壓縮機(jī)電機(jī)起動(dòng)理論

MotorStartTheory電機(jī)起動(dòng)原理T-2005-11001MSTLowSlipvFullSlip低滑移與滿滑移0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)WhenapplyingACspeeddrivesthemotor‘slowslipperformancecharacteristicsareimportant.當(dāng)使用AC速度驅(qū)動(dòng)電機(jī)低滑移時(shí)，性能特征是十分重要的。Incontrast,whenapplyingsoftstartersthemotor‘sperformanceatalllevelsofslipisimportant.相反，當(dāng)使用軟起動(dòng)器時(shí)，在滿滑移水平下的電機(jī)性能是十分重要的。SoftStartAmotor‘sstartperformancecharacteristicssetthelimitsofwhatcanbeachievedwitheitherafullvoltageorreducedvoltagestarter.電機(jī)起動(dòng)性能規(guī)定使用全電壓起動(dòng)器或降壓起動(dòng)器能達(dá)到的極限值。

Itisespeciallyimportanttoconsidermotorstartcharacteristicswhenseekingto:

-MinimisestartcurrentMaximisestarttorque當(dāng)嘗試以下方式時(shí)考慮電機(jī)起動(dòng)特性尤其重要：

-將起動(dòng)電流降至最小

-將起動(dòng)扭矩增至最大

MotorPerformance電機(jī)性能Rotordesignaffectsstartingperformance.轉(zhuǎn)子的設(shè)計(jì)影響起動(dòng)性能。

Statordesignaffectsfullspeedperformance.定子的設(shè)計(jì)影響全速性能。Theshape,positionandmaterialoftherotorbarsaffectthecurrentdrawnandtorqueproducedduringmotorstarting.轉(zhuǎn)子桿的形狀、位置和材料影響引入電流和電機(jī)起動(dòng)時(shí)產(chǎn)生的扭矩。MotorPerformance電機(jī)性能Amotor‘sstartperformancecanbeidentifiedbyexaminingthemotordatasheet.電機(jī)起動(dòng)性能可通過檢查電機(jī)數(shù)據(jù)表得到確認(rèn)。Thetabledetailsselectedperformancedataforarangeof110kWmotors.數(shù)據(jù)表詳述了110kW電機(jī)系列選用的性能數(shù)據(jù)。TypicalMotorData典型電機(jī)數(shù)據(jù)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).全電壓起動(dòng)條件下最大電機(jī)起動(dòng)電流是由電機(jī)鎖定轉(zhuǎn)子電流（LRC）確定的。LRClevelsvaryconsiderablybetweenmotors.LRC等級(jí)在電機(jī)間有顯著變化。

Intheexample,MotorHwilldraw55%morecurrentatstartthanMotorE.在實(shí)例中，電機(jī)H引入的起動(dòng)電流比電機(jī)E多55%。

StartCurrent起動(dòng)電流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.電機(jī)起動(dòng)扭矩性能是由電機(jī)的鎖定轉(zhuǎn)子扭矩（LRT）圖表示的。

LRTlevelsvaryconsiderablybetweenmotors.LRT等級(jí)在各個(gè)電機(jī)間有顯著變化。

Intheexample,MotorAproducestwiceasmuchtorqueduringstartasMotorI.在實(shí)例中，電機(jī)A起動(dòng)時(shí)產(chǎn)生的扭矩是電機(jī)I的兩倍。StartTorque起動(dòng)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.確定電機(jī)起動(dòng)性能時(shí)必須合并考慮LRC&LRT。Theexampledoesthisbyrankingthemotorsaccordingtothetorqueproducedat3xFLC.實(shí)例中的作法是根據(jù)3×FLC產(chǎn)生的扭矩對(duì)電機(jī)排序。LRC&LRTWorkTogetherLRC&LRT同時(shí)運(yùn)轉(zhuǎn)

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.扭矩減少值是電流降底值的平方。

MotorsB&Gproducealmostthesametorqueatfullvoltage.電機(jī)B和G在滿電壓情況下產(chǎn)生的扭矩幾乎相同。MotorBproduces60%morestarttorqueat3xFLC.電機(jī)B在3xFLC條件下產(chǎn)生的起動(dòng)扭矩多60％。

ReducedVoltageStartingAmplifiesMotorDifferences降壓起動(dòng)擴(kuò)大電機(jī)差異SampleOfTypical110kWMotorsMotor LRC LRT TORQUE (%FLC) (%FLT) @3XFLC A 600

263 65.8 B 600

190 C 570

150 D 660

190

Followtheexampleandcalculatethestarttorqueat3xFLCformotorsB,C&D.依照實(shí)例，計(jì)算電機(jī)B、C和D在3xFLC條件下的起動(dòng)扭矩。HowToCalculateStartTorque如何計(jì)算起動(dòng)扭矩StartTorque=LRTxStartCurrentLRC()2()2300%600%65.8%=x263%47.541.539.3SelectingamotorwithlowLockedRotorCurrent(LRC)andhighLockedRotorTorque(LRT)will:選擇低鎖定轉(zhuǎn)子電流（LRC）和高鎖定轉(zhuǎn)子扭矩（LRT）電機(jī)將：Reducestartcurrent.-降低起動(dòng)電流

