A large cross-section compact sealed conductor for dc submarine cable and a forming method

Abstract

This invention discloses a large-section compact sealed conductor for DC submarine cables and its forming method, comprising a center conductor, a first layer of shaped monofilaments, a second layer of shaped monofilaments, N layers of outer shaped monofilaments, and a composite water-blocking system; N is greater than or equal to 1; the first layer of shaped monofilaments consists of several Z-shaped monofilaments tightly twisted together outside the center conductor, with the angle between the inclined planes of adjacent Z-shaped monofilaments being between 85° and 95°; the twisting pitch of the Z-shaped monofilaments is controlled to be 12 to 16 times the pitch circle diameter of the center conductor; the composite water-blocking system comprises a semi-conductive resistive grease with a viscosity of 8500 to 11500 cP and an expandable water-blocking yarn, wherein the filling amount of the water-blocking yarn in the composite water-blocking system occupies 20 to 30% of the gap volume of the Z-shaped monofilaments; the surface roughness of the Z-shaped monofilaments is Ra = 1.0 to 2.0 μm.

Description

Technical Field

[0001] This invention belongs to the field of high voltage DC submarine cable manufacturing technology, specifically relating to a large cross-section compact sealed conductor for DC submarine cables and its forming method. Background Technology

[0002] Current technologies typically treat water-blocking functionality as a separate, added component. Whether it's the water-blocking tape wrapped around the conductor or the water-blocking powder or adhesive filling the interlayer, it's physically separate from the main conductor structure (irregularly shaped single wires). It's difficult to ensure that the water-blocking material completely fills every microscopic gap, especially at complex junctions where irregularly shaped single wires interlock and in the central region of the conductor, where unfilled microchannels are easily present. Under the mechanical and thermal stresses of cable bending, vibration, and temperature changes, the external water-blocking tape may shift, and the internal water-blocking powder or adhesive may become unevenly distributed due to long-term aging or the "mouse hole effect," resulting in differences in water-blocking performance at different locations within the cable and a decline over time.

[0003] To improve conductor cross-sectional utilization and water-blocking performance, existing technologies have developed stranded wire structures based on trapezoidal or "Z-shaped" single wires. Regarding water-blocking solutions, the mainstream technology currently involves filling the gaps between conductor layers with water-blocking adhesive, or using a composite water-blocking technology combining modified water-blocking silicone rubber and semi-conductive water-blocking binding tape to achieve a certain depth of water-blocking capability, such as adapting to water depths of 200 meters. Another related technology is a layer-by-layer compacted conductor structure. By precisely controlling the conductor stranding pitch and pressure parameters, and embedding water-absorbing and expanding water-blocking materials between layers, the compaction coefficient of the conductor can be increased, resulting in a significant improvement in longitudinal water-blocking performance.

[0004] Currently, the internal gaps of compact conductors are extremely small, making it difficult for traditional water-blocking materials to completely penetrate, resulting in "dry zones." Traditional water-blocking materials (such as water-blocking powder and some water-blocking adhesives) mainly rely on swelling upon contact with water to form a physical barrier—a "passive response" mechanism. This means they only become effective when moisture has already penetrated the material's location. Their water-blocking mechanism is relatively simple. This passive protection mode is ill-suited to rapid or continuous moisture penetration, especially under harsh environments such as high pressure and high humidity. If the expansion rate lags behind the water ingress rate, water-blocking failure may occur. Furthermore, some water-blocking powder dissolves and is lost upon contact with water, and water-blocking adhesives, after swelling, lack sufficient structural strength and are easily ruptured by water pressure, further reducing long-term reliability. Therefore, traditional water-blocking methods have significant shortcomings in response time, duration of action, and structural stability, making it difficult to meet the full life-cycle sealing performance requirements of high-end cables. Summary of the Invention

[0005] This invention provides a large-section compact sealed conductor for DC submarine cables and a forming method thereof, which at least solves the technical problem that the high water resistance sealing performance, high structural stability and ultra-high voltage electrical performance of cable conductors in existing deep-sea and high-capacity flexible DC transmission systems cannot be designed in a coordinated manner.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a large-section compact sealed conductor cable for DC submarine cables, comprising a center conductor, a first layer of shaped monofilaments, a second layer of shaped monofilaments, N layers of outer shaped monofilaments, and a composite water-blocking system; where N is greater than or equal to 1; The first layer of irregular monofilament consists of several Z-shaped irregular monofilaments tightly twisted together outside the central conductor, with the angle between the inclined planes of adjacent Z-shaped irregular monofilaments being between 85° and 95°; The twisting pitch of the Z-shaped profiled single wire is controlled to be 12 to 16 times the pitch circle diameter of the central conductor. The composite water-blocking system includes a semi-conductive resistive grease with a viscosity of 8500 to 11500 cP and an expandable water-blocking yarn. The filling amount of the water-blocking yarn in the composite water-blocking system occupies 20 to 30% of the gap volume of the Z-shaped profiled single wire. The surface roughness of the Z-shaped irregular single-line surface is Ra = 1.0~2.0μm; The second layer of shaped monofilament consists of several S-shaped monofilaments twisted together outside the first layer of shaped monofilaments. The radius of curvature of the inner arc surface of the S-shaped monofilament matches the outer contour of the inner Z-shaped monofilament. The included angle of the inclined plane of the S-shaped monofilament is between 85° and 95°.

[0007] Preferably, the center conductor is a copper rod with a diameter of 7 to 9 mm.

[0008] Preferably, the N outer irregular monofilaments are a third irregular monofilament, a fourth irregular monofilament, a fifth irregular monofilament, and a sixth irregular monofilament.

[0009] Preferably, the twisting tension gradient of the third layer of shaped monofilaments to the sixth layer of shaped monofilaments increases by 5% to 10% layer by layer, controlling the overall equivalent filling coefficient to be above 0.95.

[0010] Preferably, the composite water-blocking system comprises a semi-conductive resistive grease and an expandable water-blocking yarn. The semi-conductive resistive grease comprises a butyl rubber matrix, carbon black, organobentonite, a silane coupling agent, and an organic solvent. The butyl rubber matrix, carbon black, organobentonite, silane coupling agent, and organic solvent are mixed in a weight ratio of 100:30~40:15~25:1.5~3.0:50~100 to obtain the semi-conductive resistive grease. The proportion of the lower viscosity grease (8000-9500 cP) is 100:30~33:15~18:2.5~3.0:75~100, and the proportion of the higher viscosity grease (9500-11500 cP) is 100:37~40:22~25:1.5~2.0:50~75.

[0011] Preferably, the expandable water-blocking yarn is spun from superabsorbent polymer fibers and polyester filaments in a core-spun yarn structure.

