Cable foamed filler strip

Abstract

The utility model discloses a cable foamed filling strip, including the conductor by trapezoidal annealing copper monofilament stranding, its outside is covered with coaxial inner semiconductive layer, insulating layer, outer semiconductive layer, buffer tape layer, copper band shielding layer, inner sheath, double -deck reverse steel tape armoring and high -resistance no -halogen outer sheath, the fan -shaped ceramicizable polyolefin foamed filling strip of built -in steel wire rope is arranged between the adjacent conductive wire core, the cable has low thermal resistance, low loss characteristic under normal temperature, the foamed strip ceramicization is rapid when the fire, makes integral thermal resistance instantaneous rise >=5 times, and the cooperation double -deck reverse steel tape armoring realizes hundred meters vertical difference self -supporting, the distributed optical fiber is inlayed in buffer tape layer, can real -time monitoring conductor temperature. The utility model discloses compact structure, energy -conserving and environment -friendly, fire -resistant, high mechanical strength, is applicable to high -rise building, tunnel and high difference power supply and distribution system.

Description

Technical Field

[0001] This utility model relates to the field of cable foam filler strip technology, and in particular to a cable foam filler strip. Background Technology

[0002] In medium and high voltage power cables, the gaps between the cable cores are typically filled with filler ropes, filler strips, or ripped polypropylene fibers to ensure a round cable shape and prevent sheath material from seeping in. However, existing filler materials generally have the following shortcomings:

[0003] 1. Poor structural roundness

[0004] Traditional round or flat filler ropes are prone to creating gaps during cabling, resulting in a "plum blossom" shaped cable cross-section and uneven sheath extrusion thickness, which wastes materials and affects the appearance.

[0005] 2. Heavy weight and inconvenient construction

[0006] PP filler rope or recycled filler strip has a high density, and its weight per meter is 4-6 times that of the same volume of foam material. The labor intensity of handling and laying is high, and a special large-diameter laying frame is required.

[0007] 3. Insufficient flame retardant / fire resistant properties

[0008] Conventional filler ropes soften and drip at high temperatures, failing to form a heat insulation barrier; recycled filler strips contain impurities and release large amounts of smoke and corrosive gases when exposed to fire, failing to meet the low-smoke, halogen-free requirements for tunnels, subways, and other similar applications.

[0009] Therefore, developing a lightweight, flame-retardant, self-supporting, and rounded fan-shaped foam filler strip has become a technical challenge that the industry urgently needs to solve. Utility Model Content

[0010] The purpose of this invention is to provide a cable foam filler strip, thereby solving the aforementioned problems existing in the prior art.

[0011] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0012] It includes at least one conductive core; and on the outside of the conductive core, an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a buffer wrapping layer, a copper strip shielding layer, an inner sheath, a steel strip armor, and an outer sheath are arranged coaxially in sequence.

[0013] A fan-shaped foam filler strip is provided between adjacent conductive cores. The cross-section of the fan-shaped foam filler strip is an isosceles sector with a sector angle α = 64.747°. The width of the fan-shaped foam filler strip is 30mm-45mm, and the height is 13mm-20mm. The outer arc of the fan-shaped foam filler strip is in contact with the inner surface of the buffer wrapping layer, and the inner arc is in contact with the outer surface of the conductive core at three points. A load-bearing element is embedded longitudinally along the central axis inside the strip, and together with the steel strip armor, they form a mechanical reinforcement system.

[0014] In some specific embodiments, the center of the fan-shaped foam filler strip is made of polyurethane foam material for flame retardancy;

[0015] The outer skin of the fan-shaped foam filler strip is an embossed PE film, fire-resistant film, ceramicized film, or semi-conductive film.

[0016] The overall density of the fan-shaped foam filler strips is between 0.08 and 0.15 g / cm³. 3 .

[0017] In some specific embodiments, the fan-shaped foam filler strip is a fan-shaped ceramizable polyolefin foam strip, which is embedded between adjacent conductive cores and buffer wrapping layers to make the core filling rate ≥96%, and transforms into a continuous honeycomb ceramic body at 650 ℃ or above to block external heat sources.

[0018] In some specific embodiments, the load-bearing element is one or more thin-diameter steel wire ropes, which are buried longitudinally along the cable at the central axis of the fan-shaped foam strip; the steel wire ropes and steel strip armor share the tensile force, achieving a self-bearing safety factor of ≥5 for a 100m vertical drop.

[0019] In some specific embodiments, the steel strip armor is located between the inner sheath and the outer sheath, and adopts a double-layer reverse wrapping stainless steel strip, with the inner layer on the right and the outer layer on the left, with an overlap rate of ≥15%, and a sliding isolation membrane is provided between the layers to prevent thermal expansion and bulging during a fire.

[0020] In some specific embodiments, the copper strip shielding layer is made of copper strip with a thickness of 0.1mm–0.15mm and a wrapping overlap rate of ≥15%. It is formed by welding to create a continuous grounding loop to reduce the temperature rise caused by short-circuit current.

[0021] In some specific embodiments, the buffer wrapping layer is located between the outer semiconductive layer and the copper strip shielding layer. It is made of low-smoke halogen-free flame-retardant fiberglass tape with an overlap of 20%–25%, and is used to absorb thermal expansion and provide buffer insulation in case of fire.

[0022] In some specific embodiments, distributed optical fibers are embedded between the buffered wrapping layer and the copper strip shielding layer for real-time monitoring of conductor temperature, with a temperature measurement accuracy of ±1℃ and a spatial resolution of ≤0.5m.

[0023] In some specific embodiments, the inner sheath is located between the copper strip shielding layer and the steel strip armor, and is formed by extrusion of thermoplastic halogen-free flame-retardant polyolefin with an oxygen index ≥38; the outer sheath is located outside the steel strip armor, and is formed by extrusion of irradiated cross-linked halogen-free flame-retardant polyolefin with an oxygen index ≥42 and a combustion smoke density Ds(4min) ≤150.

[0024] In some specific embodiments, the conductive core includes an annealed copper conductor with a trapezoidal cross-section and an inner semiconductive layer, an insulating layer, and an outer semiconductive layer that are tightly wrapped around it in sequence; the inner semiconductive layer is bonded to the conductor without gaps, and a thermal expansion gap of 0.3mm–1mm is formed between the outer semiconductive layer and the buffer wrapping layer to reduce the normal thermal resistance.

[0025] The beneficial effects of this utility model are:

[0026] Compared with the prior art, the present invention has the following significant advantages:

[0027] The structure is neat and round: the fan-shaped foam filler strip is attached to the cable core at three points, and the cable has a regular shape after being formed. No additional shaping is required to ensure that the sheath is extruded evenly and reduce material waste.

[0028] Lightweight: The foamed matrix has a low density and a light overall weight, making handling and laying easier, while also reducing the load on cable trays and supports due to the cable's own weight.

[0029] Fire adaptive: It maintains elastic buffer at room temperature and rapidly ceramicizes when exposed to high temperatures, forming a continuous heat insulation layer that blocks the penetration of flames and heat into the interior, thus extending the fire resistance time.

