A cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method

Abstract

The present invention belongs to the technical field of cable materials, and specifically discloses a crosslinked polyethylene insulating material for extra-high voltage cables and a preparation method thereof. By weight, the polyethylene insulating material comprises the following raw materials: 70-100 parts of low-density polyethylene, 0.4-1.2 parts of antioxidant, and 1.5-5.5 parts of composite crosslinking agent; wherein, the antioxidant contains a polycyclic conjugated structure, and the polyethylene insulating material has a good ability to inhibit the accumulation of space charge, improving the breakdown voltage level of the cable.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable materials, and particularly relates to a cross-linked polyethylene insulating material for extra-high voltage cables and a preparation method thereof. Background Art

[0002] With the development of the ocean and the promotion of new urbanization, more and more high-voltage DC cable projects have been put into operation. The role of the insulating material in the cable is to cover the outside of the conductive material, prevent current leakage, and ensure the safety and reliability of the cable during transmission. In recent years, extruded insulation cables have become the mainstream technology for high-voltage DC cables due to their advantages such as short production cycle, low environmental impact, and convenient installation and maintenance.

[0003] Extruded insulation cables mainly include polypropylene thermoplastic elastomer insulated cables and polyethylene insulated cables. Among them, cross-linked polyethylene insulating materials have excellent insulation performance, simple laying, and convenient maintenance, and have currently become the absolute mainstream of cables in China. In industrial applications, cross-linked polyethylene mainly has silane cross-linking method, peroxide cross-linking method, radiation cross-linking method, and ultraviolet cross-linking method that has emerged in recent years. Among them, the peroxide cross-linking method is widely used in the insulation cross-linking of current medium-voltage and extra-high voltage power cables due to its fewer restrictions.

[0004] However, under the action of long-term high-voltage direct current, a large amount of space charges will accumulate inside the cross-linked polyethylene for high-voltage DC cables, resulting in distortion of the electric field distribution inside the insulation layer and leading to breakdown. Patent CN 115651105B discloses a graft-modified cross-linked polyethylene water tree-resistant insulating material, its preparation method and application. The two-step blending method reduces the pore defects inside the insulating material and effectively improves the water tree resistance and electrical properties of the material. However, although the first step of this method uses less DCP cross-linking agent to reduce the gel caused by the self-cross-linking of low-density polyethylene, in the second step of cross-linking, in order to ensure the high cross-linking degree of the insulating material, the content of the cross-linking agent added is usually high. When extruding for a long time, too much cross-linking agent will decompose, resulting in pre-cross-linking or old gel points, reducing the insulation extrusion production cycle and production efficiency of the cable, causing a large amount of production waste, and increasing the production cost of the cable. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention selects low-density polyethylene as the main component, adds antioxidants and composite cross-linking agents, and maximally guarantees the purity of the insulating material, and prepares and synthesizes a cross-linked polyethylene insulating material for extra-high voltage cables, improving the breakdown voltage level of the cable.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In the first aspect of the present invention, a crosslinked polyethylene insulating material for extra-high voltage cables is provided. By weight, it comprises the following raw materials: 70-100 parts of low-density polyethylene, 0.4-1.2 parts of antioxidant, and 1.5-5.5 parts of composite crosslinking agent; wherein, the antioxidant contains a polycyclic conjugated structure.

[0008] The higher the voltage grade of a power cable, the more likely it is to have insulation breakdown, resulting in insulation failure. Therefore, for power cables with higher voltage grades, the requirements for the purity and impurity content of the insulating material are higher. In this regard, the basic components of the insulating material in this application are pure polyethylene, crosslinking agent, and antioxidant, ensuring the purity of the insulating material to the greatest extent.

[0009] In some embodiments, the melt flow index of the low-density polyethylene at 190 °C and 2.16 kg is 1.0-3.0 g / 10 min.

