压缩机电机起动理论.pptx

Motor Start Theory1Motor Start Theory电机起动原理电机起动原理T-2005-11001MSTMotor Start Theory2Low Slip v Full Slip低滑移与满滑移低滑移与满滑移0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)When applying AC speed drives the motors low slip performance characteristics are important.当使用当使用AC速度驱动电机低滑移时，速度驱动电机低滑移时，性能特征是十分重要的。性能特征是十分重要的。In contrast,when applying soft starters the motors performance at all levels of slip is important.相反相反，当使用软起动器时当使用软起动器时，在满滑移在满滑移水平下的电机性能是十分重要的。水平下的电机性能是十分重要的。Soft StartMotor Start Theory3A motors start performance characteristics set the limits of what can be achieved with either a full voltage or reduced voltage starter.电机起动性能规定使用全电压起动器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。或降压起动器能达到的极限值。It is especially important to consider motor start characteristics when seeking to:-Minimise start current-Maximise start torque当尝试以下方式时考虑电机起动特性当尝试以下方式时考虑电机起动特性尤其重要：尤其重要：-将起动电流降至最小将起动电流降至最小-将起动扭矩增至最大将起动扭矩增至最大 Motor Performance电机性能电机性能Motor Start Theory4Rotor design affects starting performance.转子的设计影响起动性能。转子的设计影响起动性能。Stator design affects full speed performance.定子的设计影响全速性能。定子的设计影响全速性能。The shape,position and material of the rotor bars affect the current drawn and torque produced during motor starting.转子杆的形状、位置和材料影响引入转子杆的形状、位置和材料影响引入电流和电机起动时产生的扭矩。电流和电机起动时产生的扭矩。Motor Performance电机性能电机性能 Motor Start Theory5A motors start performance can be identified by examining the motor data sheet.电机起动性能可通过检查电机数据表电机起动性能可通过检查电机数据表得到确认。得到确认。The table details selected performance data for a range of 110kW motors.数据表详述了数据表详述了110kW电机系列选用的电机系列选用的性能数据。性能数据。Typical Motor Data典型电机数据典型电机数据Motor SpeedFLCLRCLRT%FLTorque(rpm)(amps)(%FLC)(%FLT)Efncy 3xFLCA14701916002639365.8B147518460019093.547.5C14751915701509241.6D148018766019094.539.2E14701855501209236F14701916701509330.1G14801907802009429.6H147518285022093.527.4I14801906701209424Sample Of Typical 110kW MotorsMotor Start Theory6Maximum motor start current under full voltage start conditions is defined by the motors Locked Rotor Current(LRC).全电压起动条件下最大电机起动电流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（是由电机锁定转子电流（LRC）确定确定的。的。LRC levels vary considerably between motors.LRC等级在电机间有显著变化。等级在电机间有显著变化。In the example,Motor H will draw 55%more current at start than Motor E.在实例中，电机在实例中，电机H引入的起动电流比引入的起动电流比电机电机E多多55%。Start Current起动电流起动电流Motor SpeedFLCLRCLRT%FLTorque(rpm)(amps)(%FLC)(%FLT)Efncy 3xFLCA14701916002639365.8B147518460019093.547.5C14751915701509241.6D148018766019094.539.2E14701855501209236F14701916701509330.1G14801907802009429.6H147518285022093.527.4I14801906701209424LRC ranges from 550%to 850%Sample Of Typical 110kW MotorsMotor Start Theory7Motor start torque performance is indicated by the motors Locked Rotor Torque(LRT)figure.电机起动扭矩性能是由电机的锁定转电机起动扭矩性能是由电机的锁定转子扭矩（子扭矩（LRT）图表示的。图表示的。LRT levels vary considerably between motors.LRT等级在各个电机间有显著变化。等级在各个电机间有显著变化。In the example,Motor A produces twice as much torque during start as Motor I.在实例中，电机在实例中，电机A起动时产生的扭矩起动时产生的扭矩是电机是电机I的两倍。的两倍。Start Torque起动扭矩起动扭矩Motor SpeedFLCLRCLRT%FLTorque(rpm)(amps)(%FLC)(%FLT)Efncy 3xFLCA14701916002639365.8B147518460019093.547.5C14751915701509241.6D148018766019094.539.2E14701855501209236F14701916701509330.1G14801907802009429.6H147518285022093.527.4I14801906701209424LRT ranges from 120%to 263%Sample Of Typical 110kW MotorsMotor Start Theory8LRC&LRT must be considered together when determining a motors start performance.确定电机起动性能时必须合并考虑确定电机起动性能时必须合并考虑LRC&LRT。The example does this by ranking the motors according to the torque produced at 3 x FLC.实例中的作法是根据实例中的作法是根据3FLC产生的扭产生的扭矩对电机排序。