High-voltage cable insulating material and preparation process thereof

Abstract

The invention discloses a high-voltage cable insulating material and a preparation method thereof. The material is composed of a crosslinked polyethylene matrix, nano silicon particles coated with polyethylene glycol on the surfaces, nano silicon dioxide particles modified by a silane coupling agent, an antioxidant and a coupling agent, the particle size of the nano silicon is 1-10 nm, the mass ratio of the nano silicon particles to the silane coupling agent is 1.0-2.0%, the particle size of the nano silicon dioxide is 20-50 nm, the mass ratio of the nano silicon dioxide particles to the silane coupling agent is 3.0-5.0%, and the mass ratio of the nano silicon particles to the coupling agent is 1: 2-1: 4. The preparation method comprises the following steps: respectively carrying out surface modification and coating on the nano filler, realizing uniform dispersion of the nano filler in a matrix by adopting a two-step blending process, and then carrying out irradiation crosslinking and molding. According to the invention, through compounding and synergism of nano silicon and nano silicon dioxide, the dielectric strength and heat-conducting property of the material are remarkably improved, partial discharge is effectively inhibited, the service life is prolonged, and the material is suitable for insulation of high-voltage cables of 500kV and above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable materials, in particular to a high-voltage cable insulation material and a preparation process thereof. BACKGROUND

[0002] When used as a high-voltage cable insulation material, traditional cross-linked polyethylene (XLPE) has the problems of limited dielectric strength (usually 30-35 kV / mm), poor thermal conductivity (thermal conductivity coefficient of about 0.3 W / m·K), high partial discharge (usually 50-100 pC) due to easy accumulation of space charge, and insufficient long-term thermal aging life (about 40 years) in the application of 500 kV and above voltage grades. In the prior art, there are schemes for modifying with single nano-silicon (Si) particles, which can improve the thermal conductivity (to about 0.8 W / m·K) and breakdown field strength to a certain extent, but the nano-silicon is easy to be oxidized and deactivated, the process is complex and the cost increases greatly; there are also schemes for modifying with single nano-silicon dioxide (SiO2), which performs well in improving dielectric properties (breakdown field strength can reach 42-45 kV / mm) and suppressing partial discharge, but the thermal conductivity coefficient is limited (about 0.9 W / m·K), which is difficult to meet the stringent requirements of super-high voltage cables on heat dissipation performance. At present, there is no disclosed technical scheme for compounding nano-silicon and nano-silicon dioxide in a specific ratio and process and applying them to high-voltage cable insulation materials to solve the above-mentioned comprehensive performance bottlenecks. SUMMARY

[0003] (I) Technical problem

[0004] The present application provides a high-voltage cable insulation material capable of synergistically improving dielectric strength, thermal conductivity, significantly suppressing partial discharge, and prolonging service life, and a preparation method thereof.

[0005] (II) Technical content

[0006] To solve the above technical problems, the technical scheme of the present application is as follows: a high-voltage cable insulation material, comprising the following components by mass percentage:

[0007] 93.0-94.0wt% of cross-linked polyethylene (XLPE) matrix;

[0008] 1.0-2.0wt% of nano-silicon particles with a particle size of 1-10 nm;

[0009] 3.0-5.0wt% of nano-silicon dioxide particles with a particle size of 20-50 nm;

[0010] 0.3-0.7wt% of coupling agent;

[0011] 0.3-0.7wt% of antioxidant;

[0012] The mass ratio of the nanosilicon to the nanosilica is 1:2 to 1:4.

[0013] Further, the surface of the nanosilicon particles is coated with polyethylene glycol (PEG).

[0014] Further, the nanosilica particles are modified by a silane coupling agent, which is KH-560.

[0015] Further, the antioxidant is a complex system of hindered phenol and phosphite with a mass ratio of 2:1.

[0016] Further, the total mass percentage of nanosilicon and nanosilica in the insulating material is not more than 6wt%.

[0017] Further, the insulating material further comprises 0.1-0.3wt% of MgO nanoparticles.

[0018] Further, the surface hydroxyl content of the nanosilica is less than 5%, and the water content is less than 0.05%.

[0019] Further, the insulating material is structurally distributed in a gradient filler, wherein the inner layer has a higher content of nanosilica than the outer layer, and the outer layer has a higher content of nanosilicon than the inner layer.

[0020] Another aspect of the present application provides a method for preparing a high-voltage cable insulating material, comprising the following steps:

[0021] S1, ball milling of nanosilicon particles under nitrogen protection, controlling the particle size to be less than 10nm, and performing polyethylene glycol coating;

[0022] S2, wet modification of nanosilica particles by a silane coupling agent, and vacuum drying at 80℃ for 4 hours;

[0023] S3, dispersion by a two-step blending method: first, pre-mixing the modified nanosilica with the XLPE matrix, and then adding the coated nanosilicon particles and antioxidants for secondary blending;

[0024] S4, irradiation crosslinking of the mixed material, with an irradiation dose of 150-200kGy, and a crosslinking degree of not less than 90%;

[0025] S5, molding by a three-layer co-extrusion process, with an insulating layer thickness of not less than 25mm, and an eccentricity of less than 5%.

