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FachgebietHochspannungstechnik
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)
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FachgebietHochspannungstechnik
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 ofeach overvoltage class, for which the expected low failure rate of the equipment is notexceeded over its full lifetime.
Derived from the representative overvoltages Urp by the coordination factor Kc.
[IEC 60071-1]
Typical forGermany:0.1% per year 1 failure in1000 years
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
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"
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FachgebietHochspannungstechnik
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!)
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FachgebietHochspannungstechnik
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 zoneedges (increased current density)
dry band
flashover of the dry band
enlargement of the dry band by arc heating
(max. temperature at foot points)
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FachgebietHochspannungstechnik
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 bridgedby partial arcs
voltage bridged
voltage drop increased
for further details see HVT 2!
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FachgebietHochspannungstechnik
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= ds ... specific layer conductivity
ds... thickness of layer
K= 5 S "light to medium pollution"K= 10 S "medium to heavy pollution"K= 40 S "very heavy pollution"
Influence of layer conductivityInfluence of layer conductivity for details see IEC 60507
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 10 -
Determination of layer conductivity frommeasured conductance and insulator geometry
Determination of layer conductivity frommeasured conductance and insulator geometry
Performance of Insulators under Pollution
2 dd
d d / 2
r s KG
l l r
= =
Measurement of conductance Gof the full insulator
shed core
creepage
distance lk
insulator length lV
Gl
=general:
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 11 -
Performance of Insulators under Pollution
k
0
d
2
l
KG
l
r
=
k
0
d
2
l
lF
r=
G... conductance of total insulator surface
form factor"form factor"
K= FGK= FG
(IEC 60507*))
form factor to be determined by
graphical procedure, describedin IEC 60507
Determination of layer conductivity frommeasured conductance and insulator geometry
Determination of layer conductivity frommeasured conductance and insulator geometry
*) IEC 60507, 2nd Ed. 1991-04: "Artificial pollution tests onhigh-voltage insulators to be used on a.c. systems"
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FachgebietHochspannungstechnik
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
fo, rain
0.7 ... 0.9 fo, dry
Ufo, polluted 0.2 ... 0.3 Ufo,dry
An overhead line insulator must be desigend about five times as long asrequired 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
L-E = 100 kV
d = 5 kV/cm l = 20 cm would be sufficient (dry!)
Actual length: ca. 1100 mm
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 13 -
pCountermeasuresCountermeasures
Performance of Insulators under Pollution
ShedsSheds
s ... flashover or arcing distance
lk ... creepage distance
li ... insulator length
p ... shed overhang
t ... shed spacing
Terms ...
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 15 -
Actual Situation for IEC 60815 (as per February 2009)
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 16 -
Actual Situation for IEC 60815
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 17 -
Actual Situation for IEC 60815
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
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 worsewith increasing diameter!
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 20 -
Performance of Insulators under Pollution
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FachgebietHochspannungstechnik
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 areasAll 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 sea2)
II - Medium
- Areas with industries not producing particularly polluting smoke and/or with averagedensity of houses equipped with heating plants- Areas with high density of houses and/or industries but subjected to frequent windsand/or rainfall
- Areas exposed to wind from the sea but not too close to the coast (at least severalkilometres distant) 2)
III - Heavy- Areas with high density of industries and suburbs of large cities with high density ofheating 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 smokeproducing particularly thick conductive deposits- Areas generally of moderate extent, very close to the coast and exposed to sea-sprayor to very strong and polluting winds from the sea- Desert areas, characterized by no rain for long periods, exposed to strong windscarrying 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 dispersalby 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
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 23 -
Performance of Insulators under Pollution
Recommendations of IEC 60815 - ExampleShed profilesShed profiles
c 30 mm
p1p2 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/stlt = total creepage distancest = arcing distance (arcing horns not considered)
IEC 60815
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 25 -
Performance of Insulators under Pollution
Shed profilesShed profiles Example of user'sexperience
From:
Raouf Znaidi: "ServiceExperience and MaintenanceRequirements for Different Typesof Insulators in Tunisia", WorldCongress on Insulators, Arrestersand Bushings, Hong Kong, Nov.27-30, 2005
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
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
-varistors
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 31 -
From an EPRI Questionnaire in North America (publ. in 2003)
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 33 -
From an EPRI Questionnaire in North America (publ. in 2003)
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 34 -
From an EPRI Questionnaire in North America (publ. in 2003)
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FachgebietHochspannungstechnik
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 isHydrophobicityHydrophobicity
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FachgebietHochspannungstechnik
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!
