Polypropylene insulated submarine cable and manufacturing method thereof

Abstract

The invention relates to the field of power transmission, in particular to a polypropylene insulated submarine cable and a manufacturing method thereof. The polypropylene insulated submarine cable comprises a plurality of single-core wire cores, and the outer walls of the plurality of single-core wire cores are tangent to each other; each single wire core sequentially comprises an aluminum conductor, a thermoplastic insulating layer and a lead-free waterproof layer from inside to outside. The thermoplastic insulating layer wraps the aluminum conductor; the lead-free waterproof layer wraps the thermoplastic insulating layer; wherein the thermoplastic armor layer wraps the plurality of single-core wire cores. By adopting the thermoplastic insulating layer and the lead-free waterproof layer, the cable has the advantages of being good in environmental protection property, low in production energy consumption, excellent in water tree aging resistance and the like.

Description

Technical Field

[0001] This invention relates to the field of power transmission, and in particular to a polypropylene insulated submarine cable and its manufacturing method. Background Technology

[0002] As the global energy transition continues to accelerate, the large-scale development of clean energy, represented by wind power and photovoltaics, has become an inevitable trend. Deep-sea wind power, with its significant advantages of more stable wind resources, greater installed capacity potential, and less impact on nearshore ecology and shipping, is gradually becoming the core direction for the in-depth development of the offshore wind power industry. Against this backdrop, the power transmission system of offshore wind farms, as a key hub for energy transmission, directly determines the overall benefits of the project through its technical performance and economic viability.

[0003] The 35kV medium-voltage submarine cables commonly used in traditional offshore wind power have gradually revealed a series of significant shortcomings when facing the power transmission demands of large-scale, deep-sea wind farms: First, transmission losses are high; during long-distance power transmission, the lower voltage level generates substantial Joule heat loss, resulting in energy waste. Second, the number of collector circuits is redundant; to meet the power collection needs of large-scale units, a greater number of cable circuits must be laid, not only occupying significant offshore route resources but also greatly increasing system complexity. Third, laying and maintenance costs are high; the submarine laying, protection, and subsequent maintenance of multi-circuit cables require greater investment in equipment and manpower, severely restricting the economic viability of deep-sea wind power projects. Clearly, 35kV submarine cables are no longer adequate for the efficient, economical, and intensive power transmission requirements of large-scale, deep-sea wind farms.

[0004] Currently, although the 66kV submarine cables used in some projects have achieved an upgrade in voltage level, their core structure still uses cross-linked polyethylene (XLPE) as insulation material and lead sheath as waterproof sheath. This traditional design still has many prominent defects in practical applications:

[0005] I. Serious environmental deficiencies: The lead contained in the lead sheath can easily be released into the marine environment or soil during accidental damage during the production and laying of submarine cables, or during the recycling process after decommissioning, causing persistent heavy metal pollution. This is contrary to the current global clean energy industry's green and low-carbon development concept and is also difficult to meet the increasingly stringent environmental regulations.

[0006] Second, high energy consumption and high cost in production: The preparation of XLPE insulation material requires a complex chemical cross-linking process. This process is not only lengthy and inefficient, but also consumes a large amount of heat and electricity. It is estimated that its comprehensive energy consumption is more than 30% higher than that of thermoplastic insulation materials. At the same time, the special equipment and chemical additives required for the cross-linking process further increase the overall production cost of submarine cables.

[0007] 3. Poor resistance to water tree aging: Under the combined effects of long-term seawater immersion and electric field, XLPE materials are prone to the gradual formation of water trees—a type of dendritic micro-defect caused by moisture penetration—within the insulation. The continuous growth of water trees will continuously degrade the insulation performance of the material, eventually leading to cable insulation breakdown, significantly shortening the service life of submarine cables, and increasing the later operation and maintenance risks and costs of deep-sea wind power projects.

[0008] Fourth, the weight per unit length is too high: The density of lead is as high as 11.34 g / cm³, which is much higher than that of commonly used polymer sheath materials. The lead sheath structure directly leads to a significant increase in the weight per unit length of the submarine cable. This not only increases the difficulty and cost of transporting and hoisting the submarine cable, but also places higher demands on the load capacity of the submarine laying equipment. Under complex seabed topography, problems such as laying difficulties and excessive cable sag are very likely to occur. Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present invention is to overcome the problems in the prior art, thereby providing a polypropylene insulated submarine cable and a method for manufacturing the same.

[0010] In a first aspect, a polypropylene insulated submarine cable is provided, comprising:

[0011] Multiple single-core wires, the outer walls of the multiple single-core wires being tangent to each other; each single-core wire, from the inside out, includes an aluminum conductor, a thermoplastic insulation layer, and a lead-free waterproof layer; the thermoplastic insulation layer encloses the aluminum conductor; the lead-free waterproof layer encloses the thermoplastic insulation layer;

[0012] The armor layer encases multiple single-core wires.

[0013] In one embodiment of the present invention, the aluminum conductor comprises multiple aluminum single wires stranded together in layers; each layer of aluminum single wires is filled with semiconducting resistive adhesive.

[0014] In one embodiment of the present invention, each layer of the aluminum single wire is wrapped with a semiconducting resistive water strip, and the semiconducting resistive water strip is covered with a semiconducting tertrol strip.

[0015] In one embodiment of the present invention, the thermoplastic insulating layer comprises a conductor shielding layer, a main insulating layer, and an insulating shielding layer, which are simultaneously formed by a three-layer co-extrusion process using blended modified polypropylene material; the thicknesses of the conductor shielding layer and the insulating shielding layer are 1.0 mm to 1.7 mm, respectively; and the thickness of the main insulating layer is 10 mm to 12 mm.

[0016] In one embodiment of the present invention, the lead-free waterproof layer includes a water-blocking buffer layer, a metal shielding layer, and a semi-conductive insulating sheath; the water-blocking buffer layer includes a first resistive water-resistant tape wrapping layer and a second semi-conductive water-resistant tape wrapping layer; the metal shielding layer includes a copper wire and copper strip layer disposed between the first resistive water-resistant tape wrapping layer and the second semi-conductive water-resistant tape wrapping layer, and an aluminum-plastic composite tape covering the second semi-conductive water-resistant tape wrapping layer, wherein the plastic layer of the aluminum-plastic composite tape faces the semi-conductive insulating sheath.

[0017] In one embodiment of the present invention, the thickness of the semiconductive insulating sheath is 5mm-8mm.

[0018] In one embodiment of the present invention, the armor layer comprises, from the inside out, an adhesive strap, an inner lining, zinc-aluminum alloy steel wire, and an outer sheath.

[0019] In one embodiment of the present invention, it further includes a plurality of fillers and an optical unit disposed within the fillers; the fillers are filled between two adjacent single-core wires.

[0020] Secondly, a method for manufacturing a polypropylene insulated submarine cable as described above is provided, comprising the following steps:

[0021] S1. Multiple aluminum single wires are twisted together in layers. After each layer of aluminum single wires is twisted together, semiconducting resistive water adhesive is injected through a semiconductor adhesive extruder to obtain an aluminum conductor.

