Accurate Measurement of Tower Grounding Resistance for Single-Tower and Multi-Tower Parallel Scenarios Based on the Clamp Meter Method: For the Sustainable Operation of Towers

Abstract

Transmission tower grounding safety is a critical element that significantly impacts the reliability and sustainability of power grids. Tower grounding resistance is a significant grounding characteristic parameter. In order to accurately measure the grounding resistance of towers using the clamp meter method in both single-tower and multi-tower parallel scenarios, this paper establishes theoretical calculation models for measuring tower grounding resistance using the clamp meter method. Considering the interaction between the artificial grounding device and the tower foundation, this paper models and simulates transmission towers and lightning shield wires, analyzing the influencing factors on the grounding resistance measurement results using the clamp meter method in both single- and multi-tower parallel scenarios. The results show that for single towers, the clamp meter measurement results increase with decreasing foundation root spacing and increasing length of the artificial device’s extension lines, but the changes are relatively small. In multi-tower grounding scenarios, due to the shunting effect of the parallel branches formed by the towers and lightning shield wires, the value is smaller than in single-tower grounding scenarios. Changing the number of parallel towers and the type of lightning shield wire produces little effect on the measurement results. However, changes in soil resistivity have the most significant impact. Therefore, correction formulas for the impact of soil resistivity on clamp meter measurements are proposed and then verified by applying them to field tests.

1. Introduction

When verifying the grounding performance of towers for their sustainable operation, precise measurement of their grounding resistance is essential to determine compliance with standards [1,2,3]. Lower tower grounding resistance plays a significant role in maintaining a reliable power supply [4]. If the grounding resistance does not meet the requirements, a ground short-circuit fault in the transmission line can generate a high fault potential, causing significant safety risks to nearby personnel and equipment. Traditionally, the grounding resistance of towers is measured by using the three-electrode method, which requires setting up a test electrode of at least tens of meters, making it time-consuming and labor-intensive [5]. Moreover, if the tower is located in mountainous areas, the conventional three-electrode testing method becomes difficult to implement [6]. The potential drop method for measuring grounding resistance requires repeated measurements, involves a large workload, and makes it challenging to plot the potential drop curve [7]. The high-frequency parallel method does not comprehensively consider the influence of field soil properties and measurement current frequency on the inductive effect of the grounding electrode, making it less adaptable to field conditions [8]. In contrast, the clamp meter method does not require auxiliary electrodes. It is only necessary to disconnect the grounding downlead of the measuring tower, leaving one downlead, and use a clamp meter around this grounding downlead to take readings, which significantly reduces the workload for measurement personnel [9].

As for the grounding device of towers, the literature [10] has conducted simulation modeling and analysis of typical tower foundation grounding in layered soil. The literature [11] has equivalently modeled the tower foundation as a cylinder and proposed a method for calculating the grounding impedance of the tower foundation. But in practice, the tower grounding consists of both an artificial and a tower foundation grounding device; their mutual influence should be considered. Another study simplified the calculation of tower grounding resistance by considering self-resistance and mutual resistance coefficients [12]. However, the clamp meter method gains the overall resistance within the entire current flow loop [13]. For a single tower without a connected lightning shield wire, the artificial and tower foundation grounding device form a series loop through the grounding downlead, the main material of the tower foot, and the soil [14]. For multi-tower scenarios, previous studies usually consider the current flow loop formed by the measuring tower and adjacent towers connected through lightning shield wires. The measurement reflects the equivalent impedance of the tower body, the lightning shield wire, and the adjacent towers on both sides [15]. The literature [16] has analyzed the impact of various factors on the grounding resistance testing of single-tower and multi-tower scenarios. However, the analysis is not comprehensive enough, as it does not consider the influence of different foundation grounding and artificial grounding device sizes on mutual inductance and the final test results. Additionally, for factors with a significant impact, no correction formulas for the measurement results have been provided and used in field tests.

Therefore, in order to measure tower grounding resistance more accurately using a clamp meter, theoretical deductions are conducted and theoretical formulas of the errors are derived considering both single- and multi-tower scenarios in Section 2. However, the values of self-resistance and mutual resistance in these formulas are unknown in practice, making it impossible to calculate the correction formulas theoretically. Thus, simulations of the clamp meter test results under different influencing factors are further performed. Correction formulas for the factors with a significant impact are fitted in Section 3 and Section 4. Finally, a case study is conducted in Section 5 to verify the feasibility of the proposed correction method.

