Protection strategy for undersea MTDC grids

Many point to point HVDC lines are already in operation in several countries. However, the development of multi-terminal DC grids is slowed by the lack of efficient control and protection strategies that can be applied on such grids. This article deals with the protection aspect of those networks. Indeed, the resort to Voltage Source Converters (VSC) changes the constraints since the short circuit current can flow through the freewheel diodes in case of the event of a DC fault. Also, since several links are considered, selectivity rules need to be investigated in order to maintain the healthy part of the grid in operation. A protection plan is proposed and its robustness and limitations are investigated.