Nano-composite polypropylene insulating material ultrahigh-voltage cable and preparation process thereof

Abstract

The invention discloses a nano-composite polypropylene insulating material ultrahigh-voltage cable and a preparation process thereof, and belongs to the technical field of ultrahigh-voltage cables, the cable comprises a conductor, an insulating layer, a shielding layer and a sheath layer, the insulating layer is prepared from a composite material containing polypropylene matrix resin, a nano-modified filler, a space charge inhibitor and the like, and the shielding layer is prepared from a composite material containing polypropylene matrix resin; the conductor is of a multi-segmentation fan-shaped stranded structure, and the sheath layer is made of a low-smoke halogen-free flame-retardant polyolefin material; according to the preparation process, ultrasonic-microwave synergistic modification of the nano filler is adopted, premixing, melting granulation, three-layer co-extrusion molding, precise cross-linking and gradient cooling post-treatment are performed, and the gel content is 60-80%, and the insulation eccentricity is smaller than or equal to 0.5%. The breakdown strength of the cable is larger than or equal to 350 kV / mm, the space charge accumulation amount is greatly reduced, the long-term working temperature reaches 105 DEG C or above, the process is controllable, industrialization is easy, and the cable is suitable for ultrahigh-voltage power transmission of 110 kV or above.

Description

Technical Field

[0001] This invention relates to the field of ultra-high voltage cable technology, and in particular to an ultra-high voltage cable with nano-composite polypropylene insulation material and its preparation process. Background Technology

[0002] With the rapid development of the power industry, 110kV and above ultra-high voltage transmission lines have become the core carriers for long-distance energy transmission. The insulation performance of cables directly determines the safety and stability of the transmission system. Currently, the mainstream insulation material for ultra-high voltage cables is cross-linked polyethylene. However, this material has defects such as low temperature resistance, poor aging resistance, and high dielectric loss. Moreover, by-products are easily generated during the cross-linking process, leading to space charge accumulation and electric field distortion, which in turn causes insulation aging, breakdown, and other faults.

[0003] Polypropylene (PP) has become an ideal substitute for ultra-high voltage cable insulation materials due to its high melting point, excellent chemical stability, good dielectric properties, and low raw material cost. However, pure PP suffers from insufficient mechanical strength and significant low-temperature brittleness, requiring nanocomposite modification to improve its performance. However, nanofillers are prone to agglomeration and have poor dispersion in the PP matrix, resulting in unsatisfactory modification effects. Furthermore, precise control of the PP crosslinking reaction is difficult; insufficient crosslinking leads to insufficient mechanical strength and heat resistance, while excessive crosslinking results in brittleness and decreased dielectric properties. In addition, existing PP insulated cable manufacturing processes suffer from problems such as large insulation layer eccentricity, significant conductor skin effect, and easy accumulation of space charge, limiting its application in ultra-high voltage power transmission.

[0004] While existing technologies include research on nanocomposite polypropylene insulation materials, most focus on formulation optimization or single modification methods, failing to achieve synergistic improvement in material properties and cable forming processes. Furthermore, they haven't effectively addressed core technical challenges in ultra-high voltage cables such as space charge accumulation and insulation eccentricity. Therefore, developing an ultra-high voltage cable with superior overall performance, a controllable manufacturing process, and the ability to suppress space charge accumulation using nanocomposite polypropylene insulation materials, along with its manufacturing process, has become crucial for the industry's development. Summary of the Invention

[0005] The technical problem to be solved by this invention is that current cable nanofillers suffer from agglomeration, difficulty in controlling cross-linking degree, accumulation of space charge, and large insulation eccentricity.

[0006] The technical solution adopted by this invention to solve its technical problem is: a nano-composite polypropylene insulation material ultra-high voltage cable, comprising a conductor, an insulation layer covering the outside of the conductor, and a sheath layer. The insulation layer is prepared from nano-composite polypropylene insulation material, which, by weight, comprises: 60-80 parts of polypropylene matrix resin, 5-15 parts of nano-modified filler, 0.5-3 parts of crosslinking agent, 0.1-1 parts of antioxidant, 1-5 parts of compatibilizer, 0.1-0.8 parts of lubricant, and 0.2-1 parts of space charge inhibitor; the space charge inhibitor is nano-zirconia with a particle size of 10-30 nm, and modified by KH-570 silane coupling agent.