[0022] S2. Add the blended polypropylene granules to a three-color screw extruder. After plasticization by the screw, the conductor shielding layer, the main insulation layer, and the insulation shielding layer are simultaneously extruded through a die to obtain a thermoplastic insulation layer. The thermoplastic insulation layer is then laminated onto the aluminum conductor.

[0023] S3. Apply a lead-free waterproof layer to the aluminum conductor in step S2.

[0024] S4. The aluminum conductor composite armor layer in step S3.

[0025] In one embodiment of the present invention, in step S2, the heat transfer medium of the three-color screw extruder is oil liquid, the extrusion temperature is 220℃-240℃, and the traction speed is 5m / min-8m / min.

[0026] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0027] 1. The polypropylene insulated submarine cable of the present invention has significantly improved environmental performance: it completely replaces the lead sheath structure and reduces heavy metal pollution; the recyclability of PP (polypropylene) material reaches 95%, which is 30% higher than that of XLPE.

[0028] 2. The economic optimization of the polypropylene insulated submarine cable described in this invention: production energy consumption is reduced by 35% compared to XLPE submarine cable, unit length cost is reduced by 25%, and laying efficiency is increased by 40%.

[0029] 3. The reliability of the polypropylene insulated submarine cable described in this invention is enhanced: its radial water-blocking performance meets the IEC 63026:2019 standard, and its water absorption rate is ≤0.03% after 28 days; its water tree resistance life reaches 40 years, which is 15 years longer than that of XLPE.

[0030] 4. The polypropylene insulated submarine cable of the present invention has the advantage of lightweight design: the weight per unit length is reduced by 35% compared with the traditional structure, making it suitable for high-capacity power transmission in deep sea areas. Attached Figure Description

[0031] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0032] Figure 1 This is a cross-sectional view of the polypropylene insulated submarine cable of this invention;

[0033] Figure 2 This is a schematic diagram of a single-core wire in this invention;

[0034] Figure 3 This is a schematic diagram of the aluminum conductor in this invention;

[0035] Figure 4 This is a schematic diagram of the extrusion of the semiconducting resistive water-based adhesive in this invention;

[0036] Figure 5 This is a schematic diagram of the stranding of a single-layer aluminum conductor in this invention; Figure 6 This is a schematic diagram of the aluminum conductor stranding in this invention; Figure 7 This is a schematic diagram of aluminum conductor wire drawing in this invention; Figure 8 This is a schematic diagram of the aluminum conductor water-blocking adhesive and water-blocking tape wrapping in this invention.

[0037] Explanation of reference numerals on the accompanying drawings:

[0038] 1. Aluminum conductor; 2. Conductor shielding layer; 3. Main insulation layer; 4. Insulating shielding layer; 5. First semi-conductive resistive water tape wrapping layer; 6. Copper wire and copper tape layer; 7. Second semi-conductive resistive water tape wrapping layer; 8. Aluminum-plastic composite tape; 9. Semi-conductive insulating sheath; 10. Filler; 11. Adhesive wrapping tape; 12. Inner lining layer; 13. Zinc-aluminum alloy steel wire; 14. Outer sheath layer;

[0039] 100. Semiconductor adhesive extruder; 101. Pipeline;

[0040] 200. Wire drawing mechanism;

[0041] 301. First frame winch; 302. Second frame winch; 303. Third frame winch; 304. Fourth frame winch;

[0042] 401. First water-blocking tape wrapping mechanism; 402. Second water-blocking tape wrapping mechanism; 403. Third water-blocking tape wrapping mechanism; 404. Fourth water-blocking tape wrapping mechanism. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] In deep-sea wind power transmission systems, traditional submarine cables commonly use cross-linked polyethylene (XLPE) as insulation and lead as a waterproof sheath. However, this structure makes the insulation material prone to water tree defects under the long-term combined action of electric fields and seawater, leading to insulation breakdown. The lead sheath poses a risk of heavy metal contamination, and the high-density material results in a large weight per unit length. The complexity of the cross-linking process leads to high energy consumption, making it difficult to meet the high-efficiency, environmentally friendly, and economical requirements of large-scale deep-sea wind farms. Specifically, water tree aging directly reduces the service life of the submarine cable, the lead contamination risk conflicts with environmental regulations, and the heavy weight increases the difficulty and cost of installation.

[0045] For example, in the power transmission projects of large-scale deep-sea wind farms, when submarine cables are laid in areas with complex seabed topography, the lead sheath is prone to damage due to mechanical stress during the laying process, leading to seawater infiltration. Simultaneously, the cross-linked polyethylene insulation layer is affected by moisture and electric fields during long-term operation, causing water tree defects to gradually expand and eventually resulting in localized insulation failure. Furthermore, the redundant design of multi-circuit cables occupies limited submarine routing resources, increasing system complexity and maintenance workload, thereby affecting the reliability and economic efficiency of the wind farm.

[0046] If the above problems are not solved, the failure rate of submarine cables will continue to rise, leading to an increased risk of power transmission system outages and making it difficult to control operation and maintenance costs; heavy metal pollution may cause lasting damage to marine ecosystems, which is inconsistent with the concept of sustainable development; in addition, high-energy-consuming production processes and weight issues will further restrict the large-scale application of deep-sea wind power projects, thus making the promotion of clean energy face technical bottlenecks.

[0047] In this regard, combined with Figures 1 to 4 This embodiment proposes a polypropylene insulated submarine cable, comprising:

[0048] Multiple single-core wires, the outer walls of the multiple single-core wires being tangent to each other; each single-core wire includes, from the inside out, an aluminum conductor 1, a thermoplastic insulation layer and a lead-free waterproof layer; the thermoplastic insulation layer wraps the aluminum conductor 1; the lead-free waterproof layer wraps the thermoplastic insulation layer; wherein, a thermoplastic armor layer wraps the multiple single-core wires.

[0049] For ease of understanding, the following explains some key terms in this embodiment:

[0050] Polypropylene insulated submarine cables are cables specifically designed for underwater environments, particularly for transmitting electrical energy in the ocean. The core insulation material of these cables is made of polypropylene, designed to provide excellent electrical insulation and mechanical protection while adapting to the complex operating conditions on the seabed.

[0051] A single-core cable is the basic unit of a cable, typically consisting of a conductor and surrounding insulation and other protective layers. In a multi-core cable, multiple single-core cables are combined together to transmit electrical energy.

[0052] Aluminum conductor 1 is the part of the cable used to transmit current. Aluminum, as a conductor material, is used in power cables due to its good conductivity, relatively low density, and cost.

[0053] Thermoplastic insulation is a dielectric material wrapped around a conductor. Its main function is to isolate the conductor, prevent current leakage, and withstand operating voltage. Thermoplastic materials are characterized by softening when heated and hardening when cooled, allowing for repeated molding and shaping, which facilitates cable manufacturing and recycling.