[0030] Mechanical reinforcement: The built-in load-bearing elements and double-layer reverse steel belt armor work together to achieve high drop self-support, eliminating the need for additional slings and simplifying construction. Attached Figure Description

[0031] Figure 1 This is a cross-sectional schematic diagram of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of the fan-shaped filler strip and the steel wire rope of this utility model;

[0033] Figure 3 This is a schematic diagram of another embodiment of the sector-shaped filler strip of this utility model.

[0034] In the attached diagram, 1 is the outer sheath; 2 is the steel strip armor; 3 is the inner sheath; 4 is the fan-shaped foam filler strip; 5 is the buffer wrapping layer; 6 is the copper strip shielding layer; 7 is the outer semiconductive layer; 8 is the insulating layer; 9 is the inner semiconductive layer; and 10 is the conductor. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the scope of the present utility model.

[0036] Reference Figure 1 and Figure 2 The cable foam filler strip shown includes at least one conductive core; an inner semiconductive layer 9, an insulation layer 8, an outer semiconductive layer 7, a buffer wrapping layer 5, a copper tape shielding layer 6, an inner sheath 3, a steel tape armor 2, and an outer sheath 1 are arranged coaxially outside the conductive core in sequence.

[0037] A fan-shaped foam filler strip 4 is installed between adjacent conductive cores. The cross-section of the fan-shaped foam filler strip 4 is an isosceles sector with a sector angle α = 64.747°. The width of the fan-shaped foam filler strip 4 is 30mm-45mm, and the height is 13mm-20mm. The outer arc of the fan-shaped foam filler strip 4 is attached to the inner surface of the buffer wrapping layer 5, and the inner arc is in three-point contact with the outer surface of the conductive core. A load-bearing element is embedded longitudinally along the central axis inside, forming a mechanical reinforcement system together with the steel strip armor 2. A detailed description of this structure from different perspectives is as follows:

[0038] Conductor 10: Located at the very center of the cable, it is composed of multiple annealed copper monofilaments with trapezoidal cross-sections concentrically twisted together. The elongation of the monofilaments is ≥35%, and the conductor fill factor is ≥99%. There are no gaps between the trapezoidal monofilaments, which makes the overall outer diameter of the conductor 6%–10% smaller than that of a circular conductor of the same cross-section, thereby reducing the insulation thickness and reducing normal operating losses by 5%–8%.

[0039] Inner semiconductive shielding layer 9: It is tightly wrapped around the outer surface of conductor 10 by extrusion, with a thickness of 0.6mm–0.8mm. The material is graphene composite semiconductive material, which is used to uniform electric field and suppress partial discharge.

[0040] Insulation layer 8: Extruded outside the inner semiconductive layer 9, made of ultra-clean cross-linked polyethylene (XLPE), with a rated operating temperature of 90℃ and a short-time overload temperature of up to 250℃.

[0041] Outer semiconductive layer 7: Extruded outside the insulating layer 8, with a thickness of 0.6mm–0.8mm, and the material is the same as that of the inner semiconductive layer (9), forming a three-layer co-extrusion structure of “conductor-insulation-outer shield” to ensure uniform electric field.

[0042] II. Buffer band layer 5

[0043] Located outside the outer semiconductive layer 7, it is made of low-smoke halogen-free flame-retardant glass fiber tape with an overlap of 20%–25%. Its main function is:

[0044] Absorbs the thermal expansion of the insulating layer;

[0045] In the event of a fire, it forms a heat insulation buffer to prevent cracking between the outer semiconductive layer 7 and the copper strip shielding layer 6 due to thermal stress.

[0046] Provides space for laying distributed optical fibers.

[0047] III. Copper tape shielding layer 6

[0048] A soft copper strip with a thickness of 0.10mm–0.15mm is used to wrap around the buffer wrapping layer 5 with an overlap rate of ≥15%. The two sides of the copper strip are continuously laser-welded into a closed cylinder to form a low-impedance grounding loop, which can quickly discharge short-circuit current and reduce fault temperature rise during single-phase grounding faults.

[0049] IV. Fan-shaped foam filler strip 4

[0050] Location: Located in the gap between adjacent conductive cores and completely wrapped by the buffer wrapping layer 5.

[0051] Structural shape: fan-shaped cross-section, angle 60°–72°, with three points of contact with the outer edge of the conductive core, so that the roundness of the cable core is ≥96%.

[0052] Material: Ceramizable polyolefin foam matrix, thermal conductivity at room temperature ≤0.18W / (m·K), density 0.45 g / cm³–0.55g / cm³.

[0053] effect:

[0054] Normal characteristics: low thermal conductivity, lightweight, reducing the overall heat capacity of the cable;

[0055] Fire resistance: Rapid ceramization at temperatures above 650 ℃, with volume shrinkage of <5%, forming a continuous honeycomb ceramic shell, which instantly increases the overall thermal resistance of the cable by ≥5 times, preventing flames and heat from penetrating into the conductor, and providing a fire resistance time of ≥90min.

[0056] V. Load-bearing components

[0057] Structure: One or more high-strength galvanized steel wire ropes with a diameter of φ1.0mm–φ1.5mm are laid in a straight line along the longitudinal direction of the cable at the central axis of the fan-shaped foam filler strip 4;

[0058] Connection method: The two ends of the wire rope are crimped and fixed to the metal clamps of the cable terminal, forming a "double tensile system" together with the steel strip armor 2;

[0059] effect:

[0060] It bears the weight of the cable itself and the tensile force during laying;

[0061] In conjunction with the double-layer reverse steel strip armor 2, the cable's self-bearing safety factor is ≥5 under a vertical drop of 100m, eliminating the need for additional slings;

[0062] During a fire, the ceramicized fan-shaped foam filler strip 4 hardens, while the steel wire rope retains its tensile strength, preventing the cable from breaking due to its own weight.

[0063] VI. Steel Belt Armor 2

[0064] Location: Between the inner sheath 3 and the outer sheath 1;

[0065] Structure: Double-layer stainless steel strip, thickness 0.2mm–0.3mm, inner layer wrapped to the right and outer layer wrapped to the left, overlap rate 15%–20%;

[0066] Connection relationship: The interlayer is coated with a 0.1mm–0.2mm high-temperature resistant sliding isolation film, which allows the steel strip to slide relative to each other during thermal expansion and contraction, preventing bulging;

[0067] effect:

[0068] Mechanical protection: Resisting external impacts and compression;

[0069] Tensile strength: Shares axial tensile force with the wire rope;

[0070] Electromagnetic shielding: Reduces external electromagnetic interference.

[0071] VII. Inner Sheath 3

[0072] Located between the copper strip shielding layer 6 and the steel strip armor 2, it is made of thermoplastic halogen-free flame-retardant polyolefin extrusion, with a thickness of 2.0mm–3.0mm and an oxygen index ≥38, serving as a moisture-proof, chemical corrosion-proof, and secondary insulation layer.

[0073] 8. Outer Sheath 1

[0074] Located on the outside of the steel strip armor 2, it is extruded from irradiated cross-linked halogen-free flame-retardant polyolefin with a thickness of 2.5mm–4.0mm, oxygen index ≥42, smoke density Ds(4min)≤150, halogen acid gas release ≤5mg / g, and has Class A flame retardancy and Class B1 fire resistance, protecting the cable from mechanical damage and environmental corrosion.

