A water treeing resistant crosslinked polyethylene insulated power cable and a method of making the same

Abstract

The application relates to the field of crosslinked polyethylene insulated power cables, and particularly discloses a water treeing resistant crosslinked polyethylene insulated power cable and a preparation method thereof. The power cable comprises a cable core and a sheath layer from inside to outside, the cable core comprises a conductor, an inner non-metal semi-conductive shielding layer, a crosslinked polyethylene insulation layer, an outer non-metal semi-conductive shielding layer and a metal shielding layer from inside to outside, and the sheath layer comprises a polyvinyl chloride sheath layer and a polyvinyl chloride outer coating layer from inside to outside; the crosslinked polyethylene insulation layer is prepared by extrusion of water treeing resistant composite masterbatch and DCP crosslinking agent. The preparation method comprises the following steps: preparing the water treeing resistant composite masterbatch; preparing the cable core; and preparing the sheath layer. The water treeing resistant crosslinked polyethylene insulated power cable can resist water treeing and simultaneously maintain good tensile strength and elongation at break.

Description

Technical Field

[0001] This application relates to the field of cross-linked polyethylene insulated power cables, and more specifically, to a water-tree resistant cross-linked polyethylene insulated power cable and its preparation method. Background Technology

[0002] With the sustained and rapid development of my country's economy, the demand for urban electricity load is increasing daily. Power cables, due to their fully enclosed and flexible structure, have relatively low requirements for laying space and external environment, thus their application scale is continuously expanding. Cross-linked polyethylene (XLPE) cables have excellent electrical and mechanical properties, high heat resistance, low operation and maintenance workload, no leakage, and do not require oil or gas supply equipment. Since the 1960s, cable manufacturers and power supply departments worldwide have paid widespread attention to XLPE insulated cables, which have largely replaced oil-paper insulated cables.

[0003] The basic components of a power cable mainly consist of three parts: the conductor, the insulation layer, and the sheath. The cable insulation layer is made of cross-linked polyethylene, where linear molecular structures are processed into a network structure under high-energy particle radiation or chemical cross-linking agents. This effectively improves the cable's electrical performance, heat resistance, and mechanical properties. The quality and level of insulation in a power cable determine its service life.

[0004] Water treeing is a persistent and prominent problem in the actual operation of XLPE power cables. Water treeing is essentially the formation of micro-cracks (containing moisture) in the insulation layer under the combined effects of a humid environment and an electric field. It gradually reduces the cable's breakdown strength, and in severe cases, leads to insulation failure, causing power outages or even fires. Extensive field data shows that the breakdown voltage of XLPE cables decreases by an average of over 13% after 5 years of operation, and by over 20% after 10 years.

[0005] Existing technologies attempt to directly melt-blend single nanoparticles, such as nano-magnesium oxide, with polyethylene. This process is indeed simple and has a certain effect against water tree aging. However, as the magnesium oxide content increases from 0 to 3 parts, the water tree length of the composite material decreases significantly, and the tensile strength also increases. However, this comes at the cost of sacrificing the material's flexibility, resulting in a continuous decrease in its elongation at break. This reduces the bending and tensile strength of the cable insulation layer, making it prone to cracking and affecting the mechanical reliability during installation and use. This poses a potential threat to the long-term service life of XLPE power cables. Summary of the Invention

[0006] To effectively alleviate the water treeing aging problem of the insulation layer of polyethylene insulated power cables, while maintaining the good tensile strength and elongation at break of the composite material, this application provides a water treeing-resistant cross-linked polyethylene insulated power cable and its preparation method.

[0007] In a first aspect, this application provides a water-tree resistant, aging-resistant cross-linked polyethylene insulated power cable, employing the following technical solution:

[0008] A water-tree aging resistant cross-linked polyethylene insulated power cable, the power cable comprising, from the inside out, a cable core and a sheath; the cable core comprising, from the inside out, a conductor, an inner non-metallic semi-conductive shielding layer, a cross-linked polyethylene insulation layer, an outer non-metallic semi-conductive shielding layer, and a metallic shielding layer; the sheath comprising, from the inside out, a polyvinyl chloride sheath layer and a polyvinyl chloride outer sheath layer.

