Function of slow grounding mechanism:

More than 90% of the fault rate of EHV lines is single-phase ground fault, while 80% of single-phase ground fault is transient fault. In China, single-phase reclosing is mostly used to eliminate single-phase ground fault in 330kV  550kV lines to improve system stability  power supply reliability.

The success of single-phase reclosing depends on the self extinguishing of the secondary arc at the fault point. The secondary arc of the transmission line below 220kV can self extinguish within this time. The secondary arc of the line above 330kV needs to be extinguished by HSGS fast grounding switch.

Secondary arc current: refers to the current supplied to the fault phase by electrostatic coupling  electromagnetic coupling between fault phase  sound phase  possible adjacent lines when circuit breakers at both ends of fault phase trip after single-phase grounding fault occurs.