CN103293419A - A Method for Evaluating Impulse Characteristics of Grounding Devices - Google Patents

Abstract

The invention discloses an evaluation method of grounding device impact performance. The method includes the steps of firstly, determining physical parameters of a grounding device in actual operation; secondly, building an equivalent numerical model, and calculating capacitance, inductance and conductivity of an element; thirdly, using a PSCAD/EMTDC simulation platform to evaluate impact features of impact current testing models; fourthly, drawing a device impact grounding resistance variation curve graph under different lightening current amplitude, different soil resistance, different size and different burying depth; fifthly, comparing grounding resistance with the curve graph to judge whether the grounding resistance accords with the curve variation range or not. By the method, grounding device grounding resistance impact features of a 10kV distribution line can be evaluated accurately.

Description

A Method for Evaluating Impulse Characteristics of Grounding Devices

technical field

The invention relates to a technique for evaluating the grounding impact characteristics of a grounding device, in particular to a method for evaluating the grounding impact characteristics of a grounding device.

Background technique

In the power system, lightning strike is one of the main causes of flashover of transmission and distribution lines. In areas with a relatively high trip rate in my country, the number of trips caused by lightning strikes accounts for about 40%-70% of the total trip times of high-voltage lines. In order to prevent people from electric shock, ensure the normal operation of the power system, and prevent lightning strikes and static electricity, a certain grounding system is required. The operation experience and theoretical analysis at home and abroad show that effectively reducing the grounding resistance of towers is the most effective measure to improve the protection effect of direct lightning strikes on transmission lines.

The size of the grounding resistance is not only related to the geometric size and shape structure of the grounding electrode, but also related to the structure of the earth and the resistivity of the soil. When the lightning impulse current flows, it is also related to the amplitude and waveform of the impulse current flowing through the grounding electrode. But for the tower lightning protection grounding of 10kV distribution network, due to the large amplitude of lightning current and high equivalent frequency, the current density flowing through the grounding device will increase, and a series of complicated transition processes will be caused due to the current impact characteristics . Therefore, the lightning strike tower, lightning protection line or lightning strike line passes through the arrester, and the ground potential formed by the lightning current flowing through the grounding device to the ground is the impact grounding resistance rather than the power frequency grounding resistance.

Due to the complex structure of the 10kV distribution line grid structure, multiple points and wide areas, and low overall insulation level, the tower grounding device is usually installed and erected together with the arrester, so it is affected by the environment of the installation site, soil resistivity, corrosion of the device itself, and unreasonable embedding. Influenced, causing the grounding resistance of the tower to exceed the regulation standard. When lightning strikes a 10kV distribution line, the lightning current will generate a high voltage drop on the grounding device, which will increase the secondary failure rate of the arrester and greatly affect the normal operation of the 10kV distribution network. Improving the grounding device is the guarantee to protect the distribution lines and grid equipment, especially the arrester, from fault current and lightning current damage in the power system.

The present invention considers the magnitude of the lightning current after the lightning overvoltage of the 10kV distribution line passes through the arrester, and adopts the establishment of a π-type circuit model to calculate the electrical parameters of the grounding device components for the grounding device under different lightning impulse currents, and establishes PSCAD/EMTDC The equivalent model for simulating the soil spark effect, through the horizontal-vertical grounding device of the 10kV distribution line, when the lightning current flows, the relationship between the impact resistance and the soil resistivity, the amplitude of the lightning current and the buried depth of the grounding device, The impact characteristics of common 10kV distribution line grounding devices are obtained, which provides a basis for rationally optimizing the layout of grounding devices in actual engineering and reducing the lightning tripping rate of distribution lines.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, to provide a method for evaluating the resistance characteristics of a horizontal-vertical grounding device, aiming at the law of the impact characteristics of a horizontal-vertical grounding device in a 10kV distribution line, in order to correctly evaluate The influence of the horizontal-vertical grounding device in different meteorological conditions, geographical conditions, structure size and installation process on the impact characteristics of the grounding device in 10kV power distribution. The mathematical model is used for calculation and analysis, and this method is proposed by combining the lightning current, the change of soil resistivity, and the difference in the impact characteristics of the grounding device with the buried depth. The evaluation of the impulse characteristics of horizontal-vertical grounding devices in 10kV distribution lines is applicable to the reconstruction and construction of grounding devices for 10kV distribution lines and the lightning protection risk assessment of 10kV distribution lines.