[0075] IX. Distributed Optical Fiber

[0076] Installation location: Lay between the buffer wrapping layer 5 and the copper tape shielding layer 6, spirally wound along the entire length of the cable, with a pitch of 0.5m–1.0m;

[0077] Connection: The optical fiber is connected to the monitoring platform through temperature demodulators at both ends of the cable;

[0078] Function: Real-time monitoring of conductor temperature, with a temperature measurement accuracy of ±1℃ and a spatial resolution of ≤0.5m, enabling early warning and precise location of faults.

[0079] Through the synergy of the above layers, the cable of this utility model has low thermal resistance, low loss and high conductivity during normal operation; in case of fire, it achieves high fire resistance and self-support through ceramicized fan-shaped foamed filler strip 4 and double-layer reverse steel strip armor 2; distributed optical fiber provides online temperature monitoring, and the overall design meets the stringent requirements of high-rise buildings, shafts and tunnels.

[0080] In some specific embodiments, the center of the fan-shaped foam filler strip 4 is made of polyurethane foam material for flame retardancy;

[0081] The outer skin of the fan-shaped foam filler strip 4 is an embossed PE film, fire-resistant film, ceramicized film, or semi-conductive film.

[0082] The overall density of the fan-shaped foam filler strip 4 is between 0.08 and 0.15 g / cm³. 3 .

[0083] The fan-shaped foam filler strip 5 adopts a core-skin double-layer integrated structure:

[0084] 1. Core Material: Closed-cell rigid polyurethane foam containing phosphorus and nitrogen flame-retardant elements in its molecular chain. A cyclopentane / water composite foaming agent is injected during foaming to form uniform micropores with a pore size of 80–150µm and a closed-cell rate >90%. The polyurethane itself has an oxygen index ≥28, resulting in rapid surface charring during combustion and inhibiting flame spread; the closed-cell structure prevents heat and smoke penetration. The core layer accounts for 70–80% of the total cross-section, providing a lightweight skeleton and elastic support.

[0085] 2. The outer skin continuously covers the outer periphery of the core layer, with a thickness of 0.15–0.25 mm, and can be any of the following functional membranes:

[0086] Embossed PE film: The surface is rolled with diamond or wavy patterns to increase the coefficient of friction and prevent cable slippage; it is resistant to acids and alkalis and is moisture-proof.

[0087] Fire-resistant membrane: Made of mica composite polyolefin, it releases water of crystallization when exposed to fire, forming a heat insulation barrier.

[0088] Ceramicized membrane: Silicone rubber base, which transforms into hard-shell ceramic at temperatures above 600 °C, and works synergistically with the polyurethane core layer to improve fire resistance integrity.

[0089] Semiconducting film: Carbon black-filled EVA, volume resistivity 10³–10 4 Ω·cm is used to equalize the electric field and suppress partial discharge. The outer skin is bonded to the core layer without adhesive through hot melt co-extrusion, and the edges are heat-sealed, resulting in a seamless finish.

[0090] 3. Overall density: core layer density 0.05–0.08 g / cm³, outer sheath density 0.90–1.05 g / cm³; after weighting by cross-sectional area, the overall density of the entire filler strip is 0.08–0.15 g / cm³, which is only 1 / 6–1 / 10 of that of traditional PP rope, significantly reducing cable weight and reducing transportation and laying load.

[0091] 4. Key Process Points: Extrusion-Foaming Integrated Molding: First, flame-retardant polyurethane raw materials and foaming agents are mixed by twin screws and injected into the fan-shaped mold cavity for foaming; then, functional films are co-extruded online, cooled and shaped, and then pulled and wound up to finally obtain continuous, jointless fan-shaped foamed filler strips.

[0092] In some specific embodiments, the conductive core includes an annealed copper conductor 10 with a trapezoidal cross section and an inner semiconducting layer 9, an insulating layer 8, and an outer semiconducting layer 7 that are tightly wrapped around it in sequence; the inner semiconducting layer 9 is bonded to the conductor 10 without gaps, and a thermal expansion gap of 0.3mm–1mm is formed between the outer semiconducting layer 7 and the buffer wrapping layer 5 to reduce the normal thermal resistance.

[0093] In this embodiment, one, conductor 10

[0094] Cross-sectional shape: isosceles trapezoid, vertex angle 88°–90°, waist inclination angle 6°–8°; relationship between the height h and the base b: h = (0.55–0.65)b.

[0095] Material: TR grade annealed oxygen-free copper rod, copper content ≥99.95%, conductivity ≥101% IACS.

[0096] Hinged structure:

[0097] The center has one trapezoidal monofilament;

[0098] The first layer has 6 roots, the second layer has 12 roots, the directions between layers are opposite, and the nodule diameter ratio is 18–22;

[0099] The monofilament is annealed at 580 ℃ for 3 hours, with an elongation of ≥35% and a hardness of HV55–65.

[0100] Dimensional accuracy: The thickness tolerance of the trapezoidal monofilament is ±0.02mm, and the width tolerance is ±0.03mm, ensuring that the outer diameter deviation of the conductor 10 after stranding is ≤0.2mm.

[0101] Fill factor: Due to the seamless interlocking of the trapezoidal cross section, the fill factor of the stranded conductor is ≥99%, which is 6%–10% smaller than that of a circular conductor with the same cross section, and increases the current carrying capacity by 3%–5%.

[0102] II. Inner Semiconductor Layer 9

[0103] Location: Extruded directly onto the outer periphery of conductor 10, with a thickness of 0.6mm–0.8mm.

[0104] Material: Graphene-composite semi-conductive cross-linked polyethylene (volume resistivity 20–100 Ω·cm).

[0105] Process: During the three-layer co-extrusion, the surface temperature of the inner semiconductive layer 9 and the conductor 10 is simultaneously controlled at 120 ℃±5 ℃ to ensure that the molten material fully fills the gap between the monofilaments and achieves "gapless bonding".

[0106] Function:

[0107] A uniform electric field suppresses local discharge caused by burrs on the conductor surface.

[0108] Reduce the contact thermal resistance between the conductor and the insulation layer, R_th ≤ 0.05K·m / W.

[0109] III. Insulation layer 8

[0110] Material: Ultra-clean cross-linked polyethylene (XLPE), impurity particles ≤50μm, dielectric constant 2.3, tgδ≤0.0005.

[0111] Thickness: Designed according to 12 / 20kV voltage level, nominal thickness 4.5mm, thinnest point ≥4.05mm.

[0112] Crosslinking process: dry crosslinking, vulcanizing tube temperature 380 ℃–420 ℃, nitrogen pressure 0.8–1.0 MPa, degree of crosslinking ≥82%.

[0113] Function: Provides main insulation, withstands short-time voltage of 1min / 110 kV, operates at a long-term temperature of 90℃, and does not break down under overload conditions of 250℃ / 5s.

[0114] IV. Outer Semiconductor Layer 7

[0115] Location: Coaxially extruded outside the insulating layer 8, with a thickness of 0.6mm–0.8mm, and the material is the same as that of the inner semiconductive layer (9).

[0116] Thermal expansion gap: The outer diameter of the outer semiconductive layer 7 is 0.3mm–1mm smaller than the inner diameter of the buffer wrapping layer 5, forming an annular air / buffer layer gap (Δd).

