Short circuit analysis on a simple power system network: the “characteristic” currents method

In this paper a short circuit analysis is performed on a simple power system using the characteristic currents method. Assuming as reference the IEC 909, the characteristic currents method modifies the calculation of the initial symmetrical fault currents corresponding to the 1/2 cycle symmetrical fault currents discussed in the ANSI/IEEE Standards C37.010-1979 and C37.13-1981. The approach is based on the correlation between the impedance of each power device and the inverse of a new parameter which is defined as the short circuit characteristic current of the component itself. The use of the characteristic currents as parameters make the short circuit analysis easier and allow an immediate perception of what is calculated. Moreover, this method is particularly suitable to be implemented on a spreadsheet program and for the application to an approximate evaluation of the short circuit currents which is helpful during the preliminary design as well as in verifying and testing the electric power systems in buildings. For verification, comparisons are made between the values calculated with the characteristic currents and appropriate ANSI/IEEE Standards