高电压设备测试（High Voltage Equipment Testing）（英文版） 课件 Project 4 High Voltage New Technology

《HighVoltageEquipmentTesting》HotWashingOperatingWorksheet：OperatingWorksheet：TableofContents01Followme02Workshop03Training01FollowmeⅠ.OverviewofhotwashingAsatmosphericpollutionwillbeattachedtothemagneticcolumnoftheinsulatingporcelainvase,therainydaysarepronetopollution,whichcanleadtoinsulationbreakdownseriouslycausedbyshortcircuitsorgroundingaccidents,soitisnecessarytocleantheinsulatingpartofthesubstationequipmentregularlyinordertopreventthepollutionoftheequipment,toavoidthereductionoftheinsulationoftheequipment,whichwillleadtothebreakdownorshortcircuitdisconnectionaccidents,suchasshowninFigure4-1.Figure4-1

Isolatingswitchinshort-circuitdisconnectionaccidentⅠ.OverviewofhotwashingUsually,theelectricalequipmentworksinastrongelectricloadforalongtime.Thecomprehensivepollutantscausedbytheenvironment,oxidation,andslowcorrosioncausethecontactresistanceoftheelectricalequipmentcontactstoincreasesignificantly,andthearcingisseriouswhenthecontactsact,resultinginhigh-temperatureablation,damagetotheelectricalappliances,andevenaccidents.Powerequipmentoperatinginastrongelectromagneticfield,duetolong-termoutdoorexposure,hasastrongaffinityforvariouspollutantsintheenvironment.Ⅰ.OverviewofhotwashingOvertime,alayerofdirtaccumulates,posingthebiggestriskof“pollutionflashover”and“fogflashover.”Thisleadstosignificantdirectandindirecteconomiclosseseachyear.Therefore,itisnecessarytotimelyremovedust,oilstains,moisture,salt,andotherpollutantsfromvariouselectricalequipmentsuchasoverheadinsulatorsandrodinsulatorsofrailwaycatenarysystems,asshowninFigure4-2,inordertoreduceflashoverfaultsandpollutionflashoversofthesupportinsulatorsofthecatenarysystem.Figure4-2

ThesupportinsulatoroftheOCSexperiencingpollutionflashoverⅠ.OverviewofhotwashingItisimportanttoprioritizecleaningtheinsulatorsofthelineinthesubstation,theporcelainbottlesofthesupportcolumnsfordisconnectingswitches,andthebushingsofswitchtransformersinthesubstation.However,allconductivemetalpartswithinthestation,suchasthepowerlines,transformerbodies,andknifeswitchcontacts,shouldnotbecleaned.Itisalsocrucialtopreventwaterusedforcleaningfromenteringtheterminalboxesandavoidwateringresssecondarywiring,asshowninFigure4-3and4-4.Figure4-3

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kVstationtransformerFigure4-4

Theon-sitelayoutofincominglinesatasubstationⅠ.OverviewofhotwashingFigure4-5illustratestheon-sitehotwashingsceneatasubstation.Figure4-5

SubstationhotwashingscenesiteⅡ.Thefunctionsofhotwashing(1)Preventandeliminatepollutionflashoversandfogflashoversinpowerequipment,reducingandavoidingthesignificanteconomiclossescausedbypoweroutages.(2)Helpimprovetheelectricalinsulationvalueoftheequipmentandmitigatesecondarypollution.Itrestoresthenormalsurfaceimpedanceofcircuitboardsandcomponents,providingspecialprotectionandensuringthattheequipmentoperatesinoptimalconditions.Ⅱ.Thefunctionsofhotwashing(3)Reducethecontactresistanceofelectricalequipmentcontacts,reducethepowerconsumptionofelectricalequipment,andimprovetheworkingefficiencyofequipment.(4)Restorethenormalheatdissipationcapacityofelectronicequipment,reducethepowerconsumptionofelectricalequipment,andimprovetheworkingefficiencyofequipment.(5)Reducetheeconomiclossescausedbypoweroutagemaintenanceequipmentgreatly.02WorkshopⅠ.OperatingProceduresforHotWashing1.BasicSecurityMeasuresAnyoneenteringthelivecleaningandmaintenancesiteshouldweartheprescribedworkinguniformandcomplywiththerelevantsafetyregulationsoftheuser(suchaswearingasafetyhelmetwithafaceshield).Cleaningtoolsusedshouldhaveinsulatinghandles,andtheexposedconductivepartsshouldbeinsulatedtopreventaccidentalshortcircuitsduringoperation.Duringwork,insulatingshoes,cottonlong-sleevedworkclothes,andglovesshouldbeworn,andtheoperationshouldbeconductedwhilestandingonaninsulatingmatordryinsulatingmaterial.Figure4-6showspersonnelwearinginsulatingprotectivegearoperatingahandheldwatergun.Ⅰ.OperatingProceduresforHotWashingFigure4-6

