Crosslinked polyethylene insulated and sheathed self-repairing cable for mining and method for manufacturing same

Abstract

The present application relates to the technical field of crosslinked polyethylene cable, in particular to a mine-used crosslinked polyethylene insulated armored self-repairing cable and a manufacturing method thereof, comprising a center conductor unit, a crosslinked polyethylene insulation layer, a shielding layer and an armored layer are sequentially wrapped outside the center conductor unit from inside to outside, and an outer sheath layer is extruded outside the armored layer; the shielding layer comprises a semi-conductive shielding layer wrapped outside the crosslinked polyethylene insulation layer, and a copper tape shielding layer wrapped outside the semi-conductive shielding layer. The present application improves the heat dissipation performance of the cable by setting a composite conductor structure in the center conductor unit and cooperating with graphene heat dissipation filaments and paraffin heat absorption and dissipation layers, effectively reduces the temperature of the cable during operation, reduces the failure caused by overheating, and prolongs the service life of the cable; the armored layer and the copper tape shielding layer are multi-point equipotential grounding through segmented conductive adhesive strips, which can effectively shield electromagnetic interference and limit the diffusion of fault current.

Description

Technical Field

[0001] This invention relates to the field of cross-linked polyethylene cable technology, and in particular to cross-linked polyethylene insulated armored self-healing cables for mining and their manufacturing methods. Background Technology

[0002] In coal mining operations, the stability and security of power supply are crucial for the normal operation of production activities. Traditional mining cables have revealed numerous drawbacks in practical use, severely hindering the efficient and safe operation of coal mining. These drawbacks are as follows:

[0003] First, poor heat dissipation performance: Traditional mining cables have relatively simple conductor structures, mostly consisting of a single metal conductor, lacking efficient heat dissipation measures. In underground coal mines, cables need to operate under high loads for extended periods, generating a large amount of heat as current flows through the conductor.

[0004] Due to poor heat dissipation, the internal temperature of the cable continues to rise, which not only accelerates the aging of the insulation material and reduces its service life, but also greatly increases the risk of fires and other safety accidents. Taking a common ordinary copper core cable as an example, when transmitting high-power electrical energy for a long time, the conductor temperature can reach over 80°C, far exceeding the safe operating temperature range.

[0005] Secondly, the shielding and grounding effects are inadequate: Underground coal mines contain numerous electrical devices that generate complex electromagnetic interference. Traditional cables have insufficient shielding design, making it difficult to effectively resist this interference and affecting the stability and accuracy of power transmission.

[0006] At the same time, if the grounding method is unreasonable and multi-point equipotential grounding cannot be achieved, the fault current can easily spread when a local fault occurs in the cable, causing a wider power outage and even endangering personnel safety.

[0007] Given these problems with traditional mining cables, it is necessary to develop a new type of mining cable with efficient heat dissipation, self-healing function, and good shielding and grounding performance. Summary of the Invention

[0008] To solve one of the above-mentioned technical problems, the present invention adopts the following technical solution: a mining cross-linked polyethylene insulated armored self-healing cable, comprising a central conductor unit, wherein a cross-linked polyethylene insulation layer, a shielding layer, and an armor layer are sequentially wrapped around the outside of the central conductor unit from the inside out, and an outer sheath layer is extruded on the outside of the armor layer.

[0009] The shielding layer includes a semi-conductive shielding layer wrapped around the outside of the cross-linked polyethylene insulation layer, and a copper strip shielding layer wrapped around the outside of the semi-conductive shielding layer.

[0010] The armor layer and the copper strip shielding layer are connected by segmented conductive adhesive strips to achieve multi-point equipotential grounding.

[0011] Based on any of the above technical solutions, a further optimization is made as follows: the armor layer includes steel strips intermittently wrapped around the periphery of the copper strip shielding layer along the length of the cable, with gaps between adjacent steel strip sections and isolated by insulating material, and conductive connection points are provided on the isolated sections.

[0012] Setting conductive connection points can limit the spread of fault current in the event of localized damage, thereby improving the safety and reliability of the cable.

[0013] Based on any of the above technical solutions, a further optimization is made as follows: the central conductor unit includes several tightly wound spiral composite conductors, and heat dissipation filaments are spirally wound around the periphery of the composite conductors; the composite conductor includes a copper conductor layer, a heat-absorbing and heat-dissipating layer is sprayed onto the inner wall of the cavity of the copper conductor layer, and an aluminum conductor layer is extruded onto the outer wall of the copper conductor layer.

[0014] Based on any of the above technical solutions, a further optimization is made as follows: a plurality of gap cavities are provided between the outer wall of the copper conductor layer and the inner wall of the aluminum conductor layer, and each gap cavity extends along the length direction of the composite conductor and is extruded together with the forming of the aluminum conductor layer.

[0015] Based on any of the above technical solutions, a further optimization is made of graphene material, and a layer of thermally conductive silicone grease is coated on the surface of the heat dissipation filament.

[0016] When the temperature rises to the phase change temperature of the thermal grease, it can release the latent heat of phase change to balance the internal temperature of the cable.

[0017] Based on any of the above technical solutions, a further optimization is made: the method for preparing the cross-linked polyethylene insulation layer includes the following steps:

[0018] Raw material formulation preparation: Take 80 parts of low-density polyethylene, 1 part of dicumyl peroxide as a crosslinking agent, 1 part of boron nitride nanoparticles, an appropriate amount of chelated cyclic aromatic ketone grafting agent, and 0.5 parts of microcapsule repair agent.

[0019] Raw material pretreatment and mixing: LDPE, boron nitride nanoparticles, and microcapsule repair agent are vacuum dried at 80°C for 4 hours to remove volatile substances from the raw materials and avoid affecting the performance of the final insulation layer;

[0020] Place the dried raw material into a twin-screw extruder. Set the temperature of the first stage to 120℃, the temperature of the second stage to 130℃, the temperature of the third stage to 140℃, and the screw speed to 200 r / min to ensure thorough and uniform mixing.

[0021] During this process, the microcapsule repair agent is uniformly dispersed in the other raw material system, laying the foundation for the subsequent formation of a uniform self-healing insulating layer.

[0022] Insulation layer extrusion molding: control the temperature of the barrel melting section at 100℃, the homogenization section at 120℃, the flange section at 105℃, the die head at 105℃, the traction speed at 10m / min, and the die head pressure at 20MPa to ensure a melt flow rate of 0.5g / 10min; during the extrusion process, all raw materials are fully melted, mixed, and extruded to form a preliminary insulation layer structure, with the microencapsulated repair agent evenly distributed inside the insulation layer;

[0023] Crosslinking process: Dry crosslinking method is adopted. In a 10 bar nitrogen pressurized pipeline, the temperature is raised to 200℃ and the crosslinking time is 40 minutes.

[0024] The cross-linking process forms a cross-linked structure between polyethylene molecular chains, enhancing the mechanical properties and stability of the insulation layer. At the same time, it ensures that the microencapsulated repair agent exists stably in the cross-linked insulation layer network, without affecting the cross-linking reaction or prematurely releasing the repair agent due to the high temperature and pressure during the cross-linking process.

[0025] Post-processing and testing: Degas at 50℃ for 48 hours to remove volatile small molecules remaining in the insulation layer during preparation, thereby improving the electrical properties of the insulation layer;

[0026] Thermal elongation test and breakdown field strength test are conducted on the insulation layer to evaluate whether the thermal and electrical insulation properties of the insulation layer meet the requirements;

[0027] Online X-ray inspection revealed a porosity of 0.3%, and infrared spectroscopy was used to monitor the cross-linking degree, which was 86%, ensuring a dense internal structure and that the degree of cross-linking met the standards for the insulation layer.

[0028] Self-healing performance testing: Simulate micro-damage tests on the insulation layer, such as using a specific microneedle puncture tool to create micro-pinhole damage on the surface of the insulation layer, observe the release of the repair agent and the damage repair effect, evaluate the self-healing ability through microscopic observation, electrical performance testing and other means, and record the repair time and the degree of recovery of the electrical performance of the insulation layer after repair.

[0029] Based on any of the above technical solutions, a further optimization is made as follows: the microcapsule repair agent is an epoxy resin-based repair agent, which consists of an inner core material and an outer wall material, with the wall material coating the core material; the core material includes bisphenol A type epoxy resin and polyetheramine D230 in a mass ratio of 4:1-6:1; the wall material includes urea-formaldehyde resin (urea to formaldehyde molar ratio of 1:1.5) and melamine-formaldehyde resin (melamine to formaldehyde molar ratio of 1:2-1:3).

[0030] The wall material can stably encapsulate the repair agent when the insulation layer is in normal use, and it can rupture and release the internal repair agent core material when subjected to minor damage.

[0031] This invention also provides a method for manufacturing a mining cross-linked polyethylene insulated armored self-repairing cable, wherein the mining cross-linked polyethylene insulated armored self-repairing cable adopts the above-mentioned mining cross-linked polyethylene insulated armored self-repairing cable, and the manufacturing method includes the following steps:

[0032] Manufacturing of the center conductor unit:

[0033] First, the copper conductor layer is repeatedly drawn into a tubular structure with a cavity. Then, an aluminum conductor layer is formed on the outer wall of the copper conductor layer through an extrusion process. During the extrusion process, a die head of the corresponding shape is selected to form a gap cavity extending along the length of the composite conductor. The copper conductor layer is kept in a fixed-axis rotation state and a flowing paraffin phase change material is injected into its cavity under high pressure, so that the inner wall of the cavity of the copper conductor layer forms a heat absorption and heat dissipation layer after cooling.

[0034] Then, a stranding machine is used to tightly wind several composite conductors into a spiral, and a heat dissipation filament made of graphene and coated with thermal grease is spirally wound around the outside to complete the fabrication of the central conductor unit.

[0035] Cross-linked polyethylene insulation layer preparation: After molding, the preliminary insulation layer is placed in a 10 bar nitrogen pressurized pipeline and heated to 200°C for dry cross-linking for 40 minutes using a heating device; after cross-linking, the insulation layer is placed in a vacuum drying oven and degassed in a vacuum environment at 50°C for 48 hours.

[0036] Shielding layer preparation: On the outside of the cross-linked polyethylene insulation layer, a semi-conductive shielding layer and a copper strip shielding layer are wrapped sequentially using a wrapping device;

[0037] Armor layer preparation: The steel strip is intermittently wrapped around the outside of the copper strip shielding layer along the length of the cable using a wrapping equipment. The steel strips are wrapped between adjacent sections and isolated by insulating material. Conductive connection points are set at the isolation sections using a spot welding machine.

[0038] Then, the segmented conductive connection points are connected to the armor layer and the copper strip shielding layer to achieve multi-point equipotential grounding;

[0039] Outer sheath preparation: After the above structure is completed, the outer sheath is extruded on the outside of the armor layer using an extruder.

