l8 surge arresters

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Surge Arresters

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Surge ArrestersSurge Arresters

Gaps and gaplessGaps and gapless Silicon Carbide and Metal OxideSilicon Carbide and Metal Oxide ClassClass Tests and RatingsTests and Ratings InstallationInstallation Field testing and FailuresField testing and Failures

IEEE C62.11-1999

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I=kVa

No Gap:

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Series Gap:

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Shunt Gap:

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I=kVa

Silicon Carbide Arresters:

Silicon carbide blocks

Duty Cycle Rating

Protective level

ma Ln Current ka

Arr

este

r vol

tage

Metal Oxide BlocksG

radi

ng c

ircui

trySeries Gaps

Operating voltage

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Silicon Carbide ArresterSilicon Carbide Arrester

Valve Block

Gap Elements

Gap Elements

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Silicon Carbide ArrestersSilicon Carbide Arresters Blocks cannot conduct continuouslyBlocks cannot conduct continuously Series gapsSeries gaps Fast transients cause the series gaps to short over and insert the Fast transients cause the series gaps to short over and insert the

silicon carbide blocks silicon carbide blocks Gaps must reseal after the arrester operates (grading circuitry)Gaps must reseal after the arrester operates (grading circuitry) Duty cycle ratingDuty cycle rating is the maximum 60hz voltage where the gaps is the maximum 60hz voltage where the gaps

can still re-seal against power follow currentcan still re-seal against power follow current Subject to external contamination Subject to external contamination Doble study shows that 50% of silicon carbide arresters tested Doble study shows that 50% of silicon carbide arresters tested

cannot meet original protection characteristicscannot meet original protection characteristics Problem with moisture contamination and gaps changing Problem with moisture contamination and gaps changing

characteristicscharacteristics Oldest SiC arresters do not have a pressure relief ratingOldest SiC arresters do not have a pressure relief rating

9GE Thyrite

Westinghouse LVS

Brown is down!!

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Arrester Class:

IEEE C62.11-1999

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Arrester Class:Arrester Class: The key test for determining class is the Pressure Relief Test: The key test for determining class is the Pressure Relief Test: Arrester must vent at or below the rated current for both the high and Arrester must vent at or below the rated current for both the high and

low current valueslow current values Parts of the arrester must not fall outside a circle with the radius equal Parts of the arrester must not fall outside a circle with the radius equal

to the height of the arrester (it can fall down!)to the height of the arrester (it can fall down!)

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Metal Oxide arrestersMetal Oxide arresters Station Class Metal Oxide arresters were first Station Class Metal Oxide arresters were first

introduced around 1980 for transmission applicationsintroduced around 1980 for transmission applications Originally three varieties:Originally three varieties:

– Gapless – Westinghouse 4” discsGapless – Westinghouse 4” discs– Shunt gap – General Electric 3” discsShunt gap – General Electric 3” discs– Series gap – Ohio Brass 3” discsSeries gap – Ohio Brass 3” discs

Today all station class arresters are gaplessToday all station class arresters are gapless Intermediate and distribution ratings introduced in Intermediate and distribution ratings introduced in

mid 80s (gapless)mid 80s (gapless) Polymer housings introduced in 90s Polymer housings introduced in 90s

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MOV MOV Design Design TestsTests

Arrester class

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Tests and RatingsTests and Ratings Protective CharacteristicsProtective Characteristics

– Discharge currentDischarge current– Lightning impulseLightning impulse– Switching impulseSwitching impulse

Arrester SurvivalArrester Survival– MCOVMCOV– Temporary over-voltage (TOV)Temporary over-voltage (TOV)– Duty Cycle (accelerated aging)Duty Cycle (accelerated aging)– Transmission line dischargeTransmission line discharge– Pressure Relief tests (arrester class)Pressure Relief tests (arrester class)

» Porcelain vs polymerPorcelain vs polymer

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Discharge Current:Discharge Current:The surge current that flows through an arrester. In a gapless arrester the peak voltage that appears across the arrester at the discharge current is the protective level.A series of 8/20 current waves are used with the peakamplitudes listed below:

• 1500a• 3000a• 5000a• 10000a• 15000a (500kv only)• 20000a (distribution & subtransmission - unshielded)• 40000aThese points are used to compare to the equipment BIL.

