Experimental studies of the HEAF (High Energy Arc Fault) fire event for high voltage switchgears

Successive fire due to a HEAF (High Energy Arc Fault) event in a high voltage metal-clad switchgear was identified at the Onagawa nuclear power plant after the Great East Japan Earthquake in March 2011. During HEAF event, hot gas heated in the metal enclosure due to the arc flash will be emitted out of the enclosure or to adjacent enclosure, and has a potential to damage the surrounding equipment. In light of this, we executed internal arc tests with full scale high/low voltage metal-enclosed switchgear components (non-arc proof type, copper bus conductor), and evaluated arcing energy, the mechanical damage of the switchgear and the surrounding equipment due to the impulsive pressure and the possibility of successive fire occurrence. In case of high voltage switchgear, when the arcing energy exceeded 27 MJ, successive fire was identified. Especially, in the case where the arc flash was discharged in the circuit breaker room, a 2-second arcing duration in a three-phase short-circuit current with 18.9 kA (measured arcing energy over 40 MJ) caused successive fire which required extinguishment. Furthermore, we analyzed details of enclosure pressure, damage to a metal enclosure and gas emissions from a broken enclosure using CFD (Computational Fluid Dynamics code) and impact analysis code, and investigated their applicability to the numerical approach for the HEAF event. (author)