A medium-voltage DC cable resistant to repeated current surges and its manufacturing method

Abstract

This application relates to the field of cable processing, specifically disclosing a medium-voltage DC cable resistant to repeated current impacts and its manufacturing method. The medium-voltage DC cable resistant to repeated current impacts includes a conductor, an insulating composite layer, a fiber tape, a copper strip, and a protective layer. The conductor is formed by stranding a central layer, a secondary layer, and an outer layer. The central layer consists of 19 round copper single wires forming a 1+6+12 structure. The secondary layer consists of 18 copper single wires rolled into a T-shape and arranged around the periphery of the central layer. The outer layer consists of 24 copper single wires rolled into a Z-shape and arranged around the periphery of the secondary layer. The manufacturing method is as follows: the central layer, secondary layer, and outer layer are stranded to obtain the conductor; an insulating composite layer is co-extruded onto the conductor surface and then radially cross-linked to obtain the core; a fiber tape coated with a semiconductor colloid is applied to the surface of the core, wrapped with a copper strip, and finally a polymer material is applied as a protective layer. After radial cross-linking, the finished cable is obtained. This cable has the advantages of being resistant to repeated high-voltage current impacts, lightweight, and capable of handling high-load DC propulsion systems.

Description

Technical Field

[0001] This application relates to the field of cable processing, and more specifically, it relates to a medium-voltage DC cable resistant to repeated current surges and a method for its preparation. Background Technology

[0002] With social development and technological progress, advanced vehicles such as large unmanned ships and heavy-duty drones have become new tracks in the transportation field. In the past, AC networking of equipment had the problems of low utilization and poor accuracy. Therefore, these devices usually have DC networking electric propulsion systems (±270V, 1.5kV, 3kV, 6kV, etc.). The electric propulsion system that uses high-voltage DC thrusters to drive propellers or other propulsion devices has the core function of efficiently and stably converting electrical energy into mechanical thrust. It is widely used in fields such as ships and aircraft with high requirements for energy efficiency and reliability. In addition to being able to perform high-efficiency energy conversion, these application conditions have put forward new requirements for cable design, such as lightweight design, reliability requirements under high current repeated pulse conditions, high control accuracy requirements for transmission current, and greater current load requirements for the same cross-section.

[0003] However, the design of existing high-voltage DC cable products in the industry usually refers to the structural design of AC cables, and the manufacturing process is not refined. In particular, the structural design and process control of the insulation layer are poor, resulting in no improvement in product weight and load, unstable high-voltage DC pulse resistance (breakdown in 20-2000 tests), and inability to meet the high-precision operation requirements of unmanned ships and drones.

[0004] Analysis of the existing cable structure, material selection, process and performance parameter design reveals that the cable cannot meet the requirements of lightweight, high load, high voltage DC pulse resistance and high precision current control. The main reasons are as follows: (1) Factors affecting cable lightweighting: The existing cable assembly consists of seven parts, including a circular conductor with multiple nominal diameter round copper wires twisted together, a conductor shielding layer of fixed thickness, an insulation layer of nominal thickness, an insulation shielding layer of nominal thickness, a metal shielding layer of nominal diameter, and an outer sheath of nominal thickness. The cable composition is simple, and the existing structural design and material selection can no longer effectively reduce the cable weight. There must be a new design idea for the structure or the selection of lighter materials, but the product performance must meet the requirements. (2) Factors affecting cable high load: Generally, to improve the cable load capacity, the cable conductive cross section can be increased or the insulation material temperature rating can be improved. Increasing the cable conductive cross section will inevitably increase the cable outer diameter, which has a greater impact on lightweighting. Alternatively, the insulation material temperature rating can be improved. For every 10°C increase in insulation operating temperature, the current carrying capacity of the same cross section can be increased by about 10%. According to GB / T12706, the rated voltage is 1kV to 35kV extruded insulation. The insulation materials given in the power cable and accessories, among which cross-linked polyethylene XLPE, ethylene propylene rubber (EPR and HEPR) have a working temperature of 90℃, which cannot meet the higher load requirements under the same cross section. At the same time, ethylene propylene rubber has a higher density than cross-linked polyethylene, and is not suitable as the insulation requirement for lightweight cables; (3) Factors affecting the cable's resistance to high voltage DC pulse and the realization of high-precision current control: First, process influence: The existing cable insulation adopts continuous extrusion of extrusion equipment. The three-layer co-extrusion process of semi-conductive conductor shield, insulation and semi-conductive insulation shield is the key process of cable products. At present, the GB standard specifies that the insulation eccentricity control index is within 10%, but the insulation eccentricity problem is one of the important indicators of cable quality. If controlled according to the national standard, the maximum electric field strength of the insulation layer will also change significantly under the high voltage DC pulse state, resulting in uneven current distribution, increased resistance, and inability to achieve high-precision current control; In addition, for every 1% increase in eccentricity, the cable temperature rise increases by 2-3℃, causing electric field distortion and a decrease in breakdown voltage; For example, when the eccentricity of a 10kV cable exceeds 8%, the withstand voltage value decreases by 25%, which cannot meet the requirements of high voltage DC pulse. Extrusion process control and eccentricity index design are key to this type of cable; secondly, the influence of metal shielding type: existing metal shielding types of cables include copper tape wrapping and copper wire braided shielding. Under repeated impacts from high voltage DC, copper wire braided shielding exhibits high electromagnetic force and may even deform, while copper tape is relatively stable. In combination with lightweight design, wrapping structure should be considered.

