## 4 The FEM Model  
The FEM model was made using Altair Flux 3D commercial software (release 2018.1.3). Second-order Differential Equation (8) was solved by dividing the area under consideration into smaller parts, first- or second-order finite elements. \[div([\sigma]grad(V))=0 \tag{8}\]  
[\(\sigma\)] is the tensor of the conductivity of the medium and \(V\) is the electric potential. As mentioned, the soil data for the preparation of the FEM model are presented in Table 4 (the best parameters of the three-layer model) for TP1 and in Table 6 (the best parameters of the four-layer model) for TP2. When modeling, we need to follow a few basic rules, presented in Figure 7, such as the following: \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**OF and Parameters**} & \multicolumn{3}{c}{**ABC**} \\ \cline{2-4}  & & **Three-Layer** & **Four-Layer** \\ \hline \(h_{1}\) (m) & B & 0.544 & 0.561 \\ \hline \(\rho_{2}\) (\(\Gamma\)m) & B & 4771.3 & 4960.7 \\ \hline \(h_{2}\) (m) & B & 2.834 & 2.777 \\ \hline \(\rho_{3}\) (\(\Gamma\)m) & B & 179.4 & 143.0 \\ \hline \(h_{3}\) (m) & B & - & 12.009 \\ \hline \(\rho_{4}\) (\(\Gamma\)m) & B & - & 310.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: _Cont._  
Figure 6: Measured and calculated apparent resistivities for TP2. * On the top surface, it is necessary to specify the boundary condition \"tangential electric\"; that is, the current can flow only along the surface of the earth and not pass from it. * On the bottom and side surfaces, the Dirichlet boundary condition potential \(V=0\) was set. The bottom and side surfaces of the model should be spaced sufficiently so as not to affect the distribution of potential in the vicinity of the earthing system. Figure 7 shows that the FEM model is made to a depth of 100 m and has dimensions on an area of 100 \(\times\) 100 m, so that the edge on which the boundary condition potential \(V=0\) is placed is sufficiently far from the grounding system. * A fault current is injected into the grounding system, which we received as information from ELES, d.o.o. It depends on the position of the distribution pole in relation to the other elements of the power system. Figure 7 shows the placement of the boundary conditions across individual surfaces of the FEM model. The dimensions of the model are also visible and were determined according to the size of the grounding system under consideration. A variable finite element mesh was used, which is denser in the area of the poles and sparser toward the outer surfaces of the model. The 2D basic mesh shown in Figure 8a was created and extended to the depth shown in Figure 8b. The final mesh is shown in Figure 8c. The number of nodes in the mesh is at a rank of 300,000, and the number of finite elements is at a rank of 580,000. Different numbers of nodes and finite elements were used for different widths of the protective foil. The finite elements used were prisms, resulting in a smaller number of finite elements than if tetrahedra elements were used. The geometry coordinates of test poles TP1 and TP2 were obtained in GPS coordinates. Several local coordinate systems were used for modeling. It is important for changing the width of the protective film (_fiv_) to be as easy as possible, because their optimal dimensions are the subject of this research. The coordinate systems (CSs) used are shown in Figure 9, which were as follows:  
* Coordinate systems CS1, CS2, CS3, and CS4 were used to distance the edge of the foil correctly from the pole legs. * Coordinate systems CSG1 and CSG2 are of particular importance. They are placed at the end point of the grounding, and their \(y\) component points in the direction of  
Figure 7: Basic characteristics of the FEM model. the grounding. They were used to distance the foil properly from the ground. The presented position proved to be the best for proper modeling of the size of the foil. * The CS\({}_{\text{C}}\) coordinate system was used to post-process the results.