Maloperation prevention study of zero sequence direction protection to broken-line faults of parallel circuits on same tower

A maloperation prevention method of zero sequence direction longitudinal protection was presented in this paper directing at broken-line faults of double-circuit transmission lines on a same tower. Firstly, the maloperation reasons were analyzed in detail. Then, the zero sequence direction amplitude-comparison criterion and the negative sequence direction amplitude-comparison criterion were constructed. The zero sequence criterion is used to detect earth faults sensitively and the negative sequence criterion is used to avoid maloperation of zero sequence criterion resulting from electrical and magnetic coupling during broken-line period. Meanwhile, the zero sequence current threshold and negative sequence current and voltage threshold were set for insuring the reliability of the whole protection scheme. The interior fault logic is that the zero sequence direction criterions of the two sides of lines both reveal forward direction. If that occurs, the zero sequence longitudinal protection acts and the fault line is removed. Otherwise, the protection will not act. Finally, the simulation results demonstrated the availability of the presented protection method.