Method for evaluating the effectiveness of lightning protection structures of multilayer insulating-conductive composites

Abstract

The application discloses a method for evaluating the performance of a lightning protection structure of a multilayer insulating-conducting composite material, which comprises the following steps: S1, establishing a three-dimensional electric field analysis finite element model of the multilayer composite material structure; S2, setting different lightning attachment key criteria to determine the lightning attachment state; S3, simulating the gradual approaching process of lightning leaders to extract the electric field intensity evolution data of each key position; S4, determining the sequence of the occurrence of the upgoing leaders at each position of the whole material-protection structure, determining the sequence of the occurrence of the lightning strikes, and determining the final lightning attachment path of the whole material-protection structure; and S5, comparing the electric field intensity of the key positions in the area under the conditions of having the protection structure and not having the protection structure to evaluate the protection performance of the protection structure. The method for evaluating the performance of the lightning protection structure of the multilayer insulating-conducting composite material can realize the prediction of the lightning attachment positions and the breakdown paths under the conditions of not having the protection and having the protection by establishing a multilayer dielectric field response model and quantifying the attachment criteria.

Description

Technical Field

[0001] This invention belongs to the field of lightning protection technology, specifically relating to a method for evaluating the effectiveness of lightning protection structures made of multilayer insulating-conductive composite materials. Background Technology

[0002] Composite materials with functions such as wave absorption and wave transmission are used as shell structures for equipment such as missiles and aircraft. They usually exist in the form of multi-layered lay-up or sandwich structures. The surface insulation structure, honeycomb (or foam core filler), and the underlying metal components together form a complex laminated system. Traditional lightning strike damage analysis is mostly based on the "surface adhesion" assumption, which believes that the lightning strike starts from the material surface and the lightning current diffuses along the surface and then propagates inward.

[0003] However, for complex laminated structures containing multiple material layers and interfaces, the lightning strike process often exhibits the characteristics of "dielectric breakdown-attachment": the lightning leader preferentially develops along the path with the largest electric field gradient and the lowest dielectric impedance. Due to the micro-geometric features such as sharp corners and thin walls, the core dielectric layer causes local electric field enhancement, forming an electric field enrichment region, which becomes an "electric field amplifier". This leads to the lightning penetrating the surface layer and developing along the interior of the sandwich layer and attaching to the bottom metal.

[0004] In the existing technology, there is a lack of quantitative evaluation methods for the "breakdown first, then adhesion" characteristics of such complex structures, making it difficult to accurately determine the protection range and effectiveness of protective structures (diverter bars, embedded lightning arresters). Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating the effectiveness of lightning protection structures made of multilayer insulating-conductive composite materials. By establishing a multilayer dielectric electric field response model and quantifying adhesion criteria, the method enables the prediction of lightning adhesion locations and breakdown paths under different conditions of no protection and protection.

[0006] The technical solution adopted in this invention is: a method for evaluating the effectiveness of lightning protection structures made of multilayer insulating-conductive composite materials, the specific method of which is as follows: S1. Establish a three-dimensional electric field analysis finite element model of a multilayer composite material structure including a protective structure, a surface insulating dielectric layer, a sandwich dielectric layer, and a metal backing plate; S2. Set different key criteria for lightning attachment to determine the lightning attachment status; S3. Simulate the gradual approach process of the lightning leader and extract the electric field intensity evolution data at each key location; S4. Based on the order in which the upward leader appears at each location of the entire material-protection structure, determine the order in which the lightning strike occurs, and determine the final lightning attachment path of the entire material-protection structure. S5. Compare the electric field intensity at key locations in the region under different conditions with and without a protective structure to evaluate the protective effectiveness of the protective structure.

[0007] The invention is further characterized by: The specific method for S1 is as follows: The finite element model for the three-dimensional electric field analysis of the multilayer composite material structure is established using the finite element method. In the case of a protective structure, the finite element model for the three-dimensional electric field analysis of the multilayer composite material structure also includes a shunt strip or an embedded lightning rod. The simulation parameters for each layer of material are set, such as conductivity, dielectric constant, insulation strength, and corona initiation threshold of the metal material; a rod electrode simulating a lightning leader is set above the three-dimensional electric field analysis finite element model of the multilayer composite material structure. The initial distance between the rod electrode and the surface of the protective structure is 1m, and an equivalent voltage excitation is applied to the electrode.

