Crosslinked polyethylene insulated power cable wrapped by high-water-resistance buffer layer and preparation method of crosslinked polyethylene insulated power cable

Abstract

The invention relates to the technical field of power cables, in particular to a cross-linked polyethylene insulated power cable wrapped by a high-water-resistance buffer layer and a preparation method of the cross-linked polyethylene insulated power cable wrapped by the high-water-resistance buffer layer, and the cross-linked polyethylene insulated power cable is prepared from the following raw materials in parts by weight: 100 parts of ethylene-vinyl acetate copolymer; 15 to 25 parts of conductive carbon black; 20 to 30 parts of sodium polyacrylate; and 10 to 15 parts of nano montmorillonite. Through the high-water-resistance buffer layer and innovative process design, the problems existing in a traditional cable are solved, and the water-resistance layer effectively blocks a water permeation path through composite water absorption and a nano barrier; nitrogen doping and dispersion optimization of conductive carbon black ensure the stability of resistivity; a plasma interface activation and microcapsule cross-linking technology improves interlayer bonding force and cross-linking uniformity, gradient degassing and low-temperature cross-linking are adopted in the preparation process, the production cycle is shortened, energy consumption is reduced, meanwhile, material degradation is avoided, the cable has high water resistance and long service life, and reliability and safety of power grid operation are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power cables, in particular to a cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer and a preparation method thereof. Background Art

[0002] Power cables are the core carriers for transmitting and distributing electric energy. They are widely used in scenarios such as urban power grids, industrial equipment, building power supply and offshore wind power. They need to operate stably for a long time in complex environments such as high voltage, high humidity, and temperature changes. Especially in high-voltage direct current transmission (HVDC) and renewable energy grid-connected systems, the insulation performance, mechanical strength and weather resistance of cables are more stringent.

[0003] However, in general, traditional cross-linked polyethylene (XLPE) insulated cables often face defects such as uneven cross-linking degree and interface stratification. Residual gas in the cross-linking process forms micropores, exacerbating the risk of partial discharge; the resistivity fluctuations of the semi-conductive layer cause electric field distortion and accelerate material degradation. In addition, the traditional process relies on high-temperature steam cross-linking, which has high energy consumption and long production cycle, and is not environmentally friendly enough.

[0004] Based on this, the present invention provides a cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer and a preparation method thereof to solve the above-mentioned technical problems. Summary of the Invention

[0005] The object of the present invention is to provide a cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer and a preparation method thereof, so as to solve the problems mentioned in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The invention provides a cross-linked polyethylene insulated power cable with a high water-resistance buffer layer. The cross-linked polyethylene insulated power cable is composed of the following raw materials in parts by weight: 100 parts of ethylene-vinyl acetate copolymer; 15-25 parts of conductive carbon black; 20-30 parts of sodium polyacrylate; 10-15 parts of nano-montmorillonite; 5-8 parts of maleic anhydride-grafted polyethylene; 0.5-1.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; 1-2 parts of calcium stearate; 15-20 parts of aluminum hydroxide; 1-2 parts of dicumyl peroxide; 0.5-1 part of gamma-aminopropyltriethoxysilane; 2-4 parts of polyethylene wax; 3-5 parts of nano-silicon dioxide; and 0.5-1 part of 2-hydroxy-4-methoxybenzophenone.

[0008] Preferably, the sodium polyacrylate is prepared by polymerizing acrylic acid monomers through plasma activation under nitrogen protection, followed by rapid neutralization with sodium hydroxide in a vacuum environment, and nanocellulose is grafted onto the surface to improve water absorption.

[0009] Preferably, the nano-montmorillonite is prepared by exfoliating natural montmorillonite into a single-layer structure in supercritical carbon dioxide, and then grafting and modifying it with γ-aminopropyltriethoxysilane under an ultrasonic field, and the interlayer spacing is expanded to 3.5-4.0 nm.

[0010] Preferably, the conductive carbon black is prepared by cracking natural gas in an electric arc furnace to generate primary particles, which are then nitrogen-doped and surface-coated with polyvinyl pyrrolidone.

