A kind of dirty self-adapting extra-high voltage transmission line low corona noise composite conductor and preparation method

Abstract

The application discloses a kind of dirty self-adaptive extra-high voltage transmission line low corona noise composite conductor and preparation method, belong to extra-high voltage transmission technical field.The composite conductor includes center steel core, gradient conductive buffer layer and corona-resistant self-cleaning composite coating from inside to outside in sequence, gradient conductive buffer layer is made of polymer matrix composite material doped with different concentration conductive filler, its conductivity is gradient reduced from inside to outside, and electric field homogenization is realized by gradient conductivity passive shunt mechanism;Corona-resistant self-cleaning composite coating is composed of fluorocarbon resin, nanometer titanium dioxide, nanometer silicon dioxide and corona-resistant additive, with super-hydrophobic self-cleaning, photocatalytic degradation and corona-resistant aging function.The application solves the technical problems that existing noise reduction conductor cannot dynamically adjust electric field distribution under self-adaptive dirty state, noise reduction fails under dirty weather and self-cleaning coating has poor durability, and can maintain excellent low corona noise performance under clean and dirty conditions.

Description

Technical Field

[0001] This invention relates to the field of ultra-high voltage power transmission technology, and in particular to a pollution-adaptive low corona noise composite conductor for ultra-high voltage power transmission lines and its preparation method. Background Technology

[0002] With the deepening implementation of my country's energy strategy, ultra-high voltage (UHV) transmission lines, as the backbone of long-distance, high-capacity power transmission, have experienced rapid development. By 2025, my country had built a UHV transmission network of ten vertical and ten horizontal lines, with a transmission mileage exceeding 50,000 kilometers, playing a crucial role in ensuring energy security and optimizing energy allocation. However, the corona audible noise generated during the operation of UHV transmission lines has become increasingly prominent, becoming one of the key factors restricting the construction and operation of UHV lines.

[0003] Audible corona noise refers to the noise emitted when the electric field strength on the surface of a conductor exceeds the breakdown field strength of air, causing air ionization and corona discharge. Ultra-high voltage (UHV) transmission lines have high voltage levels and large electric field strength on the conductor surface, making corona discharge more pronounced. The resulting audible noise not only affects the normal lives and health of residents near the lines but may also trigger environmental disputes and increase the difficulty and cost of line construction. The corona noise problem is particularly serious in industrialized and densely populated areas such as eastern and southern my country, and has become a major constraint on the environmental impact assessment and approval of UHV lines.

[0004] Surface contamination of power transmission lines is a significant cause of the sharp deterioration in audible corona noise. During actual operation, transmission lines inevitably become contaminated by pollutants such as industrial dust, vehicle exhaust, sea salt particles, and agricultural dust, forming a contamination layer on the conductor surface. The presence of this contamination layer leads to severe distortion of the electric field on the conductor surface, a sudden increase in local field strength, a significant enhancement in corona discharge intensity, and a substantial rise in audible noise levels. Studies have shown that under severely polluted conditions, the audible noise level of ultra-high voltage (UHV) transmission lines can be 10-15 dB(A) higher than under clean conditions, far exceeding the national environmental noise emission standards.

[0005] Currently, the main technical measures for reducing audible corona noise in ultra-high voltage (UHV) transmission lines include using expanded diameter conductors, split conductors, and soft aluminum conductors. Expanded diameter conductors reduce the surface electric field intensity by increasing the equivalent diameter of the conductor, thereby reducing corona discharge. Split conductors reduce the surface electric field by splitting a single-phase conductor into multiple sub-conductors and utilizing the electric field shielding effect between the sub-conductors. These technologies can achieve certain noise reduction effects under clean conditions, but their effectiveness decreases significantly under polluted conditions. This is because the electric field distribution of existing noise-reducing conductors is fixed in design and cannot be dynamically adjusted according to the pollution state of the conductor surface. When the conductor surface is polluted, the pollution layer changes the electric field distribution on the conductor surface, leading to a sudden increase in local field strength and a sharp deterioration in corona noise, which existing noise-reducing conductors cannot effectively cope with. The problem of high corona noise in high-voltage transmission lines under severe weather conditions can be addressed to some extent by cleaning and applying hydrophobic coatings. This reduces noise and environmental pollution and is applicable to various conductor types. There is some research on this topic; for example, CN110853844A discloses a method and apparatus for reducing audible corona noise in transmission lines. This method includes pre-treating the transmission conductor to remove dirt from its surface; spraying a hydrophilic coating onto the pre-treated conductor surface; and curing the hydrophilic coating. By pre-treating the transmission conductor to remove dirt, spraying a hydrophilic coating onto its surface, and then curing it, the coating thickness, appearance, and contact angle are assessed to determine if they meet requirements. If not, the coating is reapplied to form a water film, thereby reducing electric field distortion and noise. CN107961964A discloses a method for reducing audible corona noise in high-voltage transmission lines, comprising the following steps: S1. Cleaning the surface of the high-voltage transmission line; S2. Uniformly spraying a hydrophobic coating onto the surface of the high-voltage transmission line; By cleaning the surface of the high-voltage transmission line and uniformly spraying the hydrophobic coating, including grinding, cleaning with hydrophilic organic solvents, cleaning with pure water, and drying, the thickness and contact angle of the hydrophobic coating are ensured, reducing electric field distortion and noise, effectively reducing the accumulation of water droplets and dirt on the surface of the transmission line, thereby reducing the electric field distortion on the surface of the conductor, thereby increasing the corona initiation voltage of the high-voltage transmission line, and thus reducing the audible corona noise of the high-voltage transmission line under severe weather conditions. CN115725237B discloses a thermally conductive superhydrophobic coating, its preparation method, and its application. By combining silica with fluorosilane coupling agents and boron nitride powder with vinyl silicone oil and other materials, a thermally conductive superhydrophobic coating is prepared, solving the problems of poor coating adhesion and high cost on high-voltage transmission lines. It achieves efficient corona noise suppression and superhydrophobicity with a water roll-off angle of less than 10°. This thermally conductive superhydrophobic coating can be used to suppress corona noise in high-voltage cables.CN115505198A discloses a conductor coating material, a coated conductor, and a method for preparing the same. The modified cross-linked polyethylene (CXL) is prepared using raw materials A and B. Component A includes LLDPE, a cross-linking agent, rheology masterbatch, and a copper inhibitor. Component B includes LLDPE, a catalyst, rheology masterbatch, an antioxidant, an ultraviolet absorber, carbon black masterbatch, and PE color masterbatch. Through the synergistic effect of the components in components A and B of the modified CXL, and the addition of thermally conductive fillers, a dielectric barrier is formed to suppress corona discharge. Furthermore, the weather resistance of the material is improved through ultraviolet absorbers and antioxidants. This solves the problems of corona discharge and contamination in DC power transmission, significantly reducing corona loss and improving the electromagnetic environment, thus extending the service life of the conductor. However, the above solution still has several problems and is difficult to apply in practice.