[0054] A lead-free waterproof layer is a protective structure placed outside the insulation layer. Its function is to prevent moisture from penetrating into the cable, protecting the insulation layer and conductor from the effects of a humid environment, thereby maintaining the long-term stable operation of the cable. This waterproof layer is lead-free and meets environmental protection requirements.

[0055] The armor layer is the outermost mechanical protective structure of the cable, used to enhance the cable's tensile, impact and abrasion resistance, and protect the internal structure from external mechanical damage, especially during submarine laying and operation.

[0056] This embodiment provides a polypropylene insulated submarine cable, the main technical features of which are described in detail below:

[0057] The submarine cable comprises multiple single-core conductors. These single-core conductors can be arranged in various geometries; for example, they can be twisted together to form a compact cable bundle. In one implementation, the outer walls of the multiple single-core conductors are designed to be tangential, meaning they are in close contact across the cross-section, thus forming a relatively compact overall structure that helps reduce the overall diameter of the cable.

[0058] The internal structure of each single-core wire, from the inside out, includes an aluminum conductor 1, a thermoplastic insulation layer, and a lead-free waterproof layer. The aluminum conductor 1, as the core of electrical power transmission, can be composed of a single solid aluminum rod or multiple stranded aluminum wires. For example, multiple circular cross-section aluminum wires can be concentrically stranded to obtain the required conductive cross-sectional area and a certain degree of flexibility.

[0059] A thermoplastic insulation layer is designed to wrap around the exterior of the aluminum conductor 1. This insulation layer can be formed from a single thermoplastic polymer material through an extrusion process, for example, by melting polypropylene granules at high temperature, extruding them through a die, and then cooling and solidifying them onto the surface of the aluminum conductor 1. The primary function of this insulation layer is to provide electrical isolation, ensuring that current is transmitted within the conductor without leakage.

[0060] The lead-free waterproof layer is designed to wrap around the outside of the thermoplastic insulation layer. This waterproof layer can consist of one or more materials; for example, it can be formed by extrusion or wrapping a polymer material with good water-blocking properties. This waterproof layer is designed to effectively prevent external moisture from penetrating into the insulation and conductor, thereby protecting the electrical performance of the cable and extending its service life.

[0061] In addition, the submarine cable includes a lightweight armor layer designed to encase multiple single-core wires. This armor layer can be formed from one or more layers of material through extrusion or wrapping processes. The primary function of this armor layer is to provide additional mechanical strength and protection to the entire cable, enabling it to withstand external pressure, impact, and abrasion in the submarine environment.

[0062] Furthermore, the lead-free waterproof layer in this embodiment replaces the lead sheath structure commonly used in traditional submarine cables. This improvement directly solves the heavy metal pollution problem caused by lead sheaths, making the cable more environmentally friendly throughout its entire lifecycle, from production and laying to decommissioning and recycling. Simultaneously, because lead has a much higher density than polymer materials, the application of the lead-free waterproof layer significantly reduces the cable's weight per unit length. During the laying process at location A, the reduced weight means lower transportation and hoisting difficulties, and a corresponding reduction in the load capacity requirements of the laying equipment, thereby improving laying efficiency and reducing related costs.

[0063] Overall, this embodiment, by employing a polypropylene thermoplastic insulation layer and a lead-free waterproof layer, effectively overcomes the technical challenges of existing submarine cables in terms of environmental protection, production economy, long-term reliability, and weight, while ensuring power transmission performance. This technical solution provides a more efficient, economical, and environmentally friendly power transmission solution for the construction of large-scale deep-sea wind farms, demonstrating significant technological progress.

[0064] This embodiment further proposes that the aluminum conductor 1 includes multiple aluminum single wires stranded together in layers; the spaces between each layer of aluminum single wires are filled with semiconducting resistive water adhesive.

[0065] The aluminum conductor 1 is the core component of the cable used for current transmission, and it consists of multiple thin aluminum single wires. These aluminum single wires are not simply bundled together, but are layered and twisted according to a specific geometric arrangement. For example, concentric twisting can be used, where the central strand is twisted first, and then one or more layers of aluminum single wires are twisted around it, with each layer twisting in an alternating or identical direction. This layered twisting structure, compared to solid conductors or simple bundled conductors, significantly improves the conductor's flexibility, making it easier to bend during laying and operation, while also effectively dispersing external mechanical stress and improving the conductor's fatigue resistance. The semiconducting resistive adhesive is a gel-like material that combines semiconductivity and water-blocking properties. Its semiconductivity ensures that the filler material does not adversely affect the electric field distribution of the conductor, avoiding local electric field concentration, while its water-blocking performance is crucial. This adhesive is filled in the gaps between the layered twisted aluminum single wires. The filling method can be to inject or coat the colloid between the aluminum single wires by extrusion or coating during the stranding process, ensuring that the colloid can fully wet and fill all gaps that may form moisture channels.

[0066] This embodiment designs the aluminum conductor 1 as a multi-layered stranded aluminum single-wire structure, and fills the spaces between each layer of aluminum single wires with semi-conductive resistive adhesive, thus constructing a composite conductor with excellent conductivity, mechanical flexibility, and internal water-blocking capability. The layered stranded aluminum single-wire structure gives the conductor good bending performance and tensile strength, adapting to the complex laying and operating environment of submarine cables. Simultaneously, the filling with semi-conductive resistive adhesive physically isolates the tiny gaps between the aluminum single wires, forming effective water-blocking barriers. When the cable's outer sheath is damaged and moisture attempts to penetrate along the conductor's axis, the semi-conductive resistive adhesive filling each layer of aluminum single wires immediately takes effect, preventing further moisture diffusion. The semi-conductivity ensures that the filling material does not introduce additional electric field distortion or partial discharge risks, maintaining the conductor's electrical performance. This structural design allows the aluminum conductor 1 to maintain high conductivity while significantly enhancing its long-term reliability and safety in underwater environments, effectively preventing cable failures caused by moisture diffusion along the conductor's interior.

[0067] This embodiment further proposes that each layer of aluminum single wire is wrapped with a semiconducting resistive water strip, and the semiconducting resistive water strip is covered with a semiconducting Tedoron strip.

[0068] Among them, the semi-conductive water-resistant tape is a strip material that combines semi-conductive and water-blocking properties. Its semi-conductive properties help smooth the electric field and reduce local electric field concentration, thereby improving the electrical performance and operational reliability of the cable. Its water-blocking properties are achieved through an internal water absorption and expansion mechanism; when in contact with water, the water-absorbing material in the tape expands rapidly, effectively filling the gaps and preventing water from penetrating longitudinally along the conductor. This semi-conductive water-resistant tape can be made by impregnating or coating a non-woven fabric substrate with semi-conductive particles (such as carbon black) and a water-absorbing resin (such as superabsorbent polymer), or by combining a polymer film with a semi-conductive coating with a water-absorbing layer. The semi-conductive terephthalic acid tape is a strip material with terephthalic acid (polyethylene terephthalate, PET) as the base material, endowing it with semi-conductive properties. Terephthalic acid itself has excellent mechanical strength, abrasion resistance, and dimensional stability, providing good physical support and protection for the internal structure of the cable. By making it semi-conductive, the tape can further optimize the electric field distribution, suppress partial discharge, and provide a uniform potential transition interface for the subsequent insulating layer. This semi-conductive tertrol tape can be made from PET film through surface coating or co-extrusion of a semi-conductive polymer layer, or by weaving or non-woven PET fibers followed by semi-conductive treatment.

