Carbon fiber reinforced overhead insulated cable and its preparation method

Abstract

This invention discloses an overhead insulated cable with a carbon fiber reinforced core and its manufacturing method. The cable includes a carbon fiber composite reinforcing core, a conductor layer, and an insulation layer arranged sequentially from the inside out. The reinforcing core is composed of an inner layer of high-modulus carbon fiber and an outer layer of high-strength carbon fiber. The conductor layer is made of trapezoidal soft aluminum profiled wire stranded in layers and pre-twisted. The surface of the insulation layer is provided with an integrally formed raised identification ridge, containing phase sequence color masterbatch. This invention balances rigidity and toughness through a double-layer reinforcing core structure, reduces the outer diameter and suppresses fretting wear through a high-fill-coefficient profiled conductor, and achieves permanent phase sequence identification through physical identification ridges. The manufacturing method employs a two-step pultrusion, pre-twisting, three-layer co-extrusion with identification ridge forming, and segmented cooling steps, effectively solving the problems of large sag, low current carrying capacity, and easy failure of phase sequence identification in existing overhead cables.

Description

Technical Field

[0001] This invention relates to the field of wire and cable technology, and in particular to overhead insulated cables with carbon fiber reinforced cores and their preparation methods. Background Technology

[0002] In applications such as urban power grid renovation, rural power grid upgrades, and long-span transmission lines, traditional steel-cored aluminum stranded wire or ordinary overhead insulated cables can no longer fully meet the requirements for capacity expansion and reliable operation. Carbon fiber composite reinforcing core, as a new type of high-strength, lightweight material, is gradually being introduced into the field of overhead cables to replace traditional steel cores due to its advantages such as high tensile strength, low specific gravity, low coefficient of linear expansion, and corrosion resistance.

[0003] In terms of the structural design of existing overhead insulated cables using carbon fiber composite reinforcing cores, most adopt a single modulus or single strength grade of carbon fiber combined with a resin matrix. This makes it difficult to achieve an optimal balance in the overall performance of the reinforcing core. Specifically, while high-modulus carbon fiber provides good rigidity to resist tensile deformation, its elongation at break is relatively low, and when combined with the conductor layer, it is prone to interfacial stress concentration due to bending or uneven stress. On the other hand, although high-strength carbon fiber has good toughness, its insufficient modulus may lead to significant creep under long-term operating tension, thus affecting the long-term sag stability of the cable. A single-structure reinforcing core cannot simultaneously meet the requirements of rigidity and toughness. In terms of conductor structure, existing carbon fiber core overhead cables mostly use a structure of ordinary round aluminum wire layered stranding. Due to the large gaps between the round wires, the conductor fill factor is low, which not only results in a larger cable outer diameter, increasing wind load and icing load, but also makes the point contact structure between the round wires more prone to fretting wear during long-term operation. Meanwhile, there is a significant difference in the coefficient of thermal expansion between the carbon fiber reinforcing core and the metal conductor layer. When load fluctuations cause temperature changes, relative slippage or gaps can easily occur between the conductor layer and the reinforcing core, affecting the overall mechanical properties and current-carrying stability of the cable. Regarding phase sequence identification in overhead cables, existing overhead insulated cables typically use black weather-resistant insulation material extruded into shape. While this provides good resistance to UV aging, phase sequence identification mainly relies on surface painting or extruded color strips. Paint markings are prone to fading and peeling in outdoor environments, resulting in a short lifespan; extruded color strips, although relatively durable, are still difficult to clearly identify at long distances or in poor lighting conditions, causing inconvenience for line construction and maintenance.

[0004] Therefore, in response to the problems mentioned above, this invention proposes an overhead insulated cable with a carbon fiber reinforced core and its preparation method. Summary of the Invention

[0005] To overcome the problems of existing carbon fiber reinforced overhead cables, such as the difficulty in balancing the rigidity and toughness of the reinforcing core, the low conductor fill factor leading to a large outer diameter and fretting wear, the slippage between the reinforcing core and the conductor layer due to thermal expansion differences, and the easy failure of outdoor phase sequence identification marks, this invention proposes an overhead insulated cable with a carbon fiber reinforced core and its manufacturing method. This cable uses a double-layer structure reinforcing core composed of an inner high-modulus carbon fiber and an outer high-strength carbon fiber, which balances rigidity and interface bonding performance. At the same time, it adopts a conductor structure with trapezoidal soft aluminum wire stranded in layers, which improves the fill factor and optimizes the fit with the reinforcing core. In addition, a raised identification ridge containing color masterbatch is integrally formed on the surface of the insulation layer, realizing a permanent phase sequence identification function, thereby comprehensively improving the overall performance of the overhead cable.

[0006] The technical solution of this invention is: an overhead insulated cable with a carbon fiber reinforced core, comprising a carbon fiber composite reinforcing core, a conductor layer, and an insulation layer arranged sequentially from the inside out, wherein: The carbon fiber composite reinforcing core includes a reinforcing core body and a heat-resistant resin layer covering the outside of the reinforcing core body; The reinforcing core body includes an inner carbon fiber layer and an outer carbon fiber layer. The inner carbon fiber layer is formed by impregnating high-modulus carbon fiber with a first thermosetting resin matrix and curing it. The outer carbon fiber layer is formed by impregnating high-strength carbon fiber with a second thermosetting resin matrix and curing it. The outer carbon fiber layer tightly covers the outside of the inner carbon fiber layer. The conductor layer is composed of multiple trapezoidal soft aluminum wire monofilaments twisted in layers on the outside of the carbon fiber composite reinforcing core, and the twisting direction of the trapezoidal soft aluminum wire monofilaments matches the winding angle of the outer carbon fiber layer. The insulating layer includes a semiconductive shielding layer extruded outside the conductor layer and a weather-resistant cross-linked polyethylene insulating layer extruded outside the semiconductive shielding layer. The outer surface of the weather-resistant cross-linked polyethylene insulating layer is provided with an integrally formed raised identification ridge along the axial direction. The identification ridge contains a color masterbatch that is different from the color of the insulating layer body and is used to identify the phase sequence.

[0007] Preferably, the first thermosetting resin matrix is ​​a bismaleimide resin or a cyanate ester resin with a glass transition temperature ≥250℃, and the second thermosetting resin matrix is ​​a modified epoxy resin system with a fracture toughness KIC ≥1.5MPa·m. 2 .

[0008] Preferably, the high-modulus carbon fiber has a tensile modulus ≥350GPa, the high-strength carbon fiber has a tensile strength ≥4500MPa, and the thickness ratio of the inner carbon fiber layer to the outer carbon fiber layer is 1:2 to 1:1.5.

[0009] Preferably, the trapezoidal soft aluminum profile monofilament has a trapezoidal cross-section, and the fill factor of the stranded conductor layer is ≥96%; the elongation of the trapezoidal soft aluminum profile monofilament after annealing is ≥20%.

[0010] Preferably, the semiconductive shielding layer is an extruded cross-linkable semiconductive polyolefin material, and its peel force with the conductor layer and the outer carbon fiber layer is controlled between 5N and 15N.

[0011] Preferably, the cross-section of the identification ridge is semi-circular or triangular, and the identification ridge is continuously distributed in a spiral shape along the cable axis, with a spiral pitch of 10 to 20 times the outer diameter of the cable.

[0012] This invention proposes a method for preparing an overhead insulated cable with a carbon fiber reinforced core, comprising the following steps: S1, the reinforcing core is prepared using a two-step pultrusion process: S11, high-modulus carbon fiber yarn is impregnated with a first thermosetting resin in a first glue tank, introduced into a pultrusion mold for preforming, and pre-cured at 120℃-150℃ to form an inner carbon fiber layer. S12, high-strength carbon fiber yarn is impregnated with a second thermosetting resin in a second glue tank and guided to the outside of the pre-cured inner carbon fiber layer. Together they enter the main molding mold and are cured in a stepped temperature range of 180℃-220℃, so that the outer carbon fiber layer tightly covers and bonds to the inner carbon fiber layer. After curing, it is drawn and cooled to obtain a carbon fiber composite reinforcing core. The surface of the carbon fiber composite reinforcing core after drawing and cooling is surface activated by an online corona treatment device to increase the friction with the conductor layer. S2, the annealed aluminum rod is extruded into trapezoidal soft aluminum profile monofilaments through a continuous extrusion press. Multiple trapezoidal soft aluminum profile monofilaments are stranded in layers on the outside of the carbon fiber composite reinforcing core through a tubular stranding machine or a frame stranding machine. During the stranding process, the tension is controlled at 5%-8% of the tensile strength. After stranding, the conductor layer is pressed tightly by a die to make the conductor layer fit tightly against the reinforcing core. The stranding of the trapezoidal soft aluminum profile monofilaments adopts a pre-twisting process, that is, the monofilaments are pre-twisted according to the stranding pitch before stranding, so that the long base of the trapezoidal cross section of the monofilament is tightly fitted with the surface of the reinforcing core without gaps after stranding. S3, the conductor core is extruded simultaneously through a three-layer co-extrusion die head to form a semi-conductive shielding layer and a weather-resistant cross-linked polyethylene insulation layer. At the same time as the weather-resistant cross-linked polyethylene insulation layer is extruded through a die with a special-shaped hole at the die head to form an identification ridge. The extruded material of the identification ridge is a base resin with added colored masterbatch. The die for extruding the identification ridge is a combined die, including a die sleeve body for forming the outer diameter of the insulation layer and a ridge forming block that can be detachably installed on one side of the discharge end of the die sleeve body. The size and shape of the identification ridge can be adjusted by changing the ridge forming block of different specifications. S4. The cable with the insulation layer is cross-linked through a continuous vulcanization pipeline. The cross-linking temperature is controlled at 220℃-260℃. After cross-linking, it is cooled to 90℃-100℃ by high-pressure water at 1.0MPa-1.2MPa, and then cooled to below 40℃ by a normal temperature water bath to avoid internal stress concentration.

