Mineral-insulated flexible fire-resistant intelligent early warning cable and its preparation method

Abstract

This invention relates to the field of power cable technology, specifically to a mineral-insulated flexible fire-resistant intelligent early warning cable and its manufacturing method, comprising: a first optical fiber structure, including a loose tube and a stainless steel strip spirally wound around the loose tube; a conductor, stranded on the outer wall of the first optical fiber structure; a mineral insulation layer, tightly pressed against the outer wall of the conductor; a metal sheath layer, covering the surface of the mineral insulation layer; and an oxygen barrier layer, extruded onto the surface of the metal sheath layer. This invention places optical fibers at three different radial positions: the center of the conductor, the metal sheath layer, and the inner side of the outer sheath, forming a complete temperature acquisition link from the heat source to the outside environment. The three temperature data are interconnected through the inherent heat conduction path of the cable, enabling maintenance personnel to simultaneously obtain the cable core temperature, the metal sheath temperature, and the surface environmental reference temperature, providing a physical basis for distinguishing different heat source types such as internal overload, external fire, and insulation aging.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, and more specifically to mineral-insulated flexible fire-resistant intelligent early warning cable and its preparation method. Background Technology

[0002] Mineral-insulated cables, due to their excellent fire resistance, are widely used in critical locations with extremely high fire safety requirements, such as nuclear power plants, high-rise buildings, subway tunnels, and petrochemical facilities. Their basic structure consists of a copper conductor, a tightly compacted magnesium oxide mineral insulation layer, and a metal sheath. Utilizing the natural high-temperature resistance of inorganic materials, the cable can maintain its integrity for extended periods under flame exposure. To address the shortcomings of traditional mineral-insulated cables, such as excessive rigidity and difficulty in bending during installation, the industry has developed flexible mineral-insulated cables. By adding a corrugated metal sheath or a composite flame-retardant filler layer outside the mineral insulation layer, the mechanical flexibility of the cable is improved, making it more adaptable to complex installation environments while still meeting fire resistance requirements.

[0003] In the promotion and application of mineral-insulated cables, how to further enhance their fire safety early warning capabilities has become a key technological focus in this field. Relying solely on the passive fire-resistant properties of the cable material itself cannot meet the demands of modern facilities for proactive safety early warning. Therefore, the industry has gradually introduced distributed fiber optic temperature sensing technology, integrating temperature-sensing fibers into the cable structure to achieve real-time monitoring of the cable's operating temperature. When the cable's temperature rises abnormally due to overload or external fire sources, the monitoring system can promptly issue an early warning signal, providing a basis for fire-fighting coordination and emergency response. Currently, combining fiber optic temperature sensing technology with mineral-insulated cables has become one of the mainstream technical routes for improving the proactive fire protection capabilities of cable systems.

[0004] However, simply detecting the operating temperature of a cable using optical fibers is not an effective way to provide early warning of the cable's fire resistance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies. The first aspect of this invention proposes a technical solution: a mineral-insulated flexible fire-resistant intelligent early warning cable, comprising: The first optical fiber structure includes a loose tube and a stainless steel strip spirally wound around the outside of the loose tube. The conductor is twisted to the outer wall of the first optical fiber structure; A mineral insulating layer is pressed tightly against the outer wall of the conductor; A metal sheath layer covers the surface of the mineral insulating layer; An oxygen barrier layer is extruded onto the surface of the metal sheath layer; A flame-retardant layer is wrapped around the outer wall of the inner sheath layer; Inner sheath layer, covering the outer wall of the flame-retardant layer; An outer sheath layer, which covers the outer wall of the inner sheath layer; The inner sheath layer and the outer sheath layer are provided with a second optical fiber structure. The metal sheath layer includes a wrapped metal strip. The surface of the metal strip is pre-formed with grooves distributed along its length direction. A third optical fiber structure is embedded in the grooves. The first optical fiber structure, the second optical fiber structure, and the third optical fiber structure are located at three different radial positions in the cable. The first optical fiber structure is used to detect the first temperature at the center of the conductor, the second optical fiber structure is used to detect the second temperature between the outer sheath layer and the inner sheath layer, and the third optical fiber structure is used to detect the third temperature of the metal sheath layer. The surface of the metal strip is provided with a self-locking structure, so that when the metal strip is wrapped according to a predetermined overlap rate, the front and rear strips of the metal strip are fixed to each other in the axial direction of the cable, and the third optical fiber structure is wound on the outside of the mineral insulation layer with a fixed pitch.