PersonnelwearinginsulatingprotectivegearoperatingahandheldwatergunⅠ.OperatingProceduresforHotWashing2.SelectionofWaterResistanceRateandWaterColumnThepollutionintensityiscalledsaltdensity,whichreferstothemassofpollutantssuchascigaretteash,cementdust,andchemicalmaterialsthatadheretotheinsulationsurfaceofelectricalequipmentperunitareaduetoexternalenvironmentalpollution.Itisusedtomeasurethedegreeofinsulationcontamination,anditsunitismg/cm2.Ⅰ.OperatingProceduresforHotWashingThereisadifferenceininsulationbetweenwaterusedforhotwashingandordinarywater.Commonwatercontainsimpurities,andtapwateranddrinkingwateralsocontainvariousmineralions,whichcanconductelectricity.However,thewaterusedforhotwashingisindustriallyfilteredandhasaveryhighresistivity,equivalenttoaninsulatingmedium.Thisisthesafetystandardforhotwashing.Thewaterusedforhotwashingcannotbedrunkbyhumans.Ⅰ.OperatingProceduresforHotWashingBeforetheoperationofhotwashing,thecontaminationoftheinsulatorshouldbemastered.WhenthesaltdensityisgreaterthanthecriticalsaltdensityinTable4-1,itisgenerallynotsuitableforhotwashing,otherwise,thewaterresistancerateshouldbeincreased.hotwashingisnotsuitableforarrestersandpoorlysealedequipment.Table4-5

WaterResistivityandSpecificCreepageDistanceⅠ.OperatingProceduresforHotWashingTheresistivityofwaterusedforhotwashingisgenerallynotlessthan1,500·cm.Whenflushing220

kVsubstations,theresistivityofthewatershouldnotbelowerthan3,000·cm,anditshouldcomplywiththerequirementsinTable4-1.Beforeeachflushingoperation,theresistivityofthewatershouldbemeasuredusingaqualifiedresistivitymeter.Watersamplesshouldbetakenatthewateroutletformeasurement.Ifwateriscollectedincontainerssuchaswatertrucks,theresistivityofthewatershouldbemeasuredforeachbatch.Theresistivityofthewaterhasasignificantimpactonensuringthepersonalsafetyoftheoperatorsandthesafetyoftheequipment.Ⅰ.OperatingProceduresforHotWashingTheresistivityofwaterhasasignificantimpactonensuringthepersonalsafetyoftheoperatorsandthesafetyoftheequipment.Thisinfluenceismainlyreflectedintheinsulationlevelbetweenthewaterresistivityandthewatercolumn.Differentheightsofwatercolumnsanddifferentwaterresistivitiescorrespondtodifferentpowerfrequencydischargevoltages.Figure4-7showstherelationshipbetweenwaterresistivityanditspowerfrequencydischargevoltage.Figure4-7

