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ID:55175084
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页数:5页
时间:2020-04-30
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1、TransformerOneofthemostvaluableapparatusinelectricpowersystemisthetransformer,foritenablesustoutilizedifferentvoltagelevelsacrossthesystemforthemosteconomicalvalue.Generationofpoweratthesynchronousmachinelevelisnormallyatarelativelylowvoltage,whichismostdesirableeconomicall
2、y.Steppingupofthisgeneratedvoltagetohighvoltage,extra-highvoltageoreventoultra-highvoltageisdonethroughpowertransformerstosuitthepowertransmissionrequirementtominimizelossesandincreasethetransmissioncapacityofthelines.Thistransmissionvoltagelevelisthensteppeddowninmanystage
3、sfordistributionandutilizationpurposes.Atransformerisastaticdevicefortransferringelectricenergyfromonecircuittoanotherelectromagnetically,thatis,byinductioninsteadofbyconduction.Itsusualfunctionistotransferenergybetweencircuitsofdifferentvoltage.Atransformerhasamagneticcore
4、onwhichtherearetwoormorewindings.Thesewindingsareinsulatedfromeachotherandfromground.Inautotransformers,however,thewindingsareconnectedtogether.Theassemblyofcoreandcoilsisnormallyinsulatedandcooledbyimmersioninmineraloilorothersuitableliquidwithinanenclosingtank.Connectiont
5、othewindingsisbymeansofinsulatingbushings,usuallythroughthecover.The“ratiooftransformation”isdeterminedbytherelativenumberofturnsineachofhewindings.Thisisknownasthe“turnratio”anditistheratiooftheno-loadvoltages.Whentheunitiscarryingload,theratiooftheactualvoltagesisslightly
6、differentbecauseofthedropcausedbytheflowof1oadcurrentthroughtheimpedanceofthetransformerwindings.Atratedload,thisdropisknownasthe"voltageregulation".Theamountofvoltagedropvarieswiththepowerfactoroftheoutputevenwhenthekilovolt-amperesremainconstant.Practicallyallpowertransfo
7、rmersandmanydistributiontransformershavetapsinoneormorewindingsforchangingtheturnratio.Changingtheratioisdesirablefortworeasonstocompensateforvaryingvoltagedropinthesystemandtoassurethatthetransformeroperatesasnearlyaspossibleatthecorrectcoredensity.Forthelatterpurpose,thet
8、apsshouldbeinthewindingsubjecttothevoltagevariation.De-energizedtapchangersareused
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