[0013] The beneficial effects of this invention are: 1. This invention employs a double-layer reinforcing core structure composed of an inner layer of high-modulus carbon fiber and an outer layer of high-strength carbon fiber, and adjusts the thickness ratio of the inner and outer layers and the resin system to ensure that the reinforcing core has high tensile modulus. This ensures long-term sag stability and high fracture toughness to resist construction bending and impact loads, significantly improving the overall mechanical performance and service life of the cable.

[0014] 2. This invention achieves a conductor fill factor of over 96% by employing trapezoidal soft aluminum wire with layered stranding and pre-twisting process, significantly reducing the cable outer diameter and thus lowering wind and ice load. Simultaneously, it optimizes the point contact between the single wires into surface contact, effectively suppressing fretting wear and increased contact resistance during long-term operation. Furthermore, by matching the stranding direction with the outer winding angle of the reinforcing core, it eliminates torsional stress, solving the problems of loose conductor structure, poor thermal stability, and slippage at the interface with the reinforcing core.

[0015] 3. This invention transforms phase sequence identification from a traditional reliance on surface coating to a dual permanent identifier combining physical structure and built-in color by integrally molding a raised identification ridge containing color masterbatch on the surface of the insulation layer and optimizing its cross-sectional shape and spiral distribution parameters. This solves the problems of easy paint fading and difficult color stripe identification in outdoor environments, and greatly improves the convenience and reliability of line construction and maintenance.

[0016] 4. This invention employs a two-step pultrusion molding process to separately control the curing of the inner and outer layers, combined with online corona treatment to enhance the interfacial bonding force, and uses a modular mold to achieve flexible extrusion of the identification ridges. At the same time, it uses a high-pressure water and normal water segmented cooling process to eliminate insulation internal stress, solving problems such as the interface bonding of the double-layer reinforcing core, the twisting and turning of the profile, the cumbersome replacement of the identification ridge molding, and the thermal stress cracking of the insulation layer, thus ensuring the consistency of product quality and the high efficiency of production. Attached Figure Description

[0017] Figure 1 The diagram shown is a cross-sectional structural diagram of the carbon fiber reinforcing core of the present invention. Figure 2 The diagram shown illustrates the preparation process of the carbon fiber reinforcing core of this invention.

[0018] Explanation of reference numerals in the attached drawings: 1. Fiber composite reinforcing core; 11. Inner carbon fiber layer; 12. Outer carbon fiber layer; 13. Heat-resistant resin layer; 2. Conductor layer; 21. Trapezoidal soft aluminum profile monofilament; 3. Insulation layer; 31. Semi-conductive shielding layer; 32. Weather-resistant cross-linked polyethylene insulation layer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1 This invention provides an embodiment of an overhead insulated cable with a carbon fiber reinforced core: The present invention comprises a carbon fiber composite reinforcing core 1, a conductor layer 2, and an insulating layer 3 arranged sequentially from the inside out.

[0021] In this embodiment, the carbon fiber composite reinforcing core 1 will be described in detail: The carbon fiber composite reinforcing core 1 includes a reinforcing core body and a heat-resistant resin layer 13 covering the outside of the reinforcing core body. The reinforcing core body adopts a double-layer composite structure design, including an inner carbon fiber layer 11 and an outer carbon fiber layer 12.

[0022] The inner carbon fiber layer 11 is formed by impregnating high-modulus carbon fiber with a first thermosetting resin matrix and curing it. High-modulus carbon fiber refers to carbon fiber with a tensile modulus ≥350GPa, preferably carbon fiber with a modulus between 350-450GPa. This type of carbon fiber has extremely high elastic modulus, which can provide excellent rigid support for the reinforcing core. When subjected to long-term tension of overhead lines, it can effectively resist tensile deformation and ensure the sag stability of the cable. As the skeleton of the reinforcing core, the inner layer bears the main tensile load. The first thermosetting resin matrix is ​​preferably bismaleimide resin or cyanate ester resin with a glass transition temperature (Tg) ≥250℃. The purpose of choosing a high-temperature resin system is that the temperature of the carbon fiber composite core may reach above 100℃ during operation due to conductor heating and sunlight exposure. The temperature is even higher during short-circuit faults. Using a high-Tg resin can ensure that the resin matrix does not soften under high-temperature conditions, thereby ensuring that the rigidity of the inner carbon fiber layer is maintained.

[0023] The outer carbon fiber layer 12 is formed by impregnating high-strength carbon fiber with a second thermosetting resin matrix and curing it. The outer carbon fiber layer 12 tightly covers the outside of the inner carbon fiber layer 11. High-strength carbon fiber refers to carbon fiber with a tensile strength ≥ 4500 MPa, preferably with a strength between 4500-5500 MPa. This type of carbon fiber has excellent fracture toughness and impact resistance. The outer carbon fiber layer protects the inner high-modulus carbon fiber, preventing brittle fracture during bending or impact. Simultaneously, as the interface layer in direct contact with the conductor layer, it needs to possess good interfacial bonding properties. The second thermosetting resin matrix is ​​preferably a modified epoxy resin system with a fracture toughness KIC ≥ 1.5 MPa·m. 2 Modified epoxy resin has good compatibility with high-strength carbon fiber. The composite material formed after curing has moderate modulus and excellent toughness, which can buffer the stress transmission between the conductor layer and the reinforcing core. At the same time, its high fracture toughness makes the outer layer less prone to microcracks when subjected to local pressure or bending, thereby preventing the penetration of moisture or corrosive media.