[0006] In addition, some existing technologies have researched self-cleaning conductors, reducing contamination adhesion by spraying hydrophobic or photocatalytic coatings onto the conductor surface. However, these self-cleaning coatings can only reduce contamination accumulation to a certain extent and cannot completely prevent contamination formation. Moreover, they cannot eliminate the influence of contamination already adhering to the conductor surface on the electric field distribution. Therefore, when there is a certain amount of contamination on the conductor surface, the corona noise problem still exists. More importantly, the durability of existing self-cleaning coatings under ultra-high voltage environments is seriously problematic. Long-term corona discharge on the surface of ultra-high voltage conductors generates large amounts of ozone and nitrogen oxides (NOx). x These strong oxidizing substances will accelerate the oxidative degradation of the coating, causing the coating to powder, crack, and peel off after 1-2 years of operation, losing its self-cleaning function.

[0007] In summary, existing noise-reducing conductors cannot dynamically adjust the electric field distribution to adapt to pollution conditions, and are prone to noise reduction failure under polluted weather conditions; self-cleaning coatings have poor durability under ultra-high voltage environments and are prone to aging and failure. Therefore, there is an urgent need to develop a new type of ultra-high voltage transmission conductor that can adapt to pollution conditions, maintain low corona noise levels under both clean and polluted conditions, and has excellent durability. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a pollution-adaptive low corona noise composite conductor for ultra-high voltage transmission lines and its preparation method. This solves the technical problems of existing noise-reducing conductors being unable to dynamically adjust the electric field distribution in response to pollution conditions, noise reduction failure in polluted weather, and poor durability of self-cleaning coatings.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A pollution-adaptive ultra-high voltage transmission line low corona noise composite conductor includes a central steel core, a gradient conductive buffer layer, and a corona-resistant self-cleaning composite coating arranged sequentially from the inside out. The gradient conductive buffer layer covers the outer surface of the central steel core and has a gradient structure in which the conductivity gradually decreases from the inside to the outside, with a conductivity variation range of 10. 4 S / m~10 -6 S / m; The corona-resistant self-cleaning composite coating is applied to the outer surface of the gradient conductive buffer layer, with a thickness of 10-50 μm.

[0010] This design employs a gradient conductivity approach, utilizing the conductivity difference between the contaminant layer and the outer layer of the conductor to achieve natural current shunting and electric field homogenization. It requires no external drive or active control, ensuring extremely high reliability. When the conductor surface is clean, current primarily flows through the inner layer with higher conductivity, while the outer, lower-conductivity layer acts as insulation, resulting in a uniform electric field distribution and low corona noise on the conductor surface. When contaminants accumulate on the conductor surface, forming a high-resistivity contaminant layer, the resistivity of this layer is typically around 10⁻⁶. 6 -10 10 The conductivity is between Ω·m, which is much higher than that of the outer layer of the gradient conductive buffer layer (10). -6 -10 0 According to Ohm's law, current will choose the path of least resistance. In this case, the current is forced to transfer from the high-conductivity inner layer to the low-conductivity outer layer, and then flows into the contamination layer through the outer layer. Since the current is radially distributed in the gradient conductivity buffer layer, the current density in the outer layer decreases with increasing radius, and the electric field strength in the outer layer also decreases with increasing radius. Therefore, the electric field strength on the surface of the conductor is significantly reduced, thus suppressing corona discharge. The current is forced to transfer from the high-conductivity inner layer to the low-conductivity outer layer, naturally reducing the electric field strength on the outer surface, achieving a "passive adaptive" electric field homogenization effect.

[0011] Furthermore, the gradient conductive buffer layer is made of a polymer-based composite material doped with different concentrations of conductive filler, with the doping concentration of the conductive filler gradually decreasing from the inside to the outside, forming a conductivity gradient. The total thickness of the gradient conductive buffer layer is 0.5-3 mm, divided into 3-10 gradient layers, each with a thickness of 50-1000 μm, and the conductivity ratio between adjacent gradient layers is 10-100. This conductivity ratio range ensures effective current shunting and electric field equalization under different levels of contamination.

[0012] Furthermore, the outermost conductivity σ_outer of the gradient conductive buffer layer satisfies the relationship ρ_pollution, which is the typical resistivity of a heavily polluted layer: σ_outer × ρ_pollution ≥ 10. 3 At that time, the diversion effect was particularly significant.

[0013] Furthermore, the conductive filler is selected from one or more combinations of carbon nanotubes, graphene, carbon black, and carbon fibers. These conductive fillers possess excellent electrical and mechanical properties, achieving high conductivity at relatively low filler concentrations. Among them, carbon nanotubes and graphene have extremely high aspect ratios and specific surface areas, enabling them to form highly efficient conductive networks within the polymer matrix, making them ideal fillers for preparing gradient conductive buffer layers.

[0014] The polymer matrix is ​​selected from one or more combinations of polyethylene, polypropylene, polyvinyl chloride, epoxy resin, polyurethane, silicone rubber, and polyimide. These polymer materials have good weather resistance, corrosion resistance, and mechanical properties, making them suitable for long-term use in harsh outdoor environments. Polyethylene and polypropylene have excellent processing properties, making them suitable for preparing gradient conductive buffer layers using multilayer co-extrusion processes; epoxy resin and polyurethane have good adhesion and mechanical strength, making them suitable for preparing gradient conductive buffer layers using a layer-by-layer coating method; silicone rubber and polyimide have excellent high and low temperature resistance and corona resistance, making them suitable for use under extreme environmental conditions.