RelationshipbetweenwaterresistivityandpowerfrequencydischargevoltageⅠ.OperatingProceduresforHotWashingToolsforhotwashingusewatercolumnsasthemaininsulation,whilewaterpipesandinsulationoperatingrodsserveasauxiliaryinsulation.Thewatercolumnisthekeycomponentthatwithstandsvoltage,buttheinsulationofthewatercolumnmainlydependsonitslength.Atthesametime,thediameterofthewatergunnozzlealsohasasignificantimpactontheinsulation.Ⅰ.OperatingProceduresforHotWashingLarge,medium,andsmallhotwashingtoolswithwatercolumnsasthemaininsulation(thosewithnozzlediametersof3

mmandbelowarecalledsmallwaterwashers;thosewithdiametersof4–8

mmarecalledmediumwaterwashers;thosewithdiametersof9

mmandabovearecalledlargewaterwashers).ThelengthofthewatercolumnbetweenthewatergunnozzleandthechargedelectrodemustnotbelessthantherequirementsspecifiedinTable4-2.Bothlargeandmedium-sizedwater-flushinggunnozzlesshouldbereliablygrounded.Table4-2

DistancebetweenthewatergunnozzleandthechargedelectrodeⅠ.OperatingProceduresforHotWashingIftheinsulationperformanceoftheinsulatorisfoundtobereduced,itshouldbereplacedfirstbeforeconsideringotherwork.Ifthereisnoreliabletechnicalmeansofidentification,damagedandlow-valueinsulationshouldnotbesubjectedtohotwashing.Whenwashinginsulators,attentionshouldbepaidtothewinddirection.Itisnecessarytowashthedownwindsidefirstandthentheupwindside.Forinsulatorsarrangedinupperandlowerlayers,thelowerlayershouldbewashedfirst,followedbytheupperlayer.Thewashingangleshouldalsobeconsideredtopreventnearbyinsulatorsfromexperiencingflashoverinthesplashingwatermist.Differentwashingsequenceswillresultindifferentinsulationsurfaceconditions,whichwillaffecttheflashovervoltage.Ⅰ.OperatingProceduresforHotWashingOnemethodistowashthelayerssequentiallyfrombottomtotoporfromtheconductorsideoutward,minimizingthewettingofthesplashingsurfaceandavoidingwettingofotherlayersofdirt.Anothermethodistowashfromtoptobottom,whichmayresultinpartialwettingoftheinsulationsurfacebeforetheupperlayerofdirtiscompletelywashedoff.Figure4-8showsafieldwheresequentialflushingisperformed.Ⅰ.OperatingProceduresforHotWashingHotwashingshouldgenerallybeconductedingoodweatherconditions.Itisnotsuitabletoconducthotwashingwhenthewindspeedexceeds4levels,thetemperatureisbelow0C,duringrainy,snowy,sandstorm,foggy,orthunderstormweather.Therefore,thereisnocontaminationofthewaterusedforhotwashingduringoperation.However,thewaterthathaspassedthroughthewashingequipmentmaywashawaythedirtonthesurfaceoftheinsulationequipment,makingthewaternolongerclean.Figure4-8

WashthesiteinsequenceⅠ.OperatingProceduresforHotWashingThesafetydistancebetweenapersonandachargedobjectmustnotbelessthantheregulationsspecifiedinTable4-3.Table4-3

VoltageLevelsandHumanSafetyDistancesⅠ.OperatingProceduresforHotWashingTheabove“safedistance”includestheminimumdistancebetweenthecleaningoperator’smetaltools(suchassprayguns,etc.)andtheenergizedequipmentbeingcleaned.Therefore,duringthehotwashingprocess,boththesupervisorandtheoperatormustpayattentiontotheirpositions,asshowninFigure4-9.Figure4-9

