Short-circuit analysis in industrial and commercial power systems: the “characteristic” currents approach

For short-circuit analysis in industrial and commercial power systems, a new approach of the ohmic method in such a form as to facilitate, as far as possible, its use and the realization of its evaluation is suggested. The `characteristic' current method, by replacing the impedance of each equipment with the corresponding value of the `characteristic' current, permits the application of the impedance properties to the inverse of the current values, either in meshed or nonmeshed networks. In order to achieve the correct design, rating and protection coordination of the whole power system, it is necessary to know and calculate step by step the values of short circuit current for each system component, from the utility or local generating connection point until the branch-circuits and the utilization equipments. The proposed approach assumes the above mentioned short-circuit current directly as calculation and comparison parameters. With the `characteristic' currents as parameters the short-circuit analysis of substantial radial systems is made easier and a better matching of power system design requirements is permitted