A torsion-resistant crosslinked polyethylene insulated cable

Abstract

This invention relates to the field of cable technology and discloses a torsion-resistant cross-linked polyethylene (XLPE) insulated cable suitable for scenarios involving intermittent winding and static cycles, such as cable logistics warehousing and mobile emergency equipment. Existing technologies, designed for continuous winding, cannot address the residual stress generated by the rigidity of cross-linked polyethylene in intermittent scenarios, nor the aging and crack propagation problems caused by the coupling of residual stress with the environment. This invention incorporates a gradient porous stress-relieving layer outside the conductor, releasing residual stress and strengthening interfacial bonding through modulus transition and chemical adhesion; the XLPE insulation layer is modified with EVA to reduce rigidity and reinforced with nano-silica; and a self-healing layer containing directional microcapsules and carbon nanotubes is incorporated outside the insulation layer to achieve precise crack repair and anti-aging, reducing insulation cracks, conductor breakage, and shielding failure during intermittent winding and static cycles, ensuring the cable's reliability in the target scenarios.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and more particularly to a torsion-resistant cross-linked polyethylene insulated cable. Background Technology

[0002] Cross-linked polyethylene (XLPE) insulated cables are power cables with cross-linked polyethylene as the insulation layer. Due to the cross-linked three-dimensional network structure, they have good temperature resistance, insulation strength and mechanical properties, and are widely used in medium and high voltage power transmission, industrial control and new energy fields. Torsional performance is the core indicator of XLPE cables under dynamic conditions. When the cable is subjected to torsional force, problems such as insulation layer cracking, conductor strand breakage or shielding failure may occur. 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. Among these, winding is a core operating condition, where the cable needs to be stored and laid by rotating with the equipment or reel. Existing technologies are mostly designed for continuous winding scenarios. For example, CN119381072B discloses a torsion-resistant cable for 35kV wind turbines. It addresses the technical problem of insulation layer cracking and conductor wire breakage that easily occur when the cable rotates with the wind turbine. It creatively adds toughening materials to the insulation layer and uses a solution of stranding the conductors in the same direction and embedding a Kevlar braided layer. Through structural and material improvements, it addresses the risk of structural failure during cable use.

[0004] However, in scenarios such as cable logistics warehousing and emergency equipment during movement, there are intermittent winding and static cyclic conditions. During winding, XLPE cables cannot release plastic micro-deformation due to cross-linking rigidity, resulting in residual stress in the cable. During static periods, the residual stress couples with environmental temperature and humidity, accelerating cable aging. For example, temperature fluctuations exacerbate cross-linking bond breakage, and moisture triggers stress-induced water treeing. Furthermore, during the next winding, new stress is superimposed on old residual stress, leading to the accumulation and propagation of cracks in the top box. Existing anti-torsion technologies for continuous winding cannot address the residual stress and coupled aging problems during static periods, resulting in a reduced 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 existing technology. The present invention proposes a torsion-resistant cross-linked polyethylene insulated cable.

[0006] To achieve the above objectives, this application adopts the following technical solution: a torsion-resistant cross-linked polyethylene insulated cable, comprising, from the inside out, a conductor layer, a stress-relieving layer, an insulation layer, a self-healing layer, a shielding layer, and an outer sheath; the stress-relieving layer is a gradient porous composite structure, including an inner porous layer and an outer dense layer distributed radially along the cable; nano-hollow glass microspheres are dispersed in the inner porous section, and nano-calcium carbonate is dispersed in the outer dense section; the substrate of the stress-relieving layer is silane-modified butyl rubber, which can undergo a condensation reaction with the insulation layer to form covalent bonds; the self-healing layer contains microcapsules oriented at 45° along the cable axis, the microcapsules being a coupling structure of core material and wall material, the core material being a silane coupling agent, and the wall material being urea-formaldehyde resin, the core material being able to undergo a ring-opening reaction with the insulation layer; the self-healing layer also contains a three-dimensional thermally conductive network formed by single-walled carbon nanotubes.

[0007] Preferably, the stress relief layer comprises, 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 comprises, by weight, 85-90 parts cross-linked polyethylene resin, 10-14 parts ethylene-vinyl acetate, 0.8-1.0 parts dicumyl peroxide, 0.6-0.8 parts trimethylolpropane trimethacrylate, and 2-2.5 parts nano-silica, wherein the vinyl acetate content in the ethylene-vinyl acetate is 16%-20%.

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

[0010] Preferably, the shielding layer comprises, by weight, 92-95 parts of semi-conductive polyethylene, 3-4 parts of chopped carbon fiber, 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 45-55 Ω·cm, the length of the chopped carbon fiber is 0.15-0.25 mm, 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 stranded outside the central elastic reinforcing core. The copper monofilament layer has an inner layer of copper monofilaments and an outer layer of copper monofilaments arranged radially. The inner layer of copper monofilaments surrounds the central elastic reinforcing core in a right-handed bundle, and the outer layer of copper monofilaments surrounds the inner layer of copper monofilaments in a left-handed re-twisting manner.

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

[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 a gradient transition of elastic modulus from the conductor layer to the insulating layer through the inner porous layer and the outer dense layer.

[0014] Preferably, the outer protective layer comprises, by weight, 80-84 parts polyvinyl chloride resin, 10-14 parts dioctyl phthalate, 3.5-4.0 parts calcium-zinc stabilizer, 0.3-0.5 parts antioxidant 1010, and 1.5-2.0 parts carbon black. The calcium-zinc stabilizer has a calcium content of 18%-22% and a zinc content of 4%-6%. The carbon black has a particle size of 28-32 nm.

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

[0016] The technical effects and advantages of this invention are as follows: This invention improves torsional resistance through the synergistic effect of the stress-relieving layer and the XLPE insulation layer. The stress-relieving layer achieves a smooth modulus transition between the conductor and the insulation layer with its gradient porous structure, reducing interfacial stress concentration. Simultaneously, it enhances interlayer bonding through silane chemical bonding, preventing peeling during resting. The insulation layer weakens the cross-linking rigidity of XLPE through hydrogen bonding, improving its micro-deformation capability and absorbing winding torsional stress. During intermittent winding and resting cycles, it reduces the accumulation of residual stress in the insulation layer, lowers the probability of insulation crack initiation, and ensures the integrity of the cable insulation structure. This makes it suitable for repeated winding requirements in scenarios such as cable logistics warehousing and mobile emergency equipment.

[0017] In this invention, a composite design of directional microcapsules and carbon nanotube networks achieves synergistic crack repair and anti-aging. The directional microcapsules are arranged according to the propagation path of cable torsional cracks, and can accurately release the repair agent when the crack appears, reacting with XLPE to close the crack. The carbon nanotubes transfer the frictional heat of winding, assisting the microcapsules to complete the repair in a low-temperature environment, and at the same time, work with carbon black to delay the oxidative aging of XLPE. This allows cracks generated in the cable during intermittent winding to be repaired, alleviates the problem of low-temperature repair failure, reduces the impact of insulation aging on performance, and extends the service life of the cable in intermittent winding and static cycle scenarios. Attached Figure Description

[0018] The disclosure of this 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 this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 Schematic diagram of the overall cable structure provided by the present invention Figure 1 ; Figure 2 Schematic diagram of the overall cable structure provided by the present invention Figure 2 ; Figure 3 Provided by the present invention Figure 2 A magnified schematic diagram of the cable structure at point A in the middle; Figure 4 A schematic diagram of the layered structure at 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, as 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 Implementation

[0020] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0021] Example 1

[0022] An embodiment of the present invention is combined with Figures 1-5The diagram shows an anti-torsion cross-linked polyethylene insulated cable, comprising, from the inside out, a conductor layer 1, a stress-relieving layer 2, an insulation layer 3, a self-healing layer 4, a shielding layer 5, and an outer sheath 6. The conductor layer 1 has a central elastic reinforcing core 11, which is made of modified nylon. Six inner copper monofilaments 12 are stranded around the outer side of the central elastic reinforcing core 11, and twelve outer copper monofilaments 13 are stranded around the outer side of the inner copper monofilaments 12. The copper monofilaments are Class 5 soft copper. The stress-relieving layer 2 comprises the following materials in parts by weight: 80 parts silane-modified butyl rubber, 6 parts nano-hollow glass microspheres, 12 parts nano-calcium carbonate, 2.5 parts silane coupling agent KH-550, and 0.6 parts antioxidant 1010. The insulation layer 3 comprises the following materials in parts by weight: 88 parts XLPE resin, 12 parts ethylene-vinyl acetate, 0.9 parts dicumyl peroxide, and 0.7 parts... The self-healing layer 4 comprises 72 parts by weight of epoxy-modified acrylate, 23 parts by weight of directional microcapsules, 0.9 parts by weight of single-walled carbon nanotubes, 0.6 parts by weight of antioxidant 168, and 2.8 parts by weight of carbon black; the shielding layer 5 comprises 94 parts by weight of semi-conductive polyethylene, 3.5 parts by weight of chopped carbon fibers, 2.3 parts by weight of maleic anhydride-grafted polyethylene, and 0.5 parts by weight of antioxidant 1010; the outer sheath 6 comprises 82 parts by weight of PVC resin, 12 parts by weight of dioctyl phthalate, 3.8 parts by weight of calcium-zinc stabilizer, 0.4 parts by weight of antioxidant 1010, and 1.8 parts by weight of carbon black.

[0023] It should be noted that in conductor layer 1, the modified nylon material contains 5 wt% POE elastomer, has a tensile strength exceeding 45 MPa, an elongation at break greater than 280%, and the diameter of the Class 5 soft copper is approximately 0.4 mm, with a conductivity greater than 97% according to international annealed copper standards; the nano-hollow glass microspheres in stress relief layer 2 have a particle size of approximately 8 μm and a density of 0.35 g / cm³. 3The particle size of nano-calcium carbonate is approximately 50 nm; in insulating layer 3, the proportion of vinyl acetate in ethylene-vinyl acetate is 18%, and the melt flow rate after melting is measured to be 2.5 g / 10 min. The lower the value, the higher the melt viscosity and the worse the flowability, which means better mechanical strength and tear resistance; the purity of dicumyl peroxide is 98%, and the purity of trimethylolpropane trimethacrylate is 99%; the particle size of nano-silica is approximately 50 nm; in self-healing layer 4, the epoxy value of epoxy-modified acrylate is measured to be 0.5 eq / 100g, that is, 0.5 equivalent epoxy groups are contained in every 100 grams of resin. The higher this value, the higher the crosslinking density of the material after curing. The larger the particle size, the better; the core material of the directional microcapsule is silane coupling agent KH-560, and the wall material is urea-formaldehyde resin with a particle size of about 10 μm; the carbon black particle size is about 20 nm; in the shielding layer 5, the volume resistivity of the semi-conductive polyethylene was measured to be 50 Ω·cm; the length of the short-cut carbon fiber is 0.2 mm, and the tensile strength reaches 3000 MPa; the grafting rate of maleic anhydride grafted polyethylene is 1.2%. It should be further noted that the grafting rate is not necessarily better the higher it is, as excessively high grafting rates can lead to degradation of the polyethylene main chain; in the outer protective layer 6, the purity of dioctyl phthalate is 99%; the calcium-zinc stabilizer contains 20% calcium and 5% zinc; the carbon black particle size is about 30 nm, which is different from the carbon black particle size in the self-healing layer 4.