The purpose of the present invention is achieved through the following technical solutions, a method for evaluating the impact characteristics of a grounding device, comprising the following steps:

1. For an existing horizontal-vertical grounding device in a 10kV distribution line, measure the horizontal body using galvanized flat steel (as shown in Figure 1 horizontal body 3), and the vertical body using galvanized angle steel (as shown in attached Figure 1 The length of each segment of the vertical body 4); and measure the buried depth of the horizontal body from the ground, and the soil resistivity in the area;

2. Calculate the numerical parameters of the horizontal body and vertical body of the grounding device, and build the equivalent calculation model of the grounding device according to the equivalent circuit model shown in Figure 2;

(1) Calculate the inductance L ₀ of each section length of the horizontal body and the vertical body, and the inductance per unit length of the grounding body of each section, the formula is as follows:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: μ ₀ is the magnetic permeability coefficient of vacuum, which can be taken as μ ₀ =4π×10 ^-7 in the practical range, r _ef is the radius of the grounding body, and l is the length of each grounding body;

(2) Calculate the inductance C ₀ of each segment length of the horizontal body and the vertical body, and the capacitance of each segment grounding body unit length to the infinite zero plane, the formula is as follows:

C ₀ =ερG ₀ (2)

In the formula, ε is the dielectric constant of the soil, which can be taken as ε=9×8.86× ^10-12 F/m in the practical range;

(3) Calculate the conductance G ₀ of each segment length of the horizontal body and the conductance G ₁ of each segment length of the vertical body, the formula is as follows:

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="no\; l"\; filenames="HDA00003279511800022.png"\; state="\{\{state\}\}">no</figure-callout></span><figure-callout\; id="2"\; label="no\; l"\; filenames="HDA00003279511800022.png"\; state="\{\{state\}\}">\; </figure-callout>}\frac{{\mathrm{<span\; class="notranslate">\; </span>}}^{}}{}\frac{{\mathrm{<span\; class="notranslate">l</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; hr</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.61</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.31</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula, ρ is the soil resistivity, h is the buried depth of the grounding body, and _ref is the equivalent radius.

3. Use the PSCAD/EMTDC simulation platform to test the impact characteristics of the impact current test model including:

(1) Draw the change curves of the impact grounding resistance of the device under different lightning current amplitudes of 30kA, 50kA, and 70kA;

(2) Draw the impact grounding resistance change curve of the device under different soil resistivities of 50Ω/m, 100Ω/m, and 150Ω/m;

(3) Draw the impact grounding resistance change curve of different grounding device sizes including the number of branches from 2 to 8;

(4) Draw the change curve of the impact grounding resistance of the device at different buried depths from 0.6m to 1.2m;

4. Measure the grounding resistance of the grounding device actually running in the 10kV distribution line; draw the measured grounding resistance as a change curve and compare it with attached drawings 3, 4, 5, and 6 to see if it conforms to the curve change Within the range and whether it conforms to the continuous change law of the curve.

Working principle of the present invention: the present invention at first according to the actual structural characteristics of the horizontal-vertical grounding device of 10kV distribution line, measures the horizontal body that adopts galvanized flat steel, and the vertical body that adopts galvanized angle steel each section length, the distance from the ground The buried depth and the soil resistivity of the area, the distributed parameter model is used to calculate the equivalent element value of the actual model, and the inductance, capacitance and conductance of each segment length of the horizontal body and vertical body of the grounding device are calculated. Then establish a π-type circuit simulation model on the PSCAD/EMTDC simulation platform, use the PSCAD/EMTDC simulation platform to test the impact characteristics of the model, and draw the impact grounding resistance of the device with different lightning current amplitudes, different soil resistivities, and different buried depths Change curve diagram; finally, compare the actual operating data of the grounding device with the drawn curve, whether it is within the scope of the curve change and whether it conforms to the continuous change law of the curve, considering the economy and applicability for the transformation and construction of the 10kV distribution line Select the most suitable shape and embedding depth of the grounding device.

