A 35KV cross-linked polyethylene insulated power cable and its preparation method

Abstract

The present invention discloses a 35KV cross-linked polyethylene insulated power cable and a preparation method thereof. The 35KV cross-linked polyethylene insulated power cable comprises, from the inside out, a conductor, a first semi-conductive layer, a cross-linked polyethylene insulation layer, a second semi-conductive layer, a copper tape shielding layer, a hollow aluminum column protective layer, a rubber protective layer, a non-magnetic metal tape armor layer, and a PVC protective sleeve. The preparation method comprises the following steps: S1, preparation of a cross-linked polyethylene base material; S2, preparation of a PVC protective sleeve base material; S3, three-layer co-extrusion fully enclosed cross-linking; S4, protective layer coating; S5, molding. The present invention adds a semi-conductive layer to the outside of the conductor, so that a smooth interface is formed between the cross-linked polyethylene insulation layer and the high voltage potential and the low voltage potential. By adding a protective layer to the outside of the semi-conductive layer, the cable can be effectively prevented from being deformed by external forces, and the shear force and pressure on the cable can be effectively unloaded.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene cables, in particular to a 35KV cross-linked polyethylene insulated power cable and a preparation method thereof. Background Art

[0002] Cross-linked polyethylene insulated power cables generally use chemical or physical methods to transform polyethylene molecules from a linear molecular structure to a three-dimensional network structure, and from thermoplastic polyethylene to thermosetting cross-linked polyethylene, thereby improving the wear resistance, high temperature resistance, aging resistance and other properties of cross-linked polyethylene insulated power cables.

[0003] Whether conventional cables or cross-linked polyethylene (XLPE) insulated power cables, they all require an insulation layer. The rapid development of the domestic cable industry has created broad market prospects for cable insulation materials in my country. High-voltage and environmentally friendly cable materials are particularly in high demand. Taking the supply specifications for 35kV cables as an example, the production of each kilometer of 35kV cable requires approximately 3-4 tons of insulation material, with a total demand exceeding 300kt. Currently, domestic production capacity for 10-35kV cross-linked polyethylene (XLPE) insulated cables is substantial, with over 100 production lines operating, most of which utilize chemical cross-linking. The majority of these production lines are foreign, but these lines are often the same company's products. Few domestic companies independently develop cross-linked polyethylene (XLPE) insulated power cables, and the current domestically developed 35kV XLPE insulated power cables still lag significantly behind foreign products.

[0004] The difficulty of the research lies in the cross-linking method of polyethylene. The more commonly used cross-linking methods are radiation cross-linking, peroxide cross-linking and silane cross-linking. How to select a suitable cross-linking method and optimize and improve it is a problem that needs to be considered at present. Summary of the Invention

[0005] In response to the above-mentioned problems, the present invention provides a 35KV cross-linked polyethylene insulated power cable and a preparation method thereof.

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

[0007] A 35KV cross-linked polyethylene insulated power cable, comprising, from the inside out, a conductor, a first semi-conductive layer, a cross-linked polyethylene insulation layer, a second semi-conductive layer, a copper tape shielding layer, a hollow aluminum column protective layer, a rubber protective layer, a non-magnetic metal tape armor layer, and a PVC protective sheath;

[0008] The hollow aluminum column protective layer is formed by a number of closely arranged hexagonal hollow aluminum columns, and one side surface of two adjacent hexagonal hollow aluminum columns is adhered to each other and movably connected by a connecting assembly. The connecting assembly is a number of groups arranged at intervals in the hexagonal hollow aluminum columns, and the connecting assembly includes a first support plate, a second support plate and a connecting plate connecting the first support plate and the second support plate. The connecting plate is slidably connected to the first support plate, and the connecting plate is fixedly connected to the middle of the second support plate. The first support plate and the second support plate are respectively fixedly arranged on the inner walls of two adjacent hexagonal hollow aluminum columns. A first slot for the connecting plate to pass through is provided on the side surface of a hexagonal hollow aluminum column where the first support plate is located, and a second slot for the connecting plate to pass through and rotate is provided on the side surface of a hexagonal hollow aluminum column where the second support plate is located.

[0009] Furthermore, the thickness of the second support plate is 30% to 40% of the thickness of the first support plate, the lengths of the first support plate, the second support plate and the connecting plate are all 3 to 4 times the radius of the circumscribed circle of the hexagonal hollow aluminum column, and the spacing between two adjacent groups of connecting components is 2 to 3 times the length of the connecting plate.

[0010] Note: By optimizing the thickness of the first support plate, the second support plate, and the length of the first support plate, the second support plate, and the connecting plate, the cable can be effectively prevented from being deformed by external forces while ensuring the overall structural stability of the hollow aluminum column protective layer. The shear force and pressure on the cable can be effectively unloaded, and the manufacturing cost can be saved to the greatest extent by selecting less materials.

[0011] Furthermore, the first support plate is made of aluminum alloy, the second support plate is made of phosphor bronze, the first semi-conductive layer is made of acetylene black, the second semi-conductive layer is made of furnace black, and the non-magnetic metal belt armor layer is made of stainless steel.