[0024] This embodiment also provides a method for producing a torsion-resistant cross-linked polyethylene insulated cable, including the following steps: Step S1: Preparing conductor layer 1. First, modified nylon granules are extruded into a central elastic reinforcing core 11 using an extruder. Then, soft copper monofilaments with a diameter of 0.4 mm are stranded using a process of 6 strands right-handed stranding in the inner layer and 12 strands left-handed stranding in the outer layer. The stranding tension is controlled at 300N±20N, ultimately forming conductor layer 1. It should be noted that the extrusion temperature in this step should be controlled at 190-200℃. Too high a temperature will cause nylon degradation and a decrease in tensile strength, while too low a temperature will result in incomplete molding. The temperature of each zone of the extruder needs to be adjusted to 195℃±3℃. In the stranding process, the inner layer stranding pitch ratio is 17 times. If it is too large, the strands will loosen, leading to an increase in the DC resistance of the conductor. If it is too small, the conductor rigidity will increase, and the torsion resistance will decrease. The outer layer stranding pitch ratio is 13 times.

[0025] Step S2: Preparation of stress-relieving layer 2. Weigh silane-modified butyl rubber, nano-hollow glass microspheres, and other raw materials according to weight. Mix them in an internal mixer at 110-120℃ for 8-10 minutes. Co-extrude the mixture onto the conductor layer 1 using a co-extruder to form a gradient structure consisting of an inner high-elasticity porous layer and an outer high-adhesion dense layer, with a total thickness of 0.4 mm. It should be noted that excessively high mixing temperatures in this step will cause premature vulcanization of the butyl rubber, while excessively low temperatures will result in uneven material dispersion. The optimal temperature is 115℃±2℃. The coating speed is best controlled at 6 m / min, and the cooling water temperature at 28℃±2℃. The total thickness of stress-relieving layer 2 is 0.4 mm, with the inner porous layer 21 having a thickness of 0.2 mm and a porosity of approximately 28%, and the outer dense layer 22 having a thickness of 0.2 mm and a porosity of approximately 4%. To address the interfacial stress problem between conductor layer 1 and insulating layer 3, this step focuses on a synergistic mechanism involving chemical adhesion, gradient modulus transition, and porous elasticity transition.

[0026] Specifically, the silane-modified butyl rubber molecular chain contains silanol groups (-Si-OH) at its ends. When it comes into contact with the XLPE insulation layer 3, the hydroxyl groups (-Si-OH) can undergo a condensation reaction with the hydroxyl groups (-OH) on the XLPE molecular chain to form stable siloxane covalent bonds (-Si-OC-). This covalent bond can significantly enhance the interfacial bonding force between the two layers, avoiding interlayer delamination caused by residual stress during the resting process. Unlike the van der Waals forces dominated by traditional physical bonding, the interfacial forces of chemical bonding are dominated by covalent bonds, resulting in better interfacial stability. The elastic modulus of the copper conductor is higher than that of the XLPE insulation layer 3, and direct contact will cause stress concentration at the interface. The gradient structure of the inner highly elastic porous layer and the outer highly adhesive dense layer allows for a smooth transition of the conductor from high modulus to medium modulus. This avoids abrupt stress changes at a single interface, ensuring that residual stress is evenly distributed and gradually released along the gradient direction, reducing the risk of stress locking within the insulation layer 3. The honeycomb-like pores of the inner highly elastic porous layer possess elastic recovery characteristics. During winding, the pores undergo elastic deformation under torsional stress, absorbing some torsional energy. When at rest, the pores elastically recover, releasing the absorbed energy and further reducing residual stress in the XLPE insulation layer 3. Simultaneously, the porous structure can accommodate trace amounts of small molecule products generated by interfacial chemical reactions, such as water produced by condensation reactions, preventing interfacial bulging caused by product accumulation.

[0027] Step S3: Preparation of Insulation Layer 3. Weigh XLPE resin, EVA, and other raw materials according to weight, and melt-blend them in a twin-screw extruder at 140-150℃. Extrude the blend onto the stress-relieving layer 2 in an insulation extruder, and then vulcanize it in a vulcanizing tube at 165℃ for 50 minutes to finally form an insulation layer 3 with a thickness of 3.4 mm. The degree of crosslinking is controlled at 70%±2%. It should be noted that the melt blending in this step is controlled within the above temperature range. Too high a temperature will cause premature decomposition of DCP and insufficient crosslinking, while too low a temperature will result in uneven mixing of raw materials. It is best to control it at 145℃±3℃. The extrusion temperature of the extruder is controlled at 165-175℃, and the die pressure is 15MPa±2MPa. According to experimental results, 50 minutes is the optimal vulcanization time. If it is too short, the degree of crosslinking is only 60%, resulting in insufficient temperature resistance. If it is too long, the degree of crosslinking exceeds 80%, resulting in increased rigidity and decreased torsional resistance.

[0028] To improve torsional rigidity without sacrificing the insulation performance of XLPE, this step reduces rigidity through chemical modification while supplementing strength through material physical properties. Specifically, the ester groups (-COO-) in the ethylene-vinyl acetate (EVA) molecular chain are polar groups that form hydrogen bonds with the hydroxyl groups (-OH) on the XLPE molecular chain. XLPE's poor torsional rigidity stems from the high rigidity of its cross-linked three-dimensional network structure. The formation of hydrogen bonds weakens the intermolecular forces within the XLPE cross-linked network, breaking the fixed constraints of some rigid cross-linking points. This allows the XLPE molecular chain to have a certain degree of micro-displacement capability under torsional stress, thereby reducing overall rigidity and improving torsional micro-deformation performance. Nano-silica, a high-hardness inorganic particle, when uniformly dispersed in the XLPE matrix, can fill the tiny gaps between XLPE molecular chains through particle reinforcement, while limiting excessive molecular chain displacement. This avoids a decrease in the strength of insulation layer 3 due to EVA modification while maintaining the original high insulation strength of XLPE. More specifically, the interface between nanoparticles and 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.

[0029] By controlling the amount of dicumyl peroxide (DCP) and the vulcanization time, the degree of crosslinking of XLPE is limited to a specific range. Excessive crosslinking will result in an overly dense network structure and increased rigidity; insufficient crosslinking will compromise temperature resistance. A suitable degree of crosslinking can find a balance between rigidity and flexibility, ensuring that the insulation layer 3 does not soften under high-temperature winding friction and does not become brittle at room temperature.

[0030] Step S4: Preparation of self-healing layer 4. Weigh epoxy-modified acrylate, oriented microcapsules, and other raw materials according to weight, stir in a high-speed mixer at 60-70℃ for 5-8 minutes, and coat the outside of insulation layer 3 using a coating machine. The microcapsules are oriented at 45° along the cable axis, with an array density of approximately 950 capsules / mm². 2It should be noted that excessively high stirring temperature in this step will cause the microcapsules to rupture prematurely and the core material to leak, while excessively low temperature will result in uneven dispersion of carbon nanotubes. It is best to control the temperature at 65℃±2℃; the coating thickness should be 0.25mm, the curing temperature should be controlled at 90℃±3℃, and the curing time should be 35min.

[0031] To address the cracking problem caused by intermittent winding, this step guides the crack path and utilizes a chemical material to release self-healing agents. Specifically, according to the theory of materials mechanics, when a cable is subjected to torsional stress, the shear stress reaches its maximum value along a direction at a 45° angle to the cable axis, and cracks preferentially propagate along this direction. In this embodiment, the microcapsules are oriented at a 45° angle, allowing the crack to precisely contact and trigger microcapsule rupture during crack propagation. The oriented structure ensures that the microcapsules match the crack path, avoiding repair failure due to capsule positional deviation. The microcapsule core material, the silane coupling agent KH-560, contains epoxy groups (-C2H3O-). After the crack triggers capsule rupture, the epoxy groups can undergo a ring-opening reaction with the hydroxyl groups (-OH) on the XLPE molecular chain to generate stable ether bonds (-OC-). This reaction gradually fills the cracks, allowing the molecular chains of the XLPE insulation layer 3 to reconnect, achieving self-healing of the cracks and preventing moisture and dust from penetrating along the cracks during the resting process. Single-walled carbon nanotubes have extremely high thermal conductivity, and the frictional heat generated during winding can be quickly transferred to the microcapsule wall material, i.e., urea-formaldehyde resin, through the carbon nanotubes. The softening point of urea-formaldehyde resin decreases with increasing temperature; heat transfer allows the wall material to soften even at low temperatures, ensuring that the microcapsules can rupture due to stress during low-temperature winding, solving the problem of low repair efficiency of traditional self-healing layers 4 at low temperatures. The core cause of aging in the XLPE insulation layer 3 is the breakage of molecular chains caused by free radicals and the destruction of cross-linking bonds caused by ultraviolet radiation. The conjugated structure of carbon nanotubes can capture free radicals generated during aging, such as oxygen free radicals, preventing them from attacking the XLPE molecular chains. Carbon black has excellent ultraviolet absorption capabilities, blocking ultraviolet radiation from penetrating into the XLPE interior, inhibiting photo-oxidative aging, and extending the lifespan of the insulation layer 3 during resting.

[0032] Step S5: Prepare shielding layer 5. Weigh semi-conductive polyethylene, chopped carbon fiber, and other raw materials according to weight, and mix them in an internal mixer at 130-140℃ for 10-12 minutes; then extrude them onto the self-healing layer 4 through an extruder, controlling the volume resistivity to 80Ω·cm ± 10Ω·cm. It should be noted that excessively high mixing temperature in this step will cause carbon fiber oxidation and a decrease in conductivity, while excessively low temperature will result in uneven mixing and insufficient shielding performance. It is best to control the temperature at 135℃ ± 3℃; the extrusion temperature should be controlled at 170-180℃, and the thickness should be 1.0 mm.

[0033] To ensure the shielding layer 5 does not fail during winding, this step enhances interfacial bonding through a combination of materials and chemical reactions. Specifically, semi-conductive polyethylene itself has low tensile strength and is prone to breakage due to torsional tension during winding. Short-cut carbon fibers, being high-strength fibers, when uniformly dispersed within the semi-conductive polyethylene matrix, can bear some tensile stress through fiber bridging. When the shielding layer 5 is under tension, the carbon fibers can transfer stress from the polyethylene matrix to themselves, preventing the matrix from breaking due to stress concentration, thereby improving the tensile strength of the shielding layer 5 and ensuring shielding continuity during winding. The anhydride groups (-CO-O-CO-) on the maleic anhydride-grafted polyethylene molecular chains are active groups that can undergo esterification with the epoxy groups in the epoxy-modified acrylate of the self-healing layer 4 to form covalent bonds. This reaction eliminates the interfacial gap between the shielding layer 5 and the self-healing layer 4, preventing moisture and salt spray from penetrating along the interface during static placement and causing oxidation failure of the shielding layer 5. Simultaneously, it ensures that the shielding layer 5 does not peel off from the self-healing layer 4 when the cable is twisted, maintaining stable shielding performance.

[0034] Step S6: Prepare the outer protective layer 6. Weigh out PVC resin, dioctyl phthalate and other raw materials according to the weight parts, melt extrude them in a single screw extruder at 150-160℃, and extrude them onto the outside of the shielding layer 5.

