Anti-torsion cross-linked polyethylene insulated cable

Abstract

The invention relates to the technical field of cables, and discloses an anti-torsion cross-linked polyethylene insulated cable, which is suitable for cable logistics storage, mobile emergency equipment and other scenes with intermittent winding and standing circulation. The problems of residual stress generated by crosslinking rigidity of crosslinked polyethylene in an intermittent scene and aging and crack propagation caused by coupling of the residual stress and the environment cannot be solved. The stress slow-release layer with the gradient porous structure is arranged outside the conductor, residual stress is released through modulus transition and chemical bonding, and interface bonding is strengthened; the XLPE insulating layer is modified by EVA to reduce rigidity and is reinforced by nano silicon dioxide; the self-repairing layer containing the directional microcapsules and the carbon nanotubes is arranged outside the insulating layer, accurate crack repairing and aging resistance are achieved, insulating cracks, conductor wire breakage and shielding failure in intermittent winding and standing circulation can be reduced, and the use reliability of the cable in a target scene is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, in particular to a torsion-resistant cross-linked polyethylene insulated cable. Background Art

[0002] Cross-linked polyethylene (XLPE) insulated cable is a power cable with cross-linked polyethylene as the insulation layer. Due to the cross-linked three-dimensional mesh structure, it brings good temperature resistance, insulation strength and mechanical properties. It is widely used in medium and high voltage power transmission, industrial control and new energy fields. Torsion resistance is the core indicator of XLPE cable in dynamic working conditions. When the cable is subjected to torsional force, it is prone to problems such as insulation cracks, loose conductor strands and broken wires, or shielding layer failure. The industry now basically improves torsional resistance through material modification and structural optimization.

[0003] In practical applications, scenarios such as wind turbine tower yaw, industrial roller rotation, and cable logistics warehousing all place high demands on the torsional resistance of XLPE cables. Winding is the core working condition, and the cable needs to be stored and laid as the equipment or reel rotates. Existing technologies are mostly designed for continuous winding scenarios. For example, announcement number CN119381072B discloses a torsion-resistant cable for 35kV wind turbines. In order to solve the technical problems of insulation cracking and conductor breakage when the cable rotates with the wind turbine, the invention creatively adds toughening material to the insulation layer, twists the conductors in the same direction and embeds them in the Kevlar braid layer. The structural failure risk of the cable during use is addressed through structural and material improvements.

[0004] However, in scenarios such as cable logistics storage and mobile emergency equipment, there are intermittent winding and static cycle conditions. During winding, XLPE cables cannot release plastic micro-deformations due to cross-linking rigidity, resulting in residual stress in the cable. During the static period, the residual stress coupled with the ambient temperature and humidity accelerates cable aging. For example, temperature fluctuations will aggravate the breakage of cross-linking bonds, and moisture will induce stress-induced water treeing. The new stress is superimposed on the old residual stress during the next winding, resulting in the accumulation and expansion of cracks. The existing anti-torsion technology for continuous winding cannot handle the static residual stress and coupled aging problems, resulting in a shortened service life of XLPE cables during intermittent winding and static cycles. This technological gap needs to be filled. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art. The present invention provides a torsion-resistant cross-linked polyethylene insulated cable.

[0006] In order to achieve the above-mentioned objectives, the present application adopts the following technical solutions: a torsion-resistant cross-linked polyethylene insulated cable, which comprises, from the inside to the outside, a conductor layer, a stress relief layer, an insulating layer, a self-repairing layer, a shielding layer and an outer sheath; the stress relief layer is a gradient porous composite structure, comprising an inner porous layer and an outer dense layer distributed along the radial direction of the cable, nano hollow glass microbeads are dispersed in the inner porous section, and nano calcium carbonate is dispersed in the outer dense section. The substrate of the stress relief layer is silane-modified butyl rubber, which can undergo a condensation reaction with the insulating layer to form a covalent bond; the self-repairing layer is provided with microcapsules distributed at a 45° angle along the cable axis, the microcapsules are a coupling structure of a core material and a wall material, the core material is a silane coupling agent, the wall material is a urea-formaldehyde resin, and the core material can undergo a ring-opening reaction with the insulating layer; the self-repairing layer is also provided with a three-dimensional thermal conductive network formed by single-walled carbon nanotubes.

[0007] Preferably, the stress relief layer is composed of materials including, by weight, 75-85 parts of silane-modified butyl rubber, 5-7 parts of nano hollow glass microspheres, 10-14 parts of nano calcium carbonate, 2-3 parts of silane coupling agent KH-550 and 0.5-0.7 parts of antioxidant 1010.

[0008] Preferably, the insulating layer is composed of 85-90 parts by weight of cross-linked polyethylene resin, 10-14 parts of ethylene vinyl acetate, 0.8-1.0 parts of dicumyl peroxide, 0.6-0.8 parts of trimethylolpropane trimethacrylate and 2-2.5 parts of nano-silicon dioxide, and the content of vinyl acetate in ethylene vinyl acetate is 16%-20%.

[0009] Preferably, the constituent materials of the self-healing layer include, by weight, 70-75 parts of epoxy-modified acrylate, 20-25 parts of oriented microcapsules, 0.8-1.0 parts of single-walled carbon nanotubes, 0.5-0.7 parts of antioxidant 168 and 2.5-3.0 parts of carbon black, the epoxy value of the epoxy-modified acrylate is 0.45-0.55eq / 100g, and the particle size of the carbon black is 18-22nm.

[0010] Preferably, the components of the shielding layer include, by weight, 92-95 parts of semi-conductive polyethylene, 3-4 parts of chopped carbon fibers, 2-2.5 parts of maleic anhydride grafted polyethylene, and 0.4-0.6 parts of antioxidant 1010. The volume resistivity of the semi-conductive polyethylene is 45-55Ω·cm, the length of the chopped carbon fibers is 0.15-0.25mm, and the grafting rate of the maleic anhydride grafted polyethylene is 1.0%-1.4%.

[0011] Preferably, the conductor layer includes a central elastic reinforcing core and a copper monofilament layer twisted on the outside of the central elastic reinforcing core. The copper monofilament layer is radially arranged with an inner layer of copper monofilaments and an outer layer of copper monofilaments. The inner layer of copper monofilaments is wrapped around the central elastic reinforcing core in a right-handed bundle twisting manner, and the outer layer of copper monofilaments is wrapped around the inner layer of copper monofilaments in a left-handed double twisting manner.

[0012] Preferably, the central elastic reinforcement core is made of modified nylon, which contains 4%-6% by mass of POE elastomer; the inner copper monofilament and the outer copper monofilament are both Class 5 soft copper, the diameter of the copper monofilament is 0.35-0.45mm, the bundle-twisted pitch-to-diameter ratio of the inner copper monofilament is 16-18 times, and the re-twisted pitch-to-diameter ratio of the outer copper monofilament is 12-14 times.

