Procedure for Selection of Switchgear Parameters for Safe Operation of Electric Distribution Network

Abstract

One of the major hazards of short circuit is “Arc Flash” incidence which is established when current flows through ionized air that eventually leads to expelled molten metal in the form of arcs. This results in very high ambient temperature around the switchgear connecting system. The best approach to mitigate the lethal and hazardous action of this thermal outbreak is by adopting appropriate sizing of the switchgear to withstand the expected 3-phase current-induced temperature excursion; so as to avoid the attendant system fault occurrence. In an attempt to determine the choice of the switchgear selection for this task, the power network protection analysis is modeled by the conventional techniques using the electrical load flow and short circuit analysis. The ensuing model is then treated to transient fault analysis protocols using various fault current values for the selection of appropriate size of the overcurrent protective devices (OCPD). This is thus simulated using Electrical Transient Analyzer Program (ETAP). From this development, a series of numerical results is obtained, in respect of the system short circuit capacity, under various operating conditions. When these results are compared with the industrial standard practices for effective operation of the distribution network, it is discovered that the switchgear equipment operates safely at a region within which its electrical current capacity is calibrated with much higher magnitude than the system’s short circuit capacity. Hence for resilience against the arc flash induced network failure, it can then be concluded that the network should be subjected to a well calibrated and high precision electrically resilient, but thermally stable, current-based switchgear selection.