[0040] Based on any of the above technical solutions, a further optimization is made as follows: during the preparation of the central conductor unit, when the composite conductor is wound by the stranding machine, a periodically varying tension is applied, with the tension variation range being 5-10N and the period being 30-60 seconds.

[0041] This method allows the composite conductor to be wound more tightly and evenly, improving the structural stability and conductivity of the central conductor unit while avoiding damage to the conductor due to excessive tension.

[0042] Based on any of the above technical solutions, a further optimization is made as follows: In the cross-linking process of cross-linked polyethylene insulation layer, while nitrogen is introduced into the cross-linking pipeline, an inert gas (such as argon) with a volume fraction of 1%-3% is mixed in; the gas is mixed in proportion before being introduced.

[0043] The introduction of inert gas can change the microenvironment of the cross-linking reaction, promote the cross-linking of polyethylene molecular chains, improve the uniformity of cross-linking degree, reduce defects generated during the cross-linking process, improve the electrical performance and self-healing performance of the insulation layer, and eliminate the need for large-scale modification of the cross-linking equipment, only requiring the addition of a gas pre-mixing step.

[0044] Based on any of the above technical solutions, a further optimization is made: during the fabrication of the shielding layer, ultrasonic vibration of the copper strip is used during the wrapping process to ensure a tight fit between the copper strip and the semi-conductive shielding layer, thereby enhancing the shielding effect.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] 1. This invention greatly improves the heat dissipation performance of the cable by setting a composite conductor structure in the central conductor unit, setting a gap cavity between the copper conductor layer and the aluminum conductor layer, and combining it with graphene heat dissipation filaments and paraffin heat absorption and heat dissipation layer, effectively reducing the temperature of the cable during operation, reducing failures caused by overheating, and extending the service life of the cable.

[0047] 2. The cross-linked polyethylene insulation layer used in this invention incorporates a microcapsule repair agent. When the insulation layer suffers minor damage, the microcapsules rupture to release the repair agent for repair, thereby improving the self-healing ability of the insulation layer, reducing leakage and short-circuit faults caused by insulation layer damage, and ensuring the safety and stability of power transmission.

[0048] 3. The shielding layer of the present invention adopts a combination of a semi-conductive shielding layer and a copper strip shielding layer, and the armor layer and the copper strip shielding layer achieve multi-point equipotential grounding through segmented conductive adhesive strips, which can effectively shield electromagnetic interference, limit the spread of fault current, and improve the anti-interference ability and operational safety of the cable in complex electromagnetic environments.

[0049] 4. The armor layer of the present invention adopts intermittent gap wrapping with steel strip and sets conductive connection points in the isolation section. This structure can limit the spread of fault current when there is local damage, avoid the expansion of fault, and enhance the safety and reliability of the cable.

[0050] 5. The present invention improves the structural stability and conductivity of the central conductor unit, the electrical properties and self-healing properties of the insulation layer, and the shielding effect of the shielding layer by applying periodically varying tension during the preparation of the central conductor unit, mixing in inert gas during the cross-linking of the cross-linked polyethylene insulation layer, and using ultrasonic vibration during the fabrication of the shielding layer, respectively. Attached Figure Description

[0051] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or components are generally identified by similar reference numerals. In the drawings, the elements or components are not necessarily drawn to scale.

[0052] Figure 1 This is a schematic diagram of the cross-sectional structure of the cross-linked polyethylene insulated armored self-healing cable for mining according to the present invention.

[0053] Figure 2 This is a schematic diagram of the layout structure of the present invention, in which adjacent steel strips are separated by insulating material.

[0054] In the diagram, 1 is the copper conductor layer; 2 is the heat absorption and dissipation layer; 3 is the aluminum conductor layer; 4 is the semi-conductive shielding layer; 5 is the copper strip shielding layer; 6 is the conductive adhesive strip; 7 is the steel strip; 8 is the gap cavity; 9 is the heat dissipation filament; 10 is the cross-linked polyethylene insulation layer; 11 is the outer sheath layer; and 12 is the insulating material. Detailed Implementation

[0055] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore merely examples and should not be used to limit the scope of protection of the present invention. The specific structure of the present invention is as follows: Figures 1-2 As shown in the image.

[0056] Example 1: A mining cross-linked polyethylene insulated armored self-healing cable includes a central conductor unit, on the outside of which a cross-linked polyethylene insulation layer 10, a shielding layer, and an armor layer are wrapped sequentially from the inside to the outside, and an outer sheath layer 11 is extruded on the outside of the armor layer.

[0057] The shielding layer includes a semi-conductive shielding layer 4 wrapped around the outside of the cross-linked polyethylene insulation layer 10, and a copper strip shielding layer 5 wrapped around the outside of the semi-conductive shielding layer 4.

[0058] The armor layer and the copper strip shielding layer 5 are connected by segmented conductive adhesive strips 6 to achieve multi-point equipotential grounding.

[0059] This invention relates to a cross-linked polyethylene insulated armored self-healing cable for mining and its manufacturing method, aiming to solve numerous problems associated with mining cables in complex underground environments and comprehensively improve cable performance. Through unique structural design and manufacturing processes, it achieves efficient heat dissipation, self-healing, and excellent shielding and grounding performance, ensuring the safety, stability, and efficiency of power transmission in coal mines, reducing production interruptions and safety accidents caused by cable faults, lowering maintenance costs, and improving the overall efficiency and safety of coal mining operations.

[0060] The central conductor unit conducts current, cross-linked polyethylene insulation prevents current leakage, the shielding layer blocks electromagnetic interference, the armor layer enhances mechanical strength and assists grounding, and the outer sheath provides additional protection. Segmented conductive strips connect the armor layer and the copper tape shielding layer, ensuring all parts of the cable are at the same potential and preventing faults caused by potential differences. This multi-layered design provides comprehensive protection and functional support. The shielding layer reduces the impact of electromagnetic interference on internal signal and current transmission, ensuring stable power transmission; multi-point equipotential grounding effectively reduces the risk of leakage and improves safety; the armor layer enhances the cable's mechanical strength, enabling it to withstand the complex physical environment of underground environments, such as compression and tension.

[0061] The use of segmented conductive rubber strips to achieve multi-point equipotential grounding provides a more uniform and reliable grounding effect compared to traditional grounding methods, and can more effectively limit fault current. This unique grounding design offers greater safety in the field of mining cables.

[0062] Based on any of the above technical solutions, a further optimization is made as follows: the armor layer includes a steel strip 7 that is intermittently wrapped around the periphery of the copper strip shielding layer 5 along the length of the cable, with gaps between adjacent sections of the steel strip 7 and isolated by an insulating material 12, and conductive connection points are provided on the isolated sections of the insulating material 12.

[0063] The steel strips are intermittently wrapped and isolated by insulating material, which reduces electrical connections between the steel strips while ensuring mechanical strength. The conductive connection points of the isolated section remain electrically connected under normal conditions. When local damage occurs, it can limit the fault current to flow only in a small area, preventing the fault from spreading.

[0064] It effectively improves the safety and reliability of cables. When a cable is partially damaged, it prevents the fault current from spreading widely, reducing the risk of large-scale power outages and minimizing the impact on coal mine production; at the same time, it does not affect the overall mechanical properties and grounding function of the cable. In addition to the mechanical protection provided by the armor layer, it adds a fault current limiting function, enhancing the cable's ability to cope with emergencies; and strengthening the cable's adaptability and safety under complex operating conditions.

[0065] Setting conductive connection points can limit the spread of fault current in the event of localized damage, thereby improving the safety and reliability of the cable.

[0066] Based on any of the above technical solutions, the following further optimization is made: the central conductor unit includes several tightly wound spiral composite conductors, and heat dissipation filaments 9 are spirally wound around the periphery of the composite conductors; the composite conductor includes a copper conductor layer 1, a heat absorption and heat dissipation layer 2 is sprayed onto the inner wall of the cavity of the copper conductor layer 1, and an aluminum conductor layer 3 is extruded onto the outer wall of the copper conductor layer 1.

[0067] The composite conductor combines the excellent electrical conductivity of copper with the low density and high thermal conductivity of aluminum. The copper conductor layer provides a stable conductive path, while the aluminum conductor layer assists in heat dissipation and shares some of the current conduction load. The heat-absorbing and heat-dissipating layers absorb and dissipate the heat generated by the conductor, and the heat-dissipating filaments further enhance the heat dissipation effect; thus improving both the conductor's conductivity and heat dissipation performance. The composite conductor structure reduces resistance and power loss; the efficient heat dissipation design effectively lowers the cable's operating temperature, extends its service life, and reduces failures caused by overheating. It achieves the dual functions of power transmission and efficient heat dissipation, improving the overall performance of the central conductor unit.

[0068] Based on any of the above technical solutions, a further optimization is made as follows: a plurality of gap cavities 8 are provided between the outer wall of the copper conductor layer 1 and the inner wall of the aluminum conductor layer 3, and each gap cavity 8 extends along the length direction of the composite conductor and is extruded together with the forming of the aluminum conductor layer 3.

[0069] The gap cavity forms a space filled with air or other gases within the composite conductor. Utilizing the low thermal conductivity and flowability of gases, it serves as insulation and auxiliary heat dissipation. During cable operation, heat can be conducted through the gap cavity to the heat dissipation filaments and then dissipated, enhancing heat dissipation and further reducing the cable's operating temperature. The presence of the gap cavity reduces direct heat conduction between the copper and aluminum conductor layers, optimizing the heat dissipation path and improving the cable's heat dissipation efficiency. The gap cavity provides an additional heat dissipation channel for the cable, enhancing its overall heat dissipation function.

[0070] Based on any of the above technical solutions, a further optimization is made of graphene material, and a layer of thermally conductive silicone grease is coated on the surface of the heat dissipation filament 9.

[0071] When the temperature rises to the phase change temperature of the thermal grease, it can release the latent heat of phase change to balance the internal temperature of the cable.

[0072] Graphene possesses extremely high thermal conductivity, enabling rapid heat transfer. Thermal grease enhances heat conduction at room temperature. When the temperature rises to its phase transition temperature, a phase transition occurs, absorbing a significant amount of heat. This latent heat release balances the internal temperature of the cable, preventing overheating. This significantly improves the cable's heat dissipation capacity, especially as cable temperature rises. The phase transition of the thermal grease effectively mitigates the temperature increase, protecting the cable's internal structure and insulation performance, and extending its service life.

[0073] It provides efficient heat dissipation for cables, playing a crucial role in temperature regulation, especially when dealing with peak cable heating.

[0074] Based on any of the above technical solutions, a further optimization is made: the preparation method of the cross-linked polyethylene insulation layer 10 includes the following steps:

[0075] Raw material formulation preparation: Take 80 parts of low-density polyethylene, 1 part of dicumyl peroxide as a crosslinking agent, 1 part of boron nitride nanoparticles, an appropriate amount of chelated cyclic aromatic ketone grafting agent, and 0.5 parts of microcapsule repair agent.

