The Analysis and Solution of Current Differential Protection Maloperation for Transmission Line with High Series Compensation Degree

Abstract

With the increasing integration of huge-size generators and tighter interconnection among power grids, in internal fault, the fault current of Series Compensated (SC) lines may be reversed. At this time, the differential protection of SC lines may fail to operate due to insufficient sensitivity. In this research analyzes the reasons for the current reverse in SC lines and its effect on differential protection. The operation characteristics of differential protection are studied by focusing on multiple factors, including different series compensation degree, fault types, system operation mode, power angle difference, fault points, and transition resistance. An improved criterion based on the current amplitudes and phases on both sides of the series compensated lines is proposed. Further, to strengthen the operation characteristics of differential protection, the triple-fold line is chosen to improve the sensitivity for internal faults in this paper. The criterion is effective to improve the protection sensitivity of SC lines during internal fault. The PSCAD/EMTDC simulation and the power system dynamic physics simulation demonstrates that protection sensitivity is obviously increased in the improved scheme.