Slip Ring Induction Motor


Thread Starter


there is a slip ring IM of 50 KW used for hoist purpose in overhead crane. currently it is kept as spare. its a repaired one and its very old from which on test run a humming sound (more than normal) is coming, but current and other things like stator and rotor resistance is normal. can anybody suggest the reasons for this humming noise? is it due to uneven air gap and harmonics ? can i put it to service if required?

it is used for lifting loads.

Phil Corso, PE

Responding to Ritesh's 20-Oct (20:53) query... it could be an open-rotor circuit:

1) What are stator-voltage and stator-current values?

2) What are rotor-voltage and rotor-current values?

3) Does intensity of humming sound vary during starting period?

4) Have you tried uncoupled starting with slip-rings shorted?

Regards, Phil Corso ([email protected])
You said the motor has been repaired. A likely cause for increased sound (if it is the normal 120Hz buzz, maybe with overlays) is due to some over-eager burnout when the original winding was removed. That leads to looseness in the core laminations and can be the cause of extra noise.