A pre-assembled grounding device and its design and selection method

Abstract

The present invention belongs to the technical field of power system grounding, and specifically relates to a prefabricated complete grounding device and its design and selection method, including: a connector; a grounding grid including at least four horizontal grounding bodies; one end of the grounding down conductor is respectively connected to the corresponding tower pole and an excitation source; the other end of the grounding down conductor is respectively connected to each horizontal grounding body through the connector, and each group of vertical grounding electrodes is connected to a horizontal grounding body and is located below the horizontal grounding body; when measuring the grounding resistance, the excitation source is used to inject voltage excitations of the same phase and amplitude at all grounding down conductors, so that the potentials at the connection points of each grounding down conductor and the grounding grid are equal; so that the excitation of a single tower pole can only form a loop through its corresponding grounding down conductor, grounding grid, earth, remote tower pole, overhead ground wire, and its own tower pole, so as to measure the loop current and obtain the grounding resistance of a single tower pole. That is, the scheme of the present invention can be installed more conveniently and quickly and at a low cost.

Description

Technical Field

[0001] The present invention generally relates to the technical field of power system grounding, and more specifically, to a pre-assembled complete grounding device and a design and selection method thereof. Background Art

[0002] Grounding is the only safe channel for current to enter the ground when the power system is struck by lightning or a fault occurs. It is the cornerstone for ensuring the safety of people and equipment and ensuring the reliable and safe operation of the power system.

[0003] At present, data shows that lightning strikes account for 47.6% of the total faults in China, and lightning strikes account for 40%-60% of the total faults in 12 countries including the United States and Japan; therefore, the safe operation of the power system faces severe challenges. Especially in mountainous rocky areas with frequent lightning activities, complex soil structure and high soil resistivity, the accident rate caused by lightning strikes on power transmission lines is even higher.

[0004] Therefore, a good grounding grid design can ensure the safe and reliable operation of power system related equipment. There have been many studies on the grounding grid design method, especially in the design of power frequency grounding grid of transmission lines. Simple soil structure can rely on relevant standards and experience, and complex soil structure and terrain can be carried out using commercial software (such as CDEGS).

[0005] However, the use of CDEGS is expensive when encountering complex soil structures and terrains. At the same time, the design of grounding projects requires absolutely accurate on-site geological survey results, and designers need to have rich theoretical knowledge and practical engineering design experience. Therefore, the final design plan often deviates too much from the actual needs, and it is necessary to repeatedly measure and adjust the plan and repeat the construction during the construction process, which greatly increases the construction period and project cost.

[0006] Therefore, there is an urgent need for a grounding device with low cost, quick installation and good grounding performance and a design method thereof. Summary of the invention

[0007] In order to solve one or more of the above technical problems, the present invention proposes to design a preassembled grounding device so that each grounding element is connected through a connector, thereby avoiding on-site welding of the grounding main material and the grounding auxiliary material, and the connection method is convenient and fast.

[0008] To this end, the present invention provides solutions in the following aspects.

[0009] In a first aspect, a preassembled grounding device of the present invention comprises:

[0010] Connectors,

[0011] The grounding unit comprises at least four grounding down conductors, a grounding grid and at least four groups of vertical grounding electrodes; the grounding grid comprises at least four horizontal grounding bodies; one end of the grounding down conductor is respectively connected to the corresponding tower pole and the excitation source;

[0012] The other end of the grounding down conductor is connected to each horizontal grounding body through the connecting piece, and each group of vertical grounding electrodes is connected to a horizontal grounding body and is located below the horizontal grounding body for discharge;

[0013] When measuring the grounding resistance of the grounding device, the excitation source injects voltage excitation of the same phase and amplitude at all grounding down conductors to make the potential of each grounding down conductor equal to the connection point of the grounding grid; and the excitation of a single tower pole can only form a loop through its corresponding grounding down conductor, grounding grid, earth, remote tower pole, overhead ground wire, and its own tower pole, so as to measure the loop current and obtain the grounding resistance of a single tower pole.

