A novel pilot protection principle for VSC-HVDC cable lines based on fault component current

A novel pilot protection principle for VSC-HVDC cable lines based on fault component current is presented in this paper. In the transient process of cable line, if a fault occurs over the cable line, the current measured at both convert stations would have the same changing direction and the sign of the fault component current at both convert stations are the same to each other; otherwise, if a fault occurs beyond the cable line, the current measured at two convert stations would have the opposite changing direction and the sign of the fault component current at both convert stations are opposite to each other. According to this characteristic, the directional element can be located at both convert stations and state signal can be sent to the other station. Thus, the pilot protection principle can be implemented only using two terminal current. In addition, the setting principle is proposed based on fault component current in this paper. The proposed pilot protection principle is simple, reliable, and practical. It can be implemented with a low sampling rate and doesn't need the current data synchronization seriously. At the same time, various faults are simulated by using the system of VSC-HVDC built in PSCAD/EMTDC, in which frequency-dependent parameter cable line model is adopted. The simulation results show that the method can identify the fault reliably and rapidly in different conditions only using the current measured at both convert stations and has sufficient sensitivity for high resistance ground fault. It can replace the traditional rate of voltage change protection and traveling wave protection as the main protection of VSC-HVDC cable lines.