Analysis of closed-form ground-return impedances for short-circuit studies in overhead distribution systems

The objective of this study is to evaluate the applicability of the most widely used closed-form ground-return impedance formulas in short-circuit analyses of distribution systems and to identify the critical network configurations in which the choice of impedance model significantly affects the short-circuit results. The methodology adopted in this research is organized into three stages. First, an algorithm was developed to implement and compare several closed-form Earth-return impedance formulations, and its performance was validated using benchmark data reported in the literature. Second, a short-circuit analysis algorithm was designed and verified against reference results published by the IEEE Power and Energy Society. Finally, multiple short-circuit studies were performed on several IEEE distribution test feeders. The findings reveal that most closed-form Earth-return impedance models provide adequate accuracy for both balanced and unbalanced short-circuit analyses. However, for single-phase line-to-ground faults, the choice of closed-form impedance formulation is critical to obtaining accurate short-circuit results.