矩对电机排序。LRC&LRT Work TogetherLRC&LRT同时运转同时运转 Motor SpeedFLCLRCLRT%FLTorque(rpm)(amps)(%FLC)(%FLT)Efncy 3xFLCA14701916002639365.8B147518460019093.547.5C14751915701509241.6D148018766019094.539.2E14701855501209236F14701916701509330.1G14801907802009429.6H147518285022093.527.4I14801906701209424Sample Of Typical 110kW MotorsTorque developed at 3 x FLCMotor Start Theory9Motor SpeedFLCLRCLRT%FLTorque(rpm)(amps)(%FLC)(%FLT)Efncy 3xFLCA14701916002639365.8B147518460019093.547.5C14751915701509241.6D148018766019094.539.2E14701855501209236F14701916701509330.1G14801907802009429.6H147518285022093.527.4I14801906701209424Torque is reduced by the square of the current reduction.扭矩减少值是电流降底值的平方。扭矩减少值是电流降底值的平方。Motors B&G produce almost the same torque at full voltage.电机电机B和和G在满电压情况下产生的扭在满电压情况下产生的扭矩几乎相同。矩几乎相同。Motor B produces 60%more start torque at 3 x FLC.电机电机B在在3 x FLC条件下产生的起动扭条件下产生的起动扭矩多矩多60。Reduced Voltage Starting Amplifies Motor Differences降压起动扩大电机差异降压起动扩大电机差异 Sample Of Typical 110kW MotorsMotor Start Theory10MotorLRCLRTTORQUE(%FLC)(%FLT)3 X FLCA60026365.8B600190C570150D660190 Follow the example and calculate the start torque at 3 x FLC for motors B,C&D.依照实例依照实例，计算电机计算电机B、C和和D在在3 x FLC条件下的起动扭矩。条件下的起动扭矩。How To Calculate Start Torque如何计算起动扭矩如何计算起动扭矩 Start Torque=LRT xStart CurrentLRC()2()2300%600%65.8%=x263%47.541.539.3Motor Start Theory11Selecting a motor with low Locked Rotor Current(LRC)and high Locked Rotor Torque(LRT)will:选择低锁定转子电流（选择低锁定转子电流（LRC）和高锁和高锁定转子扭矩（定转子扭矩（LRT）电机将：电机将：-Reduce start current.-降低起动电流降低起动电流-Increase start torque.-增加起动扭矩增加起动扭矩-Reduce soft starter cost.-降低软起动器的成本降低软起动器的成本Summary总结总结Motor Start Theory12Current rises instantaneously to LRC levels.This causes a current transient that can have undesirable effects on the supply.电流瞬间上升至电流瞬间上升至LRC水平，由此引起水平，由此引起的电流瞬变可对电源产生不良的影响的电流瞬变可对电源产生不良的影响Current gradually falls as motor speed increases.电机速度增加时电流下降。电机速度增加时电流下降。Motor loading affects only the time taken for acceleration,not the magnitude of current which is always LRC.电机负载只影响加速所需的时间电机负载只影响加速所需的时间，而而不影响始终为不影响始终为LRC的的电流值。电流值。Full Voltage Starting满满电压起动电压起动0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Motor Start Theory13Full Voltage Starting满电压起动满电压起动0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Torque rises instantaneously to LRT levels.This causes a torque transient that can be damaging.电流瞬间上升至电流瞬间上升至LRC水平，由此引起水平，由此引起的电流瞬变具有破坏性。的电流瞬变具有破坏性。Typical torque falls from LRT to Pull Out Torque before rising to Breakdown Torque just before full speed.电机达到满速前，典型转矩在升至失电机达到满速前，典型转矩在升至失步转矩前由步转矩前由LRT降至脱扣力矩。降至脱扣力矩。Motor Start Theory140501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Full Voltage Starting Limitations满电压起动限制满电压起动限制1.Current transient 电流瞬变电流瞬变 12.Current magnitude 电流值电流值 23.Torque transient 扭矩瞬变扭矩瞬变 344.Torque magnitude 扭矩值扭矩值 Reduced voltage starting attempts to overcome these limitations by applying the voltage gradually.降压起动通过逐渐利用满电压的方式降压起动通过逐渐利用满电压的方式力图克服这些限制。力图克服这些限制。Motor Start Theory150501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Reduced Voltage Starting降压起动降压起动IST=LRT xTSTLRC()2Reduces start torque by the square of the current reduction.起动扭矩减少值是电流降低值的平方。起动扭矩减少值是电流降低值的平方。Current can only be reduced to the point where torque output from the motor exceeds the torque required by the load.电流只能降到电机扭矩输出超过负载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要求的扭矩的那个点Reduces start current.降低起动电流。降低起动电流。Motor Start Theory16Reduced Voltage Starting降压起动降压起动To be effective,a reduced voltage starter must allow the motor to accelerate to around 90%speed before applying full voltage.