[0008] The key criteria for different lightning attachments defined in S2 include the following aspects: Upward leader initiation criterion, surface flashover or air breakdown criterion, surface insulation dielectric breakdown criterion, and protective structure lightning protection criterion; By setting different key criteria for lightning attachment, the lightning attachment status is determined.

[0009] In the upward leader initiation criterion, under the influence of the rod electrode and its surrounding environment, a position will appear on the metal component where the surface electric field intensity reaches the corona initiation threshold of the metal material. This indicates that the position has the potential to generate an upward leader, and this is used as the basis for determining the leader initiation order, as follows: For metal backplates, the criteria are as follows: (1); in, The surface electric field strength of the metal backing plate; For protective structures, the criteria are as follows: (2); in, The surface electric field strength refers to the electric field strength of the lightning protection structure on the surface of a multilayer composite material.

[0010] The criteria for determining surface flashover or air breakdown specifically include the following aspects: Surface flashover criterion for sandwich dielectric layers: Tangential electric field strength on the surface of the sandwich dielectric layer. Greater than the tangential flashover threshold of the sandwich dielectric layer surface ,Right now: (3); Then, surface flashover occurs within the sandwich layer; Air breakdown criterion: Electric field strength of the air gap between the lower surface of the surface insulation material and the metal backing plate. Greater than the breakdown electric field strength of air ,Right now: (4); This indicates the formation of a penetrating discharge channel; in, The value is 3kV / mm.

[0011] The specific criteria for determining the breakdown of the surface insulating dielectric are as follows: If the normal electric field strength inside the surface insulation material Insulation strength greater than or equal to that of the surface insulation material ,Right now: (5); If the maximum normal electric field strength is located, the surface insulation dielectric breakdown is determined to have occurred at that location.

[0012] The specific criteria for determining lightning protection structure are as follows: When the lightning protection structure is a surface shunt bar or an embedded lightning rod, the structure is deemed to be effectively lightning-blocking if the following conditions are met: First, the surface halo criterion must be met: the surface electric field strength of the lightning protection structure on the surface of the multilayer composite material. Greater than or equal to the corona induction threshold of metallic materials Furthermore, the surface electric field strength of the lightning protection structure covered with multi-layer composite materials The surface electric field strength is greater than that of the metal backing plate. ,Right now: (6); (7); Secondly, the leader maintenance condition must be met: the average electric field strength in the air domain above the surface of the protective structure. Greater than or equal to the field strength required to sustain along the leader evolution path : (8); Furthermore, it does not meet the criteria for surface flashover or air breakdown, or the criteria for breakdown of surface insulating dielectric. If so, the protective structure is deemed to have effectively blocked the lightning strike.

[0013] The specific method for S3 is as follows: Using parametric scanning, the distance between the rod electrode and the surface of the lightning protection structure is gradually reduced, with the step size adjustable from 100mm to 10mm, to simulate the downward development process of the lightning leader. The electric field intensity curves at key locations such as the surface insulating dielectric layer, the core layer, the metal back plate, and the protection structure are extracted as a function of the electrode position, and the critical distance at which each criterion is first met is recorded.

[0014] In S5, when evaluating the protective effectiveness of a protective structure, for structures equipped with shunt strips or embedded lightning arresters, the evolution of electric field intensity at key locations on the surface of the protective structure and in unprotected areas is compared during the electrode's downward movement: If the surface of the protective structure always preferentially meets the lightning strike criterion, and the electric field of the surface insulating medium within the area of ​​the composite material surface that is expected to be protected from direct lightning strikes defined by the protective structure is always lower than the insulation strength, then the protection is deemed effective. If, at a certain critical distance, the electric field of the surface insulating medium within the protection range exceeds the insulation strength, the protection is deemed to have failed. The spacing of the protective structures corresponding to this critical distance is the maximum effective protection spacing. By repeatedly simulating the changes in the spacing of the protective structure, the critical spacing at which the protection fails can be obtained.

