Improved multi-level protection scheme for ground faults in low resistance grounding systems

This study addresses the issues of poor selectivity, low sensitivity, and protection failure under high-resistance ground faults in existing low resistance grounding systems. We analyze the characteristics of zero-sequence current following single-phase ground faults in low resistance grounding systems and propose a high-sensitivity multi-level protection scheme based on zero-sequence current through coordinated longitudinal protection. This scheme resolves the issue of protection failure due to relatively low fault currents caused by high resistance by reducing the settings of the protection for outlet lines, branches, and boundary protections while extending their operating time. For high-resistance ground faults exceeding 1500 Ω, the scheme accurately identifies the faulted line and delays disconnection by comparing the magnitudes of zero-sequence currents at the exits of each line and the neutral line, thereby improving the accuracy of fault location. The feasibility and reliability of the proposed multi-level protection scheme for ground faults are validated through simulations conducted on a typical low resistance grounding distribution network structure.