[0069] In the aforementioned layered stranded aluminum single-wire structure, each layer of aluminum single wire is wrapped with a semi-conductive resistive water tape, and then covered with a semi-conductive terylene tape, forming a multi-layered protective conductor structure. After the aluminum single wires are stranded, a semi-conductive resistive water tape is first tightly wrapped around the outside of each layer. This semi-conductive resistive water tape not only provides an additional semi-conductive layer, further homogenizing the electric field, but more importantly, its internal water-absorbing and expanding material can rapidly expand upon contact with moisture, forming an effective physical barrier to prevent moisture from diffusing longitudinally along the conductor. Subsequently, a semi-conductive terylene tape is tightly covered on the outside of this semi-conductive resistive water tape. This semi-conductive terylene tape, with its excellent mechanical properties, provides additional mechanical support and protection for the internal semi-conductive resistive water tape and aluminum single-wire structure, preventing loosening or damage to the internal structure due to external forces during cable manufacturing, transportation, and laying. Simultaneously, its semi-conductive properties, working synergistically with the internal semi-conductive resistive water tape, jointly construct a more stable and uniform electric field environment, effectively suppressing local electric field concentration, thereby improving the electrical reliability of the cable. This layered structural design allows the aluminum conductor 1 to maintain good conductivity while significantly enhancing its watertightness and mechanical stability, ensuring the long-term stable operation of the submarine cable in harsh environments.

[0070] Combination Figure 4 , Figure 6 , Figure 7 and Figure 8In this embodiment, the aluminum conductor 1 is designed as a four-layer aluminum single-wire structure. The four-layer aluminum single-wire structure is prepared sequentially by a wire drawing mechanism 200, an aluminum wire spool, a first frame stranding machine 301, a semiconductor adhesive extruder 100, a first water-blocking tape wrapping mechanism 401, a second frame stranding machine 302, a semiconductor adhesive extruder 100, a second water-blocking tape wrapping mechanism 402, a third frame stranding machine 303, a semiconductor adhesive extruder 100, a third water-blocking tape wrapping mechanism 403, a fourth frame stranding machine 304, a semiconductor adhesive extruder 100, and a fourth water-blocking tape wrapping mechanism 404. Specifically, the four-layer aluminum single-wire structure adopts concentric layered stranding. The forming of each layer follows a closed loop of "first bonding and sealing, then wrapping for water resistance, and finally stranding the next layer". The overall process is as follows: the aluminum rod is drawn into an aluminum single wire of a specified diameter using the wire drawing mechanism 200 and wound onto an aluminum wire spool → the first layer of aluminum single-wire structure is stranded using the first frame stranding machine 301 → the semiconductor adhesive is extruded and bonded using the semiconductor adhesive extruder 100 → the water-resistant tape is wrapped using the first water-resistant tape wrapping mechanism 401 → the second layer of aluminum single-wire structure is stranded using the second frame stranding machine 302. → Use semiconductor adhesive extruder 100 to extrude semiconductor adhesive for bonding and sealing → Use second water-blocking tape wrapping mechanism 402 to wrap water-blocking tape → Use third frame stranding machine 303 to strand the third layer of aluminum single wire structure → Use semiconductor adhesive extruder 100 to extrude semiconductor adhesive for bonding and sealing → Use third water-blocking tape wrapping mechanism 403 to wrap water-blocking tape → Use fourth frame stranding machine 304 to strand the fourth layer of aluminum single wire structure → Use semiconductor adhesive extruder 100 to extrude semiconductor adhesive for bonding and sealing → Use fourth water-blocking tape wrapping mechanism 404 to wrap water-blocking tape.

[0071] Among them, the semiconductor adhesive fills the gaps between the strands, achieving continuous interlayer conductivity, and at the same time bonds the water-blocking tape to the conductor, preventing water from migrating longitudinally along the gaps.

[0072] Water-blocking tape: Provides a radial water-blocking barrier, which, together with adhesive, forms a dual water-blocking system of "adhesive + tape", suitable for high water pressure environment on the seabed.

[0073] Frame stranding machine: It realizes the regular stranding of each layer of aluminum single wire, controls the pitch and tension, and ensures the roundness of the conductor and the stability of the structure.

[0074] This embodiment further proposes that the thermoplastic insulation layer includes a conductor shielding layer 2, a main insulation layer 3, and an insulation shielding layer 4, which are simultaneously formed by a three-layer co-extrusion process using blended modified polypropylene material; the thicknesses of the conductor shielding layer 2 and the insulation shielding layer 4 are 1.0 mm to 1.7 mm, respectively; and the thickness of the main insulation layer 3 is 10 mm to 12 mm.

[0075] Among them, blended modified polypropylene materials refer to materials whose physical, chemical, or electrical properties are improved by blending polypropylene with other polymers or additives. For example, the flexibility and impact resistance of the material can be improved by blending with elastomers, or its dielectric properties and thermal stability can be enhanced by adding nanofillers. This material selection aims to optimize the overall performance of the insulation layer, making it more suitable for the harsh working environment of submarine cables. Three-layer co-extrusion is an advanced extrusion molding technology that simultaneously extrudes materials with different properties through three independent extruders and composites them in a die to form an insulation layer with a three-layer structure. This process ensures a tight bond between the layers, high interface quality, and effectively avoids defects such as delamination and bubbles, thereby improving the overall reliability of the insulation layer. Simultaneous molding refers to the conductor shielding layer 2, the main insulation layer 3, and the insulating shielding layer 4 being completed in one extrusion process, forming a continuous, seamless whole. This molding method not only improves production efficiency, but more importantly, it ensures excellent interfacial bonding between the layers, minimizing interface defects, which is crucial for suppressing partial discharge and improving insulation strength.

[0076] In this embodiment, the blended modified polypropylene material includes 85 wt% polypropylene, 10 wt% nano-SiO2 and 5 wt% water-resistant resin.

