Question about winding(s) on a 2 speed motor

[spciesla]

I was at a conference last week and we were discussing a vibration problem on a 2 speed motor / fan. The motor experiences a vibration spike when the speed is changed. The vibration is observed by shaft relative (proximity) probes. One of the questions posed, was is this "real" vibration or some type of measurement anomaly. There was a bit of discussion and brain storming. Someone suggests that the motor speed is changed by using different windings and that the windings might have different magnetic centers, thereby causing a jolt to the system when the speed is changed. It sounds interesting on the surface, but I'm pretty light on motor design, so I don't have any idea.

Note that this is not my motor / fan, so I don't have any other relevant facts.

What's your opinion?

 

[jraef]

The problem is, there are multiple ways to attain a two speed AC induction motor. The comment on having a different magnetic center might apply to a two speed two winding motor, but would not apply to one of the 3 different ways to accomplish a two speed one winding motor.

But if this vibration anomaly is a transient event that only occurs momentarily during transition from low to high speed, I would interpret that as simply a torque transient because in the higher speed, you will be giving the motor a step change in torque, regardless of how it is accomplished. If that transient vibration is a problem, you can use soft starters to reduce the torque transient, or use a VFD in lieu of a two speed motor.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

The magnetic centers are largely dependent on the stator iron and the rotor iron.
Given the very high ratio between the magnetic permeability of iron and air, even if one winding of a two winding motor has different lengths of end turns, the effect on the magnetic center will be minimal.
I agree with jraef. Torque transients.

Bill
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