[0024] The thickness ratio of the inner carbon fiber layer 11 to the outer carbon fiber layer 12 is preferably 1:2 to 1:1.5. If the inner layer is too thin, the overall modulus of the reinforcing core will be insufficient, leading to increased sag in long-span lines. If the outer layer is too thin, the interfacial bonding performance and impact resistance of the reinforcing core will decrease, making the inner fibers prone to damage during construction and layout due to excessively small bending radii. Within this ratio range, the overall tensile modulus of the reinforcing core can be guaranteed to reach above 120 GPa, while its minimum bending radius can be guaranteed to be less than 20 times the cable outer diameter.

[0025] The heat-resistant resin layer 13 covers the outermost part of the reinforcing core body. This resin layer can be the same as or have good compatibility with the second thermosetting resin. Its function is to form a dense protective layer on the surface of the reinforcing core, fill the tiny pits on the surface of the carbon fiber, make the surface of the reinforcing core smoother, facilitate the stranding of the subsequent conductor layer, and further improve the corrosion resistance of the reinforcing core.

[0026] In this embodiment, conductor layer 2 will be described in detail: The conductor layer 2 consists of multiple trapezoidal soft aluminum profile monofilaments 21 stranded in layers around the carbon fiber composite reinforcing core 1. These trapezoidal soft aluminum profile monofilaments are made by annealing aluminum rods and then continuously extruding them into trapezoidal cross-sections. The trapezoidal cross-section design allows adjacent monofilaments to fit face-to-face, significantly improving the fill factor of the conductor layer. The trapezoidal soft aluminum profile monofilament 21 has an elongation of ≥20% after annealing. This high elongation means the aluminum monofilament has excellent flexibility after annealing, making it easy to deform during stranding and allowing it to tightly adhere to the reinforcing core surface and adjacent monofilaments. Simultaneously, bending stress caused by wind vibration during use is effectively released, thus preventing fatigue fracture.

[0027] The stranding direction of the trapezoidal soft aluminum wire monofilament 21 is matched with the winding angle of the outer carbon fiber layer 12 to eliminate torsional stress. Here, "matching" refers to comprehensively considering the production process parameters of the carbon fiber composite core when designing the stranding pitch. Specifically, during pultrusion, although the outer carbon fibers are mainly axially aligned, they may have a winding angle of 1°-3° in some processes. By adjusting the stranding direction and pitch of the conductor layer, the torsional torque generated during conductor layer stranding can be made opposite to the direction of the residual torsional torque inside the reinforcing core, thereby achieving torque balance in the finished cable. Cables treated in this way will not rotate in a free-hanging state, reducing additional stress on the fittings.

[0028] After stranding, conductor layer 2 needs to undergo compression molding to further compact the conductor layer, achieving a fill factor of ≥96%, which is far higher than the 75%-85% fill factor of traditional round stranded conductors. With a high fill factor, the cable outer diameter can be reduced by 5%-8% for the same conductor cross-sectional area, thereby reducing wind and ice loads. Simultaneously, surface contact between individual wires replaces point contact, reducing contact resistance and significantly decreasing fretting wear during long-term operation.

[0029] In this embodiment, the insulating layer 3 will be described in detail: The insulating layer 3 includes a semiconductive shielding layer 31 extruded outside the conductor layer 2 and a weather-resistant cross-linked polyethylene insulating layer 32 extruded outside the semiconductive shielding layer 31.

[0030] The semi-conductive shielding layer 31 is an extruded cross-linkable semi-conductive polyolefin material. Its function is to uniformly distribute the electric field on the conductor surface and prevent partial discharge at the interface between the conductor and the insulation layer. This invention precisely controls the peel force of the semi-conductive shielding layer. Specifically, the peel force between the semi-conductive shielding layer 31 and the conductor layer 2 and the outer carbon fiber layer 12 is controlled between 5N and 15N. If the peel force is too low, the shielding layer is prone to detaching from the conductor when the cable bends or undergoes thermal expansion and contraction, forming an air gap that leads to discharge. If the peel force is too high, peeling becomes difficult when making cable termination joints, potentially damaging the conductor or reinforcing core. By adjusting the formulation and extrusion process of the semi-conductive shielding layer, its peel force is controlled within the above range, ensuring both the reliability of electrical performance and ease of construction.

[0031] The weather-resistant cross-linked polyethylene insulation layer 32 is made of cross-linked polyethylene material with added ultraviolet absorbers and antioxidants, which has good outdoor aging resistance. Its thickness is designed according to different voltage levels, generally between 3.4mm and 20mm.

