Resistance reduction design method for wind turbine generator grounding system

Abstract

The invention discloses a wind turbine generator grounding system resistance reduction design method, which comprises the following steps: firstly determining a grounding resistance target value, then designing a wind turbine generator grounding system according to the target value, and the system comprises a fan main grounding grid, a resistance reduction grounding grid and a grounding wire connected with the resistance reduction grounding grid. During design, other surrounding grounding systems should be taken into consideration to form a large-scale grounding grid. In addition, a connecting ground wire of the main grounding grid and the resistance-reducing grounding grid needs to be buried and laid, the shape of the resistance-reducing grounding grid is designed according to the terrain, the landform and the soil structure, and the grounding resistance value is lower than that of the main grounding grid. In order to further reduce the grounding resistance, a mixture of a resistance reducing agent and conductive cement can be paved at the bottom of the horizontal grounding body. The grounding grid is preferably arranged in a place with small soil resistivity and large grounding grid area. The design method improves the stability and safety of the grounding system of the wind turbine generator.

Description

Technical Field

[0001] The invention belongs to the field of electric power, and more specifically relates to a resistance reduction design method for a grounding system of a wind turbine generator set. Background Art

[0002] Wind power is a clean and renewable energy source with little environmental pollution and abundant resources. With the development of wind power technology, wind turbines have gradually developed from the ground to the ocean and have developed rapidly in recent decades. However, during the operation of wind turbines, due to the rotation of wind turbines and the operation of electrical equipment, certain electromagnetic noise and electromagnetic radiation will be generated. If there is no effective grounding system to eliminate this electromagnetic interference, it will affect the operational stability of the wind turbines, may cause operational failures of the wind turbines, and even affect the service life of the wind turbines.

[0003] In addition, during the operation of wind turbines, overvoltage or overcurrent may occur due to lightning, electrical faults, etc. If there is no grounding system to conduct these overvoltage or current to the ground, it will pose a threat to the electrical equipment of the wind turbine and may even cause serious consequences such as fire or casualties. In this case, it is of great practical significance to design a grounding system suitable for wind turbines to eliminate electromagnetic interference and prevent overvoltage.

[0004] However, since wind turbines are usually located in open areas, the resistivity of the ground soil is relatively high, which makes the calculation and design of grounding resistance complicated. The traditional grounding system design method mainly reduces the total resistance of the grounding system by using resistance reducing agents or increasing the area of ​​the grounding body, but the application effect of these methods in wind turbines is not ideal. Therefore, it is of great practical significance to design a new wind turbine grounding system resistance reduction design method to improve the stability and safety of wind turbine operation and reduce equipment damage and failure. Summary of the invention

[0005] The main technical problem solved by the present invention is how to design a grounding system in a wind turbine that effectively reduces grounding resistance, improves electromagnetic interference suppression performance and safe operation stability, especially for wind turbines located in soil conditions with high resistivity, the design effect is particularly important. In addition, the design method should also consider long-term stability and economic benefits, so that the grounding system can maintain a low grounding resistance in long-term operation, and can also be achieved under the premise of controllable economic costs.

[0006] In order to achieve the above object, the present invention is implemented by adopting the following technical scheme: the method comprises:

[0007] Determine the target value of grounding resistance, and then design the grounding system of the wind turbine according to the target value of grounding resistance;

[0008] The wind turbine main grounding grid, resistance reduction grounding grid and their connected grounding wires are designed as a complete grounding system.

[0009] In one solution, the grounding system takes other grounding systems that are not far away into consideration in the design to form a large grounding network.

[0010] In one solution, the connecting ground wire between the main grounding grid and the resistance-reducing grounding grid is laid underground to reduce line resistance and play a role in reducing resistance of the horizontal grounding body.

[0011] In one scheme, the resistance reduction grounding grid is designed to be an "H" shaped grounding grid based on the specific conditions of the terrain, landform and soil structure.

[0012] In one solution, the grounding resistance value of the resistance reduction grounding grid is lower than that of the main grounding grid, thereby achieving the purpose of resistance reduction.

