High-voltage fire-resistant cable

Abstract

The invention relates to the field of cables, and discloses a high-voltage fire-resistant cable, which comprises an outer layer, a skeleton structure is arranged in the outer layer, a plurality of groups of wire cores are arranged between the skeleton structure and the outer layer at equal intervals, and a reinforcing core is arranged in the skeleton structure. A middle fireproof layer adopts a ceramic silicone rubber composite system (containing 25 parts of phlogopite, 8 parts of nanometer aluminum oxide and a ceramic accelerant) with an optimized proportion, a hard protective shell with the density being larger than or equal to 1.8 g / cm < 3 > can be rapidly ceramized at the temperature of 320 DEG C, the synergistic flame-retardant effect of surface layer high-flame-retardant PVC (the oxygen index is 32) is matched, and the flame-retardant effect is good; the cable can continuously block heat permeation in flame of 950-1000 DEG C for 180 minutes, the temperature of the inner layer is stably controlled to be below 180 DEG C and is far lower than the insulation tolerance limit of a cable core, the pain point of'rapid failure in fire 'of a traditional cable is thoroughly solved, and golden rescue time is won for power emergency guarantee in key scenes such as high-rise buildings and subway tunnels.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cables, in particular to a high-voltage fire-resistant cable. BACKGROUND

[0002] With the acceleration of social energy transformation and industrialization and urbanization, the power load of enterprises and residents continues to rise, and higher requirements are put forward for the safety and stability of power transmission systems. As the key carrier of power transmission, the performance of power cables is directly related to the reliability of power supply. Once an accident occurs in a power cable, not only will it cause a large area power outage and affect the social production and life order, but also it may cause serious safety accidents such as fire, causing huge economic losses and personal injuries.

[0003] In the conventional power cable structure, a metal armor layer is often provided to enhance mechanical strength, improve corrosion resistance, achieve shielding protection, and prolong service life.

[0004] As a metal material, the corrugated aluminum sheath cannot be integrally formed and needs to be assembled to the cable by welding. The high temperature generated during the welding process is easy to cause thermal damage to the internal cable structure, especially the insulation layer, reducing the insulation performance and service life of the cable. To avoid this problem, the inner surface of the aluminum sheath is usually designed in a corrugated shape, but this raises new hidden dangers. Due to the thermal expansion and contraction characteristics of metal, air gaps are easy to appear between the insulation shielding layer and the semi-conductive water-blocking layer during the operation of the cable. The existence of these air gaps causes a floating potential between the corrugated aluminum sheath and the insulation shielding layer, and further causes a potential difference between the metal sheath and the insulation shielding layer, resulting in partial discharge. Although the amount of single partial discharge is small, it will gradually erode the main insulation layer of the cable over a long period of time, and in severe cases, it may even cause cable breakdown and cause safety accidents.

[0005] The 500kV extra-high voltage water-blocking power cable disclosed in Chinese patent application CN103345965A takes certain measures in the radial direction, such as setting a semi-conductive buffer water-blocking layer, a corrosion-resistant asphalt layer, and a seamless corrugated metal sheath, but the air gap problem between the corrugated metal sheath and the water-blocking layer has not been effectively solved, and the risk of partial discharge caused by floating potential still exists, affecting the long-term stable operation of the cable.

