Assessment of Load Characteristics in Short-Circuit Studies of Distribution Substations

Abstract

This paper evaluates the influence of electrical loads on the distribution of currents under both normal and fault operating conditions in distribution substations. Static and dynamic loads are modeled using equivalent impedance components, where dynamic loads are represented by the Conventional Load Model, Exponential Load Model, Polynomial Load Model, and Comprehensive Load Model. The Newton-Raphson method is applied for power flow analysis to determine current distribution under normal operating states. In addition, the IEC short-circuit calculation method is adopted to analyze fault current distribution in the entire system under short-circuit conditions. A five-bus test system, in which the load can switch between static and composite (static + dynamic), is proposed to investigate current distribution under different operating conditions. Simulations are performed in ETAP for both normal and fault modes, considering static loads and composite loads. The results highlight current distribution across the system, clarifying the ability of dynamic loads to contribute to fault currents during short-circuit conditions, unlike static loads. The contributions of this study provide insights for designers and operators in understanding how electrical load characteristics affect the performance of protection devices in distribution substations.