[0013] Preferably, the elastic modulus of the inner porous layer of the stress relief layer is 10-14 MPa, the elastic modulus of the outer dense layer is 50-54 MPa, and the elastic modulus of the insulating layer is 550-610 MPa. The stress relief layer forms an elastic modulus gradient transition from the conductor layer to the insulating layer through the inner porous layer and the outer dense layer.

[0014] Preferably, the constituent materials of the outer protective layer include, by weight, 80-84 parts of polyvinyl chloride resin, 10-14 parts of dioctyl phthalate, 3.5-4.0 parts of calcium zinc stabilizer, 0.3-0.5 parts of antioxidant 1010 and 1.5-2.0 parts of carbon black, the mass fraction of calcium element in the calcium zinc stabilizer is 18%-22%, the mass fraction of zinc element is 4%-6%, and the particle size of carbon black is 28-32nm.

[0015] Preferably, the polar groups on the ethylene-vinyl acetate molecular chains in the insulating layer form intermolecular forces with the cross-linked polyethylene molecular chains, weakening the rigidity of the cross-linked network. Surface-modified inorganic nanoparticles are also dispersed in the insulating layer. The inorganic nanoparticles supplement the structural strength of the insulating layer through interfacial bonding with the cross-linked polyethylene molecular chains.

[0016] The technical effects and advantages of the present invention are as follows: In the present invention, the torsion resistance is improved by the synergistic cooperation between the stress relief layer and the XLPE insulation layer. The stress relief layer uses a gradient porous structure to achieve a smooth transition in the modulus between the conductor and the insulation layer, reducing interfacial stress concentration. At the same time, the interlayer bonding is enhanced through silane chemical bonding to avoid peeling during static operation. The insulation layer weakens the XLPE cross-linking rigidity through hydrogen bonds, improving the micro-deformation ability of the insulation layer and absorbing the winding torsional stress. During the intermittent winding and static cycle, the accumulation of residual stress in the insulation layer is reduced, the probability of insulation crack initiation is reduced, and the integrity of the cable insulation structure is guaranteed. The cable is adapted to the repeated winding requirements in scenarios such as cable logistics warehousing and mobile emergency equipment.

[0017] In the present invention, the synergy of crack repair and anti-aging is achieved through the composite design of oriented microcapsules and carbon nanotube networks. The oriented microcapsules are arranged according to the expansion path of the cable torsional cracks, and can accurately release the repair agent when the cracks appear, reacting with XLPE to achieve crack closure; the carbon nanotubes transfer the friction heat of winding to assist the microcapsules in completing the repair in a low-temperature environment, and at the same time cooperate with carbon black to delay the oxidation aging of XLPE, so that the cracks generated in the intermittent winding of the cable can be repaired, the problem of low-temperature repair failure is alleviated, the impact of insulation aging on performance is reduced, and the service life of the cable in intermittent winding and static cycle scenarios is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The disclosure of the present invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. In the drawings, the same reference numerals are used to refer to the same components: Figure 1 The overall structure of the cable provided by the present invention is schematically shown Figure 1 ; Figure 2 The overall structure of the cable provided by the present invention is schematically shown Figure 2 ; Figure 3 The present invention provides Figure 2 A schematic diagram of the enlarged structure of the cable at point A in the middle; Figure 4 A schematic diagram of the layered structure of the cable end provided by the present invention; Figure 5 This is a schematic diagram of the internal structure after the shielding layer and the outer protective layer are cut apart provided by the present invention.

[0019] Legend: 1. Conductor layer; 11. Central elastic reinforcing core; 12. Inner copper monofilament; 13. Outer copper monofilament; 2. Stress relief layer; 21. Inner porous layer; 22. Outer dense layer; 3. Insulation layer; 4. Self-healing layer; 5. Shielding layer; 6. Outer sheath. DETAILED DESCRIPTION

[0020] It is easy to understand that, based on the technical solution of the present invention, those skilled in the art can propose a variety of interchangeable structural methods and implementation methods without changing the essential spirit of the present invention. Therefore, the following specific embodiments and drawings are merely illustrative of the technical solution of the present invention and should not be regarded as the entire invention or as a limitation or restriction of the technical solution of the present invention. Example 1

[0021] One embodiment of the present invention combines Figure 1-Figure 5The figure shows a torsion-resistant cross-linked polyethylene insulated cable, which comprises, from the inside to the outside, a conductor layer 1, a stress relief layer 2, an insulating layer 3, a self-repairing layer 4, a shielding layer 5, and an outer sheath 6. A central elastic reinforcing core 11 is arranged in the center of the conductor layer 1. The central elastic reinforcing core 11 is made of modified nylon. Six inner copper monofilaments 12 are twisted on the outside of the central elastic reinforcing core 11, and twelve outer copper monofilaments 13 are twisted on the outside of the inner copper monofilament 12. The copper monofilaments are Class 5 soft copper. The stress relief layer 2 comprises the following materials in parts by weight: 80 parts of silane-modified butyl rubber, 6 parts of nano hollow glass microspheres, 12 parts of nano calcium carbonate, 2.5 parts of silane coupling agent KH-550, and 0.6 parts of antioxidant 1010. The insulating layer 3 comprises the following materials in parts by weight: 88 parts of XLPE resin, 12 parts of ethylene vinyl acetate, 0.9 parts of diisopropyl benzene peroxide, 0.7 The self-repairing layer 4 includes the following materials in parts by weight: 72 parts of epoxy-modified acrylate, 23 parts of oriented microcapsules, 0.9 parts of single-walled carbon nanotubes, 0.6 parts of antioxidant 168 and 2.8 parts of carbon black; the shielding layer 5 includes the following materials in parts by weight: 94 parts of semi-conductive polyethylene, 3.5 parts of chopped carbon fibers, 2.3 parts of maleic anhydride-grafted polyethylene and 0.5 parts of antioxidant 1010; the outer protective layer 6 includes the following materials in parts by weight: 82 parts of PVC resin, 12 parts of dioctyl phthalate, 3.8 parts of calcium zinc stabilizer, 0.4 parts of antioxidant 1010 and 1.8 parts of carbon black.