Compared with the prior art, the present invention has the following advantages and effects:

1. The equivalent calculation model of the 10kV distribution line grounding device of the present invention is simple, and can well simulate the operation of the grounding device under the action of lightning current.

2. The present invention can obtain the change rule of the impulse characteristics of the horizontal-vertical grounding device of the 10kV power distribution line under different lightning impulse currents.

3. The present invention can obtain the change rule of the impact characteristics of the horizontal-vertical grounding device of the 10kV power distribution line under different geographical and meteorological conditions of different lightning impulse currents and different soil resistivities.

4. The present invention can obtain the change rule of the impact characteristics of the horizontal-vertical grounding device of 10kV distribution line under different buried depths, different numbers of branches, different specifications and installation process conditions.

5. Adopting the law of impact characteristics under different conditions of the present invention can provide a basis for rationally optimizing the layout of grounding devices in actual lightning protection renovation projects and reducing the lightning tripping rate of power distribution lines.

Description of drawings

Figure 1 is a schematic diagram of a horizontal-vertical grounding device for a 10kV distribution line.

Figure 2 is a diagram of the impact resistance curve change under different soil resistivities.

Fig. 3 is a graph showing the change of impulse resistance curves under different lightning current amplitudes.

Fig. 4 is a graph showing the change of impact resistance curves under different branch numbers.

Figure 5 is a graph showing the change of impact resistance curves under different embedding depths.

Fig. 6 is an equivalent circuit diagram of an element model of a grounding device.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

1. It is aimed at an existing horizontal-vertical structure grounding device in a 10kV power distribution line, as shown in Figure 1, the impact current 1, the ground 2, the horizontal body 3, and the vertical body 4, and the construction is measured according to the actual situation The length of each segment of the grounding body in construction or renovation, the buried depth and the soil resistivity determine the actual model structure of the grounding device.

2. The conductor of the grounding device uses the distributed parameter model for numerical calculation processing, and uses the conductor resistance per unit length R ₀ , self-inductance L ₀ , leakage conductance to ground G ₀ , and capacitance to ground C ₀ to describe the branch (as shown in Figure 2 parameters).

3. Build an equivalent numerical model to calculate the capacitance, inductance and conductance of components. L ₀ and C ₀ are the inductance per unit length of the lossy wire and the capacitance to the infinite zero plane respectively, G ₀ and G ₁ are the conductance of the horizontal and vertical grounding bodies, and the formula is as follows:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: μ ₀ is the magnetic permeability coefficient of vacuum, which can be taken as μ ₀ =4π×10 ^-7 in the practical range, r _ef is the radius of the grounding body, and l is the length of each grounding body.

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="l"\; filenames="HDA00003279511800022.png"\; state="\{\{state\}\}">l</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; hr</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.61</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.31</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, ρ is the soil resistivity, h is the buried depth of the grounding body, and _ref is the equivalent radius.

The capacitance of the unit length of each grounding body to the infinite zero plane is:

C ₀ =ερG ₀ , (4)

In the formula, ε is the dielectric constant of the soil, which can be taken as ε=9×8.86× ^10-12 F/m in the practical range.

Since the electric field strength at the boundary of the spark area is the critical breakdown field strength of the soil, the equivalent radius of each conductor after considering the spark discharge can be obtained by the formula:

$\mathrm{<span\; class="notranslate">\; J</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;I</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;l</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;\&Delta;<figure-callout\; id="2"\; label="l"\; filenames="HDA00003279511800022.png"\; state="\{\{state\}\}">l</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; IE</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

In the formula, J is the current density flowing through the conductor, △I is the current flowing through the conductor to the earth, △l is the length of each conductor, ρ is the soil resistivity, and _Ec is the critical breakdown field strength of the soil.

4. Establish a PSCAD/EMTDC model for simulation calculations based on the above conditions, use a π-type circuit to simulate the grounding device, and use an ideal current source to simulate the lightning current waveform. The lightning current waveform adopts 2.6/50μs, and the double exponential expression is:

I=AI _m [exp(-αt)-exp(-βt)], (7)

5. On the PSCAD/EMTDC model, use the formula (5) (6) to calculate the different capacitance, inductance and conductance of the components by changing the soil resistivity, and draw it when the soil resistivity is 50Ω/m, 100Ω/m, and 150Ω/m The change curve of the grounding resistance is shown in Figure 3.