PositionsofpersonnelatthewashingsiteⅡ.WaterWashingVehicleDuetotheexposureofinsulatorsofelectrifiedrailwayoverheadcontactlinestotheexternalenvironmentthroughouttheyear,suspendedparticles,dust,smoke,andotherexternalsubstancesintheaircanadheretothem,formingaccumulateddirt.Thedirttightlybondswiththesurfaceoftheinsulatorsovertime,makingitdifficulttocleanevenwithnaturalwindandrain.Inhumidweather,somesaltcompoundsdissolveandtransformintoconductivewaterfilmsolutions.Ⅱ.WaterWashingVehicleTheaccumulateddirtonthesurfaceoftheinsulatorscontinuestoabsorbmoistureinharshweatherconditions,leadingtoanincreasingleakagecurrent.Thiscancausepollutionflashoversoftheinsulatorsundernormaloperatingvoltage,resultinginwidespreadandprolongedpowerfailuresthatposeaseriousthreattorailwaytransportationsafety.Currently,themainmethodusedindomesticelectrifiedrailwaypowersupplysectionstocleaninsulatorsismanualwipingduringpoweroutagesoftheoverheadcontactsystem.However,thismethodhasdrawbackssuchashighlaborintensity,lowefficiency,andpoorsafety.Manualwaterwashingbypersonnelalsoinvolvesaheavyworkloadandhighsafetyrisks.Ⅱ.WaterWashingVehicleInordertoremovetheaccumulateddirtonthesurfaceofcontactsysteminsulators,therailwaypowersupplydepartmenthasintroducedwater-washingvehiclesforinsulators.Thesevehicleseffectivelyhandlethecontaminantsontheinsulatorsoftheelectrifiedrailwayoverheadlines.Figure4-10showsanexampleofacontactsystemwaterwashingvehicle,andFigure4-11depictstheon-siteoperationofthewaterwashingvehicleforthecontactsystem.Figure4-10

OverheadContactSystemWaterWashingVehicleFigure4-11

On-siteOperationoftheOverheadContactSystemWaterWashingVehicleⅡ.WaterWashingVehicleDustcanaccumulateontheinsulatorsofthecontactsystem,causingthemtobecomedirty.Whenceramicinsulatorsareheavilysoiled,simplewashingmaynotmeetthecleanlinessstandards.Forinsulatorsthatareoutofreachontheoutersideofthelines,aclothisusedtocleanstubbornareas.Thehotwashingprocessbeginsataspeedof5kilometersperhour,targetingtheinsulatorslocated6metersabovetheground.Inthesouthernpowergrid,intelligenthot-washingoperationvehicleshavebeendeployedforon-siteoperations.Figure4-12showsanexampleofarobot-intelligenthot-washingoperationvehicle.Ⅱ.WaterWashingVehicleFigure4-12

Robot-intelligenthot-washingoperationvehicle03Training

Training1.Pleaseexplainthehotwashing._____________________________________________________________________________《HighVoltageEquipmentTesting》Thissectionisover.《HighVoltageEquipmentTesting》HighVoltageLiveDetection主讲人：何发武（副教授）OperatingWorksheet：TableofContents01Followme02Workshop03Training01FollowmeⅠ.OverviewofLiveDetectionStatemonitoringiswidelyusedinthepowersystem,andelectricalequipmenttestingismainlydividedintoonlinemonitoringandlivedetection.Onlinemonitoringreferstothecontinuousanduninterruptedautomaticdetectionoftheelectricalstateoftheliveoperationofelectricalequipmentthroughtestinginstrumentswhiletheequipmentisinoperation.Itcandetectpotentialequipmentfailures,especiallyinthestatusdetectionofintelligentsubstations,whereitplaysanextremelyimportantrole.Livedetectionreferstothemonitoringofequipmentstatuson-sitewithoutapoweroutage.Itisoneoftheeffectivemeasuresforreal-timeanduninterruptedmonitoringanddiscoveringequipmentdefects.High-voltagelivedetectionrealizestheall-aroundmonitoringofhigh-voltageequipmentthroughsensorsanddatatransmissiontechnologies.Ⅰ.OverviewofLiveDetectionThedifferencebetweenlivedetectionandpoweroutagedetectionliesinwhetherpoweroutagedetectionisusedtoconfirmtheelectricalperformanceoftheequipment.poweroutagedetectionisalsocalledpreventivetestingofpowerequipment.Theobjectsoflivedetectioninclude:transmissionline,transformer,circuitbreaker,disconnectswitch,instrumenttransformer,bushing,lightningarrester,powercapacitor,GIS,reactor,powercable,andothermajorprimaryequipment,asshowninFigure4-13.Itcandetecttheproblemsofprimaryelectricalequipmentintheoperationstate,includingpartialdischarge,overheatingfaults,gasleakagefaults,etc.,toavoidmajoraccidents.Ⅰ.OverviewofLiveDetectionThesignificanceoflivedetectionistodetectthehiddendefectsthatmayexistinequipmentduringlong-termoperationwhiletheequipmentisrunning,whichcanbetimelyidentified,treatedaccordingtothelevelandtypeoffaults,andflexiblyarrangemaintenancecycles,reducepoweroutages,andimproveequipmentreliability.Figure4-13

