Addressing Distance Relay Mal‐Operation in Low‐Inertia Grids: A PLL‐Informed Power Swing Assessment

ABSTRACT

The increasing penetration of inverter‐based resources (IBRs) has substantially reduced system inertia and altered power swing characteristics, thereby posing significant challenges to conventional impedance‐based power swing detection (PSD) methods employed in distance relays. In particular, the fast dynamic behaviour of IBR‐dominated grids often leads to high‐frequency power swings that cannot be reliably detected using traditional schemes, potentially resulting in relay maloperation. To address these challenges, this paper proposes a novel network‐aware PLL interaction index, denoted as , which is derived analytically from the synchronous reference frame phase‐locked loop (SRF‐PLL) model and grid parameters. The proposed index is integrated into the conventional PSD logic to enable accurate discrimination between stable and unstable power swings. A key advantage of the proposed approach is its independence from PLL control settings, relying solely on locally measured electrical quantities, which ensures robust, fast, and practical implementation in existing commercial distance relays. Comprehensive time‐domain simulations conducted on both a two‐bus test system and the IEEE 9‐bus benchmark network demonstrate that the proposed method significantly enhances detection reliability, selectivity, and speed compared to traditional PSD techniques. The superior performance is particularly evident under low‐inertia conditions and high‐frequency power swing scenarios, highlighting the effectiveness of the proposed scheme for modern inverter‐dominated power systems.