Graft-modified insulating material for high-voltage direct-current cross-linked polyethylene insulated cable and preparation method of graft-modified insulating material

Abstract

The invention discloses a grafting modified insulating material for a high-voltage direct-current cross-linked polyethylene insulated cable and a preparation method of the grafting modified insulating material, and belongs to the field of insulating layers of power transmission equipment. The problem of space charge injection and accumulation of a cable insulation layer under the action of a direct-current electric field can be effectively inhibited. According to the preparation method, dicumyl peroxide is taken as an initiator, a crosslinking reaction is initiated at high temperature and high pressure, a certain amount of polar molecular compound is grafted on a molecular chain of a crosslinked polyethylene material while the polyethylene material is crosslinked, and the preparation of the grafted crosslinked polyethylene insulating layer is completed. According to the method disclosed by the invention, the capture point of the carrier is injected, and a uniform and compact charge dot matrix is formed on the surface of the insulating layer to inhibit further injection of space charges, so that the effect of inhibiting accumulation of the space charges is achieved.

Description

Technical Field

[0001] This invention belongs to the field of insulation layers for power transmission equipment, and more specifically, relates to a grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables and its preparation method. Background Technology

[0002] Cross-linked polyethylene (XLPE) is widely used in power cable insulation due to its excellent electrical and mechanical properties and low price. However, with the construction and development of remote suburban and offshore energy centers such as wind and solar power, the long-distance transmission of power generation and loads increasingly favors high-voltage direct current (HVDC) transmission systems. If traditional AC insulation materials are still used as the insulation layer for HVDC cables, space charge accumulation is easily generated under the stress of long-term electric fields and temperature gradients, seriously threatening cable operation safety and failing to meet the requirements of higher-capacity HVDC cables. Grafting modification with polar organic molecules containing unsaturated double bonds can effectively avoid these problems. Furthermore, the molecular weight of the grafted polar molecules is generally small, and even a small amount of doping can achieve significant improvement. Organic fillers similar to the base polyethylene resin have better compatibility in the production of insulation materials / cable insulation, which is of great significance for further improving the voltage rating of HVDC cable insulation materials. Summary of the Invention

[0003] The purpose of this invention is to propose a method for preparing cross-linked polyethylene insulation material grafted with unsaturated double bonds and modified with polar organic molecules. This invention can effectively suppress the space charge injection and accumulation problem in cable insulation layers under a DC electric field. This invention achieves the mixing of polar organic molecules containing unsaturated double bonds and cross-linking agents through an impregnation process, solving the problem of quantitative mixing and addition of low-dose polar organic molecules. Simultaneously, the polar groups in the obtained grafted and modified cross-linked polyethylene serve as electrodes to inject charge carriers into the sample, forming a uniform and dense charged lattice on the surface of the insulation layer, thereby suppressing further space charge injection and achieving the effect of suppressing space charge accumulation.

[0004] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a graft-modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, extrusion and cross-linking in parts by weight: 100 parts of low-density polyethylene 0.1–1.0 parts of polar organic molecules containing unsaturated double bonds 1.0–3.0 parts of dicumyl peroxide Antioxidant 0.01 to 0.7 parts. The thermoplastic polyethylene mentioned in step one is low-density polyethylene with a melt flow rate of 1.0~2.5g / 10min (190℃, 2.16kg).

[0005] Furthermore, the low-density polyethylene is commercially available low-density polyethylene produced by high-pressure processing.

[0006] Furthermore, polar organic molecules containing unsaturated double bonds should have an unsaturated double bond structure, a polar functional group structure, and a melting point below 80°C.

[0007] Further specifying, the polar organic molecule containing unsaturated double bonds is one of methyl acrylate (MA), butyl acrylate (BA), methyl methacrylate (MMA), dimethylaminoethyl acrylate (DMAEA), N-ethylmaleimide (NEM), diethylaminoethyl methacrylate, 1-allyl-1H-indole-2,3-dione, and diacetone acrylamide.

