## 2 Characteristics of Surface Potential Distribution for DC Grounding Electrode
### Distribution of Current in the Feeder Rods of a DC Grounding Electrode  
Referring to Figure 1, an electromagnetic simulation model of the DC grounding electrode was established using the standard grounding electrode software CDEGS 15.4. The relevant parameters for the grounding electrode simulation are set as shown in the table below:  
According to the parameter settings in Table 1, the straight part of the single-ring DC grounding electrode is 250 m long, and the ring area is composed of two semicircles with a radius of 60 m. Each feeder rod is a cylindrical iron rod with a length of 1.5 m and a diameter of 50 mm. The interval between adjacent feeder rods is 0.5 m, and the buried depth of the grounding electrode is 4 m. Each feeder rod is numbered, and there are a total of 434 feed rods. The numbered results are shown in Figure 2. The red dots in the figure are filter wells, which are marked to facilitate subsequent segmentation processes. In reality, on the polar ring of the grounding electrode, a filter well is set up at an interval of 50 m, which is used to introduce surface water into the electrode, keep the electrode moist, and remove the gas generated by the operation of the grounding electrode. The filter well is generally arranged directly above the electrode, so the laying direction of the underground DC grounding electrode can be roughly estimated according to the location of the filter well. In the CDEGS software, the bus injection current is set to 1500 A. The total number of DC grounding electrode feeder rods is N, and N = 434 in this model. Observe the current distribution of each feeder rod and draw the current distribution diagram of the feeder rod. \begin{table}
\begin{tabular}{c c} \hline \hline
**Name** & **Parameter Information** \\ \hline Soil & Resistivity: 30 \(\Omega\cdot\)m \\  & uniform soil \\  & Resistivity: 0.3 \(\Omega\cdot\)m \\  & Width \(\times\) Height: 0.8 \(\times\) 0.8 m \\  & Resistivity: 1.68 \(\times\) 10\({}^{-6}\)\(\Omega\cdot\)m \\ Feeder rod & Length: 1.5 m; Diameter: 50 mm \\  & Injected current & 1500 A \\  & Feeder rod interval & 0.5 m \\  & Buried depth of feed element & 4 m \\  & Single-ring elliptical structure \\  & & Length of the straight section: 250 m \\  & Radius of the ring: 60 m \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters for DC grounding electrode [19; 20; 21]. Figure 1: DC grounding electrode schematic diagram. The distribution of the distribution current (\(I_{in}\)) of each feeder rod in the DC grounding electrode is drawn, as shown in Figure 3. The distribution current of all feeder rods in the DC grounding electrode ranges from 3.25 A to 3.90 A. The minimum distribution current mainly appears in the middle of the straight-line area, and the maximum distribution current is mainly concentrated in the area with the largest curvature of the ring. The average value of the overall distribution current is 3.4567 A. In summary, for the DC grounding electrode under normal conditions, it can be approximated that the current distribution of all feeder rods is evenly distributed. When the DC grounding electrode is partially broken, the current distribution of the remaining part of the feeder rod is analyzed. According to Figure 2, the polar ring of the grounding electrode is mainly divided into a straight-line area and a ring area, so we need to consider the situation that the two areas break respectively and then analyze the current distribution of the DC grounding electrode when one is broken in the straight-line area and the ring area respectively and when multiple are broken. (1) Two groups of cases are set under break 1. The first group is the breakage of the feeder rod numbered 257 in the straight-line area. The second group is the breakage of the feeder rod numbered 389 in the ring area. (2) Two cases are set under the three broken rods. The first group is the breakage of three feeder rods numbered 277-279 in the straight-line area. The second group is the breakage of three feeder rods numbered 387-389 in the ring area.