[0012] Note: By selecting elastic phosphor bronze as the material of the second support plate, the second support plate can be deformed to a certain extent, thereby improving the shear resistance of the cable when subjected to shear stress.

[0013] Furthermore, the connecting plate is slidably connected to the slide groove provided in the middle of the first support plate through a slider, and limit plates are provided at the upper and lower ends of the slider. Limit grooves for docking with the limit plates are provided at the upper and lower ends of the slide groove. The length of the slider is 15% to 30% of the length of the connecting plate, and the width of the slide groove is 60% to 75% of the width of the first support plate.

[0014] Note: The arrangement of the slider and the slide groove enables relative sliding between the connecting plate and the first support plate, thereby further improving the pressure resistance of the cable.

[0015] Furthermore, the cross section of the first slot is rectangular, the cross section of the second slot is an isosceles trapezoid, and the angle between the second slot and the connecting plate is 30° to 60°.

[0016] Note: The cross-sectional shape of the first slot and the second slot can cooperate with the second support plate to complete deformation and cooperate with the slider and the slide groove to complete relative sliding.

[0017] The method for preparing a 35KV cross-linked polyethylene insulated power cable as described in any one of the above comprises the following steps:

[0018] S1. Preparation of a cross-linked polyethylene base material: 75-85 parts by weight of polyethylene, 0.3-2 parts by weight of a cross-linking agent, 0.05-1 parts by weight of a cross-linking aid, and 0.05-0.1 parts by weight of a stabilizer are mixed, and the mixture is stirred at 150-160° C. for 1-2 hours at a stirring speed of 700-800 rpm. Subsequently, the temperature is lowered to 40-50° C., 0.3-0.5 parts by weight of carboxylated single-walled carbon nanotubes are added, and stirring is continued for 1-2 hours at a stirring speed of 1000-1200 rpm to obtain a cross-linked polyethylene base material;

[0019] S2. Preparation of PVC protective cover base material: 45-50 parts by weight of PVC resin, 1-2 parts by weight of antioxidant, 0.5-1 parts by weight of stabilizer, and 0.2-0.4 parts by weight of plasticizer are mixed, and stirred at 110-120° C. for 1-2 hours at a stirring speed of 400-500 rpm to obtain the PVC protective cover base material;

[0020] S3, three-layer co-extrusion fully enclosed crosslinking: Under vacuum sealing conditions, acetylene black, the cross-linked polyethylene base material obtained in step S1, and furnace carbon black are extruded and coated on the outside of the wire through a three-layer co-extrusion die head of a screw extruder, wherein the extrusion thickness of the acetylene black is 0.5-0.7 mm, the extrusion thickness of the cross-linked polyethylene base material is 2.3-3.22 mm, and the extrusion thickness of the furnace carbon black is 0.5-0.7 mm, to form a first semiconductive layer, a cross-linked polyethylene insulating layer, and a second semiconductive layer;

[0021] S4. Protective layer coating: First, prefabricate the hollow aluminum column protective layer, arrange the hexagonal hollow aluminum columns in sequence, install the connection assembly between two adjacent hexagonal hollow aluminum columns, then wrap copper tape around the outside of the second semi-conductive layer to obtain a copper tape shielding layer, install the prefabricated hollow aluminum column protective layer outside the copper tape shielding layer, extrude a rubber protective layer outside the hollow aluminum column protective layer, and wrap a stainless steel tape around the rubber protective layer to obtain a non-magnetic metal tape armor layer;

[0022] S5. Molding: Extruding the PVC protective cover base material obtained in step S2 outside the non-magnetic metal tape armor layer to produce a PVC protective cover.

[0023] Furthermore, the crosslinking agent in step S1 is 2,5-dimethyl-2,5-di-tert-butyl peroxide hexane or diisopropylbenzene hydroperoxide, the crosslinking aid is trimethylolpropane trimethacrylate, the stabilizers in steps S1 and S2 are both free radical inhibitors, the antioxidant in step S2 is bisphenol A, and the plasticizer is diisodecyl phthalate.

[0024] Description: By further limiting the cross-linking agent, cross-linking auxiliary agent, stabilizer, antioxidant and plasticizer, the prepared cross-linked polyethylene base material and PVC protective cover base material are made more stable.

[0025] Furthermore, the preparation method of carboxylated single-walled carbon nanotubes in step S1 is: dissolving 4 to 5 parts by weight of single-walled carbon nanotubes in 25 to 28 parts by weight of deionized water, adding 1 to 2 parts by weight of a 50% hydrobromic acid solution, stirring for 10 to 15 minutes at a stirring speed of 500 to 750 rpm, adding a 90% oxalic acid solution, continuing to stir for 6 to 8 hours at a stirring speed of 750 to 1000 rpm, filtering and washing three times with deionized water to obtain carboxylated single-walled carbon nanotubes.

[0026] Description: By adding carboxylated single-walled carbon nanotubes to the cross-linked polyethylene base material, the flame retardant effect of the cable can be further improved. The preparation method of carboxylated single-walled carbon nanotubes has been optimized, which can improve the compatibility between carboxylated single-walled carbon nanotubes and the cross-linked polyethylene base material and enable a stable mixture of the two.