[0005] In summary, existing cables cannot meet the requirements of high-voltage DC propulsion systems. Under the influence of high-voltage DC pulses, the cables lack reliability. Furthermore, in terms of product structure design, key process control, and performance index design, they cannot meet the high requirements of unmanned ships and aircraft for lightweighting, energy efficiency, and reliability. At the same time, the conductors of existing conventional products are generally multiple strands of round copper single wires twisted together to form a conductor. The twisting of all round copper single wires not only increases the gaps between them, but also makes the outer diameter of the conductor too large.

[0006] Therefore, there is an urgent need to develop a new type of cable that meets the advantages of DC propulsion systems that can withstand repeated high-voltage current surges or precise current control, are lightweight, and can handle large loads. Summary of the Invention

[0007] In order to prepare a new type of cable that meets the advantages of being resistant to repeated high-voltage current surges or precise current control, lightweight, and capable of handling heavy loads in DC propulsion systems, this application provides a medium-voltage DC cable resistant to repeated current surges and its preparation method.

[0008] In a first aspect, this application provides a medium-voltage DC cable resistant to repeated current surges, employing the following technical solution: A medium-voltage DC cable resistant to repeated current surges, the cable comprising a conductor, an insulating composite layer, a fiber tape, a copper strip, and a protective layer; the conductor is formed by stranding a central layer, a secondary layer, and an outer layer, wherein the central layer is composed of 19 round copper single wires forming a 1+6+12 structure, the secondary layer is composed of 18 copper single wires rolled into a T-shape and arranged on the periphery of the central layer, and the outer layer is composed of 24 copper single wires rolled into a Z-shape and arranged on the periphery of the secondary layer.

[0009] By adopting the above technical solutions and limiting the conductor structure, not only can the gap between individual wires inside the conductor be reduced, but the outer diameter of the conductor can also be reduced, the amount of insulation and sheathing can be reduced, and the weight of the cable can be reduced, resulting in the advantage of being lightweight.

[0010] After pure circular single wires are twisted together, there are natural gaps between the single wires, and the filling coefficient is usually only about 80%-85%. T-type and Z-type stranded wires are shaped wire structures that can fill the gaps between circular single wires through complementary contours, increasing the overall fill factor to over 90%. With significantly reduced gaps, the probability of electric field distortion decreases, and partial discharge is suppressed, thereby improving the conductor's ability to withstand repeated high-voltage current impacts. Furthermore, repeated high-voltage current impacts are accompanied by periodic heating and cooling of the conductor, causing thermal expansion and contraction deformation. A purely circular stranded structure is loose, and after long-term deformation, single wire misalignment and loose strands are prone to occur, leading to increased local resistance, heat accumulation, and accelerated insulation aging. However, with a circular + T-type + Z-type stranded structure, the different shapes of wires interlock, resulting in tighter interlayer bonding and stronger overall structural stability. After repeated thermal expansion and contraction, misalignment and loose strands are less likely to occur, maintaining stable conductivity over a long period and extending the lifespan to withstand impacts. Simultaneously, the circular + T-type + Z-type stranded structure improves surface smoothness. For high-voltage cables, the superposition of insulation composite layers, fiber tapes, copper metal tapes, and protective layers further reduces the risk of partial discharge breakdown under high-voltage impacts.

[0011] The circular + T-type + Z-type stranded structure allows for a larger effective conductive area and lower DC resistance for the same nominal cross-sectional area, making it more suitable for the needs of high-load DC systems to reduce transmission losses. Compared with ordinary pure circular concentric stranding, the combination of strands can reduce the final conductor diameter by about 9%, making the overall regularity closer to that of a solid conductor, which is more suitable for DC propulsion systems with high integration requirements. At the same time, the combination of T-type and Z-type joints on the circular outer periphery usually makes the stranding direction of adjacent layers opposite. On the one hand, it can avoid the outer single wire from embedding into the inner structure due to the same stranding direction, which would destroy the circular regularity. On the other hand, the rotational torque of each layer cancels each other out, preventing loose strands from looping. The conductor structure is more stable during operation, with less resistance fluctuation, which is more conducive to precise current control.

