A high temperature resistant and bending resistant medium voltage cable

Abstract

The present invention relates to the field of cable technology, and discloses a high-temperature resistant and bend-resistant medium-voltage cable. The medium-voltage cable of the present invention comprises a cable core, an isolation sheath, a metal armor layer, and an outer sheath from the inside out; the cable core is formed by twisting a plurality of insulated wire cores; the insulated wire core is a copper conductor and a conductor shielding layer, an insulation layer, and an insulation shielding layer wrapped around the outside of the copper conductor; the cable has excellent high-temperature resistance and bending resistance, wherein the outer sheath is prepared with linear low-density polyethylene, polypropylene, and modified linear low-density polyethylene as main raw materials, and functional additives such as composite flame retardants and compatibilizers are added; the introduction of modified linear low-density polyethylene in the outer sheath, while retaining the excellent bending resistance and flexibility of polyethylene, also improves the high-temperature resistance of the outer sheath, so that the medium-voltage cable can be used in high-temperature environments.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and in particular to a high-temperature resistant and bending-resistant medium-voltage cable. Background Art

[0002] With the rapid development of renewable energy power generation, rail transit, industrial automation, and other fields, medium-voltage cables, as core components of power transmission, are facing increasingly complex operating environments. For example, in photovoltaic power plants, cables are exposed to high temperatures and strong ultraviolet radiation for long periods of time; in rail transit, cables are frequently subjected to mechanical bending, vibration, and temperature rise. Traditional medium-voltage cable materials (such as standard cross-linked polyethylene or polyvinyl chloride) easily soften at high temperatures, and repeated bending can easily cause cracking of the insulation layer, shedding of the conductor shielding layer or outer sheath, and damage, seriously affecting the cable's reliability and service life.

[0003] The long-term operating temperature of traditional polyethylene (PE) materials is typically below 70°C. While cross-linked polyethylene (XLPE) can withstand temperatures between 90°C and 105°C, it is still susceptible to molecular chain breakage and crystalline damage under short-term overload or high-temperature thermal radiation, resulting in reduced insulation resistance and an increased risk of breakdown. Existing modification methods (such as adding inorganic fillers or chemical cross-linking) can partially improve temperature resistance, but often at the expense of flexibility. For example, high levels of aluminum hydroxide fillers can improve temperature resistance, but they can also lead to brittleness, making it difficult to meet bending radius requirements. Therefore, developing new cables that combine high-temperature resistance, bending resistance, and ease of processing has become a key path to breaking through industry bottlenecks. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-temperature resistant and bending-resistant medium-voltage cable.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A high-temperature resistant and bend-resistant medium-voltage cable comprises a cable core arranged in sequence from the inside out, an isolation jacket extruded on the outside of the cable core, a metal armor layer wrapped around the isolation jacket, and an outer sheath extruded on the metal armor layer; the cable core is formed by twisting a plurality of insulated wire cores; the insulated wire core is formed by a conductor shielding layer, an insulating layer, and an insulating shielding layer sequentially wrapped around the outside of a copper conductor;

[0007] The isolation sleeve is made of polyvinyl chloride, the metal armor layer is two layers of galvanized steel tape, the conductor shielding layer is a cross-linked EVA conductor shielding material, the insulation layer is a thermoplastic polyurethane elastomer, and the insulation shielding layer is formed by longitudinally wrapping a copper tape and then braiding it with aramid yarn;

[0008] The outer protective layer comprises the following raw materials in parts by weight: 40-60 parts of linear low-density polyethylene, 10-20 parts of polypropylene, 15-25 parts of modified linear low-density polyethylene, 5-10 parts of compatibilizer, 8-15 parts of composite flame retardant, 2-3 parts of lubricant, and 1-2 parts of antioxidant;

[0009] Furthermore, the compatibilizer is maleic anhydride grafted POE;

[0010] Furthermore, the lubricant is PE wax;

[0011] Furthermore, the antioxidant is one of antioxidant 1010, antioxidant 1024 or antioxidant 168;

[0012] Furthermore, the composite flame retardant is a mixture of magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate and melamine phosphate, wherein the mass ratio of magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate and melamine phosphate is 2:3:5:3;

[0013] The modified linear low density polyethylene is prepared by the following steps:

[0014] Step A1: Acryloyl chloride is mixed and stirred in dichloromethane, and then added dropwise to p-nitrobenzyl alcohol. Triethylamine is then added, and the mixture is heated to 45-55° C. and refluxed for 3-4 hours. The mixture is filtered, washed, and dried to obtain an acrylate derivative.