The manufacturers’ published information shall state for eacharrester rating the maximum discharge voltage for each discharge current listed. IEEE C62.11-1999

IV

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A typical discharge current called the “classifying current” is used to determine the lightning and switching surge protective levels. These currents vary depending on the nominal system voltage:

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Lightning Protective Levels:Lightning Protective Levels: LPL - An 8x20 lightning impulse discharge current is passed through the arrester LPL - An 8x20 lightning impulse discharge current is passed through the arrester

to determine the discharge voltages. to determine the discharge voltages. The current magnitude is the classifying current for the appropriate system The current magnitude is the classifying current for the appropriate system

voltage. It simulates the current magnitude and shape that the arrester would voltage. It simulates the current magnitude and shape that the arrester would have to shunt to ground due to a lightning stroke coming in on the 138kv line.have to shunt to ground due to a lightning stroke coming in on the 138kv line.

Example: an arrester applied on a 138kv system should use a 10ka 8x20 u-sec Example: an arrester applied on a 138kv system should use a 10ka 8x20 u-sec classifying current. This produces 164.9kv at the arrester. This is the protective classifying current. This produces 164.9kv at the arrester. This is the protective level (LPL).level (LPL).

The voltage protective level coordinates with the equipment “BIL” withstand The voltage protective level coordinates with the equipment “BIL” withstand valuevalue

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Front-of-Wave Protective Front-of-Wave Protective Levels:Levels:

FOW – Three current impulses (1 u-sec, 2 u-sec and 8 u-sec rise) are FOW – Three current impulses (1 u-sec, 2 u-sec and 8 u-sec rise) are passed through the arrester and the three crest voltages are plotted against passed through the arrester and the three crest voltages are plotted against time. time.

Again the current magnitude is the appropriate impulse classifying Again the current magnitude is the appropriate impulse classifying current.current.

The Front-of -Wave protective level is the point on the curve at .5 u-The Front-of -Wave protective level is the point on the curve at .5 u-secondsseconds

This protective level coordinates with the equipment “chopped wave” This protective level coordinates with the equipment “chopped wave” withstandwithstand

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Switching Surge Protective Switching Surge Protective Levels:Levels:

A discharge current of 45-60 u-secs rise time is passed A discharge current of 45-60 u-secs rise time is passed through the arrester to determine the discharge voltagethrough the arrester to determine the discharge voltage

The magnitude is the switching surge classifying The magnitude is the switching surge classifying current for the appropriate system voltagecurrent for the appropriate system voltage

This protective level coordinates with the equipment This protective level coordinates with the equipment switching surge withstandswitching surge withstand

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Tests and RatingsTests and Ratings Protective CharacteristicsProtective Characteristics

– Discharge currentDischarge current– Lightning impulseLightning impulse– Switching impulseSwitching impulse

Arrester SurvivalArrester Survival– MCOVMCOV– Temporary over-voltage (TOV)Temporary over-voltage (TOV)– Duty Cycle (accelerated aging)Duty Cycle (accelerated aging)– Transmission line dischargeTransmission line discharge– Pressure Relief tests (arrester class)Pressure Relief tests (arrester class)

» Porcelain vs polymerPorcelain vs polymer

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Be sure MCOV value is correct

Class must also be Correct

MOV NameplateMOV Nameplate

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MCOV MCOV – Maximum Continuous Operating Voltage – Maximum Continuous Operating Voltage rating is the maximum designated root-mean-rating is the maximum designated root-mean-squared (rms) value of power frequency voltage that squared (rms) value of power frequency voltage that may be applied continuously between the terminals may be applied continuously between the terminals of the arrester.of the arrester.(Note this is phase to ground rms volts!)(Note this is phase to ground rms volts!)