[0009] The cross-linked polyethylene insulation layer is obtained by extrusion of water-resistant composite material masterbatch and DCP cross-linking agent. The water-resistant composite material masterbatch comprises the following raw materials in parts by weight:

[0010] 100 portions of LDPE;

[0011] 1-1.5 parts of nano-magnesium oxide;

[0012] 3-5 parts of modified aluminosilicate fiber;

[0013] 5-6 parts of flexible buffer;

[0014] Antioxidant 300, 0.3-0.5 parts.

[0015] By adopting the above technical solution, since the cable core consists of a conductor, an inner non-metallic semi-conductive shielding layer, a cross-linked polyethylene insulation layer, an outer non-metallic semi-conductive shielding layer, and a metallic shielding layer from the inside out, it provides all-round protection for the conductor. The inner non-metallic semi-conductive shielding layer can uniformly distribute the electric field on the surface of the conductor, eliminate the air gap between the conductor and the insulation layer, reduce partial discharge and electric field concentration, and suppress the initiation of water trees on the inner surface of the insulation layer from the source. The outer non-metallic semi-conductive shielding layer can uniformly distribute the electric field on the outer surface of the insulation layer, and together with the inner shielding layer, they form a symmetrical electric field structure of "shielding-insulation-shielding", reducing the electric field distortion inside the insulation layer.

[0016] The cross-linked polyethylene insulation layer is extruded from an anti-water-tree composite masterbatch and a DCP cross-linking agent. The anti-water-tree composite masterbatch uses LDPE as the matrix material and incorporates nano-magnesium oxide, modified aluminosilicate fibers, and a flexible buffer. Nano-magnesium oxide can form deep traps in the amorphous regions of XLPE, capturing space charges and suppressing electric field distortion, thereby inhibiting water tree initiation and growth. The modified aluminosilicate fibers are short-cut, non-spherical fibers that serve as a mechanical reinforcement skeleton, bearing stress and resisting large-scale crack propagation. The fiber's "maze effect" also increases the diffusion path of water molecules, forming a barrier and aiding in anti-water-tree protection. The flexible buffer promotes the dispersion of fillers and fibers, acting as a compatibilizer, and also forms a flexible network to absorb impact energy, thus providing a buffering effect. Modified aluminosilicate fibers and flexible buffers complement each other, combining rigidity and flexibility to produce a synergistic mechanical effect. The microstructure entanglement of modified aluminosilicate fibers and flexible buffers forms an interfacial bond, which can produce an interfacial synergistic effect. The trapping effect of nano-magnesium oxide, the physical barrier of modified aluminosilicate fibers, and the water transport properties of flexible buffers form a triple protection of "chemical inhibition-physical barrier-waterproofing". Therefore, it can effectively alleviate the water treeing aging problem of polyethylene insulated power cable insulation layer, while maintaining the good tensile strength and elongation at break of composite materials.

[0017] Optionally, the flexible buffer includes at least one of liquid polybutadiene and SEBS.

[0018] By adopting the above technical solutions, SEBS can be used as an elastomer network to absorb impact energy and improve elongation at break and impact resistance; liquid polybutadiene (LPB) can be used as a flexible buffer and dispersant to wet the filler surface, promote dispersion, and compensate for rigidity.

[0019] Optionally, the flexible buffer comprises liquid polybutadiene and SEBS in a weight ratio of 1:1.

[0020] By adopting the above technical solution, the flexible molecular chains of liquid polybutadiene complement the elastic network of SEBS, further absorbing impact energy.

[0021] Optionally, the modified aluminum silicate fiber is prepared by synergistic modification of aluminum silicate fiber through alkali etching and KH550 grafting.

[0022] By employing the above technical solutions, alkaline etching increases the surface roughness of the fiber, creating more physical anchoring points. KH550 grafting introduces –NH2, providing chemical bonding, enabling the modified aluminosilicate fiber to form a physical / chemical bond with liquid polybutadiene and polyethylene, thus improving interfacial compatibility. Liquid polybutadiene not only provides flexibility compensation, but its low molecular weight also acts as a "secondary interfacial compatibilizer," further wetting and penetrating the fiber surface to form a strong mechanical interlock.

[0023] Optionally, the water-resistant composite material masterbatch further includes 0.1 to 0.5 parts by weight of octaisobutylPOSS.