[0035] It should be noted that excessively high melt extrusion temperatures in this step will lead to PVC degradation and decreased mechanical properties, while excessively low temperatures will make extrusion difficult. The optimal temperature range is 155℃±3℃. Similarly, excessively high temperatures for the outer sheath 6 will also cause PVC degradation and decreased mechanical properties, while excessively low temperatures will make extrusion difficult. The cooling water temperature should be controlled at 25℃±2℃. To improve the environmental adaptability of the outer sheath 6, this step utilizes a combination of physical toughening and chemical anti-aging reactions to enhance protective performance. Specifically, PVC resin itself is relatively rigid and prone to cracking during winding and twisting. Dioctyl phthalate, as a plasticizer, can insert between PVC molecular chains, weakening the van der Waals forces and giving the PVC molecular chains a certain degree of sliding ability, thereby reducing the rigidity of PVC and increasing its flexibility. This toughening effect allows the outer sheath 6 to undergo elastic deformation when the cable twists, preventing cracking and improving abrasion resistance. PVC is prone to deHClation at high temperatures, leading to molecular chain degradation and decreased mechanical properties. Calcium-zinc stabilizers can inhibit the chain reaction of HCl removal by reacting with HCl produced by PVC degradation. At the same time, their metal ions can combine with unstable chlorine atoms on the PVC molecular chain to prevent molecular chain breakage, thereby inhibiting the thermal aging of PVC. The outer sheath 6 is formed into a dense structure by extrusion process, which can physically block external moisture, dust, oil and other impurities from entering the cable interior and prevent impurities from reacting with the internal functional layer during the static process, thereby protecting the overall performance stability of the cable.

[0036] Comparative Example 1: To investigate the influence of the gradient porous structure of the stress relief layer 2 and the chemical bonding design of the silane coupling agent on the interface bonding performance, residual stress control capability 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 and interlayer peeling at the interface between the conductor and the XLPE insulation layer 3.

[0037] Compared with Example 1, the difference in Comparative Example 1 is that the stress relief layer 2 is replaced with a single layer of pure butyl rubber. This single layer of pure butyl rubber does not contain nano-hollow glass microspheres, nano-calcium carbonate, or silane coupling agent KH550. Only pure butyl rubber is used as the raw material, and its thickness remains at 0.4 mm. Correspondingly, in preparation step S2, only pure butyl rubber is weighed when the raw material is weighed. There is no need to control the dispersion of nanoparticles during the mixing process. The mixing temperature is still controlled at 115℃±2℃, the coating speed is maintained at 6 m / min, and the cooling water temperature is 28℃±2℃. The remaining preparation steps and parameters are completely consistent with those in Example 1.

[0038] The cables prepared in Example 1 and Comparative Example 1 were subjected to performance tests, specifically testing the interface adhesion, residual stress of insulation layer 3, interlayer peeling rate after standing, and crack occurrence rate of insulation layer 3.

[0039] Specifically, the interfacial adhesion test refers to GB / T 17748-2020 "General Test Methods for Materials Used in Cables and Optical Fibers", testing the interfacial adhesion between the cable conductor layer 1 and the XLPE insulation layer 3. Samples are taken radially from the cable, and a 180° peel test is performed using a peel tester, recording the force value during the stable peeling stage. The residual stress test of the insulation layer 3 refers to DL / T1573-2016 "Guidelines for Condition Evaluation of Power Cables". After the cable is wound once and left to stand for 10 days, the residual stress value of the XLPE insulation layer 3 is tested at room temperature using a stress relaxation tester. The interlayer peel rate test after standing refers to GB / T According to 2951.31-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 31: Test Methods for Polyvinyl Chloride Mixtures - High Temperature Pressure Test - Cracking Resistance Test", after the cable has undergone 5 winding and resting cycles, a 1m sample is cut along the length of the cable to observe the peeling between conductor layer 1 and XLPE insulation layer 3, and the peeling length is calculated as a percentage of the total length. The crack occurrence rate test of insulation layer 3 is conducted in accordance with DL / T 1915-2018 "Condition-Based Maintenance Procedures for Power Cable Lines". After the cable has undergone 5 winding and resting cycles, the surface and interior cracks of XLPE insulation layer 3 are observed using a high-magnification microscope, and the proportion of samples with cracks to the total number of tested samples is counted. The specific test results are shown in Table 1.

[0040] .

[0041] The specific reasons for the aforementioned performance differences include the following analysis: From the perspective of interfacial adhesion, the silane-modified butyl rubber of the stress-relieving layer 2 in Example 1 contains silanol groups. These silanol groups can undergo a condensation reaction with the hydroxyl groups on the molecular chain of the XLPE insulating layer 3 to form stable siloxane covalent bonds. This chemical bonding significantly enhances the interfacial bonding force, achieving an interfacial adhesion of 3.2 N / cm. In contrast, the single-layer pure butyl rubber used in Comparative Example 1 does not contain a silane coupling agent and cannot form covalent bonds with the XLPE insulating layer 3. The interfacial bonding relies solely on the van der Waals forces between the butyl rubber and the XLPE. The strength of the interaction force is lower than that of the covalent bond, thus the interfacial adhesion decreases significantly to 1.1 N / cm. Analysis of the residual stress difference in the insulating layer 3 shows that the stress relief layer 2 in Example 1 adopts a gradient porous structure, while the single-layer pure butyl rubber layer in Comparative Example 1 has a homogeneous structure without a gradient modulus transition design. The difference in elastic modulus between the conductor and the XLPE insulating layer 3 cannot be alleviated, and the torsional stress generated during winding is directly transmitted to the XLPE insulating layer 3. Furthermore, the pure butyl rubber layer lacks the energy absorption and release function of a porous structure, resulting in the inability to effectively release the residual stress, which is ultimately locked inside the XLPE insulating layer 3, with a residual stress value as high as 7. 0.8MPa; Regarding the interlayer peeling rate after resting, Example 1, with its high interfacial adhesion and low residual stress, effectively resists the relative sliding tendency at the interface during winding and resting cycles, resulting in an interlayer peeling rate of only 2% after 5 cycles; while Comparative Example 1, on the one hand, has low interfacial adhesion, failing to provide sufficient constraint to prevent interlayer sliding, and on the other hand, has high residual stress in the insulating layer 3. During resting, the residual stress continues to act on the interface, pushing the conductor layer 1 and the XLPE insulating layer 3 to separate relative to each other. The combination of these two factors leads to a significant increase in the interlayer peeling rate to 28%; Regarding the crack incidence rate of the insulating layer 3, Example 1... 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 buffer, thereby reducing the concentration of stress inside the insulation layer 3 and thus reducing the probability of crack occurrence. After 5 cycles, the crack occurrence rate is only 5%. In contrast, the XLPE insulation layer 3 in 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 propagation of microcracks. After 5 winding and resting cycles, the microcracks gradually develop into visible cracks, resulting in a crack occurrence rate of 35%.