[0015] The beneficial effects of this invention are: (1) The lightning protection structure effectiveness evaluation method of the multilayer insulating-conductive composite material of the present invention breaks through the limitations of the traditional "surface adhesion" assumption and proposes a quantitative evaluation method oriented towards the "dielectric breakdown-adhesion" mechanism, which is applicable to lightning protection analysis of complex structures such as honeycomb and foam interlayer; (2) The lightning protection structure of the multilayer insulating-conductive composite material of the present invention establishes a multilayer criterion system including upward leader initiation, surface flashover or air breakdown, dielectric breakdown and lightning protection, which has clear physical meaning and is easy to apply in engineering. (3) The method for evaluating the effectiveness of lightning protection structure of multilayer insulating-conductive composite material of the present invention realizes the quantitative prediction of the protection range of the protection structure, obtains the effective spacing of the protection structure through simulation, reduces the cost of trial and error, provides a basis for lightning protection design such as shunt bar layout and lightning arrester burial location, and the method is highly versatile and can be extended to various multilayer composite material structures. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method for evaluating the effectiveness of the lightning protection structure of the multilayer insulating-conductive composite material of the present invention; Figure 2 This is a schematic diagram of the three-dimensional electric field analysis finite element model of the multilayer insulating-conductive composite material structure of the present invention; Figure 3 This is a schematic diagram of the diversion strip protection structure and protection range model in the evaluation method of this invention; Figure 4 This is an example graph showing the variation of electric field strength of each layer with electrode position under unprotected conditions in the evaluation method of this invention; Figure 5 This is a simulated electric field distribution diagram of the shunt strip protection structure in the performance evaluation method of this invention; Figure 6This is a schematic diagram of the embedded lightning arrester protection structure in the performance evaluation method of the present invention; Figure 7 This is a simulated electric field distribution diagram of the embedded lightning arrester protection structure in the performance evaluation method of this invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] The present invention provides a method for evaluating the effectiveness of lightning protection structures made of multilayer insulating-conductive composite materials, such as... Figure 1 As shown, the specific method is as follows: S1. Establish a three-dimensional finite element model for electric field analysis of a multilayer composite material structure including a protective structure, a surface insulating dielectric layer, a sandwich dielectric layer, and a metal backing plate; the specific method is as follows: The finite element model for the three-dimensional electric field analysis of the multilayer composite material structure is established using the finite element method. In the case of a protective structure, the finite element model for the three-dimensional electric field analysis of the multilayer composite material structure also includes a shunt strip or an embedded lightning rod. The simulation parameters for each layer of material are set, such as conductivity, dielectric constant, insulation strength, and corona initiation threshold of the metallic material. A rod electrode simulating a lightning leader is placed above the three-dimensional electric field analysis finite element model of the multilayer composite material structure. The initial distance between the rod electrode and the surface of the protective structure is 1m. An equivalent voltage excitation (e.g., 550kV) is applied to the electrode. The three-dimensional electric field analysis finite element model of the multilayer composite material structure is as follows: Figure 2 As shown.

[0019] The initial distance between the aforementioned rod electrode and the surface of the protective structure is 1m, which is specifically set according to the attachment point test requirements in SAE ARP 5416B-2025 Aircraft Lightning Test Methods.

[0020] The key physical quantities involved in this invention, their typical values, and sources are shown in Table 1.

[0021] Table 1. Symbols and Explanations of Key Physical Quantities

[0022] Among them, the tangential flashover threshold of the sandwich dielectric layer surface is shown in Table 1. Because the sandwich wall of honeycomb and other sandwich structures contains a solid medium, its surface flashover field strength is usually lower than that of uniform air breakdown field strength. In engineering, 1 / 2 to 1 / 3 of the air breakdown field strength is often taken as the surface flashover threshold.

