Seasonal variations in soil electrical resistivity significantly impact the design and safety of earthing systems in electrical substations. This paper introduces a novel approach to modelling soil electrical resistivity, enhancing the accuracy and reliability of earthing system design across diverse climatic conditions.
Our methodology dynamically incorporates the effects of soil temperature and moisture levels throughout the year, adjusting measured resistivity values to determine a worst-case scenario based on average annual temperature, rainfall, and snowfall for a given location. Unlike existing methods, which only consider soil temperature, our approach accounts for the combined effects of both temperature and moisture on soil electrical resistivity.
By addressing these seasonal fluctuations, our new calculation methods provide a more comprehensive assessment of earthing system performance, enabling engineers to optimise designs for both cold and hot climates. This ensures consistent safety standards regardless of geographical location or seasonal extremes. The enhanced modelling technique which produces better estimations of the seasonal variation effects offers several key advantages including improved accuracy in predicting earthing resistance, ground potential rise and step-and-touch voltages.
We present a comprehensive method for predicting soil models on any day of the year, assuming a horizontally stratified soil model and associated measurement day are available. Our approach involves modelling soil moisture dynamics using a soil moisture velocity equation (SMVE), which accounts for depth-dependent variations and integrates key factors like infiltration rate, evapotranspiration, and drainage. This model allows for recursive calculation of soil moisture over time intervals, providing a steady-state solution aligned with periodic rainfall patterns.
By integrating soil moisture data with resistivity measurements, we derive a moisture-based correction factor for soil resistivity, which varies linearly with depth up to a critical depth. This advanced seasonal analysis can significantly enhance safety in electrical substation design, reducing the risk of electrical hazards and improving overall system reliability. Our methodology provides a robust foundation for earthing system calculations, contributing to the development of safer and more resilient electrical infrastructure across various climatic zones.