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1、电气工程专业英语姓名：吕海龙学号：20080345班级：08电气专业：电气工程及其自动化ElectricDevicesandSystemsAlthoughtransformershavenomovingparts,theyareessentialtoelectromechanicalenergyconversion.Theymakeitpossibletoincreaseordecreasethevoltageleverthatresultsinlowcosts,andcanbedistributedandusedsafely.Inadditio
2、n,theycanprovidematchingofimpedances,andregulatetheflowofpowerinanetwork.Whenweseeatransformeronautilitypoleallweisacylinderwithafewwiresstickingout.Thesewiresenterthetransformerthroughbushingsthatprovideisolationbetweenthewiresandthetank.Insidethetanktheseisanironcorelinking
3、coils,mostprobablymadewithcopper,andinsulated.Thesystemofinsulationisalsoassociatedwiththatofcoolingthecore/coilassembly.Oftentheinsulationispaper,andthewholeassemblymaybeimmersedininsulatingoil,usedtobothincreasethedielectricstrengthofthepaperandtotransferbeatfromthecore-coi
4、lassemblytotheouterwallsofthetanktoair.Figureshowsthecutoutofatypicaldistributiontransformer.Fewidealversionsofhumanconstructionsexist,andthetransformeroffersnoexception.Anidealtransformerisbasedonverysimpleconcepts,andalargenumberofassumptions.Thisisthetransformeronelearnsab
5、outinhighschool.Letustakeanironcorewithinfinitepermeabilityandtwocoilswoundaroundit,onewithN1andtheotherwithN2turns,asshowninfigure.Allthemagneticfluxistoremainintheiron.Weassignsotsatoneterminalofeachcoilinthefollowingfashion:ifthefluxinthecorechanges,inducingavoltageintheco
6、ils,andthedottedterminalofonecoilispositivewithrespectitsotherterminal,soisthedottedterminaloftheothercoil.Or,thecorollarytothis,currentintodottedterminalsproducesfluxinthesamedirection,Assumethatsomehowatimevaryingfluxisestablishedintheiron.Thenthefluxlinkagesineachcoilwillb
7、e.Voltageswillbeinducedinthesetwocoil.Ontheotherhand,currentsflowinginthecoilsarerelatedtothefieldintensityH.ifcurrentsflowinginthedirectionshown,i1intothedottedterminalofcoil1,andi2outofthedottedterminalofcoil2.werecognizethatthisispracticallyimpossible,butsoistheexistenceof
8、anidealtransformer.Equationsdescribethisidealtransformer,atwoportnet