[0023] S2. Determine key criteria for lightning attachment: Set different key criteria for lightning attachment to determine the lightning attachment status; The specific aspects of setting different key criteria for lightning attachment include the following: Upward leader initiation criterion, surface flashover or air breakdown criterion, surface insulation dielectric breakdown criterion, and protective structure lightning protection criterion; By setting different key criteria for lightning attachment, the lightning attachment status is determined.

[0024] In the upward leader initiation criterion, under the influence of the rod electrode and its surrounding environment, a position will appear on the metal component (such as an aluminum plate or shunt bar) where the surface electric field intensity reaches the corona initiation threshold of the metal material. This indicates that the position has the potential to generate an upward leader, and this is used as the basis for determining the leader initiation order, as follows: For metal backplates, the criteria are as follows: (1); in, The surface electric field strength of the metal backing plate; For protective structures, the criteria are as follows: (2); in, The surface electric field strength refers to the electric field strength of lightning protection structures on multi-layer composite materials, such as shunt strips or embedded lightning arresters. The criteria for determining surface flashover or air breakdown specifically include the following aspects: Surface flashover criterion for sandwich dielectric layers (such as honeycomb sandwich layers): Tangential electric field strength on the surface of the sandwich dielectric layer. Greater than the tangential flashover threshold of the sandwich dielectric layer surface ,Right now: (3); Then, surface flashover occurs within the sandwich layer; Air breakdown criterion: Electric field strength of the air gap between the lower surface of the surface insulation material and the metal backing plate. Greater than the breakdown electric field strength of air ,Right now: (4); This indicates the formation of a penetrating discharge channel; in, The value is 3kV / mm.

[0025] The specific criteria for determining the breakdown of the surface insulating dielectric are as follows: If the normal electric field strength inside the surface insulating material (such as fiberglass) Insulation strength greater than or equal to that of the surface insulation material ,Right now: (5); If the maximum normal electric field strength is located, the surface insulation dielectric breakdown is determined to have occurred at that location.

[0026] The specific criteria for determining lightning protection structure are as follows: When the lightning protection structure is a surface shunt bar or an embedded lightning rod, the structure is deemed to be effectively lightning-blocking if the following conditions are met: First, the surface halo criterion must be met: the surface electric field strength of the lightning protection structure on the surface of the multilayer composite material. Greater than or equal to the corona induction threshold of metallic materials Furthermore, the surface electric field strength of the lightning protection structure covered with multi-layer composite materials The surface electric field strength is greater than that of the metal backing plate. ,Right now: (6); (7); Secondly, the leader maintenance condition must be met: the average electric field strength in the air domain above the surface of the protective structure. Greater than or equal to the field strength required to sustain along the leader evolution path : (8); Furthermore, it does not meet the criteria for surface flashover or air breakdown, or the criteria for breakdown of surface insulating dielectric. If so, the protective structure is deemed to have effectively blocked the lightning strike.

[0027] S3. Simulate the gradual approach process of the lightning leader and extract the electric field intensity evolution data at each key location; The specific method is as follows: Establish a simulation model containing flow dividers, such as Figure 3 As shown, parametric scanning is used to gradually reduce the distance between the rod electrode and the surface of the lightning protection structure, with the step size adjustable from 100mm to 10mm, to simulate the downward development process of the lightning leader; the electric field intensity curves at each key location, such as the surface insulating dielectric layer, the core layer, the metal back plate, and the protection structure, are extracted as a function of the electrode position, and the critical distance at which each criterion is first met is recorded.

[0028] Typical curves are as follows Figure 4 As shown, Figure 4 The key points A, B, and C are marked, corresponding to the critical distances for corona initiation of the metal backplate (aluminum alloy), flashover of the sandwich dielectric (honeycomb), and breakdown of the insulating dielectric (glass fiber), respectively.