[0027] Furthermore, in step S3, the thickness relationship between the first semiconductive layer, the cross-linked polyethylene insulating layer, and the second semiconductive layer is determined according to the following formula:

[0028] H1+H2=2.3H0

[0029] Wherein, H1 is the thickness of the first semiconducting layer, H2 is the thickness of the second semiconducting layer, and H0 is the thickness of the cross-linked polyethylene insulation layer;

[0030] The value of H0 is determined by the following formula:

[0031]

[0032] Wherein, L is the length of the metering section of the extruder, p is the pressure of the cross-linked polyethylene base material melt, D is the screw diameter, H is the screw groove depth, is the helix angle, η is the viscosity of the cross-linked polyethylene base material melt, and Q is the extrusion pressure.

[0033] Description: By optimizing and adjusting the thickness relationship between the first semiconductive layer, the cross-linked polyethylene insulation layer, and the second semiconductive layer, and correlating them with the metering section length and extrusion pressure of the extruder, the first and second semiconductive layers form equipotentials with the conductor and the copper tape shielding layer, respectively, so that a smooth interface is formed between the cross-linked polyethylene insulation layer and the high voltage potential and the low voltage potential, thereby eliminating burrs or protrusions on the surface of the metal conductor, uniforming the interface electric field distribution, suppressing excessive local field strength, and preventing partial discharge.

[0034] The beneficial effects of the present invention are:

[0035] (1) The cross-linked polyethylene insulated power cable of the present invention forms a smooth interface between the cross-linked polyethylene insulation layer and the high voltage potential and the low voltage potential by adding a semi-conductive layer to the outside of the conductor, thereby eliminating burrs or protrusions on the surface of the metal conductor, uniforming the interface electric field distribution, suppressing excessive local field strength, and preventing local discharge; and by adding a protective layer to the outside of the semi-conductive layer, the overall structure of the hollow aluminum column protective layer is ensured to be stable, and the cable can be effectively prevented from being deformed by external forces, and the shear force and pressure on the cable can be effectively unloaded, and the manufacturing cost can be saved to the greatest extent by selecting fewer materials.

[0036] (2) The cross-linked polyethylene insulated power cable of the present invention uses elastic phosphor bronze as the material of the second support plate, which enables the second support plate to complete a certain degree of deformation, thereby improving the shear resistance of the cable when subjected to shear stress; and the setting of the slider and the slide groove enables relative sliding between the connecting plate and the first support plate, thereby further improving the pressure resistance of the cable.

[0037] (3) The preparation method of the cross-linked polyethylene insulated power cable of the present invention further limits the cross-linking agent, cross-linking aid, stabilizer, antioxidant and plasticizer, thereby making the prepared cross-linked polyethylene base material and PVC protective sheath base material more stable; by adding carboxylated single-walled carbon nanotubes to the cross-linked polyethylene base material, the flame retardant effect of the cable can be further improved, and the preparation method of the carboxylated single-walled carbon nanotubes is optimized, which can improve the compatibility between the carboxylated single-walled carbon nanotubes and the cross-linked polyethylene base material, so that the two can be stably mixed; by optimizing and adjusting the thickness relationship between the first semi-conductive layer, the cross-linked polyethylene insulation layer and the second semi-conductive layer, and correlating them with the metering section length and extrusion pressure of the extruder, the first and second semi-conductive layers form equipotentials with the conductor and the copper tape shielding layer, respectively, so that a smooth interface is formed between the cross-linked polyethylene insulation layer and the high voltage potential and the low voltage potential, which plays a role in eliminating burrs or protrusions on the surface of the metal conductor, uniforming the interface electric field distribution, suppressing excessive local field strength, and preventing local discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1This is a schematic diagram of the internal structure of the cross-linked polyethylene insulated power cable of the present invention;

[0039] Figure 2 This is a schematic diagram of the connection structure of the protective layer of the hollow aluminum column of the cross-linked polyethylene insulated power cable of the present invention;

[0040] Figure 3 This is a schematic diagram of the internal structure of the hexagonal hollow aluminum column of the cross-linked polyethylene insulated power cable of the present invention;

[0041] Figure 4 This is a schematic diagram of the internal structure of the cross-linked polyethylene insulated power cable of the present invention when the hexagonal hollow aluminum column deflects up and down;

[0042] Figure 5 This is a schematic diagram of the internal structure of the cross-linked polyethylene insulated power cable of the present invention when the hexagonal hollow aluminum column deviates left and right;

[0043] Figure 6 This is a schematic diagram of the connection structure between the hexagonal hollow aluminum column slider and the slide groove of the cross-linked polyethylene insulated power cable of the present invention;

[0044] Figure 7 The present invention is a flow chart of a method for preparing a cross-linked polyethylene insulated power cable.

