Definite time overcurrent protection for distribution networks based on piecewise linear modeling and a fault distance coefficient

To reduce carbon emissions, renewable energy sources such as photovoltaic, wind, and biomass are increasingly integrated into power systems. Most of these resources are connected via inverters and classified as inverter-interfaced distributed generators (IIDGs). However, large-scale integration of IIDGs significantly alters fault current characteristics, thereby degrading the performance of conventional overcurrent protection schemes. Despite these challenges, overcurrent protection without communication remains widely adopted due to its simplicity and cost-effectiveness, creating a practical need for performance improvement. This paper presents an overcurrent protection method based on piecewise linear IIDG modeling and a fault distance coefficient. Since fault current characteristics are essential for protection settings, the relationship between fault current and fault location is analytically derived in the presence of multiple IIDGs, and the conditions for monotonicity are identified. To enhance protection performance under IIDG integration, a protection range coefficient is used to replace the traditional reliability factor, resulting in improved selectivity, sensitivity, and speed. Fault current is calculated non-iteratively using a piecewise-linear IIDG model combined with a voltage estimation and correction mechanism, which enables fast, simple, and offline implementation. Simulation results confirm that the proposed method provides reliable performance and is well suited for distribution networks with high IIDG penetration.