Modified medium voltage arc flash incident energy calculation method

IEEE Standard 1584-2002 provides a guide for conducting arc-flash hazard analyses for low voltage and medium voltage systems. However, users need to be aware that the models in the guide were based on the measurements of arc incident energy under a specific set of test conditions combined with theoretical work. In the medium voltage arc flash analysis, the incident energy calculation, according to the guide, is a function of system voltage, gap between conductors, the distance from the possible arc point to the worker, the bolted three-phase fault and the arc clearing time from the source-side protecting device. However, the effect of fault current decaying was not considered in the current guide. According to IEEE (Institute of Electrical and Electronic Engineers) recommended short circuit calculation method, the fault contributions from generators, induction and synchronous motors would usually decay over the short circuit period based on their short circuit time constants and excitation system. Therefore, the calculated incident energy from short circuit point of view would be higher than the value if the effect of decaying current were considered.