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Appendix D CE|VFD-S Series
C-6 Revision August 2006, SE08, SW V2.61
E. If 100% continuous torque is required at low speed, it may be necessary to use a special
inverter duty motor.
F. Motor dynamic balance and rotor endurance should be considered if the operating speed
exceeds the rated speed (60Hz) of a standard motor.
G. 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.
H. 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.
I. The motor fan will be very noisy when the motor speed exceeds 50 or 60Hz.
Special motors:
A. Pole-changing (Dahlander) motor:
The rated current is different 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).
B. 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.
C. 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.