Medium voltage power cable without armour

Abstract

This invention provides an unarmored medium-voltage power cable, belonging to the field of cables, comprising: a cable core; an electrothermal layer covering the outer periphery of the cable core; a phase change heat dissipation layer covering the outer periphery of the electrothermal layer, the phase change heat dissipation layer being composed of a composite phase change material with a mass ratio of lauric acid:expanded graphite:graphene of 6:3:1, and a phase change temperature range of 40℃ to 50℃; an oxygen barrier layer covering the outer periphery of the phase change heat dissipation layer; a sheath layer covering the outer periphery of the oxygen barrier layer, the sheath layer being made of PVC flame-retardant material; and an electrothermal layer comprising: an electrothermal film covering the outer periphery of the filler layer. The purpose is to solve the problem that existing unarmored medium-voltage power cables cannot simultaneously meet the characteristics of high temperature resistance, high flame retardancy, and cold resistance. The technical effect achieved is to realize an unarmored medium-voltage power cable structure that can simultaneously meet the characteristics of high temperature resistance, high flame retardancy, and cold resistance.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and more particularly to an unarmored medium-voltage power cable. Background Technology

[0002] As power systems place increasingly higher demands on cable performance, traditional medium-voltage cables are prone to embrittlement in extreme low-temperature environments and exhibit problems such as high smoke toxicity and insufficient flame retardancy in fire scenarios. This situation is particularly prominent in mining, high-altitude and cold regions, and the new energy sector. These scenarios place special requirements on cables, necessitating that they simultaneously meet characteristics such as high temperature resistance, high flame retardancy, and cold resistance to ensure the safety and environmental friendliness of power transmission.

[0003] Medium-voltage cables generally refer to power cables with a rated voltage between 6kV and 35kV. Not all of these cables are armored. Unarmored cables are typically used in protected environments, such as cable trays or conduits, and indoor power distribution systems. However, the flexibility and electrical performance of existing unarmored medium-voltage power cables are severely affected in low-temperature environments, making them prone to cracking and other faults, which in turn interfere with the stability of power transmission. Furthermore, due to the lack of appropriate insulation structures, they cannot meet the requirements for energy saving and stable power supply in some scenarios that require insulation. Summary of the Invention

[0004] This invention provides an unarmored medium-voltage power cable to solve the defects of existing unarmored medium-voltage power cables that cannot simultaneously meet the characteristics of high temperature resistance, high flame retardancy, and cold resistance, and realizes an unarmored medium-voltage power cable structure that can simultaneously meet the characteristics of high temperature resistance, high flame retardancy, and cold resistance.

[0005] This invention provides an unarmored medium-voltage power cable, comprising: Cable inner core; An electrothermal layer, including an electrothermal film, the electrothermal film covering the outer periphery of the inner core of the cable; The phase change heat dissipation layer is wrapped around the outer periphery of the electrothermal layer. The phase change heat dissipation layer is composed of a composite phase change material with a mass ratio of lauric acid: expanded graphite: graphene of 6:3:1. The phase change temperature range of the phase change heat dissipation layer is 40℃ to 50℃. An oxygen barrier layer covers the outer periphery of the phase change heat dissipation layer; The sheath layer, which covers the oxygen-barrier outer perimeter, is made of flame-retardant PVC material.

[0006] In addition, the armorless medium-voltage power cable according to the present invention may also have the following additional technical features: In some embodiments of the present invention, the cable core includes: conductor; An insulating layer is formed and covers the outer periphery of the conductor. A filler layer covers the outer periphery of the insulating layer, and the heating layer covers the outer periphery of the filler layer.

[0007] In some embodiments of the present invention, it further includes: A first shielding layer is disposed between the insulating layer and the conductor; A second shielding layer is disposed between the filling layer and the insulating layer; The third shielding layer is disposed between the second shielding layer and the filling layer.

[0008] In some embodiments of the present invention, it further includes: A heat dissipation mesh is placed between the oxygen barrier layer and the phase change heat dissipation layer.

[0009] In some embodiments of the present invention, it further includes: The first fiberglass strip is placed between the oxygen barrier layer and the heat dissipation mesh; The second fiberglass strip is placed between the oxygen barrier layer and the sheath layer.

