Recently we experienced failure of a 132 kw, 2 pole LT motor installed 6 months back running normal. On opening the motor we found inter turn short circuit on the NDE side overhang portion of winding.

What may have caused this failure?

 

If the winding shorted between turns it could have been damaged while running by something hitting it or a bad varnish jog. The varnish is the life of an electric motor. After the motor is wound you tye the winding in then dip and bake it to cure the varnish. This varnish is what keeps the winding from vibrating while running. If the varnish is no good when it heats up it will let the turns vibrate against each other an cause a premature winding failure. If the winding has single phased in a 2 pole motor 2 sets of coils will have gotten hot and they will be 180 degrees a part.

 

If your power system is a grounded WYE the cause could be from harmonics. If your power system is an ungrounded DELTA the cause could be transient voltage spikes. If you are operating this motor from an adjustable speed drive the problem may be both harmonics and voltage spikes.

You have not explained the application, voltage, frequency or brand. You may simply be overloading it causing overheating or the last repair may be suspect. Electrical devices have a half-life due to heat. As they are operated at 7 1/2 to 10 degrees hotter than their ratings their life is cut in half.

Our electric motor repairs due to winding failure has reduced about 95% after we installed a Phaseback system power filter. You can find more information about this at the following link: http://www.phaseback.com

I hope this helps.