[0022] It should be noted that in the conductor layer 1, the modified nylon material contains 5wt% POE elastomer, the tensile strength exceeds 45MPa, the elongation at break is greater than 280%, the diameter of the Class 5 soft copper is about 0.4mm, and the conductivity is greater than 97% according to the international annealed copper standard; the particle size of the nano hollow glass microspheres in the stress relief layer 2 is about 8μm, and the density is 0.35g / cm 3, the particle size of nano calcium carbonate is about 50nm; in the insulating layer 3, the proportion of vinyl acetate in ethylene vinyl acetate is 18%, and the melt flow rate of the material after melting is measured to be 2.5g / 10min. The lower the value, the greater the melt viscosity and the worse the fluidity, that is, the better the mechanical strength and tear resistance; the purity of diisopropyl benzene peroxide is 98%, and the purity of trimethylolpropane trimethacrylate is 99%; the particle size of nano silicon dioxide is about 50nm; in the self-healing layer 4, the epoxy value of epoxy-modified acrylate is measured to be 0.5eq / 100g, that is, every 100 grams of resin contains 0.5 equivalents of epoxy groups. The higher the value, the higher the cross-linking density of the material after curing. The larger the directional microcapsule, the core material is silane coupling agent KH-560, and the wall material is urea-formaldehyde resin with a particle size of about 10 μm; the particle size of carbon black is about 20 nm; in the shielding layer 5, the volume resistivity of the semi-conductive polyethylene is measured to be 50 Ω·cm; the length of the chopped carbon fiber is 0.2 mm, and the tensile strength is 3000 MPa; the grafting rate of maleic anhydride grafted polyethylene is 1.2%. It should be further explained that the higher the grafting rate is, the better. On the contrary, a too high grafting rate will lead to degradation of the polyethylene main chain; in the outer protective layer 6, the purity of dioctyl phthalate is 99%; the calcium content in the calcium zinc stabilizer is 20%, and the zinc content is 5%; the particle size of carbon black is about 30 nm, which is different from the carbon black particle size in the self-healing layer 4.

[0023] This embodiment also provides a method for producing a torsion-resistant cross-linked polyethylene insulated cable, comprising the following steps: Step S1: Preparing a conductor layer 1. Modified nylon particles are first extruded through an extruder to form a central elastic reinforcing core 11. Soft copper monofilaments with a diameter of 0.4 mm are then twisted in a process of 6 strands in a right-hand bundle in the inner layer and 12 strands in a left-hand double-twisted outer layer. The twisting tension is controlled to 300N±20N, ultimately forming the conductor layer 1. It should be noted that the extrusion temperature in this step must be controlled between 190-200°C. Too high a temperature will cause nylon degradation and reduce tensile strength, while too low a temperature will result in incomplete molding. The temperature of each zone of the extruder must be adjusted to 195°C±3°C. During the twisting process, the inner layer bundle pitch ratio is 17 times. A too high a temperature will cause loose strands and increase the DC resistance of the conductor. A too low a temperature will increase the rigidity of the conductor and reduce torsion resistance. The outer layer double-twisted pitch ratio is 13 times.

[0024] Step S2: Prepare the stress relief layer 2. Weigh silane-modified butyl rubber, nano-hollow glass microspheres, and other raw materials by weight and mix them in an internal mixer at 110-120°C for 8-10 minutes. Coat the conductive layer 1 with a co-extruder to form a gradient structure with an inner highly elastic porous layer and an outer highly adhesive dense layer, with a total thickness of 0.4 mm. It should be noted that mixing temperatures that are too high in this step will cause premature vulcanization of the butyl rubber, while too low will result in uneven dispersion of the raw materials. It is best to control the temperature within 115°C ± 2°C. The coating speed is best controlled at 6 m / min, and the cooling water temperature is controlled at 28°C ± 2°C. The stress relief layer 2 has a total thickness of 0.4 mm, of which the inner porous layer 21 is 0.2 mm thick and has a porosity of approximately 28%, and the outer dense layer 22 is 0.2 mm thick and has a porosity of approximately 4%. To address the interfacial stress between the conductive layer 1 and the insulating layer 3, this step is designed around a synergistic mechanism involving chemical bonding, gradient modulus excess, and porous elasticity excess.

[0025] Specifically, the silane-modified butyl rubber contains silanol (-Si-OH) groups at the molecular chain ends. When it subsequently comes into contact with the XLPE insulation layer 3, the hydroxyl groups (-Si-OH) react with the hydroxyl groups (-OH) on the XLPE molecular chain to form stable siloxane covalent bonds (-Si-OC-). This covalent bond significantly strengthens the interfacial adhesion between the two layers, preventing interlayer delamination caused by residual stress during static bonding. Unlike traditional physical bonding, which is dominated by van der Waals forces, chemical bonding is dominated by covalent bonds, resulting in greater interface stability. The elastic modulus of the copper conductor is higher than that of the XLPE insulation layer 3, and direct contact can lead to stress concentration at the interface. The gradient structure of an inner, highly elastic porous layer and an outer, highly adhesive, dense layer achieves a low modulus in the inner layer through the combination of an elastomer substrate and a porous structure, while the outer layer maintains a medium modulus by filling it with nano-calcium carbonate. This allows for a smooth transition from high modulus to medium modulus in the conductor, avoiding sudden stress changes at a single interface. This allows residual stress to be evenly distributed along the gradient and gradually released, reducing the risk of stress lock-in within the insulation layer 3. The honeycomb pores in the inner, highly elastic porous layer exhibit elastic recovery properties. During winding, the pores deform elastically under torsional stress, absorbing some of the torsional energy through deformation. When standing still, the pores elastically recover, releasing the absorbed energy and thereby reducing residual stress in the XLPE insulation layer 3. Furthermore, the pore structure can accommodate trace small molecular products produced by interfacial chemical reactions, such as water from condensation reactions, preventing bulging at the interface due to product accumulation.

[0026] Step S3: Prepare the insulation layer 3. XLPE resin, EVA, and other raw materials are weighed by weight and melt-blended in a twin-screw extruder at 140-150°C. The blend is extruded onto the stress relief layer 2 in the insulation extruder, and then vulcanized in a vulcanizing tube at 165°C for 50 minutes to form an insulation layer 3 with a thickness of 3.4 mm. The cross-linking degree is controlled to 70% ± 2%. It should be noted that the melt blending in this step is controlled within the above-mentioned temperature range. Too high a temperature will cause premature decomposition of DCP and insufficient cross-linking, while too low a temperature will result in uneven mixing of the raw materials. It is best to control it within 145°C ± 3°C. The extrusion temperature of the extruder is controlled at 165-175°C, and the die pressure is 15MPa ± 2MPa. Based on experimental results, the vulcanization time is 50 minutes, and if it is too short, the cross-linking degree is only 60%, which is insufficient in heat resistance. If it is too long, the cross-linking degree exceeds 80%, which increases rigidity and reduces torsional resistance.

[0027] To improve torsional resistance without sacrificing XLPE's insulating properties, this step reduces rigidity through chemical modification while simultaneously enhancing strength through the material's physical properties. Specifically, the ester groups (-COO-) in the ethylene-vinyl acetate (EVA) molecular chains are polar groups that form hydrogen bonds with the hydroxyl groups (-OH) on the XLPE molecular chains. XLPE's poor torsional resistance stems from the strong rigidity of its cross-linked three-dimensional network. The formation of hydrogen bonds weakens the intermolecular forces within the XLPE cross-linked network, breaking the rigid constraints of some rigid crosslinks and allowing the XLPE chains to undergo a certain degree of micro-displacement under torsional stress. This reduces overall rigidity and improves torsional micro-deformation resistance. Nano-silica is a high-hardness inorganic particle. When uniformly dispersed in the XLPE matrix, it fills the tiny gaps between XLPE molecular chains through its particle reinforcement effect and limits excessive molecular chain displacement. This prevents the strength loss of the insulation layer 3 caused by EVA modification while maintaining the XLPE's inherent high insulating strength. More specifically, the interface between the nanoparticles and the XLPE molecular chains forms a composite structure of rigid particles and a flexible matrix through the interaction of van der Waals forces and hydrogen bonds.