[0008] Further specifying, the antioxidant is one of antioxidant 1010, antioxidant 1035, and antioxidant 300, or a combination of several of them in any ratio.

[0009] Another objective of this invention is to provide a method for preparing the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables.

[0010] A method for preparing a grafted modified insulation material for high-voltage direct current cross-linked polyethylene insulated cables includes the following steps: Step 1: Place low-density polyethylene and antioxidant in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then transfer to a shaking tank, add dicumyl peroxide and polar organic molecules containing unsaturated double bonds, mix evenly in the shaking tank to complete the impregnation process, and obtain a polyethylene composition; Step 3: Transfer the polyethylene composition obtained in Step 2 to a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at a certain temperature to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. Step 4: While the three-layer cable material obtained in Step 3 is being extruded, the cable conductor is wrapped in it. The three-layer cable material and the cable conductor wrapped in it pass through a cross-linking pipe with a certain pressure and temperature at a certain core running speed to obtain a high-voltage DC cable. The polyethylene composition is cross-linked in the cross-linking pipe to obtain a cross-linked polyethylene insulation layer.

[0011] Further specifying, the shaking temperature in step 2 is 80 ℃, and the mixing process is 6 hours.

[0012] Further specifying, the extrusion temperature of the three-layer co-extrusion in step 3 is 110 ℃~120 ℃.

[0013] Further specifying, the operating speed of the wire core in step 4 is 1.4 m / min to 1.6 m / min.

[0014] Further specifying, the pressure of the cross-linking pipe described in step 4 is 14 bar to 16 bar, and the temperature is 270 ℃ to 330 ℃.

[0015] The present invention has the following beneficial effects: Polyethylene materials can avoid the introduction of substances by grafting small molecule organic compounds for modification. For low-dose addition, the impregnation method makes it easier to achieve precise mixing, which has greater industrial prospects in production and manufacturing.

[0016] The cross-linked polyethylene insulating layer prepared by the method of this invention introduces polar molecules into the basic cross-linked polyethylene formulation, which are then embedded into the material via covalent bonds. This creates fixed and uniformly distributed deep traps within the material. Under the action of high-voltage direct current, the initial charge carriers in the material can be trapped to form a charged lattice, suppressing further charge injection into the insulating layer by the electrodes, improving the problem of space charge accumulation in the insulating layer, and homogenizing the electric field distortion within the insulating layer.

[0017] This invention provides a method for preparing grafted cross-linked polyethylene insulation layers for high-voltage DC cables. The method employs a chemical cross-linking approach, using dicumyl peroxide as an initiator to initiate a cross-linking reaction under high temperature and pressure. Simultaneously with the cross-linking of the polyethylene material, a certain amount of polar molecular compounds are grafted onto the molecular chains of the cross-linked polyethylene material, thus completing the preparation of the grafted cross-linked polyethylene insulation layer. The preparation method provided by this invention is simple, requires inexpensive raw materials and equipment, is suitable for large-scale production, and is compatible with current industrial cable manufacturing processes.

[0018] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0019] Figure 1 The space charge distribution of XPLE was prepared by the method in Comparative Example 1; Figure 2 The space charge distribution of XPLE-g-MA was prepared using the method described in Example 1; Figure 3 The space charge distribution of XPLE-g-MMA was prepared using the method described in Example 2; Figure 4 The space charge distribution of XPLE-g-DMAEA was prepared using the method described in Example 3; Figure 5 The space charge distribution of XPLE-g-NEM was prepared using the method described in Example 4. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0021] The low-density polyethylene described below is commercially available low-density polyethylene produced by the high-pressure process, specifically 2220H, manufactured by Yangzi Petrochemical-BASF Co., Ltd.

[0022] Example 1: This embodiment uses grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, impregnation, extrusion and cross-linking: 100 parts of low-density polyethylene 0.3 parts methyl acrylate 1.8 parts of dicumyl peroxide Antioxidant 10100.3 parts.

