Protecao Interconexao

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CEPSE – Curso de Especialização em 
Proteção de Sistemas Elétricos 
 
 
PROTEÇÃO DA 
INTERCONEXÃO 
 
 
 
 
 
 
 
Instrutor: Ricardo Abboud 
Campinas, 7 de março de 2009 
1
Proteção da Interconexão
Torna-se cada vez mais comum uma planta industrial que possui geração própria conectada
à concessionária em alta-tensão e que opera em
paralelo ou isoladamente para suprir uma parte de seu consumo de energia elétrica.
Essa geração é feita basicamente por turbinas a gás, turbinas inseridas no ciclo de vapor 
e usando bagaço de cana como combustível nas indústrias de açúcar e álcool, onde a
potência desses geradores varia muito, podendo ser maior que o consumo da própria 
indústria.
A proteção a ser instalada no ponto de interconexão requer um estudo detalhado e criterioso 
para evitar danos pessoais e aos equipamentos e a melhor aplicação depende de vários 
fatores, como por exemplo o sistema de aterramento, o fluxo de potência na interconexão 
para condições normais de operação, o layout da interconexão, o npivel de tensão, a 
topologia da rede, etc. 
2
22
Considerações sobre a Interconexão
� Sistema de Potência
� Segurança das equipes de trabalho
� Qualidade no fornecimento de energia 
para os consumidores
� Religamento automático
� Geração Distribuída
� Danos ao gerador
Interconnection protection is to protect both the PS and DG.
On the PS side, the utility is concerned with the personnel safety. The DG introduces a new 
source for which the utility personnel will have to take into account in their operations practices.
To protect the PS and the utility customers, the utility requires the DG to isolate as soon as a 
problem is detected on either side of the interconnecting breaker. This is to minimize the 
disturbance to the utility customers being served off of the interconnecting line.
The utility is also concerned about fast restoration of service to its customers. Automatic
reclosing of the utility breaker cannot take place until the DG is off-line.
3
3
REDES DE DISTRIBUIÇÃO x 
GERAÇÃO DISTRIBUÍDA
� Redes de distribuição foram projetadas para 
operação radial
� Não há normatização nacional (a cargo de cada 
concessionária)
� Alguns acessantes não compreendem os 
requisitos das concessionárias e vice-versa
� Aelutância do acessante em aceitar os esquemas 
de proteção impostos pela concessionária
� Discussão sobre os custos da conexão 
4
4
IMPACTOS DA GERAÇÃO 
DISTRIBUÍDA NA DISTRIBUIÇÃO
� Coordenação dos dispositivos de 
proteção
� Substituição/relocação dos dispositivos 
de proteção
� Sobretensões em equipamentos (1.73 
vn), trafo delta-triângulo
� Problemas com regulação de tensão
5
5
IMPACTOS DA GERAÇÃO 
DISTRIBUÍDA NA DISTRIBUIÇÃO
� Inversão do fluxo de potência para a 
transmissão
� Elevação da potência de curto-circuito
� Recondutoramento dos alimentadores
� Ilhamento - operação isolada
� Restabelecimento/Religamento
6
6
circuito 1
circuito 2
falta
IfDR = 600 A
Isistema
CB 1
CB 2
cargareligador
I
II
V
IV
IMPACTOS DA GERAÇÃO 
DISTRIBUÍDA NA DISTRIBUIÇÃO
7
77
Proteção da Interconexão
� Sobre/Subtensão
� Sobre/Subfreqüência
� Verificação de Sincronismo
� Direcional de Potência
� Oscilação de Potência
� Sobrecorrente, Direcional, Distância
� Salto Vetor
Interconnecting DG with PS requires application of specific protection functions to protect 
both the PS and the distributed resource from abnormal operating conditions.
Depending on the PS requirements, some or all of the following protection functions might 
be required on interconnection applications:
• Over-/undervoltage.
• Over-/underfrequency.
• Synch-check.
• Reverse power.
• Out-of-step.
• Directional overcurrent.
8
88
Layout da Interconexão
G
LOAD
LOAD
LOAD Interconnection
Breaker
UtilityConcessionária
CARGA
CARGA
Disjuntor de 
Interconexão
CARGA
Different layouts are used to connect the DG to the PS at different voltage levels.
A common layout is shown here where the DG is connected to a load bus through a breaker. 
Local load is served off of this bus. DG is connected to the PS through the interconnection 
breaker (IB).
On the PS side, there could be load being served off of the interconnecting line. It is apparent 
here that any disturbance at the DG will affect the customers being served off of the 
interconnecting line.
For disturbances on the PS side of the IB, the DG might want to separate from the PS and be 
able to serve its own load.
Depending on the operating mode, it is desirable to be able to synchronize across the IB as 
well as the generator breaker. With the DG off-line, the local load off of the DG bus is fed 
from the PS through the IB. DG can come online and synchronize across the DG breaker. In 
the event the IB opens and the DG is online, DG can synchronize back to the PS across the 
IB. This assumes DG is sized to carry the local load.
Overcurrent protection will be required on the IB depending on the DG type and size. Due to 
coordination issues and very different fault current availability for faults on both sides of the 
breaker, it might be desirable to use directional overcurrent relays in both directions.
A concern with applying overcurrent relays on DG is that due to the time constant of the 
DG, the fault current contribution from the DG to a fault on the PS will decrease dramatically 
and might not last long enough for a time-overcurrent relay to operate. Application of 
voltage-controlled/restraint overcurrent relays is an option.
9
99
Layout da Interconexão
G
LOAD
LOAD
LOAD Interconnection
Breaker
UtilityConcessionária
CARGA
CARGA
Disjuntor de 
Interconexão
CARGA
In this layout, the DG is connected to the PS through a transformer. The transformer 
connection will dictate what type of ground fault protection will be applied on the high side 
of the transformer. Different transformer connections are discussed later.
10
1010
Layout da Interconexão
A B
C
11
1111
Layout da Interconexão
A B
C
12
1212
Layout da Interconexão
A B
C
13
13
Funções de Proteção 
a Aplicar Depende 
da Conexão do Trafo 
e do Intercâmbio de 
Energia
Dependendo do tipo de conexão do transformador de interligação, diferentes funções de 
proteção serão requeridas.
14
1414
Ilhamento
G
LOAD
LOAD
LOAD Interconnection
Breaker
Utility
Disjuntor
Aberto
Concessionária
CARGA
CARGA
Disjuntor de 
Interconexão
CARGA
In the event of a utility main breaker trip, DG can be islanded serving utility load.
Normally, the utility does not allow the DG to operate on an island carrying utility load.
