Arc Flash Energy Reduction—Case Studies

This paper discusses the use of high-speed circuit interruption to achieve extremely fast arcing fault clearance, resulting in a significant reduction of arc flash incident energy. High-speed interruptions can create problems such as loss of selectivity and unintended production losses. To prevent nuisance tripping, protective zones are created, and circuit breakers are assigned primary and backup protective zones. Circuit breakers use high-speed circuit interruption for faults within the primary protective zone, and their speed of operation is retarded or restrained for faults outside the primary protective zone. Waveform recognition of the fault current due to downstream current-limiting devices, where they exist, enables the protection zone to extend to downstream remote equipment. This paper concludes with a description of solutions used on two installations where the incident energy was reduced from a level of “extremely dangerous” to a level much lower than that defined for “everyday work clothing” personal protective equipment (PPE) (8 cal/cm²). This reduction was achieved across three levels of equipment without compromising selectivity and, therefore, unnecessary outages.