# Detecting Grounding Grid Orientation: Transient Electromagnetic Approach
## 4 Performance Evaluation and Results' Analysis
### Grounding Grid with Unequal Mesh Spacing  
Demonstrating the feasibility of TEM for orientation detection of an unequally spaced grounding grid, Figure 11 is taken into account. In this figure, conductors are labeled \(C_{1}\) to \(C_{12}\) and nodes 1 to 9. The dimensions of meshes \(M_{1}\) and \(M_{2}\) were 2.5 m \(\times\) 2 m, and those of \(M_{3}\) and \(M_{4}\) were 1.5 m \(\times\) 2 m. Consider Node 5 as a pole and moving the transmitter coil along the circle from point \(P_{1}\) to \(P_{8}\).  
Figure 10: Average magnetic field intensity \(\overline{H_{z}}\) along \(P_{1}\) to \(P_{8}\) related to Figure 8. Here, diagonal conductor \(C_{13}\) is indicated by low \(\overline{H_{z}}\) at \(P_{6}\).  
Figure 9: Equivalent resistivity \(\rho_{r}\) of Figure 8. High \(\rho_{r}\) at \(P_{6}\) validates the presence of diagonal conductor \(C_{13}\). Unequal magnetic coupling due to an unequal mesh size results in low \(\rho_{r}\) at \(P_{5}\) and \(P_{7}\).  
In Figure 11, when the transmitter loop was at measuring point \(P_{1}\) with an angle of \(0^{\circ}\) and coordinates (4.5,3), currents \(I_{3}\) and \(I_{4}\) flowed in conductor \(C_{4}\) in the opposite direction and canceled each other out. Thus, the current was less and so was the recorded magnetic field at measuring point \(P_{1}\). At points \(P_{2}\) and \(P_{8}\) with angles \(45^{\circ}\) and \(315^{\circ}\), respectively, the downward electromagnetic signal coupled extensively with mesh \(M_{4}\) and \(M_{3}\), thus inducing large eddy currents in the meshes. The recorded magnetic field at measuring points \(P_{2}\) and \(P_{8}\) was almost equal and higher than at measuring point \(P_{1}\). Furthermore, when the transmitter loop was at measuring point \(P_{3}\) with an angle of \(90^{\circ}\), currents \(I_{3}\) and \(I_{2}\) flowed in conductor \(C_{10}\) with an unequal magnitude and did not cancel each other completely. This was because of unequal magnetic coupling in meshes \(M_{4}\) and \(M_{2}\). Thus, the recorded magnetic field at measuring point \(P_{3}\) was less than at point \(P_{2}\), but higher than at point \(P_{4}\). Similarly, the recorded magnetic field at measuring point \(P_{7}\) was less than at point \(P_{8}\), but higher than at point \(P_{6}\).  
Figure 12 and Table 1 illustrate that due to weak magnetic coupling, the recorded magnetic field at measuring points \(P_{4}\) and \(P_{6}\) was almost equal and smaller than at measuring points \(P_{2}\) and \(P_{8}\). Thus, the size of grounding grid meshes \(M_{1}\) and \(M_{2}\) was greater than the size of meshes \(M_{3}\) and \(M_{4}\).  
Figure 11: Grounding grid with an unequal mesh configuration. The dimensions of meshes \(M_{1}\) and \(M_{2}\) are 2.5 m \(\times\) 2 m and \(M_{3}\) and \(M_{4}\) are 1.5 m \(\times\) 2 m.  
Figure 12: Average magnetic field intensity \(\overline{H_{z}}\) along \(P_{1}\) to \(P_{8}\) related to Figure 11. The large size of meshes \(M_{1}\) and \(M_{2}\) results in weak magnetic coupling, and therefore, \(\overline{H_{z}}\) at \(P_{4}\) and \(P_{6}\) is less than \(\overline{H_{z}}\) at \(P_{2}\) and \(P_{8}\).  
Graphs of the equivalent resistivity \(\rho_{r}\) and average magnetic field intensity \(\overline{H_{z}}\) illustrated the presence of conductors \(C_{3}\) and \(C_{4}\) along the x-axis and conductors \(C_{9}\) and \(C_{10}\) along the y-axis. It was deduced that the grounding grid was oriented parallel to the plane of the Earth.