A Novel Method for Calculating Resistance of Grounding Schemes Buried in Homogenous and Two-Layer Soils Based on Current Sphere Simulation Technique and Concept of Images

Abstract

This paper is aimed at proposing a novel method for calculating the resistance-to-ground of three grounding-schemes under known applied-voltage. The schemes include a vertical rod(s), and square/rectangular grids with and without rods. The schemes are buried in a homogenous-soil or two-layer soil with an interface-plane separating the soil layers. The calculation method is based on the current-sphere-simulation-technique (CSST) along with the concept of images. The currents in the vertical-rod and the grid-conductors are simulated by current- spheres of diameters the same as the rod or conductor. The interface-plane between soil-layers is simulated by two sets of equal number of current-spheres. Satisfaction of Dirichlet boundary-condition at the scheme-surface and normal current-density continuity along with the potential-equality boundary-conditions the interface-plane formulates a set of equations, whose solution determines the currents of the simulation-spheres. The sum of sphere-currents simulating the ground-scheme represents the current injected into the surrounding-soil for evaluating the scheme grounding-resistance. The calculated grounding-resistance by the proposed-method agreed with those obtained from COMSOL and CYMGRD with a deviation up to 13.2% for the investigated three grounding-schemes.