In case of ground fault in a double-circuit transmission line

there is the problem that the zero-sequence current due to the increase or splitting may meet the high-sensitivity zero-sequence inverse-time limit protection setting of non-faulted lines and cause the circuit breaker in mal-operation. In view of this problem

the distribution mechanism of zero-sequence current in the case of a ground fault on a double-circuit line in a high-voltage AC system as well as the cause of possible mal-operation of the zero-sequence inverse-time over-current protection of adjacent non-fault lines are analyzed.A highly sensitive ground distance criterion is proposed to increase the zero-sequence inverse-time limit over-current selectivity. Combining the criteria and current distribution characteristics

a zerosequence inverse-time limit over-current adaptive acceleration strategy is proposed.In this method

the zero-sequence acceleration coefficient is adaptively changed to ensure the priority action of the fault line

and to avoid disorderly mal-operation of circuit breaker of adjacent non-fault line protection. The simulation result shows that the optimization of the zero-sequence inverse time-over-current protection optimization promotes the feasibility of its setting consistency

and reduces the risk of mal-operation of adjacent non-fault line circuit breakers.