[0011] Preferably, the maleic anhydride grafted polyethylene is prepared by dynamic solid-phase grafting of low-density polyethylene and maleic anhydride in a twin-screw extruder, and simultaneously introducing di-tert-butyl peroxide to initiate a free radical reaction.

[0012] Preferably, the nano-silica is synthesized from ethyl orthosilicate in an ethanol-water mixture by a sol-gel method, and then hydrophobically modified in fluorosilane vapor.

[0013] Preferably, the pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is prepared by microwave-assisted esterification of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and pentaerythritol in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid.

[0014] Preferably, the dicumyl peroxide is prepared by reacting cumene with oxygen under ultraviolet light catalysis to generate hydroperoxide, which is then coated with copolymer microcapsules with polystyrene-maleic anhydride as the wall material.

[0015] Based on the above power cable formula components, the present invention also proposes a method for preparing a cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer, comprising the following steps:

[0016] S1. Premix 15-25 parts of conductive carbon black with 2-4 parts of polyethylene wax in a high-speed mixer for 10-15 minutes at 60°C to break up carbon black agglomerates through shear force to form a uniform pre-dispersion; dehydrate 20-30 parts of sodium polyacrylate and 10-15 parts of nano-montmorillonite in a vacuum drying oven for 2 hours to ensure a moisture content of ≤0.1%; add 100 parts of ethylene-vinyl acetate copolymer, 5-8 parts of maleic anhydride-grafted polyethylene, and 1-2 parts of calcium stearate to a high-speed mixer, raise the temperature to 70°C, and mix for 5 minutes to form a viscous matrix;

[0017] S2. Segmented temperature controlled extrusion:

[0018] Feeding section in zone 1: temperature 80-90°C, adding pre-treated conductive carbon black-polyethylene wax pre-dispersion;

[0019] Second zone melting section: temperature 150-160℃, add sodium polyacrylate, nano-montmorillonite and 15-20 parts of aluminum hydroxide in sequence;

[0020] Zone 3 mixing section: temperature 170-180°C, inject 0.5-1 parts of γ-aminopropyltriethoxysilane and 3-5 parts of nano-silica, and achieve directional dispersion of nano-fillers through the high shear zone;

[0021] Homogenization section 4: Temperature 160-170°C, add 0.5-1.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.5-1 part of 2-hydroxy-4-methoxybenzophenone;

[0022] Finally, the melt is filtered through a 200-mesh filter and then enters the melt pump for pressure stabilization to ensure that the extrusion pressure fluctuation is ≤±0.5MPa;

[0023] S3. The extruded buffer layer with a thickness of 1.0-1.5 mm and the cross-linked polyethylene insulation layer are wrapped in a concentric circle structure at a wrapping speed of 20-30 m / min and a wrapping tension of 10-15 N. The surface of the insulation layer is bombarded with argon plasma to generate polar groups and enhance the bonding strength of the buffer layer.

[0024] S4. Raise the temperature to 65-70°C in a nitrogen environment for 10-15 minutes to rupture the dicumyl peroxide microcapsules and release active oxygen, initiating a cross-linking reaction;

[0025] Gradient degassing:

[0026] The first stage: degassing at 70℃ and vacuum degree 100Pa for 2 hours to remove methane and other small molecular gases;

[0027] The second stage: degassing at 60℃ and vacuum degree 50Pa for 4 hours to ensure the porosity of the insulation layer is ≤0.01%;

[0028] S5. After the cable has cooled naturally to room temperature, argon arc welding is used to continuously weld a 2mm thick aluminum strip to a corrugation depth of 5mm. The outer diameter tolerance after corrugation is ±0.1mm. Epoxy resin is applied to the inside of the aluminum strip and hot-air cured. Finally, a flame-retardant sheath containing 20-30 parts of aluminum hydroxide is co-extruded over the cross-linked layer. The sheath thickness is 4.0-5.0mm. The extruder zone temperatures are as follows: Zone 1: 125°C; Zone 2: 145°C; Zone 3: 165°C; Zone 4: 175°C; Zone 5: 170°C; Zone 6: 165°C; and the die head: 160°C.

[0029] S6. Perform performance tests on the prepared cable samples.

