72.5 kV Vacuum Bottle Switchgear Testing

[VLFit]

AC Withstand testing 72 kV vacuum sg. The test voltage is 160 kVac (factory or field?) Can someone tell me the expected current draw at that test voltage? We have to purchase >160 kVac hipots but need the kVA rating needed. Thank you.

 

[mvcjr]

Good day!

Never heard of a 72.5-kV vacuum bottle.

As far as I know, vacuum bottles are only up to 34.5 kV. Above 34.5 kV, SF6 gas is used as interrupting medium. Can you please share any literature on your equipment. I may have been out of pace with technology developments.

Thanks.

 

[jghrist]

Hitachi makes 72 kV vacuum circuit breakers. I don't know what the factory tests are, but I'd be very cautious about high voltage testing of 72 kV VCBs. There can be x-ray emissions during testing.

 

[VLFit]

On a vacuum breaker, or N2, rated for 72.5 kVac, the 1 minute Withstand test is usually performed at 140 kVac rms. The worry about x-rays is usually a holdover from the days of DC testing. Old DC hipots were often designed with half wave rectification and often with no capacitive output filtering to hold the voltage at peak. The voltmeter was calibrated to read the Average voltage output, which could be only 45% of the peak. The meter says you are dc testing at 30 kV but it is really 67 kVdc peak. xrays are created and bottles fail the test that wouldn't fail if tested properly. Test at the voltages and levels dictated by the present standards and xrays should not be a concern. Use AC.