[0015] Furthermore, the corona-resistant self-cleaning composite coating is composed of the following components by mass percentage: 60-80% fluorocarbon resin, 5-20% nano-titanium dioxide, 5-15% nano-silica, 1-8% corona-resistant additive, and 1-5% coupling agent. This coating not only possesses superhydrophobic self-cleaning and photocatalytic degradation functions, but also exhibits excellent corona aging resistance, enabling long-term stable operation under ultra-high voltage environments. There is a significant synergistic effect between the gradient conductive buffer layer and the corona-resistant self-cleaning composite coating. First, the corona-resistant self-cleaning composite coating reduces the adhesion of contaminants, lowering the impact of contaminants on the electric field of the conductor surface. This allows the gradient conductive buffer layer to operate under lighter contamination conditions, further improving the electric field homogenization effect. Second, the gradient conductive buffer layer reduces the electric field strength on the conductor surface, reducing the intensity of corona discharge. This not only reduces corona noise but also reduces the amount of ozone and nitrogen oxides generated by corona discharge, thereby mitigating the erosion of the corona-resistant self-cleaning composite coating and extending its service life. Finally, the two combine to form a complete contamination adaptive system. The corona-resistant, self-cleaning composite coating reduces dirt accumulation; the gradient conductive buffer layer automatically adjusts the electric field distribution even in the presence of small amounts of dirt. Together, these two elements enable the composite conductor to maintain excellent low corona noise performance under various environmental conditions.

[0016] Further, the nano-titanium dioxide is nitrogen-doped anatase type with a particle size of 10-50 nm; the nano-silica is fumed silica with a particle size of 5-30 nm; the corona-resistant additive is selected from one or more combinations of nano-alumina, nano-zinc oxide, and mica powder; and the coupling agent is a silane coupling agent. Fluorocarbon resin provides excellent weather resistance, corrosion resistance, and hydrophobicity, serving as the matrix material for the coating. Nano-titanium dioxide exhibits photocatalytic activity under ultraviolet light irradiation, capable of decomposing organic pollutants adhering to the surface of the wire; preferably, the nano-titanium dioxide can be nitrogen-doped anatase type nano-titanium dioxide, which can extend its photoresponse range to the visible light region, significantly improving the photocatalytic efficiency under low light conditions. Nano-silica further improves the hydrophobicity and wear resistance of the coating, forming a micro-nano composite rough structure. Nano-silica particles form nanoscale protrusions on the coating surface, while micron-sized fluorocarbon resin particles form micron-sized protrusions; the combination of the two forms a micro-nano composite rough structure. This structure traps a large amount of air, creating an air cushion between water droplets and the coating surface, thus achieving a superhydrophobic effect. When rain falls on the coating surface, it forms spherical water droplets that roll off, carrying away surface contaminants. When nano-titanium dioxide is exposed to ultraviolet or visible light, it generates electron-hole pairs. Electrons react with oxygen in the air to generate superoxide anion radicals, while holes react with water molecules to generate hydroxyl radicals. These highly oxidizing radicals can decompose organic pollutants attached to the coating surface, converting them into carbon dioxide and water.

[0017] Corona-resistant additives can form a dense barrier layer on the coating surface, effectively blocking the erosion of the coating by ozone and nitrogen oxides generated by corona discharge, significantly improving the coating's resistance to corona aging. Coupling agents are used to improve the interfacial compatibility between nanofillers and the polymer matrix, improving the mechanical properties and durability of the coating. The corona aging resistance function is achieved by adding corona-resistant additives. Corona-resistant additives such as nano-alumina, nano-zinc oxide, and mica powder have high dielectric constants and corona resistance, and can form a dense barrier layer on the coating surface. When ozone and nitrogen oxides generated by corona discharge erode the coating, this barrier layer can effectively prevent their penetration, protecting the polymer matrix inside the coating from oxidative degradation. Simultaneously, these corona-resistant additives can also absorb the energy generated by corona discharge, converting it into heat energy and dissipating it, thereby reducing damage to the coating.

[0018] Furthermore, the thickness of the corona-resistant self-cleaning composite coating is 10-50 μm. This thickness range ensures sufficient self-cleaning function and durability without affecting the electrical performance of the conductor.

[0019] Furthermore, the central steel core is a high-strength galvanized steel core or an aluminum-clad steel core with a diameter of 5-20mm, providing the mechanical strength required for the conductor.

[0020] The present invention also provides a method for preparing the above-mentioned composite conductor, comprising the following steps: S1. Pretreatment of the central steel core: The central steel core is degreased, derusted and phosphated to remove surface oil and oxide layer, form a uniform phosphate film and improve the adhesion between the coating and the steel core.

[0021] S2. Preparation of gradient conductive buffer layer: A gradient conductive buffer layer is prepared on the outer surface of the central steel core by layer-by-layer coating or multilayer co-extrusion. The doping concentration of conductive filler in each layer is controlled to form a gradient structure with gradually decreasing conductivity from the inside to the outside.

[0022] S3. Preparation of corona-resistant self-cleaning composite coating: Fluorocarbon resin, nano titanium dioxide, nano silica, corona-resistant additive and coupling agent are mixed in proportion, an appropriate amount of solvent is added, and the mixture is stirred evenly to prepare a corona-resistant self-cleaning coating; then, the corona-resistant self-cleaning coating is sprayed onto the outer surface of the gradient conductive buffer layer by high-pressure airless spraying method, and after curing, a corona-resistant self-cleaning composite coating is formed.

[0023] S4. Post-processing: The prepared composite wires are heated and cured and surface-treated to remove surface burrs and defects, and the final product is obtained.

[0024] Further, in step S2, the layer-by-layer coating method specifically refers to: Prepare polymer composite material solutions with different concentrations of conductive filler; The composite materials were coated on the outer surface of the central steel core in descending order of conductive filler concentration. After each coat is applied, cure it at 60-120℃ for 0.5-2 hours before applying the next coat. After all layers are coated, cure at 120-180℃ for 2-6 hours to form a gradient conductive buffer layer.