[0007] The polypropylene matrix resin is homopolymer polypropylene with a melt index of 0.5-2 g / 10 min and isotacticity ≥95%; the nano-modified filler is nano-silica modified with a silane coupling agent or organically modified sodium-based montmorillonite, with nano-silica particle size of 10-50 nm and specific surface area of ​​100-300 m2 / g, and organically modified sodium-based montmorillonite interlayer spacing ≥3 nm.

[0008] The crosslinking agent is a compound of dicumyl peroxide and trimethylolpropane trimethacrylate, with a mass ratio of 1:1-3; the antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, with a mass ratio of 1:1-2; the compatibilizer is maleic anhydride-grafted polypropylene with a grafting rate of 0.5-2%; and the lubricant is calcium stearate or ethylene bis-stearamide.

[0009] The conductor is a multi-segmented, tightly stranded fan-shaped conductor with 6-12 segments and a stranding pitch ratio of 10-15. A reinforcing core tube is provided at the center of the conductor to house the internal temperature monitoring and heat dissipation efficiency by introducing fluid. The sheath is a low-smoke, halogen-free, flame-retardant polyolefin sheath with an oxygen index ≥32%.

[0010] A process for preparing an ultra-high voltage cable with nano-composite polypropylene insulation material includes the following steps: S1. Preparation of nano-modified fillers: The nano-fillers and space charge inhibitors were modified with silane coupling agents by ultrasonic-microwave synergistic modification method to obtain modified nano-fillers and modified space charge inhibitors. S2. Preparation of premix: Polypropylene matrix resin, modified nanofiller, modified space charge inhibitor, antioxidant, compatibilizer and lubricant are added to a high-speed mixer and mixed to obtain a premix; S3. Melt blending and granulation: The premixed material is added to a twin-screw extruder, and a crosslinking agent is added to the side feeder. After melt blending, the material is extruded and granulated to obtain nano-composite polypropylene insulating particles. S4. Cable forming: A three-layer co-extrusion process is adopted. After preheating the conductor stranded on the outside of the reinforcing core tube, the insulation layer, shielding layer and sheath layer are extruded in sequence to achieve seamless coverage between the insulation layer and the conductor. S5. Crosslinking treatment: The formed cable is subjected to warm water bath or steam crosslinking, and the crosslinking parameters are controlled to make the gel content of the insulation material 60-80%; S6. Post-processing: The cross-linked cable is subjected to segmented cooling, intelligent tension control and performance testing to obtain the finished ultra-high voltage cable.

[0011] The specific operation of the ultrasonic-microwave synergistic modification method described in step S1 is as follows: the nanofiller / space charge inhibitor is added to anhydrous ethanol and ultrasonically dispersed at a power of 300-500W and a frequency of 20-40kHz, while simultaneously being irradiated with microwaves at a power of 200-400W and a frequency of 2450MHz for 30-60 minutes to obtain a dispersion with a mass concentration of 5-10%; 2-5% by mass of silane coupling agent is added to the nanofiller / space charge inhibitor and the mixture is stirred at 60-80℃ for 2-4 hours; after centrifugation, the mixture is vacuum dried to obtain the modified product.

[0012] In step S2, the mixing temperature of the high-speed mixer is 80-100℃, the rotation speed is 1000-1500r / min, and the mixing time is 10-20min; in step S3, the length-to-diameter ratio of the twin-screw extruder is 36:1-40:1, the screw speed is 300-500r / min, the temperature of each section is 160-190℃, and the water cooling temperature is 20-30℃.

[0013] The three-layer co-extrusion process described in step S4 adopts a high-precision temperature control system and multi-screw collaborative extrusion, with a temperature control accuracy of ±1℃, an insulation layer extrusion pressure of 80-120MPa, a holding pressure of 50-80MPa, a holding time of 5-15s, a processing temperature of 170-200℃, and a cable insulation eccentricity of ≤0.5%.

[0014] In step S5, the crosslinking treatment temperature is 160-180℃, the pressure is 0.1-0.3MPa, and the crosslinking time is 1-3h. The gel content is detected by Soxhlet extraction, and the amount of crosslinking agent, crosslinking temperature, or crosslinking time is adjusted according to the detection results.

[0015] In step S6, segmented cooling adopts gradient water cooling, with cooling water temperatures of 60-70℃, 40-50℃, and 20-30℃ respectively, and a cooling rate of 5-8℃ / min; the tension fluctuation range of intelligent tension control is ≤±5%; performance testing includes insulation layer breakdown strength, dielectric loss, and space charge accumulation testing, among which the room temperature DC breakdown strength is ≥350kV / mm, and the space charge accumulation at 90℃ is reduced by more than 90% compared with cross-linked polyethylene.

