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Appendix C How to Select the Right AC Motor Drive|
C-6 Revision August 2008, 2ELE, V1.02
7. Motor torque characteristics vary when an AC Motor Drive instead of commercial power
supply drives the motor. Check the load torque characteristics of the machine to be
connected.
8. Because of the high carrier frequency PWM control of the VFD series, pay attention to the
following motor vibration problems:
Resonant mechanical vibration: anti-vibration (damping) rubbers should be
used to mount equipment that runs at varying speed.
Motor imbalance: special care is required for operation at 50 or 60 Hz and
higher frequency.
To avoid resonances, use the Skip frequencies.
9. The motor fan will be very noisy when the motor speed exceeds 50 or 60Hz.
Special motors:
1. Pole-changing (Dahlander) motor:
The rated current is differs from that of a standard motor. Please check before operation
and select the capacity of the AC motor drive carefully. When changing the pole number
the motor needs to be stopped first. If over current occurs during operation or
regenerative voltage is too high, please let the motor free run to stop (coast).
2. Submersible motor:
The rated current is higher than that of a standard motor. Please check before operation
and choose the capacity of the AC motor drive carefully. With long motor cable between
AC motor drive and motor, available motor torque is reduced.
3. Explosion-proof (Ex) motor:
Needs to be installed in a safe place and the wiring should comply with the (Ex)
requirements. Delta AC Motor Drives are not suitable for (Ex) areas with special
precautions.
4. Gear reduction motor:
The lubricating method of reduction gearbox and speed range for continuous operation
will be different and depending on brand. The lubricating function for operating long time
at low speed and for high-speed operation needs to be considered carefully.
5. Synchronous motor:
The rated current and starting current are higher than for standard motors. Please check
before operation and choose the capacity of the AC motor drive carefully. When the AC