[0024] By adopting the above technical solution, the octaisobutyl POSS particle size is smaller than the diameter of the polyethylene molecular chain entanglement tubes. It can be inserted into the molecular chain network without becoming a stress concentration point, without destroying the integrity of the molecular chain network. On the contrary, it can simultaneously improve strength and toughness through nano-reinforcement effect, playing a significant role even with a very small amount added. Moreover, it is easy to disperse after synergistic effect with SEBS. In addition, liquid polybutadiene acts as both a compatibilizer for SEBS / POSS and a wetting and dispersing agent for fibers, achieving "dual effect with one agent". This allows octaisobutyl POSS in the LDPE matrix to not only have the conventional flame retardant effect, but also play a non-obvious crack resistance role. The raw materials can form a five-component multi-level synergistic network: chemical trap (nano magnesium oxide) / nano rigid skeleton (octaisobutyl POSS) / elastic network (SEBS) / flexible buffer (LPB) / macro fiber skeleton (modified aluminosilicate fiber), effectively alleviating the contradiction between water tree resistance and mechanical properties.

[0025] Optionally, the preparation method of the water-resistant composite material masterbatch is as follows: premix LDPE, nano magnesium oxide, antioxidant 300 and SEBS until uniform; add liquid polybutadiene and continue mixing until uniform; add modified aluminum silicate fiber and continue mixing until uniform; melt blend and extrude granulation.

[0026] By adopting the above technical solution and finally adding modified aluminum silicate fiber and blending at low speed, fiber breakage can be effectively alleviated.

[0027] Optionally, the preparation method of the water-tree resistant composite material masterbatch is as follows: premix LDPE, nano magnesium oxide, antioxidant 300, SEBS, and octaisobutylPOSS until uniform; add liquid polybutadiene and continue mixing until uniform; add modified aluminum silicate fiber and continue mixing until uniform; melt blend and extrude granulation.

[0028] Secondly, this application provides a method for preparing a water-tree resistant, aging-resistant cross-linked polyethylene insulated power cable, employing the following technical solution:

[0029] A method for preparing a water-tree resistant, aging-resistant cross-linked polyethylene insulated power cable includes the following steps:

[0030] Preparation of water-tree resistant composite masterbatch;

[0031] Water-resistant composite material masterbatch and DCP crosslinking agent are mixed uniformly at a weight ratio of 100:1.8 to form crosslinked polyethylene insulation layer material. Through a three-layer co-extrusion process, the inner non-metallic semi-conductive shielding layer, crosslinked polyethylene insulation layer and outer non-metallic semi-conductive shielding layer are simultaneously extruded and coated onto the conductor. Dry crosslinking, cooling and shaping, and degassing are performed. A metal shielding layer is then coated on the outer non-metallic semi-conductive shielding layer to obtain the cable core.

[0032] A polyvinyl chloride (PVC) sheath layer and a PVC outer sheath layer are extruded sequentially over the cable core to form a protective layer.

[0033] By adopting the above technical solution, the power cable produced can maintain good tensile strength and elongation at break of the composite material while resisting water tree aging.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. This application integrates five functional layers—anti-water tree (nano MgO), nano-reinforcement (octaisobutyl POSS), elastic toughening (SEBS), flexible buffer (LPB), and macro-fiber reinforcement (modified aluminum silicate fiber)—into the same insulating material, forming a complete protective network from nano to micro, comprehensively resolving the contradiction between mechanical and electrical properties, and achieving the effect of maintaining good tensile strength and elongation at break of the composite material while resisting water tree aging.

[0036] 2. This application introduces ultra-low dosage of octaisobutyl POSS, utilizing its nanoscale size smaller than the diameter of polyethylene entangled pipes to significantly improve modulus and crack resistance without sacrificing elongation at break, while maintaining controllable cost. Octaisobutyl POSS is used in combination with SEBS and LPB to construct a three-level structure of "nanorigid skeleton (POSS) / elastic network (SEBS) / flexible buffer matrix (LPB)," mimicking the multi-level composite principle of eggshells (nanocrystalline grains / organic matrix / interface layer) to achieve a balance of rigidity and flexibility. Liquid polybutadiene is used simultaneously as a flexibility compensator and dispersant to promote the uniform dispersion of octaisobutyl POSS, SEBS, and modified aluminosilicate fibers, simplifying the process. Nano-MgO and octaisobutyl POSS together form a space charge trap, exhibiting better anti-water treeing performance than a single MgO system.