[0045] Among them, 1-conductor, 2-first semi-conductive layer, 3-cross-linked polyethylene insulation layer, 4-second semi-conductive layer, 5-copper tape shielding layer, 6-hollow aluminum column protective layer, 61-hexagonal hollow aluminum column, 62-first support plate, 621-first slot, 622-slide groove, 623-limiting slot, 63-second support plate, 631-second slot, 64-connecting plate, 65-slider, 651-limiting plate, 7-rubber protective layer, 8-non-magnetic metal tape armor layer, 9-PVC protective layer. DETAILED DESCRIPTION

[0046] Example 1

[0047] like Figure 1 As shown, a 35KV cross-linked polyethylene insulated power cable comprises, from the inside out, a conductor 1, a first semi-conductive layer 2, a cross-linked polyethylene insulation layer 3, a second semi-conductive layer 4, a copper tape shielding layer 5, a hollow aluminum column protective layer 6, a rubber protective layer 7, a non-magnetic metal tape armor layer 8, and a PVC protective sheath 9;

[0048] like Figure 2 、 3As shown, the hollow aluminum column protective layer 6 is composed of a number of hexagonal hollow aluminum columns 61 arranged closely, and one side of two adjacent hexagonal hollow aluminum columns 61 is attached to each other and can be movably connected through a connecting component. The specific movable connection method is: the vertical sliding of the two adjacent hexagonal hollow aluminum columns 61 when they are subjected to vertical extrusion deformation, and the opposite displacement of the two adjacent hexagonal hollow aluminum columns 61 when they are subjected to shear stress deformation; the connecting component is a number of groups of spaced apart sets in the hexagonal hollow aluminum columns 61, and the connecting component includes a first support plate 62, a second support plate 63 and a connecting plate. A connecting plate 64 is connected to the first support plate 62 and the second support plate 63. The connecting plate 64 is slidably connected to the first support plate 62 and fixedly connected to the middle of the second support plate 63. The first support plate 62 and the second support plate 63 are respectively fixedly arranged on the inner walls of two adjacent hexagonal hollow aluminum columns 61. A first slot 621 for passing the connecting plate 64 is provided on the side of one of the hexagonal hollow aluminum columns 61 where the first support plate 62 is located. A second slot 631 is provided on the side of one of the hexagonal hollow aluminum columns 61 where the second support plate 63 is located for passing the connecting plate 64 and rotating.

[0049] like Figures 3-5 As shown, the thickness of the second support plate 63 is 35% of the thickness of the first support plate 62. The lengths of the first support plate 62, the second support plate 63, and the connecting plate 64 are all 3.5 times the radius of the circumscribed circle of the hexagonal hollow aluminum column 61. The spacing between two adjacent groups of connecting components is 2.5 times the length of the connecting plate 64. The first support plate 62 is made of aluminum alloy, the second support plate 63 is made of phosphor bronze, the first semi-conductive layer 2 is made of acetylene black, the second semi-conductive layer 4 is made of furnace carbon black, and the non-magnetic metal tape armor layer 8 is made of stainless steel.

[0050] like Figures 3 to 6 As shown, the connecting plate 64 is slidably connected to the slide groove 622 provided in the middle of the first support plate 62 through the slider 65, and the upper and lower ends of the slider 65 are provided with limit plates 651. The upper and lower ends of the slide groove 622 are provided with limit grooves 623 for docking with the limit plates 651. The length of the slider 65 is 24% of the length of the connecting plate 64, and the width of the slide groove 622 is 67% of the width of the first support plate 62. The cross-section of the first slot 621 is rectangular, and the cross-section of the second slot 631 is an isosceles trapezoid. The angle between the second slot 631 and the connecting plate 64 is 45°.

[0051] Example 2

[0052] This embodiment differs from embodiment 1 in that:

[0053] The thickness of the second support plate 63 is 30% of the thickness of the first support plate 62. The lengths of the first support plate 62, the second support plate 63, and the connecting plate 64 are all three times the radius of the circumscribed circle of the hexagonal hollow aluminum column 61. The spacing between two adjacent sets of connecting components is twice the length of the connecting plate 64. The first support plate 62 is made of aluminum alloy, the second support plate 63 is made of phosphor bronze, the first semi-conductive layer 2 is made of acetylene black, the second semi-conductive layer 4 is made of furnace carbon black, and the non-magnetic metal tape armor layer 8 is made of stainless steel.

[0054] The connecting plate 64 is slidably connected to the slide groove 622 provided in the middle of the first support plate 62 through the slider 65. The slider 65 is provided with a limit plate 651 at both the upper and lower ends. The slide groove 622 is provided with a limit groove 623 at both the upper and lower ends for docking with the limit plate 651. The length of the slider 65 is 15% of the length of the connecting plate 64, and the width of the slide groove 622 is 60% of the width of the first support plate 62. The cross-section of the first slot 621 is rectangular, and the cross-section of the second slot 631 is an isosceles trapezoid. The angle between the second slot 631 and the connecting plate 64 is 30°.

[0055] Example 3

[0056] This embodiment differs from embodiment 1 in that:

[0057] The thickness of the second support plate 63 is 40% of the thickness of the first support plate 62. The lengths of the first support plate 62, the second support plate 63, and the connecting plate 64 are all four times the radius of the circumscribed circle of the hexagonal hollow aluminum column 61. The spacing between two adjacent sets of connecting components is three times the length of the connecting plate 64. The first support plate 62 is made of aluminum alloy, the second support plate 63 is made of phosphor bronze, the first semiconductive layer 2 is made of acetylene black, the second semiconductive layer 4 is made of furnace carbon black, and the non-magnetic metal tape armor layer 8 is made of stainless steel.

