Cross-linked polyethylene insulated halogen-free flame-retardant special cable and preparation method thereof

Abstract

The present invention discloses a cross-linked polyethylene insulated halogen-free flame-retardant special cable and a preparation method thereof. The cable comprises an insulated conductor, a central filling layer, a halogen-free flame-retardant filling rope, a polyester tape, a non-metallic inner sheath, a metal wire shielding layer, an isolation layer, an armor layer and a non-metallic outer sheath. The cable adopts a modified halogen-free flame-retardant filling rope, and a flame-retardant coating is coated on the surface of the PP mesh filling rope to improve the oxygen index and the flame-retardant and smoke-suppressing performance. At the same time, an enhanced heat dissipation design is adopted in the center of the cable core, and a flexible central filling layer is formed by a phase change layer and a high-temperature resistant modified silicone rubber. The high-temperature resistant modified silicone rubber covers the phase change layer to form a core-shell heat-conducting structure, and the modified high-thermal conductivity silicone rubber of the shell part is used for high-efficiency heat conduction and the core part phase changes to absorb heat, thereby improving the temperature resistance and insulation aging resistance of the cable. The design of the present invention can improve the anti-aging, flame-retardant and smoke-suppressing properties of the cable, so that it can maintain long-term stability and safety in power transmission and distribution applications.

Description

Technical Field

[0001] The invention belongs to the technical field of electric wires and cables, and specifically relates to a cross-linked polyethylene insulated halogen-free flame-retardant special cable and a preparation method thereof. Background Art

[0002] Cables are divided according to voltage levels, mainly including low-voltage cables (rated voltage below 1kV), medium-voltage cables (rated voltage 1kV to 35kV) and high-voltage cables (rated voltage above 35kV, especially above 110kV). Medium-voltage power cables play a key role in urban power distribution systems, underground pipe corridors and new energy power collection systems, industrial fields and various power applications. Medium-voltage cables usually adopt a multi-core (three-core, four-core, five-core, etc.) twisted conductor structure. After cabling, fire protection, insulation, armor, sheath and other functional layers are further prepared to form a high-temperature resistant, flame-retardant and insulated cable structure. Especially in underground power distribution, industrial use, long-distance, high-power power transmission applications, higher voltage tolerance is required, and higher standards are set for the high-temperature flame retardancy and service life of the cable, requiring the cable to have long-term stability and safety.

[0003] When medium-voltage cables are transmitting power normally, the temperature is above 60°C for a long time, and even above 130°C for a short time. Being at high temperature for a long time will cause irreversible aging of the insulation layer, resulting in the risk of failure, causing stability and safety risks. In order to obtain stable and efficient heat-resistant and fire-retardant effects in the prior art, inorganic flame retardants such as hydrated alumina and magnesium oxide are added to the insulation layer and sheath materials of the cable. They have low costs and mature preparation technologies, but these additions will change the properties of the insulation material, resulting in conflicts in extrusion pressure and temperature, and put forward higher requirements for the extrusion process. The temperature cannot be too high to cause the added inorganic flame retardant to decompose, reduce its flame retardant properties and produce pores on the extruded surface, causing defects. At the same time, if the temperature is too low, the material cannot be completely plasticized, the extrusion effect is poor, and the comprehensive properties (mechanical properties) of the extruded insulation layer and sheath are adversely affected. Summary of the invention

[0004] The purpose of the present invention is to provide a cross-linked polyethylene insulated halogen-free flame-retardant special cable, which improves the anti-aging, flame-retardant and smoke-suppression properties of the cable and enables it to maintain long-term stability and safety in power transmission and distribution applications.

