Insulation enhanced superconducting cable and preparation method thereof

Abstract

The invention belongs to the technical field of superconducting, and relates to an insulation enhanced superconducting cable and a preparation method thereof. The method comprises the following steps: firstly, reinforcing a superconducting wire rod through a NiCoCr / Cu composite matrix, and carrying out multi-channel coating and on-line monitoring by adopting BN modified polyimide paint to form a uniform insulating layer; and then wrapping and hot pressing are carried out by using a B-stage epoxy-impregnated aromatic polyamide tape to construct an insulation enhanced structure. Stranded cable forming is carried out through tension control and a numerical control positioning die, and the composite cable is formed by combining the core wire and the multiple layers of insulation reinforced wires. Finally, through secondary wrapping and pretension braiding protection, the superconducting cable with the coverage area larger than or equal to 99.9% and the void ratio smaller than 1% is obtained, the withstand voltage between strands is larger than 5000V, the withstand voltage between cables is larger than 7000V, the mechanical stability and the thermal management performance are remarkably improved, and the superconducting cable is suitable for being applied to high-field magnets and fast pulses.

Description

Technical Field

[0001] This invention belongs to the field of superconducting technology and relates to an insulation-enhanced superconducting cable and its preparation method. Background Technology

[0002] Superconducting magnets can generate high-intensity, highly stable magnetic fields, and have become key components in major scientific facilities such as nuclear magnetic resonance imaging, particle accelerators, and nuclear fusion experiments, as well as high-end medical equipment. Low-temperature superconducting materials, such as NbTi and Nb3Sn, possess stable superconducting properties, excellent electromagnetic properties, and mature engineering processing capabilities in low-temperature environments, making them core materials for constructing large-scale strong magnetic field systems.

[0003] The performance of superconducting cables directly affects the field strength, safety, and cost of the magnets. Fast pulse magnets, as crucial components, are widely used in high-energy physics research, controlled nuclear fusion devices, pulsed power systems, and advanced medical equipment. Their operating characteristic is the ability to carry rapidly increasing currents within an extremely short time to generate a transiently strong magnetic field. This leads to high-voltage transient electric fields between winding turns, layers, and ground, which can easily trigger partial discharge breakdown. This poses a significant challenge to the development of high-insulation superconducting cables.

[0004] Taking a typical "1+6" type primary cable as an example, its structure consists of one central strand surrounded by six outer strands. Current superconducting cable manufacturing technologies still face the following technical bottlenecks when applied to higher-performance magnets: insufficient and unstable insulation between strands, mainly due to the limited insulation performance of the wire itself and the susceptibility of the insulation layer to damage during stranding; insufficient and inconsistent insulation to ground, primarily caused by uneven insulation layers and internal air gaps; limited current-carrying capacity, as the oxygen-free copper matrix is ​​relatively soft, making the wire susceptible to damage down to the core wire level during stranding, leading to core breakage; furthermore, low yield, as these quality issues often result in scrapped insulated cables and magnet failure, leading to excessively high manufacturing costs and hindering the large-scale production of high-strand insulated superconducting cables.

[0005] Therefore, there is an urgent need in this field to develop a new method for manufacturing superconducting cables that can effectively improve insulation performance and stability while maintaining a high critical current density, and optimize the manufacturing process to meet the higher reliability requirements of future high-end magnet devices for superconducting cables. Summary of the Invention

[0006] To address the problems and deficiencies in the existing technology, the present invention provides an insulation-enhanced superconducting cable and its preparation method.

[0007] In a first aspect, the present invention provides a method for preparing an insulation-reinforced superconducting cable, comprising: loading an NbTi alloy rod into a NiCoCr / Cu composite tube, and then vacuum-sealing, hot-extruded, and drawing it to form a superconducting single-core rod; placing the single-core rod as a component into an oxygen-free copper sheath, and then assembling and drawing it to form a superconducting wire; coating the surface of the superconducting wire with an insulating varnish and then curing it to obtain an insulated superconducting wire; wrapping the insulated superconducting wire with polyaramid fiber tape impregnated with B-stage epoxy resin and then hot-pressing it to obtain an insulation-reinforced superconducting wire; stranding the insulation-reinforced superconducting wire with a core wire to form a composite cable with a concentric n-layer structure centered on the core wire; and then wrapping the insulated superconducting wire with polyaramid fiber tape impregnated with B-stage epoxy resin and then weaving fibers on the surface of the composite cable to obtain a superconducting cable.

[0008] Where n is a positive integer not greater than 5; For the nth layer (n≥2), the maximum number of insulated and reinforced superconducting wires it contains is (n-1)×6. The total number of the insulated reinforced superconducting wire and the core wire is 1 + 3n × (n - 1).

