iso v 13

Prévia do material em texto

Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 1 -
Procedure for Insulation Coordination in Four Steps 
[IEC 60071-1]
Flow chart acc. to IEC 60071-1
(Figure 1)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 2 -
Procedure for Insulation Coordination in Four Steps 
Determination of the coordination withstand voltages Ucw
• The coordination withstand voltages are the lowest values of withstand voltages of 
each overvoltage class, for which the expected low failure rate of the equipment is not 
exceeded over its full lifetime.
• Derived from the representative overvoltages Urp by the coordination factor Kc.
[IEC 60071-1]
Typical for 
Germany:
0.1% per year
� 1 failure in 
1000 years
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 3 -
Insulation Strength Characteristics
Factors influencing the dielectric strength of the insulation:
• magnitude, shape, duration and polarity of the applied voltage
• electric field distribution in the insulation
• homogeneous or non-homogeneous electric field
• electrodes adjacent to the considered gap and their potential
• type of insulation
• gaseous
• liquid
• solid
• combination of two or all of them
• impurity content and the presence of local inhomogeneities
• physical state of the insulation
• temperature
• pressure
• other ambient conditions
• mechanical stress
• history of the insulation (aging, damage)
• chemical effects
• conductor surface effects
Factors influencing the dielectric strength of the insulation:
• magnitude, shape, duration and polarity of the applied voltage
• electric field distribution in the insulation
• homogeneous or non-homogeneous electric field
• electrodes adjacent to the considered gap and their potential
• type of insulation
• gaseous
• liquid
• solid
• combination of two or all of them
• impurity content and the presence of local inhomogeneities
• physical state of the insulation
• temperature
• pressure
• other ambient conditions
• mechanical stress
• history of the insulation (aging, damage)
• chemical effects
• conductor surface effects
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 4 -
Insulation Strength Characteristics
Standard atmospheric conditions acc. to IEC 60060-1
Temperature: 20 °C
Pressure: 1013 hPa
Absolute humidity: 11 g/m3
Temperature: 20 °C
Pressure: 1013 hPa
Absolute humidity: 11 g/m3
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 5 -
Insulation Strength Characteristics
Topics to be covered in the following:
• Insulators under polluted conditions
• Probability of flashover (Normal and Weibull distributions)
• Behavior of parallel insulation
• Coordination procedure: deterministic and statistical approach
• Correction with altitude of installation
• Clearances in air; "gap factors"
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 6 -
Pre-conditionsPre-conditions
Performance of Insulators under Pollution
• Surface layers
• dust
• carbon black
• salt (coastal areas)
• chemicals (industry, rural areas: fertilizers)
• dust
• carbon black
• salt (coastal areas)
• chemicals (industry, rural areas: fertilizers)
• no problem in dry condition
• after long rain periods: only moderate effect on flashover performance
• most critical:
Humidification after a long dry periodHumidification after a long dry period
“typical“ time of the day for insulator flashovers: morning hours (dew!)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 7 -
Development of pollution flashoverDevelopment of pollution flashover
Performance of Insulators under Pollution
dry zone by inhomogeneity of the layer
enlargement of the dry zone by heating of the zone
edges (increased current density)
dry band
flashover of the dry band
enlargement of the dry band by arc heating
(max. temperature at foot points)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 8 -
Development of pollution flashoverDevelopment of pollution flashover
Performance of Insulators under Pollution
Voltage distribution
a) with dry bands b) dry bands bridged
by partial arcs
voltage bridged
voltage drop increased
���� for further details see HVT 2!
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 9 -
Performance of Insulators under Pollution
Layer conductivity K is the most important parameter!Layer conductivity K is the most important parameter!