[0029] S4. Determine the lightning attachment location of the entire material-protection structure: Based on the order in which the upward leader appears at each location of the entire material-protection structure (i.e., the order in which the threshold is met), determine the order in which the lightning strike occurs, and determine the final lightning attachment path of the entire material-protection structure. For example, if the surface electric field strength of the metal backplate first reaches the corona initiation threshold of the metal material, then the sandwich dielectric layer satisfies the surface flashover condition, and finally the surface insulating dielectric breaks down, then the lightning attachment path is determined to be: the upward leader starts from the metal backplate → develops along the honeycomb → breaks down the surface layer → finally attaches to the backplate. Figure 4 The key points are marked in order; S5. Compare the electric field intensity at key locations in the region under different conditions with and without a protective structure to evaluate the protective effectiveness of the protective structure.

[0030] When evaluating the protective effectiveness of a protective structure, for structures equipped with shunt strips or embedded lightning arresters, the evolution of electric field intensity at key locations on the surface of the protective structure and in unprotected areas during electrode descent is compared: If the surface of the protective structure always preferentially meets the lightning strike criterion, and the electric field of the surface insulating medium within its protection range is always lower than the insulation strength, then the protection is deemed effective; where the protection range refers to the area of ​​the composite material surface that is expected to be protected from direct lightning strikes, defined by the protective structure (such as between two parallel shunt strips, or a specified radius area centered on the embedded lightning arrester).

[0031] If, at a certain critical distance, the electric field of the surface insulating medium within the protection range exceeds the insulation strength, the protection is deemed to have failed. The spacing of the protective structures corresponding to this critical distance is the maximum effective protection spacing. By repeatedly simulating the changes in the spacing of the protective structure (such as the spacing of the diverter strips or the location of the lightning arrester), the critical spacing at which the protection fails can be obtained.

[0032] Example 1 This example is a lightning adhesion assessment of an unprotected insulating surface-sandwich dielectric-metal backing three-layer composite structure: A three-layer structure model was established according to the parameters in Table 2, consisting of insulating material (glass fiber, 5.5 mm thick in this embodiment), sandwich dielectric material (honeycomb, 19 mm thick), and metal backing plate (aluminum, 0.5 mm thick in this embodiment). A voltage of 550 kV was applied to the rod electrode, and the rod electrode gradually moved towards the protective structure to simulate the downward process of the leader tip. The simulation results are as follows: When the electrode distance is 351 mm, the electric field on the upper surface of the metal backing exceeds the corona induction threshold of the metal material (8.9 kV / mm). When the electrode distance is 391 mm, the honeycomb sandwich layer reaches the surface flashover condition (air surface flashover field strength 1 × 10⁻⁶). 6 V / m); When the electrode distance is 123mm, the normal electric field intensity inside the surface glass fiber is... Exceeding its insulation strength (10kV / mm); Based on this, the lightning attachment path was determined to be: the leader starts from the metal backplate → develops along the honeycomb sandwich wall → breaks through the fiberglass insulation layer → attaches to the metal backplate; subsequent experimental verification was consistent with the simulation results.

[0033] Table 2 Material parameters for each layer in this embodiment

[0034] Example 2 Parallel flow dividers (8mm wide, made of aluminum) were placed on the surface of the laminate, with spacing of 470mm and 600mm respectively. The simulation results are as follows. Figure 5 As shown in the figure: When the spacing is 470mm, the surface of the shunt bar preferentially meets the lightning protection conditions (field strength > corona initiation threshold of metal material and leader maintenance conditions) during the downward movement of the electrode. The electric field of the fiberglass layer within the protection range is always lower than the insulation strength of the fiberglass, and the protection is effective.

[0035] When the spacing is 600mm, the electric field of the fiberglass layer exceeds the insulation strength after the electrode moves downward to a certain distance, and the protection fails.

[0036] Experimental verification: When the spacing was 470mm, all 12 discharges adhered to the shunt strip; when the spacing was 600mm, the composite board broke down, which is consistent with the simulation results.

[0037] Example 3 Evaluation of the protective effectiveness of embedded lightning arresters: A metal lightning arrester (a φ20mm cylinder at the top and an M8 screw at the bottom) is embedded in the center of the laminate. The simulation model is as follows: Figure 6 As shown; simulation results are as follows Figure 7 As shown in the figure, the simulation results show that within a 1m range of the electrode downwards, the electric field on the surface of the lightning arrester preferentially satisfies the surface corona initiation criterion (or lightning arrest criterion), and the electric field above it satisfies the leader maintenance condition, while the electric field of the metal back plate is almost zero and is always far below the corona initiation threshold of the metal material. The lightning arrester can effectively protect the entire plate.