[0009] Furthermore, in the method for preparing the insulation-enhanced superconducting cable provided by the present invention, the preparation of the insulating varnish includes: treating boron nitride with a silane coupling agent to obtain aminated boron nitride; coating the aminated boron nitride with polydopamine to obtain modified boron nitride; dispersing boron nitride in N-methylpyrrolidone to obtain a boron nitride dispersion; adding the boron nitride dispersion to polyamic acid and stirring under vacuum to obtain the insulating varnish; The solid content of boron nitride in polyamic acid is 1%~5%; The dispersion rate was 5000 rpm, and the time was 1 hour; The vacuum stirring time is 2-4 hours.

[0010] Furthermore, in the method for preparing the insulation-enhanced superconducting cable provided by the present invention, the NiCoCr / Cu composite tube is composed of a NiCoCr alloy layer and an oxygen-free copper layer, and the thickness of the NiCoCr alloy layer and the oxygen-free copper layer is the same. The hot extrusion temperature is 600~800℃, and the extrusion ratio is 5:1~15:1.

[0011] Furthermore, in the preparation method of the insulation-enhanced superconducting cable provided by the present invention, the curing includes: staying at 100~150℃ for 2~4 hours and staying at 300~400℃ for 1~5 hours.

[0012] Furthermore, in the method for preparing the insulation-enhanced superconducting cable provided by the present invention, the wrapping method is a semi-overlapping wrapping with an angle of 30°~60° and a tension of 5~20N.

[0013] Furthermore, in the method for preparing the insulation-enhanced superconducting cable provided by the present invention, the hot pressing speed is 0.5~2m / min, the temperature is 160℃~200℃, and the dwell time is 30~120s; The contact pressure between the polyaramid fiber tape impregnated with Class B epoxy resin and the surface of the insulated superconducting wire is 0.5~2MPa.

[0014] Furthermore, in the method for preparing the insulation-reinforced superconducting cable provided by the present invention, the core wire is a copper core wire or an insulation-reinforced superconducting wire. The preparation of the copper core wire includes: stretching an oxygen-free copper rod into an oxygen-free copper wire; coating the surface of the oxygen-free copper wire with the insulating varnish described in claim 2, and holding it at 100~150℃ for 2~4 hours and at 300~400℃ for 1~5 hours to obtain the copper core wire; the residual resistivity of the oxygen-free copper rod is >1000.

[0015] Furthermore, in the method for preparing the insulation-enhanced superconducting cable provided by the present invention, the overall porosity of the composite cable is ≤±1%, and the concentricity error is ≤±0.02mm; During the stranding process, the tension of the core wire is 10~25N, and the tension of the insulated reinforced superconducting wire is 5~15N.

[0016] Furthermore, in the method for preparing the insulation-enhanced superconducting cable provided by the present invention, the braiding angle is 45°±1° and the preload is 0.1~0.3N.

[0017] Secondly, the present invention provides an insulation-enhanced superconducting cable, which is prepared by the above-described method for preparing an insulation-enhanced superconducting cable; The superconducting cable has a strand withstand voltage >5000V and a cable-to-cable withstand voltage >7000V.

[0018] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: (1) NiCoCr / Cu composite tube is used to strengthen NbTi alloy rods, which improves the strength of NbTi superconducting wires themselves, reduces the damage to micron-scale NbTi core wires of the multi-core wires during multi-level stranding, thereby reducing the loss of critical current density and preserving the high performance of the wires.

[0019] (2) BN dispersion-modified polyimide varnish is used to improve the thermal conductivity, withstand voltage rating, and mechanical properties of the insulating varnish. The insulating varnish is evenly applied to the surface of the superconducting wire and core material using a multi-coat thin-coat method. After coating, the polyaramid tape impregnated with B-stage epoxy is tightly wrapped around the surface of the insulated superconducting wire and composite cable in a semi-overlapping manner using a wrapping machine, establishing multi-level insulation protection. Through these three processes, the insulation performance of the superconducting wire is significantly improved, and the damage tolerance is greatly increased.

[0020] (3) During the cable stranding process, CNC concentric positioning molds and circumferentially distributed adaptive guide grooves are used to strictly constrain the centering and tension of the composite cable. CCD and matrix eddy current detection systems are used to monitor the surface damage of the insulated superconducting wire and repair the damaged points in a timely manner. Combined with the insulation process of the insulated superconducting wire, the insulation problem between the various insulated superconducting wires in the superconducting cable is completely solved, and the insulation performance between the various insulated superconducting wires in the superconducting cable is significantly improved (>5000V).

[0021] (4) Using fibers, at a preset angle, and by increasing the pre-tightening force, the fibers are tightly woven onto the surface of the composite cable to achieve final protection. This significantly improves the insulation of the superconducting cable to ground, and the insulation withstand voltage is stably greater than 7000V.

