section 4: Protection and Logic Functions. Describes the operating 
characteristic of each protection element, using logic diagrams and 
text, and explains how to calculate element settings; describes contact 
output logic, automation, and report settings.
Section 5: Metering and Monitoring. Describes the operation of each 
metering function; describes the monitoring functions.
Section 6: Settings. Describes how to view, enter, and record settings for 
protection, control, communications, logic and monitoring.
Section 7: Communications. Describes how to connect the SEL-751 to a 
PC for communication; shows serial port pinouts; lists and defines 
serial port commands. Describes the communications port interfaces
and protocols supported by the relay for serial and Ethernet.
Section 8: Front-Panel Operations. Explains the features and use of the 
front panel, including front-panel command menu, default displays, 
and automatic messages. Describes in detail the two-line display 
(2 x 16 characters) and the touchscreen display (5-inch, color, 
800 x 480 pixels).
Section 9: Bay Control. Describes how to configure and design the bay 
control screens for SEL-751 relays with the touchscreen display 
(5-inch, color, 800 x 480 pixels).
Section 10: Analyzing Events. Describes event type, messages, event 
summary data, standard event reports, and Sequential Events Recorder 
(SER) report.
Section 11: Testing and Troubleshooting. Describes relay test procedures, 
relay self-test, and relay troubleshooting.
Appendix A: Firmware, ICD, and Manual Versions. Lists the present relay 
firmware version and details differences between the present and 
previous versions. Provides a record of changes made to the manual 
since the initial release.
xxvi
SEL-751 Relay Instruction Manual Date Code 20200603
Preface
Manual Overview
Appendix B: Firmware Upgrade Instructions. Describes the procedure to 
update the firmware stored in flash memory.
Appendix C: SEL Communications Processors. Provides examples of how 
to use the SEL-751 with SEL communications processors for total 
substation automation solutions.
Appendix D: DNP3 Communications. Describes the DNP3 protocol support
provided by the SEL-751.
Appendix E: Modbus Communications. Describes the Modbus protocol 
support provided by the SEL-751.
Appendix F: EtherNet/IP Communications. Describes the EtherNet/IP 
support provided by the SEL-751.
Appendix G: IEC 61850 Communications. Describes IEC 61850 
implementation in the SEL-751.
Appendix H: IEC 60870-5-103 Communications. Describes the 
IEC 60870-5-103 protocol support provided by the SEL-751.
Appendix I: DeviceNet Communications. Describes the use of DeviceNet 
(data-link and application protocol) over CAN (hardware protocol).
Appendix J: MIRRORED BITS Communications. Describes how SEL protective 
relays and other devices can directly exchange information quietly, 
securely, and with minimum cost.
Appendix K: Synchrophasors. Describes the Phasor Measurement Control 
Unit (PMCU), and accessing synchrophasor data through the use of 
IEEE C37.118 Protocol.
Appendix L: Relay Word Bits. Lists and describes the Relay Word bits 
(outputs of protection and control elements).
Appendix M: Analog Quantities. Lists and describes the Analog Quantities 
(outputs of analog elements).
Appendix N: Cybersecurity Features. Describes a number of features to 
help meet cybersecurity design requirements.
SEL-751 Relay Command Summary. Briefly describes the serial port 
commands that are fully described in Section 7: Communications.
Safety Information
Dangers, Warnings, 
and Cautions
This manual uses three kinds of hazard statements, defined as follows:
DANGER
Indicates an imminently hazardous situation 
that, if not avoided, will result in death or 
serious injury.
WARNING
Indicates a potentially hazardous situation 
that, if not avoided, could result in death or 
serious injury.
CAUTION
Indicates a potentially hazardous situation 
that, if not avoided, may result in minor or 
moderate injury or equipment damage.
xxvii
Date Code 20200603 Instruction Manual SEL-751 Relay
Preface
Manual Overview
Safety Symbols The following symbols are often marked on SEL products.
Safety Marks The following statements apply to this device.
CAUTION
Refer to accompanying documents.
ATTENTION
Se reporter à la documentation.
Earth (ground) Terre
Protective earth (ground) Terre de protection
Direct current Courant continu
Alternating current Courant alternatif
Both direct and alternating current Courant continu et alternatif
Instruction manual Manuel d’instructions
General Safety Marks
CAUTION
There is danger of explosion if the battery is incorrectly replaced. 
Replace only with Rayovac no. BR2335 or equivalent recommended by 
manufacturer. See Owner's Manual for safety instructions. The battery 
used in this device may present a fire or chemical burn hazard if 
mistreated. Do not recharge, disassemble, heat above 100°C or 
incinerate. Dispose of used batteries according to the manufacturer’s 
instructions. Keep battery out of reach of children.
ATTENTION
Une pile remplacée incorrectement pose des risques d’explosion. 
Remplacez seulement avec un Rayovac no BR2335 ou un produit 
équivalent recommandé par le fabricant. Voir le guide d’utilisateur 
pour les instructions de sécurité. La pile utilisée dans cet appareil peut 
présenter un risque d’incendie ou de brûlure chimique si vous en faites 
mauvais usage. Ne pas recharger, démonter, chauffer à plus de 100°C 
ou incinérer. Éliminez les vieilles piles suivant les instructions du 
fabricant. Gardez la pile hors de la portée des enfants.
CAUTION
To ensure proper safety and operation, the equipment ratings, 
installation instructions, and operating instructions must be checked 
before commissioning or maintenance of the equipment. The integrity 
of any protective conductor connectionmust be checked before 
carrying out any other actions. It is the responsibility of the user to 
ensure that the equipment is installed, operated, and used for its 
intended function in the manner specified in this manual. If misused, 
any safety protection provided by the equipment may be impaired.
ATTENTION
Pour assurer la sécurité et le bon fonctionnement, il faut vérifier les 
classements d’équipement ainsi que les instructions d’installation et 
d’opération avant la mise en service ou l’entretien de l’équipement. Il 
faut vérifier l’intégrité de toute connexion de conducteur de 
protection avant de réaliser d’autres actions. L’utilisateur est 
responsable d’assurer l’installation, l’opération et l’utilisation de 
l’équipement pour la fonction prévue et de la manière indiquée dans 
ce manuel. Une mauvaise utilisation pourrait diminuer toute 
protection de sécurité fournie par l'équipement.
For use in Pollution Degree 2 environment. Pour l'utilisation dans un environnement de Degré de Pollution 2.
Ambient air temperature shall not exceed 50°C (122°F). La température de l'air ambiant ne doit pas dépasser 50°C (122°F).
For use on a flat surface of a Type 1 enclosure. Destiné à l'utilisation sur une surface plane d'un boîtier de 
Type 1.
Terminal Ratings
Wire Material
Use 75°C (167°F) copper conductors only.
Tightening Torque
CT Terminal Blocks: 0.9–1.4 Nm (8–12 in-lb)
Compression Plug: 0.5–1.0 Nm (4.4–8.8 in-lb)
Compression Plug Mounting Ear Screw: 
0.18–0.25 Nm (1.6–2.2 in-lb)
Spécifications des bornes
Type de filage
Utiliser seulement des conducteurs en cuivre spécifiés à 
75°C (167°F).
Couple de serrage
CT bornes : 0,9–1,4 Nm (8–12 livres-pouce)
Fiche à compression : 0,5–1,0 Nm (4,4–8,8 livres-pouce)
Vis à oreille de montage de la fiche à compression : 
0,18–0,25 Nm (1,6–2,2 livres-pouce)
xxviii
SEL-751 Relay Instruction Manual Date Code 20200603
Preface
Manual Overview
Compliance Approvals
Hazardous Locations Approvals
The SEL-751 is UL certified for hazardous locations to Canadian and U.S. 
standards. In North America, the relay is approved for Hazardous Locations 
Class I, Division 2, Groups A, B, C, and D, and temperature class T3C in the 
maximum surrounding air temperature of 50°C.
The SEL-751 shall be installed in an indoor or outdoor (extended) locked 
enclosure that provides a degree of protection to personnel against access to 
hazardous parts. In either environment, the relay shall be protected from direct 
sunlight, precipitation, and full wind pressure.
To comply with the requirements of the European ATEX standard for 
hazardous location, the SEL-751 shall be installed in an ATEX-certified 
enclosure with a tool-removable door or cover that provides a degree of 
protection not less than IP54, in accordance with EN 60079-7. The enclosure 
shall be limited to the surrounding air temperature range of 
–20°C  Ta  +50°C. The enclosure should be certified to these requirements 
or be tested for compliance as part of the complete assembly. The enclosure 
must be marked “WARNING—Do not open when an explosive atmosphere is 
present.”
Hazardous Locations Safety Marks 
WARNING – EXPLOSION HAZARD
Open circuit before removing cover.
AVERTISSEMENT – DANGER D'EXPLOSION
Ouvrir le circuit avant de déposer le couvercle.
WARNING – EXPLOSION HAZARD
Substitution of components may impair suitability for Class I, 
Division 2.
AVERTISSEMENT – DANGER D'EXPLOSION
La substitution de composants peut détériorer la conformité à 
Classe I, Division 2.
Ambient air temperature shall not exceed –20°C  Ta  +50°C. La température de l’air ambiant ne doit pas dépasser 
–20°C  Ta  +50°C.
xxix
Date Code 20200603 Instruction Manual SEL-751 Relay
Preface
Manual Overview
The figure shows the compliance label that is located on the left side of the 
device.
Product Compliance Label
for the SEL-751
2350 NE HOPKINS CT, PULLMAN WA 99163 15
9
–1
4
79
.
MADE IN USA
PATENTS:
Capacitors should be safely discharged 
during decommissioning.
selinc.com/patents/123876
IND. CONT. EQ.
FOR USE IN
HAZ. LOC.
(E470448)
IND. CONT. EQ.
·
CL I, DIV 2; GP A, B, C, D; T3C
-20°C Tamb +50°C
CA • US:
HAZARDOUS LOCATIONS
Complies with 21 CFR 1040.10 and 1040.11,
except for deviations pursuant to Laser
Notice No. 50, dated June 24, 2007.
This device complies with Part 15 of the FCC 
Rules. Operation is subject to the following
two conditions: (1) this device may not cause
harmful interference, and (2) this device must 
accept any interference received, including 
interference that may cause undesired 
operation.
B
Other Safety Marks (Sheet 1 of 2)
DANGER
Disconnect or de-energize all external connections before opening this 
device. Contact with hazardous voltages and currents inside this 
device can cause electrical shock resulting in injury or death.
DANGER
Débrancher tous les raccordements externes avant d’ouvrir cet 
appareil. Tout contact avec des tensions ou courants internes à 
l’appareil peut causer un choc électrique pouvant entraîner des 
blessures ou la mort.
DANGER
Contact with instrument terminals can cause electrical shock that can 
result in injury or death.
DANGER
Tout contact avec les bornes de l’appareil peut causer un choc 
électrique pouvant entraîner des blessures ou la mort.
WARNING
Use of this equipment in a manner other than specified in this manual 
can impair operator safety safeguards provided by this equipment.
AVERTISSEMENT
L’utilisation de cet appareil suivant des procédures différentes de 
celles indiquées dans ce manuel peut désarmer les dispositifs de 
protection d’opérateur normalement actifs sur cet équipement.
WARNING
Have only qualified personnel service this equipment. If you are not 
qualified to service this equipment, you can injure yourself or others, 
or cause equipment damage.
AVERTISSEMENT
Seules des personnes qualifiées peuvent travailler sur cet appareil. Si 
vous n’êtes pas qualifiés pour ce travail, vous pourriez vous blesser 
avec d’autres personnes ou endommager l’équipement.
WARNING
Before working on a CT circuit, first apply a short to the secondary 
winding of the CT.
AVERTISSEMENT
Avant de travailler sur un circuit TC, placez d’abord un court-circuit sur 
l’enroulement secondaire du TC.
xxx
SEL-751 Relay Instruction Manual Date Code 20200603
Preface
Manual Overview
WARNING
This device is shipped with default passwords. Default passwords 
should be changed to private passwords at installation. Failure to 
change each default password to a private password may allow 
unauthorized access. SEL shall not be responsible for any damage 
resulting from unauthorized access.
AVERTISSEMENT
Cet appareil est expédié avec des mots de passe par défaut. A 
l’installation, les mots de passe par défaut devront être changés pour 
des mots de passe confidentiels. Dans le cas contraire, un accès non-
autorisé á l’équipement peut être possible. SEL décline toute 
responsabilité pour tout dommage résultant de cet accès non-
autorisé.
WARNING
To install an option card, the relay must be de-energized and then re-
energized. When re-energized, the relay will reboot. Therefore, de-
energize the protected equipment before installing the option card to 
prevent damage to the equipment.
AVERTISSEMENT
Pour installer une carte à option, le relais doit être éteint et ensuite 
rallumé. Quand il est rallumé, le relais redémarrera. Donc, il faut 
éteindre l’équipement protégé avant d’installer la carte à option pour 
empêcher des dégats à l’équipement.
WARNING
Do not perform any procedures or adjustments that this instruction 
manual does not describe.
AVERTISSEMENT
Ne pas appliquer une procédure ou un ajustement qui n’est pas décrit 
explicitement dans ce manuel d’instruction.
WARNING
During installation, maintenance, or testing of the optical ports, use 
only test equipment qualified for Class 1 laser products.
AVERTISSEMENT
Durant l’installation, la maintenance ou le test des ports optiques, 
utilisez exclusivement des équipements de test homologuéscomme 
produits de type laser de Classe 1.
WARNING
Overtightening the mounting nuts may permanently damage the relay 
chassis.
AVERTISSEMENT
Une pression excessive sur les écroux de montage peut endommager 
de façon permanente le chassis du relais.
CAUTION
Equipment components are sensitive to electrostatic discharge (ESD). 
Undetectable permanent damage can result if you do not use proper 
ESD procedures. Ground yourself, your work surface, and this 
equipment before removing any cover from this equipment. If your 
facility is not equipped to work with these components, contact SEL 
about returning this device and related SEL equipment for service.
ATTENTION
Les composants de cet équipement sont sensibles aux décharges 
électrostatiques (DES). Des dommages permanents non-décelables 
peuvent résulter de l’absence de précautions contre les DES. 
Raccordez-vous correctement à la terre, ainsi que la surface de travail 
et l’appareil avant d’en retirer un panneau. Si vous n’êtes pas équipés 
pour travailler avec ce type de composants, contacter SEL afin de 
retourner l’appareil pour un service en usine.
CAUTION
Looking into optical connections, fiber ends, or bulkhead connections 
can result in hazardous radiation exposure.
ATTENTION
Regarder vers les connecteurs optiques, les extrémités des fibres 
oules connecteurs de cloison peut entraîner une exposition à des 
rayonnements dangereux.
CAUTION
Use of controls or adjustments, or performance of procedures other 
than those specified herein, may result in hazardous radiation 
exposure.
ATTENTION
L’utilisation de commandes ou de réglages, ou l’application de tests de 
fonctionnement différents de ceux décrits ci-après peuvent entraîner 
l’exposition à des radiations dangereuses.
CAUTION
Do not connect power to the relay until you have completed these 
procedures and receive instruction to apply power. Equipment damage 
can result otherwise.
ATTENTION
Ne pas mettre le relais sous tension avant d’avoir complété ces 
procédures et d’avoir reçu l’instruction de brancher l’alimentation. Des 
dommages à l’équipement pourraient survenir autrement.
Other Safety Marks (Sheet 2 of 2)
xxxi
Date Code 20200603 Instruction Manual SEL-751 Relay
Preface
Manual Overview
General Information
Typographic 
Conventions
There are many ways to communicate with the SEL-751. The three primary 
methods are:
➤ Using a command line interface on a PC terminal emulation 
window.
➤ Using the two-line display front-panel menus and pushbuttons 
or the touchscreen display.
➤ Using QuickSet.
The instructions in this manual indicate these options with specific font and 
formatting attributes. The following table lists these conventions.
Trademarks All brand or product names appearing in this document are the trademark or 
registered trademark of their respective holders. No SEL trademarks may be 
used without written permission. 
SEL trademarks appearing in this manual are shown in the following table.
Examples This instruction manual uses several example illustrations and instructions to 
explain how to effectively operate the SEL-751. These examples are for 
demonstration purposes only; the firmware identification information or 
settings values included in these examples may not necessarily match those in 
the present version of your SEL-751.
Example Description
STATUS Commands typed at a command line interface on a PC.
<Enter> Single keystroke on a PC keyboard.
<Ctrl+D> Multiple/combination keystroke on a PC keyboard.
Start > Settings PC dialog boxes and menu selections.
The > character indicates submenus.
ENABLE Relay front- or rear-panel labels and pushbuttons.
Main > Meters Relay front-panel LCD menus and relay responses.
The > character indicates submenus.
ACSELERATOR Architect® SEL-2407®
ACSELERATOR QuickSet® SELOGIC®
Arc Sense™ SYNCHROWAVE®
Best Choice Ground Directional Element® time-overlight®
MIRRORED BITS®
xxxii
SEL-751 Relay Instruction Manual Date Code 20200603
Preface
Manual Overview
Product Labels The following two labels are the product labels for the high-voltage and low-
voltage power supply options. The product label is located on the left side 
panel of the product. The label shows the serial number, model number, and 
the ratings of the product.
Product Labels for the SEL-751
LED Emitter The following table shows LED information specific to the SEL-751 
(see Figure 2.9 for the location of the ports using these LEDs on the relay).
(High-Voltage Supply) (Low-Voltage Supply)
SEL-751 LED Information
Item
Fiber-Optic 
Ethernet Port 1 (1A, 1B)
Port 2
Arc-Flash 
Channel 1—8
Mode Multimode Multimode Multimode
Wavelength 1300 nm 820 nm 640 nm
Source LED LED LED
Connector type LC ST V-pin
Typical output power –15.7 dBm –16 dBm –12 dBm
CAUTION
Use of controls, adjustments, or 
performance of procedures other than 
those specified herein may result in 
hazardous radiation exposure.
CAUTION
Looking into optical connections, fiber 
ends, or bulkhead connections can 
result in hazardous radiation 
exposure.
xxxiii
Date Code 20200603 Instruction Manual SEL-751 Relay
Preface
Manual Overview
The following figure shows the LED location specific to the SEL-751 
(see Figure 2.9 for the complete rear-panel drawing).
SEL-751 LED Locations
Environmental 
Conditions and 
Voltage Information
The following table lists important environmental and voltage information.
LED Safety Warnings and Precautions
➤ Do not look into the end of an optical cable connected to an 
optical output.
➤ Do not look into the fiber ports/connectors.
➤ Do not perform any procedures or adjustments that are not 
described in this manual.
➤ During installation, maintenance, or testing of the optical 
ports only use test equipment classified as Class 1 laser 
products.
➤ Incorporated components such as transceivers and laser/LED 
emitters are not user serviceable. Units must be returned to 
SEL for repair or replacement.
Arc-Flash Detection 
LEDs for Self-Test
Fiber-Optic
Ethernet
Port LEDs
i5364a
Fiber-Optic 
Serial Port LED
Condition Range/Description
Indoor/outdoor use Indoor
Altitudea As high as 2000 m
Temperature
IEC Performance Rating
(per IEC/EN 60068-2-1 and IEC/EN 60068-2-2)
–40° to +85°C
Relative humidity 5% to 95%
xxxiv
SEL-751 Relay Instruction Manual Date Code 20200603
Preface
Manual Overview
Wire Sizes and 
Insulation
For wiring connections, use 105°C-rated wiring. Wire sizes for grounding 
(earthing), current, voltage, and contact connections are dictated by the 
terminal blocks and expected load currents. You can use the following table as 
a guide in selecting wire sizes. Refer to the application note Wiring SEL-2400, 
SEL-2200, and SEL-700 Series Devices (AN2014-08) for wiring and 
termination guidance. Strip the wires 8 mm (0.31 in) for installation and 
termination.
Instructions for 
Cleaning and 
Decontamination
Use a mild soap or detergent solution and a damp cloth to carefully clean the 
SEL-751 chassis when necessary. Clean the touchscreen display gently with a 
moist cotton cloth. Avoid using abrasive materials, polishing compounds, and 
harsh chemical solvents (such as xylene or acetone) on any surface of the 
relay.
Copyrighted Software The product includes copyrighted software licensed under the TI BSD End 
User Agreement, reproduced as follows:
Software License Agreement
Copyright © 2010 Texas Instruments Incorporated - http://www.ti.com/
Redistribution and use in source and binary forms, with or without 
modification, are permitted provided that the following conditions are met:
Redistributions of source code must retain the original copyright notice, 
this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the original copyright 
notice, this list of conditions and the following disclaimer in the 
documentation and/or other materials provided with the distribution.
Neither the name of Texas Instruments Incorporated nor the names of its 
contributorsmay be used to endorse or promote products derived from 
this software without specific prior written permission.
Main supply voltage fluctuations As high as ±10% of nominal 
voltage
Overvoltage Category II
Pollution Degree 2
Atmospheric pressure 80 to 110 kPa
a Consult the factory for derating specifications for higher altitude applications.
Condition Range/Description
Connection Type
Wire Size Insulation 
VoltageMinimum Maximum
Grounding (Earthing) 18 AWG (0.80 mm2) 14 AWG (2.10 mm2) 300 V min
Current 16 AWG (1.30 mm2) 12 AWG (3.30 mm2) 300 V min
Potential (Voltage) 18 AWG (0.80 mm2) 14 AWG (2.10 mm2) 300 V min
Contact I/O 18 AWG (0.80 mm2) 14 AWG (2.10 mm2) 300 V min
RTDa
a See Table 2.18: Typical Maximum RTD Lead Length.
28 AWG (0.08 mm2) 16 AWG (1.30 mm2) 300 V min
Other 18 AWG (0.80 mm2) 14 AWG (2.10 mm2) 300 V min
xxxv
Date Code 20200603 Instruction Manual SEL-751 Relay
Preface
Manual Overview
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 
CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED 
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 
THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY 
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 
USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE 
USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
OF SUCH DAMAGE.
Technical Support We appreciate your interest in SEL products and services. If you have ques-
tions or comments, please contact us at:
Schweitzer Engineering Laboratories, Inc.
2350 NE Hopkins Court
Pullman, WA 99163-5603 U.S.A. 
Tel: +1.509.338.3838 
Fax: +1.509.332.7990 
Internet: selinc.com/support
Email: info@selinc.com
https://selinc.com/support
https://selinc.com/support
https://selinc.com/support
mailto:info@selinc.com
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Date Code 20200603 Instruction Manual SEL-751 Relay
Section 1
Introduction and Specifications
Overview
The SEL-751 Feeder Protection Relay provides a comprehensive combination 
of protection, fault-locating features, monitoring, control, and communication 
in an industrial package. The base relay includes current, voltage, frequency, 
and power protection elements. Arc-flash detector-based, RTD-based, 
directional control-based, and high-impedance-based fault detection 
protection are available as options.
This manual contains the information necessary to install, set, test, operate, 
and maintain any SEL-751. You need not review the entire manual to perform 
specific tasks. 
Features
Protection Features The SEL-751 protection features depend on the model selected. The models 
are configured with specific current/voltages input cards. The current/voltage 
inputs cards are located in Slot Z and Slot E in the relay.
Slot Z cards are assigned a two-digit code beginning with the number “8” (for 
300 Vac phase voltage inputs), with the letter “L” (for 8 Vac LEA phase 
voltage inputs), or with the letter “A” (for no ac voltage inputs). The second 
number represents the phase and neutral CT ratings in the SEL-751 Model 
Options Table (MOT, see Models, Options, and Accessories). For example, 
“81” in the MOT for Slot Z indicates a SELECT 4 ACI/3 AVI card with 
three-phase ac current inputs (1 A nominal), neutral ac current input 
(1 A nominal), and three-phase ac voltage inputs (300 Vac).
Slot E cards are assigned a two-digit code beginning with the number “7” (for 
300 Vac voltage inputs) or the letter “L” (for 8 Vac LEA phase voltage inputs) 
in the SEL-751 Model Options Table (MOT). For example, “70” in the MOT 
for Slot E indicates a SELECT 2 AVI/4 AFDI card with Vsync (300 Vac), 
Vbat (300 V) input, and 4 arc-flash detection inputs.
Table 1.1 shows the phase and neutral current ratings choices for the different 
SEL-751 MOT choices. Phase current inputs are 1 A or 5 A nominal rating 
and neutral current inputs are 1 A, 5 A, or 200 mA nominal rating.
Table 1.1 Phase and Neutral Current Ratings Selection for the SEL-751 
Models (Sheet 1 of 2)
Current Rating MOT String Digit Number 15
1 Amp Phase, 1 Amp Neutral 1
1 Amp Phase, 5 Amp Neutral 2
1 Amp Phase, 200 mA Neutral 3
1.2
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Features
Table 1.2 shows current (ACI) and voltage (AVI) card selection for the 
SEL-751 models.
The SEL-751 offers an extensive variety of protection features, depending on 
the model and options selected. Table 1.3 lists the protection features available 
in different models.
5 Amp Phase, 5 Amp Neutral 5
5 Amp Phase, 1 Amp Neutral 6
5 Amp Phase, 200 mA Neutral 7
Table 1.1 Phase and Neutral Current Ratings Selection for the SEL-751 
Models (Sheet 2 of 2)
Current Rating MOT String Digit Number 15
Table 1.2 Current (ACI) and Voltage (AVI) Card Selection for SEL-751 Models
Model Description
Slot Z Card Option
(MOT String Digital 
Number 14, 15)
Slot Z Inputs
Slot E Card 
Option 
(MOT String 
Digits Number 
12, 13)
Slot E Inputs
Base SEL-751 AC Currents Only 4 ACI
(A1, A2, A3, A5, A6, A7)
IA, IB, IC, IN None (0X) None
SEL-751 With AC Voltages (300 Vac) 4 ACI/3 AVI
(81, 82, 83, 85, 86, 87)
IA, IB, IC, IN, 
VA, VB, VC
None (0X) None
SEL-751 With LEA AC Voltages (8 Vac) 4 ACI/3 AVI
(L1, L2, L3, L5, L6, L7)
IA, IB, IC, IN, 
VA, VB, VC
None (0X) None
SEL-751 With AC Phase Voltages (300 Vac), 
Vsync (300 Vac), Vbat (300 V) Input, and 
4 Arc-Flash Detections Inputs
4 ACI/3 AVI
(81, 82, 83, 85, 86, 87)
IA, IB, IC, IN, 
VA, VB, VC
2 AVI/4 AFDI 
(70)
VS, VBAT, AF1, 
AF2, AF3, AF4
SEL-751 With LEA AC Phase Voltages 
(8 Vac), LEA Vsync (8 Vac), Vbat (300 V) 
Input, and 4 Arc-Flash Detection Inputs
4 ACI/3 AVI
(L1, L2, L3, L5, L6, L7)
IA, IB, IC, IN, 
VA, VB, VC
2 AVI/4 AFDI 
(L0)
VS, VBAT, AF1, 
AF2, AF3, AF4
Table 1.3 SEL-751 Protection Elements (Sheet 1 of 3)
Protection Element
Slot Z 4 ACI Card 
(Current Only Model) 
With 1 A or 5 A 
Neutral Channel
Slot Z 4 ACI/3 AVI 
Card With 1 A or 5 A 
Neutral Channel
Slot Z 4 ACI/3 AVI 
Card With 200 mA 
Neutral Channel
50P Max. Phase Overcurrent X X X
67P Max. Phase Overcurrent With 
Directional Control
Xa Xb
50Q Neg.-Seq. Overcurrent X X X
67Q Neg.-Seq. Overcurrent With 
Directional Control
Xa Xb
50G Residual Overcurrent X X X
67G Residual Overcurrent With 
Directional Control
Xa Xb
50N Neutral Overcurrent X X X
67N Neutral Overcurrent With 
Directional Control
Xb
50INC Incipient Cable Fault X X X
1.3
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Features
51mP Phase Time Overcurrent 
(m = A, B, C)
X X X
51P Max. Phase Time Overcurrent X X X
51P Max. Phase Time Overcurrent With 
Directional Control
Xa Xb
51G Residual Time Overcurrent X X X
51G Residual Time Overcurrent With 
Directional Control
Xa Xb
51Q Neg.-Seq. Time Overcurrent X X X
51Q Neg.-Seq. Time Overcurrent With 
Directional Control
Xa Xb
51N Neutral Time Overcurrent X X X
51N Neutral Time Overcurrent With 
Directional Control
Xb
SEF Sensitive Earth Fault X
HBL Second- and Fifth-Harmonic 
Blocking
X X X
FLOC Fault Locator X X
27 Undervoltage 
(Phase, Phase-to-Phase, Vsync)
X X
59 Overvoltage (Phase, 
Phase-to-Phase, Seq., Vsync)
X X
27I Inverse Time Undervoltage X X
59I Inverse Time Overvoltage X X
60LOP Loss of Potential X X
32 Directional Power X X
49T IEC Thermal (line/cable) X X X
55 Power Factor X X
78VS Vector Shift X X
81 Over- and Underfrequency X X X
81R Rate-of-Change of Frequency X X
81RF Fast Rate-of-Change of Frequency X X
25 Synchronism Check Xc Xc
BF Breaker Failure X X X
49RTD RTDs Xd Xd Xd
79 Reclosing Xd Xd Xd
Table 1.3 SEL-751 Protection Elements (Sheet 2 of3)
Protection Element
Slot Z 4 ACI Card 
(Current Only Model) 
With 1 A or 5 A 
Neutral Channel
Slot Z 4 ACI/3 AVI 
Card With 1 A or 5 A 
Neutral Channel
Slot Z 4 ACI/3 AVI 
Card With 200 mA 
Neutral Channel
1.4
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Features
Front-Panel Options The SEL-751 offers four front-panel HMI layouts that are model and option 
dependent. Table 1.4 lists the HMI options for the SEL-751 front panel.
Monitoring Features ➤ Event summaries that contain relay ID, date and time, trip 
cause, and current/voltage magnitudes
➤ Event reports including filtered and raw analog data
➤ Sequential Events Recorder (SER)
➤ Compatibility with SEL-3010 Event Messenger
➤ A complete suite of accurate metering functions
➤ Breaker wear monitoring
➤ Load profile report
➤ HIF compressed event report (option)
Communications and 
Control Features ➤ EIA-232, front-panel port
➤ EIA-232, EIA-485, single or dual, copper or fiber-optic 
Ethernet, and fiber-optic rear-panel EIA-232 ports
➤ Built-in web server
➤ IRIG-B time-code input
➤ Modbus RTU slave, Modbus TCP/IP, Simple Network Time 
Protocol (SNTP), IEEE 1588-2008 firmware-based Precision 
Time Protocol (PTP), DNP3 serial, DNP3 LAN/WAN, 
HIF AST High-Impedance Fault (HIF) Detec-
tion With Arc Sense Technology
Xd Xd
AFD Arc-Flash Detection Xd Xd Xd
a Available when ordered with the directional option. The 1 A/5 A neutral channel is suitable for solidly grounded systems and also 
impedance-grounded systems, depending on the available fault current level.
b Available when ordered with the directional option. The 200 mA neutral channel is suitable for ungrounded, low-impedance grounded, 
high-impedance grounded, and Petersen coil grounded applications.
c Available with the 2 AVI/4 AFDI card in Slot E.
d Available as ordering options.