[0077] Conductor shielding layer 2 is a semi-conductive layer adjacent to aluminum conductor 1. Its main function is to homogenize the electric field on the conductor surface and eliminate electric field concentration caused by microscopic unevenness on the conductor surface, thereby suppressing partial discharge. This layer is usually composed of a polypropylene matrix blended with conductive fillers such as conductive carbon black. Main insulation layer 3 is the most important part of the thermoplastic insulation layer. Its main function is to provide the main insulation strength and isolate high voltage. This layer typically uses high-purity blended modified polypropylene material, which has excellent dielectric properties, low dielectric loss, and good heat resistance. Insulating shielding layer 4 is a semi-conductive layer located outside the main insulation layer 3. Its function is to homogenize the electric field on the outer surface of the main insulation layer 3 and form good electrical contact with the lead-free waterproof layer, further suppressing partial discharge and protecting the main insulation layer 3 from external electric field stress. Similar to conductor shielding layer 2, this layer is also composed of a polypropylene matrix blended with conductive fillers. The conductor shielding layer 2 and the insulating shielding layer 4 have thicknesses of 1.0mm-1.7mm, respectively. This thickness range is optimized to ensure that the shielding layers can effectively and uniformly distribute the electric field, while avoiding excessive thickness leading to material waste and an excessively large cable diameter, or insufficient thickness resulting in poor shielding performance. For example, it can be set to 1.2mm or 1.5mm. The main insulation layer 3 has a thickness of 10mm-12mm. This thickness range is determined based on the cable's rated voltage level and the dielectric strength of the insulation material. Sufficient insulation thickness is crucial for ensuring the long-term safe operation of the cable; it can withstand the electric field stress under high voltage and prevent insulation breakdown. For example, it can be set to 10.5mm or 11.5mm.

[0078] This embodiment effectively improves the insulation performance of submarine cables by designing the thermoplastic insulation layer as a composite layer with specific materials and structures. Specifically, outside the aluminum conductor 1, a conductor shielding layer 2 is first set. Its semi-conductive properties smooth the electric field on the surface of the aluminum conductor 1, eliminating the tip discharge effect and providing a uniform electric field environment for the subsequent main insulation layer 3. Next, the main insulation layer 3, as the primary insulating medium, withstands the main voltage stress during cable operation due to its excellent dielectric properties. Further outward, the insulating shielding layer 4, also with its semi-conductive properties, smooths the electric field on the outer surface of the main insulation layer 3 and forms good electrical contact with the external lead-free waterproof layer, further suppressing electric field distortion and partial discharge. These three layers are simultaneously formed through a three-layer co-extrusion process, ensuring a tight physical and chemical bond between each layer, minimizing interface defects, and thus avoiding partial discharge and insulation aging caused by interface problems. The use of blended modified polypropylene materials gives the entire insulation layer superior heat resistance, pressure resistance, and aging resistance, enabling it to operate stably for a long time in the high-pressure, high-temperature, and high-humidity submarine environment. This refined layered structure and material optimization enable the thermoplastic insulation layer to efficiently manage the electric field distribution, significantly improving the insulation reliability and service life of the cable, thereby solving the problem of partial discharge and insulation failure that traditional insulation layers are prone to in complex environments.

[0079] This embodiment further proposes that the above-mentioned lead-free waterproof layer includes a water-blocking buffer layer, a metal shielding layer, and a semi-conductive insulating sheath 9; the water-blocking buffer layer includes a first resistive water tape wrapping layer 5 and a second semi-conductive water tape wrapping layer 7; the metal shielding layer includes a copper wire and copper tape layer 6 disposed between the first resistive water tape wrapping layer 5 and the second semi-conductive water tape wrapping layer 7 and an aluminum-plastic composite tape 8 covering the second semi-conductive water tape wrapping layer 7, and the plastic layer of the aluminum-plastic composite tape 8 faces the semi-conductive insulating sheath 9.

[0080] The lead-free waterproof layer is a composite structure used to prevent moisture from entering the cable, protecting the conductor and insulation from water erosion, while also providing some mechanical protection and electromagnetic shielding. This layer can be composed of various materials, such as water-blocking materials, metallic shielding materials, and sheathing materials, to meet the complex challenges of the seabed environment.

[0081] The water-blocking buffer layer is an important component of the lead-free waterproof layer. Its main function is to prevent water penetration and provide cushioning and support for the subsequent metal shielding layer. This layer can be composed of water-absorbing and swelling materials, water-blocking tape wrapping layers, or water-blocking fiber layers to achieve effective water-blocking function.

[0082] The first water-blocking tape wrapping layer 5 is a conductive water-blocking tape formed by wrapping. Its function is to provide initial water blocking while also providing some electric field homogenization or a grounding path. This layer can be made of materials such as carbon black-filled semi-conductive non-woven fabric or conductive expansion tape.

[0083] The second semi-conductive water-blocking tape wrapping layer 7 is another type of semi-conductive water-blocking tape wrapping layer. Its function is to further enhance the water-blocking effect and provide semi-conductive shielding, which helps to achieve a uniform electric field distribution. This layer can be made of materials such as semi-conductive expansion tape or semi-conductive non-woven fabric.

[0084] The metallic shielding layer is a crucial structure used to provide electromagnetic shielding, preventing external electromagnetic interference from affecting the internal signals of the cable, and limiting the outward diffusion of the internal electric field. This layer can be composed of metal wires, metal strips, metal foils, or metal braids to ensure the cable's electromagnetic compatibility.

[0085] The copper wire and strip layer 6 is a layer composed of copper wire and / or copper strip. Its function is to provide the main electromagnetic shielding function and grounding path, and it has good conductivity. This layer can be implemented by means of copper wire braiding mesh, copper strip longitudinal wrapping, or copper wire spiral wrapping.

[0086] Aluminum-plastic composite tape 8 is a strip material composed of aluminum foil and a plastic layer. Its function is to provide additional water barrier and electromagnetic shielding, while the plastic layer provides insulation and corrosion protection. This tape can be made in various forms, such as a composite of polyester film and aluminum foil, or a composite of polypropylene film and aluminum foil.

[0087] The semi-conductive insulating sleeve 9 is an insulating sleeve with semi-conductive properties. Its function is to provide external mechanical protection, insulation, and further electric field homogenization. This sleeve can be extruded from semi-conductive polyethylene, semi-conductive polypropylene, or semi-conductive rubber materials.

[0088] The plastic layer of the aluminum-plastic composite tape 8 is oriented in a specific lamination direction towards the semi-conductive insulating sheath 9 to ensure good contact between the plastic layer and the semi-conductive insulating sheath 9, thereby providing superior adhesion, insulation performance, or corrosion prevention. This is achieved by wrapping the aluminum-plastic composite tape 8 with the plastic side facing outwards.

[0089] This embodiment achieves comprehensive protection for submarine cables by designing the lead-free waterproof layer as a multi-layered composite structure. The first and second semi-conductive water-resistant tape wrapping layers 5 and 7 in the water-blocking buffer layer work together to form an effective initial water-blocking barrier and provide preliminary management of the electric field. Building upon this, the copper wire and copper tape layer 6 in the metallic shielding layer provides strong electromagnetic shielding and grounding capabilities, while the outer aluminum-plastic composite tape 8 further enhances the water-blocking effect and electromagnetic shielding capability. Its plastic layer's specific structure facing the semi-conductive insulating sheath 9 optimizes the performance of the interlayer interface. The outermost semi-conductive insulating sheath 9 not only provides mechanical protection and insulation but also improves electric field homogenization, ensuring the overall performance of the entire lead-free waterproof layer in withstanding high water pressure, preventing water penetration, providing electromagnetic shielding, and possessing mechanical strength. This meticulously layered and synergistic design enables the cable to operate stably for extended periods in harsh submarine environments, effectively solving the problem that a single waterproof structure cannot fully meet multiple stringent requirements.

