CALCULATING THE IMPEDANCE OF A GROUNDING SYSTEM

Following up previous research, concerning low frequency electromagnet ic emission from a grounding system [1], the authors suggest methodolo gy which allows a complete electromagnetic study by finite Element Met hod (FEM) of a grounding system in the significant frequential spectru m of a stroke of lightning or a short circuit (f less than or equal to 1MHz). In this study, as well as calculating the electromagnetic fiel d at any point in space (ground or air), we shall pay particular atten tion to variation with frequency of the impedance of a grounding syste m. Suggested modelling will take into account eddy currents in buried conductors and ground- and non-linear phenomena (ionization of the gro und) around the buried conductors when high currents flow via the eart h. It will also deal with the displacement currents when their effect becomes noticeable in the earth for high frequency. The interest of th is work lies in providing data needed to implement an optimal groundin g system in non-homogenous medium. All the results of calculations wil l be compared with measurements made by the French Electricity Board ( EDF, France).