[0013] In one scheme, the resistance reducing agent and the conductive cement are mixed and stirred, and then spread horizontally on the bottom of the horizontal grounding body to reduce the grounding resistance.

[0014] In one plan, grounding grids are set up first in areas with lower soil resistivity and larger grounding grid areas.

[0015] In one solution, the resistance-reducing grounding grid relies on horizontal grounding bodies to reduce grounding resistance, vertical grounding bodies play a fixing role, and the buried bottom depth does not exceed 2m.

[0016] Beneficial effects of the present invention:

[0017] 1. By designing and analyzing the main grounding grid of the wind turbine, the resistance-reducing grounding grid and the connected grounding wires as a complete grounding system, the grounding area is increased and a lower grounding resistance is achieved, thereby improving the suppression effect of electromagnetic noise and ensuring the stable operation of the wind turbine.

[0018] 2. After mixing the resistance reducing agent and conductive cement, spread it horizontally at the bottom of the horizontal grounding body. This not only greatly reduces the grounding resistance, but also prevents the resistance reducing agent from dissipating, making the grounding resistance value stable for a long time.

[0019] 3. The design method is adapted to local conditions. According to the specific conditions of terrain, landform and soil structure, a suitable shape of the resistance-reducing grounding grid is designed to effectively reduce the grounding resistance.

[0020] 4. While greatly improving the operating stability and safety of the equipment, the grounding system designed by the present invention adopts an economical, simple and easy-to-implement design method, so that the wind turbine can operate safely and stably in remote areas with high resistivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the equivalent circuit diagram of the wind turbine grounding system;

[0022] Figure 2 It is the curve diagram of horizontal grounding body R=f(x). DETAILED DESCRIPTION

[0023] In order to facilitate understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are provided in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0024] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the present invention in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0025] The general concept of the present invention is:

[0026] The main grounding grid of the wind turbine, the resistance-reducing grounding grid and the connected grounding wires are designed and analyzed as a complete grounding system. If conditions permit, even other grounding systems not far away can be included in the design considerations to form a large grounding grid. Each point is equivalent to greatly increasing the grounding area, which can effectively and stably reduce the grounding resistance value;

[0027] Make full use of the connecting conductors between grounding grids: The connecting ground wires between the main grounding grid and the resistance-reducing grounding grid should be laid underground as much as possible. The first function is to provide electrical penetration. When the distance is far, materials with high conductivity or larger specifications should be used to reduce line resistance. The second function is to reduce resistance of the horizontal grounding body. If used well, it can contribute 10% to 30% to reducing grounding resistance.

[0028] By adopting laying methods such as burying as deep as possible or increasing the horizontal width, the grounding modules designed in the shape of two horizontal conductors are horizontally laid, which is equivalent to improving the soil resistivity around the conductor and increasing the capacitance of the grounding body.

[0029] Take measures according to local conditions and make full use of geographical advantages: According to the analysis of the terrain, landform and soil structure of the plot, the plot is suitable for the production and installation of a horizontal resistance-reducing grounding grid, which is laid along both sides of the highway to form an "H"-shaped grounding grid. The resistance-reducing grounding grid mainly relies on the horizontal grounding body to reduce the grounding resistance, and the vertical grounding body mainly plays a fixing role. The bottom end of the buried depth should not exceed 2m, that is, the vertical grounding electrode is buried in the upper soil; the grounding resistance value of the resistance-reducing grounding grid should be lower than that of the main grounding grid, so as to achieve the purpose of resistance reduction.

[0030] Give full play to the role of resistance reduction materials: After the resistance reduction agent and conductive cement are mixed and stirred, they are spread horizontally at the bottom of the horizontal grounding body, forming a special laying method similar to concrete. First, the width of the horizontal grounding body is equivalently increased, the effective area of ​​the grounding body is expanded, the grounding body's capacitance to the ground is increased, the soil resistivity around the grounding body is reduced, and the grounding resistance is effectively reduced. Second, the resistance reduction agent is solidified and laid over a wide surface, which can avoid the dispersion of the resistance reduction agent, reduce soil erosion in the grounding grid landfill soil, and make the grounding resistance value stable for a long time.

