Appendix C How to Select the Right AC Motor Drive|Revision August 2008, 03VE, SW V2.04 C-5C.3 How to Choose a Suitable MotorStandard motorWhen using the AC Motor Drive to operate a standard 3-phase induction motor, take thefollowing precautions:1. The energy loss is greater than for an inverter duty motor.2. Avoid running motor at low speed for a long time. Under this condition, the motortemperature may rise above the motor rating due to limited airflow produced by themotor’s fan. Consider external forced motor cooling.3. When the standard motor operates at low speed for long time, the output load must bedecreased.4. The load tolerance of a standard motor is as follows:3 6 20 6010082706050060%40%25%torque(%)continuousFrequency (Hz)Load duty-cycle5. If 100% continuous torque is required at low speed, it may be necessary to use a specialinverter duty motor.6. Motor dynamic balance and rotor endurance should be considered once the operatingspeed exceeds the rated speed (60Hz) of a standard motor.7. Motor torque characteristics vary when an AC Motor Drive instead of commercial powersupply drives the motor. Check the load torque characteristics of the machine to beconnected.8. Because of the high carrier frequency PWM control of the VFD series, pay attention to thefollowing motor vibration problems:
