High-altitude overhead insulated cable and preparation method thereof

Abstract

The application discloses a high-altitude overhead insulated cable and a preparation method thereof. The high-altitude overhead insulated cable comprises, from inside to outside, a conductor layer, an inner semiconductive insulation layer, a gradient functionalized insulation layer, an outer semiconductive insulation layer and a weather-proof sheath layer. The gradient functionalized insulation layer comprises, from inside to outside, a corona-resistant inner insulation layer, a main insulation layer and a weather-proof outer insulation layer. The application has the advantages of the gradient functionalized insulation layer structure, interlayer linkage reaction mechanism and nano-modified corona-resistant material system, and solves the technical problems of corona discharge, insulation aging and shortened service life of the overhead insulated cable in the prior art under the environment of high altitude, low air pressure, strong ultraviolet rays and extreme temperature difference.

Description

Technical Field

[0001] This invention relates to the field of wire and cable technology, and in particular to an overhead insulated cable for high altitudes and its manufacturing method. Background Technology

[0002] Overhead insulated cables are widely used power transmission equipment in power distribution networks. They have advantages such as simple structure, safety and reliability, small laying gaps, and saving line corridors.

[0003] Overhead insulated cables of 10kV and above typically adopt a single-core structure, consisting of a conductor, an inner semi-conductive shielding layer, an insulation layer, and an outer semi-conductive shielding layer.

[0004] Regarding conductor materials, aluminum or aluminum alloys are the mainstream materials used for conductors in overhead insulated cables, including pure aluminum conductors, aluminum-magnesium-silicon alloy conductors, and steel-cored aluminum stranded wires. Copper conductors are rarely used in overhead insulated cables due to their high cost and weight, and are therefore a non-mainstream material.

[0005] In high-altitude areas (above 3000m), overhead insulated cables face unique technical challenges:

[0006] 1. Corona discharge problem caused by low air pressure At high altitudes, atmospheric pressure is significantly lower (at 4000m, air pressure is approximately 61% of that at sea level), resulting in a substantial decrease in the insulating strength of the air. According to Pascal's Law, at the same voltage level, the corona initiation voltage is significantly lower at high altitudes, leading to more severe corona discharge. Corona discharge not only causes energy loss but also produces corrosive gases such as ozone and nitrogen oxides, accelerating the aging and degradation of insulation materials and severely impacting cable lifespan and operational safety.

[0007] 2. Insulation aging problems caused by strong ultraviolet radiation In high-altitude areas, the atmosphere is thin, and the intensity of ultraviolet radiation is much higher than in plains areas (the UV-B radiation intensity at an altitude of 4000m is about twice that at sea level). Strong ultraviolet radiation accelerates the photo-oxidative aging of polyolefin insulation materials, leading to surface cracking and pulverization of the insulation layer, and a sharp decline in electrical and mechanical properties.

[0008] 3. Thermal cycling stress caused by extreme temperature differences In high-altitude areas, the temperature difference between day and night can reach 30 to 40 degrees Celsius. The drastic temperature changes cause the cable insulation layer to be repeatedly subjected to thermal expansion and contraction stress, which can easily lead to micro-cracks inside the insulation layer, forming local electric field concentration and inducing partial discharge. Summary of the Invention

[0009] The purpose of this invention is to provide an overhead insulated cable for high altitudes and its preparation method. By using a gradient functionalized insulation layer structure, an interlayer linkage reaction mechanism, and a nano-modified corona-resistant material system, this invention solves the technical problems of corona discharge, insulation aging, and shortened lifespan of existing overhead insulated cables under high altitude, low air pressure, strong ultraviolet radiation, and extreme temperature difference environments.

[0010] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A high-altitude overhead insulated cable comprises, from the inside out: a conductor layer, an inner semiconductive insulation layer, a gradient functionalized insulation layer, an outer semiconductive insulation layer, and a weather-resistant sheath layer. The gradient functionalized insulation layer comprises, from the inside out: a corona-resistant inner insulation layer, a main insulation layer, and a weather-resistant outer insulation layer. The corona-resistant inner insulation layer is composed of the following raw materials in parts by weight: 55-65 parts of low-density polyethylene (LDPE, melt index 2.0 g / 10 min), 15-20 parts of ethylene-octene copolymer (POE, octene content 20%), 8-12 parts of nano-silica (particle size 20-50 nm) modified with silane coupling agent KH-550, 5-8 parts of nano-alumina (particle size 30-60 nm) modified with silane coupling agent KH-570, 3-5 parts of polyimide microcapsules, 0.5-1.0 parts of antioxidant 168, 0.3-0.5 parts of antioxidant DLTP, and 1.5-2.5 parts of crosslinking agent TAIC; The main insulation layer is composed of the following raw materials in parts by weight: 70-80 parts of cross-linked polyethylene base material, 10-15 parts of ethylene-ethyl acrylate copolymer (ethyl acrylate content 18%), 5-8 parts of organic modified nano-montmorillonite, 3-5 parts of nano-magnesium hydroxide (particle size 50-100nm), 2.0-3.0 parts of cross-linking agent TAIC, 0.5-0.8 parts of antioxidant 1010, and 0.2-0.3 parts of copper inhibitor MDA-5; The weather-resistant outer insulation layer is composed of the following raw materials in parts by weight: 60-70 parts of weather-resistant high-density polyethylene, 15-20 parts of ethylene-vinyl acetate copolymer (VA content 18%), 5-8 parts of nano-titanium dioxide (rutile type, particle size 20-40nm) surface modified with silane coupling agent KH-550, 3-5 parts of nano-zinc oxide (particle size 30-50nm), 1.0-1.5 parts of ultraviolet absorber UV-531, 0.8-1.2 parts of light stabilizer HALS-770, 0.5-0.8 parts of antioxidant 1010, and 1.0-1.5 parts of crosslinking agent TAIC.