2. Principle of Clamp Meter Measurement

The clamp meter method generates a test current in the grounding loop through the principle of electromagnetic induction. The power coil A induces an electromotive force E in the loop under test, generating a current I, which is measured by the measuring coil B. For the loop resistance Z, we have Z = E/I.

2.1. Theoretical Calculation Principle

The artificial grounding device, commonly referred to as the grounding electrode of towers, consists of metal components such as buried round steel and angle steel, which are connected to the tower through the grounding downlead. The tower foundation grounding device includes elements like a rebar embedded in reinforced concrete. From the perspective of the lightning current discharge, the two devices are connected in parallel. Due to the interaction between these two parts, the following equation is established:

$$\left\{\begin{array}{c}{V}_1=R_{11}{I}_1+R_{12}{I}_2\\ V_2=R_{21}{I}_1+R_{22}{I}_2\end{array}\right.$$

(1)

where V₁ is the potential of the artificial grounding device; V₂ is the potential of the tower foundation grounding device; I₁ and I₂ are the currents dissipated by the artificial and tower foundation grounding device, respectively; R₁₁ and R₂₂ are their self-resistances; R₁₂ and R₂₁ are the mutual resistances between them.

This paper studies TS-type grounding network towers, which consist of a closed rectangular frame with four radial lines. The theoretical current shunting scenario is shown in Figure 1.

From the equivalent circuit shown in Figure 1, it can be seen that, under normal conditions, when current flows through the tower body into the grounding devices, the artificial grounding device and the tower foundation grounding device are in parallel. Because the voltage drop across the bonding conductor is negligible, their potentials are equal. Therefore:

$$\left\{\begin{array}{c}{V}_1=V_2\\ I_{\mathrm{total}}=I_1+I_2\\ R_{12}=R_{21}\end{array}\right.$$

(2)

where the total current flowing into the ground is I_total.

By combining Equations (1) and (2), the theoretical calculation value of the grounding resistance of the transmission tower can be obtained as follows [16]:

$$R_{\mathrm{t}}={\displaystyle \frac{V_1}{I_{\mathrm{total}}}}={\displaystyle \frac{R_{11}{R}_{22}-R_{12}^2}{R_{11}+R_{22}-2R_{12}}}$$

(3)

where R_t is the theoretical calculation value of the grounding resistance of the transmission tower.

2.2. Theoretical Formula of Clamp Meter Measurement Considering a Single Tower

If the test transmission tower does not need to be connected to the lightning shield wire, or if it is constructed and awaiting operation but not yet connected, the test current in the clamp meter method flows through the loop of the artificial and the tower foundation grounding device. The schematic diagram for measuring the grounding resistance of the tower is shown in Figure 2.

From the figure, the artificial and tower foundation grounding device are in series. The following equations can be derived:

$$\left\{\begin{array}{c}{V}_1=V_2+E\\ I_1=-I_2\\ R_{12}=R_{21}\end{array}\right.$$

(4)

where E is the force generated by the clamp meter on the grounding down lead.

By combining Equations (1) and (4), the measured grounding resistance considering only one tower can be obtained as follows [16]:

$$R_{\mathrm{c}}={\displaystyle \frac{E}{I_1}}=R_{11}+R_{22}-2R_{12}$$

(5)

where R_c is the measured grounding resistance considering a single tower.

The transformation ratio between the clamp meter measurement value and the theoretical calculation value can be obtained as follows:

$${\eta }_{\mathrm{s}}={\displaystyle \frac{R_{\mathrm{c}}}{R_{\mathrm{t}}}}={\displaystyle \frac{(R_{11}+R_{22}-2R_{12}{)}^2+R_{12}^2-R_{11}{R}_{22}}{R_{11}{R}_{22}-R_{12}^2}}+1$$

(6)

where ${\eta }_{\mathrm{s}}$ is the transformation ratio in a single-tower grounding scenario.

2.3. Theoretical Formula of Clamp Meter Measurement Considering Multiple Towers

If the tested tower is connected to adjacent towers through the lightning shield wire, one part of the current flows through the loop of the artificial and tower foundation grounding device. Another part flows from the base of the tested tower to the top, then through the lightning shield wire to other towers. For a situation where the current disperses through multiple towers into the ground, the following equations can be derived:

$$\left\{\begin{array}{c}{V}_1=R_{11}{I}_1+R_{21}{I}_2+R_{31}{I}_3+\cdots +R_{n1}{I}_n\\ V_2=R_{12}{I}_1+R_{22}{I}_2+R_{32}{I}_3+\cdots +R_{n2}{I}_n\end{array}\right.$$

(7)

where R₃₁, …, R_n1 represent the mutual resistances between the artificial grounding device of the tested tower and the grounding device of the other towers; R₂₃, …, R_2n represent the mutual resistances between the foundation grounding device of the tested tower and the grounding device of the other towers.