[0022] (5) The preparation method provided by the present invention enables the mass production of insulation-enhanced superconducting cables, improves the yield, and significantly reduces costs.

[0023] (6) The significant improvement in the insulation performance of superconducting cables can break through the current carrying density limit of superconducting cables, increase the magnetic field strength, reduce the risk of magnetic field failure, and ensure the long-term stable operation of the magnet.

[0024] (7) The preparation method provided by the present invention can significantly improve the insulation performance of superconducting cables and reduce the insulation thickness of existing superconducting cables, which is more conducive to the lightweight development of magnets and broadens the application boundaries of superconducting magnets. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the "1+6" superconducting cable prepared in Example 1. In this diagram, 1 represents the superconducting wire, 2 represents the enamel layer, 3 represents the braided layer, 4 represents the wrapping layer, and 5 represents the copper core wire.

[0026] Figure 2 This is a schematic diagram of the "1+6+12" superconducting cable prepared in Example 2. In this diagram, 1 represents the superconducting wire, 2 represents the enamel layer, 3 represents the braided layer, and 4 represents the wrapping layer.

[0027] Figure 3 This is a schematic diagram of the "1+6+12+18" superconducting cable prepared in Example 3. In this diagram, 1 represents the superconducting wire, 2 represents the enamel layer, 3 represents the braided layer, and 4 represents the wrapping layer. Detailed Implementation

[0028] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0029] The method for preparing the superconducting cable of the present invention is as follows: S1. Place an NbTi alloy rod as the superconducting core material in a NiCoCr / Cu composite tube (composed of a NiCoCr alloy layer and an oxygen-free copper layer, with the NiCoCr alloy layer and the oxygen-free copper layer having the same thickness, and the atomic ratio of elements such as Ni, Co, and Cr in the NiCoCr alloy layer being maintained). Seal the two ends of the composite tube with oxygen-free copper end caps (vacuum degree <10). -3 The composite rod is formed by hot extrusion (600~800℃, extrusion ratio 5:1~15:1). This hot extrusion achieves a strong metallurgical bond between the NbTi alloy rod and the NiCoCr / Cu composite tube, resulting in a single-core rod. Through multiple drawing passes, the single-core rod is processed into a superconducting single-core rod with a diameter of 1~20mm. Using the superconducting single-core rod as a component, it is placed in an oxygen-free copper sheath and processed a second time to produce composite ingots with several to tens of thousands of cores. These composite ingots are then processed through multiple drawing passes to produce superconducting wires.

[0030] S2. Modified boron nitride nanopowder was added to N-methylpyrrolidone (NMP) at 1%–5% of the solid content of polyamic acid. The mixture was pre-dispersed at 5000 rpm for 1 hour, followed by ball milling to obtain a BN dispersion. The BN dispersion was added to polyamic acid and stirred under vacuum for 2–4 hours to obtain a uniform, bubble-free insulating varnish. The insulating varnish was then applied to the surface of the superconducting wire using a multi-pass coating process, with staged curing to form a uniform varnish layer, thus creating the insulated superconducting wire. Specifically, the wire was first held at a low temperature of 100–150°C for 2–6 hours to allow the NMP solvent to evaporate slowly and uniformly. Subsequently, it was held at a high temperature of 300–400°C for 1–5 hours to completely convert the polyamic acid into polyimide, enhancing the molecular chain rigidity and improving the thermal stability and insulation performance of the varnish layer. The thickness of each varnish layer was controlled at 2 μm. During the coating process, an online eddy current flaw detector and a pinhole monitoring system were used to inspect the near-surface of the insulated superconducting wire and the varnish film for defects, and repairs were made promptly.

[0031] S3. Using polyaramid fiber tape (tape) impregnated with Class B epoxy resin, tightly wrap it around the surface of the insulated superconducting wire at a wrapping angle of 30°~60° and in a semi-overlapping manner, with a wrapping tension of 5N~20N. After wrapping, a hot-pressing process is used to firmly bond the tape to the surface coating of the insulated superconducting wire, forming a uniform and continuous insulating reinforcement layer (wrapping layer) on the surface of the superconducting wire, which is the insulated reinforced superconducting wire. The hot-pressing speed is 0.5~2m / min, the temperature is 160℃~200℃, the residence time is 30~120s, and the contact pressure between the tape and the surface coating of the insulated superconducting wire is 0.5~2MPa. The diameter tolerance between the insulated reinforced superconducting wire and the superconducting wire is within ±0.02mm.