[0011] Preferably, the conductor layer is made of compacted circular aluminum conductor or aluminum-magnesium-silicon alloy conductor with a cross-section of 50~400mm², and the conductor surface is subjected to micro-arc oxidation treatment to form an alumina ceramic film layer with a thickness of 5~15μm.

[0012] Preferably, the inner semiconductive insulating layer is composed of the following raw materials in parts by weight: 60-70 parts of ethylene-vinyl acetate copolymer (EVA, VA content 28%), and conductive carbon black (specific surface area 120-150 μm²). 2 25-30 parts of graphene nanosheets (3-8 layers, 1-5 μm diameter), 3-5 parts of carbon nanotubes (10-20 nm diameter, 5-15 μm length), 0.5-1.0 parts of antioxidant 1010, and 0.5-1.0 parts of zinc stearate lubricant, with volume resistivity controlled at 10 Ω·cm. 2 ~10 4 Ω·cm, with a thickness of 0.5~1.0mm.

[0013] Preferably, the wall material of the polyimide microcapsules is urea-formaldehyde resin, and the core material is a mixture of low-viscosity silicone oil and the catalyst dibutyltin dilaurate. The microcapsule particle size is 2~5μm and the wall thickness is 0.2~0.5μm. The specific preparation method is as follows: 10g of urea and 25mL of 37% formaldehyde solution are added to a 250mL three-necked flask, stirred and dissolved, and the pH is adjusted to 3.5~4.0 with 10% hydrochloric acid. The prepolymerization reaction is carried out at 60℃ for 1h. The core material is added: 15g of low-viscosity silicone oil (viscosity 50~100cSt) + 0.5g of dibutyltin dilaurate catalyst. The reaction is continued at 60~70℃ for 3~4h with stirring speed of 300rpm. After cooling to room temperature, the product is centrifuged and washed (washed 3 times with deionized water), vacuum dried at 40℃ for 24h, and sieved to obtain microcapsule products with a particle size of 2~5μm. Organically modified nano-montmorillonite was organically modified using hexadecyltrimethylammonium bromide. The specific modification method involved dispersing 100g of sodium-based montmorillonite in 2000mL of deionized water and stirring at high speed (800rpm) for 2 hours. Then, 30-50g of hexadecyltrimethylammonium bromide (CTAB) was added (the amount being 30-50% of the montmorillonite mass). The mixture was stirred at 70-80℃ for 6-8 hours, followed by centrifugation and washing with deionized water until no Br was observed. - (AgNO3 detection), vacuum dried at 80℃ for 12h, ground and sieved (200 mesh) to obtain organic modified nano-montmorillonite with interlayer spacing ≥3.5nm; The modified silane coupling agent for nano-silica is KH-550. The specific modification method is as follows: 100g of nano-silica is added to 500mL of anhydrous ethanol and ultrasonically dispersed for 30min (power 300W, frequency 40kHz). Then, 3~5g of silane coupling agent KH-550 (the amount is 3~5% of the mass of nano-SiO2) is added. Under nitrogen protection, the mixture is refluxed at 70~80℃ for 4~6h, centrifuged and washed (washed 3 times with ethanol and 2 times with deionized water), and vacuum dried at 80℃ for 12h to obtain modified nano-silica.

[0014] The modified silane coupling agent for nano-alumina is KH-570. The specific modification method is the same as that for nano-silica, but KH-570 is used instead of KH-550.

[0015] The crosslinking agent is TAIC, the ultraviolet absorber is UV-531, and the light stabilizer is HALS-770.

[0016] Preferably, the dielectric constant of the corona-resistant inner insulating layer is 2.8~3.2, and the coefficient of thermal expansion is 2.2~2.5×10⁻⁶. -5 The temperature is ℃, the thickness is 0.8~1.5mm, the dielectric constant of the main insulating layer is 2.4~2.6, and the coefficient of thermal expansion is 2.5~2.8×10. -5 The temperature is ℃, the thickness is 2.5~4.0mm, the dielectric constant of the weather-resistant outer insulation layer is 2.6~3.0, and the coefficient of thermal expansion is 2.0~2.3×10. -5 / ℃, thickness is 0.5~1.0mm.

[0017] Preferably, the outer semiconductive insulating layer is composed of the following raw materials in parts by weight: 60-70 parts of ethylene-vinyl acetate copolymer (EVA, VA content 28%), and conductive carbon black (specific surface area 120-150 μm²). 2 28-32 parts ( / g) of graphene nanosheets (3-8 layers, 1-5μm diameter), 3-5 parts of carbon nanotubes (10-20nm diameter, 5-15μm length), 0.5-1.0 parts of antioxidant 1010, and 0.5-1.0 parts of lubricant zinc stearate, with volume resistivity controlled at 10. 1 ~10 3 Ω·cm, with a thickness of 0.5~1.0mm.

[0018] Preferably, the weather-resistant sheath layer is composed of the following raw materials in parts by weight: weather-resistant linear low-density polyethylene (density 0.920 g / cm³). 3 55-65 parts, 15-20 parts of ethylene-octene elastomer, 10-15 parts of metallocene polyethylene, 2.5-3.5 parts of carbon black (N330, particle size 26-30nm), 3-5 parts of nano titanium dioxide (rutile type), 0.5-1.0 parts of antioxidant 1010, 0.5-1.0 parts of light stabilizer HALS-944, 0.5-1.0 parts of lubricant polyethylene wax, with a thickness of 1.5-2.5mm.

[0019] A method for manufacturing an overhead insulated cable for high-altitude applications includes the following steps: Conductor surface treatment: Aluminum-magnesium-silicon alloy conductors or steel-cored aluminum stranded conductors are subjected to micro-arc oxidation treatment with a pulse voltage of 200~400V, a frequency of 50~500Hz, an electrolyte of sodium silicate 10~20g / L + potassium hydroxide 2~5g / L, and a treatment time of 10~30min to form an alumina ceramic film layer on the conductor surface. Mixing and granulation of each layer of materials: The raw materials for the inner semi-conductive insulation layer, corona-resistant inner insulation layer, main insulation layer, weather-resistant outer insulation layer, outer semi-conductive insulation layer, and weather-resistant sheath layer are added to a Banbury mixer in proportion and mixed. Granulation is then performed using an extruder. The mixing temperatures for the inner semi-conductive insulation layer are 140-150℃, 40 rpm, and 15-20 min; for the corona-resistant inner insulation layer, 130-140℃, 35 rpm, and 10-15 min; for the main insulation layer, 125-135℃, 30 rpm, and 12-15 min; for the weather-resistant outer insulation layer, 140-150℃, 35 rpm, and 10-12 min; for the outer semi-conductive insulation layer, 140-150℃, 40 rpm, and 15-20 min; and for the weather-resistant sheath layer, 150-160℃, 40 rpm, and 15-20 min. Extrusion of the inner semi-conductive insulating layer: A single-screw extruder is used, with extrusion temperatures of 130℃ in the feeding section, 140℃ in the compression section, 150℃ in the homogenization section, and 155℃ in the die head. The extrusion speed is 8~12m / min, and the extrusion thickness is 0.5~1.0mm. Three-layer co-extrusion molding: A three-layer co-extrusion extrusion unit is used to sequentially co-extrude the corona-resistant inner insulation layer, the main insulation layer, and the weather-resistant outer insulation layer on the conductor layer; Online electron beam irradiation crosslinking: The extruded cable core is crosslinked by electron beam irradiation under nitrogen protection by passing it through an online electron accelerator irradiation device; Extrusion of the outer semiconductive insulating layer: A single-screw extruder is used, with an extrusion temperature of 140~160℃, an extrusion speed of 5~15m / min, and an extrusion thickness of 0.5~1.0mm; Weather-resistant sheath extrusion: using a single-screw extruder, extrusion temperature 160~180℃, extrusion speed 5~15m / min, extrusion thickness 1.5~2.5mm; Cooling: Segmented cooling water tanks are used for cooling. The first segment is 60~70℃, the second segment is 40~50℃, and the third segment is 20~30℃, which can produce overhead insulated cables for high altitude.

[0020] Preferably, the extrusion temperatures of each layer in the three-layer co-extrusion molding step are as follows: feeding section 120~140℃, compression section 140~160℃, homogenization section 160~180℃, and die head 170~190℃; the extrusion speed is 5~15m / min; the interlayer interface temperature between the corona-resistant inner insulation layer and the main insulation layer is 165~175℃; the interlayer interface temperature between the main insulation layer and the weather-resistant outer insulation layer is 170~180℃; the interlayer contact time is ≥30s; and the co-extrusion die head is connected to a vacuum degassing device with a vacuum degree ≤-0.08MPa.

[0021] In the online electron beam irradiation crosslinking step: electron beam energy 1.5~2.5MeV, beam current intensity 20~50mA, irradiation dose 80~150kGy, linear velocity 10~30m / min, rapid cooling after irradiation, cooling rate ≥20℃ / s, using a three-stage cooling water tank: the first stage 60~70℃, the second stage 40~50℃, and the third stage 20~30℃.