[0038] Test verification: After 10 discharges of each polarity, the electric arcs adhered to the pre-embedded lightning arrester.

[0039] Example 4 The present invention provides a method for evaluating the effectiveness of lightning protection structures made of multilayer insulating-conductive composite materials, such as... Figure 1 As shown, the specific method is as follows: S1. Establish a three-dimensional finite element model for electric field analysis of a multilayer composite material structure including a protective structure, a surface insulating dielectric layer, a sandwich dielectric layer, and a metal backing plate; the specific method is as follows: The finite element model for the three-dimensional electric field analysis of the multilayer composite material structure is established using the finite element method. In the case of a protective structure, the finite element model for the three-dimensional electric field analysis of the multilayer composite material structure also includes a shunt strip or an embedded lightning rod. The simulation parameters for each layer of material are set, such as conductivity, dielectric constant, insulation strength, and corona initiation threshold of the metallic material. A rod electrode simulating a lightning leader is placed above the three-dimensional electric field analysis finite element model of the multilayer composite material structure. The initial distance between the rod electrode and the surface of the protective structure is 1m. An equivalent voltage excitation (e.g., 550kV) is applied to the electrode. The three-dimensional electric field analysis finite element model of the multilayer composite material structure is as follows: Figure 2 As shown.

[0040] S2. Determine key criteria for lightning attachment: Set different key criteria for lightning attachment to determine the lightning attachment status; S3. Simulate the gradual approach process of the lightning leader and extract the electric field intensity evolution data at each key location; S4. Determine the lightning attachment location of the entire material-protection structure: Based on the order in which the upward leader appears at each location of the entire material-protection structure (i.e., the order in which the threshold is met), determine the order in which the lightning strike occurs, and determine the final lightning attachment path of the entire material-protection structure. S5. Compare the electric field intensity at key locations in the region under different conditions with and without a protective structure to evaluate the protective effectiveness of the protective structure.

[0041] Example 5 Based on Example 4, this embodiment sets different key criteria for lightning attachment in S2, specifically including the following aspects: Upward leader initiation criterion, surface flashover or air breakdown criterion, surface insulation dielectric breakdown criterion, and protective structure lightning protection criterion; By setting different key criteria for lightning attachment, the lightning attachment status is determined.

[0042] In the upward leader initiation criterion, the surface electric field intensity at any location of a metal component (such as an aluminum plate or shunt bar) reaches the corona initiation threshold of the metal material under the influence of the rod electrode and its surrounding environment. At this point, the position possesses the potential for an upward leader to occur, and it serves as the basis for determining the leader initiation sequence, as detailed below: For metal backplates, the criteria are as follows: (1); in, The surface electric field strength of the metal backing plate; For protective structures, the criteria are as follows: (2); in, The surface electric field strength refers to the electric field strength of a lightning protection structure on a multilayer composite material surface, such as a shunt bar or a lightning rod.

[0043] The criteria for determining surface flashover or air breakdown specifically include the following aspects: Surface flashover criterion for sandwich dielectric layers (such as honeycomb sandwich layers): Tangential electric field strength on the surface of the sandwich dielectric layer. Greater than the tangential flashover threshold of the sandwich dielectric layer surface ,Right now: (3); Then, surface flashover occurs within the sandwich layer; Air breakdown criterion: Electric field strength of the air gap between the lower surface of the surface insulation material and the metal backing plate. Greater than the breakdown electric field strength of air ,Right now: (4); This indicates the formation of a penetrating discharge channel; in, The value is 3kV / mm.

[0044] The specific criteria for determining the breakdown of the surface insulating dielectric are as follows: If the normal electric field strength inside the surface insulating material (such as fiberglass) Insulation strength greater than or equal to that of the surface insulation material ,Right now: (5); If the maximum normal electric field strength is located, the surface insulation dielectric breakdown is determined to have occurred at that location.

