Super-fireproof low-voltage power cable based on porous vacuum silicon and alumina fiber composite insulation structure

Abstract

The invention relates to the technical field of cables, and provides an ultra-fire-resistant low-voltage power cable based on a porous vacuum silicon and alumina fiber composite insulation structure. The objective of the invention is to solve the technical problem that high fire-resistant reliability, structural flexibility, installation adaptability and environmental protection safety are difficult to meet at the same time under extreme fire working conditions due to limited heat insulation performance, large structural rigidity and insufficient material environmental protection performance of a conventional low-voltage fire-resistant cable. According to the technical scheme, each insulating wire core is composed of a conductor and a composite insulating structure, and each composite insulating structure sequentially comprises a porous vacuum silicon composite belt wrapping layer, an aluminum oxide fiber braid layer and a ceramic polyolefin extrusion layer from inside to outside; wherein the porous vacuum silicon composite belt wrapping layer comprises a nano porous silicon material layer facing the conductor and a polyester film layer back to the conductor, and the alumina fiber woven layer is formed by weaving alumina continuous fiber yarns; and gaps of cable cores of the multi-core cable are filled with special-shaped alumina fiber felts, and the outer layer of the multi-core cable is sequentially lapped with a basalt fiber belt and extruded with a low-smoke halogen-free flame-retardant polyolefin sheath.

Description

Technical Field

[0001] This invention relates to the field of cable technology and provides an ultra-fire-resistant low-voltage power cable based on a porous vacuum silicon and alumina fiber composite insulation structure. Background Technology

[0002] Currently, the main fire-resistant technologies used in low-voltage fire-resistant power cables include mica tape wrapping, mineral insulation, and ceramicized silicone rubber structures. Mica tape wrapping typically involves wrapping mica tape around the conductor insulation layer and applying a sheath. However, mica is prone to detachment and pulverization at high temperatures, resulting in a fire resistance time that usually does not exceed 1.5 hours (according to GB / T 19216.21 standard). Furthermore, it is susceptible to structural disintegration under intense combustion or vibration conditions, leading to short circuits. Mineral insulation, using magnesium oxide powder as the insulating material and a copper sheath as the protective layer, offers excellent fire resistance, but suffers from complex manufacturing processes, high costs, heavy weight, stringent installation bending radius requirements, and difficult joint treatment. It also tends to absorb moisture in humid environments, leading to a decline in insulation performance. The ceramicized silicone rubber structure is achieved by extruding or wrapping ceramicized silicone rubber around the conductor. At high temperatures, a ceramic hard shell can be formed. However, the thermal conductivity of this hard shell is usually higher than 0.5 W / m·K, which has limited effect on blocking the heat conduction from the external high temperature to the conductor core. It is difficult to meet the heat insulation requirements in ultra-high temperature (such as above 950℃) environments for a long time (such as more than 3 hours).

[0003] In summary, while existing technologies such as mica tape wrapping, mineral insulation, and single-layer ceramicized silicone rubber can ensure the continuity of power supply in flames to a certain extent, they have significant shortcomings or cannot simultaneously meet the requirements for extreme heat insulation to cope with prolonged ultra-high temperature environments, lightweight and flexible structures, environmentally friendly and non-toxic properties, and comprehensive mechanical performance. Especially in scenarios with extremely high fire resistance requirements for cables (e.g., more than 3 hours) and limited installation space, such as data centers, nuclear power plant containment structures, and the core tubes of super high-rise buildings, existing technologies cannot simultaneously meet the comprehensive demands of high performance and ease of installation and maintenance. Therefore, there is an urgent need for a solution with superior performance and easier installation and maintenance. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of existing low-voltage fire-resistant power cables, which are difficult to achieve simultaneously high fire resistance reliability (conductor continuous energization), structural flexibility (small bending radius installation), installation adaptability (lightweight, easy laying) and environmental safety (low smoke and halogen-free) under ultra-long-term (≥3 hours) and ultra-high temperature (≥950℃) fire conditions due to limited thermal insulation performance (such as high thermal conductivity of ceramicized layer and easy powdering of mica tape), high structural rigidity (such as heavy weight and demanding bending radius of mineral-insulated cables) and insufficient environmental friendliness of materials (such as toxic gas release of halogen-containing materials).

