During No load run test we found

1. unbalanced NLA

A=137.8A, B=144.6A, C=147.5A while Supply was A-B=380.3V, B-C=381.6V, C-A=380.9V

2. Motor frame temperature after running was reached to 62C same like DE & NDE bearing housing temperature. Also at lead cables the temperature was up-to 72C.

We rewound the motor in our shop.

Is it normal or there are problems in winding?


Original Post

The current unbalance doesn't sound unusual to me.   A very small voltage unbalance can create a larger current unbalance, especially when unloaded.

The bearing temperatures don't sound alarming (assuming they were stabilized, in absence of any comparison info). Frame and leads, tougher to say.

btw, what is the horsepower and speed of this motor?  (I'm curious if 140A is a reasonable no-load current).

How long was the motor running to reach those temperatures?

Switch 2 of the power leads supplying the motor.  If the variations in amperage readings stay in the same spot, it is caused by your incoming power.  If there variations move with the phases switched, it is caused by the motor.

In any case there is only a 7% variation.  I forget what the allowable limit is, but I believe this is ok.

Rule of thumb is the motor should pull about 1/3rd of the rated FLA running under no load.  You are slightly under that at nearly 1/4.  No problem seen there.

Are the resistance between phases even, and a nice sin wave on the Surge?

For 20 minutes running time, the temperature readings given don't sound like a cause for concern.  What was the ambient temperature at the time? Motor appears to be TEFC, was the cooling fan and fan cover installed during the test run?

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