[0031] A wind turbine grounding system resistance reduction design method includes:

[0032] (1) Grounding resistance: The main electrical parameter describing the performance of the grounding device, which refers to the sum of the resistance of the grounding body or natural grounding body to the ground and the resistance of the grounding wire. The power frequency alternating current flowing into the earth through the grounding body is called the power frequency grounding resistance current. Generally, unless otherwise specified, the grounding resistance refers to the power frequency grounding resistance, which is generally represented by the symbol R and the unit is Ω.

[0033] (2) Soil resistivity: The average value of soil resistance per unit length, generally represented by the symbol ρ, with the unit of Ω·m. It is used to describe the conductive properties of the earth. It is a commonly used parameter in grounding engineering design and directly affects the grounding resistance of the grounding device, the ground potential distribution of the grounding grid, the step voltage and the contact voltage of the equipment.

[0034] (3) The earth has conductive and capacitive properties: The earth has conductive properties. One type of conductive property is electronic conductivity. When there are conductive or semiconductor materials in the geology, such as metal mines, electronic conductivity will be exhibited. However, the earth mainly exhibits ionic conductivity, that is, the ionic conductivity formed by the dissociation of various inorganic salts or acids and alkalis in the soil.

[0035] (4) The earth is equivalent to a large capacitor. Various electromagnetic energies can be filled in it. The grounding body forms a capacitor device with the earth. The relationship between the grounding resistance and the grounding capacitance of the grounding body can be derived from Gauss's theorem:

[0036] R=ρε / C

[0037] Where R: grounding resistance of the grounding body, Ω

[0038] C: Capacitance of the grounding body, F

[0039] ρ: soil resistivity, Ω·m

[0040] ε: Dielectric constant of the ground, F / m

[0041] Therefore, reducing soil resistivity and increasing the area of ​​the grounding grid are the main methods to reduce grounding resistance.

[0042] (5) Due to the conductive and capacitive properties of the earth, the wind turbine main grounding grid, the resistance reduction grounding grid and the grounding wires connected to them can be simulated as a device in an industrial frequency AC circuit, and they are in a parallel relationship.

[0043] (6) According to experimental and theoretical calculation analysis, when a vertical grounding electrode is added to a horizontal grounding electrode to form a composite grounding electrode, the resistance reduction efficiency of the grounding electrode decreases with the increase of the length of the horizontal grounding electrode. When the length of the horizontal grounding electrode is in the range of 12-75m, the vertical grounding electrode can reduce the grounding resistance by about 25-30%; when the length exceeds 75m, the resistance reduction efficiency is greatly reduced.

[0044] Calculation formula for drag reduction engineering design

[0045] (1) When the soil has two horizontal profiles, the grounding resistance calculation formula of the horizontal grounding grid is:

[0046]

[0047] Equivalent resistivity calculation formula:

[0048] ρ d =Sρ1ρ2 / (S1ρ2+S2ρ1)

[0049] Where: S1, S2: grounding grid area covering ρ1, ρ2 soil resistivity, m 2

[0050] S; total area of ​​grounding grid.

[0051] (2) Calculation formula for horizontal grounding body:

[0052]

[0053] Where ρ: soil resistivity, Ω·m;

[0054] l: total length of grounding body, m;

[0055] h: depth of horizontal grounding electrode, m;

[0056] d: diameter of horizontal grounding electrode, m;

[0057] B: Shape factor of horizontal grounding electrode.

[0058] (3) Single vertical grounding electrode

[0059]

[0060] Where l: vertical grounding length, m;

[0061] d: equivalent diameter of vertical grounding electrode, m;

[0062] ρ: upper soil resistivity, Ω·m.

