A crosslinked polyethylene insulated power cable and a method for producing the same

Abstract

This invention relates to the field of power cable manufacturing technology, and provides a cross-linked polyethylene insulated power cable and its manufacturing method. From the inside out, the cable comprises a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, and an outer sheath layer. The outer sheath layer comprises the following components in parts by weight: 55-70 parts polyvinyl chloride, 15-30 parts thermoplastic polyurethane, 12-18 parts plasticizer, 0.3-0.5 parts antioxidant, 0.8-1.6 parts lubricant, 15-20 parts filler, 1-3 parts compatibilizer, and 0.5-1.0 parts coupling agent. The filler includes porous mineral-supported metal composite oxide. By introducing a specific proportion of porous mineral-supported metal composite oxide as a functional filler, and utilizing the catalytic carbonization effect of yttrium tin during thermal decomposition and the synergistic effect of porous minerals insulating heat and oxygen, the limiting oxygen index of the outer sheath is significantly improved, fundamentally enhancing its flame retardant performance.

Description

Technical Field

[0001] This invention relates to the field of power cable manufacturing technology, specifically to a cross-linked polyethylene insulated power cable and its manufacturing method. Background Technology

[0002] Cross-linked polyethylene (XLPE) insulated power cables have become core equipment in the power transmission field, especially in high-voltage and ultra-high-voltage power grids and power supply systems in special environments (such as coal mines and ships), due to their excellent electrical, heat resistance, and mechanical properties. With the increasing voltage levels of power grids and the growing complexity of application environments, higher requirements are being placed on the reliability, safety, and service life of cables.

[0003] Currently, in the mainstream production methods of cross-linked polyethylene insulated power cables, most existing processes employ conventional three-layer co-extrusion + dry cross-linking. Vertical cross-linking tubes are often temperature-controlled as a whole, which can easily lead to uneven cross-linking distribution in the insulation layer. Furthermore, the cooling stage often uses single-medium co-current cooling, which can easily cause internal stress concentration in the insulation layer, ultimately resulting in high cable insulation eccentricity (often exceeding 3% in conventional processes). This makes it difficult to meet the power frequency breakdown field strength requirements of ultra-high voltage power grids. Additionally, finished product testing is mostly offline sampling inspection, leading to delayed feedback on quality issues and potentially causing batch defects. The production of substandard products is due to the fact that traditional outer sheaths are mostly made of polyvinyl chloride as the base material, combined with conventional inorganic fillers such as heavy calcium carbonate and talc. These fillers can only achieve weak flame retardancy through physical barriers, without catalytic char formation, and have poor interfacial bonding with the organic matrix. This easily leads to the limiting oxygen index of the outer sheath being less than 25%, and the vertical burning rating only reaching V-2 level. At the same time, the mechanical properties decrease significantly with the increase of filler content. In addition, the compatibility of various additives in conventional outer sheath formulations is poor, and precipitation and migration are prone to occur during high-temperature extrusion and long-term use, further reducing the service life of the cable. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a cross-linked polyethylene insulated power cable and its preparation method, which solves the problem that, in terms of material application, the flame-retardant effect and flame spread suppression ability of traditional outer sheath materials still need to be improved when exposed to fire, and cannot fully meet safety standards.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a cross-linked polyethylene insulated power cable, comprising, from the inside out, a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, and an outer sheath layer; the outer sheath layer comprises the following components in parts by weight: 55-70 parts of polyvinyl chloride, 15-30 parts of thermoplastic polyurethane, 12-18 parts of plasticizer, 0.3-0.5 parts of antioxidant, 0.8-1.6 parts of lubricant, 15-20 parts of filler, 1-3 parts of compatibilizer, and 0.5-1.0 parts of coupling agent, wherein the filler comprises porous mineral-supported metal composite oxide.

[0006] Preferably, the porous mineral in the porous mineral-supported metal composite oxide is perlite, and the metal composite oxide is yttrium-tin composite oxide. The molar ratio of yttrium to tin in the yttrium-tin composite oxide is (1.2-1.5):1. The filler also includes wollastonite powder, and the mass ratio of the porous mineral-supported metal composite oxide to wollastonite powder is 1:(1.8-2.8).

[0007] Preferably, the plasticizer includes epoxidized soybean oil and trioctyl trimellitate, the compatibilizer is maleic anhydride-grafted polyethylene, and the coupling agent includes silane coupling agent and titanate coupling agent.