[0012] Preferably, for Z-twisting, the stranded conductor is placed vertically, and the direction of the spiral inclination of the single wires on its surface is observed. If this direction is consistent with the direction of the middle stroke of the English letter "Z," that is, sloping from the upper left to the lower right, it is Z-twisting, also known as right-hand twisting. Similarly, for S-twisting, the conductor is placed vertically, and if the direction of the spiral inclination of the single wires on its surface is consistent with the direction of the middle stroke of the English letter "S," that is, sloping from the upper right to the lower left, it is S-twisting, also known as left-hand twisting.

[0013] Secondly, the present invention provides a method for forming a large-section compact sealed conductor cable for DC submarine cables, comprising the following steps: (1) Paying and tension control: A multi-disc frame stranding machine is used. Each pay-off reel is equipped with an independent tension control system consisting of a magnetic powder brake or a servo motor to set the tension of each single wire. (2) Single-line preheating: Before the single line enters the coating unit, the surface of the single line is preheated by an online induction heating coil; (3) Simultaneous coating of water-resistant paste: A coating system consisting of a multi-channel precision metering pump and a micro-orifice nozzle is used. The nozzle is aimed at the side of the single line that is about to mesh to spray semi-conductive water-resistant paste in a fixed point and in a fixed quantity. (4) Synchronous guidance of water-blocking yarn: The expansion type water-blocking yarn is precisely guided into the twisting point according to a preset pattern through the yarn guide that rotates synchronously with the twisting head. The synchronization error, that is, the phase difference between the rotation of the yarn guide and the twisting head, is controlled within 1°. (5) Precision pre-twisting and dynamic continuous pressing: The coated and guided single wires are pre-twisted in the twisting head according to the preset pitch, and then enter the multi-roller combination continuous pressing mold. The mold consists of 3-5 sets of tungsten carbide rollers, which apply radial and circumferential pressure to the center conductor. The pressure is 20~24 MPa. The mold inlet is heated online at a temperature of 85~95℃. (6) Online monitoring and feedback: This is achieved by a laser diameter measuring instrument and an online X-ray real-time imaging system. The laser diameter measuring instrument monitors the outer diameter of the conductor in real time and feeds the data back to the tension control system. The tension is dynamically fine-tuned to compensate for the fluctuation of the outer diameter. The online X-ray real-time imaging system performs non-destructive testing on the formed center conductor to identify voids >0.1mm³.

[0014] Preferably, in step (1), the tension of each single wire is set to 17~19N.

[0015] Preferably, in step (2), the surface of the single wire is preheated to 45~55℃.

[0016] Preferably, in step (3), the amount of the semiconducting resistive paste applied is 0.95~1.05g / m, and the nozzle positioning accuracy is ±0.2 mm.

[0017] The beneficial effects of this invention are as follows: 1. This invention redesigns the intrinsic water-blocking structure of the cable conductor and applies a composite water-blocking system of semiconducting water-resistant paste and expanding water-blocking yarn during the conductor stranding process. It directly and synchronously implants and fills the microscopic gaps between irregular single wires, making it an inherent and inseparable part of the conductor, thereby achieving intrinsic water blocking from the inside of the conductor.

[0018] 2. This invention employs an integrated sealing system design, simultaneously embedding and filling all gaps with semi-conductive resistive sealant and expandable water-blocking yarn during the twisting process. The semi-conductive resistive sealant provides an immediate, moisture-independent, paste-like seal, blocking all gaps immediately. The expandable water-blocking yarn acts as a second line of defense, providing strong, active backup water-blocking pressure. This dual mechanism ensures that even if trace amounts of moisture breach the first line of defense, they will be quickly contained locally, forming a deep water-blocking system that significantly increases reliability. This allows the water-blocking system to coexist and grow with the conductor structure, achieving an endogenous structure where the conductor is the water-blocking body. This eliminates blind spots in protection at the source, ensuring the uniformity and long-term stability of water-blocking performance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of a large-section compact sealed conductor structure provided in an embodiment of the present invention; Figure 2A flowchart of the integrated continuous molding process for a large-section compact sealed conductor provided in an embodiment of the present invention; Figure 3 The diagram shows the angle of the inclined plane of the irregular monofilament in the large-section compact sealed conductor provided in the embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1. Center conductor; 2. First layer of irregularly shaped monofilament; 3. Second layer of irregularly shaped monofilament; 4. Third layer of irregularly shaped monofilament; 5. Fourth layer of irregularly shaped monofilament; 6. Fifth layer of irregularly shaped monofilament; 7. Sixth layer of irregularly shaped monofilament; 8. Composite water-blocking system. Detailed Implementation

[0022] In this invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" are generally understood in conjunction with the accompanying drawings and the directions shown in actual applications.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0026] The applicant of this invention has discovered that, in order to improve conductor cross-sectional utilization and water-blocking performance, the industry has developed stranded structures based on trapezoidal or "Z-shaped" single wires. Regarding water-blocking solutions, the current mainstream technology involves filling the gaps between conductor layers with water-blocking adhesive, or using a composite water-blocking technology combining modified water-blocking silicone rubber and semi-conductive water-blocking binding tape to achieve a certain depth of water-blocking capability, such as adapting to water depths of 200 meters. Another related technology is a layer-by-layer compacted conductor structure. By precisely controlling the conductor stranding pitch and pressure parameters, and embedding water-absorbing and expanding water-blocking materials between layers, the compaction coefficient of the conductor can be increased, resulting in a significant improvement in longitudinal water-blocking performance.

[0027] The internal gaps of compact conductors are extremely small, making it difficult for traditional water-blocking materials to completely penetrate, resulting in "dry zones." Traditional water-blocking materials (such as water-blocking powder and some water-blocking adhesives) mainly rely on swelling upon contact with water to form a physical barrier—a passive response mechanism. This means they only become effective when water has already seeped into the material's location. Their water-blocking mechanism is relatively simple. This passive protection mode is ill-suited to rapid or continuous water penetration, especially under harsh environments such as high pressure and high humidity. If the expansion rate lags behind the water ingress rate, water-blocking failure may occur. Furthermore, some water-blocking powder dissolves and is lost upon contact with water, and water-blocking adhesives, after swelling, lack sufficient structural strength and are easily ruptured by water pressure, further reducing long-term reliability. Irregularly shaped conductors (such as Z-shaped, T-shaped, or fan-shaped conductors with non-circular cross-sections) are difficult to seal completely. The microscopic grooves and irregular gaps between irregularly shaped conductors cannot be completely filled by water-blocking tapes or adhesives, forming a potential capillary network. These channels are physically separated from the water-blocking material, allowing seawater to easily and rapidly diffuse axially once it intrudes. This also exacerbates the risk of corrosion, as moisture trapped in the gaps between irregularly shaped wires creates a closed electrolytic environment, accelerating electrochemical corrosion. Furthermore, the aging process is irreversible and difficult to monitor; internal water ingress, corrosion, or thermal aging occurs at the core of the conductor, making it difficult to detect early using conventional online monitoring methods (such as DTS and partial discharge monitoring), and the faults are often sudden.