[0012] Preferably, the 1+6+12 structure is as follows: 6 copper single wires are evenly wrapped around 1 copper single wire, and 12 copper single wires are evenly wrapped around 6 copper single wires.

[0013] By adopting the above technical solution, the residual torque generated by the stranding between the layers can cancel each other out, and repeated impacts by high voltage current are less likely to cause cable twisting, avoiding the problem of local resistance increase and overheating breakdown caused by twisting, thereby improving the effect of resisting repeated impacts by high voltage current; and after stranding, the layers of the conductor have a high interlayer friction due to mechanical interlocking effect, which is less likely to cause conductor bending and compression deformation under high voltage impact, ensuring the structural stability of the cable; at the same time, the structure of each layer of the conductor is concentrically arranged, which can avoid partial discharge caused by the distortion of the gap electric field during repeated impacts of high voltage current, delay insulation aging, and improve long-term impact resistance reliability.

[0014] Preferably, the insulating composite layer is formed by co-extrusion of three layers: a semiconducting conductor shield, an insulating layer, and a semiconducting insulating shield. The insulating material in the insulating layer contains the following raw materials in parts by weight: 50-70 parts HDPE, 50-70 parts LLDPE, 5-10 parts EVA, 1-4 parts antioxidant, 0.2-0.5 parts copper inhibitor, 0.2-0.5 parts light stabilizer, and 1-2 parts crosslinking sensitizer.

[0015] By adopting the above technical solution, the insulation layer, along with the semi-conductive conductor shield and the semi-conductive insulating shield, is wrapped around the conductor surface. The semi-conductive conductor shield can homogenize the electric field on the conductor surface, avoiding the risk of insulation breakdown caused by the accumulation of electric field on the conductor surface. The semi-conductive insulating shield can homogenize the electric field on the inner surface of the metal shield, avoiding the risk of insulation breakdown caused by the accumulation of electric field on the inner surface of the metal shield. The insulating material in the insulation layer uses polyethylene as the base material, which ensures good insulation effect while having good flexibility and mechanical strength. Combined with the toughening and bonding effect of EVA, it can improve the adhesion stability of the insulation layer on the conductor surface. With the addition of a copper-resistant agent, the copper-resistant agent forms a stable complex with the copper conductor, reducing the aging rate of the insulation layer and improving the contact stability between the insulation layer and the copper conductor. With the addition of a crosslinking sensitizer, the crosslinking reaction of polyethylene is promoted, increasing the crosslinking density. The crosslinked polyethylene can improve heat resistance, thus meeting the requirements for use in high-temperature and medium-voltage DC cables.

[0016] Preferably, the antioxidant comprises 0.5-2 parts of hindered phenolic primary antioxidant and 0.5-2 parts of thioester secondary antioxidant.

[0017] By adopting the above technical solution, the hindered phenolic primary antioxidant is combined with thioester auxiliary antioxidant to improve the oxidation resistance of the insulation layer and ensure the durability of the cable.

[0018] Preferably, the crosslinking sensitizer is triallyl isocyanurate.

[0019] By adopting the above technical solution, the crosslinking efficiency of triallyl isocyanurate can be improved during the irradiation crosslinking process. After crosslinking, the volume resistivity of the insulation layer is increased and the dielectric constant is more stable. It can still maintain excellent electrical insulation under long-term high temperature environment, meeting the insulation requirements of high-voltage cables. It can also significantly improve the heat resistance, mechanical strength and solvent resistance of the insulation layer, making it less prone to melting and deformation under long-term operation, thus improving the current carrying capacity and service life of the cable. Furthermore, the crosslinked structure is more stable, which can improve the insulation layer's resistance to environmental stress cracking and heat aging, making it suitable for the long-term use requirements of outdoor cables.

[0020] Preferably, the insulating material further includes 2-4 parts compatibilizer, 1-2 parts EPDM, and 1-4 parts nanofiller.

[0021] By employing the above technical solution, nanoparticles can fill the residual micropores and grain boundary gaps in the polyethylene matrix, significantly reducing the internal voids of the insulation layer. Under high-voltage impact, voids are the source of electric field distortion and partial discharge; reducing defects directly lowers the partial discharge initiation voltage and delays insulation aging. Furthermore, the surface of the nanofiller can introduce deep traps to capture space charges accumulated during the impact process, preventing space charge accumulation from causing electric field distortion, reducing the damage to the insulation structure from a single impact, and extending the lifespan under long-term repeated impacts. Additionally, the nanofiller can restrict the movement of polyethylene molecular chains, improving structural stability. As a flexible rubber component, EPDM is dispersed in the matrix in the form of microparticles. On the one hand, it can buffer the thermal stress generated by thermal expansion and contraction, and avoid stress concentration that can cause cracks. On the other hand, when microcracks are generated, EPDM microparticles can absorb the impact energy through the craze-shear yielding mechanism, prevent the crack from propagating, prevent the crack from developing into a breakdown channel, and ensure the structural stability of the insulation layer.