[0008] A method for preparing a cross-linked polyethylene insulated power cable includes the following steps:

[0009] Step 1: Pre-treat the conductor, including preheating the conductor;

[0010] Step 2: Feed the pretreated conductor into the three-layer co-extrusion die head, and sequentially cover the conductor with a conductor shielding layer, a cross-linked polyethylene insulation layer, and an insulation shielding layer to form a three-layer structure;

[0011] Step 3: Pass the wire core covered with the three-layer structure through a vertical cross-linking tube for dry cross-linking;

[0012] Step 4: Perform gradient cooling on the cross-linked wire core. The gradient cooling includes a first cooling stage and a second cooling stage performed sequentially. In the first cooling stage, a first cooling medium is used for counter-current cooling, and in the second cooling stage, a second cooling medium is used for co-current cooling.

[0013] Step 5: Perform online non-destructive testing on the cooled cable, and adjust the process parameters of the three-layer co-extrusion die head in Step 2 in real time based on the test results;

[0014] Step 6: Preparation of outer sheath and cabling.

[0015] Preferably, in step one, the pretreatment further includes precision twisting, pressing and polishing, and the preheating temperature is 90℃~110℃.

[0016] Preferably, in step two, the cross-linked polyethylene insulation layer is formed from an insulating material, and the moisture content of the insulating material is less than 35 ppm.

[0017] Preferably, in step three, the vertical cross-linking pipe is divided into multiple independent heating zones along the axial direction. The temperature of each heating zone is independently controlled by a temperature control system, and the temperature of each heating zone shows a curve distribution of first rising and then falling along the direction of cable travel.

[0018] Preferably, the vertical cross-linking pipe is divided into 7 heating zones. Along the cable travel direction, the temperatures of the 7 heating zones are as follows: Zone 1 180℃~220℃, Zone 2 260℃~300℃, Zone 3 280℃~320℃, Zone 4 260℃~300℃, Zone 5 240℃~280℃, Zone 6 220℃~260℃, and Zone 7 180℃~220℃.

[0019] Preferably, in step four, the first cooling medium is cooling nitrogen, the second cooling medium is cooling water, the temperature of the cooling nitrogen is 15℃~25℃, and the temperature of the cooling water is 20℃~25℃.

[0020] Preferably, in step five, the online non-destructive testing uses an X-ray inspection system to detect the cable's eccentricity and internal impurities. The process parameters include the concentricity adjustment parameters of the three-layer co-extrusion die head.

[0021] This invention provides a cross-linked polyethylene insulated power cable and its preparation method. It has the following beneficial effects:

[0022] 1. This invention optimizes the material formulation of the outer sheath layer. By introducing a specific proportion of porous mineral-loaded metal composite oxide as a functional filler, and utilizing the catalytic carbonization effect of yttrium tin during thermal decomposition and the synergistic effect of porous minerals insulating heat and oxygen, the limiting oxygen index of the outer sheath is significantly improved, thereby fundamentally enhancing its flame retardant performance. This effectively solves the safety risk problem of cables in flammable and explosive environments. At the same time, by optimizing the filler combination and controlling its ratio, a synergistic improvement in flame retardancy and mechanical strength is also achieved.

[0023] 2. This invention ensures the smoothness and dimensional stability of the conductor surface by introducing precision stranding, compaction, and preheating in the conductor pretreatment stage, laying the foundation for subsequent uniform extrusion. Combined with the multi-temperature zone precise temperature control of the vertical cross-linking tube and the gradient cooling process of rapid counter-current shaping followed by slow stress relief in the co-current flow, the problem of stress concentration and uneven distribution in the insulation layer is effectively solved. The cable prepared in this way can control the insulation eccentricity at an extremely low level, and key indicators such as power frequency breakdown field strength and lightning impulse level are better than national standards, meeting the high reliability requirements of ultra-high voltage power grids.

[0024] 3. This invention integrates an online non-destructive testing and real-time feedback system at the end of the preparation method. This system can monitor key quality indicators such as eccentricity and impurities of the finished cable in real time, and automatically feed the data back to the adjustment device of the three-layer co-extrusion die head to form a closed-loop control. The online non-destructive testing and real-time feedback system realizes an automated closed loop of "detection, judgment, and adjustment", with a detection resolution of 0.01mm. It can instantly detect quality problems such as eccentricity and internal impurities and quickly adjust process parameters, avoiding the lag of traditional offline sampling inspection.