[0090] This embodiment further proposes that the thickness of the semi-conductive insulating sheath 9 is 5mm-8mm. Here, "thickness" refers to the radial dimension of the semi-conductive insulating sheath 9, i.e., the distance from its inner surface to its outer surface. This thickness range is designed to ensure that the semi-conductive insulating sheath 9 provides sufficient mechanical protection while considering material cost, overall cable diameter, and flexibility. One implementation method is to precisely control the dimensions of the extrusion die and the process parameters of the extruder during the extrusion molding of the semi-conductive insulating sheath 9, ensuring that the radial thickness of the sheath consistently falls between 5mm and 8mm. Another implementation method is to perform real-time or sampling inspection using online or offline thickness measurement equipment after the semi-conductive insulating sheath 9 is extruded, ensuring that its thickness meets the 5mm-8mm range requirement, and adjusting or rejecting batches that do not meet the requirements.

[0091] This embodiment limits the thickness of the semi-conductive insulating sheath 9 in the lead-free waterproof layer of the aforementioned polypropylene insulated submarine cable to within the range of 5mm-8mm. This allows the semi-conductive insulating sheath 9 to provide sufficient mechanical protection for the internal water-blocking buffer layer and metal shielding layer, effectively resisting physical damage from external environmental factors such as compression, impact, and abrasion, thereby protecting the cable's integrity and long-term operational reliability. Simultaneously, this thickness range avoids material waste and the problems of excessively thick sheaths leading to excessively large cable diameters and increased weight, which is beneficial for cable manufacturing, transportation, and laying. Furthermore, an appropriate sheath thickness helps maintain the overall flexibility of the cable, ensuring its adaptability to complex seabed terrain. By precisely controlling the thickness of the semi-conductive insulating sheath 9, the cable's structural design and cost-effectiveness are optimized while providing the necessary protective functions.

[0092] This embodiment further proposes that the armor layer of the above-mentioned polypropylene insulated submarine cable includes, from the inside out, an adhesive wrapping tape 11, an inner lining layer 12, a zinc-aluminum alloy steel wire 13, and an outer sheath layer 14.

[0093] The adhesive tape 11 is a strip-shaped material with adhesive properties or that achieves adhesion through heating, pressure, or other means. Its main function is to fix the components within the armor layer together, providing initial structural stability, preventing interlayer slippage or displacement, and offering some cushioning or sealing. The material of the adhesive tape 11 can be selected based on the required adhesive strength, temperature resistance, water resistance, etc., and can be, for example, self-adhesive polyester tape, hot melt adhesive tape, or non-woven fabric tape coated with adhesive.

[0094] The inner lining layer 12 is located outside the adhesive tape 11 and serves to support and isolate subsequent structural layers. Its main function is to provide a flat, uniform support surface for the external zinc-aluminum alloy steel wire 13, preventing direct contact between the wire and the internal structure. It also acts as a buffer, insulates, or blocks water. The material of the inner lining layer 12 can be polypropylene nonwoven fabric, polyester film, or extruded polyethylene layer; its thickness and material selection depend on the required mechanical strength, flexibility, and protective performance.

[0095] Zinc-aluminum alloy steel wire 13 is a metal wire made by coating a steel wire substrate with a zinc-aluminum alloy layer. As the main load-bearing component of the armor layer, zinc-aluminum alloy steel wire 13 provides excellent mechanical strength and tensile strength, protecting the internal structure of the cable from external mechanical damage. The zinc-aluminum alloy coating gives it excellent corrosion resistance, extending the cable's service life in seawater environments. Zinc-aluminum alloy steel wire 13 can be a single or multiple stranded steel wires, with its diameter and number designed according to the required mechanical strength and flexibility of the cable. The coating can be hot-dip galvanized aluminum alloy or electro-galvanized aluminum alloy.

[0096] The outer sheath 14 is located on the outermost side of the armor layer and is in direct contact with the external environment. Its main function is to provide final mechanical protection, abrasion resistance, corrosion resistance, UV resistance, and water resistance, ensuring the long-term reliable operation of the cable in the submarine environment. The material of the outer sheath 14 can be extruded polyethylene (PE), polyvinyl chloride (PVC), or polyurethane (PU) and other polymer materials. Its thickness, hardness, and additives (such as UV stabilizers and flame retardants) are selected according to the specific application environment and standard requirements.

[0097] This embodiment designs the armor layer as a multi-layered structure, with each layer working closely together. The adhesive tape 11 first ensures the stability of the internal structure and interlayer adhesion, providing a solid foundation for subsequent layers. The inner lining layer 12 provides buffering and support between the adhesive tape 11 and the zinc-aluminum alloy steel wire 13, avoiding stress concentration. Most importantly, the zinc-aluminum alloy steel wire 13, as the main load-bearing component, significantly improves the cable's tensile strength and impact resistance, while its zinc-aluminum alloy coating provides excellent corrosion resistance, effectively resisting seawater erosion. The outermost outer sheath layer 14 provides comprehensive external protection against abrasion, ultraviolet radiation, and further corrosion. This layer-by-layer reinforcement structure from the inside out allows the entire armor layer to function as a whole, effectively meeting the harsh challenges of the seabed environment, significantly improving the overall protective performance and reliability of the cable, and overcoming the shortcomings of a single armor layer in terms of mechanical strength, corrosion resistance, and long-term stability.

[0098] This embodiment further proposes that the above-mentioned polypropylene insulated submarine cable also includes multiple fillers 10 and optical units disposed within the fillers 10; the fillers 10 are filled between two adjacent single-core wires.

[0099] The filler 10 is a structure used to fill the internal gaps of the cable. Its main function is to stabilize the overall structure of the cable, prevent internal components from shifting or deforming under external pressure or bending stress, and provide mechanical protection for the optical unit. The filler 10 can be made of various materials, such as polymer materials like polypropylene and polyethylene, or elastic materials like rubber and silicone. Its shape is usually designed to fit tightly against the outer wall of adjacent single-core wires; for example, it can be fan-shaped, triangular, or irregularly shaped to maximize the use of the gaps between the single-core wires. In this embodiment, the filler 10 uses polypropylene (PP) granules with a melt index of 3g / 10min-5g / 10min, coated by a ring extruder.

