Crosslinked polyethylene insulated halogen-free flame-retardant special cable

Abstract

The utility model discloses a cross-linked polyethylene insulated halogen-free flame-retardant special cable. The cable comprises insulated conductors, a central filling layer, halogen-free flame-retardant filling ropes, a polyester tape, a non-metal inner sheath, a metal wire shielding layer, an isolating layer, an armor layer and a non-metal outer sheath. The cable adopts the modified halogen-free flame-retardant filling rope, and the surface of the PP net-shaped filling rope is coated with the flame-retardant coating, so that the oxygen index is improved, and the flame-retardant smoke suppression performance is improved. Meanwhile, the center of the cable core adopts an enhanced heat dissipation design, a flexible center filling layer is formed by a phase change layer and high-temperature-resistant modified silicone rubber, the phase change layer is coated with the high-temperature-resistant modified silicone rubber to form a core-shell heat conduction structure, and the modified high-heat-conduction silicone rubber of the shell part is used for high-efficiency heat conduction and phase-change heat absorption of the core part. And the temperature resistance and the insulation aging resistance of the cable are improved. Through the design of the utility model, the anti-aging, flame-retardant and smoke-suppressing performance of the cable can be improved, so that the cable can maintain long-term stability and safety in power transmission and distribution application.

Description

Technical Field

[0001] The utility model belongs to the technical field of electric wires and cables, and in particular relates to a cross-linked polyethylene insulated halogen-free flame-retardant special cable. Background Art

[0002] Cables are classified by voltage level, primarily into low-voltage cables (rated voltage below 1 kV), medium-voltage cables (rated voltage 1 kV to 35 kV), and high-voltage cables (rated voltage above 35 kV, especially above 110 kV). Medium-voltage power cables play a key role in urban power distribution systems, underground pipeline corridors, new energy power collection systems, industrial sectors, and various power applications. Medium-voltage cables typically utilize a multi-core (three-core, four-core, five-core, etc.) twisted conductor structure. After cabling, they are further coated with functional layers such as fire protection, insulation, armor, and sheathing to create a high-temperature resistant, flame-retardant, and insulated cable structure. This is particularly true for underground power distribution, industrial applications, and long-distance, high-power power transmission, which require higher voltage tolerance and impose high standards on the cables' high-temperature resistance, flame retardancy, and service life, requiring them to provide long-term stability and safety.

[0003] During normal power transmission, medium-voltage cables experience temperatures exceeding 60°C for extended periods, and even exceeding 130°C for short periods. This prolonged exposure to high temperatures can cause irreversible aging of the insulation layer, leading to the risk of failure and potentially posing stability and safety risks. To achieve stable and efficient heat-resistant and fire-retardant properties, existing technologies often add inorganic flame retardants such as hydrated alumina and magnesium oxide to the insulation and sheath materials of cables. While these are low-cost and readily available, their additions can alter the insulation's performance, creating a conflict between extrusion pressure and temperature. These additions also place high demands on the extrusion process, requiring the temperature to be kept within a safe range, preventing the inorganic flame retardants from decomposing and reducing their flame retardant properties, creating pores on the extruded surface, and causing adverse effects. Furthermore, temperatures that are too low prevent the material from being fully plasticized, resulting in poor extrusion performance and adversely affecting the overall mechanical properties of the extruded insulation and sheath. Summary of the Invention

[0004] The purpose of the utility model is to provide a cross-linked polyethylene insulated halogen-free flame-retardant special cable, which improves the cable's anti-aging, flame retardant and smoke suppression properties, so that it can 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 multiple copper wires, a conductor shielding layer extruded onto the outside of the copper conductor, and an irradiated 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] Halogen-free flame-retardant filling ropes are 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 ropes are filled, and polyester tapes are wrapped around the outer peripheries of the insulated conductors and the halogen-free flame-retardant filling ropes to form a round cable core structure;

[0009] A non-metallic inner sheath is extruded onto 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 on the outer surface of the metal wire shielding layer;

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

[0013] The non-metallic outer sheath is made of polyolefin sheath material extruded 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, and the phase change layer adopts a cylindrical structure formed by a shaped organic phase change material with high latent heat, which 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 with resin to form an ATH coating;

[0019] The ceramic fireproof layer adopts organic silicon polymer and siloxane-containing coating material 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 with a braiding density greater than 80% and a braiding angle of 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 the oxidation of the copper wire.