为确保有效运行为确保有效运行，降压起动器须使电降压起动器须使电机在使用满电压之前加速到机在使用满电压之前加速到90左右左右 Below this speed the current will step through to almost LRC levels thus removing any benefit from the reduced voltage starter.如果低于此速度如果低于此速度，电流将逐步达到电流将逐步达到LRC水平，从而失去降压起动器的任水平，从而失去降压起动器的任何优点。何优点。0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Small Reductionat 50%speedLarge Reductionat 95%speedMotor Start Theory17Electromechanical 机电机电-Auto-transformer 自耦变压器自耦变压器-Primary Resistance 一次电路电阻一次电路电阻-Star/Delta 星形星形/三角形三角形Electronic 电子电子-Soft Start 软起动软起动Reduced Voltage Starters降压起动器降压起动器Motor Start Theory18Auto-transformers自耦变压器自耦变压器Thermal Overload3 PhaseAuto Transformer(B)Start Contactor(A)Start ContactorRunContactor3 MThe Auto-transformer Starter employs an auto-transformer to reduce the voltage during the start period.The transformer has a range of output voltage taps that can be used to set the start voltage.超动期间超动期间自耦变压器起动器使用自耦变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。开关，可用以设置起动电压。The motor current is reduced by the start voltage reduction,and further reduced by the transformer action resulting in a line current less than the actual motor current.电机电流随起动电压下降而降低，且通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。线路电流小于电机实际电流。Motor Start Theory190501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)60%Tap 60%分接头分接头Auto-transformers自耦变压器自耦变压器Limitations:-Limited voltage taps-Limited number of starts per hour-Torque reduced at all speeds-Costly限制：限制：-限定电压分接头限定电压分接头-限定每小时的起动次数限定每小时的起动次数-在所有速度下扭矩值降低在所有速度下扭矩值降低-价值高价值高 Motor Start Theory200501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)50%Tap 50%分接头分接头The initial start voltage is set by tap selection,and the start time is controlled by a timer.If the start voltage is too low,or the start time incorrectly set,the transition to full voltage will occur with the motor at less than full speed,resulting in a high current and torque step.初始起动电压是由分接头选择设定的，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，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全速之时，因此导致高电流和扭矩步进。进。Auto-transformers自耦变压器自耦变压器Motor Start Theory21Primary Resistance一次电路电阻一次电路电阻RUNCONTACTORMOTOROVERLOADTHERMALSTARTRESISTORSLINECONTACTOR3 MResistors are connected in series with each phase,between the isolation contactor and the motor.The voltage drop across the resistors results in a reduced voltage applied to the motor,thus reducing start current and torque.电阻器与隔离接触器和电机之间的每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。降压，从而降低起动电流和扭矩。Motor Start Theory22Set for 4 x FLC start current.设置设置4 x FLC起动电流。起动电流。Primary Resistance一次电路电阻一次电路电阻0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Limitations:-Difficult to change resistance-Dissipate a lot of heat-Limited number of starts per hour-Start characteristics change between starts if resistors have not totally cooled-Hard to start high inertia loads限制：限制：-很难改变电阻很难改变电阻-大量散热大量散热-限定每小时的起动次数限定每小时的起动次数-如果电阻器没有完全冷却，起动特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性会在各起动间发生差异-难以起动高惯性负载难以起动高惯性负载 Motor Start Theory23Primary Resistance一次电路电阻一次电路电阻0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Set for 3.5 x FLC start current.设置设置3.5 x FLC起动电流。起动电流。Start voltage is determined by the resistors used.If the resistance is too high there will be insufficient torque to accelerate the motor to full speed.起动电压是由所使用的电阻器确定起动电压是由所使用的电阻器确定的。如果电阻太高，则扭矩不足以的。如果电阻太高，则扭矩不足以加速电机达到全速。加速电机达到全速。The reduced voltage start time is controlled by a preset timer.If the time is too short,the motor will not have achieved full speed before the resistors are bridged.