K = κ·ds κ ... specific layer conductivity
ds ... thickness of layer
K = 5 µS "light to medium pollution"
K = 10 µS "medium to heavy pollution"
K = 40 µS "very heavy pollution"
Influence of layer conductivityInfluence of layer conductivity ���� for details see IEC 60507
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 10 -
Determination of layer conductivity from
measured conductance and insulator geometry
Determination of layer conductivity from
measured conductance and insulator geometry
Performance of Insulators under Pollution
2 dd
d d / 2
r s KG
l l r
pi κ
pi
⋅ ⋅
= =
Measurement of conductance G
of the full insulator
shed core
creepage
distance lk
insulator length l VG
l
κ
=general:
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 11 -
Performance of Insulators under Pollution
k
0
d
2
l
KG
l
rpi
=
∫
k
0
d
2
l lF
rpi
= ∫
G ... conductance of total insulator surface
“form factor"“form factor"
K = F·GK = F·G
(IEC 60507*))
form factor to be determined by
graphical procedure, described
in IEC 60507
Determination of layer conductivity from
measured conductance and insulator geometry
Determination of layer conductivity from
measured conductance and insulator geometry
*) IEC 60507, 2nd Ed. 1991-04: "Artificial pollution tests on
high-voltage insulators to be used on a.c. systems"
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 12 -
Decrease in flashover voltage by conductive layersDecrease in flashover voltage by conductive layers
Performance of Insulators under Pollution
ûfo, rain ≈ 0.7 ... 0.9 · ûfo, dry
Ufo, polluted ≈ 0.2 ... 0.3 · Ufo,dry
An overhead line insulator must be desigend about five times as long as 
required to withstand operating stresses under dry conditions!
An overhead line insulator must be desigend about five times as long as 
required to withstand operating stresses under dry conditions!
Um = 123 kV
ûL-E = 100 kV 
ûd = 5 kV/cm � l = 20 cm would be sufficient (dry!)
Actual length: ca. 1100 mm
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 13 -
p
CountermeasuresCountermeasures
Performance of Insulators under Pollution
ShedsSheds
s ... flashover or arcing distance
lk ... creepage distance
li ... insulator length
p ... shed overhang
t ... shed spacing
Terms ...
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 14 -
p
Performance of Insulators under Pollution
li derived from required standard
lightning impulse voltage strength
(ud, LI ca. 5.5 kV/cm)
lk from requirement on specific
creepage distance (IEC 60815*))
31 mm/kV for „very heavy" pollution severity (IV)
25 mm/kV for „heavy" pollution severity (III)
20 mm/kV for "medium" pollution severity (II)16 mm/kV for "light" pollution severity (I)
31 mm/kV for „very heavy" pollution severity (IV)
25 mm/kV for „heavy" pollution severity (III)
20 mm/kV for "medium" pollution severity (II)
16 mm/kV for "light" pollution severity (I)
∆ = 20%
Reference value is Um, i.e.
the phase to-phase-voltage!
Reference value is Um, i.e.
the phase to-phase-voltage!
CountermeasuresCountermeasures
Note: IEC 60815 applicable to porcelain 
insulators; so far no standard on polymeric 
insulators available **)
*) IEC 60815, 1st Ed. 1986: "Guide for the selection of 
insulators in respect of polluted conditions" **) **) see next slide 
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 15 -
Actual Situation for IEC 60815 (as per February 2009) 
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 16 -
Actual Situation for IEC 60815
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 17 -
Actual Situation for IEC 60815
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 18 -
Actual Situation for IEC 60815
Example of a change in IEC 60815-1:2008 compared with 60815:1986
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 19 -
Performance of Insulators under Pollution
31 mm/kV for „very heavy" pollution severity (IV)
25 mm/kV for „heavy" pollution severity (III)
20 mm/kV for "medium" pollution severity (II)
16 mm/kV for "light" pollution severity (I)
31 mm/kV for „very heavy" pollution severity (IV)
25 mm/kV for „heavy" pollution severity (III)
20 mm/kV for "medium" pollution severity (II)
16 mm/kV for "light" pollution severity (I)
CountermeasuresCountermeasures
Correction of these values necessary depending on insulator's average diameter Dm *)
Correction factor kD (derived from service experience):
*) for definition of Dm see IEC 60815
Dm (mm) kD
< 300 1
300 - 500 1.1
> 500 1.2
Pollution performance gets worse
with increasing diameter!
