Grounding system impedance characterization using FEM

Abstract

The exact knowledge of the grounding system impedance, including its expected variability, is a matter of paramount importance in the design of medium and high voltage infrastructures. The principles underlining the physical processes involved in grounding are well established and so are the engineering concepts regarding safe operation of the grounded systems. Quite a few theoretical expressions are widely used in the project stage of any installation. Unfortunately, these expressions are only valid for simple geometries and simplified material characteristics. Uncertainty arise from the intrinsic complexity of the grounding environment: buried grids and rods, reinforced concrete foundations surrounding them, weather dependent and non-uniform soil characteristics, etc To overcome these limitations, in this paper the finite element method is applied to obtain the grounding impedance and the potential distribution around a real grounding system excited with sinusoidal currents at several frequencies. Additionally, for validating purposes, a single vertical ground rod has been simulated and compared with the results obtained by other authors. FEM commercial software, in addition to some specific purpose user functions, has been used. The method presented in this paper can be applied to any real geometry, electrode configuration and type of soil