The Role of Circuit Breaker Technology in Protecting Low Voltage Direct Current (DC) Grids

The increasing penetration of direct current (DC) components in our alternating current (AC) dominated grid revives Thomas Edison’s concept of DC grids. A switchover to DC grids offers many advantages; an elimination of conversion steps, an increased power transfer capability, an active control of the power flow, and a simplified interconnection.

Two topologies for low voltage DC grids exist, a two-wire unipolar and a three-wire, bipolar configuration. The latter, allows the connection of devices on two different voltage levels, and surpasses the many other advantages offered by a unipolar DC grid.

However, these DC grids are more dynamic causing them to quickly become unstable during a fault. Furthermore, the interruption of a DC stresses the contacts of traditional mechanical circuit breakers. Therefore, the implementation of these DC grids requires a different approach to circuit breaker design where speed and DC interruption are key elements.

This research focusses on the design of a fast switching circuit breaker capable of interrupting bidirectional fault currents in bipolar DC grids, hence maintaining the grid stability during fault conditions. The testing will be carried out on a system level, instead of the usual device level, consequently ensuring the compatibility of the circuit breaker in the DC grid. Additionally, this research contributes to the understanding of DC grid fault protection by communicating best practices.