[0006] Furthermore, traditional high-voltage cables also face challenges in terms of insulation material performance and structural design. As voltage levels increase, insulation thickness increases accordingly, making it difficult to fully expel gases and cross-linking byproducts during vacuum degassing. Even with extended degassing time, some gases and cross-linking byproducts remain on the inner side of the insulation, leading to inconsistent degassing levels on the inner and outer sides, affecting the cable's partial discharge, aging, and breakdown performance. Simultaneously, during operation, the dielectric of the insulation layer in high-voltage power cables is subjected to a combined electro-thermal effect, accelerating material aging and causing phenomena such as partial discharge and electrical treeing, ultimately potentially leading to through-breakdown of the insulation layer. For high-voltage DC cables, the conductor core continuously injects space charge into the insulation layer during operation. These charges gradually accumulate in the insulation layer, distorting the electric field and increasing the local field strength, further accelerating the aging and breakdown of the insulation material. Moreover, in the actual partial discharge detection of high-voltage power cables, the time from the occurrence of partial discharge to the growth of electrical trees causing through-breakdown is short, making it difficult to obtain effective partial discharge information and issue an alarm in time before the cable breaks down. Therefore, we propose a high-voltage fire-resistant cable. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a high-voltage fire-resistant cable that solves the aforementioned problems.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a high-voltage fire-resistant cable, comprising an outer layer, wherein a skeleton structure is provided inside the outer layer, and multiple sets of wire cores are equidistantly arranged between the skeleton structure and the outer layer, and a reinforcing core is provided inside the skeleton structure.

[0009] Preferably, the outer layer includes a surface layer, an intermediate refractory layer, and an inner layer, wherein the surface layer is disposed on the outside of the intermediate refractory layer, and the inner layer is disposed on the inside of the intermediate refractory layer.

[0010] Preferably, the skeleton structure includes a central tube and partitions integrally formed at equal intervals on the outside of the central tube, with gaps between adjacent partitions, the wire core is disposed in the gaps, and an arc-shaped filler block is filled between the wire core and the inner wall of the inner layer.

[0011] Preferably, a reinforcing core is inserted into the interior of the central tube.

[0012] Preferably, the surface layer is composed of polyvinyl chloride resin, flame retardant, plasticizer, stabilizer, lubricant and antioxidant, and its weight percentage composition is as follows: 85 parts polyvinyl chloride resin, 3-8 parts flame retardant, 12 parts plasticizer, 3 parts stabilizer, 0.8 parts lubricant and 0.2 parts antioxidant.

[0013] Preferably, the intermediate refractory layer is composed of a ceramicized silicone rubber matrix, mica powder, nano-alumina, ceramicization accelerator, coupling agent, and vulcanizing agent, with the following weight percentage proportions: 100 parts ceramicized silicone rubber matrix, 25 parts mica powder, 8 parts nano-alumina, 3 parts ceramicization accelerator, 1.2 parts coupling agent, and 2.5 parts vulcanizing agent.

[0014] Preferably, the inner layer comprises a base resin, a crosslinking agent, an antioxidant, a copper inhibitor, and a lubricant, with the following weight percentage proportions: 100 parts base resin, 3.5 parts crosslinking agent, 0.6 parts antioxidant, 0.2 parts copper inhibitor, and 0.5 parts lubricant.

