电气专业英文文献

AnExpertSystemforTransformerFaultDiagnosisUsingDissolvedGasAnalysis1.INTRODUCTIONThepowertransformerisamajorapparatusinapowersystem,anditscorrectfunctioningitsvitaltominimizesystemoutages,manydeviceshaveevolvedtomonitortheserviceabilityofpowertransformers.Thesedevices,suchas,Buchholzrelaysordifferentialrelays,respondonlytoaseverepowerfailurerequiringimmediateremovalofthetransformerfromservice,inwhichcase,outagesareinevitable.Thus,preventivetechniquesforearlydetectionfaultstoavoidoutageswouldbevaluable.Inthisway,analysisofthemixtureofthefaultygasesdissolvedininsulationoilofpowertransformerhasreceivedworldwiderecognitionasaneffectivemethodforthedetectionofoncipientfaults.ManyresearchersandelectricalutilitieshavereportedontheirexperienceanddevelopedinterpretativecriteriaonthebasisofDGA.However,criteriatendtovaryfromutilitytoutility.Therefore,transformerdiagnosisisstillintheheuristicstage.Forthisreason,knowledge-basedprogrammingisasuitableapproachtoimplementinsuchadiagnosticproblem.BasedontheinterpretationofDGA,aprototypeofanexpertsystemfordiagnosisofsuspectedtransformerfaultsandtheirmaintenanceproceduresisproposed.Thesignificantsourceinthisknowledgebaseisthegasratiomethod.Somelimitationsofthisapproachareovercomebyincorporatingthediagnosticprocedureandthesyntheticexpertisemethod.Furthermore,databasesadoptedfromTPC'Sgasrecordsoftransformersareincorporatedintotheexpertsystemtoincreasethepracticalperformance.Uncertaintyofdiagnosisismanagedbyusingfuzzysetconcepts.Thisexpertsystemisconstructedwithrulebasedknowledgerepresentation,sinceitcanbeexpressedbyexperts.Theexpertsystembuildingtool,knowledgeEngineeringSystem(KES),isusedinthedevelopmentoftheknowledgesystembecause,ithasexcellentman-machineinterfacethatprovidessuggestions.Moreover,itsinferencestrategyissimilartotheMYCIN.Afamousrule-basedexpertsystemusedformedicaldiagnosis.Theuncertaintyofhumanqualitativediagnosticexpertise,e.g.,keygasanalysis,andanotherquantitativeimprecision,suchas,normsthresholdandgasratioboundariesetc.,aresmoothedbyappropriatefuzzymodels.Withtheresultsofsuchimplementation,differentcertaintyfactorswillbeassignedtothecorrespondingexpertisevariables.Bothevent-driven(forwardchaining)andgoal-driven(backwardchaining)inferencesareusedintheinferenceenginetoimprovetheinferenceefficiency.Todemonstratethefeasibilityoftheproposedexpertsystem,aroundhundredsofTPChistoricalgasrecordshavebeentested.Itisfoundthatmoreappropriatefaultytypesandmaintenancesuggestionscansupportthemaintenancepersonalstoincreasetheperformanceoftransformerdiagnosis.2.DEVELOPMENTOFDIAGNOSISANDINTERPRETATIONLikemanydiagnosticproblems,diagnosisofoil-immersedpowertransformerisaskilledtask.Atransformermayfunctionwellexternallywithmonitors,whilesomeincipientdeteriorationmayoccurinternallytocauseafatalprobleminthelatterdevelopment.AccordingtoaJapaneseexperience,nearly80%ofallfaultsresultfromincipientdeteriorations.Therefore,faultsshouldbeidentifiedandavoidedattheearliestpossiblestagebysomepredictivemaintenancetechnique.DGAisoneofthemostpopulartechniquesforthisproblem.Faultgasesintransformersaregenerallyproducedbyoildegradationandotherinsulatingmaterial,e.g.,celluloseandpaper.Theoretically,ifanincipientoractivefaultispresent,theindividualdissolvedgasconcentration,gassingrate,totalcombustiblegas(TCG)andcellulosedegradationareallsignificantlyincreased.Byusinggaschromatographytoanalysethegasdissolvedinatransformer'sinsulatingoil,itbecomesfeasibletojudgetheincipientfaulttypes.Thisstudyisconcernedwiththefollowingrepresentativecombustiblegases;hydrogen(H2),methane(C2H2),ethane(C2H6),ethylene(C2H2)andcarbonmonoxide(C0).ManyinterpretativemethodsbasedonDGAtothenatureofincipientdeteriorationhavebeenreported.Evenundernormaltransformeroperationalconditions,someofthesegasesmaybeformedinside.Thus,itisnecessarytobuildconcentrationnormsfromasufficientlylargesamplingtoassessthestatistics.TPCinvestigatedgasdatafrompowertransformerstoconstructitscriteria.Thedevelopedknowledgebaseinthispaperispartiallybasedonthesedata.Onthehand,Dornerburgdevelopedamethodtojudgedifferentfaultsbyratingpairsofconcentrationsofgases,e.g.,CH/H,GH/C3H4,withapproximatelyequalsolubilityandfusioncoefficients.Rogersestablishedmarecomprehensiveratiocodestointerpretthethermalfaulttypeswiththeoreticalthermodynamicassessments.Thisgasratiomethodwaspromisingbecauseiteliminatedtheeffectofoilvolumeandsimplifiedthechoiceofunits.Moreover,itsystematicallyclassifiedthediagnosisexpertiseinatableform.Table1displaystheratiomethodasproposedbyRogers.Thedissolvedgasmayvarywiththenatureandseverityofdifferentfaults.Byanalyzingtheenergydensityoffaults,it'spossibletodistinguishthreebasicfaultprocesses:overheating(pyrolysis),corona(partialdischatge)andarcingdischarge.Coronaandarcingarisefromelectricalfaults,whileoverheatingisathermalfault.Bothtypesoffaultsmyleadtodeterioration,whiledamagefromoverheatingistypicallylessthanthatfromelectricalstress.Infect,differentgastrendsleadtodifferentfaultytypes,thekeygasmethodisidentified.Forexample,largeamountsofCHandHareprodu