This paper introduces and analyzes the failure of a 220 kV circuit-breaker in a 220 kV substation on May 8

2008.According to the fault recording、disassembly inspection and simulation calculation

it is found that the failure reason is CB insulation breakdown caused by lightning strike

and appropriates countermeasures are put forward.It suggests that a lightning impulse arrester should be installed at the line side whether it is hot standby or not

and research on testing method of arc-quenching chamber internal defects should be developed.