转移者教科书章变压器ntroduction节11 transformer.pptx

11-TransformersTextbookChapter23

TransformerIntroduction(Section23.1)Iron-CoreTransformers:TheIdealModel(Section23.2)ReflectedImpedance(Section23.3)TransformerRatings(Section23.4)TransformerApplications(Section23.5)

IntroductionTransformerConstructionTightlyCoupledCircuitFaraday’sLaw

IntroductionAtransformerisamagneticallycoupledcircuit,i.e.,acircuitinwhichthemagneticfieldproducedbytime-varyingcurrentinonecircuitinducesvoltageinanotherItconsistsoftwocoilswoundonacommoncore

IntroductionAlternatingcurrentinonewindingestablishesaflux,whichlinkstheotherwindingandinducesavoltageinitPowerflowsfromonecircuittotheotherviathemediumofthemagneticfield

IntroductionNoelectricalconnectionexistsbetweenthetwosides;ThepowersupplysideiscalledtheprimaryThewindingfromwhichpoweristakeniscalledthesecondaryPowercanflowineitherdirection,i.e.,primaryandsecondarycanbeexchanged

ConstructionTwobroadcategories,iron-coreandair-coreIron-coretransformersaregenerallyusedforlowfrequencyapplicationssuchaspowerandlowfrequencyapplicationsIron(transformersteel)isusedforcoresbecauseitincreasesthecouplingbetweencoilsbyprovidinganeasypathformagneticflux

ConstructionThecoretype(rightup)andtheshelltype(rightdown)areshownThecoresofbothtypesaremadefromlaminationsofsheetsteel,insulatedfromeachotherbythincoatingsofceramicorothermaterialtominimizeeddycurrentlosses

ConstructionIronhasconsiderablepowerlossduetohysteresisandeddycurrentsathighfrequenciesandisnotusefulasacorematerialforfrequencyabove50kHz

ConstructionForhigh-frequencyapplications,suchasinradiocircuits,air-coreandferrite-coreareusedFerrite,amagneticmaterialmadefrompowderedironoxide,greatlyincreasescouplingbetweencoilswhilemaintaininglowlosses

TightlyCoupledCircuitMostofthefluxproducedbyo