[0032] The weather-resistant cross-linked polyethylene insulation layer 32 has an integrally formed raised identification ridge along its axial direction on its outer surface. This ridge contains a color masterbatch, distinct from the insulation layer itself, used to identify the phase sequence. Workers achieve permanent phase sequence identification through both physical structure (raised ridge) and color (built-in masterbatch). The insulation layer itself is typically black (carbon black is added to improve weather resistance), while the identification ridge can use phase sequence colors such as red, yellow, and green. The cross-section of the identification ridge is semi-circular or triangular. A semi-circular cross-section allows for better molding flow and less stress concentration at the corners; a triangular cross-section is easier to identify visually and tactilely. There can be one or more identification ridges. For multi-phase cable systems, different phase sequences can be distinguished by the number, spacing, or color combination of the identification ridges. Furthermore, the identification ridges are continuously distributed in a spiral along the cable axis, with a spiral pitch 10 to 20 times the cable's outer diameter. This spiral design ensures that the identification ridges are visible when the cable is suspended at any angle, and the stress concentration generated by the spiral ridges when the cable bends is less than that of the straight ridges.

[0033] Please see Figure 2 This invention describes a method for preparing an overhead insulated cable with a carbon fiber reinforced core, specifically: (1) A two-step pultrusion molding process is used to prepare the reinforcing core. First, high-modulus carbon fiber yarn is drawn from the yarn rack, sorted by the yarn collecting plate, and then enters the first glue tank to be impregnated with the first thermosetting resin. The first thermosetting resin is bismaleimide resin or cyanate ester resin, and its viscosity is controlled at 800-1500 mPa·s (60℃) to ensure that the fiber is fully impregnated. After impregnation, the carbon fiber enters the preforming mold, and the excess resin is removed and pre-shaped by the extrusion action of the mold. Then, it is pre-cured in the heated pre-curing mold at 120℃-150℃ to form the inner carbon fiber layer 11. The pre-curing temperature should not be too high, and the time should be controlled at 2-5 minutes to allow the resin to reach the gel state. Incomplete curing is to allow chemical bonding with the second layer in the future.

[0034] The high-strength carbon fiber yarn is then impregnated with a second thermosetting resin in a second adhesive bath. The second thermosetting resin is a modified epoxy resin system with a viscosity controlled at 500-1000 mPa·s (50℃), exhibiting good fluidity to facilitate thorough impregnation of the high-strength carbon fiber. After impregnation, the high-strength carbon fiber is uniformly coated onto the pre-cured inner carbon fiber layer 11 via a guiding device, and both layers enter the main molding die. The main molding die is divided into multiple heating zones with a stepped temperature increase from 180℃ to 220℃, allowing the outer carbon fiber layer 12 to gradually cure while the inner carbon fiber layer 11 continues to complete its final curing. Interdiffusion and co-crosslinking of resin molecules occur at the interface between the inner and outer layers, achieving a strong chemical bond. The cured reinforcing core is then led out from the mold outlet, pulled by a traction machine, and cooled to room temperature via a cooling water bath to obtain the carbon fiber composite reinforcing core 1.

[0035] After traction cooling, the surface of the carbon fiber composite reinforcing core 1 undergoes surface activation treatment using an online corona treatment device. Corona treatment uses a high-voltage electric field to ionize air and generate plasma, which acts on the surface of the reinforcing core, introducing polar groups to increase surface energy and thus significantly increasing the frictional force with the subsequent conductor layer 2. The surface tension after treatment should reach above 50 mN / m.

[0036] (2) The aluminum rod is annealed in a continuous annealing furnace at a temperature controlled between 350℃ and 400℃ to achieve an elongation of over 20%. The annealed aluminum rod is then extruded through a trapezoidal die to form trapezoidal soft aluminum profile monofilaments 21. Multiple trapezoidal soft aluminum profile monofilaments 21 are then layered and stranded onto the outside of the carbon fiber composite reinforcing core 1 using a tubular stranding machine or a frame stranding machine. During the stranding process, the tension must be strictly controlled, set at 5%-8% of the monofilament's tensile strength. Excessive tension will cause the monofilaments to thin or be damaged, while insufficient tension will result in loose stranding.

[0037] This invention pre-twists the monofilaments according to a set stranding pitch before stranding. Specifically, a pre-twisting device is installed on the pay-off frame of the stranding machine, causing the monofilaments to twist at a certain angle along the stranding direction before entering the stranding point. During stranding, the long base of the pre-twisted monofilament's trapezoidal cross-section can achieve a tight fit with the surface of the reinforcing core and the side edges of adjacent monofilaments, without any gaps. After stranding, the conductor layer is compacted by a die with a die aperture slightly smaller than the outer diameter of the conductor layer. Pressure further densifies the conductor layer, achieving a fill factor of over 96%.

[0038] The wire core with conductor layer 2 is extruded simultaneously through a three-layer co-extrusion die head to form a semi-conductive shielding layer 31 and a weather-resistant cross-linked polyethylene insulation layer 32. While the weather-resistant cross-linked polyethylene insulation layer 32 is being extruded, an identification ridge is formed by extruding through a die with a special-shaped hole at the die head. The extruded material of the identification ridge is a base resin with added colored masterbatch, and the color of the masterbatch is determined according to the phase sequence.