[0015] Compared with the prior art, the present invention provides a high-voltage fire-resistant cable with the following advantages: I. Ultimate fire resistance protection, building a solid safety barrier: The "double protective barrier" under high temperatures: The middle fire-resistant layer adopts an optimized ratio of ceramicized silicone rubber composite system (containing 25 parts phlogopite, 8 parts nano alumina and ceramicization accelerator), which can quickly ceramicize at 320℃ to form a hard protective shell with a density ≥1.8g / cm³. Combined with the synergistic flame-retardant effect of the surface high flame-retardant PVC (oxygen index 32), it can block heat penetration for 180 minutes in a flame of 950-1000℃. The inner layer temperature is stably controlled below 180℃, which is far below the insulation tolerance limit of the wire core. This completely solves the pain point of "rapid failure in fire" of traditional cables and buys golden rescue time for power emergency protection in critical scenarios such as high-rise buildings and subway tunnels. Low-smoke, halogen-free, environmentally friendly and safe: Both the surface and inner layers are made of environmentally friendly materials without heavy metal additives (such as calcium-zinc composite stabilizers and odorless crosslinking agents). No toxic smoke is released during fire combustion, and the smoke toxicity level reaches "ZA1 level" (the safest level) in GB / T 20284-2006. This can reduce secondary damage at the fire scene, and is especially suitable for hospitals, schools and other places with strict environmental and safety requirements. II. Significant improvement in electrical performance, ensuring long-term stable operation: Significantly improved insulation reliability: The inner XLPE insulation layer achieves an optimal crosslinking degree of 75-80% through precise proportioning (3.5 parts DCP crosslinking agent, 0.2 parts copper inhibitor), with a volume resistivity of 5×10¹. 4 -1×10¹ 5 With a dielectric loss tangent (tanδ) as low as 0.0006-0.0008 Ω・cm, compared to traditional XLPE insulation layers, the insulation resistance constant is increased by more than 50%, and the dielectric strength is increased by 17%-33%. It can effectively resist electric field distortion under 35kV high voltage conditions and avoid power outage accidents caused by insulation breakdown. Blocking the risk of partial discharge: The skeleton structure adopts a central tube + equidistant partition design, and the core and inner layer are filled with arc-shaped filler blocks, which completely eliminates the problem of "air gap between insulation shield and sheath" in traditional corrugated metal sheathed cables. The partial discharge caused by floating potential is reduced to ≤1pC (far lower than the 5pC required by the national standard GB / T 12706-2020), which solves the risk of long-term partial discharge eroding the main insulation from the root, and extends the service life of the cable from the traditional 20 years to more than 30 years. III. Mechanical performance adaptation reduces laying and maintenance costs: The structural advantages of flexibility and toughness: the outer PVC layer has an elongation at break of ≥160%, and the inner XLPE layer has an elongation at break of ≥350%. Combined with the normal flexibility of the ceramicized silicone rubber matrix (bending radius ≥8 times the cable outer diameter without cracks), it can adapt to bending installation in narrow spaces (such as cable wells and wall conduits). During installation, the tensile strength is ≥16MPa (outer layer) and ≥22MPa (inner layer), which can resist external impacts such as dragging and squeezing, reducing the breakage rate during construction. The construction qualification rate is increased from 85% of traditional cables to over 98%. Weather-resistant and corrosion-resistant "all-scenario adaptability": After 1000h xenon lamp aging, the surface layer retains ≥80% of its mechanical properties and can withstand 72h immersion in 5% acid and alkali solutions without bubbling or peeling; the inner XLPE layer has an insulation resistance decrease rate of only 15%-20% after resistant to damp heat aging (40℃, 93% RH), and can operate stably in the corrosive environment of chemical industrial parks and extreme outdoor climates (high temperature, heavy rain), reducing the number of maintenance and repairs caused by environmental erosion and reducing the average annual maintenance cost by 30%-40%. IV. Structural design optimization, balancing lightweight and scalability: Lightweight and space-saving: Abandoning the metal armor layer of traditional cables, mechanical strength support is achieved through "reinforcing core + skeleton structure" (the reinforcing core is inserted into the central tube, with a compressive strength ≥12MPa). The overall weight of the cable is reduced by 25%-30% compared to armored cables of the same specification. This not only reduces the labor costs of transportation and laying, but also reduces the load on cable trays, indirectly reducing infrastructure investment. Flexible core expansion: The gap between the partitions in the skeleton structure can be flexibly adjusted according to the number of cores (supporting 3-6 sets of cores arranged at equal intervals). The arc-shaped filler block can be adapted to cores of different diameters. It can meet the customized needs of different voltage levels and core numbers from 10kV to 35kV without redesigning the mold, shortening the product development cycle and improving the response speed to market demands. V. Addressing industry pain points and driving technological upgrades: Breaking through the limitations of traditional materials: The "normal temperature flexibility - high temperature ceramicization" characteristics of ceramicized silicone rubber solve the contradiction of traditional fire-resistant cables being "either flexible but not fire-resistant, or fire-resistant but brittle and hard"; the addition of an inner copper-resistant agent blocks the catalytic degradation of XLPE by copper ions, filling the technical gap of "insufficient copper resistance of high-voltage cables". In line with future development trends: All product performance meets the latest standards of the International Electrotechnical Commission (IEC) such as 60332-3 and 60502-1, and is also compatible with the requirements for environmentally friendly cables under my country's "dual carbon" goals. It can replace imported high-end high-voltage fire-resistant cables, promote the transformation of the domestic cable industry from "mass manufacturing" to "high-end intelligent manufacturing", and reduce the dependence on imports of power equipment in key areas. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 for Figure 1 A magnified view of part A in the diagram.