15
15
Religamento
� Configuração (a), linha radial e expressa, religamento 
pode ser retardado 
� Configuração (b) o religamento automático de alta 
velocidade requerido, vital o bom desempenho do sistema 
de proteção 15
(a) (b)
No que concerne ao religamento automático da linha de transmissão da 
concessionária, é um dos aspectos que deve ser cuidadosamente 
analisado. Caso ocorra o religamento antes que o paralelismo com o 
autoprodutor tenha sido desfeito este corre o risco de sérios danos. O 
esquema de proteção por transferencia de disparo (transfer trip), que 
necessita de um canal de telecomunicação, praticamente elimina o 
paralelismo forçado, entretanto, tem um custo elevado, o que torna a sua 
adoção pouco atrativa para a maioria dos casos
Na configuração a), por se tratar de uma linha radial, o religamento 
automático pode ser retardado e isso certamente não causará grandes 
transtornos ao sistema da concessionária. Já na configuração b) o 
religamentoautomático de alta velocidade é uma exigência do sistema de 
transmissão. Para este caso é vital o bom desempenho do sistema de 
proteção no ponto de interligação do autoprodutor.
16
1616
Transformadores Delta-Estrela
� Normalmente usados pelas 
concessionárias
� Melhora a distribuição da carga
� Bloqueia a circulação de corrente de 
seqüência-zero para faltas no lado de BT
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
S H L
Utilities use delta-wye transformers extensively in utility systems to connect transmission 
and subtransmission systems to distribution systems and large three-phase customer loads. 
This transformer configuration offers several beneficial effects, including improving load 
balance and blocking zero-sequence current flow, which simplifies ground fault protection.
This slide shows a simplified one-line diagram representing a typical connection from a 
utility source substation to a customer load through a delta-wye transformer. The delta-wye
transformer could be located at a utility-owned distribution substation, or the delta-wye
transformer could be located at a customer-owned substation. The line could be radial, as 
shown in this figure, or it could be networked to another source substation with the delta-
wye transformer tapped on the line between the two substations. The line may very likely 
supply other customer loads or utility substations. Protective relaying, appropriate to detect 
line faults and trip the associated line breaker, is installed at the utility source substation.
17
1717
Diagramas de 
Componentes
Simétricas
� Usados para 
analisar as faltas
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Diagrama de Seqüência Positiva
Z1S Z1L Z1T
Carga Z1
Diagrama de Seqüência Negativa
Z2S Z2L Z2T
Carga Z2
Diagrama de Seqüência Zero
Z0S Z0L
Z0T Carga Z0
S H L
S H L
S H L
S H L
This slide shows the sequence component networks needed to analyze balanced and 
unbalanced fault conditions that occur on the utility line. Note that the representation for 
the delta-wye transformer in the zero-sequence network includes an open circuit between 
terminals H and L. This open circuit prevents the flow of zero-sequence current through the 
transformer, which is a characteristic of the delta-wye transformer.
The fundamental equations for deriving phase currents (IA, IB, and IC) and phase-to-neutral 
voltages (VA, VB, and VC) are as follows:
IA = I1 + I2 + I0 IB = a2I1 + aI2 + I0 IC = aI1 + a2I2 + I0
VA = V1 + V2 + V0 VB = a2V1 + aV2 + V0 VC = aV1 + a2V2 + V0
Where unity operator a = 1 ∠120 degrees.
18
1818
Falta Trifásica 
na Linha com 
Geração 
Distribuída 
Paralela
� A corrente 
circula 
somente no 
diagrama de 
seqüência-
positiva
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Z1S Z1L Z1T
Z2S Z2L Z2T
Z0S Z0L
Z0T
3φ
V1L
I1>0 I1>0
I2=0 I2=0
I0=0
I0=0
Ger
Carga
Z1
E1G
Z1G
I1>0
Carga
Z2
I2=0
Z2G
Carga
Z0
Z0G
V0S V0H V0L
S
S
S
S H
H
H
H
L
L
L
L
V2H
V1HV1S
V2S V2L
19
1919
Falta Trifásica 
na Linha com 
Geração e com 
o Disjuntor da 
Concessionária 
Aberto
� A corrente continua 
a circular no 
diagrama de 
seqüência-positiva
� A Geração 
Distribuída é ilhada
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Z1S Z1L Z1T
Z2S Z2L Z2T
Z0S Z0L
Z0T
3φ
V1L
I1=0 I1>0
I2=0 I2=0
I0=0
I0=0
Ger
Carga
Z1
E1G
Z1G
I1>0
Carga
Z2
I2=0
Z2G
Carga
Z0
Z0G
V0S V0H V0L
S
S
S
S H
H
H
H
L
L
L
L
V2H
V1HV1S
V2S V2L
20
2020
Falta Fase-Fase 
na Linha com 
Geração 
Distribuída 
Paralela
� A corrente 
circula 
somente nos 
diagramas de 
seqüência 
positiva e 
negativa
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Z1S Z1L Z1T
Z2S Z2L Z2T
Z0S Z0L
Z0T
φ –φ
V1L
I1>0 I1>0
I2>0 I2>0
I0=0
I0=0
Ger
Carga
Z1
E1G
Z1G
I1G>0
Carga
Z2
I2>0
Z2G
Carga
Z0
Z0G
V0S V0H V0L
S
S
S
S H
H
H
H
L
L
L
L
V2H
V1HV1S
V2S V2L
21
2121
Falta Fase-Fase 
na Linha com 
Geração 
Distrib. e com o 
Disjuntor da 
Concessionária 
Aberto
� A corrente 
continua a circular 
nos diagramas de 
seqüência positiva 
e negativa
� A Geração 
Distribuída é ilhada
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Z1S Z1L Z1T
Z2S Z2L Z2T
Z0S Z0L
Z0T
φ –φ
V1L
I1=0 I1=–I2
I2=0
I0=0
I0=0
Ger
Carga
Z1
E1G
Z1G
I1>0
Carga
Z2
I2>0
Z2G
Carga
Z0
Z0G
V0S V0H V0L
S
S
S
S H
H
H
H
L
L
L
L
V2H
V1HV1S
V2S V2L
I2=–I1
22
2222
Faltas entre Fases São Detectáveis
� A conexão delta-estrela propicia a 
circulação das correntes de seqüência 
positiva e negativa para faltas entre 
fases.
� A proteção da interconexão pode usar 
proteção de distância e sobrecorrente 
direcional para detectar faltas
23
23
Utilização de função 
de sobrecorrente para 
detecção de faltas 
multifases na linha de 
interligação 
24
2424
Necessidade de Elementos Direcionais
G
LOAD
LOAD
LOAD Interconnection
Breaker
Utility
F1 F2
A
B
Concessionária
CARGA
CARGA
Disjuntor de 
Interconexão
CARGA
A contribuição do gerador para curto-circuito em F1 é
muito menor que a contribuição da concessionária 
para curto em F2
25
25
Falta Trifásica em uma Linha Radial
Falta Trifásica Sólida
d
L
Linha
Radial
For a perfect three-phase fault, only the positive sequence impedance is involved in the 
calculations. With the usual convention, the phase “a” voltage and current are equal to the 
positive-sequence voltage and current.