[0032] S4. The insulated and reinforced superconducting wires (strands) and core wires are stranded to form a composite cable. During the stranding process, it is ensured that each insulated and reinforced superconducting wire is symmetrically arranged around the core wire, so that the concentricity error of the composite cable does not exceed ±0.02mm, and the overall porosity fluctuation range is controlled within ±1%. At the same time, the tension of the copper core wire is maintained at 10~25N and the tension of the insulated and reinforced superconducting wires is maintained at 5~15N through a tension control system to ensure structural uniformity. Subsequently, the composite cable is subjected to online inspection and real-time repair. Circumferential synchronous imaging and non-destructive testing methods are used to identify and repair defects such as scratches and pinholes in the surface paint layer, ensuring the integrity of the insulation layer.

[0033] S5. A polyaramid fiber tape (strip) impregnated with B-stage epoxy resin is used to wrap and reinforce the composite cable (wrapping layer), ensuring a tight bond between the tape and the surface of the composite cable to obtain a reinforced composite cable. Subsequently, fibers are used as the braiding material to braid and protect the surface of the reinforced composite cable, forming a braided layer, ultimately yielding a superconducting cable (cable). During the braiding process, the braiding angle is 45°±1°, and a preload of 0.1~0.3N is applied to ensure a tight fit between the fibers and the reinforced composite cable. The braiding adopts an "inward-facing" arrangement, ultimately achieving a braided layer coverage area ratio ≥99.9% and a porosity <1%. This braided layer effectively enhances the overall mechanical stability and thermal management performance of the superconducting cable, not only preventing loosening of the internal wrapping tape during subsequent processing or operation but also significantly reducing the flow resistance of the cooling medium.

[0034] In step S2, the method for preparing modified boron nitride includes: stirring with a silane coupling agent (such as γ-aminopropyltriethoxysilane) at 60-80°C for 10-16 hours, followed by filtration, washing, and drying to obtain aminated boron nitride. The aminated boron nitride is then coated with polydopamine to obtain modified boron nitride.

[0035] In S4, the core wires used include two types: copper core wires and insulated superconducting wires. The copper core wires are made from high-purity oxygen-free copper rods with a residual resistivity ratio (RRR) > 1000, which are drawn into oxygen-free copper wires and then coated with insulating varnish. This coating process is consistent with the preparation method of the insulated superconducting wires in S2. The copper core wires serve as the centerline of the superconducting cable, enhancing its thermal conductivity and acting as a current shunt in the event of superconductivity failure.

[0036] In step S5, the fiber is selected from any one of aramid fiber, ultra-high molecular weight polyethylene fiber, and glass fiber. Specifically, the aramid fiber is Kevlar or Twaron; the ultra-high molecular weight polyethylene fiber is Dyneema or Spectra; and the glass fiber is alumina fiber or basalt continuous fiber.

[0037] The superconducting cable manufacturing method provided by this invention can produce a superconducting cable with n layers. The nth layer (n≥2) has a maximum of (n-1)×6 strands; correspondingly, the total number of strands and core wires in the superconducting cable is 1+3n×(n-1). Theoretically, n can be any positive integer with no upper limit; however, in engineering applications, n is usually limited to ≤5. Too many layers will lead to an exponential increase in AC loss, and the cable's mechanical strength will be too high, making it difficult to bend and affecting practical use. Based on this manufacturing method, a series of superconducting cables with increasing layer numbers, such as "1+6", "1+6+12", "1+6+12+18", and "1+6+12+18+24", can be manufactured. For clarity, the following embodiments will specifically use three representative structures, "1+6", "1+6+12", and "1+6+12+18", as examples.

[0038] Example 1 This embodiment provides a method for preparing a "1+6" superconducting cable.

[0039] The preparation method of the "1+6" superconducting cable described in this embodiment is as follows: S1. A 200mm diameter, 200mm long NbTi alloy rod is placed as the superconducting core material in a NiCoCr / Cu composite tube with an outer diameter of 250mm, an inner diameter of 200mm, and a length of 200mm (the thickness of both the NiCoCr alloy layer and the oxygen-free copper layer is 25mm, the Fe, C, and O content in the NiCoCr alloy layer is <5ppm, and the O content in the oxygen-free copper layer is <5ppm). Oxygen-free copper end caps are used to seal both ends of the composite tube (vacuum degree <10). -3The NbTi alloy rod and the NiCoCr / Cu composite tube are hot-extruded (600℃, extrusion ratio 5:1) to form a composite rod. The composite rod is then hot-extruded to achieve a strong metallurgical bond between the NbTi alloy rod and the NiCoCr / Cu composite tube, resulting in a single-core rod. After multiple drawing processes, the single-core rod is made into a superconducting single-core rod with a diameter of 20mm. Using the superconducting single-core rod as a component, it is placed in an oxygen-free copper sheath and processed a second time to produce composite ingots with several to tens of thousands of cores. These composite ingots are then drawn through multiple drawing processes to produce superconducting wires. A high-purity oxygen-free copper rod with a residual resistivity (RRR-273 / 10K) > 1000 is selected and drawn into an oxygen-free copper wire (2mm in diameter) as the centerline of the superconducting cable.