The mutual resistances of the grounding device between the other towers and the tested tower are very small, and can be neglected. Therefore:

$$\left\{\begin{array}{c}{V}_1=R_{11}{I}_1+R_{21}{I}_2\\ V_2=R_{12}{I}_1+R_{22}{I}_2\end{array}\right.$$

(8)

The schematic diagram of the grounding resistance test considering multiple towers is shown in Figure 3.

From the figure, the following equations can be derived:

$$\left\{\begin{array}{l}\begin{array}{c}{V}_1=V_2+E\\ I_1+I_2+I_{\mathrm{s}}=0\\ R_{12}=R_{21}\end{array}\\ \left|I_1\right|=\left|I_2\right|+\left|I_{\mathrm{s}}\right|\end{array}\right.$$

(9)

where I_s represents the current shunted away from the tested tower.

The actual measured grounding resistance is the loop resistance, which can be obtained as follows:

$$R_{\mathrm{c}}={\displaystyle \frac{E}{I_1}}=R_{11}+R_{22}-2R_{12}+{\displaystyle \frac{(R_{22}-R_{21})I_{\mathrm{s}}}{I_1}}$$

(10)

The transformation ratio between the clamp meter measurement value and the theoretical calculation value can be obtained as follows:

$${\eta }_{\mathrm{m}}={\displaystyle \frac{R_{\mathrm{c}}}{R_{\mathrm{t}}}}={\displaystyle \frac{(R_{11}+R_{22}-2R_{12}{)}^2+R_{12}^2-R_{11}{R}_{22}+(I_{\mathrm{s}}/I_1)(R_{22}-R_{21})(R_{11}+R_{22}-2R_{12})}{R_{11}{R}_{22}-R_{12}^2}}+1$$

(11)

where ${\eta }_{\mathrm{m}}$ is the transformation ratio in a multi-tower grounding scenario.

When I_s is 0, the above equation represents the transformation ratio expression for a single tower. Due to the presence of other towers, I_s is not 0, and according to Equation (9), when I₁ is positive, I_s is negative. Therefore, under the same conditions, the transformation ratio for a multi-tower grounding is lower than that for a single tower.

3. Simulation Calculation for Clamp Meter Measurement in Single-Tower Grounding Scenario

3.1. Model Development

It is necessary to perform detailed modeling of the two grounding components of towers. CDEGS 15.4 is used for modeling. The upright tower foundation is a common type and is used in this study. The reinforcement consists of 24φ16 main rebars, each 3.8 m long, and 16φ8 stirrup rebars, each 2.8 m long. The slab part consists of 48 φ48 bottom slab rebars, each 3.9 m long. The tower foundation is 0.9 m high exposed above ground and is located within a concrete block with a resistivity of 2000 Ω·m. The artificial grounding device is modeled as a closed square frame with rays, made of φ12 round steel. The grounding down lead is equivalent to a cylindrical conductor with a radius of 5.5 mm. The main material of the tower foot is equivalent to a cylindrical conductor with a radius of 16.5 mm.

A short section of the conductor is connected to the grounding down lead, and a current excitation is applied. By directly calculating it with software, the theoretical values of the tower grounding resistance can be obtained. According to the above principle of the clamp meter method, when the grounding downlead is disconnected until only one remains, the artificial and tower foundation grounding device are in a single loop. A voltage excitation is applied to a certain segment of the conductor in the middle of the grounding down lead, and the current through the same conductor is measured. The clamp meter resistance measurement value is then obtained. The constructed model is shown in Figure 4.

3.2. Results Analysis

Based on the theoretical formulas in Section 2, the error in the clamp meter method primarily originates from the artificial and foundation grounding devices when measuring a single tower. In practice, this is mainly influenced by the soil resistivity and the size relationship between the artificial and foundation grounding devices. The following sections provide a detailed analysis of these factors.

