NewRecognitionMethodofLightningInterferenceinLongDistancevsc.docx

New Recognition Method of Lightning Interference in Long Distance vscAbstractWiththeincreaseofvoltagelevelandtransmissioncapacity,flexibleDCsystemshaveputforwardhigherrequirementsforlineprotection.Especiallyforlong-distance,large-capacityflexibleDCsystems,theprotectionofthelineplaysakeyroleinthestabilityoftheentiresystem.Lightner;Thedifferenceofforwardwavebetweentwocurrentlinemodulesisalsolarge,butitisfarsmallerthanthatoffaultlightning.Thedifferenceissimilartothelowresistancegroundshortcircuit.Thedifferencebetweenpole-to-poleshortcircuitisbetweenlowresistancegroundshortcircuitandhighresistancegroundshortcircuit.Furthercomparisonoftheimagesshowsthattheimagesofshort-circuitfaultsandinter-polefaultsarequitedifferentfromthoseofdirectlightningfaults.Intheeventofafailurecausedbyadirectstrikeoflightning,thedifferencebetweentheforwardwavesofthetwoendsofthecurrentappearsneedle-likeontheimage.Thedifferencebetweentheforwardwaveofgroundingshortcircuitandthatofinter-polefaultismoregentlethanthatofdirectlightningimage.Accordingtothecharacteristicsofforwardwavedifferencesignalsofcurrentoftwoterminalmodesincaseoffaultlightningstrike,non-faultlightningstrike,inter-electrodeshortcircuitandgroundshortcircuit:Thesignalchangingabruptlyandshapedlikeaneedlewithsupremedifferentials.Thisisfaultylightningstroke.Afterfailure,thesignalmutationin2msisneedle-likeandthedifferenceisrelativelylarge,whichisnon-faultlightningstroke.Thesignalchangesslowlyandthedifferenceislessthanorclosetothenon-faultlightningstrikearevariousshort-circuitfaults,wecanuseamethodtoqualitativelydealwiththisfeature.IV.PRINCIPLEANDCRITERIONOFTHEPROTECTIONA.DetectionoftheDegreeofSignalMutationTheprotectionprincipleproposedinthispaperinvolvesthesingularitydetectionofsignalsanddetectionofthemagnitudeofsignalchanges.Thecommonlyusedmethodsincludetheearlyproposedderivationorcorrelationfunctionandvarioussignaltime-frequencyanalysismethodsproposedinrecentyears,whicharerepresentedbywavelettransformandStransform.Thewavelettransformmethodusesthewaveletmodulusmaximumtocalibratethesignalmutation,andiswidelyusedinvarioustravelingwaveprotectionmethods.Wavelettransformhasapowerfulde-noisingcapability,goodtime-frequencylocalizationperformanceandamulti-scaleanalysiscapability.Soitisverysuitableforanalyzingnon-periodicsingularsignals,suchasfaulttravelingwaves.Inthispaper,weusewavelettransformtodetectthedegreeofsignalmutation67.B.PrincipleofWaveletTransformIfacontinuoussignalf(t)isasignalwithlimitedenergy,thenthewavelettransformofthesignalf(t)basedonagivenwaveletbasisfunction(t)is:0,)()(1),(,adtttfabaWbaf(3)Where:)(1)(,abtatba(4)Where,adenotesthescalefactor,bdenotesthetranslationfactor,ba,representsfunctionsacquiredafterthewavelet2022ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.2022CICED2022PaperNo.202205280000299Page3/61820basisfunctionundergoesexpansion,contractionandtranslation,ba,denotestheconjugatefunctionofba,.Thereisaone-to-onecorrespondencebetweenwavelettransformmodulusmaximumandsignalsingularities.Theamplitudeofthewavelettransformmodulusmaximumarepositivelycorrelatedwiththeintensitiesofthesignalmutations.Theoccurrencetimesofthemodulusmaximumareconsistentwiththetimeswhenthesignalmutationsoccur.Themodulusmaximumalsohavethesamepolarityasthesignalmutations8.C.TheWaveletTransformResultsofSignalsat2msaftertheFaultOccursFig.14inter-electrodeshortcircuitoccursattheexitofthelineFig.15inter-electrodeshortcircuitoccursinthemiddleofthelineFig.16single-phaselow-resistanceearthingshortcircuitoccursattheexitofthelineFig.17single-phasehigh-resistanceearthingshortcircuitoccursattheexitofthelineFig.18single-phaselow-resistanceearthingshortcircuitoccursinthemiddleofthelineFig.19single-phasehigh-resistanceearthingshortcircuitoccursinthemiddleofthelineFig.20faultlightningstrikeoccursattheexitofthelineFig.21faultlightningstrikeoccursinthemiddleofthelineFig.22Non-faultlightningstrikeoccursattheexitofthelineFig.23Non-faultlightningstrikeoccursinthemiddleofthelineItcanbeseenfromtheaboveresultsthatwhensingle-phasegroundshort-circuitoccurs,themodulusmaximumofthewavelettransformcoefficientsarealllessthan0.1inthelengthofthe2msdatawindow;wheninter-electrodeshort-circuitoccurs,thelargestmodulusmaximumofthewavelettransformcoefficientsinthelengthofthe2msdatawindowiscloseto0.1,butmuchsmallerthan0.2;Whensubjectedtolightningstrike,themodulusmaximumofthewavelettransformcoefficientsinthelengthofthe2msdatawindowarefarlargerthan0.2,andthelargerthelightningcurrentamplitudeis,thelargerthemodulusmaximumis.SowecansetthefixedvaluesofA,BandWs(K).Where,AandBarethevaluesdeterminedaftertheactualsystemissimulated:Aisthevaluethattheshort-circuitfaultcurrentcannotexceed,thatis,theupperlimitofshort-circuitfaultcurrent;Bisthelowerlimitoflightning-strikefaultcurrent.Ws(K)isthewavelettransformcoefficientswithinthelengthofthe2msdatawindowafterafaultoccurs.WhenAkWsMAX)((5)2022ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.2022CICED2022PaperNo.202205280000299Page4/61821Wecanidentify。