[0017] In the diagram: 1. Surface layer; 2. Intermediate fire-resistant layer; 3. Inner layer; 4. Central tube; 5. Reinforcing core; 6. Wire core; 7. Arc-shaped filler block. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figures 1-2 A high-voltage fire-resistant cable includes an outer layer, an inner skeleton structure, multiple sets of wire cores 6 equidistantly arranged between the skeleton structure and the outer layer, and a reinforcing core 5 arranged inside the skeleton structure.

[0020] Furthermore, the outer layer includes a surface layer 1, an intermediate refractory layer 2, and an inner layer 3. The surface layer 1 is disposed on the outside of the intermediate refractory layer 2, and the inner layer 3 is disposed on the inside of the intermediate refractory layer 2.

[0021] Furthermore, the skeleton structure includes a central tube 4 and partitions integrally formed at equal intervals on the outside of the central tube 4. There is a gap between two adjacent partitions, and the wire core 6 is set in the gap. An arc-shaped filler block 7 fills the space between the wire core 6 and the inner wall of the inner layer 3.

[0022] Furthermore, a reinforcing core 5 is inserted inside the central tube 4.

[0023] Furthermore, the surface layer 1 is composed of polyvinyl chloride resin, flame retardant, plasticizer, stabilizer, lubricant and antioxidant, and its weight percentage composition is as follows: 85 parts polyvinyl chloride resin, 3-8 parts flame retardant, 12 parts plasticizer, 3 parts stabilizer, 0.8 parts lubricant and 0.2 parts antioxidant.

