A novel pilot directional backup protection scheme based on transient currents for HVDC lines

Abstract

For HVDC transmission lines, the backup protection cannot respond to internal faults quickly. To solve this problem, a novel pilot directional backup protection scheme is proposed in this paper. Firstly, the fault characteristic of transient currents on both sides of DC bus is analyzed. When forward traveling-wave of current reaches a DC bus, the transient current integration at the back side of the bus over a short time is larger than that at the front side. However, when backward traveling-wave reaches the bus, the current integration at the back side is smaller than that at the front side. Therefore, fault direction can be determined by comparing the transient currents on both sides of DC bus. Then, internal faults can be distinguished from external faults by comparing fault directions at two ends of DC lines, and faulty poles can be selected by comparing the transient currents of two poles. Lastly, to test the performance of the novel protection proposed in this study, a ±800 kV HVDC system is built in PSCAD/EMTDC. Comprehensive test studies show that the proposed protection scheme not only can identify internal faults and select faulty poles correctly and quickly, but also can respond to high resistance ground faults.