[0063] (4) Electrical relationship between horizontal grounding body and vertical grounding body composite grounding grid:

[0064]

[0065] Where R 11 : Self-grounding resistance of n vertical grounding bodies in parallel, Ω;

[0066] R 22 : Self-grounding resistance of horizontal grounding body, Ω;

[0067] R12: Mutual grounding resistance between horizontal grounding body and vertical grounding body, Ω.

[0068] in

[0069] Where ρ: soil resistivity, Ω·m;

[0070] l1: vertical grounding electrode length, m;

[0071] l2: horizontal grounding electrode length, m.

[0072] Embodiment 1:

[0073] Take the resistance reduction design of the 4# wind turbine in a certain project as an example.

[0074] (1) Calculation of design value of grounding resistance of resistance-reducing grounding grid

[0075] (1) The terrain between the wind turbine platform of the 4# wind turbine and the location of the resistance reduction grounding grid is a steep slope at the top and a gentle slope at the bottom. The landform is exposed limestone with mixed shrubs. The soil is humus soil with a shallow soil layer. Because soil resistivity testing is difficult, according to data and soil condition analysis, it can be approximately considered that the upper soil resistivity is between 3000 and 4000Ω·m, taking ρ1=3500Ω·m, and the lower soil resistivity is the upper soil resistivity of the 1# plot, taking ρ2=600Ω·m. The two are distributed in half of the area. According to formula 4.8, the equivalent resistivity is: ρ d =1024Ω·m.

[0076] (2) The distance between the main grounding grid of the wind turbine and the 1# plot is about 120m. The connecting conductor is laid in the form of a composite grounding body composed of a horizontal grounding body and a vertical grounding body. The horizontal grounding body is made of 60 hot-dip galvanized flat steel with an equivalent diameter of d = 0.5b = 0.03m and an average burial depth of 0.3m. According to formula 4.9, since the lower end is approximately in a "Y" shape, B is taken as 0, and the grounding resistance of the horizontal grounding body connecting the resistance-reducing grounding grid and the main grounding grid conductor is calculated to be R" = R 22 =19.4Ω.

[0077] Because the connecting conductor is attached with a vertical grounding body, the length of the horizontal grounding body exceeds 75m, and resistance reduction measures are taken. The resistance reduction efficiency of the vertical grounding body factor can be taken as 30%, so the grounding resistance value R of the composite grounding body is 22 =13.6Ω.

[0078] (3) The grounding resistance value R1 of the main grounding grid of the 4# fan is taken as the average value of 30Ω detected over three years, and the standard value of the grounding resistance of the grounding system is R=4Ω. The power frequency electrical characteristics of the grounding system can be equivalent to Figure 1 Circuit diagram shown.

[0079] According to Kirchhoff's law, the grounding resistance R2 of the resistance-reducing grounding grid is derived as follows:

[0080] R2=RR1R 22 / (R1R 22 -RR 22 -RR1)=6.98Ω

[0081] The design value of the grounding resistance of the resistance-reducing grounding grid is no more than 6.98Ω, which meets the standard.

[0082] (2) Calculation of resistance reduction grounding grid

[0083] The horizontal grounding body is made of 60×6mm hot-dip galvanized flat steel and resistance reduction material with a width of b=0.8m and a thickness of 0.3m, which is equivalent to the equivalent diameter of the flat steel d=0.5b=0.4m. The horizontal grounding body is laid in the upper soil with a burial depth of 0.8m, ρ=ρ1ψ=600Ω.

[0084] It can be deduced that the function f(x) = 95.5ln 3.125x 2 / x. For curve description, see Figure 2 shown.

[0085] From the curve, it can be found that when the total length of the horizontal grounding electrode is 100m, the grounding resistance is about 9.88Ω. The resistance reduction grounding grid uses a horizontal grounding electrode and a vertical grounding electrode to form a composite grounding electrode. The resistance reduction efficiency of the horizontal grounding electrode is 30%, and the grounding resistance value of the resistance reduction grounding grid can be reduced to 6.9. That is, when the total length of the installed composite grounding electrode is not less than 100m, the resistance reduction target can be achieved.