CapacitorandreactorwithcompensationfunctionintractionnetworkⅡ.ThebasicmethodoflivedetectionThecurrentlivedetectiontechnologymainlyincludesthetransformer,GISandSF6circuitbreakerpartialdischargetest,transformeroilchromatography,capacitiveequipmentcapacityanddielectriclosschargedtest,zincoxidearresterleakagecurrent,ultrasonicdetection,ultravioletacousticimaging,infraredimagingdetectionmethodandsoon.Ⅱ.Thebasicmethodoflivedetection1.UltrasonicMethodWhentherearegaps,cracks,delaminations,interlayers,andotherdefectsinthemetalofelectricalequipmentsuchastransformers,high-voltageswitchgear,GIS,etc.,ultrasonicwavespropagatetotheinterfacebetweenthemetalandthedefect,resultinginpartialorcompletereflection.Theseultrasonicwavescannotbeheardbyhumans.Ultrasonictestingisamethodthatutilizesinstrumentstoreceiveultrasonicsignalsthatundergorefractionandreflectionattheinterfaceofinsulatingmaterials.Afterconversionandprocessingbyelectroniccircuits,itcandetectdefectssuchascracksandfracturesintheinsulatingmaterials.Thismethodhasthefunctionofrelativelylocatingfaults,andthechangesinwaveformcharacteristicscorrespondtothedepth,position,andsizeofthedefects.Ⅱ.ThebasicmethodoflivedetectionTheultrasonicmethodcandetectinternalfaultsinequipmentbyemittingandreceivingultrasonicsignals.Itcanalsodetectequipmentfaultsbyonlyreceivingultrasonicandelectromagneticwaveinformationemittedduringlocalizeddischargefaultsinsidetheequipment.Thefrequencyofultrasonicwavesisintherangeof20to100kHz.TheresultsaredisplayedindB(mV)values,curves,orimages,providingfunctionssuchasfaultidentificationandlocalization.Acoustic-opticmeasurementcombinesacousticmeasurementandfiberopticmeasurement.Whenpartialdischargeoccursinsideatransformer,itgeneratesultrasonicwavesthatexertpressureontheinstalledopticalfibersinsidethetransformer,causingdeformation.Thisleadstochangesinthelengthoftheopticalfibersandtheirrefractiveindex.Bydemodulatingthemodulatedwaveform,thesourceanddischargelocationoftheultrasonicwavescanbedetectedusingademodulator,providingaccuratetechnicalsupportformaintenance.Ⅱ.Thebasicmethodoflivedetection2.InfraredandultravioletimagingmethodThermalfaultsinpowerequipmentcanbedividedintoexternalthermalfaultsandinternalthermalfaults.Externalthermalfaultsincludeheatingcausedbyresistancechangesatwireconnections,connectors,etc.Internalthermalfaultsincludeunevendistributionofthermalelectricfieldscausedbyheatingatcontactconnectionpointsofsolid,liquid,andgasdielectricsinsidetheequipment.Ⅱ.ThebasicmethodoflivedetectionInfraredimagingisanon-contactdetectiontechniquethatallowsthevisualizationofdefectsthatarenotvisibletothenakedeye.Itcanprovideclearvisualimagesofthesedefects,enablingreal-timeandonlinemonitoringanddiagnosisofmostelectricalequipmentfaults.Inhigh-voltagemeasurementscenarios,infraredimagingisparticularlysensitivetodefectssuchasresistancelosses,corelosses,dielectriclosses,temperaturedifferencescausedbyunevenvoltagedistribution,andtemperaturedifferencescausedbyoil-immersedequipmentwithoildeficiency.Ⅱ.ThebasicmethodoflivedetectionTheprincipleoftheinfraredimagingmethodisthatthetemperaturefieldofdifferentpartsofhighvoltageelectricalequipmentinoperationcanbejudgedaccuratelybyusingtheinfraredthermalimagingmethodanddifferentcolorstodistinguishanddisplaywhetherthereistoohighlocaltemperatureonthesurfaceandinsideofpowerequipment.Todeterminewhethertheequipmenthasinsulationdefectssuchasdielectriclossorresistanceloss,itisparticularlysensitivetoearlyfaultdefectsandtheinsulationstatusofelectricalequipment.Thedisadvantageisthatduetothesmallinfraredpenetrationability,therearesomelimitations,mostofthenon-conductivematerialpenetrationthicknessislessthan1

