A Review of Commonly Used DC Arc Models

The dc arc hazard is a great concern to industry. Quantitative arc hazard assessments are performed on dc systems to determine a nearby worker´s potential incident energy exposure during an arcing event. Four viable dc assessment methods are reviewed in this paper. The most widely used model for predicting dc incident energy is based on Lee´s theoretical arc model; the electrical arc power is determined from the maximum power transfer theorem, and the arc is depicted as a spherical radiant source with uniform heat transmission in all directions. Like Lee´s model, Ammerman´s model assumes complete conversion of electrical arc energy into thermal energy, but arc power is determined from an iterative technique constrained by arc power and circuit characteristics. Ammerman incorporates multiplying factors which account for the higher incident energies associated with arcing in enclosures. Based on dc arc testing, the applicability of an existing software package has been extended to dc systems through multiplying factors, and equations for dc rail and transit systems have also been developed. Model derivation is examined in this paper for suitability to arcing in general and dc specifically. Model performance is assessed using the available limited data (ac or dc). Example calculations are provided.