[0016] The beneficial effects of this invention are: (1) By introducing space charge inhibitor nano-zirconia and combining it with ultrasonic + microwave synergistic modification of nano-fillers, the present invention enables the room temperature DC breakdown strength of the insulating material to be ≥350kV / mm, the accumulated space charge at 90℃ to be reduced by more than 90% compared with cross-linked polyethylene, the long-term working temperature to be above 105℃, the aging resistance and dielectric properties to be greatly improved, and the problems of easy accumulation of space charge and electric field distortion of traditional polypropylene insulating materials are solved. (2) The ultrasonic-microwave synergistic modification method breaks through the limitations of single ultrasonic modification, realizes efficient dispersion of nanoparticles, effectively solves the problem of nanofiller agglomeration, enhances the interfacial bonding force between nanofiller and polypropylene matrix, and gives full play to the modification effect of nanofiller. (3) A crosslinking control system of compound crosslinking agent + side feeding addition + real-time detection of gel content is adopted to accurately control the gel content at 60-80%, avoid material performance defects caused by excessive or insufficient crosslinking, and ensure excellent mechanical strength and flexibility of the insulating material. (4) The three-layer co-extrusion process combined with high-precision temperature control and multi-screw synergistic extrusion technology makes the cable insulation eccentricity ≤0.5%; the multi-segment fan-shaped tightly stranded conductor effectively reduces the skin effect; segmented cooling and intelligent tension control avoid internal stress and deformation of the cable, and improve the overall forming quality of the cable; (5) The prepared ultra-high voltage cable has low conductor resistance, excellent insulation performance and good flame retardancy. It is suitable for 110kV and above ultra-high voltage transmission lines. Moreover, the preparation process is highly controllable and easy to industrialize, which has good economic and social benefits. (6) One end of the reinforced core tube is connected to an external flow pump to draw the fluid in the middle outward. The air inlet of the reinforced core tube and the external flow pump is connected through an external flow pipe. Temperature sensor and flow sensor are set at the air inlet to monitor temperature and flow, greatly improving functionality. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Figure 1 This is a schematic diagram of the cross-sectional structure of the ultra-high voltage cable made of nanocomposite polypropylene insulation material of the present invention.

[0019] Figure 2 This is a structural schematic diagram of the end position of the present invention.

[0020] Figure 3 This is a process flow diagram for preparing ultra-high voltage cables using nanocomposite polypropylene insulation material according to the present invention.

[0021] In the diagram: 1. Conductor, 2. Insulation layer, 3. Shielding layer, 4. Sheath layer, 5. Reinforcing core tube, 6. External flow pump, 7. External flow tube, 8. Temperature sensor, 9. Flow sensor. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Figure 1 , Figure 2 and Figure 3 The illustrated ultra-high voltage cable with nano-composite polypropylene insulation material includes a conductor 1, an insulation layer 2 covering the outside of the conductor 1, and a sheath layer 4 covering the outside of the insulation layer 2. The insulation layer 2 is made of nano-composite polypropylene insulation material. One end of the reinforcing core tube 5 can be connected to an external flow pump 6 to draw fluid from the middle section outwards. An external flow pipe 7 connects the reinforcing core tube 5 and the air inlet of the external flow pump 6. A temperature sensor 8 and a flow sensor 9 are installed at the air inlet for temperature and flow monitoring. The external flow pump 6 controls the single-time pumping flow rate based on a preset internal fluid volume in the cable. Normally, continuous temperature regulation and heat dissipation are achieved through pumping. When a significant temperature change occurs, pumping is stopped, and then a single pumping cycle is performed. Based on the pumping time and temperature changes—for example, when the pumping time reaches halfway, the flow rate reaches halfway, and the temperature reaches its maximum value—it can be determined that the high-temperature location is approximately in the middle section.

[0025] Example 1, Material formulation: By weight, 70 parts homopolymer polypropylene with a melt index of 1 g / 10 min and isotacticity of 96%; 10 parts modified nano-silica with a particle size of 20 nm and a specific surface area of ​​200 m². 2 / g, 2 parts crosslinking agent with DCP:TMPTMA=1:2, 0.5 parts antioxidant with 1010:168=1:1.5, 3 parts PP-g-MAH with a grafting rate of 1%, 0.4 parts calcium stearate, 0.5 parts modified nano-zirconia with a particle size of 20nm, modified with KH-570.