[0025] 4. This invention adds antioxidants and compatibilizers to the outer sheath formulation, which effectively inhibits thermo-oxidative aging and additive migration. With the synergistic design of each layer, the cable can be used stably in a temperature range of -40℃ to 90℃, and its aging resistance is improved to more than 15 years (compared to about 8 to 10 years for traditional cables). At the same time, the outer sheath has excellent wear resistance and corrosion resistance, making it suitable for complex outdoor, underground, and humid environments, and significantly reducing the later maintenance costs of the cable. Attached Figure Description

[0026] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0027] 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 only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Please see the appendix Figure 1 This invention provides a cross-linked polyethylene insulated power cable, comprising, from the inside out, a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, and an outer sheath layer. The outer sheath layer comprises the following components in parts by weight: 55-70 parts of polyvinyl chloride, 15-30 parts of thermoplastic polyurethane, 12-18 parts of plasticizer, 0.3-0.5 parts of antioxidant, 0.8-1.6 parts of lubricant, 15-20 parts of filler, 1-3 parts of compatibilizer, and 0.5-1.0 parts of coupling agent. The filler comprises porous mineral-supported metal composite oxide.

[0029] Specifically, the preferred weight proportions of the components of the outer sheath layer are: 60 parts polyvinyl chloride (PVC), 20 parts thermoplastic polyurethane (TPU), 15 parts plasticizer, 0.4 parts antioxidant, 1.2 parts lubricant, 18 parts filler, 2 parts compatibilizer, and 0.8 parts coupling agent. The antioxidant selected is hindered phenolic antioxidant 1010, and the lubricant is a compound system of zinc stearate and polyethylene wax in a mass ratio of 1:2, which can balance internal and external lubrication effects and avoid problems such as sticking to the mold and surface roughness during extrusion. PVC is the base material. The PVC body provides basic flame retardancy and moldability, while thermoplastic polyurethane (TPU) enhances the elasticity, abrasion resistance, and low-temperature toughness of the outer sheath. The mass ratio of the two should be controlled at (2.5~4.5):1 (corresponding to the formula weight range). When PVC is 60 parts and TPU is 20 parts (mass ratio 3:1), the optimal balance between flame retardancy and mechanical properties can be achieved. If the proportion of TPU is too high, it will reduce the limiting oxygen index of the outer sheath, and if the proportion of PVC is too high, it will lead to increased brittleness and decreased elongation at break of the outer sheath.

[0030] Plasticizer: Epoxidized soybean oil and trioctyl trimellitate are compounded in a mass ratio of 1:1, with a total amount of 12 to 18 parts. Epoxidized soybean oil has both plasticizing and flame-retardant effects, while trioctyl trimellitate is a high-efficiency, temperature-resistant plasticizer that can prevent the outer sheath from plasticizing and shrinking under high temperature conditions. The compounding of the two has no migration or precipitation problems.

[0031] Coupling agent: Silane coupling agent (KH550) + titanate coupling agent (NDZ-105) are compounded in a mass ratio of 1:1, with a total amount of 0.5 to 1.0 parts. The silane coupling agent enhances the chemical bonding force between the filler and the resin, while the titanate coupling agent reduces the surface energy of the filler and prevents agglomeration. The two work together to improve the dispersibility of the filler.

[0032] Lubricant: Zinc stearate and polyethylene wax are compounded in a mass ratio of 1:2, with a total amount of 0.8 to 1.6 parts. Zinc stearate is an internal lubricant to reduce the viscosity of the resin melt, while polyethylene wax is an external lubricant to prevent sticking to the mold during extrusion, thus achieving both internal and external lubrication effects.

[0033] Antioxidant: Hindered phenolic antioxidant 1010 is preferred, with an addition amount of 0.3 to 0.5 parts. It can inhibit the thermo-oxidative aging of the outer sheath during high-temperature extrusion and long-term use, and improve the service life of the cable.

[0034] Compatibilizer: Maleic anhydride-grafted polyethylene, added in amounts of 1 to 3 parts. Its polar groups can combine with PVC, TPU and inorganic fillers respectively, improving the compatibility of the multiphase system and preventing delamination and cracking of the outer sheath.

[0035] The porous mineral in the porous mineral-supported metal composite oxide is perlite, and the metal composite oxide is yttrium-tin composite oxide. The molar ratio of yttrium to tin in the yttrium-tin composite oxide is (1.2-1.5):1. The filler also includes wollastonite powder, and the mass ratio of the porous mineral-supported metal composite oxide to wollastonite powder is 1:(1.8-2.8). The plasticizer includes epoxidized soybean oil and trioctyl trimellitate. The compatibilizer is maleic anhydride-grafted polyethylene. The coupling agent includes silane coupling agent and titanate coupling agent.

