no load current
no load current
(OP)
three phase motor, 4kv, 39amps FLA, 200hp?, running at FLA unloaded (uncoupled) from coal pulverizer (mill). repair shop ran unloaded at 31amps. what's my problem?
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RE: no load current
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: no load current
You mentioned the motor repair shop; what repairs were performed at the shop? No load currents should be significantly less than FLA. (1/2 to 1/3) If the rated FLA is 39, I would expect the shop to see about 1/2 that during their test run.
Thanks,
Jeff
RE: no load current
RE: no load current
If your motor has 20 or more poles, nothing is wrong, the magnetizing current is so large that almost matches the full load current figure. Test the motor under full load to verify that the final current under load stays into the nameplate 39 amperes. Remember that the magnetizing current is 90° out of phase to the voltage and the load current is in phase to the voltage. The final total current is the vectorial addition of both currents.
RE: no load current
Thanks, Jeff
RE: no load current
I think Gunnar is probably correct that a difference in voltage is the most likely culprit.
Of course, it's also possible that your indications are wrong or the shop's indication were. Your indications probably rely on installed CTs that were sized for your motor. Who knows what the shop used? Were the meters in cal, what is their accuracy in this range? Etc.
You may be able to find data from the MFG on no load current of the motor. At least then you'd have a third data point to work with.
Regards,
JB