26
26
Ajuste e Alcance do Relé de Sobrecorrente
� Elemento de Fase Instantâneo (50) Normalmente Ajustado para 
Alcançar Faltas em até 80% do Comprimento Total da Linha
0.8L
L
11 )8.0( LS
AJUSTE
ZZ
E
I
+
≈
Linha
Radial
Falta Trifásica Sólida
� Ajuste do Relé 
Calculado para um Valor 
Determinado de ZS1
A phase instantaneous overcurrent element is set to detect fault currents up to 80% of the 
line length. This gives enough security margin (20%) to avoid non-selective operation for 
faults beyond the remote bus. The relay setting is calculated for a given value of the 
equivalent ZS1.
27
27
Problema do Relé de Sobrecorrente
11 )8.0( LS
AJUSTE
ZZ
E
I
+
≈
11
)(
)8.0(
LS
LIMITEFALTA
ZZ
E
I
+′
=
� O Relé Opera Quando Ocorre a Seguinte 
Condição:
AJUSTEaFALTA
III >=
� À Medida que Zs1 Altera, o “Alcance” do Relé Vai 
Alterar, Uma Vez Que o Ajuste é Fixo
As the system topology behind the substation bus changes, ZS1 changes. As a result, the 
relay “reach” will change. The only way to avoid non-selective operations for faults beyond 
the remote bus is to calculate the instantaneous setting for the worst case value of ZS1, which 
results in a shorter reach of the instantaneous element for all other system configurations. It 
is highly probable that the system presents the worst case value for relatively short periods 
of time, meaning that the relay reach will be permanently sacrificed for a situation which 
occurs for short periods. This is a disadvantage of instantaneous overcurrent relays.28
2828
Geração Distribuída:
Criando a Fonte Delta Não Esperada
� Dependendo da quantidade de geradores 
em operação a Ifalta muda, comprometendo 
a coordenação ou a detecção de falta pelo 
relé de sobrecorrente
Geradores
Concessionária
Ifalta
29
29
Princípio do Relé de Distância
Falta Trifásica 
Sólida
d
L
Linha
Radial21
Considerando que o Relé seja Especificado para
Operar Quando:
||||)8.0(|| 1 aLa IZV ≤
Va, Vb, Vc
Ia, Ib, Ic
Suppose that it is possible to design a relay which operates not when the current is larger 
than a given threshold, but when the phase voltage is less than the current times a constant, 
as shown in the figure.
This relay requires voltage and current information.
30
30
Utilização de Relés de Distância 
para Detecção de Faltas
( )
MTM
ZZ ϕϕ −≤ cos
ZM
Z
R
ϕ
ϕMT
X
( )
MTM
ZIV ϕϕ −≤ cosOpera quando:
There are three traditional distance elements: impedance-type, reactance-type, and mho-type 
distance elements.
The figure shows the operation equation and operating characteristic of a mho distance 
element. The characteristic is the locus of all apparent impedance values for which the relay 
element is on the verge of operation. The operation zone is located inside the circle, and the 
resraint zone is the region outside the circle.
The mho characteristic is a circle passing through the origin of the impedance plane. The 
mho element operates for impedances inside the circle. The characteristic is oriented 
towards the first quadrant which is wehre forward faults are located. For reverse faults, the 
apparent impedance lies in the third quadrant and represents a restraint condition. The fact 
that the circle passes through the origin is an indication of the mho elements inherent 
directionality. However, close-in bolted faults result in a very small voltage at the relay 
which may result in a loss of the voltage polarizing signal. This needs to be taken into 
consideration when selecting the appropriate mho element polarizing quantity.
There are typically two settings in a mho element: the characteristic diameter, ZM, and the 
angle of this diameter with respect to the R axis, ϕMT. The angle is equivalent to the 
maximum torque angle of a directional element. The mho element presents its longest reach 
(greatest sensitivity) when the apparent impedance angle ϕ coincides with ϕMT. 
Normally, ϕMT is set close to the protected line impedance angle to ensure maximum relay 
sensitivity for faults and minimum sensitivity for load conditions.
31
31
Temporização e Coordenação do
Relé de Distância
1 2 3 4 5 6
Zona 1
Zona 2
Zona 3
Tempo de Operação
B CA
Zona 1 é Instantânea
So far, a directional distance relay, which operates instantaneously and is set to reach less 
than 100% of the protected line, has been described. Two important principles of protection 
have been missing:
1. What happens for a fault on the protected line that is beyond the reach of the relay?
2. If the relay operates instantaneously, it cannot be used as a remote back-up for a relay 
protecting a line adjacent to the remote substation.
These two problems are overcome by adding time delay distance relays. This is 
accomplished by using the distance relay to start a definite time timer. The output of the 
timer can then be used as a tripping signal.
The figure shows how a second zone (or step) is added to each of the directional impedance 
relays. A third zone, with a larger delay, can also be added. 
The operation time of the second zone is usually around 0.3 seconds and the third zone 
around 0.6 seconds. However, the required time depends on the particular application.
The ohmic reach of each zone also depends on the particular power system. The figure and 
the next slide show a typical reach scheme for three zones. 
What about Circuit Breakers 2, 4 and 5?
32
32
Alcance dos Elementos MHO 
Ajustes do Relé
X
R
B
C
A
Zona 1
Zona 2
Zona 3
Relés em A
(52-1)
The slide shows how the instantaneous Zone 1, and the delayed Zones 2 and 3 look in a 
complex impedance plane if MHO units are used for all three zones. Note the reference to 
buses A, B and C of the previous slide, which indicate that the distance elements correspond 
to the relays associate with Circuit Breaker 1, located a Substation A.
33
33
Utilização de função 
de distância para 
detecção de faltas 
multifases na linha de 
interligação 
34
34
Efeito do Infeed
21
V I
Falta
'
L
'
L ZIZIV +=
'
LL
'
L
'
L ZZZ
I
I
ZIVZ +>+==
O Infeed Causa o Subalcance do Relé
'
LZLZ
'I
A generation source connected between the relay location and the fault point affects the 
value of the impedance a distance relay estimates. This is called the infeed effect. The 
intermediate generation source causes the relay to see the impedance of the adjacent line 
multiplied by a factor. This factor is the ratio of the current in the adjacent line to the relay 
current. The infeed-effect factor is, in general, a complex number with a magnitude greater 
than unity. The infeed effect results in the relay estimating an impedance value greater than 
the real impedance between the relay and the fault, ZL + ZL. This inaccurate impedance 
value estimation produces distance relay underreach.
35
35
Linhas Multiterminais
Za
I I’
S R
T
K
ZL1
Z’L1
F1
I’’
Relé 3Relé 2
R
e
lé
 1
Zb
bbL
Z
I
I
ZZZ
APARENTE ''
'
1 ++=
Impedância Vista Relé 1:
Lines with more than two branches connected to different sources are called 
multi-terminal lines. The figure shows the typical case of a three-terminal line. 
The current distribution for faults at different points of the system (i.e. F1 and 
F2) depends on the relative impedances of the line segment, the sources’
strength and the pre-fault load flow.