[0025] Further, in step S2, the multilayer co-extrusion method specifically refers to: Multiple extruders were used to extrude polymer composite melts with different concentrations of conductive filler. The melt layers are simultaneously extruded through a multi-layer co-extrusion die head and coated onto the outer surface of the central steel core. After cooling and solidification, a conductive buffer layer with a gradient structure is formed; The temperature of the multilayer co-extrusion process is 150-250℃, and the extrusion speed is 5-20m / min.

[0026] Compared with the prior art, the present invention has the following significant advantages: 1. This invention employs a gradient conductivity design, utilizing the conductivity difference between the contamination layer and the outer layer of the conductor to achieve natural current shunting and electric field homogenization. No external drive or active control is required, resulting in extremely high reliability. Test results show that under contamination conditions, the maximum electric field intensity on the surface of the composite conductor of this invention only increases slightly, remaining between 18-20 kV / cm, with an electric field non-uniformity coefficient of less than 1.21, effectively suppressing electric field distortion caused by contamination.

[0027] 2. This invention can automatically adjust the electric field distribution according to the degree of contamination on the conductor surface, maintaining a low surface electric field strength under both clean and contaminated conditions, significantly reducing corona noise and radio interference. Under clean conditions, the audible noise level of the composite conductor of this invention is more than 13 dB(A) lower than that of ordinary steel-cored aluminum stranded wire; under artificially contaminated conditions, the audible noise only increases by 3.1-3.7 dB(A), far lower than the 13 dB(A) of existing technologies, meeting national environmental noise emission standards. This invention develops a novel corona-resistant self-cleaning composite coating, adding corona-resistant additives to the traditional self-cleaning coating, effectively blocking the erosion of the coating by ozone and nitrogen oxides generated by corona discharge, extending the service life by more than 50% compared to existing self-cleaning coatings.

[0028] 3. The gradient conductive buffer layer and the corona-resistant self-cleaning composite coating in this invention work synergistically. The corona-resistant self-cleaning composite coating reduces the adhesion of contaminants and minimizes their impact on the electric field of the conductor surface; while the gradient conductive buffer layer automatically adjusts the electric field distribution even with a small amount of contaminants, further reducing corona noise. The combination of these two elements enables the composite conductor to maintain excellent low corona noise performance under various environmental conditions. Furthermore, the manufacturing process of this invention is mature, requires no special equipment, and is easily industrialized. This invention effectively solves the corona problem of UHV conductors without increasing the conductor diameter or the number of splits, significantly reducing line construction costs and operation and maintenance expenses. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein. The reagents used herein may be commercially available related products, and performance testing standards refer to industry or national standards.

[0031] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0032] Example 1 This embodiment provides a pollution-adaptive, low-corona-noise composite conductor for ultra-high voltage transmission lines, the structure of which is as follows: Central steel core: High-strength galvanized steel core with a diameter of 12mm; Gradient conductive buffer layer: 5-layer structure with a total thickness of 1.5mm; First layer: Epoxy resin matrix doped with 15wt% multi-walled carbon nanotubes, with an electrical conductivity of 8×10⁻⁶. 3 S / m, thickness 300μm; second layer: epoxy resin matrix doped with 10wt% multi-walled carbon nanotubes, conductivity 5×10 2 The first layer has a conductivity of 20 S / m and a thickness of 300 μm; the second layer consists of an epoxy resin matrix doped with 5 wt% multi-walled carbon nanotubes, with a conductivity of 20 S / m and a thickness of 300 μm; the third layer consists of an epoxy resin matrix doped with 2 wt% multi-walled carbon nanotubes, with a conductivity of 1 × 10⁻⁶ S / m and a thickness of 300 μm. -1 S / m, thickness 300μm; fifth layer: epoxy resin matrix doped with 0.5wt% multi-walled carbon nanotubes, conductivity 5×10 -4 S / m, thickness is 300μm.

[0033] Corona-resistant self-cleaning composite coating: 25μm thick, composed of the following components by weight percentage: fluorocarbon resin FEVE 70%, nitrogen-doped anatase nano-titanium dioxide (20nm particle size) 15%, fumed silica nano-silica (15nm particle size) 10%, nano-alumina 3%, silane coupling agent KH-550 2%. Preparation method: (1) Pretreatment of the central steel core: The high-strength galvanized steel core with a diameter of 12mm is ultrasonically cleaned with acetone and anhydrous ethanol for 15 minutes to remove surface oil stains; then pickled with 10% hydrochloric acid solution for 10 minutes to remove the surface oxide layer; then rinsed with deionized water and dried at 80℃; finally, it is placed in phosphating solution for phosphating treatment for 15 minutes to form a uniform phosphating film, then rinsed with deionized water and dried at 100℃ for later use.

[0034] (2) Preparation of gradient conductive buffer layer: The gradient conductive buffer layer was prepared by a layer-by-layer coating method. The specific steps are as follows: Prepare epoxy resin composite solutions with five different carbon nanotube concentrations: Mix epoxy resin E-51, curing agent methyltetrahydrophthalic anhydride, and accelerator DMP-30 at a mass ratio of 100:80:1, and then add 15wt%, 10wt%, 5wt%, 2wt%, and 0.5wt% of multi-walled carbon nanotubes respectively. Add an appropriate amount of acetone as a solvent, stir at high speed for 30 minutes, and ultrasonically disperse for 1 hour to obtain a uniform composite solution. Coat each layer of composite material on the outer surface of the pretreated central steel core in order of carbon nanotube concentration from high to low. After each layer is coated, cure at 80℃ for 1 hour, and then coat the next layer. After all five layers are coated, cure at 150℃ for 4 hours to form a gradient conductive buffer layer with a thickness of 1.5 mm.

[0035] (3) Preparation of corona-resistant self-cleaning composite coating: The above-mentioned fluorocarbon resin FEVE, nitrogen-doped anatase nano titanium dioxide, fumed nano silica, nano alumina and silane coupling agent were mixed, and an appropriate amount of ethyl acetate was added as a solvent. The mixture was stirred at high speed for 30 minutes and ultrasonically dispersed for 1 hour to prepare a corona-resistant self-cleaning coating with a solid content of 40%. The corona-resistant self-cleaning coating was uniformly sprayed on the outer surface of the gradient conductive buffer layer by high pressure airless spraying method. The spraying pressure was 0.5 MPa and the spraying distance was 20 cm. After spraying, the coating was placed at room temperature for 30 minutes and then cured at 120℃ for 1 hour to form a corona-resistant self-cleaning composite coating with a thickness of 25 μm.