[0022] Compatibilizers can improve the compatibility and bonding of materials such as polyethylene, nanofillers, and EPDM, and increase the density of cross-linked structures, thereby improving the stability and mechanical properties of the insulation layer.

[0023] Preferably, the nanofiller is composed of branched polyethyleneimine-modified hydroxyapatite microspheres and polyethylene glycol diacrylate-modified mesoporous silica in a mass ratio of 1:1-2.

[0024] By adopting the above technical solution, hydroxyapatite microspheres and mesoporous silica utilize their filling and rigid support effects to form a support network within the cross-linked network, improving the strength and impact resistance of the insulation layer. Furthermore, branched polyethyleneimine and polyethylene glycol diacrylate can be radiation-crosslinked. Branched polyethyleneimine exhibits a three-dimensional dendritic structure with primary, secondary, and tertiary amino groups, resulting in more reaction sites and promoting the formation of the cross-linked network. Combined with the polyethylene cross-linked network, this further improves the density of the cross-linked network structure within the insulation layer. HDPE and LLDPE blends have significant differences in melt flowability, leading to uneven extrusion thickness and difficulty in controlling eccentricity. The constraint of the high-density three-dimensional cross-linked network controls the flow and ensures uniformity, thereby reducing the processing shrinkage rate of the insulation layer and ensuring the structural stability and mechanical properties of the insulation layer.

[0025] Branched polyethyleneimine-modified hydroxyapatite microspheres have a high surface amino content, which can connect with materials such as polyethylene, improve the interfacial bonding force between the filler and the matrix, and reduce interfacial defects. After being modified with polyethylene glycol diacrylate, mesoporous silica has unsaturated double bonds grafted on its surface, which can participate in the cross-linking reaction of the insulation layer during the cross-linking process, further enhance the interfacial bonding, prevent crack propagation, improve the tensile strength and impact resistance of the insulation layer, and at the same time improve thermal stability and reduce the risk of insulation layer deformation at high temperatures.

[0026] Branched polyethyleneimine-modified hydroxyapatite microspheres contain polar amino groups, while polyethylene glycol diacrylate-modified mesoporous silica contains polar ester bonds. Both can enhance the overall polarity of the insulating matrix, improve the wettability of the insulating melt on the copper conductor surface, reduce the voids between the insulating layer and the conductor interface, make the interface adhesion tighter, and improve the bonding effect between the insulating layer and the conductor. Furthermore, branched polyethyleneimine-modified hydroxyapatite microspheres and polyethylene glycol diacrylate-modified mesoporous silica can adjust the thermal expansion coefficient of the insulating layer, making it less prone to interface debonding and cracking under repeated high-voltage current impacts, thus ensuring adhesion stability.

[0027] Preferably, the compatibilizer is maleic anhydride-grafted polyethylene.

[0028] By adopting the above technical solution, the compatibility between the nanofiller and polyethylene material in the insulation layer is improved, thereby enhancing the mechanical properties and durability of the insulation layer.

[0029] Secondly, this application provides a method for manufacturing a medium-voltage DC cable resistant to repeated current surges, employing the following technical solution: A method for manufacturing a medium-voltage DC cable resistant to repeated current surges includes the following steps: S1, the middle layer, the second layer and the outer layer are twisted together to obtain a conductor; S2. After co-extruding an insulating composite layer on the conductor surface, radiation cross-linking is performed to obtain the wire core; S2. Apply a fiber tape coated with semiconductor colloid to the surface of the core, wrap it around, apply a copper strip, and finally apply a polymer material as a protective layer. After radiation cross-linking, the finished cable is obtained.

[0030] Preferably, the S2 radiation crosslinking controls the thermal elongation range to 50-100%, resulting in a wire core.

[0031] By adopting the above technical solutions, the radiation cross-linking combined with the thermal extension range ensures the coating effect of the insulation composite layer, reduces partial discharge caused by electric field distortion under repeated impacts of high voltage current, delays insulation aging, and improves long-term impact resistance stability. The fiber tape of semiconductor colloid combined with the metal copper tape can form mechanical protection for the inner insulation layer, avoiding damage to the insulation layer during subsequent processing and laying. In addition, the copper tape can prevent moisture from penetrating into the conductor, prevent water treeing from causing insulation aging, improve long-term operational structural stability, and withstand repeated impacts. The outer protective layer can improve the cable's scratch resistance, impact resistance, and heat aging resistance, extending the cable's service life.