[0036] Specifically, the preferred molar ratio of yttrium to tin in the yttrium-tin composite oxide is 1.3:1, and the preferred mass ratio of porous mineral-supported metal composite oxide to wollastonite powder is 1:2.3. Epoxidized soybean oil and trioctyl trimellitate are compounded at a mass ratio of 1:1 as a plasticizer, providing both plasticizing and flame-retardant auxiliary effects. KH550 is selected as the silane coupling agent, and NDZ-105 is selected as the titanate coupling agent; the two are compounded at a mass ratio of 1:1 to effectively improve the interfacial bonding force between the filler and the organic matrix. Perlite is first calcined and activated at 800–900℃ for 2 hours, ground to 200–300 mesh, and then the yttrium-tin composite oxide is loaded onto its surface using the sol-gel method, dried at 110–120℃, and then subjected to a 500–600 mm heat treatment. The target filler was obtained by calcination at ℃ for 3 hours. Wollastonite powder was dried at 100-110℃ to remove water and then ground to 300-400 mesh to improve the dispersibility of the filler in the matrix. The porous mineral-loaded metal composite oxide was perlite-loaded yttrium-tin composite oxide. After activation by calcination at 800-900℃, the porosity of the perlite reached over 70%, achieving physical insulation of heat and oxygen. The yttrium-tin composite oxide (Y-Sn) served as the catalytic carbonization core. Yttrium lowered the polymer thermal decomposition temperature and promoted carbon layer formation, while tin stabilized the carbon layer structure. The molar ratio of the two was controlled at 1.2-1.5:1. If the proportion of yttrium was too low, the catalytic carbonization effect would be insufficient; if it was too high, the compatibility between the filler and the matrix would decrease. The composite oxide is a perlite-supported yttrium-tin composite oxide. After calcination and activation at 800–900℃, the perlite has a porosity of over 70%, achieving physical insulation against heat and oxygen. The yttrium-tin composite oxide (Y-Sn) serves as the catalytic carbonization core. Yttrium lowers the polymer thermal decomposition temperature and promotes carbon layer formation, while tin stabilizes the carbon layer structure. The molar ratio of the two is controlled at 1.2–1.5:1. If the proportion of yttrium is too low, the catalytic carbonization effect will be insufficient; if it is too high, the compatibility between the filler and the matrix will decrease. The perlite is first calcined and activated at 800–900℃ for 2 hours, then ground to 200–300 mesh. The yttrium-tin composite oxide is then loaded onto its surface using the sol-gel method, followed by drying at 110–120℃ and 5… It is prepared by calcination at 00-600℃ for 3 hours; after drying and removing water at 100-110℃, the wollastonite powder is ground to 300-400 mesh to improve the interfacial bonding force with the organic matrix. Through the composite filler system of perlite-loaded yttrium tin composite oxide and wollastonite powder, the limiting oxygen index of the outer sheath is increased to 31.8%-32.5% (compared to only about 24% for traditional products), the vertical combustion rating reaches UL94V-0, and the smoke density (Dsmax) is reduced to 185-192 (compared to over 300 for traditional products). There is no dripping or release of highly toxic smoke during combustion, which fully meets the flame retardant safety standards for flammable and explosive special environments such as coal mines, ships, and high-rise buildings, and solves the core problems of "poor flame retardant effect and high smoke density" of traditional outer sheaths.

[0037] A method for preparing a cross-linked polyethylene insulated power cable includes the following steps:

[0038] Step 1: Pre-treatment of the conductor, which includes preheating the conductor, precision stranding, compaction and polishing, and the preheating temperature is 90℃~110℃;

[0039] First, the copper / aluminum conductor monofilaments are precisely stranded (stretching pitch ratio of 10-15), then compressed (compression coefficient 0.9-0.95), followed by polishing (using a steel wire wheel for polishing, surface roughness Ra≤0.8μm), and finally preheating. To avoid oxidation of the conductor surface caused by preheating before processing, hot air circulation preheating is used at a temperature of 90℃-110℃ for 15-20 minutes to ensure uniform internal temperature of the conductor, eliminate surface moisture, and prevent air gaps from forming during subsequent wrapping.

[0040] Step 2: Feed the pretreated conductor into the three-layer co-extrusion die head, and sequentially coat the conductor with a conductor shielding layer, a cross-linked polyethylene insulation layer, and an insulation shielding layer to form a three-layer structure. The cross-linked polyethylene insulation layer is formed from insulating material with a moisture content of less than 35 ppm.

[0041] The extrusion process employs a high-pressure three-layer co-extrusion die head with a concentricity adjustment accuracy of ±0.01mm. The extruder is a single-screw extruder with a screw length-to-diameter ratio of 25–30:1 and a rotation speed of 30–50 r / min. The conductor shielding material and the insulating shielding material are semi-conductive granules with melt flow index matching that of the cross-linked polyethylene insulation material. The cross-linked polyethylene insulation material undergoes vacuum drying, with the moisture content strictly controlled below 35ppm to prevent air bubbles from forming during the cross-linking process. The three-layer coating is carried out simultaneously, and the extrusion temperature is controlled in stages (120–140℃ for shielding material and 140–160℃ for insulation material). After coating, the core surface is smooth, without scratches or bulges.

