Crosslinked polyethylene insulated fire resistant power cable with a voltage rating of 35 kV and below

Abstract

The application relates to the technical field of power cables, and discloses a 35kV and below rated voltage cross-linked polyethylene insulated fire-resistant power cable which comprises, from inside to outside, a cable core, an inner flame-retardant layer, a fire-resistant layer, an oxygen isolation layer, a middle flame-retardant layer, an inner sheath layer, a wrapping layer, an armoring layer, an outer flame-retardant layer and an outer sheath layer; the cable core comprises, from inside to outside, a conductor, an inner shielding layer, a cross-linked polyethylene insulation layer, an outer shielding layer and a metal shielding layer; the number of the cable cores is three; a filling rope is arranged between the cable core and the inner flame-retardant layer; the raw material of the cross-linked polyethylene insulation layer comprises polyethylene, modified inorganic porous particles and a cross-linking agent; the modified inorganic porous particles are obtained by modifying inorganic porous particles with amino silane and then with sorbitol. Through the technical scheme, the problems of easy water tree and poor fire resistance of the cross-linked polyethylene insulated power cable in the related art are solved.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, specifically to a cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below. Background Technology

[0002] Power cables can be classified according to their insulation materials into polyvinyl chloride (PVC) insulated power cables, cross-linked polyethylene (XLPE) insulated power cables, polyethylene (PE) insulated power cables, and rubber insulated power cables, among which XLPE insulated power cables are the most widely used. XLPE insulated power cables utilize chemical or physical methods to transform the linear molecular structure of polyethylene into a three-dimensional network structure. Cross-linking significantly improves mechanical strength, thermal aging resistance, and environmental stress resistance, giving the cable excellent electrical properties and chemical corrosion resistance. With the widespread application of XLPE insulated power cables, cable faults such as water treeing urgently need to be addressed.

[0003] Furthermore, as people pay increasing attention to personal and property safety, higher requirements are being placed on the fire resistance of cross-linked polyethylene (XLPE) insulated power cables. When XLPE insulated power cables have good fire resistance, they can maintain power supply for a certain period of time under combustion conditions after a fire occurs, providing electrical energy and control signals for firefighting and personnel evacuation, thereby greatly reducing fire losses.

[0004] Therefore, it is of great significance to develop a fire-resistant, water-tree-resistant cross-linked polyethylene insulated power cable. Summary of the Invention

[0005] This invention proposes a cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below, which solves the problems of water treeing and poor fire resistance in cross-linked polyethylene insulated power cables in related technologies.

[0006] The technical solution of the present invention is as follows:

[0007] A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below comprises, from the inside out, a cable core, an inner flame-retardant layer, a fire-resistant layer, an oxygen barrier layer, a middle flame-retardant layer, an inner sheath layer, a wrapping layer, an armor layer, an outer flame-retardant layer, and an outer sheath layer; the cable core comprises, from the inside out, a conductor, an inner shielding layer, a cross-linked polyethylene insulation layer, an outer shielding layer, and a metal shielding layer; the number of cable cores is 3; a filler rope is provided between the cable cores and the inner flame-retardant layer; the raw materials of the cross-linked polyethylene insulation layer include polyethylene, modified inorganic porous granules, and a cross-linking agent; the modified inorganic porous granules are obtained by first modifying inorganic porous granules with aminosilane and then with sorbitol.

[0008] In the cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below of the present invention, the conductor material can be copper or aluminum, preferably copper conductor, because copper conductor has better electrical properties, mechanical strength, continuity and corrosion resistance compared with aluminum.

[0009] In the cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below of the present invention, the metal shielding layer can be a copper wire shielding layer or a copper tape shielding layer, preferably a copper tape shielding layer.

[0010] As a further technical solution, the inner flame-retardant layer, the middle flame-retardant layer, and the outer flame-retardant layer are each independently a low-smoke halogen-free flame-retardant strip.

[0011] As a further technical solution, the refractory layer is a ceramicized polyolefin oxygen barrier material.

[0012] As a further technical solution, the oxygen barrier layer is a low-smoke, halogen-free, flame-retardant polyolefin oxygen barrier material.

[0013] As a further technical solution, the wrapping layer is a double-sided ceramicized armor strip.