[0039] (4) The cable with the insulation layer is cross-linked through a continuous vulcanization pipeline. The cross-linking temperature is controlled at 220℃-260℃, and the cross-linking medium can be high-temperature nitrogen or steam. At this temperature, the cross-linking agent in the polyethylene molecular structure will decompose to generate free radicals, which will promote the formation of a three-dimensional network structure of polyethylene molecular chains, thereby giving the insulation layer higher heat resistance and mechanical properties.

[0040] After cross-linking, the cable enters the cooling section, where a segmented cooling process is employed to avoid stress concentration. Specifically, the cable is first cooled by high-pressure water at 1.0MPa-1.2MPa, rapidly reducing its temperature to 90℃-100℃. The high-pressure water ensures thorough penetration of the cooling water onto the cable surface, improving cooling efficiency, while the high-pressure environment suppresses bubble formation. The cable then enters a room-temperature water bath, where it is cooled to below 40℃, completing the final cooling process. The first stage of this segmented cooling method involves rapid cooling to quickly lower the high temperature after cross-linking, preventing excessive polyethylene crystallinity that could lead to insulation brittleness. The second stage involves slow cooling to ensure a uniform decrease in the cable's internal temperature, reducing thermal stress caused by temperature differences and preventing shrinkage voids or cracks in the insulation layer.

[0041] This invention provides Embodiment 1: In this example, the carbon fiber composite reinforcing core 1 adopts a double-layer composite structure. The inner carbon fiber layer 11 is made of high-modulus carbon fiber with a tensile modulus of 380 GPa, impregnated with bismaleimide resin (Tg=260℃), and pre-cured at 130℃ for 3 minutes; the outer carbon fiber layer 12 is made of high-strength carbon fiber with a tensile strength of 4900 MPa, impregnated with a modified epoxy resin system (KIC=1.6 MPa·m). 2 The main curing temperature is set to a stepped increase of 190℃-210℃-230℃, the thickness ratio of the inner layer to the outer layer is 1:1.8, and the diameter of the reinforcing core is 5.0mm.

[0042] The conductor layer 2 is made of trapezoidal soft aluminum wire monofilaments 21 twisted together, with an elongation of 25% after annealing. The twisting adopts a pre-twisting process, with a twisting pitch of 150mm and a twisting direction to the left, matching the winding angle of the outer layer fiber of the reinforcing core. After compaction, the outer diameter of the conductor layer is 12.5mm, with a fill factor of 97.2%.

[0043] The insulation layer 3 includes a semi-conductive shielding layer 31 with a thickness of 0.5 mm and a measured peel force of 8 N; and a weather-resistant cross-linked polyethylene insulation layer 32 with a thickness of 3.4 mm, a triangular cross-section for identification edges, a spiral pitch of 200 mm, and red masterbatch.

[0044] This invention provides Embodiment 2: In this example, the carbon fiber composite reinforcing core 1 adopts a double-layer composite structure. The inner carbon fiber layer 11 is made of high-modulus carbon fiber with a tensile modulus of 420 GPa, impregnated with cyanate ester resin (Tg=280℃), and pre-cured at 140℃ for 4 minutes. The outer carbon fiber layer 12 is made of high-strength carbon fiber with a tensile strength of 5200 MPa, impregnated with a modified epoxy resin system (KIC=1.8 MPa·m). 2The main curing temperature is set to a stepped increase of 200℃-220℃-240℃, the thickness ratio of the inner layer to the outer layer is 1:2.0, and the diameter of the reinforcing core is 8.0mm.

[0045] Conductor layer 2 is made of trapezoidal soft aluminum wire monofilament 21 twisted together, with an elongation of 28% after annealing. The twisting adopts a pre-twisting process, with a twisting pitch of 220mm and a twisting direction of right. The outer diameter of the conductor layer after compaction is 20.0mm, and the fill factor is 97.8%.

[0046] The insulation layer 3 includes a semi-conductive shielding layer 31 with a thickness of 0.8 mm and a measured peel force of 12 N; a weather-resistant cross-linked polyethylene insulation layer 32 with a thickness of 8.0 mm; and an identification ridge with a semi-circular cross-section, a spiral pitch of 350 mm, and using green masterbatch.

[0047] This invention provides comparative examples: This example provides six sets of comparative examples to compare with Embodiments 1 and 2 above, thereby verifying the effectiveness of the present invention. Specifically: Comparative Example 1 uses a single carbon fiber reinforcing core, only high-strength carbon fiber impregnated with modified epoxy resin, and omits the inner high-modulus carbon fiber layer. The reinforcing core diameter is 5.0 mm, and the other structures are the same as in Example 1.

[0048] Comparative Example 2 uses a single carbon fiber reinforcing core, only high-modulus carbon fiber impregnated with bismaleimide resin, and omits the outer high-strength carbon fiber layer. The reinforcing core diameter is 5.0 mm, and the other structures are the same as in Example 1.

