Flashovers or even explosions of switchgears fixed on substations and power plant at the voltage rank of 220 kV or below

which were caused by lightning intrusive waves

have taken place frequently in east China in recent years.In July 2007

this kind of event occurred because of lightning strike on the 220 kV transmission line

which generated the circuit breaker flashover and current transformer dielectric breakdown.This paper simulates the accident considering the running condition

and obtains the lightning over-voltages by the software EMTP.According to the over-vohage values

the reasons of the accident are analysed

and some protection methods from over-voltage due to lightning intrusive wave are presented by installing MOAs at both ends of the 220 kV transmission lines.