In order to describe the process of insulation destruction of GIS under lightning impulse voltage

we proposed a novel method of transient insulation numerical analysis. A combination of the electromagnetic transient analysis method and optimized charge simulation method（CSM） was put forward to calculate and analyze the transient insulation characteristics of a 550 kV GIS under lightning impulse voltage. The instantaneous insulation of GIS was characterized to provide a theoretical basis for insulation optimization design of GIS. The results show that

compared to the calculation results by traditional insulation analysis method

the calculated electric field strength peak values of GIS by the proposed method is increased by about 8%. Within 0～15 μs

though the voltage of GIS does not approach to its peak value

there exists severe electric field distortion caused by the sharp voltage variation with higher probability of GIS insulation breakdown. Additionally

for the GIS insulation structure optimization design

it is advisable to restrain the change rate of electric field strength amplitude in order to reduce the probability of insulation breakdown.