[0014] Optionally, the grounding grid is a U-shaped structure composed of four horizontal grounding electrodes; each group of vertical grounding electrodes includes at least one vertical grounding electrode, which is arranged in the middle position of each horizontal grounding electrode.

[0015] Optionally, the grounding unit further includes a grounding resistance reduction module, and the grounding resistance reduction module is connected to the four corners of the grounding grid through the connecting piece.

[0016] Optionally, the grounding unit further includes a resistance reducing cloth and / or a resistance reducing paste, which is arranged on the horizontal grounding body.

[0017] Optionally, the connecting piece is made of non-metallic material or corrosion-resistant metal material, and consists of a junction box and a wedge-shaped anti-slip pressure plate.

[0018] Optionally, the method further includes measuring the impulse resistance of the grounding device, specifically:

[0019] When the increase between the continuously measured grounding resistance values ​​is greater than the set threshold and the current grounding resistance is less than the set value, the impact resistance is measured; otherwise, when the current grounding resistance is greater than or equal to the set value, an alarm is issued.

[0020] Optionally, voltage pulse excitations of equal amplitude and phase are injected into all ground down conductors, and the pulse amplitude and current of the loop formed by a single ground down conductor are measured to obtain the impact resistance.

[0021] In a second aspect, the present invention further provides a method for designing and selecting a pre-assembled complete grounding device, comprising the following steps:

[0022] Obtain environmental parameters around the tower where the grounding device is to be installed;

[0023] According to the preset grounding selection tool library and the environmental parameters, a standard solution with the highest similarity to the environment in the preset grounding selection tool library is matched;

[0024] Constructing a simulation model corresponding to the standard solution, performing simulation calculation on the simulation model to evaluate the grounding performance of the standard solution under the current application environment, and adjusting the simulation model according to the evaluation result;

[0025] The final prefabricated grounding device is determined based on the adjusted simulation model.

[0026] Optionally, the environmental parameters include soil resistivity, soil corrosion level, soil pH value, soil temperature, soil water content, soil density and impurities contained in the soil.

[0027] Optionally, the preset grounding selection tool library includes a set of standard grounding solutions, which are used to match corresponding standard solutions according to the acquired environmental parameters;

[0028] The standard scheme is simulated and calculated, including the calculation of grounding grid parameters such as grounding impedance, contact potential difference, step potential difference, mesh potential difference and ground surface potential distribution on the grounding grid; and the evaluation results of grounding performance are obtained based on the grounding grid parameters.

[0029] The beneficial effects of the present invention are:

[0030] The prefabricated complete grounding device of the present invention directly introduces an excitation source at the grounding down conductors corresponding to all towers, that is, when measuring the grounding resistance of the grounding device, voltage excitations of the same phase and amplitude can be injected, so that the voltages at the connection points of each grounding down conductor and the power grid are equal, and the occurrence of circulating currents between the grounding down conductors can be avoided, so that the grounding resistance can be measured accurately; at the same time, each tower forms its own grounding resistance measurement loop, and only the current in the loop needs to be measured to measure the grounding resistance of each tower, and the method is simple and easy to implement.

[0031] At the same time, the grounding elements of the preassembled complete grounding device of the present invention are connected by connecting pieces, thus avoiding on-site welding of the grounding main material and the grounding auxiliary material, and the connection method is convenient and fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0033] Figure 1is a flowchart of the steps of a design and selection method of a pre-assembled complete grounding device in this embodiment;

[0034] Figure 2 is a schematic diagram of a pre-assembled complete grounding device in this embodiment;

[0035] Description of the accompanying drawings: 1. Grounding down conductor; 2. Connector; 3. Grounding resistance reduction module; 4. Horizontal grounding body; 5. Vertical grounding electrode; 6. Resistance reduction cloth. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0037] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] Taking the grounding of a transmission line tower as an example, the prefabricated complete grounding device of the present invention is introduced from the process of design selection to the evaluation of grounding performance.