[0042] Comparative Example 2: To investigate the effects of EVA modification and nano-silica reinforcement design in this invention on the torsional micro-deformation resistance, insulation strength and crack control effect of XLPE insulation layer 3, and to verify the necessity of this modification design in solving the problems of poor torsional performance and easy crack initiation caused by the cross-linking rigidity of XLPE, this comparative example 2 was set up.

[0043] Compared with Example 1, the difference in Comparative Example 2 is that the EVA-modified XLPE insulation layer 3 is replaced with a pure XLPE insulation layer 3. The pure XLPE insulation layer 3 uses only XLPE resin as raw material and does not add ethylene-vinyl acetate or nano silica. Its thickness is still 3.4 mm. Correspondingly, in the preparation step S3, only XLPE resin, dicumyl peroxide and trimethylolpropane trimethacrylate are weighed when weighing raw materials. There is no need to control the dispersion of EVA and nano silica. The melt blending temperature is still controlled at 145℃±3℃, the extrusion temperature is 165-175℃, the die pressure is 15MPa±2MPa, the vulcanization is carried out at 165℃ for 50 min in the vulcanizing tube, and the degree of crosslinking is controlled at 70%±2%. The remaining preparation steps and parameters are completely consistent with those in Example 1.

[0044] The cables prepared in Example 1 and Comparative Example 2 were subjected to performance tests, specifically testing the elastic modulus of XLPE insulation layer 3, the micro-deformation of insulation layer 3 during winding, the crack depth of insulation layer 3, and the insulation breakdown voltage.

[0045] Specifically, the elastic modulus test of XLPE insulation layer 3 is conducted according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". At room temperature, dumbbell-shaped samples are cut from 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 insulation layer 3 during winding is conducted according to GB / T29631-2013 "Insulation and sheathing materials for low-voltage cables - Part 1: General requirements". The cable is wound at a torsion angle of 120° / m, and the maximum micro-deformation of XLPE insulation layer 3 during winding is measured using a laser displacement sensor. The crack depth test of insulation layer 3 is conducted according to DL / T1915-2018 "Conditional maintenance procedures for power cable lines". After five winding-and-resting cycles, thin sheet samples are cut radially from insulation layer 3, and the maximum crack depth is observed and measured using a high-magnification microscope at 500x magnification. The insulation breakdown voltage test is conducted according to GB / T According to 1408.1-2016 "Test Methods for Electrical Strength of Insulating Materials - Part 1: Tests at Power Frequency", the breakdown voltage of cable insulation layer 3 was tested using the oil immersion method under normal temperature and pressure, with a voltage ramp rate of 2kV / s. The voltage value at breakdown was recorded. The specific test results are shown in Table 2.

[0046] .

[0047] The specific reasons for the aforementioned performance differences include the following analysis: Regarding the difference in the elastic modulus of the XLPE insulation layer 3, in Example 1, the formation of hydrogen bonds weakens the intermolecular forces within the XLPE crosslinked network, reducing overall rigidity, and the elastic modulus is controlled at 580 MPa; Comparative Example 2 uses pure XLPE insulation layer 3, without the hydrogen bonding effect of EVA, so the rigidity of the XLPE crosslinked network is not weakened, the constraint between molecular chains is strong, and it cannot buffer external forces through micro-displacement of molecular chains, resulting in an elastic modulus as high as 800 MPa, far higher than Example 1; Regarding the micro-deformation of the insulation layer 3 during winding, Example 1, due to the XLPE... The PE insulation layer 3 has a low elastic modulus and strong micro-displacement capability of its molecular chains. During winding, it can absorb torsional stress through the sliding of molecular chains and slight deformation of the insulation layer 3, with a micro-deformation of up to 15%. In contrast, the pure XLPE insulation layer 3 in Comparative Example 2 has a high elastic modulus, and its molecular chains are tightly bound by a cross-linked network, preventing effective sliding. During winding, it can only produce a 5% micro-deformation, and most of the torsional stress cannot be buffered by deformation, acting directly on the interior of the insulation layer 3, which can easily cause potential safety hazards. Regarding the crack depth of the insulation layer 3, the EVA modification in Example 1 disperses torsional stress through deformation, reducing stress concentration. At the same time, the nano-silica particles... The reinforcement fills the tiny gaps between XLPE molecular chains, preventing the initiation and propagation of microcracks. Therefore, after 5 winding-and-resting cycles, the crack depth is only 0.1 mm. In contrast, the pure XLPE insulation layer 3 of Comparative Example 2 lacks the above-mentioned dual protection. On the one hand, its micro-deformation capability is poor, and torsional stress easily forms a concentrated area inside the insulation layer 3, especially near the interface between the insulation layer 3 and the stress relief layer 2. Stress concentration will continuously induce microcracks. On the other hand, without the reinforcement and barrier of nano-silica, the microcracks will rapidly propagate into the insulation layer 3. After 5 cycles, the crack depth reaches 0.5 mm, destroying the integrity of the insulation layer 3. Integrity; Analysis of insulation breakdown voltage differences shows that in Example 1, the nano-silica particles uniformly disperse the electric field, preventing the electric field from concentrating inside the insulation layer 3. At the same time, the EVA modification does not destroy the insulating nature of XLPE, so the insulation breakdown voltage remains at 41kV. In Comparative Example 2, the pure XLPE insulation layer 3 has a large crack depth, and air or moisture from the outside easily accumulates inside the crack. These impurities cause the electric field to concentrate at the crack tip, significantly reducing the local insulation strength. Moreover, without the electric field dispersion effect of nano-silica, the overall electric field distribution of the insulation layer 3 is uneven, ultimately causing the breakdown voltage to drop to 28kV, which cannot meet the requirements for safe operation.

