In the light of insulation breakdown events caused by UHV circuit breaker closing unloaded GIS bus when commissioning process of UHV GIS equipment in recent years

in this paper

effects on switching overvoltage when closing unloaded GIS bus caused by the pre-breakdown of the circuit breaker is researched. And the results suggest: 1) if without considering the pre-breakdown of the circuit breaker

the 2% statistics overvoltage is 1.58 p.u.

while with considering the pre-breakdown

the overvoltage would be up to 1.8 p.u.; 2)The rise time of the first transient overvoltage wave is 0.3 μs

less than the standard lightning impulse rising time; 3)The fast transient overvoltage did not exceed switching impulse protective level of UHV GIS equipments

but the hidden defects of equipments would be excited easily with the effect of the overvoltage

even cause insulation accident. Based on the simulation results and the researches on the insulation characteristics of GIS equipment at home and abroad

this paper puts forward some opinions and suggestions are put forward to prevent the insulation breakdown

and the research conclusions of this paper can be used as reference for the design of AC UHV GIS equipment and insulation accident prevention.