[0036] (4) Post-processing: The prepared composite wire is heated and cured at 120°C for 2 hours, and then the surface is trimmed to remove surface burrs and defects to obtain the final product.

[0037] Example 2 This embodiment provides a pollution-adaptive, low-corona-noise composite conductor for ultra-high voltage transmission lines, the structure of which is as follows: Central steel core: Aluminum-clad steel core with a diameter of 15mm; Gradient conductive buffer layer: 7-layer structure, with a total thickness of 2mm; First layer: Polyurethane matrix doped with 12wt% graphene, with an electrical conductivity of 6×10⁻⁶. 3 The first layer has a conductivity of S / m and a thickness of 286μm; the second layer is a polyurethane matrix doped with 8wt% graphene, with a conductivity of 3×10⁻⁶. 2 The first layer has a conductivity of 80 S / m and a thickness of 286 μm; the second layer has a conductivity of 80 S / m and a thickness of 286 μm; the third layer has a conductivity of 20 S / m and a thickness of 286 μm; the fourth layer has a conductivity of 20 S / m and a thickness of 286 μm; the fifth layer has a conductivity of 1.5 wt% graphene doped with a polyurethane matrix and a conductivity of 3 × 10⁻⁶ S / m and a thickness of 286 μm. 0 S / m, thickness 286μm; sixth layer: polyurethane matrix doped with 0.8wt% graphene, conductivity 5×10 -1 S / m, thickness 286μm; seventh layer: polyurethane matrix doped with 0.2wt% graphene, conductivity 2×10 -4 S / m, thickness is 286μm.

[0038] Corona-resistant self-cleaning composite coating: 30μm thick, composed of the following components by weight percentage: fluorocarbon resin FEVE 75%, nitrogen-doped anatase nano-titanium dioxide (30nm particle size) 12%, fumed silica nano-silica (10nm particle size) 8%, nano-zinc oxide 3%, silane coupling agent KH-560 2%. Preparation method: (1) Pretreatment of the central steel core: same as in Example 1.

[0039] (2) Preparation of gradient conductive buffer layer: The gradient conductive buffer layer was prepared by multi-layer co-extrusion method. The specific steps are as follows: Seven single-screw extruders were used to extrude polyurethane composite melts with different graphene concentrations. The extrusion temperature was 160-180℃. The melts of each layer were extruded simultaneously through the seven-layer co-extrusion die head and uniformly coated on the outer surface of the pretreated central steel core. After cooling and solidification in a water-cooling tank, a conductive buffer layer with a gradient structure with a thickness of 2mm was formed. The extrusion speed was 8m / min.

[0040] (3) Preparation of corona-resistant self-cleaning composite coating: Except for the particle size of raw materials and the proportion of components, the rest are the same as in Example 1.

[0041] (4) Post-processing: Same as in Example 1.

[0042] Example 3 This embodiment provides a pollution-adaptive, low-corona-noise composite conductor for ultra-high voltage transmission lines, the structure of which is as follows: Central steel core: High-strength galvanized steel core with a diameter of 10mm; Gradient conductive buffer layer: 3-layer structure, with a total thickness of 1mm; First layer: Silicone rubber matrix doped with 25wt% carbon black, with an electrical conductivity of 3×10⁻⁶. 3 S / m, thickness is 333μm; second layer: silicone rubber matrix doped with 15wt% carbon black, conductivity is 2×10 1 S / m, thickness 333μm; third layer: silicone rubber matrix doped with 5wt% carbon black, conductivity 1×10 -3 S / m, thickness is 333μm.

[0043] Corona-resistant self-cleaning composite coating: 20μm thick, composed of the following components by weight percentage: fluorocarbon resin FEVE 65%, nitrogen-doped anatase nano-titanium dioxide (15nm particle size) 20%, fumed silica nano-silica (20nm particle size) 10%, mica powder 3%, silane coupling agent KH-570 2%. Preparation method: (1) Pretreatment of the central steel core: same as in Example 1.

[0044] (2) Preparation of gradient conductive buffer layer: The gradient conductive buffer layer was prepared by a layer-by-layer coating method. The specific steps are as follows: Prepare three silicone rubber composite solutions with different carbon black concentrations: Mix methyl vinyl silicone rubber and vulcanizing agent benzoyl peroxide at a mass ratio of 100:2, and then add 25wt%, 15wt%, and 5wt% carbon black respectively. Add an appropriate amount of n-hexane as a solvent, stir at high speed for 30 minutes, and ultrasonically disperse for 1 hour to obtain a uniform composite solution; Coat each layer of composite material on the outer surface of the pretreated central steel core in order of carbon black concentration from high to low; After each layer is coated, cure at 60℃ for 2 hours, and then coat the next layer; After all three layers are coated, cure at 120℃ for 6 hours to form a gradient conductive buffer layer with a thickness of 1 mm.

[0045] (3) Preparation of corona-resistant self-cleaning composite coating: Except for the particle size of raw materials and the proportion of components, the rest are the same as in Example 1.

[0046] (4) Post-processing: Same as in Example 1.

[0047] Example 4 This embodiment provides a pollution-adaptive, low-corona-noise composite conductor for ultra-high voltage transmission lines, the structure of which is as follows: Central steel core: High-strength galvanized steel core with a diameter of 12mm; Gradient conductive buffer layer: 3-layer structure with a total thickness of 0.5mm; First layer: Polyethylene matrix doped with 8wt% carbon nanotubes, with an electrical conductivity of 1×10⁻⁶. 4 S / m, thickness 200μm; second layer: polyethylene matrix doped with 3wt% carbon nanotubes, conductivity 1×10 2S / m, thickness 150μm; third layer: polyethylene matrix doped with 0.5wt% multi-walled carbon nanotubes, conductivity 1×10 -6 S / m, thickness is 150μm.

[0048] Corona-resistant self-cleaning composite coating: 30μm thick, composed of the following components by weight percentage: fluorocarbon resin FEVE 72%, nitrogen-doped anatase nano-titanium dioxide (25nm particle size) 10%, fumed silica nano-silica (12nm particle size) 12%, nano-alumina 4%, silane coupling agent KH-550 2%. Preparation method: (1) Pretreatment of the central steel core: same as in Example 1.