Example 145kv to ground = 83.7kv so the minimum Example 145kv to ground = 83.7kv so the minimum MCOV for our 138 kv system is 84kvMCOV for our 138 kv system is 84kvThis is the most important criteria for correct This is the most important criteria for correct applicationapplication

IEEE C62.11-1999

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Temporary Over-voltage Curves: Temporary Over-voltage Curves: MOVs can MOVs can tolerate voltages over MCOV for short periodstolerate voltages over MCOV for short periodsCheck the actual manufactures curves for each arrester.Check the actual manufactures curves for each arrester.Note curves for “prior duty” and “no prior duty”. The “prior dutyNote curves for “prior duty” and “no prior duty”. The “prior dutycurve is for previous transmission switching duty.curve is for previous transmission switching duty.

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Duty Cycle Rating Duty Cycle Rating – Arrester is raised to an – Arrester is raised to an elevated 60hz voltage (duty cycle rating) and elevated 60hz voltage (duty cycle rating) and operated 20 times at the impulse classifying current. operated 20 times at the impulse classifying current. If it doesn’t go into thermal runaway it passes the If it doesn’t go into thermal runaway it passes the test. Basically this is equivalent to the old duty cycle test. Basically this is equivalent to the old duty cycle rating for silicon carbide arresters. rating for silicon carbide arresters.

Example: an 84kv MCOV translates to a 108kv duty Example: an 84kv MCOV translates to a 108kv duty cycle rating. A 98kv MCOV is a 120kv duty cycle.cycle rating. A 98kv MCOV is a 120kv duty cycle.This test coupled with the high current discharge test This test coupled with the high current discharge test simulates accelerated aging of the blocks.simulates accelerated aging of the blocks.

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Metal Oxide Arrester Ratings:

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Switching Switching Surges:Surges:

Z0= L/C

Voltage doubles when closing in on an open line = 2 P.U. at open line terminal

Assume that High Speed Re-closing traps a negative 1 P.U. charge on the Assume that High Speed Re-closing traps a negative 1 P.U. charge on the line. Then when the breaker re-closes the maximum voltage at the open end line. Then when the breaker re-closes the maximum voltage at the open end

can approach a maximum of can approach a maximum of 3.5 - 4.0 P.U.3.5 - 4.0 P.U. for multiple reflections depending for multiple reflections depending on damping (R):on damping (R):

Trapped charge = -1.0 P.U.Trapped charge = -1.0 P.U.

3.5 P.U.

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Transmission Line Discharges:Transmission Line Discharges:

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When an arrester discharges a switching surge the When an arrester discharges a switching surge the blocks heat up. Switching surges last much longer blocks heat up. Switching surges last much longer than lightning surges and so the arresters must than lightning surges and so the arresters must dissipate more energy.dissipate more energy.

Repetitive discharges can cause the arrester to fail Repetitive discharges can cause the arrester to fail if there isn’t enough time between to allow for if there isn’t enough time between to allow for coolingcooling

The transmission discharge test assures the The transmission discharge test assures the arrester will tolerate a standard amount of energyarrester will tolerate a standard amount of energy

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Surge impedance Line Length

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The arrester is subjected to 20 surges:The arrester is subjected to 20 surges:– Six consecutive-one minute to cool-six more-Six consecutive-one minute to cool-six more-

one minute-six more-one minute-two moreone minute-six more-one minute-two more The arrester passes if:The arrester passes if:

– discharge test is successfuldischarge test is successful– Power loss is within specs (leakage current)Power loss is within specs (leakage current)

Transient Network Analysis studies use a value of Transient Network Analysis studies use a value of 7 kilojoules/kv of MCOV rating for transmission 7 kilojoules/kv of MCOV rating for transmission arrestersarresters

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Pressure Relief Tests:Pressure Relief Tests:

If an arrester fails internally the arc creates rapidly expandingIf an arrester fails internally the arc creates rapidly expandinggasses that can cause the housing to explode violently unlessgasses that can cause the housing to explode violently unlessthe pressure is vented. Arresters are rated on the fault currentthe pressure is vented. Arresters are rated on the fault currentmagnitude that can pass through the housing. They must vent magnitude that can pass through the housing. They must vent successfully at or below the rated current:successfully at or below the rated current:

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Arc Arc Chutes:Chutes:

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Seal plates

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Failed 396kv arrester at Black Oak substationFailed from prolonged 60hz over-voltage:

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This arrester actually failed according to the This arrester actually failed according to the standard. The pieces didn’t scatter very far!standard. The pieces didn’t scatter very far!

