Modeling the Dynamic Behavior of DC Arcs

AC arc flash hazards were recognized in 1982 and introduced into OSHA and NFPA 70E soon thereafter. DC arc flash hazards were being considered by 2007 and introduced into the 2012 NFPA 70E. Two methods were introduced in NFPA 70E to estimate dc incident energy, with little data available. In general, these methods overestimate the hazard when compared to recent laboratory data. This article will provide a high-level overview of (a) the current understanding of high-current, dc arc physics, (b) models presently used in performing dc incident energy analyses, and (c) recent laboratory studies to measure DC arc flash parameters for several voltages. This latest information will then be used to evaluate the accuracy of some existing dc arc hazard assessments, and to propose improved approaches to modeling the dynamic behavior of short, high-current, free-air arcs. These dynamic models proposed help to better predict the extinction behavior of such arcs. This work is applicable to slow risetime arcs, such as produced by dc power supplies, battery banks, super capacitors, and solar voltaic systems. It is not applicable to capacitor discharges as the fast risetime produces a supersonic shock wave and the arc behavior is beyond the scope of this article. Data analyzed is from the battery bank and electric transportation applications.