[0024] Please refer to Table 1 below: Table 1: Specific proportions of surface layer 1: Component Name Specific Specification Weight Parts Function Description Polyvinyl Chloride Resin Type SG-5 (average polymerization degree 1000-1100) 85 Base material, providing basic mechanical properties and processability, ensuring structural stability after surface layer molding Flame Retardant Di-santimony trioxide (Sb203, purity > 99.5%) + Aluminum hydroxide (Al(OH)3, particle size 1-3 μm) 3-8 Compound flame retardant system: antimony trioxide as a synergistic flame retardant, can react with PVC decomposition products to generate flame-retardant gas; aluminum hydroxide decomposes and releases water vapor at high temperature, dilutes flammable gas, and the 1:2.7 ratio of the two can achieve the best flame-retardant synergistic effect Plasticizer Dioctyl phthalate (DOP, purity ≥99%) 12 Reduces the intermolecular forces of PVC, improves the flexibility of the surface layer, makes the surface layer less likely to crack when the cable bends, and improves the processing fluidity, facilitating extrusion molding Stabilizer Calcium-zinc composite stabilizer (Ca content 8-10%, Zn content 2-3%) 3 Inhibits thermal degradation of PVC during processing and use (avoids PVC aging due to high temperature HCl production), prolongs the service life of the surface layer, and is environmentally friendly without heavy metal pollution, meeting cable material environmental protection standards Lubricant Stearic acid (SA, purity ≥98%) 0.8 Reduces friction between materials and equipment during processing, prevents surface roughness, scratches, and other defects during surface layer molding, and ensures smooth surface appearance Antioxidant 1010 (tetra [beta- (3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester) 0.2 Inhibits performance degradation of PVC due to oxidation during long-term use, improves the surface layer's aging resistance, and is particularly suitable for cable applications in outdoor or high-temperature environments Basic physical properties: Thickness: 1.5mm (compatible with 10-35kV high-voltage cable specifications, balancing protection and lightweight). Tensile strength: ≥16MPa (higher than the standard of 15MPa for conventional PVC materials, and can withstand deformation caused by minor external impacts or compression). Elongation at break: ≥160% (ensuring no surface cracks when the cable is bent at a radius ≥12 times its outer diameter). Hardness (Shore A): 85±3 (ensuring surface scratch resistance while avoiding excessive hardness that could lead to brittle fracture). Flame retardant properties: Oxygen Index (OI): 32 (Tested according to GB / T 2406.2-2009, which is higher than the flame retardant requirement of "Oxygen Index ≥ 30". It requires an oxygen concentration of more than 32% in the air to burn, which greatly reduces the risk of fire spread). Vertical burning performance: Meets the requirements of "single cable vertical burning test" in GB / T 18380.1-2022, with a burning time of ≤30s and the burning drippings not igniting the degreased cotton below. Environmental resistance: Aging resistance: After aging at 100℃ for 168 hours, the tensile strength retention rate is ≥85%, and the elongation at break retention rate is ≥80% (meeting the requirements for long-term use of cables in high-temperature environments). Chemical corrosion resistance: After immersion in 5% hydrochloric acid solution and 5% sodium hydroxide solution for 72 hours, there is no blistering or peeling on the surface, and the tensile strength change rate is ≤±10% (it can resist acid and alkali corrosion and is suitable for special scenarios such as chemical and metallurgical industries); Weather resistance: After 1000 hours of xenon lamp aging test (simulating outdoor ultraviolet radiation), there is no obvious discoloration on the surface (color difference ΔE≤3), and the mechanical property retention rate is ≥80% (suitable for high-voltage cables laid outdoors). Formula design basis: Flame retardancy is a priority: by precisely controlling the compounding ratio of flame retardants, the oxygen index is increased to 32 without sacrificing flexibility, meeting the core requirements of "flame retardant and low smoke" for high-voltage cables, and avoiding the generation of large amounts of toxic smoke in the event of a fire; Processing and usage balance: 12 parts of plasticizer ensure good material flowability during extrusion molding, while avoiding surface "stickiness" due to excessive plasticizer; 3 parts of calcium-zinc stabilizer meet the thermal stability requirements without affecting mechanical properties by adding too much. Scene adaptability: Antioxidants and weather-resistant components are added to address the complex environments that high-voltage cables may face, such as outdoor, chemical, and high-temperature environments, to ensure that the surface layer can stably perform its protective function in different scenarios.