[0028] By controlling the amount of dicumyl peroxide (DCP) and the curing time, the crosslinking degree of XLPE is limited to a specific range. Excessive crosslinking results in an overly dense network structure and increased rigidity, while too low a crosslinking degree cannot guarantee heat resistance. The appropriate crosslinking degree strikes a balance between rigidity and flexibility, ensuring that the insulation layer 3 does not soften under the high temperatures of winding friction and does not become brittle when left at room temperature.

[0029] Step S4: Prepare the self-repairing layer 4. Weigh the epoxy-modified acrylate, oriented microcapsules and other raw materials by weight, stir them in a high-speed mixer at 60-70°C for 5-8 minutes, and coat them on the outside of the insulation layer 3 using a coating machine. The microcapsules are oriented at 45° along the cable axis, with an array density of about 950 / mm. 2It should be noted that in this step, if the stirring temperature is too high, the microcapsules will rupture prematurely and the core material will leak. If it is too low, the carbon nanotubes will be unevenly dispersed. It is best to control it at 65℃±2℃; the coating thickness is 0.25mm, the curing temperature is controlled at 90℃±3℃, and the curing time is 35min.

[0030] To solve the crack problem of intermittent winding, this step guides the crack path and releases self-repair in conjunction with chemical materials. Specifically, according to the theory of material mechanics, when the cable is subjected to torsional stress, the shear stress reaches its maximum value along the direction of 45° to the cable axis, and the crack will preferentially expand along this direction. In this embodiment, the microcapsules are arranged in a 45° direction, which allows the cracks to precisely contact and trigger the microcapsule rupture during the expansion process. The directional structure can match the microcapsules with the crack path, avoiding repair failure caused by capsule position deviation; the microcapsule core material silane coupling agent KH-560 contains epoxy groups (-C2H3O-). After the crack triggers the capsule to rupture, the epoxy groups can undergo a ring-opening reaction with the hydroxyl groups (-OH) on the XLPE molecular chain to form a stable ether bond (-OC-). This reaction gradually fills the cracks, reconnecting the molecular chains of the XLPE insulation layer 3 and enabling self-healing of the cracks, preventing moisture and dust from intruding along the cracks during storage. Single-walled carbon nanotubes have extremely high thermal conductivity, allowing frictional heat generated during winding to be rapidly transferred through the carbon nanotubes to the microcapsule wall material, which is urea-formaldehyde resin. The softening point of urea-formaldehyde resin decreases with increasing temperature. This heat transfer allows the wall material to soften even at low temperatures, ensuring that the microcapsules can withstand stress-induced rupture during low-temperature winding, thus resolving the low repair efficiency of the traditional self-healing layer 4 at low temperatures. The core cause of aging in the XLPE insulation layer 3 is free radical-induced molecular chain breakage and UV-induced crosslinking bond destruction. The conjugated structure of the carbon nanotubes captures free radicals generated during aging, such as oxygen radicals, preventing them from attacking the XLPE molecular chains. Carbon black has excellent UV absorption, blocking UV rays from penetrating the XLPE interior, inhibiting photo-oxidation aging and extending the life of the insulation layer 3 during storage.

[0031] Step S5: Prepare shielding layer 5. Weigh semi-conductive polyethylene, chopped carbon fibers, and other raw materials by weight and mix them in an internal mixer at 130-140°C for 10-12 minutes. Extruder overlay the self-healing layer 4, controlling the volume resistivity to 80 Ω·cm ± 10 Ω·cm. It should be noted that excessively high mixing temperatures in this step can lead to oxidation of the carbon fibers and a decrease in conductivity, while excessively low temperatures can result in uneven mixing and insufficient shielding performance. Ideally, the temperature should be controlled at 135°C ± 3°C. The extrusion temperature should be controlled at 170-180°C, with a thickness of 1.0 mm.

[0032] To ensure that shielding layer 5 does not fail during the winding process, this step enhances interfacial bonding through a combination of materials and chemical reactions. Specifically, semi-conductive polyethylene itself has low tensile strength and is susceptible to breakage due to torsional stretching during winding. Chopped carbon fibers are high-strength fibers. When evenly dispersed in the semi-conductive polyethylene matrix, they can absorb some of the tensile stress through a fiber bridging effect. When shielding layer 5 is subjected to tension, the carbon fibers transfer stress from the polyethylene matrix to themselves, preventing stress concentration and fracture in the matrix. This improves the tensile strength of shielding layer 5 and ensures shielding continuity during winding. The anhydride groups (-CO-O-CO-) on the maleic anhydride-grafted polyethylene molecular chains are active groups that undergo an esterification reaction with the epoxy groups in the epoxy-modified acrylate in self-healing layer 4, forming covalent bonds. This reaction eliminates interfacial gaps between shielding layer 5 and self-healing layer 4, preventing oxidation failure of shielding layer 5 caused by moisture and salt spray intrusion along the interface during static operation. It also ensures that shielding layer 5 does not delaminate from self-healing layer 4 when the cable is twisted, maintaining stable shielding performance.

[0033] Step S6: preparing the outer protective layer 6. Weigh PVC resin, dioctyl phthalate and other raw materials according to weight, melt and extrude them in a single-screw extruder at 150-160°C, and extrude them onto the outside of the shielding layer 5.

[0034] It should be noted that in this step, if the melt extrusion temperature is too high, it will cause the PVC to degrade and the mechanical properties to decrease. If it is too low, it will be difficult to extrude. It is best to control it at 155℃±3℃. If the thickness temperature of the outer sheath 6 is too high, it will cause the PVC to degrade and the mechanical properties to decrease. If it is too low, it will be difficult to extrude. It needs to be controlled at 155℃±3℃. The temperature of the cooling water is controlled at 25℃±2℃. In order to improve the environmental adaptability of the outer sheath 6, this step achieves an improvement in protection performance through the synergistic effect of physical toughening and chemical reaction anti-aging. Specifically, the PVC resin itself is very rigid and prone to cracking when winding and twisting. Dioctyl phthalate, as a plasticizer, can be inserted between the PVC molecular chains, weakening the van der Waals force between the molecular chains, giving the PVC molecular chains a certain sliding ability, thereby reducing the rigidity of the PVC and improving its flexibility. This toughening effect can make the outer sheath 6 undergo elastic deformation when the cable is twisted, avoiding cracking, while improving friction resistance. PVC is prone to de-HCl reaction at high temperatures, resulting in molecular chain degradation and a decrease in mechanical properties. The calcium zinc stabilizer can react with HCl produced by PVC degradation to inhibit the chain reaction of de-HCl. At the same time, its metal ions can combine with unstable chlorine atoms on the PVC molecular chain to prevent the molecular chain from breaking, thereby inhibiting the thermal aging of PVC. The outer sheath 6 adopts an extrusion process to form a dense structure, which can physically block external impurities such as water vapor, dust, and oil from invading the interior of the cable, avoiding the reaction of impurities with the internal functional layer during the static process, thereby protecting the overall performance of the cable.