[0049] (2) Preparation of gradient conductive buffer layer: The gradient conductive buffer layer was prepared by multi-layer co-extrusion method. The specific steps are as follows: Three single-screw extruders were used to extrude polyethylene composite melts with different carbon nanotube concentrations. The extrusion temperature was 180-200℃. The melts of each layer were extruded simultaneously through the three-layer co-extrusion die head and uniformly coated on the outer surface of the pretreated central steel core. After cooling and solidification in a water-cooling tank, a conductive buffer layer with a gradient structure with a thickness of 0.5mm was formed. The extrusion speed was 10m / min.

[0050] (3) Preparation of corona-resistant self-cleaning composite coating: Except for the particle size of raw materials and the proportion of components, the rest are the same as in Example 1.

[0051] (4) Post-processing: Same as in Example 1.

[0052] Example 5 This embodiment provides a pollution-adaptive, low-corona-noise composite conductor for ultra-high voltage transmission lines, the structure of which is as follows: Central steel core: Aluminum-clad steel core with a diameter of 15mm; Gradient conductive buffer layer: 5-layer structure with a total thickness of 0.8mm; First layer: Polypropylene matrix doped with 10wt% graphene, with an electrical conductivity of 1×10⁻⁶. 4 The first layer has a conductivity of S / m and a thickness of 150μm; the second layer is a polypropylene matrix doped with 5wt% graphene, with a conductivity of 1×10⁻⁶. 3 The first layer has a conductivity of S / m and a thickness of 150μm; the second layer is a polypropylene matrix doped with 2wt% graphene, with a conductivity of 1×10⁻⁶. 1 The fourth layer consists of a polypropylene matrix doped with 0.8 wt% graphene, with an electrical conductivity of 1 × 10⁻⁶ S / m and a thickness of 150 μm. -1 The fifth layer consists of a polypropylene matrix doped with 0.2 wt% graphene, with an electrical conductivity of 1 × 10⁻⁶ S / m and a thickness of 150 μm. -6S / m, thickness 200μm. Corona-resistant self-cleaning composite coating: thickness 40μm, composed of the following components by mass percentage: fluorocarbon resin FEVE 68%, nitrogen-doped anatase nano titanium dioxide (particle size 18nm) 13%, fumed silica nano (particle size 16nm) 11%, nano zinc oxide 5%, silane coupling agent KH-560 3%. Preparation method: (1) Pretreatment of the central steel core: same as in Example 1.

[0053] (2) Preparation of gradient conductive buffer layer: The gradient conductive buffer layer was prepared by multi-layer co-extrusion method. The specific steps are as follows: Five single-screw extruders were used to extrude polypropylene composite melts with different graphene concentrations. The extrusion temperature was 200-220℃. The melts of each layer were extruded simultaneously through the five co-extrusion die heads and uniformly coated on the outer surface of the pretreated central steel core. After cooling and solidification in a water cooling tank, a conductive buffer layer with a gradient structure with a thickness of 0.8mm was formed. The extrusion speed was 8m / min.

[0054] (3) Preparation of corona-resistant self-cleaning composite coating: Except for the particle size of raw materials and the proportion of components, the rest are the same as in Example 1.

[0055] (4) Post-processing: Same as in Example 1.

[0056] Comparative Example 1 This comparative example uses ordinary steel-cored aluminum stranded wire, model LGJ-400 / 35, which consists of a central steel core and an outer layer of aluminum stranded wire, without a gradient conductive buffer layer and a corona-resistant self-cleaning composite coating.

[0057] Comparative Example 2 This comparative example is an existing expanded diameter conductor, model LGKK-600, which consists of a central steel core, a support layer, and an outer aluminum stranded wire, without a gradient conductive buffer layer and a corona-resistant self-cleaning composite coating.

[0058] Comparative Example 3 This comparative example is a steel-cored aluminum stranded wire, model LGJ-400 / 35, coated with a common self-cleaning coating. The outer surface of the ordinary steel-cored aluminum stranded wire is coated with a common self-cleaning coating with a thickness of 25 μm. The common self-cleaning coating consists of the following components by weight percentage: 75% fluorocarbon resin, 15% common anatase nano-titanium dioxide, 8% fumed silica, 2% silane coupling agent KH-550, and contains no corona-resistant additives.

[0059] Comparative Example 4 This comparative example is a composite wire containing only a gradient conductive buffer layer. Its structure is basically the same as that of Example 1, except that it does not have a corona-resistant self-cleaning composite coating.

[0060] The wire samples prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to comprehensive performance tests, including corona audible noise test, surface electric field distribution test, corona initiation voltage test, self-cleaning performance test, corona aging resistance test, and mechanical performance test.

[0061] Audible corona noise was tested in a corona cage at a voltage of 1000kV (phase voltage of an ultra-high voltage AC line). Audible noise levels were measured under both clean and artificially polluted conditions. The artificial pollutant was prepared using the solid-layer method, with a pollutant concentration of 0.1 mg / cm³. 2 (Equivalent salt density) and 0.5 mg / cm 2 (Dense gray) simulates typical pollution conditions in an eastern industrial region. Audible noise was measured using an A-weighted sound level meter, with the measurement point 1m from the conductor surface. Test results are shown in Table 1.

[0062] Table 1. Audible corona noise levels of conductors under different conditions (dB (A))

[0063] As shown in Table 1, under clean conditions, the audible noise levels of the composite conductors in Examples 1-5 are significantly lower than those in the comparative examples, indicating that the composite conductors of the present invention have excellent low corona noise performance under clean conditions. Under artificially polluted conditions, the audible noise levels of Comparative Examples 1 and 2 increase significantly, reaching 68.9 dB(A) and 61.5 dB(A) respectively, far exceeding the national environmental noise emission standards.

[0064] Comparative Example 4 (containing only the gradient conductive buffer layer) had an audible noise level of 44.6 dB(A) under clean conditions and 49.8 dB(A) under dirty conditions, representing a noise increase of 5.2 dB(A). Although this was a significant improvement over Comparative Examples 1-3, it was not as good as the Example. This indicates a synergistic effect between the gradient conductive buffer layer and the corona-resistant self-cleaning composite coating. The corona-resistant self-cleaning composite coating can reduce dirt adhesion and further reduce corona noise under dirty conditions.