[0028] To address the aforementioned issues, this application provides a large-section compact sealed conductor cable for DC submarine cables, comprising a center conductor 1, a first layer of shaped monofilaments 2, a second layer of shaped monofilaments 3, N layers of outer shaped monofilaments, and a composite water-blocking system 8; where N is greater than or equal to 1. The first layer of shaped monofilament consists of several Z-shaped monofilaments tightly twisted together outside the central conductor, with the angle between the inclined planes of adjacent Z-shaped monofilaments between 85° and 95°. Figure 3 ); The stranding pitch of the aforementioned Z-shaped profiled single wire is controlled to be 12 to 16 times the pitch circle diameter of the central conductor. The aforementioned composite water-blocking system includes a semi-conductive resistive grease with a viscosity of 8500 to 11500 cP and an expandable water-blocking yarn. The filling amount of the water-blocking yarn in the aforementioned composite water-blocking system occupies 20 to 30% of the gap volume of the Z-shaped profiled single wire. The surface roughness of the aforementioned Z-shaped irregular single-line surface is Ra = 1.0~2.0μm; The second layer of shaped monofilament consists of several S-shaped monofilaments twisted together outside the first layer of shaped monofilaments. The radius of curvature of the inner arc surface of the S-shaped monofilament matches the outer contour of the inner Z-shaped monofilament. The included angle of the inclined plane of the S-shaped monofilament is between 85° and 95°. Figure 3 ).

[0029] The embodiments provided by this invention include a center conductor, a first layer of shaped monofilaments, a second layer of shaped monofilaments, N layers of outer shaped monofilaments, and a composite water-blocking system; N is greater than or equal to 1. The multi-layer shaped monofilament Z-shaped or S-shaped stranding structure significantly reduces the voids inside the conductor, further improving the fill factor. The compact structure reduces the overall cable outer diameter, saving materials and reducing manufacturing and laying costs for the same current carrying capacity, further improving the conductor's compactness and fill factor. The layered stranding of shaped monofilaments helps achieve a more uniform temperature field and stress distribution, avoiding localized overheating, further improving current distribution, and reducing the skin effect. The multi-layer shaped monofilament structure can form a self-supporting skeleton, improving the overall rigidity and tensile strength of the conductor, adapting to the high-tension conditions in deep-sea laying. The design of the center conductor and multi-layer stranding effectively disperses external mechanical stress, prevents deformation, and further enhances the mechanical strength and tensile performance of the sealed conductor cable. Combined with a composite water-blocking system, the multi-layered tightly twisted structure itself reduces the longitudinal penetration channels of water. Even if the outer sheath is damaged, it can effectively prevent seawater from spreading longitudinally along the conductor, which can further improve the reliability and lifespan of the submarine cable.

[0030] In the embodiments provided by the present invention, the first layer of irregular monofilament is composed of several Z-shaped irregular monofilaments tightly twisted together outside the central conductor, and the angle between the inclined planes of adjacent Z-shaped irregular monofilaments is between 85° and 95°. The angle can be any one or any two of the following values: 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, and 95°. The contour is precisely designed to ensure that the angle between the inclined planes of adjacent single lines is between 85° and 95°, forming a stable wedge-shaped meshing structure. If the angle between the inclined planes is too small (<85°), a V-shaped slit will be formed, and the water-blocking paste will be easily squeezed out and difficult to retain. In addition, the expansion pressure of the expanding yarn will be released quickly along the inclined plane, making it difficult to form an effective sealing internal pressure. If the angle between the inclined planes is too large (>95°), the various irregular single lines will be in close parallel contact, the gap entrance will be narrow, and the paste will be difficult to flow into the depth, easily forming filling voids. An angle between 85° and 95° is conducive to the flow and retention of the paste. When the expanding yarn expands or the conductor is squeezed, the pressure can be converted into a normal clamping force on the inclined plane, enhancing the self-locking of the structure. The combination of this structure and the composite water-blocking system increases the effective contact area between the paste and the single line. Combined with the preheating process, the effective wetting area of ​​the paste is increased by approximately 30-50%, significantly enhancing adhesion. Simultaneously, the radial shrinkage force generated during paste curing is converted into normal compressive stress on the inclined surface, improving internal pressure retention efficiency by over 60%, forming a durable and tight interface, and enhancing the structure's mechanical self-locking and pressure transmission.

[0031] In the embodiments provided by this invention, the stranding pitch of the Z-shaped profiled single wire is controlled to be 12 to 16 times the diameter of the central conductor's pitch circle, which can be one or any two of 12, 13, 14, 15, and 16 times. The composite water-blocking system includes a semi-conductive resistive grease with a viscosity of 8500 to 11500 cP and an expandable water-blocking yarn, which can be one or any two of 8500 cP, 9000 cP, 9500 cP, 10000 cP, 10500 cP, 11000 cP, and 11500 cP. The filling amount of the water-blocking yarn in the composite water-blocking system occupies 20 to 30% of the gap volume of the Z-shaped profiled single wire to achieve optimal compactness. If the pitch is too small (<12 times), the conductor rigidity is too high, the bending performance is poor, and the water-blocking yarn will be overloaded. Stretching and compression may damage its structure, affecting its expansion performance, and compressing the axial space left for the paste to flow and fill. If the pitch is too large (>16 times), the axial gap between the irregular single threads increases, resulting in a loose structure, poor mechanical stability, and the water-blocking yarn may not be able to make good contact with the single thread in the excessively large gaps. Furthermore, the water-blocking paste is prone to uneven axial distribution under gravity or centrifugal force. A pitch of 12-16 times provides a stable spiral winding path for the water-blocking yarn and also provides a channel for the uniform distribution of the paste along the axial direction. To fill complex gaps (when the pitch is too small or too large), a water-blocking paste with extremely low viscosity (e.g., <5000 cP) is required, but this can easily lead to sagging during installation and loss before curing, with a filling rate that may be less than 70%. When this pitch is combined with a composite water-blocking system, a medium-to-high viscosity paste (8500-11500 cP) is used. Under twisting pressure, this viscosity paste can flow fully into the wedge-shaped gaps without being easily thrown out or excessively flowing axially, achieving a gap volume filling rate of >95%. Meanwhile, the twisting pitch defines a uniform and stable gap volume. The diameter and filling amount of the water-blocking yarn are designed to occupy 20-30% of the gap volume. During expansion, its volume expansion rate (≥300%) is converted into a radial sealing pressure of up to 1.5~2.5 MPa, which is efficiently utilized due to the limited gap space.

[0032] In the embodiments provided by the present invention, the surface roughness of the Z-shaped irregular single wire is Ra = 1.0~2.0μm, which can be one or any two of 1.0μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, and 2.0μm; this facilitates mechanical interlocking with the paste; reduces the fluidity between the paste and the wire; reduces the possibility of uneven distribution of the paste; thereby improving the axial distribution of the water-blocking paste under gravity or centrifugal force; and improving the water-blocking effect.

