Delta Electronics VFD-G C.3 How to Choose a Suitable Motor, torque%, 25% 40% 60% 100, continuous

Appendix C How to Select the Right AC Motor Drive

4.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 operate a standard 3-phase induction motor, take the following 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 motor temperature may rise above the motor rating due to limited airflow produced by the motor’s fan. Consider external forced motor cooling.

3.When the standard motor operates at low speed for long time, the output load must be decreased.

4.The load tolerance of a standard motor is as follows:

Load duty-cycle

torque(%)

25% 40% 60%

100

82

70
60	continuous
50

0 3 6 20 60

Frequency (Hz)

5.If 100% continuous torque is required at low speed, it may be necessary to use a special inverter duty motor.

6.Motor dynamic balance and rotor endurance should be considered once the operating speed exceeds the rated speed (60Hz) of a standard motor.

Revision July 2008, EG03, SW V1.06 C-5