## 2 Characteristics of Surface Potential Distribution for DC Grounding Electrode
### Characteristics of Surface Potential Distribution for DC Grounding Electrodes
#### 2.3.2 Breakage in the Ring Region  
The ring area is the same as the straight-line part, and a filter well is set up at an interval of 50 m. In the ring area on one side, five filter wells numbered 6-10 divide the ring part into four sections. The corresponding arc length and center angle of each section are the same, and the number of buried grounding electrodes is basically the same. It can be seen that one side of the ring is composed of four units. Similarly, the two sides of the ring are composed of eight units. Therefore, we only need to make a specific analysis of one of the units. The feeder rod buried between filter wells 6 and 7 is taken as the unit. In the unit, different numbers of continuous broken feeder rods are set up to observe the surface potential distribution characteristics under normal conditions and after a certain number of fractures. The results are shown in Figure 10. The range of surface potential change affected by the breaking of the local area of the grounding electrode is calculated, and the results are shown in Figure 11.  
According to the results in Figure 11, it can be seen that the range of surface potential change affected by the breaking of the feeder rod is approximately circular, and the farther the distance, the smaller the change: when one feeder rod is broken, the surface potential change in the radius of 6 m is greater than 1 V; when there are three feeder rods broken, the surface potential change in the radius of about 14 m is greater than 1 V; the more the number of continuous faults, the wider the area of surface potential change. Based on the results presented in Figure 8, with the objective of detecting the breakage of one feeder rod, it is noted that the breakage of a single feeder rod induces a surface potential change greater than 1 V within a radius of approximately 12 m. Therefore, a measurement interval of 10 m is set in the straight-line region. In Figure 7, the installation orientation of the grounding electrode can be determined using the filter wells numbered 1 to 6, with a spacing of 50 m between adjacent wells. The measurement plan is as follows: (1) First \begin{table}
\begin{tabular}{c c} \hline \hline
**Range of Potential Variation** & \(\mathbf{\Delta U\geq 1\ V}\) \\ \hline one feeder rod broken & 12 m \\ three feeder rods broken & 28 m \\ five feeder rods broken & 39 m \\ ten feeder rods broken & 50 m \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The range of surface potential changes influenced after breakage in the straight region. Figure 10: Surface potential distribution after breakage between filter wells 6 and 7 in the ring region. (**a**) Under normal operating conditions; (**b**) One feeder rod broken; (**c**) Three feeder rods broken; (**d**) Five feeder rods broken; (**e**) Ten feeder rods broken. of all, measurement points are arranged at each of the infiltration wells numbered 1 to 6; (2) Subsequently, 4 measurement points are evenly distributed between each pair of adjacent infiltration wells, totaling 20 additional measurement locations. Thus, 26 measurement points are required along one side of the straight-line region of the DC grounding electrode, and a total of 52 measurement points on both sides, to complete the inspection of the operational status of the DC grounding electrode in the straight-line region. In the ring area of the grounding electrode, because the direction of the grounding electrode is not known, the measurement points cannot be arranged along the laying route of the grounding electrode. According to the influence of the ground electrode broken in the ring area on the surface potential, the measurement points are finally arranged on the line AB between the filter wells. According to Figure 11a, the maximum distance between connection AB and the grounding electrode is 4.6 m, and the radius of action that affects the potential change is about 6 m when one of the feeder rods is broken, which can detect whether the grounding electrode is broken on the connection AB.