## AC Hipot of Large Generator Coils - uF ratings?

## AC Hipot of Large Generator Coils - uF ratings?

(OP)

The problem with using power frequency AC test sets to perform AC Withstand testing and Partial Discharge and Tan Delta/Power Factor testing is the high kVA capacity required if your test winding is high in capacitance. VLF can be used to help minimize this power. Question: is there a source somewhere that shows the typical uF ratings of stator windings, and others, of typical size motor and generator coils? Maybe a few for windings with a kVac input voltage of 2.4, 4.16, 13.2, 25, etc, I know there are a million possibilities but if perhaps any model listings of vendors that might show the capacitance along with all the other specs. Or, how about just for hydro generators. thank you.

## RE: AC Hipot of Large Generator Coils - uF ratings?

1 - Estimate total surface area A of coil insulation in contact with slot iron. It would be something like number of slots times slot length times (slot width plus twice slot depth)

2 - Estimate groundwall insulation thickness T (use something like 0.001" thickness per 50 to 100 volts if you don't have anything better)

3 - Estimate relative constant e_r dielectric constant of groundwall insulation (3 - 4 once impregnated...not sure about green coils)

4 - Calculate C ~ e_r*e_0 * A / T

This would be estimate capacitance to ground when installed and I assume (?) you will simulate this configuration during test. Once again sorry if I've missed your mark.

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(2B)+(2B)' ?

## RE: AC Hipot of Large Generator Coils - uF ratings?

I am familiar with calculating the capacitance like you illustrate. This assumes that one has the coil in possession or the data for a specific coil. I am more looking for any data that shows the range of capacitance's for several voltage classes of generators for the purpose of predicting the kVA needed to test the object. I know there are too many possibilities to what I ask, but if even a dozen samples can be had it would help. For instance: does GE or some other producer have a chart of the test voltage and power requirements, or the actual uF ratings of the coils, for a commonly used list of generators with a 6 kV or 13.2 kV input and up to maybe 100 mW. Maybe it doesn't exist and the AC power requirements from a hipot must be calculated each time for each specific motor. Thanks anyway for your reply.

## RE: AC Hipot of Large Generator Coils - uF ratings?

Now I understand you are more interested in the winding of whole machine.

Knowing capacitance of machine to ground is important in electrical protection. I'm sure I've seen some graph summaries of that and posted some here on eng-tips. Let me see if I can find that.

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(2B)+(2B)' ?

## RE: AC Hipot of Large Generator Coils - uF ratings?

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(2B)+(2B)' ?

## RE: AC Hipot of Large Generator Coils - uF ratings?

## RE: AC Hipot of Large Generator Coils - uF ratings?

Muthu

www.edison.co.in

## RE: AC Hipot of Large Generator Coils - uF ratings?

## RE: AC Hipot of Large Generator Coils - uF ratings?

Did a AC HV test on a 250 MW, 11 KV hydro machine stator today. 23 KV, 12.5 A at 50 Hz = 1.74uF per phase.

Muthu

www.edison.co.in