﻿ 直流接地极土壤电阻率建模方法研究

# 直流接地极土壤电阻率建模方法研究Research on Soil Resistivity Modeling Method of DC Grounding Electrode

Abstract: The DC ground electrode is an important part of the DC transmission project. The distribution of the soil resistivity around it directly affects the parameter design and operation and maintenance of the ground electrode. In order to ensure the normal operation of the ground electrode and avoid af-fecting the personal safety and equipment performance near the ground electrode, it is necessary to test and model the soil resistivity around the ground electrode. In this paper, the four-pole method and the magnetotelluric method are used to test the soil resistivity around the ground electrode. The results obtained by these two test methods are compared, and the respective advantages and disadvantages of these two methods in soil resistivity testing are comprehensively analyzed. The soil resistivity is modeled by the inversion software independently developed by our team. Finally, the grounding resistance value calculated according to the soil model is in good agreement with the reference value, which verifies the reliability and accuracy of the method.

1. 引言

2. 四极电法和大地电磁法的测试原理

2.1. 四极电法

Figure 1. Schematic diagram of soil resistivity measurement

${V}_{A}=\frac{I\rho }{2\pi x}$ (1)

${V}_{B}=-\frac{I\rho }{2\pi x}$ (2)

${V}_{B}=\frac{I\rho }{2\pi }\left(\frac{1}{{a}_{1}}-\frac{1}{{a}_{2}}\right)$ (3)

${V}_{D}=\frac{I\rho }{2\pi }\left(\frac{1}{{a}_{2}}-\frac{1}{{a}_{4}}\right)$ (4)

${U}_{CD}=\frac{I\rho }{2\pi }\left(\frac{1}{{a}_{1}}-\frac{1}{{a}_{2}}-\frac{1}{{a}_{3}}+\frac{1}{{a}_{4}}\right)$ (5)

$\rho =\frac{2\pi R}{\frac{1}{{a}_{1}}-\frac{1}{{a}_{2}}-\frac{1}{{a}_{3}}+\frac{1}{{a}_{4}}}$ (6)

$R=\frac{{U}_{CD}}{I}$ (7)

2.2. 大地电磁法

$p=\frac{1}{2\pi }\sqrt{\frac{10\rho }{f}}\approx 503\sqrt{\frac{\rho }{f}}$ (8)

3. 土壤电阻率现场测试

3.1. 现场选址

Figure 2. Longqing ground electrode and Linqing ground electrode share the Qingtai pole site

Figure 3. L1, L2 measuring line position

Figure 4. L3 survey line, MT survey point location

Figure 5. V5-2000 system magnetic sensors and electrodes

3.2. 测试结果及反演

3.2.1. 四级法土壤电阻率测试结果与反演

Table 1. Measurement results of L1 and L2

Table 2. L3 measurement results

Figure 6. The main interface of the soil inversion software

Figure 7. Inversion results of L1 survey line

Table 3. Inversion of soil layering model by L1 survey line

Table 4. L2 line inversion soil layering model

Table 5. L3 line inversion soil layering model

3.2.2. 大地电磁法MT土壤电阻率测试结果

Table 6. MT inversion soil layering model

4. 土壤电阻率综合分析与验证

4.1. 土壤电阻率测试方法的分析比较

Table 7. Recommended soil resistivity

4.2. 土壤电阻率测试结果的验证

Figure 8. Simulation model of DC ground electrode

Figure 9. Electric potential distribution on the surface of the ground conductor

4.3. 小结

5. 结论

1) 由于龙泉、团林共用青台接地极址位于耕地区域，接地极附近土壤的电阻率普遍较低。大部分区域的土壤电阻率低于30 Ω∙m，电阻率最高区域的土壤电阻率为66.9 Ω∙m；

2) 在120 m范围内，四极法测量土壤电阻率的精度较高；在120 m以下时，土壤电阻率突然增大，反演结果均方根误差过大。表明四极法对浅层土壤电阻率测试的精度较高，随着测试深度的增加，大地电磁法的优势越来越明显；

3) 利用反演得到的土壤模型，仿真计算得到接地极的接地电阻值为0.21 Ω，与该接地极前期测试得到的接地电阻值为0.028~0.029 Ω吻合较好，进一步验证了本文提出的土壤电阻率建模方法的有效性和可靠性。

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