Calculation of short circuit currents for sizing electrical equipment

Selection of electrical equipment is influenced by the expected magnitudes of the short-circuit currents to which they will be exposed. The widely used application guides ANSI/IEEE C37.010-1979 and C37.5-1979 for AC high-voltage circuit breakers, as well as the IEC standard used in Europe, recommend procedures for determining circuit-breaker duty. These procedures utilize approximate calculations of fault currents. The authors present a method for more accurately approximating fault currents. Calculation of short-circuit currents by the proposed method and by the ANSI method are compared for an industrial power system.<>