Engineers can typically calculate settings for distance and/or directional 
overcurrent relays for all faults. The help of computer programs is important. 
The main difficulty when these calculations comes from the fact that the 
system’s configuration can substantially change if, for example, one of the 
sources is out of service. 
For more complicated cases, there could be infeed and/or outfeed conditions. 
The final consequence is an extra delay in schemes with no communications, 
since Zone 1 reach must be restricted to avoid selectivity problems. 
Multi-ended line protection are more effectively protected by line differential or 
directional comparison schemes using reliable communication links.
36
36
Lins
138.kV 
T#Bertin
138.kV 
T#Tropical
138.kV 
Promissão
138.kV 
Cogera
138.kV 
T#Cogera
138.kV 
Cogera
13.8kV 
 5324P-77 
 0.0P0 
 26.9P-7 
 43.4P-5 
 1595P-84 
 1.9P-5 
 25.5P-6 
 5.9P-5 
 6.2P9 
 7080P-117
 2335P100 
 1982P101 
 708P-87 
 354P93 
 354P93 
 1634P-77 
 1982P-79 1982P101 1982P-79 
 708P93 
 2335P-80 1634P103 
 1982P101 1982P-79 
 3540P-117
 3540P-117
CURTO-CIRCUITO 3F NA BARRA DE LINS
EXTENSÃO: 46 km
ESTRUTURA: MET-TIPO K-T22
CAA-477.0 MCM HAWK
CABO-GUARDA: 2 CAG 5/16”
3F - 2096.2@-82.3° MVA
1F - 2484.7@-83.6° MVA
3F - 1148.3@-76.7° MVA
1F - 814.5@-78.9° MVA
Z+=0.13424+0.45764 Ω/km
Z0=0.44021+1.69427 Ω/km
TR1//TR2
15/20/25 MVA
2 x 37,5 MVA
37
37
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
-5
-10
-15 -10 -5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130
PMS-LIN-21 Type=SEL 321Mho
 PTR=1200.0 CTR=160.0 Min I= 0.50A
 Zone 1: Z=2.48 sec Ohm @ 73.7 deg. T=0.0sZone 2: Z=4.37 sec Ohm @ 73.7 deg. T=0.50s
 Zone 3: Z=5.83 sec Ohm @ 73.7 deg. T=1.00s
Line Z= 2.92@ 73.7 sec Ohm ( 21.87 Ohm)
Apparent impedances plotted:
 (Vb-Vc)/(Ib-Ic)= 3.54@71.9 sec Ohm (26.55 Ohm).
 (Vc-Va)/(Ic-Ia)= 3.54@71.9 sec Ohm (26.55 Ohm).
 (Va-Vb)/(Ia-Ib)= 3.54@71.9 sec Ohm (26.55 Ohm).
Relay response: Zone 2 tripped. Delay=0.50s.
 B-C UNIT: Zone 2 Tripped.
 C-A UNIT: Zone 2 Tripped.
 A-B UNIT: Zone 2 Tripped.
Fault Description:
3LG Bus fault on:
 Lins 138. kV
IMPEDÂNCIA APARENTE VISTA POR PROMISSÃO
Relé 21 instalado no terminal da SE 
Promissão detecta a falta na zona 2 
corretamente, idependentemente do 
infeed
38
38
Lins
138.kV 
T#Bertin
138.kV 
T#Tropical
138.kV 
Promissão
138.kV 
Cogera
138.kV 
T#Cogera
138.kV 
Cogera
13.8kV 
 9601P-83 
 0.0P-27 
 3469P-90 
 13.3P-9 
 13.6P-3 13.0P-3 
 11.6P-8 
 11.8P-3 
 5.8P12 
 8882P-118
 1061P99 
 622P104 
 888P-88 
 444P92 
 444P92 
 209P-50 
 622P-76 622P-76 622P104 
 888P92 
 209P130 1061P-81 
 622P-76 622P104 
 4441P-118
 4441P-118
CURTO-CIRCUITO 3F NA BARRA DE PROMISSÃO
39
39
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
-5
-10
-15 -10 -5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130
LIN-PMS Type=SEL 321Mho
 PTR=1200.0 CTR=160.0 Min I= 0.50A
 Zone 1: Z=2.48 sec Ohm @ 73.7 deg. T=0.0s
 Zone 2: Z=4.37 sec Ohm @ 73.7 deg. T=0.50s
 Zone 3: Z=5.83 sec Ohm @ 73.7 deg. T=1.00s
Line Z= 2.92@ 73.7 sec Ohm ( 21.87 Ohm)
Apparent impedances plotted:
 (Vb-Vc)/(Ib-Ic)= 8.67@47.6 sec Ohm (65.00 Ohm).
 (Vc-Va)/(Ic-Ia)= 8.67@47.6 sec Ohm (65.00 Ohm).
 (Va-Vb)/(Ia-Ib)= 8.67@47.6 sec Ohm (65.00 Ohm).
All relay units are restrained. Delay=9999s.
Fault Description:
3LG Bus fault on:
 Promissão 138. kV
IMPEDÂNCIA APARENTE VISTA POR LINS
Relé 21 instalado no terminal da SE 
Lins não detecta a falta devido ao 
efeito infeed
40
40
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
-5
-10
-15
-45 -40 -35 -30 -25 -20 -15 -10 -5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105
REGIÃO DE 
CARGA
ZL
X
R
Zcarga
kV
2
MVA
ZONAS DE PROTEÇÃO E A IMPEDÂNCIA DA CARGA
Uma alternativa é aumentar o 
alcance do relé 21 da SE Lins, mas 
isto pode causar a atuação para 
condição de carga
41
4141
Falta Fase-Terra 
na Linha com 
Geração 
Distribuída 
Paralela
� A corrente circula 
nos diagramas de 
seqüência 
positiva, negativa 
e zero
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Z1S Z1L Z1T
Z2S Z2L Z2T
Z0S Z0L
Z0T
φ – G
V1L
I1>0 I1>0
I2>0 I2>0
I0>0
I0=0
Carga
Z1
E1G
Z1G
I1>0
Carga
Z2
I2>0
Z2G
Carga
Z0
Z0G
V0S V0H V0L
S
S
S
S H
H
H
H
L
L
L
L
V2H
V1HV1S
V2S V2L
Ger
Symmetrical component analysis shows us that the distributed generator contributes fault 
current to all three types of line faults, through the delta-wye transformer, when the utility 
source breaker is closed and the two sources are operating in parallel. For each fault type, 
the generator contributes only positive-sequence, or positive- and negative-sequence current 
to the fault because the delta connected winding permits the flow of positive- and negative-
sequence current, and blocks the flow of zero-sequence current. The only path for zero 
sequence current to flow is through the grounded utility source.
42
4242
Falta Fase-Terra 
na Linha com 
Geração Distrib. e 
com o Disjuntor da 
Concessionária 
Aberto
� Todas as correntes 
são interrompidas 
quando o disjuntor 
da fonte da 
concessionária 
abre (?)
