ungrounded capacitor

[ronald]

We have a capacitor bank connected in wye float ground on a 23kv line. but its body were grounded.
We have performed a hipot testing and test show that they are ok for installation.recently the fuse on phase B blow. We replaced the blown fuse but at the moment of restoration of that phase, the phase A also blow.The rated voltage of capacitor is 14.4kv.
Can anyone give me an idea whats the cause of fuse blowing. There was no abnormalities in the line when we tried to restore the bank. Thanks and Good day.

 

[bennie]

Re: ungrounded capacitor

The voltage ratings are too low. Try the next size 15,125 KV. The capacitors should be shot if the fuse melted.

A floating wye bank will see higher voltage than the nominal voltage to ground.

Are the capacitors single bushing or two bushing?

 

[ronald]

Re: ungrounded capacitor

thanks for your reply. Yup the capacitors has two bushing.

 

[bennie]

Re: ungrounded capacitor

Ronald: I am making a wild guess. When one fuse operates, the voltage increases on the other two phases. Capacitors are designed to operate at 110% of their rating. More than that will cause an arc through the dielectric. A floating wye has a domino effect, after one failure.