[0033] In the embodiments provided by this invention, the second layer of shaped monofilaments consists of several S-shaped monofilaments twisted together outside the first layer of shaped monofilaments. The radius of curvature of the inner arc surface of the S-shaped monofilaments matches the outer contour of the inner Z-shaped monofilaments. The included angle of the inclined plane of the S-shaped monofilaments is between 85° and 95°, and can be one or any two of 85°, 88°, 89°, 90°, 91°, 92°, and 95°. This achieves a seamless overlap. Its outer arc surface ultimately forms an approximately perfect cylindrical surface.

[0034] Optionally, in one embodiment, the aforementioned center conductor is a copper rod with a diameter of 7-9 mm, which can be one or any combination of 7 mm, 7.5 mm, 8 mm, 8.5 mm, and 9 mm; it is located at the very center of the conductor. Its function is to provide mechanical support, bear most of the tension during the laying and operation of the submarine cable, and prevent plastic deformation of the conductor.

[0035] Optionally, in one embodiment, the aforementioned N outer irregularly shaped monofilaments are a third, fourth, fifth, and sixth irregularly shaped monofilament layer, resulting in a more uniform heat conduction path, avoiding localized hot spots, and helping to suppress space charge accumulation. The tight interlocking of the layers forms a labyrinthine water-blocking path, significantly extending the water penetration time. Combined with the composite water-blocking system, even if the outer sheath is damaged, it can effectively prevent seawater from spreading longitudinally along the conductor for several kilometers, preventing the entire cable from failing.

[0036] Optionally, in one embodiment, the stranding tension gradient of the aforementioned third to sixth layers of shaped monofilaments increases by 5% to 10% layer by layer, controlling the overall equivalent fill factor to be above 0.95. Simultaneously, the bending stiffness ratio is aimed to approach 1, giving the stranded conductor mechanical properties close to those of a solid conductor. The tension gradient adjustment method is as follows: in the stranding machine's control system, tension parameters are set for each pay-off reel from the third to the sixth layer, with the third layer as the tension base, increasing by 5-8% for the fourth layer, 7-9% for the fifth layer, and 10% for the sixth layer. The fill factor adjustment method is as follows: to achieve a fill factor above 0.95, tension control and die compression need to work together, with the outer diameter of each layer reduced by 0.5-1.0 mm after passing through the winding die.

[0037] Optionally, in one embodiment, the above-mentioned composite water-blocking system includes a semi-conductive resistive grease and an expandable water-blocking yarn. The semi-conductive resistive grease includes a butyl rubber matrix, carbon black, organobentonite, silane coupling agent, and organic solvent. The butyl rubber matrix, carbon black, organobentonite, silane coupling agent, and organic solvent are mixed in a weight ratio of 100:30~40:15~25:1.5~3.0:50~100 to obtain the above-mentioned semi-conductive resistive grease. The above weight ratios can be any one or any two of the following: 100:30:15:1.5:50, 100:35:20:2.0:60, 100:38:21:2.3:70, 100:40:25:3.0:100; wherein the viscosity paste ratio for 8000-9500 cP is 100:30~33:15~18:2.5~3.0:75~100, and can be any one or any two of the following: 100:30:15:2.5:75, 100:31:16:2.6:80, 100:32:17:2.8:85, 100:33:18:3.0:100; 9500-11500 cP The viscosity paste ratio of cP is 100:37~40:22~25:1.5~2.0:50~75, which can be one or any two of the following: 100:37:22:1.5:50, 100:38:23:1.7:60, 100:39:24:1.8:65, 100:40:25:2.0:75. This semiconducting resistive paste not only has excellent water-blocking and sealing performance, but also has semiconductor characteristics, which can uniformly shape the electric field on the conductor surface, avoid local electric field concentration, further suppress the accumulation of space charge at the conductor-insulator interface, and form a good electro-thermal-mechanical transition with the conductor and insulation layer. Butyl rubber has the best air tightness and water tightness among all rubbers, and can effectively prevent moisture penetration for a long time. It also has good flexibility and adhesion, and can maintain elasticity at low temperatures (such as -2°C in the deep sea), closely adhering to the surface of irregular monofilaments and filling micro gaps. Carbon black imparts semiconductor properties. By controlling the carbon black content and dispersibility, the volume resistivity of the paste is precisely adjusted, achieving electric field homogenization. This further enhances the paste's shear resistance, preventing flow or delamination during application or operation. It also aids in conductor heat dissipation, reducing the risk of hot spots. Organic bentonite forms a three-dimensional network structure when static, making the paste gel-like and non-flowing; under dynamic shear (such as stranding or application), it thins, facilitating construction and filling. It also assists in water blocking, expanding upon contact with water to further block potential seepage channels, improving the storage stability of the composite water-blocking system and preventing carbon black sedimentation and component leaching. Silane coupling agents form molecular bridges between the inorganic filler and the organic rubber matrix, improving dispersion uniformity and bonding strength. This also enhances the hydrolysis resistance of the composite water-blocking system, reducing moisture erosion at the filler-matrix interface and extending the water-blocking life. Furthermore, it improves adhesion, allowing the paste to adhere more firmly to the surface of the metal conductor, preventing delamination and void formation.Organic solvents control the viscosity of the paste, ensuring good flowability during extrusion or injection processes and fully wetting the gaps between multilayer profiled monofilaments. They also promote component dispersion, helping carbon black and bentonite to distribute evenly, preventing agglomeration, and allowing for controlled volatilization. Some solvents can moderately volatilize during subsequent heating crosslinking or vacuum treatment, allowing the paste to ultimately solidify into a stable gel state. The composite water-blocking system includes a semi-conductive resistive water-based paste and an expandable water-blocking yarn, possessing a dual water-blocking mechanism. The semi-conductive resistive water-based paste fills microscopic gaps, providing a long-term static seal. The expandable water-blocking yarn expands rapidly upon contact with water, sealing macroscopic damage channels. The composite water-blocking system exhibits complementary electrical properties. The water-blocking yarn, as an insulating material, only serves a physical water-blocking function; the semi-conductive resistive water-based paste also performs an electric field homogenization function. The combination of the two does not affect the overall electric field distribution.

[0038] In some embodiments, the semiconducting resistive grease is formulated by mixing a butyl rubber matrix, carbon black (conductive phase), organobentonite (water-blocking phase), silane coupling agent, and organic solvent in a specific weight ratio. It provides instant sealing and electric field control. The working viscosity of the grease is controlled between 8500 and 11500 cP, ensuring proper gap geometry matching. Excessively high viscosity (η>15,000 cP) prevents the filling of wedge-shaped sharp corners during twisting; excessively low viscosity (η<7,000 cP) makes it easily ejected by centrifugal force. Its volume resistivity is controlled at 10. 2 ~10 4 Ω·cm helps to smooth the electric field distribution on the conductor surface. The proportions of each component affect the volume change during curing. Excessive shrinkage (e.g., >5%) will generate tensile stress at the interface, forming microcracks; while insufficient shrinkage will not provide enough internal shrinkage pressure. The optimized formulation should control the volume shrinkage rate at 1-3% to generate beneficial, moderate internal shrinkage pressure (approximately 0.5-1.0 MPa), enhancing interfacial tightness without compromising adhesion. The amount of silane coupling agent used can form chemical bonds between the paste and the copper single-wire surface, significantly reducing interfacial contact resistance, ensuring electrical continuity of the semiconductor layer, and avoiding electric field distortion due to interfacial defects. After optimization, the interfacial resistance should be less than the bulk resistance of the paste. The ratio of butyl rubber matrix to organobentonite determines the cohesive strength of the cured paste and its adhesion to the metal, ensuring an adhesion strength of at least 2 MPa to the copper single-wire to prevent debonding under thermomechanical stress.

