245 kV SF6 Circuit Breaker and Air Insulated Bus Field Testing

[rcw retired EE]

Is an AC overpotential test common for air insulated 230 kV substation commissioning?

A utility's spec calls for "AC Hi-pot Test of Circuit Breaker and Applicable Bus Sections" in a checklist attachment to their generic circuit breaker installation specification that is used for breakers from 5 KV-500 kV. The AC test voltages are not specified, so the utility engineer requested we replicate the circuit breaker factory test (425 kV AC for 3 minutes). Field tests are usually 75% of factory tests= 75% x 425 kV = 319kV AC.

I haven't been able to locate a 300kV + AC hypot.

The utility's substation maintenance staff doesn't recall doing any AC overpotential test other than Doble power factor insulation tests at 10 kV.

Our normal 230 kV field testing protocol is a full set of Doble power factor tests at 10 kV AC and a DC insulation resistance test plus any manufacturer required or recommended tests. The breaker manufacturer does not list any overpotential tests in their O&M manual.

The >100kV test equipment I've seen are variable frequency resonant units that come on two semi-truck trailers and require a minimum circuit capacitance to build the voltage. A breaker with 8 feet of bare cable on either side is not much cpacitance, I don't think we could get that style to work.

If AC overpotential testing is common, I would have expected there to be more than a handful of "portable" AC High Pot test sets in North America.

Thanks in advance for any feedback.

 

[DTR2011]

Short answer - No. In my experience in the USA.

I have seen specifications calling for such tests and questioned them. Some have removed this requirement when the difficulty was explained and as you mentioned, many utilities do not perform such tests. With difficulty comes cost, of course.

The reality is that the VA requirements for such a test set does not exist (as portable field equipment). There are DC test sets that are more readily available in something semi portable.

If AC is a must, you may want to investigate backfeeding a VT (if an Iron device is available). Of course, safety factors would have to be accounted for. This will get you to nominal, if the V/Hz is known from the OEM, perhaps 1.1-1.2 * Vo is possible. A big Variac (or similar) is required.

I understand your pain. Some years ago, I had a 34.5 kV metal clad switchgear to HyPot. The biggest AC Hypot I could rent did not have sufficient VA and would trip out. Contacted the SWGR vendor and they could not test it with their shop equipment either.

My company has a VLF cable test set. If I can remove VT's, I will often use this as at least a proof test.

The HV AC Test equipment, I have used in conjunction with the OEM on HV GIS. The capacitance was known and it was a resonant test.

If you absolutely have to create this high of a voltage and the VT backfeed won't fly, you could try HV cable testers / installers as a service. They may have the huge rigs you described.

 

[dpmac]

Advanced Testing Systems has HV Series Resonant Test Sets in North America.
50KV-20VA to 700kV-5MVA

http://www.advtest.com