[0006] Preferably, the self-locking structure includes: A first curled portion is provided at the front edge of the metal strip; The second coiled portion is located at the center of the front part of the metal strip; The third coiled portion is provided at the connection between the front and rear sections of the metal strip; The fourth coiled section is located at the center of the rear part of the metal strip. The third curled portion forms an outward first opening that mates with the first curled portion, the second curled portion forms an inward second opening, and the fourth curled portion forms an inward third opening, which is the groove. When the metal strip is wrapped, the front strip body covers the surface of the rear strip body, and the first curled portion is embedded in the outward first opening of the third curled portion, while the second curled portion covers the surface of the fourth curled portion.

[0007] Preferably, the cross-section of the third opening is Ω-shaped, and the opening diameter is smaller than the diameter of the third optical fiber structure. The third optical fiber structure includes an optical fiber core, a buffer layer, and a protective layer. The buffer layer covers the outer wall of the optical fiber core, and the protective layer covers the outer wall of the buffer layer.

[0008] Preferably, the optical fiber core comprises a multi-core optical fiber, the buffer layer comprises an aerogel layer, and the protective layer comprises a metal tube; The porous ceramic layer or aerogel layer has a lower thermal conductivity than the protective layer and the material in contact with the outer wall of the protective layer, forming a low thermal conductivity intermediate layer in the radial direction of the third optical fiber structure.

[0009] Preferably, the first coiled portion is configured as a non-closed ring structure, giving it elastic deformation capability. The third coiled portion is configured to generate elastic deformation when the cable is bent, so that stress is released through the deformation of the third coiled portion and the first coiled portion when the cable is bent, while maintaining the flexibility of the cable.

[0010] Preferably, the oxygen barrier layer includes a ceramicized silicone rubber oxygen barrier layer, the outer surface of which is a smooth cylindrical surface, and the flame retardant layer includes a multilayer mica tape wrapped around the smooth cylindrical surface.

[0011] Preferably, the multi-core optical fiber includes a first optical fiber for temperature measurement and a second optical fiber for humidity monitoring.

[0012] Preferably, the inner sheath layer includes a first low-smoke halogen-free flame-retardant polyolefin layer, the outer sheath layer includes a second low-smoke halogen-free flame-retardant polyolefin layer, and the second optical fiber structure is embedded between the first low-smoke halogen-free flame-retardant polyolefin layer and the second low-smoke halogen-free flame-retardant polyolefin layer for measuring the cable surface temperature and serving as an environmental reference.

[0013] Preferably, the conductor is a multilayer compacted conductor; the gap formed by the spiral winding of the stainless steel strip in the first optical fiber structure is filled with high-temperature resistant and waterproof sealant to prevent moisture from seeping into the conductor area along the first optical fiber structure.

[0014] A second aspect of this invention provides a technical solution: a method for preparing the aforementioned mineral-insulated flexible fire-resistant intelligent early warning cable, comprising the following steps: Step S1: Prepare the first optical fiber structure by placing the optical fiber core inside the loose tube, spirally wrapping a stainless steel strip around the outside of the loose tube, and filling the gaps in the spiral with high-temperature resistant and waterproof sealant. Step S2: Strand conductors on the outer wall of the first optical fiber structure to form a conductor core with a central optical fiber; Step S3: Fill the outer wall of the conductor with mineral insulating powder and press it with a mold to form a mineral insulating layer; Step S4: Prefabricate a metal strip and simultaneously form a first coiled section, a second coiled section, a third coiled section and a fourth coiled section on the surface of the metal strip through a rolling process, wherein the fourth coiled section forms a groove with an Ω-shaped cross section; Step S5: Embed the third optical fiber structure into the Ω-shaped groove of the fourth coiled part, so that the protective layer is tightly attached to the inner wall of the groove; Step S6: Wrap the metal tape with the embedded third optical fiber structure around the surface of the mineral insulation layer with a predetermined overlap ratio, and embed the first curled part of the front tape into the first opening of the third curled part of the rear tape to form a self-locking structure. At the same time, the second curled part covers the surface of the fourth curled part to form a metal sheath layer. Step S7: Extrude ceramicized silicone rubber onto the surface of the metal sheath layer to form an oxygen barrier layer; Step S8: Wrap multiple layers of mica tape around the surface of the oxygen barrier layer to form a flame-retardant layer; Step S9: Extrude a first low-smoke halogen-free flame-retardant polyolefin onto the surface of the flame-retardant layer to form an inner sheath layer, lay a second optical fiber structure on the surface of the inner sheath layer, and then extrude a second low-smoke halogen-free flame-retardant polyolefin onto the surfaces of the inner sheath layer and the second optical fiber structure to form an outer sheath layer.