Table 1.3 SEL-751 Protection Elements (Sheet 3 of 3)
Protection Element
Slot Z 4 ACI Card 
(Current Only Model) 
With 1 A or 5 A 
Neutral Channel
Slot Z 4 ACI/3 AVI 
Card With 1 A or 5 A 
Neutral Channel
Slot Z 4 ACI/3 AVI 
Card With 200 mA 
Neutral Channel
Table 1.4 SEL-751 Front-Panel Options
Model/Display Descriptiona
Front-Panel Option 
(MOT String Digit 
Number 16)
Number of 
Pushbuttons
LED Type
SEL-751 With Two-Line Display
(2 x 16 characters)
1 4 Tricolor
SEL-751 With Two-Line Display
(2 x 16 characters)
0 8 Tricolor
SEL-751 With Touchscreen Display
(5-inch, color, 800 x 480 pixels)
A 8 Tricolor
SEL-751 With Touchscreen Display
(5-inch, color, 800 x 480 pixels)
B 4 Tricolor
a For ordering options, refer to the SEL-751 MOT.
1.5
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Models, Options, and Accessories
Ethernet FTP, Telnet, MIRRORED BITS, Event Messenger, 
IEC 61850 Edition 2, IEC 60870-5-103, DeviceNet, 
EtherNet/IP, and Synchrophasors with C37.118 Protocol
➤ SEL ASCII, Compressed ASCII, Fast Meter, Fast Operate, Fast 
SER, and Fast Message Protocols
➤ Programmable Boolean and math operators, logic functions, 
and analog compare
Language Support ➤ The standard relay front-panel overlay is in English; a Spanish 
overlay is available as an ordering option. Text displayed on the 
HMI display will correspond to the ENGLISH or SPANISH 
ordering option.
➤ All of the ASCII command responses can be displayed in 
English or Spanish. When you set the port setting LANG to 
either ENGLISH or SPANISH, the SEL-751 ASCII commands 
display in the corresponding language.
➤ The web server reports can be displayed in English or Spanish 
by setting the Ethernet Port 1 setting LANG to either 
ENGLISH or SPANISH.
Models, Options, and Accessories
Models Complete ordering information is not provided in this instruction manual. See 
the latest Model Option Table for the SEL-751 at selinc.com, under Support > 
Product Literature > Ordering Information (Model Option Tables). Options 
and accessories are as follows:
SEL-751 Base Unit ➤ Front panel with two-line display or with touchscreen display
➢ Four programmable pushbuttons, each with two tricolor 
LEDs 
➢ Eight target tricolor LEDs (six programmable)
➢ Operator control interface
➢ EIA-232 port
➤ Power supply card with two digital inputs and three digital 
outputs (Slot A)
➤ Processor and communications card (Slot B)
➢ EIA-232 serial port with IRIG-B time-code input
➤ Three expansion slots for optional cards (Slots C, D, E)
➤ Four ac current inputs (1 A/5 A/200 mA neutral only) (Slot Z)
➤ Protocols
➢ Modbus RTU
➢ SEL ASCII and Compressed ASCII
➢ SEL Fast Meter, Fast Operate, Fast SER, Fast Message
➢ Ymodem File Transfer
➢ SEL MIRRORED BITS
➢ Event Messenger
➢ Synchrophasors with C37.118
➤ Breaker wear monitoring
https://selinc.com
1.6
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Models, Options, and Accessories
Options ➤ Firmware options
➢ Autoreclosing control
➢ Directional control for overcurrent elements (solid or 
low-impedance grounded systems only)
➢ Advanced directional control for overcurrent elements 
(low-impedance grounded systems; ungrounded, high-
impedance grounded systems; and Petersen coil-
grounded systems—requires 200 mA neutral CT) 
➢ HIF detection using Arc Sense technology
➤ Current/Voltage input options (see Table 1.1 and Table 1.2)
➤ 2 AVI/4 AFDI card option with
➢ Synchronism-check voltage input (300 V or 8 V LEA)
➢ DC station battery monitor
➢ 4 arc-flash detector inputs
➤ 8 AFDI card option
➢ 8 arc-flash detector inputs
➤ Input/output (I/O) options 
➢ Additional digital I/O (4 DI/4 DO, 4 DI/3 DO, 8 DI, 
8 DO, 3 DI/4 DO/1 AO, 14 DI)
➢ Additional analog I/O (4 AI/4 AO, 8 AI)
➢ 10 RTD inputs
➤ Front-panel HMI options (see Table 1.4)
➤ Communications options (protocol/ports)
➢ EIA-485/EIA-232/Fiber-optic EIA-232/Ethernet ports 
(single/dual, copper or fiber-optic)
➢ SNTP
➢ FTP
➢ PTP (firmware-based)
➢ PRP
➢ Modbus TCP/IP 
➢ IEC 61850 Edition 2
➢ IEC 60870-5-103
➢ EtherNet/IP
➢ DNP3 serial and LAN/WAN
➢ DeviceNet (Note: This option has been discontinued 
and is no longer available as of September 25, 2017.)
➤ Language options
➢ The relay supports English or Spanish language as an 
ordering option
1.7
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Applications
Accessories Contact your Technical Service Center or the SEL factory for additional detail 
and ordering information for the following accessories:
➤ External RTD protection
➢ SEL-2600 RTD Module (with ST option only)
➢ A simplex 62.5/125 µm fiber-optic cable with ST 
connector for connecting the external RTD module to 
the SEL-751
➤ SEL-2505 Remote I/O Module (with SEL-2812 compatible ST 
fiber-optic port) for connection to relay fiber-optic serial Port 2, 
or use SEL-2505 with EIA-232 (DB-9) serial port to connect to 
EIA-232 Port 3 on the relay.
➤ SEL-C804 and SEL-C814 Multimode Fiber-Optic Arc-Flash 
Detection (AFD) Sensors and Accessories
➤ SEL-751 Configurable Labels
➤ Rack-Mounting Kits
➢ For one relay
➢ For two relays 
➢ For one relay and a test switch
➤ Wall-Mounting Kits
➤ Bezels for Retrofit
➤ Replacement Rear Connector Kit
➤ Dust Protection Kit
➤ Relay Wire Termination Kits—See Application Note 
AN2014-08.
For all SEL-751 mounting accessories for competitor products, including 
adapter plates, visit selinc.com/applications/mountingselector/.
Applications
The SEL-751 Feeder Protection Relay has many power system protection, 
monitoring, and control applications. Figure 1.1 shows some of the typical 
protection applications for the SEL-751. You can use the SEL-751 directional 
and nondirectional overcurrent functions to protect virtually any power system 
circuit or device including lines, feeders, transformers, capacitor banks, 
reactors, and generators. Over- and underfrequency, over- and undervoltage, 
and synchronism-check elements are well suited for applications at distributed 
generation sites.Directional power elements in the SEL-751 also make the 
relay suitable for utility or customer interface protection where customer 
generation is present.
You can use powerful SELOGIC control equations in all SEL-751 models to 
provide custom protection and control applications. SEL application guides 
and technical support personnel are available to help with unique applications.
https://selinc.com/applications/mountingselector/
1.8
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Applications
Figure 1.1 SEL-751 Feeder Protection Relay Applied Throughout the Power System
Section 2: Installation includes ac and dc connection diagrams for various 
applications. The following is a list of other possible application scenarios:
➤ With internal or external RTD module for thermal protection
➤ With arc-flash detection and protection
➤ HIF detection and protection for feeders
Transformer Bank 
Protection 
Core-Balance
Current Transformer
N
N
Trip
AB
C
ABC
VABC VS
VABC
VS
Distribution Bus
Distributed Generation
Fast Bus Trip Scheme
Utility Distribution 
Feeder Protection 
and Reclosing 
Industrial Distribution
Feeder Protection 
AB
C
AB
C
Trip
Trip
Distribution Bus 
Protection
52
52
52
52
52
Trip and
Close
SEL-751
SEL-751
SEL-751
SEL-751
SEL-751
SEL-751
G
1.9
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Getting Started
Figure 1.2 shows typical current connections. Refer to Section 2: Installation 
for additional applications and the related connection diagrams.
Figure 1.2 Typical Current Connections
Getting Started
Understanding basic relay operation principles and methods will help you use 
the SEL-751 effectively. This section presents the fundamental knowledge 
you need to operate the SEL-751, organized by task. These tasks help you 
become familiar with the relay and include the following:
➤ Powering the Relay
➤ Establishing Communication
➤ Checking the Relay Status
➤ Setting the Date and Time
Perform these tasks to gain a fundamental understanding of relay operation.
Powering the Relay Power the SEL-751 with 110–240 Vac, 110–250 Vdc or 24–48 Vdc, 
depending on the part number.
➤ Observe proper polarity, as indicated by the +/H (Terminal A01) 
and the –/N (Terminal A02) on the power connections.
➤ Connect the ground lead; see Grounding (Earthing) 
Connections on page 2.24.
➤ Once connected to power, the relay does an internal self-check 
and the ENABLED LED illuminates.
SEL-751
The current transformers and the SEL-751 
chassis must be grounded in the relay cabinet.
A
B
C
IN
IC
IB
IA
Z08
Z07
Z06
Z05
Z04
Z03
Z02
Z01
52
FEEDER
BUS
1.10
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Getting Started
Establishing 
Communication
The SEL-751 has three EIA-232 serial communications ports. The following 
steps require PC terminal emulation software and an SEL-C234A Cable 
(or equivalent) to connect the SEL-751 to the PC. See Section 7: 
Communications for further information on serial communications 
connections and the necessary cable pinout.
Step 1. Connect the PC and the SEL-751 by using the serial 
communications cable.
Step 2. Apply power to both the PC and the relay.
Step 3. Start the PC terminal emulation program.
Step 4. Set the PC terminal emulation program to the communications 
port settings listed in the Default Value column of Table 1.5. 
Also, set the terminal program to emulate either VT100 or 
VT52 terminals.
Step 5. Press the <Enter> key on the PC keyboard to check the 
communications link.
You will see the = prompt at the left side of the computer screen 
(column 1). 
If you do not see the = prompt, check the cable connections, 
and confirm that the settings in the terminal emulation program 
are the default values in Table 1.5.
Step 6. Type QUIT <Enter> to view the relay report header.
You will see a computer screen display similar to Figure 1.3. If 
you see jumbled characters, change the terminal emulation type 
in the PC terminal emulation program.
Step 7. Type ACC <Enter> and the appropriate password 
(see Table 7.40 for factory-default passwords) to go to 
Access Level 1.
Step 8. Type QUIT <Enter> to view the relay report header.
Table 1.5 SEL-751 Serial Port Settings
Description Setting Label Default Value
SPEED SPEED 9600
DATA BITS BITS 8
PARITY PARITY N
STOP BITS STOP 1
PORT TIMEOUT T_OUT 5
HWDR HANDSHAKING RTSCTS N
=>QUIT <Enter>
Feeder xyz Date: 03/10/2011 Time: 10:31:43
Station 1 Time Source: Internal
=
Figure 1.3 Response Header
1.11
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Getting Started
Checking the 
Relay Status
Use the STA serial port command to view the SEL-751 operational status. 
Note that offsets are shown only when the relay is online and tracking 
frequency. If the DC offset exceeds a warning threshold, the analog value has 
a “w” next to it. Analog channel dc offset and monitored component status are 
listed in the status report depicted in Figure 1.4.
If a communications card with the DeviceNet protocol is present, the status 
report depicted in Figure 1.5 applies. If a communications card with Modbus 
RTU protocol is present, the status report depicted in Figure 1.4 applies.
=>>STA <Enter>
SEL-751 Date: 01/24/2017 Time: 14:06:58.751
FEEDER RELAY Time Source: Internal
Serial Num = 012345678901234
FID = SEL-751-X386-V0-Z007002-D20170116 CID = B3B2
PART NUM = 751301B6X6X7081A23X
SELF TESTS (W=Warn)
 FPGA GPSB HMI RAM ROM CR_RAM NON_VOL CLOCK CID_FILE +0.9V +1.2V
 OK OK OK OK OK OK OK OK OK 0.90 1.20
 +1.5V +1.8V +2.5V +3.3V +3.75V +5.0V -1.25V -5.0V BATT
 1.50 1.80 2.50 3.33 3.74 5.04 -1.25 -5.01 3.10
Option Cards
 CARD_C CARD_D CARD_E CARD_Z
 OK OK OK OK
Offsets
 IA IB IC IN VA VB VC VS
 12 12 12 8 -4 -7 -5 -7
 Relay Enabled
=>>
Figure 1.4 STA Command Response—No Communications Card or EIA-232/
EIA-485 Communications Card
=>STA <Enter>
SEL-751 Date: 03/14/2011 Time: 14:03:48.984
FEEDER RELAY Time Source: Internal
Serial Num = 000000000000000
FID = SEL-751-X139-V0-Z001001-D20110309 CID = 05A2
PART NUM = 751501BA3CA70860230
SELF TESTS (W=Warn)
 FPGA GPSB HMI RAM ROM CR_RAM NON_VOL CLOCK CID_FILE +0.9V +1.2V
 OK OK OK OK OK OK OK OK OK 0.90 1.20
 +1.5V +1.8V +2.5V +3.3V +3.75V +5.0V -1.25V -5.0V BATT
 1.50 1.80 2.51 3.35 3.77 4.98 -1.26 -5.04 3.04
Option Cards
 CARD_C CARD_D CARD_E CARD_Z
 OK OK OK OK
DeviceNet
 DN_MAC_ID ASA DN_RATE DN_STATUS
 4 1a25 df42h AUTO 0000 0000
Offsets
 IA IB IC IN VA VB VC VS
 12 12 12 8 -4 -7 -5 -7
 Relay Enabled
=>
Figure 1.5 STA Command Response—Communications Card/DeviceNet 
Protocol
1.12
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Getting Started
Table 7.51 provides the definition of each status report designator and 
Table 11.8 shows all the self-tests performed by the relay. The beginning of 
the status report printout (see Figure 1.5) contains the relay serial number, 
firmware identification string (FID), and checksum string (CID). These strings 
uniquely identify the relay and the version of the operating firmware.
Setting the 
Date and Time
DAT (Date Command)
Viewing the Date
Type DAT <Enter> at the prompt to view the date stored in the SEL-751. If 
the date stored in the relay is July 29, 2010, and the DATE_F setting is MDY, 
the relay replies:
7/29/2010
If the DATE_F setting is YMD, the relay replies:
2010/7/29If the DATE_F setting is DMY, the relay replies:
29/7/2010
Changing the Date
Type DAT followed by the correct date at the prompt to change the date stored 
in the relay. For example, to change the date to May 2, 2010 
(DATE_F := MDY), enter the following at the action prompt:
DAT 5/2/10
You can separate the month, day, and year parameters with spaces, commas, 
slashes, colons, and semicolons.
TIM (Time Command)
Viewing the Time
Enter TIM at the prompt to view the time stored in the SEL-751. The relay 
replies with the stored time. For example
13:52:44
This time is 1:52 p.m. (and 44 seconds).
Changing the Time
Enter TIM followed by the correct time at the action prompt to change the 
time stored in the relay. For example, to change the time to 6:32 a.m., enter the 
following at the prompt:
TIM 6:32:00
You can separate the hours, minutes, and seconds parameters with spaces, 
commas, slashes, colons, and semicolons.
1.13
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Specifications
Specifications
Compliance
Designed and manufactured under an ISO 9001 certified quality 
management system
47 CFR 15B, Class A
Note: This equipment has been tested and found to comply with the 
limits for a Class A digital device, pursuant to part 15 of the FCC 
Rules. These limits are designed to provide reasonable protection 
against harmful interference when the equipment is operated in a 
commercial environment. This equipment generates, uses, and can 
radiate radio frequency energy and, if not installed and used in 
accordance with the instruction manual, may cause harmful 
interference to radio communications. Operation of this equipment in 
a residential area is likely to cause harmful interference in which case 
the user will be required to correct the interference at his own 
expense.
UL Listed to U.S. and Canadian safety standards (File E212775, 
NRGU, NRGU7)
Note: UL has not yet developed requirements for products intended to 
detect and mitigate an arc flash; consequently, UL has not evaluated 
the performance of this feature. While UL is developing these 
requirements, it will place no restriction on the use of this product for 
arc-flash detection and mitigation. For test results performed by an 
independent laboratory and other information on the performance and 
verification of this feature, please contact SEL customer service.
CE Mark
RCM Mark
Hazardous Locations
UL Certified for Hazardous Locations to U.S. and Canadian standards 
CL 1, DIV 2; GP A, B, C, D; T3C, maximum surrounding air 
temperature of 50°C (File E470448)
EU
EN 60079-0:2012 + A11:2013, EN 60079-7:2015, 
EN 60079-15:2010, EN 60079-11:2012
Ambient air temperature shall not exceed –20°C  Ta  +50°C
Note: Where so marked, ATEX and UL Hazardous Location 
Certification tests are applicable to rated supply specifications only 
and do not apply to the absolute operating ranges, continuous thermal, 
or short circuit duration specifications.
General
AC Current Input
INOM = 200 mA, 1 A, or 5 A secondary, depending on the model.
Measurement Category: II
Phase and Neutral Currents
INOM = 5 A 
Continuous Rating: 3 • INOM @ 85°C 
4 • INOM @ 55°C
A/D Measurement Limit: 217 A peak (154 A rms symmetrical)
Saturation Current Rating: Linear to 96 A symmetrical
1-Second Thermal: 500 A
Burden (per phase): <0.1 VA @ 5 A
INOM = 1 A
Continuous Rating: 3 • INOM @ 85°C
4 • INOM @ 55°C
A/D Measurement Limit: 43 A peak (31 A rms symmetrical) 
Saturation Current Rating: Linear to 19.2 A symmetrical
1-Second Thermal: 100 A
Burden (per phase): <0.01 VA @ 1 A
INOM = 200 mA
Continuous Rating: 4 A, linear to 4 A symmetrical
A/D Measurement Limit: 20 A peak (14 A rms symmetrical)
1-Second Thermal: 500 A
Burden (per phase): <0.01 VA @ 0.2 A
AC Voltage Input
VNOM (L-L) Setting Range: 20–250 V (if DELTA_Y:= DELTA)
20–480 V (if DELTA_Y := WYE)
300 Vac Voltage Inputs
Rated Continuous Voltage: 300 Vac (phase-to-neutral)
10-Second Thermal: 600 Vac (phase-to-neutral)
Low-Energy Analog (LEA) Voltage Inputs
Rated Continuous Voltage: 8 Vac (phase-to-neutral)
Nominal LEA Voltage: 0.5–6.8 Vrms (phase-to-neutral)
Input Range: ±12 Vpeak
10-Second Thermal: 300 Vac (phase-to-neutral)
Burden: 0.0001 VA
Input Impedance: 2 M single-ended (phase-to-neutral)
4 M differential (phase-to-phase)
Power Supply
Relay Start-Up Time: Approximately 5–10 seconds (after 
power is applied until the ENABLED 
LED turns on)
High-Voltage Supply
Rated Supply Voltage: 110–240 Vac, 50/60 Hz
110–250 Vdc
Input Voltage Range 
(Design Range):
85–264 Vac
85–300 Vdc
Power Consumption: <50 VA (ac)
<25 W (dc)
Interruptions: 50 ms @ 125 Vac/Vdc
100 ms @ 250 Vac/Vdc
Low-Voltage Supply
Rated Supply Voltage: 24–48 Vdc
Input Voltage Range 
(Design Range):
19.2–60.0 Vdc
Power Consumption: <25 W (dc)
Interruptions: 10 ms @ 24 Vdc
50 ms @ 48 Vdc
Burden
Input Impedance 
(Per Phase)
Input Impedance 
(Phase-to-Phase)
Vphase 0.008 VA @ 120 Vac 2 M 4 M
Vbat/Vs 0.003 VA @ 120 Vac 5 M
1.14
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Specifications
Fuse Ratings
Low-Voltage Power Supply Fuse
Rating: 3.15 A
Maximum Rated Voltage: 300 Vdc, 250 Vac
Breaking Capacity: 1500 A at 250 Vac
Type: Time-lag T
High-Voltage Power Supply Fuse
Rating: 3.15 A
Maximum Rated Voltage: 300 Vdc, 250 Vac
Breaking Capacity: 1500 A at 250 Vac
Type: Time-lag T
Output Contacts
General
The relay supports Form A, B, and C outputs.
Dielectric Test Voltage: 2500 Vac
Impulse Withstand Voltage 
(UIMP): 5000 V
Mechanical Durability: 100,000 no-load operations
Standard Contacts
Pickup/Dropout Time: 8 ms (coil energization to contact 
closure)
DC Output Ratings
Rated Operational Voltage: 250 Vdc
Rated Voltage Range: 19.2–275 Vdc
Rated Insulation Voltage: 300 Vdc
Make: 30 A @ 250 Vdc per IEEE C37.90
Continuous Carry: 6 A @ 70°C
4 A @ 85°C
1-Second Thermal: 50 A
Contact Protection: 360 Vdc, 115 J MOV protection across 
open contacts
Breaking Capacity (10,000 Operations) per IEC 60255-0-20:1974:
24 Vdc 0.75 A L/R = 40 ms
48 Vdc 0.50 A L/R = 40 ms
125 Vdc 0.30 A L/R = 40 ms
250 Vdc 0.20 A L/R = 40 ms
Cyclic (2.5 Cycles/Second) per IEC 60255-0-20:1974:
24 Vdc 0.75 A L/R = 40 ms
48 Vdc 0.50 A L/R = 40 ms
125 Vdc 0.30 A L/R = 40 ms
250 Vdc 0.20 A L/R = 40 ms
AC Output Ratings
Maximum Operational 
Voltage (Ue) Rating: 240 Vac
Insulation Voltage (Ui) Rating 
(excluding EN 61010-1): 300 Vac
1-Second Thermal: 50 A
Contact Rating Designation: B300
B300 (5 A Thermal Current, 300 Vac Max)
Maximum Current Max VA
Voltage 120 Vac 240 Vac —
Make 30 A 15 A 3600
Break 3 A 1.5 A 360
PF < 0.35, 50–60 Hz
Utilization Category: AC-15
Voltage Protection Across 
Open Contacts:
270 Vac, 40 J
Fast Hybrid (High-Speed, High-Current Interrupting)
DC Output Ratings
Rated Operational Voltage: 250 Vdc
Rated Voltage Range: 19.2–275 Vdc
Rated Insulation Voltage: 300 Vdc
Make: 30 A @ 250 Vdc per IEEE C37.90
Carry: 6 A @ 70°C
4 A @ 85°C
1-Second Thermal: 50 A
Open State Leakage Current: <500 µA
MOV Protection (maximum 
voltage): 250 Vac/330 Vdc
Pickup Time: <50 s, resistive load
Dropout Time: <8 ms, resistive load
Breaking Capacity (10,000 Operations) per IEC 60255-0-20:1974:
48 Vdc 10.0 A L/R = 40 ms
125 Vdc 10.0 A L/R = 40 ms
250 Vdc 10.0 A L/R = 20 ms
Cyclic Capacity (4 Cycles in 1 Second, Followed by 2 Minutes Idle for 
Thermal Dissipation) per IEC 60255-0-20:1974:
48 Vdc 10.0 A L/R = 40 ms
125 Vdc 10.0 A L/R = 40 ms
250 Vdc 10.0 A L/R = 20 ms
AC Output Ratings
See AC Output Ratings for Standard Contacts.
Optoisolated Control Inputs
When Used With DC Control Signals
Pickup/Dropout Time: Depends on the input debounce settings
250 V: ON for 200.0–312.5 Vdc
OFF below 150 Vdc
220 V: ON for 176–275 Vdc
OFF below 132 Vdc
125 V: ON for 100.0–156.2 Vdc
OFF below 75 Vdc
110 V: ON for 88.0–137.5 Vdc
OFF below 66 Vdc
48 V: ON for 38.4–60.0 Vdc
OFF below 28.8 Vdc
24 V: ON for 15–30Vdc
OFF below 5 Vdc
When Used With AC Control Signals
Pickup Time: 2 ms
Dropout Time: 16 ms
250 V: ON for 170.6–312.5 Vac
OFF below 106 Vac
220 V: ON for 150.2–275 Vac
OFF below 93.3 Vac
AC-15
Operational Voltage (Ue) 120 Vac 240 Vac
Operational Current (Ie) 3 A 1.5 A
Make Current 30 A 15 A
Break Current 3 A 1.5 A
Electromagnetic loads > 72 VA, PF < 0.3, 50–60 Hz
1.15
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Specifications
125 V: ON for 85–156.2 Vac
OFF below 53 Vac
110 V: ON for 75.1–137.5 Vac
OFF below 46.6 Vac
48 V: ON for 32.8–60 Vac
OFF below 20.3 Vac
24 V: ON for 14–30 Vac
OFF below 5 Vac
Current Draw at Nominal DC 
Voltage:
2 mA (at 220–250 V)
4 mA (at 48–125 V)
10 mA (at 24 V)
Rated Impulse Withstand 
Voltage (Uimp): 4000 V
Analog Output (Optional)
1 A0 4 A0
Current: 4–20 mA ±20 mA
Voltage: — ±10 V
Load at 1 mA: — 0–15 k
Load at 20 mA: 0–300  0–750 
Load at 10 V: — >2000 
Refresh Rate: 100 ms 100 ms
% Error, Full Scale, at 25°C: <±1% <±0.55%
Select From: Analog quantities available in the relay
Analog Inputs (Optional)
Maximum Input Range: ±20 mA
±10 V
Operational range set by user
Input Impedance: 200 (current mode)
>10 k (voltage mode)
Accuracy at 25°C
With User Calibration: 0.05% of full scale (current mode)
0.025% of full scale (voltage mode)
Without User Calibration: Better than 0.5% of full scale at 25°C
Accuracy Variation With 
Temperature:
±0.015% per °C of full-scale 
(±20 mA or ±10 V)
Arc-Flash Detectors (Optional)
Multimode fiber-optic receiver/transmitter pair
Fiber Type: 1000 µm diameter, 640 nm wavelength, 
plastic, clear-jacketed, or black-
jacketed
Connector Type: V-pin
Frequency and Phase Rotation
System Frequency: 50, 60 Hz
Phase Rotation: ABC, ACB
Frequency Tracking: 15–70 Hz
Time-Code Input
Format: Demodulated IRIG-B
On (1) State: Vih 2.2 V
Off (0) State: Vil  0.8 V
Input Impedance: 2 k
Synchronization Accuracy
Internal Clock: ±1 µs
Synchrophasor Reports 
(e.g., MET PM): ±10 µs
All other reports: ±5 ms
SNTP Accuracy: ±2 ms
PTP Accuracy: ±1 ms
Unsynchronized Clock Drift 
Relay Powered: 2 minutes per year typical
Communications Ports
Standard EIA-232 (2 ports)
Location: Front Panel
Rear Panel
Data Speed: 300–38400 bps
EIA-485 Port (optional)
Location: Rear panel
Data Speed: 300–19200 bps
Ethernet Port (optional)
Single/Dual 10/100BASE-T copper (RJ45 connector)
Single/Dual 100BASE-FX (LC connector)
EIA-232 Multimode Fiber-Optic Port (Optional)
Location: Rear panel
Data Speed: 300–38400 bps
Fiber-Optic Ports Characteristics
Port 1 (or 1A, 1B) Ethernet
Wavelength: 1300 nm
Optical Connector Type: LC
Fiber Type: Multimode
Link Budget: 16.1 dB
Typical TX Power: –15.7 dBm
RX Min. Sensitivity: –31.8 dBm
Fiber Size: 62.5/125 µm
Approximate Range: ~6.4 km
Data Rate: 100 Mbps
Typical Fiber Attenuation: –2 dB/km
Port 2 Serial
Wavelength: 820 nm
Optical Connector Type: ST
Fiber Type: Multimode
Link Budget: 8 dB
Typical TX Power: –16 dBm
RX Min. Sensitivity: –24 dBm
Fiber Size: 62.5/125 µm
Approximate Range: ~1 km
Data Rate: 5 Mbps
Typical Fiber Attenuation: –4 dB/km
 Channels 1-8 Arc-Flash Detectors (AFDI)
Diagnostic Wavelength: 640 nm
Optical Connector Type: V-pin
Fiber Type: Multimode
Typical TX Power: –12 dBm
1.16
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Specifications
Point Sensor
Minimum Receive 
Sensitivity: –52.23 dB
Point Sensor Diagnostic 
Worst Case Loss: –28 dB
Link Budget: 12.23 dB
Black-Jacketed Fiber Worst 
Case Loss: –0.19 dBm
Black-Jacketed Fiber Typical 
Loss: –0.17 dBm
ST or V-Pin Connector Splice 
Loss: –2.00 dB
Approximate Range: As much as 35 m 
Fiber Sensor
Minimum Receive 
Sensitivity: –29.23 dB
Link Budget: 17.23 dB
Clear-Jacketed Fiber Worst 
Case Loss: –0.19 dBm
Clear-Jacketed Fiber Typical 
Loss: –0.17 dBm
ST or V-Pin Connector Splice 
Loss: –2.00 dB
Approximate Range: As much as 70 m 
Optional Communications Cards
Option 1: EIA-232 or EIA-485 communications 
card
Option 2: DeviceNet communications card
Communications Protocols
SEL, Modbus RTU and TCP/IP, DNP3 serial and LAN/WAN, FTP, 
Telnet, SNTP, IEEE 1588-2008 firmware-based PTP, IEC 61850 
Edition 2, IEC 60870-5-103, EtherNet/IP, PRP, MIRRORED BITS, 
EVMSG, IEEE C37.118 (synchrophasors), and DeviceNet
Operating Temperature
IEC Performance Rating: –40 to +85C (–40 to +185F)
(per IEC/EN 60068-2-1 and 
IEC/EN 60068-2-2)
Note: Not applicable to UL applications.
Note: The front-panel display is impaired for temperatures below 
–20°C and above +70°C.
DeviceNet Communications 
Card Rating: +60°C (+140°F) maximum
Optoisolated Control Inputs: As many as 26 inputs are allowed in 
ambient temperatures of 85°C or less
As many as 34 inputs are allowed in 
ambient temperatures of 75°C or less
As many as 44 inputs are allowed in 
ambient temperatures of 65°C or less
Operating Environment
Insulation Class: 1
Pollution Degree: 2
Overvoltage Category: II
Atmospheric Pressure: 80–110 kPa
Relative Humidity: 5%–95%, noncondensing
Maximum Altitude Without 
Derating (Consult the 
Factory for Higher Altitude 
Derating): 2000 m
Dimensions
144.0 mm (5.67 in) x 192.0 mm (7.56 in) x 147.4 mm (5.80 in)
Weight
2.7 kg (6.0 lb)
Relay Mounting Screw (#8-32) Tightening Torque
Minimum: 1.4 Nm (12 in-lb)
Maximum: 1.7 Nm (15 in-lb)
Terminal Connections
Terminal Block
Screw Size: #6
Ring Terminal Width: 0.310-inch maximum
Terminal Block Tightening Torque
Minimum: 0.9 Nm (8 in-lb)
Maximum: 1.4 Nm (12 in-lb)
Compression Plug Tightening Torque
Minimum: 0.5 Nm (4.4 in-lb)
Maximum: 1.0 Nm (8.8 in-lb)
Compression Plug Mounting Ear Screw Tightening Torque
Minimum: 0.18 Nm (1.6 in-lb)
Maximum: 0.25 Nm (2.2 in-lb)
Product Standards
Electromagnetic 
Compatibility:
IEC 60255-26:2013
IEC 60255-27:2013
UL 508
CSA C22.2 No. 14-05
Type Tests
Environmental Tests
Enclosure Protection: IEC 60529:2001 + CRDG:2003
IP65 enclosed in panel 
(2-line display models)
IP54 enclosed in panel 
(touchscreen models)
IP50 for terminals enclosed in the dust-
protection assembly (protection 
against solid foreign objects only) 
(SEL Part #915900170). The 10°C 
temperature derating applies to the 
temperature specifications of the relay.
