壓縮機電機起動理論

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

Itisespeciallyimportanttoconsidermotorstartcharacteristicswhenseekingto:

-MinimisestartcurrentMaximisestarttorque當(dāng)嘗試以下方式時考慮電機起動特性尤其重要：

-將起動電流降至最小

-將起動扭矩增至最大

MotorPerformance電機性能Rotordesignaffectsstartingperformance.轉(zhuǎn)子的設(shè)計影響起動性能。

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

Intheexample,MotorHwilldraw55%morecurrentatstartthanMotorE.在實例中，電機H引入的起動電流比電機E多55%。

StartCurrent起動電流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.電機起動扭矩性能是由電機的鎖定轉(zhuǎn)子扭矩（LRT）圖表示的。

LRTlevelsvaryconsiderablybetweenmotors.LRT等級在各個電機間有顯著變化。

Intheexample,MotorAproducestwiceasmuchtorqueduringstartasMotorI.在實例中，電機A起動時產(chǎn)生的扭矩是電機I的兩倍。StartTorque起動扭矩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.確定電機起動性能時必須合并考慮LRC&LRT。Theexampledoesthisbyrankingthemotorsaccordingtothetorqueproducedat3xFLC.實例中的作法是根據(jù)3×FLC產(chǎn)生的扭矩對電機排序。LRC&LRTWorkTogetherLRC&LRT同時運轉(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B和G在滿電壓情況下產(chǎn)生的扭矩幾乎相同。MotorBproduces60%morestarttorqueat3xFLC.電機B在3xFLC條件下產(chǎn)生的起動扭矩多60％。

ReducedVoltageStartingAmplifiesMotorDifferences降壓起動擴大電機差異SampleOfTypical110kWMotorsMotor LRC LRT TORQUE (%FLC) (%FLT) @3XFLC A 600

263 65.8 B 600

190 C 570

150 D 660

190

Followtheexampleandcalculatethestarttorqueat3xFLCformotorsB,C&D.依照實例，計算電機B、C和D在3xFLC條件下的起動扭矩。HowToCalculateStartTorque如何計算起動扭矩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）電機將：Reducestartcurrent.-降低起動電流

Increasestarttorque.-增加起動扭矩

Reducesoftstartercost.-降低軟起動器的成本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電源產(chǎn)生不良的影響Currentgraduallyfallsasmotorspeedincreases.電機速度增加時電流下降。Motorloadingaffectsonlythetimetakenforacceleration,notthemagnitudeofcurrentwhichisalwaysLRC.電機負(fù)載只影響加速所需的時間，而不影響始終為LRC的電流值。FullVoltageStarting滿電壓起動0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)FullVoltageStarting滿電壓起動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.電機達到滿速前，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IST=LRTxTSTLRC()2Reducesstarttorquebythesquareofthecurrentreduction.起動扭矩減少值是電流降低值的平方。Currentcanonlybereducedtothepointwheretorqueoutputfromthemotorexceedsthetorquerequiredbytheload.電流只能降到電機扭矩輸出超過負(fù)載要求的扭矩的那個點Reducesstartcurrent.降低起動電流。ReducedVoltageStarting降壓起動Tobeeffective,areducedvoltagestartermustallowthemotortoacceleratetoaround90%speedbeforeapplyingfullvoltage.

為確保有效運行，降壓起動器須使電機在使用滿電壓之前加速到90％左右

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

at50%speedLargeReduction

at95%speedElectromechanical

機電-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ReducedVoltageStarters降壓起動器Auto-transformers自耦變壓器ThermalOverload3Phase

AutoTransformer(B)StartContactor(A)StartContactorRunContactor3~MTheAuto-transformerStarteremploysanauto-transformertoreducethevoltageduringthestartperiod.Thetransformerhasarangeofoutputvoltagetapsthatcanbeusedtosetthestartvoltage.超動期間自耦變壓器起動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)置起動電壓。Themotorcurrentisreducedbythestartvoltagereduction,andfurtherreducedbythetransformeractionresultinginalinecurrentlessthantheactualmotorcurrent.電機電流隨起動電壓下降而降低，且通過變壓器的作用進一步降低最后產(chǎn)生的線路電流小于電機實際電流。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

- 限定每小時的起動次數(shù)

- 在所有速度下扭矩值降低

- 價值高

0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)50%Tap50%分接頭Theinitialstartvoltageissetbytapselection,andthestarttimeiscontrolledbyatimer.Ifthestartvoltageistoolow,orthestarttimeincorrectlyset,thetransitiontofullvoltagewilloccurwiththemotoratlessthanfullspeed,resultinginahighcurrentandtorquestep.初始起動電壓是由分接頭選擇設(shè)定的，而起動時間是由定時器控制的。如果起動電壓太低或起動時間設(shè)置不正確，變至滿電壓的過程將發(fā)生在電機未達全速之時，因此導(dǎo)致高電流和扭矩步進。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之間的每一相實行串接。電阻器降壓導(dǎo)致電機降壓，從而降低起動電流和扭矩。Setfor4xFLCstartcurrent.設(shè)置4xFLC起動電流。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

- 限定每小時的起動次數(shù)

- 如果電阻器沒有完全冷卻，起動特性會在各起動間發(fā)生差異

- 難以起動高慣性負(fù)載

PrimaryResistance一次電路電阻0501001502002503001009080706050403020100SLIP(%)FULLLOADTORQUE(%)0100200300400500600700CURRENT(%)Setfor3.5xFLCstartcurrent.設(shè)置3.5xFLC起動電流。Startvoltageisdeterminedbytheresistorsused.Iftheresistanceistoohightherewillbeinsufficienttorquetoacceleratethemotortofullspeed.起動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達到全速。Thereducedvoltagestarttimeiscontrolledbyapresettimer.Ifthetimeistooshort,themotorwillnothaveachievedfullspeedbeforetheresistorsarebridged.降壓起動時間是由預(yù)置計時器控制的。如果時間太短，電機不會在電阻器跨接之前達到全速。

Star/Delta星形/三角形Motor

3~ThermalOverloadStarContactorDeltaContactorMainContactorThemotorisinitiallyconnectedinstarconfigurationandthen,afterapresettime,themotorisdisconnectedfromthesupplyandreconnectedindeltaconfiguration.Thecurrentandtorqueinthestarconfigurationareonethirdofthefullvoltagecurrentandtorquewhenthemotorisconnectedindelta.電機最初以星形配置進行連接，然后，在預(yù)設(shè)時間之后，電機會與電源斷開，并再次以三角形配置進行連接。當(dāng)電機以三角形連接時，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)起動器以轉(zhuǎn)換