会员注册 | 登录 | 微信快捷登录 QQ登录 微博登录 | 帮助中心 人人文库renrendoc.com美如初恋!
站内搜索 百度文库

热门搜索: 直缝焊接机 矿井提升机 循环球式转向器图纸 机器人手爪发展史 管道机器人dwg 动平衡试验台设计

   首页 人人文库网 > 资源分类 > DOC文档下载

外文翻译--异步电动机起动的方法和问题.doc

  • 资源星级:
  • 资源大小:62.00KB   全文页数:12页
  • 资源格式: DOC        下载权限:注册会员/VIP会员
您还没有登陆,请先登录。登陆后即可下载此文档。
  合作网站登录: 微信快捷登录 支付宝快捷登录   QQ登录   微博登录
友情提示
2:本站资源不支持迅雷下载,请使用浏览器直接下载(不支持QQ浏览器)
3:本站资源下载后的文档和图纸-无水印,预览文档经过压缩,下载后原文更清晰   

外文翻译--异步电动机起动的方法和问题.doc

INDUCTIONMOTORSTARTINGMETHODSANDISSUESAbstractManymethodscanbeusedtostartlargeACinductionmotors.Choicessuchasfullvoltage,reducedvoltageeitherbyautotransformerorWyesDelta,asoftstarter,orusageofanadjustablespeeddrivecanallhavepotentialadvantagesandtradeoffs.Reducedvoltagestartingcanlowerthestartingtorqueandhelppreventdamagetotheload.Additionally,powerfactorcorrectioncapacitorscanbeusedtoreducethecurrent,butcaremustbetakentosizethemproperly.Usageofthewrongcapacitorscanleadtosignificantdamage.Choosingtheproperstartingmethodforamotorwillincludeananalysisofthepowersystemaswellasthestartingloadtoensurethatthemotorisdesignedtodelivertheneededperformancewhileminimizingitscost.Thispaperwillexaminethemostcommonstartingmethodsandtheirrecommendedapplications.IndexTermsmotorstarting.Reducedvoltagestartautotransformer,wyesdelta,powerfactorcorrectionI.INTRODUCTIONThereareseveralgeneralmethodsofstartinginductionmotorsfullvoltage,reducedvoltage,wyesdelta,andpartwindingtypes.Thereducedvoltagetypecanincludesolidstatestarters,adjustablefrequencydrives,andautotransformers.These,alongwiththefullvoltage,oracrossthelinestarting,givethepurchaseralargevarietyofautomotiveswhenitcomestospecifyingthemotortobeusedinagivenapplication.Eachmethodhasitsownbenefits,aswellasperformancetradeoffs.Properselectionwillinvolveathoroughinvestigationofanypowersystemconstraints,theloadtobeacceleratedandtheoverallcostoftheequipment.Inorderfortheloadtobeaccelerated,themotormustgenerategreatertorquethantheloadrequirement.Ingeneraltherearethreepointsofinterestonthemotorsspeedtorquecurve.ThefirstislockedrotortorqueLRTwhichistheminimumtorquewhichthemotorwilldevelopatrestforallangularpositionsoftherotor.ThesecondispulluptorquePUTwhichisdefinedastheminimumtorquedevelopedbythemotorduringtheperiodofaccelerationfromresttothespeedatwhichbreakdowntorqueoccurs.ThelastisthebreakdowntorqueBDTwhichisdefinedasthemaximumtorquewhichthemotorwilldevelop.Ifanyofthesepointsarebelowtherequiredloadcurve,thenthemotorwillnotstart.Thetimeittakesforthemotortoacceleratetheloadisdependentontheinertiaoftheloadandthemarginbetweenthetorqueofthemotorandtheloadcurve,sometimescalledacceleratingtorque.Ingeneral,thelongerthetimeittakesforthemotortoacceleratetheload,themoreheatthatwillbegeneratedintherotorbars,shortingringandthestatorwinding.Thisheatleadstoadditionalstressesinthesepartsandcanhaveanimpactionmotorlife.II.FULLVOLTAGEThefullvoltagestartingmethod,alsoknownasacrossthelinestarting,istheeasiestmethodtoemploy,hasthelowestequipmentcosts,andisthemostreliable.Thismethodutilizesacontroltocloseacontactorandapplyfulllinevoltagetothemotorterminals.Thismethodwillallowthemotortogenerateitshigheststartingtorqueandprovidetheshortestaccelerationtimes.Thismethodalsoputsthehigheststrainonthepowersystemduetothehighstartingcurrentsthatcanbetypicallysixtoseventimesthenormalfullloadcurrentofthemotor.Ifthemotorisonaweakpowersystem,thesuddenhighpowerdrawcancauseatemporaryvoltagedrop,notonlyatthemotorterminals,buttheentirepowerbusfeedingthestartingmotor.Thisvoltagedropwillcauseadropinthestartingtorqueofthemotor,andadropinthetorqueofanyothermotorrunningonthepowerbus.Thetorquedevelopedbyaninductionmotorvariesroughlyasthesquareoftheappliedvoltage.Therefore,dependingontheamountofvoltagedrop,motorsrunningonthisweakpowerbuscouldstall.Inaddition,manycontrolsystemsmonitorundervoltageconditions,asecondpotentialproblemthatcouldtakearunningmotorofflineduringafullvoltagestart.Besideselectricalvariationofthepowerbus,apotentialphysicaldisadvantageofanacrossthelinestartingisthesuddenloadingseenbythedrivenequipment.Thisshockloadingduetotransienttorqueswhichcanexceed600ofthelockedrotortorquecanincreasethewearontheequipment,orevencauseacatastrophicfailureiftheloadcannothandlethetorquesgeneratedbythemotorduringstaring.A.CapacitorsandStartingInductionmotorstypicallyhaveverylowpowerfactorduringstartingandasaresulthaveverylargereactivepowerdraw.SeeFig.2.Thiseffectonthesystemcanbereducedbyaddingcapacitorstothemotorduringstarting.Thelargereactivecurrentsrequiredbythemotorlagtheappliedvoltageby90electricaldegrees.Thisreactivepowerdoesntcreateanymeasurableoutput,butisrathertheenergyrequiredforthemotortofunction.TheproductoftheappliedsystemvoltageandthisreactivepowercomponentcanbemeasuredinVARSvoltamperereactive.Thecapacitorsacttosupplyacurrentthatleadstheappliedvoltageby90electricaldegrees.Theleadingcurrentssuppliedbythecapacitorscancelthelaggingcurrentdemandedbythemotor,reducingtheamountofreactivepowerrequiredtobedrawnfromthepowersystem.Toavoidovervoltageandmotordamage,greatcareshouldbeusedtomakesurethatthecapacitorsareremovedasthemotorreachesratedspeed,orintheeventofalossofpowersothatthemotorwillnotgointoageneratormodewiththemagnetizingcurrentsprovidedfromthecapacitors.Thiswillbeexpandedoninthenextsectionandintheappendix.B.PowerFactorCorrectionCapacitorscanalsobeleftpermanentlyconnectedtoraisethefullloadpowerfactor.Whenusedinthismannertheyarecalledpowerfactorcorrectioncapacitors.Thecapacitorsshouldneverbesizedlargerthanthemagnetizingcurrentofthemotorunlesstheycanbedisconnectedfromthemotorintheeventofapowerloss.Theadditionofcapacitorswillchangetheeffectiveopencircuittimeconstantofthemotor.Thetimeconstantindicatesthetimerequiredforremainingvoltageinthemotortodecayto36.8ofratedvoltageafterthelossofpower.Thisistypicallyonetothreesecondswithoutcapacitors.Withcapacitorsconnectedtotheleadsofthemotor,thecapacitorscancontinuetosupplymagnetizingcurrentafterthepowertothemotorhasbeendisconnected.Thisisindicatedbyalongertimeconstantforthesystem.Ifthemotorisdrivingahighinertiaload,themotorcanchangeovertogeneratoractionwiththemagnetizingCurrentfromthecapacitorsandtheshaftdrivenbytheload.Thiscanresultinthevoltageatthemotorterminalsactuallyrisingtonearly50ofratedvoltageinsomecases.Ifthepowerisreconnectedbeforethisvoltagedecaysseveretransientscanbecreatedwhichcancausesignificantswitchingcurrentsandtorquesthatcanseverelydamagethemotorandthedrivenequipment.Anexampleofthisphenomenonisoutlinedintheappendix.Ill.REDUCEDVOLTAGEEachofthereducedvoltagemethodsareintendedtoreducetheimpactofmotorstartingcurrentonthepowersystembycontrollingthevoltagethatthemotorseesattheterminals.Itisveryimportanttoknowthecharacteristicsoftheloadtobestartedwhenconsideringanyformofreducedvoltagestarting.Themotormanufacturerwillneedtohavethespeedtorquecurveandtheinertiaofthedrivenequipmentwhentheyvalidatetheirdesign.Thecurvecanbebuiltfromaninitial,orbreakawaytorque,asfewasfourotherdatapointsthroughthespeedrange,andthefullspeedtorqueforthestartingcondition.Acentrifugalorsquarecurvecanbeassumedinmanycases,buttherearesomeapplicationswherethiswouldbeproblematic.Anexamplewouldbescrewcompressorswhichhaveamuchhighertorquerequirementatlowerspeedsthanthemorecommoncentrifugalorfanload.SeeFig.3.Byunderstandingthedetailsoftheloadtobestartedthemanufacturercanmakesurethatthemotorwillbeabletogeneratesufficienttorquetostarttheload,withthestartingmethodthatischosen.A.AutotransformerThemotorleadsareconnectedtothelowervoltagesideofthetransformer.Themostcommontapsthatareusedare80,65,and50.At50voltagethecurrentontheprimaryis25ofthefullvoltagelockedrotoramps.Themotorisstartedwiththisreducedvoltage,andthenafterapresetconditionisreachedtheconnectionisswitchedtolinevoltage.Thisconditioncouldbeapresettime,currentlevel,busvolts,ormotorspeed.Thechangeovercanbedoneineitheraclosedcircuittransition,oranopencircuittransitionmethod.Intheopencircuitmethodtheconnectiontothevoltageisseveredasitischangedfromthereducedvoltagetothelinelevel.Careshouldbeusedtomakesurethattherewillnotbeproblemsfromtransientsduetotheswitching.Thispotentialproblemcanbeeliminatedbyusingtheclosedcircuittransition.WiththeclosedcircuitmethodthereisacontinuousVoltageappliedtothemotor.Anotherbenefitwiththeautotransformerstartingisinpossiblelowervibrationandnoiselevelsduringstarting.Sincethetorquegeneratedbythemotorwillvaryasthesquareoftheappliedvoltage,greatcareshouldbetakentomakesurethattherewillbesufficientacceleratingtorqueavailablefromthemotor.Aspeedtorquecurveforthedrivenequipmentalongwiththeinertiashouldbeusedtoverifythedesignofthemotor.Agoodruleofthumbis

注意事项

本文(外文翻译--异步电动机起动的方法和问题.doc)为本站会员(英文资料库)主动上传,人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。 若此文所含内容侵犯了您的版权或隐私,请立即通知人人文库网(发送邮件至[email protected]或直接QQ联系客服),我们立即给予删除!

温馨提示:如果因为网速或其他原因下载失败请重新下载,重复下载不扣分。

[email protected] 2015-2017 人人文库网网站版权所有
苏ICP备12009002号-5