[0100] An optical unit is a component used to transmit optical signals, with optical fiber at its core. An optical unit may include one or more optical fibers, which are typically encapsulated in a protective sheath to prevent mechanical damage and environmental corrosion. The main function of an optical unit is to achieve high-speed, high-capacity data communication, compensating for the shortcomings of traditional cables in data transmission capabilities. Optical units can use single-mode or multimode optical fibers, the specific choice depending on the required transmission distance and bandwidth. The protective sheath can be made of materials such as stainless steel or PBT (polybutylene terephthalate) to provide sufficient strength and corrosion resistance. The filler element 10 is placed between adjacent single-core wires, meaning it is positioned within the gaps formed by the arrangement of multiple single-core wires. This structural design fully utilizes the available space inside the cable, allowing the optical unit to be integrated with the power transmission wires in the same cable, thus achieving integrated power and data transmission. Simultaneously, the arrangement of the single-core wires provides support and positioning for the filler element 10, ensuring the stability and safety of the optical unit within the cable.

[0101] This embodiment achieves effective integration of power transmission and optical communication by placing filler elements 10 between multiple single-core conductors of a polypropylene insulated submarine cable and housing the optical unit within the filler elements 10. Specifically, when multiple single-core conductors are arranged tangentially inside the cable, gaps are formed between them. These gaps are designed to accommodate the filler elements 10, which provide a stable installation space and necessary mechanical protection for the optical unit. The material and shape of the filler elements 10 are optimized to fit tightly against the outer wall of the single-core conductors, effectively filling the gaps inside the cable, enhancing the overall structural stability of the cable, and preventing mechanical stress damage such as compression and bending to the optical unit during cable manufacturing, laying, and operation. Under the protection of the filler elements 10, the optical unit can stably transmit optical signals, thereby adding high-speed data communication capabilities to the submarine cable without significantly increasing the cable's outer diameter or complexity. This integrated design allows a single cable to simultaneously undertake the tasks of power transmission and information transmission, greatly simplifying the deployment and maintenance of submarine engineering projects and improving the overall efficiency and reliability of the system.

[0102] This embodiment also discloses a manufacturing method for manufacturing the polypropylene insulated submarine cable, comprising the following steps:

[0103] S1. Multiple aluminum single wires are stranded in layers. After each layer of aluminum single wires is stranded, a semiconducting resistive water adhesive is injected through a semiconductor adhesive extruder 100 to obtain an aluminum conductor 1. Specifically, the semiconductor adhesive extruder 100 extrudes the semiconducting resistive water adhesive through a pipe 101, and the extrusion process is used to integrally form each layer of aluminum single wires and the semiconducting resistive water adhesive. Further, a semiconducting resistive water tape is wrapped around the aluminum conductor 1, and a semiconducting terylene tape is covered on the outside of the semiconducting resistive water tape to form a triple radial water barrier.

[0104] S2. Add the blended polypropylene granules to a three-color screw extruder. After plasticization by the screw, the conductor shielding layer 2, the main insulation layer 3, and the insulation shielding layer 4 are simultaneously extruded through a die to obtain a thermoplastic insulation layer. The thermoplastic insulation layer is then laminated onto the aluminum conductor 1. Specifically, the thicknesses of the conductor shielding layer 2 and the insulation shielding layer 4 are 1.0mm-1.7mm, the thickness of the main insulation layer 3 is 10mm-12mm, the working temperature reaches 105℃, and the water tree resistance is improved by 50% compared to XLPE.

[0105] S3. Apply a lead-free waterproof layer to the aluminum conductor 1 in step S2. Specifically, the lead-free waterproof layer includes a water-blocking buffer layer, a metal shielding layer, and a semi-conductive insulating sheath 9. The water-blocking buffer layer includes a first semi-conductive water-resistant tape wrapping layer 5 and a second semi-conductive water-resistant tape wrapping layer 7. The metal shielding layer includes a copper wire / tape layer 6 disposed between the first and second semi-conductive water-resistant tape wrapping layers 5 and 7, and an aluminum-plastic composite tape 8 covering the second semi-conductive water-resistant tape wrapping layer 7, with the plastic layer of the aluminum-plastic composite tape 8 facing the semi-conductive insulating sheath 9. The wrapping tension of the first and second semi-conductive water-resistant tape wrapping layers 5 and 7 is controlled between 50N and 80N, with an overlap rate ≥50%. The copper wire / tape layer 6 is made of 16 Φ1.2mm copper wires evenly tied together with a pitch of 100mm-150mm. The longitudinal wrapping of the aluminum-plastic composite tape 8 is achieved using ultrasonic welding, with a welding strength ≥15N / mm.

[0106] S4. The composite armor layer of the aluminum conductor 1 in step S3; specifically, the armor layer, from the inside out, includes an adhesive wrapping tape 11, an inner lining layer 12, a zinc-aluminum alloy steel wire 13, and an outer sheath layer 14, with a weight per unit length reduced by 40% compared to the lead sheath structure. Specifically, the diameter of the zinc-aluminum alloy steel wire 13 is 2.0mm-2.5mm, and the wrapping pitch is 15-20 times the diameter of the submarine cable. An infrared heating device is used to preheat the polypropylene outer sheath layer 14, with the temperature controlled at 100℃-120℃, to improve the wrapping tightness.

[0107] The aforementioned manufacturing process replaces the traditional cross-linking process with direct extrusion molding of thermoplastic polypropylene, eliminating the complex chemical cross-linking steps and effectively reducing production energy consumption and equipment investment. The three-layer co-extrusion process simultaneously forms the conductor shielding layer 2, the main insulation layer 3, and the insulation shielding layer 4, ensuring the uniformity of the insulation structure and the interfacial bonding strength, fundamentally suppressing the generation of water tree defects. The application of a lead-free waterproof layer completely eliminates the risk of heavy metal pollution from lead sheaths, while also reducing the weight per unit length of the cable. Through the above technical solutions, the overall energy consumption of the submarine cable manufacturing process is reduced by more than 30% compared to traditional processes, and the resistance to water tree aging is significantly improved, providing an efficient, environmentally friendly, economical, and reliable power transmission infrastructure solution for large-scale deep-sea wind farms.

[0108] This embodiment further proposes that in step S2, the heat transfer medium of the three-color screw extruder is oil liquid, the extrusion temperature is 220℃-240℃, and the traction speed is 5m / min-8m / min.

[0109] In this three-color screw extruder, the heat transfer medium is oil. This medium is used to heat or cool the extruder barrel and screw to maintain the polymer temperature during extrusion. Compared to water or steam, oil has a higher boiling point and better thermal stability, providing stable and uniform temperature control. This ensures that the blended modified polypropylene material is heated evenly during extrusion, avoiding localized overheating or uneven cooling, thus guaranteeing the quality of the extruded product. The extrusion temperature is 220℃-240℃, a crucial range for the blended modified polypropylene material to fully melt, plasticize, and maintain appropriate viscosity. At this temperature, the material can smoothly pass through the die to form a uniform insulating layer, while avoiding material degradation due to excessively high temperatures or poor plasticization due to excessively low temperatures. This temperature is typically precisely regulated using heating and cooling zones on the extruder, along with temperature sensors and controllers. The traction speed is 5m / min-8m / min, directly affecting the dimensional accuracy, surface quality, and production efficiency of the extruded product. Within this speed range, sufficient time is ensured for the extruded insulation layer to stabilize in dimensions before cooling and curing, while avoiding excessive stretching and thinning due to excessive speed or low production efficiency due to excessively slow speed. The traction speed is typically controlled by the motor speed of the traction machine and precisely adjusted via a frequency converter.