[0032] In summary, this application has the following beneficial effects: 1. The conductors of existing conventional products are generally multiple round copper single wires twisted together to form a conductor. The twisting of all round copper single wires not only increases the gaps between them, but also makes the outer diameter of the conductor too large. This application not only reduces the gaps between the single wires inside the conductor, but also reduces the outer diameter of the conductor, reduces the amount of insulation and sheathing, reduces the weight of the cable, and has the advantage of being lightweight.

[0033] 2. After circular + T-shaped + Z-shaped stranding, the wires of different shapes are interlocked, the interlayer bonding is tighter, the overall structural stability is stronger, and it is not easy to misalign or loosen the strands after repeated thermal expansion and contraction. It can maintain stable conductivity for a long time and has a longer lifespan to withstand impact. At the same time, the circular + T-shaped + Z-shaped stranding structure can improve the surface smoothness. For high-voltage cables, it can make the extruded semi-conductive conductor shielding layer evenly adhere to the conductor surface, avoid the protrusions on the purely circular stranded surface from piercing the semiconductor layer, reduce the electric field concentration problem caused by semiconductor layer defects, and further reduce the risk of partial discharge breakdown under high voltage impact. Attached Figure Description

[0034] Figure 1 These are conductor structure diagrams of Embodiment 1 and Comparative Example 1 of this application; Figure 2 This is a diagram of the insulation extrusion process during the cable manufacturing process of Embodiment 1 of this application; Figure 3 This is a cross-sectional view of the cable in Embodiment 1 of this application. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] Preparation examples of nanofillers Preparation Example 1: The nanofiller was prepared using the following method: Branched polyethyleneimine was placed in water and stirred until completely dissolved to obtain a 2% (w / w) branched polyethyleneimine solution. 100g of hydroxyapatite microspheres were placed in 1000g of the branched polyethyleneimine solution. The average particle size of the hydroxyapatite microspheres was 5μm. The microspheres were ultrasonically dispersed at 60℃ for 30min, and then stirred at 200r / min for 2h to separate the hydroxyapatite microspheres. After drying and dispersion, branched polyethyleneimine-modified hydroxyapatite microspheres with an average particle size of less than 10μm were obtained. Polyethylene glycol diacrylate was dissolved in water and stirred until completely dissolved to obtain a 2% (w / w) polyethylene glycol diacrylate solution. 100g of mesoporous silica was placed in the polyethylene glycol diacrylate solution. The average particle size of the mesoporous silica was 100nm. It was ultrasonically dispersed at 60℃ for 30min, and then stirred at 200r / min for 2h to separate the mesoporous silica. After drying and dispersion, polyethylene glycol diacrylate modified mesoporous silica with an average particle size of less than 200nm was obtained. The nanofiller was obtained by mixing branched polyethyleneimine-modified hydroxyapatite microspheres and polyethylene glycol diacrylate-modified mesoporous silica at a mass ratio of 1:1.5.

[0037] Preparation Example 2: The difference between this preparation example and Preparation Example 1 is that: The nanofiller was obtained by mixing branched polyethyleneimine-modified hydroxyapatite microspheres and polyethylene glycol diacrylate-modified mesoporous silica at a mass ratio of 1:1.

[0038] Preparation Example 3: The difference between this preparation example and Preparation Example 1 is that: The nanofiller was obtained by mixing branched polyethyleneimine-modified hydroxyapatite microspheres and polyethylene glycol diacrylate-modified mesoporous silica at a mass ratio of 1:2.

[0039] Preparation examples of insulating materials Preparation Example 4: The insulating material was prepared using the following method: 60 kg of HDPE, 60 kg of LLDPE, 8 kg of EVA, 2 kg of antioxidant, 0.4 kg of copper inhibitor, 0.3 kg of light stabilizer, and 1.6 kg of crosslinking sensitizer were weighed, mixed, and then extruded and granulated using a twin-screw extruder to obtain an insulating material. The EVA contained 15% VA. The antioxidants included 1 kg of hindered phenolic primary antioxidant and 1 kg of thioester secondary antioxidant. The hindered phenolic primary antioxidant was antioxidant 1076, and the thioester secondary antioxidant was antioxidant DLTDP. The copper inhibitor was antioxidant 1024. The light stabilizer was light stabilizer 622. The crosslinking sensitizer was triallyl isocyanurate. The extruder temperatures were 145℃ in zone 1, 155℃ in zone 2, 155℃ in zone 3, 170℃ in zone 4, 175℃ in zone 5, 180℃ in zone 6, 190℃ in zone 7, and 195℃ in zone 8.