� A Geração 
Distribuída é ilhada
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Diagramas de Componentes Simétricas
E1S
Z1S Z1L Z1T
Z2S Z2L Z2T
Z0S Z0L
Z0T
φ – G
V1L
I1=0 I1=0
I2=0 I2=0
I0=0
I0=0
Ger
Carga
Z1
E1G
Z1G
I1>0
Carga
Z2
I2=0
Z2G
Carga
Z0
Z0G
V0S V0H V0L
S
S
S
S H
H
H
H
L
L
L
L
V2H
V1HV1S
V2S V2L
Symmetrical component analysis shows us that the distributed generator contributes fault 
current to all three types of line faults, through the delta-wye transformer, when the utility 
source breaker is closed and the two sources are operating in parallel. For each fault type, 
the generator contributes only positive-sequence, or positive- and negative-sequence current 
to the fault because the delta connected winding permits the flow of positive- and negative-
sequence current, and blocks the flow of zero-sequence current.
With the utility source breaker open, the generator only contributes current to three-phase 
and phase-to-phase line faults. With the utility source ground connection isolated by the 
open breaker, the delta connected winding opens the zero-sequence current path, blocking 
current flow for single phase-to-ground line faults. Or does it?
43
4343
Faltas à Terra Podem Persistir Após a 
Abertura do Disjuntor da Fonte da 
Concessionária
� A capacitância shunt do sistema 
fornece o caminho para a seqüência-
zero da corrente de falta à terra
� A magnitude da corrente é insuficiente 
para que a proteção baseada em 
corrente detecte a falta
44
4444
Geração Distribuída:
Criando a Fonte Delta Não Esperada
� Qual o impacto que isto tem no 
sistema da concessionária?
Linha
Transformador
CargaSubestação da
Fonte da
Concessionária
Ger
S H L
The interconnection of “distributed generation” to utility distribution circuits adds a new 
complication to the design and operation of utility systems. Both the utility and distributed 
generation owner must assure that the installation is designed and constructed to provide 
safe, reliable, and economical operation. The utility and the distributed generation owner 
must jointly ensure that: (1) the distributed generation operation does not harm or damage 
the utility; (2) the operation does not cause problems for other utility customers; and (3) the 
safety of personnel and the public is not jeopardized by the operation of customer-owned 
distributed generation. These concerns must be addressed in the design and operation of the 
distributed generation/utility interface.
45
4545
A Isolação da Falta é Essencial
� Mantém a segurança
� Protege os equipamentos
� Minimiza as interrupções do fornecimento 
dos serviços para o consumidor
� Restabelece a qualidade de energia 
requerida para os circuitos não faltosos
� Elimina faltas transitórias para permitir o 
restabelecimento automático
Isolation is an important concept that is used extensively on electric power systems to 
ensure safe and reliable operation: safe from the standpoint that protective devices 
automatically de-energize and isolate faulty equipment or downed conductors to protect the 
public and also to protect utility operating and maintenance personnel who get called upon 
to make repairs, reliable from the standpoint that customers expect, and regulatory bodies 
dictate, that electric power be delivered within prescribed voltage limits to prevent damage 
and maintain proper operation of customer utilization equipment. Power system faults in 
grounded systems cause significant voltage sags and swells that violate these prescribed 
limits. Isolating and de-energizing the faulty power system element restores proper power
delivery to most customers and interrupts power delivery to customers on the faulty circuit.In this case, a few customers with no power is preferable to having many customers with 
inadequate power quality.
Because many power system faults are temporary, utilities often supplement the protective 
relaying on lines with automatic reclosing. Successful automatic restoration limits the 
duration of a power interruption to as little as a few cycles for those few affected customers 
who are served from the faulted line. If one or more successive automatic reclosing
operations are unsuccessful, the circuit is left de-energized and out of service until crews 
can inspect the circuit, find the problem, and make appropriate repairs.
46
4646
Detecção do Ilhamento
� Detecta condições anormais após a 
abertura do disjuntor da fonte da 
concessionária
� Sobrefreqüência/subfreqüência
� Sobretensão/subtensão
� Direcional de potência
� Salto Vetor (?????)
47
4747
Proteção Básica do Ilhamento
To Utility
Source
32
Gen
Loads
62
27
59
81O
81U
62
62
62
62
1 or 3
Directional Power
Undervoltage
Overvoltage
Overfrequency
Underfrequency
*
* Optional
*
2 or 3
Para a Fonte da
Subtensão
Cargas
Concessionária
Sobretensão
Sobrefreqüência
Subfreqüência
Direcional de Potência
* Aplicação depende do fluxo 
de potência
2 ou 3
Ger
Islanding protection relies on a sufficient mismatch between distributed generation capacity 
and connected load on the isolated “island” to cause the frequency to quickly drop if the 
load is greater than the generation or to quickly rise if the generation exceeds the connected 
load. Voltage magnitude, on the other hand, may not change significantly due to 
generation/load mismatch.
Three-phase and phase-to-phase line faults may cause significant voltage depression on 
more than one phase, making them relatively easy to detect using undervoltage protection. 
Single phase-to-ground faults, however, may present a problem. As we discussed earlier, 
distributed generation does not contribute to phase-to-ground line faults with the utility 
source breaker open. An undervoltage condition exists for the time it takes the utility 
source relaying to trip the line breaker, but then the voltage may return to near normal on 
the secondary side of the delta-wye transformer.
Typical islanding protection is shown in this slide. These relay elements are typically set 
just above and below the nominal frequency and voltage operating ranges to detect 
abnormal operating conditions. Short time delays of one second or less are typically used to 
help ride through brief frequency and voltage transients caused by power system faults 
beyond the utility substation source line or on load circuits within the customer’s facility.
48
4848
Detecção do Ilhamento Por Função 
Direcional de Potência
� No caso de não haver exportação de 
energia em condições normais de 
operação, pode-se utilizar uma função 32 
que detecte a inversão do fluxo de potência 
quando do ilhamento
� Necessário que haja outras cargas 
conectadas na mesma linha
� Proteção dependente da quantidade de 
cargas conectadas na linha no momento do 
ilhamento
49
4949
O Relé de Potência Detecta o 
Ilhamento Através da Carga da Linha
Para a Fonte da
Concessionária
32
+–
Cargas da Linha
da Concessionária
Ajustes do
Relé de Potência Reversa
Limiar da Partida da Potência Fornecida
Abaixo das Cargas da Linha da Concessionária
+ Q
– Q
Região de
Não Atuação
Região
de Trip
+ P– P
Ger
Carga
Limite de Partida da Potência Reversa
Abaixo das Cargas da Linha da Concessionária
Caso em que não há
exportação de energia
Reverse power relays may be added to supplement the over-/undervoltage and frequency 
relays where the interconnection normally has a net power import level. Reverse power 
relays may also be added when the interconnection does not normally export power and the 
utility line has sufficient attached load to pick up the reverse power relay during islanded 
conditions. This slide shows the application of an optional directional power relay to detect 
islanding using a reverse power pickup threshold that is less than the minimum utility line 
load.
