AC Synchronous Motor Question

[SmokinJoeR]

I have a 3755HP 6600V AC Synchronous Motor and I was wondering if it is ok to run this motor at a stator voltage of 4160V continuously?


Are there side effects of operating a synch motor at lower than rated stator voltage?

The excitation requirements for this machine is taken care of fully so that isn't a problem.

Any help is appreciated.

Joe

 

[jraef]

Even on a synchronous motor, the torque will vary by the sqare of the voltage reduction. So in your case, you are applying 63% rated design voltage so your effective motor torque will drop to roughly 40% of rated. Assuming the frequency is the same, then you now have a 1490HP motor for all intents and purposes. If you load it any more than that, it will over load and/or stall, which has some very bad consequences for synchronous motors.


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[electricpete]

During normal full-voltage full-load operation, you have margin to pole slip. The question is how much margin do you have left (if any) after you reduce voltage. Also if you have steady (vs pulsating) load, you might be able to take a little credit for that. Maybe OEM can help with an evaluation.

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[electricpete]

By the way, I would think would increasing the excitation voltage to top end of the band would buy back some margin to pole slip (assuming you can tolerate this machine putting out the vars).... wouldn't it?

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[waross]

You are going to have to reduce the excitation proportionally to the reduction of the voltage to maintain unity power factor.
The motor at full load does not use the maximum available torque. If 40% of the original starting torque will still start the motor you have a good chance that it will be able to develop 3755HP x (4160V/6600V) = 2367 HP.


Bill
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