Vacuum bottle in gas insulated switchgear

[leoliu]

I was asked to have the vacuum circuit breaker tested during routine maintenance process in the MV gas insualted switchgear. But there is no access to do the test on vaccum CB in these Siemense 8DA10 series GIS. The insulation testing, hi-pot test can be done at main circuit level with CB closed. Does have any experience on this? How to check the VCB on routine base.

 

[collies99]

Vacuum bottle integrity test is performed with the contacts open and an AC hipot is placed across the open contact, all untested phase grounded. The leakage current is measured for trending purpose but it is really a pass-fail test.

if the hipot test set does not trip-out, the bottle is good.

Test value as per manufacturer's recommended level, or as per NETA standard in its absence. Test values the same for acceptance or maintenance and they are at .75 of factory test level.

 

[leoliu]

Thanks a lot for your reply, Collies99. But My vaccum bottle is in GIS assembly. The CB can not be racked out. The only way I can think of is applied the testing to the cable termial with CB open. Have anyone done this?

 

[Zogzog]

As collies99 mentioned a hipot test is really just a go/no-go test and won't tell you much more than if your bottle has failed or not, which you would know the first time you open the breaker. Only real VI test is a MAC test that allows you to measure the pressure remaining in the bottle and therefore predict remaining life, but you need access to the VI to do that test as well.

 

[collies99]

Hi Leoliu
Yes you have to place the breaker in the Open state snd configure the bus such as that you can energized one side of the breaker with the AC hipot test set.

The leakage current through the vacuum medium is then measured at the opposite terminal to ground. You csn either do this will a micro-ammeter or use the guard leaf from the test set. If provisioned with fisterer connectors, you need the mating end for proper connection.

Depending on the KV class you may need special connectors if your gear is provisioned with fisterrer connector, else if I am correct from a quick google of your breaker, isolate the cables and make connection there. The other side could probably be connected to the grounding switch provided there is an external connection to ground to break where leakage current can be taken. Switch is grounded so it connects to the bus side as in a feeder breaker, else you need an outage where the main bus needs to be energized and the leakage measurement taken at the load side breaker connection point.