Predetermination of lateral length to prevent overvoltage problems due to open conductors in three-phase systems

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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-