Selectivity of Zero-Sequence Current Backup Protection and Improvement Based on Wide Area Measurement System

For complicated power grid, the inverse time zero-sequence current protection is widely used, which can better solve the relay settings problem. In most cases, due to the natural distribution of the zero-sequence current, the selectivity of the protection can be guaranteed; however, in some cases it cannot. In this chapter, the selectivity of the zero-sequence current backup protection under the condition of internal ground fault on the double-circuit transmission lines was analyzed in detail. Studies showed that in this case the protection of the non-fault line of the double-circuit lines can operate correctly. However, when the system zero-sequence parameters and the location of the fault point met certain conditions, both the protections of the adjacent lines on the two sides of the double-circuit transmission lines had the possibility of unselective mal-operation. In order to solve this problem, improved method based on wide area measurement system was proposed. The use of multi-point zero-sequence voltage in this method can improve the selectivity and the speed of the backup protection. At last, PSCAD simulation was carried out to verify the correctness of the analysis.