[0023] The cross-linked polyethylene insulated halogen-free flame-retardant special cable of the above embodiment of the utility model 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 power transmission task of the main trunk in urban power supply and industrial power consumption, especially in the application in industry and underground pipeline corridors, which puts forward higher requirements on the temperature resistance, fire retardancy and anti-aging long-term stability of the cable. In addition to the design of halogen-free and low- In addition to the high-smoke 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 high-efficiency heat conduction, and the high latent heat of the core part is used for phase change heat absorption to achieve efficient heat 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 at the same time, and 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

[0024] Figure 1 It is a structural schematic diagram of a cross-linked polyethylene insulated halogen-free flame-retardant special cable according to an embodiment of the present utility model.

[0025] Figure 2 It is a structural schematic diagram from another angle of the cross-linked polyethylene insulated halogen-free flame retardant special cable according to an embodiment of the present utility model.

[0026] 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 utility model. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0028] {Example 1}

[0029] Combine Figure 1 、 Figure 2 、 Figure 3 The cross-linked polyethylene insulated, halogen-free, flame-retardant special cable shown in the embodiment is a medium-voltage cable design with a rated voltage range of 1-35 kV. The cable structure of this embodiment includes an insulated conductor 1, a central filler layer 2, a halogen-free, flame-retardant filler cord 3, a polyester tape 4, a non-metallic inner sheath 5, a metal wire shield 6, an isolation layer 7, an armor layer 8, and a non-metallic outer sheath 9.

[0030] The insulated conductor 1 comprises a copper conductor 11 formed by twisting a plurality of copper wires, a conductor shielding layer 12 extruded on the outside of the copper conductor 11 , and an irradiated cross-linked polyethylene insulation layer 13 .

[0031] In the embodiments of the present invention, the copper wire is annealed oxygen-free copper wire. Annealing makes the oxygen-free copper wire soft and has high conductivity, RRR value, and conductive properties. Multiple strands of copper wire are twisted together using a frame-type stranding machine to produce the copper conductor 11. The conductor has a compaction coefficient greater than 90% and a twist pitch ratio between 8 and 20.

[0032] 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 an extrusion thickness of 1-1.5 mm to eliminate the air gap on the surface of the conductive core, improve the ability to resist partial discharge and tree discharge, and uniformly distribute the electric field on the surface of the conductive core, thereby reducing the maximum working field strength on the conductor surface increased by the wire guide effect.

[0033] An irradiated cross-linked polyethylene (XLPE) insulation layer 12 is extruded on the basis of the conductor shielding layer 12 to improve the heat resistance, temperature resistance, flame retardancy, smoke suppression and aging resistance of the cable conductor. The extrusion thickness is 2-3.5mm.

[0034] 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 that of the radiation cross-linked polyethylene insulation layer 13 .

[0035] 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 a halogen-free flame retardant filling rope 3 is filled in the gap.

[0036] As an optional embodiment, the core filling layer 2 comprises a flexible core filling layer composed of a phase change layer 21 and a high-temperature-resistant modified silicone rubber 22. The high-temperature-resistant modified silicone rubber 22 encapsulates the phase change layer 21, forming a core-shell thermally conductive structure. This provides flexible support and improved heat resistance, enhancing the cable's temperature resistance (medium-voltage cables maintain temperatures above 60°C year-round during normal power transmission, and even exceeding 130°C for short periods) and aging resistance, preventing insulation aging and potential stability and safety risks from long-term high-temperature exposure. Furthermore, the conductor shielding layer 12 acts as a thermal barrier, preventing the impact of conductor temperature rise on the main shielding layer, the XLPE insulation.