IP20 for terminals and the relay rear 
panel
Vibration Resistance: IEC 60255-21-1:1988
IEC 60255-27:2013, Section 10.6.2.1
Endurance: Class 2
Response: Class 2
Shock Resistance: IEC 60255-21-2:1988
IEC 60255-27:2013, Section 10.6.2.2
IEC 60255-27:2013, Section 10.6.2.3
Withstand: Class 1
Response: Class 2
Bump: Class 1
Seismic (Quake Response): IEC 60255-21-3:1993
IEC 60255-27:2013, Section 10.6.2.4
Response: Class 2
1.17
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Specifications
Cold: IEC 60068-2-1:2007
IEC 60255-27:2013, Section 10.6.1.2
IEC 60255-27:2013, Section 10.6.1.4
–40°C, 16 hours
Dry Heat: IEC 60068-2-2:2007
IEC 60255-27:2013, Section 10.6.1.1
IEC 60255-27:2013, Section 10.6.1.3
85°C, 16 hours
Damp Heat, Steady State: IEC 60068-2-78:2001
IEC 60255-27:2013, Section 10.6.1.5
40°C, 93% relative humidity, 10 days
Damp Heat, Cyclic: IEC 60068-2-30:2001
IEC 60255-27:2013, Section 10.6.1.6
25° to 55°C, 95% relative humidity, 
6 cycles
Change of Temperature: IEC 60068-2-14:2009
IEC 60255-1:2010, Section 6.12.3.5
–40° to +85°C, ramp rate 1°C/min, 
5 cycles
Dielectric Strength and Impulse Tests
Dielectric (Hi-Pot): IEC 60255-27:2013, Section 10.6.4.3
IEEE C37.90-2005
1.0 kVac on analog outputs, Ethernet 
ports
2.0 kVac on analog inputs, IRIG
2.5 kVac on contact I/O
3.6 kVdc on power supply, IN and VN 
terminals
Impulse: IEC 60255-27:2013, Section 10.6.4.2
0.5 J, 5 kV on power supply, contact
I/O, ac current, and voltage inputs
0.5 J, 530 V on analog outputs
IEEE C37.90:2005
0.5 J, 5 kV
0.5 J, 530 V on analog outputs
RFI and Interference Tests
Electrostatic Discharge 
Immunity:
IEC 61000-4-2:2008
IEC 60255-26:2013;Section 7.2.3
IEEE C37.90.3:2001
 Severity Level 4
 8 kV contact discharge
 15 kV air discharge
Radiated RF Immunity: IEC 61000-4-3:2010
IEC 60255-26:2013; Section 7.2.4
10 V/m
IEEE C37.90.2-2004
20 V/m
Fast Transient, Burst 
Immunitya:
IEC 61000-4-4:2011
IEC 60255-26:2013; Section 7.2.5
4 kV @ 5.0 kHz
2 kV @ 5.0 kHz for comm. ports
Surge Immunitya: IEC 61000-4-5:2005
IEC 60255-26:2013; Section 7.2.7
2 kV line-to-line
4 kV line-to-earth
Surge Withstand Capability 
Immunitya:
EN 61000-4-18:2010
IEC 60255-26:2013; Section 7.2.6
2.5 kV common mode
1 kV differential mode
1 kV common mode on comm. ports
IEEE C37.90.1-2002
2.5 kV oscillatory
4 kV fast transient
Conducted RF Immunity: IEC 61000-4-6:2008
IEC 60255-26:2013; Section 7.2.8
10 Vrms
Magnetic Field Immunity: IEC 61000-4-8:2009
IEC 60255-26:2013, Section 7.2.10
Severity Level:
1000 A/m for 3 seconds
100 A/m for 1 minute; 50/60 Hz
IEC 61000-4-9: 2001
Severity Level: 1000 A/m
IEC 61000-4-10:2001
Severity Level: 100 A/m 
(100 kHz and 1 MHz)
Power Supply Immunity: IEC 61000-4-11:2004
IEC 61000-4-17:1999
IEC 61000-4-29:2000
IEC 60255-26:2013, Section 7.2.11
IEC 60255-26:2013, Section 7.2.12
IEC 60255-26:2013, Section 7.2.13
EMC Emissions
Conducted Emissions: IEC 60255-26:2013 Class A
FCC 47 CFR Part 15.107 Class A
ICES-003 Issue 6
EN 55011:2009 + A1:2010 Class A
EN 55022:2010 + AC:2011 Class A
EN 55032:2012 + AC:2013 Class A
CISPR 11:2009 + A1:2010 Class A
CISPR 22:2008 Class A
CISPR 32:2015 Class A
Radiated Emissions: IEC 60255-26:2013 Class A
FCC 47 CFR Part 15.109 Class A
ICES-003 Issue 6
EN 55011:2009 + A1:2010 Class A
EN 55022:2010 + AC:2011 Class A
EN 55032:2012 + AC:2013 Class A
CISPR 11:2009 + A1:2010 Class A
CISPR 22:2008 Class A
CISPR 32:2015 Class A
Processing Specifications and Oscillography
AC Voltage and 
Current Inputs: 32 samples per power system cycle
Frequency Tracking Range: 15–70 Hz
Digital Filtering: One-cycle cosine after low-pass analog 
filtering. Net filtering (analog plus 
digital) rejects dc and all harmonics 
greater than the fundamental.
Protection and 
Control Processing:
Processing interval is 4 times per power 
system cycle (except for math 
variables and analog quantities, which 
are processed every 25 ms). Analog 
quantities for rms data are derived 
from data averaged from the previous 
8 cycles.
Arc-Flash Processing: Arc-Flash light is sampled 32 times per 
cycle
Arc-Flash current, light, and 2 fast 
hybrid outputs are processed 16 times 
per cycle
Oscillography
Length: 15, 64, or 180 cycles
Sampling Rate: 16 samples per cycle unfiltered
4 samples per cycle filtered
Trigger: Programmable with Boolean expression
1.18
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Specifications
Format: ASCII and Compressed ASCII
Binary COMTRADE (32 samples per 
cycle unfiltered)
Time-Stamp Resolution: 1 ms
Time-Stamp Accuracy: ±5 ms
Sequential Events Recorder
Time-Stamp Resolution: 1 ms
Time-Stamp Accuracy (With 
Respect to Time Source) for 
all Relay Word bits except 
those corresponding to 
digital inputs (INxxx) and 
arc-flash elements 
(TOLx/50xAF/OUTxxx): ±5 ms
Time-Stamp Accuracy (With 
Respect to Time Source) for 
Relay Word bits 
corresponding to digital 
inputs (INxxx) and arc-flash 
elements (TOLx/50xAF/
OUTxxx): 1 ms
Relay Elements
Instantaneous/Definite-Time Overcurrent (50P, 50G, 50N, 50Q)
Pickup Setting Range, A Secondary:
5 A models: 0.25–100.00 A, 0.01 A steps
1 A models: 0.05–20.00 A, 0.01 A steps
200 mA model: 0.01–4.00 A, 0.01 A steps (50N)
Accuracy: ±3% of setting plus ±0.02 • INOM A 
secondary (steady state)
±5% of setting plus ±0.02 • INOM A 
secondary (transient)
±6% of setting plus ±0.02 • INOM A 
secondary (transient for 50Q)
Time Delay: 0.00–400.00 seconds, 0.01 seconds 
steps
Pickup/Dropout Time: <1.5 cycles
Arc-Flash Instantaneous Overcurrent (50PAF, 50NAF)
Pickup Setting Range, A Secondary:
5 A models: 0.50–100.00 A, 0.01-A steps
1 A models: 0.10–20.00 A, 0.01 A-steps
Accuracy: 0 to +10% of setting plus ±0.02 • INOM 
A secondary (steady state pickup)
Pickup/Dropout Time: 2–5 ms/1 cycle
Arc-Flash Time-Overlight (TOL1–TOL8)
Pickup Setting Range, % of 
Full Scale:
3.0–80.0% (point sensor)
0.6–80.0% (fiber sensor)
Pickup/Dropout Time: 2–5 ms/1 cycle
Inverse-Time Overcurrent (51P, 51G, 51N, 51Q)
Pickup Setting Range, A Secondary:
5 A models: 0.25–24.00 A, 0.01 A steps
1 A models: 0.05–4.80 A, 0.01 A steps
200 mA models: 10.00–960.00 mA, 0.01 mA steps (51N)
Accuracy: ±5% of setting plus ±0.02 • INOM A 
secondary (steady state pickup)
Time Dial
U.S.: 0.50–15.00, 0.01 steps
IEC: 0.01–1.50, 0.01 steps
Accuracy: ±1.5 cycles, plus ±4% between 2 and 30 
multiples of pickup (within rated 
range of current)
IEC Thermal Element (49IEC)
Setting Range: Trip pickup, 1%–150%
Alarm pickup, 1%–100%
Pickup Accuracy: ±2% (for I  INOM)
±5% (for 0.4 • INOM < I < INOM)
Time to Trip/Reset Accuracy: ±5% plus ±0.5 s of the calculated value
Undervoltage (27P, 27PP, 27S)
Setting Range: OFF, 2.00–300.00 V (phase elements, 
phase-to-phase elements with delta 
inputs or synchronism voltage input) 
OFF, 2.00–520.00 V (phase-to-phase 
elements with wye inputs)
Accuracy: ±1% of setting plus ±0.5 V
Time Delay: 0.00–120.00 seconds, 0.01-second steps
Pickup/Dropout Time: <1.5 cycles
Overvoltage (59P, 59PP, 59G, 59Q, 59S)
Setting Range: OFF, 2.00–300.00 V (phase elements, 
phase-to-phase elements with delta 
inputs or synchronism voltage input) 
OFF, 2.00–520.00 V (phase-to-phase 
elements with wye inputs)
Accuracy: ±1% of setting plus ±0.5 V
Time Delay: 0.00–120.00 seconds, 0.01-second steps
Pickup/Dropout Time: <1.5 cycles
Inverse-Time Undervoltage (27I)
Setting Range: OFF, 2.00–300.00 V (phase elements, 
positive-sequence elements, phase-to-
phase elements with delta inputs or 
synchronism-check voltage input)
OFF, 2.00–520.00 V (phase-to-phase 
elements with wye inputs)
Accuracy: ±1% of setting plus ±0.5 V
Time Dial: 0.00–16.00 s
Accuracy: ±1.5 cyc plus ±4% between 0.95 and 
0.1 multiples of pickup 
Inverse-Time Overvoltage (59I)
Setting Range: OFF, 2.00–300.00 V (phase elements, 
sequence elements, or phase-to-phase 
elements with delta inputs or 
synchronism voltage input)
OFF, 2.00–520.00 V (phase-to-phase 
elements with wye inputs)
Accuracy: ±1% of setting plus ±0.5 V
Time Dial: 0.00–16.00 s
Accuracy: ±1.5 cyc plus ±4% between 1.05 and 
5.5 multiples of pickup
1.19
Date Code 20200603 Instruction Manual SEL-751 Relay
Introduction and Specifications
Specifications
Harmonic Blocking 
Pickup Range (% of 
fundamental): 5%–100%
Pickup Accuracy (A secondary): 
5 A models: ±5% plus ±0.10 A of harmonic current
1 A models: ±5% plus ±0.02 A of harmonic current
Time Delay Accuracy: ±0.5% plus ±0.25 cycle
Vector Shift (78VS)
Pickup Setting Range: 2.0°–30.0°, 0.1-degree increment
Accuracy: ±10% of the pickup setting, ±1 degree
Voltage Supervision 
Threshold: 
20.0%–100.0% • VNOM
Pickup Time: <3 cycles
Power Elements (32)
Instantaneous/Definite Time, 
Three-Phase Elements Type:
+W, –W, +VAR, –VAR
Pickup Setting Range, VA Secondary:
5 A models: 1.0–6500.0 VA, 0.1 VA steps
1 A models: 0.2–1300.0 VA, 0.1 VA steps
Accuracy: ±0.10 A • (L-L voltage secondary) plus 
±5% of setting at unity power factor 
for power elements and zero power 
factor for reactive power elements 
(5 A nominal)
±0.02 A • (L-L voltage secondary) plus 
±5% of setting at unity power factor 
for power elements and zero power 
factor for reactive power elements 
(1 A nominal)
Time Delay: 0.0–240.0 seconds, 0.1-second steps
Pickup/Dropout Time: <10 cycles
Power Factor (55)
Setting Range: OFF, 0.05–0.99
Accuracy: ±5% of full scale 
for current  0.5 • INOM
Time Delay: 1–240 seconds, 1-second steps
Frequency (81)
Setting Range: Off, 15.00–70.00 Hz
Accuracy: ±0.01 Hz (V1 >60 V) with voltage 
tracking
±0.05 Hz (I1 >0.8 • INOM) with current 
tracking
Time Delay: 0.00–400.00 seconds, 0.01-second steps
Pickup/DropoutTime: <4 cycles
Rate-of-Change of Frequency (81R)
Setting Range: OFF, 0.10–15.00 Hz/s
Accuracy: ±100 mHz/s, plus ±3.33% of pickup
Time Delay: 0.10–60.00 seconds, 0.01-second steps
Synchronism Check (25)
Pickup Range, Secondary 
Voltage: 0.00–300.00 V
Pickup Accuracy, Secondary 
Voltage:
±1% plus ±0.5 V
(over the range of 2–300 V)
Slip Frequency Pickup Range: 0.05 Hz–0.50 Hz
Slip Frequency Pickup 
Accuracy: ±0.02 Hz
Phase Angle Range: 0°–80°
Phase Angle Accuracy: ±4°
Load-Encroachment Detection
Pickup Setting Range
5 A Model: 0.10–128.00  secondary, 
0.01  steps
1 A Model: 0.50–640.00  secondary, 
0.01  steps
Forward Load Angle: –90° to +90°
Forward Load Angle: +90° to +270°
Accuracy
Impedance Measurement: ±5% plus ±0.5 
Angle Measurement: ±3°
Station Battery Voltage Monitor
Operating Range: 0–350 Vdc (300 Vdc for UL purposes)
Pickup Range: 20.00–300.00 Vdc
Pickup accuracy: ±2% of setting plus ±2 Vdc
Timers
Setting Range: Various
Accuracy: ±0.5% of setting plus ±1/4 cycle
RTD Protection
Setting Range: Off, 1°–250°C
Accuracy: ±2C
RTD Open-Circuit Detection: >250°C
RTD Short-Circuit Detection: <–50°C
RTD Types: PT100, NI100, NI120, CU10
RTD Lead Resistance: 25  max. per lead
Update Rate: <3 s
Noise Immunity on RTD 
Inputs: 
As high as 1.4 Vac (peak) at 50 Hz or 
greater frequency
RTD Fault/Alarm/Trip Time 
Delay:
Approx. 12 s
Metering
Accuracies are specified at 20C, nominal frequency, ac currents within 
(0.2–20.0) • INOM A secondary, and ac voltages within 50–250 V 
secondary (1.33–6.67 V secondary with 8 V LEA option), unless 
otherwise noted.
Phase Currents: ±1% of reading, ±1° (±2.5° at 0.2–0.5 A 
for relays with INOM = 1 A)
Three-Phase Average Current: ±1% of reading
IG (Residual Current): ±2% of reading, ±2° (±5.0° at 0.2–0.5 A 
for relays with INOM = 1 A)
IN (Neutral Current): ±1% of reading, ±1° (±2.5° at 0.2–0.5 A 
for relays with INOM = 1 A)
±1.6 mA and ±1% (0.04–4.0 A) (0.2 A 
nominal channel IN current input)
I1 Positive-Sequence Current: ±2% of reading
3I2 Negative-Sequence 
Current: ±2% of reading
System Frequency: ±0.01 Hz of reading for frequencies 
within 15–70 Hz (V1 > 60 V)
Line-to-Line Voltages: ±1% of reading, ±1° for voltages
1.20
SEL-751 Relay Instruction Manual Date Code 20200603
Introduction and Specifications
Specifications
Three-Phase Average 
Line-to-Line Voltage:
±1% of reading for voltages within 
24–264 V
Line-to-Ground Voltages: ±1% of reading, ±1° for voltages within 
24–264 V (0.64–7.04 V for LEA 
inputs)
Three-Phase Average 
Line-to-Ground Voltages:
±1% of reading for voltages within 
24–264 V (0.64–7.04 V for LEA 
inputs)
Voltage Imbalance (%): ±2% of reading
V1 Positive-Sequence 
Voltage:
±2% of reading for voltages within 
24–264 V (0.64–7.04 V for LEA 
inputs)
3V2 Negative-Sequence 
Voltage:
±2% of reading for voltages within 
24–264 V (0.64–7.04 V for LEA 
inputs)
Real Three-Phase Power 
(kW): ±3% of reading for 0.10 < pf < 1.00
Reactive Three-Phase Power 
(kVAR): ±3% of reading for 0.00 < pf < 0.90
Apparent Three-Phase Power 
(kVA): ±3% of reading
Power Factor: ±2% of reading
RTD Temperatures: ±2°C
Energy Meter 
Accumulators: Separate IN and OUT accumulators 
updated once per second, transferred 
to nonvolatile storage 4 times per day
ASCII Report Resolution: 0.001 MWh
Accuracy: The accuracy of the energy meter 
depends on applied current and power 
factor as shown in the power metering 
accuracy specifications above. The 
additional error introduced by 
accumulating power to yield energy is 
negligible when power changes slowly 
compared to the processing rate of 
once per second.
Synchrophasor Accuracy
Maximum Message Rate
Nominal 60 Hz System: 60 messages per second
Nominal 50 Hz System: 50 messages per second
The voltage accuracy specifications are only applicable for the model 
options with standard voltage inputs (not applicable to LEA option).
The current accuracy specifications are applicable for all 1 A and 5 A 
options.
Note: For the SEL-751 current only model, the accuracy specifications 
for currents are only applicable when the applied signal frequency 
equals FNOM.
Accuracy for Voltages
Level 1 compliant as specified in IEEE C37.118 under the following 
conditions for the specified range.
Conditions
➤ At maximum message rate
➤ When phasor has the same frequency as the positive-sequence 
voltage
➤ Frequency-based phasor compensation is enabled PHCOMP := Y)
➤ The narrow bandwidth filter is selected (PMAPP := N)
Range
Frequency: ±5.0 Hz of nominal (50 or 60 Hz)
Magnitude: 30 V–250 V
Phase Angle: –179.99° to 180.00°
Out-of-Band Interfering 
Frequency (Fs): 10 Hz  Fs  (2 • FNOM)
Accuracy for Currents
Level 1 compliant as specified in IEEE C37.118 under the following 
conditions for the specified range.
Conditions
➤ At maximum message rate
➤ When phasor has the same frequency as the positive-sequence 
voltage
➤ Frequency-based phasor compensation is enabled 
(PHCOMP := Y)
➤ The narrow bandwidth filter is selected (PMAPP := N)
Range
Frequency: ±5.0 Hz of nominal (50 or 60 Hz)
Magnitude: (0.4–2) • INOM (INOM = 1 A or 5 A)
Phase Angle: –179.99° to 180.00°
Out-of-Band Interfering 
Frequency (Fs): 10 Hz  Fs  (2 • FNOM)
a Front port serial cable (non-fiber) lengths assumed to be <3 m.
Date Code 20200603 Instruction Manual SEL-751 Relay
Section 2
Installation
Overview
The first steps in applying the SEL-751 Feeder Protection Relay are installing 
and connecting the relay. This section describes common installation features 
and requirements.
To install and connect the relay safely and effectively, you must be familiar 
with relay configuration features and options. You should carefully plan relay 
placement, cable connections, and relay communication.
This section contains drawings of typical ac and dc connections to the 
SEL-751. Use these drawings as a starting point for planning your particular 
relay application.
The instructions for using the versatile front-panel custom label option are 
available on the SEL-751 product page on the SEL website. With custom 
labels, you can use SELOGIC control equations and slide-in configurable 
front-panel labels to change the function and identification of target LEDs.
Relay Placement
Proper placement of the SEL-751 helps to ensure years of trouble-free 
protection. Use the following guidelines for proper physical installation of the 
SEL-751.
Physical Location The SEL-751 is EN 61010-1 certified at Installation/Overvoltage Category II 
and Pollution Degree 2. This allows mounting of the relay in a sheltered 
indoor environment that does not exceed the temperature and humidity ratings 
for the relay. The SEL-751 is required to be mounted in an indoor or outdoor 
(extended) locked enclosure that provides a degree of protection to personnel 
against access to hazardous parts. In either environment, the relay shall be 
protected from direct sunlight, precipitation, and full wind pressure.
You can place the relay in extreme temperature and humidity locations. 
(See Operating Temperature and Operating Environment on page 1.16.) 
For EN 61010-1 certification, the SEL-751 rating is 2000 m (6562 ft) above 
mean sea level.
To comply with the requirements of the European ATEX standard for 
hazardous locations, the SEL-751 shall be installed in an ATEX-certified 
enclosure with a tool-removable door or cover that provides a degree of pro-
tection not less than IP54, in accordance with EN 60079-0. The enclosure 
shall be limited to the surrounding air temperature range of –
20°C  Ta  +50°C. The enclosure should be certified to these requirements 
or be tested for compliance as part of the complete assembly. The enclosure 
must be marked “WARNING—Do not open when an explosive atmosphere is 
2.2
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
present.” In North America, the relay is approved for Hazardous Locations 
Class I, Division 2, Groups A, B, C, and D,and temperature class T3C with a 
maximum surrounding air temperature of 50°C.
Relay Mounting To flush mount the SEL-751 in a panel, cut a rectangular hole with the dimen-
sions shown in Figure 2.1. Use the supplied front-panel gasket for protection 
against dust and water ingress into the panel. The relay is rated IP 65 when 
the two-line display model is enclosed in a panel and rated IP54 when the 
touchscreen display model is enclosed in a panel.
For extremely dusty environments, use the optional IP50-rated terminal dust-
protection assembly (protection against solid foreign objects only) 
(SEL Part #915900170). The 10°C-temperature derating applies to the tem-
perature specifications of the relay.
Figure 2.1 Relay Panel-Mount Dimensions
Refer to Section 1: Introduction and Specifications, Models, Options, and 
Accessories for information on mounting accessories.
I/O Configuration
Your SEL-751 offers flexibility in tailoring I/O to your specific application. In 
total, the SEL-751 has six rear-panel slots, labeled as Slots A, B, C, D, E, and Z. 
Slots A, B, and Z are base unit slots, each associated with a specific function. 
Optional digital/analog I/O, communications, RTD, and voltage cards are 
available for the SEL-751. Figure 2.2 shows the slot allocations for the cards.
Because installations differ substantially, the SEL-751 offers a variety of card 
configurations to provide options for the many diverse applications. Choose 
the combination of option cards most suited for your application from the fol-
lowing selection.
7.36 
(187.0)
5.47 
(139.0)
i9089b
2.3
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
SELECT Power Supply With I/O (Slot A)
SELECT Processor and 
Communications Card (Slot B)
SELECT I/O Expansion Card (Slot C)
SELECT I/O Expansion Card (Slot D)
SELECT I/O Expansion Card (Slot E)
SELECT 4 ACI/3 AVI Card (Slot Z)
Rear-Panel Slot
A B C D E Z
Software 
Reference
1
(e.g., OUT101)
3
(e.g., IN301)
4
(e.g., OUT401)
5
(e.g., AI501)
Description
Power supply and
I/O carda
CPU/comm. 
cardb
Comm. or input/
outputc card
Input/outputc
or RTD card
Input/outputc or 
voltage/arc-flash 
card
4 ACI/3 AVI 
card in base 
unit
Card Type
SELECT EIA-232/485 
SELECT DeviceNet 
SELECT 3 DI/4 DO/1 AO (one card per relay)   
SELECT 4 DI/4 DO   
SELECT 4 DI/3 DO (1 Form B, 2 Form C)   
SELECT 8 DI   
SELECT 8 DO   
SELECT 8 AI   
SELECT 14 DI   
SELECT 4 AI/4 AO (one card per relay)   
SELECT 10 RTD 
SELECT 2 AVI/4 AFDI (MOT…x70x…) 
SELECT 2 AVI/4 AFDI (MOT…xL0x…) 
SELECT 8 AFDI (MOT…x77x…) 
2.4
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
Figure 2.2 Slot Allocations for Different Cards
Power Supply Card 
PSIO/2 DI/3 DO 
(Slot A)
Select appropriate power supply option for the application:
➤ High Voltage: 110–240 Vac, 110–250 Vdc, 50/60 Hz 
➤ Low Voltage: 24–48 Vdc
Select the appropriate digital input voltage option: 125 Vdc/Vac, 24 Vdc/Vac, 
48 Vdc/Vac, 110 Vdc/Vac, 220 Vdc/Vac, or 250 Vdc/Vac.
This card is supported in Slot A of the SEL-751. It has two digital inputs and 
three digital outputs (two normally open Form A contact outputs and one 
Form C output). Table 2.1 shows the terminal designation for the 
PSIO/2 DI/3 DO card.
SELECT 4 ACI/3 AVI (MOT…x81/82/83/85/86/87x…) 
SELECT 4 ACI/3 AVI (MOT…xL1/L2/L3/L5/L6/L7x…) 
SELECT 4 ACI (MOT...xA1/A2/A3/A5/A6/A7x...) 
a Power supply, two inputs, and three outputs.
b IRIG-B, EIA-232/485, fiber-optic serial and/or Ethernet ports (the IRIG-B input option is available on terminals B01, B02 for all models 
except models with a fiber-optic Ethernet port (Port 1) and dual copper Ethernet port (Port 1) that have Port 3 as an EIA-232 serial port and 
can input IRIG-B via the EIA-232 port and an SEL communications processor). IRIG-B input is also supported via Port 2 (EIA-232 fiber-optic 
serial port).
c Digital or analog.
Rear-Panel Slot
A B C D E Z
Software 
Reference
1
(e.g., OUT101)
3
(e.g., IN301)
4
(e.g., OUT401)
5
(e.g., AI501)
Description
Power supply and
I/O carda
CPU/comm. 
cardb
Comm. or input/
outputc card
Input/outputc
or RTD card
Input/outputc or 
voltage/arc-flash 
card
4 ACI/3 AVI 
card in base 
unit
Card Type
Table 2.1 Power Supply Inputs (PSIO/2 DI/3 DO) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Description
Ground connection
A01, A02 Power supply input terminals
A03, A04 OUT101, driven by OUT101 SELOGIC 
control equation
A05, A06 OUT102, driven by OUT102 SELOGIC 
control equation
A07, A08, A09 OUT103, driven by OUT103 SELOGIC 
control equation
A10, A11 IN101, drives IN101 element
A12, A11 IN102, drives IN102 element
A 100
OUT_0 1
OUT_02
IN_0 1
IN_02
10
1 1
08
12
INPUTS:
05
06
04
03
02
0 1
GND
+/H
—/N
P
O
W
E
R
OUT_03
09
07
2.5
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
Communications 
Ports (Slot B)
Select the communications ports necessary for your application from the 
base-unit options shown in Table 2.2.
PORT F supports the following protocols:
➤ SELBOOT
➤ Modbus RTU Slave
➤ SEL ASCII and Compressed ASCII
➤ SEL Settings File Transfer
➤ Event Messenger
➤ C37.118 (Synchrophasor Data)
PORT 1 (Ethernet) supports the following protocols:
➤ C37.118 (Synchrophasor Data)
➤ Modbus TCP/IP
➤ EtherNet/IP
➤ DNP3 LAN/WAN
➤ IEC 61850
➤ Simple Network Time Protocol (SNTP)
➤ Precision Time Protocol (PTP)
➤ FTP
➤ Telnet
PORT 2 and PORT 3 support the following protocols:
➤ Modbus RTU Slave
➤ SEL ASCII and Compressed ASCII
➤ SEL Fast Meter
➤ SEL Fast Operate
➤ SEL Fast SER
➤ SEL Fast Message Unsolicited Write
➤ SEL Settings File Transfer
➤ SEL MIRRORED BITS (MBA, MBB, MB8A, MB8B, MBTA, 
MBTB)
➤ Event Messenger
Table 2.2 Communications Ports
Port Location Feature Description
F Front Panel Standard Nonisolated EIA-232 serial port
1 Rear Panel Optional (Single/Dual) Isolated 10/100BASE-T
Ethernet copper port or 100BASE-FX
Ethernet fiber-optic port
2 Rear Panel Optional Isolated multimode fiber-optic serial 
port with ST connectors
3 Rear Panel Standard Either nonisolated EIA-232 or isolated 
EIA-485 serial port
2.6
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
➤ DNP3 Level 2 Outstation
➤ C37.118 (Synchrophasor Data)
➤ IEC 60870-5-103
Communications Card 
(Slot C)
Either the DeviceNet (see Appendix I: DeviceNet Communications) or the 
EIA-232/ EIA-485 communications card is supported in Slot C. The 
EIA-232/EIA-485 card provides one serial port with one of the following two 
serial port interfaces:
➤ Port 4A, an isolated EIA-485 serial port interface
➤ Port 4C, a nonisolated EIA-232 serial port interface, supporting 
the +5 Vdc interface
Select either EIA-232 or EIA-485 functionality through use of the Port 4 
Setting COMM Interface. Table 2.3 shows the port number, interface, and type 
of connector for the two protocols.
The communications card supports all of the following protocols:
➤ Modbus RTU Slave
➤ SEL ASCII and Compressed ASCII
➤ SEL Fast Meter
➤ SEL Fast Operate
➤ SEL Fast SER
➤ SEL Fast Message Unsolicited Write
➤ SEL Settings File Transfer
➤ SEL MIRRORED BITS (MBA, MBB, MB8A, MB8B, MBTA, 
MBTB)
➤ Event Messenger
➤ DNP3 Level 2 Outstation
➤ C37.118 (Synchrophasor Data)
➤ IEC 60870-5-103
Current Card (4 ACI) MOT…xA1x…(1 A phase, 1 A neutral CTs), or …xA5x…(5 A phase, 
5 A neutral CTs), or …xA2x…(1 A phase, 5 A neutral CTs), or …xA6x… 
(5 A phase, 1 A neutral CTs) or …xA3x…(1 A phase, 200 mA neutral CTs), 
or …xA7x…(5 A phase, 200 mA neutral CTs). Supported in Slot Z of the 
SEL-751, this card has current inputs for three-phase CTs, neutral current CT.
The 4 ACI current card inputs terminal designation for the card is as shown in 
Table 2.4. 
Table 2.3 Communications Card Interfaces and Connectors
Port Interface Connectors
4A EIA-485 5-pin Euro 
4CEIA-232 D-sub
NOTE: After any change, be sure to 
thoroughly test the settings.