[0005] According to the first aspect of the present invention, a cross-linked polyethylene insulated halogen-free flame-retardant special cable is provided, comprising:

[0006] An insulated conductor, comprising a copper conductor formed by twisting a plurality of copper wires, a conductor shielding layer extruded outside the copper conductor, and a radiation cross-linked polyethylene insulation layer;

[0007] A central filling layer, comprising a phase change layer and a high temperature resistant modified silicone rubber to form a flexible central filling layer, wherein the high temperature resistant modified silicone rubber covers the phase change layer to form a core-shell heat conducting structure;

[0008] A halogen-free flame-retardant filling rope is filled in the gaps between the plurality of insulated conductors, so that when the plurality of insulated conductors are twisted around the central filling layer to form a cable core, the halogen-free flame-retardant filling rope is filled, and a polyester tape is wrapped around the outer periphery of the insulated conductors and the halogen-free flame-retardant filling rope to form a round cable core structure;

[0009] A non-metallic inner sheath is extruded on the outer surface of the tape layer formed by the polyester tape;

[0010] A metal wire shielding layer, woven on the outer surface of the non-metallic inner sheath;

[0011] An isolation layer, extruded and wrapped around the outer surface of the metal wire shielding layer;

[0012] An armor layer is wrapped around the outer surface of the isolation layer and is isolated from the metal wire shielding layer by the isolation layer;

[0013] The non-metallic outer sheath is extruded with a polyolefin sheath material on the outer surface of the armor layer to form the overall external protection of the cable.

[0014] As an optional embodiment, the high temperature resistant modified silicone rubber is a copolymer of a silicone rubber matrix and an insulating thermal conductive material, the phase change layer is a cylindrical structure formed by a high latent heat shaped organic phase change material, and is wrapped by the high temperature resistant modified silicone rubber to form a concentric core-shell thermal conductive structure;

[0015] As an optional embodiment, the halogen-free flame-retardant filling rope is a PP mesh filling rope and is coated with a flame-retardant coating on the surface to increase its oxygen index to above 45%.

[0016] As an optional embodiment, the flame retardant coating coated on the surface of the halogen-free flame retardant filling rope adopts one of ATH coating, MDH coating and ceramic fireproof layer;

[0017] The ATH coating is formed by combining aluminum hydroxide powder and resin;

[0018] The MDH coating is formed by combining magnesium hydroxide powder and resin;

[0019] The ceramic fireproof layer adopts organic silicon polymer and siloxane-containing coating materials to form a stable ceramic layer at high temperature to isolate oxygen and heat.

[0020] As an optional embodiment, the metal wire shielding layer adopts a copper wire braided shielding layer, the braiding density is greater than 80%, and the braiding angle is 45° to 55°.

[0021] As an optional embodiment, the armor layer is made of steel tape wrapped around the outer surface of the isolation layer at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25%.

[0022] As an optional embodiment, the isolation layer is formed by PVC extrusion, so that metal isolation is formed between the copper wire braided shielding layer and the steel belt, delaying and reducing oxidation of the copper wire.

[0023] According to a second aspect of the present invention, a method for preparing a cross-linked polyethylene insulated halogen-free flame-retardant special cable is provided, comprising the following steps:

[0024] Step 1: Prepare the insulated conductor

[0025] A conductor shielding layer and an irradiated cross-linked polyethylene insulation layer are extruded on the outer surface of a copper conductor formed by twisting a plurality of copper wires by a double-layer co-extrusion process to form a conductor with a conductor shield and insulation coated on the periphery, and then the conductor with a conductor shield and insulation coated on the periphery is electron irradiated;

[0026] Step 2: Twisting and preparing cable core

[0027] The irradiated multiple insulated conductors, the central filling layer and the multiple halogen-free flame-retardant filling ropes are twisted into a cable to form a round cable core structure, the central filling layer is filled in the center, the multiple halogen-free flame-retardant filling ropes are filled in the gaps between the multiple insulated conductors, and are wrapped around the outer periphery of the cable core structure by polyester tape to form a wrapping layer; the central filling layer is a prefabricated part, and a cylindrical organic phase change material with high latent heat is wrapped with high-temperature resistant modified silicone rubber to form a concentric core-shell heat-conducting structure;

[0028] Step 3, extruding a polyethylene or polyvinyl chloride inner protective layer on the outer surface of the tape layer;

[0029] Step 4: Use a braiding machine to braid a copper wire shielding layer on the outer surface of the inner sheath, with a copper wire braiding density greater than 80% and a braiding angle of 45° to 55°;

[0030] Step 5, extrude PVC on the outer surface of the copper wire shielding layer as an isolation layer;

[0031] Step 6: Wrap the steel tape on the outer surface of the isolation layer at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25% to form a steel tape armor layer.

