HV DC testing 2

[genRman]

Could some learned gentleman please advise where I might obtain reference material for HV DC testing of rotating electrical machines.
It is recognised practice to verify the condition of a synchronous generators main stator winding insulation system with a High Voltage AC withstand test at (2x Vs) +1kV
when in new condition.

However, when testing the generator in field conditions, I understand that it is recognised that a DC test at 1.7x the AC rms value, will provide an adequate alternative.
I am looking for some guidance on levels of testing and determining winding condition (using withstand tests, Tan Delta & polarization Index tests)

The clear advantages are one of test plant size and portability, coupled with the limit of damage sustained if a failure occours, which would then have to be rectified.

Some words of wisdom, any database on typical results obtained vrs generator rating , etc would be much apreciated.
If we are to go down this line of HV DC testing, are there any pitfalls to be avoided in terms of instrumentation/ supply sizing etc?

Many thanks

GenRman

 

[electricpete]

You talk about field conditions. For field testing of a service-aged machine, you should reduce the test levels approx 2/3 of those that you mention. 2E+1kv ac and 1.7*(2E+1)kv dc apply only to factory testing of new machines.

IEEE 95 is the IEEE Guide for DC hipot of rotating machines.

There is included a discussion of several "step voltage test" methods where voltage is slowly increased and leakage current is plotted vs voltage. Deviation above a linear increase may signal the beginning of breakdwon This provides some additional diagnostic value beyond the simple go-no test. It is a useful test for dc since leakage current is more directly measurable... it cannot be performed for ac since capacitive current overwhelms leakage current.

The best on-line info I know of is at:

http://www.usbr.gov/power/data/fist/fist3~1/vol3-1.pdf

 

[genRman]

Thanks electricpete,
since posting the inquiry I found the exact site you have provided & obtained some very informative data on the oposing techniques.