[0010] In some embodiments of the present invention, the electrothermal layer further includes: The wire core is spirally wound onto the heating film.

[0011] In some embodiments of the present invention, the electrothermal layer further includes: The temperature control chip is integrated into the heating film, and the heating film and the wire core are electrically connected to the temperature control chip.

[0012] In some embodiments of the present invention, it further includes: Temperature sensor, which is integrated on the heating film or conductor, is electrically connected to the temperature control chip.

[0013] In some embodiments of the present invention, the PVC flame-retardant material of the sheath layer is composed of 65 to 72 parts of polyvinyl chloride resin, 22 to 28 parts of nano magnesium hydroxide, 8 to 12 parts of phosphorus-nitrogen composite flame retardant, 18 to 22 parts of cold-resistant plasticizer, 3 to 5 parts of nano titanium dioxide, 5 to 8 parts of heat stabilizer, 1 to 2 parts of antioxidant and 0.8 to 1.2 parts of lubricant.

[0014] In some embodiments of the present invention, the particle size of nano-magnesium hydroxide is between 30 nm and 50 nm; The particle size of nano-titanium dioxide is between 20nm and 30nm.

[0015] In summary, this application offers the following beneficial technical effects: The combined use of an electrothermal film and a phase-change heat dissipation layer enables the cable to heat rapidly in low-temperature environments and effectively dissipate heat in high-temperature environments, thereby ensuring the cable operates within a suitable temperature range and indirectly improving power supply stability and equipment lifespan. The use of a flame-retardant PVC sheath effectively suppresses the generation of dense smoke, reducing the harm of toxic fumes to personnel and the environment, and providing favorable conditions for fire rescue. Ultimately, the cable of this application simultaneously meets the requirements of high temperature resistance, high flame retardancy, and cold resistance. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A schematic diagram of the structure of an unarmored medium-voltage power cable according to some embodiments of the present invention is shown.

[0017] Figure label: 1. Conductor; 2. First shielding layer; 3. Insulating layer; 4. Second shielding layer; 5. Third shielding layer; 6. Filling layer; 7. Wrapping layer; 8. Electrothermal layer; 9. Phase change heat dissipation layer; 10. Heat dissipation mesh; 11. First fiberglass tape; 12. Oxygen barrier layer; 13. Second fiberglass tape; 14. Sheath layer. Detailed Implementation

[0018] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0019] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “” used herein may also indicate the inclusion of the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated, unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0020] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0021] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "over," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure is flipped, an element described as "below other elements or features" or "below other elements or features" would subsequently be oriented "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may also be rotated 90 degrees or in other orientations, and the spatial relative descriptors used in the text will be interpreted accordingly.

[0022] like Figure 1As shown, according to an embodiment of the first aspect of the present invention, an unarmored medium-voltage power cable is provided, comprising a cable core, a wrapping layer 7, an oxygen barrier layer 12, an electric heating layer 8, a phase change heat dissipation layer 9, and a sheath layer 14. The cable core comprises a conductor 1, an insulation layer 3, and a filling layer (6). The insulation layer 3 covers the outer periphery of the conductor 1, the filling layer 6 covers the outer periphery of the insulation layer 3, the electric heating layer 8 comprises an electric heating film, the electric heating film covers the outer periphery of the filling layer 6, the wrapping layer 7 is disposed between the electric heating layer 8 and the filling layer 6, the phase change heat dissipation layer 9 covers the outer periphery of the electric heating layer 8, the oxygen barrier layer 12 covers the outer periphery of the phase change heat dissipation layer 9, and the sheath layer 14 covers the outer periphery of the oxygen barrier.

[0023] In the above experimental example, it should be noted that conductor 1 is a compacted round copper conductor with a fill factor greater than or equal to 92%; specifically, there are three conductors 1; the filler layer 6 is a ceramicized silicone rubber flame-retardant filler strip with an oxygen index ≥ 45%; the phase change heat dissipation layer 9 is made of a phase change heat dissipation material with a coating thickness of 0.8mm to 1.2mm; the sheath layer 14 is embedded with a carbon fiber sensor network and a wireless transmission module; the oxygen barrier layer 12 is a low-smoke halogen-free high flame-retardant polyolefin oxygen barrier layer; and the sheath layer 14 is made of PVC flame-retardant material.