[0010] Through the specific selection of low-density polyethylene in this application, the probability of crosslinked network formation will be increased in the early stage of crosslinked network formation, reducing the dosage of the crosslinking agent. However, the easy crosslinking in the early stage will also cause molecules to entangle with each other, resulting in a reduction in crosslinking sites between molecules and a decrease in crosslinking density.

[0011] In some embodiments, the composite crosslinking agent comprises dicumyl peroxide, di-tert-butyl peroxide cumene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0012] In some embodiments, the mass ratio of dicumyl peroxide, di-tert-butyl peroxide cumene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane is 1:(0.33-0.39):(0.17-0.26).

[0013] In this application, the dosage of the crosslinking agent is reduced through the compounding of crosslinking agents. Their different decomposition rates make the free radical generation rate more gentle, improve the crystalline structure inside polyethylene, increase the crystallinity, reduce the existence of amorphous regions that are prone to form electrical trees, and the perfect crystal structure helps to reduce the accumulation of space charges and accelerate the heat dissipation process.

[0014] However, after the high-temperature decomposition of dicumyl peroxide, substances such as acetophenone, methane, and cumyl alcohol will be produced; di-tert-butyl peroxide cumene will also produce by-products such as aromatic diols and aromatic diketones. During the processing of ordinary cables, under the action of high temperature, a small part of these crosslinking by-products escapes, and most of them remain in non-penetrable voids or adhere to polymer chains. After the cable is powered on, they slowly escape from the insulation layer to form insulation air holes, posing a safety hazard. While the crosslinking density of polyethylene in the early stage of this application is relatively low, which can promote the discharge of a part of the by-products.

[0015] In some embodiments, the preparation steps of the antioxidant are as follows:

[0016] S1. Under the protection of an inert gas, resorcinol, fatty aldehyde, hydrochloric acid and absolute ethanol are stirred at 60-80 °C for 8-14 h, cooled to room temperature, washed, recrystallized 1-2 times with an acetone-n-hexane solution, and vacuum dried at 40-60 °C to constant weight to obtain a white powder;

[0017] S2. The white powder obtained in step S1 is dissolved in an acetone-n-hexane solution, an inert gas is introduced, and at 1-4 °C, a β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride-n-hexane solution and a triethylamine-n-hexane solution are simultaneously added dropwise. After the addition is completed, the mixture is stirred for 20-40 min, heated to 30-50 °C, and kept warm for 18-30 h. After the heat preservation is completed, first perform rotary evaporation, then add toluene and stir. After suction filtration, continue rotary evaporation to obtain a crude product;

[0018] S3. The crude product obtained in step S2 is added dropwise to ice ether at a rotation speed of 400-600 rpm. After the addition is completed, let it stand, perform suction filtration, wash, and vacuum dry at 25-35 °C to constant weight to obtain the antioxidant.

[0019] Crosslinked polyethylene is the most commonly used main insulation for current high-voltage cables. Industrially, antioxidants are usually added to improve its processing characteristics and long-term electrical characteristics. In actual applications, the molecular weights of traditional antioxidants are generally relatively small, and there are defects such as poor thermal stability, easy volatilization, and poor migration resistance during processing and use, resulting in the antioxidants not achieving the expected antioxidant effect and thus being unable to inhibit or slow down the aging of polymer materials; while some commercial macromolecular antioxidants have problems with limited antioxidant performance due to poor fusion with crosslinked polyethylene.

[0020] In the first aspect, the antioxidant of the present application has a polycyclic conjugated structure, making it not easy to volatilize, resistant to migration and hydrolysis during use, meeting the processing requirements of cross-linked polyethylene materials; in the second aspect, the cross-linked polyethylene added with this antioxidant can effectively inhibit the accumulation of space charge, alleviating the local electric field distortion in the polymer caused by the continuously accumulating space charge during the use of the cable, and thus improving the breakdown resistance of the insulating material. The possible reason is that this antioxidant changes the crystalline morphology of cross-linked polyethylene, reducing the formation of grain boundary defects, or the dipole charge center of the strong polar group in the antioxidant leads to the generation of traps, binding the mobile charges in the material and preventing them from accumulating in large quantities under the influence of the electric field, thereby inhibiting the generation of space charge; in the third aspect, since peroxide cross-linking mainly controls its cross-linking degree by heating temperature, when the cross-linking degree is inappropriate, the heat resistance of cross-linked polyethylene is poor and cannot meet the requirements of long-term use of the cable. However, the antioxidant of the present application will undergo electron migration during the cross-linking process to generate a relatively stable structure, thereby increasing the oxidation induction time and oxidation onset temperature.

