Optimized Instantaneous Protection Settings: Improving Selectivity and Arc-Flash Protection

In today´s power distribution systems, the protection methods do not provide full selectivity and instantaneous fault clearing for expected fault current, including lower-magnitude arcing currents simultaneously. This article discusses two methods that may change that. The first method is a selectivity analytical technique useful with many circuit breaker (CB) trips currently available in the industry. The second method is a new CB trip technology. Both methods allow switch gear CBs to use sensitive instantaneous settings and maintain selectivity when used in upstream current-limiting (CL) molded case CBs (MCCBs), CL motor circuit protectors (MCPs), or CL fuses in downstream equipment such as motor control centers (MCCs).