[0037] 3. The method of this application produces a power cable that can resist water tree aging while maintaining good tensile strength and elongation at break of the composite material. Detailed Implementation

[0038] The present application will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments shall be performed under conventional conditions or conditions recommended by the manufacturer, and the raw materials used in the following embodiments shall be commercially available unless otherwise specified.

[0039] LDPE, melt index (MI) of 2.0 g / 10 min, brand: Shanghai Petrochemical, model: DJ200.

[0040] Nano-sized magnesium oxide with an average particle size of 50 nm.

[0041] Aluminosilicate fiber, chopped, 2mm in length.

[0042] Liquid polybutadiene (LPB), Mn2000, was purchased from Kunshan Castel Polymer Materials Co., Ltd.

[0043] Octaisobutyl POSS (octaisobutyl cage-like polysilsesquioxane), with a particle size of 1.5 nm, was purchased from Shaanxi Xingbei Aike Biotechnology Co., Ltd.

[0044] DCP (diisopropylbenzene peroxide), brand name: Hongbaoli.

[0045] Preparation example of modified aluminosilicate fibers

[0046] Preparation Example 1

[0047] The preparation method of modified aluminosilicate fibers is as follows:

[0048] Pretreatment: Take 10 kg of chopped aluminosilicate fibers with a length of 2 mm, soak them in 0.1 mol / L HCl solution for 6 hours to remove surface impurities, wash with deionized water until neutral, and dry at 100℃.

[0049] Alkali etching modification: The pretreated aluminum silicate fiber is immersed in a 1 mol / L NaOH solution and treated at 80°C for 12 hours. It is then washed with deionized water until neutral and dried at 100°C.

[0050] KH550 grafting modification: Prepare a modification solution according to the ratio of distilled water:KH550 silane coupling agent:ethanol = 80:1:10 (volume ratio), stir evenly, immerse the alkaline etched aluminum silicate fiber in it, and treat at 80℃ for 12 hours.

[0051] Post-processing: Remove the aluminum silicate fiber, wash with ethanol to remove unreacted coupling agent, and cure at 120°C for 30 minutes to obtain modified aluminum silicate fiber, which is then sealed and stored for later use.

[0052] Example

[0053] Example 1

[0054] A water-tree aging resistant cross-linked polyethylene insulated power cable includes, from the inside out, a cable core and a sheath. The cable core consists of, from the inside out, a conductor, an inner non-metallic semi-conductive shielding layer, a cross-linked polyethylene insulation layer, an outer non-metallic semi-conductive shielding layer, and a metallic shielding layer. The sheath consists of, from the inside out, a polyvinyl chloride sheath layer and a polyvinyl chloride outer sheath layer.

[0055] The cross-linked polyethylene insulation layer is obtained by extrusion of water-tree resistant composite masterbatch and DCP cross-linking agent. The water-tree resistant composite masterbatch includes the following raw materials: LDPE; nano-magnesium oxide; modified aluminum silicate fiber prepared in Preparation Example 1; flexible buffer, liquid polybutadiene and SEBS in a weight ratio of 1:1; antioxidant 300. The amount of each raw material is detailed in Table 1.

[0056] A method for preparing a water-tree resistant, aging-resistant cross-linked polyethylene insulated power cable includes the following steps:

[0057] Preparation of water-tree resistant composite masterbatch: LDPE, nano-magnesium oxide, antioxidant 300, and SEBS were premixed at 1000 rpm for 10 minutes until homogeneous, so that the nano-magnesium oxide and SEBS were initially dispersed; liquid polybutadiene was slowly added, and mixing was continued at 1000 rpm for 8 minutes until homogeneous, so that LPB was uniformly adsorbed on the surface of powder and resin particles; modified aluminum silicate fiber was added, the speed was reduced to 400 rpm, and low-speed mixing was carried out for 5 minutes until homogeneous, avoiding fiber breakage, to obtain a premix; the premix was melt-blended at 120℃, extruded and granulated to a particle diameter of 3 mm; dried at 80℃ for 4 hours to remove residual moisture.

