Determining the arc fault hazard of an electrical installation requires calculating the available arc current, then deriving the energy incident to a person standing a certain distance away. Calculation methods used in NFPA70e and derived from IEEE Std 1584 consider the arc current to be constant until it is interrupted by some device, so that the accumulated incident energy is directly proportional to the arc duration. If the fault is sourced fully or partly by a synchronous generator, this assumption is invalid, since the available current from the generator will decrease exponentially with time. The decay of current will lead to inaccurate estimates of the energy level of the arc, either because the current will be lower than calculated (resulting in lower energy), or because the arc will not be interrupted as quickly (resulting in higher energy). A full power system analysis with the dynamics of the generator(s) included will give a more accurate result, but may be too expensive or time-consuming. This paper proposes a simplified approximation of the generator dynamics that extends the IEEE 1584 methods to account for the generator decrement curve. It is hoped that the proposed method will form the basis for further discussion and eventual incorporation of this or some similar method in the standard

This content is only available via PDF.
You can access this article if you purchase or spend a download.