Capacitor bank switching problem

[Arevaengineer]

Dear All

Following is a problem, Can anyone help

1800kVAR,6.6kV Capacitor bank when switched on through a vacuum contactor rated 11kV,400A,AC4 gives a loud noise like a gunshot.remains energized normally and when swithced off same thing happens.
No visible marks of insulation oil leakage on the capacitor bank, no damage to insulator.
Do i need to check the switching chamber of the contactor,if yes at what voltage.It is under operation since 1995 but was last swithced on a year ago.
What else to look for?
Same thing happens to the stage 3 bank but with lesser sound
Thanks to anyone who can solve the mystery.

 

[busbar]

Is the contactor specifically intended and rated for capacitor switching? Have insulation-resistance—specifically bottle vacuum integrity—been performed with satisfactory results?

Contactor-manufacturer’s application and maintenance literature, along with NETA 2001 Maintenance Testing Specs may be useful references.

 

[jbartos]

Suggestion: The vacuum contactors have special rating when it comes to capacitive load switching. Seek the contactor manufacturer tech support.
Visit

http://www.jenningstech.com/pdf/cont/rp173.pdf

for a sample of Capacitive MVAR rating of a vacuum contactor

 

[Rodmcm]

I would think that a gunshot discharge is the sound of a flashover, this maynot be in the breaker but could be across cable connections ( phase to phase and phase to earth). I would suggest a thourough physical check of all HV connections from stabs to final terminations. Vaccuum contactors, especially older ones, did suffer from not cuting current at the zero displacement angle and there were reports of damage to motors when used as a starter. First stop should be the manufacturer.

 

[swgrmfg]

A few questions for Arevaengineer:

1. Where is the physical source of the noise. The Cap or the VCTT?
2. Are the Caps connected in Wye or Delta? If in Wye, are they single or double bushing? If single bushing, is the bank effectively grounded?
3. Do you have a series reactor in line with the Cap bank?
4. Are all electrical connections in this circuit (cables, lugs, bolts, etc...) mechanically sound?

GH