[0030] Preferably, the performance test in step S6 includes resistivity detection and water resistance performance test.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention solves the problems existing in traditional cables through a high water-resistance buffer layer and innovative process design. The water-resistance layer effectively blocks the water penetration path through composite water absorption and nano-barriers; the conductive carbon black nitrogen doping and dispersion optimization ensure the stability of resistivity; plasma interface activation and microcapsule cross-linking technology improve the interlayer bonding strength and cross-linking uniformity. The preparation process adopts gradient degassing and low-temperature cross-linking to shorten the production cycle and reduce energy consumption, while avoiding material degradation. The cable has both high water resistance and long life, and is suitable for harsh environments such as high voltage, high humidity and offshore, significantly improving the reliability and safety of power grid operation. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] 1. Materials:

[0035] The material components of the cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer of the present invention are commercially available unless otherwise specified:

[0036] The invention provides a cross-linked polyethylene insulated power cable with a high water-resistance buffer layer. The cross-linked polyethylene insulated power cable is composed of the following raw materials in parts by weight: 100 parts of ethylene-vinyl acetate copolymer; 15-25 parts of conductive carbon black; 20-30 parts of sodium polyacrylate; 10-15 parts of nano-montmorillonite; 5-8 parts of maleic anhydride-grafted polyethylene; 0.5-1.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; 1-2 parts of calcium stearate; 15-20 parts of aluminum hydroxide; 1-2 parts of dicumyl peroxide; 0.5-1 part of gamma-aminopropyltriethoxysilane; 2-4 parts of polyethylene wax; 3-5 parts of nano-silicon dioxide; and 0.5-1 part of 2-hydroxy-4-methoxybenzophenone.

[0037] Among them, it should be noted that sodium polyacrylate is prepared by initiating polymerization of acrylic acid monomers through plasma activation under nitrogen protection, and then quickly neutralizing with sodium hydroxide in a vacuum environment, and nanocellulose is grafted on the surface to improve water absorption.

[0038] Among them, it should be noted that nano-montmorillonite is prepared by exfoliating natural montmorillonite into a single-layer structure in supercritical carbon dioxide, and then grafting and modifying it with γ-aminopropyltriethoxysilane under an ultrasonic field, and the interlayer spacing is expanded to 3.5-4.0nm.

[0039] It should be noted that conductive carbon black is produced by cracking natural gas in an electric arc furnace to generate primary particles, which are then nitrogen-doped and surface-coated with polyvinyl pyrrolidone.

[0040] It should be noted that the maleic anhydride grafted polyethylene is prepared by dynamic solid-phase grafting of low-density polyethylene and maleic anhydride in a twin-screw extruder, and simultaneously introducing di-tert-butyl peroxide to initiate a free radical reaction.

[0041] It should be noted that nano-silica is synthesized from ethyl orthosilicate in an ethanol-water mixture by a sol-gel method, and then hydrophobically modified in fluorosilane vapor.

[0042] It should be noted that pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is prepared by microwave-assisted esterification of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and pentaerythritol in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid.

[0043] It should be noted that dicumyl peroxide is prepared by reacting cumene with oxygen under ultraviolet light to generate hydroperoxide, which is then encapsulated in copolymer microcapsules with polystyrene-maleic anhydride as the wall material.

[0044] 2. Process:

[0045] Based on the above power cable formula components, the present invention also proposes a method for preparing a cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer, comprising the following steps:

[0046] S1. Premix 15-25 parts of conductive carbon black with 2-4 parts of polyethylene wax in a high-speed mixer for 10-15 minutes at 60°C to break up carbon black agglomerates through shear force to form a uniform pre-dispersion; dehydrate 20-30 parts of sodium polyacrylate and 10-15 parts of nano-montmorillonite in a vacuum drying oven for 2 hours to ensure a moisture content of ≤0.1%; add 100 parts of ethylene-vinyl acetate copolymer, 5-8 parts of maleic anhydride-grafted polyethylene, and 1-2 parts of calcium stearate to a high-speed mixer, raise the temperature to 70°C, and mix for 5 minutes to form a viscous matrix;