mm.Therefore,infraredrayscanonlydetectthecharacteristicthermalelectricfielddistributionformedonthesurfaceoftheequipment,andcannotdetecttheinternaloperationstatefromtheoutsideoftheequipment.Ⅱ.ThebasicmethodoflivedetectionThecommonfaultsofhighvoltageequipmentdetectedbyinfraredimagingmethodareasshowninTable4-4.Table4-4

CommonFaultsDetectedbyInfraredImaginginHigh-VoltageEquipmentⅡ.ThebasicmethodoflivedetectionUltravioletimagingmethodismainlybasedonthetheoryofcoronadischarge.Whenhigh-voltageequipmentexperiencescoronadischarge,itemitsultravioletradiation.Afterbeingreceivedandprocessedbyanultravioletcamera,theimageoverlapswithvisiblelightimagesandisdisplayedonthescreen.Thisallowsfordirectobservationofsurfacedischargeofhigh-voltageequipment,determiningthelocation,shape,andintensityofcoronadischarge.Therefore,itcandetectinsulationdefectssuchasequipmentdamage,dirt,partialdischargecausedbycarbonization,erosiondamage,andinsulationdegradation,accuratelydeterminingthehealthconditionoftheequipment.Ⅱ.ThebasicmethodoflivedetectionThewavelengthofinfraredisintherangeof8–14m,whilethewavelengthrangeofultravioletisintherangeof40–400