50
5050
Detecção do Ilhamento Por Função de 
Subpotência
� No caso de sempre haver importação 
de energia em condições normais de 
operação, pode-se utilizar uma função 
37 que detecte a subpontência no 
ponto de interconexão
� Geração nunca é suficiente para suprir 
as próprias cargas
51
5151
O Dropout do Relé de Potência Fornecida Detecta 
o Ilhamento por Perda da Potência Recebida
Ajustes da Perda de Potência Recebida
Limiar para Desatuação da Potência Recebida
Abaixo do Nível de Mínima Potência a Importar
+ Q
– Q
Região de
Não Atuação
Região
de Trip
+ P– P
Para a Fonte da
Concessionária
32
Ger
Carga
+–
Limite do Dropout da Potência Fornecida
Abaixo do Nível Mínimo de Potência Recebida
This slide shows the application of an optional directional power relay to detect islanding 
when the import power falls below the minimum import level.
52
5252
Proteção da Interconexão com Detecção de 
Faltas à Terra no Lado Delta
Para a Fonte da
Concessionária
51
Ger
Cargas
67
47
27/59
Direcional de Potência
Sobrecorrente Direcional ou Distância (21)
Desbalanço de Corrente
de Fase
Sobrecorrente
Não-Direcional
*
* Opcional
46
32
1 ou 3
*
Proteção do
Ilhamento
Proteção dos
Equipamentos
Proteção Contra
Faltas
81O/
81U
27/59
Desbalanço de
Tensão de Fase
Sub / Sobretensão
de Fase
Sobre /
Subfreqüência
ou 59N ou
27A, B, C e
59A, B, C
25
31 ou 3 2 ou 3
25
To detect sustained ground faults on the high side of the delta-wye transformer, single-
phase or three-phase VTs are needed on the high side of the transformer.
53
5353
Detecção de Faltas à Terra com um Único TP
0
27/59
F2
F3
F1
No Fault
F1
F2
F3
27
—
—
—
X
59
—
X
X
—
27 59
VNOM
(F1)
1.73 • VNOM
Voltage
Islanded
(F2, F3)
Paralleled
(F2, F3)
Sem Falta
Tensão
Ilhado
Paralelado
A common application using a single-phase transformer, connected phase-to-ground, is 
shown in this slide. This application uses a single-phase under-/overvoltage relay element 
(device 27/59) to detect a ground fault. As discussed earlier, the faulted phase voltage is 
zero, and the unfaulted phase voltages are 1.73 times nominal, when supplied from a delta 
source. The undervoltage element can be set at some fraction of nominal voltage, 50%, for 
example. The overvoltage element can be set above nominal voltage, 130%, for example. 
The undervoltage element picks up if the fault is on the same phase as the VT connection, 
and the overvoltage element picks up if the fault is on one of the other two phases. A timer 
is generally required to provide a coordinating time delay on the output of the undervoltage
element because the undervoltage condition could be the result of a fault external to the 
utility source line. Sufficient time delay must be used to permit external faults to clear 
before tripping. The need for an extended coordinating time delay on the overvoltage
element is unnecessary because sustained high voltage above the overvoltage relay pickup 
level can only occur after the utility source breaker opens. A short time delay, around a few 
cycles, should be sufficient to ride through any high voltage transients caused by lightning 
and switching surges. Fast tripping can be accomplished for faults on the two phases that 
the VT is not connected to.
The single-phase voltage transformer is exposed to 1.73 times the nominal phase-to-ground 
voltage, so it should be rated for line-to-linevoltage, even though it is connected phase-to-
ground. If the magnetizing impedance of the transformer is approximately the same as the 
shunt capacitive reactance of the corresponding phase, ferroresonance is possible. 
Recommended practice calls for a loading resistor connected in parallel with the under-
/overvoltage relay to damp resonant oscillations [Reference: “Protection Relaying Principles 
and Applications,” by J. Lewis Blackburn]. Note that this scheme has a significant ground 
fault sensitivity limitation. In addition, blown potential fuse conditions are difficult to 
differentiate from solid ground faults. Overcoming these limitations requires additional
VTs.
54
5454
Detecção de Faltas à Terra com TP 
Trifásico Delta Aberto (“Broken-Delta”)
59N
F2
F3
F1
3V0
This slide shows three-phase VTs connected in a wye/broken delta connection. 
55
5555
Detecção de Faltas à Terra com
TP Trifásico Delta Aberto (“Broken-Delta”)
No Fault
F1
F2
F3
59N
—
X
X
X
3V0
3pu
Islanded
3V0
1pu
Paralleled
0
59N
(No Fault)
Islanded
(F1, F2, F3)
3V0
Paralleled
(F1, F2, F3)
1
3
Sem Falta
Ilhado
Paralelado
(Sem Falta)
Ilhado
Paralelado
With the broken-delta connection, 3V0 zero-sequence voltage develops across the terminals of the broken 
delta windings. A single overvoltage element, 59N, connected across the broken delta terminals provides 
excellent ground fault detection. Under normal unfaulted conditions, there is no voltage across the open 
corner of the broken delta winding:
3V0 = VA + VB + VC 
= 1 ∠ 0° + 1 ∠–120° + 1 ∠ 120°
= 0
During paralleled operation, a solid ground fault produces 1 per unit of 3V0 zero-sequence voltage across the 
broken delta connection:
3V0 = VA + VB + VC
= 0 + 1 ∠–120° + 1 ∠ 120° (assuming a phase A fault)
= 1 ∠ 180°
During islanded operation, a single phase-to-ground line fault produces 3 per unit 3V0 zero-sequence voltage 
across the broken delta connection:
3V0 = VA + VB + VC
= 0 + 1.73 ∠–150° + 1.73 ∠ 150°
= 3 ∠ 180°
Setting the 59N pickup threshold above 1 per unit and below 3 per unit provides secure detection for a 
sustained ground fault during an islanded condition. There is no need for an extended coordinating time delay, 
so fast tripping can be accomplished for a ground fault on any phase.
Each of the three single-phase voltage transformers may be exposed to 1.73 times nominal phase-to-ground 
voltage during an islanded condition, so they should be rated for line-to-line voltage, even though they are 
connected phase-to-ground. If the magnetizing impedance of each transformer is approximately the same as 
the shunt capacitive reactance of the corresponding phase, ferroresonance is possible. Recommended practice 
calls for a loading resistor connected in parallel with the 59N relay to dampen resonant oscillations 
[Reference: “Protection Relaying Principles and Applications,” by J. Lewis Blackburn].
The broken-delta VT connection has some disadvantages that warrant review, but are not directly relevant to 
this discussion. Appendix A in the associated paper includes a more detailed discussion about the broken-delta 
VT connection.
