In this paper, we investigate effect of horizontally two-layered soil on the equivalent circuit of grounding grids in comparison with hemogenثous soils. In extracting equivalent circuit, vector fitting method is applied to input impedance of the grid computed via the finite element method (FEM). The simulation results show that the input impedance of the grounding grids in horizontally two-layered soils is placed between the individual ones in hemogenثous soils with conductivity values of the first and second layers. This fact show that importance of including different layers of soil in extracting equivalent circuit which can be imported to EMTP software for accurate transient analyses of power systems under lightning return strokes.
