Capacitor switching phenomenon for EHV circuit breaker

While, shunt capacitor bank are extensively used to improve loading of the transmission lines as well as to support system voltages. As these capacitor banks are frequently switched in and out of duty, enegisation and de-energisation of these bank causes transient voltages are produced. The concerns on energisation are overvoltage and inrush current, while for de-energisation is restriking.

Switching of capacitor bank, Capacitor bank because of their concentrated capacitance, in contrast with distributed capacitance, generally draws much more current than unloaded cable or line- in practical cases up to several hundred of ampere. Switching of Capacitor bank causes a very high rate of rise of transient recovery voltage across circuit breaker contacts. With improvements in circuit breaker technology, modern SF6 circuit breakers have been designed with less number of interrupter per pole. This causes, modern circuit breaker operates with higher voltage stress in the dielectric recovery region after current interruption. Catastrophic failures of circuit Breaker during shunt reactor and capacitor bank de-energisation. In those cases, evidence of cumulative re-strikes has been found to be the main cause of interrupter failure.