# Detecting Grounding Grid Orientation: Transient Electromagnetic Approach
## 2 Related Work  
There has been growing interest in fault diagnosis as excavation is resource intensive both in terms of time and effort. Recent studies on fault diagnosis of the grounding grid can be categorized into electric network methods [11; 12; 13; 14], electromagnetic methods [15; 16; 17; 18], electrochemical detection methods [19], and transient electromagnetic methods [16; 20]. Electrical network methods are based on the surface potential difference and port resistance. These methods have low accuracy as the surface potential difference and port resistance are very small even if the grid is broken. Electromagnetic methods are based on processing the surface magnetic intensity once the current is injected in the grid. The accuracy of these methods depends on soil resistivity. Once the soil condition is changed, re-measurements are required. Grounding grid corrosion level is easily detected by the electrochemical method by measuring the electrochemical properties between grounding conductors and soil. However, this method fails to diagnose breakpoints in the grounding grid. In the transient electromagnetic method, equivalent resistivity is calculated by performing fast inversion calculations on the secondary magnetic field. Faults in the grounding grid are diagnosed from the distribution of equivalent resistivity. Figure 1: Grounding grid and its characteristics. The configuration or topology plays a vital role in the performance of the grounding grid. It is also an essential requirement for fault diagnosis. Although the drawing layout of the grounding grid shows its complete configuration, it is prone to human error, leading to spoilage or loss. Research on the configuration detection of the grounding grid is limited. The derivative method was used by [21; 22] to measure the grounding grid configuration. The drawback associated with the derivative method is the occurrence of false peaks due to the surrounding electromagnetic environment. The transient electromagnetic method (TEM) was used by [23] to determine the grounding grid configuration. Measuring points with high equivalent resistivity and low magnetic intensity showed the presence of the grounding conductor. Furthermore, the wavelet edge based detection technique was utilized by [24] to image the configuration of the grounding grid. Currently employed methods of configuration detection have assumed grounding grid orientation parallel to the substation boundary. This makes the grounding grid orientation parallel in the plane of the Earth. Practically, the orientation of unknown grounding grids is not known. In such a scenario, existing configuration detection methods fail to deliver accurate results [10]. Although [25] utilized magnetic detection electrical impedance tomography (MDEIT) to measure grounding grid configuration irrespective of its orientation, this method requires numerous measurements. Figure 2 illustrates the parallel and non-parallel orientation of the grounding grid with respect to the substation boundary. The literature on grounding grid orientation detection is extremely limited. Existing methods regarding orientation detection only include the derivative method [10; 26]. This method is based on the derivative of the surface magnetic flux density and the concept of locating the geometrical object in the polar plane. The derivative method [10; 26] performs well only when the substation electromagnetic environment (EME) is ignored, otherwise the method collapses. The effect of EME on the derivative method is illustrated in Figure 3. This figure is comprised of the following: Figure 3a is the original signal (magnetic flux density \(\vec{B}_{z}\)) from the grid [26]; Figure 3b is the surrounding EME signal; Figure 3c is the magnetic flux density \(\vec{M}_{z}\) when \(\vec{B}_{z}\) and EME signals are combined; and Figure 3d is the derivative of \(\vec{M}_{z}\). False peaks along true peaks are originated, distorting the result completely. The incorrect resulting consequences come from the EME enhancement due to the derivative.