压缩机电机起动理论

MotorStartTheory电机起动原理T-2005-11001MSTLowSlipvFullSlip低滑移与满滑移0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)WhenapplyingACspeeddrivesthemotor‘slowslipperformancecharacteristicsareimportant.当使用AC速度驱动电机低滑移时，性能特征是十分重要的。Incontrast,whenapplyingsoftstartersthemotor‘sperformanceatalllevelsofslipisimportant.相反，当使用软起动器时，在满滑移水平下的电机性能是十分重要的。SoftStartAmotor‘sstartperformancecharacteristicssetthelimitsofwhatcanbeachievedwitheitherafullvoltageorreducedvoltagestarter.电机起动性能规定使用全电压起动器或降压起动器能达到的极限值。

Itisespeciallyimportanttoconsidermotorstartcharacteristicswhenseekingto:

-MinimisestartcurrentMaximisestarttorque当尝试以下方式时考虑电机起动特性尤其重要：

-将起动电流降至最小

-将起动扭矩增至最大

MotorPerformance电机性能Rotordesignaffectsstartingperformance.转子的设计影响起动性能。

Statordesignaffectsfullspeedperformance.定子的设计影响全速性能。Theshape,positionandmaterialoftherotorbarsaffectthecurrentdrawnandtorqueproducedduringmotorstarting.转子杆的形状、位置和材料影响引入电流和电机起动时产生的扭矩。MotorPerformance电机性能Amotor‘sstartperformancecanbeidentifiedbyexaminingthemotordatasheet.电机起动性能可通过检查电机数据表得到确认。Thetabledetailsselectedperformancedataforarangeof110kWmotors.数据表详述了110kW电机系列选用的性能数据。TypicalMotorData典型电机数据Motor Speed FLC LRC LRT %FL Torque (rpm) (amps) (%FLC) (%FLT) Ef’ncy @3xFLC A 1470 191 600

263 93 65.8 B 1475 184 600

190 93.5 47.5 C 1475 191 570

150 92 41.6 D 1480 187 660

190 94.5 39.2 E 1470 185 550

120 92 36 F 1470 191 670

150 93 30.1 G 1480 190 780

200 94 29.6 H 1475 182 850

220 93.5 27.4 I 1480 190 670

120 94 24SampleOfTypical110kWMotorsMaximummotorstartcurrentunderfullvoltagestartconditionsisdefinedbythemotor‘sLockedRotorCurrent(LRC).全电压起动条件下最大电机起动电流是由电机锁定转子电流（LRC）确定的。LRClevelsvaryconsiderablybetweenmotors.LRC等级在电机间有显著变化。

Intheexample,MotorHwilldraw55%morecurrentatstartthanMotorE.在实例中，电机H引入的起动电流比电机E多55%。

StartCurrent起动电流Motor Speed FLC LRC LRT %FL Torque (rpm) (amps) (%FLC) (%FLT) Ef’ncy @3xFLC A 1470 191 600

263 93 65.8 B 1475 184 600

190 93.5 47.5 C 1475 191 570

150 92 41.6 D 1480 187 660

190 94.5 39.2 E 1470 185 550

120 92 36 F 1470 191 670

150 93 30.1 G 1480 190 780

200 94 29.6 H 1475 182 850

220 93.5 27.4 I 1480 190 670

120 94 24LRCrangesfrom550%to850%SampleOfTypical110kWMotorsMotorstarttorqueperformanceisindicatedbythemotor‘sLockedRotorTorque(LRT)figure.电机起动扭矩性能是由电机的锁定转子扭矩（LRT）图表示的。

LRTlevelsvaryconsiderablybetweenmotors.LRT等级在各个电机间有显著变化。

Intheexample,MotorAproducestwiceasmuchtorqueduringstartasMotorI.在实例中，电机A起动时产生的扭矩是电机I的两倍。StartTorque起动扭矩Motor Speed FLC LRC LRT %FL Torque (rpm) (amps) (%FLC) (%FLT) Ef’ncy @3xFLC A 1470 191 600

263 93 65.8 B 1475 184 600

190 93.5 47.5 C 1475 191 570

150 92 41.6 D 1480 187 660

190 94.5 39.2 E 1470 185 550

120 92 36 F 1470 191 670

150 93 30.1 G 1480 190 780

200 94 29.6 H 1475 182 850

220 93.5 27.4 I 1480 190 670

120 94 24LRTrangesfrom120%to263%SampleOfTypical110kWMotorsLRC&LRTmustbeconsideredtogetherwhendeterminingamotor‘sstartperformance.确定电机起动性能时必须合并考虑LRC&LRT。Theexampledoesthisbyrankingthemotorsaccordingtothetorqueproducedat3xFLC.实例中的作法是根据3×FLC产生的扭矩对电机排序。LRC&LRTWorkTogetherLRC&LRT同时运转

Motor Speed FLC LRC LRT %FL Torque (rpm) (amps) (%FLC) (%FLT) Ef’ncy @3xFLC A 1470 191 600