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 20 -
Performance of Insulators under Pollution
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 21 -
Performance of Insulators under Pollution
Pollution level Examples of typical environments 
I - Light 
- Areas without industries and with low density of houses equipped with heating plants 
- Areas with low density of industries or houses but subjected to frequent winds and/or 
rainfall 
- Agricultural areas 1) 
- Mountainous areas 
All these areas shall be situated at least 10 km to 20 km from the sea and shall not be 
exposed to winds directly from the sea 2) 
II - Medium 
- Areas with industries not producing particularly polluting smoke and/or with average 
density of houses equipped with heating plants 
- Areas with high density of houses and/or industries but subjected to frequent winds 
and/or rainfall 
- Areas exposed to wind from the sea but not too close to the coast (at least several 
kilometres distant) 2) 
III - Heavy 
- Areas with high density of industries and suburbs of large cities with high density of 
heating plants producing pollution 
- Areas close to the sea or in any case exposed to relatively strong winds from the sea 2) 
IV - Very heavy 
- Areas generally of moderate extent, subjected to conductive dusts and to industrial smoke 
producing particularly thick conductive deposits 
- Areas generally of moderate extent, very close to the coast and exposed to sea-spray 
or to very strong and polluting winds from the sea 
- Desert areas, characterized by no rain for long periods, exposed to strong winds 
carrying sand and salt, and subjected to regular condensation 
 
1) Use of fertilizers by spraying, or the burning of crop residues, can lead to a higher pollution level due to dispersal 
by wind. 
2) Distances from sea coast depend on the topography of the coastal area and on the extreme wind conditions. 
 
IEC 60815:1986, Table 1IEC 60815:1986, Table 1
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 22 -
Shed profilesShed profiles
Performance of Insulators under Pollution
Some typical shed profiles (from IEC 60815; explanation of the parameters see there).
From left to right: normal shed profile, alternating shed profile, underrib sheds (fog profile),
cap-and-pin insulators
Some typical shed profiles (from IEC 60815; explanation of the parameters see there).
From left to right: normal shed profile, alternating shed profile, underrib sheds (fog profile),
cap-and-pin insulators
IEC 60815
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 23 -
Performance of Insulators under Pollution
Recommendations of IEC 60815 - ExampleShed profilesShed profiles
c ≥ 30 mm
p1 – p2 ≥ 15 mm
s/p1 ≥ 0.65 (in case of plain, non-underripped sheds)
lx/dx < 5
C.F. ≤ 3.5 (pollution classes I + II)
≤ 4 (pollution classes III + IV)
C.F.= creepage factor = lt/st
lt = total creepage distance
st = arcing distance (arcing horns not considered)
IEC 60815
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 24 -
Performance of Insulators under Pollution
Recommendations of IEC 60815 - ExampleShed profilesShed profiles
α ≥ 5 °specified
IEC 60815
No specification for bottom side angle;
however, ≥ 2 °"advisable" in case of sheds
without underribs
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 25 -
Performance of Insulators under Pollution
Shed profilesShed profiles Example of user's
experience
From:
Raouf Znaidi: "Service 
Experience and Maintenance 
Requirements for Different Types 
of Insulators in Tunisia", World 
Congress on Insulators, Arresters 
and Bushings, Hong Kong, Nov. 
27-30, 2005
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 26 -
Cleaning, greasing, coating of insulatorsCleaning, greasing, coating of insulators
Performance of Insulators under Pollution
Some particular sites require regular cleaning of the insulators.
Extreme situation:
„Maritime desert climate with industrial pollution“
(e.g.: petrochemical facilities in Saudi-Arabia)
Extreme situation:
„Maritime desert climate with industrial pollution“
(e.g.: petrochemical facilities in Saudi-Arabia)
But also in Middle Europe in the vicinity of industrial facilities (steel 
works, petrochemistry)
���� for further details see HVT 2!
