Impact of climatic variations on seasonal changes of earthing resistance

Abstract

Seasonal soil-moisture flux causes time-varying soil resistivity and earthing resistance, which can compromise the safety of power-system earthing installations. Using representative sites in South Africa and Nigeria under comparable climates, this paper quantifies how temperature and relative humidity drive changes in topsoil suction and influence variation in subsoil resistivity and earthing resistance. The sites span four Köppen-Geiger climate classes: Aw (tropical savanna), BSh (hot semi-arid steppe), BWh (hot desert), and Cwb (subtropical highland). To study climate effects, a two-layer subsoil (silty top layer over sandy clay) with two earthing configurations: bare vertical rod and earthing enhancement material (EEM) embedded rod is modelled in COMSOL Multiphysics and simulated under the monthly suction values computed from the monthly average temperature and humidity data (1991-2021) of the sites. From postprocessing, the resistance of bare and EEM-embedded rods was computed and compared with analytical equivalents. Results show consistent resistance reduction with EEM across months and climates. Earthing sites in BWh and BSh exhibit wider suction ranges and larger resistance variations than those in Aw and Cwb. Similar climate classes show comparable seasonal patterns, but their rainfall days and sunshine hours provide plausible contextual differences in resistance magnitude and variation.