56
5656
Detecção de Faltas à Terra com
TP Trifásico Estrela-Estrela
59
F2
F3
F1
B
C
A
59 59
B CA
This slide shows three-phase VTs connected in a wye-wye connection. Individual phase
overvoltage relay elements (59A, 59B, and 59C) are connected to their respective secondary 
phases. And, like the previous connection, each of the three single-phase voltage 
transformers may be exposed to 1.73 times the nominal phase-to-ground voltage during an 
islanded condition, so they should be rated for line-to-line voltage, even though they are 
connected phase-to-ground. If the magnetizing impedance of each transformer is 
approximately the same as the shunt capacitive reactance of the corresponding phase,
ferroresonance is possible. Recommended practice calls for a loading resistor connected to 
each secondary phase to dampen resonant oscillations [Reference: “Protection Relaying 
Principles and Applications,” by J. Lewis Blackburn].
57
5757
Detecção de Faltas à Terra com
TP Trifásico Estrela-Estrela
No Fault
F1
F2
F3
27
—
A
B
C
59
—
B, C
A, C
A, B
0
59
VNOM
1.73 • VNOM
Voltage
Islanded unfaulted phases
(F1, F2, F3)
Paralleled unfaulted
phases (F1, F2, F3)
27 Faulted
 phase (F1, F2, F3)
Sem Falta
Tensão
Fases “boas” Ilhadas
Fases “boas”
Paraleladas (F1, F2, F3)
(F1, F2, F3)
Fase
Defeituosa (F1, F2, F3)
For solid ground faults, this connection offers faulted phase identification by knowing 
which phases experience high voltage during an islanded condition. This protection can be 
supplemented with individual phase undervoltage elements (27A, 27B, and 27C). Like the 
previous two connections, there is no need for an extended coordinating time delay, so fast 
tripping can be accomplished for a ground fault on any phase.
58
58
Função Salto de Vetor
Essa função tem por finalidade detectar as situações em que ocorre o ilhamento do sistema 
devido à perda da concessionária. 
esse princípio consta basicamente de, ocorrido o distúrbio, memorizar um ciclo de tensão
de pré-evento e, posteriormente, medir a diferença de tempo entre as passagens pelo zero
das tensões de pré e pós evento, utilizando uma referência interna que é sempre ligada à
freqüência fundamental.
O ângulo do Salto de Vetor é dado por:
Esta proteção necessita de um critério bastante complexo e preciso em seus ajustes para 
evitar operações indevidas. Possui total dependência do fluxo de potência ativa 
intercambiada entre os dois sistemas para que essas medições sejam efetivas ( fluxo mínimo 
entre 10 a
15 % da potência nominal da planta ). Em condições de baixo intercâmbio de energia a 
proteção não é efetiva.
Transitórios podem causar a atuaçao incorreta da proteção.
59
59
Trafo estrela aterrado 
lado da 
concessionária, pode-
se utilizar relés de 
sobrecorrente de 
neutro para detecção 
de faltas monofásicas
60
6060
Trafo Estrela Aterrado Lado 
Concessionária
� Existe contribuição de seq zero para faltas na 
linha mesmo com o gerador fora de operação, 
causa atuação 51G
� Pode aumentar de maneira significativa o nível de 
curto-circuito na concessionária, mesmo para 
pequenos geradores, pois a contribuição de seq 
zero depende da impedância do trafo.
� Pode causar sérios problemas de coordenação no 
sistema de proteção da concessionária.
61
6161
Abertura e Monitoração
Usando as Comunicações
79 Gen
TxTrip Rx
Tx
52a
Status
Rx (Optional)
Tx
Gen
Status
Rx
S
SCADA
Trip
Estado
52a
Ger
Estado
Ger
(Opcional)
Communication between the utility source substation and the distributed generation site 
provides backup for islanding protection and assurance that the distributed generation is 
indeed disconnected from the utility system before the utility source breaker is reclosed, as 
shown in the above slide (Figure 26 in the paper). The communications link is set up to 
directly transfer trip either the customer main interconnect breaker or the generator 
breaker(s) when the utility source breaker trips. In the other direction, the status of the 
customer main interconnect breaker and/or generator breaker status is sent to the utility 
source substation to confirm that the distributed generation source is isolated before
reclosing the substation line breaker. This information can also be linked to the utility 
SCADA system to provide status information to utility operators. Traditional 
communications links required to accomplish this communication can be expensive, but 
new, more affordablecommunications options are available.
For short distances, a fiber-optic communications channel offers excellent speed and 
immunity from ground potential rise and electromagnetic interference. Direct 
communication between the relays at each site can be established through fiber-optic 
transceivers that plug directly into the communications port on selected relays or into 
remote I/O devices that can be wired to devices with conventional contact inputs and 
outputs.
Unlicensed spread spectrum radio offers another option if the two sites are within about 10 
miles of each other, and a line-of-sight path exists between them. Spread spectrum radio, 
while not quite as fast as a fiber channel, has very good speed and excellent immunity to 
ground potential rise and electromagnetic interference generated by power system faults and 
switching transients. Radios are available that interface directly with selected relays and 
remote I/O devices.
62
6262
Abertura e Monitoração
Usando as Comunicações
A B
C
DJ1 DJ2
DJ5 DJ6
DJ4DJ3
A teleproteção se torna mais complicado dependendo do layout da interconexão,
Neste exemplo são requeridos quatro canais de comunicação, não considerando 
redundância, o que pode representar um custo muito elevado de implementação.
O DJ5 deve ser aberto sempre que ocorrer a abertura dos disjuntores DJ1 e DJ2 e o 
religamento destes últimos só pode ocorrer quando o DJ5 estiver aberto. Funçoes de 
detecção de linha morta podem ser utilizadas, adicionalmente, para garantia do não 
religamento dos disjuntores DJ1 e DJ2 quando o DJ5 estiver fechado e o gerador em 
operação.
63
6363
Oscilação de Potência
� Faltas no Sistema
� Chaveamento de Linhas
� Alterações Súbitas das Cargas
Out-of-step condition or loss of synchronism is caused by system faults, line switching, 
and sudden changes in load while the mechanical inputs remain relatively constant.
Generators in a power system are continually adjusting to changing system conditions. 
When these changes are too severe, loss of synchronism can occur. 
Once an out-of-step condition occurs, the two parts need to be separated and 
resynchronized.
During an out-of-step condition, the system will experience fluctuating currents and 
voltages that can cause substantial damage to the generator shaft.
64
6464
Conceitos de Energia Elétrica
VS
P
VR
X
VS
VR
δ
Em um Sistema 
Sem Perdas:
δsen
X
VV
PPP
RS
RS
===
X
VV
P RSMAX =
In a lossless system, active power transfer depends on the voltage manitudes, the series 
reactance, and the angle between the voltages or power angle, δ. The direction of active power 
depends on the sign of δ: power flows from the line end having the leading voltage to the line 
end having the lagging voltage.
To increase the power transfer capability of the power system you can raise the system voltage 
level, reduce the series reactance, or apply a combination of both. The reactance can be 
reduced by adding interconnecting lines or connecting series capacitors in transmission lines.