3.2.1. Simulation Results under Different Soil Resistivities

To study the impact of soil resistivity on the measurement results, the foundation root spacing is set to 9 m, and the length of the device’s extension lines is set to 18 m. By varying the soil resistivity, the relationship between the theoretical value and the measured value is obtained, as shown in

Table 1. Theoretical value and measured value under different soil resistivities.

Soil Resistivity (Ω·m)	Theoretical Value (Ω)	Measured Value (Ω)	Transformation Ratio ηs
10	0.214	3.11	14.54
50	0.868	5.923	6.824
100	1.686	7.945	4.713
300	4.927	10.784	2.189
500	8.137	13.136	1.614
700	11.300	14.670	1.298
900	14.709	16.681	1.134
1100	16.659	17.364	1.042
1300	18.643	19.011	1.020
1500	20.830	20.737	0.996
2000	26.045	24.188	0.929
3000	35.514	31.139	0.877
4000	44.320	37.581	0.848
5000	53.073	43.679	0.823

.

In subsequent studies examining the impact of the size relationship between the artificial and foundation grounding devices, the soil resistivity is set to 500 Ω·m. Therefore, the transformation ratio 1.61 corresponding to a soil resistivity of 500 Ω·m is used as the baseline value. By calculating the relative transformation ratio under different soil resistivities, the influence of this single factor can be highlighted. The relative transformation ratio between the theoretical value and the measured value is illustrated in Figure 5.

From Figure 5, it can be seen that as the soil resistivity increases, the rate of increase in the clamp meter measurement value is less than the rate of increase in the theoretical calculation value, because the rate of increase in R₁₁ and R₂₂ is higher than the rate of increase in R₁₂ and R₂₁. It causes a rapid decrease in the ratio. However, the decreasing trend gradually slows down. By fitting the above data, the fitted formula is:

$${\eta }_{\mathrm{s},\mathrm{r}}={\displaystyle \frac{12.61+0.02\gamma }{1+ 0.04\gamma }}$$

(12)

where $\gamma$ is the soil resistivity and ${\eta }_{\mathrm{s},\mathrm{r}}$ is the relative transformation ratio when the soil resistivity changes in the case of a single tower.

3.2.2. Simulation Results under Different Artificial and Foundation Grounding Device Sizes

To study the impact of the foundation root spacing on measurement results, the soil resistivity is set to 500 Ω·m, the length of the device’s extension lines is set to 18 m, and the variation range of the foundation root spacing is from 5 m to 13 m. The ratio of the diagonal length of the foundation grounding electrode to the diagonal length of the artificial grounding device is defined as the length ratio β. The impact of the length ratio on the transformation ratio between the theoretical value and the measured value is illustrated in Figure 6.

From Figure 6, it can be seen that the transformation ratio coefficient is negatively correlated with the foundation root spacing. This is because, with the increase in the foundation root spacing, the dispersal area of the foundation expands, leading to a decrease in its self-resistance R₂₂. In the case where the size of the artificial device remains unchanged, an increase in the size of the concrete causes an increase in the mutual resistance R₁₂. The reduction in the first term of the numerator in the error increment (R₁₁ + R₂₂ − 2R₁₂)² is more significant than the reduction in the third term R₁₁R₂₂, resulting in a gradual decrease in the transformation ratio coefficient.

To study the impact of the artificial device’s extension line length on measurement results, the soil resistivity is set to 500 Ω·m, the foundation root spacing is set to 9 m, and the variation range of the extension line length is from 0 m to 50 m. The impact of the artificial device’s extension line length on measurement results is shown in Figure 7.

From Figure 7, it can be seen that the transformation ratio coefficient is negatively correlated with the length of the artificial device’s extension lines.

Due to the foundation root spacing being set to 9 m, and the length of the device’s extension lines being set to 18 m in the study of the impact of soil resistivity, this length ratio is defined as the baseline value, which allows for consideration of a single influencing factor. The results of combining the two-length ratio changing scenarios are shown in Figure 8.

It can be observed that when the length ratio varies within the common range of 0.2 to 0.6, the difference in the relative transformation ratio is within 10%, indicating that the impact is not significant.

4. Simulation Calculation for Clamp Meter Measurement in Multi-Tower Grounding Scenario

4.1. Model Development

The measurement considering multiple towers primarily studies the shunting effect of adjacent towers. Compared to the single-tower measurement, additional parallel branches include the tower body of the tested tower, the lightning shield wire, other towers and their grounding device. Therefore, the model of towers and lines is established in ATP 6.0.