[0058] The connecting plate 64 is slidably connected to the slide groove 622 provided in the middle of the first support plate 62 through the slider 65. The slider 65 is provided with a limit plate 651 at both the upper and lower ends. The slide groove 622 is provided with a limit groove 623 at both the upper and lower ends for docking with the limit plate 651. The length of the slider 65 is 30% of the length of the connecting plate 64, and the width of the slide groove 622 is 75% of the width of the first support plate 62. The cross-section of the first slot 621 is rectangular, and the cross-section of the second slot 631 is an isosceles trapezoid. The angle between the second slot 631 and the connecting plate 64 is 60°.

[0059] Working principle:

[0060] The following briefly describes the working principle of the protection mode of the hollow aluminum column protective layer 6 for power cables of the present invention.

[0061] When the power cable is in use, when it is subjected to vertical extrusion deformation, the rubber protective layer 7 squeezes the hollow aluminum column protective layer 6, such as Figure 4 As shown, at this time, the slider 65 slides inside the slide groove 622, and the limit plate 651 slides inside the limit groove 623, thereby causing the connecting plate 64 to slide inside the first slot 621, and the two hexagonal hollow aluminum columns 61 slide relative to each other, thereby offsetting the extrusion force;

[0062] When the power cable is deformed by shear stress, the rubber protective layer 7 squeezes the hollow aluminum column protective layer 6, such as Figure 5 As shown, at this time, the two hexagonal hollow aluminum columns 61 are offset, and the connecting plate 64 pulls the second support plate 63 to deform the second support plate 63, thereby offsetting the shear stress. When the shear stress is eliminated, the second support plate 63 is reset, and the two hexagonal hollow aluminum columns 61 are reset at the same time and restored to their original state.

[0063] Example 4

[0064] This embodiment is a method for preparing a 35KV cross-linked polyethylene insulated power cable in Example 1, comprising the following steps:

[0065] S1. Preparation of cross-linked polyethylene base material: 80 parts by weight of polyethylene, 1 part by weight of a cross-linking agent, 0.5 parts by weight of a cross-linking aid, and 0.5 parts by weight of a stabilizer are mixed, and the mixture is stirred at 155° C. for 1.5 hours at a stirring speed of 750 rpm. Subsequently, the temperature is lowered to 45° C., 0.4 parts by weight of carboxylated single-walled carbon nanotubes are added, and the mixture is stirred for 1.5 hours at a stirring speed of 1100 rpm to obtain a cross-linked polyethylene base material, wherein the cross-linking agent is 2,5-dimethyl-2,5-di-tert-butylperoxide hexane or diisopropylbenzene hydroperoxide, the cross-linking aid is trimethylolpropane trimethacrylate, and the stabilizers are all free radical inhibitors;

[0066] The preparation method of carboxylated single-walled carbon nanotubes is as follows: 4.5 parts by weight of single-walled carbon nanotubes are dissolved in 26 parts by weight of deionized water, 1.5 parts by weight of a 50% hydrobromic acid solution is added, and the mixture is stirred for 12 minutes at a stirring speed of 600 rpm. A 90% oxalic acid solution is added, and the mixture is stirred for 7 hours at a stirring speed of 800 rpm. After filtration, the mixture is washed three times with deionized water to obtain carboxylated single-walled carbon nanotubes.

[0067] S2. Preparation of PVC protective cover base material: 48 parts by weight of PVC resin, 1.5 parts by weight of antioxidant, 0.7 parts by weight of stabilizer, and 0.3 parts by weight of plasticizer were mixed, and stirred at 115° C. for 1.5 hours at a stirring speed of 450 rpm to obtain the PVC protective cover base material. The stabilizers were all free radical inhibitors, the antioxidant was bisphenol A, and the plasticizer was diisodecyl phthalate.

[0068] S3, three-layer co-extrusion fully enclosed crosslinking: Under vacuum sealing conditions, acetylene black, the cross-linked polyethylene base material obtained in step S1, and furnace carbon black are extruded and coated on the outside of the wire 1 through the three-layer co-extrusion die head of a screw extruder. The extrusion thickness of the acetylene black is 0.6 mm, the extrusion thickness of the cross-linked polyethylene base material is 2.76 mm, and the extrusion thickness of the furnace carbon black is 0.6 mm, forming a first semiconductive layer 2, a cross-linked polyethylene insulating layer 3, and a second semiconductive layer 4;

[0069] The thickness relationship between the first semiconductive layer 2, the cross-linked polyethylene insulating layer 3 and the second semiconductive layer 4 is determined according to the following formula:

[0070] H1+H2=2.3H0

[0071] Wherein, H1 is the thickness of the first semiconducting layer 2, H2 is the thickness of the second semiconducting layer 4, and H0 is the thickness of the cross-linked polyethylene insulation layer 3;

[0072] The value of H0 is determined by the following formula:

[0073]

[0074] Wherein, L is the length of the metering section of the extruder, p is the pressure of the cross-linked polyethylene base material melt, D is the screw diameter, H is the screw groove depth, is the helix angle, η is the viscosity of the cross-linked polyethylene base material melt, and Q is the extrusion pressure;

