第七章____电机控制系统(双语)

7电机控制系统7.1控制符号7.2电机开关控制7.3电机的控制设备7.4电机起动系统7.5正、反转控制7.6动力制动7ElectricalMachineControlSystem7电机控制系统Thepreviouschaptershavedealtprimarilywiththetypesandcharacteristicsofelectricalmachines.Thischapterprovidesanoverviewofseveralpowercontrolsystemswhichareusedwithelectricalmachines.在前面的章节中我们主要讨论了电机的类型和特性。本章对在电机中使用的几个功率控制系统给出了一个概略的介绍。7.1ControlSymbolsItisnecessarytobecomefamiliarwiththeelectricalsymbolswhicharecommonlyusedwithmachinecontrolsystems.SomecommonmachinecontrolsymbolsareinFig.7.1.7.1控制符号有必要熟悉一下电机控制系统中常使用的电气符号。一些常见的电机控制符号如图7.l所示。7.2MachineControlwithSwitchesAnimportanttypeofelectricalmachinecontrolistheswitch.Manytypesofswitchesareusedtocontrolelectricalmachines.Thefunctionofaswitchistoturnacircuitonoroff;however,manymorecomplexswitchfunctionscanbeperformed.7.2电机开关控制电机控制的一个重要元件就是开关。许多类型的开关都被用来控制电机。开关的功能是使一个电路接通或断路；但是，也能实施很多更复杂的开关功能。7.2.1ToggleswitchesAmongthesimplesttypeofswitchesaretoggleswitches.ThesymbolsforseveralkindsoftoggleswitchesareshowninFig.7.2.Noticethesymbolsthatareusedforvarioustypesoftoggleswitches.7.2.2PushbuttonswitchesPushbuttonswitchesarecommonlyusedformachinecontrol.7.2.1拨动开关最简单的开关类型是拨动开关。几类拨动开关的符号如图7.2所示。注意各种类型拨动开关的符号。7.2.2按钮开关按钮开关一般用在电机控制中。Manymachinecontrolapplicationsusepushbuttonsasameansofstarting,stopping,orreversingamotor.Pushbuttonsaremanuallyoperatedtocloseoropenamachinecontrolcircuit.Thereareseveraltypesofpushbuttonsusedforthecontrolofmachines.Pushbuttonsareusuallymountedinenclosurescalledmotorcontrolstations.许多电机控制的应用都用按钮作为电机起动、停止或反转的一种手段。手动操作按钮来闭合或打开一个电机控制电路。有好几种用来控制电机的按钮。按钮通常安装在叫电机控制台的机壳上。Ordinarily,pushbuttonsareeitherthenormallyclosed(NC)ornormallyopen(NO)types.However,thereareafewmodifications.Anormallyclosedpushbuttoniscloseduntilitisdepressedmanuallyandwillopenacircuitwhenitisdepressed.通常，按钮不是常闭(NC)类型就是常开(NO)类型。但是有一些修改。一个常闭按钮通常是关闭的直到它被用手按下，当它被按下后将断开一个电路。Thenormallyopenpushbuttonisopenuntilitismanuallydepressedand,then,onceitisdepressed,itwillcloseacircuit.The“start”pushbuttonofamotorcontrolstationisofNOtype,whilethe“stop”switchesofNCtype.常开按钮一直开着直到它被手动按下，并且一旦它被压下，它将闭合一个电路。电机控制台上的“开始”按钮是常开类型的，而“停止”开关为常闭类型。7.2.3RotaryswitchesAnothercommontypeofswitchistherotaryswitch.Manydifferentswitchingcombinationscanbewiredbyusingarotaryswitch.Theshaftofarotaryswitchisattachedtosetsofmovingcontacts.7.2.3旋转开关另一个普通的开关类型是旋转开关。许多不同的开关组合能通过使用一个旋转开关连接在一起。旋转开关的转轴与一系列运动触点相连。