Since the clamp meter method involves high-frequency test currents, the transmission line adopts the Jmarti model [17], with the tower height setting at 27 m and the tower span at 200 m. The tower uses the multi-wave resistance model for simulation, dividing it into the main material, diagonal material, and cross-arm parts [18,19]. We apply excitation at different positions on the single tower. The self-resistance of the artificial and foundation grounding device, as well as the mutual resistance between them, can be computed. The model of the grounding resistance test considering multi-towers is established, as shown in Figure 9.

4.2. Results Analysis

Based on the derived formulas in Section 2, in the case of multiple towers, the measurement is also related to the current shunted away from the tested tower. Therefore, the factors influencing the measurement error include the paralleling tower number and the type of lightning shield wire.

4.2.1. Simulation Results under Different Paralleling Tower Numbers

The theoretical grounding resistance value is 8.932 Ω and the lightning shield wire model is JLB35-120. By varying the paralleling tower numbers in the simulation model, the results are shown in

Table 2. Calculation results under different numbers of parallel towers.

Theoretical Value of Grounding Resistance (Ω)	Number of Towers on One Side	Measured Value of Clamp Meter Method (Ω)	Transformation Ratio ηm
8.932	1	6.887	0.771
8.932	2	6.609	0.740
8.932	3	6.498	0.727
8.932	4	6.435	0.720
8.932	5	6.402	0.717

.

The above results show that the more parallel towers there are, the more parallel loops are formed, resulting in a smaller equivalent resistance and thus a smaller measurement value. However, when the paralleling tower number exceeds 3, the increase in the number of towers has a minimal impact on the transformation ratio.

4.2.2. Simulation Results under Different Types of Lightning Shield Wires

The theoretical grounding resistance value is 8.932 Ω and the number of parallel towers on one side is set to 4; different types of lightning shield wires are used. The results are listed in

Table 3. Simulation results with different lightning shield wires.

Theoretical Value of Grounding Resistance (Ω)	Type of Lightning Shield Wire	Measurement Value of Clamp Meter Method (Ω)	Transformation Ratio ηm
8.932	JLB35-120 Double Circuit Line	6.435	0.720
8.932	JLB35-120 Single Circuit Line	6.439	0.721
8.932	JLB20A-50 Double Circuit Line	6.464	0.724
8.932	JLB20A-50 Single Circuit Line	6.468	0.725

.

The simulation indicates that double lightning shield wires or lightning shield wires with a larger outer diameter reduce the total loop resistance, resulting in a smaller measurement value. However, the impact of the lightning shield wire form on the measurement value is relatively small.

4.2.3. Impact of Soil Resistivity on Multi-Tower Measurement Results

Given the significant impact of soil resistivity on the transformation ratio for single-tower grounding, it is also crucial to consider this factor when performing clamp meter measurements in multi-tower grounding scenarios. In the simulation, the tower span is set to 200 m, the tower height is set to 40 m, and the double circuit lightning shield wire has a DC resistance of 2.86 Ω/km. The foundation root spacing is set to 9 m, and the length of the device’s extension lines is set to 18 m. By calculating the resistance values for each tower and incorporating them into the multi-tower simulation model, the transformation ratio under different soil resistivities for multi-tower grounding can be obtained as shown in

Table 4. Transformation ratio under different soil resistivities for multi-tower grounding.

Soil Resistivity (Ω·m)	Self-Resistance of Artificial Grounding Device/Ω	Self-Resistance of Tower Foundation Grounding Device/Ω	Mutual Resistance /Ω	Theoretical Value of Grounding Resistance (Ω)	Measured Current/A	Measured Value of Clamp Meter Method (Ω)	Transformation Ratio ηm
10	0.214	0.216	3.029	0.139	3.802	2.630	12.291
50	0.875	6.119	0.676	0.868	2.697	3.708	4.272
100	1.704	8.533	1.335	1.686	2.375	4.211	2.497
300	5.014	13.394	4.069	4.927	1.813	5.516	1.119
500	8.318	17.819	6.813	8.137	1.410	7.092	0.872
700	11.618	21.374	9.510	11.300	1.172	8.532	0.755
900	14.913	27.199	13.113	14.709	0.987	10.132	0.689
1100	16.982	28.898	14.671	16.659	0.953	10.493	0.630
1300	18.872	32.905	16.836	18.643	0.858	11.655	0.625
1500	21.162	35.790	18.601	20.830	0.775	12.903	0.619
2000	26.340	44.162	23.733	26.045	0.686	14.577	0.560
3000	35.891	58.860	32.547	35.514	0.526	19.011	0.535
4000	44.660	73.475	41.172	44.320	0.439	22.779	0.514
5000	53.379	87.842	49.811	53.073	0.378	26.455	0.498

.

