The earthing switch at line side of double-circuit transmission lines on same tower needs the capability of switching induced current.To design the auxiliary circuit of B-type earthing switch
the authors analyze the characteristics of different auxiliary circuit structures and the influences of different kinds of arc interrupter media on the design.The essentials of B-type HVAC earthing switch design are offered according to the specification of insulation system
and the working principle of the auxiliary circuit is introduced.