[0032] Step 7: Extruding a polyolefin sheath material on the outer surface of the steel belt armor layer to prepare an outer sheath.

[0033] Thus, the cross-linked polyethylene insulated halogen-free flame-retardant special cable of the present invention is prepared.

[0034] The cross-linked polyethylene insulated halogen-free flame-retardant special cable of the above embodiment of the present invention, on the one hand, adopts a modified halogen-free flame-retardant filling rope, and a flame-retardant coating (especially ATH coating, MDH coating, ceramic fireproof layer) is coated on the surface of the pp mesh filling rope to increase its oxygen index to above 45%, thereby improving the flame retardant and smoke suppression performance; on the other hand, the medium-voltage power cable undertakes the main power transmission tasks in urban power supply and industrial power consumption, especially in the application in industry and underground pipe gallery, which puts forward higher requirements on the temperature resistance, fire retardancy and anti-aging long-term stability of the cable. In addition to designing the filling layer with halogen-free, low-smoke and high In addition to flame-retardant filling, an enhanced heat dissipation design is also used in the center of the cable core. The flexible central filling layer is composed of a phase change layer and a high-temperature resistant modified silicone rubber. The high-temperature resistant modified silicone rubber covers the phase change layer to form a core-shell thermal conductive structure. The modified high thermal conductivity silicone rubber of the shell part is used for efficient heat conduction, and the high latent heat of the core part is used for phase change heat absorption, to achieve efficient thermal conduction and heat dissipation, improve the temperature resistance of the cable, and optimize the core structure to a shaped cylindrical organic phase change material structure. The external wrapping is used to avoid flow while the core-shell thermal conductive structure is used to buffer the cable core to improve the mechanical properties of the cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic structural diagram of a cross-linked polyethylene insulated halogen-free flame-retardant special cable according to an embodiment of the present invention.

[0036] Figure 2 It is a schematic structural diagram from another angle of the cross-linked polyethylene insulated halogen-free flame-retardant special cable according to an embodiment of the present invention.

[0037] Figure 3 It is a schematic diagram of the cross-sectional structure of a cross-linked polyethylene insulated halogen-free flame-retardant special cable according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0039] {Example 1}

[0040] Combination Figure 1 , Figure 2 , Figure 3 The cross-linked polyethylene insulated halogen-free flame-retardant special cable of the embodiment shown belongs to the medium voltage cable design, and the rated voltage range is 1-35kV. The cable structure of this embodiment includes an insulated conductor 1, a central filling layer 2, a halogen-free flame-retardant filling rope 3, a polyester tape 4, a non-metallic inner sheath 5, a metal wire shielding layer 6, an isolation layer 7, an armor layer 8 and a non-metallic outer sheath 9.

[0041] The insulated conductor 1 comprises a copper conductor 11 formed by twisting a plurality of copper wires, a conductor shielding layer 12 extruded outside the copper conductor 11 , and a radiation cross-linked polyethylene insulation layer 13 .

[0042] In the embodiment of the present invention, the copper wire material is annealed oxygen-free copper wire material, and the oxygen-free copper wire is annealed to make it soft and have high conductivity, RRR value and conductive performance. A plurality of copper wires are twisted by a frame-type twisting machine to obtain a copper conductor 11, the conductor has a compression coefficient greater than 90%, and a twisting pitch ratio between 8 and 20.

[0043] The conductor shielding layer 12 adopts a semi-conductive shielding layer, such as a polyolefin semi-conductive shielding material (a polymer of thermoplastic polypropylene and conductive carbon black), which is extruded on the outer surface of the copper conductor 11 to form a thin layer with a thickness of 1-1.5 mm to eliminate the air gap on the surface of the conductive core, improve the ability to resist local discharge and tree discharge, and make the electric field on the surface of the conductive core uniform, thereby reducing the maximum working field strength on the conductor surface increased by the wire guide effect.