[0075] S4. Protective layer coating: First, prefabricate the hollow aluminum column protective layer 6, arrange 30 hexagonal hollow aluminum columns 61 in sequence, install a connection assembly between two adjacent hexagonal hollow aluminum columns 61, then wrap copper tape around the outside of the second semi-conductive layer 4 to obtain a copper tape shielding layer 5, install the prefabricated hollow aluminum column protective layer 6 on the outside of the copper tape shielding layer 5, extrude a rubber protective layer 7 on the outside of the hollow aluminum column protective layer 6, and wrap a stainless steel tape around the outside of the rubber protective layer 7 to obtain a non-magnetic metal tape armor layer 8;

[0076] S5. Molding: The PVC protective sheath base material obtained in step S2 is extruded onto the outside of the non-magnetic metal tape armor layer 8 to produce a PVC protective sheath 9.

[0077] Example 5

[0078] This embodiment differs from embodiment 1 in that:

[0079] The method parameters in step S1 are different.

[0080] S1. Preparation of cross-linked polyethylene base material: 75 parts by weight of polyethylene, 0.3 parts by weight of a cross-linking agent, 0.05 parts by weight of a cross-linking aid, and 0.05 parts by weight of a stabilizer were mixed, and the mixture was stirred at 150° C. for 1 h at a stirring speed of 700 rpm. The temperature was then lowered to 40° C., 0.3 parts by weight of carboxylated single-walled carbon nanotubes were added, and the mixture was stirred for 1 h at a stirring speed of 1000 rpm to obtain a cross-linked polyethylene base material, wherein the cross-linking agent was 2,5-dimethyl-2,5-di-tert-butylperoxide hexane or diisopropylbenzene hydroperoxide, the cross-linking aid was trimethylolpropane trimethacrylate, and the stabilizers were all free radical inhibitors;

[0081] The preparation method of carboxylated single-walled carbon nanotubes is as follows: 4 to 5 parts by weight of single-walled carbon nanotubes are dissolved in 25 parts by weight of deionized water, 1 to 2 parts by weight of a 50% hydrobromic acid solution is added, and the mixture is stirred for 10 minutes at a stirring speed of 500 rpm. A 90% oxalic acid solution is added, and the mixture is stirred for 6 hours at a stirring speed of 750 rpm. After filtration, the mixture is washed three times with deionized water to obtain carboxylated single-walled carbon nanotubes.

[0082] Example 6

[0083] This embodiment differs from embodiment 1 in that:

[0084] The method parameters in step S1 are different.

[0085] S1. Preparation of cross-linked polyethylene base material: 85 parts by weight of polyethylene, 2 parts by weight of a cross-linking agent, 1 part by weight of a cross-linking aid, and 0.1 parts by weight of a stabilizer are mixed, and the mixture is stirred at 160° C. for 2 h at a stirring speed of 800 rpm. Subsequently, the temperature is lowered to 50° C., 0.5 parts by weight of carboxylated single-walled carbon nanotubes are added, and the mixture is stirred for 2 h at a stirring speed of 1200 rpm to obtain a cross-linked polyethylene base material, wherein the cross-linking agent is 2,5-dimethyl-2,5-di-tert-butylperoxide hexane or diisopropylbenzene hydroperoxide, the cross-linking aid is trimethylolpropane trimethacrylate, and the stabilizers are all free radical inhibitors;

[0086] The preparation method of carboxylated single-walled carbon nanotubes is as follows: 5 parts by weight of single-walled carbon nanotubes are dissolved in 28 parts by weight of deionized water, 2 parts by weight of a 50% hydrobromic acid solution is added, and the mixture is stirred for 15 minutes at a stirring speed of 750 rpm, 90% oxalic acid solution is added, and the stirring is continued for 8 hours at a stirring speed of 1000 rpm. After filtration, the mixture is washed three times with deionized water to obtain carboxylated single-walled carbon nanotubes.

[0087] Example 7

[0088] This embodiment differs from embodiment 1 in that:

[0089] The method parameters in step S2 are different.

[0090] S2. Preparation of PVC protective cover base material: 45 parts by weight of PVC resin, 1 part by weight of antioxidant, 0.5 parts by weight of stabilizer and 0.2 parts by weight of plasticizer were mixed, and stirred at 110°C for 1 hour at a stirring speed of 400 rpm to obtain the PVC protective cover base material. The stabilizers were all free radical inhibitors, the antioxidant was bisphenol A, and the plasticizer was diisodecyl phthalate.

[0091] Example 8

[0092] This embodiment differs from embodiment 1 in that:

[0093] The method parameters in step S2 are different.

[0094] S2. Preparation of PVC protective cover base material: 50 parts by weight of PVC resin, 2 parts by weight of antioxidant, 1 part by weight of stabilizer and 0.4 parts by weight of plasticizer were mixed, and stirred at 120°C for 2 hours at a stirring speed of 500 rpm to obtain the PVC protective cover base material. The stabilizers were all free radical inhibitors, the antioxidant was bisphenol A, and the plasticizer was diisodecyl phthalate.

[0095] Example 9

[0096] This embodiment differs from embodiment 1 in that:

[0097] The method parameters in step S3 are different.

