Shunt capacitor

as a reactive power compensation device

performs frequent switching with the variation of reactive load in power system. Due to the high reignition rate of the vacuum circuit breaker for the switching

the restrike is likely to occur in case of switching shunt capacitor. In this paper

a study is performed on the serious accidents of bulges and oil injection of two-phase capacitors in a 330 kV substation in northwest China when 35 kV capacitor at the low voltage side is switched by vacuum circuit breaker. The cause of the fault is analyzed and obtained by such means as inspection at site

over-voltage theory analysis and electromagnetic transient simulation analysis. The simulation wave-forms are in good agreement with the accident recording wave-forms

which verifies the accuracy of the proposed accident occurrence process

and proves that the sustaining reignition of the vacuum circuit breaker is the fundamental cause of the capacitor failure. Finally

improvement measures are proposed to reduce the occurrence probability of restrike of vacuum circuit breaker and avoid occurrence of the restrike in the switching of shunt capacitor.