Study of Overvoltage Protection and Insulation Coordination for MMC Based HVDC

This paper focus on overvoltage protection and insulation coordination in Modular Multilevel Converter based HVDC system planning. An overvoltage protection scheme, which bases on the topology used inTransbay project by Siemens, is proposed in this paper. Thescheme draws fromthe characteristics of MMC-HVDC systems and the research results in classic HVDC systems, byplacing arresters at some key locations in the MMC-HVDC converter station.With this scheme, the overvoltage at those key pointscan be limitedto an acceptable range and hence protect the key equipment concerned. Since all the DC lines of the project are undersea cables, no lighting overvoltage is considered and 14 faults which could happen are carefully selected to serve as the verification conditions for the insulation design. Based on the PSCAD/EMTDC simulations and the deterministic method, the specified withstand voltage levels of the critical equipment in the converter station is calculated.