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1、AWaveletBasedApproachforFastDetectionofInternalFaultinPowerTransformersThepowertransformerisoneofthemostexpensiveelementsofpowersystemanditsprotectionisanessentialpartoftheoverallsystemprotectionstrategy.Thedifferentialprotectionprovidesthebestprotectionforpowert

2、ransformer.Itsoperationprincipleisbasedonthispointthatthedifferentialcurrentduringaninternalfaultishigherthannormalcondition.But,alargetransientcurrent(inrushcurrent)cancausemal-operationofdifferentialrelays.Then,studiesfortheimprovementofthetransformerprotection

3、havefocusedondiscriminationbetweeninternalshortcircuitfaultsandinrushcurrentsintransformers.Themagnetizinginrushcurrenthasalargesecondorderharmoniccomponentincomparisontointernalfaults.Therefore,sometransformerprotectionsystemsaredesignedtohaltoperatingduringthei

4、nrushcurrentbysensingthislargesecondorderharmonic.Thesecondharmoniccomponentinthemagnetizinginrushcurrentstendtoberelativelysmallinmodernlargepowertransformersbecauseofimprovementsinthepowertransformercorematerials.Also,ithasbeenseenthatthefaultcurrentcancontainh

5、ighersecondorderharmonicsthantheinrushcurrentduetononlinearfaultresistance,CTsaturation.thedistributedcapacitanceinthetransmissionline,whichtransformerisconnectedto,orduetotheuseofextrahighvoltageundergroundcables.Variousmethodshavebeensuggestedforovercomingthisp

6、rotectionsystemmal-operation.Thispaperpresentsawaveletbasedmethodfordiscriminationamonginrushcurrent,internalshortcircuit,externalshortcircuitandenergizinganditisnotaffectedbyCTsaturationanditisabletodetectinternalfaultswhiletransformerenergization.UnlikeArtifici

7、alNeuralNetworkandFuzzylogicbasedalgorithms.Thisapproachisnotsystemdependent.Theoperatingtimeoftheschemeislessthan10ms.TheDaubechiesmotherwaveletisusedwithasamplerateof5kHz.Then,thedifferentialcurrentsofthethreephasesaredecomposedintotwodetailsandonlythesecondlev

8、elwillbeconsideredbyusingdb5motherwavelet.DiscreteWaveletTransformThewavelettransformisapowerfultooltoextractinformationfromthenon-stationarysignalssimultaneou