[0035] Comparative Example 1: In order to explore the effects of the gradient porous structure of the stress relief layer 2 and the chemical bonding design of the silane coupling agent in the present invention on the interface bonding performance, residual stress control ability and integrity of the insulation layer 3 of the cable under intermittent winding and static cycle scenarios, and to verify the necessity of this structure and chemical bonding design in solving the problems of stress concentration at the interface between the conductor and the XLPE insulation layer 3 and static interlayer delamination, this comparative example 1 is specially set up.

[0036] Compared with Example 1, the difference of this comparative example 1 is that the stress relief layer 2 is replaced by a single-layer pure butyl rubber layer, to which nano hollow glass microbeads, nano calcium carbonate and silane coupling agent KH550 are not added, and only pure butyl rubber is used as the raw material, and its thickness remains at 0.4 mm; accordingly, in the preparation step S2, only pure butyl rubber is weighed when the raw materials are weighed, and there is no need to control the dispersion of nanoparticles during the mixing process. The mixing temperature is still controlled at 115°C ± 2°C, the coating speed is maintained at 6 m / min, and the cooling water temperature is 28°C ± 2°C. The remaining preparation steps and parameters of each step are completely consistent with those of Example 1.

[0037] The performance tests of the cables prepared in Example 1 and Comparative Example 1 were carried out, specifically testing the interface adhesion, the residual stress of the insulation layer 3, the interlayer peeling rate after standing, and the crack incidence rate of the insulation layer 3.

[0038] Specifically, the interface adhesion test refers to GB / T 17748-2020 "General test methods for materials for electric cables and optical cables", and the interface adhesion between the cable conductor layer 1 and the XLPE insulation layer 3 is tested. The sample is cut in the radial direction of the cable, and a 180° peeling test is performed using a peeling tester, and the force value in the stable peeling stage is recorded; the residual stress test of the insulation layer 3 refers to DL / T1573-2016 "Guidelines for Status Evaluation of Power Cables". After the cable is wound once, it is left to stand for 10 days, and the residual stress value of the XLPE insulation layer 3 is tested at room temperature using a stress relaxation tester; the interlayer peeling rate test after standing refers to GB / T 2951.31-2008 "General test methods for insulation and sheathing materials of electric and optical cables - Part 31: Special test methods for polyvinyl chloride mixtures - High temperature pressure test - Cracking resistance test". After the cable has been wound and rested for five times, a 1-meter specimen is cut from the cable length. The peeling between the conductor layer 1 and the XLPE insulation layer 3 is observed, and the ratio of the peeling length to the total length is calculated. The crack incidence rate test of the insulation layer 3 is tested with reference to DL / T 1915-2018 "Code for Condition-Based Maintenance of Power Cable Lines". After the cable has been wound and rested for five times, a high-power microscope is used to observe the cracks on the surface and inside the XLPE insulation layer 3, and the ratio of the number of specimens with cracks to the total number of specimens tested is calculated. The specific test results are shown in Table 1.

[0039] .

[0040] The specific reasons for the above performance differences include the following analysis: From the perspective of interface adhesion differences, the silane-modified butyl rubber of the stress relief layer 2 in Example 1 contains silanol groups, which can react with the hydroxyl groups on the molecular chain of the XLPE insulating layer 3 to form a stable siloxane covalent bond. This chemical bonding can significantly improve the interface bonding force, making the interface adhesion reach 3.2N / cm; while the single-layer pure butyl rubber used in this comparative example 1 does not contain a silane coupling agent and cannot form a covalent bond with the XLPE insulating layer 3. The interface bonding relies solely on the van der Waals force between the butyl rubber and the XLPE. The strength of the interaction is lower than that of the covalent bond, so the interfacial adhesion drops significantly to 1.1N / cm; from the analysis of the residual stress difference in the insulating layer 3, the stress relief layer 2 of Example 1 adopts a gradient porous structure, while the single-layer pure butyl rubber layer of Comparative Example 1 is a homogeneous structure without a gradient modulus transition design. The elastic modulus difference between the conductor and the XLPE insulating layer 3 cannot be alleviated, and the torsional stress generated during winding is directly transferred to the XLPE insulating layer 3. The pure butyl rubber layer has no porous structure for energy absorption and release, resulting in the inability to effectively release the residual stress, which is eventually locked inside the XLPE insulating layer 3, with a residual stress value of up to 7 .8MPa; in terms of the interlayer peeling rate after standing, Example 1 can effectively resist the relative sliding tendency at the interface during the winding and standing cycle by virtue of its higher interface adhesion and lower residual stress, so the interlayer peeling rate after 5 cycles is only 2%; while in Comparative Example 1, on the one hand, the interface adhesion is low and it cannot provide sufficient restraint to prevent interlayer sliding. On the other hand, the residual stress of the insulating layer 3 is high. When standing, the residual stress will continue to act on the interface, pushing the conductor layer 1 and the XLPE insulating layer 3 to separate relatively. The superposition of these two factors causes the interlayer peeling rate to rise significantly to 28%; as for the crack incidence rate of the insulating layer 3, the implementation In Example 1, the stress relief layer 2 can reduce the residual stress of the XLPE insulation layer 3 through gradient modulus transition and porous buffering, reduce the concentration of stress inside the insulation layer 3, and thus reduce the probability of crack occurrence. After 5 cycles, the crack incidence rate is only 5%; while the XLPE insulation layer 3 of Comparative Example 1 is subjected to higher residual stress. These residual stresses will form stress concentration areas inside the insulation layer 3, especially near the interface between the insulation layer 3 and the conductor. Stress concentration will continuously induce the generation and expansion of microcracks. After 5 winding and static cycles, the microcracks gradually develop into visible cracks, causing the crack incidence rate to increase to 35%.

[0041] Comparative Example 2: This comparative example 2 was conducted to investigate the effects of the EVA modification and nano-silica reinforcement design of the present invention on the torsional micro-deformation resistance, insulation strength, and crack control of the XLPE insulation layer 3, and to verify the necessity of this modification design in solving the problems of poor torsional resistance and easy crack initiation caused by the cross-linked rigidity of XLPE.

[0042] Compared with Example 1, the difference of this comparative example 2 is that the EVA-modified XLPE insulation layer 3 is replaced by a pure XLPE insulation layer 3. The pure XLPE insulation layer 3 uses only XLPE resin as a raw material, without adding ethylene vinyl acetate and nano-silica, and its thickness remains at 3.4 mm; accordingly, in the preparation step S3, when weighing the raw materials, only XLPE resin, diisopropylbenzene peroxide and trimethylolpropane trimethacrylate are weighed, and there is no need to perform dispersion control of EVA and nano-silica. The melt blending temperature is still controlled at 145°C ± 3°C, the extrusion temperature is 165-175°C, the head pressure is 15 MPa ± 2 MPa, the vulcanization tube is vulcanized at 165°C for 50 min, and the crosslinking degree is controlled to 70% ± 2%. The remaining preparation steps and parameters of each step are completely consistent with Example 1.