降压起动时间是由预置计时器控制降压起动时间是由预置计时器控制的。如果时间太短，电机不会在电的。如果时间太短，电机不会在电阻器跨接之前达到全速。阻器跨接之前达到全速。Motor Start Theory24Star/Delta星形星形/三角形三角形Motor3ThermalOverloadStarContactorDeltaContactorMainContactorThe motor is initially connected in star configuration and then,after a preset time,the motor is disconnected from the supply and reconnected in delta configuration.The current and torque in the star configuration are one third of the full voltage current and torque when the motor is connected in delta.电机最初以星形配置进行连接，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。满电压电流和扭矩的三分之一。Motor Start Theory25Limitations:-No adjustment possible.-Open transition switching between star and delta causes damaging current and torque transients.限制：限制：-不能调节。不能调节。-星形和三角形之间的开路瞬变会破星形和三角形之间的开路瞬变会破坏电流和扭矩瞬变坏电流和扭矩瞬变Star/Delta星形星形/三角形三角形0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Insufficient torque to accelerate this load in star configuration.不足的扭矩以星形配置加速该负载不足的扭矩以星形配置加速该负载Motor Start Theory26Open Transition SwitchingOccurs when the starter goes through an open circuit stage in the switching sequence.Stage 1 connection to the reduced voltage;2 disconnect from the reduced voltage(open circuit);3 connect to the full voltage.Open transition starting causes severe current&torque transients that can be more detrimental to the supply and the mechanical equipment than full voltage starting.When the motor is spinning and then disconnected from the supply,it acts as a generator.Output voltage can be the same amplitude as the supply.At the time of reclose there can still be significant voltage present at the motor terminals.Voltage generated by the motor at the instant of reclose may be equal to the supply voltage but exactly out of phase.This equates to reclosing with twice the supply voltage on the motor.The result is a current of twice locked rotor current and a torque transient of four times locked rotor torque.Motor Start Theory27开路瞬变转换开路瞬变转换 当起动器以转换顺序通过开路段时发生。1连接降压；2与降压（开路）断开；3连接满电压。开路瞬变起动造成严重的电流和扭矩瞬变，这对电源和机械设备可能比满电压起动更加有害。当电机旋转、然后与电源断开时，起到发电机的作用。输出电压可与电源振幅相同。再合闸时，仍可有明显的电压出现在电机终端。再合闸瞬间电机产生的电压可与电源电压相等但正好失相。这等于再合闸电机上有两倍的电源电压。这一结果是两倍锁定转子电流的电流和四倍锁定转子扭矩的扭矩瞬变。Motor Start Theory28Soft Starter软起动器软起动器MotorOverloadAC SwitchesContactorM3 Soft Starters control the voltage applied to the motor by the use of solid state AC switches(SCRs)in series with the supply to the motor.软起动器通过与电机电源串接的固态软起动器通过与电机电源串接的固态AC开关（开关（ACR）控制电机电压。控制电机电压。Motor Start Theory29-Minimum possible start current-No current steps-No torque steps-Good start torque characteristics-起动电流可达最低起动电流可达最低-没有电流步进没有电流步进-没有扭矩步进没有扭矩步进-良好的起动扭矩特性良好的起动扭矩特性 Soft Starter软起动器软起动器0501001502002503001009080706050403020100SLIP(%)FULL LOAD TORQUE(%)0100200300400500600700CURRENT(%)Motor Start Theory30Motor characteristics set the limits of what can be achieved with a soft starter.电机特性决定软起动器所能达到的极电机特性决定软起动器所能达到的极限。限。Pay special attention to motor characteristics when:在以下情况下要特别注意电机特性在以下情况下要特别注意电机特性:-it is important to minimise start current-将起动电流降至最低是十分重要的将起动电流降至最低是十分重要的-it is important to maximise start torque-将起动扭矩增至最大是十分重要的将起动扭矩增至最大是十分重要的-dealing with large motors(200kW+)-涉及大型电机（涉及大型电机（200kW+）Summary总结总结Motor Start Theory31Soft start is technically the best reduced voltage starting system.技术上技术上，软起动是最佳的降压起动系软起动是最佳的降压起动系统。统。Star/Delta starting is the cheapest and most commonly employed reduced voltage starting system.However its performance characteristics are damaging.星形星形/三角形起动是最廉价和最通用三角形起动是最廉价和最通用的降压起动系统。但其运作性能有破的降压起动系统。但其运作性能有破坏性。坏性。Summary总结总结