[0040] S2. Modified boron nitride nanopowder was added to N-methylpyrrolidone (NMP) at 1% of the polyamic acid solid content. The mixture was pre-dispersed at 5000 rpm for 1 hour, followed by ball milling to obtain a BN dispersion. The BN dispersion was added to the polyamic acid and stirred under vacuum for 2 hours to obtain a uniform, bubble-free insulating varnish. The insulating varnish was applied to the surfaces of superconducting wires and oxygen-free copper wires using a multi-pass coating process. A uniform varnish layer was formed through staged curing, resulting in insulated superconducting wires and copper core wires. Specifically, the process involved first holding the varnish at a low temperature of 150°C for 2 hours to allow the NMP solvent to evaporate slowly and uniformly, followed by holding it at a high temperature of 300°C for 1 hour to completely convert the polyamic acid into polyimide, enhancing the molecular chain rigidity and improving the thermal stability and insulation performance of the varnish layer. The thickness of each varnish layer was controlled at 2 μm. During the coating process, an online eddy current flaw detector and a pinhole monitoring system were used to inspect the near-surface and varnish layer of the insulated superconducting wires and copper core wires for defects, and repairs were made promptly.

[0041] S3. Using polyaramid fiber tape (tape) impregnated with Class B epoxy resin, tightly wrap it around the surface of the insulated superconducting wire at a 30° wrapping angle and in a semi-overlapping manner, with a wrapping tension of 5N. After wrapping, a hot-pressing process is used to firmly bond the tape to the surface coating of the insulated superconducting wire, forming a uniform and continuous insulating reinforcement layer (wrapping layer) on the surface of the superconducting wire, which is the insulated reinforced superconducting wire. The hot-pressing speed is 0.5m / min, the temperature is 160℃, the residence time is 120s, and the contact pressure between the tape and the surface coating of the insulated superconducting wire is 0.5MPa. The diameter tolerance between the insulated reinforced superconducting wire and the superconducting wire is within ±0.02mm.

[0042] S4. Using a customized CNC concentric positioning mold, six insulated reinforced superconducting wires (strands) and one copper core wire (strand) are precisely stranded in a single synchronous feed to obtain a composite cable. Figure 1The system employs a customized CNC concentric positioning mold with six adaptive guide grooves evenly distributed circumferentially. This forces each insulated superconducting wire to be symmetrically arranged around the copper core wire, ensuring the concentricity error of the composite cable does not exceed ±0.02mm and the overall porosity fluctuation is controlled within ±1%. During the cable stranding process, a dual-path independent tension feedback system monitors and dynamically adjusts the tension of the copper core wire and the insulated superconducting wire in real time, maintaining a copper core wire tension of 25N and an insulated superconducting wire tension of 15N to ensure structural uniformity. Subsequently, the composite cable undergoes online inspection and immediate repair. Six circumferentially distributed high-speed CCD cameras and flexible eddy current array probes work together to accurately identify and locate scratches and pinhole defects on the paint layer surface. For identified localized damage, the system can trigger an immediate repair mechanism to ensure the integrity of the paint layer meets subsequent application requirements.

[0043] S5. A polyaramid fiber tape (tape) impregnated with B-stage epoxy resin is used to wrap and reinforce the composite cable (wrapping layer), ensuring a tight bond between the tape and the composite cable surface to obtain a reinforced composite cable. Subsequently, aramid fiber (Kevlar) is used as the braiding material, and a CNC braiding machine is used to braid and protect the surface of the reinforced composite cable, forming a braided layer, ultimately obtaining a "1+6" superconducting cable. During the braiding process, the braiding angle is precisely controlled at 45°±1° via an encoder and servo motor linkage system. A preload of 0.3N is applied to the fibers through an elastic guide wheel mechanism, ensuring a tight fit between the fibers and the reinforced composite cable. The braiding spindles adopt an "inward-facing" arrangement, ultimately achieving a braided layer coverage area ratio ≥99.9% and a porosity <1%.

[0044] Example 2 This embodiment provides a method for preparing a "1+6+12" superconducting cable.

