Auxiliary Branch for Hybrid DC Circuit Breaker in Flexible DC Grid to Reduce Fault Breaking Time and Arrester Capacity Demand

Considering the voltage source characteristics of the converters in the flexible DC grid, the current-limiting reactors are usually placed on the DC line terminals to limit the fault current rising speed. However, the current-limiting reactors will deteriorate the operation of the hybrid DC circuit breakers, leading to prolonged fault breaking time and increased arrester capacity demand. Therefore, a simple but effective auxiliary branch is designed for hybrid DC circuit breakers in this paper to solve these problems. The auxiliary branch is composed of a diode valve and an energy-consuming resistor connected in series, which does not require active control and can be put into operation automatically. By configuring the proposed auxiliary branch to cooperate with the hybrid DC circuit breaker, the fault breaking time and the arrester capacity demand of the hybrid DC circuit breaker can be significantly reduced, which accelerates the fault recovery speed, decreases the overcurrent time of the fragile semiconductor components, and reduces the breaker investment costs. Extensive simulations in PSCAD/EMTDC software are conducted to verify the effectiveness of the proposed auxiliary branch.