tn—c系统、tn—s系统、tn—c—s系统

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1、TN—C系统、TN—S系统、TN—C—S系统Thetn~csystem,thetn~ssystem,thetn—c—ssystemAccordingtothecurrentnationalstandardspecificationsfordesignoflow-voltagedistribution(GB50054),thedefinitionoflow-voltagedistributionsystemcanbedividedintothreekinds,namely,TN,TT,ITthreeforms.In

2、thiscase,thefirstcapitalTindicatesthedirectgroimdingoftheneutralpointofthepowertransformer・Iindicatesthatthepowertransformerhasaneutralpoint(orahighimpedancegrounding)・ThesecondcapitalTindicatesthattheoutershelloftheelectricalequipmentisdirectlygrounded,butis

3、notconnectedtothegroundingsystemofthegrid・Nindicatesthattheoutershelloftheelectricalequipmentisconnectedtothegroundingneutrallineofthesystem・TNsystem:theneutralpointofthepowertransformerisconnectedtotheneutralline・TTsystem:theneutralgroundofthepowertransforme

4、r,theelectricequipmentcaseisprotectedtoground.ITsystem:thepowertransformerisnotgroundedinneutral(orthroughhighimpedaneegrounding),andtheelectricdevicecaseisprotectedbytheshel1.TNsystemPowertransformerneutralpointgroundingpowersystem,accordingtotheelectricaleq

5、uipmentexposedconductivepartsconnectedtothesystemofdifferentwaysandcanbedividedintothreecategories:namelyTN-Csystem,TN-Ssystem,TN-C-Ssystem.Thefollowingaredescribedrespective!y.1,TN-CsystemThecharacteristicis:theneutralgroundofthepowertransformer,theprotectio

6、nofthezeroline(PE)andtheworkingzeroline(N).,(1)itistheuseofneutralpointgroundingsystemofneutralline(zero)asafaultcurrentbackflowconductor,whenphaselinetotouchtheshelloftheelectricalequipment,electricityflowsthroughthezerolinefaultbacktothepoint,becauseofthesh

7、ortcircuitcurrentisbig,sotheovercurrentprotectorcanbeusedtocutoffthepowersupply.Thetn-csystemgenerallyUSESzero-sequencecurrentprotection;(2)TN-Csystemissuitableforthebasicbalancedthree-phaseloadsituation,ifthethree-phaseunbalancedload,theunbalancecurrentofPEN

8、line,addsomeloadequipmentcausedbyharmoniccurrentwillbeintothePEN,toneutralNcharged,andislikelytobehigherthan50v,itnotonlymakestheequipmentcasingcharged,notforpersonalsafety,butalsounablet