[0015] Furthermore, in step A1, the molar ratio of acryloyl chloride to p-nitrobenzoic acid is 1:1;

[0016] Step A2: piperazine and an acrylate derivative were mixed uniformly in a methanol-water solution, respectively designated as solution 1 and solution 2; solution 2 was slowly added to solution 1, and the mixture was heated to 60° C. and stirred for 2-3 hours. Pd / C and hydrazine hydrate were then added in sequence, and the mixture was refluxed at 80° C. and stirred for 6 hours. The mixture was filtered, and water was added and stirred for 10 minutes. The mixture was filtered again, dried in vacuo, and recrystallized to obtain a piperazine derivative;

[0017] Furthermore, in step A2, the usage ratio of solution 1, solution 2, Pd / C, hydrazine hydrate and water is 30 mL:30 mL:0.5-1 g:5-8 g:100 mL;

[0018] Furthermore, in step A2, the amount ratio of piperazine, methanol and water in solution 1 is 0.01-0.02 mol:15 mL:15 mL, and the amount ratio of acrylate derivative, methanol and water in solution 2 is 0.011-0.022 mol:15 mL:15 mL;

[0019] Step A3: Mix a piperazine derivative and maleic anhydride in N,N-dimethylformamide (DMF) to obtain solution 3 and solution 4, respectively; slowly add solution 3 dropwise to solution 4, react at room temperature for 2 hours, add anhydrous sodium acetate and hydroquinone, stir for 10-20 minutes, add acetic anhydride, and heat to 50°C for 2-4 hours. Filter, wash, dry, and recrystallize to obtain a maleimide-piperazine derivative.

[0020] Furthermore, in step A3, the usage ratio of solution 3, solution 4, anhydrous sodium acetate, hydroquinone and acetic anhydride is 50 mL:50 mL:0.5-1.5 g:0.7-2.1 g:1.2-3.6 mL;

[0021] Furthermore, in step A3, the amount ratio of the piperazine derivative to DMF in solution 3 is 0.01-0.03 mol:50 mL, and the amount ratio of maleic anhydride to DMF in solution 4 is 0.01-0.03 mol:50 mL;

[0022] Step A4: Stirring the irradiated linear low-density polyethylene, sodium dodecylsulfonate, a maleimide-piperazine derivative, and water at 60° C. for 40-50 minutes, introducing nitrogen, and heating to 90° C. Benzoyl peroxide was added three times, and the reaction was continued for 8-10 hours. The product was filtered, washed, and dried to obtain a modified linear low-density polyethylene.

[0023] Furthermore, in step A4, the ratio of irradiated linear low-density polyethylene, sodium lauryl sulfate, maleimide-piperazine derivative, water and benzoyl peroxide is 25-50 g: 0.3-0.6 g: 10-20 g: 200 mL: 0.015-0.03 g.

[0024] The outer protective layer is prepared by the following steps:

[0025] Raw materials are weighed according to weight, and linear low-density polyethylene, polypropylene, modified linear low-density polyethylene, compatibilizer, composite flame retardant, lubricant and antioxidant are added into a blender and stirred evenly, and then transferred to a single-screw extruder for extrusion to obtain an outer protective layer;

[0026] Furthermore, the temperature of each section of the single-screw extruder is as follows: section 1: 170-180°C, section 2: 170-180°C, section 3: 175-185°C, die head: 175-185°C, and the screw speed is 30-50rpm.

[0027] Beneficial effects of the present invention:

[0028] The medium-voltage cable prepared by the present invention has excellent high-temperature resistance and bending resistance. The outer sheath is prepared with linear low-density polyethylene, polypropylene and modified linear low-density polyethylene as main raw materials, and functional additives such as composite flame retardants and compatibilizers are added. The introduction of modified linear low-density polyethylene in the outer sheath not only retains the excellent bending resistance and flexibility of polyethylene, but also improves the high-temperature resistance of the outer sheath, so that the medium-voltage cable can be used in high-temperature environments.

[0029] The medium-voltage cable prepared by the present invention adopts cross-linked EVA conductor shielding material and thermoplastic polyurethane elastomer as the conductor shielding layer and insulation layer in sequence, which not only has shielding and insulation functions, but also has good mechanical properties and durability, so that the conductor shielding layer and insulation layer will not fall off when the cable is repeatedly bent.