[0058] Water-resistant composite material masterbatch and DCP crosslinking agent are mixed uniformly at a weight ratio of 100:1.8 to form crosslinked polyethylene insulation layer material. Through a three-layer co-extrusion process, the inner non-metallic semi-conductive shielding layer, crosslinked polyethylene insulation layer and outer non-metallic semi-conductive shielding layer are simultaneously extruded and coated onto the conductor. Dry crosslinking, cooling and shaping, and degassing are performed. A metal shielding layer is then coated on the outer non-metallic semi-conductive shielding layer to obtain the cable core.

[0059] A polyvinyl chloride (PVC) sheath layer and a PVC outer sheath layer are extruded sequentially over the cable core to form a protective layer.

[0060] Example 2

[0061] The difference between this embodiment and Embodiment 1 is that the amount of each raw material used is different, as detailed in Table 1.

[0062] Example 3

[0063] The difference between this embodiment and Embodiment 1 is that the amount of each raw material used is different, as detailed in Table 1.

[0064] Example 4

[0065] The difference between this embodiment and Embodiment 2 is that the flexible buffer is only liquid polybutadiene.

[0066] Example 5

[0067] The difference between this embodiment and Embodiment 2 is that the flexible buffer is only SEBS.

[0068] Example 6

[0069] The difference between this embodiment and Embodiment 2 is that the water-resistant composite material masterbatch also includes octaisobutyl POSS. The amount of each raw material is detailed in Table 1.

[0070] A method for preparing a water-tree aging-resistant cross-linked polyethylene insulated power cable differs from Example 2 in that the preparation method of the water-tree resistant composite material masterbatch is as follows: LDPE, nano-magnesium oxide, antioxidant 300, SEBS, and octaisobutylPOSS are premixed at 1000 rpm for 10 minutes until homogeneous, so that the nano-magnesium oxide, SEBS, and octaisobutylPOSS are initially dispersed; liquid polybutadiene is slowly added, and mixing continues at 1000 rpm for 8 minutes until homogeneous, so that LPB is uniformly adsorbed on the surface of powder and resin particles; modified aluminum silicate fiber is added, the rotation speed is reduced to 400 rpm, and low-speed mixing is carried out for 5 minutes until homogeneous, avoiding fiber breakage, to obtain a premix; the premix is ​​melt-blended at 120°C, extruded and granulated to a particle diameter of 3 mm; and dried at 80°C for 4 hours to remove residual moisture.

[0071] Example 7

[0072] The difference between this embodiment and Embodiment 6 is that the amount of octaisobutyl POSS used is different, as detailed in Table 1.

[0073] Example 8

[0074] The difference between this embodiment and Embodiment 6 is that the amount of octaisobutyl POSS used is different, as detailed in Table 1.

[0075] Comparative Example

[0076] Comparative Example 1

[0077] The difference between this comparative example and Example 2 is that the water-tree resistant composite material masterbatch does not contain modified aluminum silicate fiber, flexible buffer, or nano magnesium oxide, as detailed in Table 1.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 2 is that the anti-water tree composite material masterbatch does not contain modified aluminum silicate fiber or flexible buffer, and the amount of nano magnesium oxide is different, as detailed in Table 1.

[0080] Comparative Example 3

[0081] The difference between this comparative example and Example 2 is that the water-resistant composite material masterbatch does not contain modified aluminum silicate fibers.

[0082] Comparative Example 4

[0083] The difference between this comparative example and Example 2 is that unmodified aluminum silicate fibers are used in the water-resistant composite material masterbatch.

[0084] Comparative Example 5

[0085] The difference between this comparative example and Example 2 is that the water-tree resistant composite material masterbatch does not contain a flexible buffer.

[0086] Table 1. Amounts of each raw material in the water-tree resistant composite masterbatch of each embodiment and comparative example.

[0087] LDPE / kg Nano magnesium oxide / kg Modified aluminosilicate fiber / kg Liquid polybutadiene / kg SEBS / kg Antioxidant 300 / kg Octaisobutyl POSS / kg Example 1 100 1 3 2.5 2.5 0.3 0 Example 2 100 1.2 5 3 3 0.5 0 Example 3 100 1.5 4 3 3 0.4 0 Example 4 100 1.2 5 6 0 0.5 0 Example 5 100 1.2 5 0 6 0.5 0 Example 6 100 1 5 3 3 0.5 0.1 Example 7 100 1 5 3 3 0.5 0.3 Example 8 100 1 5 3 3 0.5 0.5 Comparative Example 1 100 0 0 0 0 0.5 0 Comparative Example 2 100 3 0 0 0 0.5 0 Comparative Example 3 100 1.2 0 3 3 0.5 0 Comparative Example 4 100 1.2 Unmodified, 5 3 3 0.5 0 Comparative Example 5 100 1.2 5 0 0 0.5 0

[0088] Performance testing

[0089] Detection methods

[0090] For the cables in each embodiment and comparative example, samples were cut from the cross-linked insulation layer to obtain XLPE test samples.

