A novel pilot differential protection for HVDC transmission line based on the differential voltage

The HVDC transmission system has played an important role in modern power system. In traditional HVDC transmission line protection, the differential protection is invulnerable to high fault resistance, but its time delay is too long due to the distributed capacitance current. In order to solve this problem, a novel pilot differential protection is proposed in this paper. The compensating voltage on the setting point on the line can be calculated by using the voltage and current at two terminals of the line, separately. The difference value of the compensating voltages calculated by the voltage and current at rectifier side terminal and the inverter side terminal are defined as the differential voltage in this paper. When external fault occurs, the compensating voltage on the setting point calculated by the rectifier side terminal and inverter side terminal should be almost the same, so the differential voltage should be relatively small. However, when internal fault occurs, the compensating voltage on the setting point calculated by the two terminals are different, so the differential voltage should be relatively large. The analysis proves that the differential voltage can be used to identify the fault. A ±800 kV UHVDC system is modeled for simulation in PSCAD/EMTDC, and the correctness and effectiveness of the proposed protection method is verified.