Generating simple‐to‐apply comprehensive engineering recommendation for earthing safety in systems with solidly earthed neutral

Abstract

This study presents the procedure of generating simple-to-apply engineering recommendation for earthing systems and boundaries for setting of earth faults relay protection in power systems with solidly earthed neutral. The simple rules are based on ‘the worst case analyses’. Motivation for this work was simplification of the engineering process with acceptable deviation from economic optimum. Another reason is addressing the specific problems occurring in studied arid desert terrains conditions, which are described in this study. The analyses are based on calculation of earth fault current, its distribution over multiple earthing systems along the power line connected via protective conductor, tripping time dependent on relay curve, and allowed step and touch voltages depending on tripping time and characteristics of soil and optional additional surface material. For these calculations, the Excel/VBA software tool is developed and used. Different topologies of earthing systems (with grounding contours, rods, with/without backfill materials, etc.) considering layout of equipment in substation are studied using finite-elements software in order to determine the ratio of touch and step voltages to ground potential rise – GPR. The methodology is explained through a prominent case study of overhead line with overhead ground wire and metallic poles in the rural area.