[0044] An irradiated cross-linked polyethylene (XLPE) insulation layer 13 is extruded on the basis of the conductor shielding layer 12 to improve the heat resistance, temperature resistance, flame retardancy, smoke suppression and anti-aging properties of the cable conductor. The extrusion thickness is 2-3.5 mm.

[0045] The conductor shielding layer 12 and the radiation cross-linked polyethylene insulation layer 13 are extruded by a double-layer co-extrusion process, and the thickness of the conductor shielding layer 12 is smaller than the thickness of the radiation cross-linked polyethylene insulation layer 13 .

[0046] In an embodiment of the present invention, in order to improve the heat resistance and mechanical properties of the medium voltage cable, a central filling layer 2 is filled into the center of multiple insulated conductors, that is, multiple insulated conductors are twisted into a cable around the central filling layer 2 and halogen-free flame retardant filling rope 3 is filled in the gap.

[0047] As an optional embodiment, the central filling layer 2 is composed of a phase change layer 21 and a high temperature resistant modified silicone rubber 22 to form a flexible central filling layer. The high temperature resistant modified silicone rubber 22 covers the aforementioned phase change layer 21 to form a core shell heat conductive structure, achieving flexible support and heat resistance improvement, improving the temperature resistance of the cable (the medium voltage cable is above 60°C all year round when transmitting power normally, and even above 130°C for a short time) and anti-aging performance, avoiding the aging of the insulation under high temperature for a long time and causing stability and safety risks. At the same time, the conductor shielding layer 12 is used as a thermal barrier to avoid the impact of the conductor thermal temperature rise on the main shielding layer XLPE insulation layer.

[0048] In a preferred embodiment, the high temperature resistant modified silicone rubber 22 adopts a copolymer of a silicone rubber matrix and an insulating thermal conductive material. The phase change layer 21 adopts a cylindrical structure formed by a high latent heat shaped organic phase change material, which is wrapped by the high temperature resistant modified silicone rubber 22 to form a concentric core-shell thermal conductive structure, that is, a core-shell structure. The PCM core structure is covered by the high thermal conductivity shell as a whole, and the PCM core structure with high latent heat is used to achieve passive management of the heat of the inner conductor, thereby improving the heat resistance and insulation aging resistance of the cable.

[0049] As an optional solution, the insulating thermal conductive material uses at least one of boron nitride, silicon nitride, aluminum nitride, silicon carbide, aluminum oxide, and magnesium oxide, and uses dispersed powder to copolymerize with the silicone rubber matrix to form a highly thermally conductive modified silicone rubber. It should be understood that the highly thermally conductive modified silicone rubber used in the present invention is prepared by using commercially available modified silicone rubber or custom commission, wherein the mass ratio of the insulating thermal conductive material added is less than 0.5%, and spherical powder is used.

[0050] Combination Figure 1 , Figure 3 As shown, the halogen-free flame retardant filling rope 3 is filled in the gaps between the multiple insulated conductors 1, so that when the multiple insulated conductors 1 are twisted into a cable core around the aforementioned central filling layer 2, they are filled with the halogen-free flame retardant filling rope 3, and the polyester tape 4 is wrapped around the outer periphery of the insulated conductors 1 and the halogen-free flame retardant filling rope 3 to form a round cable core structure.

[0051] In the embodiment of the present invention, the halogen-free flame-retardant filling rope 3 is a PP mesh filling rope, and a flame-retardant coating is coated on the surface to increase its oxygen index to above 45%.

[0052] As an optional example, the flame retardant coating coated on the surface of the halogen-free flame retardant filling rope 3 adopts one of ATH coating, MDH coating and ceramic fireproof layer.

[0053] ATH coating is formed by combining aluminum hydroxide powder with resin.

[0054] MDH coating is formed by combining magnesium hydroxide powder and resin.

[0055] The aforementioned ceramic fireproof layer adopts organic silicon polymer and siloxane-containing coating materials to form a stable ceramic layer at high temperature to isolate oxygen and heat.

