~APPENDIX A~
- 82 -
(4) Selections of motor
A. Standard motors
a. The load should be a standard three phase induction motor.
b. Motor can not be operated at low speed for a long time, because
that the low speed of cooling fan will result high temperature.
This is improved by using the motor with independence fan.
c. The characteristics of the standard three phase induction motor
(NEMA B) are shown as followings.
d. As the speed of motor is greater than 60 Hz, the torque is
decrease drastically.
e. Is the insulation of motor good or not? The minimum
requirement is 100 M
Ω
at 500 V.
B. Special motors
a. Synchronous motor: Starting current is greater than that of
standard induction motor. V/F ratio is lower than that of
standard induction motor. The ratings of inverter should be
increased.
b. Waterproof motor: The rated current is greater than that of
standard induction motor. And the V/F pattern and the
limitation of minimum speed should be mentioned. Sometimes,
the insulation may be poor due to the sand and the other
objects.
c. Explosion proof motor: RM5G series is not designed against
explosion. In installation, operation and maintenance, care must
be made for safety considerations.
Percentage of slip rate
100 80 60 40 20 0
300
200
100
0
Torque
Max. Speed
Constant
Torque
0
Wmb
Pm
Pm
T
Ta
Percentage of full -load
Percentage of synchronous speed
Constant
horsepower