[0048] Comparative Example 3: To investigate the influence of the synergistic design of directional microcapsules, single-walled carbon nanotubes and carbon black in the self-healing layer 4 of this invention on the cable crack repair capability, low-temperature repair efficiency and anti-aging performance of XLPE insulation layer 3, and to verify the necessity of this design in solving the problems of cracks not being able to heal themselves, low-temperature repair failure and accelerated aging under intermittent winding scenarios, this comparative example 3 was set up.

[0049] Compared with Example 1, the difference in Comparative Example 3 is that the self-healing layer 4 is replaced with a common epoxy-modified acrylate coating. This common epoxy-modified acrylate coating uses only epoxy-modified acrylate as raw material, without adding oriented microcapsules, single-walled carbon nanotubes and carbon black, and its thickness remains at 0.25 mm. Correspondingly, in preparation step S4, only epoxy-modified acrylate is weighed when weighing raw materials, and there is no need to control the arrangement of oriented microcapsules and the dispersion of carbon nanotubes. The stirring temperature of the high-speed mixer is still controlled at 65℃±2℃, the coating speed is the same as in Example 1, the curing temperature is 90℃±3℃ and the curing time is 35 min unchanged, and the remaining preparation steps and parameters are completely consistent with those in Example 1.

[0050] The cables prepared in Example 1 and Comparative Example 3 were subjected to performance tests, specifically the crack repair rate, repair efficiency at -10℃, oxidation induction period of XLPE insulation layer 3 after 10 days of rest, and the probability of insulation failure after 5 winding-rest cycles.

[0051] Specifically, the crack repair rate test was conducted according to DL / T 1915-2018 "Condition-Based Maintenance Procedures for Power Cable Lines". Artificial cracks with a depth of 0.3 mm were pre-fabricated in the cable insulation layer 3. After standing for 48 hours, the crack closure was observed using a high-magnification microscope at 500x magnification, and the proportion of repaired crack length to initial crack length was calculated. The repair efficiency test at -10℃ was conducted according to GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11: General Test Methods - Thickness and Dimensional Measurements - Mechanical Properties Tests". The above crack repair test was repeated at -10℃, and the proportion of microcapsule rupture triggering repair was statistically analyzed. The oxidation induction period test of XLPE insulation layer 3 after 10 days of standing was conducted according to GB / T According to 19466.2-2004 "Differential Scanning Calorimetry for Plastics - Part 2: Determination of Glass Transition Temperature", the oxidation induction time of XLPE insulation layer 3 was tested using a differential scanning calorimeter at 200℃ in an oxygen atmosphere. The insulation failure probability test after 5 winding-and-resting cycles was conducted according to DL / T 1573-2016 "Guidelines for Condition Evaluation of Power Cables". After 5 winding-and-resting cycles, a withstand voltage test was performed at the rated voltage. For a 10kV cable, a voltage of 17.5kV was applied for 1 minute, and the proportion of samples that failed the withstand voltage test was recorded. Specific test results are shown in Table 3.

[0052] .

[0053] The specific reasons for the aforementioned performance differences include the following analysis: Regarding the difference in crack repair rate, the self-healing layer 4 of Example 1 contains oriented microcapsules, which can trigger capsule rupture and release the repair agent when the crack propagates, achieving self-healing. In contrast, the ordinary epoxy-modified acrylate coating of Comparative Example 3 lacks oriented microcapsules and has no source of repair agent; the 0.3mm crack cannot be filled through chemical reaction, and after 48 hours, the crack remains in its initial state, resulting in a repair rate of 0%. In terms of repair efficiency at -10℃, Example 1 relies on the high thermal conductivity of single-walled carbon nanotubes to transfer the frictional heat from the winding to the microcapsule wall material, allowing the wall material to soften and crack even at low temperatures. Comparative Example 3, lacking single-walled carbon nanotubes, experiences no heat transfer at low temperatures, and neither the microcapsules nor the coating itself can produce a repair effect, resulting in a repair efficiency of 0%. For the XLPE oxidation induction period after 10 days of resting, in Example 1, carbon nanotubes can capture free radicals generated by XLPE aging, and carbon black can absorb ultraviolet light; the two work synergistically to delay aging. In Comparative Example 3, these two components are absent, making the XLPE molecular chains susceptible to free radical attack and ultraviolet damage, accelerating the rate of cross-link breakage, and shortening the oxidation induction period from 290 min to 150 min, significantly increasing the aging rate. Analysis of the insulation failure probability after 5 cycles shows that Example 1, by repairing cracks to prevent moisture intrusion and extending insulation life through anti-aging design, has a failure probability of only 3%. In Comparative Example 3, due to the lack of crack repair and accelerated aging, cracks gradually expand and introduce impurities, leading to the destruction of the integrity of insulation layer 3, a decrease in withstand voltage performance, and ultimately 45% of the samples failing the withstand voltage test, resulting in a significantly increased failure probability.

[0054] Comparative Example 4: To investigate the effects of the short-cut carbon fiber reinforcement and maleic anhydride-grafted polyethylene chemical bonding design of the shielding layer 5 in this invention on the tensile strength, winding fracture resistance, interfacial bonding stability and oxidation resistance 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 under intermittent winding scenarios, interfacial peeling and oxidation failure when stationary, this comparative example 4 was set up.

[0055] Compared with Example 1, the difference in Comparative Example 4 is that the semiconductive shielding layer 5 containing chopped carbon fibers and maleic anhydride-grafted polyethylene is replaced with a pure semiconductive polyethylene shielding layer 5. This pure semiconductive polyethylene shielding layer 5 uses only semiconductive polyethylene and antioxidant 1010 as raw materials, without adding chopped carbon fibers and maleic anhydride-grafted polyethylene, and its thickness remains 1.0 mm. Correspondingly, in the preparation step S5, only semiconductive polyethylene and antioxidant 1010 are weighed when weighing the raw materials. There is no need to control the dispersion of chopped carbon fibers and design the interface bonding of maleic anhydride-grafted polyethylene. The mixing temperature is still controlled at 135℃±3℃, the extrusion temperature is 170-180℃, and the volume resistivity control target is 80Ω・cm±10Ω・cm. The remaining preparation steps and parameters are completely consistent with those in Example 1.