[0015] Compared with the prior art, the advantages of the present invention are as follows: This invention places optical fibers at three different radial positions on the cable: the conductor center, the metal sheath layer, and the inner side of the outer sheath. This forms a complete temperature acquisition link from the heat source to the outside world. The three temperature data are interconnected through the inherent heat conduction path of the cable, providing intermediate state information during the heat transfer process without the need for additional algorithms. This multi-radial-point temperature acquisition structure enables maintenance personnel to simultaneously obtain the cable core temperature, metal sheath temperature, and surface environmental reference temperature. This provides a physical basis for distinguishing different heat source types such as internal overload, external fire, and insulation aging, overcoming the deficiency of existing single-point temperature measurement in determining the nature of the heat source.

[0016] This invention simultaneously forms a self-locking coil and an Ω-shaped groove on a metal strip through a rolling process, embedding the third optical fiber structure into the Ω-shaped groove. This self-locking structure allows the metal strip to form an axially fixed, sealed tubular sheath without welding or bundling after wrapping, simplifying the manufacturing process. At the same time, the elastic locking action of the Ω-shaped groove precisely positions the third optical fiber structure on the inner wall of the metal sheath, ensuring that the optical fibers are evenly distributed with a fixed pitch along the cable length, which is beneficial for the spatial consistency of distributed temperature measurement. In addition, the metal strip and the metal protective layer of the third optical fiber structure are in direct contact, forming a low thermal resistance heat transfer path, ensuring that the measured temperature truly reflects the actual temperature of the metal sheath layer.

[0017] The third optical fiber structure of this application incorporates a porous ceramic or aerogel buffer layer, which has a thermal conductivity significantly lower than that of the metal protective layer and metal tape material, forming a known and constant low thermal conductivity intermediate layer in the radial direction of the optical fiber. Therefore, when heat is transferred from the metal sheath to the fiber core, this intermediate layer generates a measurable micro-temperature difference, and the heat flux density flowing through this location can be accurately calculated through calibration. This enables the third optical fiber structure to simultaneously possess temperature measurement and heat flux sensing capabilities, allowing for cross-verification with data from the conductor's central optical fiber, thereby improving the reliability of cable thermal condition assessment. Attached Figure Description

[0018] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the structure of the mineral-insulated flexible fire-resistant intelligent early warning cable shown in an embodiment of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the mineral-insulated flexible fire-resistant intelligent early warning cable shown in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the metal sheath layer shown in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the metal strip shown in an embodiment of the present invention; Figure 5 This is a perspective view of the metal strip shown in an embodiment of the present invention; Figure 6 This is a schematic diagram of the third optical fiber structure shown in an embodiment of the present invention. Detailed Implementation

[0019] To better understand the technical content of this invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0020] {Example 1} Combination Figures 1 to 3 As shown, the first aspect of the present invention proposes a technical solution: a mineral-insulated flexible fire-resistant intelligent early warning cable, comprising a first optical fiber structure 1, a conductor 2, a mineral insulation layer 3, a metal sheath layer 4, an oxygen barrier layer 5, a flame-retardant layer 6, an inner sheath layer 7, and an outer sheath layer 9. The first optical fiber structure 1 includes a loose tube and a stainless steel tape spirally wound around the loose tube. Thus, the loose tube provides protection for the internal optical fiber core, preventing mechanical compression, while the armor layer formed by the spiral wrapping of the stainless steel tape not only protects the optical fiber from compression by subsequent stranded conductors but also utilizes the high elastic modulus of stainless steel to maintain the optical fiber's central position.

[0021] Preferably, the gaps formed by the spiral winding of the stainless steel strip in the first optical fiber structure 1 are filled with high-temperature resistant and waterproof sealant. The spiral gaps can be filled with sealant in subsequent processes to prevent moisture from seeping into the conductor 2 area along the first optical fiber structure 1.

[0022] Furthermore, conductor 2 is stranded on the outer wall of the first optical fiber structure 1, mineral insulation layer 3 is pressed tightly against the outer wall of conductor 2, and metal sheath layer 4 is covered on the surface of mineral insulation layer 3.

[0023] Optionally, the mineral insulation layer 3 is formed by compacting magnesium oxide powder, serving both electrical insulation and thermal conductivity. The metal sheath layer 4 provides a mechanical seal and fire barrier, while also acting as an intermediate medium for thermal conduction.

[0024] In this configuration, conductor 2 is a multilayer compacted conductor. This allows the first optical fiber structure 1 to be securely wrapped around the center, ensuring that the optical fiber and conductor bend synchronously without relative slippage, and the multilayer compacted conductor also possesses radial water-blocking capability.

[0025] Furthermore, the oxygen barrier layer 5 is extruded onto the surface of the metal sheath layer 4, the flame retardant layer 6 is wrapped around the outer wall of the oxygen barrier layer 5, the inner sheath layer 7 is wrapped around the outer wall of the flame retardant layer 6, and the outer sheath layer 9 is wrapped around the outer wall of the inner sheath layer 7.