[0024] The technical effect achieved by the above experimental example is that by using PVC flame-retardant material to make the sheath layer 14, the sheath layer 14 can effectively suppress the generation of dense smoke, reduce the harm of toxic smoke to personnel and the environment, and provide favorable conditions for fire rescue.

[0025] The combination of insulation layer 3, filling layer 6, wrapping layer 7, oxygen barrier layer 12 and PVC sheath layer 14 gives the power cable good flame retardant properties, effectively preventing the spread of flames and improving the safety of power facilities.

[0026] The combination of the electric heating film and the phase change heat dissipation layer 9 enables the cable to heat up rapidly in low-temperature environments and dissipate heat effectively in high-temperature environments. This allows for bidirectional temperature control, including both cooling and heating, even without armor, keeping the cable within a suitable operating temperature range. This indirectly improves power supply stability and equipment lifespan. Ultimately, the cable can simultaneously meet the requirements of high temperature resistance, high flame retardancy, and cold resistance.

[0027] Optional, such as Figure 1 As shown, the unarmored medium-voltage power cable also includes a first shielding layer 2 and a second shielding layer 4. The first shielding layer 2 is disposed between the insulation layer 3 and the conductor 1, and the second shielding layer 4 is disposed between the filler layer 6 and the insulation layer 3.

[0028] In the above optional embodiments, it should be noted that the first shielding layer 2 is a conductor shielding layer, and each conductor 1 is covered with a conductor shielding layer on its outer periphery. Each conductor shielding layer is covered with an insulating layer 3 on its outer periphery. The second shielding layer 4 is an insulating shielding layer, and each insulating layer 3 is covered with an insulating shielding layer on its outer periphery.

[0029] The advantages of the above optional embodiments are as follows: by covering the outer periphery of the conductor 1 with the first shielding layer 2, the sharp point effect and burr effect on the surface of the conductor 1 can be effectively eliminated, making the electric field distribution more uniform, avoiding the accelerated insulation aging caused by excessive local field strength, and extending the service life of the insulation layer 3.

[0030] The second shielding layer 4 is located between the insulation layer 3 and the filling layer 6. It can enclose the electric field on the outer surface of the insulation layer 3 within the shielding layer, preventing the electric field from spreading to the outside and interfering with surrounding equipment. At the same time, it blocks external electromagnetic signals from intruding into the inside of the cable, thus improving the anti-interference capability.

[0031] The first shielding layer 2 and the second shielding layer 4 work together to form a complete shielding system, which not only ensures the stability of the electric field between the conductor 1 and the insulation layer 3, but also strengthens the electromagnetic isolation of the insulation layer 3 from the outside world, greatly reduces the probability of partial discharge, and enhances the safety and reliability of the cable operation. It is suitable for high voltage and strong electromagnetic environment scenarios.

[0032] Optional, such as Figure 1 As shown, it also includes a third shielding layer 5, which is disposed between the second shielding layer 4 and the filling layer 6.

[0033] In the above optional embodiments, it should be noted that the third shielding layer 5 is a metal shielding layer.

[0034] The advantages of the above optional embodiments are as follows: by setting the third shielding layer 5, the electromagnetic signals that are not completely blocked by the second shielding layer 4 can be intercepted for a second time, which greatly reduces the interference of the external strong electromagnetic environment on the internal signals of the cable, and at the same time prevents the cable's own electric field from spreading to the outside, thus avoiding electromagnetic interference to surrounding equipment.

[0035] In addition, the third shielding layer 5 of the metal shielding layer can fill the gap between the second shielding layer 4 and the filling layer 6, reduce the interface electric field fluctuation caused by the loose structure of the filling layer 6, and at the same time, with the help of the physical strength of the metal, provide mechanical protection for the insulating shielding layer, reducing the risk of damage to the insulating layer 3 caused by the filling layer 6 being squeezed or minor external impacts.

