Evaluation of the Residual Current Breaker (RCB) influence on the optimal sizing of hybrid HVDC circuit breakers

The increasing adoption of HVDC systems based on half-bridge modular multilevel converters hints at the need for fast and reliable fault interruption solutions. Hybrid HVDC circuit breakers (DCCBs) have emerged as a leading candidate, combining rapid current interruption with effective energy absorption. Metal Oxide Surge Arresters (MOSAs) are integral to these designs, providing counter-voltage generation and dissipation of fault energy. Residual current breakers (RCBs) are conventionally integrated with the main DCCB to ensure full galvanic isolation by eliminating residual fault currents that persist after the fault interruption transient. This paper shows that RCBs also play a crucial role in preventing transientinduced re-ignition in the MOSA branches of the DCCB, which can otherwise lead to severe energy overstress and increased breaker sizing. Ensuring fast, coordinated operation of RCBs with the main DCCB is therefore essential to optimize breaker performance and cost.