[0026] Among them, the oxygen barrier layer 5 prevents external oxygen from penetrating into the metal sheath layer, thus preventing oxidation at high temperatures. The flame retardant layer 6 forms a ceramicized protective shell in the flame, slowing down the transfer of heat inward.

[0027] The inner sheath layer 7 and the outer sheath layer 9 are provided with a second optical fiber structure 8. The metal sheath layer 4 includes a wrapped metal strip 41. The surface of the metal strip 41 is pre-formed with grooves distributed along its length direction. A third optical fiber structure 42 is embedded in the grooves.

[0028] Thus, the inner sheath layer 7 and the outer sheath layer 9 provide overall mechanical protection and low-smoke, halogen-free flame-retardant properties. The second optical fiber structure 8, located between the inner and outer sheaths, can measure the cable surface temperature as an environmental reference; the third optical fiber structure 42 is embedded in the groove of the metal sheath for precise measurement of the temperature of the metal sheath layer.

[0029] The first optical fiber structure 1, the second optical fiber structure 8, and the third optical fiber structure 42 are located at three different radial positions in the cable. The first optical fiber structure 1 is used to detect the first temperature at the center of the conductor 2, the second optical fiber structure 8 is used to detect the second temperature between the outer sheath layer 9 and the inner sheath layer 7, and the third optical fiber structure 42 is used to detect the third temperature of the metal sheath layer 4.

[0030] Thus, the temperature data from three different radial locations together constitute the radial temperature distribution information of the cable.

[0031] It should be understood that, since the first optical fiber structure 1 is located at the center of the heat source and the third optical fiber structure 42 is located at the outer boundary of the main thermal resistance layer (mineral insulation layer 3), the temperature difference ΔT between the two is significant. 13 The heat flux density Q flowing through the mineral insulation layer (determined by the load current I²R) satisfies the following relationship: ΔT 13 =Q×R min , where R min This represents the equivalent thermal resistance of the mineral insulation layer. Through long-term monitoring of ΔT... 13The change in the ratio of / Q can be used to quantitatively assess the aging state of the mineral insulation layer. When the ratio increases irreversibly, it indicates a decrease in the thermal conductivity of the mineral insulation layer.

[0032] Meanwhile, the temperature difference ΔT between the third temperature and the second temperature 32 The combined thermal resistance of the oxygen barrier layer 5 and the flame retardant layer 6 is reflected. When this temperature difference increases abnormally under a constant load, it indicates that the outer fire-resistant structure may be delaminating or damaged.

[0033] Therefore, the temperature data from these three radial locations together constitute a complete cable thermal health monitoring network, enabling traditional single temperature early warning to be upgraded to multi-layer structural condition assessment.

[0034] It should be understood that when an external fire occurs, the temperature of the second optical fiber will rise sharply first, while the temperature of the first optical fiber will lag behind; when an internal overload occurs, the temperature of the first optical fiber will rise first, while the temperature of the second optical fiber will lag behind. This layered physical structure naturally endows the three temperature data with different time response characteristics and amplitude relationships, thus providing a structural basis for external devices to distinguish anomaly types without relying on complex algorithms.

[0035] Furthermore, the surface of the metal strip 41 is provided with a self-locking structure, so that when the metal strip 41 is wrapped according to a predetermined overlap rate, the front strip body 411 and the rear strip body 413 of the metal strip 41 are fixed to each other in the cable axial direction, and the third optical fiber structure 42 is wound on the outside of the mineral insulation layer 3 according to a fixed pitch.

[0036] Thus, by setting a self-locking structure, the metal strip can remain axially fixed without welding or bundling after wrapping, simplifying the process and improving reliability. At the same time, the fixed pitch ensures that the third optical fiber structure 42 is evenly distributed along the cable length, enabling continuous axial temperature measurement.

[0037] Furthermore, the self-locking structure enables the metal strip layer to form a continuous and sealed tubular structure in the circumferential direction, which can serve as a fire barrier and also be used for precise positioning of the third optical fiber structure 42.

[0038] Because the third optical fiber structure 42 is engaged in the groove of the metal tape, and the metal tape has a fixed wrapping pitch, the third optical fiber structure 42 forms a helix with a known pitch along the cable length. This ensures the consistency of spatial sampling during distributed temperature measurement and avoids signal attenuation caused by abrupt changes in the fiber bending radius. Simultaneously, the metal tape is in direct contact with the protective layer of the third optical fiber structure 42, forming a good heat conduction path, ensuring that the temperature measured by the third optical fiber structure 42 accurately reflects the temperature of the metal sheath layer, rather than a localized hot spot.