[0023] The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this embodiment is carried out according to the following steps: Step 1: Place low-density polyethylene and antioxidant 1010 in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then add dicumyl peroxide and methyl acrylate to a shaking tank, mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, realize the mixing of materials, and obtain a polyethylene composition. Step 3: Place the polyethylene composition obtained in Step 2 into a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at 120 °C to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. In steps 4 and 3, the three-layer cable material obtained is extruded while the cable conductor is wrapped within it. The three-layer cable material and the cable conductor wrapped within it pass through a cross-linking pipe with a core running speed of 1.5 m / min and a pressure of 16 bar and a temperature of 300 ℃ to obtain a high-voltage DC cable. The polyethylene composition is cross-linked within the cross-linking pipe to obtain a grafted cross-linked polyethylene insulation layer (XPLE-g-MA).

[0024] Example 2: This embodiment uses grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, impregnation, extrusion and cross-linking: 100 parts of low-density polyethylene 0.4 parts of methyl methacrylate 1.8 parts of dicumyl peroxide Antioxidant 10100.3 parts.

[0025] The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this embodiment is carried out according to the following steps: Step 1: Mix low-density polyethylene and antioxidant 1010 uniformly in a parallel twin-screw extruder at a temperature of 190°C, and then pelletize. Step 2: Then add dicumyl peroxide and methyl methacrylate to a shaking tank, mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, realize the mixing of materials, and obtain a polyethylene composition. Step 3: Place the polyethylene composition obtained in Step 2 into a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at 120 °C to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. In steps 4 and 3, the three-layer cable material obtained is extruded while the cable conductor is wrapped within it. The three-layer cable material and the cable conductor wrapped within it pass through a cross-linking pipe with a core running speed of 1.5 m / min and a pressure of 16 bar and a temperature of 300 ℃ to obtain a high-voltage DC cable. The polyethylene composition is cross-linked within the cross-linking pipe to obtain a grafted cross-linked polyethylene insulation layer (XPLE-g-MMA).

[0026] Example 3: This embodiment uses grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, impregnation, extrusion and cross-linking: 100 parts of low-density polyethylene 0.3 parts dimethylaminoethyl acrylate 1.8 parts of dicumyl peroxide Antioxidant 10100.3 parts.

[0027] The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this embodiment is carried out according to the following steps: Step 1: Place low-density polyethylene and antioxidant 1010 in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then add dicumyl peroxide and dimethylaminoethyl acrylate to a shaking tank, and mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, thereby achieving the mixing of materials and obtaining a polyethylene composition. Step 3: Place the polyethylene composition obtained in Step 2 into a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at 120 °C to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. In steps 4 and 3, the three-layer cable material obtained is extruded while the cable conductor is wrapped within it. The three-layer cable material and the cable conductor wrapped within it pass through a cross-linking pipe with a core running speed of 1.5 m / min and a pressure of 16 bar and a temperature of 300 ℃ to obtain a high-voltage DC cable. The polyethylene composition is cross-linked within the cross-linking pipe to obtain a grafted cross-linked polyethylene insulation layer (XPLE-g-DMAEA).

[0028] Example 4: This embodiment uses grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, impregnation, extrusion and cross-linking: 100 parts of low-density polyethylene 0.3 parts of N-ethylmaleimide 1.8 parts of dicumyl peroxide Antioxidant 10100.3 parts.

[0029] The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this embodiment is carried out according to the following steps: Step 1: Place low-density polyethylene and antioxidant 1010 in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then add it to the shaking tank, add dicumyl peroxide and N-ethylmaleimide, and mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, realize the mixing of materials, and obtain a polyethylene composition. Step 3: Place the polyethylene composition obtained in Step 2 into a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at 120 °C to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. In steps 4 and 3, the three-layer cable material obtained is extruded while the cable conductor is wrapped within it. The three-layer cable material and the cable conductor wrapped within it pass through a cross-linking pipe with a core running speed of 1.5 m / min and a pressure of 16 bar and a temperature of 300 ℃ to obtain a high-voltage DC cable. The polyethylene composition is cross-linked within the cross-linking pipe to obtain a grafted cross-linked polyethylene insulation layer (XPLE-g-NEM).