[0045] The preparation method of the "1+6+12" superconducting cable described in this embodiment is as follows: S1. A 400mm diameter, 1200mm long NbTi alloy rod is placed as the superconducting core material in a NiCoCr / Cu composite tube with an outer diameter of 480mm, an inner diameter of 400mm, and a length of 1200mm (the thickness of both the NiCoCr alloy layer and the oxygen-free copper layer is 40mm, the Fe, C, and O content in the NiCoCr alloy layer is <5ppm, and the O content in the oxygen-free copper layer is <5ppm). Oxygen-free copper end caps are used to seal both ends of the composite tube (vacuum degree <10). -3The composite rod is formed by hot extrusion (800℃, extrusion ratio 15:1). After hot extrusion, a strong metallurgical bond is achieved between the NbTi alloy rod and the NiCoCr / Cu composite tube, resulting in a single-core rod. Through multiple drawing processes, the single-core rod is made into a superconducting single-core rod with a diameter of 1 mm. Using the superconducting single-core rod as a component, it is placed in an oxygen-free copper sheath and processed a second time to produce composite ingots with several to tens of thousands of cores. The composite ingots are then processed through multiple drawing processes to produce superconducting wires.

[0046] S2. Modified boron nitride (BN) nanopowder was added to N-methylpyrrolidone (NMP) at 5% of the polyamic acid solid content. The mixture was pre-dispersed at 5000 rpm for 1 hour, followed by ball milling to obtain a BN dispersion. The BN dispersion was added to the polyamic acid and stirred under vacuum for 4 hours to obtain a uniform, bubble-free insulating varnish. The insulating varnish was then applied to the surface of the superconducting wire using a multi-pass coating process, with staged curing to form a uniform varnish layer, thus creating the insulated superconducting wire. Specifically, the wire was first held at a low temperature of 100℃ for 3 hours to allow the NMP solvent to evaporate slowly and uniformly. Subsequently, it was held at a high temperature of 400℃ for 3 hours to completely convert the polyamic acid into polyimide, enhancing the molecular chain rigidity and improving the thermal stability and insulation performance of the varnish layer. The thickness of each varnish layer was controlled at 2 μm. During the coating process, an online eddy current flaw detector and a pinhole monitoring system were used to inspect the near-surface of the insulated superconducting wire and the varnish layer for defects, and repairs were made promptly.

[0047] S3. Using polyaramid fiber tape (tape) impregnated with Class B epoxy resin, tightly wrap it around the surface of the insulated superconducting wire at a 30° wrapping angle and in a semi-overlapping manner, with a wrapping tension of 20N. After wrapping, a hot-pressing process is used to firmly bond the tape to the surface coating of the insulated superconducting wire, forming a uniform and continuous insulating reinforcement layer (wrapping layer) on the surface of the superconducting wire, which is the insulated reinforced superconducting wire. The hot-pressing speed is 2m / min, the temperature is 200℃, the residence time is 30s, and the contact pressure between the tape and the surface coating of the insulated superconducting wire is 2MPa. The diameter tolerance between the insulated reinforced superconducting wire and the superconducting wire is within ±0.02mm.

[0048] S4. Using a customized CNC concentric positioning mold, one insulated reinforced superconducting wire (core wire), six insulated reinforced superconducting wires (first layer), and twelve insulated reinforced superconducting wires (second layer) are precisely stranded into a single layer through a single synchronous feed to obtain a composite cable. Figure 2The customized CNC concentric positioning mold features 6 and 12 adaptive guide grooves evenly distributed circumferentially, forcing each insulated superconducting wire to be symmetrically arranged around the core wire, ensuring the concentricity error of the composite cable does not exceed ±0.02mm and the overall porosity fluctuation is controlled within ±1%. During the cable stranding process, a dual-path independent tension feedback system monitors and dynamically adjusts the tension of the core wire and the insulated superconducting wire in real time, maintaining a core wire tension of 10N and an insulated superconducting wire tension of 5N to ensure structural uniformity. Subsequently, the composite cable undergoes online inspection and immediate repair. Six sets of circumferentially distributed high-speed CCD cameras and flexible eddy current array probes work together to accurately identify and locate scratches and pinhole defects on the paint layer surface. For identified local damage, the system can trigger an immediate repair mechanism to ensure the integrity of the paint layer meets subsequent application requirements.

[0049] S5. A polyaramid fiber tape (tape) impregnated with B-stage epoxy resin is used to reinforce the composite cable by wrapping it (wrapping layer), ensuring a tight bond between the tape and the composite cable surface, resulting in a reinforced composite cable. Subsequently, ultra-high molecular weight polyethylene fiber (Dyneema) is used as the braiding material, and a CNC braiding machine is used to braid and protect the surface of the reinforced composite cable, forming a braided layer, ultimately obtaining a "1+6+12" superconducting cable. During the braiding process, the braiding angle is precisely controlled at 45°±1° via an encoder and servo motor linkage system. A preload of 0.1N is applied to the fibers through an elastic guide wheel mechanism, ensuring a tight fit between the fibers and the reinforced composite cable. The braiding spindles adopt an "inward-facing" arrangement, ultimately achieving a braided layer coverage area ratio ≥99.9% and a porosity <1%.

