Delta Electronics VFD-EL series, User Manual, Page: 179 / 181

Appendix C How to Select the Right AC Motor Drive
|
| |
|
Revision 2016/03, 6ELE, V1.14
C-4
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:
3 6 20 60
100
82
70
60
50
0
60%
40%
25%
to
rq
u
e
(%
)
continuous
Frequency (Hz)
Load duty-cycle
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.
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.