[0022] In summary, the present invention has the following beneficial effects: 1. Because the corona-resistant inner insulation layer, main insulation layer, and weather-resistant outer insulation layer of this invention all contain an allyl or vinyl crosslinking agent (TAIC), during the electron beam irradiation crosslinking process, the TAIC molecules in each layer not only form a crosslinking network within their respective layers, but more importantly, due to the mutual diffusion and entanglement of molecular chains at the interlayer interfaces during the three-layer co-extrusion, the free radicals generated by irradiation can cross the interlayer interfaces and form interlayer CC chemical bonds between the three layers. This interlayer chemical bond transforms the three-layer insulating material from physical contact to chemical bonding, increasing the interlayer peel strength by more than three times.

[0023] 2. In this invention, the surfaces of nano-silica and nano-alumina in the corona-resistant inner insulation layer are modified with KH-550 and KH-570 silane coupling agents, resulting in amino and methacryloyloxy functional groups. The surface of the organically modified nano-montmorillonite in the main insulation layer contains long-chain alkylammonium ions. In the molten state of the three-layer co-extrusion, the amino groups on the surface of the nano-silica in the corona-resistant inner insulation layer form hydrogen bonds with the hydroxyl groups between the nano-montmorillonite layers of the main insulation layer. The methacryloyloxy groups on the surface of the nano-alumina undergo transesterification with the ethyl acrylate groups in the EEA of the main insulation layer, forming covalent bonds. This nanoparticle interface bridging effect increases the interfacial shear strength between the corona-resistant inner insulation layer and the main insulation layer by more than 50%.

[0024] 3. The weather-resistant outer insulation layer of the present invention contains UV-531 and HALS-770 light stabilizers. During electron beam irradiation and subsequent thermal aging, the octyl group in the UV-531 molecule has limited compatibility with the HDPE matrix and migrates to the main insulation layer under the action of thermal driving force. Due to the layered barrier effect of nano-montmorillonite in the main insulation layer, the migration of UV-531 is partially blocked, forming a concentration gradient distribution at the interface between the two layers. This gradient distribution extends the UV protection function from the weather-resistant outer insulation layer to the main insulation layer, forming a gradient UV protection system of "weather-resistant outer insulation layer main protection + main insulation layer layer protection". At the same time, the piperidine group in the HALS-770 molecule forms a coordination adsorption with the hydroxyl group on the surface of nano-magnesium hydroxide in the main insulation layer, so that HALS-770 is enriched on the surface of the main insulation layer, enhancing the photo-oxidation stability of the main insulation layer.

[0025] 4. The polyimide microcapsules in the corona-resistant inner insulation layer of the present invention encapsulate low-viscosity silicone oil and the catalyst dibutyltin dilaurate. When microcracks are generated by corona discharge or partial discharge: the microcapsules rupture, releasing the silicone oil and the catalyst. The low-viscosity silicone oil penetrates into the crack tip and the adjacent main insulation layer under capillary action. The Si-H groups in the silicone oil react with the hydroxyl groups on the surface of the nano-montmorillonite in the main insulation layer to form Si-O-Si bonds, which enhances the interfacial bonding at the crack. At the same time, the silicone oil reacts with moisture in the air under the action of the catalyst to form silicone rubber filler at the crack, realizing cross-layer self-repair. Attached Figure Description

[0026] Figure 1 This is a schematic cross-sectional view of the overall structure of the overhead insulated cable for high altitude use in Embodiment 1 of the present invention; Figure 2 This is a flowchart of the preparation method of the high-altitude overhead insulated cable of Embodiment 1 of the present invention; In the diagram: 1-Conductor layer, 2-Inner semiconducting insulation layer, 3-Graded functionalized insulation layer, 31-Corona resistant inner insulation layer, 32-Main insulation layer, 33-Weather resistant outer insulation layer, 4-Outer semiconducting insulation, 5-Weather resistant sheath layer. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. These embodiments do not constitute a limitation on the present invention.

[0028] Example 1: Foundation scheme (10kV / 240mm² / pure aluminum), structural cross-section as shown Figure 1 As shown, the preparation method flow is as follows: Figure 2 As shown.

[0029] Conductor layer 1: L3 pure aluminum, 19 strands / 3.2mm, compaction coefficient 0.92, micro-arc oxidation 300V / 200Hz / 20min, ceramic film 10μm.

[0030] Inner semiconductive insulating layer 2: 65 parts EVA, 28 parts N550 carbon black, 4 parts graphene, 1.5 parts CNT, 0.8 parts antioxidant 1010, and 0.7 parts zinc stearate. Mixing temperature: 145℃ / 40rpm / 18min; extrusion temperature: 150~155℃; thickness: 0.8mm.

[0031] Gradient functionalized insulating layer 3: Layer A, corona-resistant inner insulation layer 31 (1.2mm): LDPE 60 parts, POE 18 parts, modified nano SiO2 10 parts, modified nano Al2O 36 parts, polyimide microcapsules 4 parts, antioxidant 168 0.8 parts, DLTP 0.4 parts, TAIC 2.0 parts, mixed at 135℃ / 35rpm / 15min, extrusion temperature 170~175℃.

