A single-ended protection scheme based on dual voltage criteria

Offshore wind power integration via Multi-terminal flexible DC (MTDC) transmission systems represents a critical solution for offshore wind energy accommodation in China, where the secure operation of DC transmission lines is of paramount importance. To address the insufficient transition resistance withstand capability of existing single-ended protection schemes for DC lines, this paper proposes a novel single-ended protection approach based on the topological characteristics of MTDC-based offshore wind power integration systems. First, the system configuration is elaborated, featuring onshore centralized current-limiting reactor arrangement to reduce project investment costs. Subsequently, the transient characteristic differences between low-resistance and high-resistance faults in DC lines are analyzed based on which distinct single-ended protection criteria are developed to accommodate different transition resistance ranges. PSCAD/EMTDC simulation results demonstrate that the proposed protection scheme can reliably identify DC line faults using only single-ended electrical quantities, while exhibiting both fast operation speed and strong transition resistance withstand capability, thereby providing an effective safeguard for the secure operation of flexible DC-based offshore wind power integration systems.