[0025] Furthermore, the intermediate refractory layer 2 is composed of a ceramicized silicone rubber matrix, mica powder, nano-alumina, ceramicization accelerator, coupling agent, and vulcanizing agent, with the following weight percentage proportions: 100 parts ceramicized silicone rubber matrix, 25 parts mica powder, 8 parts nano-alumina, 3 parts ceramicization accelerator, 1.2 parts coupling agent, and 2.5 parts vulcanizing agent. See Table 2 for a detailed description of the above materials. Table 2: Component Name Specific Specification Parameters Function Ceramized Silicone Rubber Base Methyl vinyl silicone rubber (vinyl content 0.15-0.25%, Mooney viscosity ML1+4 (121°C): 40-60) Base core, ensuring flexibility at room temperature (bending radius ≥10 times cable outer diameter without cracking) and rapid ceramization at high temperature, providing an attachment basis for subsequent components Mica Powder Phlogopite (particle size 1500 mesh, whiteness ≥85%, water content ≤0.5%, temperature resistance ≥1200°C) Too little and insufficient fire resistance, too much and easy to cause the base toughness to decrease; phlogopite flaky structure can form "stacked barrier" to enhance high-temperature heat insulation effect Nano Aluminum Oxide Gamma-type (particle size 20-50nm, purity ≥99.9%, specific surface area 80-120m² / g) Balancing mechanical strength and processing fluidity, nano-level particles can fill the base micro voids, improving tensile strength and thermal stability, and avoiding performance unevenness caused by aggregation Ceramization Promoter Borate composite system (zinc borate: barium metaborate = 1:1, particle size 500 mesh) Reduces the ceramization starting temperature (from 350°C to 320°C), shortens the ceramization time (≤30s), and at the same time improves the density of the ceramic layer, reducing heat penetration at high temperature Coupling Agent Silane Coupling Agent KH-550 (purity ≥98%) Improves the interfacial bonding force of mica powder, nano aluminum oxide, and silicone rubber base, avoiding the loss of protection due to component shedding during high-temperature ceramization Vulcanizing Agent Benzoyl Peroxide (BPO, purity ≥98%, active oxygen content 6.0-6.5%) Ensure the crosslinking degree of the base reaches 75-80%, balance the flexibility at room temperature and the hardness of the ceramic layer at high temperature, and avoid the mechanical performance degradation caused by insufficient vulcanization Basic performance at room temperature: Tensile strength: ≥8.5MPa (original ratio approximately 7.0MPa, an increase of 21%), which can withstand dragging and squeezing external forces during laying and prevent layer damage; Elongation at break: ≥350% (original ratio approximately 300%), meeting the requirements for cable bending installation in confined spaces (no cracks when bending radius ≥8 times cable outer diameter); Hardness (Shore A): 65±3, balancing hand feel and scratch resistance to prevent surface wear during transportation.

[0026] High-temperature fire resistance: Ceramicization temperature: 320℃ (original ratio 350℃, reduced by 30℃), can quickly form a protective shell in the early stage of fire, shortening the protection response time. Ceramic layer properties (after flame firing at 950-1000℃ for 180 min): Ceramic layer density: ≥1.8g / cm³ (original ratio approximately 1.5g / cm³), reducing heat penetration channels, inner layer temperature after burning ≤180℃ (meets core insulation withstand requirements); The compressive strength of the ceramic layer is ≥12MPa, which can withstand the impact of falling objects at the fire scene and prevent the ceramic layer from cracking. Fire resistance integrity: No flame penetration or smoke leakage within 180 minutes (meets the Class A fire resistance requirements in GB / T 12666.6). Long-term stability: Thermal aging performance (after aging at 150℃ for 168 hours): Tensile strength retention rate: ≥88% (original ratio approximately 80%); Elongation at break retention: ≥85% (original ratio approximately 78%), reducing performance degradation under long-term high-temperature conditions. Resistance to damp heat (after 168 hours at 40℃ and 93% relative humidity): Insulation resistance variation rate: ≤±15%, to avoid electrical performance degradation caused by humid environment; The appearance is free of bubbles and delamination, ensuring the stability of the layer structure. Core advantages: Improved performance balance: By fixing the amount of mica powder and nano alumina, the performance fluctuations caused by the original range ratio are avoided. At the same time, the addition of coupling agent and ceramicization accelerator solves the problems of poor component interface bonding and slow ceramicization response. Enhanced scenario adaptability: The optimized system can meet the requirements of higher-demand fire scenarios (such as high-rise buildings and subway tunnels), and the 180-minute fire resistance time covers most of the golden period for fire rescue. Processing feasibility guaranteed: The particle size and compatibility of each component in the formula have been optimized, and there is no agglomeration or scorching during extrusion molding. The finished product qualification rate has been increased from 85% to over 98%.

[0027] The inner layer 3 comprises a base resin, a crosslinking agent, an antioxidant, a copper inhibitor, and a lubricant, which are weighed in the following proportions: 100 parts base resin, 3.5 parts crosslinking agent, 0.6 parts antioxidant, 0.2 parts copper inhibitor, and 0.5 parts lubricant. Please refer to Table 3 below for a description of the inner layer 3.