[0040] Preparation Example 5: The difference between this preparation example and Preparation Example 4 is that: Weigh out 50kg of HDPE, 50kg of LLDPE, 5kg of EVA, 1kg of antioxidant, 0.2kg of copper inhibitor, 0.2kg of light stabilizer, and 1kg of crosslinking sensitizer, mix them thoroughly, and then extrude and granulate them using a twin-screw extruder to obtain an insulating material; the antioxidant includes 0.5kg of hindered phenolic primary antioxidant and 0.5kg of thioester secondary antioxidant.

[0041] Preparation Example 6: The difference between this preparation example and Preparation Example 4 is that: Weigh 70kg of HDPE, 70kg of LLDPE, 10kg of EVA, 4kg of antioxidant, 0.5kg of copper inhibitor, 0.5kg of light stabilizer, and 2kg of crosslinking sensitizer, mix them thoroughly, and then extrude and granulate them using a twin-screw extruder to obtain the insulating material. The antioxidant includes 2kg of hindered phenolic primary antioxidant and 2kg of thioester secondary antioxidant.

[0042] Preparation Example 7: The difference between this preparation example and Preparation Example 4 is that: The raw materials also include 3 kg of compatibilizer, 1.5 kg of EPDM and 2.5 kg of nanofiller. The nanofiller is the nanofiller prepared in Preparation Example 1, and the compatibilizer is maleic anhydride-grafted polyethylene.

[0043] Preparation Example 8: The difference between this preparation example and Preparation Example 7 is that: The raw materials also include 2 kg of compatibilizer, 1 kg of EPDM and 1 kg of nanofiller. The nanofiller is the nanofiller prepared in Preparation Example 2, and the compatibilizer is maleic anhydride-grafted polyethylene.

[0044] Preparation Example 9: The difference between this preparation example and Preparation Example 7 is that: The raw materials also include 4 kg of compatibilizer, 2 kg of EPDM and 4 kg of nanofiller. The nanofiller is the nanofiller prepared in Preparation Example 3 and the compatibilizer is maleic anhydride-grafted polyethylene. Example

[0045] The semiconducting conductor shielding uses semiconducting conductor shielding polymer material from Jiangyin Haijiang Polymer Materials Co., Ltd., inner shield HJ0331; the semiconducting insulating shielding uses semiconducting insulating shielding polymer material from Jiangyin Haijiang Polymer Materials Co., Ltd., outer shield HJ0631; other raw materials are all commercially available.

[0046] Example 1: A medium-voltage DC cable resistant to repeated current surges: S1. The core layer of the conductor consists of 19 round copper wires forming a 1+6+12 structure. Six copper wires are evenly wrapped around one copper wire, and twelve copper wires are evenly wrapped around six copper wires. The 1+6+12 structure is concentrically arranged. The second layer consists of 18 copper wires rolled into a T-shape and arranged around the core layer. The outer layer consists of 24 copper wires rolled into a Z-shape and arranged around the second layer. The conductor cross-section of each copper wire is 300mm². 2 The conductor has a diameter of 3.33 mm and is formed by twisting together the core layer, the second layer, and the outer layer (see conductor). Figure 3 (Sequence number 1), the conductor exhibits a 1+6+12+18+24 twisted structure (see...) Figure 1(Left side structure) S2. The conductor surface is co-extruded with three layers: a semiconducting conductor shield, an insulating layer, and a semiconducting insulating shield (see extrusion steps). Figure 2 After treatment, an insulating composite layer is formed. The insulating material used is the same as that prepared in Preparation Example 4. The nominal thickness of the insulating composite layer is 4 mm. Then, irradiation crosslinking is performed. The number of crosslinking channels is 6n, the irradiation energy is 2.7 MeV, the irradiation metering is 12 Mrad, the beam current is 30 mA, and the wire exit speed is 23 m / min. The core is obtained by controlling the thermal elongation range to 70-80%. S2. Apply a fiber tape coated with semiconductor colloid to the surface of the wire core (see...) Figure 3 (Item No. 3), evenly wrapped, with an overlap rate of 25%, and the nominal thickness of the fiber bag is 0.2mm; then a metal copper strip is applied to the surface (see...). Figure 3 (Item No. 4), with an overlap rate of 25% and a nominal thickness of 0.15mm for the copper strip; finally, a polymer material is applied as a protective layer (see...). Figure 3 (Serial number 5), the nominal thickness of the protective layer is 3mm; after radiation cross-linking, the number of cross-linking channels is 14n, the irradiation energy is 2.1MeV, the irradiation metering is 12Mrad, the beam current is 25mA, and the output speed is 17m / min, the finished cable is obtained.

