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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.Inadd
2、ition,theycanprovidematchingofimpedances,andregulatetheflowofpowerinanetwork.Whenweseeatransformeronautilitypoleallweisacylinderwithafewwiresstickingout.Thesewiresenterthetransformerthroughbushingsthatprovideisolationbetweenthewiresandthetank.Insidethetanktheseisanironcor
3、elinkingcoils,mostprobablymadewithcopper,andinsulated.Thesystemofinsulationisalsoassociatedwiththatofcoolingthecore/coilassembly.Oftentheinsulationispaper,andthewholeassemblymaybeimmersedininsulatingoil,usedtobothincreasethedielectricstrengthofthepaperandtotransferbeatfro
4、mthecore-coilassemblytotheouterwallsofthetanktoair.Figureshowsthecutoutofatypicaldistributiontransformer.Fewidealversionsofhumanconstructionsexist,andthetransformeroffersnoexception.Anidealtransformerisbasedonverysimpleconcepts,andalargenumberofassumptions.Thisisthetransf
5、ormeronelearnsaboutinhighschool.Letustakeanironcorewithinfinitepermeabilityandtwocoilswoundaroundit,onewithN1andtheotherwithN2turns,asshowninfigure.Allthemagneticfluxistoremainintheiron.Weassignsotsatoneterminalofeachcoilinthefollowingfashion:ifthefluxinthecorechanges,ind
6、ucingavoltageinthecoils,andthedottedterminalofonecoilispositivewithrespectitsotherterminal,soisthedottedterminaloftheothercoil.Or,thecorollarytothis,currentintodottedterminalsproducesfluxinthesamedirection,Assumethatsomehowatimevaryingfluxisestablishedintheiron.Thentheflu
7、xlinkagesineachcoilwillbe.Voltageswillbeinducedinthesetwocoil.Ontheotherhand,currentsflowinginthecoilsarerelatedtothefieldintensityH.ifcurrentsflowinginthedirectionshown,i1intothedottedterminalofcoil1,andi2outofthedottedterminalofcoil2.werecognizethatthisispracticallyimpo
8、ssible,butsoistheexistenceofanidealtransformer.Equationsdescribethisidealtransformer,atwoportnet
