Assessing the Discharge on High Voltage Direct Current SF6 Circuit Breaker after Arc Interruption

Distribution of the electric field in high voltage direct current (HVDC) circuit breaker is the key to study the risk of gas discharge after arc interruption. The current interruption mechanism in HVDC circuit breaker (CB) is complicated and needs an auxiliary circuit to generate current zero crossing. The transient overvoltage after arc extinguishing may increase the magnitude of electric field over the critical dielectric strength of gas medium. The dielectric strength of gas is also affected by the change of temperature and pressure during the interruption. This paper simulates the arc current and voltage for 250 kV SF6 CB using the passive commutation circuit. The Finite element method (FEM) is then used to study the electric field, pressure and temperature distributions during the opening of CB contacts after arc interruption. A comparison is carried out between the maximum electric field at different instants after arc interruption and the critical dielectric strength of SF6. This work also estimates the period of time, which the SF6 discharge takes place after the arc extinguishing.