[0042] Step 3: Pass the three-layered wire core through a vertical cross-linking tube for dry cross-linking. The vertical cross-linking tube is divided into multiple independent heating zones along the axial direction. The temperature of each heating zone is independently controlled by a temperature control system. Along the direction of cable travel, the temperature of each heating zone shows a curve distribution of first rising and then falling.

[0043] The vertical cross-linking pipe has seven independent heating zones of equal length along the axial direction. The axial length of each heating zone is 1.5-2m. Each heating zone is equipped with an independent hot air circulation module and a temperature sensor. The temperature control system is a PLC-based precise temperature control system with an accuracy of ±1℃. Along the cable travel direction, the temperatures of the seven heating zones are 180-220℃, 260-300℃, 280-320℃, 260-300℃, 240-280℃, 220-260℃, and 180-220℃, respectively. The cable core travels at a speed of 3-5m / min to ensure sufficient cross-linking of the insulation layer (cross-linking degree ≥85%). Dry nitrogen gas is continuously introduced into the cross-linking pipe as a protective gas with a purity ≥99.99% and a pressure of 0.05-0.1MPa to prevent oxidation and degradation of the insulation layer at high temperatures.

[0044] Step 4: Perform gradient cooling on the cross-linked wire core. Gradient cooling includes a first cooling stage and a second cooling stage performed sequentially. In the first cooling stage, a first cooling medium is used for counter-current cooling, and in the second cooling stage, a second cooling medium is used for co-current cooling. The first cooling medium is cooling nitrogen, and the second cooling medium is cooling water. The temperature of the cooling nitrogen is 15℃~25℃, and the temperature of the cooling water is 20℃~25℃.

[0045] Countercurrent nitrogen cooling at 15–25℃, with a nitrogen flow rate of 5–8 m / s and a cooling time of 10–15 s, is used to achieve rapid shaping of the insulation layer and suppress the generation of internal stress. Cocurrent cooling with water at 20–25℃, with a water flow rate of 3–5 m / s and a cooling time of 20–25 s, is used to achieve slow cooling of the insulation layer and eliminate residual internal stress. After cooling, the surface temperature of the wire core drops below 40℃, avoiding heat deformation during subsequent inspection and processing.

[0046] Step 5: Perform online non-destructive testing on the cooled cable, and adjust the process parameters of the three-layer co-extrusion die head in Step 2 in real time according to the test results. The online non-destructive testing uses an X-ray inspection system to detect the eccentricity and internal impurities of the cable. The process parameters include the concentricity adjustment parameters of the three-layer co-extrusion die head.

[0047] A high-resolution X-ray inspection system is adopted, with a detection resolution ≥0.01mm. The inspection speed is synchronized with the cable travel speed (3~5m / min). The inspection data is transmitted to the central control system in real time. When the cable insulation eccentricity exceeds 2% or there are impurities with a particle size greater than 0.1mm inside, it is judged as unqualified. The central control system automatically sends a command to the concentricity adjustment device of the three-layer co-extrusion die head to adjust the relative position of the inner die core and the outer die sleeve of the die head (adjustment accuracy ±0.01mm). At the same time, the extruder feeding speed is finely adjusted (adjustment range ±5r / min) until the detection indicators are restored to the qualified range, forming a closed-loop control.

[0048] Step 6: Outer sheath preparation and cabling. Polyvinyl chloride and thermoplastic polyurethane are premixed, then lubricant, antioxidant and coupling agent are added for the first mixing, then filler is added for the second mixing, and finally plasticizer and compatibilizer are added for the third mixing to obtain the outer sheath mixture. The inner lining layer and armor layer are wrapped in sequence to form a cable semi-finished product. The outer sheath mixture is extruded on the outside of the cable semi-finished product to form the outer sheath layer, and cross-linked polyethylene insulated power cable is obtained.