[0030] Example 5: This embodiment uses grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, impregnation, extrusion and cross-linking: 100 parts of low-density polyethylene 0.3 parts of diethylaminoethyl methacrylate 1.8 parts of dicumyl peroxide Antioxidant 10100.3 parts.

[0031] The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this embodiment is carried out according to the following steps: Step 1: Place low-density polyethylene and antioxidant 1010 in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then add dicumyl peroxide and diethylamino methacrylate to a shaking tank, mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, realize the mixing of materials, and obtain a polyethylene composition. Step 3: Place the polyethylene composition obtained in Step 2 into a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at 110 °C to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. In steps 4 and 3, the three-layer cable material obtained is extruded while the cable conductor is wrapped in it. The three-layer cable material and the cable conductor wrapped in it run together through a cross-linking pipe with a core speed of 1.6 m / min and a pressure of 16 bar and a temperature of 270 ℃ to obtain a high-voltage DC cable. The polyethylene composition is cross-linked in the cross-linking pipe to obtain a grafted cross-linked polyethylene insulation layer.

[0032] Example 6: This embodiment uses grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, which is made from the following raw materials by melt blending, impregnation, extrusion and cross-linking: 100 parts of low-density polyethylene 0.3 parts of 1-allyl-1H-indole-2,3-dione 1.8 parts of dicumyl peroxide Antioxidant 10100.3 parts.

[0033] The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this embodiment is carried out according to the following steps: Step 1: Place low-density polyethylene and antioxidant 1010 in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then add dicumyl peroxide and 1-allyl-1H-indole-2,3-dione to a shaking tank, mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, realize the mixing of materials, and obtain a polyethylene composition. Step 3: Place the polyethylene composition obtained in Step 2 into a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at 120 °C to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. In steps 4 and 3, the three-layer cable material obtained is extruded while the cable conductor is wrapped in it. The three-layer cable material and the cable conductor wrapped in it run together through a cross-linking pipe with a pressure of 16 bar and a temperature of 300 °C at a core running speed of 1.5 m / min to obtain a high-voltage DC cable. The polyethylene composition is cross-linked in the cross-linking pipe to obtain a grafted cross-linked polyethylene insulation layer.

[0034] Comparative Example 1: The preparation method of the grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables described in this comparative example is carried out according to the following steps: 1. Low-density polyethylene and antioxidant 1010 are uniformly mixed in the following weight proportions in a parallel twin-screw extruder at a temperature of 190°C, and then pelletized to obtain polyethylene particles containing antioxidant. 100 parts of low-density polyethylene Antioxidant 10100.3 parts; 2. Add the antioxidant-containing polyethylene particles obtained in step 1 to a shaking tank, add dicumyl peroxide in the following weight proportions, and mix evenly in the shaking tank at 80°C for 6 hours to complete the impregnation process, thereby achieving material blending and obtaining a polyethylene composition: 100 parts of polyethylene particles containing antioxidants 1.8 parts of dicumyl peroxide; 3. The polyethylene composition obtained in step 2 is placed in a three-layer co-extrusion cable extruder, and the polyethylene composition is used as the insulation material. It is co-extruded with the shielding material at 120 °C to obtain a three-layer cable material composed of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. Fourth, while the three-layer cable material obtained in step three is being extruded, the cable conductor is wrapped within it. The three-layer cable material and the cable conductor it wraps together pass through a cross-linking pipe with a core running speed of 1.5 m / min and a pressure of 16 bar and a temperature of 300°C to obtain a high-voltage DC cable. The polyethylene composition is cross-linked within the cross-linking pipe to obtain a cross-linked polyethylene insulation layer (XPLE).

[0035] Samples were taken from the cross-linked polyethylene insulation layers prepared in Examples 1, 2, 3, 4 and Comparative Example 1, respectively, for space charge distribution testing. The test was conducted using the pulse electroacoustic (PEA) method at a temperature of 80°C, with the sample subjected to a DC electric field of 40 kV / mm for 30 min for polarization.