WARNING
Before working on a CT circuit, first 
apply a short to the secondary 
winding of the CT.
2.7
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
Current/Voltage Card 
(4 ACI/3 AVI)
MOT…x81x…(1 A phase, 1 A neutral CTs), or …x85x…(5 A phase, 
5 A neutral CTs), or …x82x…(1 A phase, 5 A neutral CTs), or …x86x… 
(5 A phase, 1 A neutral CTs) or …x83x…(1 A phase, 200 mA neutral CTs), 
or …x87x…(5 A phase, 200 mA neutral CTs). Supported in Slot Z of the 
SEL-751, this card has current inputs for three-phase CTs, neutral current 
CTs, and 300 Vac voltage inputs for three-phase (wye or delta) PTs. 
MOT…xL1x…(1 A phase, 1 A neutral CTs), or …xL5x…(5 A phase, 5 A 
neutral CTs), or …xL2x…(1 A phase, 5 A neutral CTs), or …xL6x… (5 A 
phase, 1 A neutral CTs) or …xL3x… (1 A phase, 200 mA neutral CTs), or 
…xL7x…(5 A phase, 200 mA neutral CTs). Supported in Slot Z of the 
SEL-751, this card has current inputs for three-phase CTs, neutral current 
CTs, and 8 Vac LEA voltage inputs for three-phase (wye or delta) PTs.
The 4 ACI/3 AVI current/voltage card inputs terminal designation for the card 
with LEA voltage inputs and the regular voltage inputs is as shown in 
Table 2.5.
Table 2.4 Current Inputs (4 ACI) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Description
Z01
Z02
IA, A-Phase current input
Z03
Z04
IB, B-Phase current input
Z05
Z06
IC, C-Phase current input
Z07
Z08
IN, Neutral current input
Z03
Z04
IB
Z05
Z06
IC
Z07
Z08
IN
Z02
IA
Z01
ACI
WARNING
Before working on a CT circuit, first 
apply a short to the secondary 
winding of the CT.
2.8
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
Voltage/Arc-Flash 
Detection Inputs Card 
(2 AVI/4 AFDI)
MOT…x70x… Supported only in Slot E of the SEL-751, this card has 300 
Vac synchronism-check voltage input (VS), station dc battery monitor input 
(VBAT), and four fiber-optic transmit and receive inputs (AF1–AF4).
MOT…xL0x… Supported only in Slot E of the SEL-751, this card has 8 V 
LEA synchronism-check voltage input (VS), station dc battery monitor input 
(VBAT), and four fiber-optic transmit and receive inputs (AF1–AF4).
The terminal designations for both MOT…x70x… and …xL0x… are shown 
in Table 2.6.
Table 2.5 Current/Voltage Inputs (4 ACI/3 AVI) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Description
Z01
Z02
IA, A-Phase current input
Z03
Z04
IB, B-Phase current input
Z05
Z06
IC, C-Phase current input
Z07
Z08
IN, Neutral current input
Z09
Z10
Z11
Z12
VA, A-Phase voltage input
VB, B-Phase voltage input
VC, C-Phase voltage input
N, common connection for VA, VB, VC
Z03
Z04
IB
Z05
Z06
IC
Z07
Z08
IN
Z02
IA
Z01
ACI
AVI
Z09
Z 1 1
WYE
VA VA
VB VB
(COM)
VC VC
Z12 N COM
OPEN
DELTA
Z10
Table 2.6 Voltage/Arc-Flash Detection Inputs (2 AVI/4 AFDI) Card Terminal 
Designations
Side-Panel 
Connections Label
Terminal 
Number
Description
E01 VS, synchronism-check voltage input
E02 NS, common connection for synchronism-check volt-
age input
E03 VBAT+ station battery (positive) voltage input
E04 VBAT– station battery (negative) voltage input
E05 AF1 Channel TX and RX Inputs
E06 AF2 Channel TX and RX Inputs
E07 AF3 Channel TX and RX Inputs
E08 AF4 Channel TX and RX Inputs
E02
E03
E04
E 0 1
E06
E07
E08
E05
TX RX
AF 1
AF2
AF3
AF4
VS
NS
VBAT+
VBAT-
2.9
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
Eight Arc-Flash 
Detection Inputs 
(8 AFDI)
MOT…x77x… Supported only in Slot E of the SEL-751, this card has eight 
arc-flash fiber-optic transmit and receive inputs (AF1–AF8). Table 2.7 shows 
the terminal designations.
Analog Inputs Card 
(8 AI)
Supported in any nonbase unit slot (Slot C through Slot E), this card has eight 
analog inputs. Table 2.8 shows the terminal designation.
Table 2.7 Eight Arc-Flash Detection Inputs (8 AFDI) Card Terminal 
Designations
Side-Panel 
Connections Label
Terminal 
Number
Description
E01 AF1 Channel TX and RX Inputs
E02 AF2 Channel TX and RX Inputs
E03 AF3 Channel TX and RX Inputs
E04 AF4 Channel TX and RX Inputs
E05 AF5 Channel TX and RX Inputs
E06 AF6 Channel TX and RX Inputs
E07 AF7 Channel TX and RX Inputs
E08 AF8 Channel TX and RX Inputs
TX RX
0 1
02
03
04
AF 1
AF2
AF3
AF4
05 AF5
06 AF6
07 AF7
08 AF8
Table 2.8 Eight Analog Inputs (8 AI) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x = 3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 AIx01, Transducer Input x01
03, 04 AIx02, Transducer Input x02
05, 06 AIx03, Transducer Input x03
07, 08 AIx04, Transducer Input x04
09, 10 AIx05, Transducer Input x05
11, 12 AIx06, Transducer Input x06
13, 14 AIx07, Transducer Input x07
15, 16 AIx08, Transducer Input x08
NOTE: Analog inputs cannot 
provide loop power. Each analog 
output is self-powered and has an 
isolated power supply.
NOTE: The requirements of 
IEC 60255-26 and IEC 60255-27 are 
met for connection lengths less than 
10 m for analog inputs and outputs.
2.10
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
Analog Input/Output 
Card (4 AI/4 AO)
Supported in any one of the nonbase unit slots (Slot C through Slot E), this card 
has four analog inputs and four analog outputs. Table 2.9 shows the terminal 
designations.
I/O Card 
(3 DI/4 DO/1 AO)
Supported in one nonbase unit slot (Slot C, D, or E), this card has three digital 
inputs, four digital outputs, and one analog output. Table 2.10 shows the 
terminal designations.
Table 2.9 Four Analog Inputs/Four Analog Outputs (4 AI/4 AO) Card 
Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 AOx01, Analog Output x01
03, 04 AOx02, Analog Output x02
05, 06 AOx03, Analog Output x03
07, 08 AOx04, Analog Output x04
09, 10 AIx01, Transducer Input x01
11, 12 AIx02, Transducer Input x02
13, 14 AIx03, Transducer Input x03
15, 16 AIx04, Transducer Input x04
NOTE: Analog inputs cannot 
provide loop power. Each analog 
output is self powered and has an 
isolated power supply.
NOTE: Analog outputs are isolated 
from each other.
NOTE: The requirements of 
IEC 60255-26 and IEC 60255-27 are 
met for connection lengths less than 
10 meters for analog inputs and 
outputs.
AO_02
AO_0 1
AO_03
AO_04
AI_02
AI_0 1
AI_03
AI_04
08
05
06
02
04
09
03
10
1 1
12
1 3
14
15
16
07
0 1
Table 2.10 I/O (3 DI/4 DO/1 AO) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 OUTx01, driven by OUTx01 SELOGIC 
control equation
03, 04 OUTx02, driven by OUTx02 SELOGIC 
control equation
05, 06 OUTx03, driven by OUTx03 SELOGIC 
control equation
07, 08 OUTx04, driven by OUTx04 SELOGIC 
control equation
09, 10 AOx01, Analog Output 1
11, 12 INx01, drives INx01 element
13, 14 INx02, drives INx02 element
15, 16 INx03, drives INx03 element
NOTE: Analog output is self 
powered and has an isolated power 
supply.
NOTE: All digital inputs and digital 
outputs (including high-current, 
high-speed hybrid) connections are 
polarity neutral.
NOTE: The requirements of 
IEC 60255-26 and IEC 60255-27 are 
met for connection lengths less than 
10 meters for analog inputs and 
outputs.
INPUTS:
AO_0 1
IN_0 1
IN_02
IN_03
OUT_0 1
OUT_02
OUT_03
OUT_04
08
05
06
02
04
09
03
10
1 1
12
1 3
14
15
16
07
0 1
+
—
2.11
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
RTD Card (10 RTD) Supported in Slot D only, this card has 10 three-wire RTD inputs. Table 2.11 
shows the terminal designations.
I/O Card (4 DI/3 DO) Supportedin any nonbase unit slot (Slot C through Slot E), this card has four 
digital inputs, one Form B digital output (normally closed) and two Form C 
digital output contacts. Table 2.12 shows the terminal designations.
Table 2.11 RTD (10 RTD) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Description
01 RTD01 (+)
02 RTD01 (–)
03 RTD01 Comp/Shield
04 RTD02 (+)
05 RTD02 (–)
06 RTD02 Comp/Shield
07 RTD03 (+)
08 RTD03 (–)
09 RTD03 Comp/Shield
•
•
•
•
•
•
28 RTD10 (+)
29 RTD10 (–)
30 RTD10 Comp/Shield
NOTE: All comp/shield terminals are 
internally connected to relay chassis 
and ground.
NOTE: Use passive resistors to 
simulate temperatures to test the RTD 
inputs. Use of an RTD simulator can 
damage the relay.
08
05
06
04
09
20
2 1
22
23
24
25
26
27
28
29
30
10
1 1
12
1 3
14
15
16
17
18
19
07
02
03
0 1
RTD 1
COMP/ SHLD
+
—
RTD2
COMP/ SHLD
+
—
RTD3
COMP/ SHLD
+
—
RTD4
COMP/ SHLD
+
—
RTD5
COMP/ SHLD
+
—
RTD6
COMP/ SHLD
+
—
RTD7
COMP/ SHLD
+
—
RTD8
COMP/ SHLD
+
—
RTD9
COMP/ SHLD
+
—
RTD 10
COMP/ SHLD
+
—
Table 2.12 Four Digital Inputs/Three Digital Outputs (4 DI/3 DO) Card 
Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 OUTx01, driven by OUTx01 SELOGIC 
control equation
03, 04, 05 OUTx02, driven by OUTx02 SELOGIC 
control equation
06, 07, 08 OUTx03, driven by OUTx03 SELOGIC 
control equation
09, 10 INx01, drives INx01 element
11, 12 INx02, drives INx02 element
13, 14 INx03, drives INx03 element
15, 16 INx04, drives INx04 element
INPUTS:
IN_0 1
IN_02
IN_03
IN_04
OUT_0 1
OUT_02
02
04
05
09
03
OUT_0307
08
06
10
1 1
12
1 3
14
15
16
0 1
2.12
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
I/O Card (4 DI/4 DO) Supported in any nonbase unit slot (Slot C through Slot E), this card has four 
digital inputs and four outputs (all normally open). Optionally, the outputs can 
be fast hybrid (high-speed, high-current interrupting) outputs. Table 2.13 
shows the terminal designations.
I/O Card (8 DI) Supported in any nonbase unit slot (Slot C through Slot E), this card has eight 
digital inputs. Table 2.14 shows the terminal designations.
Table 2.13 Four Digital Inputs/Four Digital Outputs (4 DI/4 DO) Card 
Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 OUTx01, driven by OUTx01 SELOGIC 
control equation
03, 04 OUTx02, driven by OUTx02 SELOGIC 
control equation
05, 06 OUTx03, driven by OUTx03 SELOGIC 
control equation
07, 08 OUTx04, driven by OUTx04 SELOGIC 
control equation
09, 10 INx01, drives INx01 element
11, 12 INx02, drives INx02 element
13, 14 INx03, drives INx03 element
15, 16 INx04, drives INx04 element
NOTE: All digital inputs and digital 
outputs (including high-current, high-
speed hybrid) connections are polarity 
neutral.
INPUTS:
IN_0 1
IN_02
IN_03
IN_04
OUT_0 1
OUT_02
OUT_03
OUT_04
08
05
06
02
04
09
03
10
1 1
12
1 3
14
15
16
07
0 1
Table 2.14 Eight Digital Inputs (8 DI) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 INx01, drives INx01 element
03, 04 INx02, drives INx02 element
05, 06 INx03, drives INx03 element
07, 08 INx04, drives INx04 element
09, 10 INx05, drives INx05 element
11, 12 INx06, drives INx06 element
13, 14 INx07, drives INx07 element
15, 16 INx08, drives INx08 element
INPUTS:
08
05
06
02
04
09
03
10
1 1
12
1 3
14
15
16
07
0 1
IN_0 1
IN_02
IN_03
IN_04
IN_05
IN_06
IN_07
IN_08
2.13
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
I/O Card (8 DO) Supported in any nonbase unit slot (Slot C through Slot E), this card has eight 
digital outputs. Table 2.15 shows the terminal designations.
The 8 DO card shown previously is all Form A contacts. Refer to the SEL-751 
Model Option Table for all the variants available (8A, 8B, 4A/4B, 2A/6B, 6A/2B).
I/O Card (14 DI) Supported in any nonbase unit slot (Slot C through Slot E), this card has four-
teen digital inputs. Table 2.16 shows the terminal designations.
Table 2.15 Eight Digital Outputs (8 DO) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01, 02 OUTx01, driven by OUTx01 SELOGIC 
control equation
03, 04 OUTx02, driven by OUTx02 SELOGIC 
control equation
05, 06 OUTx03, driven by OUTx03 SELOGIC 
control equation
07, 08 OUTx04, driven by OUTx04 SELOGIC 
control equation
09, 10 OUTx05, driven by OUTx05 SELOGIC 
control equation
11, 12 OUTx06, driven by OUTx06 SELOGIC 
control equation
13, 14 OUTx07, driven by OUTx07 SELOGIC 
control equation
15, 16 OUTx08, driven by OUTx08 SELOGIC 
control equation
Table 2.16 Fourteen Digital Inputs (14 DI) Card Terminal Designations
Side-Panel 
Connections Label
Terminal 
Number
Descriptiona
a x=3, 4, or 5 if the card is installed in Slot C, D, or E, respectively.
01 
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
INx01, drives INx01 element
INx02, drives INx02 element
INx03, drives INx03 element
INx04, drives INx04 element
INx05, drives INx05 element
INx06, drives INx06 element
INx07, drives INx07 element
COM
INx08, drives INx08 element
INx09, drives INx09 element
INx10, drives INx10 element
INx11, drives INx11 element
INx12, drives INx12 element
INx13, drives INx13 element
INx14, drives INx14 element
COM
2.14
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
Card Configuration 
Procedure
Changing card positions or expanding on the initial number of cards requires 
no card programming; the relay detects the new hardware and updates the 
software accordingly (you still have to use the SET command to program the 
I/O settings).
The SEL-751 offers flexibility in tailoring I/O to your specific application. 
The SEL-751 has six rear-panel slots, labeled as Slots A, B, C, D, E, and Z. 
Slots A, B, and Z are base unit slots, each associated with a specific function. 
Optional digital/analog I/O cards are available for the SEL-751 in Slots C, D, 
and E. Optional communications cards are available only for Slot C, an RTD 
card is available only for Slot D, 1 A/5 A CT combinations for voltage/current 
and current only cards are available only on Slot Z, and voltage only cards are 
available only for Slot E. Figure 2.2 shows the slot allocations for the cards. 
Because installations differ substantially, the SEL-751 offers a variety of card 
configurations that provide options for an array of applications. Choose the 
combination of cards most suited for your application.
Swapping Optional I/O Cards
When an I/O card is moved from one slot to a different slot, the associated 
settings for the slot the card is moved from are lost. For example, if a 
4 DI/4 DO card is installed in Slot D, the SELOGIC control equation settings 
OUT401–OUT404 are available. If OUT401 = IN101 AND 51P1T, and the 
card is moved to a different slot, then the OUT401 setting is lost. This is true 
for all the digital and analog I/O cards.
Adding Cards to Slots C, D, E, and Z
The SEL-751 can be upgraded by adding as many as three cards.
Installation
Perform the following steps to install cards into Slots C, D, E, or Z of the base 
unit.
Step 1. Save the settings and event report data before installing the new 
card in the relay.
Step 2. Remove the power supply voltage from terminals A01+ and A02– 
and remove the ground wire from the green ground screw.
Step 3. Disconnect all the connection plugs.
Step 4. Remove the eight screws on the rear and remove the rear cover.
Step 5. Remove the plastic filler platecovering the slot associated with 
the card being installed.
Step 6. Insert the card in the correct slot.
Make sure the contact fingers on the printed circuit board are 
bent at an approximate 130-degree angle relative to the board 
for proper electromagnetic interference protection.
Step 7. Before reattaching the rear cover, check for and remove any 
foreign material that may remain inside the SEL-751 case.
Step 8. Carefully reattach the rear cover.
Step 9. Reinstall the eight screws that secure the rear cover to the case.
Step 10. Apply power supply voltage to terminals A01+ and A02–, and 
reconnect the ground wire to the green ground screw.
DANGER
Disconnect or de-energize all 
external connections before opening 
this device. Contact with hazardous 
voltages and currents inside this 
device can cause electrical shock 
resulting in injury or death.
2.15
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
Step 11. If the card is in the proper slot, the front panel displays the 
following:
STATUS FAIL
X Card Failure
If you do not see this message and the ENABLED LED is turned 
on, the card was inserted into the wrong slot. Begin again at 
Step 2.
Step 12. Press the ESC pushbutton.
Step 13. Press the Down Arrow pushbutton until STATUS is highlighted.
Step 14. Press the ENT pushbutton.
The front panel displays the following:
STATUS
Relay Status
Step 15. Press the ENT pushbutton.
The front panel displays the following:
Serial Num
000000000000000000000000
Step 16. Press the ENT pushbutton.
The front panel displays the following:
Confirm Hardware
Config (Enter)
Step 17. Press the ENT pushbutton.
The front panel displays the following:
Accept New Config?
No Yes
Step 18. Select Yes and press the ENT pushbutton.
The front panel displays the following:
Config Accepted
Enter to Reboot
Step 19. Press the ENT pushbutton and proceed to Step 22.
Step 20. Wait for the Device Status screen to appear, and then verify the 
new part number and tap Yes to confirm the new configuration.
Step 21. Tap OK on the notification screen to reboot the relay.
2.16
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
Step 22. Use the PARTNO command from Access Level C to enter the 
exact part number of the relay after the relay restarts and the 
ENABLED LED is turned on to indicate the option card was 
installed correctly.
After reconfiguration, the relay updates the part number, except 
for the following indicated digits. These digits remain 
unchanged, i.e., these digits retain the same character as before 
the reconfiguration. Also, a communications card installed in 
Slot C is reflected as an empty slot in the part number. A regular 
4 DI/4 DO card and a hybrid 4 DI/4 DO card have the same 
device ID. When interchanging these two cards, the part 
number for the respective slots should be updated manually. 
Use the STATUS command to view the part number.
Step 23. Update the side-panel drawing with the drawing sticker 
provided in the option card kit. If necessary, replace the rear 
panel with the one applicable for the option card and attach the 
terminal-marking label provided with the card to the rear-panel 
cover. Also, contact SEL for an updated product serial number 
label with the updated part number.
Step 24. Reconnect all connection plugs and add any additional 
wiring/connectors required by the new card.
Slot B CPU Card Replacement
When replacing the Slot B card, do the following:
1. Ensure that the card has the latest firmware from the factory.
2. Review the firmware revision history for the changes that were 
made; note that new settings added, if any, might affect existing 
settings in the relay or its application.
3. Save all settings and event reports before replacing the card.
4. If the IEC 61850 protocol option was used previously, verify 
that the IEC 61850 protocol is still operational after the 
replacement. If not, reenable it. Refer to Protocol Verification for 
Relays With IEC 61850 Option in Appendix B: Firmware 
Upgrade Instructions.
Perform the following steps to replace the existing CPU board with a new 
board:
Step 1. Turn off the power to the relay.
Step 2. Use a ground strap between yourself and the relay.
Step 3. Disconnect the terminal blocks and CT/PT wires.
Step 4. Remove the rear panel.
Step 5. Remove the main board from its slot and insert the new board.
Step 6. Attach the rear panel (new if applicable) and reconnect the 
terminal blocks and CT/PT wires.
Step 7. Apply new side stickers to the relay.
PART NUM = 751001B5X1X7086020X
2.17
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
Step 8. Turn on the relay and log in via terminal emulation software.
Step 9. Issue the STA command and accept the new configuration.
Step 10. From Access Level 2, type CAL to enter Access Level C.
Do not modify any calibration settings other than those listed in 
this procedure.
The default password for Access Level C is CLARKE.
Step 11. From Access Level C, issue the SET C command.
Step 12. Update the serial number and part number to the appropriate 
values, type END, and save the settings.
Step 13. Issue the STA C command to reboot the relay.
Step 14. Issue the STA command to verify that the serial number and 
part number of your relay are correct.
Slot A Power Supply Card
If you are replacing the power supply card, change the part number 
accordingly using the PARTNO command from Access Level C. Install new 
side stickers on the side of the relay.
Analog Input (AI) 
Voltage/Current 
Jumper Selection
Figure 2.3 shows the circuit board of an analog I/O board. Jumper x (x = 1–8) 
determines the nature of each channel. For a current channel, insert Jumper x 
in position 1–2; for a voltage channel, insert Jumper x in position 2–3.
Figure 2.3 Circuit Board of Analog I/O Board, Showing Jumper Selection
JMPX
21 3 21 3
JMPX
Position 2 – 3 = V (voltage) mode
Where "JMPX" is the jumper for AI channel "X"
Position 1 – 2 = I (current) mode 
(default position)
2.18
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
I/O Configuration
Analog Output (AO) 
Voltage/Current 
Jumper Selection
Figure 2.4 shows the locations of JMP1 through JMP4 on an analog output 
board. You can select each of the four analog output channels as either a 
current analog output or a voltage analog output.
Figure 2.4 JMP1 Through JMP4 Locations on 4 AI/4 AO Board
You need to insert three jumpers for a current analog output selection and two 
jumpers for a voltage analog output selection. For a current analog output 
selection, insert a jumper between Pins 1 and 2, Pins 5 and 6, and Pins 9 and 
10. For a voltage analog output selection, insert a jumper between Pins 3 
and 4, and Pins 7 and 8. Figure 2.5 shows JMP4 selected as a current analog 
output. The current analog output selection is the default setting for JMP1 
through JMP4. Figure 2.6 shows JMP1 selected as a voltage analog output.
Figure 2.5 Current Output Jumpers Figure 2.6 Voltage Output Jumpers
JMP1JMP2
JMP3
JMP4
9 7 5 3 1
10 8 6 4 2
JMP1–JMP4 Pin 
Numbering
NOTE: Analog inputs cannot provide 
loop power. Each analog output is self 
powered and has an isolated power 
supply.
NOTE: There is no jumper between 
Pins 5 and 6 for a voltage analog 
output selection.
9
5
1
10
6
2
JM
P4
JMP4 Selected as Current Output
7
5
3
8
6
4
JM
P1
JMP1 Selected as Voltage Output
2.19
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
I/O Configuration
Password, Breaker 
Control, and SELBOOT 
Jumper Selection
Figure 2.7 shows the major components of the Slot B card in the base unit. 
Notice the three sets of pins labeled A, B, and C.
Figure 2.7 Pins for Password, Breaker Control, and SELBOOT Jumper
Pins labeled A bypass the password requirement, pins labeled B enable 
breaker control, and pins labeled C force the relay to the SEL operating sys-
tem calledSELBOOT. In the unlikely event that the SEL-751 experiences an 
internal failure, communication with the relay may be compromised. Forcing 
the relay to SELBOOT provides you with a way to download new firmware. To 
force the relay to SELBOOT, place the jumper in position C, as shown in 
Figure 2.7 (SELBOOT Forced). After the relay is forced to SELBOOT, you can 
only communicate with it via the front-panel port.
To gain access to the Level 1, 2, or C command levels without passwords, 
place the jumper in Position A, as shown in Figure 2.7 (Password Bypassed). 
Note that you can only access command levels without passwords to the 
access level set for the MAXACC setting for the port through which you are 
communicating. Although you can gain access to Level 2 and Level C without 
passwords, the alarm contact still closes momentarily when accessing Level 2 
and Level C. See Table 2.17 for the functions of the three sets of pins and 
their jumper default positions.
Table 2.17 Jumper Functions and Default Positions
Pins Jumper Default Position Description
A Not bypassed (requires password) Password bypass
B On (breaker control enabled) Enable breaker controla
a Enable/disable serial port, front panel, and Fast Operate commands for the breaker control. 
The jumper position affects the breaker control using the OPEN or CLOSE commands and 
output contact control using the PULSE command via the serial port, the front-panel menu-
driven user interface, or the communications protocols. The jumper position does not affect 
the operation of the local bits, the remote bits, or the front-panel programmable pushbuttons.
C Not bypassed (not forced SELBOOT) SELBOOT Forced
JMP1
A B C
JMP1
A B C
JMP1
A B C
JMP1
A B C
Password
Bypassed
Default
Positions
SELBOOT
Forced
Remote
Breaker
Control
Allowed
JMP1
A B C
2.20
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Relay Connections
Relay Connections
Side-Panel and 
Rear-Panel Diagrams
The physical layout of the connectors on the side-panel and rear-panel 
diagrams of seven sample configurations of the SEL-751 are shown in 
Figure 2.8 through Figure 2.14.
Figure 2.8 Dual Fiber Ethernet With 2 AVI/4 AFDI Voltage Option With Arc-Flash 
Detector Inputs, DeviceNet Card, and Fast Hybrid 4 DI/4 DO Card (Relay MOT 751501AA3CA70850830)
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
2.21
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Relay Connections
Figure 2.9 Single Copper Ethernet, EIA-485 Communication, 8 DO (Form A) Card, 4 AI/4 AO Card, and 
2 AVI/4 AFDI Voltage Option With Arc-Flash Detector Inputs (Relay MOT 751201A2A6X70810320)
Figure 2.10 Single Copper Ethernet With EIA-232 Communication, 10 RTD Card, 4 DI/4 DO Card and 
2 AVI/4 AFDI Voltage Option Card With Arc-Flash Detector Inputs (Relay MOT 751501A1A9X70850230)
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
2.22
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Relay Connections
Figure 2.11 No Ethernet, EIA-232 Serial Communications, EIA-232/EIA-485 Communications 
Card, 8 DI Card, and 8 DO Card (Form A) (Relay MOT 751401AA03A2A850000)
Figure 2.12 Dual Copper Ethernet, 4 DI/4 DO Card, 14 DI Card, 8 AFDI With Arc-Flash Detector 
Inputs, 4 ACI/3 AVI Card With 5 A Phase, 200 mA Neutral, and Three-Phase AC Voltage Inputs (300 Vac) 
(Relay MOT 7515S1A1A4A77870671)
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
2.23
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Relay Connections
Figure 2.13 Dual Copper Ethernet, 14 DI Card, 8 DO (Form B) Card, 2 AVI/4 AFDI Card With LEA Vsync, Vbat 
Inputs, and 4 Arc-Flash Detection Inputs, 4 ACI/3 AVI Card With 5 A Phase, 200 mA Neutral, and Three-Phase 
LEA Voltage Inputs (8 Vac) (Relay MOT 751501A4A2BL0L70671)
Figure 2.14 Dual 10/100 Base-T Ethernet, EIA-232 Rear Port, Without Single Multimode ST Fiber-Optic Serial 
Port Rear, With DeviceNet Card, Fast Hybrid 4 DI/4 DO Card, 8 DI Card and 4 ACI Card (No Voltage Inputs) 
(Relay MOT 751001AA3CA3AA50F30)
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
(A) Side-Panel Input and Output Designations (B) Rear-Panel Layout
2.24
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Relay Connections
Power Connections The POWER terminals on the rear panel (A01(+/H) and A02(—/N)) must connect 
to 110–240 Vac, 110–250 Vdc or 24–48 Vdc (see Power Supply on page 1.13 
for complete power input specifications). The POWER terminals are isolated 
from chassis ground. Use 14 AWG (2.1 mm2) to 16 AWG (1.3 mm2) size wire 
to connect to the POWER terminals.
For compliance with IEC 60947-1 and IEC 60947-3, place a suitable external 
switch or circuit breaker in the power leads for the SEL-751; this device 
should interrupt both the hot (+/H) and neutral (—/N) power leads. The maxi-
mum current rating for the power disconnect circuit breaker or optional over-
current device (fuse) should be 20 A, 300 V.
Operational power is internally fused by a power supply fuse. See Field Ser-
viceability on page 2.53 for details. Be sure to use fuses that comply with 
IEC 60127-2.
Grounding (Earthing) 
Connections
You must connect the ground terminal labeled GND on the rear panel to a rack 
frame or switchgear ground for proper safety and performance. Use 14 AWG 
(2.1 mm2) to 18 AWG (0.8 mm2) wire less than 2 m (6.6 ft) in length for the 
ground connection.
Serial Ports Because all ports (F, 2, 3, and 4) are independent, you can communicate to any 
combination simultaneously. Although serial Port 4 on the optional communi-
cations card consists of an EIA-485 (4A) and an EIA-232 (4C) port, only one 
port is available at a time. Use the Port 4 communications interface 
COMMINF setting to select between EIA-485 and EIA-232.
The serial port EIA-485 plug-in connector accepts wire size 26 AWG through 
14 AWG. Strip the wires 8 mm (0.31 in) and install with a small slotted 
screwdriver. All EIA-232 ports accept 9-pin D-subminiature male connectors.
For connecting devices at distances farther than 100 ft, where metallic cable is 
not appropriate, SEL offers fiber-optic transceivers or the fiber-optic port. The 
SEL-2800 family of transceivers provides fiber-optic links between devices 
for electrical isolation and long-distance signal transmission. Contact SEL for 
further information on these products.
IRIG-B Time-Code Input
The SEL-751 IRIG-B accepts a demodulated time signal to synchronize the 
internal clock with an external source. Three options for IRIG-B signal input 
are given, but only one should be used at a time. You can use the IRIG-B (B01 
and B02) inputs, an SEL communications processor via EIA-232 serial Port 3, 
or fiber-optic serial Port 2. The available communications processors are the 
SEL-2032, SEL-2030, SEL-2020, and the SEL-2100 Logic Processor. You 
can also use the SEL-3530 Real-Time Automation Controller (RTAC) to 
provide an IRIG-B input.
The models with fiber-optic Ethernet and dual copper Ethernet do not have 
the terminals B01 and B02 for IRIG-B but have IRIG-B input via EIA-232 
Port 3. The third option for IRIG-B is via fiber-optic serial Port 2. Use an 
SEL-2812MT Transceiver to connect to the SEL-2030 or SEL-2032 and bring 
the IRIG-B signal with the EIA-232 input. Use a fiber-optic cable pair with 
ST connectors (C805, C807, or C808) to connect to Port 2 on the SEL-700G. 
Refer to Section 7: Communications for IRIG-B connection examples and for 
details about using an SEL-2401/2407/2404 as a time source.
DANGER
Contact with instrument terminals can 
cause electrical shock that can result 
in injury or death.
CAUTION
Equipment components are sensitive 
to electrostatic discharge (ESD). 