[0049] Comparative Example 3 uses a conventional round aluminum wire stranded structure for the conductor layer. The diameter of the aluminum single wire is 2.5 mm, and the filling factor after stranding is 88%. It does not use trapezoidal wire or pre-twisting process. Only other structures are the same as in Example 1.

[0050] Comparative Example 4 has an insulation layer without identification ridges and uses conventional black insulation material. Phase sequence identification is achieved by surface painting, but other structures are the same as in Example 1.

[0051] In the preparation method of Comparative Example 5, step 2 did not use the pre-twisting process; the trapezoidal wires were directly twisted together, and other parameters were the same as in Example 2.

[0052] In the preparation method of Comparative Example 6, step 4 uses a single water tank for cooling, without segmented cooling, and other parameters are the same as in Example 2.

[0053] Table 1 Test Results of Examples

[0054] Table 2 Test results for comparative examples 1-4

[0055] Tables 1 and 2 show that Comparative Example 1, using a single high-strength carbon fiber, has high tensile strength but low tensile modulus, resulting in a large sag increase at 80°C and significant sag changes at high temperatures, affecting the safe operation of the line. Comparative Example 2, using a single high-modulus carbon fiber, has a tensile modulus as high as 160 GPa and a smaller sag increase at 80°C, but its tensile strength is significantly reduced, and its minimum bending radius is large. The strength retention rate after bending is only 92%, indicating poor toughness and susceptibility to damage during construction. Example 1 uses a double-layer structure, combining the advantages of high modulus and high strength, with a tensile strength of 2850 MPa, a tensile modulus of 135 GPa, a sag increase of 12.5% ​​at 80°C, and a strength retention rate of 95% after bending. Its performance is well-balanced and excellent. Example 2 also verifies this effect. Comparative Example 3 uses conventional round wire stranding with a fill factor of only 88.5%, resulting in an increased conductor outer diameter of 13.8 mm for the same conductor cross-sectional area, which increases wind and ice loads. Comparative Example 3 showed a resistance change rate of 2.1% after heating at 120℃ for 1000 hours, significantly higher than the 0.8% of Example 1. The reason for this is that the point contact between the circular lines undergoes fretting wear and oxidation during long-term thermal cycling, increasing the contact resistance. In contrast, the trapezoidal lines in Example 1 have surface contact, resulting in more stable contact. Comparative Example 4 used surface paint for identification; after 1000 hours of salt spray testing and 1000 hours of UV aging, the paint significantly faded and peeled, losing its identification function. The identification ridge in Example 1 is an integrally formed structure with the insulation layer, containing color masterbatch. After the same tests, the color remained good, the ridge was intact, and it could still be clearly identified by color and touch.

[0056] As can be seen from the table, the peel force of Examples 1 and 2 is controlled at 8N and 12N respectively, both within the preferred range of 5N-15N. This peel force range ensures that the shielding layer and the conductor will not separate during use, and also facilitates peeling during construction, resulting in good overall performance.

[0057] Table 3 shows the test results for Comparative Examples 5 and 6.

[0058] As shown in Tables 1 and 3, Comparative Example 5, which did not employ a pre-twisting process, had a conductor fill factor of 95.1%, slightly lower than the 97.8% of Example 2. Furthermore, the conductor outer diameter was slightly larger. After the thermal cycling test, the resistance change rate of Comparative Example 5 was significantly higher than that of Example 2, indicating that without pre-twisting, there were minute gaps in the trapezoidal monofilaments, suggesting the possibility of fretting wear during long-term operation. Comparative Example 6 used a single water tank for cooling. After the thermal cycling test, slight shrinkage cracks appeared in the insulation layer, indicating stress concentration during the cooling process. Example 2 employed a segmented cooling process, first rapidly cooling to 90℃-100℃ with high-pressure water, then slowly cooling with room-temperature water. No abnormalities were observed in the insulation layer after thermal cycling, indicating that the internal stress was effectively released.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An overhead insulated electrical cable of the type having a carbon fiber reinforced core, characterized in that, It includes a carbon fiber composite reinforcing core (1), a conductor layer (2), and an insulating layer (3) arranged sequentially from the inside out, wherein: The carbon fiber composite reinforcing core (1) includes a reinforcing core body and a heat-resistant resin layer (13) covering the outside of the reinforcing core body. The reinforcing core body includes an inner carbon fiber layer (11) and an outer carbon fiber layer (12), wherein the inner carbon fiber layer (11) is formed by impregnating a first thermosetting resin matrix with high modulus carbon fiber and curing, and the outer carbon fiber layer (12) is formed by impregnating a second thermosetting resin matrix with high strength carbon fiber and curing, and the outer carbon fiber layer (12) tightly covers the outside of the inner carbon fiber layer (11). The conductor layer (2) is made of multiple trapezoidal soft aluminum wire monofilaments (21) twisted in layers on the outside of the carbon fiber composite reinforcing core (1), and the twisting direction of the trapezoidal soft aluminum wire monofilaments (21) matches the winding angle of the outer carbon fiber layer (12). The insulating layer (3) includes a semi-conductive shielding layer (31) extruded outside the conductor layer (2) and a weather-resistant cross-linked polyethylene insulating layer (32) extruded outside the semi-conductive shielding layer (31). The outer surface of the weather-resistant cross-linked polyethylene insulating layer (32) is provided with an integrally formed raised identification ridge along the axial direction. The identification ridge contains a color masterbatch that is different from the color of the insulating layer body and is used to identify the phase sequence.

