电力变压器的选择和冷却-毕业设计外文翻译2篇x.docx

电力变压器的选择和冷却-毕业设计外文翻译2篇x.docx

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本科毕业设计

外文文献及译文

文献、资料题目：

《Special English for ArchitecturalElectricEngineeringandAutomation》

文献、资料来源：

期刊（著作、网络等）文献、资料发表（出版）日期：

2006.4 院（部）：

信息与电气工程学院学院

专业：

电气工程与自动化 班级：

姓名：

学号：

指导教师：

翻译日期：

2013.6.30

山东建筑大学毕业设计外文文献及翻译

外文文献一：

Transformer

Oneofthemostvaluableapparatusinelectricpowersystemisthetransformer,foritenablesustoutilizedifferentvoltagelevelsacrossthesystemforthemosteconomicalvalue.Generationofpoweratthesynchronousmachinelevelisnormallyatarelativelylowvoltage，whichismostdesirableeconomically．Steppingupof

thisgeneratedvoltagetohighvoltage，extra-highvoltageoreventoultra-high

voltageisdonethroughpowertransformerstosuitthepowertransmissionrequirementtominimizelossesandincreasethetransmissioncapacityofthelines．Thistransmissionvoltagelevelisthensteppeddowninmanystagesfordistributionandutilizationpurposes．

Atransformerisastaticdevicefortransferringelectricenergyfromonecircuit

toanotherelectromagnetically，thatis，byinductioninsteadofbyconduction．Itsusualfunctionistotransferenergybetweencircuitsofdifferentvoltage．Atransformerhasamagneticcoreonwhichtherearetwoormorewindings．Thesewindingsareinsulatedfromeachotherandfromground．Inautotransformers，however，thewindingsareconnectedtogether．Theassemblyofcoreandcoilsisnormallyinsulatedandcooledbyimmersioninmineraloilorothersuitableliquidwithinanenclosingtank．Connectiontothewindingsisbymeansofinsulatingbushings，usuallythroughthecover.

The“ratiooftransformation”isdeterminedbytherelativenumberofturnsineachofhewindings．Thisisknownasthe“turnratio”anditistheratiooftheno-loadvoltages．Whentheunitiscarryingload,theratiooftheactualvoltagesisslightlydifferentbecauseofthedropcausedbytheflowof1oadcurrentthroughtheimpedanceofthetransformerwindings．Atratedload,thisdropisknownasthe"voltageregulation".Theamountofvoltagedropvarieswiththepowerfactoroftheoutputevenwhenthekilovolt-amperesremainconstant．

Practicallyallpowertransformersandmanydistributiontransformershavetaps

inoneormorewindingsforchangingtheturnratio．Changingtheratioisdesirable

fortworeasonstocompensateforvaryingvoltagedropinthesystemandtoassurethatthetransformeroperatesasnearlyaspossibleatthecorrectcoredensity．Forthelatterpurpose,thetapsshouldbeinthewindingsubjecttothevoltagevariation.De-energizedtapchangersareusedwhenitisexpectedthattheratiowillneedtobechangedonlyinfrequently,becauseofloadgrowthorsomeseasonalchange．Thedesiredtapisselectedbymeansofaratioadjuster（noloadtaps）．Loadtapchanger（LTC）isusedwhenchangesinratiomaybefrequentorwhenitisundesirabletode-energizethetransformertochangeatap．Itseldommakesmuchdifferencetotheuserwhichwindingorwindingsaretapped；therefore，thechoiceisusuallymadebythedesigneronthebasisofcostandgooddesign.BothwindingcurrentandvoltagemustbeconsideredwhenapplyingLTCequipment．HighvoltageandhighcurrentapplicationsrequirespecialconsiderationstoarriveatanoptimumlocationfortheLTCequipment．StepdownunitsusuallyhaveLTCinthelow-voltagewindingandde-energizedtapsinthehighvoltagewinding．

Whenenergyistobetransferredbetweentwocircuitsofnearlythesame

voltage．Theuseofautotransformersaffordscostsavingsovertwo-windingunits．Thenearerthevoltagesaretoeachother,thesmallerwillbetheautotransformerperkilovolt-ampereofoutput，andthegreaterthesavings．Thesimplicityofphasingoutsystemshasincreaseditsuse．MostautotransformersareY-connected，andithasbeenastandardAmericanpracticetoaddalowcapacity,deltawinding．Thisisfrequentlyreferredtoasa“deltatertiary“．Itsprimarypurposehasbeentoprovideaninternalpathforthethirdharmoniccurrents（requiredforexcitation），thusreducingthosecurrentsonthepowersystem．Italsohelpsto

stabilizetheneutralandtogroundthesystembetter．Inrecentyears，theuseof

shieldedtelephonecablehasreducedtherequirementsforthedeltatertiary.Becauseanautotransformerdoesnotaffordelectricalseparationbetweenthetwocircuits,disturbancesoriginatingononecircuitcanbecommunicatedtotheother．Thisdifficultyisminimizedbysolidlygroundingtheneutraloftheautotransformer.Solidlygroundingtheneutral，however,causes（amongotherthings）currentofshort-circuitmagnitudetoflowthroughthedelta-connectedtertiarywindingduringground

faultsoneithersystem.Autotransformersarenotinherentlyself-protectingand,therefore，allwindingsmustbeexaminedformechanicalstrengthasappliedtothesystemwhereth