Performance Analysis of Distance Relay in the Presence of Grid‐Forming Inverter

In recent years, renewable power plants have evolved from small‐scale units connected to distribution networks to large‐scale facilities integrated into transmission systems. These sources are typically interfaced through power electronic converters and are referred to as inverter‐based resources (IBRs). Unlike synchronous generators (SGs), IBRs exhibit different dynamic behaviour during short‐circuit faults. Their fault current contribution is limited by power electronic switches and its phase angle is determined by inverter control systems. In addition, IBRs lack the inherent inertia of synchronous generators, creating new challenges for power system protection. This paper investigates the performance of distance relays in transmission networks with high penetration of IBRs. Simulations are carried out in PSCAD for two scenarios: a system dominated by synchronous generators and a system with IBRs. The recorded signals are then analysed in MATLAB. Results show that the presence of IBRs significantly affects the apparent impedance trajectory seen by the relay. For single line‐to‐ground faults, the relay generally operates correctly; however, under high fault resistance and remote fault locations, the impedance deviation increases from about 22.1 Ω in the SG‐based system to approximately 36.8 Ω in the IBR‐based system. The effect is more severe for phase‐to‐phase and phase‐to‐phase‐to‐ground faults. For a line‐to‐line fault with 10 Ω resistance at 50% of the line, the deviation increases from about 11.7 Ω to nearly 53.9 Ω. In a line‐to‐line‐to‐ground fault at 70% of the line with 10 Ω resistance, the deviation can reach approximately 165 Ω, potentially causing relay maloperation.