Algorithm to Prevent Breaker-Failure Protection Maloperation Due to Subsidence Current

Duplication of circuit breakers (CBs) in substations is not realistic due to economic and operational constraints. In the event of failure of a CB, adjacent breakers need to be called in to isolate the fault. Typically, a breaker-failure protection (BFP) function is integrated within commercial relays to monitor such situations. However, these functions are prone to maloperation because of subsidence in current transformers (CTs) resulting from faults with significant decaying dc component. To this end, a reliable reset algorithm for the BFP function is presented. After measuring the decaying dc component within a one-cycle moving window, the proposed algorithm accurately distinguishes between the alternating pattern of fault current and exponential decaying pattern in subsidence current. Its performance remains unaffected during change in fault current level, decaying dc component, CT saturation, level of subsidence, and random noise. Effectiveness of the proposed scheme in practical scenarios is demonstrated through a hardware setup validated through error analysis. Overall performance evaluation in terms of reliability indices testifies its superiority over available techniques.