[0036] The horizontal axis represents the thickness of the test sample (μm), and the vertical axis represents the space charge density (C·m). -3 It can be seen that a large amount of negative space charge, approximately 5.8 C·m, ​​exists inside the XLPE sample during the pressurization process. -3 The space charge of the other three grafted modified materials was suppressed to varying degrees, and the space charge within the samples of the grafted modified materials at the final pressure point was less than 2 C·m. -3 In particular, the XLPE-g-DMAEA material exhibits a significant space charge shielding layer, inhibiting further charge injection into the sample. Space charge test results demonstrate that XLPE materials grafted with modified polar molecules can effectively suppress space charge accumulation and migration under long-term DC electric fields.

Claims

1. A grafted modified insulation material for high-voltage DC cross-linked polyethylene insulated cables, characterized in that, It is made from the following raw materials in parts by weight through melt blending, extrusion and crosslinking: 100 parts of low-density polyethylene 0.1–1.0 parts of polar organic molecules containing unsaturated double bonds 1.0–3.0 parts of dicumyl peroxide Antioxidant 0.01 to 0.7 parts. The thermoplastic polyethylene mentioned in step one is low-density polyethylene with a melt flow rate of 1.0~2.5g / 10min (190℃, 2.16kg).

2. The insulating material according to claim 1, characterized in that, The low-density polyethylene is commercially available low-density polyethylene produced by high-pressure processing.

3. The insulating material according to claim 1, characterized in that, Polar organic molecules containing unsaturated double bonds should have an unsaturated double bond structure, a polar functional group structure, and a melting point below 80℃.

4. The insulating material according to claim 1, characterized in that, The polar organic molecule containing unsaturated double bonds is one of the following: methyl acrylate (MA), butyl acrylate (BA), methyl methacrylate (MMA), dimethylaminoethyl acrylate (DMAEA), N-ethylmaleimide (NEM), diethylaminoethyl methacrylate, 1-allyl-1H-indole-2,3-dione, and diacetone acrylamide.

5. The insulating material according to claim 1, characterized in that, The antioxidant is one or more of antioxidant 1010, antioxidant 1035, and antioxidant 300.

6. The method for preparing the insulating material according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Place low-density polyethylene and antioxidant in a parallel twin-screw extruder, mix them uniformly at 190°C, and then pelletize them. Step 2: Then transfer to a shaking tank, add dicumyl peroxide and polar organic molecules containing unsaturated double bonds, mix evenly in the shaking tank to complete the impregnation process, and obtain a polyethylene composition; Step 3: Transfer the polyethylene composition obtained in Step 2 to a three-layer co-extrusion cable extruder, and use the polyethylene composition as the insulation material. Co-extrude it and the shielding material at a certain temperature to obtain a three-layer cable material consisting of an outer shielding layer, a polyethylene composition insulation layer, and an inner shielding layer. Step 4: While the three-layer cable material obtained in Step 3 is being extruded, the cable conductor is wrapped in it. The three-layer cable material and the cable conductor wrapped in it pass through a cross-linking pipe with a certain pressure and temperature at a certain core running speed to obtain a high-voltage DC cable. The polyethylene composition is cross-linked in the cross-linking pipe to obtain a cross-linked polyethylene insulation layer.

7. The method according to claim 6, characterized in that, The shaking temperature in step 2 is 80 ℃, and the mixing process takes 6 hours.

8. The method according to claim 6, characterized in that, The extrusion temperature of the three-layer co-extrusion in step 3 is 110 ℃~120 ℃.

9. The method according to claim 6, characterized in that, The operating speed of the wire core in step 4 is 1.4 m / min to 1.6 m / min.

10. The method according to claim 6, characterized in that, The pressure of the cross-linked pipe described in step 4 is 14 bar to 16 bar, and the temperature is 270 ℃ to 330 ℃.

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