ABSTRACT In multi‐terminal flexible direct current (DC) systems, faults on the DC line develop rapidly, posing significant challenges for traditional protection schemes in terms of both speed and reliability. To address this issue, a novel transverse protection scheme based on the transient equivalent impedance difference is proposed. This scheme is particularly relevant to systems integrating large‐scale renewable energy sources, such as wind farms, where fault characteristics can differ significantly from traditional power systems. First, considering the differences between sending‐end and receiving‐end converter stations, equivalent models of the DC sides of the converter stations are constructed. By analysing the topology of the equivalent model, analytical expressions for the voltages at the converter stations on both ends of the protected line, under different fault scenarios, are derived. Based on the differences in the voltage–current ratios during internal and external faults, the protection criterion is established using the characteristic frequency point at which the difference coefficient reaches its maximum. Finally, simulation results on the RT‐LAB platform demonstrate that the proposed protection scheme has robustness against changes in fault resistance. The total operational response time is less than 3 ms, which can meet the stringent speed requirements for DC line protection, offering a reliable solution for systems with high levels of renewable energy integration.
Ma et al. (Thu,) studied this question.