Chapter 8Appendix C How to Select the Right AC Motor Drive
|VFD-S Series
Revision August 2008, SE09, SW V2.61 C-5
D. If the stall prevention function is activated, the accel./decel. time is automatically
extended to a length that the AC Motor Drive can handle. If the motor needs to
decelerate within a certain time with high load inertia that can’t be handled by the AC
Motor Drive in the required time, either use an external brake resistor and/or brake unit,
depending on the model, (to shorten deceleration time only) or increase the capacity for
both the motor and the AC Motor Drive.
C.3 How to Choose a Suitable Motor
Standard motor
When using the AC Motor Drive to control a standard 3-phase induction motor, take the
following precautions:
A. The motor losses are greater than for an inverter duty motor.
B. Avoid running the motor at low speed for a long time. Under this condition, the motor
temperature may rise above the motor rating due to limited airflow produced by the
motor’s fan. Consider external forced motor cooling.
C. When the standard motor operates at low speed for long time, the output load must be
decreased.
D. The load tolerance of a standard motor is as follows:
3 6 20 60
100
82
70
60
50
0
60%
40%
25%
torque(%)
continuous
Frequency (Hz)
Load duty-cycle
E. If 100% continuous torque is required at low speed, it may be necessary to use a special
inverter duty motor.
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