When considering multiple towers, the transformation ratio still decreases with an increase in soil resistivity. However, comparing the results in Table 1, it can be seen that due to the shunting effect of the towers and the lightning shield wire, the clamp meter measurement results and the transformation ratio are smaller under the same resistivity. Similarly, the transformation ratio 0.87 corresponding to a soil resistivity of 500 Ω·m is used as the baseline value to highlight the influence of this single factor. The relative transformation ratio between the theoretical value and the measured value is illustrated in Figure 10.

By fitting the above data, the fitted formula under different soil resistivities for multi-tower grounding is:

$${\eta }_{\mathrm{m},\mathrm{r}}={\displaystyle \frac{29.29+0.06\gamma }{1+ 0.11\gamma }}$$

(13)

where $\gamma$ is the soil resistivity and ${\eta }_{\mathrm{m},\mathrm{r}}$ is the relative transformation ratio when the soil resistivity changes for multi-tower grounding.

5. Field Testing

Grounding resistance testing in multi-tower parallel scenarios was conducted on some typical 220 kV towers in Hubei province. The artificial grounding devices of these towers all used a square frame with rays, with a side length of 15 m and ray length of 18 m, made of φ12 round steel. Soil resistivity was measured using the four-electrode method [20], with measurements taken along the terrain surrounding the tower. Then, inversion of the soil structure was performed [21]. Since the soil resistivity obtained from field tests is stratified, the equivalent single layer soil resistivity is calculated to ensure that the tower grounding resistance is the same. The results of the soil resistivity tests are shown in

Table 5. Soil model in the area near the test tower.

Tower Number	First Layer Thickness (m)	First Layer Resistivity (Ω·m)	Second Layer Thickness (m)	Second Layer Thickness (m)	Equivalent Resistivity (Ω·m)
G4	6.79	23.66	∞	15.86	21.3
T18	9.95	18.47	∞	5839.40	76.2
T26	2.49	10.93	∞	14.80	12.4

.

Grounding resistance was measured using the clamp meter method, as shown in Figure 11.

The measured values are obtained and corrected by applying the correction formula for the influence of soil resistivity in multi-tower scenarios. The results are compared with the theoretical values, which are shown in

Table 6. Results of tower grounding resistance field measurements.

Tower Number	Soil Resistivity (Ω·m)	Measured Value (Ω)	Corrected Measured Value (Ω)	Theoretical Value of Grounding Resistance (Ω)	Error
G4	21.3	4.12	0.52	0.49	6.1%
T18	76.2	5.52	1.79	1.65	8.5%
T27	12.4	3.77	0.34	0.29	17.2%

:

It can be observed that the clamp meter measured values of grounding resistance for most towers are significantly higher than the theoretical calculated values as the soil resistivity is low, which aligns with the simulation analysis. After applying the correction using the above fitted formula, the deviation in grounding resistance is within 20%, thus verifying the feasibility of the corrected formula.

6. Conclusions

This paper establishes theoretical calculation models for measuring tower grounding resistance using the clamp meter method considering both single and multiple towers. The effects of various factors on the measurement results are analyzed through simulation. Then, correction formulas for the factors with a significant impact are proposed and validated through a field test. Through this study, tower grounding resistance is precisely measured using the clamp meter method to ensure the sustainable operation of the towers. The main conclusions are as follows:

Based on the calculation formula of difference between the clamp meter measurement and theoretical values for single- and multi-tower scenarios, it is found that due to the shunting effect in multi-tower grounding, the clamp meter measurement results are smaller than in single-tower grounding.

For single-tower grounding, soil resistivity has a greater impact on the results of the transformation ratio between the clamp meter measurement value and the theoretical value. Therefore, a fitting formula is developed, which can be used in field testing.

In multi-tower grounding scenarios, the changes in measurement results under different numbers of towers and types of lightning shield wires are not significant. Similar to single-tower grounding, the soil resistivity has a greater impact on the results, and correction formulas for different resistivities were derived.

A field test for a multi-tower was conducted and the correction formula for different soil resistivities was applied. The results showed an error of within 20% compared to the theoretical simulations, which verified the feasibility of the proposed method.