Calculating the impedance of a grounding system

Following up previous research, concerning low frequency electromagnetic emission from a grounding system [1], the authors suggest 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&leMHz). In this study, as well as calculating the electromagnetic field at any point in space (ground and air), we shall pay particular attention to variation with frequency of the impedance of a grounding system. Suggested modelling will take 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 will also deal with displacement currents when their effect becomes noticeable in the earth for high frequency. The interest of this work lies in providing data needed to implement an optimal grounding system in non-homogeneous medium. All the results of calculations will be compared with measurements made by the French Electricity Board (E.D.F., France).