263 93 65.8 B 1475 184 600

190 93.5 47.5 C 1475 191 570

150 92 41.6 D 1480 187 660

190 94.5 39.2 E 1470 185 550

120 92 36 F 1470 191 670

150 93 30.1 G 1480 190 780

200 94 29.6 H 1475 182 850

220 93.5 27.4 I 1480 190 670

120 94 24SampleOfTypical110kWMotorsTorquedevelopedat3xFLCMotor Speed FLC LRC LRT %FL Torque (rpm) (amps) (%FLC) (%FLT) Ef’ncy @3xFLC A 1470 191 600

263 93 65.8 B 1475 184 600

190 93.5 47.5 C 1475 191 570

150 92 41.6 D 1480 187 660

190 94.5 39.2 E 1470 185 550

120 92 36 F 1470 191 670

150 93 30.1 G 1480 190 780

200 94 29.6 H 1475 182 850

220 93.5 27.4 I 1480 190 670

120 94 24Torqueisreducedbythesquareofthecurrentreduction.扭矩减少值是电流降底值的平方。

MotorsB&Gproducealmostthesametorqueatfullvoltage.电机B和G在满电压情况下产生的扭矩几乎相同。MotorBproduces60%morestarttorqueat3xFLC.电机B在3xFLC条件下产生的起动扭矩多60％。

ReducedVoltageStartingAmplifiesMotorDifferences降压起动扩大电机差异SampleOfTypical110kWMotorsMotor LRC LRT TORQUE (%FLC) (%FLT) @3XFLC A 600

263 65.8 B 600

190 C 570

150 D 660

190

Followtheexampleandcalculatethestarttorqueat3xFLCformotorsB,C&D.依照实例，计算电机B、C和D在3xFLC条件下的起动扭矩。HowToCalculateStartTorque如何计算起动扭矩StartTorque=LRTxStartCurrentLRC()2()2300%600%65.8%=x263%47.541.539.3SelectingamotorwithlowLockedRotorCurrent(LRC)andhighLockedRotorTorque(LRT)will:选择低锁定转子电流（LRC）和高锁定转子扭矩（LRT）电机将：Reducestartcurrent.-降低起动电流

Increasestarttorque.-增加起动扭矩

Reducesoftstartercost.-降低软起动器的成本Summary总结CurrentrisesinstantaneouslytoLRClevels.Thiscausesacurrenttransientthatcanhaveundesirableeffectsonthesupply.电流瞬间上升至LRC水平，由此引起的电流瞬变可对电源产生不良的影响Currentgraduallyfallsasmotorspeedincreases.电机速度增加时电流下降。Motorloadingaffectsonlythetimetakenforacceleration,notthemagnitudeofcurrentwhichisalwaysLRC.电机负载只影响加速所需的时间，而不影响始终为LRC的电流值。FullVoltageStarting满电压起动0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)FullVoltageStarting满电压起动0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)TorquerisesinstantaneouslytoLRTlevels.Thiscausesatorquetransientthatcanbedamaging.电流瞬间上升至LRC水平，由此引起的电流瞬变具有破坏性。TypicaltorquefallsfromLRTtoPullOutTorquebeforerisingtoBreakdownTorquejustbeforefullspeed.电机达到满速前，典型转矩在升至失步转矩前由LRT降至脱扣力矩。

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)FullVoltageStartingLimitations满电压起动限制1.Current

transient

电流瞬变

12.Currentmagnitude

电流值

23.Torquetransient

扭矩瞬变

344.Torquemagnitude

扭矩值

Reducedvoltagestartingattemptstoovercometheselimitationsbyapplyingthevoltagegradually.降压起动通过逐渐利用满电压的方式力图克服这些限制。

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)ReducedVoltageStarting降压起动IST=LRTxTSTLRC()2Reducesstarttorquebythesquareofthecurrentreduction.起动扭矩减少值是电流降低值的平方。Currentcanonlybereducedtothepointwheretorqueoutputfromthemotorexceedsthetorquerequiredbytheload.电流只能降到电机扭矩输出超过负载要求的扭矩的那个点Reducesstartcurrent.降低起动电流。ReducedVoltageStarting降压起动Tobeeffective,areducedvoltagestartermustallowthemotortoacceleratetoaround90%speedbeforeapplyingfullvoltage.

为确保有效运行，降压起动器须使电机在使用满电压之前加速到90％左右

BelowthisspeedthecurrentwillstepthroughtoalmostLRClevelsthusremovinganybenefitfromthereducedvoltagestarter.如果低于此速度，电流将逐步达到LRC水平，从而失去降压起动器的任何优点。0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)SmallReduction

at50%speedLargeReduction

at95%speedElectromechanical

机电-Auto-transformer

自耦变压器

-PrimaryResistance

一次电路电阻-Star/Delta

星形/三角形Electronic

电子-SoftStart

软起动ReducedVoltageStarters降压起动器Auto-transformers自耦变压器ThermalOverload3Phase

AutoTransformer(B)StartContactor(A)StartContactorRunContactor3~MTheAuto-transformerStarteremploysanauto-transformertoreducethevoltageduringthestartperiod.Thetransformerhasarangeofoutputvoltagetapsthatcanbeusedtosetthestartvoltage.超动期间自耦变压器起动器使用自耦变压器降低电压。变压器有一套输出电压开关，可用以设置起动电压。Themotorcurrentisreducedbythestartvoltagereduction,andfurtherreducedbythetransformeractionresultinginalinecurrentlessthantheactualmotorcurrent.电机电流随起动电压下降而降低，且通过变压器的作用进一步降低最后产生的线路电流小于电机实际电流。0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)60%Tap60%分接头Auto-transformers自耦变压器Limitations:- Limitedvoltagetaps- Limitednumberofstartsperhour- TorquereducedatallspeedsCostly限制：