[0050] Example 3 This embodiment provides a method for preparing a "1+6+12+18" superconducting cable.

[0051] The preparation method of the "1+6+12+18" superconducting cable described in this embodiment is as follows: S1. A 300mm diameter, 600mm long NbTi alloy rod is placed as the superconducting core material in a NiCoCr / Cu composite tube with an outer diameter of 450mm, an inner diameter of 300mm, and a length of 600mm (the thickness of both the NiCoCr alloy layer and the oxygen-free copper layer is 75mm, the Fe, C, and O content in the NiCoCr alloy layer is <5ppm, and the O content in the oxygen-free copper layer is <5ppm). Oxygen-free copper end caps are used to seal both ends of the composite tube (vacuum degree <10). -3The NbTi alloy rod and the NiCoCr / Cu composite tube are hot-extruded (700℃, extrusion ratio 8:1) to form a composite rod. The composite rod is then hot-extruded (700℃, extrusion ratio 8:1) to achieve a strong metallurgical bond between the NbTi alloy rod and the NiCoCr / Cu composite tube, resulting in a single-core rod. After multiple drawing processes, the single-core rod is made into a superconducting single-core rod with a diameter of 10mm. Using the superconducting single-core rod as a component, it is placed in an oxygen-free copper sheath and processed a second time to produce composite ingots with several to tens of thousands of cores. These composite ingots are then subjected to multiple drawing processes to produce superconducting wires.

[0052] S2. Modified boron nitride (BN) nanopowder was added to N-methylpyrrolidone (NMP) at 3% of the polyamic acid solid content. The mixture was pre-dispersed at 5000 rpm for 1 hour, followed by ball milling to obtain a BN dispersion. The BN dispersion was added to the polyamic acid and stirred under vacuum for 3 hours to obtain a uniform, bubble-free insulating varnish. The insulating varnish was then applied to the surface of the superconducting wire using a multi-pass coating process, with staged curing to form a uniform varnish layer, thus creating the insulated superconducting wire. Specifically, the wire was first held at a low temperature of 120°C for 4 hours to allow the NMP solvent to evaporate slowly and uniformly. Subsequently, it was held at a high temperature of 350°C for 5 hours to completely convert the polyamic acid into polyimide, enhancing the molecular chain rigidity and improving the thermal stability and insulation performance of the varnish layer. The thickness of each varnish layer was controlled at 2 μm. During the coating process, an online eddy current flaw detector and a pinhole monitoring system were used to inspect the near-surface of the insulated superconducting wire and the varnish layer for defects, and repairs were made promptly.

[0053] S3. Using polyaramid fiber tape (tape) impregnated with Class B epoxy resin, tightly wrap it around the surface of the insulated superconducting wire at a 40° wrapping angle and in a semi-overlapping manner, with a wrapping tension of 10N. After wrapping, a hot-pressing process is used to firmly bond the tape to the surface coating of the insulated superconducting wire, forming a uniform and continuous insulating reinforcement layer (wrapping layer) on the surface of the superconducting wire, which is the insulated reinforced superconducting wire. The hot-pressing speed is 1m / min, the temperature is 180℃, the residence time is 60s, and the contact pressure between the tape and the surface coating of the insulated superconducting wire is 1MPa. The diameter tolerance between the insulated reinforced superconducting wire and the superconducting wire is within ±0.02mm.

[0054] S4. Using a customized CNC concentric positioning mold, one insulated reinforced superconducting wire (core wire), six insulated reinforced superconducting wires (first layer), twelve insulated reinforced superconducting wires (second layer), and eighteen insulated reinforced superconducting wires (third layer) are precisely stranded into a single layer through a single synchronous feed to obtain a composite cable. Figure 3The customized CNC concentric positioning mold features 6, 12, and 18 adaptive guide grooves evenly distributed circumferentially, forcing each insulated superconducting wire to be symmetrically arranged around the core wire. This ensures the concentricity error of the composite cable does not exceed ±0.02mm, and the overall porosity fluctuation is controlled within ±1%. During the cable stranding process, a dual-path independent tension feedback system monitors and dynamically adjusts the tension of the core wire and the insulated superconducting wire in real time, maintaining a core wire tension of 20N and an insulated superconducting wire tension of 10N to ensure structural uniformity. Subsequently, the composite cable undergoes online inspection and immediate repair. Six sets of circumferentially distributed high-speed CCD cameras and flexible eddy current array probes work together to accurately identify and locate scratches and pinhole defects on the paint layer surface. For identified localized damage, the system can trigger an immediate repair mechanism to ensure the integrity of the paint layer meets subsequent application requirements.

