Abstract
While multi-phase short circuits are reliably cleared by conventional overcurrent relays, single-phase-to-ground faults (SPGFs) in isolated, compensated, or resistance-grounded 6–10 kV distribution networks produce extremely low, highly distorted currents that frequently cause traditional zero-sequence protections to misoperate. Because SPGFs constitute the vast majority of network disturbances, resolving this specific low-current detection challenge remains a critical priority for grid resilience. This paper presents a preselective protection approach based on Vector Analysis of Reactive Asymmetry Current (VARAC), designed for implementation in digital relay protection and automation terminals. Instead of relying primarily on vulnerable zero-sequence quantities, the method derives diagnostic features from the reactive asymmetry structure of three-phase current phasors. A reactive asymmetry matrix is formed from pairwise imaginary cross-products, symmetrized to preserve real eigenvalues and stable modal interpretation. The dominant eigenvalue and eigenvector are then used to quantify fault intensity and directional skew through two decision features: a magnitude-based index and a normalized asymmetry ratio. This enables robust discrimination between normal and faulted operation, including low-current and compensated-fault conditions where conventional criteria lose sensitivity. Simulation and oscillographic evaluations show a clear separation between pre-fault and SPGF regimes, fast onset detection, and improved structural selectivity versus traditional zero-sequence indicators. The proposed algorithm is computationally lightweight and compatible with hierarchical distributed SCADA architectures, supporting coordinated monitoring, diagnostics, and adaptive protection functions in modern medium-voltage networks.