[0043] The performance tests of the cables prepared in Example 1 and Comparative Example 2 were conducted, specifically testing the elastic modulus of the XLPE insulation layer 3, the micro-deformation of the insulation layer 3 during winding, the crack depth of the insulation layer 3, and the insulation breakdown voltage.

[0044] Specifically, the elastic modulus test of the XLPE insulation layer 3 refers to GB / T 1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for films and sheets". Under room temperature, a dumbbell-shaped specimen is cut from the cable insulation layer 3, and the elastic modulus is tested using a universal testing machine at a tensile speed of 50 mm / min; the micro-deformation test of the insulation layer 3 during winding refers to GB / T29631-2013 "Low-voltage cable insulation and sheath materials Part 1: General provisions". The cable is wound at a torsion angle of 120° / m, and a laser displacement sensor is used to test the maximum micro-deformation of the XLPE insulation layer 3 during the winding process; the crack depth test of the insulation layer 3 refers to DL / T1915-2018 "Power Cable Line Status Inspection and Maintenance Regulations". After the cable has been wound and rested for 5 times, a thin sheet specimen is cut radially from the insulation layer 3, and a high-power microscope is used to magnify it 500 times and observe and measure the maximum depth of the crack; the insulation breakdown voltage test refers to GB / T 1408.1-2016, "Electrical Strength Test Methods for Insulating Materials - Part 1: Power Frequency Tests," tests the breakdown voltage of the cable insulation layer 3 using the oil immersion method at room temperature and pressure, with a voltage ramp rate of 2 kV / s. The voltage at breakdown is recorded. The specific test results are shown in Table 2.

[0045] .

[0046] The specific reasons for the above performance differences include the following analysis: From the perspective of the difference in the elastic modulus of the XLPE insulating layer 3, the formation of hydrogen bonds in Example 1 will weaken the intermolecular force within the XLPE cross-linked network, reduce the overall rigidity, and the elastic modulus is controlled at 580 MPa; Comparative Example 2 uses a pure XLPE insulating layer 3 without the hydrogen bonding effect of EVA, the rigidity of the XLPE cross-linked network is not weakened, the constraint effect between the molecular chains is strong, and the external force cannot be buffered by the micro-displacement of the molecular chains, resulting in an elastic modulus of up to 800 MPa, which is much higher than that of Example 1; in terms of the micro-deformation of the insulating layer 3 during winding, Example 1 is different from Example 1 due to the XLPE The PE insulating layer 3 has a low elastic modulus and a strong ability of micro-displacement of the molecular chain. During the winding process, the torsional stress can be absorbed by the sliding of the molecular chain and the slight deformation of the insulating layer 3, and the micro-deformation reaches 15%. However, the elastic modulus of the pure XLPE insulating layer 3 of comparative example 2 is large, and the molecular chain is tightly constrained by the cross-linked network and cannot slide effectively. Only 5% micro-deformation can be generated during winding. Most of the torsional stress cannot be buffered by deformation and directly acts on the inside of the insulating layer 3, which is easy to cause accident hazards. As for the crack depth of the insulating layer 3, the EVA modification in Example 1 disperses the torsional stress through deformation and reduces stress concentration. At the same time, the nano-silica particles Reinforcement, filling the tiny gaps between XLPE molecular chains, and preventing the initiation and expansion of microcracks. Therefore, after 5 winding-resting cycles, the crack depth is only 0.1mm; the pure XLPE insulation layer 3 of this comparative example 2 does not have the above-mentioned double protection. On the one hand, the micro-deformation ability is poor, and the torsional stress is easy to form a concentrated area inside the insulation layer 3, especially near the interface between the insulation layer 3 and the stress relief layer 2. The stress concentration will continuously cause microcracks; on the other hand, without the reinforcement and barrier of nano-silicon dioxide, the microcracks will quickly expand into the interior of the insulation layer 3. After 5 cycles, the crack depth reaches 0.5mm, destroying the integrity of the insulation layer 3. Integrity; From the analysis of the difference in insulation breakdown voltage, the nano-silica particles in Example 1 evenly disperse the electric field to avoid the electric field concentration inside the insulating layer 3. At the same time, the EVA modification does not destroy the insulating nature of XLPE, so the insulation breakdown voltage is maintained at 41kV; the pure XLPE insulating layer 3 in this comparative example 2 has a large crack depth, and air or water vapor from the outside easily accumulates inside the crack. These impurities will cause the electric field to concentrate at the crack tip, greatly reducing the local insulation strength; and without the electric field dispersion effect of nano-silica, the overall electric field distribution of the insulating layer 3 is uneven, which ultimately causes the breakdown voltage to drop to 28kV, which cannot meet the safe operation requirements.

[0047] Comparative Example 3: In order to explore the influence of the coordinated design of the oriented microcapsules, single-walled carbon nanotubes and carbon black of the self-healing layer 4 in the present invention on the cable crack repair ability, low-temperature repair efficiency and anti-aging performance of the XLPE insulation layer 3, and to verify the necessity of this design in solving the problems of cracks unable to self-heal, low-temperature repair failure and aggravation of static aging in intermittent winding scenarios, this comparative example 3 is specially set up.

[0048] Compared with Example 1, the difference of this comparative example 3 is that the self-repairing layer 4 is replaced by an ordinary epoxy-modified acrylate coating. The ordinary epoxy-modified acrylate coating only uses epoxy-modified acrylate as a raw material, and does not add oriented microcapsules, single-walled carbon nanotubes and carbon black, and its thickness remains at 0.25 mm; accordingly, in the preparation step S4, only epoxy-modified acrylate is weighed when the raw materials are weighed, and there is no need to control the arrangement of the oriented microcapsules and the dispersion of the carbon nanotubes. The stirring temperature of the high-speed mixer is still controlled at 65°C ± 2°C, the coating speed is the same as in Example 1, the curing temperature is 90°C ± 3°C, and the curing time is 35 min. The remaining preparation steps and parameters of each step are completely consistent with Example 1.

[0049] The cables prepared in Example 1 and Comparative Example 3 were subjected to performance tests, specifically testing the crack repair rate, repair efficiency in a low-temperature environment of -10°C, oxidation induction period of the XLPE insulation layer 3 after standing for 10 days, and insulation failure probability after 5 winding-standing cycles.