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Arrester base left on structure Arrester base left on structure after failure.after failure.

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Typical 46 kV MOV ArresterTypical 46 kV MOV Arrester

Polymer Housing

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Failed Polymer ArresterFailed Polymer Arrester

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Arrester InstallationArrester Installation

Grounding – continuous conductorGrounding – continuous conductor– Better ground improves arrester Better ground improves arrester

performanceperformance– Shortest ground lead lengthShortest ground lead length– Can monitor leakage current if the lead is Can monitor leakage current if the lead is

insulatedinsulated Lead length & ground leadLead length & ground lead Corona rings/ClearancesCorona rings/Clearances Arc chutesArc chutes SiC change-outsSiC change-outs

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Arc chutes should faceaway from other equipment or bushings

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Installed 138 kV ArresterInstalled 138 kV Arrester

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InfrastructureInfrastructureSilicon Carbide Arrester Silicon Carbide Arrester Replacement ProgramReplacement Program

Change out old SiC arresters on xfmrs starting in Change out old SiC arresters on xfmrs starting in 2006 during 5 year gauge inspections (xfmrs 2006 during 5 year gauge inspections (xfmrs 138kv and above)138kv and above)

Replace old arresters as part of xfmr/breaker Replace old arresters as part of xfmr/breaker change-outs and pin/cap insulator replacementschange-outs and pin/cap insulator replacements

If a SiC arrester fails, change out all 6If a SiC arrester fails, change out all 6 Don’t return SiC arresters to stockDon’t return SiC arresters to stock

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Arrester Arrester Maintenance, Field Maintenance, Field

Tests & FailuresTests & Failures Can’t check protective Can’t check protective

levels in the field!levels in the field! Moisture intrusionMoisture intrusion Leakage currentLeakage current Power factorPower factor MeggerMegger Thermovision Thermovision Visual inspectionsVisual inspections Failed arrestersFailed arresters

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watts

vars

Leakage Current:Measure leakage current with the arrester energizedIncreasing resistive component of the leakage current indicates blocks are failing (losses are proportional to i2)

ma

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Inspection While Out of service:Inspection While Out of service:– Weather Tight HousingWeather Tight Housing

» Check for cracks in the porcelain or tears or bulges in the Check for cracks in the porcelain or tears or bulges in the polymer.polymer.

– Clean all external surfaces of the arresterClean all external surfaces of the arrester– Coat all external weather tight housing surfaces with Coat all external weather tight housing surfaces with

silicon grease to aid in water shedding if environment silicon grease to aid in water shedding if environment is harsh.is harsh.

– Check and clean the ground connectionsCheck and clean the ground connections

Inspection and Prep for Testing:Inspection and Prep for Testing:

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Effects of Contamination:Effects of Contamination:

Contamination causes an unequal voltage distribution across the outside surface of the arrester.

In arresters with internal gaps and grading circuitry this can also cause an imbalance of voltage across the gaps and results in improper operation and premature failure of the arrester.

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watts

vars

Power Factor:Apply 10kv to terminal and measure leakage currentResistive component of leakage current indicates internal moisture contamination

10 kv

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Inspection While Out of service:Inspection While Out of service:– Electrical TestingElectrical Testing

» Power Factor TestingPower Factor Testing

Should perform upon installation to establish benchmark. Should perform upon installation to establish benchmark.

This test is generally more effective on Silicon Carbide arresters than This test is generally more effective on Silicon Carbide arresters than MOV arresters in detecting internal contamination or breakdown of MOV arresters in detecting internal contamination or breakdown of spark gaps or valve blocks. spark gaps or valve blocks.

Make the measurement with the highest voltage available on the test Make the measurement with the highest voltage available on the test set without exceeding the line to ground voltage of the arrester under set without exceeding the line to ground voltage of the arrester under test.test.

The values that are measured are the leakage current (less than 3 The values that are measured are the leakage current (less than 3 milli-amperes) and watts loss (less than 150 mW). These tests can milli-amperes) and watts loss (less than 150 mW). These tests can only be read utilizing a 10kV power factor test set.only be read utilizing a 10kV power factor test set.