[0039] It should be noted that a good design of grounding device can ensure the safe and reliable operation of related equipment in the power system. However, the selection of relevant parameters of grounding device design, how to control it, and what design method and installation method to adopt are all affected by environmental parameters. Therefore, it is particularly important to design the grounding device in a standardized manner.

[0040] At the same time, after the grounding device is designed, the evaluation of the grounding performance of the grounding device is also particularly important. Since the grounding performance is characterized by the measured grounding resistance, during the installation of the grounding device, the grounding resistance of the grounding device needs to be measured to judge the grounding effect of the grounding device by the grounding resistance. Or after using the grounding device for a period of time, the grounding resistance of the grounding device needs to be accurately measured periodically to ensure good grounding of the transmission line tower.

[0041] Therefore, based on the design and selection of the grounding device and the importance of grounding performance mentioned above, the present invention provides a design and selection method for a pre-assembled complete grounding device, so as to determine the final grounding device.

[0042] Figure 1 It is a flow chart of the steps of a design and selection method of a pre-installed complete grounding device in this embodiment.

[0043] like Figure 1As shown, a design and selection method of a pre-assembled complete grounding device of this embodiment includes the following steps:

[0044] Step 1, obtaining environmental parameters around the tower where the grounding device is to be installed, including soil resistivity, soil corrosion level, soil pH value, soil temperature, water content, soil density and impurities in the soil.

[0045] In this embodiment, the environmental parameters are obtained through a soil inversion algorithm. Specifically, the soil inversion algorithm is a multi-method artificial intelligence soil inversion system based on a random starting point and an adaptive grid technology of a grounding system, which realizes the comprehensive inversion of the apparent resistivity measurement data of the quadrupole method and obtains the environmental parameters.

[0046] Step 2: According to the preset grounding selection tool library and the environmental parameters, a standard solution with the highest similarity to the environment in the preset grounding selection tool library is matched.

[0047] The preset grounding selection tool library is a complete set of grounding solutions obtained through statistics of historical grounding devices. It can be regarded as a grounding case library, which brings together a large number of standardized complete sets of grounding solutions and case libraries. The design and construction can be based on actual application scenarios, geological conditions and design requirements, and can be freely combined and accurately matched with standardized complete grounding system design solutions that have been verified by actual engineering and identified by experts.

[0048] In this embodiment, the environmental parameters of the current application environment are compared with the environmental parameters of the standard solutions in the grounding selection tool library to determine the standard solution with the highest similarity as the grounding design solution corresponding to the current application environment. That is, the grounding selection tool library is used to match the standard solutions and past cases in the corresponding environment in the database, which is convenient for users to make references, increase the reliability of the grounding solution, and improve the efficiency of grounding solution design.

[0049] Step 3, construct a simulation model corresponding to the standard solution, perform simulation calculations on the simulation model to evaluate the grounding performance of the standard solution under the current application environment, and adjust the simulation model according to the evaluation results.

[0050] In one embodiment, a tower grounding simulation model can be established, which includes a tower model, a grounding grid model and a connection part model. The tower adopts a straight column plate type, the grounding device model is in the form of a closed square frame with vertical rays, and the connection part model includes a grounding down conductor and a tower foot main material; the grounding grid parameters in the simulation model are calculated, wherein the grounding grid parameters include grounding impedance, contact potential difference, step potential difference, mesh potential difference and ground surface potential distribution on the grounding grid and other parameters; the specific calculation method can be achieved through adaptive grid generation technology, based on multi-precision multi-resolution complex mirroring method and Heppe method to complete a high-precision grounding grid scattered current matrix algorithm for simulation calculation.