[0050] Specifically, the crack repair rate test refers to DL / T 1915-2018 "Power Cable Line Status Inspection and Maintenance Regulations", prefabricated an artificial crack with a depth of 0.3mm in the cable insulation layer 3, and after standing for 48 hours, a high-power microscope was used to observe the crack closure after magnification 500 times, and the ratio of the crack repair length to the initial crack length was calculated; the repair efficiency test at a low temperature of -10°C refers to GB / T 2951.11-2008 "General test methods for insulation and sheath materials of electric and optical cables Part 11: General test methods for thickness and overall dimensions measurement and mechanical property test", repeated the above crack repair test at a low temperature of -10°C, and counted the proportion of microcapsules that ruptured and triggered repair; the oxidation induction period test of the XLPE insulation layer 3 after standing for 10 days refers to GB / T 19466.2-2004 "Plastics - Differential Scanning Calorimetry - Part 2: Determination of Glass Transition Temperature" uses a differential scanning calorimeter to test the oxidation induction time of XLPE insulation layer 3 at 200°C in an oxygen atmosphere. The probability of insulation failure after five winding-rest cycles is tested according to DL / T 1573-2016 "Guidelines for Condition Assessment of Power Cables." After five winding-rest cycles, the cables are subjected to a withstand voltage test at rated voltage. For 10kV cables, a voltage of 17.5kV is applied for 1 minute. The percentage of samples that failed the withstand voltage test relative to the total number of samples tested is calculated. The specific test results are shown in Table 3.

[0051] .

[0052] The specific reasons for the above-mentioned performance differences include the following analysis: From the perspective of the difference in crack repair rate, the self-healing layer 4 of Example 1 contains oriented microcapsules. When the crack expands, the capsules can be triggered to rupture and release the repair agent, achieving self-healing of the crack. However, the ordinary epoxy-modified acrylate coating of Comparative Example 3 does not have oriented microcapsules and no source of repair agent. The 0.3mm crack cannot be filled through chemical reaction. After 48 hours, the crack remains in its initial state, and the repair rate is 0%. In terms of repair efficiency in a low-temperature environment of -10°C, Example 1 relies on the high thermal conductivity of single-walled carbon nanotubes to transfer the friction heat of winding to the microcapsule wall material, allowing the wall material to soften and crack even at low temperatures. However, Comparative Example 3 does not have single-walled carbon nanotubes. Without heat transfer in the low-temperature environment, neither the microcapsules nor the coating itself can produce a repair effect, resulting in a repair efficiency of 0%. Regarding the XLPE oxidation induction period after 10 days of standing, the carbon nanotubes in Example 1 can capture free radicals generated by XLPE aging, and the carbon black can absorb ultraviolet rays, and the two work together to delay aging. Comparative Example 3 does not have these two components, and the XLPE molecular chains are susceptible to free radical attack and ultraviolet damage, which accelerates the rate of cross-link bond breakage, shortening the oxidation induction period from 290 minutes to 150 minutes, and significantly improving the aging rate. Based on the analysis of the probability of insulation failure after 5 cycles, Example 1 avoids water intrusion through crack repair and extends the insulation life through anti-aging design, with a failure probability of only 3%. In Comparative Example 3, due to the lack of crack repair and aggravated aging, the cracks will gradually expand and introduce impurities, resulting in the destruction of the integrity of the insulation layer 3 and the decline of the withstand voltage performance. Ultimately, 45% of the samples failed the withstand voltage test, and the failure probability increased significantly.

[0053] Comparative Example 4: In order to explore the effects of the chopped carbon fiber reinforcement and maleic anhydride grafted polyethylene chemical bonding design of the shielding layer 5 in the present invention on the tensile strength, winding fracture resistance, interface bonding stability and antioxidant performance of the shielding layer 5, and to verify the necessity of this design in solving the problems of easy breakage of the shielding layer 5 in intermittent winding scenarios, interface peeling when standing, and oxidation failure, this comparative example 4 is specially set up.

[0054] Compared with Example 1, the difference of this comparative example 4 is that the semiconductive shielding layer 5 containing chopped carbon fibers and maleic anhydride grafted polyethylene is replaced by a pure semiconductive polyethylene shielding layer 5. The pure semiconductive polyethylene shielding layer 5 only uses semiconductive polyethylene and antioxidant 1010 as raw materials, and does not add chopped carbon fibers and maleic anhydride grafted polyethylene, and its thickness remains at 1.0 mm; accordingly, in the preparation step S5, only semiconductive polyethylene and antioxidant 1010 are weighed when the raw materials are weighed, and there is no need to perform dispersion control of the chopped carbon fibers and interface bonding design of the maleic anhydride grafted polyethylene. The mixing temperature is still controlled at 135°C ± 3°C, the extrusion temperature is 170-180°C, and the volume resistivity control target of 80Ω·cm ± 10Ω·cm remains unchanged. The remaining preparation steps and parameters of each step are completely consistent with those of Example 1.

[0055] The cables prepared in Example 1 and Comparative Example 4 were subjected to performance tests, specifically testing the tensile strength of the shielding layer 5, the breakage rate of the shielding layer 5 after winding, the adhesion between the shielding layer 5 and the self-repairing layer 4, and the oxidation rate of the shielding layer 5 after standing for 10 days.

[0056] Specifically, the tensile strength test of the shielding layer 5 refers to GB / T 1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for films and sheets", and a dumbbell-shaped specimen is cut from the shielding layer 5. The tensile strength at room temperature is tested using a universal testing machine at a tensile speed of 50 mm / min; the fracture rate test of the shielding layer 5 after winding refers to DL / T 1915-2018 "Procedure for Status Inspection and Maintenance of Power Cable Lines", and the cable is wound and left to stand for 5 times at a torsion angle of 120° / m. Three 1m specimens are cut in the length direction of the cable, and the fracture conditions of the surface and cross-section of the shielding layer 5 are observed, and the proportion of the fracture length to the total length is calculated; the adhesion test of the shielding layer 5 and the self-repairing layer 4 refers to GB / T 17748-2020, "General Test Methods for Materials for Electrical and Optical Fiber Cables," specimens containing the shielding layer 5 and self-healing layer 4 were cut radially from the cable and subjected to a 90° peel test using a peel tester. The force during the stable peeling phase was recorded. After 10 days of stagnation, the shielding layer 5 was tested for oxidation rate according to GB / T 2951.51-2017, "General Test Methods for Insulation and Sheathing Materials for Electrical and Optical Fiber Cables - Part 51: Specific Test Methods for Filling Pastes - Dropping Point, Oil Separation, Low-Temperature Brittleness, Total Acid Number, Corrosion, Dissipation Factor Tangent at 23°C, and Volume Resistivity." After 10 days of stagnation, the shielding layer 5 was stripped and sampled. The relative content of oxidized elements on the surface of the shielding layer 5 was measured using an X-ray photoelectron spectrometer, and the proportion of the oxidized area to the total test area was calculated. The specific test results are shown in Table 4.

[0057] .

