Comparative assessment of short-circuit calculation methods in inverter-dominated power systems

Abstract

The increasing integration of inverter-based resources (IBRs) in power systems raises questions regarding the applicability of short-circuit calculation methods originally developed for synchronous generation. This work evaluates the limitations of IEC 60909 in systems with high photovoltaic penetration by comparing its results with dynamic RMS and EMT simulations, used as reference, and with two alternative approaches: The Complete Method and a Fault-Ride-Through-based method. The analysis is performed on the IEEE 14-bus system considering 25% and 50% IBR penetration levels and three fault types: Three-phase, lineto-line, and single line-To-ground faults. The results show that IEC 60909 systematically overestimates short-circuit currents, with errors strongly dependent on the fault type, reaching up to 76% in single line-To-ground faults at 50% IBR penetration. The alternative methods significantly improve accuracy, but on different fault types. The FRT-based method provides the best performance for three-phase and line-To-line faults, while the Complete Method achieves higher accuracy in single line-To-ground faults. These findings suggest that no static method is uniformly suitable across all fault types, and that a complementary approach is required for short-circuit analysis in inverter-dominated systems.