When capacitor bank is switched by circuit breaker with AVC system automatic control at 35 kV side of main transformer in 220 kV substation

the transformer may be damaged due to re-gas protection action by three-phase short circuit in the switchgear panel. This paper analyzes such serious fault with combination of the recorded faulty oscillogram and the action record of arc suppression coil. By way of disassembly and test of the faulty circuit breaker

overvoltage simulation and analysis of the fault process etc

the reason of the fault is found out from the accident and in theory

corresponding prevention measures are raised.