高电压设备测试（High Voltage Equipment Testing）（英文版） 课件 Worksheet 1 Insulation Resistance Test

《HighVoltageEquipmentTesting》InsulationResistanceTest主讲人：何发武（副教授）OperatingWorksheet：OperatingWorksheet：TableofContents01Followme02Workshop03Training01FollowmeⅠ.OverviewofinsulationresistanceMeasuringtheinsulationresistance,particularlytheabsorptionratioandpolarizationindexofthetransformer,ishighlysensitiveinassessingtheoverallinsulationcondition.Thismethodeffectivelyidentifiesissueslikemoisture,surfacecontamination,andthrough-holedefectsinthetransformerinsulation.Itcanalsodetectproblemssuchasshortcircuits,grounding,orcracksintheporcelaininsulation.Insulatingmaterialswithinthetransformer,includingtheinternalironcore,clamps,andthrough-bolts,playacrucialroleinensuringinsulation.Theinsulationinthewindingsectionscanwithstandhighvoltagelevels.Ⅰ.OverviewofinsulationresistanceWhentheinsulationofthetransformeriscompromisedduetopiercing,damagetotheceramicinsulation,connectionoftheleadwiretothecasing,ortheoccurrenceofmetalshort-circuitfaults,therewillbeanoticeablechangeintheinsulationresistance.Moreover,thechangeininsulationresistancebeforeandafterequipmentdryingissignificantlylargerthanthechangeinthedissipationfactorofthedielectric.Ⅰ.OverviewofinsulationresistanceForinstance,inthe7,500

kVAtransformer,thedissipationfactormaychangeby2.5timesbeforeandafterdrying,whiletheinsulationresistancemaychangebymorethan40times.Thischangeisquiteremarkable.Therefore,evaluatingtheinsulationresistanceofcomponentsliketheironcorecaneffectivelydetectoverallmoistureinthetransformerinsulation,surfacecontaminationofcomponents,andconcentratedthrough-holedefects.Ⅰ.OverviewofinsulationresistanceTheabsorptionratioKreferstotheratiooftheinsulationresistancevalueat60secondstotheinsulationresistancevalueat15seconds.ThepolarizationindexPIreferstotheratiooftheinsulationresistancevalueat10minutestotheinsulationresistancevalueat1minuteduringtesting.K=R60/R15 (2-1)PI=R600/R60 (2-2)Ⅰ.OverviewofinsulationresistanceThepolarizationindexisanimportantparameterforassessingwhetherlargepowerequipmentisaffectedbymoisture.Forthelargetransformer,generator,powercable,andparallelcapacitor,duetotheirlargesamplecapacitanceandcompositeinsulationmaterials,theabsorptioncurrentdecaysslowly,andthepolarizationprocessoftencannotbecompletedwithin1minute.Therefore,itisnecessarytomeasurefor10minutes,andcomparedtofactorytests,theinsulationconditionisjudgedusingthepolarizationindex(PI).Ⅰ.OverviewofinsulationresistanceTaketransformersasanexample,duetotheimprovementindryingprocesses,theinsulationresistanceoftransformersisincreasingandcangenerallyreachseveraltensofthousandsofmegaohms,causingthepolarizationprocessofthetransformertobecomelonger.Therefore,thepolarizationindexshouldbemeasured,andtheabsorptionratiotestresultsshouldnotbeusedtodetermineifthetransformerisqualified.Ⅰ.OverviewofinsulationresistanceWhentheinsulationresistanceofthetransformerexceeds10,000M,thereisnoneedtoconsidertheabsorptionratioorpolarizationindex.Therefore,whenconductinginsulationresistance,absorptionratio,orpolarizationindextesting,theresultsshouldbeanalyzedandjudgedincombinationwithspecificelectricalequipment.Inthe“Regulations”,itisstipulatedthattheabsorptionratioandpolarizationindexarenotconvertedbytemperature.Ⅱ.TestStandardsAccordingtothe“RegulationsonPreventiveTestingofPowerEquipment”,itisstipulatedthattheabsorptionratioshouldnotbelessthan1.3orthepolarizationindexshouldnotbelessthan1.5asthecompliancestandard.AsshowninTable2-1,2-2.Aftermeasuringinsulationresistance,itshouldbeuniformlyconvertedto20Candcomparedwiththefactoryvalueorthevaluefromthepreviousmeasurementcycle.StatusPolarizationIndex(PI)HazardousLessthan1.0Poor1.0–1.1suspicious1.1–1.25fair1.25–2.0goodGreaterthan2.0Table2-1

