Polyphase induction motor fault finding

[popee1]

Hi Ladies & Gents,

I was wondering if you could help me. I work in the power industry and during some routine maintenance of a transformer we found the tap-changer to be faulty, where the mechanism had jammed. We have disconnected the motor from the mechanism however the motor doesn’t seem to be operating. We are getting three phases to the motor when operating the contactor and the relay for changing the phase rotation is audible when we select the motor direction. Are there any tests we can do to confirm the motor is damaged? Our 3 phase machine theory is a little sketchy. We don't have any diagrams yet, we can see the nameplate but it gives, rated hp, current, volts etc. Any help would be appreciated.

Cheers - Popee1

 

[ScottyUK]

Most motors for tapchangers have a thermal overload relay. When you apply power to the motor does the O/L relay operate?

Can you turn the motor over by hand to show it is not seized?

Test for continuity through the motor windings. There will be three separate windings if you are lucky so check they are isolated from each other using a Megger and check the winding resistances are more-or-less equal using a milliohm-meter.

Does anything smell burnt? Cooked windings have a distinctive smell.


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