2. The overhead power cable of carbon fiber reinforced core according to claim 1, characterized in that: The first thermosetting resin matrix is ​​a bismaleimide resin or a cyanate ester resin with a glass transition temperature ≥250℃, and the second thermosetting resin matrix is ​​a modified epoxy resin system with a fracture toughness KIC ≥1.5 MPa·m. 2 .

3. The overhead power cable of carbon fiber reinforced core according to claim 1, characterized in that: The high-modulus carbon fiber has a tensile modulus ≥350GPa, the high-strength carbon fiber has a tensile strength ≥4500MPa, and the thickness ratio of the inner carbon fiber layer (11) to the outer carbon fiber layer (12) is 1:2 to 1:1.

5.

4. The overhead power cable of carbon fiber reinforced core according to claim 1, characterized in that: The trapezoidal soft aluminum profile monofilament (21) has a trapezoidal cross-section, and the fill factor of its stranded conductor layer (2) is ≥96%; the elongation of the trapezoidal soft aluminum profile monofilament (21) after annealing is ≥20%.

5. The overhead power cable of carbon fiber reinforced core according to claim 1, characterized in that: The semiconductive shielding layer (31) is an extruded cross-linkable semiconductive polyolefin material, and its peel force with the conductor layer (2) and the outer carbon fiber layer (12) is controlled between 5N and 15N.

6. The overhead power cable of carbon fiber reinforced core according to claim 1, characterized in that: The cross-section of the identification ridge is semi-circular or triangular, and the identification ridge is continuously distributed in a spiral shape along the cable axis, with a spiral pitch of 10 to 20 times the outer diameter of the cable.

7. Process for the production of an overhead insulated cable with a carbon fiber reinforced core, producing an overhead insulated cable with a carbon fiber reinforced core as claimed in any of claims 1 to 6, characterized in that Includes the following steps: S1. A two-step pultrusion molding process is used to prepare the reinforcing core. First, high-modulus carbon fiber yarn is impregnated with a first thermosetting resin in a first glue tank and introduced into a pultrusion mold for pre-forming. It is pre-cured at 120℃-150℃ to form an inner carbon fiber layer (11). Then, high-strength carbon fiber yarn is impregnated with a second thermosetting resin in a second glue tank and guided to the outside of the pre-cured inner carbon fiber layer (11). Together, they enter the main molding mold and are cured in a stepwise temperature range of 180℃-220℃, so that the outer carbon fiber layer (12) tightly covers and bonds to the inner carbon fiber layer (11). After curing, it is pulled and cooled to obtain a carbon fiber composite reinforcing core (1). S2, the annealed aluminum rod is extruded into trapezoidal soft aluminum wire monofilament (21) by a continuous extrusion press. Multiple trapezoidal soft aluminum wire monofilaments (21) are stranded in layers on the outside of the carbon fiber composite reinforcing core (1) by a tubular stranding machine or a frame stranding machine. During the stranding process, the tension is controlled at 5%-8% of the tensile strength. After stranding, the conductor layer (2) is pressed tightly by a die so that it adheres tightly to the reinforcing core. S3, the wire core with conductor layer (2) is extruded simultaneously through a three-layer co-extrusion die head to form a semi-conductive shielding layer (31) and a weather-resistant cross-linked polyethylene insulation layer (32). At the same time as the weather-resistant cross-linked polyethylene insulation layer (32) is extruded, an identification ridge is formed by extruding through a die with a special hole at the die head. The extruded material of the identification ridge is a base resin with added colored masterbatch. S4 involves cross-linking the insulated cable through a continuous vulcanization pipeline, with the cross-linking temperature controlled between 220℃ and 260℃. After cross-linking, the cable is cooled in sections by high-pressure water cooling to avoid stress concentration.

8. The method of producing an overhead insulated electric cable with a carbon fiber reinforced core according to claim 7, characterized in that: In step S2, the stranding of the trapezoidal soft aluminum wire monofilament (21) adopts a "pre-twisting" process, which specifically involves pre-twisting the monofilament according to the stranding pitch before stranding, so that the long base of the trapezoidal cross section of the monofilament is tightly attached to the surface of the reinforcing core without gaps after stranding.

9. The method of producing an overhead insulated electric cable with a carbon fiber reinforced core according to claim 7, characterized in that, In step S4, the specific process of segmented cooling is as follows: first, it is cooled to 90℃-100℃ by high-pressure water of 1.0MPa-1.2MPa, and then cooled to below 40℃ by a normal temperature water bath.

10. The method of producing an overhead insulated electric cable with a carbon fiber reinforced core according to claim 7, characterized in that; In step S1, the surface of the carbon fiber composite reinforcing core (1) after traction cooling is surface activated by an online corona treatment device to increase the friction with the conductor layer (2).

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