[0047] S2. Segmented temperature controlled extrusion:

[0048] Feeding section in zone 1: temperature 80-90°C, adding pre-treated conductive carbon black-polyethylene wax pre-dispersion;

[0049] Second zone melting section: temperature 150-160℃, add sodium polyacrylate, nano-montmorillonite and 15-20 parts of aluminum hydroxide in sequence;

[0050] Zone 3 mixing section: temperature 170-180°C, inject 0.5-1 parts of γ-aminopropyltriethoxysilane and 3-5 parts of nano-silica, and achieve directional dispersion of nano-fillers through the high shear zone;

[0051] Homogenization section 4: Temperature 160-170°C, add 0.5-1.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.5-1 part of 2-hydroxy-4-methoxybenzophenone;

[0052] Finally, the melt is filtered through a 200-mesh filter and then enters the melt pump for pressure stabilization to ensure that the extrusion pressure fluctuation is ≤±0.5MPa;

[0053] S3. The extruded buffer layer with a thickness of 1.0-1.5 mm and the cross-linked polyethylene insulation layer are wrapped in a concentric circle structure at a wrapping speed of 20-30 m / min and a wrapping tension of 10-15 N. The surface of the insulation layer is bombarded with argon plasma to generate polar groups and enhance the bonding strength of the buffer layer.

[0054] S4. Raise the temperature to 65-70°C in a nitrogen environment for 10-15 minutes to rupture the dicumyl peroxide microcapsules and release active oxygen, initiating a cross-linking reaction;

[0055] Gradient degassing:

[0056] The first stage: degassing at 70℃ and vacuum degree 100Pa for 2 hours to remove methane and other small molecular gases;

[0057] The second stage: degassing at 60℃ and vacuum degree 50Pa for 4 hours to ensure the porosity of the insulation layer is ≤0.01%;

[0058] S5. After the cable has cooled naturally to room temperature, argon arc welding is used to continuously weld a 2mm thick aluminum strip to a corrugation depth of 5mm. The outer diameter tolerance after corrugation is ±0.1mm. Epoxy resin is applied to the inside of the aluminum strip and hot-air cured. Finally, a flame-retardant sheath containing 20-30 parts of aluminum hydroxide is co-extruded over the cross-linked layer. The sheath thickness is 4.0-5.0mm. The extruder zone temperatures are as follows: Zone 1: 125°C; Zone 2: 145°C; Zone 3: 165°C; Zone 4: 175°C; Zone 5: 170°C; Zone 6: 165°C; and the die head: 160°C.

[0059] S6. Perform performance tests on the prepared cable samples.

[0060] It should be noted that the performance test in step S6 includes resistivity detection and water resistance performance test.

[0061] Example 1: In this example, based on the above process, a cross-linked polyethylene insulated power cable wrapped with a high water-resistance buffer layer is prepared according to the following specific parameters. Specifically, the following steps are included:

[0062] Step S1: Raw material pretreatment and premixing:

[0063] Conductive carbon black pre-dispersion: Add 20 parts of conductive carbon black and 3 parts of polyethylene wax into a high-speed mixer at 700 rpm and 60°C, and pre-mix for 12 minutes.

[0064] Dehydration of water-blocking agent: 25 parts of sodium polyacrylate and 12.5 parts of nano-montmorillonite were dried in a vacuum drying oven (pressure ≤ 10Pa, temperature 80°C) for 2 hours, with a water content of ≤ 0.1%;

[0065] Matrix premix: Add 100 parts of ethylene-vinyl acetate copolymer, 6.5 parts of maleic anhydride grafted polyethylene, and 1.5 parts of calcium stearate into a high-speed mixer, heat to 70°C, and mix for 5 minutes to form a viscous matrix;

[0066] Step S2: Buffer layer blending and extrusion:

[0067] Segmented temperature controlled extrusion:

[0068] Zone 1 (feeding section): temperature 85°C, adding conductive carbon black-polyethylene wax pre-dispersion;

[0069] Zone 2 (melting section): temperature 155°C, add 25 parts of sodium polyacrylate, 12.5 parts of nano-montmorillonite, and 17.5 parts of aluminum hydroxide in sequence;