[0039] In an optional embodiment, combined with Figure 3 and Figure 4 As shown, the self-locking structure includes: A first curled portion 41a is provided at the edge of the front part of the metal strip 411; A second coiled portion 41b is provided at the center of the front part of the metal strip 41; A third coiled portion 412 is provided at the junction of the front belt body 411 and the rear belt body 413 of the metal belt 41; The fourth coiled section 41c is located in the center of the rear belt body 413 of the metal belt 41.

[0040] The third curled portion 412 forms an outward first opening that cooperates with the first curled portion 41a, the second curled portion 41b forms an inward second opening, and the fourth curled portion 41c forms an inward third opening, which is a groove. When the metal strip 41 is wrapped, the front strip body 411 covers the surface of the rear strip body 413, and the first curled portion 41a is embedded in the outward first opening of the third curled portion 412, while the second curled portion 41b covers the surface of the fourth curled portion 41c.

[0041] Thus, the first coiled portion 41a is embedded in the first opening of the third coiled portion 412 to form an axial lock, preventing the metal strip from coming off under force. The second coiled portion 41b covers the surface of the fourth coiled portion 41c, which not only protects the third optical fiber structure 42 embedded in the groove of the fourth coiled portion, but also allows the coiled portions to slide relative to each other when the cable is bent, avoiding plastic wrinkles in the metal strip.

[0042] Specifically, the third opening has an Ω-shaped cross-section, and its diameter is smaller than that of the third optical fiber structure 42. The Ω-shaped third opening has an elastic locking function, which can firmly embed the third optical fiber structure 42 without it falling out, while allowing slight movement during thermal expansion to avoid pressure on the optical fiber.

[0043] In a preferred embodiment, the first coiled portion 41a is configured to have a non-closed annular structure in cross-section, giving the first coiled portion 41a elastic deformation capability. The third coiled portion 412 is configured to generate elastic deformation when the cable is bent, so that when the cable is bent, stress is released through the deformation of the third coiled portion 412 and the first coiled portion 41a, and the flexibility of the cable is maintained.

[0044] Thus, the non-closed ring structure is similar to a spring. When the cable is bent, the first coiled part 41a can be stretched or compressed, and the third coiled part 412 can generate elastic flexure. The two work together to absorb the circumferential and axial stress generated by bending, preventing the metal sheath layer from undergoing permanent deformation or damaging the internal mineral insulation layer.

[0045] Furthermore, in combination Figure 6As shown, the third optical fiber structure 42 includes an optical fiber core 421, a buffer layer 422, and a protective layer 423. The buffer layer 422 covers the outer wall of the optical fiber core 421, and the protective layer 423 covers the outer wall of the buffer layer 422.

[0046] The three-layer structure of fiber core 421, buffer layer 422 and protective layer 423 provides sensing, buffering and mechanical protection functions from the inside out.

[0047] In an optional embodiment, the optical fiber core 421 includes a multi-core optical fiber, the buffer layer 422 includes an aerogel layer, and the protective layer 423 includes a metal tube.

[0048] The porous ceramic layer or aerogel layer has a lower thermal conductivity than the protective layer 423 and the material in contact with the outer wall of the protective layer 423, forming a low thermal conductivity intermediate layer in the radial direction of the third optical fiber structure 42.

[0049] It should be understood that, since the thermal conductivity of the buffer layer 422 is known and constant, while the thermal conductivity of the metal protective layer 423 and the metal strip 41 is very high, almost all the temperature drop from the metal strip 41 to the fiber core 421 occurs in the buffer layer 422. Therefore, through calibration, a definite relationship between the outer wall temperature of the protective layer and the fiber core temperature can be established.

[0050] Thus, a standard thermal resistance layer with known thermal resistance is formed through the low thermal conductivity buffer layer 422. When heat is transferred from the metal strip 41 to the fiber core 421, since the thermal resistance of the buffer layer 422 is known and constant, the heat flux density flowing through this point can be accurately calculated by measuring the slight temperature difference between the outer wall temperature of the protective layer and the fiber core temperature. Simultaneously, the porous structure is elastic, which can buffer the micro-bending loss caused by the compression of the metal sheath on the fiber core.

[0051] In a preferred embodiment, the multi-core optical fiber includes a first optical fiber for temperature measurement and a second optical fiber for humidity monitoring. The first optical fiber may be a common single-mode optical fiber, and the second optical fiber may be an optical fiber coated with polyimide or palladium.

[0052] In this way, the multi-core optical fiber not only enables temperature monitoring, but also provides an early warning of sheath damage when moisture invades the metal sheath, compensating for the lag in temperature monitoring.