[0098] S3. Three-layer co-extrusion fully enclosed cross-linking: Under vacuum sealing conditions, acetylene black, the cross-linked polyethylene base material obtained in step S1, and furnace carbon black are extruded and coated on the outside of the wire 1 through the three-layer co-extrusion head of a screw extruder. The extrusion thickness of the acetylene black is 0.7 mm, the extrusion thickness of the cross-linked polyethylene base material is 3.22 mm, and the extrusion thickness of the furnace carbon black is 0.7 mm, forming a first semiconductive layer 2, a cross-linked polyethylene insulating layer 3, and a second semiconductive layer 4.

[0099] Example 10

[0100] This embodiment differs from embodiment 1 in that:

[0101] The method parameters in step S3 are different.

[0102] S3. Three-layer co-extrusion fully enclosed cross-linking: Under vacuum sealing conditions, acetylene black, the cross-linked polyethylene base material obtained in step S1, and furnace carbon black are extruded and coated on the outside of the wire 1 through the three-layer co-extrusion head of a screw extruder. The extrusion thickness of the acetylene black is 0.7 mm, the extrusion thickness of the cross-linked polyethylene base material is 3.22 mm, and the extrusion thickness of the furnace carbon black is 0.7 mm, forming a first semiconductive layer 2, a cross-linked polyethylene insulating layer 3, and a second semiconductive layer 4.

[0103] Example 11

[0104] This embodiment differs from embodiment 1 in that:

[0105] In step S4, the number of hexagonal hollow aluminum columns 61 is different.

[0106] A hollow aluminum column protective layer 6 is prefabricated, 32 hexagonal hollow aluminum columns 61 are arranged in sequence, and a connecting component is installed between two adjacent hexagonal hollow aluminum columns 61.

[0107] Example 12

[0108] This embodiment differs from embodiment 1 in that:

[0109] In step S4, the number of hexagonal hollow aluminum columns 61 is different.

[0110] A hollow aluminum column protective layer 6 is prefabricated, 28 hexagonal hollow aluminum columns 61 are arranged in sequence, and a connecting component is installed between two adjacent hexagonal hollow aluminum columns 61.

[0111] Experimental example

[0112] Taking the method for preparing power cables in Examples 4 to 6 as an example, the performance of the cross-linked polyethylene base material prepared therefrom was tested and compared with the 35KV cross-linked insulation material standard. The results are shown in Table 1.

[0113] Table 1 Properties of cross-linked polyethylene base material of Example 4

[0114]

[0115] As can be seen from the data in Table 1, the various properties tested for the cross-linked polyethylene base materials prepared in Examples 4 to 6 of the present invention meet the standard requirements for 35 kV cross-linked insulating materials. By adding carboxylated single-walled carbon nanotubes, the volume resistivity at 20°C is improved while ensuring that the gel content meets the standard. Therefore, the method parameters in Example 4 are preferred.

Claims

1. A 35KV cross-linked polyethylene insulated power cable, characterized in that: From the inside out, it includes a conductor (1), a first semi-conductive layer (2), a cross-linked polyethylene insulation layer (3), a second semi-conductive layer (4), a copper tape shielding layer (5), a hollow aluminum column protective layer (6), a rubber protective layer (7), a non-magnetic metal tape armor layer (8), and a PVC protective sleeve (9); The hollow aluminum column protective layer (6) is formed by closely arranging a plurality of hexagonal hollow aluminum columns (61), and one side surface of two adjacent hexagonal hollow aluminum columns (61) is attached to each other and can be movably connected through a connecting assembly. The connecting assembly is a plurality of groups of hexagonal hollow aluminum columns (61) arranged at intervals. The connecting assembly includes a first support plate (62), a second support plate (63), and a connecting plate (64) connecting the first support plate (62) and the second support plate (63). The connecting plate (64) slides with the first support plate (62). Dynamic connection, the connecting plate (64) is fixedly connected to the middle of the second support plate (63), the first support plate (62) and the second support plate (63) are respectively fixedly arranged on the inner walls of two adjacent hexagonal hollow aluminum columns (61), a side surface of a hexagonal hollow aluminum column (61) where the first support plate (62) is located is provided with a first slot (621) for allowing the connecting plate (64) to pass through, and a side surface of a hexagonal hollow aluminum column (61) where the second support plate (63) is located is provided with a second slot (631) for allowing the connecting plate (64) to pass through and rotate; The thickness of the second support plate (63) is 30% to 40% of the thickness of the first support plate (62); the lengths of the first support plate (62), the second support plate (63) and the connecting plate (64) are all 3 to 4 times the radius of the circumscribed circle of the hexagonal hollow aluminum column (61); the spacing between two adjacent groups of connecting components is 2 to 3 times the length of the connecting plate (64); the first support plate (62) is made of aluminum alloy, and the second support plate (63) is made of phosphor bronze; The cross-linked polyethylene insulation layer (3) is prepared from a cross-linked polyethylene base material. The preparation method of the cross-linked polyethylene base material is as follows: 75-85 parts by weight of polyethylene, 0.3-2 parts by weight of a cross-linking agent, 0.05-1 parts by weight of a cross-linking aid, and 0.05-0.1 parts by weight of a stabilizer are mixed, and the mixture is stirred at a temperature of 150-160° C. for 1-2 hours at a stirring speed of 700-800 rpm, and then the temperature is lowered to 40-50° C., 0.3-0.5 parts by weight of carboxylated single-walled carbon nanotubes are added, and the mixture is stirred for 1-2 hours at a stirring speed of 1000-1200 rpm to obtain the cross-linked polyethylene base material.