[0070] Zone 3 (mixing section): temperature 175°C, injection of 0.75 parts of γ-aminopropyltriethoxysilane and 4 parts of nano-silica, shear rate 1200s -1 ;

[0071] Zone 4 (homogenization section): Temperature 165°C, add 1.0 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.75 part of 2-hydroxy-4-methoxybenzophenone;

[0072] Melt pressure stabilization: After the melt is filtered through a 200-mesh filter, the melt pump pressure is stabilized at 12MPa, and the pressure fluctuation is ≤±0.5MPa;

[0073] Step S3: Buffer layer wrapping and interface activation:

[0074] Wrapping process: buffer layer thickness 1.0mm, semi-conductive shielding layer resistivity 1×10³Ω·cm, cross-linked polyethylene insulation layer thickness 16mm, wrapping speed 25m / min, wrapping tension 15N;

[0075] Plasma treatment: Argon plasma power 8 kW, treatment time 45 s, peel strength 18.5 N / cm;

[0076] Step S4: Cross-linking and degassing:

[0077] Microcapsule cross-linking: Heat to 65°C in a nitrogen environment, keep warm for 12 minutes, and the cross-linking degree is 88%;

[0078] Gradient degassing:

[0079] The first stage: degassing at 70℃ and vacuum degree 100Pa for 2 hours to remove methane and other small molecular gases;

[0080] The second stage: degassing at 60℃ and vacuum degree 50Pa for 4 hours to ensure the porosity of the insulation layer is ≤0.01%;

[0081] Step S5: Cooling and jacket forming:

[0082] After the cable is cooled naturally to room temperature, argon arc welding is used to continuously weld 2mm thick aluminum strips with a corrugation depth of 5mm and an outer diameter tolerance of ±0.1mm after corrugation. Epoxy resin glue is applied on the inside of the aluminum strips and hot air cured.

[0083] Sheath co-extrusion: flame retardant sheath contains 25 parts of aluminum hydroxide, thickness 2.5 mm, extruder temperature: zone 1: 125℃; zone 2: 145℃; zone 3: 165℃; zone 4: 175℃; zone 5: 170℃; zone 6: 165℃; die head: 160℃;

[0084] Example 2: In this example, the conductive carbon black is 15 parts, the sodium polyacrylate is 20 parts, and the nano-montmorillonite is 10 parts. Other process parameters are the same as those in Example 1.

[0085] Example 3: In this example, the conductive carbon black is 25 parts, the sodium polyacrylate is 30 parts, and the nano-montmorillonite is 15 parts. Other process parameters are the same as those in Example 1.

[0086] Example 4: In this example, the wrapping tension is adjusted to 18N, the wrapping speed is adjusted to 30m / min, and the other material components and process parameters are the same as those in Example 1;

[0087] Example 5: In this example, the gradient degassing time is adjusted to 1.5 hours in the first stage and 3 hours in the second stage. Other material components and process parameters are the same as those in Example 1.

[0088] The material parameters of Examples 1-5 are shown in Table 1:

[0089] Table 1: Example material composition table

[0090] Components Example 1 Example 2 Example 3 Example 4 Example 5 Ethylene vinyl acetate copolymer 100 100 100 100 100 Conductive carbon black 20 15 25 20 20 Sodium polyacrylate 25 20 30 25 25 Nano-montmorillonite 12.5 10 15 12.5 12.5 Maleic anhydride grafted polyethylene 6.5 6.5 6.5 6.5 6.5 Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate 1.0 1.0 1.0 1.0 1.0 calcium stearate 1.5 1.5 1.5 1.5 1.5 aluminum hydroxide 17.5 17.5 17.5 17.5 17.5 Dicumyl peroxide 1.5 1.5 1.5 1.5 1.5 γ-Aminopropyltriethoxysilane 0.75 0.75 0.75 0.75 0.75 Polyethylene wax 3 3 3 3 3 Nanosilica 4 4 4 4 4 2-Hydroxy-4-methoxybenzophenone 0.75 0.75 0.75 0.75 0.75

[0091] Comparative Example 1: In this comparative example, the conductive carbon black is 10 parts, and the other process parameters are the same as those in Example 1;

[0092] Comparative Example 2: In this comparative example, the amount of sodium polyacrylate was 35 parts, and the other process parameters were the same as those in Example 1.