[0021] In some embodiments, the carbon chain length of the fatty aldehyde in step S1 is C8 - C16.

[0022] In some embodiments, the molar ratio of resorcinol to fatty aldehyde in step S1 is 1:(1.05 - 1.3).

[0023] In some embodiments, the mass ratio of the white powder to β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride in step S2 is 1:(2.15 - 2.35).

[0024] In some embodiments, the mass ratio of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride to triethylamine in step S2 is 1:(0.3 - 0.4).

[0025] In the second aspect of the present invention, a preparation method of a cross-linked polyethylene insulating material for ultra-high voltage cables is provided, which includes the following steps: low-density polyethylene, an antioxidant, and a composite cross-linking agent are melt-kneaded and extruded at 110 - 130 °C to obtain the cross-linked polyethylene insulating material for ultra-high voltage cables.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The basic components of the insulating material of the present invention are pure polyethylene, a cross-linking agent, and an antioxidant, ensuring the purity of the insulating material to the greatest extent, having a good ability to inhibit the accumulation of space charge, and improving the voltage withstand level of the cable.

[0028] 2. This application reduces the dosage of crosslinking agent through compounding crosslinking agents and improves the crystalline structure inside polyethylene. It not only reduces the existence of amorphous regions that are prone to form electrical trees, but also helps reduce the accumulation of space charge and accelerate the heat dissipation process.

[0029] 3. The crosslinking density of the polyethylene of the present invention is relatively low in the early stage, which promotes the discharge of a part of the by-products of the crosslinking agent, and the crosslinking density is improved in the later stage.

[0030] 4. The antioxidant of this application is not easy to volatilize, resistant to migration and hydrolysis during use. It can increase the oxidation induction time and oxidation onset temperature, meet the processing requirements of crosslinked polyethylene materials, and can effectively inhibit the accumulation of space charge, improving the breakdown resistance of insulating materials. Detailed Embodiment

[0031] The present invention will be described below in conjunction with specific implementation embodiments. It should be noted that the following examples are examples of the present invention, only for explaining the present invention, and not for limiting the present invention. Other combinations and various improvements within the concept of the present invention can be made without departing from the main idea or scope of the present invention.

[0032] For the convenience of those skilled in the art to implement the present invention, the following is an explanation of some raw materials and manufacturers of the examples:

[0033] Low-density polyethylene is purchased from Sinopec Beijing Yanshan Company. The melt flow index is 2.0 g / 10 min (190 °C, 2.16 kg), and the density is 0.915 g / cm 3 .

[0034] Preparation Example 1

[0035] The preparation steps of antioxidant-A are as follows:

[0036] S1. Under nitrogen protection, 100 g of resorcinol, 212 g of lauraldehyde, 140 mL of hydrochloric acid with a concentration of 20 wt%, and 960 mL of absolute ethanol are stirred at 70 °C for 10 h, cooled to room temperature, then washed 3 times with absolute ethanol, then recrystallized 2 times with a 50 v% acetone-n-hexane solution, and vacuum dried at 50 °C to constant weight to obtain a white powder;

[0037] S2. Dissolve 50 g of the white powder obtained in step S1 in 1000 mL of a 50 v% acetone-n-hexane solution, introduce nitrogen, and at 2 °C, simultaneously dropwise add a solution of 112.5 g of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride in 800 mL of n-hexane and a solution of 39.4 g of triethylamine in 470 mL of n-hexane. After the dropping is completed, stir for 30 min, raise the temperature to 40 °C, and keep warm for 25 h. After the heat preservation is completed, first perform rotary evaporation, then add toluene and stir until precipitation appears. After filtration, continue rotary evaporation to constant weight to obtain a crude product;

[0038] S3. At a rotation speed of 500 rpm, the crude product obtained in step S2 is added dropwise to 5 times its mass of ice-cold diethyl ether. After the addition is complete, let it stand until precipitation is complete, perform suction filtration, wash twice with ice-cold diethyl ether, and dry under vacuum at 30 °C to constant weight to obtain antioxidant-A.