[0086] (3) Design of structure and shape of resistance-reducing grounding grid

[0087] Depend on Figure 2 According to the trend analysis of the curve, when the length of the grounding electrode approaches 80m, the resistance reduction efficiency tends to be flat. Considering the economy and resistance reduction efficiency, a single horizontal grounding electrode should not exceed 75m. When the total length exceeds 75m, it can be laid in two or more lines.

[0088] According to the soil structure model and terrain conditions of plot 1#, the plot is suitable for installing an "H"-shaped horizontal resistance reduction grounding grid, which adopts a composite horizontal grounding grid structure consisting of horizontal grounding electrodes, vertical grounding electrodes and special resistance reduction materials. The total length of the horizontal grounding electrodes is not less than 100m, and the vertical grounding electrodes are made of L50 hot-dip galvanized angle steel, 1m long, with a spacing of not less than 5m and a burial depth of not more than 2m.

[0089] (4) How to use the drag reduction material

[0090] Grounding grid resistance reduction projects often require some special methods to achieve the resistance reduction goal. How to use resistance reduction materials in the design is an important part of engineering design and construction. Resistance reduction projects should focus on the selection and laying methods of resistance reduction materials to fully utilize and improve the performance of resistance reduction materials.

[0091] (5) Principle of resistance reduction of resistance reducing agent

[0092] According to relevant theoretical calculations and experiments, the grounding body is laid with resistance reducing agent, which has the following main functions:

[0093] 1) Increase the effective cross-section of the grounding body

[0094] a. For a hemispherical grounding electrode, according to the formula Therefore, the efficiency of reducing grounding resistance is: Where R2 is the grounding resistance after the resistance reduction agent is laid, R1: the original grounding resistance of the hemispherical grounding body, r: the radius of the hemisphere, r1: the radius from the resistance reduction agent to the center of the sphere. When r1 = 2r, ΔR = 50%, that is, when the resistance reduction agent laid reaches twice the radius of the hemisphere, the grounding resistance can be reduced by half, and the resistance reduction efficiency is 50% greater.

[0095] b. For horizontal grounding electrodes, according to the formula Calculate, the grounding resistance reduction efficiency is: Where ρ1: resistivity of resistance reducing agent; ρ2: original soil resistivity, l: horizontal grounding length; d: equivalent diameter of grounding body; d1: equivalent diameter of resistance reducing agent replacement. When the buried depth is 0.3m, a 60×6 hot-dip galvanized flat steel horizontal grounding body is installed, and a resistance reducing agent with a cross section of 1m×0.3m is laid, the resistance reducing efficiency gradually weakens with the increase of length, but the grounding resistance can also be reduced by 65%-55%.

[0096] c. For vertical grounding body grounding resistance: The grounding resistance reduction efficiency is: Where ρ1: resistivity of resistance reducing agent, ρ2: original soil resistivity, l: length of vertical grounding body, d: diameter of grounding body, d1: replacement diameter of resistance reducing agent. When installing a vertical grounding body with a diameter of φ20 and a length of 2m, laying a 0.3m diameter resistance reducing material can reduce the grounding resistance by 45.3%.

[0097] If the replacement diameter d1 is increased to be equal to the length of the vertical grounding body, it can be approximated to a hemisphere: When installing a vertical grounding electrode with a diameter of φ20 and a length of 2m, laying a 2m diameter resistance reduction material can reduce the grounding resistance by 83.3%.

[0098] 2) Reduce the ground bus line resistance and contact resistance

[0099] a. The grounding resistance of the grounding system is composed of three resistance components. The first is the resistance of the grounding busbar itself, which is represented by R X The second is the resistance characteristic of the earth around the grounding body (grid), represented by R d The third is the degree of electrical conductivity between the grounding body (grid) and the surrounding soil, which is called contact resistance and is represented by R j The grounding resistance of the grounding body (grid) is represented by R, which conforms to the relationship R = R X +R d +R j .