[0056] 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-healing layer 4, and the oxidation rate of the shielding layer 5 after standing for 10 days.

[0057] Specifically, the tensile strength test of shielding layer 5 is conducted according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". A dumbbell-shaped specimen is cut from shielding layer 5, and 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 shielding layer 5 after winding is conducted according to DL / T 1915-2018 "Maintenance Procedures for Power Cable Lines". After the cable is wound and left to stand for 5 cycles at a torsion angle of 120° / m, three 1m sections are cut along the length of the cable. The fracture condition of the surface and cross-section of shielding layer 5 is observed, and the proportion of fracture length to total length is calculated. The adhesion test between shielding layer 5 and self-healing layer 4 is conducted according to GB / T According to GB / T 2017-2020 "General Test Methods for Materials Used in Cables and Optical Fibers", a sample containing the shielding layer 5 and the self-healing layer 4 was cut radially from the cable. A 90° peel test was performed using a peel tester, and the force value during the stable peel stage was recorded. After standing for 10 days, the oxidation rate of the shielding layer 5 was tested according to GB / T 2951.51-2017 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 51: Test Methods for Filler Paste - Dropping Point, Oil Separation, Low Temperature Brittleness, Total Acid Value, Corrosion, Dielectric Loss Tangent and Volume Resistivity at 23°C". After the cable was stood for 10 days, the shielding layer 5 was peeled off and a sample was taken. The relative content of oxide elements on the surface of the shielding layer 5 was tested using X-ray photoelectron spectroscopy, and the proportion of the oxidized area to the total test area was calculated. The specific test results are shown in Table 4.

[0058] .

[0059] The specific reasons for the aforementioned performance differences include the following analysis: Regarding the difference in tensile strength of the shielding layer 5, the shielding layer 5 in Example 1 contains chopped carbon fibers, whose high strength characteristics can bear tensile stress through fiber bridging effect, improving the overall tensile strength of the shielding layer 5. In contrast, the pure semi-conductive polyethylene in Comparative Example 4 has low tensile strength, lacks fiber reinforcement, and cannot resist the torsional tensile stress during winding, with a tensile strength of only 8 MPa, far lower than that of Example 1. In terms of the fracture rate of the shielding layer 5 after winding, Example 1 relies on chopped carbon fibers to disperse tensile stress, preventing the semi-conductive polyethylene matrix from fracture due to stress concentration; after 5 cycles, the fracture rate is only 0.1%. Comparative Example 4 lacks chopped carbon fibers; during winding, the torsional tensile stress directly acts on the semi-conductive polyethylene, causing the matrix to crack, with a fracture rate as high as 22%, disrupting the continuity of the shield. Regarding the adhesion between the shielding layer 5 and the self-healing layer 4, in Example 1, the anhydride groups of the maleic anhydride-grafted polyethylene can undergo esterification with the epoxy groups of the self-healing layer 4, forming covalent bonds to enhance interfacial bonding. In Comparative Example 4, without maleic anhydride-grafted polyethylene, the interface relies solely on physical adhesion, resulting in a significant decrease in adhesion to 0.6 N / cm. During static placement, it is prone to peeling due to stress or moisture intrusion. Analysis of the oxidation rate of the shielding layer 5 after 10 days of static placement shows that the interfacial covalent bonds in Example 1 can prevent moisture and salt spray intrusion, reducing the oxidation of the shielding layer 5. In Comparative Example 4, the low interfacial adhesion allows impurities to easily penetrate along the interface, leading to the oxidation of carbon powder in the semi-conductive polyethylene, with the oxidation rate rising to 30%. This, in turn, increases the volume resistivity of the shielding layer 5, affecting its shielding performance.

[0060] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A torsion-resistant cross-linked polyethylene insulated cable, characterized in that, The cable comprises, from the inside out, a conductor layer, a stress-relieving layer, an insulation layer, a self-healing layer, a shielding layer, and an outer sheath. The stress-relieving layer is a gradient porous composite structure, consisting of an inner porous layer and an outer dense layer distributed radially along the cable. The inner porous layer contains dispersed nano-hollow glass microspheres, and the outer dense layer contains dispersed nano-calcium carbonate. The substrate of the stress-relieving layer is silane-modified butyl rubber, which can undergo a condensation reaction with the insulation layer to form covalent bonds. The self-healing layer contains microcapsules oriented at 45° along the cable axis. These microcapsules are a coupling structure of core and wall materials, with the core material being a silane coupling agent and the wall material being urea-formaldehyde resin. The core material can undergo a ring-opening reaction with the insulation layer. The self-healing layer also contains a three-dimensional thermally conductive network formed by single-walled carbon nanotubes.

2. The anti-torsion cross-linked polyethylene insulated cable according to claim 1, characterized in that: The stress relief layer comprises, 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.

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

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

5. The anti-torsion cross-linked polyethylene insulated cable according to claim 1, characterized in that: The shielding layer comprises, by weight, 92-95 parts of semi-conductive polyethylene, 3-4 parts of chopped carbon fiber, 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 45-55 Ω·cm, the length of the chopped carbon fiber is 0.15-0.25 mm, and the grafting rate of the maleic anhydride-grafted polyethylene is 1.0%-1.4%.

6. The anti-torsion 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 stranded on the outside of the central elastic reinforcing core. The copper monofilament layer has an inner layer of copper monofilaments and an outer layer of copper monofilaments arranged radially. The inner layer of copper monofilaments is wrapped around the central elastic reinforcing core in a right-hand stranded manner, and the outer layer of copper monofilaments is wrapped around the inner layer of copper monofilaments in a left-hand twisted manner.

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

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

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

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

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