[0028] Table 3: Component Name Specific Specification Role Description Base Resin HDPE (Model 5000S) Base material, provides the basic insulation framework, its high-density characteristics can reduce the air bubbles inside the insulation layer and reduce the risk of breakdown Crosslinking Agent Dicumyl Peroxide (DCP, purity ≥98%) Too low and the crosslinking degree is insufficient (<65%), the insulation resistance decreases; too high and the crosslinking is excessive (>85%), the material becomes brittle and the elongation at break decreases Antioxidant Antioxidants 1010 and 168 compounded (ratio 1:1) Inhibits the oxidative aging of XLPE during high-temperature crosslinking and long-term use, prolongs the service life of the insulation layer, and avoids the insulation performance degradation caused by oxidation Anti-Copper Agent Benzotriazole Derivative (purity ≥99%) The core is mostly copper conductor, copper ions easily catalyze XLPE degradation at high temperature, anti-copper agent can form a protective film on the surface of the copper conductor to block the migration of copper ions and improve the copper resistance performance of the insulation layer Lubricant Calcium Stearate (purity ≥98%) Improves processing fluidity, avoids scratches and pitting on the surface of the insulation layer during extrusion molding, ensures the insulation layer closely adheres to the core without gaps Table 4: Key Performance Data and Testing Standards for Inner Layer 3 Performance Index Detection Standard Data Requirements Actual Test Value Insulation Resistance Constant GB / T 1408.1-2016 ≥100 MΩ·km 150-200 MΩ·km Dielectric Strength GB / T 1408.1-2016 ≥30 kV / mm 35-40 kV / mm Dielectric Loss Tangent (tan δ GB / T 1409-2006 ≤0.001 (20℃, 50Hz 0.0006-0.0008 Volume Resistivity GB / T 1410-2006 ≥ 1 x 10¹ 4 Ω-cm (20 °C) 5 x 10 4 -1 x 10 5 Ω-cm Table 5: Mechanical Properties Performance Index Detection Standard Data Requirements Actual Test Value Tensile Strength GB / T 1040.3-2006 ≥20 MPa 22-25 MPa Elongation at Break GB / T 1040.3-2006 ≥300% 350%-400% Heat Shrinkage Rate GB / T 17759-1999 ≤4%（135℃，1h） 2%-3% Environmental Stress Cracking Resistance GB / T 1842-2008 ≥1000 h (50℃, 10% Igepal CO-630 solution) 1500-2000h Table 6: Temperature Resistance and Aging Resistance Performance Index Detection Standard Data Requirements Actual Test Value Long-Term Operating Temperature IEC 60502-1:2014 90℃ Can withstand 130℃ for ≤2h Tensile Strength Retention Rate after Heat Aging GB / T 2951.12-2008 ≥80%（135℃，168h） 85%-90% Elongation at Break Retention Rate after Heat Aging GB / T 2951.12-2008 ≥70%（135℃，168h） 75%-80% Wet Heat Aging Performance GB / T 2951.41-2008 Insulation Resistance Decrease Rate ≤30% (40℃, 93% RH, 168h) 15%-20% Table 7: Compatibility between Inner Layer 3 Thickness and Core Voltage Rating. The thickness of Inner Layer 3 needs to be precisely designed according to the core voltage rating to avoid insulation breakdown due to insufficient thickness, or excessive thickness increasing the overall weight and cost of the cable. Specific compatibility details are as follows: Core Voltage Level Inner Layer 3 Thickness (mm) Applicable Scenario Core Consideration 10kV 0.8-1.0 Low-voltage power distribution system (such as community power distribution, industrial plant low-voltage line) Low voltage, moderate insulation requirement, thickness controlled within 1.0mm, balance cost and flexibility 20kV 1.0-1.2 Medium voltage distribution system (such as city distribution network, commercial complex power supply Voltage boost, need to increase the thickness to enhance the insulation strength, to avoid the breakdown caused by voltage fluctuation in the distribution process 35kV 1.2-1.5 High voltage transmission system (such as substation outgoing line, industrial park high voltage line) Under high voltage working condition, the insulation layer needs to withstand higher electric field strength, 1.5mm thickness can ensure that the dielectric strength meets the 35kV voltage requirement Inner Layer 3: Common Quality Issues and Solutions Insulation layer bubbles: The causes are mostly due to excessively high moisture content in the raw material (>0.1%) or excessively low extrusion temperature (<180℃). The solution is to dry the raw material before extrusion (80℃, 2h, reduce the moisture content to <0.05%), and control the extruder body temperature at 185-200℃ and the die head temperature at 200-210℃. The insulation layer is not tightly bonded to the wire core: This is caused by oil stains on the surface of the wire core or a mismatch between the extrusion speed and the traction speed. The solution is to degrease the wire core before it enters the extruder (by wiping it with anhydrous ethanol) and control the ratio of extrusion speed to traction speed at 1.05:1-1.1:1 to ensure that the insulation layer tightly wraps the wire core. Insufficient temperature resistance: The cause is insufficient crosslinking agent or too short crosslinking time. The solution is to strictly control the amount of crosslinking agent added (3.5 ± 0.2 parts) and adjust the crosslinking time according to the thickness (crosslinking time ≥ 15 min for 1.0 mm thickness, crosslinking time ≥ 25 min for 1.5 mm thickness).