[0039] Optionally, in one embodiment, the aforementioned expandable water-blocking yarn is spun from superabsorbent polymer (SAP) fibers and polyester filaments in a core-spun yarn structure. During the twisting process, it is longitudinally laid within the conductor layer with every 2-3 copper single wires embedded in a single strand. This provides active and long-lasting water-blocking performance; when it absorbs water, its volume can rapidly expand to more than 300 times its original size, generating an expansion pressure of up to 1.5 MPa or more, actively squeezing and completely blocking any possible seepage channels. The expandable water-blocking yarn is not a simple filler material, but is deeply coupled with the conductor metal structure. Its key parameters are related to the improved conductor parameters (85° of Z / S type single wire). 95° inclined plane angle, 12 There is a synergistic relationship between the twist pitch (16 times the pitch ratio): the theoretical maximum expansion volume (≥300%) of the water-resistant yarn will be slightly larger than the available gap volume defined by the single-thread bevel angle and the twist tightness at its location. Optimized wedge angle (85°) The radial pressure (1.5) generated by the expansion of the yarn upon contact with water (95°) (2.5MPa) is efficiently converted into normal clamping force on the inclined plane, achieving self-locking reinforcement. The yarn diameter is controlled to 60% of the radial gap within the theoretical layer. 80% ensures the yarn is fully embedded during stranding, resulting in an expansion performance retention rate >95%. This method of embedding 2-3 copper single wires at intervals creates a periodic internal support structure with the same pitch as the conductor stranding pitch, providing additional damping without excessively increasing conductor stiffness.

[0040] This application embodiment also provides a method for forming a large-section compact sealed conductor cable for DC submarine cables, including steps S101~S106: S101. Wire feeding and tension control: A multi-disc frame stranding machine is adopted. Each wire feeding disc is equipped with an independent tension control system consisting of a magnetic powder brake or a servo motor to set the tension of each single wire. In this embodiment, closed-loop control is achieved through a servo motor, with fluctuations ≤5%, ensuring that the single thread is neither too loose nor too tight before stranding. Constant tension ensures uniform structure and stable gap geometry, avoiding defects such as excessively large or small local gaps, which could lead to insufficient paste filling and hinder the embedding of water-resistant yarn.

[0041] S102, Single-line preheating: Before the single line enters the coating unit, the surface of the single line is preheated by an online induction heating coil; In this embodiment, after preheating, the working viscosity of the paste is controlled within the optimal coating range of 8000-11000 cP, which significantly improves its capillary action ability to flow into micro-crevices and avoids incomplete filling due to high viscosity.

[0042] S103, Water-resistant paste synchronous coating: A coating system consisting of a multi-channel precision metering pump and a micro-orifice nozzle is used. The nozzle is aimed at the side of the single line that is about to mesh to spray semi-conductive water-resistant paste at a fixed point and in a fixed quantity. In this embodiment, precise and quantitative spraying of semiconducting resistance grease enables accurate and sufficient filling. Quantitative spraying ensures sufficient grease within a unit gap volume; precise lateral positioning allows the grease to be directly applied to the mating surfaces, avoiding waste and contamination; stable viscosity ensures a balance between flowability and shape retention, preventing splashing or flow interruption.

[0043] S104, Water-blocking yarn synchronous guidance: Through the yarn guide that rotates synchronously with the twisting head, the expansion-type water-blocking yarn is accurately guided into the twisting point according to a preset pattern. The synchronization error, that is, the phase difference between the rotation of the yarn guide and the twisting head, is controlled within 1°. In this embodiment, the phase difference between the rotation of the yarn guide and the twisting head is controlled within 1° to ensure that the spatial distribution of the water-blocking yarn is accurate and to prevent the water-blocking yarn from piling up, being cut by the copper wire, or being partially missing due to incorrect positioning, thereby establishing a complete and uninterrupted three-dimensional water-blocking network.

[0044] S105, Precision Pre-Twisting and Dynamic Continuous Pressing: The coated and guided single wires are pre-twisted in the twisting head according to the preset pitch, and then enter the multi-roller combination continuous pressing mold. The mold consists of 3-5 sets of tungsten carbide rollers, which apply radial and circumferential pressure to the center conductor. The pressure is 20~24 MPa. The mold inlet is heated online at a temperature of 85~95℃. In this embodiment, a progressive pressure of 20-24 MPa is applied to the conductor in both radial and circumferential directions. The mold inlet needs to be heated online to maintain the conductor temperature at 85-95°C, which promotes the initial gelation of the water-blocking paste, resulting in thixotropic flowability under pressure, which can completely squeeze out residual air bubbles and completely fill all corners.

[0045] S106. Online monitoring and feedback: This is achieved by a laser diameter gauge and an online X-ray real-time imaging system. The laser diameter gauge monitors the outer diameter of the conductor in real time, and the data is fed back to the tension control system to dynamically fine-tune the tension to compensate for fluctuations in the outer diameter. The online X-ray real-time imaging system performs non-destructive testing on the formed central conductor to identify voids >0.1mm³.

[0046] In this embodiment, an image algorithm is used to identify defects such as voids in the water-blocking paste or missing water-blocking yarn. Once an anomaly is detected, the system can trigger an alarm or automatically adjust the coating parameters of the metering pump, achieving real-time closed-loop quality control of the production process.

[0047] In some implementations, multi-reel frame stranding machines are used, with each reel equipped with an independent tension control system consisting of a magnetic powder brake or servo motor. This system sets the tension for each individual wire, with the core objective of precisely and independently controlling the tension of each wire. Independent tension control ensures that all wires feed synchronously and are subjected to balanced force, resulting in a highly symmetrical and rounded conductor cross-section, which is particularly crucial for large-section submarine cables. Precise tension control helps maintain tight adhesion between individual wires during pre-twisting, stranding, and compaction, reducing gaps and improving the overall conductor density. It also avoids the risk of wire damage and breakage; excessive tension can lead to wire thinning or even breakage, while insufficient tension can cause slack, overlap, or knotting. The independent tension system allows for setting the optimal tension value for each reel, achieving stable operation of mixed stranding. The uniformity and density of the conductor structure directly affect DC resistance, current carrying capacity, and electric field distribution. Tension consistency reduces the risk of localized hot spots and electric field distortion, improving the long-term operational reliability of submarine cables.

[0048] In some implementations, the surface of the single wire is preheated by an online induction heating coil before entering the coating unit. This improves the adhesion and interfacial bonding strength of the paste, making it easier to wet and spread on substrate surfaces at higher temperatures. Preheating also removes trace amounts of moisture, oil, or oxide film from the single wire surface, improving the physical / chemical bonding between the coating and the metal interface. Preheating the single wire removes adsorbed gases and residual volatiles from the surface, reducing air bubble entrainment during coating. It also promotes the full flow of coating material to fill the gaps between strands, forming a continuous and dense sealing layer, significantly improving longitudinal water resistance. Preheating the single wire can share some of the heat load, allowing the coating system to operate under more stable and energy-efficient conditions, which is beneficial for high-speed continuous production. Since the paste has poor fluidity, if the substrate temperature is too low, it is difficult to fully wet complex stranded structures. Surface preheating effectively compensates for insufficient material fluidity, ensuring that deep grooves and gaps are also completely covered.

[0049] In some implementations, a coating system consisting of a multi-channel precision metering pump and micro-orifice nozzles is employed. The nozzles are aimed at the sides where the single wires are about to engage, applying semiconducting resistive hydrogel at precise points and in precise quantities. This achieves efficient and accurate gap filling, improving longitudinal sealing performance. Precise spraying onto the sides about to engage injects the hydrogel into the future gap at the moment the single wires twist, achieving pre-filling followed by closure, significantly improving seal integrity and effectively blocking the longitudinal diffusion path of moisture along the conductor. The precision metering pump can independently control the flow rate of each spray channel (accuracy up to ±1%), ensuring that each single wire engagement area receives the appropriate amount of hydrogel. Quantitative spraying balances sealing reliability and process cleanliness, avoiding material waste and process defects. The semiconducting resistive hydrogel can make the internal potential of the conductor more uniform, suppressing space charge accumulation and reducing the risk of partial discharge under a DC electric field, while maintaining excellent thixotropic properties, aging resistance, and long-term water-blocking performance. The micro-orifice nozzle offers fast response and controllable atomization / flow. Combined with online tension and stranding speed feedback, it can achieve dynamic matching with the stranding speed. Multi-channel independent control supports differentiated spraying strategies for different positions, enabling the entire system to be integrated at the front end of the stranding wire. This allows for integrated continuous manufacturing with simultaneous stranding and sealing, further improving the conductor structure stability and long-term operational reliability.

[0050] In some implementations, an expandable water-blocking yarn is precisely guided into the stranding point according to a preset pattern using a yarn guide that rotates synchronously with the stranding head. The synchronization error, i.e., the phase difference between the rotation of the yarn guide and the stranding head, is controlled within 1°, enabling high-precision and high-reliability embedding of the expandable water-blocking yarn into a large-section, compact conductor. The highly stable spatial relative position between the yarn guide and the stranding point ensures that the water-blocking yarn is always accurately fed into the designed position, avoiding offset, tangling, or misalignment. This allows the water-blocking yarn to smoothly and without tension abrupt changes into the stranding structure, maintaining the consistency of the conductor's outer diameter and meeting the stringent requirements for conductor roundness in subsequent extrusion insulation layers.

[0051] In some embodiments, the coated and guided single wires are initially stranded at a preset pitch in a stranding head, and then enter a multi-roller combination continuous pressing die. The die consists of 3-5 sets of tungsten carbide rollers, which apply radial and circumferential pressure to the central conductor, with a pressure of 20-24. The pressure can be any value within the range of 20MPa, 21MPa, 22MPa, 23MPa, 24MPa, or any combination thereof. The mold inlet is heated online at a temperature of 85~95℃, specifically within the range of 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, or any combination thereof. Microscopic gaps still exist in the conductors after initial stranding, especially at the meshing points of irregularly shaped single wires. High voltage is applied continuously from multiple directions through multiple sets of tungsten carbide rollers, causing controllable plastic deformation of the single wires, resulting in a tight fit. The fill factor can be increased to ≥97%, significantly superior to conventional stranding, meeting the comprehensive requirements of DC submarine cables for low resistance, small outer diameter, and high mechanical strength. After moderate heating, the yield strength of the single wire decreases while its ductility increases. 85~95℃ falls within the low-temperature heat-assisted range, avoiding excessive softening or oxidation of the material and effectively reducing the force required for crimping, thus reducing equipment load. Simultaneously, it promotes the softening and flow of the coated semiconducting resistive grease and expanded water-blocking yarn, better filling residual micro-gaps and forming a dense sealing layer. Using 3-5 sets of tungsten carbide rollers to apply pressure in stages avoids excessive local deformation, cracking, or surface scratches in single wires, ensuring uniform pressure transmission and high conductor roundness. The extremely low porosity inside the conductor suppresses space charge accumulation and local field distortion under a DC electric field. The semiconducting sealing layer bonds tightly to the metal surface under hot pressing, further homogenizing the potential distribution and reducing the risk of aging during long-term operation.

[0052] In some implementations, this is achieved using a laser diameter gauge and an online real-time X-ray imaging system. The laser diameter gauge monitors the conductor's outer diameter and tension in real time, enabling high-precision control of the outer diameter consistency; dynamic closed-loop feedback actively compensates for process disturbances. A stable outer diameter avoids uneven insulation layer thickness, eccentricity, or interface gaps, improving insulation reliability and production yield. The online real-time X-ray imaging system performs non-destructive testing on the formed center conductor to identify voids >0.1 mm³, achieving non-destructive, online, and highly sensitive identification of internal defects.

[0053] In some implementations, the tension of each single wire is set to 17~19N, which can be one or any two of 17N, 17.5N, 18N, 18.5N, and 19N. Within this range, it is sufficient to maintain stable feeding of the single wire during high-speed feeding and stranding processes, while avoiding excessive stretching that would lead to reduced wire diameter, increased resistance, or work hardening. If the tension is too low (<15N), the single wire is prone to loosening, resulting in overlapping, serpentine, or uneven gaps at the stranding point, affecting the filling factor. If the tension is too high (>20N), the single wire is overstretched, which may cause uneven deformation of the inner layer single wires under pressure or shorten the outer layer pitch, destroying the preset stranding geometry; and increasing the rebound stress during crimping, reducing the final compactness. A stable tension of 17~19N ensures that the coating is not subjected to additional stretching during feeding, and that it is subjected to stable force when entering the multi-roller crimping die, avoiding the extrusion or uneven distribution of the paste.

[0054] In some embodiments, in step (2) above, the single-line surface is preheated to 45~55°C, which can be one or any two of the following values: 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, and 55°C. This can reduce the interfacial tension between the coating and the substrate, improve the spreadability and wettability of the paste on the metal surface, and further enhance the physical adsorption and chemical compatibility of the coating with the aluminum / copper alloy surface, thereby improving long-term adhesion.

