Study on Submarine Cable Overvoltage in Multi-terminal MMC-HVDC System of Offshore Wind Power

With the development of offshore wind power towards large-scale and deep-sea areas, the use of multi-terminal MMC-HVDC for offshore wind power is becoming a trend. The DC submarine cable, as the connection unit of MMC-HVDC converter stations, plays a crucial role in the safety and reliability of the whole system. This paper establishes a computation model of an overvoltage of the submarine cable, which is a ±500kV offshore wind power three-terminal MMC-HVDC in the simulation software. 16 types of faults are considered, including the grid side of the transformer, the valve side of the transformer, the valve side of the bridge arm reactor, and the DC side. As a conclusion, the maximum overvoltage of the submarine cable between the two offshore converter stations is 1.93p.u., and the maximum overvoltage of the common DC submarine cable is 2.07p.u., both caused by a single-pole ground fault at the outlet of the converter station. The results can provide an important reference for improving the operational safety of submarine cables in future practical projects.