[0039] Preparation Example 2

[0040] The preparation steps of antioxidant-B are as follows:

[0041] The difference between this preparation example and Preparation Example 1 is that: in step S1, 168 g of lauraldehyde is replaced by 115 g of hexanal.

[0042] Preparation Example 3

[0043] The preparation steps of antioxidant-C are as follows:

[0044] The difference between this preparation example and Preparation Example 1 is that: in step S1, 168 g of lauraldehyde is replaced by 308 g of stearaldehyde.

[0045] Preparation Example 4

[0046] The preparation steps of antioxidant-D are as follows:

[0047] The difference between this preparation example and Preparation Example 1 is that: in step S1, the amount of lauraldehyde used is 184 g.

[0048] Preparation Example 5

[0049] The preparation steps of antioxidant-E are as follows:

[0050] The difference between this preparation example and Preparation Example 1 is that: in step S1, the amount of lauraldehyde used is 248 g.

[0051] Preparation Example 6

[0052] The preparation steps of antioxidant-F are as follows:

[0053] The difference between this preparation example and Preparation Example 1 is that: in step S2, the amount of white powder used is 45 g.

[0054] Preparation Example 7

[0055] The preparation steps of antioxidant-G are as follows:

[0056] The difference between this preparation example and Preparation Example 1 is that: in step S2, the amount of white powder used is 55 g.

[0057] Example 1

[0058] A crosslinked polyethylene insulating material for extra-high voltage cables, by weight, comprises the following raw materials: 85 parts of low-density polyethylene, 0.8 part of antioxidant-A, and 3.5 parts of a composite crosslinking agent;

[0059] The composite crosslinking agent comprises 2.2 parts of dicumyl peroxide, 0.8 part of di-tert-butyl peroxyisopropylbenzene, and 0.5 part of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane;

[0060] The preparation method of the crosslinked polyethylene insulating material for extra-high voltage cables in this example comprises the following steps: Mixing and extruding low-density polyethylene, antioxidant-A, dicumyl peroxide, di-tert-butyl peroxyisopropylbenzene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane at 120°C to obtain the crosslinked polyethylene insulating material for extra-high voltage cables.

[0061] Example 2

[0062] A crosslinked polyethylene insulating material for extra-high voltage cables, by weight, comprises the following raw materials: 70 parts of low-density polyethylene, 0.4 part of antioxidant-A, and 1.5 parts of a composite crosslinking agent;

[0063] The composite crosslinking agent comprises 1 part of dicumyl peroxide, 0.33 part of di-tert-butyl peroxyisopropylbenzene, and 0.17 part of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane;

[0064] The preparation method of the crosslinked polyethylene insulating material for extra-high voltage cables in this example comprises the following steps: Mixing and extruding low-density polyethylene, antioxidant-A, dicumyl peroxide, di-tert-butyl peroxyisopropylbenzene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane at 110°C to obtain the crosslinked polyethylene insulating material for extra-high voltage cables.

[0065] Example 3

[0066] A crosslinked polyethylene insulating material for extra-high voltage cables, by weight, comprises the following raw materials: 100 parts of low-density polyethylene, 1.2 parts of antioxidant-A, and 5.5 parts of a composite crosslinking agent;

[0067] The composite crosslinking agent comprises 3.3 parts of dicumyl peroxide, 1.29 parts of di-tert-butyl peroxyisopropylbenzene, and 0.91 part of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane;

[0068] The preparation method of the cross-linked polyethylene insulating material for extra-high voltage cables in this embodiment includes the following steps: Mix and extrude low-density polyethylene, antioxidant-A, diisopropylbenzene peroxide, di-tert-butyl peroxyisopropylbenzene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane at 130 °C to obtain the cross-linked polyethylene insulating material for extra-high voltage cables.