[0055] In some embodiments, in step (3) above, the coating amount of the semiconducting resistive paste is 0.95~1.05 g / m, which can be one or any two of the following values: 0.95 g / m, 0.96 g / m, 0.97 g / m, 0.98 g / m, 0.99 g / m, 1.0 g / m, 1.01 g / m, 1.02 g / m, 1.03 g / m, 1.04 g / m, and 1.05 g / m. The nozzle positioning accuracy is ±0.2 mm, ensuring the optimal balance between sealing function and electrical performance, and maintaining the consistency and roundness of the conductor outer diameter. This further improves material utilization and reduces manufacturing costs. High positioning accuracy ensures that the relative position of each nozzle and the corresponding single wire remains constant, maintaining synchronization even under high-speed rotating twisting head, avoiding cross-spraying, missed spraying, or overlapping accumulation.

[0056] Preferably, the irregularly shaped monofilament twisted structure in this invention is deeply coupled with the composite water-blocking system to form a dynamically adaptable functional network. The water-blocking system is designed with a gradient to accommodate different gap sizes and stress states at different levels: for the inner layer (layers within the Z-shaped profile) with large curvature and small gaps, a low-viscosity (8000-9500 cP) and highly permeable semi-conductive water-blocking paste is used. The ratio of the low-viscosity paste (8000-9500 cP) is 100: 30~33: 15~18: 2.5~3.0: 75~100, and the ratio of the high-viscosity paste (9500-11500 cP) is 100: 37~40: 22~25: 1.5~2.0: 50~75. It is combined with water-blocking yarn with low linear density and a low Tex value of 33 tex to 67 tex, tightly embedded to ensure filling; for the outer layer with gentle curvature (layers other than Z-shaped irregularities), a water-blocking paste with higher viscosity and high thixotropy (such as 9500-11500 cP) is used to prevent sagging, and combined with water-blocking yarn with a higher linear density of 1500 tex to 2000 tex. The fundamental advantage of this synergistic design is that it enables the conductor to achieve complete filling and sealing from the inside out without dead corners, strictly controlling the longitudinal water permeability length to within one meter, and achieving a leapfrog improvement in mechanical stability, electrical reliability and waterproof sealing performance.

[0057] The present invention will be described in detail below through embodiments.

[0058] Example 1 A large-section compact sealed conductor cable for DC submarine cables includes a center conductor, a first layer of shaped monofilaments, a second layer of shaped monofilaments, a third layer of shaped monofilaments, a fourth layer of shaped monofilaments, a fifth layer of shaped monofilaments, a sixth layer of shaped monofilaments, and a composite water-blocking system.

[0059] The center conductor is a copper rod with a diameter of 8.0 mm, located at the very center of the conductor.

[0060] The first layer of shaped monofilaments consists of several Z-shaped monofilaments tightly twisted together outside the central conductor, with the angle between the inclined planes of adjacent Z-shaped monofilaments being 93°. The twisting pitch of the Z-shaped monofilaments is controlled to be 15.5 times the pitch circle diameter of the central conductor. The composite water-blocking system is a paste with a viscosity of 8500~11500 cP, and the filling amount of the composite water-blocking system occupies 27% of the gap volume of the Z-shaped monofilaments. The surface roughness of the Z-shaped monofilaments is Ra = 1.8μm. The second layer of shaped monofilaments consists of several S-shaped monofilaments twisted together outside the first layer of shaped monofilaments. The radius of curvature of the inner arc surface of the S-shaped monofilaments matches the outer contour of the inner Z-shaped monofilaments. The angle between the inclined planes of the S-shaped monofilaments is 93°.

[0061] The semiconducting resistive water-based paste is composed of butyl rubber matrix, carbon black (conductive phase), organobentonite (water-blocking phase), silane coupling agent, and organic solvent in a weight ratio of 100:35:20:2:50, mixed together. The lower viscosity paste (8800 cP) has a ratio of 100:31:163:2.6:80, and the higher viscosity paste (10500 cP) has a ratio of 100:38:23:1.8:63.

[0062] The expandable water-blocking yarn is spun from superabsorbent polymer (SAP) fibers and polyester filaments in a core-spun yarn structure.

[0063] A method for forming a large-section compact sealed conductor cable for DC submarine cables includes the following steps: (1) Paying and tension control: A multi-disc frame stranding machine is used. Each pay-off reel is equipped with an independent tension control system consisting of a magnetic powder brake or a servo motor to set the tension of each single wire. The tension of each single wire is set to 18.3N. Under this tension, the equivalent fill factor of the stranded conductor reaches 0.962, the outer diameter fluctuation of the conductor is controlled within ±0.03mm, and the interlayer radial pressure is tested to be 2.85MPa.

[0064] (2) Single-line preheating: Before the single line enters the coating unit, the surface of the single line is preheated by an online induction heating coil; the surface of the single line is preheated to 51°C. At this temperature, the temperature difference between the interface of the paste and the single line is less than 3°C. The measured shear bond strength after coating reaches 2.86 N / mm², the micro-interface is dense and without gaps, and the bond strength retention rate is still above 92% after 300 hours of damp heat aging.

[0065] (3) Simultaneous application of water-resistant paste: A coating system consisting of a multi-channel precision metering pump and a micro-orifice nozzle is used. The nozzle is aimed at the side of the single line that is about to engage and sprays semi-conductive resistive water paste at a fixed point and in a fixed quantity. The coating amount of semi-conductive resistive water paste is 1.02 g / m, and the nozzle positioning accuracy is ±0.2 mm. After testing, the filling coverage rate reached 98.5%.

[0066] (4) Synchronous guidance of water-blocking yarn: The expansion type water-blocking yarn is precisely guided into the twisting point according to a preset pattern through the yarn guide that rotates synchronously with the twisting head. The synchronization error, that is, the phase difference between the rotation of the yarn guide and the twisting head, is controlled within 1°. (5) Precision pre-stranding and dynamic continuous crimping: The coated and guided single wires are pre-stranded in the stranding head according to a preset pitch, and then enter a multi-roller combination continuous crimping mold. The mold consists of 3-5 sets of tungsten carbide rollers, which apply radial and circumferential pressure to the center conductor. The pressure is 22.4 MPa. The mold inlet is heated online at a temperature of 91.3℃. Under these parameters, the equivalent filling factor of the stranded conductor reaches 0.965, the interlayer contact area increases by 28%, and the measured tensile strength of the conductor is 15.3% higher than that of the uncrimped state. After 200 thermal cycles, the conductor structure shows no relaxation and the outer diameter change rate is less than 0.05%. (6) Online monitoring and feedback: This is achieved by a laser diameter measuring instrument and an online X-ray real-time imaging system. The laser diameter measuring instrument monitors the outer diameter of the conductor in real time and feeds the data back to the tension control system. The tension is dynamically fine-tuned to compensate for the fluctuation of the outer diameter. The online X-ray real-time imaging system performs non-destructive testing on the formed center conductor to identify voids >0.1mm³.