[0049] Preparation of outer sheath mixing materials (high-speed mixer):

[0050] Premix: PVC + TPU, 60-70℃, 10-15 min, initial fusion;

[0051] First mixing: Add lubricant, antioxidant, and coupling agent, heat to 80-90℃, and mix for 15-20 minutes to ensure uniform dispersion of the additives;

[0052] Second mixing: Add the filler, heat to 90-100℃, and disperse the filler by high-speed shear for 20-25 minutes;

[0053] Third mixing: Cool to 70-80℃, add plasticizer and compatibilizer, 10-15 minutes, to prevent plasticizer from evaporating at high temperature;

[0054] Granulation: Granulate using a twin-screw extruder to a particle size of 2-3 mm, then dry for later use;

[0055] Preparation of auxiliary layer:

[0056] Inner liner: Low-smoke halogen-free polyolefin material, extruded using a single-screw extruder at an extrusion temperature of 140–170℃, with a thickness of 0.5–1.0 mm;

[0057] Armor layer: galvanized steel strip with gaps, steel strip thickness 0.3-0.5mm, armor gap 1-2mm, providing both mechanical protection and heat dissipation;

[0058] Outer sheath extrusion: The outer sheath granules are extruded onto the outside of the armor layer using a single screw extruder. The barrel temperature is controlled in stages at 160℃, 175℃, 190℃, and 180℃, while the die head temperature is 175~180℃. The extrusion speed is 3~5m / min, synchronized with the cable travel speed. After extrusion, the cable is water-cooled at 20~25℃ for shaping, and finally, the finished cable is obtained.

[0059] Specifically, the X-ray inspection system has a detection resolution of no less than 0.01 mm, and the detection speed is synchronized with the cable travel speed. Detection data is transmitted to the central control system in real time. If the cable eccentricity exceeds 2% or impurities larger than 0.1 mm are detected inside, the central control system will automatically send a command to the concentricity adjustment device of the three-layer co-extrusion die head to adjust the relative position of the inner die core and outer die sleeve, while simultaneously fine-tuning the extruder's feeding speed until the detection indicators return to the acceptable range. All mixing is carried out in a high-speed mixer. In the premixing stage of PVC and thermoplastic polyurethane, the mixing temperature is 60–70℃, and the mixing time is 10–15 minutes to allow the two resins to initially fuse. The first mixing temperature is raised to 80–90℃, and the mixing time is 15–20 minutes to allow the additives to be evenly dispersed in the resin matrix. The second mixing temperature is raised to 90–100℃, and the mixing time is 20–25 minutes, utilizing a high-speed mixer. Shear force ensures thorough dispersion of the filler, preventing agglomeration. The third mixing stage involves cooling to 70-80℃, adding plasticizer and compatibilizer, and mixing for 10-15 minutes to prevent plasticizer volatilization at high temperatures. After mixing, the mixture is granulated using a twin-screw extruder to obtain outer sheath granules with a particle size of 2-3 mm. The inner lining layer uses low-smoke halogen-free polyolefin material, extruded using an extruder at an extrusion temperature of 140-170℃. The armor layer uses galvanized steel strip with gaps, a steel strip thickness of 0.3-0.5 mm, and an armor gap of 1-2 mm, providing both mechanical protection and heat dissipation. The outer sheath granules are extruded onto the outside of the armor layer using a single-screw extruder. The extruder barrel temperature is controlled in stages at 160℃, 175℃, 190℃, and 180℃, while the die head temperature is 175-180℃. The extrusion speed is synchronized with the cable travel speed at 3-5 m / min. After extrusion, the cable is water-cooled and shaped at a cooling water temperature of 20-25℃, ultimately yielding the finished cable.

[0060] The vertical cross-linking pipe is divided into 7 heating zones. Along the direction of cable travel, the temperatures of the 7 heating zones are as follows: Zone 1 180℃~220℃, Zone 2 260℃~300℃, Zone 3 280℃~320℃, Zone 4 260℃~300℃, Zone 5 240℃~280℃, Zone 6 220℃~260℃, and Zone 7 180℃~220℃.

[0061] Specifically, the seven heating zones are arranged at equal lengths along the axial direction of the vertical cross-linking pipe, with the axial length of each heating zone being 1.5 to 2 meters. Each heating zone is equipped with an independent hot air circulation module and a temperature sensor. The temperature control system uses a PLC for precise temperature control with an accuracy of ±1°C. Dry nitrogen is continuously introduced into the cross-linking pipe as a protective gas, with a purity of not less than 99.99%, to prevent oxidation and degradation of the insulation layer at high temperatures. The travel speed of the cable core in the cross-linking pipe is controlled at 3 to 5 meters per minute to ensure full cross-linking of the insulation layer.

[0062] To better illustrate the formulation implementation scheme of the cross-linked polyethylene insulated power cable of the present invention, the following examples are provided:

[0063] Example 1:

[0064] This embodiment provides a cross-linked polyethylene insulated power cable, the structure of which, from the inside out, includes a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, and an outer sheath layer.