Undetectable permanent damage can 
result if you do not use proper ESD 
procedures. Ground yourself,your 
work surface, and this equipment 
before removing any cover from this 
equipment. If your facility is not 
equipped to work with these 
components, contact SEL about 
returning this device and related SEL 
equipment for service.
2.25
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Relay Connections
Ethernet Port
The SEL-751 can be ordered with an optional single/dual 10/100BASE-T or 
100BASE-FX Ethernet port. Connect to Port 1 of the device by using a 
standard RJ45 connector for the copper port and an LC connector for the fiber-
optic port.
Fiber-Optic Serial Port
The optional fiber-optic serial port is compatible with the SEL-2812 Fiber-
Optic Transceivers with IRIG-B, the SEL-2814 Fiber-Optic Transceivers, or 
the SEL-2600 RTD Module.
I/O Diagram A more functional representation of two of the control (I/O) connections is 
shown in Figure 2.15 and Figure 2.16.
Figure 2.15 Control I/O Connections—4 AI/4 AO Option in Slot D and Fiber-Optic Port in Slot B
Fiber-Optic Cable
to SEL-2600 Series
+IRIG-B
–IRIG-B
IRIG-B
PS
A01
A02
–/N
+/H
External 
Contacts
SEL-751 Relay
RX
D07
+ 
As Many as Four
Analog Outputs
D08
— 
B01 B02
IN
10
1
IN
10
2
A10
A11
A12 A07
A08
OU
T1
03
+ 
D15
— 
D16
D02
— 
— 
D10
D01
+ 
+ 
D09
A03
A04
OU
T1
01
A05
A06
OU
T1
02
A09
TX
As Many as Four
Analog Inputs
AO401 AO404
AI401 AI404
+ +
+ +
NOTE: All digital inputs 
and digital outputs 
(including high-current, 
high-speed hybrid) 
connections are polarity 
neutral.
2.26
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Relay Connections
Figure 2.16 Control I/O Connections—Internal RTD Option in Slot D
RTD Wiring Table 2.18 shows the maximum cable lengths for the RTD connections that 
satisfy the 25-ohm limit required for connecting to SEL devices.
Refer to application guide AG2017-09: Applying Various Types of RTDs With 
SEL Devices. This application guide specifies the correct connection of two-
wire, three-wire, and four-wire RTDs to three-terminal SEL measurement 
devices.
RTD wiring recommendations:
1. Use shielded twisted pair cables for RTD wiring.
2. Connect the RTD_CAL wire to the RTD CAL/SHIELD 
Terminal on the SEL device. This will eliminate any wiring 
resistance error.
3. Make sure the RTD mounting ear screws are snug and secure.
PS
A01
A02
–/N
+/H
External
Contacts
SEL-751 RelayIN1
01
IN
10
2
A10
A11
A12
+IRIG-B
–IRIG-B
IRIG-B
B01 B02
A07
A08
OU
T1
03
A03
A04
OU
T1
01
A05
A06
OU
T1
02
A09
D03
COMP/
SHLD
D02
—
D01
+
RTD01
D30
COMP/
SHLD
D29
— 
D28
+ 
RTD10
As Many as Ten
RTD Inputs
• The chassis ground connector located on the rear-panel card Slot A must always be connected to the local ground mat.
• Power supply rating (110–240 Vac, 110–250 Vdc or 24–48 Vdc) depends on the relay part number.
• Optoisolated Inputs IN101 and IN102 are standard and are located on the card in Slot A.
• All optoisolated inputs are single-rated: 24, 48, 110, 125, 220, or 250 Vac/Vdc. Standard Inputs IN101/102 can have a different
 rating then the optional IN401/402/403/404 (not shown).
• Output Contacts OUT101, OUT102, and OUT103 are standard and are located on the card in Slot A.
• The analog (transducer) outputs shown are located on the optional I/O expansion card in Slot D.
• The fiber-optic serial port is located on the card in Slot B. A Simplex 62.5/125 um fiber-optic cable is necessary for connecting
 to an SEL-2600 RTD Module. This fiber-optic cable should be 1000 meters or shorter.
NOTE: All RTD 
comp/shield terminals are 
internally connected to 
the relay chassis and 
ground.
Table 2.18 Typical Maximum RTD Lead Length
RTD Lead AWG Maximum Length (meters)
28 116 m
26 184 m
24 290 m
22 455 m
20 730 m
18 1155 m
16 1848 m
NOTE: RTD inputs are not internally 
protected from electrical surges. 
External protection is recommended 
if surge protection is necessary.
2.27
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Use Relay Wire Termination Kits—see Application Note AN2014-08—and 
avoid fitting multiple wires into a single terminal, the bird-caging effect of 
stranded wires, and bulky wire bundles.
Analog Output Wiring Connect the two terminals of the analog output as shown in Figure 2.17. Also 
connect the analog output cable shield to ground at the relay chassis ground, 
programmable logic controller (PLC), or meter location. Do not connect the 
shield to ground at both locations.
Figure 2.17 Analog Output Wiring Example
AC/DC Control Connection Diagrams
This section describes fail-safe versus nonfail-safe tripping, describes voltage 
connections, and provides the ac and dc wiring diagrams.
Fail-Safe/Nonfail-Safe 
Tripping
Figure 2.18 shows the output OUT103 relay coil and Form C contact. When the 
relay coil is de-energized, the contact between A07 and A08 is open while the 
contact between A07 and A09 is closed.
Figure 2.18 Output OUT103 Relay Output Contact Configuration
The SEL-751 provides fail-safe and nonfail-safe trip modes (setting 
selectable) for all output contacts. The following occurs in fail-safe mode:
➤ The relay coil is energized continuously if the SEL-751 is 
powered and operational.
➤ When the SEL-751 generates a trip signal, the relay coil is 
de-energized.
➤ The relay coil is also de-energized if the SEL-751 power supply 
voltage is removed or if the SEL-751 fails (self-test status is 
FAIL).
NOTE: Connection of dc voltage to 
the analog output terminals could 
result in damage to the relay.
Analog Output
Relay Chassis Ground
Meter
or
PLC
AO_0 1
02
0 1
Contacts shown with 
OUT103 relay coil de-energized
A07
A08 A09
OUT103
Relay Coil
NOTE: Fast hybrid contacts are 
designed for fast closing (50 s) 
only. Fail-safe mode operating time 
(time to open the contacts) for 
fast-hybrid contacts is <8 ms (the 
same time as for a normal output 
contact).
2.28
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
Figure 2.19 shows fail-safe and nonfail-safe wiring methods to control 
breakers.
Figure 2.19 Breaker Trip Coil Connections With OUT103FS := Y and 
OUT103FS := N
High-Speed, High-
Current Interrupting 
DC Tripping Outputs
High-speed outputs are optimized for direct tripping of power circuit breakers. 
They operate in less than 50 µs, work with dc trip coil circuits, are polarity 
insensitive and capable of making 30 A, and can interrupt 10 A with an 8 ms 
dropout time. High-speed outputs are implemented as hybrid circuits, each of 
which consists of the parallel combination of a high-current, solid-state switch 
and an electromechanical bypass relay. Avoid using high-speed outputs to 
drive highly sensitive, high-input-resistance electronic inputs (e.g., <2 mA 
electronic circuits) unless such inputs are connected in parallel with a low-
resistance load (e.g., a breaker trip coil). 
Avoid connecting multiple high-speed outputs in parallel when driving highly 
sensitive electronic inputs. Keep wiring short, and use fiber-based MIRRORED 
BITS communications to bridge longer distances.
Voltage Connections With the voltage inputs option, you can connect the ac voltages directly, use a 
wye-wye VT connection (set DELTA_Y := WYE), an open-delta VT 
connection (set DELTA_Y := DELTA), or a single-phase VT (set 
SINGLEV := Y). Figure 2.20 and Figure 2.21 show the methods of 
connecting single-phase and three-phase voltages.
When the voltage inputs to the relay are connected in wye as shown in 
Figure 2.21 (a): Direct Connection, Figure 2.21 (b): Wye-Wye VT Connec-
tions With LEA Inputs) or Figure 2.21 (c): Wye-Wye VT Connection, the relay 
computes the zero-sequence voltage as the following:
3V0 = VA + VB + VC
When the voltage inputs to the relay are connected via an open-delta VT as 
shown in Figure 2.21 (d)–Figure 2.21 (f), the relay cannot calculate zero-
sequence voltage (3V0). Relay functions that require zero-sequencevoltage 
may be disabled, unless another 3V0 voltage source is supplied to the relay 
via terminal VS-NS and VSCONN is set to 3V0 as in Figure 2.21 (e) and 
Figure 2.21 (f). With setting VSCONN := 3V0, voltage input VS (terminals 
VS, NS) expects 3V0 voltage (VS = 3V0 = VA + VB + VC) with the polarity 
shown in the figures. Setting VSCONN := 3V0 disables the synchronism-
check element. To enable synchronism check element set VSCONN := VS. 
Set VSCONN accordingly per your application needs.
Nonfail-safe
OUT103FS = N
52A
Breaker Trip CoilTC
A08
A07A07
52A
Fail-Safe
(Electrically Held Open)
OUT103FS= Y
Breaker Trip CoilTC
A09
NOTE: Contacts shown with OUT103 relay coil de-energized
NOTE: Current limiting fuses in 
direct-connected voltage applications 
are recommended to limit short-
circuit arc-flash incident energy.
2.29
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Some installations do not have all three voltage phases available to connect to 
the relay as shown in Figure 2.20 (a) and Figure 2.20 (b). In such cases set 
DELTA_Y to WYE or DELTA according and set SINGLEV := Y. In those 
cases the relay will disable some of the voltage based functions as specified in 
Table 4.4.
Figure 2.20 Single-Phase Voltage Connections
(a) Single Phase-Neutral VT Connection
(DELTA_Y := WYE and SINGLEV := Y)
EO1
EO2
A B C
ZO9
Z10
Z11
Z12
SEL-751
F1
(b) Single Phase-Phase VT Connection
(DELTA_Y := DELTA and SINGLEV := Y)
A B C
EO1
EO2
ZO9
Z10
Z11
Z12
SEL-751
F1
VS
NS
VA
VB
VC
N
VS
NS
VA
VB
VC
N
2.30
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
Figure (b) shows LEA inputs, which support only wye-wye connections. Refer to Under- and Overvoltage Functions on 
page 4.100 and LEA Ratio and Angle Correction Factors (Global Settings) on page 4.9 for the LEA settings and ratio 
correction factor calculations.
Figure (d) shows an open-delta VT connection with B-Phase (Z10) grounded. You can choose to ground A-Phase or 
C-Phase instead of B-Phase, as shown in figures (e) and (f), provided all other connections remain as shown. Terminals 
E01 or E02 can be used to input VAB voltage from the bus to the VS/NS input on the relay with NS terminal grounded. 
Figure 2.21 Voltage Connections
LE
A 
Se
ns
or
Note: N terminal must be connected to ground. This 
is normally accomplished inside the sensor.
(e) Open-Delta and Broken-Delta (3V0) VT Connections 
(Set DELTA_Y := DELTA and VSCONN := 3V0) 
A B C
ZO9
Z10
Z11
Z12
F2
F3
F4
Broken-Delta
VA
VB
VC
E02
E01
SEL-751
(f) Open-Delta and Broken-Delta (3V0) VT Connections
(Set DELTA_Y := DELTA and VSCONN := 3V0)
A B C
ZO9
Z10
Z11
Z12Broken-Delta
VA
VB
VC
E02
E01
SEL-751
F1
F2
F4
(a) Direct Connection (Grounded System)
(Set DELTA_Y := WYE)
F1, F2, and F3 are fuses
EO1
EO2
A B C
ZO9
Z10
Z11
Z12
F1
F3
F2
SEL-751
(c) Wye-Wye VT Connection 
(Set DELTA_Y := WYE and VSCONN := VS )
EO1
EO2
A B C
ZO9
Z10
Z11
Z12
F1
F3
F2
SEL-751
(d) Open-Delta VT Connection 
(Set DELTA_Y := DELTA and VSCONN := VS)
EO1
EO2
A B C
ZO9
Z10
Z11
Z12
F1
F3
SEL-751
(b) Wye-Wye Connected LEA Sensors 
(Set DELTA_Y := WYE )
A
B
C
EO1
EO2
ZO9
Z10
Z11
Z12
SEL-751
VS
NS
VA
VB
VC
N
VS
NS
VA
VB
VC
N
VS
NS
VA
VB
VC
N
VA
VC
NN
VA
VB
VC
N
VS
NS
VA
VB
VC
VS
NS
VB
VS
NS
2.31
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Potential Transformer 
Ratios and PT 
Nominal Secondary 
Voltage Settings
The relay setting PTR is the overall potential ratio from the primary system to 
the relay phase voltage inputs VA-VB-VC-N. For example, on a 12.5 kV 
phase-to-phase primary system with wye-connected 7200:120 V PTs (setting 
DELTA_Y := WYE, and the relay wired as shown in Figure 2.21 (c)), the 
correct PTR setting is 60. For the same 12.5 kV system connected through 
12470:115 V PTs in an open-delta configuration (setting 
DELTA_Y := DELTA, and the relay wired as shown in Figure 2.21 (d), 
Figure 2.21 (e) or Figure 2.21 (f)), the correct PTR setting is 108.44.
Single-phase voltage connections follow the same rationale. Refer to 
Figure 2.20 (a) and Figure 2.20 (b). For example, with a single-phase voltage 
connection to the VA-N terminals (DELTA_Y := WYE and SINGLEV := Y) 
from a 12.5 kV phase-to-phase primary system with a line-neutral connected 
7200:120 V PT, the correct PTR setting is 60. For the same 12.5 kV system 
connected through 12470:115 V PTs in a line-to-line configuration 
(DELTA_Y := DELTA and SINGLEV := Y) the correct PTR setting is 
108.44.
The relay setting PTRS is the overall potential ratio from the synchronizing or 
broken-delta voltage source to the relay VS-NS voltage inputs. For example, 
in a synchronism-check application (setting VSCONN := VS), with phase-to-
ground voltage connected from a 12.5 kV phase-to-phase primary system 
through a 7200:120 V PT, the correct PTRS setting is 60.
In an application that uses a broken-delta PT connection to create a 3V0 zero-
sequence voltage signal (setting VSCONN := 3V0 and the relay VS-NS termi-
nals wired as shown in Figure 2.21 (e) or Figure 2.21 (f)) with three PTs con-
nected wye (primary)/broken delta (secondary) with ratios of 7200:120, the 
correct PTRS setting is 60. If the application includes a step-down trans-
former in addition (not show in the figure), it must also be included in the 
overall PTRS ratio calculation. If a 400:250 step-down instrumentation trans-
former is in the circuit, the correct PTRS setting would be 60 • 1.6 = 96.00.
Settings PTR and PTRS are used in the event report and METER commands 
to report power system values in primary units. Settings PTR and PTRS are 
also used when the setting VSCONN := 3V0, to scale the measured VS volt-
age into the same voltage base as voltage inputs VA-VB-VC-N for certain 
directional functions in Section 4: Protection and Logic Functions. If no VTs 
are connected to voltage inputs VA-VB-VC-N, make setting PTR the same 
value as setting PTRS. The ratio of the PTRS and PTR settings (PTRS/PTR) 
must be less than 1000 and greater than 0.001 when VSCONN := 3V0. The 
relay setting VNOM is the nominal secondary voltage connected to voltage 
inputs VA-VB-VC-N. For wye-connected or delta-connected PTs, VNOM is 
the phase-to-phase secondary voltage value. 
For example, for a 10 kV (phase-to-phase) system with wye-connected VTs 
rated 7200:120 V (PTR := 60), the setting for VNOM would be: 
10000 V/60 = 166.66 V. For a 12.5 kV (phase-to-phase) system with open-
delta connected VTs rated 14000:115 V (PTR := 121.74), the setting for 
VNOM would be 12500 V/121.74 = 102.68 V. 
The SEL-751 automatically sets VNOM := OFF and hides the setting when 
the setting SINGLEV := Y. In Table 4.4, a setting of SINGLEV := OFF is 
shown to disable/turn-off a number of features. Effectively, VNOM := OFF 
signifies that a full three-phase voltage source is not connected to voltage 
inputs VA-VB-VC-N. Even with VNOM := OFF, voltage can still be con-
nected to voltage inputs VA-VB-VC-N (for example, single-phase voltage 
connected to voltage input VA-N), as discussed. 
2.32
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
Station DC Battery 
Monitor
Use the station dc battery monitor (one of the options available with the 
Voltage Card options) in the SEL-751 to alarm for undervoltage and 
overvoltage dc battery conditions and to view how station dc battery voltage 
fluctuates during tripping, closing, and other dc control functions. The 
monitor measures station dc battery voltage applied to the rear-panel terminals 
E03 (VBAT+) and E04 (VBAT–) of the SELECT 2 AVI/4 AFDI voltage/arc-
flash card in Slot E. Refer to Section 5: Metering and Monitoring for details 
on the station dc battery monitor function and settings. 
AC/DC Connections 
and Applications
Figure2.22 shows typical phase and neutral current connections for a feeder 
application. Figure 2.23 through Figure 2.32 show ac/dc connection diagrams 
for various applications. See Figure 2.20 and Figure 2.21 for other voltage 
connections.
Figure 2.22 Typical Current Connections
SEL-751
The current transformers and the SEL-751 
chassis must be grounded in the relay cabinet.
A
B
C
IN
IC
IB
IA
Z08
Z07
Z06
Z05
Z04
Z03
Z02
Z01
52
FEEDER
BUS
2.33
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Voltages are necessary for voltage elements, synchronism-check elements, voltage-polarized directional elements, fault 
location, and metering (e.g., voltage, KW, KVAR). INxxx and OUTxxx indicate user-configurable optional digital inputs and 
outputs. Voltage channel VS is shown connected with VSCONN := VS for use in voltage and synchronism-check elements 
and voltage metering. You can use the VS voltage channel for other voltage inputs such as 3VO from a broken delta PT 
connection by setting VSCONN := 3V0 for use with zero-sequence voltage polarized directional elements. Setting 
VSCONN := 3V0 disables synchronism-check elements.
Channel IN provides current IN for the neutral ground overcurrent elements. Separate from Channel IN, the residual 
ground overcurrent elements operate from the internally derived residual current IG (IG = 3I0 = IA + IB + IC). But in this 
residual connection example, the neutral ground and residual ground overcurrent elements operate the same because 
IN = IG.
Figure 2.23 SEL-751 Provides Overcurrent Protection and Reclosing for a Distribution Feeder 
(Includes Fast Bus Trip Scheme) (Delta-Connected PTs)
TC
Trip
Coil
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure 
Trip 
Circuit
IC OUTxxx
IN
FEEDER
52
(+)
OUTxxx
(+)
52A
to Annunciator, RTU,
SEL-2032/2030/2020,
or SEL-3530 RTAC
to Bus Relay
(Fast Bus Trip Scheme)
ALARM
OUT101
(+)
(—)
Breaker StatusINxxx
VCN VB VA
VS
NS
Forward 
Tripping 
Direction
2.34
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
Voltages are necessary for voltage elements, synchronism-check elements, voltage-polarized directional elements, fault 
location, and metering (e.g., voltage, KW, KVAR). INxxx and OUTxxx indicate user-configurable optional digital inputs and 
outputs. Voltage channel VS is shown connected with VSCONN := VS for use in voltage and synchronism-check elements 
and voltage metering. You can use VS voltage channel for other voltage inputs such as 3VO from a broken delta PT 
connection by setting VSCONN := 3V0 for use with zero-sequence voltage polarized directional elements. Setting 
VSCONN := 3V0 disables synchronism-check elements.
Channel IN provides current IN for the neutral ground overcurrent elements. Separate from Channel IN, the residual 
ground overcurrent elements operate from the internally derived residual current IG (IG = 3I0 = IA + IB + IC). But in this 
residual connection example, the neutral ground and residual-ground overcurrent elements operate the same because 
IN = IG.
Although automatic reclosing is probably not necessary in this example, output contact OUT102 can close the circuit 
breaker via initiation from various means (serial port communications, optoisolated input assertion, etc.) with desired 
supervision (e.g., synchronism check).
INxxx is shown for use with a fast bus trip scheme. The fast bus trip scheme is often referred to as a reverse-interlocking 
or zone-interlocking scheme.
Figure 2.24 SEL-751 Provides Overcurrent Protection for a Distribution Bus (Includes Fast Bus Trip Scheme) 
(Wye-Connected PTs)
TC
Trip
Coil
52A
(+)
(—) Trip
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
CC
Close
Coil
52B
(+)
(—) Close
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker
Failure
Trip
Circuit
IC OUTxxx
IN
BUS
52
(+)
52A
to Annunciator, RTU,
SEL-2032/2030/2020,
or SEL-3530 RTAC
From Feeder Relays
(Fast Bus Trip Scheme)
ALARM
OUT101
(+)
(—)
Breaker StatusINxxx
(—)
INxxx
VCN VB VA
VS
NS
A
B
C
Forward 
Tripping 
Direction
2.35
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Voltage Channel VS does not need to be connected. Here, it is shown connected for use in voltage and synchronism-
check elements and voltage metering. See Figure 2.21 (d and e) on for synchronism-check VS connection (VSCONN := 
VS) and broken-delta VS connection (VSCONN := 3V0).
In this example, current Channel IN provides current polarization for a directional element used to control ground 
overcurrent elements. Separate from Channel IN, the residual ground overcurrent elements operate from the internally 
derived residual current IG (IG = 3I0 = IA + IB + IC).
Figure 2.25 Transmission Line Directional Overcurrent Protection and Reclosing With Current-Polarization 
Source Connected to Channel IN (Wye-Connected PTs)
TC
Trip
Coil
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
Fo
rw
ar
d 
Tr
ip
pi
ng
 D
ire
ct
io
n
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure Trip 
CircuitIC OUTxxx
IN
VS
NS
LINE
52
(+)
52A
to Annunciator, RTU, 
SEL-2032/2030/2020, 
or SEL-3530 RTAC
OUT101
ALARM
(+)
(—)
Breaker StatusINxxx
(+)
(—) From Feeder Relays 
(Fast Bus Trip Scheme)INxxx
TRANSFORMER BANK
VCN VB VA
2.36
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
Voltages are necessary for voltage elements, synchronism-check elements, voltage-polarized directional elements, fault 
location, and metering (e.g., voltage, KW, KVAR). INxxx and OUTxxx indicate user-configurable optional digital inputs and 
outputs.
Although automatic reclosing is probably not necessary in this example, output contact OUT102 can close the circuit 
breaker via initiation from various means (serial port communications, optoisolated input assertion, etc.), with desired 
supervision (e.g., hot bus check). 
For sensitive earth fault (SEF) applications, the SEL-751 should be ordered with channel IN rated at 0.2 A nominal. See 
AC Current Input specifications on page 1.13. See neutral ground overcurrent element pickup specifications in Table 4.9 
and Table 4.16.
Figure 2.26 SEL-751 Provides Overcurrent Protection for a Delta-Wye Transformer Bank (Wye-Connected PTs)
TC
Trip
Coil
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure 
Trip 
Circuit
IC OUTxxx
IN
52
(+)
52A
to Annunciator, RTU,
SEL-2032/2030/2020,
or SEL-3530 RTAC
ALARM
OUT101
(+)
(—)
Breaker StatusINxxx
n
b a c
(Low-Side)
VCN VB VA
Forward 
Tripping 
Direction
2.37
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
Voltages are necessary for voltage elements, synchronism-check elements, voltage-polarized directional elements, fault 
location, and metering (e.g., voltage, KW, KVAR). INxxx and OUTxxx indicate user-configurable optional digital inputs and 
outputs.
Although automatic reclosing is probably not necessary in this example, output contact OUT102 can close the circuit 
breaker via initiation from various means (serial port communications, optoisolated input assertion, etc.), with desired 
supervision (e.g., hot bus check).
Figure 2.27 SEL-751 Provides Overcurrent Protection for a Transformer Bank With a Tertiary 
Winding (Wye-Connected PTs)
TC
Trip
Coil
52A
(+)
(—) Trip
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
CC
Close
Coil
52B
(+)
(—) Close
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker
Failure
Trip
Circuit
IC OUTxxx
IN
(+)
52A
to Annunciator, RTU,
SEL-2032/2030/2020,
or SEL-3530 RTAC
ALARM
OUT101
(+)
(—)
Breaker StatusINxxx
n
a
(Low-Side)(Tertiary)
c b
N
52
VCN VB VA
Forward 
Tripping 
Direction
2.38
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
A core-balance current transformer is often referred to as a zero-sequence, ground fault, or window current transformer.
Pass neutral (N) through the core-balance CT only if the neutral is brought out and it is grounded only at the source.
Voltages are necessary for voltage elements, synchronism-check elements, voltage-polarized directional elements, fault 
location, and metering (e.g., voltage, KW, KVAR). INxxx and OUTxxx indicate user-configurable optional digital inputs and 
outputs.
Although automatic reclosing is probably not necessary in this example, output contact OUT102 can close the circuit 
breaker via initiation from various means (serial port communications, optoisolated input assertion, etc.), with desired 
supervision.
Figure 2.28 SEL-751 Provides Overcurrent Protection for an Industrial Distribution Feeder 
(Core-Balance Current Transformer Connected to Channel IN)
TC
Trip
Coil
52A
(+)
(—) Trip
CircuitIA
SEL-751 RELAY
OUT103
CC
Close
Coil
52B
(+)
(—) Close
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker
Failure
Trip
Circuit
IC OUTxxx
IN
52
(+)
52A
to Annunciator, RTU,
SEL-2032/2030/2020,
or SEL-3530 RTAC
ALARM
OUT101
(+)
(—)
Breaker StatusINxxx
FEEDER
AN B C
A
B
C
N
BUS
Forward 
Tripping 
Direction
2.39
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
A core-balance current transformer is often referred to as a zero-sequence, ground fault, or window current transformer.
The lower CT wiring option (with the core-balance current transformer) is the preferred option (greater sensitivity; no 
false residual currents due to CT saturation, etc.).
Directional control for a low-impedance grounded system is selected with setting ORDER containing S. Directional 
control for a high-impedance grounded system is selected with setting ORDER := U (see Table 4.20–Table 4.22). 
Nondirectional sensitive earth fault (SEF) protection is also available.
Figure 2.29 SEL-751 Provides Overcurrent Protection for a High-Impedance or Low-Impedance 
Grounded System (Wye-Connected PTs)
TC
Trip
Coil
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
Fo
rw
ar
d 
Tr
ip
pi
ng
 D
ire
ct
io
n
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure 
Trip 
Circuit
IC OUTxxx
OUT101
IN
FEEDER
52
(+)
52A
ALARM
(+)
(—)
Breaker StatusINxxx
IA
Fo
rw
ar
d 
Tr
ip
pi
ng
 D
ire
ct
io
n
IB
IC
IN
AN B C
CT Wiring Options
Pass neutral (N) through 
core-balance CT only if neutral 
is brought out and it is 
grounded only at the source
Low-Impedance
or
High-Impedance
Grounded
+
+
to Annunciator, RTU,
or SEL Communications 
Processor
VCN VB VA
2.40
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
A core-balance current transformer is often referred to as a zero-sequence, ground fault, or window current transformer.
Directional control for a Petersen coil-grounded system is selected with setting ORDER containing P (see Table 4.20–
Table 4.22). Nondirectional sensitive earth fault (SEF) protection is also available.
Figure 2.30 SEL-751 Provides Overcurrent Protection for a Petersen Coil-Grounded System 
(Wye-Connected PTs)
TC
Trip
Coil
52A
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
Fo
rw
ar
d 
Tr
ip
pi
ng
 D
ire
ct
io
n
Co
re
-B
al
an
ce
 C
T
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure 
Trip 
Circuit
IC OUTxxx
OUT101
FEEDER
A B c
52
(+)
ALARM
(+)
(—)
Breaker StatusINxxx
IN
Petersen
Coil
TRANSFORMER BANK
+
+
to Annunciator, RTU,
or SEL Communications Processor
VCN VB VA
2.41
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
AC/DC Control Connection Diagrams
A core-balance current transformer is often referred to as a zero-sequence, ground fault, or window current transformer.
Directional control for an ungrounded system is selected with setting ORDER := U (see Table 4.20–Table 4.22). 
Nondirectional sensitive earth fault (SEF) protection is also available.
Figure 2.31 SEL-751 Provides Overcurrent Protection for an Ungrounded System (Wye-Connected PTs)
TC
Trip
Coil
52A
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
OUT103
Fo
rw
ar
d 
Tr
ip
pi
ng
 D
ire
ct
io
n
Co
re
-B
al
an
ce
 C
T
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure 
Trip 
Circuit
IC OUTxxx
OUT101
FEEDER
A B c
52
(+)
ALARM
(+)
(—)
Breaker StatusINxxx
IN
Ungrounded
TRANSFORMER BANK
+
+
to Annunciator, RTU,
or SEL Communications Processor
VCN VB VA
2.42
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
AC/DC Control Connection Diagrams
A core-balance current transformer is often referred to as a zero-sequence, ground fault, or window current transformer.
Directional control for an ungrounded system is selected with setting ORDER := U (see Table 4.20—Table 4.22). 
Nondirectional sensitive earth fault (SEF) protection is also available.
The voltage inputs can accept open-delta PT (three-wire) connection (as shown) when setting DELTA_Y := DELTA. 
VB must be externally tied to N, as shown.
The zero-sequence voltage 3V0 (from the “broken-delta” connection) is shown coming from a step-down 
instrumentation transformer, and connecting to voltage input VS-NS. To use this connection, make setting VSCONN := 
3V0. Make group setting PTRS as shown in Section 4: Protection and Logic Functions.
The step-down transformer is required when the maximum expected residual voltage exceeds the relay voltage channel 
rating. 
The polarity of voltage input VS-NS connection should be verified prior to placing the relay into service. 
Figure 2.32 SEL-751 Provides Overcurrent Protection for an Ungrounded System (Open-Delta Connected PTs, 
Broken-Delta 3V0 Connection)
TC
Trip
Coil
52A
(+)
(—) Trip 
CircuitIA
C
B
A
SEL-751 RELAY
VS
NS
OUT103
Fo
rw
ar
d 
Tr
ip
pi
ng
 D
ire
ct
io
n
Co
re
-B
al
an
ce
 C
T
CC
Close
Coil
52B
(+)
(—) Close 
CircuitIB OUT102
86
Lock
Out
86B
(+)
(—) Breaker 
Failure 
Trip 
Circuit
IC OUTxxx
OUT101
FEEDER
A B c
52
(+)
Step-Down 
Transformer 
(Some 
Applications)
ALARM
(+)
(—)
Breaker StatusINxxx
IN
Ungrounded
Broken-Delta
TRANSFORMER BANK
Open-Delta
52A
+
+
to Annunciator, RTU,
or SEL Communications Processor
VCN VB VA
2.43
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Arc-Flash Protection
Arc-Flash Protection
System Installation This section describes an arc-flash system installation, the sensor 
characteristics, and an arc-flash application. Refer to Section 4: Protection 
and Logic Functions for a description of arc-flash protection and the relay 
settings. Section 11: Testing and Troubleshooting gives a description of the 
commissioning tests to verify the installation. Also, refer to Application Guide 
AG2011-01: Using the SEL-751 and SEL-751A for Arc-Flash Detection, 
available on the SEL website, for more details.