[0032] B-layer main insulation layer 32 (3.5mm): 75 parts XLPE, 12 parts EEA, 6 parts organic modified nano montmorillonite, 4 parts nano magnesium hydroxide, 1.2 parts DCP, 1.2 parts TAIC, 0.4 parts antioxidant 1010, 0.25 parts MDA-5, mixed at 130℃ / 30rpm / 15min (DCP added at 125℃), extrusion temperature 170~175℃.

[0033] C-layer weather-resistant outer insulation layer 33 (0.8mm): 65 parts weather-resistant HDPE, 18 parts EVA, 26 parts modified nano-TiO, 4 parts nano-ZnO, 1.2 parts UV-531, 1.0 part HALS-770, 0.6 parts antioxidant 1010, and 1.2 parts TAIC. Mixing temperature: 145℃ / 35rpm / 12min; extrusion temperature: 180~185℃.

[0034] Outer semiconductive insulation 4: Same as inner semiconductive insulation layer 2, 30 parts carbon black, extrusion temperature 150~160℃, thickness 0.8mm.

[0035] Weather-resistant jacket layer 5: LLDPE 60 parts, POE 18 parts, mPE 12 parts, N330 3.0 parts, nano TiO2 4 parts, antioxidant 1010 0.8 parts, HALS-944 0.8 parts, polyethylene wax 0.8 parts. Mixing temperature 155℃ / 40rpm / 18min, extrusion temperature 170~180℃, thickness 2.0mm.

[0036] Irradiation crosslinking: 2.0 MeV, 35 mA, 120 kGy, 20 m / min, N2 protection, cooling rate ≥ 20 °C / s.

[0037] Example 2: High corona resistance formulation (10kV / 185mm² / pure aluminum) Differences from Example 1: Layer A: Nano SiO2 increased to 12 parts, nano Al2O3 increased to 8 parts, polyimide microcapsules increased to 5 parts, and 2 new nano boron nitride (50nm) parts were added; Layer B: Nano-montmorillonite increased to 8 parts, nano-magnesium hydroxide increased to 5 parts; The thickness of layer B is increased to 4.5mm; The irradiation dose was increased to 140 kGy.

[0038] Example 3: 20kV Thick Insulation Scheme (20kV / 300mm) 2 (pure aluminum) Differences from Example 1: Conductor layer 1: 37 strands / 3.2mm, compaction coefficient 0.93, micro-arc oxidation 380V / 300Hz / 28min, ceramic film 14μm; Layer A: 1.5mm; Layer B: 5.5mm (8 parts nano-montmorillonite, 5 parts nano-magnesium hydroxide); C layer: 1.0mm (UV-531 1.5 parts, HALS-770 1.2 parts); Irradiation dose: 140 kGy; Spark detection voltage: 15kV.

[0039] Example 4: 35kV long span (35kV / 400mm² / steel-cored aluminum stranded wire) Differences from Example 1: Conductor layer 1: Steel-cored aluminum stranded wire (7 steel cores + 30 aluminum wires), compaction coefficient 0.93, micro-arc oxidation 400V / 350Hz / 30min, ceramic film 15μm; Layer A: 1.5mm (5 parts of polyimide microcapsules); Layer B: 6.5mm (8 parts nano-montmorillonite); Layer C: 1.2mm (1.5 parts UV-531, 1.2 parts HALS-770); Irradiation dose: 150 kGy; Spark detection voltage: 20kV.

[0040] Example 5: Heavy icing zone (10kV / 150mm² / aluminum-magnesium-silicon alloy) Differences from Example 1: Conductor layer 1: aluminum-magnesium-silicon alloy (Mg 0.8%, Si 0.5%), 19 strands / 3.0mm, micro-arc oxidation 360V / 280Hz / 26min, ceramic film 13μm; Layer A: POE increased to 20 copies; Layer B: Replace 5 copies of EEA with POE; Weather-resistant sheath layer 5: POE increased to 20 parts, mPE increased to 15 parts.

[0041] Example 6: Ultra-weather-resistant formula (10kV / 240mm² / pure aluminum) Differences from Example 1: C layer: 60 parts weather-resistant HDPE, 15 parts EVA, 28 parts modified nano TiO, 5 parts nano ZnO, 1.5 parts UV-531, 1.2 parts HALS-770, and 2 parts newly added nano cerium oxide (CeO2, 30nm); Weather-resistant sheath layer 5: Nano TiO2 increased to 5 parts, HALS-944 increased to 1.0 parts, and 0.5 parts of carbon nanotubes added.

[0042] Performance Testing and Comparative Analysis Interlayer linkage reaction verification test Test 1: Verification of translayer chemical bonding (FTIR-ATR)

[0043] Test 2: Verification of Nanoparticle Interface Bridging (TEM+EDS)

[0044] Test 3: UV-531 gradient migration validation (HPLC)

[0045] Test 4: Self-healing cross-layer penetration testing (SEM+EDS) After artificially creating microcracks: silicone oil penetrates the B layer to a depth of approximately 50 μm, and Si-O-Si bonds are formed at the crack (FTIR 1080 cm⁻¹). - ¹).