[0030] The modified linear low-density polyethylene prepared by the present invention introduces imide rings and piperazine rings into the linear low-density polyethylene by grafting modification, and utilizes the synergistic effect of the two to improve the high-temperature resistance of the outer sheath; wherein, the imide ring is a typical high-temperature resistant group, and its rigid aromatic heterocyclic structure can effectively hinder the thermal motion of the polyethylene molecular chain at high temperature, thereby improving the overall thermal deformation temperature and thermal stability of the material; the piperazine ring contains two nitrogen atoms, which can enhance the interaction between molecular chains through polar action or hydrogen bonding, reduce the slip of the molecular chains at high temperature, and thus inhibit the softening of the cable at high temperature; in addition, the free carbon-carbon double bonds in the modified linear low-density polyethylene can also undergo cross-linking reaction with polyethylene and polypropylene to form a three-dimensional network structure, and the cross-linking structure can effectively limit the slip of the molecular chain, significantly improve the thermal deformation temperature, creep resistance and bending resistance of the material, and at the same time delay melting and decomposition at high temperature. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0032] Example 1: Modified linear low density polyethylene was prepared by the following steps:

[0033] Step A1: 0.1 mol of acryloyl chloride was mixed and stirred in 100 mL of dichloromethane, and then added dropwise to 0.1 mol of p-nitrobenzyl alcohol. Triethylamine was then added, and the mixture was heated to 45° C. and refluxed for 3 h. The mixture was filtered, washed, and dried to obtain an acrylate derivative.

[0034] Step A2, piperazine and an acrylate derivative were mixed uniformly in a methanol aqueous solution, respectively, and recorded as solution 1 and solution 2; 30 mL of solution 2 was slowly added to 30 mL of solution 1, and the mixture was heated to 60 ° C and stirred for 2 h, and then 0.5 g of Pd / C and 5 g of hydrazine hydrate were added in sequence, refluxed and stirred at 80 ° C for 6 h, filtered, added with 100 mL of water and stirred for 10 min, filtered twice, vacuum dried, and recrystallized to obtain a piperazine derivative, wherein the amount ratio of piperazine, methanol and water in the solution 1 is 0.01 mol: 15 mL: 15 mL, and the amount ratio of the acrylate derivative, methanol and water in the solution 2 is 0.011 mol: 15 mL: 15 mL;

[0035] Step A3, the piperazine derivative and maleic anhydride were mixed in DMF, respectively, and recorded as solution 3 and solution 4; 50 mL of solution 3 was slowly added dropwise to 50 mL of solution 4, and the mixture was reacted at room temperature for 2 h. 0.5 g of anhydrous sodium acetate and 0.7 g of hydroquinone were added and stirred for 10 min. 1.2 mL of acetic anhydride was added, and the mixture was heated to 50 ° C. and reacted for 2 h. The mixture was filtered, washed, dried, and recrystallized to obtain a maleimide-piperazine derivative. The amount ratio of the piperazine derivative to DMF in the solution 3 was 0.01 mol:50 mL, and the amount ratio of maleic anhydride to DMF in the solution 4 was 0.01 mol:50 mL;

[0036] Step A4: 25 g of irradiated linear low-density polyethylene, 0.3 g of sodium dodecylsulfonate, 10 g of a maleimide-piperazine derivative, and 200 mL of water were stirred at 60 ° C for 40 min, nitrogen was introduced, and the temperature was raised to 90 ° C. 0.015 g of benzoyl peroxide was added three times, and the reaction was continued for 8 h. The mixture was filtered, washed, and dried to obtain a modified linear low-density polyethylene.

[0037] Example 2: Modified linear low density polyethylene was prepared by the following steps:

[0038] Step A1: 0.1 mol of acryloyl chloride was mixed and stirred in 100 mL of dichloromethane, and then added dropwise to 0.1 mol of p-nitrobenzyl alcohol. Triethylamine was then added, and the mixture was heated to 50° C. and refluxed for 3.5 hours. The mixture was filtered, washed, and dried to obtain an acrylate derivative.