[0037] In a preferred embodiment, the high-temperature-resistant modified silicone rubber 22 is a copolymer of a silicone rubber matrix and an insulating thermally conductive material. The phase change layer 21 is a cylindrical structure formed from a shaped organic phase change material with high latent heat. This cylindrical structure is encased in the high-temperature-resistant modified silicone rubber 22 to form a concentric core-shell thermally conductive structure, or core-shell structure. The highly thermally conductive shell completely encases the PCM core, passively managing the heat of the internal conductor through the high latent heat PCM core, thereby improving the cable's heat resistance and resistance to insulation aging.

[0038] As an optional solution, the insulating and thermally conductive material comprises at least one of boron nitride, silicon nitride, aluminum nitride, silicon carbide, aluminum oxide, and magnesium oxide, with the dispersed powder copolymerized 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 this invention is prepared using commercially available modified silicone rubber or custom-made materials, with the insulating and thermally conductive material added at a weight ratio of less than 0.5% and in spherical powder form.

[0039] Combine 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.

[0040] 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 applied on the surface to increase the oxygen index thereof to above 45%.

[0041] As an optional example, the flame retardant coating coated on the surface of the halogen-free flame retardant filling rope 3 is one of ATH coating, MDH coating, and ceramic fireproof layer.

[0042] ATH coating is formed by combining aluminum hydroxide powder with resin

[0043] The MDH coating is formed by combining magnesium hydroxide powder with resin to form an ATH coating.

[0044] 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.

[0045] Combine Figure 1 、 3 As shown, the non-metallic inner protective layer 5 is made of polyethylene or polyvinyl chloride sheath material and is extruded on the outer surface of the tape layer formed by the aforementioned polyester tape 4.

[0046] Combine Figure 1 、 3 As shown, the metal wire shielding layer 6 is woven on the outer surface of the aforementioned non-metallic inner sheath 5.

[0047] 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°.

[0048] Combine 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 tape.

[0049] Combine 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.

[0050] As an optional embodiment, the armor layer 8 is wrapped around the outer surface of the aforementioned isolation layer 7 using steel strips at a wrapping angle of 30° to 40° and an overlap rate of 15% to 25%.

[0051] The non-metallic outer sheath 9 is made of polyolefin sheath material and is extruded onto the outer surface of the aforementioned armor layer 8 to form the overall external protection of the cable.

[0052] {Example 2}

[0053] 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:

[0054] Step 1: Prepare the insulated conductor

[0055] A conductor shielding layer 12 and a radiation-cross-linked polyethylene insulation layer 13 are extruded from the outer surface of a copper conductor 11 formed by twisting multiple copper wires using a double-layer co-extrusion process to form a conductor with a conductor shield and insulation coated on the outer surface; the conductor with the conductor shield and insulation coated on the outer surface is subjected to electron irradiation under radiation cross-linking conditions of a temperature of 140-150° C. and a certain radiation dose;

[0056] Step 2: Twisting to prepare the cable core

[0057] 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, and the multiple halogen-free flame-retardant PP mesh filling ropes are filled in the gaps between the multiple insulated conductors 1. The polyester tape is wrapped around the outer periphery of the cable core structure to form a wrapping layer. The aforementioned central filling layer 2 is a prefabricated 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.

[0058] Step 3: Extrude a polyethylene inner protective layer on the outer surface of the tape layer with a thickness of 1.5-2.5 mm;

[0059] Step 4: Use a braiding machine to weave 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 weaving density is greater than 80%, and the weaving angle is 45° to 55°.

[0060] Step 5: Extrude PVC on the outer surface of the copper wire shielding layer as an isolation layer;

[0061] Step 6: Wrap the steel tape around 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.