[0065] A combination of finite element analysis software and electric field sensors was used to measure the electric field distribution on the surface of the conductor, and to calculate the maximum electric field strength and the electric field non-uniformity coefficient. The test conditions were the same as those for corona audible noise testing. The test results are shown in Table 2.

[0066] Table 2. Maximum surface electric field strength (kV / cm) and electric field non-uniformity coefficient of conductors under different conditions

[0067] As shown in Table 2, under clean conditions, the maximum surface electric field intensity of the composite conductors in Examples 1-5 is significantly lower than that in Comparative Examples 1-3, and the electric field non-uniformity coefficient is also smaller, indicating a more uniform electric field distribution. This is because the presence of the gradient conductive buffer layer allows the current to be mainly transmitted through the inner layer with higher conductivity, resulting in a uniform electric field distribution on the conductor surface and thus reducing the intensity of corona discharge.

[0068] Under artificial contamination conditions, the maximum surface electric field intensity of Comparative Examples 1-3 increased significantly, and the electric field non-uniformity coefficient also increased significantly, indicating that the electric field was severely distorted. In contrast, the maximum surface electric field intensity of the composite conductors in Examples 1-5 only increased slightly, and the electric field non-uniformity coefficient was also smaller, indicating that the gradient conductive buffer layer can effectively suppress the electric field distortion caused by contamination, automatically adjust the electric field distribution, and make the electric field return to uniformity.

[0069] The maximum electric field strength on the surface of Comparative Example 4 was 17.8 kV / cm under clean conditions and 20.6 kV / cm under dirty conditions, with an electric field non-uniformity coefficient of 1.28. Although this was a significant improvement over Comparative Examples 1-3, it was not as good as Examples 1-5. This further demonstrates the synergistic effect between the gradient conductive buffer layer and the corona-resistant self-cleaning composite coating.

[0070] Corona initiation voltage tests were performed on wire samples in an artificial climate chamber. Test conditions: temperature 25℃, relative humidity 80%, and contamination level 0.1 mg / cm³. 2 (Equivalent salt density). The corona initiation voltage was measured using ultraviolet imaging. The voltage at which the ultraviolet imager detects the first corona discharge point is the corona initiation voltage. The test results are shown in Table 3.

[0071] Table 3. Test results of corona initiation voltage of conductors (kV)

[0072] As can be seen from Table 3, the corona initiation voltage of the composite wires in Examples 1-5 is significantly higher than that in Comparative Examples 1-4. This indicates that the composite wires of the present invention can effectively suppress the occurrence of corona discharge and significantly improve the corona initiation voltage.

[0073] The self-cleaning performance test consisted of two parts: superhydrophobic performance testing and photocatalytic performance testing. Superhydrophobic performance testing: The water contact angle and roll-off angle of the coating were measured using a contact angle meter. Measurements were taken at five different locations for each sample, and the average value was recorded. Photocatalytic performance testing: The photocatalytic performance of the coating was evaluated through a photocatalytic degradation experiment of methylene blue. The wire samples were immersed in a 10 mg / L methylene blue solution and subjected to degradation experiments under both ultraviolet and visible light irradiation. After 24 hours, the absorbance of the solution was measured, and the degradation rate of methylene blue was calculated. The test results are shown in Table 4.

[0074] Table 4 Performance test results of self-cleaning coating

[0075] As shown in Table 4, the water contact angle of the corona-resistant self-cleaning composite coatings in Examples 1-5 is greater than 150° and the roll-off angle is less than 10°, exhibiting excellent superhydrophobic properties. This allows rainwater to form droplets on the surface of the conductor and roll off, carrying away surface dirt and effectively reducing dirt accumulation. Regarding photocatalytic performance, the coatings in the examples achieved a degradation rate of over 90% for methylene blue under ultraviolet light irradiation within 24 hours and over 85% under visible light irradiation. In contrast, the ordinary self-cleaning coating in Comparative Example 3 achieved a degradation rate of 88.6% under ultraviolet light irradiation, comparable to the examples, but its degradation rate under visible light irradiation was only 65.3%, far lower than the examples. This is because the present invention uses nitrogen-doped anatase nano-titanium dioxide as a photocatalyst, which extends its photoresponse range to the visible light region, significantly improving the photocatalytic efficiency under low light conditions.

[0076] The wire samples underwent a combined salt spray-UV-corona discharge aging test, with a total aging time of 1000 hours. Aging conditions: salt spray concentration 5%, temperature 35℃; UV light intensity 0.89W / m. 2 @340nm, temperature 60℃; corona voltage 1000kV, current 1mA. The water contact angle, corona initiation voltage, and coating adhesion of the coating were measured before and after aging. The test results are shown in Table 5.

[0077] Table 5 Results of Corona Aging Resistance Test

[0078] As shown in Table 5, after 1000 hours of combined aging test, the water contact angle of the corona-resistant self-cleaning composite coatings in Examples 1-5 remained above 125°, and the coating adhesion remained above 3.5 MPa. In contrast, the water contact angle of the ordinary self-cleaning coating in Comparative Example 3 dropped to 98°, losing its superhydrophobic properties; the corona initiation voltage decreased by 19.2%, and the coating adhesion was only 1.2 MPa, showing obvious powdering and peeling phenomena.

[0079] This demonstrates that the corona-resistant self-cleaning composite coating of the present invention exhibits excellent corona aging resistance and can operate stably for a long time under ultra-high voltage conditions. This is mainly attributed to the corona-resistant additives added to the coating, which can form a dense barrier layer on the coating surface, effectively blocking the erosion of the coating by ozone and nitrogen oxides generated by corona discharge.

[0080] The tensile strength, elongation, and fatigue resistance of the conductor were tested. Tensile strength and elongation were tested according to GB / T 1179-2017 "Round Wire Concentric Stranded Overhead Conductors"; fatigue resistance was tested according to GB / T 2317.3-2008 "Test Methods for Electrical Fittings Part 3: Thermal Cycling Test" at a frequency of 10 Hz and a stress ratio of 0.1. The number of cycles at conductor breakage was recorded. The test results are shown in Table 6.