[0005] To achieve the above objectives, the present invention employs the following technical means:

[0006] This invention provides an insulated wire core, comprising a conductor and a composite insulation structure covering the conductor, characterized in that: the composite insulation structure comprises, from the inside out, a porous vacuum silicon composite tape wrapping layer, an alumina fiber braided layer, and a ceramicized polyolefin extrusion layer; in the porous vacuum silicon composite tape wrapping layer, the side facing the conductor is a porous vacuum silicon material layer with a nanoscale pore structure, and the side facing away from the conductor is a polyethylene terephthalate film layer; the alumina fiber braided layer is woven from continuous alumina fiber yarn.

[0007] In the above scheme, the porosity of the porous vacuum silicon material is above 97%, and the pore size is 10~40nm.

[0008] In the above scheme, the Al2O3 mass content in the alumina fiber braided layer is not less than 72%.

[0009] The present invention also provides a low-voltage power cable, comprising at least one of the aforementioned insulated cores. When multiple insulated cores are included, the gaps between the cores are filled with alumina fiber felt, the cores are wrapped with basalt fiber tape, and the outermost layer is a low-smoke halogen-free flame-retardant polyolefin sheath.

[0010] In the above scheme, the alumina fiber felt is an irregular semi-circular structure adapted to the gap between the cable cores.

[0011] Because the present invention employs the above-mentioned technical means, it has the following beneficial effects:

[0012] Compared with existing technologies, this invention introduces a multi-layer composite structure consisting of a "porous vacuum silicon super heat insulation layer," an "alumina fiber braided insulation layer," and a "ceramization layer," resulting in the following significant advantages:

[0013] 1. Revolutionary fire resistance performance: Due to the adoption of a multi-layer composite mechanism that combines "passive super heat insulation" and "active ceramic sealing", each layer complements and works synergistically at high temperatures, making the fire resistance limit of the cable far exceed the 90-minute requirement of national standards (such as GB / T 19216.21), easily reaching more than 180 minutes, and even meeting the most stringent international standards such as BS6387 CWZ level.

[0014] 2. Superior comprehensive mechanical properties: Due to the replacement of rigid metal sheaths (such as MI cables) with flexible alumina fiber braided layers and ceramicized polyolefins, and the optimization of cabling structure, the bending performance of this cable is significantly better than that of mineral-insulated cables. Its minimum bending radius can reach 10-12 times the cable outer diameter, and the weight is reduced by about 30%-50%, which greatly improves the convenience of installation and the range of applicable scenarios.

[0015] 3. Excellent environmental protection and safety: All major materials (alumina fiber, basalt fiber, ceramicized polyolefin, etc.) are inorganic or halogen-free low-smoke polymers, which do not release toxic hydrogen halide gas when burning. The smoke density is low and the light transmittance is high, providing valuable time for personnel evacuation and fire rescue in the event of a fire.

[0016] 4. Significant economic efficiency and technological feasibility: The manufacturing process of this invention is mainly based on mature cable manufacturing equipment (such as wrapping machines, braiding machines, extruders, and cabling machines). Unlike MI cables, it does not require special powder filling and die casting processes. The production process is simplified, the production efficiency is high, and it is conducive to large-scale production. The manufacturing cost has a huge advantage over mineral-insulated cables.

[0017] 5. This invention systematically integrates the passive super insulation of the porous vacuum silicon composite tape wrapping layer, the structural support and morphological maintenance of the alumina fiber braided layer 3, the active ceramic sealing of the ceramicized polyolefin extrusion layer, the gap thermal blocking of the alumina fiber felt, and the external reinforcement of the basalt fiber tape. Each layer forms a dynamic functional relay during the thermal evolution of a fire: the porous vacuum silicon composite tape wrapping, as the ultimate thermal insulation unit adjacent to the conductor, relies on the nanoporous structure to deeply attenuate the residual heat flow that penetrates the outer protection layer, controlling the thermal load on the conductor surface within a safe threshold, and directly ensuring the continuity of the conductor's power supply during ultra-long-term fires; the alumina fiber braided layer provides a rigid skeleton during the softening stage of the ceramicized layer, preventing the ceramic shell from cracking and maintaining the geometry of the core; the filling felt and wrapping tape work together to block the diffusion path of heat within the cable core. This combination is not a simple superposition of the functions of each layer (such as only increasing the thickness of the insulation layer or using ceramic materials alone), but rather a precise match between material properties and structural positions, enabling the "insulation-support-sealing-filling-reinforcement" links to create an interdependent and functionally amplified effect. For example, the alumina fiber braided layer independently undertakes the task of high-temperature resistance, provides an indispensable forming substrate for the ceramic layer, and together with the porous vacuum silicon layer, constructs a low thermal conductivity pathway. If any link is missing, the integrity and durability of the overall fire-resistant system will be significantly weakened. Thus, this invention solves the core contradiction in the prior art of balancing ultra-long-term fire resistance reliability, structural flexibility, installation adaptability, and environmental safety, producing a synergistic effect of "structural stability ensuring functional realization, and functional realization supporting structural survival," achieving a fundamental improvement in fire resistance performance and comprehensive engineering applicability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cable structure of the present invention;