[0046] Comprehensive performance test Table 1. Comparison of corona performance (altitude 4000m)

[0047] Table 2 Comparison of Weather Resistance

[0048] Table 3 Comparison of Electrical Performance

[0049] Table 4 Mechanical properties and thermal cycling performance

[0050] Table 5 Summary of Key Performance of Each Embodiment

[0051] Extreme temperature difference thermal cycling stress test In high-altitude areas, the diurnal temperature range can reach 30-40℃, and in extreme cases, it can exceed 50℃. Under repeated thermal expansion and contraction, the cable insulation layer experiences thermal cycling stress, which can easily lead to interlayer delamination, microcrack propagation, and insulation performance degradation. This invention effectively alleviates thermal cycling stress through a gradient thermal expansion coefficient design and a cross-layer chemical bonding mechanism. The following is a systematic thermal cycling stress verification test: Test 5: Thermal Cycling Test Conditions and Procedures Based on GB / T 2951.21-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 21: Test Methods for Elastomer Compounds - Thermal Elongation Test" and IEC 60811-2-1, design a thermal cycling test scheme:

[0052] Test equipment: High and low temperature alternating damp heat test chamber (temperature range -60℃~+150℃, temperature fluctuation ±0.5℃).

[0053] Test 6: Changes in interlayer peel strength after thermal cycling Interlayer peel strength is a key indicator for evaluating the stability of interfacial bonding under thermal cycling stress. After thermal cycling tests on conventional XLPE cables and the cable of this invention, the interlayer peel strength was tested according to ASTM D1876.

[0054] The results show that after 1500 thermal cycles, the peel strength between the AB layers of the cable of this invention still maintains 82.2% of the initial value, and the peel strength between the BC layers remains at 83.3%, with no delamination. The interlayer chemical bonding and nano-interface bridging mechanisms significantly improve the interfacial thermal cycling resistance.

[0055] Test 7: Insulation layer dimensional stability after thermal cycling The radial shrinkage and axial elongation of the insulation layer under thermal cycling stress directly affect the fit between the cable and the joint, as well as the electric field distribution. Test method: Mark a baseline on the insulation layer surface, and measure the rate of dimensional change after thermal cycling.

[0056]

[0057] The thermal expansion coefficient gradient of the three insulating layers in this invention is matched (layer A: 2.2~2.5×10⁻⁶). -5 / ℃, B layer 2.5~2.8×10 -5 / ℃, C layer 2.0~2.3×10 -5 / °C), the deformation of each layer is coordinated and consistent, avoiding internal stress concentration and dimensional distortion caused by mismatched thermal expansion.

[0058] Test 8: Change of dielectric properties after thermal cycling Thermal cycling stress may induce interfacial defects and microcracks, leading to changes in dielectric constant and dielectric loss. Test method: A broadband dielectric spectrometer (frequency range 10 - ²~10 6 Hz) is used to test the dielectric parameters before and after thermal cycling.

[0059]

[0060] After 1000 thermal cycles, the cable of the present invention has a dielectric constant change rate of only 1.2%, a dielectric loss increase of 31%, and a volume resistivity decrease of 12.5%; while the conventional cable has a dielectric constant change rate of 10.3%, a dielectric loss increase of 134%, and a volume resistivity decrease of 66.7%. The gradient matching of thermal expansion coefficients effectively inhibits the generation of interfacial micro-defects.

[0061] Test 9: Extreme high and low temperature shock test Simulate extreme sudden weather changes in high-altitude areas (such as sudden clearing after hail, sudden temperature drop at night), and carry out high and low temperature shock test:

[0062] Test results:

[0063] Test 10: Microstructure analysis after thermal cycling (SEM+EDS) Scanning electron microscope observation and energy spectrum analysis are performed on the cable insulation layer after 1500 thermal cycles:

[0064] Test 11: Actual measurement and verification of thermal expansion coefficient A thermomechanical analyzer (TMA) is used with a heating rate of 5°C / min and a temperature range of -50°C to +120°C to test the actual thermal expansion coefficient of each layer:

[0065] The measured thermal expansion coefficients show a gradient distribution of Layer A < Layer B, Layer C < Layer B, which interacts with the dielectric constant gradient to achieve smooth electric field transition and thermal stress relief.

[0066] Test 12: Thermal cycling-corona combined aging test In high-altitude environments, thermal cycling stress and corona aging often act simultaneously, and a combined aging test is designed:

[0067] Test results:

[0068] Combined aging tests show that the cable of this invention maintains excellent insulation performance and interface stability under the combined effects of thermal cycling and corona discharge, while conventional cables deteriorate rapidly under dual stress.

[0069] This invention achieves a comprehensive improvement in the performance of high-altitude overhead insulated cables through the following technological innovations: 1. Material System: A nano-SiO2 / Al2O3 synergistic corona-resistant system was constructed. High-energy electrons were captured through interface traps to suppress the initiation of electrical treeing. The self-healing technology of polyimide microcapsules was used to achieve active repair of corona damage, realizing a three-in-one ultraviolet protection system of "nano-TiO2 / ZnO + UV-531 + HALS".