Figure 2.33 shows main system components comprising: current input card, 
the arc-flash/voltage input card with sensor terminal block, and the fiber-
optic-based point-sensor assembly. Figure 2.10 shows the rear-panel layout 
and the side-panel I/O designations for a relay model with the 2 AVI/4 AFDI 
card for arc-flash protection. Figure 2.12 shows the rear-panel layout and the 
side-panel I/O designations for a relay model with the 8 AFDI card. Installa-
tion instructions for the 8 AFDI card are similar to the 2 AVI/4 AFDI card.
Figure 2.33 SEL-751 With an Arc-Flash Option Card and Fiber-Optic Based 
Point Sensor
Light-Sensor 
Installation
An arc-flash system installation starts by selecting the best sensor location 
and the safestpath for bringing the sensor fibers back to the relay. The actual 
sensor location varies depending on the type of switchgear being protected. 
Although arc-flash light is easily reflected off painted surfaces, make sure to 
avoid shadows/light obstruction caused by the insulating baffles or moving 
parts of the breaker truck assembly. 
While fiber-optic sensors are inherently nonconductive, they are not intended 
for direct contact with energized parts, and must be suspended within 25 mm 
(1 in) of the grounded surface. Make sure to observe the original high-voltage 
2.44
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Arc-Flash Protection
clearance and creepage requirements. Sensors should be permanently affixed 
through the use of supplied mounting grommets or permanent cable ties. 
Figure 2.34 shows an example of a typical black-jacketed fiber installation. 
Figure 2.34 Black-Jacketed Fiber installation Example
Fiber-bending radius must be kept greater than 50 mm (2 in). Care should be 
exercised when crossing from a moving part (such as control cabinet door) to 
a stationary switchgear enclosure. Use standard wiring practices with bundled 
fibers and well-defined strain relief points. Additional attention is necessary 
to prevent moving parts, such as a breaker truck assembly, from inadvertently 
damaging the arc-flash sensor fibers. Although easily detected by the sensor 
diagnostics, such problems can be eliminated through careful installation 
planning. Once routed, fiber sensors are connected to the SEL-751 as shown 
in Figure 2.33.
Point-Sensor 
Installation 
The point-sensor is optimized for monitoring confined switchgear spaces 
where the distance between sensors and the potential sources of arc (ener-
gized parts) can be kept below 2 m. Such spaces typically include breaker 
compartments, outgoing and incoming cable compartments, and potential 
transformer (PT) compartments. Figure 2.35 shows a schematic diagram of 
the point-sensor assembly and Figure 2.36 shows the point-sensor dimen-
sions.
Figure 2.35 Point-Sensor Assembly
Black-Jacketed Fiber Zipcord Duplex
V-Pin
Terminators
Dual V-Pin
Latch Sensors
1–35 Meters
2.45
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Arc-Flash Protection
Figure 2.36 Point-Sensor Dimensions
The sensor is mounted flush on the switchgear cabinet wall, using a standard 
1/4-inch hole. Mounting steps are shown in Figure 2.37.
Figure 2.37 Point-Sensor Installation
1. Mounting Grommet Insertion
(1/4” diameter hole)
2. Sensor Insertion
(1/4” diameter hole)
0.519 in
(13.17 mm)
1.199 in
(30.46 mm)
0.087 in
(2.2 mm)
0.140 in
(3.56 mm)
0.547 in
(13.9 mm)
0.400 in
(10.16 mm)
0.250 in
(6.35 mm)
0.169 in
(4.3 mm)
1/4” diameter hole
1/4” diameter hole
2.46
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Arc-Flash Protection
The point sensor is omnidirectional with a slight loss of sensitivity at the fiber 
entry point. Figure 2.38 through Figure 2.40 show the sensor directivity 
pattern. The point sensor must be located in clear view of the energized parts, 
which are most likely to cause an arc-flash event. 
Figure 2.38 Point-Sensor Directivity (0–360° Around the Mounting Plane)
Figure 2.39 Point-Sensor Directivity (Front to Back, Above the Mounting 
Plane)
120%
100%
80%
60%
40%
0°
350° 10°
340° 20°
330° 30°
320° 40°
310° 50°
300° 60°
290° 70°
280° 80°
270° 90°
260° 100°
250° 110°
240° 120°
230° 130°
220° 140°
210° 150°
200° 160°
190° 170°
180°
120%
100%
80%
60%
40%
0°
350° 10°
340° 20°
330° 30°
320° 40°
310° 50°
300° 60°
290° 70°
280° 80°
270° 90°
260° 100°
250° 110°
240° 120°
230° 130°
220° 140°
210° 150°
200° 160°
190° 170°
180°
2.47
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Arc-Flash ProtectionFigure 2.40 Point-Sensor Directivity (Left to Right, Above the Mounting 
Plane)
Fiber Sensor 
Installation
The clear-jacketed fiber sensor is optimized for monitoring of large distrib-
uted resources, such as switchgear system bus enclosures. The clear-jacketed 
fiber sensor is omnidirectional and can be mounted in close proximity to the 
switchgear enclosure walls. Figure 2.41 shows a schematic diagram of the 
clear-jacketed fiber sensor. Figure 2.42 shows a clear-jacketed fiber sensor 
mounting example photo.
 
Total loop length = 2 • A + B (allowed range 3 to 70 meters)
 Range for A: 1 to 30 meters
 Range for B: 1 to 50 meters
Figure 2.41 Clear-Jacketed Fiber Sensor Assembly
120%
100%
80%
60%
40%
0°
350° 10°
340° 20°
330° 30°
320° 40°
310° 50°
300° 60°
290° 70°
280° 80°
270° 90°
260° 100°
250° 110°
240° 120°
230° 130°
220° 140°
210° 150°
200° 160°
190° 170°
180°
i8004c
Dual V-Pin
Latch
V-Pin
Terminators
V-Pin or
ST Splice
Connector
“A” Meters 
“B” Meters 
Clear-Jacketed Fiber
Black-Jacketed Fiber Zipcord Duplex
2.48
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Arc-Flash Protection
Figure 2.42 Clear-Jacketed Fiber Sensor Mounting Example
A clear-jacketed fiber sensor consists of the major components shown in 
Figure 2.43. Two connector options (V-pin and ST) are available to transition 
from the black-jacketed to the clear-jacketed fiber section, as shown in 
Figure 2.44. The ST connector option is generally superior because of positive 
locking.
Figure 2.43 Clear-Jacketed Fiber Sensor Components (V-Pin Style)
For correct operation, a clear-jacketed fiber sensor must be located within 2 m 
of the arcing site, with at least 0.5 m of the fiber sensor exposed to the light. 
The maximum length of the clear-jacketed fiber sensor is limited to 70 m and 
includes both, clear-jacketed fiber and black-jacketed fiber sections (the 
black-jacketed section is counted twice because of its dual-fiber construction). 
Transition between the two sections is accomplished by using a connector 
splice as shown in Figure 2.44.
Figure 2.44 Clear-Jacketed Fiber Sensor Showing Transition From Clear- to Black-Jacketed Fiber Section
Clear-Jacketed 
Fiber Sensor 
Clear-Jacketed Fiber 
Transition Connectors 
(V-Pin)
Connector Splice 
Bushing (V-Pin)
Black-Jacketed 
Fiber Section
ST Connection (3/8” diameter hole) V-Pin Connection (5/16” diameter hole)
5/16” diameter hole
3/8” diameter hole
2.49
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Arc-Flash Protection
The clear-jacketed fiber loop should be returned through the same general 
area as the forward path, providing dual opportunity to sense the same arc-
flash event. This approach ensures that the maximum distance between the 
relay and the light-producing event remains below 35 m, irrespective of the 
SEL-751 dual V-pin connector orientation. 
Application Example Figure 2.45 shows a typical switchgear application example with one incom-
ing and two radial (outgoing) feeders. All three feeders are protected with an 
SEL-751 controlling Breakers 1, 2, and 3. Radial feeder Breakers 2 and 3 
must be tripped for downstream faults, normally located in the outgoing cable 
termination compartment. To obtain better coverage, multiple sensors can be 
installed in the same compartment, as shown in the lower right corner of the 
Figure 2.45 with sensors marked LS1 and LS2. 
Bus compartment and the outgoing breaker compartments for Breakers 2 and 
3 are protected by the incoming feeder Breaker 1, with Sensors LS1, LS2, and 
LS3 connected directly to the incoming feeder relay (upper right hand corner 
of Figure 2.45). Sensor LS1 is implemented as a clear-jacketed fiber loop 
enclosing entire length of the bus. 
When desired, you can use radial feeder relays sensors (such as LS3 con-
nected to the lower right hand relay) to transfer trip the upstream breaker. 
Logic equations for this function are shown in Output Logic Programming in 
Section 4: Protection and Logic Functions.
Figure 2.45 Switchgear Application Example
Ordering Arc-Flash 
Fiber Sensors 
Arc-flash fiber sensors can be ordered with or without splices. To configure 
the standard multimode fiber-optic arc-flash detection point and fiber-loop 
sensor cable assemblies without additional splice connectors, use the C804 
Multimode Fiber-Optic Arc-Flash Detection (AFD) Sensors Model Option 
Table (MOT). For multimode fiber optic arc-flash detection sensors with addi-
CAUTION
Before placing the arc-flash 
protection system in service, first 
make sure all the sensors are 
correctly installed, and then execute 
the AFT command to initiate a self-
test.
3 2
1
LS2
LS3
LS3LS1
LS1
LS2
Bus
LS1—LS4 are arc-flash detection inputs, point or clear-jacketed fiber sensors.
SEL-751
SEL-751SEL-751
2.50
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Arc-Flash Protection
tional splice connectors, refer to the SEL-C814 Arc-Flash Detection (AFD) 
Fiber Cables and Accessories MOT. The losses and budget values shown in 
Table 2.19 are typical values.
Link Optical Loss Calculation Examples
This example shows a bare-fiber sensor with two V-Pin or ST connectors and 
an A dimension of 15 meters and a B dimension of 40 meters. Two connectors 
is the standard configuration, as shown in Figure 2.46.
Table 2.19 Optical Budget Calculations
Link Budgeta
a Link budget is calculated after allowing for the losses of the dual V-pin latch. When using a 
point sensor it allows for the sensor loss as well.
Loss Datab
b Link losses are calculated by adding up the fiber loss and the splice connector losses. The link 
losses should be less than the link budget.
Bare-Fiber Sensor 17 dB ST connector splice 2 dB
Point Sensor 12.25 dB V-Pin connector splice 2 dB
Bare-fiber 0.175 dB/m
Jacketed fiber0.175 dB/m
Table 2.20 SEL-C804 and SEL-C814 Arc-Flash Detection Cable 
Specifications 
Specifications
Cable
Black Jacket, Zipcord Clear Jacket, Simplex
Operating Temperature –40° to +85°C –55° to +85°C
Core Material PMMA PMMA
Cladding Material Fluorinated Polymer Fluorinated Polymer
Core Diameter 980 m 980 m
Cladding Diameter 1000 m 1000 m
Jacket Material PVC Polyethylene
Outer Cable Diameter 2.2 mm x 4.3 mm 
(0.087 in x 0.17 in)
2.20 mm
(0.087 in)
Weight/Unit Length 11 g/m (0.008 lb/ft) 4 g/m (0.003 lb/ft)
Maximum Cable Pull Tension 140 N (9.6 lb/ft) 70 N (4.8 lb/ft)
Maximum Connector Pull Tension 43.8 N (3.0 lb/ft) 43.8 N (3.0 lb/ft)
Minimum Bend Radius 25 mm (0.98 in) 25 mm (0.98 in)
Attenuation (Loss) 0.175 dB/m 0.175 dB/m
NOTE: Jacketed fiber in a zipcord 
duplex configuration includes two 
fiber lengths. Loss calculations must 
account for the total length of the 
fiber. This is accounted for in the 
examples as a “x 2” multiplier.
Link Budget 17 dB
– (2 dB x # of connector splices) –4 dB
– (0.175 dB/m x A dimension x 2) –5.25 dB
– (0.175 dB/m x B dimension) –7 dB
Total Link Losses = –16.25 dB
2.51
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Arc-Flash Protection
Figure 2.46 Bare-Fiber Sensor Assembly With Two Splices
This example shows a point sensor with an A dimension of 30 m, as shown in 
Figure 2.47. 
Figure 2.47 Point Sensor Assembly
Splice connectors can be added for the arc-flash fiber sensors to meet the 
shipping needs for large switchgears that require multiple splits for transpor-
tation. For multimode fiber-optic arc-flash detection sensors with additional 
splice connectors, refer to the SEL-C814 Arc-Flash Detection (AFD) Fiber 
Cables and Accessories MOT.
Ordering Examples Using the SEL-C814 Model Option Table
This example of a bare-fiber sensor with four ST connectors and an A 
dimension of 15 meters, as shown in Figure 2.48, shows the part numbers 
generated using an SEL-C814 MOT and the link optical loss calculations. Two 
connectors is the standard configuration.
Link Budget 12.25 dB
– (0.175 dB/m x A dimension x 2) –10.5 dB
Total Link Losses = –10.5 dB
V-Pin
Terminators
B Meters 
Clear-Jacketed Fiber
Dual V-Pin
Latch
V-Pin or
ST Splice
Connector
A Meters 
Black-Jacketed Fiber Zipcord Duplex
Black-Jacketed Fiber Zipcord Duplex
V-Pin
Terminators
Dual V-Pin
Latch Sensors
1–35 Meters
Link Budget 17 dB
– (2 dB x # of connector splices) –8 dB
– (0.175 dB x A dimension x 2) –5.25 dB
Link Losses = available for B meters 3.75 dB
÷ (0.175 dB/m) 21.42 meters
maximum B dimension
2.52
SEL-751 Relay Instruction Manual Date Code 20200603
Installation
Arc-Flash Protection
Figure 2.48 Bare-Fiber Sensor Assembly With Two Additional ST Splice 
Connectors
This example of a point sensor with two V-pin connectors, as shown in 
Figure 2.49, shows the part numbers generated using an SEL-C814 MOT and 
the link optical loss calculations.
Figure 2.49 Point Sensor Assembly With Two V-Pin Splice Connectors
Link Budget 12.25 dB
– (2 dB x # of connector splices) –4 dB
Link Losses = available for A meters 8.25 dB
÷ (2 x 0.175 dB/m) 23.6 meters
maximum A dimension
B Meters 
A Meters 
P/N C814CSS007
P/N C814CSS007
P/N C814CSS007
Note: To complete the fiber assembly, you will also need to 
order two ST Connector Splice bushings with P/N 915900151 
ST-ST Connector 
Terminated Clear-Jacketed 
Fiber, Simplex Cable 
P/N C814CSS007
Dual V-Pin Latch-V-Pin 
Terminated Black-Jacketed 
Fiber, Zipcord Duplex Cable
P/N C814BSL015
Black-Jacketed 
Fiber Zipcord 
Duplex
V-Pin
Terminators
Dual V-Pin 
Latch
ST Connector 
Splices
Clear-Jacketed Fiber
Black-Jacketed 
Fiber Zipcord 
Duplex
V-Pin
Terminators
Sensor
01-35 Meters
A Meters
V-Pin Connector 
Splices
Dual V-Pin 
Latch
Note: To complete the fiber assembly, you will also need to order two ST connector 
splice bushings with P/N 915900148. 
Dual V-Pin Latch-V-Pin Terminated 
Black-Jacketed Fiber 
Zipcord Duplex Cable
P/N C814BVL006 
V-Pin to Point Sensor Terminated 
Black-Jacketed Fiber 
Zipcord Duplex Cable
P/N C814BVP017
2.53
Date Code 20200603 Instruction Manual SEL-751 Relay
Installation
Field Serviceability
Field Serviceability
The SEL-751 firmware can be upgraded in the field; refer to Appendix B: 
Firmware Upgrade Instructions for firmware upgrade instructions. You may 
know when a self-test failure has occurred by configuring an output contact to 
create a diagnostic alarm as explained in Section 4: Protection and Logic 
Functions. By using the metering functions, you can determine whether the 
analog front-end (not monitored by relay self-test) is functional. Refer to 
Section 11: Testing and Troubleshooting for detailed testing and 
troubleshooting information.
The only two components that can be replaced in the field are the power sup-
ply fuse and the real-time clock battery. A lithium battery powers the clock 
(date and time) if the external power source is lost or removed. The battery is 
a 3 V lithium coin cell, Rayovac BR2335 or equivalent. At room temperature 
(25°C), the battery will operate nominally for 10 years at rated load. When the 
relay is powered from an external source, the battery experiences a low self-
discharge rate. Thus, battery life can extend well beyond 10 years. The battery 
cannot be recharged.
Fuse Replacement To replace the power supply fuse, perform the following steps:
Step 1. De-energize the relay.
Step 2. Remove the eight rear-panel screws and the relay rear panel.
Step 3. Remove the Slot A printed circuit board.
Step 4. Locate the fuse on the board.
Step 5. Remove the fuse from the fuse holder.
Step 6. Replace the fuse with a BUSS S505 3.15A (ceramic), 
Schurter T 3.15A H 250V, or equivalent.
Step 7. Insert the printed circuit board into Slot A.
Step 8. Replace the relay rear panel and energize the relay.
Real-Time Clock 
Battery Replacement
To replace the real-time clock battery, perform the following steps:
Step 1. De-energize the relay.
Step 2. Remove the eight rear-panel screws and the relay rear panel.
Step 3. Remove the Slot B printed circuit board.
Step 4. Locate the battery clip (holder) on the board. 
Step 5. Carefully remove the battery from beneath the clip. 
Properly dispose of the old battery.
Step 6. Install the new battery with the positive (+) side facing up.
Step 7. Insert the printed circuit board into Slot B.
Step 8. Replace the relay rear panel and energize the relay.
Step 9. Set the relay date and time.
CAUTION
Equipment components are sensitive 
to electrostatic discharge (ESD). 
Undetectable permanent damage can 
result if you do not use proper ESD 
procedures. Ground yourself, your 
work surface, and this equipment 
before removing any cover from this 
equipment. If your facility is not 
equipped to work with these 
components, contact SEL about 
returning this device and related SEL 
equipment for service.
DANGER
Disconnect or de-energize all external 
connections before opening this 
device. Contact with hazardous 
voltages and currents inside this 
device can cause electrical shock 
resulting in injury or death.
CAUTION
There is danger of explosion if the 
battery is incorrectly replaced. 
Replace only with Rayovac 
no. BR2335 or equivalent 
recommended by manufacturer. See 
Owner’s Manual for safety 
instructions. The battery used in this 
device may present a fire or chemical 
burn hazard if mistreated. Do not 
recharge, disassemble, heat above 
100°C or incinerate. Dispose of used 
batteries according to the 
manufacturer’s instructions. Keep 
battery out of reach of children.
This page intentionally left blank
Date Code 20200603 Instruction Manual SEL-751 Relay
Section 3
PC Interface
Overview
The SEL-751 Feeder Protection Relay can communicate with your computer 
in three different ways.
➤ The web server requires a web browser (Microsoft Internet 
Explorer, Mozilla FireFox, Google Chrome, etc.) and an 
Ethernet cable. The relay must havethe Ethernet port option. 
Refer to Web Server for functional details and capabilities.
➤ The SEL software solution requires downloading 
ACSELERATOR QuickSet SEL-5030 Software (via Compass) to 
your computer. Communication to the relay is accomplished 
through a serial or Ethernet port. Refer to QuickSet Software on 
page 3.11 for functional details and capabilities.
➤ The ASCII command line requires PC-based terminal 
emulation software (HyperTerminal, Tera Term, etc.), a serial 
or Ethernet port, and a serial or Ethernet cable to connect to the 
relay. Refer to Section 7: Communications for ASCII 
commands and supported functions.
Web Server
Connection and Login 
to Web Server
The web server provides a GUI for the relay without loading any software on 
your PC. The GUI is contained in the relay firmware. To connect to the web 
server of the SEL-751, the relay and your PC must be connected to the same 
Ethernet network. The network can be of any size, from a company-wide 
network to a direct-connect from your PC to the relay. The connection from 
the relay is through the Ethernet port of the relay (Port 1). To start 
communicating with the relay, you must enter a valid IP address (SET P 1 
IPADDR) and valid default router (SET P 1 DEFRTR) via a relay serial port. 
Be sure to obtain the IP address and default router from your IT resource to 
avoid network conflicts (e.g., duplicate IP addresses).
The SEL-751 comes pre-loaded with settings that enable you to communicate 
with the relay over a simple network. The network consists of connecting the 
SEL-751 (via Port 1) directly to the Ethernet port of your computer. Connect 
to Ethernet Port 1 of the relay by using a standard RJ45 connector for the 
copper port and an LC connector for the fiber-optic port. This connection 
requires that the computer not be connected to any other network (see 
Figure 3.1).
NOTE: We have tested the web 
server for correct operation and 
formatting with the following 
browsers: Internet Explorer 8, 
Firefox 14, and Chrome 5.
There are a wide variety of browsers 
available. While most browsers have 
the same functionality, we cannot 
guarantee the correct operation and 
formatting for all of them.
3.2
SEL-751 Relay Instruction Manual Date Code 20200603
PC Interface
Web Server
Figure 3.1 Direct Connection of an SEL-751 to a Computer
The default IP address is 192.168.1.2 and the default router is 192.168.1.1. 
Once the network is configured, as shown in Figure 3.1, you can connect to 
the web server in the relay by entering 192.168.1.2 in the address bar of your 
web browser (see Figure 3.2).
Figure 3.2 Login Page of Web Server for an SEL-751
The Login page of the web server allows you to access either Access Level 1 
(ACC) or Access Level 2 (2AC). The menu item you select under Access 
Level determines the access level at which you enter the web server 
(see Figure 3.3). For factory-default passwords, refer to Table 7.40.
Meter, Reports, Communications, Relay Status, and Settings (show only) 
require Access Level 1 or 2. System requires Access Level 2. The reports 
shown in each category are based on the part number and settings. For 
example, if the relay does not support arc flash, the Meter Light report is not 
available.
Cat 5e Cable 
(SEL-C627M or Equivalent)
SEL-751NOTE: For relays with a fiber-optic 
Ethernet port, use a commercially 
available 100BASE-FX to 
100BASE-TX media converter to 
interface with a PC RJ45 port. Use 
an SEL-C808 62.5/125 m 
Multimode Fiber-Optic Cable to 
connect to Port 1 of the relay.
3.3
Date Code 20200603 Instruction Manual SEL-751 Relay
PC Interface
Web Server
 
Figure 3.3 Select Access Level 2 From the Web Server Login
Meter The web server offers a convenient method for displaying all the metering 
reports stored in the relay. Located on the navigation pane, the Meter menu 
lists each of the available metering reports. When you select a metering report 
from the Meter menu, the corresponding report is displayed (see Figure 3.4).
 
Figure 3.4 Fundamental Meter Report Webpage
Reports The SEL-751 collects and stores a variety of data and statistics from the power 
system. These data are stored and reported through a series of reports. Located 
on the navigation pane, the Report menu lists each of the reports stored in the 
relay (Event Reports, HIF Event Reports, Sequential Events Recorder, Load 
Profile, and Breaker Monitor). When you select a report from the Reports 
menu, its corresponding report is displayed.
NOTE: All metering reports 
automatically update. To disable the 
updates, select the Disable Page Refresh 
button at the bottom of the display 
window.
3.4
SEL-751 Relay Instruction Manual Date Code 20200603
PC Interface
Web Server
Event Reports
Event reports stored in the SEL-751 can be exported in three different formats 
(binary COMTRADE, raw CEV, or filtered CEV). When you select Event 
Reports, a list of all the event reports presently stored in the relay is shown 
(see Figure 3.5).
After selecting the event format to be used, select the event report to export by 
clicking on the event needed. When prompted, you can open or save the event.
In addition to retrieving events, the Event Reports page allows you to clear all 
the events stored in the relay or to trigger events. Clear Event Report History 
erases the events from the nonvolatile memory of the relay. Trigger Event 
Report commands the relay to do an event capture of the present voltages and 
currents detected by the relay (see Figure 3.5).
Figure 3.5 Event Report Webpage
3.5
Date Code 20200603 Instruction Manual SEL-751 Relay
PC Interface
Web Server
HIF Event Reports
When the SEL-751 is ordered with the Arc Sense technology (AST) option for 
high-impedance fault (HIF) detection, the relay provides HIF reports. When 
you select HIF Event Reports from the Reports menu, a list of the HIF event 
reports available in the relay is shown. In addition to retrieving events, the HIF 
Event Reports page allows you to clear all the HIF events stored in the relay or 
to trigger an event.
Figure 3.6 HIF Event Report Webpage
Sequential Events Recorder
In addition to event reports, the SEL-751 collects and stores time-stamped 
data for assertion and deassertion of the Relay Word bits. These data are 
captured in the Sequential Events Recorder (SER) and can be exported 
through the web server.
When you select Sequential Events Recorder, a list of all the SER records 
presently stored in the relay displays (see Figure 3.7). The SER report stored 
in the SEL-751 can be downloaded or cleared by clicking the appropriate 
button at the bottom of the webpage.
 
Figure 3.7 Sequential Events Recorder Report Webpage
3.6
SEL-751 Relay Instruction Manual Date Code 20200603
PC Interface
Web Server
Load Profile 
The SEL-751 collects and stores time-stamped data of the analog quantities. 
These data are reported in the load profile report. When you select Load 
Profile, a list of all the load profile records presently stored in the relay 
displays (see Figure 3.8). You can export or clear the load profile report stored 
in the SEL-751 by using the two buttons at the bottom of the display window.
 
Figure 3.8 Load Profile Webpage
Breaker Monitor Report
The breaker monitor in the SEL-751 helps in scheduling circuit breaker 
maintenance (see Breaker Monitor). When you select Breaker Monitor, the 
breaker monitor report presently stored in the relay displays (see Figure 3.9). 
The breaker monitor report stored in the SEL-751 can be downloaded with the 
Download Breaker Monitor Report button.
Figure 3.9 Breaker Wear Monitor Webpage
3.7
Date Code 20200603 Instruction Manual SEL-751 Relay
PC Interface
Web Server
Communications You can view the Ethernet port configuration details, including the MAC 
address of the relay, by clicking Communications > Ethernet 
(see Figure 3.10). Click Clear Ethernet Statistics to clear PACKETS, 
BYTES, and ERRORS data. Refer to Section 7: Communicationsfor 
additional details on the Ethernet command.
 
Figure 3.10 MAC Address
Relay Status The Relay Status menu lists the status report pages available through the web 
server (Self-Tests, Relay Word Bits, and SELOGIC Counters). When you select 
a status report from the Relay Status menu, the corresponding status report 
displays.
Self-Tests
The SEL-751 has continual diagnostics that verify the status of the relay 
hardware. The results of these diagnostics can be viewed by selecting Relay 
Status > Self-Tests in the navigation pane. When you select Relay Status > 
Self-Tests, the status of the relay, including the serial number, part number, 
and self-tests results, are displayed (see Figure 3.11).
 
Figure 3.11 Self-Tests Webpage
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Web Server
Relay Word Bits
The web server can display the present state of the Relay Word bits of the 
relay. Select Relay Word Bits to display the state of all the Relay Word bits 
(see Figure 3.12). Relay Word bits shown in yellow are asserted. This 
webpage is updated automatically; you can disable the automatic updates by 
clicking Disable Page Refresh. Scroll up or down to view the remaining 
Relay Word bits not visible on the screen.
 
Figure 3.12 Relay Word Bits Webpage
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Web Server
SELOGIC Counters
When you select Relay Status > SELogic Counters, the count of each of the 
enabled SELOGIC counters displays (see Figure 3.13). A counter is only 
displayed when it is enabled.
 
Figure 3.13 SELOGIC Counters Webpage
Settings When you select Settings on the navigation pane, a list of all the available 
settings classes in the SEL-751 displays. Select a class of settings to view each 
of the settings in that class (Group, Logic, Global, Report, etc.). Figure 3.14 
shows the Group 1 settings class of Settings.
 
Figure 3.14 Group 1 Settings Webpage
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Web Server
System
File Management
The web server offers a convenient method for upgrading the relay firmware 
(Access Level 2). Select System > File Management (on the navigation 
pane) to upgrade your relay firmware (see Figure 3.15).
When preparing to upgrade the relay firmware you must first download the 
new relay firmware. The firmware is designated with a .zds extension. Click 
Browse to navigate to and select the firmware you want to send to the relay, 
and click Upgrade Firmware to start the upgrade process (see Figure 3.15). 
See Appendix B: Firmware Upgrade Instructions for the complete firmware 
upgrade procedure.
Figure 3.15 Upgrade Relay Firmware From the File Management Webpage
Language Support The web server reports can be displayed in English or Spanish by setting the 
Ethernet Port 1 setting LANG to either ENGLISH or SPANISH.
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QuickSet Software
QuickSet Software
This section describes how to get started with the SEL-751 and QuickSet. SEL 
provides many PC software solutions (applications) to support the SEL-751 
and other SEL devices. Table 3.1 lists SEL-751 software solutions.
QuickSet is a powerful setting, event analysis, and measurement tool that aids 
in setting, applying, and using the SEL-751. Table 3.2 shows the suite of 
QuickSet applications provided for the SEL-751.
Table 3.1 SEL Software Solutions 
Part Number Product Name Description
SEL-5010 SEL-5010 Relay Assistant Software Manages a connection directory and settings of 
multiple devices
SEL-5030 ACSELERATOR QuickSet SEL-5030 Software See Table 3.2
SEL-5032 ACSELERATOR Architect SEL-5032 Software Configures IEC 61850 communications
SEL-5036 ACSELERATOR Bay Screen Builder SEL-5036 Software Designs and manages bay screens in conjunction 
with SEL-5030 for the SEL-751 with color 
touchscreen display
SEL-5040 ACSELERATOR Report Server SEL-5040 Software Automatically retrieves, files, and summarizes 
reports
SEL-5078-2 SEL-5078-2 SYNCHROWAVE Central Visualization and 
Analysis Software
Provides power system situational awareness by 
translating data into visual information; displays 
and analyzes time-synchronized synchrophasor 
data and relay event reports
SEL-5601-2 SEL-5601-2 SYNCHROWAVE Event Software Plots COMTRADE and SEL Compressed ASCII 
format event report oscillography; performs custom 
calculations on analog, digital, and complex 
quantities; and analyzes the Impedance Plane for 
distance element (mho) operation, the Alpha Plane 
for differential element (78L) operation, and the 
Bewley Lattice for traveling-wave data
SEL-5801 SEL-5801 Cable Selector Selects the proper SEL cables for your application
Table 3.2 QuickSet Applications (Sheet 1 of 2)
Application Description
Rules-Based 
Settings Editor
Provides online or offline device settings that include 
interdependency checks. Use this feature to create and manage 
settings for multiple devices in a database.
HMI Provides a summary view of device operation. Use this feature to 
simplify commissioning testing.
Design Templatesa Allows you to customize device settings to particular applications 
and store those settings in Design Templates. You can lock settings 
to match your standards or lock and hide settings that are not used.
Event Analysis Provides oscillography and other event analysis tools.
Bay Control Allows you to design new bay screens and edit existing bay screens 
by launching Bay Screen Builder for SEL-751 relays with the color 
touchscreen display.