[0076] Low-density polyethylene (LDPE) serves as the base material, providing insulation properties. Dicumyl peroxide initiates a cross-linking reaction, causing the polyethylene molecular chains to form a cross-linked structure, enhancing the mechanical properties and stability of the insulation layer. Boron nitride nanoparticles improve the thermal conductivity and heat resistance of the insulation layer. Chelated cyclic aromatic ketone grafting agents improve the compatibility between materials. Microencapsulated repair agents are used for self-repair when the insulation layer is damaged.

[0077] Raw material pretreatment and mixing: LDPE, boron nitride nanoparticles, and microcapsule repair agent are vacuum dried at 80°C for 4 hours to remove volatile substances from the raw materials and avoid affecting the performance of the final insulation layer;

[0078] Place the dried raw material into a twin-screw extruder. Set the temperature of the first stage to 120℃, the temperature of the second stage to 130℃, the temperature of the third stage to 140℃, and the screw speed to 200 r / min to ensure thorough and uniform mixing.

[0079] During this process, the microcapsule repair agent is uniformly dispersed in the other raw material system, laying the foundation for the subsequent formation of a uniform self-healing insulating layer.

[0080] Vacuum drying removes volatile substances, preventing them from forming bubbles in the insulation layer or affecting material properties. The twin-screw extruder operates at different temperature ranges and speeds, ensuring thorough mixing of the raw materials and uniform distribution of the microcapsule repair agent, thus guaranteeing subsequent self-healing functionality. This improves the quality and performance stability of the insulation layer. Removing volatile substances reduces internal defects in the insulation layer, and uniform mixing allows each raw material to perform at its optimal level, ensuring the effective realization of the self-healing function.

[0081] Insulation layer extrusion molding: control the temperature of the barrel melting section at 100℃, the homogenization section at 120℃, the flange section at 105℃, the die head at 105℃, the traction speed at 10m / min, and the die head pressure at 20MPa to ensure a melt flow rate of 0.5g / 10min; during the extrusion process, all raw materials are fully melted, mixed, and extruded to form a preliminary insulation layer structure, with the microencapsulated repair agent evenly distributed inside the insulation layer;

[0082] Crosslinking process: Dry crosslinking method is adopted. In a 10 bar nitrogen pressurized pipeline, the temperature is raised to 200℃ and the crosslinking time is 40 minutes.

[0083] The cross-linking process forms a cross-linked structure between polyethylene molecular chains, enhancing the mechanical properties and stability of the insulation layer. At the same time, it ensures that the microencapsulated repair agent exists stably in the cross-linked insulation layer network, without affecting the cross-linking reaction or prematurely releasing the repair agent due to the high temperature and pressure during the cross-linking process.

[0084] The dry crosslinking method is carried out under nitrogen pressure. High temperature decomposes dicumyl peroxide to generate free radicals, which initiate crosslinking of polyethylene molecular chains, forming a three-dimensional network structure. Nitrogen protection prevents oxidation and ensures the stability of the microcapsule repair agent during the crosslinking process. This significantly enhances the mechanical properties and stability of the insulation layer, enabling it to better withstand mechanical stress and environmental influences. Simultaneously, it ensures that the microcapsule repair agent retains its self-healing function after the insulation layer is crosslinked, without being damaged or prematurely released. Through the crosslinking process, the initially formed insulation layer is transformed into an insulation structure with high strength and stability, while retaining its self-healing function.

[0085] Post-processing and testing: Degas at 50℃ for 48 hours to remove volatile small molecules remaining in the insulation layer during preparation, thereby improving the electrical properties of the insulation layer;

[0086] Thermal elongation test and breakdown field strength test are conducted on the insulation layer to evaluate whether the thermal and electrical insulation properties of the insulation layer meet the requirements;

[0087] Online X-ray inspection revealed a porosity of 0.3%, and infrared spectroscopy was used to monitor the cross-linking degree, which was 86%, ensuring a dense internal structure and that the degree of cross-linking met the standards for the insulation layer.

[0088] Self-healing performance testing: Simulate micro-damage tests on the insulation layer, such as using a specific microneedle puncture tool to create micro-pinhole damage on the surface of the insulation layer, observe the release of the repair agent and the damage repair effect, evaluate the self-healing ability through microscopic observation, electrical performance testing and other means, and record the repair time and the degree of recovery of the electrical performance of the insulation layer after repair.

[0089] Vacuum degassing removes residual volatile small molecules, reducing their impact on electrical performance. Thermal elongation testing, breakdown field strength testing, X-ray detection of porosity, and infrared spectroscopy monitoring of crosslinking degree are used to assess the insulation layer's performance from different angles and determine if it meets requirements.

[0090] Based on any of the above technical solutions, a further optimization is made as follows: the microcapsule repair agent is an epoxy resin-based repair agent, which consists of an inner core material and an outer wall material, with the wall material coating the core material; the core material includes bisphenol A type epoxy resin and polyetheramine D230 in a mass ratio of 4:1-6:1; the wall material includes urea-formaldehyde resin (urea to formaldehyde molar ratio of 1:1.5) and melamine-formaldehyde resin (melamine to formaldehyde molar ratio of 1:2-1:3).

[0091] The wall material can stably encapsulate the repair agent when the insulation layer is in normal use, and it can rupture and release the internal repair agent core material when subjected to minor damage.

