高電壓設備測試（High Voltage Equipment Testing）（英文版） 課件 Worksheet 5 Partial Discharge Test

《HighVoltageEquipmentTesting》PartialDischargeTest主講人：何發(fā)武（副教授）OperatingWorksheet：

OperatingWorksheet：

TableofContents01Followme02Workshop03Training01FollowmeⅠ.CausesofPartialDischargeElectricalequipmentusedinthepowergrid,suchastransformer,instrumenttransformer,reactor,GISmotor,cable,andcapacitor,aredesignedtowithstandspecificinsulationvoltagelevelscorrespondingtotheiroperatingvoltages.Undernormalconditions,theirinsulationperformancecanwithstandtheoperatingvoltage.Duetopoorinsulationmanufacturingprocesses,theremaybedefectssuchasbubbles,impurities,cracks,orinsulationdampnessandagingafterlong-termoperation.Suchflawedinsulationispronetoexhibitperiodicpartialdischargeswhensubjectedtohigh-voltagealternatingelectricfields.Ⅰ.CausesofPartialDischargeAlthoughtheenergyreleasedduringpartialdischargesissmallanddoesnotimmediatelyaffecttheinsulationstrengthoftheelectricalequipment,itcangraduallydegradetheinsulationperformance.Eventually,thisdegradationcanleadtoinsulationbreakdown,significantlyimpactingthesafeoperationandreliabilityofthepowergrid.Topreventequipmentfailures,itisessentialtoconductregularpartialdischargedetectiononelectricalequipment.Thishelpsidentifypotentialcableequipmentrisks,evaluatetheoverallhealthofcables,andmitigatetheoccurrenceofequipmentmalfunctions,asshowninFigure2-7.Ⅰ.CausesofPartialDischargePartialdischargeservesasanearlywarningsignforimpendingfaultsinelectricalequipment,suchastransformers.Duringtheinitialstage,partialdischargestypicallyhavelowintensityandprogressslowly.Beforecompleteinsulationbreakdownoccurs,partialdischargescanpersistforseveralmonthsorevenyears.Detectingpartialdischargespromptlyallowsfortimelyintervention,thusminimizingtheriskofseriousaccidents.Figure2-28illustratestheeffectsanddetectionmethodsofpartialdischargeinpowerequipment.Ⅰ.CausesofPartialDischargeFigure2-27

ProcessfromPartialDischargetoBreakdownFigure2-28

EffectsanddetectionmethodsofpartialdischargeⅠ.CausesofPartialDischargePartialdischargereferstothephenomenonofnon-penetratingdischargebetweenelectrodesinalocalpositionduringtheoperationofhigh-voltageelectricalequipment,whichdoesnotcausecompleteinsulationbreakdown.Partialdischargeincludesthreedischargeforms,namelyinternaldischarge(insidethedielectric),surfacedischarge(onthesurfaceofthedielectric),andcoronadischarge(atthetipoftheelectrode).Long-termoccurrenceofpartialdischargeunderoperatingvoltagecaneventuallyleadtoinsulationaccidentsinequipmentduetothecumulativeeffects.Partialdischargeisoneofthemaintenancemethodsforpreventingelectricalequipmentfailures,andthereforeneworoperatingequipmentshouldalsobetestedregularlyasrequired.Figure2-29,2-30showsGISultra-highfrequencypartialdischargelivedetection.Ⅰ.CausesofPartialDischargeFigure2-29

GISFigure2-30

GISultra-highfrequencypartialdischargelivedetectionⅠ.CausesofPartialDischargeTherearemainlytwomethodsforon-sitepartialdischargetesting:offlinepartialdischargewithstandvoltagetestandonlinepartialdischargelivetest.Theofflinepartialdischargewithstandvoltagetestisaimedat220

kVmaintransformers,GIS,etc.Itappliesanon-partialdischargetesttransformerwith1.1timesthepowerfrequencywithstandvoltagetest.Non-partialdischargetesttransformersaretransformerswithoutpartialdischarge.Currently,therearetwotypesofnon-partialdischargetransformers,oneisaninflatabletesttransformer,andtheotherisanoil-immersedtesttransformer.Itisdifficulttomakeothertesttransformersintonon-partialdischargetransformers.Ⅰ.CausesofPartialDischargeThehigh-voltageleadofthewithstandvoltageequipmentshouldbeequippedwithacorrugatedpipe;theoutdoorterminalsofthetestphaseandnon-testphaseofthewithstandvoltagecableshouldbeequippedwithanequalizingring,andthenon-testphaseterminalshouldbegrounded.Theofflinepartialdischargetestisusedtocheckwhethertheelectricalequipmentstructureisreasonable,thelevelofcraftsmanshipisgoodorbad,andinternalinsulationdefects,includinglocalexcessiveelectricfieldstrengthinsidetheinsulation,sharpcornersonmetalcomponents,impuritiesmixedintheinsulation,internalmetalgrounding,poorelectricalconnectionbetweenconductivemedia,andotherlocaldefects.Ⅰ.CausesofPartialDischargeTransformerpartialdischargeisusuallycarriedoutafterdestructivetesting,anditisconductedforfaultsfoundon-siteintransformersof220

