Selectivity in DC-Microgrids: The Reaction Time Gap

Short-circuit behavior in DC-microgrids differs significantly from AC systems, increasing the use of hybrid and solid-state circuit breakers. Due to much shorter breaking times, the delay between the fault occurring and breaker reaction must be considered for selectivity. This reaction time gap - resulting from delays in detection and actuation - is introduced and discussed in detail in this paper. While often negligible in AC systems, it becomes critical in fast DC protection. If not properly accounted for, this delay may compromise protection selectivity and lead to cascading switchoff operations within the system. The paper analyzes how current slopes and grid dynamics interact with breaker delays, affecting coordination. Countermeasures concerning reaction and short-circuit dynamics are discussed to mitigate the reaction time gap and ensure selective protection in DCmicrogrids.