Dielectric recovery characteristics of SF₆ circuit breaker under repeated lightning strikes

Repeated lightning strikes are multiple discharges with intervals ranging from a few milliseconds to hundreds of milliseconds. During the recovery phase after the circuit breakers interrupt the initial lightning short-circuit current, if repeated lightning strikes occur, deficient dielectric recovery can result in circuit breaker breakdown or system disturbances. This study aims to clarify the dielectric recovery characteristics of SF₆ circuit breakers under repeated lightning strikes. Firstly, a magneto-hydro-dynamic (MHD) arc model is developed in ANSYS Fluent to simulate and analyze the spatiotemporal evolution of the physical field during current interruptions. Then, based on the proposed dielectric strength evaluation method, the dielectric recovery processes are investigated and compared under different contact rebounds, arcing time and interrupting currents. Finally, the validity of the method is further verified through repeated lightning strike experiments. Research indicates that contact rebound may be the primary reason for circuit breaker breakdown under repeated lightning strikes, with a rebound distance of 6.5 mm resulting in a 28.3 % reduction in dielectric strength. The validated dielectric strength evaluation method aids in understanding the post-arc recovery phase and calculating the withstand capacity, offering valuable insights for circuit breaker design.