[0056] Combination Figure 1 , 3 As shown, the non-metallic inner protective layer 5 is made of polyethylene or polyvinyl chloride sheath material, which is extruded on the outer surface of the tape layer formed by the aforementioned polyester tape 4.

[0057] Combination Figure 1 , 3As shown, the metal wire shielding layer 6 is woven on the outer surface of the aforementioned non-metallic inner sheath 5.

[0058] As an example, the metal wire shielding layer 6 is a copper wire braided shielding layer with a braiding density greater than 80% and a braiding angle of 45° to 55°.

[0059] Combination Figure 1 , 3 As shown, the isolation layer 7 is extruded on the outer surface of the aforementioned metal wire shielding layer 6. The isolation layer 7 is formed by PVC extrusion, so that metal isolation is formed between the copper wire braided shielding layer and the steel belt.

[0060] Combination Figure 1 , 3 As shown, the armor layer 8 is wrapped around the outer surface of the aforementioned isolation layer 7 and is isolated from the metal wire shielding layer 6 by the aforementioned isolation layer 7.

[0061] As an optional embodiment, the armor layer 8 is made of steel tape wrapped around the outer surface of the aforementioned isolation layer 7 at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25%.

[0062] The non-metallic outer sheath 9 is made of polyolefin sheath material and is extruded on the outer surface of the aforementioned armor layer 8 to form the overall external protection of the cable.

[0063] {Example 2}

[0064] According to an embodiment of the present invention, a method for preparing a cross-linked polyethylene insulated halogen-free flame-retardant special cable is disclosed, comprising the following steps:

[0065] Step 1: Prepare the insulated conductor

[0066] A conductor shielding layer 12 and a radiation cross-linked polyethylene insulation layer 13 are extruded on the outer surface of a copper conductor 11 formed by twisting multiple copper wires by a double-layer co-extrusion process to form a conductor with a conductor shield and insulation coated on the periphery; the conductor with a conductor shield and insulation coated on the periphery is subjected to electron irradiation under radiation cross-linking conditions of a temperature of 140-150° C. and a certain radiation dose;

[0067] Step 2: Twisting and preparing cable core

[0068] The irradiated multiple insulated conductors 1, the central filling layer 2 and the multiple halogen-free flame-retardant PP mesh filling ropes are twisted into a cable to form a round cable core structure, the central filling layer 2 is filled in the center, the multiple halogen-free flame-retardant PP mesh filling ropes are filled in the gaps between the multiple insulated conductors 1, and are wrapped around the outer periphery of the cable core structure by polyester tape to form a wrapping layer; the aforementioned central filling layer 2 is a prefabricated part, and a cylindrical organic phase change material with high latent heat is wrapped with a high-temperature resistant modified silicone rubber 22 to form a concentric core-shell heat-conducting structure;

[0069] Step 3: Extruding a polyethylene inner protective layer on the outer surface of the tape layer, with a thickness of 1.5-2.5 mm;

[0070] Step 4: Use a braiding machine to braid a copper wire shielding layer on the outer surface of the inner sheath, the diameter of the copper wire is 0.5-0.8 mm, the copper wire braiding density is greater than 80%, and the braiding angle is 45° to 55°;

[0071] Step 5, extrude PVC on the outer surface of the copper wire shielding layer as an isolation layer;

[0072] Step 6: Wrap the steel tape on the outer surface of the isolation layer at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25% to form a steel tape armor layer.

[0073] Step 7: Extruding a polyolefin sheath material on the outer surface of the steel belt armor layer to prepare an outer sheath with a thickness of 2-2.5 mm.

[0074] The insulated conductor 1 uses a copper conductor 11 formed by twisting multiple copper wires as the main conductor core. The copper wire is made of annealed oxygen-free copper wire material. After annealing, the oxygen-free copper wire is made soft and has high conductivity, RRR value and conductive performance.

[0075] A plurality of copper wires are twisted together by a frame-type twisting machine to obtain a copper conductor 11, the compression coefficient of the conductor is greater than 90%, and the twisting pitch ratio is 12.