[0069] Example 4

[0070] This embodiment provides a cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method. The specific implementation method is the same as that of Example 1, except that: Antioxidant-A is replaced by an equal amount of Antioxidant-B.

[0071] Example 5

[0072] This embodiment provides a cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method. The specific implementation method is the same as that of Example 1, except that: Antioxidant-A is replaced by an equal amount of Antioxidant-C.

[0073] Example 6

[0074] This embodiment provides a cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method. The specific implementation method is the same as that of Example 1, except that: Antioxidant-A is replaced by an equal amount of Antioxidant-D.

[0075] Example 7

[0076] This embodiment provides a cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method. The specific implementation method is the same as that of Example 1, except that: Antioxidant-A is replaced by an equal amount of Antioxidant-E.

[0077] Example 8

[0078] This embodiment provides a cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method. The specific implementation method is the same as that of Example 1, except that: Antioxidant-A is replaced by an equal amount of Antioxidant-F.

[0079] Example 9

[0080] This embodiment provides a cross-linked polyethylene insulating material for extra-high voltage cables and its preparation method. The specific implementation method is the same as that of Example 1, except that: Antioxidant-A is replaced by an equal amount of Antioxidant-G.

[0081] Example 10

[0082] A cross-linked polyethylene insulating material for extra-high voltage cables, by weight, comprises the following raw materials: 85 parts of low-density polyethylene, 0.8 part of antioxidant-A, and 3.5 parts of a composite cross-linking agent;

[0083] The composite crosslinking agent contains 2.5 parts of dicumyl peroxide and 1 part of diisopropylbenzene peroxide tert-butyl;

[0084] The preparation method of the crosslinked polyethylene insulating material for extra-high voltage cables in this example is the same as that in Example 1.

[0085] Example 11

[0086] A crosslinked polyethylene insulating material for extra-high voltage cables, by weight, comprises the following raw materials: 85 parts of low-density polyethylene, 0.8 part of antioxidant-A, and 3.5 parts of a composite crosslinking agent;

[0087] The composite crosslinking agent contains 2.7 parts of dicumyl peroxide and 0.8 part of 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane;

[0088] The preparation method of the crosslinked polyethylene insulating material for extra-high voltage cables in this example is the same as that in Example 1.

[0089] Performance test:

[0090] 1. Gel content test:

[0091] Take 0.3 g of the crosslinked polyethylene insulating material of each example, record its mass as m1, wrap it with a 120-mesh copper mesh, immerse it in xylene solution, extract it with a reflux extractor at 160 °C for 4 h, take out the sample, rinse it 3 times with absolute ethanol, then place it in a vacuum drying oven at 100 °C and dry it to constant weight, weigh the mass of the crosslinked polyethylene insulating material after drying, record it as m2, and calculate the gel content (C gel ) of the crosslinked polyethylene insulating material, C gel =(m2 / m1)×100%, and the gel content represents the crosslinking degree of polyethylene.

[0092] 2. DC breakdown test:

[0093] Measure the DC breakdown field strength of the crosslinked polyethylene insulating material of each example at 50 °C. During the measurement process, use a uniform voltage increase method, and the voltage increases at a rate of 1000 V / s until the sample is broken down, and record the breakdown voltage.

[0094] The results are shown in Table 1.

[0095] Table 1 Performance test results

[0096]

[0097]

[0098] It can be seen from the data in Table 1 that the crosslinked polyethylene insulating materials of Examples 1-3 have a high gel content and a high DC breakdown voltage, indicating that their crosslinking degree and withstand voltage level are relatively high.