Thesemovingcontactstouchdifferentsetsofstationarycontactswhicharemountedonceramicsegmentswhentherotaryshaftisturnedtodifferentpositions.Theshaftcanlockintoplaceinanyofseveralpositions.Rotaryswitchesareusuallycontrolledbymanuallyturningtherotaryshaftclockwiseorcounterclockwise.当转轴被转到不同位置时，这些运动触点与装在瓷片上的一系列不同静止触点接触。轴能位于几个位置中的任何一个。旋转开关通常通过手动顺时针或逆时针方向转动转轴来控制。Aknobisnormallyfastenedtotheendoftherotaryshafttopermiteasierturningoftherotaryshaft.7.2.4LimitswitchesLimitswitchesaremerelyon/offswitchesthatusemechanicalmovementtocauseachangeintheoperationoftheelectricalcontrolcircuitofamachine.旋钮通常被固定在转轴的末端以便能轻松地转动转轴。7.2.4限位开关限位开关仅仅是用机械运动来引起电机的电子控制电路操作变化的开/关开关。Theelectricalcurrentdevelopedasaresultofthemechanicalmovementisusedtolimitmovementofthemachineortomakesomechangeinitsoperationalsequence.Limitswitchesareoftenusedinsequencing,routing,sorting,orcountingoperationsinindustry.机械运动产生的电流被用来限制电机的运动，或者对它的运行顺序进行一些变化。在工业中，限位开关长被用于顺序、行程、分类或计数操作。Often,theyareusedinconjunctionwithhydraulicorpneumaticcontrols,electricalrelays,orothermotor-operatedmachinerysuchasdrillpresses,lathesorconveyorsystems.Inthismostbasicform,alimitswitchconvertsmechanicalmotionintoanelectricalcontrolcurrent.Noticethecam,whichisanexternalpartthatisusuallymountedonamachine.他们常被用于与液体或气动控制，继电器或其它诸如钻床、车床或传送带系统等电动机驱动的机械相联。在其最基本的形式中，限位开关把机械运动转换成电子控制电流。注意凸轮通常安装在电机上，是一个外部零件。Thecamappliesforcetoanactuatorofthelimitswitch.TheactuatoristhepartofthelimitswitchthatcausetheinternalNOorNCcontactstochangestate.Theactuatoroperatesduetoeitherlinearorrotarymotionofthecam,whichappliesforcetothelimitswitch.凸轮给限位开关的执行机构提供力。执行机构是限位开关的一部分，它引起其内部的常开或常闭触点改变状态。由于给限位开关提供力的凸轮的线性或旋转运动，执行机构才得以运行。Theothertermsassociatedwithlimitswitchesarepretravelandovertravel.Pretravelisthedistancethattheactuatormustmovetochangethenormallyopenornormallyclosedstateofthelimit-switchcontacts.Overtravelisthedistancetheactuatormovesbeyondthepointwherethecontactschangestate.其他的与限位开关有关术语是预行程和过行程。预行程是执行机构运动而改变限位开关触点常开或常闭状态的距离。过行程是执行机构在触点改变状态时运动的距离。Bothpretravelandovertravelsettingsareimportantinmachinesetupswherelimitswitchesareused.7.2.5TemperatureswitchesTemperatureswitchesarecommontypesofcontroldevices.Thecontrolelementofatemperatureswitchcontainsaspecificamountofliquid.在使用限位开关的电机设置中预行程和过行程的设定都很重要。7.2.5温度开关温度开关是控制元件里的常见类型。温度开关的控制元件包括特定数量的液体。Theliquidincreasesinvolumewhentemperatureincreases.Thuschangesintemperaturecanbeusedtochangethepositionofasetofcontactswithinthetemperature-switchenclosure.Temperatureswitchesmaybeadjustedthroughoutarangeoftemperaturesetting.当温度增加时，液体体积增加。这样温度的变化能被用来改变温度开关机壳内的一组触点的位置。温度开关可以调整温度设定的范围。7.2.6PressureswitchesAnothertypeofelec