[0058] The specific reasons for the above-mentioned performance differences include the following analysis: From the perspective of the difference in tensile strength of the shielding layer 5, the shielding layer 5 of Example 1 contains chopped carbon fibers, whose high strength can bear tensile stress through the fiber bridging effect, thereby improving the overall tensile strength of the shielding layer 5. The pure semi-conductive polyethylene of Comparative Example 4 has low tensile strength and is not reinforced by fibers, so it cannot withstand the torsional tensile stress during winding. Its tensile strength is only 8 MPa, which is much lower than that of Example 1. In terms of the breakage rate of the shielding layer 5 after winding, Example 1 relies on chopped carbon fibers to disperse the tensile stress, avoiding stress concentration fracture of the semi-conductive polyethylene matrix. After 5 cycles, the breakage rate is only 0.1%. Comparative Example 4 does not have chopped carbon fibers. The torsional tensile stress acts directly on the semi-conductive polyethylene during winding, causing cracking of the matrix. The breakage rate is as high as 22%, destroying the continuity of the shield. Regarding the adhesion between the shielding layer 5 and the self-repairing layer 4, the anhydride groups of the maleic anhydride grafted polyethylene in Example 1 can undergo an esterification reaction with the epoxy groups of the self-repairing layer 4, forming covalent bonds to enhance interfacial bonding. Comparative Example 4 does not have maleic anhydride grafted polyethylene, and the interface relies solely on physical adhesion, resulting in a significant drop in adhesion to 0.6 N / cm. It is susceptible to peeling due to stress or moisture intrusion when left stationary. Analysis of the oxidation rate of the shielding layer 5 after 10 days of standing shows that the interfacial covalent bonds in Example 1 can block the intrusion of moisture and salt spray, reducing oxidation of the shielding layer 5. Comparative Example 4 has low interfacial adhesion, and impurities easily penetrate along the interface, leading to oxidation of the carbon powder in the semi-conductive polyethylene. The oxidation rate rises to 30%, thereby increasing the volume resistivity of the shielding layer 5 and affecting the shielding performance.

[0059] The technical scope of the present invention is not limited to the contents of the above description. Those skilled in the art can make various deformations and modifications to the above embodiments without departing from the technical idea of ​​the present invention, and these deformations and modifications should all fall within the protection scope of the present invention.

Claims

1. A torsion-resistant cross-linked polyethylene insulated cable, characterized in that: From the inside to the outside, it includes a conductor layer, a stress relief layer, an insulating layer, a self-repairing layer, a shielding layer and an outer sheath; the stress relief layer is a gradient porous composite structure, including an inner porous layer and an outer dense layer distributed along the radial direction of the cable, nano hollow glass microbeads are dispersed in the inner porous section, and nano calcium carbonate is dispersed in the outer dense section. The substrate of the stress relief layer is silane modified butyl rubber, which can undergo a condensation reaction with the insulating layer to form a covalent bond; the self-repairing layer is provided with microcapsules distributed at a 45° angle along the cable axis, the microcapsules are a coupling structure of a core material and a wall material, the core material is a silane coupling agent, and the wall material is urea-formaldehyde resin, and the core material can undergo a ring-opening reaction with the insulating layer; the self-repairing layer is also provided with a three-dimensional thermal conductive network formed by single-walled carbon nanotubes.

2. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The stress relief layer is composed of materials, by weight, including 75-85 parts of silane-modified butyl rubber, 5-7 parts of nano hollow glass microspheres, 10-14 parts of nano calcium carbonate, 2-3 parts of silane coupling agent KH-550 and 0.5-0.7 parts of antioxidant 1010.

3. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The insulating layer is composed of 85-90 parts by weight of cross-linked polyethylene resin, 10-14 parts of ethylene vinyl acetate, 0.8-1.0 parts of dicumyl peroxide, 0.6-0.8 parts of trimethylolpropane trimethacrylate and 2-2.5 parts of nano-silicon dioxide, wherein the content of vinyl acetate in the ethylene vinyl acetate is 16%-20%.

4. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The components of the self-healing layer include, by weight, 70-75 parts of epoxy-modified acrylate, 20-25 parts of oriented microcapsules, 0.8-1.0 parts of single-walled carbon nanotubes, 0.5-0.7 parts of antioxidant 168 and 2.5-3.0 parts of carbon black. The epoxy value of the epoxy-modified acrylate is 0.45-0.55eq / 100g, and the particle size of the carbon black is 18-22nm.

5. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The shielding layer is composed of 92-95 parts by weight of semi-conductive polyethylene, 3-4 parts of chopped carbon fibers, 2-2.5 parts of maleic anhydride grafted polyethylene, and 0.4-0.6 parts of antioxidant 1010. The volume resistivity of the semi-conductive polyethylene is 45-55Ω·cm, the length of the chopped carbon fibers is 0.15-0.25mm, and the grafting rate of the maleic anhydride grafted polyethylene is 1.0%-1.4%.

6. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The conductor layer includes a central elastic reinforcing core and a copper monofilament layer twisted around the outside of the central elastic reinforcing core. The copper monofilament layer is radially arranged with an inner layer of copper monofilaments and an outer layer of copper monofilaments. The inner layer of copper monofilaments is wrapped around the central elastic reinforcing core in a right-handed bundle twisting manner, and the outer layer of copper monofilaments is wrapped around the inner layer of copper monofilaments in a left-handed double twisting manner.

7. The torsion-resistant cross-linked polyethylene insulated cable according to claim 6, characterized in that: The central elastic reinforcement core is made of modified nylon, which contains 4%-6% by mass of POE elastomer; the inner copper monofilament and the outer copper monofilament are both Class 5 soft copper, the diameter of the copper monofilament is 0.35-0.45mm, the bundle-twisted section diameter ratio of the inner copper monofilament is 16-18 times, and the complex-twisted section diameter ratio of the outer copper monofilament is 12-14 times.

8. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The elastic modulus of the inner porous layer of the stress relief layer is 10-14 MPa, the elastic modulus of the outer dense layer is 50-54 MPa, and the elastic modulus of the insulating layer is 550-610 MPa. The stress relief layer forms an elastic modulus gradient transition from the conductor layer to the insulating layer through the inner porous layer and the outer dense layer.

9. The torsion-resistant cross-linked polyethylene insulated cable according to claim 1, characterized in that: The outer protective layer is composed of materials, by weight, including 80-84 parts of polyvinyl chloride resin, 10-14 parts of dioctyl phthalate, 3.5-4.0 parts of calcium zinc stabilizer, 0.3-0.5 parts of antioxidant 1010 and 1.5-2.0 parts of carbon black. The mass fraction of calcium element in the calcium zinc stabilizer is 18%-22%, the mass fraction of zinc element is 4%-6%, and the particle size of the carbon black is 28-32nm.

10. The torsion-resistant cross-linked polyethylene insulated cable according to claim 3, characterized in that: The polar groups on the ethylene-vinyl acetate molecular chains in the insulating layer form intermolecular forces with the cross-linked polyethylene molecular chains, weakening the rigidity of the cross-linked network. Surface-modified inorganic nanoparticles are also dispersed in the insulating layer. The inorganic nanoparticles supplement the structural strength of the insulating layer through interfacial bonding with the cross-linked polyethylene molecular chains.

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