2. A 35KV cross-linked polyethylene insulated power cable according to claim 1, characterized in that: The first semi-conductive layer (2) is made of acetylene carbon black, the second semi-conductive layer (4) is made of furnace carbon black, and the non-magnetic metal belt armor layer (8) is made of stainless steel.

3. A 35KV cross-linked polyethylene insulated power cable according to claim 1, characterized in that: The connecting plate (64) is slidably connected to a slide groove (622) provided in the middle of the first support plate (62) through a slider (65); a limit plate (651) is provided at both upper and lower ends of the slider (65); a limit groove (623) for docking with the limit plate (651) is provided at both upper and lower ends of the slide groove (622); the length of the slider (65) is 15% to 30% of the length of the connecting plate (64); and the width of the slide groove (622) is 60% to 75% of the width of the first support plate (62).

4. A 35KV cross-linked polyethylene insulated power cable according to claim 1, characterized in that: The cross-section of the first slot (621) is rectangular, the cross-section of the second slot (631) is an isosceles trapezoid, and the angle between the second slot (631) and the connecting plate (64) is 30° to 60°.

5. The method for preparing a 35KV cross-linked polyethylene insulated power cable according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Preparation of a cross-linked polyethylene base material: 75-85 parts by weight of polyethylene, 0.3-2 parts by weight of a cross-linking agent, 0.05-1 parts by weight of a cross-linking aid, and 0.05-0.1 parts by weight of a stabilizer are mixed, and the mixture is stirred at 150-160° C. for 1-2 hours at a stirring speed of 700-800 rpm. Subsequently, the temperature is lowered to 40-50° C., 0.3-0.5 parts by weight of carboxylated single-walled carbon nanotubes are added, and stirring is continued for 1-2 hours at a stirring speed of 1000-1200 rpm to obtain a cross-linked polyethylene base material; S2. Preparation of PVC protective cover base material: 45-50 parts by weight of PVC resin, 1-2 parts by weight of antioxidant, 0.5-1 parts by weight of stabilizer, and 0.2-0.4 parts by weight of plasticizer are mixed, and stirred at 110-120° C. for 1-2 hours at a stirring speed of 400-500 rpm to obtain the PVC protective cover base material; S3, three-layer co-extrusion fully enclosed cross-linking: under vacuum sealing conditions, acetylene carbon black, the cross-linked polyethylene base material obtained in step S1, and furnace carbon black are extruded and coated on the outside of the conductor (1) through the three-layer co-extrusion head of the screw extruder, the extrusion thickness of the acetylene carbon black is 0.5-0.7 mm, the extrusion thickness of the cross-linked polyethylene base material is 2.3-3.22 mm, and the extrusion thickness of the furnace carbon black is 0.5-0.7 mm, forming a first semi-conductive layer (2), a cross-linked polyethylene insulating layer (3), and a second semi-conductive layer (4); S4, protective layer coating: first, prefabricate a hollow aluminum column protective layer (6), arrange the hexagonal hollow aluminum columns (61) in sequence, install a connection assembly between two adjacent hexagonal hollow aluminum columns (61), then wrap a copper tape around the outside of the second semi-conductive layer (4) to obtain a copper tape shielding layer (5), install the prefabricated hollow aluminum column protective layer (6) outside the copper tape shielding layer (5), extrude a rubber protective layer (7) outside the hollow aluminum column protective layer (6), and wrap a stainless steel tape around the outside of the rubber protective layer (7) to obtain a non-magnetic metal tape armor layer (8); S5. Molding: Extruding the PVC protective sheath base material obtained in step S2 outside the non-magnetic metal belt armor layer (8) to produce a PVC protective sheath (9).

6. The method for preparing a 35KV cross-linked polyethylene insulated power cable according to claim 5, characterized in that: The crosslinking agent in step S1 is 2,5-dimethyl-2,5-di-tert-butylhexane peroxide or diisopropylbenzene hydroperoxide, the crosslinking aid is trimethylolpropane trimethacrylate, the stabilizers in steps S1 and S2 are both free radical inhibitors, the antioxidant in step S2 is bisphenol A, and the plasticizer is diisodecyl phthalate.

7. The method for preparing a 35KV cross-linked polyethylene insulated power cable according to claim 5, characterized in that: The preparation method of carboxylated single-walled carbon nanotubes in step S1 is as follows: 4 to 5 parts by weight of single-walled carbon nanotubes are dissolved in 25 to 28 parts by weight of deionized water, 1 to 2 parts by weight of a 50% hydrobromic acid solution is added, and the mixture is stirred for 10 to 15 minutes at a stirring speed of 500 to 750 rpm. A 90% oxalic acid solution is added, and the mixture is stirred for 6 to 8 hours at a stirring speed of 750 to 1000 rpm. After filtration, the mixture is washed three times with deionized water to obtain carboxylated single-walled carbon nanotubes.

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