[0093] Comparative Example 3: In this comparative example, no microencapsulated crosslinking agent was used, and uncoated dicumyl peroxide was directly added. Other process parameters were the same as those in Example 1.

[0094] Comparative Example 4: In this comparative example, the nano-montmorillonite was replaced by unmodified natural montmorillonite, and the other process parameters were the same as those in Example 1.

[0095] Comparative Example 5: In this comparative example, no dicumyl peroxide crosslinking agent was added, and other process parameters were the same as those in Example 1;

[0096] The material parameters of Comparative Examples 1-5 are shown in Table 2:

[0097] Table 2: Comparative Example Material Composition Table

[0098] Components Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Ethylene vinyl acetate copolymer 100 100 100 100 100 Conductive carbon black 10 20 20 20 20 Sodium polyacrylate 25 35 25 25 25 Nano-montmorillonite 12.5 12.5 12.5 12.5 (natural montmorillonite) 12.5 Maleic anhydride grafted polyethylene 6.5 6.5 6.5 6.5 6.5 Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate 1.0 1.0 1.0 1.0 1.0 calcium stearate 1.5 1.5 1.5 1.5 1.5 aluminum hydroxide 17.5 17.5 17.5 17.5 17.5 Dicumyl peroxide 1.5 1.5 1.5 (unwrapped) 1.5 0 γ-Aminopropyltriethoxysilane 0.75 0.75 0.75 0.75 0.75 Polyethylene wax 3 3 3 3 3 Nanosilica 4 4 4 4 4 2-Hydroxy-4-methoxybenzophenone 0.75 0.75 0.75 0.75 0.75

[0099] 3. Performance test:

[0100] According to the process of the embodiment and the comparative example, a power cable sample was prepared and its performance was tested, and the steps were as follows:

[0101] a. Conduct pH, average water blocking rate, tensile strength before aging, moisture content, and resistivity tests according to T / CAS-374. Thermal aging test parameters are: aging temperature at 100°C, duration of 168 hours, and tensile strength change rate less than 20%;

[0102] b. Peel strength test according to ASTM D903 180° peel test;

[0103] c. Cross-linking degree test according to IEC 60811-501 gel content method;

[0104] The performance data of the power cable samples prepared in Examples 1-5 and Comparative Examples 1-5 are recorded in Tables 3 and 4;

[0105] Table 3: Example performance data

[0106] Test items Example 1 Example 2 Example 3 Example 4 Example 5 Volume resistivity (Ω·cm) 1.2×10³ 2.5×10³ 8×10² 1.1×10³ 1.0×10³ pH 7.2 7.2 7.2 7.2 7.2 Average water blocking rate (mm / h) 15.0 12.3 11.0 13.0 9.0 Tensile strength before aging (N / mm) 8.0 7.0 7.2 7.0 6.8 Moisture content (%) 1.6 2.6 2.3 3.0 2.9 Peel strength (N / cm) 18.5 14.0 20.2 19.8 21.0 Degree of cross-linking (%) 88 82 90 89 91

[0107] Table 4: Comparative Example Performance Data

[0108] Test items Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Volume resistivity (Ω·cm) 1.2×10³ 1.2×10³ 1.2×10³ 1.2×10³ Failure pH 7.2 7.2 7.2 7.2 7.2 Average water blocking rate (mm / h) 15.0 15.0 15.0 21.0 19.0 Tensile strength before aging (N / mm) 2.6 8.0 8.0 8.0 3.6 Moisture content (%) 1.6 5.2 1.6 1.6 5.5 Peel strength (N / cm) 18.5 18.5 18.5 18.5 3.5 Degree of cross-linking (%) 88 88 65 88 0

[0109] 4. Analysis Conclusions:

[0110] According to Tables 1 to 4, in Comparative Example 1, the tensile strength before aging decreased significantly when the conductive carbon black was reduced to 10 parts. Conductive carbon black is a key reinforcing filler, and its insufficient content leads to deterioration of the mechanical properties of the material, and the tensile strength decreases compared with Example 1; in Comparative Example 2, the moisture content of sodium polyacrylate increased significantly when it was increased to 35 parts. Excessive water-absorbing resin releases moisture when dehydration is not complete, which destroys the stability of the material, and the moisture content is higher than that of Example 1; in Comparative Example 3, the crosslinking degree is reduced by canceling the microcapsule coating of diisopropyl peroxide, and the uncoated crosslinking agent decomposes prematurely during the processing, resulting in insufficient crosslinking reaction, and the crosslinking degree is lower than that of Example 1; in Comparative Example 4, the nano-montmorillonite is replaced with unmodified natural montmorillonite, and the average water blocking rate is increased. The interlayer spacing of the unmodified natural montmorillonite is small, the nano-barrier barrier fails, the water penetration is accelerated, and the water blocking rate is increased compared with Example 1. In addition, the various performances in Examples 1-5 far exceed the monitoring indicators. Therefore, compared with the comparative examples, the embodiments of the cable of the present invention are reasonable.

[0111] In summary, the material components in the embodiments of the present invention are scientific and reasonable. At the same time, the components of 20 parts of conductive carbon black, 25 parts of sodium polyacrylate, and 12.5 parts of nano-montmorillonite in Example 1 make all indicators optimal. Therefore, the material component interval and process parameter optimization of the present invention have significant synergistic effects, and the ratio within the material interval balances conductivity and dispersibility; process innovation greatly improves long-term reliability; Example 1 has the best comprehensive performance due to its balanced material ratio and process parameters, and is suitable for high-voltage cables of 110kV and above, and is the best embodiment of the present invention.

[0112] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0113] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A cross-linked polyethylene insulated power cable wrapped with a high water resistance buffer layer, characterized in that: The invention is composed of the following raw materials in parts by weight: 100 parts of ethylene-vinyl acetate copolymer; 15-25 parts of conductive carbon black; 20-30 parts of sodium polyacrylate; 10-15 parts of nano-montmorillonite; 5-8 parts of maleic anhydride-grafted polyethylene; 0.5-1.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; 1-2 parts of calcium stearate; 15-20 parts of aluminum hydroxide; 1-2 parts of dicumyl peroxide; 0.5-1 parts of gamma-aminopropyltriethoxysilane; 2-4 parts of polyethylene wax; 3-5 parts of nano-silicon dioxide; and 0.5-1 part of 2-hydroxy-4-methoxybenzophenone.

2. A cross-linked polyethylene insulated power cable wrapped with a high water resistance buffer layer according to claim 1, characterized in that: The sodium polyacrylate is prepared by polymerizing acrylic acid monomers through plasma activation under nitrogen protection, followed by rapid neutralization with sodium hydroxide in a vacuum environment, and nanocellulose is grafted onto the surface to improve water absorption.

3. The cross-linked polyethylene insulated power cable with a high water resistance buffer layer wrapped therein according to claim 2, characterized in that: The nano-montmorillonite is prepared by exfoliating natural montmorillonite into a single-layer structure in supercritical carbon dioxide, and then grafting and modifying it with gamma-aminopropyltriethoxysilane under an ultrasonic field, with the interlayer spacing expanded to 3.5-4.0nm.

4. The cross-linked polyethylene insulated power cable with a high water resistance buffer layer wrapped according to claim 1, characterized in that: The conductive carbon black is prepared by cracking natural gas in an electric arc furnace to generate primary particles, which are then nitrogen-doped and then coated with polyvinyl pyrrolidone.

5. The cross-linked polyethylene insulated power cable with a high water resistance buffer layer wrapped according to claim 1, characterized in that: The maleic anhydride grafted polyethylene is prepared by dynamically solid-phase grafting low-density polyethylene with maleic anhydride in a twin-screw extruder, and simultaneously introducing di-tert-butyl peroxide to initiate a free radical reaction.

6. The cross-linked polyethylene insulated power cable with a high water resistance buffer layer wrapped therein according to claim 1, characterized in that: The nano silicon dioxide is prepared by synthesizing ethyl orthosilicate in an ethanol-water mixture through a sol-gel method and then hydrophobically modifying it in fluorosilane vapor.

