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1、ECE421/599ElectricEnergySystems4–TransmissionLineParametersInstructor:KaiSunFall20141Introduction?Transmissionlines–Overheadlines–UndergroundCables(lessthan1%)?PropertiesCoronadischargeoninsulatorstringofa500kVline(source:wikipedia.org)–SeriesResistanc

2、e(strandingandskineffect)–SeriesInductance(magnetic&electricfields;fluxlinkageswithintheconductorcrosssectionandexternalfluxlinkages)–ShuntCapacitance(magnetic&electricfields;chargeanddischargeduetopotentialdifferencebetweenconductors)–ShuntConductance

3、(duetoleakagecurrentsalonginsulatorsorcoronadischargecausedbyionizationofair)?Line-to-linevoltagelevels–69kV,115kV,138kVand161kV(sub-transmission)–230kV,345kV,and500kV(EHV)–765kV(UHV)2OverheadTransmissionLinesShieldwires(groundwires)aregroundconductors

4、usedtoprotectthetransmissionlinesfromlightningstrikes(Source:wikipedia.organdEPRIdynamictutorial)3OverheadTransmissionLines?Materials–AAC(AllAluminumConductor),–AAAC(AllAluminumAlloyConductor)ACSR(7steeland24aluminumstrands)–ACSR(AluminumConductorSteel

5、Reinforced)–ACAR(AluminumConductorAlloyReinforced)–ACCC(AluminumConductorCompositeCore)?Whynotcopper?–Relativelowercostsandhigherstrength-to-weightratiosthancopper?Bundleconductors24/7ACSRandmodernACCCconductors–Preferredforhighvoltages,e.g.2-conductor

6、bundlesfor230kV,3-4for345-500kV,and6for765kV4Abundleof4conductorLineResistanceConsiderasolidroundconductorataspecifictemperature:?DCresistanceρ=conductorresistivityρlRdc=l=conductorlengthAA=conductorcross-sectionalarea?ACresistance–Currentisnotuniforml

7、ydistributedoverthecross-sectionalarea;currentdensityisgreatestatthesurface(skineffect)–2%higherthanDCresistanceat60Hz?TemperatureimpactSkineffect:circulatingeddytandtareinoCcurrentIWcancellingthe12currentflowinthecenterofT≈228foraluminumtheconductor.(

8、source:wikipedia.org)5InductanceofaSingleConductor?Inductancefornonmagneticmaterial:L=λ/I=Lint+=Lextλint//II+λext?Ampere’slawHxxμ0IxHx(Ix=I)BH=μ=xx02πxI:currentenclosedatradiusxxH:magneticfieldintensityxB:magneticfluxdensityxμ=4π×10-7H/