[0045] The specific criteria for determining lightning protection structure are as follows: When the lightning protection structure is a surface shunt bar or an embedded lightning rod, the structure is deemed to be effectively lightning-blocking if the following conditions are met: First, the surface halo criterion must be met: the surface electric field strength of the lightning protection structure on the surface of the multilayer composite material. Greater than or equal to the corona induction threshold of metallic materials Furthermore, the surface electric field strength of the lightning protection structure covered with multi-layer composite materials The surface electric field strength is greater than that of the metal backing plate. ,Right now: (6); (7); Secondly, the leader maintenance condition must be met: the average electric field strength in the air domain above the surface of the protective structure. Greater than or equal to the field strength required to sustain along the leader evolution path : (8); Furthermore, it does not meet the criteria for surface flashover or air breakdown, or the criteria for breakdown of surface insulating dielectric. If so, the protective structure is deemed to have effectively blocked the lightning strike.

[0046] Example 6 Based on Example 5, the specific method of S3 in this embodiment is as follows: Establish a simulation model containing flow dividers, such as Figure 3 As shown, parametric scanning is used to gradually reduce the distance between the rod electrode and the surface of the lightning protection structure, with the step size adjustable from 100mm to 10mm, to simulate the downward development process of the lightning leader; the electric field intensity curves at each key location, such as the surface insulating dielectric layer, the core layer, the metal back plate, and the protection structure, are extracted as a function of the electrode position, and the critical distance at which each criterion is first met is recorded.

[0047] Example 7 Based on Example 6, this embodiment evaluates the protective effectiveness of the protective structure by comparing the evolution of electric field intensity at key locations on the surface of the protective structure and in the unprotected area during the electrode's downward movement, for structures equipped with shunt strips or embedded lightning arresters. If the surface of the protective structure always preferentially meets the lightning strike criterion, and the electric field of the surface insulating medium within the area of ​​the composite material surface that is expected to be protected from direct lightning strikes defined by the protective structure is always lower than the insulation strength, then the protection is deemed effective. If, at a certain critical distance, the electric field of the surface insulating medium within the protection range exceeds the insulation strength, the protection is deemed to have failed. The spacing of the protective structures corresponding to this critical distance is the maximum effective protection spacing. By repeatedly simulating the changes in the spacing of the protective structure (such as the spacing of the diverter strips or the location of the lightning arrester), the critical spacing at which the protection fails can be obtained.

