In order to meet the requirements of expansion break with high insulation margin for uninterrupted power supply during GIS expansion butt joint and on-site withstand voltage

this paper introduces a 252 kV GIS uninterrupted expansion equipment with double isolation breaker

which uses two isolation breakers in series to form expansion breaker. Due to the influence of the equivalent capacitance of the breaker and the stray capacitance to the ground

the voltage ratio of the two breakers is not 1:1. In order to verify the insulation performance of the double isolation breaker

the maximum withstand voltage of the expansion breaker is analyzed first

establishes the equivalent circuit analysis model to derive the theoretical formula

then the Ansys finite element software is used as the calculation tool

and then the research and analysis method combining theoretical formula derivation and simulate calculation is used to obtain the breaker voltage distribution. The results show that

the high-voltage side is olation breaker voltage issignificantly higher than the low-voltage side. for the three-phase common box structure

the three-phase breaker voltage division ratio is slightly different

and the middle phase division voltage ratio is slightly lower. According to the calculation results

evaluate the insulation performance of the double isolated breaker

and then optimize the structure.