Increasestarttorque.-增加起動(dòng)扭矩

Reducesoftstartercost.-降低軟起動(dòng)器的成本Summary總結(jié)CurrentrisesinstantaneouslytoLRClevels.Thiscausesacurrenttransientthatcanhaveundesirableeffectsonthesupply.電流瞬間上升至LRC水平，由此引起的電流瞬變可對(duì)電源產(chǎn)生不良的影響Currentgraduallyfallsasmotorspeedincreases.電機(jī)速度增加時(shí)電流下降。Motorloadingaffectsonlythetimetakenforacceleration,notthemagnitudeofcurrentwhichisalwaysLRC.電機(jī)負(fù)載只影響加速所需的時(shí)間，而不影響始終為LRC的電流值。FullVoltageStarting滿電壓起動(dòng)0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)FullVoltageStarting滿電壓起動(dòng)0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)TorquerisesinstantaneouslytoLRTlevels.Thiscausesatorquetransientthatcanbedamaging.電流瞬間上升至LRC水平，由此引起的電流瞬變具有破壞性。TypicaltorquefallsfromLRTtoPullOutTorquebeforerisingtoBreakdownTorquejustbeforefullspeed.電機(jī)達(dá)到滿速前，典型轉(zhuǎn)矩在升至失步轉(zhuǎn)矩前由LRT降至脫扣力矩。

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)FullVoltageStartingLimitations滿電壓起動(dòng)限制1.Current

transient

電流瞬變

12.Currentmagnitude

電流值

23.Torquetransient

扭矩瞬變

344.Torquemagnitude

扭矩值

Reducedvoltagestartingattemptstoovercometheselimitationsbyapplyingthevoltagegradually.降壓起動(dòng)通過逐漸利用滿電壓的方式力圖克服這些限制。

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)ReducedVoltageStarting降壓起動(dòng)IST=LRTxTSTLRC()2Reducesstarttorquebythesquareofthecurrentreduction.起動(dòng)扭矩減少值是電流降低值的平方。Currentcanonlybereducedtothepointwheretorqueoutputfromthemotorexceedsthetorquerequiredbytheload.電流只能降到電機(jī)扭矩輸出超過負(fù)載要求的扭矩的那個(gè)點(diǎn)Reducesstartcurrent.降低起動(dòng)電流。ReducedVoltageStarting降壓起動(dòng)Tobeeffective,areducedvoltagestartermustallowthemotortoacceleratetoaround90%speedbeforeapplyingfullvoltage.

為確保有效運(yùn)行，降壓起動(dòng)器須使電機(jī)在使用滿電壓之前加速到90％左右

BelowthisspeedthecurrentwillstepthroughtoalmostLRClevelsthusremovinganybenefitfromthereducedvoltagestarter.如果低于此速度，電流將逐步達(dá)到LRC水平，從而失去降壓起動(dòng)器的任何優(yōu)點(diǎn)。0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)SmallReduction

at50%speedLargeReduction

at95%speedElectromechanical

機(jī)電-Auto-transformer

自耦變壓器

-PrimaryResistance

一次電路電阻-Star/Delta

星形/三角形Electronic

電子-SoftStart

軟起動(dòng)ReducedVoltageStarters降壓起動(dòng)器Auto-transformers自耦變壓器ThermalOverload3Phase

AutoTransformer(B)StartContactor(A)StartContactorRunContactor3~MTheAuto-transformerStarteremploysanauto-transformertoreducethevoltageduringthestartperiod.Thetransformerhasarangeofoutputvoltagetapsthatcanbeusedtosetthestartvoltage.超動(dòng)期間自耦變壓器起動(dòng)器使用自耦變壓器降低電壓。變壓器有一套輸出電壓開關(guān)，可用以設(shè)置起動(dòng)電壓。Themotorcurrentisreducedbythestartvoltagereduction,andfurtherreducedbythetransformeractionresultinginalinecurrentlessthantheactualmotorcurrent.電機(jī)電流隨起動(dòng)電壓下降而降低，且通過變壓器的作用進(jìn)一步降低最后產(chǎn)生的線路電流小于電機(jī)實(shí)際電流。0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)60%Tap60%分接頭Auto-transformers自耦變壓器Limitations:- Limitedvoltagetaps- Limitednumberofstartsperhour- TorquereducedatallspeedsCostly限制：

- 限定電壓分接頭

- 限定每小時(shí)的起動(dòng)次數(shù)