[0036] Optional, such as Figure 1 As shown, it also includes a heat dissipation mesh 10, which is disposed between the oxygen barrier layer 12 and the phase change heat dissipation layer 9.

[0037] In the above optional embodiments, it should be noted that the phase change heat dissipation layer 9 covers the outer periphery of the electrothermal film, and the heat dissipation mesh 10 is a honeycomb graphene heat dissipation mesh 10 with a thickness between 0.3 mm and 0.5 mm; the phase change heat dissipation layer 9 is composed of a composite phase change material with a mass ratio of lauric acid: expanded graphite: graphene of 6:3:1, and is prepared using microencapsulation technology, with a phase change temperature range of 40°C to 50°C.

[0038] When the cable temperature exceeds 40°C, the phase change material absorbs heat and changes from solid to liquid, storing heat; after the temperature drops, the liquid phase change material re-solidifies and releases heat, thus achieving heat buffering.

[0039] By utilizing the ultra-high thermal conductivity of graphene (greater than or equal to 5000 W / (m·K)) of the graphene heat dissipation mesh 10, heat is rapidly directed to the cable surface, thereby achieving efficient heat dissipation.

[0040] Calculations show that the heat dissipation efficiency of the power cable in this application is more than 45% higher than that of traditional cables, and it saves 45% more energy than traditional heat tracing cables. The specific calculation process is as follows: First, calculation of geometric parameters and heat dissipation area: External surface area per unit length of a conventional cable (85mm in diameter): ; The outer surface area per unit length of the cable (92mm in diameter) in this application is: ; Second, heat dissipation calculation: The thermal conductivity of the insulation layer of traditional cables is kxlpe=0.35; the thermal conductivity of ordinary PVC sheath is kpvc=0.18; and the convective heat transfer coefficient for natural convection is h=10. The thermal resistance of the insulation layer (outer diameter of conductor 1 is approximately 0.01 μm) is: ; The thermal resistance of sheath layer 14 is: ; The convection thermal resistance is: ; The total thermal resistance is: ; Heat dissipation for: ; Represents the phase change heat dissipation temperature. =40℃.

[0041] The heat dissipation of the power cable in this application calculate: The thermal conductivity of phase change heat dissipation layer 9 is kpc=0.8; the thermal conductivity of graphene heat dissipation mesh 10 is kgr=5000; the enhanced convection on the graphene surface increases the convective heat transfer coefficient to h=25; the thermal resistance of phase change heat dissipation layer 9 and graphene heat dissipation mesh 10 is calculated as follows: The outer radius of sheath layer 14 is: ; The outer radius of phase change heat dissipation layer 9 is: ; The outer radius of the graphene heat dissipation mesh 10 is: m; The thermal resistance of phase change heat dissipation layer 9 is: ; The thermal resistance of the graphene heat dissipation mesh 10 is: (Negligible); Convection thermal resistance: ; Total thermal resistance (ignoring the thermal resistance of graphene heat dissipation mesh 10): ; Heat dissipation : ; Represents the phase change heat dissipation temperature. =40℃.

[0042] Third, the percentage increase in heat dissipation efficiency: .

[0043] Optional, such as Figure 1 As shown, it also includes a first glass fiber strip 11 and a second glass fiber strip 13. The first glass fiber strip 11 is disposed between the oxygen barrier layer 12 and the heat dissipation mesh 10, and the second glass fiber strip 13 is disposed between the oxygen barrier layer 12 and the sheath layer 14.

[0044] In the above optional embodiments, it should be noted that both the first glass fiber tape 11 and the second glass fiber tape 13 are low-smoke halogen-free glass fiber tapes.

[0045] The advantages of the above optional embodiments are as follows: the arrangement of the first glass fiber tape 11 between the oxygen barrier layer 12 and the heat dissipation mesh 10 can prevent the heat dissipation mesh 10 from damaging the oxygen barrier layer 12 due to external friction, and at the same time, its high temperature resistance characteristics can be used to help the oxygen barrier layer 12 block heat transfer.

[0046] The second fiberglass tape 13 is located between the oxygen barrier layer 12 and the sheath layer 14. It can buffer the impact of the sheath layer 14 on the oxygen barrier layer 12 when it is squeezed by external force, reduce the risk of damage to the oxygen barrier layer 12, and its insulation can enhance the overall electrical safety.