[0117] Gap formation method: After extrusion, a vacuum sizing mold is used to control the outer diameter of the outer semiconductive layer 7 to D-0.3mm to D-1mm (D is the inner diameter of the buffer wrapping layer).

[0118] Interval function:

[0119] At room temperature, the air thermal resistance is 0.04 K·m / W, which significantly reduces the overall thermal resistance between the conductor, shield, and wrapping tape.

[0120] During a fire, the insulation layer and the outer semiconductive layer expand, and Δd is completely filled, preventing mechanical compression from causing insulation damage.

[0121] V. Schematic diagram of inter-layer connection relationship

[0122] Conductor 10 → Inner semiconducting layer 9 → Insulating layer 8 → Outer semiconducting layer 7 → [Δd thermal expansion gap] → Buffer wrapping layer 5.

[0123] There is no gap between the inner semiconducting layer 9 and the conductor 10, and the interfacial thermal resistance is close to zero.

[0124] A Δd is maintained between the outer semiconductive layer 7 and the buffer wrapping layer 5 to achieve the dual function of "low thermal resistance under normal conditions - fire expansion compensation".

[0125] In some specific embodiments, the fan-shaped foam filler strip 4 is a fan-shaped ceramicizable polyolefin foam strip, which is embedded between adjacent conductive cores and buffer wrapping layer 5. Its fan-shaped angle is 60°–72°, so that the cable core filling rate is ≥96%, and it is transformed into a continuous honeycomb ceramic body at 650 ℃ or above to block external heat sources.

[0126] I. Detailed Technical Features of Fan-Shaped Ceramizable Polyolefin Foam Strips (Fan-Shaped Foam Filler Strip 4)

[0127] 1. Geometric Parameters 1.1 Cross-sectional Shape: Isosceles sector, with the arc radius R matching the cable cabling radius, and the sector angle α = 60°–72° (preferably 64.747°). 1.2 Dimensional Chain: Sector height h = (D1–D2) / 2–δ, where D1 is the inner diameter of the buffer wrapping layer (measured value); D2 is the outer diameter of the three-core conductive wire; and δ is the reserved thermal expansion gap of 0.2mm. 1.3 Tolerances: Angle ±1°, height ±0.1mm, ensuring three-point contact, and cable core roundness ≥96%.

[0128] 2. Material Composition 2.1. Matrix Resin: Ethylene-vinyl acetate copolymer (EVA, VA content 18%) + linear low-density polyethylene (LLDPE) 70 / 30 blend, providing flexibility and foamability. 2.2. Ceramicizing Additives: Silicate glass powder (softening point 550 ℃) 20 phr; mica powder (aspect ratio ≥ 60) 10 phr; Al(OH)3 synergistic flame retardant 15 phr. 2.3. Foaming System: Chemical foaming agent azodicarbonamide (AC) 2.5 phr; activator ZnO 1.0 phr; surface-modified SiO2 nucleating agent 1.5 phr. 2.4. Crosslinking System: Dicumyl peroxide (DCP) 0.8 phr, ensuring structural stability after foaming.

[0129] 3. Foaming and Crosslinking Process 3.1 Mixing: Internal mixer 110 ℃ / 8min → Twin-screw extruder 120 ℃ / 6min → Single-screw extrusion 90 ℃ to form sheets. 3.2 Irradiation Pre-crosslinking: β-rays 50kGy, increasing melt strength by 30% and preventing foam collapse. 3.3 Foaming: Horizontal foaming furnace 180 ℃ / 3min, foaming ratio 2.0–2.2, closed-cell rate ≥90%, density 0.45g / cm³±0.02g / cm³. 3.4 Forming: The foamed sheets are heat-set by rolling into 60°–72° fan-shaped strips, and after dimensional stability, they are wound up for later use.

[0130] 4. Built-in load-bearing element (steel wire rope) 4.1 Specifications: 1×19 structural galvanized steel wire rope, nominal diameter 1.2 mm, tensile strength 1770MPa, breaking force ≥2.0kN. 4.2 Arrangement: The steel wire rope is laid in a straight line along the central axis of the fan shape, and is formed by one-time encapsulation with foam, with a bonding strength ≥300N / 50 mm.

[0131] 5. Thermal-physical property conversion mechanism 5.1 Room temperature performance: Thermal conductivity 0.16–0.18 W / (m·K) (25 ℃); Compression set ≤5% (70 ℃ / 24h). 5.2 Ceramization at 650 ℃: A dense Si-O-Al ceramic film forms on the surface within 5 min; after 15 min, the whole structure transforms into a continuous honeycomb ceramic body with a volume shrinkage of <5%; the thermal conductivity of the ceramic body decreases to 0.05 W / (m·K), resulting in an increase of ≥5 times in the overall thermal resistance of the cable.

[0132] 6. Fill rate verification theoretical calculation: Three cores + 3 sector strips, circular area fill rate 96.8%; Actual measurement: Slice projection method, fill rate 96.3%–97.1%, meeting the ≥96% requirement.

[0133] 7. For installation and process adaptation, the outer surface of the fan-shaped strip is sprayed with 0.02mm silicone oil to reduce the coefficient of friction of the cable to 0.15 and prevent displacement during sheath extrusion; the cable tension is 8-10N to ensure three-point contact between the fan-shaped strip and the conductive core without gaps.

[0134] In some specific embodiments, the load-bearing element is one or more thin-diameter steel wire ropes, which are buried longitudinally along the cable at the central axis of the fan-shaped foam strip; the steel wire ropes and the steel strip armor 2 share the tension, achieving a self-bearing safety factor of ≥5 for a 100m vertical drop.

[0135] I. Overall Layout Ideas for Load-Bearing Components

[0136] A geometric central axis (i.e., the centroid line connecting the fan-shaped cross-sections) is reserved inside the fan-shaped ceramizable polyolefin foam strip (fan-shaped foam filler strip 4), and 1 to 3 thin-diameter steel wire ropes are embedded along the entire longitudinal direction of the cable (see attached diagram 5-1). The steel wire ropes and the external double-layer reverse steel strip armor 2 form an "internal and external dual-path" tensile system.

[0137] Internal path – the steel wire rope directly “suspends” the conductive core;

[0138] External path – steel belt armor bears part of the tensile force and protects the internal structure.

[0139] The two paths work in parallel, so that when the cable is laid with a vertical drop of 100m, the overall safety factor is ≥5 (breaking force / working tensile force ≥5).

[0140] II. Specifications and Selection of Steel Wire Rope

[0141] Structure: 1×19 strand galvanized steel wire rope, smooth surface, oil-free hemp core, easy to co-extrude and bond with foam strips.

[0142] Nominal diameter: 1.2mm (single) or 0.8mm (double).

[0143] Tensile strength: ≥1770 MPa; breaking force of a single strand ≥2.0 kN; total breaking force of two strands ≥4.0 kN.

[0144] Elongation: ≤0.8% (before breakage), ensuring elastic elongation <80 mm under 100m vertical working conditions, without affecting electrical performance.

[0145] Anti-rotation: Uses tangential twist to reduce torque when the cable is bent.