- 在所有速度下扭矩值降低

- 價(jià)值高

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)50%Tap50%分接頭Theinitialstartvoltageissetbytapselection,andthestarttimeiscontrolledbyatimer.Ifthestartvoltageistoolow,orthestarttimeincorrectlyset,thetransitiontofullvoltagewilloccurwiththemotoratlessthanfullspeed,resultinginahighcurrentandtorquestep.初始起動(dòng)電壓是由分接頭選擇設(shè)定的，而起動(dòng)時(shí)間是由定時(shí)器控制的。如果起動(dòng)電壓太低或起動(dòng)時(shí)間設(shè)置不正確，變至滿電壓的過程將發(fā)生在電機(jī)未達(dá)全速之時(shí)，因此導(dǎo)致高電流和扭矩步進(jìn)。Auto-transformers自耦變壓器PrimaryResistance一次電路電阻RUN

CONTACTORMOTOROVERLOADTHERMALSTART

RESISTORSLINE

CONTACTOR3~MResistorsareconnectedinserieswitheachphase,betweentheisolationcontactorandthemotor.Thevoltagedropacrosstheresistorsresultsinareducedvoltageappliedtothemotor,thusreducingstartcurrentandtorque.電阻器與隔離接觸器和電機(jī)之間的每一相實(shí)行串接。電阻器降壓導(dǎo)致電機(jī)降壓，從而降低起動(dòng)電流和扭矩。Setfor4xFLCstartcurrent.設(shè)置4xFLC起動(dòng)電流。PrimaryResistance一次電路電阻0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Limitations:- Difficulttochangeresistance- Dissipatealotofheat- Limitednumberofstartsperhour- StartcharacteristicschangebetweenstartsifresistorshavenottotallycooledHardtostarthighinertialoads限制：

- 很難改變電阻

- 大量散熱

- 限定每小時(shí)的起動(dòng)次數(shù)

- 如果電阻器沒有完全冷卻，起動(dòng)特性會(huì)在各起動(dòng)間發(fā)生差異

- 難以起動(dòng)高慣性負(fù)載

PrimaryResistance一次電路電阻0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Setfor3.5xFLCstartcurrent.設(shè)置3.5xFLC起動(dòng)電流。Startvoltageisdeterminedbytheresistorsused.Iftheresistanceistoohightherewillbeinsufficienttorquetoacceleratethemotortofullspeed.起動(dòng)電壓是由所使用的電阻器確定的。如果電阻太高，則扭矩不足以加速電機(jī)達(dá)到全速。Thereducedvoltagestarttimeiscontrolledbyapresettimer.Ifthetimeistooshort,themotorwillnothaveachievedfullspeedbeforetheresistorsarebridged.降壓起動(dòng)時(shí)間是由預(yù)置計(jì)時(shí)器控制的。如果時(shí)間太短，電機(jī)不會(huì)在電阻器跨接之前達(dá)到全速。

Star/Delta星形/三角形Motor

3~ThermalOverloadStarContactorDeltaContactorMainContactorThemotorisinitiallyconnectedinstarconfigurationandthen,afterapresettime,themotorisdisconnectedfromthesupplyandreconnectedindeltaconfiguration.Thecurrentandtorqueinthestarconfigurationareonethirdofthefullvoltagecurrentandtorquewhenthemotorisconnectedindelta.電機(jī)最初以星形配置進(jìn)行連接，然后，在預(yù)設(shè)時(shí)間之后，電機(jī)會(huì)與電源斷開，并再次以三角形配置進(jìn)行連接。當(dāng)電機(jī)以三角形連接時(shí)，則星形配置電流和扭矩是滿電壓電流和扭矩的三分之一。Limitations:- Noadjustmentpossible.Opentransitionswitchingbetweenstaranddeltacausesdamagingcurrentandtorquetransients.限制：

- 不能調(diào)節(jié)。

- 星形和三角形之間的開路瞬變會(huì)破壞電流和扭矩瞬變Star/Delta星形/三角形0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Insufficienttorquetoacceleratethisloadinstarconfiguration.不足的扭矩以星形配置加速該負(fù)載OpenTransitionSwitchingOccurswhenthestartergoesthroughanopencircuitstageintheswitchingsequence.Stage[1]connectiontothereducedvoltage;[2]disconnectfromthereducedvoltage(opencircuit);[3]connecttothefullvoltage.Opentransitionstartingcausesseverecurrent&torquetransientsthatcanbemoredetrimentaltothesupplyandthemechanicalequipmentthanfullvoltagestarting.

Whenthemotorisspinningandthendisconnectedfromthesupply,itactsasagenerator.Outputvoltagecanbethesameamplitudeasthesupply.Atthetimeofreclosetherecanstillbesignificantvoltagepresentatthemotorterminals.Voltagegeneratedbythemotorattheinstantofreclosemaybeequaltothesupplyvoltagebutexactlyoutofphase.Thisequatestoreclosingwithtwicethesupplyvoltageonthemotor.Theresultisacurrentoftwicelockedrotorcurrentandatorquetransientoffourtimeslockedrotortorque.開路瞬變轉(zhuǎn)換

當(dāng)起動(dòng)器以轉(zhuǎn)換