[0039] Step A2, piperazine and an acrylate derivative were mixed uniformly in a methanol aqueous solution, respectively, and recorded as solution 1 and solution 2; 30 mL of solution 2 was slowly added to 30 mL of solution 1, and the mixture was heated to 60 ° C and stirred for 2.5 h, and then 0.75 g of Pd / C and 6.5 g of hydrazine hydrate were added in sequence, refluxed and stirred at 80 ° C for 6 h, filtered, added with 100 mL of water and stirred for 10 min, filtered twice, vacuum dried, and recrystallized to obtain a piperazine derivative, wherein the amount ratio of piperazine, methanol and water in the solution 1 is 0.015 mol: 15 mL: 15 mL, and the amount ratio of the acrylate derivative, methanol and water in the solution 2 is 0.016 mol: 15 mL: 15 mL;

[0040] Step A3, the piperazine derivative and maleic anhydride were mixed in DMF, respectively, and recorded as solution 3 and solution 4; 50 mL of solution 3 was slowly added dropwise to 50 mL of solution 4, and the mixture was reacted at room temperature for 2 h. 1 g of anhydrous sodium acetate and 1.4 g of hydroquinone were added and stirred for 15 min. 2.4 mL of acetic anhydride was added, and the mixture was heated to 50 ° C. and reacted for 3 h. The mixture was filtered, washed, dried, and recrystallized to obtain a maleimide-piperazine derivative. The amount ratio of the piperazine derivative to DMF in the solution 3 was 0.02 mol: 50 mL, and the amount ratio of maleic anhydride to DMF in the solution 4 was 0.02 mol: 50 mL;

[0041] Step A4: 40 g of irradiated linear low-density polyethylene, 0.5 g of sodium dodecylsulfonate, 15 g of a maleimide-piperazine derivative, and 200 mL of water were stirred at 60 ° C for 45 min, nitrogen was introduced, and the temperature was raised to 90 ° C. 0.023 g of benzoyl peroxide was added three times, and the reaction was continued for 9 h. The mixture was filtered, washed, and dried to obtain a modified linear low-density polyethylene.

[0042] Example 3: Modified linear low density polyethylene was prepared by the following steps:

[0043] Step A1: 0.1 mol of acryloyl chloride was mixed and stirred in 100 mL of dichloromethane, and then added dropwise to 0.1 mol of p-nitrobenzyl alcohol. Triethylamine was then added, and the mixture was heated to 55° C. and refluxed for 4 h. The mixture was filtered, washed, and dried to obtain an acrylate derivative.

[0044] Step A2, piperazine and an acrylate derivative were mixed uniformly in a methanol aqueous solution, respectively, and recorded as solution 1 and solution 2; 30 mL of solution 2 was slowly added to 30 mL of solution 1, and the mixture was heated to 60 ° C and stirred for 3 h, and then 1 g of Pd / C and 8 g of hydrazine hydrate were added in sequence, refluxed and stirred at 80 ° C for 6 h, filtered, added with 100 mL of water and stirred for 10 min, filtered twice, vacuum dried, and recrystallized to obtain a piperazine derivative, wherein the amount ratio of piperazine, methanol and water in the solution 1 is 0.02 mol: 15 mL: 15 mL, and the amount ratio of the acrylate derivative, methanol and water in the solution 2 is 0.022 mol: 15 mL: 15 mL;

[0045] Step A3, the piperazine derivative and maleic anhydride were mixed in DMF, respectively, and recorded as solution 3 and solution 4; 50 mL of solution 3 was slowly added dropwise to 50 mL of solution 4, and the mixture was reacted at room temperature for 2 h. 1.5 g of anhydrous sodium acetate and 2.1 g of hydroquinone were added and stirred for 20 min. 3.6 mL of acetic anhydride was added, and the mixture was heated to 50 ° C. and reacted for 4 h. The mixture was filtered, washed, dried, and recrystallized to obtain a maleimide-piperazine derivative. The amount ratio of the piperazine derivative to DMF in the solution 3 was 0.03 mol: 50 mL, and the amount ratio of maleic anhydride to DMF in the solution 4 was 0.03 mol: 50 mL;

[0046] Step A4: 50 g of irradiated linear low-density polyethylene, 0.6 g of sodium dodecylsulfonate, 20 g of a maleimide-piperazine derivative, and 200 mL of water were stirred at 60 ° C for 50 min, nitrogen was introduced, and the temperature was raised to 90 ° C. 0.03 g of benzoyl peroxide was added three times, and the reaction was continued for 10 h. The mixture was filtered, washed, and dried to obtain a modified linear low-density polyethylene.