[0047] Example 2: The difference between this example and Example 1 is that: S2. The conductor surface is co-extruded with three layers: a semiconducting conductor shield, an insulating layer, and a semiconducting insulating shield (see extrusion steps). Figure 2 After treatment, an insulating composite layer is formed. The insulating material used is the same as that prepared in Preparation Example 4. The nominal thickness of the insulating composite layer is 3 mm. Then, it is subjected to irradiation crosslinking. The core is obtained by controlling the thermal elongation range to 50-70%.

[0048] Example 3: The difference between this example and Example 1 is that: S2. The conductor surface is co-extruded with three layers: a semiconducting conductor shield, an insulating layer, and a semiconducting insulating shield (see extrusion steps). Figure 2 After treatment, an insulating composite layer is formed. The insulating material used is the same as that prepared in Preparation Example 4. The nominal thickness of the insulating composite layer is 5 mm. Then, it is subjected to irradiation crosslinking. The core is obtained by controlling the thermal elongation range to 80-100%.

[0049] Example 4: The difference between this example and Example 1 is that: The insulating material used was the insulating material prepared in Preparation Example 7.

[0050] Example 5: The difference between this example and Example 4 is that: The insulating material used was the insulating material prepared in Preparation Example 8.

[0051] Example 6: The difference between this example and Example 4 is that: The insulating material used was the insulating material prepared in Preparation Example 9.

[0052] Example 7: The difference between this example and Example 4 is that: In the preparation of insulating materials, the nanofiller replaces the esterified polyethyleneimine-modified hydroxyapatite microspheres with hydroxyapatite microspheres of equal mass, and replaces the polyethylene glycol-modified mesoporous silica with mesoporous silica of equal mass.

[0053] Example 8: The difference between this example and Example 4 is that: No nanofillers were added during the preparation of the insulating material.

[0054] Comparative Example Comparative Example 1: The difference between this comparative example and Example 1 is that: See conductor structure Figure 1 The structure diagram on the right is entirely made of round wires.

[0055] Performance testing 1. Performance testing of the insulation layer The insulation layer in the cable was prepared using the methods described in Examples 1-8. The tensile strength and elongation at break of the insulation layer were tested according to GB / T2951.11-2008, the thermal extension was tested according to GB / T2951.21-2008, and the volume resistivity at 20°C was tested according to GB / T31838.2-2019. The data were recorded. The change rate of tensile strength of the insulation layer was recorded after aging at 180°C for 7 days. The aging time of the insulation layer with conductor was recorded at 150°C.

[0056] Table 1 Insulation Layer Performance Test Table (In the table, " / " indicates that the corresponding embodiment did not test this item and there is no data)

[0057] 2. Performance Testing Cables were prepared using the methods of Examples 1, 4, 7-8 and Comparative Example 1, respectively. The cables were subjected to 20 impacts each on the positive and negative sides at 20kV. The area of ​​cracks and expansion cracks in the insulation layer was recorded. The larger the area of ​​cracks and expansion cracks, the less resistant the cable was to repeated impacts from high voltage current. The total area data was recorded.

[0058] Table 2 Performance Test Table

[0059] As can be seen from Examples 1-3 and Table 1, the cable prepared in this application has the advantages of being lightweight and resistant to current surges, and the insulation layer has good strength, toughness and heat resistance, which can further ensure the cable's resistance to current surges and extend the cable's service life.

[0060] As can be seen from Examples 1 and 4-6 and Table 1, compatibilizers can improve the compatibility and bonding of materials such as polyethylene, nanofillers, and EPDM. EPDM, as a flexible rubber component, ensures the strength and flexibility of the cable and can also improve the structural stability and durability of the cable.

[0061] Combining Examples 4 and 7-8 with Table 1, it can be seen that in the preparation of the insulation material in Example 7, the nanofiller replaced the esterified polyethyleneimine-modified hydroxyapatite microspheres with an equal mass of hydroxyapatite microspheres, and the mesoporous silica replaced the polyethylene glycol-modified mesoporous silica with an equal mass of mesoporous silica. Compared with Example 4, the strength of Example 7 is lower than that of Example 4, the thermal elongation is higher than that of Example 4, and the total area of ​​cracks and expansion cracks is larger than that of Example 4. This indicates that branched polyethyleneimine and polyethylene glycol diacrylate can crosslink, improve the density of the crosslinked network structure inside the insulation layer, and, together with the filling and supporting effect of hydroxyapatite microspheres and mesoporous silica, further improve the strength and heat resistance. At the same time, it increases the bonding density of the insulation layer on the conductor surface, prevents cracking, and improves the structural stability and durability of the finished cable.

