Environmental-State-Driven Robust Neutral-Point Impedance Configuration for Coastal Low-Voltage IT Systems

Coastal low-voltage isolated or impedance-earthed-neutral (IT) systems are capable of continuous power supply following the first earth fault. However, environmental erosion and converter-related system unbalance render the neutral-to-earth characteristics of such systems highly dependent on insulation performance and protective-earthing-path conditions. This paper proposes an environmental-state-driven and traceable configuration method for fixed series resistance–inductance neutral-to-earth branches. The method represents environment-dependent variations in system insulation and protective-earthing paths through temperature, humidity, salt contamination, and component aging and establishes four coupled environmental states accordingly. For each candidate neutral branch configuration, three critical indicators, i.e., neutral-point displacement voltage, first-earth-fault current, and touch voltage, are comprehensively evaluated. A common robust feasible region satisfying all prescribed environmental states is extracted through full-state constraint screening. Infeasible configuration candidates are traced to their dominant environmental states and restrictive constraints. Furthermore, a Pareto max–min selection criterion is adopted to determine the optimal configuration, which maximizes the minimum normalized safety margin without requiring additional empirical trade-off weights or online parameter retuning. A 400 V primary case study, complemented by cross-site climatic and electrical-system transferability assessments, demonstrates the applicability of the proposed framework over the investigated conditions.