Progressive Switching of Hybrid DC Circuit Breakers for Faster Fault Isolation

Achieving fast and efficient circuit protection is critical to direct current (DC) system safety with many scholars focusing on hybrid direct current circuit breakers (DCCBs) to achieve this goal. However, fault isolation speed is limited by the time required for the mechanical switch to achieve sufficient dielectric strength across the contacts. In this paper, we propose a progressive solid-state switching method for hybrid DCCBs to dynamically control the voltage potential across the mechanical switch. The proposed switching method reduces fault isolation time and limits the peak fault current during breaker operation. DC system dynamics are explored and the voltage withstand capability of a new Ultrafast Mechanical Switch is analyzed. The discovered characteristics are used to design a progressive switching method in computer simulation and it is validated experimentally with a test prototype. In the proposed design fault current is curtailed during the mechanical switch opening sequence rather than waiting until it is fully open, improving system stability.