[0026] Further, in the two-step blending method, the first pre-mixing temperature is 180-190℃, and the second blending temperature is 200-210℃.

[0027] (Three) Technical effects

[0028] The present application has the following advantages compared with the prior art:

[0029] 1. Synergistic improvement of dielectric and thermal conductivity performance: By compounding nano-silicon (high thermal conductivity) and nano-silica (excellent dielectric performance), a synergistic effect is produced, which increases the breakdown field strength of the insulation material by 40-50% (to 48-50 kV / mm) and the thermal conductivity coefficient by 230-300% (to 1.15-1.25 W / m·K), breaking through the performance bottleneck of single filler modification.

[0030] 2. Excellent partial discharge suppression effect: The combined action of nano-silicon and nano-silica effectively suppresses the accumulation of space charge, reducing the partial discharge by 80-90% (to 10-15 pC), and significantly improving the electrical safety and reliability of the cable operation.

[0031] 3. Long-term service life extension: Benefiting from the capture of free radicals by the hydroxyl groups on the surface of nano-silica and the inhibition of thermal oxidative chain scission by nano-silicon, the thermal aging life of the material is extended by 37.5-50% (equivalent life of 55-60 years), meeting the stringent requirements of ultra-high voltage power grids for long service life.

[0032] 4. Strong comprehensive cost and process feasibility: By using low-cost and easily accessible nano raw materials and through an optimized two-step dispersion process and surface modification technology, the total cost of the material increases by only about 12% while achieving performance breakthroughs, and the process has good compatibility and scalability with existing cable production lines.

[0033] 5. Good mechanical performance and environmental friendliness: The uniform dispersion of the fillers increases the tensile strength of the insulation material to 25-28 MPa and enhances the deformation resistance. The material system does not contain heavy metals, meets environmental regulations, and the insulation layer parameters are compatible with existing international standards (such as IEC60502), without the need to change the main structure of the cable. DETAILED DESCRIPTION

[0034] The present application will be further described in detail below with reference to the examples.

[0035] Example 1

[0036] A high-voltage cable insulation material, comprising the following components by mass percentage: cross-linked polyethylene (XLPE) matrix 93.0 wt%; nano-silicon particles 2.0 wt%, particle size 1-10 nm; nano-silica particles 4.3 wt%, particle size 20-50 nm; coupling agent 0.3 wt%; antioxidant 0.3 wt%; the mass ratio of nano-silicon to nano-silica is 1:2 to 1:4.

[0037] The surface of the nanometer silicon particles is coated with polyethylene glycol (PEG), the nanometer silicon dioxide particles are modified by a silane coupling agent, the silane coupling agent is KH-560, the antioxidant is a compounded system of hindered phenol and phosphite with a mass ratio of 2:1, the total mass percentage of nanometer silicon and nanometer silicon dioxide in the insulating material is not more than 6wt%, the insulating material further comprises 0.1wt% of MgO nanoparticles, the surface hydroxyl content of the nanometer silicon dioxide is less than 5%, and the water content is less than 0.05%.

[0038] The insulating material is structurally in a gradient filler distribution, wherein the inner layer nanometer silicon dioxide content is higher than the outer layer, and the outer layer nanometer silicon content is higher than the inner layer.

[0039] Another aspect of the present application provides a method for preparing a high-voltage cable insulating material, comprising the following steps: ball milling nanometer silicon particles under nitrogen protection, controlling the particle size to be less than 10nm, and performing polyethylene glycol coating; wet modification of nanometer silicon dioxide particles by a silane coupling agent, and vacuum drying at 80°C for 4 hours; dispersing by a two-step blending method: first premixing the modified nanometer silicon dioxide and the XLPE matrix, and then adding the coated nanometer silicon particles and the antioxidant for secondary blending; irradiation crosslinking of the mixed material, with an irradiation dose of 150-200kGy and a crosslinking degree of not less than 90%; and forming by a three-layer co-extrusion process, with an insulating layer thickness of not less than 25mm and an eccentricity of less than 5%.

[0040] In the two-step blending method, the first premixing temperature is 180-190°C, and the second blending temperature is 200-210°C, and dispersion is performed in a high shear section.

[0041] Example 2

[0042] A high-voltage cable insulating material, comprising the following components in mass percentage: a cross-linked polyethylene (XLPE) matrix 93.5wt%; nanometer silicon particles 1.5wt% with a particle size of 1-10nm; nanometer silicon dioxide particles 4.0wt% with a particle size of 20-50nm; a coupling agent 0.5wt%; an antioxidant 0.5wt%; and the mass ratio of the nanometer silicon and nanometer silicon dioxide is 1:2 to 1:4.

[0043] The surface of the nanometer silicon particles is coated with polyethylene glycol (PEG), the nanometer silicon dioxide particles are modified by a silane coupling agent, the silane coupling agent is KH-560, the antioxidant is a compounded system of hindered phenol and phosphite with a mass ratio of 2:1, the total mass percentage of nanometer silicon and nanometer silicon dioxide in the insulating material is not more than 6wt%, the surface hydroxyl content of the nanometer silicon dioxide is less than 5%, and the water content is less than 0.05%.

