A Basic Assessment of Arc Flash in Low Voltage AC

The empirical model provided by the IEEE1584-2018 guide interpolates intermediate values of the average arc current, incident energy, and arc-flash boundary to determine final results, corrected by factors for enclosure size and arc current variation. Various kinds of software exist to assess the risk of arc flash complying with this model. It becomes relevant to have a physical understanding of the phenomenon, examining singularly the various parameters that affect it, such as the arc-fault current, the arc flash in the air or in the enclosure, electrode gap, and the box size. At this aim, the article proposes a simplified method to calculate the arc-fault currents, the incident energy, and arc-flash boundary, assuming as reference test the IEEE 1584 results. At first, it deals with a normalized analysis of the arc-fault currents in reference to the maximum power transfer condition. This analysis highlights the basic influence of the power factor on the fault current behavior and allows to identify an operational value of the arc resistance. In the power systems of low voltage ac ≤600 V, this article proposes a tentative criterion to evaluate the incident energy, the arc-flash boundary, and to select the adequate PPE(Personal Protective Equipment). The parameters suggested by the simplified model are identified and verified, assuming as a reference of the arc-fault current calculation with the IEEE guide. The numerical results on case studies, obtained with the proposed model, are completely consistent with the results obtained with the IEEE1584-2018 guide.