nm.Thedifferencebetweenultravioletandinfraredistheirwavelength.Duetotheabilitytooperateindaylight(“day-blindband”),ultravioletimagingremainsstableandclearevenunderbrightsunlight.Itissuitablefordetectingthelocationandintensityofcoronadischarge,arcs,andsurfacepartialdischargecausedbycracks,dirt,surfacedamage,andloosenessinpowerequipment.Itisparticularlyeffectiveindetectingcoronadischargelocationsininsulators,wireconnections,equipotentialrings,andotherpowerequipmentinoverheadlinesandhigh-voltagesubstations.Duringmeasurement,attentionshouldbepaidtotheinfluenceoftemperature,humidity,airpressure,windspeed,fieldofviewangle,detectiondistance,instrumentgain,andotherfactorsontheaccuracyofcoronadischargedetectiontoreducemeasurementerrors.Ⅱ.Thebasicmethodoflivedetection3.LeakagecurrentoflightningarresterCurrently,non-gappedzincoxidelightningarresters(MetalOxideArrester,MOA)aremainlyusedinsubstations,anddampnessandagingarethemaincausesoflightningarresterfailures.Undernormaloperatingvoltage,thecurrentpassingthroughthelightningarresterisverysmall,rangingfromtenstohundredsofmicroamps(A),whichiscalledACleakagecurrentunderoperatingvoltage,alsoknownastotalcurrent.Undernormalcircumstances,thecapacitivecomponentaccountsforthemajorityofthetotalcurrent,whiletheresistivecomponentaccountsforabout10%to20%ofthetotalcurrent.Whenthelightningarresteragesorgetsdamp,itsresistivecurrentgraduallyincreases,andtheproportionofresistivecurrentinthetotalcurrentalsoincreasesaccordingly,leadingtoanincreaseinthetotalcurrent.Therefore,thischaracteristiccanbeusedtojudgetheoperatingstateofmetaloxide.Ⅱ.ThebasicmethodoflivedetectionTheincreaseinresistivecurrentreflectsthedefectsofthelightningarresterwhenitisseverelydamp,aged,orhasseriousinsulationdegradation.Bymonitoringthetotalcurrentorresistivecurrentofthelightningarresterduringoperationandcomparingtheobtaineddatawiththefactoryandhistoricaldata,insulationdefectsofthelightningarrestercanbediscovered.Inthefield,thethirdharmoniccurrentmethodisusedtoobtainthetotalcurrentfromthelightningarrestergroundingline,andthethirdharmonicisobtainedthroughathirdharmonicbandpassfilter.Bydetectingthechangesinharmoniccurrent,theagingstateofthemetaloxidelightningarrestercanbedetermined.Ⅱ.ThebasicmethodoflivedetectionTheinitialcurrentvalueofMOAreferstothecurrentvaluepassingthroughitmeasuredduringcommissioning.BymonitoringtheACleakagecurrentandresistivecomponentofthezincoxidelightningarresterunderoperatingvoltage,insulationdefectssuchasagingordampnesscanbedetermined.Thechangeinresistivecurrentflowingthroughthezincoxidelightningarresterunderratedoperatingvoltagedirectlyreflectsthequalityofitsinsulationperformance,withanincreaseinresistiveleakagecurrentbeingusedasajudgmentcriterion.Whenthefundamentalcomponentoftheresistivecurrentincreasessignificantlyandthecontentofharmonicsdoesnotincreasesignificantly,itgenerallyindicatesseverepollutionordampness.Whenthecontentofharmonicsintheresistivecurrentincreasessignificantlyandthefundamentalcomponentdoesnotincreasesignificantly,itgenerallyindicatesaging.Ⅱ.ThebasicmethodoflivedetectionThemainmethodsofMOAonlinemonitoringareshowninTable4-5.Table4-5

MainmethodsforonlinemonitoringofMOAⅡ.ThebasicmethodoflivedetectionMeasurementsaretakenunderoperatingvoltagetoassessthefullcurrentandresistivecurrent,reflectingtheconditionoftheMOA.Changesinthefullcurrentcanindicateseveremoistureingress,poorinternalcomponentcontacts,andsignificantvalveaging.However,changesinresistivecurrentaremoresensitivetoearly-stagevalveaging.Forexample,whenthepeakresistivecurrentincreasesfrom50Ato250A,theincreaseinoverallcurrentmayonlybeafewpercentagepoints.Ⅱ.ThebasicmethodoflivedetectionTomeasurethefullcurrent,acontinuousonlinemonitoringdeviceisconnectedinseriesbetweenthebottomofthelightningarresterandthegroundtomonitorthefullcurrent.Whenmeasuringtheresistivecurrent,thestabilityofthevalveplateofthelightningarrestermainlyreliesonmonitoringtheresistivecurrent.Theresistivecurrentismoresensitivetoearly-stagevalveagingandmoistureingress.Sincethecurrentvaluesofthearresterunderoperatingvoltagearesmall(intheArange),strictrequirementsareplacedonthesensor.Whenselectingaleakagecurrentsensorforthearrester,highsensitivityandgoodstabilitysensorsarechosen,takingintoaccounttheeffectsofinterphaseinterferencewhilemonitoringtheresistivecurrent.Duringmeasurements,attentionshouldbegiventoweatherconditions,voltagefluctuations,wiringmethods,electromagneticinterference,andstraycurrents,amongotherfactorsthatmayaffecttheaccuracyofthemeasurements.Ⅱ.ThebasicmethodoflivedetectionTheinfluenceofhumiditycancauseanincreaseintheexternalinsulationleakagecurrentofthearrester,leadingtosignificantchangesintheonlinemeasurementvalues.Humidityisalsoessenti