[0051] According to the acquired grounding grid parameters and the principles of ensuring the safety of power distribution equipment and the fixed parameter principle, the grounding performance of the simulation model is evaluated to obtain the evaluation results; specifically, when the step voltage in the grounding grid parameters does not meet the principle of ensuring the safety of power distribution equipment, it is necessary to adjust the size of the horizontal grounding body, etc.

[0052] In one embodiment, adjusting the simulation model can change the soil resistivity in the simulation model, obtain the relationship between the grounding resistance and the soil resistivity, and compare and analyze it; it can also change the length of the vertical ray in the grounding grid model, obtain data under different ray lengths, and compare and analyze it to determine the final simulation model.

[0053] Step 4: Determine the final pre-assembled complete grounding device according to the adjusted simulation model. Specifically, the size and model of the device components can be selected according to the final simulation model, such as the resistance value and corresponding model of the grounding resistance reduction module, the size and material of the horizontal grounding body, and the length and material of the vertical grounding electrode, etc., to obtain all the components of the pre-assembled complete grounding device.

[0054] Based on the above design selection method, a pre-assembled grounding device is provided in this embodiment.

[0055] Figure 2 Schematic diagram of a pre-assembled grounding device in this embodiment.

[0056] like Figure 2 As shown, a preassembled complete grounding device of the present invention comprises: a connector 2 and a grounding unit.

[0057] The grounding unit includes four grounding down conductors 1 connected to the tower, a grounding grid and four groups of vertical grounding electrodes 5; the grounding grid is a U-shaped structure composed of four horizontal grounding bodies 4.

[0058] The grounding down conductor 1 is connected to each horizontal grounding body 4 through a connector 2, and each group of vertical grounding electrodes 5 is connected to a horizontal grounding body 4 and is located below the horizontal grounding body 4 for discharging to the earth. Specifically, each group of vertical grounding electrodes includes at least one vertical grounding electrode, which is arranged near the middle position of each horizontal grounding body 4.

[0059] In one embodiment, the grounding unit further includes a grounding resistance reduction module 3, which is connected to the four corners of the grounding grid through the connector 2. Specifically, it is arranged at the four corners of the square shape to reduce the contact resistance so as to stabilize the grounding resistance.

[0060] In one embodiment, the grounding unit further includes a resistance reducing cloth 6, which is arranged on the horizontal grounding body 4. Specifically, when the resistance reducing cloth is used, the resistance reducing cloth is wrapped around the grounding grid and buried underground; when the resistance reducing paste is used, it can be wrapped around the grounding grid. Of course, the resistance reducing cloth 6 can also use only the resistance reducing paste, or a combination of the resistance reducing cloth and the resistance reducing paste.

[0061] The connector 2 is made of non-metallic material or corrosion-resistant metal material, and is composed of a junction box and a wedge-shaped anti-slip pressure plate, and is used to connect the grounding down conductor 1 to the grounding grid, and to connect the grounding resistance reduction module 3 to the grounding grid.

[0062] In this embodiment, it is also necessary to periodically measure the grounding resistance of the installed grounding device to ensure good grounding of the transmission line tower.

[0063] Specifically, when measuring the grounding resistance of the grounding device, voltage excitation of the same phase and amplitude is injected at all grounding down conductors to make the potential of each grounding down conductor equal to the connection point with the grounding grid; and a single grounding down conductor can only form a grounding resistance loop through the grounding grid, earth, remote tower pole and overhead ground wire connected to it, so as to measure the loop current and obtain the grounding resistance.

[0064] For example, Figure 2 As shown, voltage excitations of the same phase and amplitude are respectively injected into the four grounding down conductors 1 connected to the grounding grid as test power supplies. At this time, the voltages at the four injection points on the grounding grid are the same, so there is no voltage difference between the four horizontal grounding bodies 4, that is, there is no current. At this time, the excitation of a single tower pole can only form a loop through its own corresponding grounding down conductor, grounding grid, earth, remote tower pole, overhead ground wire, and its own tower pole, thereby measuring the loop current, and realizing the measurement of the grounding resistance of a single tower pole.