65
6565
Efeito do Tipo de Falta
δ
P
Falta Trifásica
Falta Fase-Fase-Terra
Falta Fase-Fase
Falta Fase-Terra
Sistema Normal
This figure depicts the power-angle curves for different fault types in a power system with two 
parallel lines. The most critical fault for system stability is the three-phase fault. In general, 
fault types involving more phase conductors are more critical for stability.
66
6666
Tensão Durante uma Oscilação
VS
VR
VC
Centro
Elétrico
0
90
180
270
VS
VC
VR
δ
A distance relay is affected the most by a power swing. One way to visualize why that is, is to 
consider what happens to the voltage at the theoretical electrical center of the system. In our 
simple two bus case, with no losses and no VAR flow, the voltage at the electrical center of the 
system is going to be as shown. 
67
6767
Tensão Durante uma Oscilação
VS
VR
VC
Centro
Elétrico
90
180
VS
V0
90
180
270
VS
C
δ
VRVR
As the two systems pull apart during a disturbance (the power angle “δ” gets larger), the 
voltage at the electrical center of the system becomes depressed. 
68
6868
Tensão Durante uma Oscilação
VS
VR
VC
Centro
Elétrico
0
90
180
270
VS
VC
VR
0
90
180
VS
VR
δ
The greater the swing of the power angle “δ”, the greater the voltage depression at the 
electrical center of the system. At the point that the two systems are 180 degrees apart, the 
voltage at the electrical center will be zero in magnitude. 
Coincidentally, during the part of the swing where the power angle “δ” is greatest, the current 
magnitude will be at maximum. 
Intuitively, we would expect an impedance relay to see the depressed voltage and increased 
current as a short circuit and operate. 
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6969
Oscilações para a Condição de
Perda de Sincronismo
Tensão de Seqüência Positiva
Corrente de Seqüência Positiva
Ciclos
A
m
p
e
re
s
 S
e
c
.
V
o
lt
s
 S
e
c
.
This slide shows voltage and current waveforms of an out-of-step system condition which 
evolves to a 3PH fault at cycle 30.
Notice the oscillations in the system voltage and the current during this out-of-step condition 
and that the voltage is at minimum when the current is at maximum. 
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7070
Impedância e Perda de Sincronismo
VS ZS ZL ZR VR
2
X
2
ZR
ZL
ZS
1
P
R
&
Q
VS / VR = 1
VS / VR > 1
VS / VR < 1
1
The best way to visualize and detect out-of-step phenomena is to analyze apparent impedance variations 
with time as viewed at the terminals of the generator or high voltage terminals of the step-up-transformer. 
A simple visualization of these variations in apparent impedance during and out-of-step condition is 
illustrated in this slide. 
Three impedance loci are plotted as a function of the ratio of the system voltages VS/VR which is 
assumed to remain constant during the swing. When the voltage ratio of VS/VR = 1, the impedance 
locus is a straight line PQ, which is a perpendicular bisector of the total system impedance between 1 and 
2. The angle formed by the intersection of lines 1P and 2P on line PQ is the angle of separation between 
systems. As VS advances in angle ahead of VR, the impedance locus moves from point P toward Q and 
the angle increases. 
When the locus intersects the total impedance line 12, the systems are 180 Degrees out of phase. This 
point is the electrical center of the system and represents a full three phase apparent fault at the 
impedance location. As the locus moves to the left of the system impedance line, the angular separation 
increases beyond 180 degrees and eventually the systems will be in phase once again. 
If the systems remain together, System 1 can continue to move ahead of System 2 and the whole cycle 
may repeat itself. When the locus reaches the point where the swing started, one slip cycle has been 
completed. If System 1 slows down with respect to System 2, the impedance locus will move in the 
opposite direction from Q to P. When the voltage ratio VS/VR is more than one, the electrical center will 
be above the impedance center of the system. When VS/VR is less than one, the electrical center will be 
below the impedance center of the system. 
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7171
A Perda de Sincronismo
Causa Danos ao Gerador
� A Condição de Oscilação de Potência 
Pode Resultar em Um ou em Todos os 
Itens a Seguir:
� Stresses excessivos nos enrolamentos
� Danos ao eixo devido aos torques no 
mesmo
� Magnitudes de corrente elevadas
� Temperaturas elevadas no núcleo do 
estator
An out-of-step condition causes high currents andforces on the generator windings and high 
levels of transient shaft torques. If the slip frequency of the unit with respect to the power 
system approaches a natural torsional frequency, the torques can be high enough to break 
the shaft. It is, therefore, desirable to immediately trip the unit since shaft torque levels 
build up with each subsequent slip cycle. 
This buildup is the result of the continually increasing slip frequency passing through the 
first natural torsional frequency of the shaft system. Pole slipping events can also result in 
abnormally high stator core end iron fluxes that can lead to overheating and shorting at the 
ends of the stator core. The unit’s step-up transformer will also be subjected to very high 
transient winding currents that impose high mechanical stresses on its windings.
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7272
Blinder Simples
Proteção de Perda de Sincronismo
R
X
Oscilação Estável
78R78L
Oscilação
Instável
Oscilação Estável
78Z
B AC
Single Blinder Scheme
The single blinder scheme consists of mho element 78Z, right blinder 78R, and left blinder 
78L. This scheme detects an out-of-step condition by tracking the path of positive-sequence 
impedance trajectories that pass through the protection zone. 
This scheme declares a swing unstable if it enters Area A, moves into Area B, and exits the 
mho via Area C. The blinders and the mho unit working together allow the circuit breaker to 
open at a more favorable angle for arc interruption. Swings traveling from right to left 
follow this sequence. Out-of-step trajectories traveling from left to right traverse the 
protection zone in the reverse sequence, shown in the diagram from Area C to B to A. The 
single blinder scheme distinguishes between short circuit faults and out-of-step conditions 
by tracking the path of the impedance trajectory. During short circuit faults, the impedance 
will move from the load region to inside the mho element and between the two blinders, 
almost instantaneously preventing the out-of-step function from picking up.
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7373
Blinder Duplo
Proteção de Perda de Sincronismo
R
X
Oscilação Estável
78R178R2
Oscilação
Instável
Oscilação Estável
78Z1
Double Blinder Scheme
The double blinder scheme consists of mho element 78Z1, outer resistance blinder 78R1, 
and inner resistance blinder 78R2. This scheme uses a timer 78D as part of its logic to detect 
out-of-step conditions. The scheme declares an out-of-step condition if the positive-
sequence impedance stays between the two blinders for more than 78D seconds and 
advances further inside the inner blinder. The logic issues an out-of-step trip once an out-
of-step condition is established and the positive sequence impedance exits the mho circle. 
The double blinder scheme distinguishes between short circuit faults and out-of-step 
conditions by monitoring the length of time that the impedance trajectory stays between the 
two blinders. During short circuit faults, the impedance either moves inside the inner 
blinder or goes through the two blinders almost instantaneously so that the timer does not 
time out. Either case prevents the out-of-step element from picking up.