[0146] III. Burial Location and Fixing Method

[0147] Geometric position: The wire rope is precisely positioned at the center axis of the fan-shaped foam strip (0.45h from the arc surface, where h is the height of the fan shape) to ensure minimal stress during bending.

[0148] Vertical positioning:

[0149] Every 1m, the steel wire rope and foam strip are tied together twice with 0.2mm annealed copper wire to prevent slippage during co-extrusion.

[0150] During cable laying, the wire rope should be kept at 0.2% to 0.3% pretension to eliminate slack.

[0151] End anchoring:

[0152] After stripping the outer sheath at both ends of the cable, the steel wire rope is bent 180° in the opposite direction and crimped with copper terminals;

[0153] The terminals and end metal clamps are bolted together to form a "lifting ring" type anchorage, ensuring that the tensile force is directly transmitted to the mounting bracket.

[0154] IV. Co-force model with steel belt armor 2

[0155] Force distribution calculation

[0156] Cable unit weight: W = 5.6 kg / m → Total weight of 100m section 560 kgf ≈ 5.5 kN;

[0157] Working tensile force F_w = 5.5kN;

[0158] Dual-path parallel connection: breaking force of wire rope F_s = 4.0kN, breaking force of steel belt armor F_a = 22kN;

[0159] The parallel stiffness ratio K_s / K_a≈1:5, and the actual tension distribution is: the wire rope bears ≈0.9kN, and the steel strip bears ≈4.6kN;

[0160] The safety factor = min(4.0 / 0.9, 22 / 4.6)≈4.8, which meets the requirement of ≥5.

[0161] Fire condition verification

[0162] After ceramization at 650 ℃, the compression modulus of the fan-shaped foamed strip increases by 20 times, and the relative slippage between the wire rope and the steel strip is less than 1 mm.

[0163] The ceramic body provides a rigid sheath for the wire rope, preventing local flattening and ensuring that the tensile strength is not reduced.

[0164] V. Key Points of Process Implementation

[0165] Co-extrusion process

[0166] Steel wire rope unloading → preheating to 60 ℃ → entering the foaming machine head and being coated with ceramicizable polyolefin → maintaining the central axis position through a vacuum sizing sleeve → cooling and shaping.

[0167] Tension closed-loop control

[0168] A closed-loop system using a magnetic powder brake and tension sensor is employed to ensure that the tension fluctuation of the wire rope is less than 5N.

[0169] Online testing

[0170] A laser diameter gauge is installed 1m after the foamed strip is extruded to monitor the eccentricity of the wire rope in real time, which is ≤0.3mm.

[0171] In some specific embodiments, the steel strip armor 2 is located between the inner sheath 3 and the outer sheath 1, and adopts a double-layer reverse wrapping stainless steel strip, with the inner layer on the right and the outer layer on the left, with an overlap rate of ≥15%, and a sliding isolation membrane is provided between the layers to prevent thermal expansion and bulging during a fire.

[0172] I. Position and overall structure of steel-tape armor 2 in the cable

[0173] Location: It is located between the outer side of the inner sheath 3 and the inner side of the outer sheath 1, forming a sandwich structure of "inner sheath - armor - outer sheath".

[0174] Functional partitions:

[0175] Inner sheath 3 → provides radial waterproofing, chemical corrosion resistance, and secondary insulation;

[0176] Steel belt armor 2 → Bears mechanical impact, extrusion and self-supporting tensile force of 100m vertical drop;

[0177] Outer sheath 1 → Flame retardant, weather resistant, UV resistant, and protects the armor from environmental corrosion.

[0178] II. Design and Function of Sliding Separator

[0179] Material: 0.10mm thick high-temperature resistant PTFE (polytetrafluoroethylene) film, surface treated with corona discharge, coefficient of friction ≤0.04.

[0180] structure:

[0181] A PTFE sliding membrane is continuously wrapped around the double-layer steel strips.

[0182] Film width = steel strip width + 2mm, edge folded back 1mm to prevent curling;

[0183] There is no adhesive between the film and the steel strip, allowing relative sliding between the layers.

[0184] Mechanism of action:

[0185] At room temperature: Reduces fretting wear between steel strips and reduces the "rustling" sound of the armor;

[0186] Fire at 650℃: Thermal expansion coefficient of steel strip is 17×10⁻ 6 At / ℃, the inner and outer layers generate reverse circumferential stress due to opposite directions. The sliding membrane converts in-plane shear into interlayer slip (slippage amount 0.5–1.2 mm), avoiding bulging, warping, or breakage.

[0187] III. Process Implementation Flow

[0188] Steel strip unwinding → tension closed-loop control (tension 80–120N)

[0189] Inner right-hand wrapping:

[0190] Wrap around the corner 55°±2°;

[0191] Online laser width measurement with closed-loop correction;

[0192] Insert PTFE sliding membrane:

[0193] The film unwinding tension is 20N, allowing for bonding without adhesive sticking.

[0194] Outer layer left-side wrapping:

[0195] Wrap around the corner 60°±2°;

[0196] The overlap and inner layer are staggered by ≥3mm to form a cross-locking mechanism;

[0197] Heat setting: 120 ℃ / 2 min to eliminate wrapping stress;

[0198] Online testing:

[0199] Overlap rate ±1% (laser scanning);

[0200] The height of the bulge measured by ultrasonic measurement is ≤0.1mm.

[0201] In some specific embodiments, the copper strip shielding layer 6 is made of copper strip with a thickness of 0.1mm–0.15mm and a wrapping overlap rate of ≥15%. It is formed by welding to create a continuous grounding loop to reduce the temperature rise caused by short-circuit current.

[0202] I. Overall Design Objectives of Copper Strip Shielding Layer 6

[0203] In 6–35kV medium-voltage cables, it is necessary to meet the short-circuit capacity requirements of GB / T12706 while minimizing the additional temperature rise caused by short-circuit current. This embodiment achieves this through an "ultra-thin copper strip + continuous welding" solution.

[0204] When the short-circuit current Ik = 25kA / 1s, the conductor temperature rise is ≤120K;

[0205] Under normal operating conditions, the copper strip's self-loss is ≤0.3W / m;

[0206] The total grounding resistance is ≤20mΩ to ensure rapid discharge of fault current.

[0207] II. Wrapping and Overlapping Techniques

[0208] Wrapping method: concentric wrapping, pitch = armor outer diameter × 10–12;

[0209] Overlap rate: ≥15% (actual 16%–18%), overlap length 4.0–4.5mm;

[0210] Tension control: Closed-loop servo tension 40–60N to prevent the copper strip from stretching and thinning;

[0211] Online inspection: The laser width measuring instrument monitors the overlap width in real time, and automatically corrects deviations of ±0.5mm.

[0212] III. Continuous Welding Process (forming "seamless copper tubes")

[0213] Pre-welding treatment:

[0214] Mechanical scraping is performed within 0.5mm of the copper strip edge to remove the oxide layer;

[0215] Nitrogen protection, oxygen content ≤50ppm.

[0216] Welding method:

[0217] Laser lap welding (power 300W, spot diameter 0.2mm, speed 15m / min).

[0218] The weld width is 0.3 mm, the penetration depth is 0.08 mm (≈67% of the thickness), and the tensile strength is ≥200 N / mm².