- 限定电压分接头

- 限定每小时的起动次数

- 在所有速度下扭矩值降低

- 价值高

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)50%Tap50%分接头Theinitialstartvoltageissetbytapselection,andthestarttimeiscontrolledbyatimer.Ifthestartvoltageistoolow,orthestarttimeincorrectlyset,thetransitiontofullvoltagewilloccurwiththemotoratlessthanfullspeed,resultinginahighcurrentandtorquestep.初始起动电压是由分接头选择设定的，而起动时间是由定时器控制的。如果起动电压太低或起动时间设置不正确，变至满电压的过程将发生在电机未达全速之时，因此导致高电流和扭矩步进。Auto-transformers自耦变压器PrimaryResistance一次电路电阻RUN

CONTACTORMOTOROVERLOADTHERMALSTART

RESISTORSLINE

CONTACTOR3~MResistorsareconnectedinserieswitheachphase,betweentheisolationcontactorandthemotor.Thevoltagedropacrosstheresistorsresultsinareducedvoltageappliedtothemotor,thusreducingstartcurrentandtorque.电阻器与隔离接触器和电机之间的每一相实行串接。电阻器降压导致电机降压，从而降低起动电流和扭矩。Setfor4xFLCstartcurrent.设置4xFLC起动电流。PrimaryResistance一次电路电阻0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Limitations:- Difficulttochangeresistance- Dissipatealotofheat- Limitednumberofstartsperhour- StartcharacteristicschangebetweenstartsifresistorshavenottotallycooledHardtostarthighinertialoads限制：

- 很难改变电阻

- 大量散热

- 限定每小时的起动次数

- 如果电阻器没有完全冷却，起动特性会在各起动间发生差异

- 难以起动高惯性负载

PrimaryResistance一次电路电阻0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Setfor3.5xFLCstartcurrent.设置3.5xFLC起动电流。Startvoltageisdeterminedbytheresistorsused.Iftheresistanceistoohightherewillbeinsufficienttorquetoacceleratethemotortofullspeed.起动电压是由所使用的电阻器确定的。如果电阻太高，则扭矩不足以加速电机达到全速。Thereducedvoltagestarttimeiscontrolledbyapresettimer.Ifthetimeistooshort,themotorwillnothaveachievedfullspeedbeforetheresistorsarebridged.降压起动时间是由预置计时器控制的。如果时间太短，电机不会在电阻器跨接之前达到全速。

Star/Delta星形/三角形Motor

3~ThermalOverloadStarContactorDeltaContactorMainContactorThemotorisinitiallyconnectedinstarconfigurationandthen,afterapresettime,themotorisdisconnectedfromthesupplyandreconnectedindeltaconfiguration.Thecurrentandtorqueinthestarconfigurationareonethirdofthefullvoltagecurrentandtorquewhenthemotorisconnectedindelta.电机最初以星形配置进行连接，然后，在预设时间之后，电机会与电源断开，并再次以三角形配置进行连接。当电机以三角形连接时，则星形配置电流和扭矩是满电压电流和扭矩的三分之一。Limitations:- Noadjustmentpossible.Opentransitionswitchingbetweenstaranddeltacausesdamagingcurrentandtorquetransients.限制：

- 不能调节。

- 星形和三角形之间的开路瞬变会破坏电流和扭矩瞬变Star/Delta星形/三角形0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Insufficienttorquetoacceleratethisloadinstarconfiguration.不足的扭矩以星形配置加速该负载OpenTransitionSwitchingOccurswhenthestartergoesthroughanopencircuitstageintheswitchingsequence.Stage[1]connectiontothereducedvoltage;[2]disconnectfromthereducedvoltage(opencircuit);[3]connecttothefullvoltage.Opentransitionstartingcausesseverecurrent&torquetransientsthatcanbemoredetrimentaltothesupplyandthemechanicalequipmentthanfullvoltagestarting.

Whenthemotorisspinningandthendisconnectedfromthesupply,itactsasagenerator.Outputvoltagecanbethesameamplitudeasthesupply.Atthetimeofreclosetherecanstillbesignificantvoltagepresentatthemotorterminals.Voltagegeneratedbythemotorattheinstantofreclosemaybeequaltothesupplyvoltagebutexactlyoutofphase.Thisequatestoreclosingwithtwicethesupplyvoltageonthemotor.Theresultisacurrentoftwicelockedrotorcurrentandatorquetransientoffourtimeslockedrotortorque.开路瞬变转换

当起动器以转换