[0047] Example 4: A method for preparing a high-temperature resistant and bend-resistant medium-voltage cable comprises the following steps:

[0048] Step S1: extruding a cross-linked EVA conductor shielding material onto the outside of a copper conductor to form a conductor shielding layer, extruding a thermoplastic polyurethane elastomer onto the outside of the conductor shielding layer to form an insulating layer, and longitudinally shielding the outside of the insulating layer with a copper tape and then braiding aramid yarn to form an insulating shielding layer, thereby obtaining an insulated wire core;

[0049] Step S2: gluing multiple insulated wire cores to form a cable core, extruding polyvinyl chloride on the outside of the cable core to form an isolation jacket, and wrapping two layers of galvanized steel tape on the outside of the isolation jacket to form a metal armor layer;

[0050] Step S3, weighing the raw materials by weight, adding 40 parts of linear low-density polyethylene, 10 parts of polypropylene, 15 parts of modified linear low-density polyethylene prepared in Example 1, 5 parts of maleic anhydride grafted POE, 8 parts of composite flame retardant, 2 parts of PE wax and 1 part of antioxidant 1010 to a blender and stirring evenly, transferring to a single-screw extruder for extrusion, and then extruding it on the outside of the metal armor layer to form an outer sheath, thereby obtaining a high-temperature resistant and bend-resistant medium-voltage cable. The temperatures of each section of the single-screw extruder are: section 1: 170°C, section 2: 170°C, section 3: 175°C, and die head: 175°C, and the screw speed is 30 rpm.

[0051] Example 5: A method for preparing a high-temperature resistant and bend-resistant medium-voltage cable comprises the following steps:

[0052] Step S1: extruding a cross-linked EVA conductor shielding material onto the outside of a copper conductor to form a conductor shielding layer, extruding a thermoplastic polyurethane elastomer onto the outside of the conductor shielding layer to form an insulating layer, and longitudinally shielding the outside of the insulating layer with a copper tape and then braiding aramid yarn to form an insulating shielding layer, thereby obtaining an insulated wire core;

[0053] Step S2: gluing multiple insulated wire cores to form a cable core, extruding polyvinyl chloride on the outside of the cable core to form an isolation jacket, and wrapping two layers of galvanized steel tape on the outside of the isolation jacket to form a metal armor layer;

[0054] Step S3, weighing the raw materials by weight, adding 50 parts of linear low-density polyethylene, 15 parts of polypropylene, 20 parts of modified linear low-density polyethylene prepared in Example 2, 8 parts of maleic anhydride grafted POE, 12 parts of composite flame retardant, 2.5 parts of PE wax and 1.5 parts of antioxidant 1024 to a blender and stirring evenly, transferring to a single-screw extruder for extrusion, and then extruding it on the outside of the metal armor layer to form an outer sheath, thereby obtaining a high-temperature resistant and bend-resistant medium-voltage cable. The temperatures of each section of the single-screw extruder are: section 1: 175°C, section 2: 175°C, section 3: 180°C, die head: 180°C, and the screw speed is 40 rpm.

[0055] Example 6: A method for preparing a high-temperature resistant and bend-resistant medium-voltage cable comprises the following steps:

[0056] Step S1: extruding a cross-linked EVA conductor shielding material onto the outside of a copper conductor to form a conductor shielding layer, extruding a thermoplastic polyurethane elastomer onto the outside of the conductor shielding layer to form an insulating layer, and longitudinally shielding the outside of the insulating layer with a copper tape and then braiding aramid yarn to form an insulating shielding layer, thereby obtaining an insulated wire core;

[0057] Step S2: gluing multiple insulated wire cores to form a cable core, extruding polyvinyl chloride on the outside of the cable core to form an isolation jacket, and wrapping two layers of galvanized steel tape on the outside of the isolation jacket to form a metal armor layer;

[0058] Step S3, weighing the raw materials by weight, adding 60 parts of linear low-density polyethylene, 20 parts of polypropylene, 25 parts of modified linear low-density polyethylene prepared in Example 3, 10 parts of maleic anhydride grafted POE, 15 parts of composite flame retardant, 3 parts of PE wax and 2 parts of antioxidant 168 to a blender and stirring evenly, transferring the mixture to a single-screw extruder for extrusion, and then extruding the mixture on the outside of the metal armor layer to form an outer sheath, thereby obtaining a high-temperature resistant and bend-resistant medium-voltage cable. The temperatures of each section of the single-screw extruder are: section 1: 180°C, section 2: 180°C, section 3: 185°C, die head: 185°C, and the screw speed is 50 rpm.