[0026] Preparation process: S1, Modified nanomaterials: Nano-silica and nano-zirconia were added to anhydrous ethanol and irradiated with ultrasonication at 400W and 30kHz + microwave at 300W for 45min to obtain an 8% mass concentration dispersion; 3% mass of KH-550 and KH-570 were added and stirred at 70℃ for 3h; centrifuged at 4000r / min for 12min and vacuum dried at 90℃ for 5h to obtain the modified product; S2, Premix: Add each component to a high-speed mixer and mix at 90℃ and 1200r / min for 15min; S3. Granulation: Twin-screw extruder (length-to-diameter ratio 38:1), 350r / min, temperature of each section 170-185℃, side feeding with crosslinking agent, water cooling and pelletizing at 25℃. S4, Three-layer co-extrusion: Temperature control accuracy ±1℃, insulation layer 2 extrusion pressure 100MPa, holding pressure 65MPa, holding time 10s, processing temperature 185℃, conductor 1 is an 8-segment sector stranded conductor, insulation layer 2 eccentricity 0.4%; S5, Crosslinking: Crosslinking at 170℃ and 0.2MPa for 2 hours, gel content 72%; S6. Post-processing: Gradient water cooling (65℃→45℃→25℃), cooling rate 6℃ / min, tension fluctuation ±3%, and the finished product is obtained after passing the performance test.

[0027] Example 2, material formulation: by weight, 65 parts homopolymer polypropylene with a melt index of 0.8 g / 10 min and isotacticity of 95%; 12 parts modified montmorillonite with an interlayer spacing of 3.5 nm; 1.5 parts crosslinking agent with a DCP:TMPTMA ratio of 1:1; 0.8 parts antioxidant with a 1010:168 ratio of 1:2; 4 parts PP-g-MAH with a grafting rate of 1.5%; 0.5 parts EBS; 0.8 parts modified nano-zirconia with a particle size of 15 nm, modified with KH-570.

[0028] Preparation process: Same as in Example 1. After crosslinking, the gel content of the insulating layer 2 material is 75%, the eccentricity of the insulating layer 2 is 0.3%, and the DC breakdown strength at room temperature is 365kV / mm.

[0029] The ultra-high voltage cable prepared in the above embodiments, after testing, has a space charge accumulation of more than 95% at 90℃ compared to XLPE, a long-term operating temperature of up to 110℃, a dielectric loss of insulation layer 2 of ≤0.002, and an aging resistance performance that is more than 50% higher than that of traditional polypropylene insulated cables, fully meeting the usage requirements of 110kV and above ultra-high voltage transmission lines.

[0030] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A nano-composite polypropylene insulation material ultra-high voltage cable, comprising a conductor (1), an insulation layer (2) covering the outside of the conductor (1), and a sheath layer (4), characterized in that, The insulating layer (2) is prepared from nano-composite polypropylene insulating material, which comprises, by weight: 60-80 parts of polypropylene matrix resin, 5-15 parts of nano-modified filler, 0.5-3 parts of crosslinking agent, 0.1-1 parts of antioxidant, 1-5 parts of compatibilizer, 0.1-0.8 parts of lubricant, and 0.2-1 parts of space charge inhibitor; the space charge inhibitor is nano-zirconia with a particle size of 10-30 nm, and modified by KH-570 silane coupling agent.

2. The ultra-high voltage cable with nano-composite polypropylene insulation material according to claim 1, characterized in that, The polypropylene matrix resin is homopolymer polypropylene with a melt index of 0.5-2 g / 10 min and isotacticity ≥95%; the nano-modified filler is nano-silica modified with a silane coupling agent or organically modified sodium-based montmorillonite, with a nano-silica particle size of 10-50 nm and a specific surface area of ​​100-300 m². 2 / g, with an organically modified sodium-based montmorillonite interlayer spacing ≥3nm.

3. The ultra-high voltage cable with nano-composite polypropylene insulation material according to claim 1, characterized in that, The crosslinking agent is a compound of dicumyl peroxide and trimethylolpropane trimethacrylate, with a mass ratio of 1:1-3; the antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, with a mass ratio of 1:1-2; the compatibilizer is maleic anhydride-grafted polypropylene with a grafting rate of 0.5-2%; and the lubricant is calcium stearate or ethylene bis-stearamide.