[0014] As a further technical solution, the armor layer is a galvanized steel strip.

[0015] In the cross-linked polyethylene insulation layer of the cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below of the present invention, the cross-linking agent can be any one or more conventional cross-linking agents in the art, such as peroxide, preferably diisopropylbenzene peroxide.

[0016] As a further technical solution, the modified inorganic porous granules are obtained by first modifying inorganic porous granules with aminosilane, then with sorbitol, and finally with compounds containing double bonds and ether groups.

[0017] In this invention, inorganic porous granules are first modified with aminosilane, then with sorbitol, and finally with compounds containing double bonds and ether groups. This improves the dispersibility of the inorganic porous granules in the cross-linked polyethylene insulation layer and enhances the compatibility between the inorganic porous granules and the polyethylene base material. This not only increases the mechanical strength of the cross-linked polyethylene insulation layer but also effectively inhibits the occurrence of water treeing.

[0018] As a further technical solution, the raw materials of the modified inorganic porous granules include inorganic porous granules in a mass ratio of 100:4~10:10~15:4~7, aminosilane, sorbitol, and compounds containing double bonds and ether groups.

[0019] In the cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below of the present invention, the inorganic porous granules in the cross-linked polyethylene insulation layer can be any one or more conventional inorganic porous granules in the art, preferably porous silica.

[0020] In the cross-linked polyethylene insulation layer of the cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below of this invention, the aminosilane can be any one or more amino-containing silanes in the art, such as KH-550 γ-aminopropyltriethoxysilane, KH-540 γ-aminopropyltrimethoxysilane, KH-902 γ-aminopropylmethyldiethoxysilane, KH-553 γ-aminopropylsilanetriol, KH-554 γ-aminopropylmethyldimethoxysilane, KH-590 N-phenyl-γ-aminopropyltrimethoxysilane, KH-602 N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, KH-703 N,N-Diethyl-3-aminopropyltrimethoxysilane, KH-792N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, KH-892γ-diethylenetriaminopropyltrimethoxysilane, KH-ND22γ-diethylaminomethyltriethoxysilane, KH-ND42N-phenylaminomethyltriethoxysilane, KH-170bis-(γ-trimethoxysilylpropyl)amine, KH-270bis(3-triethoxysilylpropyl)amine, KH-620hexamethyldisilazane, KH-16374-amino-3,3-dimethylbutyltrimethoxysilane, KH-7933-(2-aminoethyl)-aminopropyltriethoxysilane, KH-603 3-(N,N-dimethylaminopropyl)-aminopropylmethyldimethoxysilane, KH-556(N,N-dimethyl-3-aminopropyl)trimethoxysilane, KH-558 N-(n-butyl)-γ-aminopropyltrimethoxysilane, KH-559 N-cyclohexyl-γ-aminopropylmethyldimethoxysilane, etc., preferably KH-550 or KH-602.

[0021] In the cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below of the present invention, the compound containing double bonds and ether groups in the cross-linked polyethylene insulation layer can be any one or more compounds containing carbon-carbon double bonds and ether groups, preferably 3,4',5-trimethoxy-trans-diphenylethylene.

[0022] As a further technical solution, the preparation method of the modified inorganic porous granules includes the following steps:

[0023] S1. Disperse inorganic porous granules in water, add aminosilane, stir to carry out the first modification, and dry to obtain the first modified inorganic porous granules;

[0024] S2. The first modified inorganic porous granules are added to an aqueous solution of sorbitol, stirred for the second modification, and dried to obtain the second modified inorganic porous granules.

[0025] S3. The second modified inorganic porous granules are added to a compound solution containing double bonds and ether groups, stirred for third modification, and dried to obtain modified inorganic porous granules.

[0026] As a further technical solution, the stirring speed in step S1 is 300~500 rpm, for example, it can be 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] As a further technical solution, the stirring time in step S1 is 20~30 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] As a further technical solution, the stirring in step S2 is divided into a first stirring and a second stirring. The first stirring has a speed of 3000~5000 rpm and a time of 15~25 min, while the second stirring has a speed of 200~400 rpm and a time of 10~20 min.