Claims

1. A method for evaluating the effectiveness of lightning protection structures made of multilayer insulating-conductive composite materials, characterized in that, The specific method is as follows: S1. Establish a three-dimensional electric field analysis finite element model of a multilayer composite material structure including a protective structure, a surface insulating dielectric layer, a sandwich dielectric layer, and a metal backing plate; S2. Set different key criteria for lightning attachment to determine the lightning attachment status; S3. Simulate the gradual approach process of the lightning leader and extract the electric field intensity evolution data at each key location; S4. Based on the order in which the upward leader appears at each location of the entire material-protection structure, determine the order in which the lightning strike occurs, and determine the final lightning attachment path of the entire material-protection structure. S5. Compare the electric field intensity at key locations in the region under different conditions with and without a protective structure, and evaluate the protective effectiveness of the protective structure. The specific aspects of setting different key criteria for lightning attachment in S2 include the following: Upward leader initiation criterion, surface flashover or air breakdown criterion, surface insulation dielectric breakdown criterion, and protective structure lightning protection criterion; By setting different key criteria for lightning attachment, the lightning attachment status is determined. In the upward leader initiation criterion, under the influence of the rod electrode and its surrounding environment, a position will appear on the metal component where the surface electric field intensity reaches the corona initiation threshold of the metal material. Therefore, this position is used as the basis for determining the leading order, as follows: For metal backplates, the criteria are as follows: （1）； in, The surface electric field strength of the metal backing plate; For protective structures, the criteria are as follows: （2）； in, The surface electric field strength refers to the electric field strength of the lightning protection structure on the surface of a multilayer composite material. The criteria for surface flashover or air breakdown specifically include the following aspects: Surface flashover criterion for sandwich dielectric layers: tangential electric field strength on the surface of the sandwich dielectric layer. Greater than the tangential flashover threshold of the sandwich dielectric layer surface ,Right now: （3）； Then, surface flashover occurs within the sandwich layer; Air breakdown criterion: Electric field strength of the air gap between the lower surface of the surface insulation material and the metal backing plate. Greater than the breakdown electric field strength of air ,Right now: （4）； This indicates the formation of a penetrating discharge channel; in, The value is set to 3kV / mm; The specific criteria for determining the breakdown of the surface insulating dielectric are as follows: If the normal electric field strength inside the surface insulation material Insulation strength greater than or equal to that of the surface insulation material ,Right now: （5）； Then it is determined that the surface insulation dielectric breakdown occurs at the location of the maximum normal electric field strength; The specific lightning protection criteria for the protective structure are as follows: When the lightning protection structure is a surface shunt bar or an embedded lightning rod, the structure is deemed to be effectively lightning-blocking if the following conditions are met: First, the surface halo criterion must be met: the surface electric field strength of the lightning protection structure on the surface of the multilayer composite material. Greater than or equal to the halo threshold of metallic materials Furthermore, the surface electric field strength of the lightning protection structure covered with multi-layer composite materials The surface electric field strength is greater than that of the metal backing plate. ,Right now: （6）； （7）； Secondly, the leader maintenance condition must be met: the average electric field strength in the air domain above the surface of the protective structure. Greater than or equal to the field strength required to sustain along the leader evolution path : （8）； Furthermore, it does not meet the criteria for surface flashover or air breakdown, or the criteria for breakdown of surface insulating dielectric. If so, the protective structure is deemed to have effectively blocked the lightning strike.

2. The method for evaluating the effectiveness of the lightning protection structure of the multilayer insulating-conductive composite material according to claim 1, characterized in that, The specific method of S1 is as follows: The three-dimensional electric field analysis finite element model of the multilayer composite material structure is established using the finite element method; in the case of a protective structure, the three-dimensional electric field analysis finite element model of the multilayer composite material structure also includes a shunt strip or an embedded lightning arrester. The simulation parameters for each layer of material are set, such as conductivity, dielectric constant, insulation strength, and corona initiation threshold of the metal material; a rod electrode simulating a lightning leader is set above the three-dimensional electric field analysis finite element model of the multilayer composite material structure. The initial distance between the rod electrode and the surface of the protective structure is 1m, and an equivalent voltage excitation is applied to the electrode.

3. The method for evaluating the effectiveness of the lightning protection structure of the multilayer insulating-conductive composite material according to claim 1, characterized in that, The specific method of S3 is as follows: Using parametric scanning, the distance between the rod electrode and the surface of the lightning protection structure is gradually reduced, with the step size adjustable from 100mm to 10mm, to simulate the downward development process of the lightning leader. The electric field intensity curves at key locations of the surface insulating dielectric layer, the core layer, the metal back plate, and the protection structure are extracted as a function of the electrode position, and the critical distance at which each criterion is first met is recorded.

4. The method for evaluating the effectiveness of the lightning protection structure of the multilayer insulating-conductive composite material according to claim 3, characterized in that, In S5, when evaluating the protective effectiveness of the protective structure, for structures equipped with shunt strips or embedded lightning arresters, the evolution of electric field intensity at key locations on the surface of the protective structure and in the unprotected area is compared during the electrode's downward movement: If the surface of the protective structure always preferentially meets the lightning strike criterion, and the electric field of the surface insulating medium within the area of ​​the composite material surface that is expected to be protected from direct lightning strikes defined by the protective structure is always lower than the insulation strength, then the protection is deemed effective. If, at a certain critical distance, the electric field of the surface insulating medium within the protection range exceeds the insulation strength, the protection is deemed to have failed. The spacing of the protective structures corresponding to this critical distance is the maximum effective protection spacing. By repeatedly simulating the changes in the spacing of the protective structure, the critical spacing at which the protection fails can be obtained.

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