6. The lightning current generation module on the PSCAD/EMTDC model changes the magnitude of the lightning current amplitude, and draws the grounding resistance change curve when the lightning current amplitude is 30kA, 50kA, and 70kA, as shown in Figure 4.

7. On the PSCAD/EMTDC model, by changing the number of branches, use the formula (1) (2) (3) (4) to increase or decrease the capacitance, inductance and conductance of the component, and draw the ground resistance change curve under different sizes, As shown in Figure 5.

8. On the PSCAD/EMTDC model, calculate the conductance of the element by changing the embedding depth using the formula (2) (3), and draw the grounding resistance change curve at different embedding depths, as shown in Figure 6.

9. Measure the grounding resistance of the 10kV power distribution line of the grounding device and compare it with the accompanying drawings 3, 4, 5 and 6, and check whether it is within the variation range of the curve and whether it conforms to the continuous variation law of the curve .

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (6)

1. A method for evaluating the impact characteristics of a grounding device, comprising the following steps: Step 1: For a horizontal-vertical grounding device in a 10kV power distribution line, including several segmented horizontal bodies and vertical bodies, the horizontal body and vertical body are perpendicular to each other, measure each segment of the horizontal body and vertical body length; Step 2: measuring the embedding depth of the horizontal body described in step 1 from the ground, and the soil resistivity in the area where the grounding device is located; Step 3: Use the equivalent circuit model to build the equivalent calculation model of the horizontal body and the vertical body of the grounding device, and establish a PSCAD/EMTDC model for simulation calculation; Step 4: draw the impact resistance change curve of the grounding device; Step 5: Measure the data of the actual operation of the grounding device for evaluation. 2. evaluation method according to claim 1, is characterized in that, in described step 3, calculates the inductance per unit length of each subsection grounding body of described equivalent circuit model, and its calculation formula is as follows: ${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$ In the formula, μ ₀ is the magnetic permeability of vacuum, take μ ₀ =4π×10 ^-7 , r _ef is the radius of the grounding body, and l is the length of each grounding body. 3. The evaluation method according to claim 1, characterized in that, in the step 3, the length conductance G ₀ of each segment of the horizontal body in the equivalent circuit model is calculated, and the equivalent circuit is calculated The conductance G ₁ of each segment length of the vertical body in the model is calculated as follows: ${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; hr</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.61</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>$ ${\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ef</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.31</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>$ In the formula, ρ is the soil resistivity, h is the buried depth of the grounding body, and _ref is the equivalent radius. 4. evaluation method according to claim 1, is characterized in that, in described step 3, equivalent circuit model wherein each section grounding body unit length is to the capacitance of infinity zero plane, and its formula is as follows: C ₀ =ερG ₀ , In the formula, ε is the dielectric constant of the soil, and ε=9×8.86×10 ^-12 F/m. 5. The evaluation method according to claim 1, wherein said step 4 comprises the following steps: A. Draw the impact resistance change curve of the grounding device under different lightning current amplitudes of 30kA, 50kA, and 70kA; B. Draw the impact resistance change curve of the grounding device under different soil resistivities of 50Ω/m, 100Ω/m, and 150Ω/m; C. Draw the impact resistance change curve of the grounding device with different sizes of the grounding device including the number of branches from 2 to 8; D. Draw the impact resistance change curve of the grounding device at different buried depths from 0.6m to 1.2m. 6. The evaluation method according to claim 1, wherein said step 5 comprises the following steps: (1) Measure the grounding resistance of the grounding device under different operating conditions in the 10kV distribution line, and draw the change curve; (2) Compare the measured grounding resistance change curve with the grounding device's impact resistance change curve calculated by the simulation platform, and whether it is within the range of the grounding device's impact resistance curve calculated by the simulation platform; (3) Whether the grounding device is within the range is judged to be qualified, and the grounding device that is not within the range is judged to be unqualified, and the buried depth and size of the grounding device need to be further modified.

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