kVandabove,combinedwithDCresistancemeasurement,inducedwithstandvoltagetest,transformercharacteristictest,andothercomprehensiveanalysistodetermineitsinsulationstatus,inordertodiscoverinsulationdefectssuchasmaterialsormanufacturingprocesses.Onlinepartialdischargelivetestingistoinstalldetectioninstrumentson-sitetodetectpossiblepartialdischargeinelectricalequipmentsuchastransformers,high-voltageswitchgear,GIS,cables,etc.underoperatingvoltage.Ⅱ.PrincipleofPartialDischargeDetectionThefollowingmainlyintroduceson-siteonlinepartialdischargedetection.Themainstreammethodsforonlinepartialdischargedetectionareultra-highfrequency(UHF)andacousticemission(AE)detectiontechnology.Aspartialdischargeisakindofpulsewave,itwillproduceaseriesofphysicalphenomenaandchemicalchangessuchaslight,sound,electricalandmechanicalvibrationsintheinteriorandsurroundingspaceoftheelectricalequipment.Bydetectingthesechanges,theinsulationstateinsidetheelectricalequipmentcanbemonitored.Ⅱ.PrincipleofPartialDischargeDetectionThefrequencybandofUHFdetectionisusually300

MHzto3,000

MHz.UHFpartialdischargedetectioncandetectsuspendeddischarge,coronadischarge,freeparticledischarge,internalinsulationdischargeinequipment,etc.Duringpartialdischarge,alargeandsteeppulsecurrentisgeneratedduetotheneutralizationofpositiveandnegativecharges,whichexciteselectromagneticwavesuptoseveralGHz.ThepartialdischargeisdetectedbyreceivingtheUHFelectromagneticwavesduringthepartialdischargeprocessthroughanantennasensor.Thetwofrequenciesofpartialdischarge,namely,radiofrequencyinterference(RFI)andacousticemission(AE),areshowninFigure2-31.Ⅱ.PrincipleofPartialDischargeDetectionFigure2-31

SchematicDiagramofTwoFrequencies,RadioFrequencyinterference(RFI)and

acousticemission

(AE),forpartialdischargedetectionⅡ.PrincipleofPartialDischargeDetectionTheadvantageofUHFdetectionisitshighsensitivityandstrongresistancetolow-frequencycoronainterference.Itcanusehigh-bandwidthandhigh-sampling-rateoscilloscopestoachievetimedelaypositioningofdischargesources,thusachievingpreciselocalization.However,itsdisadvantagesarethatitissusceptibletointerferencefromUHFsignalsintheenvironmentandtheshieldingeffectofmetal.Duringonlinepartialdischargeinspection,thedetectionpositionsaregenerallyselectedineasy-to-dischargelocationsinsidetheGIS,suchascircuitbreakers,lowerpartsofhigh-voltagebushings,orbusbargaps.Ⅱ.PrincipleofPartialDischargeDetectionSincetheprincipleofUHFdetectionforpartialdischargedetectionistomeasurethehigh-frequencycurrentpulsesgeneratedbypartialdischargeintheinsulationstructureofthetestspecimenunderacertainvoltage,itisnecessarytoeliminatehigh-frequencypulsesignalscausedbyenvironmentalhightemperature,on-siteinterference,largeequipmentvibration,personnelmovement,mobilephones,engines,andotherhigh-frequencysignalsduringactualtesting.Otherwise,itwilldecreasethedetectionsensitivityandeasilycausemisjudgment.On-sitedetectionshouldbestrictlycarriedoutaccordingtoregulationsandoperatinginstructions,followingthedetectionprocess,ensuringcompletedetectionofimportantareas,preventingmissed,insufficient,orerroneousdetection.Datacollectionandanalysisshouldbecompletedon-site,combinedwithreasonableanalysisofthedetectionindicators.AsshowninFigure2-32.Ⅱ.PrincipleofPartialDischargeDetectionFigure2-32HandheldPartialDischargeInspectionInstrumentⅡ.PrincipleofPartialDischargeDetectionThehandheldpartialdischargeinspectioninstrumentintegratestwomodesofpartialdischargedetection,radiofrequencyinterference(RFI)andacousticemission(AE),andcanquicklycompleteinsulationdefectdetectionandlocalizationofvariouselectricalequipmentintheentiresubstation,includingGIS,transformer,switchgear,andcabletermination.AsshowninFigure2-33.Figure2-33