[0081] Table 6. Test results of mechanical properties of the conductors

[0082] As shown in Table 6, the tensile strength and elongation of the composite conductors in Examples 1-5 are comparable to those in Comparative Examples 1-4, meeting the mechanical performance requirements of UHV transmission lines. Meanwhile, the fatigue resistance of the composite conductors in Examples 1-5 is significantly higher than that in Comparative Examples 1-3. This is because the gradient conductive buffer layer acts as a buffer and damping layer, improving the fatigue resistance and operational reliability of the conductors.

[0083] The above provides a detailed description of a pollution-adaptive low-corona noise composite conductor for UHV transmission lines and its preparation method. This solution solves the technical problems of existing noise-reducing conductors, such as the inability to dynamically adjust the electric field distribution in response to pollution conditions, noise reduction failure in polluted weather, and poor durability of self-cleaning coatings. In this invention, there is a significant synergistic effect between the gradient conductive buffer layer and the corona-resistant self-cleaning composite coating. The combination of these two elements enables the composite conductor to maintain excellent low-corona noise performance under both clean and polluted conditions, meeting national environmental noise emission standards. The composite conductor of this invention has a simple structure and mature manufacturing process, showing promising engineering application prospects. Using the composite conductor of this invention can significantly reduce corona noise and radio interference in UHV transmission lines, improve the reliability and safety of line operation, and has significant engineering application value and significant economic and environmental benefits.

[0084] The preferred embodiments of the present invention have been described in detail above, and are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pollution-adaptive low-corona noise composite conductor for ultra-high voltage transmission lines, characterized in that, It includes a central steel core, a gradient conductive buffer layer, and a corona-resistant self-cleaning composite coating arranged sequentially from the inside out; The gradient conductive buffer layer covers the outer surface of the central steel core and has a gradient structure in which the conductivity gradually decreases from the inside to the outside, with a conductivity variation range of 10. 4 S / m~10 -6 S / m; The corona-resistant self-cleaning composite coating is applied to the outer surface of the gradient conductive buffer layer, with a thickness of 10-50 μm.

2. The low corona noise composite conductor for ultra-high voltage transmission lines according to claim 1, characterized in that, The gradient conductive buffer layer is made of polymer-based composite material doped with different concentrations of conductive filler. The doping concentration of the conductive filler gradually decreases from the inside to the outside, forming a conductivity gradient. The total thickness of the gradient conductive buffer layer is 0.5-3 mm, divided into 3-10 gradient layers, each with a thickness of 50-1000 μm, and the conductivity ratio between adjacent gradient layers is 10-100.

3. The low corona noise composite conductor for ultra-high voltage transmission lines according to claim 2, characterized in that, The outermost conductivity σ_outer of the gradient conductive buffer layer satisfies the relationship between the resistivity ρ_pollution of a typical heavily polluted layer: σ_outer × ρ_pollution ≥ 10 3 .

4. The low corona noise composite conductor for ultra-high voltage transmission lines according to claim 2, characterized in that, The conductive filler is selected from one or more combinations of carbon nanotubes, graphene, carbon black, and carbon fibers; the polymer matrix is ​​selected from one or more combinations of polyethylene, polypropylene, polyvinyl chloride, epoxy resin, polyurethane, silicone rubber, and polyimide.

5. The low corona noise composite conductor for ultra-high voltage transmission lines according to claim 1, characterized in that, The corona-resistant self-cleaning composite coating is composed of the following components by weight percentage: 60-80% fluorocarbon resin, 5-20% nano titanium dioxide, 5-15% nano silicon dioxide, 1-8% corona-resistant additive, and 1-5% coupling agent.

6. The low corona noise composite conductor for ultra-high voltage transmission lines according to claim 5, characterized in that, The nano-titanium dioxide is nitrogen-doped anatase with a particle size of 10-50 nm; the nano-silica is fumed silica with a particle size of 5-30 nm; the corona-resistant additive is selected from one or more combinations of nano-alumina, nano-zinc oxide, and mica powder; and the coupling agent is a silane coupling agent.

7. The low corona noise composite conductor for ultra-high voltage transmission lines according to claim 1, characterized in that, The central steel core is a high-strength galvanized steel core or an aluminum-clad steel core, with a diameter of 5-20mm.

8. A method for preparing a pollution-adaptive low-corona noise composite conductor for ultra-high voltage transmission lines as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Pretreatment of the central steel core: The central steel core is degreased, derusted and phosphated to remove surface oil and oxide layer and form a uniform phosphate film. S2. Preparation of gradient conductive buffer layer: A gradient conductive buffer layer is prepared on the outer surface of the central steel core by layer-by-layer coating or multilayer co-extrusion. The doping concentration of conductive filler in each layer is controlled to form a gradient structure with gradually decreasing conductivity from the inside to the outside. S3. Preparation of corona-resistant self-cleaning composite coating: Fluorocarbon resin, nano titanium dioxide, nano silica, corona-resistant additive and coupling agent are mixed in proportion, an appropriate amount of solvent is added, and the mixture is stirred evenly to prepare a corona-resistant self-cleaning coating; then, the corona-resistant self-cleaning coating is sprayed onto the outer surface of the gradient conductive buffer layer by high-pressure airless spraying method, and after curing, a corona-resistant self-cleaning composite coating is formed. S4. Post-processing: The prepared composite wires are heated and cured and surface treated to obtain the final product.

9. The preparation method according to claim 8, characterized in that, In step S2, the layer-by-layer coating method specifically refers to: Prepare polymer composite material solutions with different concentrations of conductive filler; The composite materials were coated on the outer surface of the central steel core in descending order of conductive filler concentration. After each coat is applied, cure it at 60-120℃ for 0.5-2 hours before applying the next coat. After all layers are coated, cure at 120-180℃ for 2-6 hours to form a gradient conductive buffer layer.

10. The preparation method according to claim 8, characterized in that, In step S2, the multilayer co-extrusion method specifically refers to: Multiple extruders were used to extrude polymer composite melts with different concentrations of conductive filler. The melt layers are simultaneously extruded through a multi-layer co-extrusion die head and coated onto the outer surface of the central steel core. After cooling and solidification, a conductive buffer layer with a gradient structure is formed; The temperature of the multilayer co-extrusion process is 150-250℃, and the extrusion speed is 5-20m / min.

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