Power Factor Test:Power Factor Test:

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Example:Example: During Class A Maintenance on the No. 2 During Class A Maintenance on the No. 2

transformer at Doubs Substation, the transformer at Doubs Substation, the Substation Crew decided to perform Power Substation Crew decided to perform Power Factor Testing on the high side arresters.Factor Testing on the high side arresters.

Testing revealed an abnormal test pattern Testing revealed an abnormal test pattern on the Z phase arresteron the Z phase arrester

The next slides show the test results of a The next slides show the test results of a neighboring similar arrester as well as the neighboring similar arrester as well as the results from the arrester in question.results from the arrester in question.

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Arrester DetailsArrester Details

Nameplate Data of ArresterNameplate Data of Arrester– ABBABB– EXLIMEXLIM– Style – T396SA318AAPStyle – T396SA318AAP– Serial No. 00M3001Serial No. 00M3001

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Test ResultsTest Resultson a Good Arresteron a Good Arrester

All tests were performed with the Doble Power All tests were performed with the Doble Power Factor test set at 10 kV.Factor test set at 10 kV.

Phase results (comparable to all arresters tested of Phase results (comparable to all arresters tested of the same make and model)the same make and model)mAmA WattsWatts

TopTop 0.3570.357 0.0600.060 MidMid 0.1640.164 0.0590.059 BotBot 0.3180.318 0.0830.083

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Test ResultsTest Resultson the Arrester in Questionon the Arrester in Question

Z Phase results (4/28/2003)Z Phase results (4/28/2003)mAmA WattsWatts

Z TopZ Top 0.3760.376 0.1420.142Z MidZ Mid 0.3090.309 1.5501.550Z BottZ Bott 0.0340.034 0.2110.211

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Retest ResultsRetest Resultson the Arrester in Questionon the Arrester in Question

Phase results (4/30/2003) after cleaning surfacesPhase results (4/30/2003) after cleaning surfacesmAmA WattsWatts

TopTop 0.3600.360 0.1130.113 MidMid 0.2360.236 0.9480.948 BottBott 0.3110.311 0.0100.010The retests did show a slight improvement of the The retests did show a slight improvement of the

readings after the cleaning. The middle section readings after the cleaning. The middle section was still different from a typical reading. The was still different from a typical reading. The decision was made to replace the arrester decision was made to replace the arrester assembly.assembly.

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Test ResultsTest Resultson the Arrester in Questionon the Arrester in Question

Phase results (4/30/2003) on the ground after Phase results (4/30/2003) on the ground after disassemblydisassembly

mAmA WattsWatts MidMid 0.3840.384 1.4711.471 BottBott 0.3170.317 0.0820.082The tests on the ground showed that the bottom The tests on the ground showed that the bottom

section was of typical values but the middle section was of typical values but the middle section was still different from the typical section was still different from the typical readings. The arrester was sent to ABB in readings. The arrester was sent to ABB in Youngwood, PA for further investigation. Youngwood, PA for further investigation.

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ABB InvestigationABB Investigation6/3/20026/3/2002

ABB Received the arrester sections and performed ABB Received the arrester sections and performed a voltage test on all 3 sections.a voltage test on all 3 sections.

The test applies the rated voltage to each section of The test applies the rated voltage to each section of the arrester. (118 kV for the top 2 sections and 82 the arrester. (118 kV for the top 2 sections and 82 kV for the bottom section). The resulting leakage kV for the bottom section). The resulting leakage current is then read. The expected leakage is less current is then read. The expected leakage is less than 1 mA.than 1 mA.

The top section and bottom section passed the test.The top section and bottom section passed the test. The middle section failed the test when the applied The middle section failed the test when the applied

voltage was only 44 kV (expected to reach 118 voltage was only 44 kV (expected to reach 118 kV)kV)

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Top of Middle section Arrester with Retaining plate removed and seal plate exposed.

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Under side of Seal plate after removal

Notice the corrosion and signs of moisture

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Inside arrester with Seal plate removed

Notice the corrosion and signs of moisture

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A close inspection of the seal plate revealed a crack in the plate.