Referencestandardsforassessinginsulationconditionbasedonthepolarizationindex.Ⅱ.TestStandardsTable2-2QualifiedstandardforinsulationresistancetestⅡ.TestStandardsTable2-2QualifiedstandardforinsulationresistancetestⅡ.TestStandardsTable2-2Qualifiedstandardforinsulationresistancetest02WorkshopⅠ.MeasurementmethodsDuringthemeasurement,recordtheambienttemperatureandhumidity.Measuretheinsulationresistanceandabsorptionratiosequentiallyforeachwindingwithrespecttogroundandbetweenotherwindings.Short-circuitallleadsofthewindingbeingtested,andshort-circuitandgroundallleadsofthenon-testedwindings.Thisallowsformeasuringtheinsulationconditionbetweenthetestedwindingandground,aswellasbetweenthetestedwindingandthenon-testedwindings,whileavoidingtheinfluenceofresidualchargesinthenon-testedwindingsonthemeasurement.Ⅰ.MeasurementmethodsDuringthemeasurement,recordtheambienttemperatureandhumidity.Measuretheinsulationresistanceandabsorptionratiosequentiallyforeachwindingwithrespecttogroundandbetweenotherwindings.Short-circuitallleadsofthewindingbeingtested,andshort-circuitandgroundallleadsofthenon-testedwindings.Thisallowsformeasuringtheinsulationconditionbetweenthetestedwindingandground,aswellasbetweenthetestedwindingandthenon-testedwindings,whileavoidingtheinfluenceofresidualchargesinthenon-testedwindingsonthemeasurement.Ⅰ.MeasurementmethodsFigure2-1showsthefunctionaldiagramoftheinsulationresistancetester,Figure2-2showsthewiringdiagramformeasuringtheinsulationresistanceofthehigh-voltagewindingofthehigh-voltagegenerator.Figure2-1

InsulationresistancetesterfunctiondiagramFigure2-2Wiringdiagramforinsulationresistancemeasurementofthree-Phasetransformerhigh-voltagewindingⅠ.MeasurementmethodsWhenmeasuringtheinsulationresistanceofwindingsratedat1

kVandbelow,useamegohmmeterwitharangenotexceeding0.5

kV.Forwindingswithvoltagesof2.5

kVandabove,amegohmmeterwithavoltageof1

kVor2.5

kVcanbeused.Forwindingsratedat10

kVandabove,usea5

kVinsulationresistancetesterandrecordthetopoiltemperature.Ⅰ.MeasurementmethodsAnalysisofinsulationresistancemeasurementresultsisconductedusingacomparativemethod,primarilyrelyingoncomparingtheresultswithprevioustestresultsofthistransformer.Generally,theswitchingtestvalueshouldnotbelowerthan70%ofthefactorytestvalue.Whenconvertinginsulationresistancetotheinsulationresistanceat20C,transformersupto220

kVshouldhaveavaluenotlessthan800

M,andthetransformerof500

kVshouldhaveavaluenotlessthan2,000

M.Theabsorptionratioshouldnotbelowerthan1.3.Ⅰ.MeasurementmethodsWhenmeasuringtheinsulationresistanceofwindingsratedat1