[0067] Example 2 The only difference from Example 1 is that the tension of each single wire is set to 16N, which ensures proper stranding without loosening. However, the slightly lower tension leads to a decrease in the conductor fill factor to 0.962, an increase in outer diameter fluctuation to ±0.08mm, and a drop in interlayer radial pressure to 2.41MPa. Actual measurement data shows that the interlayer slippage of the conductor in Example 2 increased by 15% after bending tests compared to Example 1, and the DC resistance was 0.32% higher. This indicates that it is slightly inferior in terms of interlayer pressure transmission and micro-gap filling when dealing with multi-layer stranding of irregularly shaped single wires, and the overall conductor structure density and electrical stability are not as good as in Example 1.

[0068] Example 3 The only difference from Example 1 is that the single-line surface was preheated to 47°C, which ensured normal coating of the paste without cold spot peeling. However, the slightly lower preheating temperature resulted in insufficient interfacial activation energy, causing the paste spreadability to decrease by about 8%. The measured shear bond strength was 2.61 N / mm², a decrease of 8.7% compared to Example 1. After damp heat aging, the bond strength retention rate was 88%, and small voids were visible at the interface. Dynamic bending tests showed that the interface debonding rate of the sample in Example 2 was 12% higher than that in Example 1 after 1000 bends. Therefore, the 51°C used in Example 1 is a more preferred preheating temperature parameter in this technical solution.

[0069] Example 4 The only difference from Example 1 is that the coating amount of the semiconducting resistive hydrogel is 1.04 g / m. This slightly higher coating amount caused slight extrusion of the hydrogel during stranding and compaction, resulting in a 1.96% increase in material consumption per unit length compared to Example 1. A trace amount of hydrogel residue was visible on the outer wall of the conductor after stranding. Microscopic observation showed that while the extruded hydrogel did not affect the water-blocking performance, it increased the cleaning requirements in subsequent processes, and the extruded hydrogel did not effectively participate in interface filling, resulting in slightly lower material utilization.

[0070] Example 5 The only difference from Example 1 is that radial and circumferential pressures of 22.4 MPa were applied to the central conductor, and the mold inlet was heated online at a temperature of 91.3°C. Actual measurements showed that the conductor fill factor was 0.951, the interlayer contact area increased by only 21%, and the tensile strength increased by 11.8%, a decrease of 23% compared to Example 1. After the same thermal cycling test, the outer diameter change rate reached 0.12%, with localized minor interlayer slippage.

[0071] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A large cross-section compact sealed conductor cable for DC submarine cables, characterized in that, It includes a central conductor, a first layer of irregularly shaped monofilaments, a second layer of irregularly shaped monofilaments, an Nth layer of outer irregularly shaped monofilaments, and a composite water-blocking system; N is greater than or equal to 1; The first layer of irregular monofilament consists of several Z-shaped irregular monofilaments tightly twisted together outside the central conductor, with the angle between the inclined planes of adjacent Z-shaped irregular monofilaments being between 85° and 95°; The twisting pitch of the Z-shaped profiled single wire is controlled to be 12 to 16 times the pitch circle diameter of the central conductor. The composite water-blocking system includes a semi-conductive resistive grease with a viscosity of 8500 to 11500 cP and an expandable water-blocking yarn. The filling amount of the water-blocking yarn in the composite water-blocking system occupies 20 to 30% of the gap volume of the Z-shaped profiled single wire. The surface roughness of the Z-shaped irregular single-line surface is Ra = 1.0~2.0μm; The second layer of shaped monofilament consists of several S-shaped monofilaments twisted together outside the first layer of shaped monofilaments. The radius of curvature of the inner arc surface of the S-shaped monofilament matches the outer contour of the inner Z-shaped monofilament. The included angle of the inclined plane of the S-shaped monofilament is between 85° and 95°.

2. Large cross-section compact sealed conductor cable for DC submarine cables according to claim 1, characterized in that, The central conductor is a copper rod with a diameter of 7 to 9 mm.

3. Large cross-section compact sealed conductor cable for DC submarine cables according to claim 1, characterized in that, The N-layer outer irregular monofilament consists of a third layer of irregular monofilament, a fourth layer of irregular monofilament, a fifth layer of irregular monofilament, and a sixth layer of irregular monofilament.

4. Large cross-section compact sealed conductor cable for DC submarine cables according to claim 3, characterized in that, The twisting tension gradient of the third layer of shaped monofilaments to the sixth layer of shaped monofilaments increases by 5% to 10% layer by layer, controlling the overall equivalent filling coefficient to be above 0.

95.

5. The large cross-section compact sealed conductor cable for DC submarine cables according to claim 1, characterized in that, The expandable water-blocking yarn is spun from superabsorbent polymer fibers and polyester filaments in a core-spun yarn structure.

6. The forming process for large cross-section compact sealed conductor cables for DC submarine cables according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Paying and tension control: A multi-disc frame stranding machine is used. Each pay-off reel is equipped with an independent tension control system consisting of a magnetic powder brake or a servo motor to set the tension of each single wire. (2) Single-line preheating: Before the single line enters the coating unit, the surface of the single line is preheated by an online induction heating coil; (3) Simultaneous coating of water-resistant paste: A coating system consisting of a multi-channel precision metering pump and a micro-orifice nozzle is used. The nozzle is aimed at the side of the single line that is about to mesh to spray semi-conductive water-resistant paste in a fixed point and in a fixed quantity. (4) Synchronous guidance of water-blocking yarn: The expansion type water-blocking yarn is precisely guided into the twisting point according to a preset pattern through the yarn guide that rotates synchronously with the twisting head. The synchronization error, that is, the phase difference between the rotation of the yarn guide and the twisting head, is controlled within 1°. (5) Precision pre-twisting and dynamic continuous pressing: The coated and guided single wires are pre-twisted in the twisting head according to the preset pitch, and then enter the multi-roller combination continuous pressing mold. The mold consists of 3-5 sets of tungsten carbide rollers, which apply radial and circumferential pressure to the center conductor. The pressure is 20~24 MPa. The mold inlet is heated online at a temperature of 85~95℃. (6) Online monitoring and feedback: This is achieved by a laser diameter measuring instrument and an online X-ray real-time imaging system. The laser diameter measuring instrument monitors the outer diameter of the conductor in real time and feeds the data back to the tension control system. The tension is dynamically fine-tuned to compensate for the fluctuation of the outer diameter. The online X-ray real-time imaging system performs non-destructive testing on the formed center conductor to identify voids >0.1mm³.

7. The forming process for large cross-section compact sealed conductor cables for DC submarine cables according to claim 6, characterized in that, In step (1), the tension of each single wire is set to 17~19N.

8. The method for forming a large-section compact sealed conductor cable for DC submarine cables according to claim 6, characterized in that, In step (2), the single-wire surface is preheated to 45-55°C.

9. The forming process for large cross-section compact sealed conductor cables for DC submarine cables according to claim 6, characterized in that, In step (3), the semi-conductive water-resistant paste is applied at 0.95-1.05 g / m, and the nozzle positioning accuracy is ±0.2 mm.

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