[0047] Optional, such as Figure 1 As shown, the heating layer 8 includes a wire core that is spirally wound on the heating film, and the wrapping layer 7 is located between the heating film and the filler layer 6.

[0048] In the above optional embodiments, it should be noted that the heating film is a flexible heating film; the flexible heating film is spirally wound around the core, the thickness of the flexible heating film is between 0.08mm and 0.12mm, it is printed with polyimide-based carbon nanotube conductive ink, and the surface resistance is between 8Ω / sq and 12Ω / sq, where Ω / sq is ohms per square meter.

[0049] Energy efficiency calculation of heating layer 8: Energy consumption E0 calculation for traditional heat tracing cables; Assume the constant power of a traditional heat tracing cable is P0 = 35 kW·h; The energy consumption of a traditional heat tracing cable in 24 hours is E0 = P0 × 24 = 840 KW; Dynamic power adjustment of energy consumption E of heating layer 8: Start-up phase (0~0.5h): Power P1 = 30KW·h; Constant temperature stage (0.5~24h): Average power P2=19.25KW·h (temperature control chip adjusts according to temperature feedback); The energy consumption for 24 hours is: E = P1 × 0.5 + P2 × 23.5 = 467.375 KW; Energy saving rate calculation: (840-467.375) / 840=44.36%; The beneficial effect of the above optional embodiments is that the cold resistance of the cable of this application is significantly improved by setting the electrothermal film.

[0050] Optional, such as Figure 1 As shown, the heating layer 8 also includes a temperature control chip, which is integrated into the heating film.

[0051] In the above optional embodiments, it should be noted that the temperature control chip is an existing intelligent temperature control chip, and the temperature control chip is communicatively connected to the wireless transmission module inside the sheath layer 14; the accuracy of the temperature control chip is ±0.1℃.

[0052] The advantages of the above optional embodiments are: by using the built-in temperature control chip in the heating film, the heating power can be automatically adjusted to maintain the internal temperature of the cable within the set temperature range.

[0053] Optional, such as Figure 1 As shown, it also includes a temperature sensor, which is integrated on the heating film or conductor 1, and the temperature sensor is electrically connected to the temperature control chip.

[0054] In the above optional embodiments, it should be noted that the temperature sensor is a platinum resistance sensor with an accuracy of ±0.2℃, and the temperature control chip is electrically connected to the heating film.

[0055] The advantages of the above optional embodiments are as follows: the cable of this application achieves the goal of not needing armoring while meeting performance requirements through the setting of phase change heat dissipation layer 9 and electrothermal layer 8, thereby reducing the weight and cost of the cable, while improving the bending performance of the cable and facilitating installation and laying.

[0056] The combination of the electric heating layer 8, the phase change heat dissipation layer 9, and the heat dissipation mesh 10 enables the temperature of the cable of this application to be dynamically adjusted in both directions, ensuring that the cable is in the optimal operating temperature range and improving power supply stability and service life.

[0057] Optional, such as Figure 1 As shown, the PVC flame-retardant material of the sheath layer 14 is composed of 65 to 72 parts of polyvinyl chloride resin, 22 to 28 parts of nano magnesium hydroxide, 8 to 12 parts of phosphorus-nitrogen composite flame retardant, 18 to 22 parts of cold-resistant plasticizer, 3 to 5 parts of nano titanium dioxide, 5 to 8 parts of heat stabilizer, 1 to 2 parts of antioxidant and 0.8 to 1.2 parts of lubricant.

[0058] The beneficial effects of the above optional embodiments are as follows: the formulation of the PVC flame-retardant material of the sheath layer 14 achieves an oxygen index of over 42% and a smoke density rating (SDR) of ≤8 through the synergistic effect of nano flame retardants and phosphorus-nitrogen flame retardants; the addition of cold-resistant plasticizers and nano titanium dioxide ensures that the elongation at break of the sheath is ≥350% at -60℃; thus, the cable of this application can still maintain good flexibility and electrical performance in low-temperature environments, is not prone to cracking and other faults, and ensures the stability of power transmission.