[0019] Figure 2 This is a schematic diagram of the insulated wire core structure of the present invention;

[0020] Explanation of reference numerals in the attached figures:

[0021] 1-Conductor, 2-Porous vacuum silicon composite tape wrapping layer, 2-1-Porous vacuum silicon material layer, 2-2-Polyethylene terephthalate film layer, 3-Alumina fiber braided layer, 4-Ceramicized polyolefin extrusion layer, 5-Alumina fiber felt, 6-Basalt fiber tape, 7-Low smoke halogen-free flame retardant polyolefin sheath. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0023] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without these specific details.

[0024] As attached Figure 1 As shown, conductor 1 transmits current; porous vacuum silicon composite tape wrapping layer 2 provides basic insulation and heat insulation; alumina fiber braided layer 3 enhances high temperature resistance and mechanical properties; ceramicized polyolefin extrusion layer 4 provides high-temperature ceramicized protection; alumina fiber felt 5 fills the insulation and stabilizing structure; basalt fiber tape 6 wrapping layer enhances fire resistance and slow release; low-smoke halogen-free flame-retardant polyolefin sheath 7 provides cable protection. These layers work together to achieve ultra-fire resistance and high reliability.

[0025] The core of the technical solution of this invention lies in a multi-layer composite insulation and fire-resistant structure that combines "active ceramic protection" with "passive super heat insulation". To facilitate those skilled in the art to better understand the technical concept of this invention, the following detailed description is provided:

[0026] I. Static Structure:

[0027] The cable, from the inside out, includes:

[0028] 1. Insulated core: It consists of conductor 1, porous vacuum silicon composite tape wrapping layer 2, alumina fiber braided layer 3, and ceramicized polyolefin extrusion layer 4.

[0029] Conductor 1: It adopts the type I or type II conductor structure conforming to GB / T 3956 standard, and is made of multiple strands of oxygen-free copper wires through regular stranding or bundling.

[0030] Porous vacuum silicon composite tape wrapping layer 2: A porous vacuum silicon composite tape tightly wrapped around the conductor, in which the porous vacuum silicon material faces inward and directly contacts the conductor, while the PET material faces outward. The porous vacuum silicon is mainly composed of nanoporous vacuum silicon. By simultaneously satisfying the conditions of a pore size of 10–40 nm (less than the mean free path of air molecules 68 nm) and a porosity greater than 97%, it can achieve a near-vacuum thermal insulation effect. Its density can be as low as 0.03 g / ml, and its thermal conductivity as low as 0.014 W / (m·K). The absence of intermolecular collisions within the fine pores results in ultra-high thermal insulation performance, providing the foundation for cable insulation and phase conductor thermal insulation. The porous vacuum silicon composite tape is composed of PET and porous vacuum silicon.

[0031] Alumina fiber braided layer 3: Composed of continuous alumina fiber yarn, it covers the outer periphery of the porous vacuum silicon composite tape wrapping layer 2. The Al2O3 content of the alumina fibers is 72% or higher, the tensile strength of a single filament is greater than 2 GPa, the tensile modulus of a single filament is greater than 170 GPa, and the dielectric strength is greater than 3.2. This braided layer tightly wraps and fixes the inner porous vacuum silicon composite tape wrapping layer 2, preventing it from loosening or being damaged. Under high temperatures in a fire, when the outer ceramicized polyolefin extrusion layer 4 softens and initiates the ceramicization reaction, this braided layer provides skeletal support, maintaining the geometric shape of the core structure and the integrity of the interlayer bonding, avoiding short circuits between conductors due to structural collapse, and simultaneously improving the overall mechanical strength, high temperature resistance, and insulation stability of the core.