[0053] In an optional embodiment, the oxygen barrier layer 5 includes a ceramicized silicone rubber oxygen barrier layer, the outer surface of which is a smooth cylindrical surface, and the flame retardant layer 6 includes a multilayer mica tape wrapped around the smooth cylindrical surface.

[0054] It should be understood that ceramicized silicone rubber is elastic at room temperature and can conform to the uneven surface of the metal sheath; after being shaped by the mold, it forms a smooth cylindrical surface, providing a flat base for the mica tape wrapping, avoiding wrinkles or breakage of the mica tape due to unevenness of the base when bending, and ensuring the integrity and fire resistance stability of the flame retardant layer 6.

[0055] Furthermore, the inner sheath layer 7 includes a first low-smoke halogen-free flame-retardant polyolefin layer, the outer sheath layer 9 includes a second low-smoke halogen-free flame-retardant polyolefin layer, and the second optical fiber structure 8 is embedded between the first low-smoke halogen-free flame-retardant polyolefin layer and the second low-smoke halogen-free flame-retardant polyolefin layer for measuring the cable surface temperature and serving as an environmental reference.

[0056] Among them, the thermal conductivity of the inner sheath layer 7 and the outer sheath layer 9 is similar. Therefore, the temperature measured by the second optical fiber structure 8 is close to the cable surface temperature and can be used as a reference for judging the environmental heat dissipation conditions.

[0057] In an optional embodiment, the thermal resistance change of the mineral insulation layer can be reflected by comparing the difference between the first and third temperatures; the combined thermal resistance of the oxygen barrier and flame retardant layers can be reflected by comparing the difference between the third and second temperatures. When the cable experiences overload, external fire, or insulation aging, the rates of change and differences between these three temperatures are different, thus providing a physical basis for external monitoring equipment to distinguish fault types.

[0058] Specifically, the surface temperature T2 provided by the second fiber structure 8, the center temperature T1 provided by the first fiber structure 1, and the metal sheath temperature T3 provided by the third fiber structure 42 constitute a complete radial temperature profile. By comparing the rate of change and amplitude of T1, T3, and T2, three typical abnormal operating conditions can be qualitatively distinguished: In the event of an external fire, temperature T2 rises first, while T1 lags behind; in the event of an internal overload, temperature T1 rises first, while T2 lags behind; and in the event of insulation aging, the temperature difference between T1 and T3 increases, but T2 remains stable. This ability to differentiate between the two is entirely determined by the physical structure of the cable, without relying on complex algorithms or historical data, thus improving the reliability and response speed of early warnings.

[0059] {Example 2} A second aspect of this invention provides a technical solution: a method for preparing the aforementioned mineral-insulated flexible fire-resistant intelligent early warning cable, comprising the following steps: Step S1: Prepare the first optical fiber structure 1 by placing the optical fiber core inside the loose tube, spirally wrapping a stainless steel strip around the outside of the loose tube, and filling the gap between the spirals with high-temperature resistant and waterproof sealant.

[0060] Specifically, after the stainless steel strip is spirally wrapped, silicone sealant is injected into the spiral gap using a vacuum injection method, which cures to form an elastic sealing layer. This ensures that the sealant is not squeezed out during conductor stranding and mineral insulation compaction, and can withstand thermal expansion and contraction without cracking.

[0061] This prevents moisture from seeping into the center of the conductor along the optical fiber channel, avoiding conductor oxidation and moisture absorption by the mineral insulation layer.

[0062] Step S2: Strand conductor 2 on the outer wall of the first optical fiber structure 1 to form a conductor core with a central optical fiber.

[0063] Step S3: Fill the outer wall of conductor 2 with mineral insulating powder and press it with a mold to form mineral insulating layer 3.

[0064] Step S4: Pre-fabricate a metal strip 41, and simultaneously form a first coiled portion 41a, a second coiled portion 41b, a third coiled portion 412 and a fourth coiled portion 41c on the surface of the metal strip 41 by a rolling process, wherein the fourth coiled portion 41c forms a groove with an Ω-shaped cross section.

[0065] In an optional embodiment, the pre-formed metal strip 41 can be rolled simultaneously on the surface of the copper strip using multi-pass precision rolling mills to form a first coiled portion 41a, a second coiled portion 41b, a third coiled portion 412, and a fourth coiled portion 41c. After rolling, annealing is required to eliminate work hardening and restore the elasticity of the copper strip.

[0066] The Ω-shaped groove has an opening width slightly smaller than the outer diameter of the third optical fiber structure, so that the optical fiber can be locked and fixed by the elasticity of the copper tape without the need for adhesive.

[0067] Step S5: Embed the third optical fiber structure 42 into the Ω-shaped groove of the fourth coiled part 41c, so that the protective layer 423 fits tightly against the inner wall of the groove.

