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1、......ElectricDevicesandSystemsAlthoughtransformershavenomovingparts,theyareessentialtoelectromechanicalenergyconversion.Theymakeitpossibletoincreaseordecreasethevoltageleverthatresultsinlowcosts,andcanbedistributedandusedsafely.Inaddition,theycanprovidematching
2、ofimpedances,andregulatetheflowofpowerinanetwork.Whenweseeatransformeronautilitypoleallweisacylinderwithafewwiresstickingout.Thesewiresenterthetransformerthroughbushingsthatprovideisolationbetweenthewiresandthetank.Insidethetanktheseisanironcorelinkingcoils,most
3、probablymadewithcopper,andinsulated.Thesystemofinsulationisalsoassociatedwiththatofcoolingthecore/coilassembly.Oftentheinsulationispaper,andthewholeassemblymaybeimmersedininsulatingoil,usedtobothincreasethedielectricstrengthofthepaperandtotransferbeatfromthecore
4、-coilassemblytotheouterwallsofthetanktoair.Figureshowsthecutoutofatypicaldistributiontransformer.Fewidealversionsofhumanconstructionsexist,andthetransformeroffersnoexception.Anidealtransformerisbasedonverysimple专业.专注.......concepts,andalargenumberofassumptions.T
5、hisisthetransformeronelearnsaboutinhighschool.Letustakeanironcorewithinfinitepermeabilityandtwocoilswoundaroundit,onewithN1andtheotherwithN2turns,asshowninfigure.Allthemagneticfluxistoremainintheiron.Weassignsotsatoneterminalofeachcoilinthefollowingfashion:ifthe
6、fluxinthecorechanges,inducingavoltageinthecoils,andthedottedterminalofonecoilispositivewithrespectitsotherterminal,soisthedottedterminaloftheothercoil.Or,thecorollarytothis,currentintodottedterminalsproducesfluxinthesamedirection,Assumethatsomehowatimevaryingflu
7、xisestablishedintheiron.Thenthefluxlinkagesineachcoilwillbe.Voltageswillbeinducedinthesetwocoil.Ontheotherhand,currentsflowinginthecoilsarerelatedtothefieldintensityH.ifcurrentsflowinginthedirectionshown,i1intothedottedterminalofcoil1,andi2outofthedottedterminal
8、ofcoil2.werecognizethatthisispracticallyimpossible,butsoistheexistenceofanidealtransformer.专业.专注.......Equationsdescribethisidealtransformer,atwoportnetwork.Thesymbol