[0032] Ceramicized polyolefin extrusion layer 4: The ceramicized polyolefin material extruded outside the alumina fiber braided layer 3 is flexible under normal conditions and ceramicized at high temperatures to form a hard protective shell. This ceramic shell is tightly bonded to the alumina fiber braided layer 3 to form a strong, insulating final fireproof barrier that completely isolates the conductor from the flame.

[0033] 2. Cable core structure: Multiple insulated wire cores (such as five cores) are twisted together to form a cable.

[0034] Filler layer: Irregular semi-circular alumina fiber felt is filled into the gaps between the cable cores to achieve tight filling, heat insulation and structural stability. It can maximize the filling of the gaps between the cable cores, eliminate air cavities, form a uniform and continuous heat insulation body, and effectively prevent the longitudinal propagation of flames and heat inside the cable core.

[0035] Basalt fiber tape wrapping reinforcement layer: Basalt fiber tape is wrapped around the outside of the filled cable core. Its tensile strength can reach more than 3500MPa, and its thermal conductivity can reach 0.04W / m·K, providing mechanical reinforcement and fire protection.

[0036] Outer sheath: Low-smoke halogen-free flame-retardant polyolefin sheath material extruded onto the outermost layer of the cable.

[0037] II. Connection Relationships and Working Principles:

[0038] Connection relationship: Each layer is composited sequentially through processes such as wrapping, braiding, extrusion, and filling. The porous vacuum silicon composite tape is in direct contact with the conductor; the alumina fiber braided layer covers the porous vacuum silicon composite tape; the ceramicized polyolefin layer covers the braided layer; after the insulated cores are cabled, the gaps are filled with alumina fiber felt, basalt fiber tape is wrapped and fixed, and finally the outer sheath is extruded.

[0039] According to the working principle of each structure in the stage of cable combustion:

[0040] Phase 1: Normal Operation (<200℃): Current flows normally through the conductor. The porous vacuum silicon composite tape and alumina fiber braided layer provide stable electrical insulation and basic thermal insulation between phases. The cable is flexible overall, making it easy to bend and lay.

[0041] Phase Two: Initial Stage of Fire / Carbonization of Outer Sheath (200℃-400℃)

[0042] External flames carbonize the outer sheath. The basalt fiber tape, with its high melting point, remains intact, forming the first physical fire barrier and preventing the flames from directly burning the cable core.

[0043] Phase 3: High Temperature Intrusion / Active Protection Activation (400℃-750℃)

[0044] Heat begins to penetrate the wrapping layer. The filling alumina fiber felt and the wrapping layer slow down heat conduction.

[0045] Key points: During the heating process from 400 degrees Celsius, as the extruded ceramicized polyolefin insulation absorbs heat and transforms from plastic to ceramic, porous vacuum silicon attenuates excess heat penetrating the ceramicized polyolefin insulation and the alumina braided layer, providing super insulation. Simultaneously, the ceramicized polyolefin extrusion layer begins to ceramicize, forming a hard shell. The alumina fiber braided layer provides support, preventing the ceramic shell from cracking.

[0046] Phase Four: Continuous combustion at ultra-high temperatures (750℃-950℃, lasting for more than 180 minutes)

[0047] At 750-950 degrees Celsius, after the extruded ceramic polyolefin insulation is fully ceramicized, the porous vacuum silicon works in conjunction with other layers to block heat transfer and continuously provide heat insulation, protecting the conductor from normal electrical conduction.

[0048] The synergistic system of "passive insulation ("porous vacuum silicon" combined with "alumina fiber felt"), "active sealing (ceramized polyolefin extrusion layer)" and "structural reinforcement ("alumina fiber braiding" combined with "basalt fiber tape")" plays a full role.

[0049] Each layer has a clearly defined function, working in a relay-like manner to cope with thermal shock: the insulation layer attenuates heat, the structural layer maintains its shape, and the ceramicized layer provides the final seal. This division of labor and cooperation is impossible to achieve with existing single-layer or double-layer structures, ensuring the long-term continuity of the circuit under extreme conditions.

