Challenges for Distance Relays in Grid Code-Compliant Inverter-Based Power Systems: A Review

The distinct fault characteristics of inverter-based systems, compared to those of synchronous generator (SG)-based power systems, can cause malfunctions in distance relays, including distance, directional, and phase selection elements. Recent updates to grid codes and standards aim to standardize the behavior of inverter-based resources (IBRs), ensuring their fault characteristics more closely resemble those of SG-based systems. These updates enable IBR-based systems to fulfill certain preconditions required for the reliable operation of distance relays, e.g., presenting a highly inductive IBR output impedance for negative-sequence quantities. However, due to fundamental limitations in IBR control and hardware, not all the preconditions for distance relays are met, even in systems compliant with updated grid codes. This paper reviews the preconditions necessary for reliable distance relay operation, identifying those that are fulfilled by grid code-compliant IBRs and those that remain unmet. It is found that, due to the unmet preconditions, the IBRs not only exacerbate pre-existing challenges in distance relay inherited from SG-based systems but also introduce IBR-specific issues. Finally, potential solutions to address the challenges caused by the unmet preconditions are shared.