400kV circuit breeaker with capacitor in parallel to the pole

[stratford]

Dear all. On site we have a 400kV circuit breaker that connects our step-Up transformer high voltage to the grid substation.
The poles of the circuit breaker have in parallel connection capacitors.
Can you explain why these capacitors are installed?
I guess they are used for precharging of the breaker.
The breaker type is Magrini Galileo 420MhMe-2.

 

[RRaghunath]

This is seen in breakers with multiple breaks. If I remember right, the capacitors distribute the restriking voltage (at the time of breaker opening) across the two arcing gaps) uniformly.

There is a buyers guide for HV circuit breakers available in ABB website. I find it quite informative.

 

[scottf]

Parallel capacitors are commonly used in breakers to limit the transient recovery voltage for close in faults. Normally called TRV capacitors.

 

[Bahram7]

Grading capacitors on multi-breaks power circuit-breakers are a necessity to distribute the recovery voltage amoung breaks. Values are in the range of 800 to 2200 pF. Even with them, the first break (on the network side) will see 15-20% more voltage during a three-phase-to-ground fault. This is taken into account during tests.
Single-break breakers may not have a capacitor unless it is recommended by the manufacturer to limit the rate-of-rise of the transient recovery voltages during short-line fauls.

Bahram7

http://www.Simtech-Intl.com