[0029] As a further technical solution, the stirring speed in step S3 is 200~400 rpm, for example, it can be 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] As a further technical solution, the stirring time in step S3 is 15~35min, for example, it can be 15min, 18min, 20min, 25min, 30min or 35min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] As a further technical solution, the mass ratio of the polyethylene, modified inorganic porous granules, and crosslinking agent is 100:10~20:1~3, for example, it can be 100:10:1, 100:10:2, 100:10:3, 100:15:1, 100:15:2, 100:15:3, 100:20:1 or 100:20:3, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] The working principle and beneficial effects of this invention are as follows:

[0033] This invention provides a cross-linked polyethylene (XLPE) insulated fire-resistant power cable with a rated voltage of 35kV and below. The cable structure, from the inside out, includes a cable core, an inner flame-retardant layer, a fire-resistant layer, an oxygen barrier layer, a middle flame-retardant layer, an inner sheath layer, a wrapping layer, an armor layer, an outer flame-retardant layer, and an outer sheath layer. The cable core, from the inside out, includes a conductor, an inner shielding layer, a XLPE insulation layer, an outer shielding layer, and a metal shielding layer. By optimizing the cable structure and incorporating a fire-resistant layer, the fire resistance of the XLPE insulated power cable is improved. Furthermore, the XLPE insulation layer of this invention uses inorganic porous granules that have been modified with aminosilane and then sorbitol, which inhibits water treeing. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] In the following embodiments and comparative examples:

[0036] The polyethylene is low-density polyethylene (LDPE) from Yanshan Petrochemical, specifically LD113.

[0037] The inorganic porous granules are fumed silica with a particle size of 500 nm and a density of 2.66 g / cm³. 3 Its specific surface area is 126.53 m². 2 / g;

[0038] A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below comprises, from the inside out, three cable cores, a first low-smoke halogen-free flame-retardant strip, a ceramicized polyolefin oxygen barrier, a second low-smoke halogen-free flame-retardant strip, a polyolefin sheath layer, a double-sided ceramicized armor strip, a galvanized steel tape armor layer, a third low-smoke halogen-free flame-retardant strip, and a low-smoke halogen-free polyolefin outer sheath layer; a filler rope is provided between the cable cores and the first low-smoke halogen-free flame-retardant strip; each cable core comprises, from the inside out, a copper conductor, an inner shielding layer, a cross-linked polyethylene insulation layer, an outer shielding layer, and a copper tape shielding layer; the inner shielding layer, the cross-linked polyethylene insulation layer, and the outer shielding layer are produced using a three-layer co-extrusion process; the cross-linked polyethylene insulation layer is prepared by the following method:

[0039] Example 1

[0040] S1. Disperse 100 parts of inorganic porous granules in 1000 parts of water, add 10 parts of KH-550 and stir at 500 rpm for 20 min, then dry to obtain the first modified inorganic porous granules;

[0041] S2. The first modified inorganic porous granules are added to a 10wt% sorbitol aqueous solution, stirred at 3000rpm for 15min, then stirred at 200rpm for 20min, and dried to obtain the second modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to sorbitol is 100:10.

[0042] S3. The second modified inorganic porous granules are added to a 35 mg / mL dimethyl sulfoxide solution of 3,4',5-trimethoxy-trans-diphenylethylene, stirred at 400 rpm for 15 min, and dried to obtain modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to 3,4',5-trimethoxy-trans-diphenylethylene is 100:5.

[0043] S4. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0044] Example 2

[0045] S1. Disperse 100 parts of inorganic porous granules in 1000 parts of water, add 4 parts of KH-602 and stir at 300 rpm for 30 min, then dry to obtain the first modified inorganic porous granules;

[0046] S2. The first modified inorganic porous granules are added to a 15wt% sorbitol aqueous solution, stirred at 5000rpm for 25min, then stirred at 400rpm for 10min, and dried to obtain the second modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to sorbitol is 100:15.

[0047] S3. The second modified inorganic porous granules are added to a 35 mg / mL dimethyl sulfoxide solution of 3,4',5-trimethoxy-trans-diphenylethylene, stirred at 200 rpm for 35 min, and dried to obtain modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to 3,4',5-trimethoxy-trans-diphenylethylene is 100:7.

