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1、Predeterminationoflaterallengthtopreventovervoltageproblemsduetoopenconductorsinthree-phasesystemsProf.S.Prusty,Ph.D.,D.I.C.,andM.Panda,M.Sc.(Eng.)Indexingterms:Transmissionanddistributionplant,Powertransmissionanddistribution,ConductorsandconductivityAbstract:Theopeningofoneo
2、rtwoconductorsinthree-phasecircuitssupplyinganungroundedtransformerproducesasteady-stateovervoltageduetoferroresonancebetweenthelateralcapacitanceandthetransformernonlinearinductance.Availablemethodsofdeterminingtheconditionsunderwhichsuchanovervoltagemayoccuraremostlybasedone
3、xperimentalstudies,andhencearelimitedinapplicationtosystemswhosedesignparametersaresimilartothoseusedinthetests.Asimpleandelegantapproach,presentedhere,revealsthatanincorrectchoiceofovervoltagelimitleadstotheselectionofanunsafelaterallength,resultinginapotentiallydangeroushigh
4、voltageacrosstheconnectedapparatusandprotectiveequipment.Generalisedmathematicalequationsaredevelopedtodeterminethesafelaterallengthasafunctionoftransformersizeforthepreventionoftheovervoltageproblemduetoopenconductorsinthree-phasesystems.Thecomputedresultsareingoodagreementwi
5、thexperimentalobservations.1IntroductionswitchorovercurrentdevicelateralTheopeningofoneortwoconductorsinathree-phasestar-ungroundedcircuitsupplyinganungroundedtransformerproducesatransformersteady-stateovervoltageduetoferroresonancebetweenthecapacitivereactanceofthecircuitsand
6、thenonlinearinductivereactanceofthetransformerundercertaincondi-tions.Thistypeofovervoltageproblemhasbeenrecog-}C0LA'jlightning*arresternisedforalongtimeandanumberofpapers[1-11]areavailableonthesubject.SincethemethodspresentedinLA
7、j/deltaconnectedpreviouspapers[1-7]ofdetermin
8、ingtheconditionforthe"/transformeroccurrenceofsuchovervoltagesasafunctionoftrans-formersizeandlaterallengtharemostlybasedonaseriesoftestsonamodejsystem,thesearelimitedinapplicationlightningarrestertosystemswhosedesignparametersaresimilartothoseusedinthetests.Inarecentpaper,St
9、aatsetal.[8]haveFig.1Equivalentcircuitrepresentationofathree-