[0100] b. The above theoretical calculations refer to R d However, if the line resistance and contact resistance are not controlled or not well controlled, the grounding resistance of the grounding system will not meet the standard after actual construction. j It is caused by the poor connection between the grounding body (net) and the surrounding soil. This is closely related to the soil used for the landfill of the grounding body. Generally, the tighter and finer the landfill soil, the better the R j The smaller the soil, the looser the soil, the more serious the soil erosion, and the j The larger the grounding area, the more fine soil should be backfilled and compacted tightly, instead of sand, gravel and construction waste. j It is also related to the surface condition of the grounding body. The smoother the grounding body, the lower the R j The smaller it is, the rougher the grounding body is. j The larger the grounding surface, the more R jIt will become larger and larger, so the grounding body should be made of hot-dip galvanized steel, one is the surface is smooth, the other is anti-corrosion. Solid physical resistance reducing agent has the function of reducing and eliminating contact resistance, one is to wrap tightly with the grounding body, the other is to dissolve easily with the surrounding soil, which can basically eliminate contact resistance.

[0101] c. The metal conductor connected to the resistance-reducing grounding (body) network has its own resistance, which is called line resistance R X , in accordance with the relationship: R X =δL / S, where δ is metal resistivity, unit Ω·m, L is the length of the metal conductor, unit m, and S is the cross-sectional area of ​​the conductor, unit m2. X There are two power frequency electrical relationships with the grounding resistance of the grounding body: when the conductor is laid in the open air and not directly buried, R X It is in series with the resistance-reducing grounding body (grid): R = R X +R d ; When the conductor is buried directly in the ground, the conductor is equivalent to a horizontal grounding body, and the grounding resistance of the conductor and the grounding resistance of the grounding body are in parallel.

[0102] Therefore, there are two ways to overcome or reduce R X Methods: First, when the resistance reduction grounding grid is far away from the main grounding grid, the grounding busbar should be made of metal materials with low resistivity and large cross-sectional area, generally hot-dip galvanized flat steel or round steel, and copper materials in special cases. Second, the connecting wire is directly buried in the ground as a horizontal grounding body, and resistance reduction technology is adopted to minimize its grounding resistance.

[0103] 3) Resistance reducing agent can improve and maintain soil conductivity

[0104] The conductivity of soil is related not only to the conductive ions contained in the soil, but also to the water content of the soil. This is because most of the inorganic salts in the soil can only dissociate into conductive ions in water, and the resistivity of the soil is generally negatively correlated with its water content. Therefore, the selected resistance reducing agent must have strong water absorption and water retention, and general physical resistance reducing agents have this property.

[0105] (6) Methods of laying resistance-reducing materials

[0106] According to the resistance reduction principle of resistance reduction materials, under the conditions of karst geology and geomorphology, the following laying methods are adopted to give full play to the role and efficiency of resistance reduction materials:

[0107] 1) The resistance-reducing grounding grid uses a resistance-reducing agent with conductive cement added. After adding water and mixing evenly on site, it is wrapped around the horizontal grounding body and spread at the bottom of the excavated trench into a cross-section of 0.9m×0.3m. After solidification, it is similar to reinforced concrete. Its functions are, first, to increase the width of the horizontal grounding body, expand the effective area of ​​the grounding body, increase the grounding body's capacitance to the ground, reduce the soil resistivity near the grounding body, and effectively reduce the grounding resistance. Second, the resistance-reducing agent is physically solidified and laid on a wide surface, which can avoid the dispersion of the resistance-reducing agent, reduce soil erosion in the landfill of the grounding grid, and make the grounding resistance value stable for a long time.

[0108] 2) The connecting wire between the main grounding grid and the resistance reduction grounding grid is installed and laid as a horizontal grounding body. The horizontal grounding module is installed along both sides of the wire and in the vertical direction of the wire. Its main functions are: first, the horizontal laying method is equivalent to increasing the width of the horizontal grounding body, expanding the effective area of ​​the grounding body, increasing the grounding body's capacitance to the ground, reducing the soil resistivity near the grounding body, and effectively reducing the grounding resistance. Second, the use of solidified resistance reduction modules is convenient for installation, and it can also prevent the dispersion of resistance reduction materials, making the resistance reduction effect long-term and stable.