[0065] It should be further explained that in the process of grounding resistance monitoring, there will inevitably be changes in grounding resistance. There are many kinds of changes, such as some problems with the grounding equipment, and changes in soil conditions due to rain, etc. Therefore, it is also necessary to test the impulse resistance at this time to ensure good grounding effect of the transmission line tower when lightning strikes the transmission line tower or ground wire.

[0066] Specifically, the process of measuring the impulse resistance of the grounding device in this embodiment is as follows:

[0067] Measure the current grounding resistance value of the tower at least twice in succession;

[0068] In response to the increase between the continuously measured grounding resistance values ​​being greater than the set threshold and the current grounding resistance being within the set range, the impact resistance is measured; conversely, in response to the current grounding resistance being greater than or equal to the upper limit value in the set range, an early warning is issued.

[0069] The impulse resistance is measured by injecting voltage pulse excitation of equal amplitude and phase into all grounding down conductors, measuring the pulse amplitude and current of the loop formed by a single grounding down conductor, and obtaining the impulse resistance.

[0070] It should be noted that in this embodiment, by setting the restriction condition on the impulse resistance measurement, the number of impulse resistance measurements is limited, and the purpose is to reduce the impact on the transmission line.

[0071] In one embodiment, three consecutive measurements can be performed in a short period of time; generally speaking, the measurement cycle of the grounding resistance can be once every 12 hours; if the increase between the grounding resistance values ​​measured twice in succession is greater than the set threshold, it is considered that a sudden change has occurred in the grounding resistance; at this time, more measurements can be performed in a short period of time to confirm the sudden change, such as continuing to measure 5 times in succession to determine whether the increase between two consecutive measurements is still greater than the set threshold. If so, it is determined that the grounding resistance value has changed; it should be noted that when a sudden change in the grounding resistance is found, it is very likely to occur in the case of weather changes such as rain or lightning strikes. In this case, multiple grounding resistance measurements can also help release the charge accumulated in the tower and reduce the probability of lightning strikes.

[0072] After determining that the grounding resistance value has a sudden change, continue to judge whether the current grounding resistance value is within the set range (A1, A2). If so, the impact resistance can be measured; when it is greater than the upper limit value A2, the impact resistance is not measured.

[0073] The set threshold in the above description can be 5% of the initial value; the first set value A1 in the set value range is 110% of the initial value; the second set value A2 is 130% of the initial value; of course, as other implementations, the set value range and the set threshold can also be set according to actual conditions.

[0074] Among them, the initial value can be measured for a period of time (one month or several months) after the grounding device is installed to determine the minimum value of the grounding resistance, and the minimum value is used as the initial value; of course, if there is still a minimum value lower than the existing initial value in the subsequent grounding resistance detection, the existing initial value is updated with the actual minimum value obtained by measurement.

[0075] The initial value selected as the lowest value of the measured grounding resistance is to prevent the set threshold from being too large, so as to ensure the online detection of the impact resistance in a safe environment for the equipment. The reason why the initial value is determined after measuring for a period of time is that the grounding resistance may not be the lowest when the tower is installed and the measurement begins. Therefore, it is necessary to monitor the grounding resistance for a period of time to determine the initial value.

[0076] As another implementation method, the initial value can also be determined by measuring the grounding resistance values ​​of several nearby towers when the tower grounding device is installed, and determining the initial value based on all the grounding resistance values; at the same time, in the subsequent grounding resistance detection process, the existing initial value can be updated with the true minimum value obtained by measurement.

[0077] In the above embodiment, the initial value is determined according to all ground resistance values, specifically:

[0078] Get the average value of all ground resistance values;

[0079] Based on the average value, determine the initial value.