[0070] 2. Structural Design: A gradient functionalized three-layer insulation structure is constructed, with each layer having a clear functional positioning and synergistic enhancement. A gradient matching design of dielectric constant is adopted to smooth the electric field distribution, and a gradient matching design of thermal expansion coefficient is used to eliminate thermal cycling stress.

[0071] 3. Interface engineering: Through interlayer linkage reaction mechanism, physical contact is transformed into chemical bonding. Cross-layer chemical bonding increases interlayer peel strength by 256%, and nanoparticle interface bridging increases interfacial shear strength by 132%.

[0072] 4. Innovative preparation process: The process adopts a three-layer co-extrusion + online electron beam irradiation crosslinking integrated process to precisely control the interlayer interface temperature and rapidly cool and lock the cross-layer chemical bond structure.

[0073] The 10kV overhead insulated cable for high altitude applications of this invention can be widely used in the following scenarios: 1. Power distribution network construction in high-altitude areas: Qinghai-Tibet Plateau (average altitude above 4000m), Yunnan-Guizhou Plateau (altitude 2000~4000m), Western Sichuan Plateau, Qilian Mountains, etc.

[0074] 2. Transmission lines in special environments: areas with strong ultraviolet radiation (Tibet, Qinghai), areas with extreme temperature differences (day-night temperature difference > 30℃), heavy icing areas, and areas with large crossings.

[0075] 3. Expected economic benefits: The service life of the cable is extended from the conventional 10 years to more than 25 years, the power loss caused by corona discharge is reduced by about 15%, the frequency of line maintenance and replacement is reduced, and the overall operation and maintenance cost is reduced by more than 60%.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. An overhead insulated cable for high-altitude applications, characterized in that, From the inside out, it includes: a conductor layer, an inner semiconducting insulating layer, a gradient functionalized insulating layer, an outer semiconducting insulating layer, and a weather-resistant sheath layer. The gradient functionalized insulating layer includes, from the inside out, a corona-resistant inner insulating layer, a main insulating layer, and a weather-resistant outer insulating layer. The corona-resistant inner insulation layer is composed of the following raw materials in parts by weight: 55-65 parts low-density polyethylene, 15-20 parts ethylene-octene copolymer, 8-12 parts nano-silica modified with silane coupling agent, 5-8 parts nano-alumina modified with silane coupling agent, 3-5 parts polyimide microcapsules, 0.8-1.5 parts antioxidant, and 1.5-2.5 parts crosslinking agent; The main insulation layer is composed of the following raw materials in parts by weight: 70-80 parts of cross-linked polyethylene base material, 10-15 parts of ethylene-ethyl acrylate copolymer, 5-8 parts of organic modified nano-montmorillonite, 3-5 parts of nano-magnesium hydroxide, 2.0-3.0 parts of cross-linking agent, 0.5-0.8 parts of antioxidant, and 0.2-0.3 parts of copper inhibitor; The weather-resistant outer insulation layer is composed of the following raw materials in parts by weight: 60-70 parts of weather-resistant high-density polyethylene, 15-20 parts of ethylene-vinyl acetate copolymer, 5-8 parts of nano-titanium dioxide surface modified with silane coupling agent, 3-5 parts of nano-zinc oxide, 1.0-1.5 parts of ultraviolet absorber, 0.8-1.2 parts of light stabilizer, 0.5-0.8 parts of antioxidant, and 1.0-1.5 parts of crosslinking agent; The dielectric constant of the corona-resistant inner insulating layer is 2.8~3.2, and the coefficient of thermal expansion is 2.2~2.5×10⁻⁶. -5 The temperature is ℃, the thickness is 0.8~1.5mm, the dielectric constant of the main insulating layer is 2.4~2.6, and the coefficient of thermal expansion is 2.5~2.8×10. -5 The temperature is ℃, the thickness is 2.5~4.0mm, the dielectric constant of the weather-resistant outer insulation layer is 2.6~3.0, and the coefficient of thermal expansion is 2.0~2.3×10. -5 / ℃, thickness is 0.5~1.0mm.

2. The overhead insulated cable for high altitude use according to claim 1, characterized in that: The conductor layer is made of compacted circular aluminum conductor or aluminum-magnesium-silicon alloy conductor with a cross-section of 50~400mm². The conductor surface is subjected to micro-arc oxidation treatment to form an alumina ceramic film layer with a thickness of 5~15μm.

3. The overhead insulated cable for high altitude use according to claim 1, characterized in that: The inner semiconductive insulating layer is composed of the following raw materials in parts by weight: 60-70 parts ethylene-vinyl acetate copolymer, 25-30 parts conductive carbon black, 3-5 parts graphene nanosheets, 1-2 parts carbon nanotubes, 0.5-1.0 parts antioxidant, and 0.5-1.0 parts lubricant, with a volume resistivity controlled at 10. 2 ~10 4 Ω·cm, with a thickness of 0.5~1.0mm.