Setting Database 
Management
QuickSet uses a database to manage the settings of multiple 
devices.
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Setup Follow the steps outlined in Section 2: Installation to prepare the SEL-751 for 
use. Perform the following steps to initiate communications:
Step 1. Connect the appropriate communications cable between the 
SEL-751 and your PC.
Step 2. Apply power to the SEL-751.
Step 3. Start QuickSet.
Communications
QuickSet uses relay communications Port 1 through Port 4, or Port F (front 
panel) to communicate with the SEL-751. Perform the following steps to 
configure QuickSet to communicate with the relay.
Step 1. Select Communications from the QuickSet main menu bar, as 
shown in Figure 3.16.
Figure 3.16 Communications Parameter Menu Selection
Step 2. Select the Parameters submenu to display the screen shown in 
Figure 3.17.
Step 3. Configure the PC port to match the relay communications 
settings.
Step 4. Configure QuickSet to match the SEL-751 default settings by 
entering Access Level 1 and Access Level 2 passwords in the 
respective text boxes.
Step 5. For network communications, select Network from the Active 
Connection Type drop-down menu and enter the network 
parameters as shown in Figure 3.18. 
For the SEL-751, always select FTP as the file transfer option.
Step 6. Exit the menu by clicking OK when finished.
Terminal Provides a direct connection to the SEL device. Use this feature to 
ensure proper communication and directly interface with the 
device.
Help Provides general QuickSet and device-specific QuickSet context 
help.
a Available only in licensed versions of QuickSet.
Table 3.2 QuickSet Applications (Sheet 2 of 2)
Application Description
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Terminal
Terminal Window
Select Communications > Terminal on the main menu bar (see Figure 3.19) 
to open the terminal window.
Figure 3.19 Communications Terminal Menu Selection
The terminal window is an ASCII interface with the relay. This is a basic 
terminal emulation. Many third-party terminal emulation programs are 
available with file transfer encoding schemes. Open the terminal window by 
either clicking Communications > Terminal or pressing <Ctrl+T>. Verify 
proper communications with the relay by opening a terminal window, pressing 
<Enter>a few times, and verifying that a prompt is received. If a prompt is 
not received, verify proper setup.
NOTE: Factory-default 
passwords for Access 
Level 1 and 2 are OTTER 
and TAIL, respectively.
Figure 3.17 Serial Port Communication 
Parameters Dialog Box
Figure 3.18 Network Communication 
Parameters Dialog Box
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Terminal Logging
To create a file that contains all terminal communications with the relay, select 
Communications > Logging > Terminal Logging, and specify a file at the 
prompt. QuickSet records communications events and errors in this file. Click 
Communications > Logging > Connection Log to view the log. Clear the 
log by selecting Communications > Logging > Clear Connection Log.
Driver and Part Number
After clicking Communications > Terminal, access the relay at Access 
Level 1. Issue the ID command to receive an identification report, as shown in 
Figure 3.20.
Locate and record the Z-number (Z001001) in the FID string. The first portion 
of the Z-number (Z001…) determines the QuickSet relay settings driver 
version when you are creating or editing relay settings files. The use of the 
driver version is discussed in more detail in Settings Editor on page 3.18. 
Compare the part number (PARTNO=7510XXXXXXXXXXXXXX) with the 
Model Option Table (MOT) to ensure the correct relay configuration. The 
SEL display package version can be found in Table A.5. The customer display 
package (CDP) version has a unique ID code based on the total number of 
seconds from 1/1/2000 to the time stamp when the CDP was created and 
downloaded to the relay via QuickSet.
Settings Database 
Management and 
Driver
QuickSet uses a database to save the relay settings. QuickSet contains sets of 
all settings files for each relay specified in the database manager. Choose 
appropriate storage backup methods and a secure location for storing the 
database files.
Database Manager
Select File > Database Manager on the main menu bar to create new 
databases and manage records within existing databases.
Settings Database
Step 1. Open the database manager to access the database. Click 
File > Database Manager. A dialog box appears. 
The default database file already configured in QuickSet is 
Relay.rdb. This database contains example settings files for the 
SEL products with which you can use QuickSet. 
Step 2. Enter a description for the database in the Database Description 
dialog box. 
=ID <Enter>
"FID=SEL-751-X397-V0-Z007003-D20170305","08BC"
"BFID=BOOTLDR-R500-V0-Z000000-D20090925","0952"
"CID=9B42","025E"
"DEVID=SEL-751","0408"
"DEVCODE=77","0316"
"PARTNO=751001B6X3X7183021X","06D9"
"CONFIG=11251201","03F0"
"SEL DISPLAY PACKAGE=1.0.32768.873","086A"
"CUSTOMER DISPLAY PACKAGE=1.542556555","099A"
"iedName =TEMPLATE","05DC"
"type =SEL_751","04B0"
"configVersion =ICD-751-R100-V0-Z001001-D20070326","0D75"
= 
Figure 3.20 Device Response to the ID Command
NOTE: The SEL display package and 
customer display package versions 
are only displayed in the touchscreen 
display model.
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Step 3. Enter special operating characteristics that describe the relay settings 
in the Settings Description text box. These can include the 
protection scheme settings and communications settings. 
Step 4. Highlight a relay or settings file listed in Settings and click the 
Copy button to create a new set of settings. 
QuickSet prompts for a new name. Be sure to enter a new 
description in Settings Description.
Copy/Move Settings Between Databases
Step 1. Select the Copy/Move Settings Between Settings Databases 
tab to create multiple databases with the database manager; 
these databases are useful for grouping similar protection 
schemes or geographic areas. 
Step 2. Click the Settings Database B button to open a relay 
database. 
Step 3. Type a filename and click Open. 
a. Highlight a device or setting in Settings Database A.
b. Click Copy or Move, and click the > button to create a 
new device or settings file in Settings Database B.
Step 4. Reverse this process to move or copy devices from the B 
database to the A database. 
Copy creates an identical device that appears in both databases. Move 
removes the device from one database and places the device in another 
database.
Create a New Database, Copy an Existing Database
To create a new database: 
Step 1. Click File > Database Manager, and then click Create New 
Database. QuickSet prompts you for a file name. 
Step 2. Type the new database name (and select a new location if the 
new location differs from the existing one), and click Save. 
QuickSet displays the message Settings [path and 
filename] was successfully created. 
Step 3. Click OK.
To copy an existing database of devices to a new database: 
Step 1. Click File > Database Manager, and select the Copy/Move 
Settings Between Databases tab.
QuickSet opens the last active database and assigns it as 
Database A. 
Step 2. Click the Open B button; QuickSet prompts you for a file 
location. 
Step 3. Type a new database name, click the Open button, and click 
Yes; the program creates a new empty database. Load devices 
into the new database as in Copy/Move Settings Between 
Databases on page 3.15.
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Settings QuickSet offers the capability of creating settings for one or more SEL-751 
relays. Store existing relay settings downloaded from SEL-751 relays with 
QuickSet, creating a library of relay settings, then modify and upload these 
settings from the settings library to an SEL-751. QuickSet makes setting the 
relay easy and efficient. However, you do not have to use QuickSet to 
configure the SEL-751; you can use an ASCII terminal or a computer running 
terminal emulation software. QuickSet provides the advantages of rules-based 
settings checks, SELOGIC control equation Expression Builder, operator 
control and metering HMI, event analysis, and help.
Settings Editor
The settings editor shows the relay settings in easy-to-understand categories. 
The SEL-751 settings structure makes setting the relay easy and efficient. 
Settings are grouped logically, and relay elements that are not used in the 
selected protection scheme are not accessible. For example, if there is only 
one analog card installed in the relay, you can access settings for this one card 
only. Settings for the other slots are dimmed (grayed) in the QuickSet menu. 
QuickSet shows all of the settings categories in the settings tree view. The 
settings tree view remains constant whether settings categories are enabled or 
disabled.
Settings Menu
QuickSet uses a database to store and manage SEL relay settings. Each unique 
relay has its own settings records. Use the File menu to open (Open) an 
existing record, create and open a new (New) record, or read (Read) relay 
settings from a connected SEL-751 and then create and open a new record. 
Click Tools > Settings > Convert to convert and open an existing record in 
the settings editor.
File > New
To make SEL-751 settings with the settings editor, click File > New on the 
main menu bar and select the SEL-751 and the latest driver version (00X) on 
the Settings Editor Selection screen, as shown in Figure 3.21.
QuickSet makes the new settings file using the driver that you specify in the 
Settings Editor Selection screen. QuickSet uses the Z-number in the FID 
string to create a particular settings file.
Table 3.3 File/Tools Menus
Menus Description
<<, >> Use these navigation menu buttons to move from one cate-
gory to the next
File > New Open a New record
File > Open Open an existing record
File > Read Read device settings and then create and open a new record
Tools > Settings > Convert Convert and open an existing record
3.17
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QuickSet SoftwareFigure 3.21 Driver Selection
After the relay model and settings driver selection, QuickSet presents the 
Device Part Number dialog box. Use this dialog box to configure the settings 
editor to produce settings for a relay with options determined by the part 
number, as shown in Figure 3.22. Click OK when finished.
Figure 3.22 Update Part Number
Figure 3.23 shows the Settings Editor screen. Check the driver version 
number in the title bar of the Settings Editor screen. Compare the QuickSet 
driver number and the first portion of the Z-number in the FID string (select 
Tools > HMI > HMI > Status). These numbers must match. QuickSet uses 
this first portion of the Z-number to determine the correct settings editor to 
display.
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QuickSet Software
Figure 3.23 New Settings Screen
File > Open
The Open menu item opens an existing device from the active database folder. 
QuickSet prompts for a device to load into the settings editor.
File > Read
When the Read menu item is selected, QuickSet uses serial protocols to read 
the device settings from the connected device. As QuickSet reads the device, a 
Transfer Status screen appears.
Tools > Settings > Convert
Use the Convert menu item (Tools > Settings) to convert from one settings 
version to another. Typically, you would use this utility to upgrade an existing 
settings file to a newer version because devices are using a newer version 
number. QuickSet provides a Convert Settings report that shows missed, 
changed, and invalid settings created as a result of the conversion. Review this 
report to determine whether changes are necessary.
Settings Editor 
Use the settings editor to enter settings. The settings editor includes the 
settings driver version (the first three digits of the Z-number) in the settings 
editor title bar.
Enter Settings
NOTE: Setting changes made during 
the edit session are not read by the 
relay unless they are transferred to 
the relay with the Send menu item.
Step 1. Click the drop-downs and the buttons in the settings tree 
view to expand and select the settings you want to change. 
Step 2. Use Tab to navigate through the settings, or click a settings 
box.
Step 3. To restore the previous value for a setting, right-click in the 
settings text box and select Previous Value. 
Device Version 
Number
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Step 4. To restore the factory-default setting value, right-click in the 
settings text box and select Default Value. 
Step 5. If you enter a setting that is out of range or has an error, 
QuickSet shows the error at the bottom of the settings editor. 
Double-click the error listing to go to the setting and enter valid 
input.
Expression Builder
SELOGIC control equations are a powerful means for customizing device 
performance. QuickSet simplifies this process with Expression Builder, a 
rules-based editor for programming SELOGIC control equations. Expression 
Builder organizes device elements, analog quantities, and SELOGIC control 
equation variables.
Access Expression Builder. Use the ellipsis button that follows the 
setting text boxes in the settings editor to create an expression, as shown in 
Figure 3.24.
Figure 3.24 Expression Created With Expression Builder
Using Expression Builder. The expression builder screen is organized into 
three main parts: the expression builder text box, the left side column, which 
contains broad categories of device elements, analog quantities, counters, 
timers, latches, and logic variables, and the right side column, which displays 
category operands for use in the expression. Directly underneath the 
expression builder text box is a row of operators that you can include in your 
expression. The operators include basic logic, rising- and falling-edge 
triggers, expression compares, and comments.
Touchscreen Settings and Bay Screen Builder
The touchscreen settings are available when the touchscreen display option is 
selected as part of the front-panel options. This option provides you with the 
ability to design bay screen one-line diagrams with the help of Bay Screen 
Builder SEL-5036 Software. For more information, refer to Bay Screens 
Design Using QuickSet and Bay Screen Builder on page 9.10.
NOTE: Be sure to enable the 
functions you need (Logic Settings > 
SELogic Enable) before using Expression 
Builder.
Ellipsis Button
Created Expression
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QuickSet Software
File > Save
Select File > Save once settings are entered into QuickSet to ensure that the 
settings are not lost.
File > Send
To transfer the edits made in the QuickSet edit session, you must send the 
settings to the relay by clicking File > Send. In the dialog box that opens, 
select the settings section(s) that you want to transfer to the relay by checking 
the appropriate box and click OK.
Edit > Part Number
Use this menu item to change the part number.
Text Files
Select Tools > Settings > Import and Tools > Settings > Export on the main 
menu bar to import or export settings from or to a text file. Use this feature to 
create a small file that can be easily stored or sent electronically.
Event Analysis QuickSet has integrated analysis tools that help you retrieve information about 
relay operations quickly and easily. Use the event information that the 
SEL-751 stores to evaluate the performance of a system (select Tools > 
Events > Get Event Files). Figure 3.25 shows the event retrieval screen.
Figure 3.25 Retrieve Events Screen
You can retrieve event files stored in the relay and transfer these files to a 
computer. For information on the types of event files and data capture, see 
Section 10: Analyzing Events. To download event files from the device, click 
Tools > Events > Get Event Files. The Event History dialog box appears, as 
shown in Figure 3.25.
View Event History
The SEL-751 is capable of capturing three types of events (4 samples/cycle 
filtered, 32 samples/cycle raw, and high-impedance fault). These events can be 
captured in either compressed ASCII (.cev) or COMTRADE format. QuickSet 
allows you to download the .cev events. Use the Event Type drop-down shown 
NOTE: HIF events are only available 
with the Arc Sense technology (AST) 
option. HIF events can take as long as 
an hour to download (at 38400 bps). 
Increase the data rate before 
downloading.
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in Figure 3.25 to select the event type. For information on how to download 
COMTRADE events from the relay, see Section 10: Analyzing Events, 
Retrieving COMTRADE Event Files.
Get Event
Highlight the event you want to view (see Figure 3.25), select the event type 
from the Event Type drop down menu (4 samples or 32 samples), and click 
Get Selected Event. QuickSet then queries where to save the file on your 
computer, as shown in Figure 3.26.
Figure 3.26 Save the Retrieved Event
When saving an event report, select a save location and a file name for your 
report. Select either Default Naming or Custom Naming. Default naming has 
predefined tags and organization, which appears in the Format text box when 
default naming is selected. You can use custom naming to create a file name 
specific to your application by selecting and organizing your own tags (listed 
in Available Tags).
View Event Files
Click Tools > Events to view an event with SYNCHROWAVE Event. You can 
view multiple events by clicking on Load Event > Add New Event in 
SYNCHROWAVE Event.
Meter and Control Click on Tools > HMI > HMI to display a screen similar to the one shown in 
Figure 3.27. The HMI tree view shows all the functions available in the HMI. 
Unlike the self-configuration of the device settings tree, the HMI tree remains 
the same regardless of the type of cards installed. For example, if no Analog 
Input card is installed, theAnalog Input function is still available, but the relay 
responds as follows:
No Analog Input Card Present.
Device Overview
The Device Overview screen provides an overview of the device. The Contact 
I/O portion of the screen displays the status of the two inputs and three outputs 
of the main board. You cannot change these assignments.
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QuickSet Software
Figure 3.27 Device Overview Screen
You can assign any Relay Word bit to the 16 user-defined target LEDs. To 
change the present assignment, double-click on the text above the square you 
want to change. After double-clicking on the text, a box with available Relay 
Word bits appears in the lower left corner of the screen. Select the appropriate 
Relay Word bit, and click the Update button to assign the Relay Word bit to 
the LED. To change the color of the LED, click in the square and make your 
selection from the color palette.
The front-panel LEDs display the status of the 24 front-panel LEDs. Use the 
front-panel settings to change the front-panel LED assignments. The 
Fundamental, Min/Max, Energy, etc., screens display the corresponding 
values.
Click on the Targets button to view the status of all the Relay Word bits. 
When a Relay Word bit has a value of 1 (RB02 = 1), the Relay Word bit is 
asserted. When a Relay Word bit has a value of 0 (RB02 = 0), the Relay Word 
bit is deasserted.
The Status and SER screens display the same information as the ASCII STA 
and SER commands.
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Figure 3.28 shows the control screen. From here, you can reset metering data; 
clear the Event History, SER, MIRRORED BITS report, or LDP; or trigger 
events. You can also reset the targets, synchronize with IRIG, or set the time 
and date. If supported, you can run arc-flash sensor diagnostic tests.
Figure 3.28 Control Screen
To control the Remote bits, click on the appropriate square, then select the 
operation from the box shown in Figure 3.29.
Figure 3.29 Remote Operation Selection
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QuickSet Software
Language Support
QuickSet has multi-language support. Click Language to choose from 
English, Spanish, French, or Chinese, as seen in Figure 3.30. Selecting any of 
these choices converts the menu items in QuickSet to the selected language.
Figure 3.30 Language Support Options
Additionally, if Spanish or English is selected from the Language menu, the 
relay settings displayed by QuickSet are converted into the corresponding 
language, as shown in Figure 3.31.
NOTE: If the SEL-751 is connected 
to any SEL communications 
processor (SEL-203x or RTAC), the 
corresponding LANG port setting 
must be set to ENGLISH.
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QuickSet Software
Figure 3.31 Spanish Settings QuickSet Display
Each communications port (serial or Ethernet) on the SEL-751 can be 
independently set to display either English or Spanish. Changing the port 
setting LANG to SPANISH or ENGLISH results in the QuickSet HMI and all 
of its available functions to display in the corresponding language. For 
example, if the Control Window is selected in the HMI while the setting 
LANG := SPANISH, QuickSet displays the Control Window (Ventana de 
Control) in Figure 3.32.
NOTE: Once the HMI screen is 
displayed in QuickSet, the LANG 
setting does not affect the displayed 
HMI. To change the language of the 
HMI, the HMI must be closed, and the 
LANG setting must be changed, and 
the HMI reopened.
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Figure 3.32 Spanish Control Window (Ventana de Control) Display
QuickSet Help Various forms of QuickSet help are available, as shown in Table 3.4. Press 
<F1> to open a context-sensitive help file with the appropriate topic as the 
default.
Table 3.4 QuickSet Help
Help Description
General QuickSet Select Help from the main menu bar.
SEL-751 Settings Select Settings Help from the Help menu bar 
while the Settings Editor is open.
Date Code 20200603 Instruction Manual SEL-751 Relay
Section 4
Protection and Logic Functions
Overview
This section describes the SEL-751 Feeder Protection Relay settings, 
including the protection elements and basic functions, control I/O logic, as well as 
the settings that control the communications ports and front-panel displays.
This section includes the following subsections:
Application Data. Lists information that you need to know about the 
protected equipment before calculating the relay settings. Lists the 
settings for protection elements included in all models of the SEL-751.
Group Settings (SET Command).
ID Settings and Configuration Settings. Lists the ID settings and the 
settings that configure the relay inputs to accurately measure and 
interpret the ac current and voltage input signals.
VNOM Range Check. Identifies the VNOM range for DELTA and WYE 
connected PT configurations.
Low-Energy Analog (LEA) Voltage Inputs. Discusses the settings 
associated with LEA voltage inputs.
Line Parameter Settings. Lists the line parameter settings for use with 
fault location and direction elements.
Fault Location. Describes the fault location enable setting.
Overcurrent Elements. Lists the settings and describes the logic associated 
with overcurrent elements.
Time-Overcurrent Elements. Lists the settings and time-overcurrent curves 
and describes the logic associated with the elements.
Directional Control. Lists the settings to configure the directional 
elements. Describes the operating characteristics, logic, and the 
configuration of directional settings for directional control of the 
overcurrent elements.
Load-Encroachment Logic. Lists the settings to configure load-
encroachment logic. Describes the operating characteristics and logic 
of the load-encroachment function and provides application examples.
High-Impedance Fault Detection With Arc Sense Technology. Lists the 
settings associated with high-impedance fault (HIF) detection.
Second- and Fifth-Harmonic Blocking Logic. Lists the settings associated 
with second- and fifth-harmonic blocking logic.
RTD-Based Protection. Lists the settings associated with the RTD inputs. 
You can skip this subsection if your application does not include RTD 
inputs.
NOTE: Each SEL-751 is shipped with 
default factory settings. Calculate 
the settings for your application to 
ensure secure and dependable 
protection. Document and enter the 
settings (see Section 6: Settings).
4.2
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Overview
IEC Thermal Elements. Lists the settings associated with IEC thermal 
elements.
Under- and Overvoltage Functions. Lists the settings associated with the 
under- and overvoltage elements.
Inverse-Time Undervoltage Protection. Lists the settings and inverse time-
undervoltage curves and describes the logic associated with the 
elements.
Inverse-Time Overvoltage Protection. Lists the settings and inverse time- 
overvoltage curves and describes the logic associated with the 
elements.
Synchronism-Check Elements. Lists the settings and describes the logic 
associated with synchronism-check elements.
Power Elements. Lists the settings and describes the logic associated with 
power elements.
Power Factor Elements. Lists the settings and describes the logic 
associated with power factor elements.
Loss-of-Potential (LOP) Protection. Lists the logic and settings associated 
with the LOP element.
Vector Shift Element. Lists the settings associated with vector shift logic.
Frequency Protection. Lists the settings and describes the logic associated 
with over- and underfrequency elements.
Rate-of-Change-of-Frequency (81R) Protection. Lists the settings and 
describes the logic associated with rate-of-change-of-frequency 
elements.
Fast Rate-of-Change-of-Frequency(81RF) Protection. Lists the settings 
and describes the logic associated with fast rate-of-change-of-
frequency elements.
Trip/Close Logic. Lists trip and close logic.
Reclose Supervision Logic. Describes the logic that supervises automatic 
reclosing when an open interval time times out—a final condition 
check right before the close logic asserts the close output contact.
Reclose Logic. Describes all the reclosing relay settings and logic 
necessary for automatic reclosing (besides the final close logic and 
reclose supervision logic described previously).
Demand Metering. Lists the settings associated with demand metering.
Logic Settings (SET L Command). Lists the settings associated with latches, 
timers, and output contacts.
Global Settings (SET G Command). Lists the settings that allow you to 
configure the relay to your power system, date format, analog inputs/
outputs, and logic equations of global nature.
General Settings. Lists the Global system settings, such as phase rotation, 
nominal frequency, date format, etc.
Event Messenger Points. Describes the configuration of event messenger 
points.
Multiple Settings Groups. Lists settings for active group selection and 
describes configuration of the active group selection via SELOGIC 
control equations.
LEA Ratio Correction Settings. Lists settings for LEA ratio and angle 
correction for phase and synchronism voltage inputs.
4.3
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Overview
Synchrophasor Measurement. Describes Phasor Measurement Unit 
(PMU) settings for C37.118 Protocol.
Time and Date Management Settings. Lists settings for time and date 
management, describes the configuration of the settings, and lists the 
supported protocols.
Breaker Failure Settings. Lists the settings and describes the logic for the 
flexible breaker failure function.
Arc-Flash Protection. Lists the settings for the arc-flash elements 
including arc-flash overcurrent and time-overlight elements.
Analog Inputs. Describes analog input functionality, lists the settings and 
gives an example.
Analog Outputs. Describes analog output functionality, lists the settings 
and gives an example. 
Station DC Battery Monitor. Describes station dc battery monitor function 
and lists the settings.
Breaker Monitor. Lists the settings and describes the breaker monitor 
function that you can use for scheduling circuit breaker maintenance.
Digital Input Debounce. Provides the settings for digital input dc debounce 
or ac debounce mode of operation.
Data Reset. Lists the data reset SELOGIC control equation settings for 
resetting targets, energy metering, max/min metering, demand 
metering and peak demand metering.
Access Control. Describes the SELOGIC control equation setting you 
would use for disabling settings changes from the relay front panel.
Time Synchronization Source. Describes the setting you would use for 
choosing IRIG1 or IRIG2 as the time synchronization source.
Disconnect Control Settings. Describes the settings and logic associated 
with the disconnects.
Local/Remote Control. Describes the local/remote breaker control 
function.
Port Settings (SET P Command). Lists the settings that configure the relay 
front- and rear-panel serial ports.
Front-Panel Settings (SET F Command). Lists the settings for the front-panel 
display, pushbuttons, and LED control.
Report Settings (SET R Command). Lists the settings for the sequential 
event reports, event, and load profile reports.
DNP Map Settings (Set D Command). Shows the DNP user map register 
settings.
Modbus Map Settings (SET M Command). Shows the Modbus user map 
register settings.
EtherNet/IP Assembly Map Settings (SET E Command). Shows EtherNet/IP 
assembly map settings.
Touchscreen Settings. The touchscreen settings apply to relays that support 
the color touchscreen display. (The settings are supported in 
ACSELERATOR QuickSet SEL-5030 Software only.)
4.4
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Application Data
See Section 6: Settings for a list of all settings (SEL-751 Settings Sheets) and 
various methods of accessing them. All current and voltage settings in the 
SEL-751 are in secondary.
NOTE: The DeviceNet port 
parameters can only be set at the rear 
of the relay on the DeviceNet card 
(see Figure I.1).
You can enter the settings by using the front-panel SET RELAY function 
(see Section 8: Front-Panel Operations), the serial port (see Section 7: 
Communications), the EIA-485 port (see Appendix E: Modbus 
Communications), or the Ethernet port (see Section 7: Communications).
Application Data
It is faster and easier for you to calculate settings for the SEL-751 if you 
collect the following information before you begin:
➤ System phase rotation and nominal frequency
➤ Current transformer primary and secondary ratings and 
connections
➤ Voltage transformer or low-energy analog (LEA) voltage 
sensor ratios and connections, if used
➤ Type and location of resistance temperature detectors (RTDs), 
if used
➤ Highest expected load current
➤ Expected fault current magnitudes for ground and three-phase 
faults
Group Settings (SET Command)
ID Settings All models of the SEL-751 have the identifier settings described in Table 4.1.
The SEL-751 prints the Relay and Terminal Identifier strings at the top of the 
responses to serial port commands to identify messages from individual relays.
Enter as many as 16 characters, including letters A–Z (not case sensitive), 
numbers 0–9, periods (.), dashes (-), and spaces. Suggested identifiers include 
the location or number of the protected feeder.
Configuration 
Settings
The CT ratio settings configure the relay to accurately scale measured values 
and report the primary quantities. Calculate the phase and neutral current CT 
ratios by dividing the primary rating by the secondary rating.
Table 4.1 Identifier Settings
Setting Prompt Setting Range
Setting Name := 
Factory Default
UNIT ID LINE 1 16 Characters RID := SEL-751
UNIT ID LINE 2 16 Characters TID := FEEDER RELAY
4.5
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.1 Phase CT Ratio Setting Calculation
Consider an application where the phase CT rating is 100:5 A.
Set CTR := 100/5 := 20.
Table 4.3 shows the voltage settings. The voltage configuration settings 
configure the relay voltage inputs to correctly measure and scale the voltage 
signals. The relay can be ordered with different secondary voltage input 
configurations—standard voltage inputs rated for 300 Vac or LEA voltage 
inputs rated for 8 Vac. Refer to Figure 2.21 for different voltage connections.
The voltage configuration settings configure the relay voltage inputs to 
correctly measure and scale the voltage signals. The relay can be ordered with 
different secondary voltage input configurations—standard voltage inputs 
rated for 300 Vac or LEA voltage inputs rated for 8 Vac. Refer to Figure 2.21 
for different voltage connections.
The PTR and PTRS settings are applicable and available for setting when the 
relay is ordered with standard voltage inputs (300 Vac). The LEA_R, 
LEA_SC, LEA_S_R, and LEA_S_SC settings are applicable to the relay with 
LEA inputs (8 Vac). The LEA_R and LEA_S_R settings are settable while the 
LEA_SC and LEA_S_SC settings are autocalculated by the relay and not 
available for setting as explained in Low-Energy Analog (LEA) Voltage Inputs. 
The DELTA_Y, VSCONN, VNOM, and SINGLEV settings are applicable to 
either of the voltage input options.
Set the phase PT ratio (PTR) setting equal to the VT ratio. The synchronism-
check voltage input VS is an optional single phase-to-neutral or phase-to-
phase voltage input. Set the synchronism-check voltage input PT ratio (PTRS) 
setting equal to the VT ratio of the VS input.
Table 4.2 CT Configuration Settings
Setting Prompt Setting Range
Setting Name := 
Factory DefaultPHASE CT RATIO 1–5000 CTR := 120
NEUTRAL CT RATIO 1–5000 CTRN := 120
Table 4.3 Voltage Configuration Settings
Setting Prompt Setting Range Setting Name := 
Factory Default
PHASE PT RATIO 1.00–10000.00 PTR := 180.00
PHASE LEA RATIO 37.50–500000.00 LEA_R := 180.00
PHASE LEA SCALE 1.00–13333.33a 
a Autocalculated.
LEA_SC := 4.80
SYNCV PT RATIO 1.00–10000.00 PTRS := 180.00
SYNCV LEA RATIO 37.50–500000.00 LEA_S_R := 180.00
SYNCV LEA SCALE 1.00–13333.33a LEA_S_SC := 4.80
XFMR CONNECTION WYE, DELTA DELTA_Y := DELTA
VS CONNECTION VS, 3V0 VSCONN := VS
LINE VOLTAGE OFF, 20.00–250.00 Vb
b The line voltage setting range is 20.00–480.00 if DELTA_Y := WYE.
VNOM := 120.00
SINGLE V INPUT Y, N SINGLEV := N
4.6
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.2 Phase VT Ratio Setting Calculations
Consider a 13.8 kV feeder application where you use 14400:120 V 
rated voltage transformers (connected in open delta).
Set PTR := 14400/120 := 120 and DELTA_Y := DELTA.
Set the phase LEA ratio (LEA_R) setting equal to the marked LEA sensor 
ratio. The synchronism-check voltage input VS is an optional single phase-to-
neutral or phase-to-phase voltage input. Set the synchronism-check voltage 
input LEA ratio (LEA_S_R) setting equal to the marked LEA sensor ratio of 
the VS input.
EXAMPLE 4.3 Phase LEA Ratio Setting Calculations
Consider a 13.8 kV feeder application where you have a 2500:1 ratio 
LEA sensor (connected in wye).
Set LEA_R := 2500/1 := 2500 and DELTA_Y := WYE.
When phase-to-phase potentials are connected to the relay, set DELTA_Y to 
DELTA. When phase-to-neutral potentials are connected to the relay, set 
DELTA_Y to WYE.
In applications where only a single voltage is available, set SINGLEV equal 
to Y. As shown in Figure 2.20, the single voltage must be connected to the 
A-phase input, but it can be an A-N or an A-B voltage. Be sure to set 
DELTA_Y equal to WYE for an A-N input or DELTA_Y equal to DELTA for 
an A-B input voltage. When you set SINGLEV equal to Y, the relay 
performance changes in the following ways:
➤ Power and Voltage Elements. When you use one voltage, the 
relay assumes that the system voltages are balanced in both 
magnitude and phase angle. Power, power factor, and positive-
sequence impedance are calculated assuming balanced 
voltages.