[0062] In Example 8, no nanofiller was added during the preparation of the insulation material. Compared with Example 4, the strength of Example 8 was lower than that of Example 4, the thermal elongation was higher than that of Example 4, and the total area of ​​cracks and expansion cracks was larger than that of Example 4. This indicates that the nanofiller can fill the micropores and grain boundary gaps remaining in the polyethylene matrix, significantly reduce the voids inside the insulation layer, reduce the damage of current impact to the insulation structure, and extend the life under long-term repeated impact. In addition, the nanofiller can restrict the movement of polyethylene molecular chains and improve the durability of the cable.

[0063] Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that all conductors in Comparative Example 1 are round wires, and the total area of ​​cracks and expansion cracks in Comparative Example 1 is larger than that in Example 1. This indicates that after the conductor is twisted in a 1+6+12 structure with round + T-shaped + Z-shaped strands, the wires of different shapes are interlocked, the interlayer bonding is tighter, the overall structural stability is stronger, and it is not easy to misalign or loosen the strands after repeated thermal expansion and contraction. It can maintain stable conductivity for a long time, giving the cable the advantage of being able to withstand repeated impacts of high voltage current and improving the service life of the cable.

[0064] 3. Mild-type test Cables were prepared using the methods of Example 1 and Comparative Example 1, respectively. The mass difference between the cable mass of Comparative Example 1 and the cable mass of Example 1 was recorded. The larger the mass difference, the better the lightweight effect of Example 1. A mass difference of 15% indicates that the prepared cable has the advantage of being lightweight.

[0065] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A medium-voltage DC cable resistant to repeated current surges, characterized in that, The cable comprises a conductor, an insulating composite layer, a fiber tape, a copper strip, and a protective layer. The conductor is made by stranding a central layer, a secondary layer, and an outer layer. The central layer is composed of 19 round copper single wires forming a 1+6+12 structure. The secondary layer is made of 18 copper single wires rolled into a T-shape and arranged around the periphery of the central layer. The outer layer is made of 24 copper single wires rolled into a Z-shape and arranged around the periphery of the secondary layer.

2. The medium-voltage DC cable resistant to repeated current surges according to claim 1, characterized in that: The 1+6+12 structure is as follows: 6 copper single wires are evenly wrapped around 1 copper single wire, and 12 copper single wires are evenly wrapped around 6 copper single wires.

3. A medium-voltage DC cable resistant to repeated current surges according to claim 1, characterized in that, The insulating composite layer is formed by co-extrusion of three layers: a semi-conductive conductor shield, an insulating layer, and a semi-conductive insulating shield. The insulating material in the insulating layer contains the following raw materials in parts by weight: 50-70 parts HDPE, 50-70 parts LLDPE, 5-10 parts EVA, 1-4 parts antioxidant, 0.2-0.5 parts copper inhibitor, 0.2-0.5 parts light stabilizer, and 1-2 parts crosslinking sensitizer.

4. A medium-voltage DC cable resistant to repeated current surges according to claim 3, characterized in that, The antioxidants include 0.5-2 parts of hindered phenolic primary antioxidants and 0.5-2 parts of thioester secondary antioxidants.

5. A medium-voltage DC cable resistant to repeated current surges according to claim 3, characterized in that, The crosslinking sensitizer is triallyl isocyanurate.

6. A medium-voltage DC cable resistant to repeated current surges according to claim 3, characterized in that, The insulating material also includes 2-4 parts compatibilizer, 1-2 parts EPDM, and 1-4 parts nanofiller.

7. A medium-voltage DC cable resistant to repeated current surges according to claim 6, characterized in that, The nanofiller consists of branched polyethyleneimine-modified hydroxyapatite microspheres and polyethylene glycol diacrylate-modified mesoporous silica in a mass ratio of 1:1-2.

8. A medium-voltage DC cable resistant to repeated current surges according to claim 6, characterized in that, The compatibilizer is maleic anhydride-grafted polyethylene.

9. A method for preparing a medium-voltage DC cable resistant to repeated current surges as described in any one of claims 1-8, characterized in that, Includes the following steps: S1, the middle layer, the second layer and the outer layer are twisted together to obtain a conductor; S2. After co-extruding an insulating composite layer on the conductor surface, radiation cross-linking is performed to obtain the wire core; S2. Apply a fiber tape coated with semiconductor colloid to the surface of the core, wrap it around, apply a copper strip, and finally apply a polymer material as a protective layer. After radiation cross-linking, the finished cable is obtained.

10. A method for manufacturing a medium-voltage DC cable resistant to repeated current surges according to claim 9, characterized in that, The S2 radiation crosslinking controls the thermal elongation range to 50-100%, resulting in a wire core.

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