[0065] The outer sheath layer comprises the following components by weight: 51 parts polyvinyl chloride, 17 parts thermoplastic polyurethane, 12.8 parts plasticizer (of which the mass ratio of epoxidized soybean oil to trioctyl trimellitate is 1:1), 0.34 parts antioxidant (hindered phenol 1010), 1.02 parts lubricant (the mass ratio of zinc stearate to polyethylene wax is 1:2), 15.3 parts filler (of which the mass ratio of porous mineral-supported metal composite oxide to wollastonite powder is 1:2.3), 1.7 parts compatibilizer (maleic anhydride-grafted polyethylene), and 0.68 parts coupling agent (the mass ratio of KH550 to NDZ-105 is 1:1).

[0066] In the porous mineral-supported metal composite oxide, the porous mineral is perlite, and the metal composite oxide is yttrium-tin composite oxide with a yttrium to tin molar ratio of 1.3:1. Perlite was activated by calcination at 850℃ for 2 hours, ground to 250 mesh, and then yttrium-tin composite oxide was loaded onto it using the sol-gel method. The mixture was then dried at 115℃ and calcined at 550℃ for 3 hours. Wollastonite powder was dried at 105℃ and ground to 350 mesh.

[0067] The cable manufacturing method is as follows:

[0068] Step 1: After the conductor is precisely stranded, compressed, and polished, it is preheated to 100°C.

[0069] Step 2: Feed the pretreated conductor into the three-layer co-extrusion die head, and sequentially cover it with a conductor shielding layer, a cross-linked polyethylene insulation layer (insulation material moisture content ≤35ppm), and an insulation shielding layer.

[0070] Step 3: The core wire is dry cross-linked through a vertical cross-linking tube. The cross-linking tube is divided into 7 heating zones with temperatures of 200℃, 280℃, 300℃, 280℃, 260℃, 240℃, and 200℃ respectively.

[0071] Step 4: Use gradient cooling, first use nitrogen gas at 20°C for countercurrent cooling, and then use water at 22°C for cocurrent cooling.

[0072] Step 5: Use an X-ray inspection system to perform online non-destructive testing and adjust the concentricity parameters of the three-layer co-extrusion die head in real time.

[0073] Step Six: The outer sheath layer mixture is premixed and mixed three times in a high-speed mixer, then granulated and extruded onto the outside of the inner lining layer and armor layer to form the finished cable.

[0074] Example 2:

[0075] The difference between this embodiment and Embodiment 1 lies in the composition and ratio of fillers in the outer sheath layer formulation, as detailed below:

[0076] The outer sheath layer comprises, by weight: 53 parts polyvinyl chloride, 20.4 parts thermoplastic polyurethane, 13.1 parts plasticizer (epoxidized soybean oil and trioctyl trimellitate in a mass ratio of 1:1), 0.41 parts antioxidant, 1.14 parts lubricant, 16.3 parts filler (of which the porous mineral-supported metal composite oxide and wollastonite powder are in a mass ratio of 1:2.0), 2.04 parts compatibilizer, and 0.73 parts coupling agent.

[0077] In the porous mineral-supported metal composite oxide, the molar ratio of yttrium to tin is 1.4:1, the activation temperature of perlite is 900℃, and the rest of the preparation process is the same as in Example 1.

[0078] The cable preparation method is the same as in Example 1.

[0079] Comparative Example 1:

[0080] The difference between this comparative example and Example 1 is that the outer sheath layer does not use porous mineral-supported metal composite oxide filler, but only conventional inorganic filler (heavy calcium carbonate), and no coupling agent is added.

[0081] The outer sheath layer comprises the following components by weight: 55 parts polyvinyl chloride, 18 parts thermoplastic polyurethane, 13 parts plasticizer (epoxidized soybean oil and trioctyl trimellitate in a mass ratio of 1:1), 0.4 parts antioxidant, 1.1 parts lubricant, 12.5 parts heavy calcium carbonate, and 1.8 parts compatibilizer.

[0082] The cable preparation method is the same as in Example 1, except that no coupling agent was used to treat the filler in the outer sheath layer mixture.

[0083] The results are shown in Table 1 below.