[0092] Under normal circumstances, the wall material stably encapsulates the core material, preventing premature leakage of the repair agent. When the insulation layer suffers minor damage, the stress at the damage point causes the wall material to crack, releasing the core material composed of bisphenol A type epoxy resin and polyetheramine D230. The core material undergoes a curing reaction at the damage site, repairing the insulation layer's damage. This effectively extends the insulation layer's service life, reduces cable faults caused by minor damage, and improves the reliability and safety of cable operation. In the complex environment of underground coal mines, cables inevitably suffer various minor scratches, punctures, and other damage. The self-healing function can promptly repair these damages, preventing small problems from escalating into serious leakage or short-circuit accidents, ensuring the continuity of power transmission, and reducing mine downtime and economic losses caused by cable faults.

[0093] Traditional cables, once their insulation is damaged, often require manual location and repair, which consumes a significant amount of manpower, resources, and time. The self-healing function of this invention can automatically repair even minor damage, greatly improving the convenience of cable maintenance and operational stability.

[0094] Example 2: Compared with Example 1, this example also includes the following technical features:

[0095] This invention also provides a method for manufacturing a mining cross-linked polyethylene insulated armored self-repairing cable, wherein the mining cross-linked polyethylene insulated armored self-repairing cable adopts the above-mentioned mining cross-linked polyethylene insulated armored self-repairing cable, and the manufacturing method includes the following steps:

[0096] Manufacturing of the center conductor unit:

[0097] First, the copper conductor layer is repeatedly drawn into a tubular structure with a cavity. Then, the aluminum conductor layer 3 is formed on the outer wall of the copper conductor layer 1 through an extrusion process. During the extrusion process, a die head of the corresponding shape is selected to form a gap cavity 8 extending along the length of the composite conductor. The copper conductor layer 1 is kept in a fixed-axis rotation state and a flowing paraffin phase change material is injected into its cavity under high pressure, so that the inner wall of the cavity of the copper conductor layer 1 forms a heat absorption and heat dissipation layer 2 after cooling.

[0098] Then, a stranding machine is used to tightly wind several composite conductors into a spiral, and a heat dissipation filament 9 made of graphene and coated with thermal grease is wound around its outer periphery to complete the fabrication of the central conductor unit.

[0099] A hollow copper conductor layer is manufactured using a drawing process, providing a foundation for subsequent processing. During the extrusion of the aluminum conductor layer, a die is used to create gap cavities, enhancing heat dissipation. Paraffin phase change material is injected into the cavities of the copper conductor layer, utilizing its phase change properties to absorb and release heat. A stranding machine winds the composite conductor and adds graphene heat-dissipating filaments, further improving heat dissipation and conductivity.

[0100] Cross-linked polyethylene insulation layer 10 was prepared. After molding, the preliminary insulation layer was placed in a 10 bar nitrogen pressurized pipeline and heated to 200°C for dry cross-linking for 40 minutes using a heating device. After cross-linking, the insulation layer was placed in a vacuum drying oven and degassed in a vacuum environment at 50°C for 48 hours.

[0101] During dry cross-linking, heating under nitrogen protection causes the polyethylene molecular chains to cross-link, enhancing the insulation layer's performance. Vacuum degassing removes residual volatile substances from the cross-linking process, further improving the insulation layer's electrical properties. After cross-linking and degassing treatments, the mechanical, stability, and electrical properties of the insulation layer are significantly improved. This better protects the cable's internal conductors, prevents current leakage, improves the cable's insulation reliability, and reduces the risk of failures due to insulation problems.

[0102] Shielding layer preparation: On the outside of the cross-linked polyethylene insulation layer 10, a semi-conductive shielding layer 4 and a copper strip shielding layer 5 are wrapped in sequence using a wrapping device;

[0103] The wrapping equipment tightly wraps a semi-conductive shielding layer and a copper tape shielding layer sequentially around the insulation layer. The semi-conductive shielding layer improves the electric field distribution, while the copper tape shielding layer blocks external electromagnetic interference, preventing it from affecting the current transmission inside the cable. This effectively shields against external electromagnetic interference, ensuring the stability and accuracy of current transmission within the cable. It reduces the impact of electromagnetic interference on other electrical equipment in the coal mine, and also prevents electromagnetic interference generated by the cable itself from adversely affecting external equipment, thus improving the compatibility and stability of the entire coal mine electrical system.

[0104] Armor layer preparation: The steel strip 7 is intermittently wrapped around the outside of the copper strip shielding layer 5 along the length of the cable using a wrapping device. The steel strip 7 is wrapped between adjacent sections and isolated by the insulating material 12. Conductive connection points are set in the isolation section using a spot welding machine.

[0105] Then, the segmented conductive connection points are connected to the armor layer and the copper strip shielding layer 5 to achieve multi-point equipotential grounding;

[0106] The wrapping equipment achieves intermittent, gap-like wrapping of the steel strip. Insulating material isolates the steel strip segments, and the conductive connection points ensure electrical continuity of the steel strip while limiting the propagation of fault current in the event of localized damage. Segmented conductive connection points connect the armor layer and the copper strip shielding layer, achieving multi-point equipotential grounding and reducing the risk of leakage.

[0107] The mechanical strength of the cable is enhanced, enabling it to withstand external forces such as compression and impact underground. Multi-point equipotential grounding and fault current limiting functions improve the cable's safety and reliability, reducing safety accidents and equipment damage caused by fault current propagation, and ensuring safe coal mine production.

[0108] Preparation of outer sheath layer 11: After the above structure is completed, the outer sheath layer 11 is extruded on the outside of the armor layer using an extruder.

