Conversion of Ungrounded Systems to High-Resistance Grounding Systems

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1、ConversionofUngroundedSystemstoHigh-ResistanceGroundingSystemsPeterE.Sutherland,SeniorMemberIEEEArshadMansoor,SeniorMemberIEEEEPRISolutions,Inc.942CorridorParkBlvd.Knoxville,TN37932Abstract—Aninnovativemethodisproposedwherechargingderivinganeutralpointthroughgroundingtransformers.

2、[1][2]currentcanbemeasuredandgroundingresistorssizedwithoutstagingafault.Overvoltageshavecauseddamagetoequipmentandvoltagetransformerfuseblowinganungrounded4.8kVdeltadistributionsystem.Threecausesaresuspected:single-II.OVERVOLTAGESINUNGROUNDEDSYSTEMSline-to-groundfaults,multiplere

3、strikesandferroresonance.Thefirstisthemostlikely.TheexistenceofferroresonancecanA.Structureofanungroundedsystembedeterminedbytakingrecordingsoftransientwaveforms.TheAnungroundedfeederinapowersystemmightlooklikesolutionevaluatedhereisconversiontoahigh-resistanceFigure1.Thesourcewou

4、ldbeadistributionsubstationgroundedsystemusingbanksofdistributiontransformerswithtransformerwithanungroundeddeltaorwyesecondary.broken-deltasecondaries.EvaluationofsystemparametersThree-phaseloadswouldalsobeungroundeddeltaorwyeshowsthatthegroundingresistanceshouldbeintherangeof0.5

5、to1.0timestheperphasecapacitivereactance.Thismethodwillconnected.Single-phaseloadswouldbeconnectedphasetorequirethatallequipmentinthe4.8kVdistributionsystemsbephase.Thetransformersandfeederconductorswillcontainratedforfullline-to-linevoltage.Groundfaultcurrentwillbedistributedcapa

6、citances,whichformtheunintentionallimitedtolessthan10A.Simulationofmultiplerestrikesshowsgroundingsystem(Figure2).Inthetransformer,thesearethatovervoltageswillbelimitedto2.5perunit.Properlysizedmostlyfromwindingstothegroundedcore.Incables,thesehigh-resistancegroundingcaneliminatef

7、erroresonance.aremostlyfromphaseconductorstogroundedshields.Inoverheadlines,thesearebothphasetophaseandphasetoKeywords;highresistancegrounding,ungroundedsystems,ground.ferroresonance,groundfaults.SourceI.INTRODUCTIONDistributionprimarycircuitstypicallyhaveoneofthefollowingwireconf

8、igurations:•three-wireungroundedY