4. The ultra-high voltage cable with nano-composite polypropylene insulation material according to claim 1, characterized in that, The conductor (1) is a multi-segmented fan-shaped tightly stranded conductor with 6-12 segments and a stranding pitch ratio of 10-15. A reinforcing core tube (5) is provided at the center of the conductor (1) to house the internal temperature monitoring and heat dissipation efficiency enhanced by introducing fluid. The sheath layer (4) is a low-smoke halogen-free flame-retardant polyolefin sheath with an oxygen index ≥32%.

5. A process for preparing an ultra-high voltage cable with nano-composite polypropylene insulation material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of nano-modified fillers: The nano-fillers and space charge inhibitors were modified with silane coupling agents by ultrasonic-microwave synergistic modification method to obtain modified nano-fillers and modified space charge inhibitors. S2. Preparation of premix: Polypropylene matrix resin, modified nanofiller, modified space charge inhibitor, antioxidant, compatibilizer and lubricant are added to a high-speed mixer and mixed to obtain a premix; S3. Melt blending and granulation: The premixed material is added to a twin-screw extruder, and a crosslinking agent is added to the side feeder. After melt blending, the material is extruded and granulated to obtain nano-composite polypropylene insulating particles. S4. Cable forming: The three-layer co-extrusion process is adopted. After the conductor (1) stranded on the outside of the reinforcing core tube (5) is preheated, the insulation layer (2), shielding layer (3) and sheath layer (4) are extruded in sequence to achieve seamless coverage between the insulation layer (2) and the conductor (1). S5. Crosslinking treatment: The formed cable is subjected to warm water bath or steam crosslinking, and the crosslinking parameters are controlled so that the gel content of the insulation layer (2) material is 60-80%; S6. Post-processing: The cross-linked cable is subjected to segmented cooling, intelligent tension control and performance testing to obtain the finished ultra-high voltage cable.

6. The preparation process according to claim 5, characterized in that, The specific operation of the ultrasonic-microwave synergistic modification method described in step S1 is as follows: the nanofiller / space charge inhibitor is added to anhydrous ethanol and ultrasonically dispersed at a power of 300-500W and a frequency of 20-40kHz, while simultaneously being irradiated with microwaves at a power of 200-400W and a frequency of 2450MHz for 30-60 minutes to obtain a dispersion with a mass concentration of 5-10%; 2-5% by mass of silane coupling agent is added to the nanofiller / space charge inhibitor and the mixture is stirred at 60-80℃ for 2-4 hours; after centrifugation, the mixture is vacuum dried to obtain the modified product.

7. The preparation process according to claim 5, characterized in that, In step S2, the mixing temperature of the high-speed mixer is 80-100℃, the rotation speed is 1000-1500r / min, and the mixing time is 10-20min; in step S3, the length-to-diameter ratio of the twin-screw extruder is 36:1-40:1, the screw speed is 300-500r / min, the temperature of each section is 160-190℃, and the water cooling temperature is 20-30℃.

8. The preparation process according to claim 5, characterized in that, The three-layer co-extrusion process described in step S4 adopts a high-precision temperature control system and multi-screw co-extrusion, with a temperature control accuracy of ±1℃. The extrusion pressure of the insulation layer (2) is 80-120MPa, the holding pressure is 50-80MPa, the holding time is 5-15s, the processing temperature is 170-200℃, and the cable insulation eccentricity is ≤0.5%.

9. The preparation process according to claim 5, characterized in that, In step S5, the crosslinking treatment temperature is 160-180℃, the pressure is 0.1-0.3MPa, and the crosslinking time is 1-3h. The gel content is detected by Soxhlet extraction, and the amount of crosslinking agent, crosslinking temperature, or crosslinking time is adjusted according to the detection results.

10. The preparation process according to claim 5, characterized in that, In step S6, the segmented cooling adopts gradient water cooling, with cooling water temperatures of 60-70℃, 40-50℃, and 20-30℃ respectively, and a cooling rate of 5-8℃ / min; the tension fluctuation range of intelligent tension control is ≤±5%; the performance test includes the insulation layer (2) breakdown strength, dielectric loss, and space charge accumulation test, of which the room temperature DC breakdown strength is ≥350kV / mm, and the space charge accumulation at 90℃ is reduced by more than 90% compared with cross-linked polyethylene.

Images