[0219] Post-weld shaping:

[0220] Argon gas cooling, weld temperature ≤80℃;

[0221] The weld seam is flattened by two sets of rolling rollers, with a height difference of ≤0.02mm, to ensure a round outer diameter.

[0222] IV. Continuous grounding loop

[0223] Electrical continuity: weld resistance ≤ 5 μΩ / m, total length resistance ≤ 20 mΩ (1 km cable);

[0224] Grounding terminal:

[0225] Strip 50mm of copper tape from both ends of the cable, fold it 180°, and then crimp it with copper lug terminals;

[0226] The terminal is tightened with an M8 bolt to the grounding busbar, and the contact resistance is ≤1mΩ;

[0227] Grounding method: Both ends are directly grounded, which can meet the requirement of not melting when the single-phase short circuit current is 25kA / 1s.

[0228] V. Short-circuit temperature rise calculation and verification

[0229] Calculation model: IEC 60949 adiabatic formula Δθ = (I²ρt) / (k²S²)

[0230] Where I= 25 kA, ρ= 1.72×10⁻ 8Ω·m, t = 1s, k = 226 A·√s / mm², S = 3.0 mm² (cross-sectional area of ​​copper strip).

[0231] Result: Δθ=108K (copper strip initial temperature 90 ℃, maximum 198 ℃), which is lower than the copper strip softening temperature of 250 ℃.

[0232] Actual measurement: After a short-circuit current of 25kA / 1s, the highest temperature on the copper strip surface was 192℃, which deviated from the calculated value by 4%, verifying the accuracy of the model.

[0233] VI. Additional Functions

[0234] Electromagnetic shielding: Continuous copper tube shielding coefficient ≥80dB (30MHz–1GHz), reducing external electromagnetic interference;

[0235] Radial water resistance: The weld is free of pores and shows no leakage after passing a longitudinal water permeability test at 1MPa / 1h;

[0236] Bending performance: The minimum bending radius of the cable is 12D (D is the outer diameter of the cable), and there are no cracks in the weld.

[0237] VII. Process Compatibility

[0238] The existing unit (steel strip armor + outer sheath extrusion) only needs to add a copper strip unwinding frame, a laser welding machine and a weld flattening device, without the need for a complete line modification.

[0239] By using "0.10–0.15mm ultra-thin copper strip + ≥15% overlap + laser continuous welding", this embodiment ensures rapid discharge of short-circuit current while controlling the copper strip's own loss, weight, and cost within the optimal range, and significantly reduces fault temperature rise, achieving highly reliable and long-life operation.

[0240] In some specific embodiments, the buffer wrapping layer 5 is located between the outer semiconductive layer 7 and the copper strip shielding layer 6, and is composed of low-smoke halogen-free flame-retardant fiberglass tape with an overlap rate of 20%–25%, used to absorb thermal expansion and provide buffer insulation in case of fire.

[0241] The buffer layer 5, located between the outer semiconductive layer 7 and the copper strip shielding layer 6, plays a crucial role in connecting the two layers. It is continuously wrapped with low-smoke, halogen-free flame-retardant fiberglass tape. The fiberglass tape is woven from alkali-free E-glass yarn, and its surface is treated with a silane coupling agent to ensure adhesion to adjacent layers and prevent fiber fuzzing. The fiberglass tape has a nominal thickness of 0.18 mm, a unit area mass of approximately 200 g / m², a tensile strength ≥800 N / 50 mm, and an elongation at break ≤3%. Under flame conditions, it does not drip or burn, producing only a very small amount of white smoke, meeting the GB / T 19666 Class A flame-retardant requirements.

[0242] The wrapping method is a concentric spiral winding, with the pitch controlled between 6 and 8 times the outer diameter of the cable layer, and the overlap rate maintained at 20%–25%, equivalent to an overlap of 4.5–5.5 mm per turn. This overlap range was determined through thermo-mechanical coupling calculations: it can absorb the circumferential elongation (approximately 0.25%) caused by thermal expansion of the insulation layer and outer semiconducting layer during long-term operation at 90°C, and also provide additional thermal insulation buffer under fire conditions at 650°C, reducing the surface temperature rise of the copper tape shielding layer by approximately 30K.

[0243] The wrapping tension is controlled in a closed loop by a servo tension arm, with a set value of 40–50N. This ensures that the tape layers fit tightly and avoids excessive compression that could deform the insulation layer. After wrapping, the surface of the fiberglass tape is preheated to 80°C, causing the micro-gaps between the tapes to fuse together and form a "semi-cured" whole. This prevents displacement and wrinkling during subsequent copper tape wrapping and sheath extrusion processes.

[0244] During a fire, the silicate fibers in the fiberglass tape begin to soften at 650 °C, forming a dense silica glass film on the surface. This film not only prevents flame penetration but also reflects heat back to the outside, reducing the temperature rise rate of the internal insulation layer by approximately 40%. Simultaneously, the porous structure of the fiberglass tape absorbs and stores some heat before softening, delaying the peak temperature rise by about 2–3 minutes, buying valuable time for evacuation and firefighting. Because the material itself is halogen-free and produces low smoke, the amount of halogen acid gas released during combustion is <5 mg / g, meeting the environmental protection and personnel safety requirements of enclosed spaces such as tunnels and subways.

[0245] In some specific embodiments, a distributed optical fiber is embedded between the buffer wrapping layer 5 and the copper strip shielding layer 6 for real-time monitoring of conductor temperature, with a temperature measurement accuracy of ±1℃ and a spatial resolution of ≤0.5m.

[0246] This distributed optical fiber is embedded in a spiral pattern between the buffer wrapping layer and the copper tape shielding layer. The spiral pitch is controlled at 8 to 10 times the outer diameter of the cable core, ensuring that the fiber does not suffer additional attenuation due to excessive bending while covering the entire length of the conductor. The optical fiber uses a low-bending-loss single-mode G.652.D core rod, wrapped with a 900μm flame-retardant tight sleeve, and then encased in a 2mm stainless steel microtube. The inner wall of the microtube is filled with thixotropic thermally conductive silicone grease, which is both waterproof and improves the thermal response speed.

[0247] During fiber optic cable installation, a 0.2% pre-stretch is maintained to prevent additional stress caused by thermal shrinkage during operation. A 3m slack is reserved at each end of the cable, and the fiber optic outlet is connected to the DTS (Distributed Temperature Demodulator) through the steel tape armor. The DTS employs Raman scattering dual-channel technology with a pulse width of 10ns, corresponding to a spatial resolution ≤0.5m; its temperature measurement accuracy reaches ±1℃ within a 25km range.

[0248] A 0.1mm thermally conductive graphite pad is placed between the optical fiber and the copper strip shielding layer. The graphite pad serves as both electromagnetic shielding buffer and rapid heat transfer, ensuring that the temperature sensed by the optical fiber is less than 2 seconds behind the actual temperature of the conductor. The stainless steel microtube outside the optical fiber is electrically isolated from the copper strip to prevent short-circuit current erosion.

[0249] During cable operation, the DTS collects the temperature distribution curve once per second, and the data is uploaded to the monitoring platform via the edge computing gateway. When the temperature of any 0.5m micro-area exceeds the set threshold (e.g., 105 ℃) or the temperature rise rate exceeds 2 ℃ / min, the platform automatically alarms and provides the precise meter mark of the fault point, with an error not exceeding ±0.5m.

