Inverted 3-phase motor surging

[rakeshkdhawan]

We have a 3-Phase brushless inverted motor. The rotor is 10.5" in diameter and 2" in length.

The rotor is made of COLD ROLLED DEEP DRAWN LOW CARBON ALLOY 1008/1010 STEEL PER ASTM A-A1008A/A109, 16 GAUGE ( .059").

This has 20 poles - 10 pole pairs. The max spped of the motor is about 500 rpm.

We see surging/pulsing which occurs once per revolution. We do not know what the cause is?

I have the following questions:

1. What does the aspect ratio (D/L) do to a motor in terms of vibration?
2. Having a 10.5" diameter steel, we do see some run out. How can run out contribute to surging/pulsing/vibration?
3. The rotor consist of 2 housings. Left housing and right housing. The right housing is single straight sheet of steel. Can that contribute to surging.
4. How do I go about finding the cause of the surging. We have looked at electrical currents. They are well balanced. We do see 10 times the rotational rpm due to electrical excitation but do not think that contributes to the mechanical issue at hand.
5. What is the effect of uneven air gap on surging/pulsing?

Any help would be greatly appreciated.

Thanks
Rakesh

 

[alexit]

This is permanent magnet DC brushless inverted motor?

Perhaps this helps some of your questions:

http://www.ansoft.com/news/articles...ing_for_Permanent_Magnet_Rotor_Validation.pdf

There are many possiblilty for surge in motor from your questions:
1. High aspect ratio means more edge effects means more control errors or inefficiency
2. poor runout or mechanincal position of poles
3. One housing has local better/worse flux density than other
5. Uneven air gap is normal only efficinecy unless also #2 or #3

4. Measure very accurate rotor velocity/acceleration and displacements in three axis, see if surge corresponds to absolute rotor position displacement respect to all axis. When can predict surge as position of rotor make change to speeds at many small interval. Does surge always occur at same absolute position? (Not in relation to electrical frequency/voltage/current.) Find why this spot is fast/slow than others...