➤ Metering. When you use one voltage, the relay displays 
magnitude and phase angle for the measured PT. The relay 
displays zero for the magnitudes of the unmeasured voltages. 
Balanced voltages are assumed for power, power factor, VG, 
and 3V2 metering.
➤ Event Reports. When you use one voltage, the unmeasured 
voltage magnitudes are reported as zero.
DELTA_Y SINGLEV Event Report Voltages
DELTA Y VAB, VBC, VCA = 0.0
WYE Y VA, VB, VC = 0.0
Table 4.4 Effect on Group Settings When SINGLEV := Y (Sheet 1 of 2) 
Identifier Settings
Group Setting Change Reason
VNOM Forced to OFF and hidden Loss-of-Potential logic 
requires three-phase voltage.
Line Parameter Settings
Z1MAG, Z1ANG, 
Z0MAG, Z0ANG, 
Z0SMAG, Z0SANG
Hidden Impedance calculations 
require three-phase voltage.
4.7
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
VNOM Range Check The relay performs a range check for the VNOM setting that depends upon the 
voltage-input delta or wye configuration. When the setting DELTA_Y is DELTA, 
then the allowed range of the VNOM is OFF, 20–250 V (l-l). When the setting 
DELTA_Y is WYE, then the allowed range of VNOM is OFF, 20–480 V (l-l). 
Note that the VNOM setting is always in line-to-line voltage, even when set 
for a wye configuration. Limit the VNOM setting to 250 V (l-l) for 
ungrounded systems and to 480 V (l-l) for solidly grounded systems when 
using WYE-connected PTs. In an ungrounded system, when there is a line-to-
ground fault, the terminal voltages can increase by a factor of as much as 1.73.
EXAMPLE 4.4 VNOM Setting Calculation for Standard Voltage 
Inputs
Consider a 10 kV (phase-to-phase) system with wye-connected VTs 
rated 7200:120 (PTR := 60).
The setting for VNOM would be VNOM := 10000/60 := 166.67.
In the case of LEA sensors, the calculated VNOM should be scaled by 
37.5 (300/8) to set VNOM at the 300 V base as shown in the following 
example. The scaling (37.5) is explained in Low-Energy Analog (LEA) Voltage 
Inputs.
Enable Settings
EDIR Setting may be forced to OFF 
and hidden
See Table SET.1: Range 
Dependencies for the EDIR 
Setting.
ELOAD, EFLOC Forced to N and hidden These functions require 
three-phase voltage.
Directional Element Settings (available when EDIR := Y or AUTO)
ORDER Refer to Table SET.2: Range 
Dependencies for the ORDER 
Setting for the ORDER setting 
dependencies on the SINGLEV 
setting.
Associated directional ele-
ment requires three-phase 
voltage.
50PDIRP, Z2F, Z2R, 
a2, k2, 50QFP, 50QRP
Hidden Associated voltage ele-
ments require three-phase 
voltage.
Overvoltage Elements
59G1P, 59G2P, 
59Q1P, 59Q2P
Forced to OFF and hidden These functions require 
three-phase voltage.
27InOQ (n = 1, 2) Refer to Table SET.3: Range 
Dependencies for 27I Operating 
Quantities
59InOQ (n = 1, 2, 3, 4) Refer to Table SET.4: Range 
Dependencies for 59I Operating 
Quantities
Vector Shift Settings
E78VS Hidden Element enable requires 
three-phase voltages
Table 4.4 Effect on Group Settings When SINGLEV := Y (Sheet 2 of 2) 
Identifier Settings
Group Setting Change Reason
4.8
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.5 VNOM Setting Calculation for LEA Voltage Inputs
Consider a 10 kV (phase-to-phase) system with a wye-connected LEA 
sensor with a ratio of 2500:1 (LEA_R := 2500).
The setting for VNOM would be VNOM := 10000/2500 • 37.5 := 150.0
Low-Energy Analog 
(LEA) Voltage Inputs
The SEL-751 can be ordered with different secondary ac input voltage 
configurations—standard voltage inputs rated for 300 V and LEA voltage 
inputs rated for 8 V. The LEA voltage inputs are suitable for C37.92 compliant 
high-impedance sensors, such as capacitive voltage dividers and resistive 
voltage dividers (see Figure 4.1).
Figure 4.1 Low-Energy Analog Voltage Sensor (Capacitive Voltage Divider)
Derived LEA Scale for 8 Vac LEA Voltage Inputs and Voltage-Related 
Settings
Irrespective of the voltage input option, standard (300 Vac) or LEA (8 Vac), 
all the voltage related settings are based at 300 V. For example, the 59 element 
pickup range for standard voltage inputs is 2.0–300.0 V and this range will 
remain the same for LEA inputs as well. To maintain the same 300 V base 
across different voltage options, such as LEA inputs, the relay scales up the 
input signal by a factor of 37.5 (300 V/8 V). Likewise, you can scale the 
Table 4.5 Main Relay Functions That Change With VNOM := OFF 
Relay Function
When VNOM :=
Numeric Value
When VNOM := OFF
Load-encroachment logic 
(enable setting ELOAD)
Available Not available
Negative-sequence and posi-
tive-sequence voltage polar-
ized directional elements
Available DIRQE is disabled, FDIRP/ RDIRP 
disabled, ground directional ele-
ment ORDER setting choice “Q” 
not selectable
Phase and negative-sequence 
element directional control
Available Not available (defaults to “nondirec-
tional” in levels DIR1–DIR4)
Loss-of-potential logic Available Not available
Voltage unbalance logic Available Not available
Vector shift element Available Not available
Voltage Divider
Voltage Input 
(8 Vac LEA Input)
C1
C2
Vpri
Vsec
SEL-751
4.9
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
voltage related pickup settings accordingly to convert the settings from 8 V to 
300 V base. Refer to Example 4.6. With LEA voltage inputs the relay sees 
8 Vac on the voltage inputs as 300 Vac secondary (8 • 37.5 = 300 V). Further, 
to realize accurate primary voltagemetering, the relay uses the derived LEA 
scales, LEA_SC and LEA_S_SC. These scale factors are autocalculated by 
the relay based on LEA_R and LEA_S_R settings, respectively. The LEA 
scale is derived as follows:
LEA_SC = LEA_R • (8/300)
where LEA_R is the marked LEA sensor ratio. 
The ratio of Vpri to Vsec of the voltage divider shown in Figure 4.1 is referred 
to as true ratio. Ideally, the marked LEA sensor ratio should equal the true 
ratio. If not, apply the following additional ratio correction factors.
For example, if an LEA sensor has an LEA sensor ratio of 1400:1,
LEA_R = 1400
LEA_SC = 1400 • 8/300 = 37.33
EXAMPLE 4.6 Voltage Setting Conversion to 300 V Base
A voltage divider (10000 ratio) is connected between a 12.47 kV 
system (7.2 kV line-to-neutral) and the LEA inputs.
7200 V / 10000 = 0.72 V
(actual voltage divider output to the 8 Vac LEA inputs; 
8 V base)
0.72 V • (300/8) = 27 V
(the relay thinks it is looking at 27 V on a 300 V base, not 
0.72 V on an 8 V base)
27 V is the nominal adjusted secondary voltage—adjusted by the 300/
8 factor from an 8 V base to a 300 V base. For this same example, if a 
0.8 V output of the 8 Vac LEA (8 V base) is deemed an overvoltage 
condition, then an overvoltage element pickup setting (e.g., 59P1P) 
could be set at 59P1P = 0.8 V • (300/8) = 30 V (300 V base).
LEA Ratio and Angle Correction Factors (Global Settings)
In the SEL-751 with LEA voltage inputs, Global settings VARCF, VBRCF, 
VCRCF, VSRCF, VAPAC, VBPAC, VCPAC, and VSPAC are applied to their 
respective voltage inputs, VA, VB, VC, and VS. These normalized secondary 
voltages are used throughout the SEL-751. Refer to Table 4.71 under Global 
Settings for these settings.
Ratio Correction Factors (RCF) for Voltage Inputs 
The ratio correction factor (RCF) settings minimize the magnitude error by 
compensating for the irregularities (on a per-phase basis) of the voltage 
dividers connected between the primary voltage system and the LEA inputs. 
The derivation of the RCF value for a voltage divider for a particular phase is 
defined as follows:
Equation 4.1
where:
Vpri = test voltage applied to the primary side of the 
voltage divider
RCF true ratiomarked ratio------------------------------
Vpri Vsec
LEA_R------------------------
Vpri
Vsec LEA_R
----------------------------------= = =
4.10
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings (SET Command)
The marked LEA sensor ratio of the voltage divider is always provided by the 
manufacturer and often the per phase RCF values are also provided.
If the voltage divider is perfect, then
Vpri / Vsec = LEA_R and RCF = 1.000
Therefore, the measured voltage divider performance equals the marked ratio 
of the voltage divider, as given by the manufacturer. But such perfect 
conditions are usually not the case.
If the voltage divider is putting out more voltage (Vsec) than nominally 
expected for an applied voltage input (Vpri), then
Vpri / Vsec < LEA_R and RCF < 1.000
An example of an RCF value less than 1.000 is found in Example 4.7. In this 
example, setting VBRCF = 0.883 brings down the too-high voltage on voltage 
input VB (0.82 V is brought down to nominal 0.72 V).
If the voltage divider is putting out less voltage (Vsec) than nominally 
expected for an applied voltage input (Vpri), then
Vpri / Vsec > LEA_R and RCF > 1.000
EXAMPLE 4.7 Normalizing Voltages With Ratio Correction Factors
A voltage divider is connected to the 8 Vac LEA voltage inputs (see 
Figure 4.1). The RCF values per phase for the voltage divider are given 
as follows:
VARCF = 1.078 (voltage input VA)
VBRCF = 0.883 (voltage input VB)
VCRCF = 1.112 (voltage input VC)
The marked ratio of the voltage divider is given as:
LEA_R = 10000
What are the true ratios of each phase of the voltage divider?
true ratio = Vpri/Vsec
Vpri and Vsec are measured in manufacturer tests to derive RCF values 
as shown in Equation 4.1 and accompanying explanation. From 
Equation 4.1:
RCF • LEA_R = Vpri/Vsec = true ratio
1.078 • 10000 = 10780 (true ratio for voltage input VA)
0.883 • 10000 = 8830 (true ratio for voltage input VB)
1.112 • 10000 = 11120 (true ratio for voltage input VC)
Note that these true ratios vary from 8830 to 11120, while the marked 
ratio of the voltage divider is given as 10000.
Consider what is happening in Example 4.7. First, assume the primary voltage 
(Vpri) is the same magnitude for each phase. When this primary voltage is run 
through the respective true ratios, the secondary voltage outputs vary widely. 
Presuming a primary voltage of 12.47 kV (7.2kV line-to-neutral), the resultant 
secondary voltages are listed below:
Vsec = resultant voltage measured on the secondary side of 
the voltage divider
True ratio = Vpri / Vsec
Marked
ratio
= LEA_R = effective nominal LEA sensor ratio of the 
voltage divider connected between the primary 
voltage system and the LEA input.
4.11
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
7200 V / 10780 = 0.67 V (true secondary voltage to voltage input VA)
7200 V / 8830 = 0.82 V (true secondary voltage to voltage input VB)
7200 V / 11120 = 0.65 V (true secondary voltage to voltage input VC)
Note that the true secondary voltages to voltage inputs VA and VC are running 
low (below the normalized secondary voltage 0.72 V = 7200 V / 10000), while 
the voltage to voltage input VB is running high (above the normalized 
secondary voltage 0.72 V). But the RCF values adjust these true secondary 
voltages to normalized secondary voltage:
0.67 V • 1.078 = 0.72 V (normalized voltage from voltage input VA)
0.82 V • 0.883 = 0.72 V (normalized voltage from voltage input VB)
0.65 V • 1.112 = 0.72 V (normalized voltage from voltage input VC)
Again, the normalized secondary voltage (0.72 V) is the same for all three 
phases in this example, because the primary voltage is assumed to be the same 
magnitude for each phase (7200 V). The relay uses these normalized 
secondary voltages for all the voltage-based protection elements and metering. 
The true secondary voltages cannot be seen (via the SEL-751) unless the RCF 
values are set to unity (RCF := 1.000).
Phase Angle Compensation (PAC) for Voltage Inputs 
Use the VAPAC, VBPAC, VCPAC, and VSPAC voltage phase-angle 
correction Global settings for the voltage inputs VA, VB, VC, and VS, 
respectively. These settings compensate for the phase error caused by the 
voltage divider and the cable connected to the relay. Use a positive phase 
angle correction setting if the resulting phase error is negative and vice versa. 
For example, if the resulting phase error on the VA input is –1.00 degree, then 
set VAPAC := 1.00 degrees.
Line Parameter 
Settings
The line would typically use line impedance settings Z1MAG, Z1ANG, 
Z0MAG, and Z0ANG in the fault locator and in automatically making 
directional element settings Z2F, Z2R, Z0F, and Z0R. Use a corresponding 
line length setting (LL) in the fault locator.
If the protected line belongs to a hybrid power system, such as shown in 
Figure 4.48, refer to Z0MTA—Zero-Sequence Maximum Torque Angle for 
information on the Z0MTA setting.
Table 4.6 Line Parameter Settings
Setting Prompt Setting Range
Setting Name := 
Factory Default
POS SQ LN Z MAG 0.10–510.00 ohmsa
a Settings ranges and default ohm values shown are for 5 A nominal CT rating. Multiply by 5 for 
1 A CTs.
Z1MAG := 2.14a
POS SQ LN Z ANG 5.00–90.00 deg Z1ANG := 68.86
ZERO SQ LN Z MAG 0.10–510.00 ohmsa Z0MAG := 6.38a
ZERO SQ LN Z ANG 5.00–90.00 deg Z0ANG := 72.47
ZERO SQ SR Z MAG 0.10–510.00 ohmsa Z0SMAG := .36a
ZERO SQ SR Z ANG 0.00–90.00 deg Z0SANG := 84.61
LINE LENGTH 0.10–999.00 LL := 0.10–999
NOTE: The relay does not require 
line impedance settings when setting 
SINGLEV= Y, and hides these settings 
from the SET and SHO commands.
4.12
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings(SET Command)
On both hybrid and solidly grounded power systems, Z0ANG must be set to 
the actual zero-sequence line angle to allow correct fault locator operation for 
forward faults involving ground.
The line impedance settings Z1MAG, Z1ANG, Z0MAG, and Z0ANG are set 
in secondary. Line impedance ( primary) is converted to secondary:
primary • (CTR/PTR) = secondary
where:
CTR = phase (IA, IB, IC) current transformer ratio
PTR = phase (VA, VB, VC) potential transformer ratio
Line length setting LL is unitless and corresponds to the line impedance 
settings. For example, if a particular line length is 15 miles, enter the line 
impedance values ( secondary) and then enter the corresponding line length:
LL = 15.00 (miles)
If this length of line is measured in kilometers rather than miles, then enter:
LL = 24.14 (kilometers)
Fault Location The relay reports the fault location if the EFLOC setting := Y and the fault 
locator operates successfully after an event report is generated. If the fault 
locator does not operate successfully, $$$$$$ is listed in the field. Fault 
location is based on the line impedance settings Z1MAG, Z1ANG, Z0MAG, 
and Z0ANG; source impedance settings Z0SMAG and Z0SANG; and 
corresponding line length setting LL. Because the fault locating function 
requires three-phase voltages, the Group setting EFLOC cannot be set to Y 
when Group setting VNOM := OFF. Similarly, the Group setting EFLOC is 
hidden and set to N internally when the Group setting SINGLEV := Y or the 
relay is ordered with no voltage inputs.
Overcurrent Elements Four levels of instantaneous/definite-time elements are available for phase, 
neutral, residual, and negative-sequence overcurrent as shown in Table 4.8 
through Table 4.11 and in Figure 4.2.
Each element can be torque controlled through the use of appropriate 
SELOGIC control equations (for example, when 50P1TC := IN401, the 50P1 
element is operational only if IN401 is asserted).
  
 

Table 4.7 Fault Locator Setting
Setting Prompt Setting Range
Setting Name := 
Factory Default
FLT LOC ENABLE Y, N EFLOC := N
Table 4.8 Maximum Phase Overcurrent Settings (Sheet 1 of 2)
Setting Prompt Setting Range
Setting Name := 
Factory Default
MAXP OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
50P1P := 10.00
50P1P := 2.00
MAXP OC TRIP DLY OFF, 0.00–400.00 sec 50P1D := 0.00
MAXP OC TRQ CON SELOGIC 50P1TC := 1
MAXP OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
50P2P := 10.00
50P2P := 2.00
4.13
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
The phase instantaneous overcurrent elements (50P1 through 50P4; see 
Figure 4.2) normally operate by using the output of the one cycle cosine-
filtered phase current. During severe CT saturation, the cosine-filtered phase 
current magnitude can be substantially reduced because of the high harmonic 
content and reduced magnitude of the distorted secondary waveform. If the 
overcurrent element relied only on the output of the cosine-filtered secondary 
current, the operation of any high-set instantaneous overcurrent element might 
be severely delayed and jeopardized. For any phase instantaneous overcurrent 
element in the SEL-751 that is set greater than eight times the relay current 
input rating (40 A in a 5 A relay), the overcurrent element also operates on the 
output of a bipolar peak detector if the current waveform is highly distorted, as 
is the case with severe CT saturation. This ensures fast operation of the 50Pn 
phase overcurrent elements even with severe CT saturation.
When the harmonic distortion index exceeds the fixed threshold, which 
indicates severe CT saturation, the phase overcurrent elements operate on the 
output of the peak detector. When the harmonic distortion index is below the 
fixed threshold, the phase overcurrent elements operate on the output of the 
cosine filter.
MAXP OC TRIP DLY OFF, 0.00–400.00 sec 50P2D := 0.00
MAXP OC TRQ CON SELOGIC 50P2TC := 1
MAXP OC TRIP LVL OFF, 0.25–100.00 Aa 
0.05–20.00 Ab
50P3P := 10.00
50P3P := 2.00
MAXP OC TRIP DLY OFF, 0.00–400.00 sec 50P3D := 0.00
MAXP OC TRQ CON SELOGIC 50P3TC := 1
MAXP OC TRIP LVL OFF, 0.25–100.00 Aa 
0.05–20.00 Ab
50P4P := 10.00
50P4P := 2.00
MAXP OC TRIP DLY OFF, 0.00–400.00 sec 50P4D := 0.00
MAXP OC TRQ CON SELOGIC 50P4TC := 1
a For INOM = 5 A.b For INOM = 1 A.
Table 4.8 Maximum Phase Overcurrent Settings (Sheet 2 of 2)
Setting Prompt Setting Range
Setting Name := 
Factory Default
NOTE: The cosine filter provides 
excellent performance in removing dc 
offset and harmonics. However, the 
bipolar peak detector has the best 
performance in situations of severe 
CT saturation when the cosine filter 
magnitude estimation is significantly 
degraded. Combining the two 
methods provides an elegant solution 
for ensuring dependable short-circuit 
overcurrent element operation.
NOTE: When using the output of 
harmonic blocking logic to torque-
control 50 elements set with a pickup 
greater than 8 • INOM, the harmonic 
blocking could nullify the peak 
detector feature of the 
corresponding 50 element. Refer to 
the Second- and Fifth-Harmonic 
Blocking Logic on page 4.89.
4.14
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings (SET Command)
The relay offers two types of ground fault detecting overcurrent elements. The 
neutral overcurrent elements (50N1T through 50N4T) operate with current 
measured by the IN input. The residual (RES) overcurrent elements (50G1T 
through 50G4T) operate with the current derived from the phase currents.
Table 4.9 Neutral Overcurrent Settings
Setting Prompt Setting Range
Setting Name := 
Factory Default
NEUT OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
0.01–4.00 Ac
a For INOM = 5 A.b For INOM = 1 A.c For INOM = 0.2 A.
50N1P := OFF
NEUT OC TRIP DLY OFF, 0.00–400.00 sec 50N1D := 0.50
NEUT OC TRQ CON SELOGIC 50N1TC := 1
NEUT OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
0.01–4.00 Ac
50N2P := OFF
NEUT OC TRIP DLY OFF, 0.00–400.00 sec 50N2D := 0.50
NEUT OC TRQ CON SELOGIC 50N2TC := 1
NEUT OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
0.01–4.00 Ac
50N3P := OFF
NEUT OC TRIP DLY OFF, 0.00–400.00 sec 50N3D := 0.50
NEUT OC TRQ CON SELOGIC 50N3TC := 1
NEUT OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
0.01–4.00 Ac
50N4P := OFF
NEUT OC TRIP DLY OFF, 0.00–400.00 sec 50N4D := 0.50
NEUT OC TRQ CON SELOGIC 50N4TC := 1
NOTE: If channel IN is rated 0.2 A 
nominal, then it is recommended that 
50NnD (n = 1–4) be set to at least a 
minimum 2-cycle time delay.
NOTE: When a switch or breaker 
closes, the three poles may not close 
at the same time, creating a 
momentary current unbalance 
condition. To override this condition 
use an overcurrent trip delay (for 
example, 50NnD := 0.05 s).
4.15
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
q To Figure 4.43; w From Figure 4.37; e From Figure 4.36; r From Figure 4.42; t Residual Current Magnitude lIGl 
is the calculated residual current. Not shown in the figure, Relay Word bit ORED50T is asserted if any of the 50PnT, 67PnT, 
50NnT, 67NnT, 50GnT, 67GnT, 50QnT or 67QnT Relay Word bits are asserted (n = 1 to 4).
Figure 4.2 Instantaneous Overcurrent Element Logic
When For Trip For Pickup Nonfunctional
EDIR := Y or AUTO Use 67PnT, 67NnT, 67QnT, 
and 67GnT
Use 67PnP, 67NnP, 67QnP, 
and 67GnP
50PnT, 50NnT, 50QnT, 50GnT, 
50PnP, 50NnP, 50QnP, and 50GnP
EDIR := N ora
a When the directional control option is not ordered and EDIR is automatically set to N and hidden.
Use 50PnT, 50NnT, 50QnT, 
and 50GnT
Use 50PnP, 50NnP, 50QnP, 
and 50GnP
67PnT, 67NnT, 67QnT, 67GnT, 
67PnP, 67NnP, 67QnP, and 67GnP
IA
IB
IC
IN
PHROT
IG
Current
Magnitude
Calculations
Settings
|IP|
(Maximum Phase Current Magnitude)
|IN|(Core-Balance Current Magnitude)
|IG|(Residual Current Magnitude)
(Negative-Sequence Current Magnitude)
|3I2|
|IA|(A-PhaseCurrent Magnitude)
|IB|(B-Phase Current Magnitude)
(C-Phase Current Magnitude)
|IC|
Negative-Sequence 
Current Calculation
50P1TC
50P1P
|IA|
50A1P
50B1P
|IC|
50C1P
Relay 
Word 
Bits
|IB|
4
5
5
5
5
5
5
5
5
50PnP
67PnT/50PnT 
50NnP
67NnT/50NnT
67NnP/50NnP
67PnP/50PnP 
|IN|
|IP|
50PnTC
67QnT/50QnT 
50GnP
67GnT/50GnT 
67GnP/50GnP 
|IG|
50QnP
|3I2|
50GnTC
50QnTC
67QnP/50QnP 
50PnD
0
50GnD
0
50NnD
0
50QnD
0
PnDIR 1
GnDIR 3
50NnTC
NnDIR 2
QnDIR
4.16
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings (SET Command)
When a core-balance CT is connected to the relay IN input, as in Figure 2.28, 
use the neutral overcurrent element to detect the ground faults. Calculate the 
trip level settings based on the available ground fault current and the core-
balance CT ratio.
Table 4.10 Residual Overcurrent Settings 
Setting Prompt Setting Range
 Setting Name := 
Factory Default
RES OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
a For INOM = 5 A.b For INOM = 1 A.
 50G1P := OFF
RES OC TRIP DLY OFF, 0.00–400.00 sec 50G1D := 0.50
RES OC TRQ CON SELOGIC 50G1TC := 1
RES OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
 50G2P := OFF
RES OC TRIP DLY OFF, 0.00–400.00 sec 50G2D := 0.50
RES OC TRQ CON SELOGIC 50G2TC := 1
RES OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
 50G3P := OFF
RES OC TRIP DLY OFF, 0.00–400.00 sec 50G3D := 0.50
RES OC TRQ CON SELOGIC 50G3TC := 1
RES OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
 50G4P := OFF
RES OC TRIP DLY OFF, 0.00–400.00 sec 50G4D := 0.50
RES OC TRQ CON SELOGIC 50G4TC := 1
Table 4.11 Negative-Sequence Overcurrent Settings
Setting Prompt Setting Range
Setting Name := 
Factory Default
NSEQ OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
a For INOM = 5 A.b For INOM = 1 A.
50Q1P := OFF
NSEQ OC TRIP DLY OFF, 0.00–400.00 sec 50Q1D := 0.2
NSEQ OC TRQ CON SELOGIC 50Q1TC := 1
NSEQ OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
50Q2P := OFF
NSEQ OC TRIP DLY OFF, 0.00–400.00 sec 50Q2D := 0.2
NSEQ OC TRQ CON SELOGIC 50Q2TC := 1
NSEQ OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
50Q3P := OFF
NSEQ OC TRIP DLY OFF, 0.00–400.00 sec 50Q3D := 0.2
NSEQ OC TRQ CON SELOGIC 50Q3TC := 1
NSEQ OC TRIP LVL OFF, 0.25–100.00 Aa
0.05–20.00 Ab
50Q4P := OFF
NSEQ OC TRIP DLY OFF, 0.00–400.00 sec 50Q4D := 0.2
NSEQ OC TRQ CON SELOGIC 50Q4TC := 1
NOTE: When a switch or breaker 
closes, the three poles may not close 
at the same time, creating a 
momentary current unbalance 
condition. To override this condition 
use an overcurrent trip delay (for 
example, 50GnD = 0.05 s).
NOTE: When a switch or breaker 
closes, the three poles may not close 
at the same time, creating a 
momentary current unbalance 
condition. To override this condition 
use an overcurrent trip delay 
(e.g., 50QnD = 0.05 s).
4.17
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
The relay offers four negative-sequence overcurrent elements to detect phase-
to-phase faults, phase reversal, single phasing, and unbalance load.
When the overcurrent trip delay (50P1D through 50P4D, 50N1D through 
50N4D, 50G1D through 50G4D and 50Q1D through 50Q4D) is set to OFF, 
the time delayed overcurrent element is disabled and the output Relay Word 
bits (50P1T through 50P4T, 50N1T through 50N4T, 50G1T through 50G4T 
and 50Q1T through 50Q4T) keep deasserted.
Pickup and Reset Time Curves
Figure 4.3 and Figure 4.4 show pickup and reset time curves applicable to all 
nondirectional instantaneous overcurrent elements with sinusoidal waveforms 
applied (60 Hz or 50 Hz relays). These times do not include output contact 
operating time and, thus, are accurate for determining element operation time 
for use in internal SELOGIC control equations. Output contact pickup/dropout 
time is approximately 4 ms (0.25 cycle for a 60 Hz relay; 0.20 cycle for a 
50 Hz relay).
NOTE: The pickup time curve in 
Figure 4.3 is not valid for conditions 
with a saturated CT, where the 
resultant current to the relay is 
nonsinusoidal.
Figure 4.3 Instantaneous Overcurrent Element Pickup Time Curve
Figure 4.4 Instantaneous Overcurrent Element Reset Time Curve
Incipient Cable Fault The incipient cable fault element is used to detect self-clearing, half- to one-
cycle overcurrent events. This type of event is most common in cable splices 
and are indicative of an impending fault. As the frequency of the events 
increases, the likelihood of a permanent fault increases, and preventative 
maintenance should be scheduled.
The logic, as detailed in Figure 4.6, detects when two consecutive raw 
samples of phase current are higher than the user-defined threshold and asserts 
the respective phase 50INCx (x = A, B, C) Relay Word bit. If the overcurrent 
clears within three half cycles, an event is recorded in the history report and 
the counter is incremented. The cable phase, total number of events on each 
phase, and time stamps of the 32 most recent events are stored in the report 
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.2 2 3 4 5 6 7 8 9 10
Applied Current (Multiples of Pickup Setting)
Pi
ck
up
 T
im
e 
(C
yc
le
s)
Maximum
Minimum
Applied Current (Multiples of Pickup Setting)
Re
se
t T
im
e 
(C
yc
le
s)
Maximum
Minimum
2
1.5
1
0.5
0
1.2 2 3 4 5 6 7 8 9 10
4.18
SEL-751 Relay Instruction Manual Date Code 20200603
Protection and Logic Functions
Group Settings (SET Command)
(see Figure 4.5), which is displayed with the HIS 50INC command (see 
Table 7.27). To reset the counter and the event report, issue the HIS 50INC C 
command.
Figure 4.6 Incipient Cable Fault Logic
The logic provides a threshold for alarm via 50IALC and a threshold for 
tripping via 50ITRC, depending on the number of detected events. These have 
corresponding Relay Word bits, 50IALCx and 50ITRCx (x = A, B, C), for 
each phase when the count on that phase is higher than the respective 
threshold.
Time-Overcurrent 
Elements
One level of inverse-time element is available for A-, B-, C-phases, and 
negative-sequence overcurrent. Also, two levels of inverse-time elements are 
available for maximum phase, neutral, and residual overcurrent. See 
Table 4.13 through Table 4.17 for available settings.
You can select from five U.S. and five IEC inverse characteristics. Table 4.18 
and Table 4.19 show equations for the curves and Figure 4.12 through 
Figure 4.21 show the curves. The curves and equations shown do not account 
for constant time adder and minimum response time (settings 51_CT and 
=>>HIS 50INC <Enter>
SEL-751 Date: 08/29/2019 Time: 11:09:24.098
FEEDER RELAY Time Source: Internal
FID=SEL-751-X470-V1-Z008004-D20190827
# DATE TIME CNTA CNTB CNTC INCF PHASE
1 08/29/2019 11:09:15.497 1 0 0 A 
2 08/29/2019 11:09:15.747 2 0 0 A 
3 08/29/2019 11:09:15.998 3 0 0 A 
4 08/29/2019 11:09:16.248 4 0 0 A 
5 08/29/2019 11:09:16.498 5 0 0 A 
LAST RESET = 08/29/2019 11:09:09.024
Figure 4.5 HIS 50INC Report Response
50IALCA
50ITRCA
50IALC
50ITRC
Reset
Counter
8
Samples
2
16
Samples
46
Samples 50INCTA
50INCA
16
1
Samples
E50INC
|IA RAW|
Relay
Word
Bit
Setting
Relay
Word
Bit
Settings
Relay
Word
Bits
Table 4.12 Incipient Cable Fault Settings
Setting Prompt Setting Range
Setting Name := 
Factory Default
50INC PU LVL OFF, 5.00–50.00 Aa
1.00–10.00 Ab
a For INOM = 5 A.b For INOM = 1 A.
E50INC := 15.00
E50INC := 3.00
50INC WARN COUNT 1–100 50IALC := 1
50INC TRIP COUNT 1–100 50ITRC := 10
4.19
Date Code 20200603 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
51_MR respectively, each assumed equal to zero). Use the 51_CT if you want 
to raise the curves by a constant time. Also, you can use the 51_MR if you 
want to ensure