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FachgebietHochspannungstechnik
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)
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FachgebietHochspannungstechnik
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 isbeing used
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FachgebietHochspannungstechnik
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
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FachgebietHochspannungstechnik
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:
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 45 -
Cyclic TestsCyclic Tests
Weather Aging Tests for Polymeric Insulators
Practical testproblem: rainand solarradiation at thesame time!
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h f l l
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FachgebietHochspannungstechnik
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 summercycle 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.
O h A i T f P l i I l
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FachgebietHochspannungstechnik
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 testspecimens are mounted on the wheel as shown in Figure A.1 below. They go through fourpositions 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 partof the cycle the insulator is dipped into a saline solution. The second part of the test cyclepermits the excess saline solution to drip off the specimen ensuring that the light wetting ofthe surface gives rise to sparking across dry bands that will form during the third part of thecycle. In that part the specimen is submitted to a power frequency voltage. In the last part ofthe cycle the surface of the specimen that had been heated by the dry band sparking isallowed to cool.
Electrical stress: The power frequency test voltage in kV is determined by dividing theactual creepage distance in millimetres by 28,6.
NaCl content of de-ionized water: 1,40 kg/m 0,06 kg/mAmbient temperature: 20 C 5 KTest 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!
Oth A i T t f P l i I l t
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FachgebietHochspannungstechnik
Overvoltage Protection and Insulation Coordination / Chapter 6 - 49 -
Wheel TestWheel Test
Other Aging Tests for Polymeric Insulators
P f f I l t d P ll ti
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FachgebietHochspannungstechnik
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 beapplied 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 insulatorsClass 4 : in general, application of NCI should be carefully checked for each
individual application
P f m nc f P l m ic Insul t s
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FachgebietHochspannungstechnik
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
Performance of Polymeric Insulators
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FachgebietHochspannungstechnik
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
Performance of Polymeric Insulators
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FachgebietHochspannungstechnik
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
Performance of Polymeric Insulators
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FachgebietHochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 54 -
Brittle fractureBrittle fracture
Performance of Polymeric Insulators
From:
M. Kuhl: "FRP Rods for Brittle Fracture Resistant CompositeInsulators",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
Performance of Insulators under Pollution
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FachgebietHochspannungstechnik 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
Performance of Insulators under Pollution
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FachgebietHochspannungstechnik 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
Performance of Insulators under Pollution
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FachgebietHochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 57 -
Solid layer methodSolid layer method
Performance of Insulators under Pollution
Test specimen is energized in a coldfog chamber and then exposed tohumidity
Test specimen is energized in a coldfog chamber and then exposed tohumidity
Layer conductivity between 3 S and 80 SLayer conductivity between 3 S and 80 S
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 tohumidity in a cold fog chamberand then energized
Test specimen is exposed tohumidity in a cold fog chamberand then energized
Test specimen must not flash over within a specified time of exposure
Test 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
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Performance of Insulators under Pollution
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FachgebietHochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 59 -
Radial Field Stress under PollutionRadial Field Stress under Pollution
Performance of Insulators under Pollution
MO column
Conductivelayer
Gas or solid
Solid
Uaxial,int
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
Porzellangehuse-Innenwand
MO discs
porcelain housing, inner wall
Photo: PD in aporcelain housedsurge arrester
Performance of Insulators under Pollution
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FachgebietHochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 60 -
Dielectric and Thermal EffectsDielectric and Thermal Effects
f m f
Internal partialdischarges
changes in internalatmosphere
risk of deterioration
of all internal parts
Internal partialdischarges
changes in internalatmosphere
risk of deterioration
of all internal parts
Risk of partialheating of internal
active elements
Risk of partialheating of internalactive elements
Risk of external flashoversRisk of external flashovers
Outer surface discharges
Risk of partial heating ofinternal active elements
Outer surface discharges
Risk of partial heating ofinternal active elements
Example: 800-kV surge arrester
Emerging Insulator Standards
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FachgebietHochspannungstechnik Overvoltage Protection and Insulation Coordination / Chapter 6 - 61 -
g g
From:
Claude de Tourreil: "New IECstandards: their Impact on futureSelection of CompositeInsulators", World Congress onInsulators, Arresters andBushings, Hong Kong, Nov. 27-30, 2005
Recommended