Design aspects of a medium voltage hybrid DC breaker

With increased demands on energy efficiency and stability, the use of direct current (DC) will have a natural place in the future smart grid. Today DC is mostly used in high voltage, high power transmission over large distances and in low voltage systems where the demands on reliability are high, e.g. data centres. New applications as wind farm collection grids and a desire to replace over-head lines with cables opens possibilities for DC distribution grids in medium voltage. The use of DC grids will require the development of DC breakers to handle fault in the grid. This paper presents the design aspects of a hybrid DC breaker for a medium voltage application. Since the hybrid topology consists of a mechanical switch as well as semiconductor components and metal oxide varistors, the design must handle trade-offs in performance and cost both for each part and also between the different components.