Sensitivity Enhancement Scheme for Zero-sequence Differential Protection Based on Double-sequence Pilot-wire Directional Elements

Non-transposed multi-circuit lines on the same tower have the characteristics of low power construction investment and strong power transmission capacity per unit corridor width, and are now widely used. Firstly, the zero-sequence components of non-transposed multi-circuit lines on the same tower are analyzed, revealing the reason for the insufficient sensitivity of zero-sequence differential protection when the setting threshold is based on avoiding the maximum unbalanced current. The longitudinal zero-sequence directional protection has the characteristics of simple principle, strong tolerance to transition resistance, easy algorithm implementation, high sensitivity, and insensitivity to system oscillations and normal load changes. Based on this, a sensitivity improvement scheme for zero-sequence differential protection using dual-sequence longitudinal directional elements is proposed. The dual-sequence longitudinal directional elements are used to determine the fault location. If it is within the zone, the zero-sequence differential protection setting is reduced, improving sensitivity while ensuring selectivity. Finally, based on the actual engineering topology parameters of a 500kV multi-circuit line on the same tower in East China, a PSCAD electromagnetic transient simulation model is established, and a large number of simulations verify the effectiveness of the proposed improvement measures.