Abstract: As an environmentally friendly switchgear, vacuum circuit breakers have a wide range of application prospects. There is a problem of uneven potential distribution in the main shielding cover of the vacuum arc extinguishing chamber in single and break vacuum circuit breakers, and the uneven potential distribution in the tank structure is more significant. To study the influence of the potential distribution of the main shielding cover on the internal insulation performance of the vacuum interrupter, this paper establishes a partial voltage model of the main shielding cover of the vacuum interrupter. COMSOL software is used to calculate and analyze the effect of the main shielding cover potential change on the internal electric field by constructing a capacitor on the outside of the vacuum interrupter to change the percentage of the main shielding cover potential in the inter fracture potential. The law of the influence of the main shielding cover potential change on the internal electric field is obtained. On this basis, power frequency and lightning impulse withstand voltage experiments were conducted on a 10kV vacuum arc extinguishing chamber under different main shielding cover voltages. Research has shown that the electric field strength inside the vacuum interrupter decreases first and then increases with the increase of the main shielding potential, and the maximum field strength inside the vacuum interrupter is the smallest when the main shielding voltage is 50%. The simulation and experimental results are basically consistent. At a contact distance of 6mm, when the potential of the main shielding cover is 50% of the inter fracture potential, the power frequency breakdown voltage increases by 5.4% and the lightning impulse voltage increases by 6.7%. This study provides reference for improving the internal insulation performance of vacuum arc extinguishing chambers and for the application of higher voltage level vacuum circuit breakers.

Key words: vacuum interrupter, main shield potential, electric field simulation, insulation performance