shorting contacts sparking (slip ring induction motor)
shorting contacts sparking (slip ring induction motor)
(OP)
there is a situation of a 15MW slip ring motor (uses liquid rotor starter) that has its slip ring shorting contacts sparking/ flashing - mostly when the motor trips from full load. On few occations they also spark during startup but this is not frequent. As a result the contacts need to be replaced now and again as they get badly damaged on the contact surface. This is a recent problem, the motors slip rings were replaced about 5 months ago as part of major overhaul. Can anyone suggests why this could be happening and what can be done to resolve this problem?





RE: shorting contacts sparking (slip ring induction motor)
Bill
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"Why not the best?"
Jimmy Carter
RE: shorting contacts sparking (slip ring induction motor)
RE: shorting contacts sparking (slip ring induction motor)
And the contacts are opened while the machine is secured.
During transition from running to secured (trip), the contacts immediately open?
In that case I would think a time delay is needed between tripping the motor and opening those contacts. Just thinking out loud (I don't work with these type machines)
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RE: shorting contacts sparking (slip ring induction motor)
Muthu
www.edison.co.in
RE: shorting contacts sparking (slip ring induction motor)
edison123, keeping the contacts closed all the time will adversely affect the starting current (will be high) and starting torque (will be low). For a slip ring motor we want to start the motor with some resistance added to the rotor circuit for high starting torque, this is then shorted out (by the rotor shorting contacts) once the motor has attained running speed. The trouble now is that as soon as the mtor trips for some condition, these shorting contacts open (as they should)but a flash also occurs accross the contact faces - destroying them in the process.
RE: shorting contacts sparking (slip ring induction motor)
Or go for a higher rated rotor shorting contacts to handle the rotor current, which is close to DC.
Muthu
www.edison.co.in
RE: shorting contacts sparking (slip ring induction motor)
I have similar HV motor, *only* 3550kW, and it have special device mounted on the shaft with small motor for shorting rings and lifting brushes when it came to the nominal speed. After tripping of the motor,device simply letting down brushes and motor is ready for new start. Your motor is bigger and it must have something similar or, like Muthu said, you must make scheme for opening rotor contactor after few second of tripping of the motor and also block start of the motor when the rotor contactor is close. Good luck!