[0059] Examples and comparative studies of the PVC flame-retardant material test results for sheath layer 14 are as follows: Dumbbell-shaped sheath specimens (thickness 1.0 mm to 2.0 mm) were prepared, pretreated in a -60°C environment for 4 hours using a low-temperature tensile testing machine, and subjected to a low-temperature tensile test at a tensile rate of 25 mm / min. The elongation at break was recorded.

[0060] In Experiment 1, the PVC flame-retardant material of the sheath layer 14 is composed of 66 parts of polyvinyl chloride resin, 23 parts of nano magnesium hydroxide, 9 parts of phosphorus-nitrogen composite flame retardant, 19 parts of cold-resistant plasticizer, 3 parts of nano titanium dioxide, 6 parts of heat stabilizer, 1 part of antioxidant and 0.8 parts of lubricant. The performance parameters of the sheath layer 14 in Experiment 1 are shown in Table 1 below.

[0061] Table 1 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 362 -60.2 25 43 2 1.48 18.2 368 -59.8 25 43 3 1.50 17.5 359 -60.1 25 43 4 1.53 18.5 371 -59.9 25 43 5 1.49 17.9 365 -60.0 25 43 In Experiment 2, the PVC flame-retardant material of the sheath layer 14 is composed of 72 parts of polyvinyl chloride resin, 28 parts of nano magnesium hydroxide, 12 parts of phosphorus-nitrogen composite flame retardant, 22 parts of cold-resistant plasticizer, 5 parts of nano titanium dioxide, 8 parts of heat stabilizer, 2 parts of antioxidant and 1.2 parts of lubricant. The performance parameters of the sheath layer 14 in Experiment 2 are shown in Table 2 below.

[0062] Table 2 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 366 -60.2 25 48 2 1.48 18.2 371 -59.8 25 48 3 1.50 17.5 362 -60.1 25 48 4 1.53 18.5 374 -59.9 25 48 5 1.49 17.9 368 -60.0 25 48 In Experiment 3, the PVC flame-retardant material of the sheath layer 14 is composed of 69 parts of polyvinyl chloride resin, 25 parts of nano magnesium hydroxide, 10 parts of phosphorus-nitrogen composite flame retardant, 20 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 7 parts of heat stabilizer, 2 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Experiment 3 are shown in Table 3 below.

[0063] Table 3 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 364 -60.2 25 45 2 1.48 18.2 369 -59.8 25 45 3 1.50 17.5 360 -60.1 25 45 4 1.53 18.5 372 -59.9 25 45 5 1.49 17.9 366 -60.0 25 45 Experimental Examples 1, 2, and 3 demonstrate that the formulation of the PVC flame-retardant material in the sheath layer 14 achieves an oxygen index of over 42% and a smoke density rating (SDR) of ≤8 through the synergistic effect of nano flame retardants and phosphorus-nitrogen flame retardants. The addition of cold-resistant plasticizers and nano titanium dioxide ensures that the elongation at break of the sheath layer 14 is ≥350% at -60℃. This enables the cable of this application to maintain good flexibility and electrical performance in low-temperature environments, making it less prone to cracking and other faults, thus ensuring the stability of power transmission.

[0064] In addition, the formulation of the PVC flame-retardant material of the sheath layer 14 achieves a smoke density rating (SDR) ≤8 through the synergistic effect of nano flame retardants and phosphorus-nitrogen flame retardants, as detailed in Table 4 below.

[0065] Table 4

[0066] Comparative Example 1: The PVC flame-retardant material of the sheath layer 14 is composed of 68 parts of polyvinyl chloride resin, 18 parts of nano magnesium hydroxide, 10 parts of phosphorus-nitrogen composite flame retardant, 20 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 6.5 parts of heat stabilizer, 1.5 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Comparative Example 1 are shown in Table 5 below.