[0109] (7) Selection and improvement of drag reduction materials

[0110] Under karst geological and geomorphic conditions, the surface soil is humus or humus clay, which is slightly acidic, loose and relatively dry; there are many underground pores, and water and soil are easily lost. Therefore, in view of these characteristics, the following aspects should be paid attention to when selecting resistance reduction materials:

[0111] 1) Choose environmentally friendly, solid physical drag reducing agent

[0112] Physical resistance reducing agents are generally made of non-electrolyte solid powders, such as charcoal, graphite, bentonite, rare earth and other physical materials with very low resistivity, either alone or mixed in equal proportions. These materials are non-toxic and have poor permeability, and will not pollute the soil or groundwater.

[0113] Its environmental protection conditions should comply with the relevant provisions of "Technical Conditions for Grounding Resistance Reduction Materials" (DL / T380-2010).

[0114] 2) Select drag-reducing materials with suitable physical and chemical properties

[0115] Strong alkalinity will increase the corrosion rate of metal materials. Weakly alkaline resistance reducing agents should be used, with a pH value of 7 < 8.5; the average corrosion rate of steel grounding electrodes should be less than 0.03mm / a. Other physical and chemical indicators should comply with the relevant provisions of DL / T380-2010.

[0116] 3) Try to choose resistance-reducing materials with low resistivity

[0117] The electrical performance indicators of resistance reduction materials should comply with the relevant provisions of DL / T380-2010. The standard requires that the resistivity of resistance reduction materials should be ≤5Ω·m, the lower the better.

[0118] 4) Select drag reduction materials with good stability and long-term performance

[0119] Generally, solid physical drag reduction materials have good stability and long-term effectiveness. You can refer to the following two conditions to select drag reduction materials:

[0120] a. After the resistance-reducing material has undergone the impact withstand test and the power frequency current withstand test, the change in the nominal resistivity value should be less than 20%;

[0121] b. The resistance-reducing material should be subjected to water loss, water immersion and hot and cold cycle tests (the combination of these tests is called a stability test), and the measured average resistivity should not be greater than its nominal resistivity.

[0122] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM).

[0123] It should be understood that the detailed description of the technical solutions of the present invention by means of the preferred embodiments is illustrative rather than restrictive. A person skilled in the art may modify the technical solutions described in the embodiments, or replace some of the technical features by equivalents, based on reading the specification of the present invention; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wind turbine grounding system resistance reduction design method, characterized by: The method includes: Determine the target value of grounding resistance, and then design the grounding system of the wind turbine according to the target value of grounding resistance; The wind turbine main grounding grid, resistance reduction grounding grid and their connected grounding wires are designed as a complete grounding system.

2. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: The grounding system described herein takes other grounding systems that are not far away into consideration in the design scope to form a large grounding network.

3. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: The connecting ground wire between the main grounding grid and the resistance-reducing grounding grid is laid underground to reduce line resistance and play a role in reducing resistance of the horizontal grounding body.

4. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: According to the specific conditions of terrain, landform and soil structure, the resistance reduction grounding grid is designed to be an "H" shaped grounding grid.

5. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: The grounding resistance value of the resistance reduction grounding grid should be lower than that of the main grounding grid, so as to achieve the purpose of resistance reduction.

6. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: After the resistance reducing agent and conductive cement are mixed and stirred, they are spread horizontally at the bottom of the horizontal grounding body to reduce the grounding resistance.

7. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: Grounding grids should be set up first in areas with lower soil resistivity and larger grounding grid areas.

8. A wind turbine grounding system resistance reduction design method according to claim 1, characterized in that: The resistance-reducing grounding grid relies on the horizontal grounding body to reduce the grounding resistance, the vertical grounding body plays a fixing role, and the buried bottom depth does not exceed 2m.

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