Capacitance Requirements for 230kV PCBs

[nightfox1925]

Hello Friends,

We have just recently reviewed 230kV SF6 power circuit breakers specification and observed that the rated Interrupting Rating of the vendor proposed power circuit breakers are less than the required S.C. value specified by BUYER. The Vendor informed us that adding some specific capacitance at suitable locations would increase the Interrupting Rating of the Power Circuit Breakers. I'm a little bit confused. Is this related to the TRV? can anyone provide me with more clear details on this subject?

 

[Skogsgurra]

I do not understand this either.

Does your man mean series capacitors? That's not easily done - and I doubt that it helps. Unless they are sized to increase impedance in the transmission line, which probably is against what you want.

SF6 breakers are (slightly) better with capacitor bank switching than most other breaker types. That's the only way I can see capacitors enter the scene. But that is not what your question was about.

No. I am confused here. But prepared to learn more if someone has a good explanation.

Gunnar Englund

http://www.gke.org

 

[nightfox1925]

We actually required dead tank, outdoor type, 230kV SF6 power circuit breakers (as applied to an outdoor switchyard) with an interrupting rating of 50kA. Their specification lately indicates "40kA w/o internal capacitance" and "50kA with internal capacitance". I heard that ABB power ciruit breakers are fitted with some capacitance to increase their interrupting capacity but for the power circuit breaker in question (AREVA), they informed me that they are not able to provide internal capacitance on their power circuit breakers. What makes it confusing is that they have informed us that providing some capacitors on specific locations at the switchyard will improve the breaker S.C. rating. Is this capacitance related with the transient recovery voltage affecting the breakers' interrupting capabilities?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[KJvR]

Yes, small shunt capacitance reduce the surge impedance and will also reduce the TRV. The breaker is limited as already stated by the TRV and by reducing the TRV you can increase the interupting capability of the breaker. You might like to refer to the IEC standards for Symmetrical rating of HV circuit breakers. I am not familiar with 230kV breakers, but on MV breakers the recommended peak withstand current is a percentage value of the Symmerical break current value. A 40kA breaker will still have a lower peak withstand capability than the 50kA breaker.

 

[dpc]

Yes, this is sometimes done to increase the interrupting rating. Makes me not want to stand too close to these when I'm in the yard.