Calculating the impedance of a grounding system

Following up previous research concerning low frequency electromagnetic emission from a grounding system [Nekhoul et al., 1995], the authors suggest a methodology which allows a complete electromagnetic study by finite element method (FEM) of a grounding system in the significant frequential spectrum of a stroke of lightning or a short circuit (f/spl les/1 MHz). In this study as well as calculating the electromagnetic field at any point in space (ground and air), we pay particular attention to variation with frequency of the impedance of a grounding system. Suggested modelling takes into account eddy currents in buried conductors and ground and non-linear phenomena (ionization of the ground) around the buried conductors when high currents flow via the earth. It also deals with displacement currents when their effect becomes noticeable in the earth for high frequency. The interest of this work lies in data needed to implement an optimal grounding system in non-homogeneous media. All the results of calculations are compared with measurements made by the French Electricity Board (E.D.F., France).