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 27 -
Semi-conducting glazingSemi-conducting glazing
Performance of Insulators under Pollution
Idea: to avoid dry-band arcing by resistive bypass
No flashover due to bypass current
surface current
Drawback: stable semiconducting glazing difficult to produce
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 28 -
Semi-conducting glazingSemi-conducting glazing
Performance of Insulators under Pollution
Under development: for composite insulators by coating filled with micro-varistors
 
µ-varistors
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 29 -
Composite insulatorsComposite insulators
Performance of Insulators under Pollution
• introduced in the beginning of the 1970s
• today „virtually" state of the art
• „problems": long time performance not yet clear,
"brittle fracture", animal attacks
Shed material:• EPDM (Ethylene-Propylene-
Diene-Monomer)
� only in distribution
• Silicone rubber (SIR)
FRP core
extruded SIR sheath
push-over SIR sheds
crimped-on metal end fitting
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 30 -
From an EPRI Questionnaire in North America (publ. in 2003)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 31 -
From an EPRI Questionnaire in North America (publ. in 2003)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 32 -
From an EPRI Questionnaire in North America (publ. in 2003)
compare this with the
"bathtub curve"of failure
���� no evidence for aging
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 33 -
From an EPRI Questionnaire in North America (publ. in 2003)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 34 -
From an EPRI Questionnaire in North America (publ. in 2003)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 35 -
HydrophobicityHydrophobicity
Performance of Insulators under Pollution
One of the most important properties of composite insulators
with regard to pollution performance is HydrophobicityHydrophobicity
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 36 -
HydrophobicityHydrophobicity
Performance of Insulators under Pollution
Advancing angle
Receding angle
= most important for characterization
of hydrophobicity
Receding angle
= most important for characterization
of hydrophobicity
Properties change under the influence of electrical field � actual research!
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 37 -
HydrophobicityHydrophobicity
Performance of Insulators under Pollution
IEC/TS 62073
Wettability classes*)
*) Based on the "STRI Guide" (of STRI, Ludvika/Sweden)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 38 -
Silicone rubber as insulator materialSilicone rubber as insulator material
Performance of Insulators under Pollution
Hydrophobicity transfer to pollution layersHydrophobicity transfer to pollution layers
Hydrophobicity only with silicone rubberHydrophobicity only with silicone rubber
Dynamics of hydrophobicityDynamics of hydrophobicity
Excellent service record so far (only few exceptions where silicone rubber is not optimal, 
e.g. under extreme coastal conditions, i.e. heavy salt layers)
Excellent service record so far (only few exceptions where silicone rubber is not optimal, 
e.g. under extreme coastal conditions, i.e. heavy salt layers)
Excellent tracking resistanceExcellent tracking resistance
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 39 -
Natural Test SitesNatural Test Sites
Weather Aging Tests for Polymeric Insulators *)
 
Example: Koeburg, RSA
Realistic test conditions, but no acceleration 
factors
���� long test times necessary (several years)
"(In)famous" test sites:
• Koeburg, RSA (Atlantic Ocean)
• Dungeness, UK (The Channel)
• Martiguez, F (Mediterranean Sea)
*) NOTE: often the term NCI = 
non ceramic insulators is 
being used
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 40 -
Natural Test SitesNatural Test Sites
Weather Aging Tests for Polymeric Insulators
Example: Dungeness, UK (Excursion 2002)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 41 -
The "Tracking and Erosion Test" acc. to IEC 61109The "Tracking and Erosion Test" acc. to IEC 61109
Weather Aging Tests for Polymeric Insulators
Similar test procedures specified e.g. for surge arresters (IEC 60099-4) and for polymeric 
insulators (IEC 62217)
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 42 -
The "Tracking and Erosion Test" acc. to IEC 61109The "Tracking and Erosion Test" acc. to IEC 61109
Weather Aging Tests for Polymeric Insulators
Examples of test chambers
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 43 -
Weather Aging Tests for Polymeric Insulators
Tracking
Erosion
The "Tracking and Erosion Test" acc. to IEC 61109The "Tracking and Erosion Test" acc. to IEC 61109
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 44 -
Cyclic TestsCyclic Tests
Weather Aging Tests for Polymeric Insulators
Cyclic tests usually consist in applying, in addition to voltage stress, various stresses in a cyclic 
manner:
- solar radiation simulation; 
- artificial rain; 
- dry heat;
- damp heat (near saturation);
- high dampness at room temperature (saturation has to be obtained);
- salt fog at low concentration.