[0050] Example 1:

[0051] Super fire-resistant five-core low-voltage power cable for rated voltage 0.6 / 1 kV

[0052] Technical content and production process:

[0053] Conductor: Annealed copper conductor conforming to GB / T 3956, with a conductor cross-section of 25 mm². 2 .

[0054] Porous vacuum silicon composite tape wrapping layer 2: A porous vacuum silicon composite tape with a thickness of 0.2 mm is used to wrap around the conductor with a 50% overlap rate.

[0055] Alumina fiber braided layer 3: Alumina fiber yarn is braided outside the wrapping layer, with a braiding density of not less than 90%.

[0056] Ceramicized polyolefin extrusion layer 4: Extrusion of 0.8 mm thick ceramicized polyolefin material to form an insulated wire core.

[0057] Cable forming: Five insulated wire cores are twisted together to form a cable core.

[0058] Filling: Fill the gaps between the cable cores with irregularly shaped semi-circular alumina fiber felt 5 to ensure a round cross-section.

[0059] Reinforcement by wrapping: 0.15mm thick basalt fiber tape 6 is wrapped around the outside of the filled cable core with a 50% overlap rate.

[0060] Outer sheath: Extruded 1.5mm thick low-smoke halogen-free flame-retardant polyolefin sheath material, conforming to GB / T 19666.

[0061] Process flow: wire drawing and annealing → conductor stranding → wrapping → braiding → extrusion → cabling → extrusion.

[0062] Implementation results:

[0063] The cable underwent a fire resistance test (flame temperature 750°C) according to GB / T 19216.21 standard, maintaining its integrity for 180 minutes and passing the voltage test. The bending radius was no greater than 12 times the cable's outer diameter, the oxygen index was greater than 40, and the smoke density and light transmittance were greater than 80%, meeting high standards of fire resistance and environmental protection requirements.

[0064] To meet the highest category CWZ requirements of BS 6387:2013 "Fire resistance test method for cable to maintain line integrity under flame conditions", Protocol C (fire resistance alone): The cable sample is placed in a flame at 950℃ ± 40℃ for 180 minutes and the cable is observed to ensure normal power supply. Protocol W (fire resistance + water spray): After burning in a flame at 650℃ ± 40℃ for 15 minutes, water spray is immediately applied for 15 minutes to simulate the harsh environment after the fire sprinkler system is started. The cable is then observed to ensure normal power supply and whether there is a short circuit between phases. Protocol Z (fire resistance + mechanical impact): While burning at 950℃, the cable is subjected to mechanical impact every 30 seconds for 15 minutes. The cable is then observed to ensure normal power supply.

Claims

1. An insulated wire core, comprising a conductor (1) and a composite insulation structure covering the conductor (1), characterized in that: The composite insulation structure comprises, from the inside out, a porous vacuum silicon composite tape wrapping layer (2), an alumina fiber braided layer (3), and a ceramicized polyolefin extrusion layer (4); in the porous vacuum silicon composite tape wrapping layer (2), the side facing the conductor (1) is a porous vacuum silicon material layer (2-1) with a nanoscale pore structure, and the side facing away from the conductor (1) is a polyethylene terephthalate film layer (2-2); the alumina fiber braided layer (3) is woven from continuous alumina fiber yarn.

2. The insulated wire core according to claim 1, characterized in that: The porous vacuum silicon material has a porosity of over 97% and a pore size of 10~40nm.

3. The insulated wire core according to claim 1, characterized in that: The Al2O3 mass content in the alumina fiber braided layer is not less than 72%.

4. An ultra-fire-resistant low-voltage power cable based on a porous vacuum silicon and alumina fiber composite insulation structure, comprising at least one insulated core as described in any one of claims 1 to 3, characterized in that: When multiple insulated cores are included, the gaps between the cores are filled with alumina fiber felt (5), the cores are wrapped with basalt fiber tape (6), and the outermost layer is a low-smoke halogen-free flame-retardant polyolefin sheath (7).

5. The low-voltage power cable according to claim 4, characterized in that: The alumina fiber felt (5) is an irregular semi-circular structure adapted to the gap between the cable cores.

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