[0068] Step S6: The metal tape 41 embedded with the third optical fiber structure 42 is wrapped around the surface of the mineral insulation layer 3 with a predetermined overlap ratio, and the first curled portion 41a of the front tape 411 is embedded in the first opening of the third curled portion 412 of the rear tape 413 to form a self-locking structure. At the same time, the second curled portion 41b covers the surface of the fourth curled portion 41c to form a metal sheath layer 4.

[0069] Specifically, on the wrapping machine, a metal tape embedded with a third optical fiber structure is spirally wrapped around the surface of a mineral insulation layer with a 45% overlap. The wrapping head is equipped with a guide wheel, which allows the first coiled portion 41a of the front tape to automatically slide into the first opening of the third coiled portion 412 of the rear tape, while the second coiled portion 41b naturally covers the fourth coiled portion 41c.

[0070] The wrapping tension is controlled at 50~80N to ensure tight self-locking without damaging the optical fiber.

[0071] Thus, the self-locking structure creates a mechanical interlock between the metal strip layers, with a tensile strength ≥500N / cm, requiring no welding, and allowing the coiled part to slide elastically when the cable is bent.

[0072] Step S7: Extruding ceramicized silicone rubber onto the surface of the metal sheath layer 4 to form an oxygen barrier layer 5. Specifically, after extruding the oxygen barrier layer, the surface is shaped using an adjustable shaping mold to make the surface of the oxygen barrier layer 5 round.

[0073] Step S8: Wrap multiple layers of mica tape around the surface of the oxygen barrier layer 5 to form a flame retardant layer 6.

[0074] Step S9: Extrude a first low-smoke halogen-free flame-retardant polyolefin onto the surface of the flame-retardant layer 6 to form an inner sheath layer 7, lay a second optical fiber structure 8 on the surface of the inner sheath layer 7, and then extrude a second low-smoke halogen-free flame-retardant polyolefin onto the surfaces of the inner sheath layer 7 and the second optical fiber structure 8 to form an outer sheath layer 9.

[0075] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A mineral-insulated flexible fire-resistant intelligent early warning cable, characterized in that, include: The first optical fiber structure (1) includes a loose tube and a stainless steel strip spirally wound around the outside of the loose tube; Conductor (2) is twisted to the outer wall of the first optical fiber structure (1); A mineral insulating layer (3) is pressed tightly against the outer wall of the conductor (2); A metal sheath layer (4) covers the surface of the mineral insulating layer (3); An oxygen barrier layer (5) is extruded onto the surface of the metal sheath layer (4); A flame-retardant layer (6) covers the outer wall of the inner sheath layer (5); The inner sheath layer (7) covers the outer wall of the flame-retardant layer (6); The outer sheath layer (9) covers the outer wall of the inner sheath layer (7); A second optical fiber structure (8) is provided between the inner sheath layer (7) and the outer sheath layer (9). The metal sheath layer (4) includes a wrapped metal strip (41). The surface of the metal strip (41) is pre-formed with grooves distributed along its length direction, and a third optical fiber structure (42) is embedded in the grooves. The first optical fiber structure (1), the second optical fiber structure (8) and the third optical fiber structure (42) are located at three different radial positions in the cable radial direction. The first optical fiber structure (1) is used to detect the first temperature at the center of the conductor (2), the second optical fiber structure (8) is used to detect the second temperature between the outer sheath layer (9) and the inner sheath layer (7), and the third optical fiber structure (42) is used to detect the third temperature of the metal sheath layer (4). The surface of the metal strip (41) is provided with a self-locking structure, so that when the metal strip (41) is wrapped according to a predetermined overlap rate, the front strip body (411) and the rear strip body (413) of the metal strip (41) are fixed to each other in the axial direction of the cable, and the third optical fiber structure (42) is wound on the outside of the mineral insulation layer (3) according to a fixed pitch.

2. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 1, characterized in that, The self-locking structure includes: The first curled portion (41a) is provided at the edge of the front strip body (411) of the metal strip (41). The second coiled portion (41b) is provided in the center of the front strip body (411) of the metal strip (41). The third coiled portion (412) is provided at the connection between the front belt body (411) and the rear belt body (413) of the metal belt (41). The fourth coiled portion (41c) is located in the center of the rear strip body (413) of the metal strip (41). The third curled portion (412) forms an outward first opening that cooperates with the first curled portion (41a), the second curled portion (41b) forms an inward second opening, and the fourth curled portion (41c) forms an inward third opening, the third opening being the groove; when the metal strip (41) is wrapped, the front strip body (411) covers the surface of the rear strip body (413), and the first curled portion (41a) is embedded in the outward first opening of the third curled portion (412), and the second curled portion (41b) covers the surface of the fourth curled portion (41c).

3. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 2, characterized in that, The third opening has an Ω-shaped cross section and the opening diameter is smaller than the diameter of the third optical fiber structure (42). The third optical fiber structure (42) includes an optical fiber core (421), a buffer layer (422), and a protective layer (423). The buffer layer (422) covers the outer wall of the optical fiber core (421), and the protective layer (423) covers the outer wall of the buffer layer (422).

4. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 3, characterized in that, The optical fiber core (421) includes a multi-core optical fiber, the buffer layer (422) includes an aerogel layer, and the protective layer (423) includes a metal tube. The porous ceramic layer or aerogel layer has a lower thermal conductivity than the protective layer (423) and the outer wall contact material of the protective layer (423), forming a low thermal conductivity intermediate layer in the radial direction of the third optical fiber structure (42).

5. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 2, characterized in that, The first coiled portion (41a) is configured to have a non-closed ring structure in cross section, so that the first coiled portion (41a) has elastic deformation capability. The third coiled portion (412) is configured to generate elastic deformation when the cable is bent, so that when the cable is bent, stress is released through the deformation of the third coiled portion (412) and the first coiled portion (41a), and the flexibility of the cable is maintained.

6. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 1, characterized in that, The oxygen barrier layer (5) includes a ceramicized silicone rubber oxygen barrier layer, the outer surface of which is a smooth cylindrical surface, and the flame retardant layer (6) includes a multilayer mica tape wrapped around the smooth cylindrical surface.

7. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 1, characterized in that, The multi-core optical fiber includes a first optical fiber for temperature measurement and a second optical fiber for humidity monitoring.

8. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 1, characterized in that, The inner sheath layer (7) includes a first low-smoke halogen-free flame-retardant polyolefin layer, and the outer sheath layer (9) includes a second low-smoke halogen-free flame-retardant polyolefin layer. The second optical fiber structure (8) is embedded between the first low-smoke halogen-free flame-retardant polyolefin layer and the second low-smoke halogen-free flame-retardant polyolefin layer and is used to measure the surface temperature of the cable and as an environmental reference.

9. The mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 1, characterized in that, The conductor (2) is a multilayer compacted conductor; the gap formed by the spiral winding of the stainless steel strip of the first optical fiber structure (1) is filled with high-temperature resistant waterproof sealant to prevent moisture from seeping into the conductor (2) area along the first optical fiber structure (1).

10. The method for preparing the mineral-insulated flexible fire-resistant intelligent early warning cable according to claim 1, characterized in that, Includes the following steps: Step S1: Prepare the first optical fiber structure (1), place the optical fiber core inside the loose tube, spirally wrap a stainless steel strip around the outside of the loose tube, and fill the spiral gap with high temperature resistant and waterproof sealant. Step S2: Strand conductor (2) on the outer wall of the first optical fiber structure (1) to form a conductor core with a central optical fiber; Step S3: Fill the outer wall of the conductor (2) with mineral insulating powder and press it with a mold to form a mineral insulating layer (3); Step S4: Prefabricate a metal strip (41), and simultaneously form a first coiled portion (41a), a second coiled portion (41b), a third coiled portion (412) and a fourth coiled portion (41c) on the surface of the metal strip (41) by a rolling process, wherein the fourth coiled portion (41c) forms a groove with an Ω-shaped cross section; Step S5: Embed the third optical fiber structure (42) into the Ω-shaped groove of the fourth coiled part (41c) so that the protective layer (423) fits tightly against the inner wall of the groove; Step S6: The metal tape (41) embedded with the third optical fiber structure (42) is wrapped around the surface of the mineral insulation layer (3) with a predetermined overlap ratio, and the first curled part (41a) of the front tape (411) is embedded in the first opening of the third curled part (412) of the rear tape (413) to form a self-locking structure. At the same time, the second curled part (41b) covers the surface of the fourth curled part (41c) to form a metal sheath layer (4). Step S7: Extrude ceramicized silicone rubber onto the surface of the metal sheath layer (4) to form an oxygen barrier layer (5); Step S8: Wrap multiple layers of mica tape around the surface of the oxygen barrier layer (5) to form a flame retardant layer (6); Step S9: Extrude a first low-smoke halogen-free flame-retardant polyolefin onto the surface of the flame-retardant layer (6) to form an inner sheath layer (7), lay a second optical fiber structure (8) on the surface of the inner sheath layer (7), and then extrude a second low-smoke halogen-free flame-retardant polyolefin onto the surfaces of the inner sheath layer (7) and the second optical fiber structure (8) to form an outer sheath layer (9).

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