[0110] This embodiment uses oil as the heat transfer medium in the three-color screw extruder, providing a stable and uniform temperature environment for the extrusion process. The high specific heat capacity and thermal conductivity of oil help to precisely control the temperature of the barrel and screw, ensuring uniform heating of the blended modified polypropylene material throughout the extrusion path and avoiding material degradation or uneven plasticization caused by localized overheating. Furthermore, by precisely controlling the extrusion temperature within the range of 220℃-240℃, the blended modified polypropylene material is ensured to fully melt and achieve optimal fluidity, allowing it to pass through the die with a uniform thickness, forming a dense and defect-free conductor shielding layer 2, main insulation layer 3, and insulating shielding layer 4. Simultaneously, by setting the traction speed to 5m / min-8m / min, sufficient time is allowed for the extruded insulation layer to stabilize its dimensions during cooling and solidification, avoiding tensile deformation or dimensional deviations in the insulation layer caused by improper traction speed. The synergistic effect of these parameters enables the thermoplastic insulation layer to be tightly bonded to the aluminum conductor 1, forming a single-core wire with excellent electrical insulation properties and mechanical strength, laying a solid foundation for the subsequent bonding of the lead-free waterproof layer and armor layer.

[0111] In one specific implementation, during the manufacturing of polypropylene insulated submarine cables, in step S2, heat transfer oil can be used as the heat transfer medium for the three-color screw extruder. This heat transfer oil exhibits good thermal stability at high temperatures. The set temperatures of each temperature zone of the extruder can be fine-tuned according to the specific grade of the blended modified polypropylene material. For example, the feeding zone temperature can be set to 200℃, the compression zone temperature to 225℃, the metering zone temperature to 235℃, and the die temperature to 230℃, ensuring that the material is fully plasticized within the range of 220℃-240℃. Simultaneously, the traction device can be a servo motor-driven tracked traction machine with a traction speed set to 6.5m / min to achieve a good match between the extrusion speed and the cooling and curing speed, thereby obtaining a dimensionally stable and smooth thermoplastic insulation layer.

[0112] By employing the aforementioned technical solutions, precisely controlling the heat transfer medium, extrusion temperature, and traction speed of the three-color screw extruder during the manufacturing process of polypropylene insulated submarine cables effectively solves the problem of unstable insulation layer quality caused by improper parameters in traditional extrusion processes. The oil liquid, acting as a heat transfer medium, provides a uniform and stable temperature field, preventing localized overheating or uneven plasticization of the polypropylene material. The optimized extrusion temperature range ensures sufficient melting and good flowability of the material, resulting in a dense and uniformly thick extruded insulation layer. A reasonable traction speed guarantees the dimensional stability of the insulation layer during cooling and solidification, reducing internal stress. These measures work together to significantly improve the electrical properties, mechanical strength, and long-term reliability of the thermoplastic insulation layer, thereby enhancing the overall quality and service life of the polypropylene insulated submarine cable.

[0113] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A polypropylene insulated submarine cable, characterized in that, include: Multiple single-core wires, the outer walls of the multiple single-core wires being tangent to each other; each single-core wire includes, from the inside out, an aluminum conductor (1), a thermoplastic insulation layer, and a lead-free waterproof layer; the thermoplastic insulation layer wraps around the aluminum conductor (1); the lead-free waterproof layer wraps around the thermoplastic insulation layer; The armor layer encases multiple single-core wires.

2. The polypropylene insulated submarine cable according to claim 1, characterized in that, The aluminum conductor (1) comprises multiple aluminum single wires stranded together in layers; each layer of aluminum single wires is filled with semiconducting resistive water adhesive.

3. The polypropylene insulated submarine cable according to claim 2, characterized in that, Each layer of the aluminum single wire is wrapped with a semiconducting resistive water strip, and the semiconducting resistive water strip is covered with a semiconducting Tedoron strip.

4. The polypropylene insulated submarine cable according to claim 1, characterized in that, The thermoplastic insulation layer includes a conductor shielding layer (2), a main insulation layer (3), and an insulation shielding layer (4) formed simultaneously by a three-layer co-extrusion process using blended modified polypropylene material; the thicknesses of the conductor shielding layer (2) and the insulation shielding layer (4) are 1.0 mm to 1.7 mm, respectively; and the thickness of the main insulation layer (3) is 10 mm to 12 mm.

5. The polypropylene insulated submarine cable according to claim 1, characterized in that, The lead-free waterproof layer includes a water-blocking buffer layer, a metal shielding layer, and a semi-conductive insulating sheath (9); the water-blocking buffer layer includes a first water-resistant tape wrapping layer (5) and a second semi-conductive water-resistant tape wrapping layer (7); the metal shielding layer includes a copper wire and copper strip layer (6) disposed between the first water-resistant tape wrapping layer (5) and the second semi-conductive water-resistant tape wrapping layer (7) and an aluminum-plastic composite tape (8) covering the second semi-conductive water-resistant tape wrapping layer (7), and the plastic layer of the aluminum-plastic composite tape (8) faces the semi-conductive insulating sheath (9).

6. The polypropylene insulated submarine cable according to claim 5, characterized in that, The thickness of the semi-conductive insulating sheath (9) is 5mm-8mm.

7. The polypropylene insulated submarine cable according to claim 1, characterized in that, The armor layer consists of, from the inside out, an adhesive strap (11), an inner lining (12), a zinc-aluminum alloy steel wire (13), and an outer sheath (14).

8. The polypropylene insulated submarine cable according to claim 1, characterized in that, It also includes multiple fillers (10) and optical units disposed within the fillers (10); the fillers (10) are filled between two adjacent single-core wires.

9. A method for manufacturing a polypropylene insulated submarine cable as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Multiple aluminum single wires are stranded in layers. After each layer of aluminum single wires is stranded, semiconducting resistive water adhesive is injected through a semiconductor adhesive extruder (100) to obtain an aluminum conductor (1). S2. Add the blended polypropylene granules to a three-color screw extruder. After plasticizing by the screw, the conductor shielding layer (2), the main insulation layer (3) and the insulation shielding layer (4) are simultaneously extruded through the die to obtain a thermoplastic insulation layer. The thermoplastic insulation layer is then composited onto the aluminum conductor (1). S3. Apply a lead-free waterproof layer to the aluminum conductor (1) in step S2; S4. Composite armor layer for aluminum conductor (1) in step S3.

10. The manufacturing method according to claim 9, characterized in that, In step S2, the heat transfer medium of the three-color screw extruder is oil liquid, the extrusion temperature is 220℃-240℃, and the traction speed is 5m / min-8m / min.

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