Simulation Study on Switching Overvoltage of Submarine Cables in Flexible DC Transmission System

With the rapid development of wind power generation, submarine cables have become a critical transmission channel for delivering offshore wind energy to onshore power stations. Because of the difficulty of submarine-cable maintenance, particular attention should be paid to their overvoltage characteristics during operation. Taking a ±200 kV DC submarine-cable project as the research background, this paper establishes a PSCAD/EMTDC model of a two-terminal MMC-HVDC submarine-cable system and compares the conductor-to-ground overvoltages caused by faults at different electrical locations. Among the investigated AC-side cases, single-line-to-ground faults on the valve sides of the connecting transformer and bridge-arm reactor produce relatively high cable overvoltages, with the bridge-arm-reactor valve-side fault reaching a maximum of 2.48 p.u. (496.48 kV). Among all investigated cases, the grounding fault on the valve side of the DC reactor produces the highest overvoltage, reaching 2.93 p.u. (586.18 kV) at approximately 30 km along the cable. After the initial transient associated with the DC-side grounding faults, the healthy-pole conductor-to-ground voltage remains at approximately 2.0 p.u. The results identify the relatively severe fault locations and cable sections requiring particular monitoring attention and provide a case-specific reference for DC submarine-cable monitoring and subsequent project-specific insulation-coordination studies.