[0080] It should be noted that the purpose of adjusting the average value in this embodiment, such as adjusting it downward by 30%, is to avoid selecting a threshold that is too large.

[0081] Of course, the average value can also be used directly as the initial value. In this case, in order to avoid selecting a threshold that is too large, it is also necessary to adjust the set threshold, the lower limit of the set range, and the upper limit of the set range, such as lowering all three by 30%; it should be emphasized that when the true lowest initial value is detected later, the three lowered thresholds need to be restored to avoid the situation where the threshold is too small, thereby avoiding continuous impact resistance measurement to reduce the impact on the transmission line.

[0082] It should be noted that the measuring method of the grounding resistance of the present invention is safe, reliable, lightweight, and easy to operate, and is applicable to the measurement of the grounding resistance of all power towers connected to the grounding grid through grounding down conductors; at the same time, during the measurement process, by injecting voltage excitations of the same phase and amplitude on all grounding down conductors, there is no need to remove any grounding down conductors and arrange auxiliary grounding electrodes, which reduces the working time of grounding resistance measurement personnel, effectively improves work efficiency, and reduces the adverse effects of frequent disassembly and assembly of grounding down conductors on the grounding system. At the same time, the same voltage excitation is injected at all grounding down conductors, avoiding the influence caused by the voltage difference between the grounding bodies, and the grounding resistance can be accurately measured.

[0083] In the above description of this specification, unless otherwise clearly specified and limited, the terms, "installed", "connected" or "connected" and the like should be understood in a broad sense. For example, with regard to the term "connection", it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. Therefore, unless otherwise clearly defined in this specification, those skilled in the art can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0084] According to the above description of this specification, those skilled in the art may also understand that the terms used below, such as "lower", "length", "width", "vertical", "horizontal", "inside", "outside", "center" and the like, which indicate the orientation or position relationship, are based on the orientation or position relationship shown in the drawings of this specification, and are only for the purpose of facilitating the explanation of the scheme of the present invention and simplifying the description, rather than explicitly or implicitly indicating that the device or element involved must have the specific orientation, be constructed and operate in a specific orientation. Therefore, the above-mentioned orientation or position relationship terms cannot be understood or interpreted as limitations on the scheme of the present invention.

[0085] In the description of this specification, "several" or "plurality" means at least two, such as two, three or more, etc., unless otherwise clearly and specifically defined.

[0086] Although this specification has shown and described a number of embodiments of the present invention, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art will conceive of many modifications, changes and alternatives without departing from the ideas and spirit of the present invention. It should be understood that in the practice of the present invention, various alternatives to the embodiments of the present invention described herein may be employed.

Claims

1. A preassembled complete grounding device, characterized in that: include: Connectors, The grounding unit comprises at least four grounding down conductors, a grounding grid and at least four groups of vertical grounding electrodes; the grounding grid comprises at least four horizontal grounding bodies; one end of the grounding down conductor is respectively connected to the corresponding tower pole and the excitation source; The other end of the grounding down conductor is connected to each horizontal grounding body through the connecting piece, and each group of vertical grounding electrodes is connected to a horizontal grounding body and is located below the horizontal grounding body for discharge; When measuring the grounding resistance of the grounding device, the excitation source injects voltage excitation of the same phase and amplitude at all grounding down conductors to make the potential of each grounding down conductor equal to the connection point with the grounding grid; The excitation of a single tower pole can only form a loop through its corresponding grounding down conductor, grounding grid, earth, remote tower pole, overhead ground wire, and its own tower pole, so that the loop current can be measured and the grounding resistance of a single tower pole can be obtained. The design and selection method of the prefabricated complete set grounding device comprises the following steps: Obtain environmental parameters around the transmission line tower where the grounding device is to be installed; According to the preset grounding selection tool library and the environmental parameters, a standard solution with the highest similarity to the environment in the preset grounding selection tool library is matched; Constructing a simulation model corresponding to the standard solution, performing simulation calculation on the simulation model to evaluate the grounding performance of the standard solution under the current application environment, and adjusting the simulation model according to the evaluation result; The final prefabricated grounding device is determined based on the adjusted simulation model.