[0250] In the fire test, the cable was subjected to a flame at 650 ℃ for 30 minutes, and the optical fiber remained intact without any breaks. The temperature measurement curve showed an error of less than 1.5 ℃ compared with the thermocouple on the armored surface, verifying the reliability of the system under extreme conditions.

[0251] In some specific embodiments, the inner sheath 3 is located between the copper strip shielding layer 6 and the steel strip armor 2, and is formed by extrusion of thermoplastic halogen-free flame-retardant polyolefin with an oxygen index ≥38; the outer sheath 1 is located outside the steel strip armor 2, and is formed by extrusion of irradiated cross-linked halogen-free flame-retardant polyolefin with an oxygen index ≥42 and a combustion smoke density Ds(4min) ≤150.

[0252] The inner sheath 3, located between the copper strip shielding layer 6 and the steel strip armor 2, is directly extruded from thermoplastic halogen-free flame-retardant polyolefin, with a thickness of 2.0mm–3.0mm. The resin matrix is ​​primarily composed of ethylene-vinyl acetate copolymer and linear low-density polyethylene, with the addition of aluminum hydroxide, magnesium hydroxide, and a phosphorus-nitrogen intumescent flame-retardant synergistic system to maintain an oxygen index above 38. The extrusion temperature is controlled at 170℃–185℃, and the melt flow rate is maintained at approximately 1.5 g / 10min, ensuring that the melt fully covers the copper strip weld while avoiding annealing and softening of the copper strip at high temperatures. The surface of the inner sheath undergoes an online spark test to ensure it is free of pinholes, providing radial water resistance, chemical protection, and secondary insulation.

[0253] The outer sheath 1, made of irradiated cross-linked halogen-free flame-retardant polyolefin, is 2.5mm–4.0mm thick. The formulation incorporates boron-zinc composite flame retardant, nano-montmorillonite, and anti-dripping agents into the EVA / LLDPE matrix. It undergoes cross-linking via electron accelerator irradiation at a dose of 150kGy, forming a three-dimensional network structure and improving heat resistance to 125℃. The measured oxygen index is ≥42, achieving UL 94V-0 rating during vertical burning. During combustion, the material surface rapidly expands into a dense char layer, inhibiting the inward diffusion of heat and oxygen. The closed micropores within the char layer effectively reduce smoke particle formation, resulting in a smoke density Ds(4 min) ≤150 and a light transmittance maintained above 60%, meeting the stringent requirements for low-smoke halogen-free materials in enclosed spaces such as tunnels and subways. The outer sheath surface is further enhanced with UV-531 and HALS light stabilizers, providing resistance to outdoor UV aging for over 20 years. Both sheaths are free of halogens, red phosphorus, and heavy metals, and the combustion products do not contain corrosive hydrogen halide gas. They comply with GB / T 19666-2019 Class A flame retardant and the EU RoHS directive.

[0254] In some specific embodiments, the trapezoidal copper monofilament of conductor 10 has an annealing elongation of ≥35% and a fill factor of ≥99%, which reduces the outer diameter of the conductor by 6%–10% compared to a circular conductor of the same cross-section, thereby reducing the insulation thickness and lowering the normal operating loss by 5%–8%.

[0255] Conductor 10 uses annealed TU2 grade trapezoidal copper monofilament. The monofilament has an isosceles trapezoidal cross-section with a vertex angle of approximately 88° and a slight inclination of 6°–8° on the waist sides. During stranding, the trapezoidal sides fit together, with interlayer gaps approaching zero, achieving a fill factor of over 99%, which is about 12 percentage points higher than traditional round monofilament stranded conductors. Due to the extremely high cross-sectional utilization, the conductor outer diameter is reduced by 6%–10% for the same cross-sectional area, directly resulting in three benefits:

[0256] Reduced insulation layer usage: With the reduced outer diameter, the thickness of the XLPE insulation layer can be reduced by 0.3mm–0.5mm, which saves material and reduces thermal resistance.

[0257] Shortened heat dissipation path: The heat diffusion distance from the conductor to the shielding layer is shortened, and the conductor's operating temperature is reduced by about 5K.

[0258] Reduced resistance loss: After annealing at 580 ℃ for 3 hours, the trapezoidal monofilament has an elongation of ≥35%, resulting in sufficient grain growth and a 3%–4% decrease in resistance per unit length. Combined with the reduction in outer diameter and resistance, the loss during normal operation is reduced by 5%–8%. The annealing process uses nitrogen protection to avoid surface oxidation, maintain the bright copper color, and ensure a tighter bond with the inner semiconductive layer during subsequent co-extrusion, eliminating interface gaps and further reducing the risk of partial discharge.

[0259] The working principle of this utility model can be summarized by four synergistic mechanisms: "low thermal resistance under normal conditions, high heat insulation in fire, self-supporting capacity over 100 meters, and online measurement throughout the entire process." The specific process is as follows:

[0260] Normal operation phase

[0261] Trapezoidal annealed copper monofilaments are tightly stranded with a fill factor ≥99%, reducing the conductor's outer diameter by 6%–10%, resulting in a simultaneous decrease in resistance and thermal resistance. The inner and outer semiconductive layers, together with XLPE insulation, form a low-loss electric field control system. The fan-shaped ceramizable polyolefin foam strip has a thermal conductivity ≤0.18W / (m·K), acting as a "low-temperature heat dissipation pad." Combined with a 0.3–1 mm thermal expansion gap, this reduces the conductor's operating temperature by 5K, resulting in an overall loss reduction of 5%–8%.

[0262] Fire Triggering Stage

[0263] When the external temperature rises to approximately 450 °C, the foaming strip begins to soften and transform into the ceramic phase; above 650 °C, silicate glass powder and mica powder melt, forming a continuous honeycomb ceramic shell within 15 minutes. The thermal conductivity drops sharply to 0.05 W / (m·K), and the overall thermal resistance of the cable increases by 5 times instantly, preventing flames and heat from penetrating inward. The temperature rise of the insulation layer is limited to the allowable range, enabling continuous power supply for 90 minutes.

[0264] Load bearing stage

[0265] The built-in fine-diameter steel wire rope is arranged along the central axis of the fan-shaped foam strip and is connected in parallel with the double-layer reverse stainless steel strip armor to bear the force. The inner steel strip runs to the right and the outer steel strip runs to the left, with an overlap rate of ≥15%. The PTFE sliding membrane between the layers allows for thermal expansion and slippage. Both share the cable's self-weight and external tension, with a safety factor of ≥5 under a 100m vertical drop, eliminating the need for additional slings.

[0266] Real-time monitoring phase

[0267] Distributed optical fibers are embedded between the buffered cladding layer and the copper strip shielding layer. Utilizing the Raman scattering principle, continuous scanning is performed with a 10ns pulse width and a spatial resolution of ≤0.5m. The system updates the temperature profile once per second. When the temperature rise rate of any 0.5m micro-area is ≥2℃ / min or the absolute temperature is ≥105℃, the platform immediately issues a location alarm with an error of <1m, enabling preventative maintenance.

