Main Breaker Switching Control and Design Optimization for A Progressively Switched Hybrid DC Circuit Breaker

The switching control and MOV design optimization in the main circuit breaker (MCB) of a progressively switched hybrid DC circuit breaker (DCCB) is presented. A progressively switched hybrid DCCB achieves faster fault isolation with reduced fault current and transient recovery voltage compared to a regular hybrid DCCB due to its modified switching strategy. Analytical model of the system dynamics during fault isolation with progressive switching is derived to demonstrate the switching scheme's effect on the energy-absorbing component, which is the metal oxide varistor (MOV), during turn-off. The developed analytical model in conjunction with the displacement curve of the fast mechanical switch of the hybrid DCCB is utilized to optimize the components of the main circuit breaker branch to reduce MOV degradation from asymmetric energy dissipation. This process also calculates when each switch stage should be turned off progressively during fault isolation. A model of the circuit breaker is built in PSCAD to validate the performance of the proposed optimization method. Experimental results are provided for a low voltage system to demonstrate reduced fault current peak in a progressive switching and near uniform energy absorption in optimally selected MOVs.