Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning an electric motor re-wind that may or may not be faulty, is answered by ABB:
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Question: Do you have a view on the following, which concerns a motor re-wind? I have just had a 127kW motor rewound for a compressor and I have a 20A imbalance in one winding. Whilst trying not to blame the motor I have checked the following:
- Phase voltage across winding 425 off-load; 421 full-load - not 1V difference between phases
- 400A busbar supplying the load - all connections clean and tight
- Moved phases on by 1. Current imbalance follows the leg (eg: the yellow phase has the problem - when the legs are moved on by one, the problem moved to the blue phase)
- The winding leg is out by 20A, but the incoming phase is out by 10A
- The windings value off-load U1 U2 = 82A; V1 V2 = 61A; W1 W2 = 62A.
- Phase amp. Red 119.3; Yellow 126.6; Blue 118.4 (greater than the permissible % difference).
As the motor heats up, the amperes increase until the overload comes in. I allowed the winding to reach 129A and still climbing before I took it off-line. When the motor is running off-load the ampere remains constant. This could be the imbalance on the leg over heating at FLC
The temperature in the air and on-load are constant, as before.
Have I missed anything before I go back to the motor company? I would be grateful for your help.
Answer: You seem to have covered most things and it points to the motor.
You could try measuring the resistance of the individual windings and comparing them to see if there is any noticeable difference.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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