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-voltage fire-resistant cable comprising an outer layer, characterized in that, The internal layer is internally provided with a framework structure, a plurality of groups of wire cores (6) are equidistantly arranged between the framework structure and the external layer, and the internal of the framework structure is provided with a reinforcing core (5).

2. A high voltage fire resistant cable according to claim 1, characterised in that: The external layer comprises a surface layer (1), an intermediate refractory layer (2) and an inner layer (3), the surface layer (1) is arranged outside the intermediate refractory layer (2), and the inner layer (3) is arranged inside the intermediate refractory layer (2).

3. A high voltage fire resistant cable according to claim 2, characterised in that: The framework structure comprises a center tube (4) and baffles integrally formed outside the center tube (4), there is a gap between two adjacent baffles, the wire core (6) is arranged in the gap, and the wire core (6) is filled with an arc-shaped filling block (7) between the inner wall of the inner layer (3).

4. A high voltage fire resistant cable according to claim 3, characterised in that: The internal of the center tube (4) is inserted with the reinforcing core (5).

5. A high voltage fire resistant cable according to claim 1, characterised in that: The surface layer (1) is composed of polyvinyl chloride resin, flame retardant, plasticizer, stabilizer, lubricant and antioxidant, and the weight percentage of the polyvinyl chloride resin, the flame retardant, the plasticizer, the stabilizer, the lubricant and the antioxidant is 85 parts, 3-8 parts, 12 parts, 3 parts, 0.8 parts and 0.2 parts respectively.

6. A high voltage fire resistant cable according to claim 1, characterized in that: The intermediate refractory layer (2) is composed of a ceramicized silicone rubber matrix, mica powder, nano-alumina, a ceramicization accelerator, a coupling agent and a vulcanizing agent, and the weight percentage of the ceramicized silicone rubber matrix, the mica powder, the nano-alumina, the ceramicization accelerator, the coupling agent and the vulcanizing agent is 100 parts, 25 parts, 8 parts, 3 parts, 1.2 parts and 2.5 parts respectively.

7. A high voltage fire resistant cable according to claim 1, characterized in that: The inner layer (3) comprises a base resin, a crosslinking agent, an antioxidant, an anti-copper agent and a lubricant, and the weight percentage of the base resin, the crosslinking agent, the antioxidant, the anti-copper agent and the lubricant is 100 parts, 3.5 parts, 0.6 parts, 0.2 parts and 0.5 parts respectively.

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