[0091] Referring to GB / T 1040.1-2025, dumbbell-shaped specimens with a thickness of 1 mm and a width of 6 mm were prepared for each XLPE test sample. Tensile strength and elongation at break were tested at a tensile speed of 50 mm / min. The test results are detailed in Table 2.

[0092] Following IEC / TS61956, the cup test method was used to accelerate the aging of water trees in each XLPE test sample for 360 hours at room temperature in a 1.0 mol / L NaCl solution at a voltage of 5 kV and a frequency of 50 Hz. After 360 hours of aging, the samples were stained with methylene blue solution, and the morphology of the water trees in each sample was observed using a metallographic microscope. The length of the longest water tree was recorded. The test results are detailed in Table 2.

[0093] Table 2 Test Results

[0094] Tensile strength (MPa) Elongation at break (%) Water tree length (μm) Example 1 23.2 505 320 Example 2 24.5 510 280 Example 3 24.3 508 290 Example 4 24.2 475 300 Example 5 24.3 485 295 Example 6 24.7 515 265 Example 7 25 520 245 Example 8 25.2 522 235 Comparative Example 1 20.8 486 760 Comparative Example 2 24.2 480 260 Comparative Example 3 22 495 450 Comparative Example 4 23.5 460 380 Comparative Example 5 25 420 350

[0095] Combining Examples 1-3 and Comparative Example 1 with Table 2, it can be seen that Example 2 achieves the optimal balance: water tree length 280 μm, elongation at break 510%, and tensile strength 24.5 MPa. In contrast, Example 1 has a longer water tree (320 μm) due to lower amounts of nano-MgO and modified aluminosilicate fiber; Example 3 has a slightly longer water tree (290 μm) and increased cost due to higher amounts of nano-MgO and lower amounts of modified aluminosilicate fiber. Therefore, Example 2, as the basic preferred formulation, has the best overall performance and cost-effectiveness.

[0096] Based on Examples 2, Comparative Examples 1-5, and Table 2, it can be seen that the absence of modified aluminosilicate fibers leads to increased water tree length and decreased tensile strength, highlighting the indispensable role of the fiber's physical barrier and mechanical framework. Modified aluminosilicate fibers significantly enhance interfacial bonding, while unmodified fibers result in increased water tree length and a significant decrease in elongation at break. The flexible agent not only toughens the fibers but also improves filler dispersion, indirectly inhibiting water treeing. Therefore, without the flexible agent, elongation at break is severely reduced, and water tree length increases considerably. Furthermore, considering all factors, the optimal combination of modified aluminosilicate fibers, the flexible agent, and nano-magnesium oxide yields the best results, significantly reducing the amount of nano-magnesium oxide required and minimizing mechanical strength loss.

[0097] Example 2 (SEBS+LPB compound) showed a significantly higher elongation at break (510%) than LPB alone (Example 4, 475%) and SEBS alone (Example 5, 485%), and also had the lowest water tree length. This demonstrates that the compound forms a more continuous and efficient flexible buffer layer, while LPB, as a dispersing agent, further improves the uniform distribution of the modified aluminosilicate fibers.

[0098] As the amount of octaisobutylPOSS increased from 0.1 parts to 0.5 parts (Examples 6-8), tensile strength and elongation at break increased simultaneously, while water tree length decreased continuously. Particularly noteworthy is that at ultra-low addition levels of 0.1-0.5 parts, octaisobutylPOSS achieved simultaneous reinforcement and toughening, with tensile strength increasing from 24.5 MPa to 25.2 MPa (+2.9%), elongation at break increasing from 510% to 522% (+2.4%), and water tree length decreasing from 280 μm to 235 μm (-16%). This is attributed to the fact that the nanocage structure of octaisobutylPOSS can insert into the polyethylene molecular chain network, acting as a physical crosslinking point to increase modulus without hindering chain movement. Simultaneously, it possesses charge trapping capabilities, forming a "double-trap" anti-water tree system with nano-MgO.

