Overall Protection Scheme for Flexible DC Distribution Lines Based on Synergy of Current Limiting Control and Protection

Due to the extremely high overcurrent after a fault in the flexible DC distribution lines, it is necessary to reduce the uses of the high breaking current circuit breakers by current limiting. However, the existing protection principles may refuse to operate after the current limiting. Therefore, the combination of current limiting technology and protection principles has become an urgent demand for the development of a DC distribution system. For this reason, this paper proposes an overall protection scheme for the flexible DC distribution lines based on the coordination of full-cycle current limiting control strategy and the correlation protection principles in order to realize the fault identification while limiting the current. The proposed full-cycle current limiting control strategy uses different current limiting links to suppress the fault current in the early, middle and late stages of the fault development, which greatly reduces the need for the high breaking current circuit breakers in the DC distribution network. Meanwhile, the protection principle of the Pearson correlation coefficient still operates reliably, simultaneously identifying faults, thus reducing the protection redundancy. Simulation results in the real time digital simulator (RTDS) show that the current limiting strategy effectively reduces the fault current and enhances the correlation between the currents on both sides of the circuit. The protection is able to reliably identify the faults without strict communication synchronization, and is not affected by the transition resistance, the data window length and the noise, having a good application prospect. © 2022 Power System Technology Press. All rights reserved.