kVandbelow,useamegohmmeterwitharangenotexceeding0.5

kV.Forwindingswithvoltagesof2.5

kVandabove,amegohmmeterwithavoltageof1

kVor2.5

kVcanbeused.Forwindingsratedat10

kVandabove,usea5

kVinsulationresistancetesterandrecordthetopoiltemperature.WhenmeasuringtheabsorptionratioKofthetransformer,theironcoremustbegrounded.Iftheironcoreisnotgrounded,insulationmaterialssuchascardboardbetweenthetransformerwindingsandthecasingareintroducedinseries,causinganincreaseinthemeasuredinsulationvalueR15,resultinginadecreaseintheabsorptionratio,whichcaneasilyleadtoanunqualifiedresult.Ⅰ.WorkspecificationWhenconductinghigh-voltagetestsonelectricalequipment,afencemustbesetuparoundtheworkarea,withasignhangingonthefencewith“NoEntry,HighVoltageDanger!”Guardsshouldbestationedthere.Onlyoneworkgroupisallowedtoperformhigh-voltagetestsononepieceofequipmentwithinaspecificelectricalconnection.Agroundingwireshouldbeinstalledonthemaintenancesideofthedisconnectionpoint,andasignwith“NoEntry,HighVoltageDanger!”shouldbehungonthehigh-voltagetestside,facingthemaintenanceworkarea.Ⅱ.TechnicalstandardsForthelargepowertransformerof35

kVandbelow,theabsorptionratioshouldnotbelowerthan1.3.Forthelargepowertransformerswithvoltagesequaltoorhigherthan60

kV,theabsorptionratioshouldbecontrollednotlowerthan1.5.Inthecommissioningtestofthepowerindustry,thecorrespondingrequirementfortheabsorptionratioisnotlowerthan1.2and1.3,respectively.Ⅲ.JudgmentandAnalysisInsulationresistancecanpartiallyreflecttheinsulationconditionofwindings.However,itisgreatlyinfluencedbyfactorssuchasinsulationstructure,operationmode,environment,equipmenttemperature,insulationoilquality,andmeasurementerrors.Therefore,duringinstallation,theinsulationresistancevalueR60sshouldnotbelowerthan70%ofthemeasuredinsulationresistancevalueduringthefactorytest.Duringpreventivetests,theinsulationresistancevalueR60sshouldnotbelowerthan50%ofthemeasuredvalueafterinstallation,majorrepairs,andpriortobeingputintooperation.Forthe500

kVtransformer,underthesametemperatureconditions,itsinsulationresistanceshouldnotbelowerthan70%ofthefactoryvalue,andtheminimumresistancevalueat20Cshouldnotbelessthan2,000

M.Ⅳ.SpecialNoticesDuetothedesignedshieldingloopinthemegohmmeter’sinternalcircuitrytoensuremeasurementaccuracy,itisimportanttocorrectlyconnectthecircuit.TheL-terminalofthelineshouldbeconnectedtotheconductivepartofthetestspecimeninsulatedfromtheground,whiletheE-terminalshouldbeconnectedtothegroundingendofthetestspecimen.Interchangingtheseconnectionsisnotallowedasitmayresultinmeasurementerrors.Ⅳ.SpecialNoticesSelectingamegohmmeterwithameasuringvoltagethatmatchestheratedvoltageofthespecimeniscrucial.Thebreakdownvoltageoftheinsulationmaterialisrelatedtotheappliedvoltage,andthemeasurementaccuracyofinsulationcharacteristicsalsodependsontheappliedvoltage.Ifthemeasuringvoltageistoolow,itwillnotaccuratelymeasuretheinsulationcondition,andifitistoohigh,itmaydamagetheinsulationofthespecimen.Ⅳ.SpecialNoticesTemperatureandhumidityshouldberecordedduringthemeasurement.Theabsorptionratioistemperature-dependent.Forverygoodinsulation,theabsorptionratioincreaseswithtemperature.Forpoorinsulationsuchasoilorpaperinsulation,theabsorptionratiodecreaseswithtemperature.Inequipmentwithseveremoisture,theinsulationresistancevariessignificantlywithtemperature.Iftheequipmenttransitionsfromoperationtoshutdown,itshouldbemeasuredaftertheinternalinsulationhascooleddowncompletely,andtheinsulationresistanceshouldbeconvertedtotheinsulationresistanceat20C.Ⅳ.SpecialNoticesForneworRepairedoil-immersedtransformers,Itwilltakedozensofhourstowaitfortheoilcirculationandbubbleescapebeforemeasuringtheinsulationresistance.Forthetransformerwithacapacityof8,000

kVAorabove,theyshouldbeleftstandingforatleast20hours,whileotherlower-capacitytransformersrequireastandingtimeofatleast5hours.Thequalityofoilinthetransformerdirectlyaffectstheinsulationresistancevalue.Thebettertheoilquality,thehighertheinsulationresistanceandthehighertheabsorptionratio.