[0048] S4. After mixing 100 parts of polyethylene and 20 parts of modified inorganic porous granules evenly, add 1 part of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0049] Example 3

[0050] S1. Disperse 100 parts of inorganic porous granules in 1000 parts of water, add 10 parts of KH-550 and stir at 500 rpm for 20 min, then dry to obtain the first modified inorganic porous granules;

[0051] S2. The first modified inorganic porous granules are added to a 10wt% sorbitol aqueous solution, stirred at 3000rpm for 15min, then stirred at 200rpm for 20min, and dried to obtain the modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to sorbitol is 100:10.

[0052] S3. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0053] Example 4

[0054] S1. Disperse 100 parts of inorganic porous granules in 1000 parts of water, add 10 parts of KH-550 and stir at 500 rpm for 20 min, then dry to obtain the first modified inorganic porous granules;

[0055] S2. The first modified inorganic porous granules are added to a 35 mg / mL dimethyl sulfoxide solution of 3,4',5-trimethoxy-trans-diphenylethylene, stirred at 400 rpm for 15 min, and dried to obtain the second modified inorganic porous granules, wherein the mass ratio of the inorganic porous granules to 3,4',5-trimethoxy-trans-diphenylethylene is 100:5.

[0056] S3. The second modified inorganic porous granules are added to a 10wt% sorbitol aqueous solution, stirred at 3000rpm for 15min, then stirred at 200rpm for 20min, and dried to obtain the modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to sorbitol is 100:10.

[0057] S4. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0058] Comparative Example 1

[0059] S1. Disperse 100 parts of inorganic porous granules in 1000 parts of water, add 10 parts of KH-550 and stir at 500 rpm for 20 min, then dry to obtain modified inorganic porous granules.

[0060] S2. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0061] Comparative Example 2

[0062] S1. Add 100 parts of inorganic porous granules to a 10wt% sorbitol aqueous solution, stir at 3000rpm for 15min, then stir at 200rpm for 20min, and dry to obtain modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to sorbitol is 100:10.

[0063] S2. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0064] Comparative Example 3

[0065] S1. 100 parts of inorganic porous granules were added to a 35 mg / mL dimethyl sulfoxide solution of 3,4',5-trimethoxy-trans-diphenylethylene, stirred at 400 rpm for 15 min, and dried to obtain modified inorganic porous granules, wherein the mass ratio of inorganic porous granules to 3,4',5-trimethoxy-trans-diphenylethylene was 100:5.

[0066] S2. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0067] Comparative Example 4

[0068] S1. Disperse 100 parts of inorganic porous granules in 1000 parts of water, add 10 parts of KH-550 and stir at 500 rpm for 20 min, then dry to obtain the first modified inorganic porous granules;

[0069] S2. The first modified inorganic porous granules were added to a 35 mg / mL dimethyl sulfoxide solution of 3,4',5-trimethoxy-trans-diphenylethylene, stirred at 400 rpm for 15 min, and dried to obtain the modified inorganic porous granules, wherein the mass ratio of the inorganic porous granules to 3,4',5-trimethoxy-trans-diphenylethylene was 100:5.

[0070] S3. After mixing 100 parts of polyethylene and 10 parts of modified inorganic porous granules evenly, add 3 parts of dicumyl peroxide and continue mixing. Co-extrude the blend with the blends of the other two layers and cross-link at 170℃ and 15MPa for 30min to obtain a cross-linked polyethylene insulation layer.

[0071] Performance testing:

[0072] (1) Water tree resistance: Referring to the method in ASTM D6097-01a "Standard Test Method for Relative Tolerance to Radial Water Tree Growth in Solid Insulating Materials", the water tree resistance of cross-linked polyethylene insulation is expressed by the water tree growth resistance (RWTG):

[0073] RWTG = L / WTL;

[0074] In the formula: L is the distance between the needle plate electrodes (L=3.2mm), and WTL is the maximum length of the water tree;

[0075] (2) Mechanical strength: The tensile strength was tested according to the method in GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Cables - Part 11: General Test Methods for Thickness and Dimensional Measurement and Mechanical Properties Test". The test sample was a dumbbell specimen with a thickness of 3 mm.

[0076] The test results are recorded in Table 1.