7. The cross-linked polyethylene insulated power cable with a high water resistance buffer layer wrapped therein according to claim 1, characterized in that: The tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester is prepared by microwave-assisted esterification of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and pentaerythritol in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid.

8. The cross-linked polyethylene insulated power cable wrapped with a high water resistance buffer layer according to claim 1, characterized in that: The dicumyl peroxide is prepared by reacting cumene with oxygen under ultraviolet catalysis to generate hydroperoxide, which is then coated with copolymer microcapsules using polystyrene-maleic anhydride as wall material.

9. The method for preparing a cross-linked polyethylene insulated power cable wrapped with a high water resistance buffer layer according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Premix 15-25 parts of conductive carbon black with 2-4 parts of polyethylene wax in a high-speed mixer for 10-15 minutes at 60°C to break up carbon black agglomerates through shear force to form a uniform pre-dispersion; dehydrate 20-30 parts of sodium polyacrylate and 10-15 parts of nano-montmorillonite in a vacuum drying oven for 2 hours to ensure a moisture content of ≤0.1%; add 100 parts of ethylene-vinyl acetate copolymer, 5-8 parts of maleic anhydride-grafted polyethylene, and 1-2 parts of calcium stearate to a high-speed mixer, raise the temperature to 70°C, and mix for 5 minutes to form a viscous matrix; S2. Segmented temperature controlled extrusion: Feeding section in zone 1: temperature 80-90°C, adding pre-treated conductive carbon black-polyethylene wax pre-dispersion; Second zone melting section: temperature 150-160℃, add 20-30 parts of sodium polyacrylate, 10-15 parts of nano-montmorillonite, and 15-20 parts of aluminum hydroxide in sequence; Zone 3 mixing section: temperature 170-180°C, inject 0.5-1 parts of γ-aminopropyltriethoxysilane and 3-5 parts of nano-silica, and achieve directional dispersion of nano-fillers through the high shear zone; Homogenization section 4: Temperature 160-170°C, add 0.5-1.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.5-1 part of 2-hydroxy-4-methoxybenzophenone; Finally, the melt is filtered through a 200-mesh filter and then enters the melt pump for pressure stabilization to ensure that the extrusion pressure fluctuation is ≤±0.5MPa; S3. The extruded buffer layer with a thickness of 1.0-1.5 mm and the cross-linked polyethylene insulation layer are wrapped in a concentric circle structure at a wrapping speed of 20-30 m / min and a wrapping tension of 10-15 N. The surface of the insulation layer is bombarded with argon plasma to generate polar groups and enhance the bonding strength of the buffer layer. S4. Raise the temperature to 65-70°C in a nitrogen environment for 10-15 minutes to rupture the dicumyl peroxide microcapsules and release active oxygen, initiating a cross-linking reaction; Gradient degassing: The first stage: degassing at 70℃ and vacuum degree 100Pa for 2 hours to remove methane small molecules; The second stage: degassing at 60℃ and vacuum degree 50Pa for 4 hours to ensure the porosity of the insulation layer is ≤0.01%; S5. After the cable has cooled naturally to room temperature, argon arc welding is used to continuously weld a 2mm thick aluminum strip to a corrugation depth of 5mm. The outer diameter tolerance after corrugation is ±0.1mm. Epoxy resin is applied to the inside of the aluminum strip and hot-air cured. Finally, a flame-retardant sheath containing 20-30 parts of aluminum hydroxide and a thickness of 4.0-5.0mm is co-extruded over the cross-linked layer. The extruder temperature in each zone is as follows: Zone 1: 125°C; Zone 2: 145°C; Zone 3: 165°C; Zone 4: 175°C; Zone 5: 170°C; Zone 6: 165°C; Die head: 160°C; S6. Perform performance tests on the prepared cable samples.

10. The method for preparing a cross-linked polyethylene insulated power cable wrapped with a high water resistance buffer layer according to claim 9, characterized in that: The performance test in step S6 includes resistivity detection and water resistance performance test.