4. The overhead insulated cable for high altitude use according to claim 1, characterized in that: The polyimide microcapsules have a wall material of urea-formaldehyde resin and a core material of a mixture of low-viscosity silicone oil and a catalyst of dibutyltin dilaurate. The microcapsule particle size is 2-5 μm and the wall thickness is 0.2-0.5 μm. The organically modified nano-montmorillonite is organically modified with hexadecyltrimethylammonium bromide, with an interlayer spacing ≥3.5 nm. The crosslinking agent is TAIC. The modified silane coupling agent for nano-silica is KH-550, the modified silane coupling agent for nano-alumina is KH-570, the ultraviolet absorber is UV-531, and the light stabilizer is HALS-770.

5. The overhead insulated cable for high altitude use according to claim 1, characterized in that: The outer semiconductive insulating layer is composed of the following raw materials in parts by weight: 60-70 parts ethylene-vinyl acetate copolymer, 28-32 parts conductive carbon black, 3-5 parts graphene nanosheets, 1-2 parts carbon nanotubes, 0.5-1.0 parts antioxidant, and 0.5-1.0 parts lubricant, with a volume resistivity controlled at 10. 1 ~10 3 Ω·cm, with a thickness of 0.5~1.0mm.

6. The overhead insulated cable for high altitude use according to claim 1, characterized in that: The weather-resistant sheath layer is composed of the following raw materials in parts by weight: 55-65 parts of weather-resistant linear low-density polyethylene, 15-20 parts of ethylene-octene elastomer, 10-15 parts of metallocene polyethylene, 2.5-3.5 parts of carbon black, 3-5 parts of nano titanium dioxide, 0.5-1.0 parts of antioxidant, 0.5-1.0 parts of light stabilizer, 0.5-1.0 parts of lubricant, and a thickness of 1.5-2.5 mm.

7. A method for preparing a high-altitude overhead insulated cable according to any one of claims 1 to 6, characterized in that, Includes the following steps: Conductor surface treatment: Aluminum-magnesium-silicon alloy conductors or steel-cored aluminum stranded conductors are subjected to micro-arc oxidation treatment with a pulse voltage of 200~400V and a frequency of 50~500Hz to form an alumina ceramic film layer on the conductor surface. Mixing and granulating the materials of each layer: The raw materials of the inner semi-conductive insulation layer, the corona-resistant inner insulation layer, the main insulation layer, the weather-resistant outer insulation layer, the outer semi-conductive insulation layer and the weather-resistant sheath layer are added to the internal mixer in proportion and mixed, and then granulated by the extruder; Extrusion of the inner semi-conductive insulating layer: A single-screw extruder is used, with extrusion temperatures of 130℃ in the feeding section, 140℃ in the compression section, 150℃ in the homogenization section, and 155℃ in the die head. The extrusion speed is 8~12m / min, and the extrusion thickness is 0.5~1.0mm. Three-layer co-extrusion molding: A three-layer co-extrusion extrusion unit is used to sequentially co-extrude the corona-resistant inner insulation layer, the main insulation layer, and the weather-resistant outer insulation layer on the conductor layer; Online electron beam irradiation crosslinking: The extruded cable core is crosslinked by electron beam irradiation under nitrogen protection by passing it through an online electron accelerator irradiation device; Extrusion of the outer semiconductive insulating layer: A single-screw extruder is used, with an extrusion temperature of 140~160℃, an extrusion speed of 5~15m / min, and an extrusion thickness of 0.5~1.0mm; Weather-resistant sheath extrusion: using a single-screw extruder, extrusion temperature 160~180℃, extrusion speed 5~15m / min, extrusion thickness 1.5~2.5mm; Cooling: Segmented cooling water tanks are used for cooling. The first segment is 60~70℃, the second segment is 40~50℃, and the third segment is 20~30℃, which can produce overhead insulated cables for high altitude.

8. The method for preparing an overhead insulated cable for high altitude use according to claim 7, characterized in that: The extrusion temperatures of each layer in the three-layer co-extrusion molding process are as follows: feeding section 120~140℃, compression section 140~160℃, homogenization section 160~180℃, and die head 170~190℃; the extrusion speed is 5~15m / min; the interlayer interface temperature between the corona-resistant inner insulation layer and the main insulation layer is 165~175℃; the interlayer interface temperature between the main insulation layer and the weather-resistant outer insulation layer is 170~180℃; the interlayer contact time is ≥30s; and the co-extrusion die head is connected to a vacuum degassing device with a vacuum degree ≤-0.08MPa.

9. The method for preparing an overhead insulated cable for high altitude use according to claim 7, characterized in that: In the online electron beam irradiation crosslinking step: the electron beam energy is 1.5~2.5MeV, the beam current intensity is 20~50mA, the irradiation dose is 80~150kGy, the linear velocity is 10~30m / min, and rapid cooling is performed after irradiation with a cooling rate ≥20℃ / s. A three-stage cooling water tank is used: the first stage is 60~70℃, the second stage is 40~50℃, and the third stage is 20~30℃.

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