Furthermore, temperature variations may cause some degree of mechanical stress, especially 
at the level of insulator interfaces and also give rise to condensation phenomena, which are 
repeated several times in the course of a cycle.
For power frequency test voltage, a test transformer shall be used. The test circuit when loaded 
with a resistive current of 250 mA (r.m.s.) on the high voltage side shall experience a maximum 
voltage drop of 5 %. The protection level shall be set at 1 A (r.m.s.).
Problem: no general agreement on one particular test!Problem: no general agreement on one particular test! Examples next slides:
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 45 -
Cyclic TestsCyclic Tests
Weather Aging Tests for Polymeric Insulators
Practical test 
problem: rain 
and solar 
radiation at the 
same time!
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 46 -
Cyclic TestsCyclic Tests
Weather Aging Tests for Polymeric Insulators
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 47 -
Cyclic TestsCyclic Tests
Weather Aging Tests for Polymeric Insulators
"EPRI" cycle: a year in service is considered to be represented by 10 days of summer 
cycle and 11 days of winter cycle. A duration of 5040 h is required for the whole test, 
10 summer/winter cycles of 21 days each.
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 48 -
Wheel Test acc. to IEC 62217Wheel Test acc. to IEC 62217
Other Aging Tests for Polymeric Insulators
The test specimens shall be cleaned with de-ionized water before starting the test. The test
specimens are mounted on the wheel as shown in Figure A.1 below. They go through four
positions in one cycle. Each test specimen remains stationary for about 40 s in each of the
four positions. The 90° rotation from one position to the next takes about 8 s. In the first part
of the cycle the insulator is dipped into a saline solution. The second part of the test cycle
permits the excess saline solution to drip off the specimen ensuring that the light wetting of
the surface gives rise to sparking across dry bands that will form during the third part of the
cycle. In that part the specimen is submitted to a power frequency voltage. In the last part of
the cycle the surface of the specimen that had been heated by the dry band sparking is
allowed to cool.
Electrical stress: The power frequency test voltage in kV is determined by dividing the 
actual creepage distance in millimetres by 28,6.
NaCl content of de-ionized water: 1,40 kg/m³ ± 0,06 kg/m³Ambient temperature: 20 °C ± 5 K
Test duration: 30 000 cycles
The test is regarded as passed, if on both test specimens:
• no tracking occurs
• for composite insulators: erosion depth is less than 3 mm and does not reach the core; if applicable
• for resin insulators: erosion depth is less than 3 mm;
• no shed, housing or interface is punctured.
���� Extremely severe test!
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 49 -
Wheel TestWheel Test
Other Aging Tests for Polymeric Insulators
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 50 -
"Silicone Bonus""Silicone Bonus"
Performance of Insulators under Pollution
For NCIs with permanent (recovering) hydrophobic characteristics a "silicone bonus" may be 
applied as a reduction factor of creepage distance (C.D.) compared with ceramic insulators:
Class 1 : 70 % … 75 % of C.D. of ceramic insulators
Class 2 : 80 % of C.D. of ceramic insulators (not applicable in coastal areas!)
Class 3 : same C.D. as for ceramic insulators
Class 4 : in general, application of NCI should be carefully checked for each
individual application
Class 1 : 70 % … 75 % of C.D. of ceramic insulators
Class 2 : 80 % of C.D. of ceramic insulators (not applicable in coastal areas!)
Class 3 : same C.D. as for ceramic insulators
Class 4 : in general, application of NCI should be carefully checked for each
individual application
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 51 -
Silicone rubber as insulator materialSilicone rubber as insulator material
Performance of Polymeric Insulators
Other problems ....
Moss, algea
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 52 -
Silicone rubber as insulator materialSilicone rubber as insulator material
Other problems ....
Animal attack (parrots, cockattoos, termites)
Example: AustraliaExample: Australia
Performance of Polymeric Insulators
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 53 -
Silicone rubber as insulator materialSilicone rubber as insulator material
Other problems ....
