ARC flash pressure measurement by physical method, effect of metal vapor on ARC blast

Abstract

Arc flash pressure waves or arc blasts have received much attention in the electrical safety industry but no consensus standard or method exists to predict the overpressure or thermoacoustic blast created by an arc. The papers to date have focused on noise (auditory damage) or equipment damage. First, we surveyed the literature for arc blast models to compare some practical measurements of arc blast with the published attempts to characterize arc blast. Second, we performed some laboratory controlled experiments to evaluate the effect of copper vapor expansion, if any, on arc blast since this is commonly taught to be a significant factor in the blast pressure. Third, we evaluated the speed of an ejected door (an unsecured door was used as a worst case scenario of door ejection) to correlate this with fault current levels, clearing times and electrode materials to see if the effect of vaporization of the metal could be detected in an unsealed but closed enclosure. Fourth, we performed arc tests in a tight enclosure to measure the internal pressure exerted on the front door with different current levels and electrode materials to look at metal vaporization effect. Fifth, we evaluated some published methods to evaluate them for promise of prediction of door ejection speed and pressure in enclosed equipment. To date, calculations from existing equations do not assist in predicting door ejection speeds or the effect on workers. We sought to provide a path forward for research to provide a practical application method of measuring arc blast and offer insight into developing an effective model which the industry could use on equipment and modeling equipment arc blast effect on a worker.