[0062] Step 7: Extrude a polyolefin sheath material onto the outer surface of the steel belt armor layer to prepare an outer sheath with a thickness of 2-2.5 mm.

[0063] Among them, 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 treatment, the oxygen-free copper wire is made soft and has high conductivity, RRR value and conductive performance.

[0064] A plurality of copper wires are twisted together by a frame-type stranding machine to produce a copper conductor 11 . The conductor has a compression coefficient greater than 90% and a twisting pitch-diameter ratio of 12.

[0065] A semi-conductive shielding layer and an irradiated cross-linked polyethylene (XLPE) insulation layer 12 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 the semi-conductive shielding material, and a modified anti-aging flame retardant and smoke-suppressing insulation material is used as the main insulating material. They are extruded on the outer surface of the copper conductor 11 to form a thin semi-conductive shielding layer (thickness of 1 mm) and an XLPE insulation layer (thickness of 2.5 mm).

[0066] 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 into a cable around the center filling layer 2 and the gaps are filled with halogen-free flame-retardant filling ropes 3.

[0067] The central filler layer 2, filling the center of the conductor, is a flexible layer composed of a phase change layer 21 and a high-temperature-resistant modified silicone rubber 22. The high-temperature-resistant modified silicone rubber 22 encapsulates the phase change layer 21, forming a core-shell thermally conductive structure. This provides flexible support and improved heat resistance, enhancing the cable's temperature resistance (medium-voltage cables typically maintain temperatures above 60°C year-round, and even briefly exceed 130°C during normal power transmission) and aging resistance. This prevents insulation aging and dendrite effects from long-term high-temperature exposure, which can pose stability and safety risks. Furthermore, the conductor shield 12 acts as a thermal barrier, preventing the impact of the conductor's thermal temperature rise on the main shielding layer, the XLPE insulation.

[0068] The high-temperature-resistant modified silicone rubber 22 is a copolymer of a silicone rubber matrix and an insulating thermally conductive material. The phase change layer 21 is a cylindrical structure formed from a shaped organic phase change material with high latent heat. This cylindrical structure is encased in the high-temperature-resistant modified silicone rubber 22 to form a concentric core-shell thermally conductive structure, or core-shell structure. The highly thermally conductive shell completely encases the PCM core, passively managing the heat of the internal conductor through the high latent heat PCM core, thereby improving the cable's heat resistance and resistance to insulation aging.

[0069] As an optional solution, the insulating thermal conductive material uses silicon nitride, a highly thermally conductive insulating material, which is dispersed in powder and copolymerized with the silicone rubber matrix to form a highly thermally conductive modified silicone rubber. The weight ratio of the insulating thermal conductive material added is less than 0.5%, and the powder is spherical.

[0070] While the present invention has been described above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A cross-linked polyethylene insulated halogen-free flame retardant special cable, characterized in that: include: An 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 an irradiated cross-linked polyethylene insulation layer (13); A central filling layer (2) is formed by 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-conducting 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, the halogen-free flame-retardant filling rope (3) is filled, 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; A non-metallic inner protective layer (5) is extruded onto the outer surface of the wrapping layer formed by the polyester tape (4); A metal wire shielding layer (6) woven on the outer surface of the non-metallic inner sheath (5); An isolation layer (7) extruded onto the outer surface of the metal wire shielding layer (6); An armor layer (8) is wrapped around the outer surface of the isolation layer (7) and is 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 of 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%; The conductor shielding layer (12) and the irradiated cross-linked polyethylene insulation layer (13) are extruded using a double-layer co-extrusion process; The metal wire shielding layer (6) adopts a copper wire braided shielding layer, the braiding density is greater than 80%, and the braiding angle is between 45° and 55°.

2. The cross-linked polyethylene insulated halogen-free flame-retardant special cable according to claim 1, characterized in that: The thickness of the conductor shielding layer (12) is smaller than the thickness of the irradiated cross-linked polyethylene insulation layer (13).

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

4. 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.

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