460V Motor failed on DC Hi-Pot test 1

[HamidEle]

thread237-8885

we failed on some 460V Hi-pot test applying 1000V DC. To me 1000v is a proper DC voltage for 460V motor as per IEEE-43 table-1.
Wondering what your thoughts are.

Thanks in advance.

 

[che12345]

Dear Mr. HamidEle (Electrical)(OP)18 Mar 20 03:02
1. " FYI, the vendor came back and recommended to use 500v to Meggaer 460v motor as it is not ...."
Agreed.
Reference: (Megger an instrument manufacturer) states that commonly used test voltage for routine maintenance for equipment rating 440-550Vac , the test voltage is 500-1000Vdc.
2. Insulation resistance value taken with 1000Vdc may differ from the value taken with 500Vdc with the same duration and temperature. They do not indicate any defect if both readings are above the generally minimum acceptable resistance value.
3. In practice, a 460Vac motor [should be able],(without any ill effect) to be tested at !000Vdc.
4. Although testing a 460Vac motor at 500Vdc seems to be low, while testing it at 1000Vdc seems to be better, but NOT necessary.
Che Kuan Yau (Singapore)

 

[LionelHutz]

megger is slang for a megohmmeter testing.

Based on talks with an individual from an old school motor shop I deal with, I would surge comparison test a questionable motor myself with no derating for it being a used motor.

 

[HamidEle]

Great discussions. Thanks everyone again for the invaluable inputs.

 

[edison123]

Hamid

As I said, the winding connection is not recognized by standards for hipot tests. The test is based on the rated voltage, not phase to ground voltage. The idea of maintenance test is to assure the motor is good for service. Better to have a test failure under controlled circumstances than to have a service failure, which leads to more expensive shutdowns and possibly more expensive damages to repair. Do the tests as per standards not as per vendor's fears.

Muthu

http://www.edison.co.in