Abstract: In order to ensure that the type test of breaking small capacitive current of 800 kV AC SF₆ ciruit breaker in UHVDC transmission system of ±800 kV and ±1 100 kV is successfully passed and the products run reliably for a long time after being put into operation, the electric field strength and gas density of the circuit breaker under different conditions are calculated by finite element method, and it is concluded that the dielectric strength of the original circuit breaker and three optimized schemes and the position of the lowest point of dielectric strength during the circuit breaker opening process are not affected by the opening speed and inflation pressure. Under the optimized scheme, the average opening speed of the circuit breaker is increased by 5.7%, which can meet the dielectric strength requirement that the peak recovery voltage reaches 2 100 kV. The test passed smoothly, and there was no re-breakdown in the breaking process, which proved that the calculation method and optimization scheme adopted had practical guiding significance.

Key words: circuit breaker, capacitive current, gas density, electric field strength, dielectric strength