[0059] Comparative Example 1: This comparative example is a medium voltage cable. The difference from Example 6 is that linear low-density polyethylene is used instead of the modified linear low-density polyethylene prepared in Example 3, and the rest are the same.

[0060] Comparative Example 2: This comparative example is a medium voltage cable. The difference from Example 6 is that N-phenylmaleimide grafted polyethylene is used instead of the modified linear low-density polyethylene prepared in Example 3. The rest are the same.

[0061] The N-phenylmaleimide grafted polyethylene was prepared by the following steps: 50 g of irradiated linear low-density polyethylene, 0.6 g of sodium dodecylsulfonate, 20 g of N-phenylmaleimide, and 200 mL of water were stirred at 60°C for 50 min, nitrogen was introduced, and the temperature was raised to 90°C. 0.03 g of benzoyl peroxide was added three times, and the reaction was continued for 10 h. The mixture was filtered, washed, and dried to obtain the N-phenylmaleimide grafted polyethylene.

[0062] Performance testing:

[0063] Bending resistance test: The medium voltage cables prepared in Examples 4-6 and Comparative Examples 1-2 were subjected to bending tests using a wire and cable bending tester (rotation speed 20 rpm). Cable samples were inserted into the specified circular holes according to their thickness and fixed in a fixture with adjusted spacing. After rotating the tester 200 times, the samples were inspected for damage and cracks.

[0064] High temperature resistance test: The medium voltage cables prepared in Examples 4-6 and Comparative Examples 1-2 were tested for tensile strength retention and elongation at break retention at 180°C for 168 hours according to GB / T 1040.1-2006.

[0065] The test results are shown in Table 1:

[0066] Table 1: Performance test results

[0067]

[0068] As can be seen from Table 1, after the bending resistance test, the medium voltage cable prepared by the present invention has no damage or cracks on the cable surface, indicating that it has excellent bending resistance. After the high temperature resistance test, after the cable is placed at 180°C for 168 hours, the tensile strength retention rate is in the range of (105.3-110.2)%, and the elongation at break retention rate is in the range of (92.5-95.1)%, indicating that it has excellent high temperature resistance.

[0069] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the scope defined by the concept of the invention, they should all fall within the scope of protection of the present invention.

Claims

1. A high temperature resistant and bending resistant medium voltage cable, characterized in that: The cable core comprises a cable core arranged in sequence from the inside to the outside, an isolation jacket is extruded on the outside of the cable core, a metal armor layer is wrapped around the isolation jacket, and an outer sheath is extruded on the metal armor layer; the cable core is formed by twisting a plurality of insulated wire cores; the insulated wire core is formed by a conductor shielding layer, an insulating layer, and an insulating shielding layer sequentially wrapped on the outside of a copper conductor; The isolation sleeve is made of polyvinyl chloride, the metal armor layer is two layers of galvanized steel tape, the conductor shielding layer is a cross-linked EVA conductor shielding material, the insulation layer is a thermoplastic polyurethane elastomer, and the insulation shielding layer is formed by longitudinally wrapping a copper tape and then braiding it with aramid yarn; The outer protective layer comprises the following raw materials in parts by weight: 40-60 parts of linear low-density polyethylene, 10-20 parts of polypropylene, 15-25 parts of modified linear low-density polyethylene, 5-10 parts of compatibilizer, 8-15 parts of composite flame retardant, 2-3 parts of lubricant, and 1-2 parts of antioxidant; The modified linear low-density polyethylene is prepared by reacting irradiated linear low-density polyethylene with a maleimide-piperazine derivative, the maleimide-piperazine derivative is prepared by reacting a piperazine derivative with maleic anhydride, the piperazine derivative is prepared by reacting piperazine with an acrylate derivative, and the acrylate derivative is prepared by reacting acryloyl chloride with p-nitrobenzyl alcohol.