[0099] Compared with Example 1, in the preparation of the antioxidant in Example 4-5, the carbon chain length of the fatty aldehyde was changed, which was not conducive to the entanglement between the fatty aldehyde and polyethylene, affected the fusion of the antioxidant and crosslinked polyethylene, and further affected the crosslinking degree and voltage withstand level of polyethylene.

[0100] Compared with Example 1, in the preparation of the antioxidant in Example 6-9, the dosage ratio between raw materials was changed, which was not conducive to the formation of the polycyclic conjugated structure of the antioxidant, affected the migration resistance during processing and use and the inhibition of space charge accumulation of the antioxidant, and reduced the crosslinking degree and voltage withstand level of polyethylene.

[0101] It can be seen from Example 1 and Examples 10-11 that the compounding of the three crosslinking agents can effectively increase the gel content; and the compounded crosslinking agents improve the crystal structure inside polyethylene, which helps to reduce the accumulation of space charge, and further improves the breakdown voltage level.

[0102] The above-described embodiments do not impose any formal restrictions on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, can make some changes or modifications to the above-disclosed technical content to form equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A crosslinked polyethylene insulating material for extra-high voltage cables, characterized in that, By weight, it contains the following raw materials: 70 - 100 parts of low-density polyethylene, 0.4 - 1.2 parts of antioxidant, and 1.5 - 5.5 parts of composite cross-linking agent; wherein, the antioxidant contains a polycyclic conjugated structure; The melt flow index of the low-density polyethylene at 190 °C and 2.16 kg is 1.0 - 3.0 g / 10 min; The composite cross-linking agent contains diisopropylbenzene peroxide, di-tert-butylperoxyisopropylbenzene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; The preparation steps of the antioxidant are as follows: S1. Under the protection of inert gas, resorcinol, fatty aldehyde, hydrochloric acid, and absolute ethanol are stirred at 60 - 80 °C for 8 - 14 h, cooled to room temperature, washed, recrystallized 1 - 2 times with acetone-n-hexane solution, and vacuum dried at 40 - 60 °C to constant weight to obtain a white powder; S2. The white powder obtained in step S1 is dissolved in acetone-n-hexane solution, inert gas is introduced, at 1 - 4 °C, a solution of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride in n-hexane and a solution of triethylamine in n-hexane are simultaneously added dropwise. After the addition is completed, it is stirred for 20 - 40 min, heated to 30 - 50 °C, and kept warm for 18 - 30 h. After the heat preservation is completed, first perform rotary evaporation, then add toluene and stir, filter by suction, and then continue rotary evaporation to obtain a crude product; S3. The crude product obtained in step S2 is added dropwise to ice ether at a rotation speed of 400 - 600 rpm. After the addition is completed, it is left standing, filtered by suction, washed, and vacuum dried at 25 - 35 °C to constant weight to obtain the antioxidant; In step S1, the carbon chain length of the fatty aldehyde is C8 - C16; A preparation method of cross-linked polyethylene insulating material for extra-high voltage cables, comprising the following steps: mixing and extruding low-density polyethylene, antioxidant, and composite cross-linking agent at 110 - 130 °C to obtain the cross-linked polyethylene insulating material for extra-high voltage cables.

2. The crosslinked polyethylene insulating material for extra-high voltage cables according to claim 1, characterized in that, The mass ratio of diisopropylbenzene peroxide, di-tert-butylperoxyisopropylbenzene, and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane is 1:(0.33 - 0.39):(0.17 - 0.26).

3. The crosslinked polyethylene insulating material for extra-high voltage cables according to claim 1, wherein In step S1, the molar ratio of resorcinol to fatty aldehyde is 1:(1.05 - 1.3).

4. The crosslinked polyethylene insulating material for extra-high voltage cables according to claim 1, characterized in that, In step S2, the mass ratio of the white powder to β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride is 1:(2.15 - 2.35).

5. The crosslinked polyethylene insulating material for extra-high voltage cables according to claim 1, wherein In step S2, the mass ratio of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl chloride to triethylamine is 1:(0.3 - 0.4).

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