[0099] However, since octaisobutyl POSS is expensive, and the detection results of Example 8 are not significantly better than those of Example 7, it is recommended to use the formulation of Example 7, which offers the best cost-performance ratio and achieves the optimal balance between performance improvement and cost control.

[0100] Therefore, the technical solution of this application reduces the amount of nano-MgO by 60%, and through the synergistic effect of modified aluminosilicate fiber, SEBS / LPB flexible agent and trace amount of octaisobutylPOSS, it achieves simultaneous improvement of three indicators: water tree resistance, elongation at break and tensile strength. This improves the pain point of reduced flexibility in the single high nano-MgO route and demonstrates a significant synergistic effect of raw material compounding.

[0101] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A water-tree resistant, aging-resistant cross-linked polyethylene insulated power cable, characterized in that, The power cable comprises, from the inside out, a cable core and a sheath. The cable core comprises, from the inside out, a conductor, an inner non-metallic semi-conductive shielding layer, a cross-linked polyethylene insulation layer, an outer non-metallic semi-conductive shielding layer, and a metallic shielding layer. The sheath comprises, from the inside out, a polyvinyl chloride sheath layer and a polyvinyl chloride outer sheath layer. The cross-linked polyethylene insulation layer is obtained by extrusion of water-resistant composite material masterbatch and DCP cross-linking agent. The water-resistant composite material masterbatch comprises the following raw materials in parts by weight: 100 portions of LDPE; 1-1.5 parts of nano-magnesium oxide; 3-5 parts of modified aluminosilicate fiber; 5-6 parts of flexible buffer; Antioxidant 300, 0.3-0.5 parts.

2. The water-tree aging-resistant cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The flexible buffer includes at least one of liquid polybutadiene and SEBS.

3. The water-tree aging-resistant cross-linked polyethylene insulated power cable according to claim 2, characterized in that, The flexible buffer comprises liquid polybutadiene and SEBS in a weight ratio of 1:

1.

4. The water-tree aging-resistant cross-linked polyethylene insulated power cable according to claim 3, characterized in that, The modified aluminum silicate fiber is prepared by synergistic modification of aluminum silicate fiber through alkali etching and KH550 grafting.

5. The water-tree aging-resistant cross-linked polyethylene insulated power cable according to claim 3, characterized in that, The water-resistant composite material masterbatch also includes 0.1 to 0.5 parts by weight of octaisobutylPOSS.

6. The water-tree aging-resistant cross-linked polyethylene insulated power cable according to claim 3, characterized in that, The preparation method of the water-tree resistant composite material masterbatch is as follows: LDPE, nano magnesium oxide, antioxidant 300 and SEBS are premixed until uniform; liquid polybutadiene is added and mixed until uniform; modified aluminum silicate fiber is added and mixed until uniform; melt blending and extrusion granulation are performed.

7. The water-tree aging-resistant cross-linked polyethylene insulated power cable according to claim 5, characterized in that, The method for preparing the water-tree resistant composite material masterbatch is as follows: LDPE, nano magnesium oxide, antioxidant 300, SEBS, and octaisobutylPOSS are premixed until uniform; liquid polybutadiene is added and mixed until uniform; modified aluminum silicate fiber is added and mixed until uniform; melt blending and extrusion granulation are then performed.

8. A method for preparing a water-tree resistant aging cross-linked polyethylene insulated power cable according to any one of claims 1 to 7, characterized in that, Includes the following steps: Preparation of water-tree resistant composite masterbatch; Water-resistant composite material masterbatch and DCP crosslinking agent are mixed uniformly at a weight ratio of 100:1.8 to form crosslinked polyethylene insulation layer material. Through a three-layer co-extrusion process, the inner non-metallic semi-conductive shielding layer, crosslinked polyethylene insulation layer and outer non-metallic semi-conductive shielding layer are simultaneously extruded and coated onto the conductor. Dry crosslinking, cooling and shaping, and degassing are performed. A metal shielding layer is then coated on the outer non-metallic semi-conductive shielding layer to obtain the cable core. A polyvinyl chloride (PVC) sheath layer and a PVC outer sheath layer are extruded sequentially over the cable core to form a protective layer.