Investigation of a Mechanical Switch within a Hybrid Circuit Breaker for Protection in DC Grids

Transmission and distribution of electrical energy has been achieved by using alternating current (AC) almost exclusively until now. Direct current (DC) pushes forward into long range energy transmission, server farms, mobility and manufacturing systems, being former AC dominated areas. With potential advantages of DC there are also different challenges like switching nominal and fault currents and ensuring that only affected parts of DC grids are disabled when failures occur.The government-funded research project Smart Modular Switchgear (SMS I) resulted in the proposal of a novel, algorithm-based low voltage DC protection system, facing those challenges. Fast, selective and reliable switching operations were achieved even with multiple distributed power supplies included in one power grid. Former results of these studies indicate that a hybrid circuit breaker (HCB) is the most suitable switch for this application. In this contribution the mechanical component of a model HCB is investigated by measuring and evaluating the on-state resistance and the interruption behavior under different load conditions and with two different contact materials. Furthermore, these results are compared to other direct current switches (DCS). Finally, the usability of the switch is discussed for the project SMS II where higher voltage levels are subject of the research focus.