Influence of soil model simplifications on the prospective touch voltage of earthing systems

The soil resistivity is a main parameter in the dimensioning process of earthing systems. In analytical calculations and in typical evaluation programs, the soil is considered uniform or layered, but in reality it has an arbitrary shaped resistivity distribution. An Electrical Resistivity Tomography (ERT) of a test area is performed, using Wenner's array configuration. The found apparent resistivity data is then used as an input parameter for the inversion modelling process to find the resistivity distribution of the test area, which will be the reference model. The prospective touch voltage and the surface potential distribution of two half spherical shaped earthing electrodes is analysed using the finite element method (FEM) software ANSYS Maxwell 3D. Seven different soil models were compared to the reference model. These models are simplified ones using the apparent resistivity and the inversion result, to compare the effect on the potential distributions.
Using the minimum apparent resistivity for a homogeneous soil and the average of each layer of the reference model for a layered model showed the smallest deviation on the potential distribution.
Further investigations will show the effect of different soil structures on the prospective touch voltage.