Animal attack (parrots, cockattoos, termites)
Example: AustraliaExample: Australia
Performance of Polymeric Insulators
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 54 -
Brittle fractureBrittle fracture
Performance of Polymeric Insulators
From:
M. Kuhl: "FRP Rods for Brittle Fracture Resistant Composite 
Insulators", 
http://www.lappinsulator.com/downloadcenter/technical.asp
Countermeasures:
• ECR glass (electro-chemical resistant)
• quality of sealing at triple point
• field stress reduction by grading rings
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 55 -
Performance of Insulators under Pollution
2 different methods:
Salt fog methodSalt fog method
Solid layer methodSolid layer method
Artificial pollution testsArtificial pollution tests
IEC standard 60507IEC standard 60507
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 56 -
Salt fog methodSalt fog method
Performance of Insulators under Pollution
Test specimen energized at operating voltage under conductive salt fog exposureTest specimen energized at operating voltage under conductive salt fog exposure
Salt mass concentration between 2.5 kg/m3 und 224 kg/m3Salt mass concentration between 2.5 kg/m3 und 224 kg/m3
(1 kg/m3 corresponds to 1 g/l)
Classification by withstand salt mass concentrationClassification by withstand salt mass concentration
Test specimen must not flash over within a specified time of exposureTest specimen must not flash over within a specified time of exposure
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 57 -
Solid layer methodSolid layer method
Performance of Insulators under Pollution
Test specimen is energized in a cold 
fog chamber and then exposed to 
humidity
Test specimen is energized in a cold 
fog chamber and then exposed to 
humidity
Layer conductivity between 3 µS and 80 µSLayer conductivity between 3 µS and 80 µS
Classification by withstand layer conductivity or withstand salt deposit densityClassification by withstand layer conductivity or withstand salt deposit density
Solid layer of specified conductivity is applied in wet condition and driedSolid layer of specified conductivity is applied in wet condition and dried
Test specimen is exposed to 
humidity in a cold fog chamber 
and then energized
Test specimen is exposed to 
humidity in a cold fog chamber 
and then energized
Test specimen must not flash over within a specified time of exposureTest specimen must not flash over within a specified time of exposure
Salt Deposit Density (SDD) between 0.03 mg/cm2 and 0.60 mg/cm2Salt Deposit Density (SDD) between 0.03 mg/cm2 and 0.60 mg/cm2
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 58 -
Performance of Insulators under Pollution
Artificial pollution testsArtificial pollution tests
Correlation between pollution level, recommended creepage distance and artificial pollution test 
parameters:
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 59 -
Radial Field Stress under PollutionRadial Field Stress under Pollution
Performance of Insulators under Pollution
MO column
Conductive
layer
Gas or solid
Solid
U
a
x
i
a
l
,
 
i
n
t
Uradial
Arises if there is an internal active part with a
given, constant axial voltage distribution; risk of
• internal PD in case of internal gas volume
• puncture in case of pure solid insulation
MO-Scheiben
Porzellangehäuse-Innenwand
MO discs
porcelain housing, inner wall
Photo: PD in a 
porcelain housed 
surge arrester
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 60 -
Dielectric and Thermal EffectsDielectric and Thermal Effects
Performance of Insulators under Pollution
Internal partial
discharges
⇒ changes in internal
atmosphere
⇒ risk of deterioration
of all internal parts
Internal partial
discharges
⇒ changes in internal
atmosphere
⇒ risk of deterioration
of all internal parts
Risk of partial
heating of internal
active elements
Risk of partial
heating of internal
active elements
Risk of external flashoversRisk of external flashovers
Outer surface discharges
⇒ Risk of partial heating of
internal active elements
Outer surface discharges
⇒ Risk of partial heating of
internal active elements
Example: 800-kV surge arrester
Fachgebiet
Hochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 61 -
Emerging Insulator Standards
From:
Claude de Tourreil: "New IEC 
standards: their Impact on future 
Selection of Composite 
Insulators", World Congress on 
Insulators, Arresters and 
Bushings, Hong Kong, Nov. 27-
30, 2005