[0077] Table 1. Test results of water tree resistance and mechanical strength of cross-linked polyethylene insulation layer

[0078]

[0079] As shown in Table 1, the RWTG of the cross-linked polyethylene insulation layers obtained in Examples 1-4 is higher than that in Comparative Examples 1-4, indicating that the use of inorganic porous granules modified with aminosilane first and then with sorbitol can suppress water treeing. Furthermore, the RWTG and tensile strength of the cross-linked polyethylene insulation layers obtained in Examples 1-2 are higher than those in the other examples and comparative examples, indicating that the modification of the inorganic porous granules with aminosilane first, then with sorbitol, and finally with compounds containing double bonds and ether groups can not only increase the mechanical strength of the cross-linked polyethylene insulation layer but also effectively suppress water treeing.

[0080] The cross-linked polyethylene insulated fire-resistant power cables with rated voltages of 35kV and below obtained in each embodiment were subjected to fire resistance tests according to the method in TICW 8-2012 "Extruded Insulated Fire-Resistant Power Cables with Rated Voltages of 6kV (Um=7.2kV) to 35kV (Um=40.5kV)". All of them passed the test, indicating that the cross-linked polyethylene insulated power cables provided by the present invention have good fire resistance.

[0081] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below, characterized in that, From the inside out, the cable consists of a cable core, an inner flame-retardant layer, a fire-resistant layer, an oxygen barrier layer, a middle flame-retardant layer, an inner sheath layer, a wrapping tape layer, an armor layer, an outer flame-retardant layer, and an outer sheath layer. The cable core, from the inside out, consists of a conductor, an inner shielding layer, a cross-linked polyethylene insulation layer, an outer shielding layer, and a metal shielding layer. There are three cable cores. A filler rope is provided between the cable cores and the inner flame-retardant layer. The raw materials for the cross-linked polyethylene insulation layer include polyethylene, modified inorganic porous granules, and a cross-linking agent. The modified inorganic porous granules are obtained by first modifying inorganic porous granules with aminosilane, then with sorbitol, and finally with compounds containing double bonds and ether groups.

2. The cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below according to claim 1, characterized in that, The conductor is a copper conductor; the metal shielding layer is a copper strip shielding layer.

3. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below as described in claim 1, characterized in that, The inner flame-retardant layer, the middle flame-retardant layer, and the outer flame-retardant layer are each independently a low-smoke halogen-free flame-retardant strip; The refractory layer is a ceramicized polyolefin oxygen barrier material; The oxygen barrier layer is a low-smoke, halogen-free, flame-retardant polyolefin oxygen barrier material.

4. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below as described in claim 1, characterized in that, The wrapping layer is a double-sided ceramicized armor strip; the armor layer is a galvanized steel strip.

5. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below as described in claim 1, characterized in that, The raw materials for the modified inorganic porous granules include inorganic porous granules in a mass ratio of 100:4~10:10~15:4~7, aminosilane, sorbitol, and compounds containing double bonds and ether groups.

6. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below according to claim 1, characterized in that, The method for preparing the modified inorganic porous granules includes the following steps: S1. Disperse inorganic porous granules in water, add aminosilane, stir to carry out the first modification, and dry to obtain the first modified inorganic porous granules; S2. The first modified inorganic porous granules are added to an aqueous solution of sorbitol, stirred for the second modification, and dried to obtain the second modified inorganic porous granules. S3. The second modified inorganic porous granules are added to a compound solution containing double bonds and ether groups, stirred for the third modification, and dried to obtain the modified inorganic porous granules.

7. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below as described in claim 6, characterized in that, In step S1, the stirring speed is 300~500 rpm and the time is 20~30 min; In step S2, the stirring is divided into a first stirring and a second stirring. The first stirring speed is 3000~5000 rpm and the time is 15~25 min. The second stirring speed is 200~400 rpm and the time is 10~20 min. In step S3, the stirring speed is 200~400 rpm and the time is 15~35 min.

8. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below as described in claim 1, characterized in that, The crosslinking agent is a peroxide.

9. A cross-linked polyethylene insulated fire-resistant power cable with a rated voltage of 35kV and below as described in claim 1, characterized in that, The mass ratio of the polyethylene, modified inorganic porous granules, and crosslinking agent is 100:10~20:1~3.

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