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Removal of first MOV Disc. Notice the surface contamination on the disc

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Removal of entire stack of MOV Discs. Notice the

surface contamination on all the discs

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Inspection While Out of service:Inspection While Out of service:– Electrical TestingElectrical Testing

» Insulation ResistanceInsulation Resistance An arrester is to act as an insulator a majority of its in service life. It An arrester is to act as an insulator a majority of its in service life. It

will only allow current to flow to ground during high voltage transients will only allow current to flow to ground during high voltage transients generally caused by lightning.generally caused by lightning.

Make the measurement with the highest voltage available on the test Make the measurement with the highest voltage available on the test set without exceeding the line to ground voltage of the arrester under set without exceeding the line to ground voltage of the arrester under test.test.

Readings should be comparable to similar arresters. The value Readings should be comparable to similar arresters. The value should be greater than 200 Mega Ohms. This test is generally more should be greater than 200 Mega Ohms. This test is generally more effective on Silicon Carbide arresters than MOV arresters in effective on Silicon Carbide arresters than MOV arresters in detecting internal contamination or breakdown of spark gaps or valve detecting internal contamination or breakdown of spark gaps or valve blocks. blocks.

MOV arresters may show a high insulation resistance value after an MOV arresters may show a high insulation resistance value after an operation but still be failed as an open circuit. operation but still be failed as an open circuit.

Megger Test:Megger Test:

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Infra-red Image of ArrestersInfra-red Image of Arresters *>24.3°

C

*<4.1°C

5.0

10.0

15.0

20.0

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Inspection While in service :Inspection While in service :– Infra red ImagingInfra red Imaging

» Infra red imaging of in-service arresters may detect damaged Infra red imaging of in-service arresters may detect damaged arrestersarresters

» Arresters while in normal service only conduct a few milli-Arresters while in normal service only conduct a few milli-amps of current, therefore, will not produce heat.amps of current, therefore, will not produce heat.

» If the arrester images indicate a rise in temperature from If the arrester images indicate a rise in temperature from ambient temperature of 5 degrees Celsius or more, ambient temperature of 5 degrees Celsius or more, replacement should be considered. replacement should be considered.

» The blocks are probably starting to fail and are conducting The blocks are probably starting to fail and are conducting too much currenttoo much current

Infrared ImagingInfrared Imaging

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Inspection While in service:Inspection While in service:– Weather Tight HousingWeather Tight Housing

» The weather tight housing is the covering of the arresterThe weather tight housing is the covering of the arrester» Generally produced from porcelain or polymer.Generally produced from porcelain or polymer.» Check for cracks in the porcelain or tears or bulges in the polymer.Check for cracks in the porcelain or tears or bulges in the polymer.

– Make certain porcelain or polymer appears clean and free of Make certain porcelain or polymer appears clean and free of any debrisany debris

– Visually inspect the ground connections from the base of the Visually inspect the ground connections from the base of the arrester. A missing connection will not allow the arrester to arrester. A missing connection will not allow the arrester to function as designed.function as designed.

» Multiple arrester operations with improperly sized wire may result in a Multiple arrester operations with improperly sized wire may result in a failure of the ground wire.failure of the ground wire.

» Improperly sized ground wire may also result in fire.Improperly sized ground wire may also result in fire.

Visual InspectionVisual Inspection

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Failure assessmentFailure assessment» Suspect ArrestersSuspect Arresters

Exercise EXTREME caution while investigating problems and Exercise EXTREME caution while investigating problems and handling suspect arresters. Sealed Silicon Carbide and MOV handling suspect arresters. Sealed Silicon Carbide and MOV arresters may be under pressure due to a build up of fault arresters may be under pressure due to a build up of fault gasses. gasses.

Visually inspect suspect arresters carefully while looking for Visually inspect suspect arresters carefully while looking for burn deposits near arc chutes on Silicon Carbide arresters. burn deposits near arc chutes on Silicon Carbide arresters.

MOV arresters may show very subtle signs of failure such as MOV arresters may show very subtle signs of failure such as deformation of the polymer covering. Generally, MOV deformation of the polymer covering. Generally, MOV arresters will fail and split the polymer covering or fracture the arresters will fail and split the polymer covering or fracture the porcelain cover. porcelain cover.

Failed Arresters:Failed Arresters:

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Thanks for your attention…… Your substation support staff!Luxor substation - 1936

l8 surge arresters

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