Short-circuit analysis and protection coordination of a 33 kV phosphate plant distribution network

Abstract

This study presents a short-circuit and protection coordination analysis of a 33 kV/0.4 kV industrial distribution network supplying a phosphate processing plant in Mauritania. Using ETAP software, the system was modeled to evaluate fault behaviors based on IEC 60909 and IEC 60255-151 standards. The study assesses the existing protection architecture and proposes an optimized digital protection framework. Simulation results indicate that the initial symmetrical short-circuit current at the 0.4 kV busbar reaches 96.5 kA, exceeding the 25-36 kA breaking capacity of the legacy equipment by nearly 300%. The analysis also investigates single-line-to-ground faults, revealing a fault current inversion phenomenon driven by the solid grounding configuration. To address these vulnerabilities, the study proposes upgrading to 150 kA-rated high-breaking-capacity switchgear and implementing advanced negative-sequence protection (ANSI 46) and transformer differential protection (ANSI 87T). This work provides a practical diagnostic framework for mitigating asymmetrical faults and optimizing protection coordination in heavy-duty industrial clusters.