[0055] S5. A polyaramid fiber tape (tape) impregnated with B-stage epoxy resin is used to wrap and reinforce the composite cable (wrapping layer), ensuring a tight bond between the tape and the composite cable surface to obtain a reinforced composite cable. Subsequently, basalt continuous fiber is used as the braiding material, and a CNC braiding machine is used to braid and protect the surface of the reinforced composite cable, forming a braided layer, ultimately obtaining a "1+6+12+18" superconducting cable. During the braiding process, the braiding angle is precisely controlled at 45°±1° via an encoder and servo motor linkage system. A preload of 0.2N is applied to the fibers through an elastic guide wheel mechanism, ensuring a tight fit between the fibers and the reinforced composite cable. The braiding spindles adopt an "inward-facing" arrangement, ultimately achieving a braided layer coverage area ratio ≥99.9% and a porosity <1%.

[0056] The superconducting cable prepared by this invention exhibits an insulation performance between strands >5000V and an insulation withstand voltage between cables >7000V, demonstrating a significant improvement in insulation performance. Furthermore, the introduction of NiCoCr enhances the low-temperature (2.5~10K) service performance of the superconducting cable, promoting the future application and development of magnet technology.

[0057] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing an insulation-reinforced superconducting cable, characterized in that, include: A superconducting single-core rod is made by inserting an NbTi alloy rod into a NiCoCr / Cu composite tube, followed by vacuum encapsulation, hot extrusion, and drawing. The single-core rod is then placed into an oxygen-free copper sheath, assembled a second time, and drawn to form a superconducting wire. An insulating varnish is coated onto the surface of the superconducting wire and cured to obtain an insulated superconducting wire. The insulated superconducting wire is then wrapped with polyaramid fiber tape impregnated with B-stage epoxy resin and subjected to hot pressing to obtain an insulation-reinforced superconducting wire. The insulated superconducting wire is twisted with the core wire to form a composite cable with a concentric n-layer structure centered on the core wire; the insulated superconducting wire is wrapped with polyaramid fiber tape impregnated with B-stage epoxy resin, and then the composite cable is woven with fibers to obtain a superconducting cable. Where n is a positive integer not greater than 5; For the nth layer (n≥2), the maximum number of insulated and reinforced superconducting wires it contains is (n-1)×6. The total number of the insulated reinforced superconducting wire and the core wire is 1 + 3n × (n - 1).

2. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The preparation of the insulating varnish includes: treating boron nitride with a silane coupling agent to obtain aminated boron nitride; coating the aminated boron nitride with polydopamine to obtain modified boron nitride; dispersing the modified boron nitride in N-methylpyrrolidone to obtain a boron nitride dispersion; adding the boron nitride dispersion to polyamic acid and stirring under vacuum to obtain the insulating varnish. The solid content of boron nitride in polyamic acid is 1%~5% wt.%; The dispersion rate was 5000 rpm, and the time was 1 hour; The vacuum stirring time is 2-4 hours.

3. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The NiCoCr / Cu composite tube is composed of a NiCoCr alloy layer and an oxygen-free copper layer, and the thickness of the NiCoCr alloy layer and the oxygen-free copper layer is the same. The hot extrusion temperature is 600~800℃, and the extrusion ratio is 5:1~15:

1.

4. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The curing process includes: holding at 100~150℃ for 2~4 hours, and holding at 300~400℃ for 1~5 hours.

5. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The wrapping method is a semi-overlapping wrapping, with an angle of 30°~60° and a tension of 5~20N.

6. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The hot pressing process is performed at a speed of 0.5~2m / min, a temperature of 160℃~200℃, and a dwell time of 30~120s. The contact pressure between the polyaramid fiber tape impregnated with B-stage epoxy resin and the surface of the insulated superconducting wire is 0.5~2MPa.

7. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The core wire is a copper core wire or an insulated reinforced superconducting wire. The preparation of the copper core wire includes: stretching an oxygen-free copper rod into an oxygen-free copper wire; coating the surface of the oxygen-free copper wire with the insulating varnish described in claim 2; holding it at 100~150℃ for 2~4 hours and at 300~400℃ for 1~5 hours to obtain the copper core wire. The residual resistivity of the oxygen-free copper rod is >1000.

8. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The overall porosity of the composite cable is ≤±1%, and the concentricity error is ≤±0.02mm; During the stranding process, the tension of the core wire is 10~25N, and the tension of the insulated reinforced superconducting wire is 5~15N.

9. The method for preparing the insulation-reinforced superconducting cable according to claim 1, characterized in that, The weaving angle is 45°±1°, and the preload is 0.1~0.3N.

10. An insulation-enhanced superconducting cable, characterized in that, The cable is prepared by the method of any one of claims 1 to 9, which is an insulation-enhanced superconducting cable. The superconducting cable has a strand withstand voltage >5000V and a cable-to-cable withstand voltage >7000V.

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