[0109] An extruder heats and melts outer sheath materials such as plastic, then extrudes them onto the outer armor layer to form a tightly wrapped outer sheath. The outer sheath protects the cable from external chemical corrosion, moisture erosion, and mechanical damage.

[0110] Based on any of the above technical solutions, a further optimization is made as follows: during the preparation of the central conductor unit, when the composite conductor is wound by the stranding machine, a periodically varying tension is applied, with the tension variation range being 5-10N and the period being 30-60 seconds.

[0111] This method allows the composite conductor to be wound more tightly and evenly, improving the structural stability and conductivity of the central conductor unit while avoiding damage to the conductor due to excessive tension.

[0112] When a stranding machine winds a composite conductor, the periodically varying tension causes the composite conductor to be subjected to different magnitudes of tension at different times. Smaller tensions prevent excessive stretching damage to the conductor, while the periodic changes in tension help the conductor to be wound more tightly and evenly, reducing gaps and loose areas.

[0113] This improves the structural stability of the central conductor unit, resulting in tighter contact between conductors, reduced contact resistance, and thus improved conductivity. Simultaneously, it prevents conductor damage caused by excessive tension, ensuring product quality, reducing scrap rates, and increasing production efficiency.

[0114] Based on any of the above technical solutions, a further optimization is made as follows: In the cross-linking process of the cross-linked polyethylene insulation layer 10, while nitrogen is introduced into the cross-linking pipe, an inert gas (such as argon) with a volume fraction of 1%-3% is mixed in; the gas is mixed in proportion before being introduced.

[0115] The introduction of inert gas can change the microenvironment of the cross-linking reaction, promote the cross-linking of polyethylene molecular chains, improve the uniformity of cross-linking degree, reduce defects generated during the cross-linking process, improve the electrical performance and self-healing performance of the insulation layer, and eliminate the need for large-scale modification of the cross-linking equipment, only requiring the addition of a gas pre-mixing step.

[0116] Inert gases (such as argon) are mixed into nitrogen, altering the gaseous atmosphere of the reaction system during the crosslinking process. The presence of inert gases affects the diffusion and reactivity of free radicals, promoting more uniform crosslinking between polyethylene molecular chains and reducing defects caused by uneven crosslinking. This significantly improves the electrical properties and self-healing properties of the insulation layer. The increased uniformity of crosslinking makes the mechanical properties and stability of the insulation layer more reliable, reducing the problem of insulation performance degradation caused by crosslinking defects and ensuring the long-term stable operation of the cable.

[0117] Based on any of the above technical solutions, a further optimization is made: during the fabrication of the shielding layer, the copper strip is ultrasonically vibrated during the wrapping process to ensure a tight fit between the copper strip and the semi-conductive shielding layer 4, thereby enhancing the shielding effect.

[0118] During the wrapping of the copper tape, the high-frequency mechanical waves generated by ultrasonic vibration cause the copper tape to vibrate slightly. This vibration promotes molecular interpenetration and tight contact between the copper tape and the semi-conductive shielding layer, eliminating gaps and air layers between them and improving the fit. This significantly enhances the shielding effect of the shielding layer. The tightly bonded copper tape and semi-conductive shielding layer can more effectively block electromagnetic interference, reduce the leakage and intrusion of interference signals, improve the cable's anti-interference capability in complex electromagnetic environments, and ensure the stability of power transmission.

[0119] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. For those skilled in the art, any alternative improvements or transformations made to the implementation of the present invention fall within the protection scope of the present invention.

[0120] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A crosslinked polyethylene insulated and sheathed self-repairing cable for mining, characterized in that: It includes a central conductor unit, and from the inside out, a cross-linked polyethylene insulation layer, a shielding layer, and an armor layer are sequentially wrapped around the outside of the central conductor unit, and an outer sheath layer is extruded on the outside of the armor layer. The shielding layer includes a semi-conductive shielding layer wrapped around the outside of the cross-linked polyethylene insulation layer, and a copper strip shielding layer wrapped around the outside of the semi-conductive shielding layer. The armor layer and the copper strip shielding layer are connected by segmented conductive adhesive strips to achieve multiple equipotential grounding points. The armor layer includes steel strips that are intermittently wrapped around the outer periphery of the copper strip shielding layer along the length of the cable. The steel strips are intermittently wrapped between adjacent sections and isolated by insulating material, and equipotential points are set on the isolated sections. The central conductor unit includes several tightly wound composite conductors spirally wound around the periphery of the composite conductors; the composite conductor includes a copper conductor layer, a heat-absorbing and heat-dissipating layer is sprayed onto the inner wall of the cavity of the copper conductor layer, and an aluminum conductor layer is extruded onto the outer wall of the copper conductor layer. The heat dissipation filament is made of graphene material, and a layer of thermally conductive silicone grease is coated on the surface of the heat dissipation filament.