TypeandseverityofpartialdischargeintransformersidentifiedbyUHFdetectionⅡ.PrincipleofPartialDischargeDetectionTheprincipleofultrasonicdetectionforpartialdischargeissimilartoUHFdetection.WhenpartialdischargeoccursinsideelectricalequipmentsuchasGIS,itgeneratessteepcurrentpulsesthatcauseinstantaneousexpansionofSF6,resultinginanexplosiveeffect.Afterthedischarge,SF6returnstoitsoriginalvolume.Thevolumechangescausedbytheexpansionandcontractionoftheinsulationduringpartialdischargecreateultrasonicwaves.Ultrasonicwaveshaveafrequencyabove20

kHz.Theypropagateintheformofsphericalwaveswiththepartialdischargepoint(source)asthecenter.Byusingsensorswithintherangeof20

kHzto100

kHzattachedtothemetalcasingofGIS,theultrasoundsignalsaredetected,enablingthelocalizationofpartialdischargeanddetectionofvibration-relateddefects(mechanicalvibrationandhysteresisvibration)aswellaspartialdischarge-relateddefects(tipdischarge,freemetalparticledischarge,suspendedpotentialdischarge).Ⅱ.PrincipleofPartialDischargeDetectionTheUHFRFImodedetectionprocessconsistsoffoursteps:frequencyscanningforfrequencydomainanalysis,timedomainanalysistodeterminethepresenceofpartialdischarge,confirmationofpartialdischargetype,andlocalizationofpartialdischargesourcethroughfrequencydomainanalysisorpowermeter.Theultrasonicmodedetectionprocessconsistsofthreesteps:detectingpartialdischargeactivitythroughbargraphmode,distinguishingpartialdischargetypesthroughphasemode,andidentifyingfreemetalparticledischargephenomenathroughpulsemode.02WorkshopⅠ.PartialDischargeOperationProcessTable2-9

OperationalstepsforpartialdischargetestingⅠ.PartialDischargeOperationProcessPartialdischargetesterisshowninFigure2-34.(a)

Frontviewofmainunit(b)SideviewofmainunitⅠ.PartialDischargeOperationProcessPartialdischargetesterisshowninFigure2-34.(c)Bottomviewofmainframe(d)TopviewofmainframeFigure2-34

PartialdischargetesterⅡ.ProcessofPartialDischargeTurnontheinstrumentandensurethattheTEVsensorisawayfromthemetalelectrodetoavoidaffectingtheself-testfunction.SelecttheTEVmode.Whilemeasuring,ensurethattheTEVprobeisincontactwiththemetalelectrodetobemeasuredandkeptvertical,asshowninFigure2-35.Figure2-35

ProcessofpartialdischargeⅡ.ProcessofPartialDischargeThemeasurementfocusisonthecentralpositionsofcableboxes,currenttransformerchambers,busbarchambers,circuitbreakers,andpotentialtransformersineachpaneloftheswitchgear.Duringthemeasurement,recordthefirstsetofreadingsateachposition.Ifthemeasuredamplitudeis10dBhigherthanthebackgroundinterferencelevelandtheamplitudeitselfisgreaterthan20dB,threeconsecutivesetsofreadingsshouldberecorded.Ⅱ.ProcessofPartialDischargeWhenconductingultrasoundmeasurements,firstturnontheinstrumentandselecttheultrasoundmodefromthemenu.Inserttheprovidedheadphonesandadjustthevolume.Thereadingswillcontinuouslyupdateonthedisplayscreen.Startbymeasuringthebackgroundnoiseandrecordit.Ifthereadingsbecometoohigh,reducethegain.Toinspecttheswitchgear,pointtheultrasoundsensortowardstheswitchgear,especiallyattheportsofcircuitbreakers,inflatablecableboxes,potentialtransformers,andairgapsinbusbarchambers.Dischargescanbeidentifiedbythehissingsoundemittedthroughtheheadphones,similartothesoundoffryingpans.Theultrasounddeviceisequippedwithalaseraimingfunction,all