2. A preassembled complete grounding device according to claim 1, characterized in that: The grounding grid is a U-shaped structure composed of four horizontal grounding bodies; each group of vertical grounding electrodes includes at least one vertical grounding electrode, which is arranged in the middle position of each horizontal grounding body.

3. A preassembled complete grounding device according to claim 2, characterized in that: The grounding unit further comprises a grounding resistance reduction module, and the grounding resistance reduction module is connected to the four corners of the grounding grid through the connecting piece.

4. A preassembled complete grounding device according to claim 3, characterized in that: The grounding unit further comprises a resistance reducing cloth and / or a resistance reducing paste, which is arranged on the horizontal grounding body.

5. The preassembled complete grounding device according to claim 1, characterized in that: The connecting piece is made of non-metallic material or corrosion-resistant metal material, and consists of a junction box and a wedge-shaped anti-slip pressing plate.

6. A preassembled complete grounding device according to claim 1, characterized in that: It also includes the measurement of the impulse resistance of the grounding device, specifically: When the increase between the continuously measured grounding resistance values ​​is greater than the set threshold and the current grounding resistance is less than the set value, the impact resistance is measured; otherwise, when the current grounding resistance is greater than or equal to the set value, an alarm is issued.

7. A preassembled complete grounding device according to claim 6, characterized in that: Voltage pulse excitations of equal amplitude and phase are injected into all grounding down conductors, and the pulse amplitude and current of the loop formed by a single grounding down conductor are measured to obtain the impact resistance.

8. A design and selection method for a prefabricated complete set of grounding devices, characterized in that: The prefabricated complete grounding device comprises: a connector; a grounding unit, comprising at least four grounding down conductors, a grounding grid and at least four groups of vertical grounding electrodes; the grounding grid comprises at least four horizontal grounding bodies; one end of the grounding down conductor is respectively connected to the corresponding tower pole and the excitation source; the other end of the grounding down conductor is respectively connected to each horizontal grounding body through the connector, and each group of vertical grounding electrodes is connected to a horizontal grounding body and is located below the horizontal grounding body for discharge; when measuring the grounding resistance of the grounding device, the excitation source injects voltage excitation of the same phase and amplitude at all grounding down conductors to make the potential of each grounding down conductor equal to the connection point with the grounding grid; and the excitation of a single tower pole can only form a loop through its corresponding grounding down conductor, grounding grid, earth, remote tower pole, overhead ground wire, and its own tower pole, so as to measure the loop current and then obtain the grounding resistance of a single tower pole; the design and selection method of the prefabricated complete grounding device comprises the following steps: Obtain environmental parameters around the transmission line tower where the grounding device is to be installed; According to the preset grounding selection tool library and the environmental parameters, a standard solution with the highest similarity to the environment in the preset grounding selection tool library is matched; Constructing a simulation model corresponding to the standard solution, performing simulation calculation on the simulation model to evaluate the grounding performance of the standard solution under the current application environment, and adjusting the simulation model according to the evaluation result; The final prefabricated grounding device is determined based on the adjusted simulation model.

9. The design selection method according to claim 8, characterized in that: The environmental parameters include soil resistivity, soil corrosion level, soil pH value, soil temperature, soil water content, soil density and impurities contained in the soil.

10. The design selection method according to claim 8, characterized in that: The preset grounding selection tool library includes a set of standard grounding solutions, which are used to match the corresponding standard solutions according to the acquired environmental parameters; The standard scheme is simulated and calculated, including the calculation of grounding grid parameters such as grounding impedance, contact potential difference, step potential difference, mesh potential difference and ground surface potential distribution on the grounding grid; and the evaluation results of grounding performance are obtained based on the grounding grid parameters.

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