Sync motor test run

[ProWinder]

I want to test run a sync motor in the shop location. I have no name plate to get information from. I know the stator is 2300 VAC, 1200 rpm. Can I test run the motor as a squirrel cage motor on 600 VAC, leaving the rotor leads open? In doing this will the rotor work as an auto transformer and build voltage in the rotor windings to the point of causing a failure to ground? I have rewound the coils on the rotor and need to test run to check the Babbitt bearings, to ensure they are not going to fail.
Thanks for any help.

 

[wayne440]

Here is a somewhat relevant thread that illustrates one probable failure mode.

http://www.eng-tips.com/viewthread.cfm?qid=403231

 

[ProWinder]

Thanks for the link. I did not find that thread when I did a search.

 

[LionelHutz]

Is the motor a brush type or brushless type?

You can not run a brush type motor with the rotor open circuit. It will produce a high enough voltage to cause insulation breakdown. Shorting isn't the best method either but it should work just to test the motor. Using a resistor that is 2-4x the field coil resistance across the leads during starting would work the best.

 

[ProWinder]

Yes it is the brush type. Thank you for the info.

 

[waross]

The normal load on the field during starting is the coil of the Polarized Field Frequency Relay. Leave the relay in the circuit or replace it with an equivalent impedance.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[krisys]

There is a confusion of whether it is synchronous motor or Slip ring induction motor. The rotor shorting is the requirement for the slip ring induction motor.

In the synchronous motor rotor main winding is meant for field. The field shall be excited by supplying the voltage either thru the brush from external source or through the pilot exciter via rotating diode.
There is another set of winding, which is auxiliary in nature, usually called as damper winding. If I remember correctly the this winding is additionally used to start the motor in induction mode.

So, if you do not give the excitation supply, the motor would run like an induction motor. Normally the starting winding is rated for short time duty. SO I am not sure, how long you can run the motor safely.

In my view, you can give a bump start, or run for few seconds (say 30 sec) and stop to check the bearing.

If you want you run continuously, you have to arrange a DC supply for the field winding.

 

[LionelHutz]

The motor will likely reluctance synchronize with no load connected. The stator current levels should be under rated with 26% of the rated voltage applied but the currents should be monitored. Still, I'm doubting that running it for a longer time will hurt the motor.