[0268] Through the above four-stage coordination, the cable automatically switches between states in scenarios of "low-loss operation - high heat insulation in fire - high drop self-support - full-process intelligent measurement", ensuring power supply safety, energy efficiency and convenient operation and maintenance.

[0269] By adopting the above-disclosed technical solution of this utility model, the following beneficial effects are obtained:

[0270] "Sudden change in thermal resistance" during fire conditions - low thermal resistance under normal conditions, high thermal resistance upon contact with fire

[0271] The fan-shaped ceramizable polyolefin foam strip has a thermal conductivity of ≤0.18W / (m·K) at room temperature, without increasing operating losses; it becomes ceramizable within 3 minutes at 650 ℃, and the honeycomb structure instantly increases the overall thermal resistance by more than 5 times, achieving 90 minutes of fire-resistant power supply, meeting the uninterrupted requirements of fire protection circuits in tunnels, shafts and high-rise buildings.

[0272] 100-meter vertical "self-supporting" structure - no slings required

[0273] The built-in fine-diameter steel wire rope and double-layer reverse stainless steel strip armor are connected in parallel to form a dual tensile resistance system. The safety factor is ≥5 under a 100m vertical drop, and it can be directly laid on site, eliminating the need for steel wire rope, hooks and maintenance, reducing construction work by 30% and costs by 15%.

[0274] Conductor energy saving "double reduction" - small outer diameter and low resistance

[0275] The trapezoidal annealed copper monofilament fill factor is ≥99%, which reduces the outer diameter of the conductor of the same cross-section by 6%–10% and the resistance by 3%–4%; the insulation layer thickness is reduced simultaneously, and the thermal resistance is reduced by another 5%–8%, resulting in a comprehensive reduction of normal operating losses by 5%–8% and significant energy savings over the life cycle.

[0276] Online "millimeter-level" temperature measurement - distributed optical fiber

[0277] Distributed optical fibers are embedded between the buffer layer and the copper strip, achieving a temperature measurement accuracy of ±1℃, a spatial resolution of ≤0.5 m, and a fault location error of <1m, enabling preventive maintenance and reducing power outage maintenance time by more than 50%.

[0278] End-to-end "Halogen-free and Low-Smoke" - Green and Safe

[0279] The oxygen index of the inner and outer sheaths is ≥38 and ≥42 respectively, the smoke density of combustion Ds (4 min) is ≤150, the halogen acid gas release is ≤5 mg / g, the light transmittance is high in fire, and the escape visibility distance is long; at the same time, it meets the RoHS and REACH environmental directives.

[0280] "Compact and lightweight" structure - convenient for transportation and installation

[0281] With a smaller outer diameter and a weight reduction of approximately 7%, the tray capacity is increased by 10%, and transportation and labor costs for installation decrease simultaneously.

[0282] The process is highly compatible – no equipment modification is required.

[0283] All key processes (trapezoidal monofilament stranding, fan-shaped foam co-extrusion, double-layer reverse armoring, and laser welding of copper strips) can be completed on existing medium-voltage cable production lines, with an investment payback period of less than 6 months.

[0284] In summary, this utility model simultaneously solves four major pain points: low loss, high fire resistance, high drop self-support, and online monitoring, forming an integrated medium-voltage cable solution that is energy-saving, safe, environmentally friendly, and easy to construct.

[0285] The above are merely preferred embodiments of this utility model. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the protection scope of this utility model.

Claims

1. A cable foam filler strip, characterized in that: It includes at least one conductive core; and on the outside of the conductive core, an inner semiconductive layer (9), an insulating layer (8), an outer semiconductive layer (7), a buffer wrapping layer (5), a copper strip shielding layer (6), an inner sheath (3), a steel strip armor (2) and an outer sheath (1) are arranged coaxially in sequence. A fan-shaped foam filling strip (4) is provided between adjacent conductive cores. The cross-section of the fan-shaped foam filling strip (4) is an isosceles fan shape with a fan angle α = 64.747°. The width of the fan-shaped foam filling strip (4) is 30mm-45mm and the height is 13mm-20mm. The outer arc of the fan-shaped foam filling strip (4) is in contact with the inner surface of the buffer wrapping layer (5), and the inner arc is in contact with the outer surface of the conductive core at three points. A load-bearing element is embedded longitudinally along the central axis inside the strip and together with the steel strip armor (2) forms a mechanical reinforcement system.

2. The cable foam filler strip according to claim 1, characterized in that: The center of the fan-shaped foam filler strip (4) is made of polyurethane foam material, which is used for flame retardancy; The outer skin of the fan-shaped foam filler strip is an embossed PE film, a fire-resistant film, a ceramicized film, or a semi-conductive film. The integrated density of the fan-shaped foamed filling strip is 0.08-0.15 g / m 3 .

3. The cable foam filler strip according to claim 2, characterized in that: The fan-shaped foam filler strip (4) is a fan-shaped ceramicizable polyolefin foam strip, which is embedded between the adjacent conductive core and the buffer wrapping layer (5).

4. The cable foam filler strip according to claim 3, characterized in that: The load-bearing element is one or more thin-diameter steel wire ropes, aramid fiber bundles, or glass fiber bundles, which are embedded longitudinally along the cable at the central axis of the fan-shaped foam strip; the load-bearing element and the steel strip armor (2) share the tensile force.

5. The cable foam filler strip according to claim 4, characterized in that: The steel strip armor (2) is located between the inner sheath (3) and the outer sheath (1), and adopts a double-layer reverse wrapping stainless steel strip, with the inner layer facing right and the outer layer facing left. A sliding isolation membrane is provided between the layers to prevent thermal expansion and bulging during a fire.

6. The cable foam filler strip according to claim 5, characterized in that: The copper strip shielding layer (6) is a copper strip with a thickness of 0.1mm–0.15mm, and is formed by welding to create a continuous grounding loop in order to reduce the temperature rise caused by short circuit current.

7. The cable foam filler strip according to claim 6, characterized in that: The buffer wrapping layer (5) is located between the outer semiconductive layer (7) and the copper strip shielding layer (6), and is made of low-smoke halogen-free flame-retardant fiberglass tape. It is used to absorb thermal expansion and provide buffer insulation during fire.

8. The cable foam filler strip according to claim 7, characterized in that: Distributed optical fibers are embedded between the buffer tape layer (5) and the copper tape shield layer (6) for real-time monitoring of conductor temperature.

9. The cable foam filler strip according to claim 8, characterized in that: The inner sheath (3) is located between the copper strip shielding layer (6) and the steel strip armor (2) and is formed by extrusion of thermoplastic halogen-free flame-retardant polyolefin; the outer sheath (1) is located outside the steel strip armor (2) and is formed by extrusion of irradiated crosslinked halogen-free flame-retardant polyolefin.

10. The cable foam filler strip according to claim 9, characterized in that: The conductive core includes an annealed copper conductor (10) with a trapezoidal cross section and an inner semiconductive layer (9), an insulating layer (8), and an outer semiconductive layer (7) that are tightly wrapped around it in sequence. The inner semiconductive layer (9) is bonded to the conductor (10) without gaps, and a thermal expansion gap of 0.3mm–1mm is formed between the outer semiconductive layer (7) and the buffer wrapping layer (5) to reduce the normal thermal resistance.

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