Design of arc Flash protection system using solid state switch, photo detection, with parallel impedance

Arc flash hazard has been a major concern for the electrical industry with incidences hospitalizing workers and severely impacting processes and profitability with lost production. It is well understood that the energy produced by an arc flash incident is proportional to the voltage, current and duration of the event. The arc flash duration is the sum of the time to detect the arc and the time to isolate. Breakthroughs have been achieved in the detection of arc flash incidences under 1 ms with photo detection and solid state technologies, however, conventional circuit breaker operation time is 84 ms and results in damages to equipment and injury to personnel. This paper describes an arc Flash protection system that has been designed that allows the detection of an arcing event by performing continuous light monitoring of the switchgear combined with a means to isolate the fault in under 9 ms with an SCR switch. The conceptual system has been developed for a 3 phase, 600 Volt system and is scalable to higher ratings. The module comprises a solid state SCR switch connected in parallel with a resistance for switching transient elimination, and combined with control circuitry connected to the system and fibre optic point sensors monitoring for arcing incidence. The system achieves high yield in incident energy limitation during an arc flash fault. Details of the development of the module are discussed.