generator winding pi test

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Thread Starter

Eric Enquist

We have 6.6kv generators that we do a polarization index test at 10kv. But all the sites that I have read say to use much lower voltage than the insulation you have, my question is what is the recommended voltage to use to get the proper results?
 
> We have 6.6kv generators that we do a polarization index test at 10kv. But all the sites that I have read say to use
> much lower voltage than the insulation you have, my question is what is the recommended voltage to use to get the proper results?

6.6kv (rms) * 1.414 = 9.3324kv peak voltage

The generator's insulation should handle a 10kv test. You should be able to find the insulation class of the generator (nameplate or last service shop) to be sure.
 
I was always taught that to derive the polarization index of a motor or generator to use 500 VDC for devices rated at approximately 500 V or less, and 1000 VDC for devices rated over 500 V. Also, motor-driven meggars are typically specified for use in deriving polarization index values. I am aware that some of the test equipment manufacturers have electronic meggars which are supposedly capable of being run for 10 minutes, but I have heard mixed results about using these devices when compared with motor-driven meggars.

By using a consistent voltage range when obtaining polarization index values the values can be compared to other similar machines measured with the same voltages.

Having said all of the above, a machine manufacturer may have different recommendations for their equipment. Consult the manuals and instructions provided by the manufacturer of the generator at your site, or consult the manufacturer directly.
 
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