Cause of motor failures?

[jmcs]

The information I'm looking for would be a chart of the temperature rise and long term effects on the motor insulation of a motor running with a voltage imbalance of .9 to 1.1 percent and current of about 5 percent. I have a customer that has had several motor failures in the past two years (same motor). The motor repair shop reports that I have read say the problem is voltage spikes, transients, lightening, etc. I have run several surveys with a power quality analyzer and have not seen any RMS spikes, etc. even during lightening storms, (motor has lightening arrestors and surge capacitors). I have seen the voltage imbalance of 1% and current of 5%, plus waveform faults with peak voltages of 580 volts phase to neutral (480Y/277 volt system), but they only last one cycle, sometimes 2 or 3 of them within a 15 cycle time frame. I think it may be capacitors switching on the primary. There is also a system voltage drop of approximately 5% every 30 to 40 minutes as the result of another motor starting which causes a 20% drop in current on the motor in question followed by the inrush current as the motor regains speed. The motor current also fluctuates up and down 4-6 amps quite rapidly. I have also caught a few partial phase losses which would single phase the motor for a short time. The question I have is could all of these things combined over time deteriorate the insulation to the point where a small voltage spike destroys the motor? If anyone is interested in seeing them, I have bitmaps of voltage and current time plots and the waveform faults.

zip file with bitmaps

http://geocities.com/pschimpf/temporary_stuff/well.zip

Jpegs

http://geocities.com/pschimpf/temporary_stuff/jeff_pq_filelist.htm

You can read more about this thread on the controls board.

Thanks to anyone who can help.

 

[RAgrawal]

you have not mentinod the rating of the motor & protection employed. Since lightining arrestor and syrge capacitors are there, there should not be any harm to the motor by voltage spikes. similarly voltage variation should also not cause any effect.

The only possible reason could be the partial phase loss (as mentioned by you) resulting in the single phasing of the motor. You should employ suitable NPS protection. I think NPS protection will certainly protect your motor.

 

[jbartos]

Suggestion to the original posting marked ///\\\:
The question I have is could all of these things combined over time deteriorate the insulation to the point where a small voltage spike destroys the motor?
///Yes, it potentially could.
See other posting in this Forum for the voltage and current imballance effects on the squirrel cage induction motor. E.g. Run1on (Electrical) Aug 19, 2001 in the Electric Motors & Controls Engineering.\\