Testing Canstack PM Motors at Higher than Rated Frequencies

[SPIGUY]

I'm trying to determine if testing small synchronous PM motors (used as timing devices in appliance controls) at high frequencies (up to 600 Hz) will damage the motor during production audit testing. These motors are rated at 115 VAC 60 Hz with a speed of 0.0037 RPM (1 RPM/271 minutes). In order to get the test completed in a timely matter the motors are thus running at 10X speed. How does increasing the frequency affect the excitation level, the voltage, and current from a theorical standpoint?

 

[jbartos]

Comments:
1. Which parameters are you testing at these motors?
2. The higher frequency will cause Eddy Current to increase and generate heat and watt losses.
3. Remagnetization losses will increase with frequency (C. P. Steinmetz's Law/Formula)
4. Bearings may be damaged by the higher frequency causing common mode currents. Some good grounding may be prudent.
5. Permanent magnet may lose some magnetism due to higher temperatures.
6. Some increased mechanical vibrations may develop.
7. Wire skin effect will take place and heat up windings.
8. Etc.

 

[rhatcher]

First, there will be no excitation for a PM motor. However, the big question in my mind is the RPM of the motor you described. A synchronous RPM at 60 hz of 0.0037 RPM would imply that the motor has almost 2 million poles. Are you sure of your info or did I leave my brain at work again? Please clarify this question. Any input from the group would be appreciated....

 

[SPIGUY]

Clarification:

Motor speed is 240 RPM. The timer speed is 0.0037 RPM with speed reduction from the motor to the timer cam achieved through a gear train. Sorry for the confusion. The test monitors timer operation only (motor start, correct motor rotation, and contact switching/timing). Individual motor voltage, current, and temperature are not recorded. I observed a customer's tester and the motors ran cool to the touch. The customer states that at the tester test conditions (208 VAC @ 600 Hz) motor current is half the level it is at 115 VAC. I'm not sure how they can maintain the motor excitation level. We are trying to develop a similar tester.