[0076] A semi-conductive shielding layer and an irradiated cross-linked polyethylene (XLPE) insulation layer 13 are extruded on the surface of the copper conductor 11 through a double-layer co-extrusion process, wherein a polymer of thermoplastic polypropylene and conductive carbon black is used as a semi-conductive shielding material, and a modified anti-aging, flame retardant and smoke-suppressing insulating material is used as the main insulating material, which are extruded on the outer surface of the copper conductor 11 to form a thin semi-conductive shielding layer (1 mm thick) and an XLPE insulation layer (2.5 mm thick).

[0077] During the cabling process, the center filling layer 2 is filled into the center of the multiple insulated conductors, that is, the multiple insulated conductors are twisted around the center filling layer 2 to form a cable and the halogen-free flame-retardant filling rope 3 is filled in the gaps.

[0078] The central filling layer 2 filled in the center of the conductor is composed of a phase change layer 21 and a high temperature resistant modified silicone rubber 22 to form a flexible central filling layer. The high temperature resistant modified silicone rubber 22 covers the aforementioned phase change layer 21 to form a core-shell heat-conducting structure, which realizes flexible support and heat resistance improvement, improves the temperature resistance of the cable (the medium voltage cable is above 60°C all year round when transmitting power normally, and even above 130°C for a short time) and anti-aging performance, and avoids the aging of the insulation and the dendrite effect caused by long-term exposure to high temperature, resulting in stability and safety risks. At the same time, the conductor shielding layer 12 is used as a thermal barrier to prevent the impact of the conductor's thermal temperature rise on the main shielding layer XLPE insulation layer.

[0079] The high temperature resistant modified silicone rubber 22 is a copolymer of a silicone rubber matrix and an insulating thermal conductive material. The phase change layer 21 is a cylindrical structure formed by a high latent heat shaped organic phase change material, which is wrapped by the high temperature resistant modified silicone rubber 22 to form a concentric core-shell thermal conductive structure, that is, a core-shell structure. The PCM core structure is covered by a high thermal conductive shell as a whole, and the PCM core structure with high latent heat is used to achieve passive management of the heat of the inner conductor, thereby improving the heat resistance and insulation aging resistance of the cable.

[0080] As an optional solution, the insulating thermal conductive material uses silicon nitride high thermal conductive insulating material, and disperses the powder to copolymerize with the silicone rubber matrix to form a highly thermally conductive modified silicone rubber. The mass ratio of the insulating thermal conductive material added is less than 0.5%, and spherical powder is used.

[0081] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A cross-linked polyethylene insulated halogen-free flame-retardant special cable, characterized in that: include: An insulated conductor (1), the insulated conductor (1) comprising a copper conductor (11) formed by twisting a plurality of copper wires, a conductor shielding layer (12) extruded outside the copper conductor (11), and a radiation cross-linked polyethylene insulation layer (13); A central filling layer (2), comprising a phase change layer (21) and a high temperature resistant modified silicone rubber (22) to form a flexible central filling layer, wherein the high temperature resistant modified silicone rubber (22) covers the phase change layer (21) to form a core-shell heat conductive structure; The halogen-free flame-retardant filling rope (3) is filled in the gaps between the plurality of insulated conductors (1), so that when the plurality of insulated conductors (1) are twisted around the central filling layer (2) to form a cable core, they are filled with the halogen-free flame-retardant filling rope (3), and a polyester tape (4) is wrapped around the outer periphery of the insulated conductors (1) and the halogen-free flame-retardant filling rope (3) to form a round cable core structure; A non-metallic inner protective layer (5) is extruded onto the outer surface of the tape layer formed by the polyester tape (4); A metal wire shielding layer (6) braided on the outer surface of the non-metallic inner protective layer (5); An isolation layer (7) extruded onto the outer surface of the metal wire shielding layer (6); An armor layer (8) wrapped around the outer surface of the isolation layer (7) and isolated from the metal wire shielding layer (6) by the isolation layer (7); A non-metallic outer sheath (9) is formed by extruding a polyolefin sheath material on the outer surface of the armor layer (8) to form an overall external protection for the cable; The halogen-free flame-retardant filling rope (3) is a PP mesh filling rope and is coated with a flame-retardant coating on the surface, and its oxygen index is above 45%.

2. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The conductor shielding layer (12) and the radiation cross-linked polyethylene insulation layer (13) are extruded by a double-layer co-extrusion process.

3. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 2, characterized in that: The thickness of the conductor shielding layer (12) is smaller than the thickness of the radiation cross-linked polyethylene insulation layer (13).

4. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The flame retardant coating coated on the surface of the halogen-free flame retardant filling rope (3) is one of an ATH coating, an MDH coating, and a ceramic fireproof layer; The ATH coating is formed by combining aluminum hydroxide powder with resin; The MDH coating is formed by combining magnesium hydroxide powder with resin; The ceramic fireproof layer adopts organic silicon polymer and siloxane-containing coating materials to form a stable ceramic layer at high temperature to isolate oxygen and heat.

5. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The metal wire shielding layer (6) is a copper wire braided shielding layer with a braiding density greater than 80% and a braiding angle of 45° to 55°.

6. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The armor layer (8) is made of steel strips wrapped around the outer surface of the isolation layer (7) at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25%.

7. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The isolation layer (7) is formed by PVC extrusion, so that metal isolation is formed between the copper wire braided shielding layer and the steel belt.

8. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The high temperature resistant modified silicone rubber (22) is a copolymer of a silicone rubber matrix and an insulating heat conductive material. The phase change layer (21) is a cylindrical structure formed by a high latent heat shaped organic phase change material, which is wrapped by the high temperature resistant modified silicone rubber (22) to form a concentric core-shell heat conductive structure.

9. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 8, characterized in that: The insulating thermal conductive material is at least one of boron nitride, silicon nitride, aluminum nitride, silicon carbide, aluminum oxide, and magnesium oxide, and is formed by copolymerizing dispersed powder with a silicone rubber matrix to form a modified silicone rubber with high thermal conductivity.

10. The method for preparing the cross-linked polyethylene insulated halogen-free flame-retardant special cable according to any one of claims 1 to 9, characterized in that: The steps include: Step 1: Prepare the insulated conductor Extruding a conductor shielding layer (12) and a radiation cross-linked polyethylene insulation layer (13) on the outer surface of a copper conductor (11) formed by twisting a plurality of copper wires by a double-layer co-extrusion process to form a conductor with a conductor shielding and insulation coated on the outer periphery; subjecting the conductor with a conductor shielding and insulation coated on the outer periphery to electron irradiation under radiation cross-linking conditions of a temperature of 150° C. and a radiation dose of 10-20 Mrd; Step 2: Twisting and preparing cable core The irradiated multiple insulated conductors (1), the central filling layer (2) and the multiple halogen-free flame-retardant filling ropes (3) are twisted into a cable to form a round cable core structure, the central filling layer (2) is filled in the center, the multiple halogen-free flame-retardant filling ropes (3) are filled in the gaps between the multiple insulated conductors (1), and are wrapped around the outer periphery of the cable core structure by a polyester tape to form a wrapping layer; the central filling layer (2) is a preformed part, and a high latent heat cylindrical organic phase change material is wrapped with a high temperature resistant modified silicone rubber (22) to form a concentric core-shell heat-conducting structure; Step 3, extruding a polyethylene or polyvinyl chloride inner protective layer on the outer surface of the tape layer; Step 4: Use a braiding machine to weave a copper wire shielding layer on the outer surface of the inner sheath, with a copper wire weaving density greater than 80% and a weaving angle of 45° to 55°; Step 5, extrude PVC on the outer surface of the copper wire shielding layer as an isolation layer; Step 6: Wrap the steel tape on the outer surface of the isolation layer at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25% to form a steel tape armor layer. Step 7: Extruding a polyolefin sheath material on the outer surface of the steel belt armor layer to prepare an outer sheath.

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