6.3kV motor winding failure in less than 1 year after re-winding
6.3kV motor winding failure in less than 1 year after re-winding
(OP)
Hello to electrical man,
I have a 1.2MW (6.3kV) motor which was re-wound last year (Oct05).
The winding was shorted again this year (Aug06) in less than ONE year after re-wound.
The shorted location is just a little dot near the winding overhung.
This motor did not show sign of overheating and it was not operating above its full load ampere.
Anyone has similar experience... please share... Thank U.
Cheers...
William
I have a 1.2MW (6.3kV) motor which was re-wound last year (Oct05).
The winding was shorted again this year (Aug06) in less than ONE year after re-wound.
The shorted location is just a little dot near the winding overhung.
This motor did not show sign of overheating and it was not operating above its full load ampere.
Anyone has similar experience... please share... Thank U.
Cheers...
William





RE: 6.3kV motor winding failure in less than 1 year after re-winding
Even if not you could still be getting voltage spikes on your motor leads from some other source. There have been several discussions in here about vacuum contactor re-strike transients that may be worth your reading. Do a Keyword Search. Here is one of the old threads, there were others if you care to look hard enough.
thread237-42676
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: 6.3kV motor winding failure in less than 1 year after re-winding
Thank U for your respond.
a. This motor is not operating on VFD. It starts on direct on-line starting.
b. We are using vacuum combination starter unit. The contactor rating is 400A whereas our FLA is 181A. Running ampere is approx. 97% (175A).
c. When you mentioned re-striking transient on CBS, do you mean during starting condition (contactor clsing)?
RE: 6.3kV motor winding failure in less than 1 year after re-winding
Gunnar Englund
www.gke.org
RE: 6.3kV motor winding failure in less than 1 year after re-winding
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: 6.3kV motor winding failure in less than 1 year after re-winding
I have checked with the vendor for my vacuum contactor.
Vacuum contactor since the 80s used low surge material on the contactor surface which basicially creates very low voltage surge that is very popular for motor starting/switching.
With such low surge, this type of vacuum contactor doesn't require any surge protection (as in C-R arrestor or surge suppressor) for motor application even with frequent switching operation.
RE: 6.3kV motor winding failure in less than 1 year after re-winding
Always be skeptical of a vendor's engineering advice. Remember who signs their paychecks!
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: 6.3kV motor winding failure in less than 1 year after re-winding
Even if the vendor is correct, a surge arrester/surge capacitor combo **at the motor terminals** is pretty cheap insurance. IEEE recommends surge protection at the motor for all medium-voltage motors, regardless of vacuum/air/whatever contactor upstream.
RE: 6.3kV motor winding failure in less than 1 year after re-winding
After rewinding, what type of acceptance tests were performed?
Air voids in critical areas could develop Partial Discharges and accelerated aging of the insulation.
RE: 6.3kV motor winding failure in less than 1 year after re-winding
We have nearly one thousand 6.3kV motors. Nearly 95% of these motors use vacuum contactor. Most of the vacuum contactors come from the same vendor.
This is the first time, we have motor winding that fails in less than one year after re-winding.
In the past, we do have winding failure, but is largely due to bearing failure which rubbed the winding or due to overloading.
Anyone has the IEEE standard number for this requirement to provide surge protection for all MV motors??
The re-winding vendor has used this motor coil manufacturer for the past 5years without any problem.
The new coils have been subjected to high voltage test starting from factory to the re-winding process. However, all these tests are considered as "GO or NO GO" test. It may not be able to detect minor "injury" to the winding in the process.
RE: 6.3kV motor winding failure in less than 1 year after re-winding
http://www.accesstd.com.au/report.htm
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: 6.3kV motor winding failure in less than 1 year after re-winding