2. A high temperature resistant and bend resistant medium voltage cable according to claim 1, characterized in that: The modified linear low density polyethylene is prepared by the following steps: Step A1, acryloyl chloride and dichloromethane are mixed and stirred uniformly, then added dropwise to p-nitrobenzyl alcohol, and triethylamine is added, and the mixture is heated to 45-55° C. and refluxed for 3-4 hours, filtered, washed, and dried to obtain an acrylate derivative; Step A2: piperazine and an acrylate derivative were mixed uniformly in a methanol-water solution, respectively designated as solution 1 and solution 2; solution 2 was slowly added to solution 1, and the mixture was heated to 60° C. and stirred for 2-3 hours. Pd / C and hydrazine hydrate were then added in sequence, and the mixture was refluxed at 80° C. and stirred for 6 hours. The mixture was filtered, and water was added and stirred for 10 minutes. The mixture was filtered again, dried in vacuo, and recrystallized to obtain a piperazine derivative; Step A3: Mix the piperazine derivative and maleic anhydride in DMF, respectively, and record them as solution 3 and solution 4; slowly add solution 3 dropwise to solution 4, react at room temperature for 2 hours, add anhydrous sodium acetate and hydroquinone, stir for 10-20 minutes, add acetic anhydride, and heat to 50°C for 2-4 hours, filter, wash, dry, and recrystallize to obtain a maleimide-piperazine derivative; Step A4: Stir the irradiated linear low-density polyethylene, sodium dodecylsulfonate, maleimide-piperazine derivative, and water at 60°C for 40-50 minutes, introduce nitrogen, and raise the temperature to 90°C. Add benzoyl peroxide three times and continue the reaction for 8-10 hours. Filter, wash, and dry to obtain modified linear low-density polyethylene.

3. The high temperature resistant and bending resistant medium voltage cable according to claim 2, characterized in that: In step A1, the molar ratio of acryloyl chloride to p-nitrobenzoic acid is 1:

1.

4. The high temperature resistant and bending resistant medium voltage cable according to claim 2, characterized in that: In step A2, the amount ratio of solution 1, solution 2, Pd / C, hydrazine hydrate and water is 30 mL:30 mL:0.5-1 g:5-8 g:100 mL, the amount ratio of piperazine, methanol and water in the solution 1 is 0.01-0.02 mol:15 mL:15 mL, and the amount ratio of the acrylate derivative, methanol and water in the solution 2 is 0.011-0.022 mol:15 mL:15 mL.

5. The high temperature resistant and bending resistant medium voltage cable according to claim 2, characterized in that: In step A3, the amount ratio of solution 3, solution 4, anhydrous sodium acetate, hydroquinone and acetic anhydride is 50 mL: 50 mL: 0.5-1.5 g: 0.7-2.1 g: 1.2-3.6 mL, the amount ratio of the piperazine derivative and DMF in the solution 3 is 0.01-0.03 mol: 50 mL, and the amount ratio of maleic anhydride and DMF in the solution 4 is 0.01-0.03 mol: 50 mL.

6. The high temperature resistant and bending resistant medium voltage cable according to claim 2, characterized in that: In step A4, the ratio of irradiated linear low-density polyethylene, sodium lauryl sulfate, maleimide-piperazine derivative, water and benzoyl peroxide is 25-50 g:0.3-0.6 g:10-20 g:200 mL:0.015-0.03 g.

7. The high temperature resistant and bending resistant medium voltage cable according to claim 1, characterized in that: The composite flame retardant is a mixture of magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate and melamine phosphate, wherein the mass ratio of magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate and melamine phosphate is 2:3:5:

3.

8. The high temperature resistant and bending resistant medium voltage cable according to claim 1, characterized in that: The compatibilizer is maleic anhydride grafted POE, the lubricant is PE wax, and the antioxidant is one of antioxidant 1010, antioxidant 1024 or antioxidant 168.

9. The high temperature resistant and bend resistant medium voltage cable according to claim 1, characterized in that: The outer protective layer The following steps are involved: Raw materials are weighed according to weight, and linear low-density polyethylene, polypropylene, modified linear low-density polyethylene, compatibilizer, composite flame retardant, lubricant and antioxidant are added into a blender and stirred evenly, and then transferred to a single-screw extruder for extrusion to obtain the outer protective layer.

10. The high temperature resistant and bending resistant medium voltage cable according to claim 1, characterized in that: In the outer protective layer, the temperature of each section of the single-screw extruder is as follows: section 1: 170-180°C, section 2: 170-180°C, section 3: 175-185°C, die head: 175-185°C, and the screw speed is 30-50rpm.

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