2. A method of manufacturing a mine crosslinked polyethylene insulated and sheathed self-repairing cable as claimed in claim 1, characterized in that, The manufacturing method includes the following steps: Manufacturing of the center conductor unit: First, the copper conductor layer is repeatedly drawn into a tubular structure with a cavity. Then, an aluminum conductor layer is formed on the outer wall of the copper conductor layer through an extrusion process. During the extrusion process, a die head of the corresponding shape is selected to form a gap cavity extending along the length of the composite conductor. The copper conductor layer is kept in a fixed-axis rotation state and a flowing paraffin phase change material is injected into its cavity under high pressure, so that the inner wall of the cavity of the copper conductor layer forms a heat absorption and heat dissipation layer after cooling. Then, a stranding machine is used to tightly wind several composite conductors into a spiral, and a heat dissipation filament made of graphene and coated with thermal grease is spirally wound around the outside to complete the fabrication of the central conductor unit. The cross-linked polyethylene insulation layer was prepared by heating the initial insulation layer to 200°C in a 10 bar nitrogen pressurization pipeline for dry cross-linking for 40 minutes. After cross-linking is completed, the insulation layer is placed in a vacuum drying oven and degassed at 50°C for 48 hours. Shielding layer preparation: On the outside of the cross-linked polyethylene insulation layer, a semi-conductive shielding layer and a copper strip shielding layer are wrapped sequentially using a wrapping device; Armor layer preparation: The steel strip is intermittently wrapped around the outside of the copper strip shielding layer along the length of the cable using a wrapping equipment. The steel strips are wrapped between adjacent sections and isolated by insulating material. An equipotential point is set at the isolation section using a spot welding machine. Then, the segmented conductive connection points are connected to the armor layer and the copper strip shielding layer to achieve grounding at multiple equipotential points; Outer sheath preparation: After the above structure is completed, the outer sheath is extruded on the outside of the armor layer using an extruder.

3. The manufacturing method according to claim 2, characterized in that: During the preparation of the central conductor unit, a periodically varying tension is applied when the composite conductor is wound in a stranding machine. The tension ranges from 5 to 10 N, and the period is 30 to 60 seconds.

4. The manufacturing method according to claim 3, characterized in that: In the cross-linking process of cross-linked polyethylene insulation, nitrogen gas is introduced into the cross-linking pipeline, and an inert gas with a volume fraction of 1%-3% is mixed in; the gas is mixed in proportion before being introduced.

5. The manufacturing method according to claim 4, characterized in that: During the fabrication of the shielding layer, ultrasonic vibration of the copper strip is used in the wrapping process to ensure a tight fit between the copper strip and the semi-conductive shielding layer, thereby enhancing the shielding effect.

6. The production method according to claim 2, wherein The method for preparing the cross-linked polyethylene insulation layer includes the following steps: Raw material formulation preparation: Take 80 parts of low-density polyethylene, 1 part of dicumyl peroxide as a crosslinking agent, 1 part of boron nitride nanoparticles, an appropriate amount of chelated cyclic aromatic ketone grafting agent, and 0.5 parts of microcapsule repair agent. Raw material pretreatment and mixing: LDPE, boron nitride nanoparticles, and microcapsule repair agent are vacuum dried at 80°C for 4 hours to remove volatile substances from the raw materials and avoid affecting the performance of the final insulation layer; Place the dried raw material in a twin-screw extruder, set the first stage temperature to 120℃, the second stage temperature to 130℃, the third stage temperature to 140℃, and the screw speed to 200r / min, and mix thoroughly and evenly. During thorough mixing, the microcapsule repair agent is uniformly dispersed in the other raw material system; Insulation layer extrusion molding: control the temperature of the barrel melting section at 100℃, the homogenization section at 120℃, the flange section at 105℃, the die head at 105℃, the traction speed at 10m / min, and the die head pressure at 20MPa to ensure a melt flow rate of 0.5g / 10min; during the extrusion process, all raw materials are fully melted, mixed, and extruded to form a preliminary insulation layer structure, with the microencapsulated repair agent evenly distributed inside the insulation layer; Crosslinking process: Dry crosslinking method is adopted. In a 10 bar nitrogen pressurized pipeline, the temperature is raised to 200℃ and the crosslinking time is 40 minutes. The cross-linking process forms a cross-linked structure between polyethylene molecular chains, enhancing the mechanical properties and stability of the insulation layer, while ensuring that the microencapsulated repair agent exists stably in the cross-linked insulation layer network. Post-processing and testing: Degas at 50℃ for 48 hours to remove volatile small molecules remaining in the insulation layer during preparation, thereby improving the electrical properties of the insulation layer; Thermal elongation test and breakdown field strength test are conducted on the insulation layer to evaluate whether the thermal and electrical insulation properties of the insulation layer meet the requirements; Online X-ray inspection revealed a porosity of 0.3%, and infrared spectroscopy was used to monitor the cross-linking degree, which was 86%, ensuring a dense internal structure and that the degree of cross-linking met the standards for the insulation layer. Self-healing performance testing: Simulate micro-damage test on the insulation layer. Use a specific microneedle puncture tool to create micro-pinhole damage on the surface of the insulation layer, observe the release of the repair agent and the damage repair effect, evaluate the self-healing ability through microscopic observation and electrical performance testing, and record the repair time and the degree of recovery of the electrical performance of the insulation layer after repair.

7. The manufacturing method according to claim 6, characterized in that: in, The microcapsule repair agent uses an epoxy resin-based repair agent, which consists of an inner core material and an outer wall material, with the wall material coating the core material. The core material includes bisphenol A type epoxy resin and polyetheramine D230 in a mass ratio of 4:1-6:

1. The wall material includes urea-formaldehyde resin and melamine-formaldehyde resin. Among them, the urea-formaldehyde resin has a urea to formaldehyde molar ratio of 1:1.5, and the melamine-formaldehyde resin has a melamine to formaldehyde molar ratio of 1:2-1:

3. The wall material can stably wrap the repairing agent when the insulation layer is normally used, and can break to release the internal repairing agent core material when slightly damaged.

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