Fault section identification using zero-sequence current carrier signaling in ungrounded power distribution systems

In isolated-neutral distribution networks, single-phase-to-earth faults generate extremely weak fault currents with complex spatial distributions, rendering conventional manual patrols inefficient and expensive. This paper derives closed-form expressions for the magnitude and phase of zero-sequence currents along feeders with radial and tree topologies, establishing segment-level criteria based on magnitude discontinuities and phase reversals. Building on these analytical results, a distributed zero-sequence current carrier-monitoring scheme is proposed: each zero-sequence current transformer is assigned a unique high-frequency carrier, mapping geographical position to a frequency signature, thereby enabling fault-section identification without additional communication infrastructure. The effectiveness of the proposed method is verified through comprehensive simulations.