[0084] Table 1:

[0085] project Limiting Oxygen Index (LOI, %) Vertical flammability rating Smoke density (Dsmax) Tensile strength (MPa) Elongation at break (%) Example 1 32.5 V-0 185 16.2 320 Example 2 31.8 V-0 192 15.8 305 Comparative Example 1 24.1 V-2 315 12.6 260

[0086] The results show that the porous mineral-supported metal composite oxide and wollastonite powder composite filler system of the present invention has a limiting oxygen index of 32.5% and 31.8%, respectively, and a vertical burning rating of V-0, with significantly lower smoke density, exhibiting excellent flame retardant performance. In contrast, Comparative Example 1, using conventional heavy calcium carbonate filler without the functional filler system of the present invention, has a limiting oxygen index of only 24.1%, a vertical burning rating of only V-2, and a smoke density as high as 315, showing significantly inferior flame retardant performance compared to the example. Furthermore, the tensile strength and elongation at break of Comparative Example 1 are also lower than those of the example, indicating that the formulation of the present invention improves flame retardant performance while also considering the mechanical properties of the material. Therefore, the porous mineral-supported metal composite oxide filler of the present invention plays a crucial role in improving the flame retardant performance of cable outer sheaths.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cross-linked polyethylene insulated power cable, characterized in that, From the inside out, it comprises a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, and an outer sheath layer. The outer sheath layer comprises the following components in parts by weight: 55-70 parts of polyvinyl chloride, 15-30 parts of thermoplastic polyurethane, 12-18 parts of plasticizer, 0.3-0.5 parts of antioxidant, 0.8-1.6 parts of lubricant, 15-20 parts of filler, 1-3 parts of compatibilizer, and 0.5-1.0 parts of coupling agent. The filler comprises porous mineral-supported metal composite oxide.

2. The cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The porous mineral in the porous mineral-supported metal composite oxide is perlite, and the metal composite oxide is yttrium-tin composite oxide. The molar ratio of yttrium to tin in the yttrium-tin composite oxide is (1.2-1.5):

1. The filler also includes wollastonite powder, and the mass ratio of the porous mineral-supported metal composite oxide to wollastonite powder is 1:(1.8-2.8).

3. The cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The plasticizer includes epoxidized soybean oil and trioctyl trimellitate, the compatibilizer is maleic anhydride-grafted polyethylene, and the coupling agent includes silane coupling agent and titanate coupling agent.

4. A method for preparing a cross-linked polyethylene insulated power cable, using a cross-linked polyethylene insulated power cable as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Pre-treat the conductor, including preheating the conductor; Step 2: Feed the pretreated conductor into the three-layer co-extrusion die head, and sequentially cover the conductor with a conductor shielding layer, a cross-linked polyethylene insulation layer, and an insulation shielding layer to form a three-layer structure; Step 3: Pass the wire core covered with the three-layer structure through a vertical cross-linking tube for dry cross-linking; Step 4: Perform gradient cooling on the cross-linked wire core. The gradient cooling includes a first cooling stage and a second cooling stage performed sequentially. In the first cooling stage, a first cooling medium is used for counter-current cooling, and in the second cooling stage, a second cooling medium is used for co-current cooling. Step 5: Perform online non-destructive testing on the cooled cable, and adjust the process parameters of the three-layer co-extrusion die head in Step 2 in real time based on the test results; Step 6: Preparation of outer sheath and cabling.

5. The method for preparing a cross-linked polyethylene insulated power cable according to claim 4, characterized in that, In step one, the pretreatment also includes precision stranding, pressing and polishing, and the preheating temperature is 90℃~110℃.

6. The method for preparing a cross-linked polyethylene insulated power cable according to claim 4, characterized in that, In step two, the cross-linked polyethylene insulation layer is formed from an insulating material, and the moisture content of the insulating material is less than 35 ppm.

7. The method for preparing a cross-linked polyethylene insulated power cable according to claim 4, characterized in that, In step three, the vertical cross-linking pipe is divided into multiple independent heating zones along the axial direction. The temperature of each heating zone is independently controlled by a temperature control system, and the temperature of each heating zone shows a curve distribution of first rising and then falling along the direction of cable travel.

8. The method for preparing a cross-linked polyethylene insulated power cable according to claim 4, characterized in that, The vertical cross-linking tube is divided into 7 heating zones. Along the direction of cable travel, the temperatures of the 7 heating zones are as follows: Zone 1 180℃~220℃, Zone 2 260℃~300℃, Zone 3 280℃~320℃, Zone 4 260℃~300℃, Zone 5 240℃~280℃, Zone 6 220℃~260℃, and Zone 7 180℃~220℃.

9. The method for preparing a cross-linked polyethylene insulated power cable according to claim 4, characterized in that, In step four, the first cooling medium is cooling nitrogen, the second cooling medium is cooling water, the temperature of the cooling nitrogen is 15℃~25℃, and the temperature of the cooling water is 20℃~25℃.

10. The method for preparing a cross-linked polyethylene insulated power cable according to claim 4, characterized in that, In step five, the online non-destructive testing uses an X-ray inspection system to detect the cable's eccentricity and internal impurities. The process parameters include the concentricity adjustment parameters of the three-layer co-extrusion die head.

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