(4.2.1)-17分裂變壓器及運行

ElectricalEquipmentandOperation12ContentsIntroductionUsedinFactoryTransformersMainTransformerUsedintheWiringoftheExpansionUnitofSmallandMedium-sizedUnits3IntroductionThesplitoperationonthelow-voltagesideoftwotransformersoperatinginparallelcanachievetheeffectoflimitingtheshort-circuitcurrent.So,canweusetwotransformerswhosereactancevaluesareidenticaltothatofatransformer,andthenconductsplitoperationontheirlow-voltageside?Obviouslythisworks.However,thecost(yuan/kVA)perunitcapacityofthetransformerincreasesasthecapacityofasingleunitdecreases.Usingtwosmaller-capacitytransformersinsteadofonelarge-capacitytransformerwillincreasetheinvestmentofthetransformeritself.Inordertosolvethiscontradiction,wegenerallyadoptsplittransformer.SplitTransformerSplitTransformerThelow-voltagewindingiscomposedofsplitwindingsofequalcapacitysplitintotwobranches.Twolow-voltagewindingsareinidenticalrelationtothehigh-voltagewinding,resultinginX2’=X2”X1≈0Thefundamentaldifferencefromthegeneralthree-windingtransformer.Theimpedancestructureisequivalenttothesplitoperationoftwoparallelsmalltransformersonthelow-voltageside.SchematicdiagramofsplittransformerstructureEquivalentcircuitdiagramofsplittransformersHighpressureLowpressureLowpressure5UsedinFactoryTransformersDuringnormaloperation:Whenashortcircuitoccursinaloadbranch(suchas2’)Thentheimpedancethatlimitstheshort-circuitcurrentflowinginto2’is:Theshort-circuitimpedancewhenashort-circuitoccursistwicethatduringnormaloperation.6UsedinFactoryTransformersAlthoughthesplittransformerisabout20%moreexpensivethantheordinaryone,ithasverygoodcurrentlimitingeffect.Itisespeciallyusedforthewiringoflargeunits,forexample,double-shaftturbo-generatorsetsorgeneratorswithdualwindings.Itisveryconvenientforthewiring.Nowadays,generally,manymedium-sizedpowerplantsusesplittransformers.Themainreasonisthataftersplittransformersareused,iftheshort-circuitcurrentcanbelimited,thereisnoneedtoinstallcurrent-limitingreactors.PlantstandbypowersupplyInterconnectingtransformer7MainTransformerUsedintheWiringoftheExpansionUnitofSmallandMedium-sizedUnitsDuringnormaloperation:Whenashortcircuitoccurs(e.g.2’):Ifanothergeneratorstopsandfailstowork,thesystemwillprovideshort-circuitcurrent.Theimpedancelimitingthisshort-circuitcurrentis:Ifthesystemfailstoprovideshort-circuitcurrent,theshort-circuitcurrentwillbeprovidedbyanothergenerator.Theimpedancelimitingthisshort-circuitcurrentis:Whenthesystemandanothergeneratorprovideshort-circuitcurrentatthesametime,X2’becomestwocurrentchannels,increasingtheimpedancesX1-2’andx2-2”thatlimittheshort-circuitcurrent.8MainwiringdiagramofahydropowerplantMainTransformerUsedintheWiringoftheExpansionUnitofSmallandMedium-sizedUnitsFactorystandby9Throughimpedance:Halfthroughimpedance:Splitimpedance:Splittingcoefficient:Generally,thesplittingcoefficientofsplittransformeris3.5.Generally,thelargertheKfinoperation,thebetteritsabilitytolimittheshort-circuitcurrent.Itcanbeseenthatthesplittransformerhastheadvantagesoflargereactancewhenshort-circuited,andsmallreactanceundernormalconditions.SplitTransformer101.Whatisthemainpurposeofthesplittransformer?