[0067] Table 5 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 360 -60.2 25 39 2 1.48 18.2 366 -59.8 25 39 3 1.50 17.5 358 -60.1 25 39 4 1.53 18.5 368 -59.9 25 39 5 1.49 17.9 365 -60.0 25 39 Comparative Example 1 shows that insufficient nano-magnesium hydroxide will reduce the flame retardant properties. In Comparative Example 2, the PVC flame-retardant material of the sheath layer 14 is composed of 68 parts of polyvinyl chloride resin, 25 parts of nano magnesium hydroxide, 6 parts of phosphorus-nitrogen composite flame retardant, 20 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 6.5 parts of heat stabilizer, 1.5 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Comparative Example 2 are shown in Table 6 below.

[0068] Table 6 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 361 -60.2 25 40 2 1.48 18.2 367 -59.8 25 40 3 1.50 17.5 360 -60.1 25 40 4 1.53 18.5 371 -59.9 25 40 5 1.49 17.9 364 -60.0 25 40 Comparative Example 2 shows that the phosphorus-nitrogen composite flame retardant is insufficient, and the expected flame retardant performance will be reduced, while other properties are relatively stable.

[0069] In Comparative Example 3, the PVC flame-retardant material of the sheath layer 14 is composed of 68 parts of polyvinyl chloride resin, 25 parts of nano magnesium hydroxide, 10 parts of phosphorus-nitrogen composite flame retardant, 15 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 6.5 parts of heat stabilizer, 1.5 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Comparative Example 3 are shown in 7 below.

[0070] Table 7 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 335 -60.2 25 45 2 1.48 18.2 337 -59.8 25 45 3 1.50 17.5 334 -60.1 25 45 4 1.53 18.5 338 -59.9 25 45 5 1.49 17.9 336 -60.0 25 45 Comparative Example 4: The PVC flame-retardant material of the sheath layer 14 is composed of 68 parts of polyvinyl chloride resin, 25 parts of nano magnesium hydroxide, 10 parts of phosphorus-nitrogen composite flame retardant, 15 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 6.5 parts of heat stabilizer, 1.5 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Comparative Example 4 are shown in Table 8 below.

[0071] Table 8 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 361 -55.2 25 45 2 1.48 18.2 366 -54.8 25 45 3 1.50 17.5 360 -55.1 25 45 4 1.53 18.5 372 -54.9 25 45 5 1.49 17.9 366 -55.0 25 45 Comparative Examples 3 and 4 show that insufficient cold-resistant plasticizer will reduce cold resistance, while other properties remain basically normal.

[0072] Comparative Example 5: The PVC flame-retardant material of the sheath layer 14 is composed of 68 parts of polyvinyl chloride resin, 25 parts of nano magnesium hydroxide, 10 parts of phosphorus-nitrogen composite flame retardant, 20 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 3 parts of heat stabilizer, 1.5 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Comparative Example 5 are shown in Table 9 below.

[0073] Table 9 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (°C) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 348 -60.2 25 41 2 1.48 18.2 351 -59.8 25 41 3 1.50 17.5 345 -60.1 25 41 4 1.53 18.5 353 -59.9 25 41 5 1.49 17.9 349 -60.0 25 41 Comparative Example 5 shows that the stabilizer is insufficient, which is expected to make the material prone to degradation during processing, affecting product quality and other properties. Comparative Example 6: The PVC flame-retardant material of the sheath layer 14 is composed of 75 parts of polyvinyl chloride resin, 25 parts of nano magnesium hydroxide, 10 parts of phosphorus-nitrogen composite flame retardant, 15 parts of cold-resistant plasticizer, 4 parts of nano titanium dioxide, 6.5 parts of heat stabilizer, 1.5 parts of antioxidant and 1 part of lubricant. The performance parameters of the sheath layer 14 in Comparative Example 6 are shown in Table 10 below.

[0074] Table 10 Style Number Thickness (mm) Tensile strength (MPa) Elongation at break (%) Test temperature (%) Tension rate (mm / min) Oxygen index (%) 1 1.52 17.8 349 -60.2 25 45 2 1.48 18.2 354 -59.8 25 45 3 1.50 17.5 347 -60.1 25 45 4 1.53 18.5 355 -59.9 25 45 5 1.49 17.9 352 -60.0 25 45 Comparative Example 6 shows that excessive polyvinyl chloride resin will result in a harder protective layer, reduced flexibility, and may also affect processing fluidity, and other properties may fluctuate.

