Earth resistivity tomography for earthing system design

Abstract

Well designed earthing systems are needed to ensure that occurring fault currents can be safely transported into the ground. Soil models are a key parameter for the dimensioning process of earthing systems. In previous research the soil is often assumed to be homogeneous or layered in its resistivity distribution. But the soil is arbitrary in its resistivity distribution. This work will give an input, which errors on the earth surface potential and step voltage will occur, if the soil model is not constructed accurately enough. Different standardized methods are used to interpret the measurement of soil resistivity to build a soil model. To get the measurement values, Wenners array is used within an earth resistivity tomography (ERT). For the interpretation, the method shown in IEEE Std. 80 will be used and compared with inversion theory. The impact of the different methods on the occurring earth surface potential and step voltages is analysed within a finite element method (FEM) simulation. It is expected, that the different methods for finding the soil model will influence the behaviour of the mentioned potentials. This analysis will help to use new methods to build up appropriate soil models for the designing process of earthing systems. The outcome can improve the efficiency of earthing systems and enhance personal safety.