Estimation of the Arc Power During a Three-Phase Arc Fault in MV Electrical Installations

Abstract

In order to determinate the pressure rise and the gas temperature due to fault arcs in electric installations, the arc power that is heating the surrounding gas of fault arcs has to be known. As the arc voltage for a given short-circuit current is a direct equivalent of the arc power, it is important to model the arc voltage properly. In order to consider the dependence of the arc voltage on gas density, the radiative effect of fault arcs on the power balance is introduced into the arc model by using the net emission coefficient as a function of gas density, arc temperature, and arc radius. The radiation model takes account of the local radiation distribution at the center of the isothermal plasma. As a consequence, the physical profile of fault arcs can be theoretically predicated. In addition, this paper introduces a calculation method to estimate the fault-arc current of a three-phase arc fault according to the characteristics of three-phase fault arcs. Along with the arc voltage, the fault-arc current can determinate the arc power of the multiphase fault arcs during an arc fault in the electrical installations. Furthermore, it is demonstrated for an example of the arc fault in a compact medium-voltage station with pressure relief openings and a pressure relief channel that the development of pressure and temperature can be simulated on a computational-fluid-dynamic-based calculation method with a reasonable and accurate arc power in electrical installations.