Overview of Protection Relay Designs in Power Systems that Integrate Grid-Forming Converters

Recent research on GFMCs (Grid-Forming Converters) with high-penetration RESs (Renewable Energy Sources) highlights their ability to mimic SGs (synchronous generators), enabling RESs to self-synchronize, share power, and support grid frequency response. However, many GFM control methods and loops significantly alter short-circuit fault characteristics, affecting traditional protection systems, especially for the functions of distance protection relays in transmission grids. Distance relays operate by calculating impedance from local voltage and current. GFMCs, with current limiters and FRT (Fault Ride Through) controllers, will modify the amplitude and phase angle of reference currents, reducing impedance below relay settings. This change affects relay sensitivity and reliability in detecting short-circuit faults. Thus, this article aims to explore the impact of GFMCs on relay protection in transmission grids and provide insights for designing new protection systems that can adapt to evolving power grids, where GFMCs and GFLCs (Grid-Following Converters) play a key role.