[0075] Optional, such as Figure 1 As shown, the particle size of nano-magnesium hydroxide is between 30 nm and 50 nm, and the particle size of nano-titanium dioxide is between 20 nm and 30 nm.

[0076] The advantages of the above optional embodiments are as follows: nano magnesium hydroxide has better dispersibility in the particle size range of 30nm to 50nm, can uniformly fill the substrate, and can quickly release crystal water when exposed to high temperature. It can exert a highly efficient flame retardant effect by absorbing heat and diluting oxygen, while avoiding the decline in the mechanical properties of the substrate due to excessive particle size.

[0077] The particle size of nano-titanium dioxide, ranging from 20nm to 30nm, gives it a larger specific surface area, which can enhance its ability to absorb and scatter ultraviolet light, improve the material's weather resistance, and at the same time assist in the catalytic degradation of surface pollutants.

[0078] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An unarmored medium-voltage power cable, characterized in that, include: Cable inner core; The heating layer (8) includes a heating film that covers the outer periphery of the inner core of the cable; A phase change heat dissipation layer (9) is wrapped around the outer periphery of the electrothermal layer (8). The phase change heat dissipation layer (9) is composed of a composite phase change material with a mass ratio of lauric acid: expanded graphite: graphene of 6:3:

1. The phase change temperature range of the phase change heat dissipation layer (9) is 40°C to 50°C. An oxygen barrier layer (12) is wrapped around the outer periphery of the phase change heat dissipation layer (9); A sheath layer (14) is wrapped around the outer periphery of the oxygen barrier layer (12), and the sheath layer (14) is made of PVC flame-retardant material.

2. The unarmored medium-voltage power cable according to claim 1, characterized in that, The cable core includes: Conductor (1); An insulating layer (3) covers the outer periphery of the conductor (1); A filling layer (6) covers the outer periphery of the insulating layer (3), and an electrothermal layer (8) covers the outer periphery of the filling layer (6).

3. The unarmored medium-voltage power cable according to claim 2, characterized in that, Also includes: A first shielding layer (2) is disposed between the insulating layer (3) and the conductor (1); The second shielding layer (4) is disposed between the filling layer (6) and the insulating layer (3); The third shielding layer (5) is disposed between the second shielding layer (4) and the filling layer (6).

4. The unarmored medium-voltage power cable according to claim 1, characterized in that, Also includes: A heat dissipation mesh (10) is disposed between the oxygen barrier layer (12) and the phase change heat dissipation layer (9).

5. The unarmored medium-voltage power cable according to claim 4, characterized in that, Also includes: A first glass fiber strip (11) is disposed between the oxygen barrier layer (12) and the heat dissipation mesh (10); A second fiberglass strip (13) is disposed between the oxygen barrier layer (12) and the sheath layer (14).

6. The unarmored medium-voltage power cable according to claim 1, characterized in that, The electrothermal layer (8) further includes: The wire core is spirally wound onto the heating film.

7. The unarmored medium-voltage power cable according to claim 6, characterized in that, The electrothermal layer (8) further includes: A temperature control chip is integrated within the heating film, and both the heating film and the wire core are electrically connected to the temperature control chip.

8. The unarmored medium-voltage power cable according to claim 7, characterized in that, Also includes: A temperature sensor is integrated on the electrothermal film or the conductor (1) and is electrically connected to the temperature control chip.

9. The unarmored medium-voltage power cable according to claim 1, characterized in that, The sheath layer (14) is made of PVC flame-retardant material; The PVC flame retardant material is composed of 65 to 72 parts of polyvinyl chloride resin, 22 to 28 parts of nano magnesium hydroxide, 8 to 12 parts of phosphorus-nitrogen composite flame retardant, 18 to 22 parts of cold-resistant plasticizer, 3 to 5 parts of nano titanium dioxide, 5 to 8 parts of heat stabilizer, 1 to 2 parts of antioxidant and 0.8 to 1.2 parts of lubricant.

10. The unarmored medium-voltage power cable according to claim 9, characterized in that, The particle size of the nano-magnesium hydroxide is between 30 nm and 50 nm. The nano-titanium dioxide particles have a size between 20 nm and 30 nm.

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