[0044] The insulating material is structurally a gradient filler distribution, wherein the inner layer has a higher content of nanosilica than the outer layer, and the outer layer has a higher content of nanosilicon than the inner layer.

[0045] Another aspect of the present application provides a method for preparing a high-voltage cable insulating material, comprising the following steps: ball milling of nanosilicon particles under nitrogen protection, controlling the particle size to be less than 10 nm, and coating with polyethylene glycol; wet modification of nanosilica particles with silane coupling agent, and vacuum drying at 80°C for 4 hours; dispersion by two-step blending method: first premixing the modified nanosilica with the XLPE matrix, then adding the coated nanosilicon particles and antioxidants for secondary blending; irradiation crosslinking of the mixed material, with an irradiation dose of 150-200 kGy and a crosslinking degree of not less than 90%; molding by three-layer co-extrusion process, with an insulating layer thickness of not less than 25 mm and an eccentricity of less than 5%.

[0046] In the two-step blending method, the first premixing temperature is 180-190°C, and the second blending temperature is 200-210°C, and dispersion is carried out in the high shear section.

[0047] The performance improvement of the high-voltage cable insulating material of the present application is based on the functional and structural synergistic effects of nanosilicon (Si) particles and nanosilica (SiO2) particles in the crosslinked polyethylene (XLPE) matrix, which are specifically manifested as:

[0048] 1. Dielectric-thermal conduction synergistic enhancement mechanism:

[0049] Thermal conduction network construction: Nanosilicon particles with high thermal conductivity (thermal conductivity coefficient about 150 W / m·K) are dispersed in the matrix and interlaced or close to nanosilica particles with better thermal conductivity than pure XLPE (thermal conductivity coefficient about 1.2 W / m·K), forming a high-efficiency three-dimensional thermal conduction network inside the insulating material. This network can quickly conduct the heat generated by conductor loss and dielectric loss during cable operation, thereby greatly reducing the heat accumulation inside the insulating layer and improving the overall thermal conductivity to 1.0-1.2 W / m·K.

[0050] Dielectric performance optimization and charge suppression: Nanosilica has extremely high volume resistivity (>10 16 Ω·cm) and extremely low dielectric loss (tanδ<0.001). It introduces a large number of nanoscale interfaces in the matrix, changes the electric field distribution through interface polarization effect, and suppresses the initiation and growth of electrical tree under high field strength. At the same time, the hydroxyl groups (-OH) on its surface can effectively capture and bind free charges, which together with nanosilicon significantly reduces the injection and accumulation of space charges. The combination of the two fundamentally improves the intrinsic withstand voltage of the material (breakdown field strength is increased to 45-50 kV / mm) and strongly suppresses partial discharge (partial discharge amount is reduced to 10-20 pC).

[0051] 2. Interface modification and long-term stability mechanism:

[0052] Dispersion and interface combination: By using polyethylene glycol (PEG) to coat nano-silicon to prevent its oxidation and agglomeration, and using silane coupling agent (KH-560) to modify the surface of nano-silicon dioxide, the compatibility and interface bonding force between the two kinds of nano-fillers and the XLPE matrix are greatly improved. This not only ensures the uniform dispersion of the fillers under the "two-step dispersion method" process (SEM shows a spacing of 50-100 nm), avoids the formation of conductive paths or stress concentration points due to agglomeration, and reduces the risk of micro-discharge and electrical breakdown caused by interface defects.

[0053] Anti-aging synergistic protection: During the thermal and oxidative aging process of the cable, the hydroxyl groups on the surface of nano-silicon dioxide can neutralize the free radicals generated by the chain scission of XLPE, delaying the degradation of the polymer; while the addition of nano-silicon inhibits the thermal and oxidative induced molecular chain scission process. Both of them work together to build a long-term protection mechanism for the matrix material, thus significantly extending the thermal aging life of the material from the traditional 40 years to 55-60 years.

[0054] 3. Integrated design of structure and performance:

[0055] Through the "two-step dispersion method" process (mixing SiO2 / XLPE first, then adding Si) and the optional gradient filler distribution design (high SiO2 content on the inner layer side of the insulation layer to optimize the electric field distribution and charge suppression, and high Si content on the outer layer side to strengthen heat dissipation), the insulation layer realizes spatial optimization configuration in dielectric performance and heat dissipation performance, further improving the overall electrical reliability and thermal stability of the cable.

[0056] Table 1 Technical index measured data

[0057]

[0058] Table 2 Performance comparison with competitors

[0059] Parameter Traditional XLPE 5 nm Si / XLPE Nano-SiO2 / XLPE Si / SiO2 / XLPE Breakdown field strength (kV / mm) 30-35 40-42 42-45 48-50 Thermal conductivity (W / m·K) 0.3 0.8 0.7-0.9 1.15-1.25 Partial discharge (pC) 50-100 20-30 20-25 10-15 Cost increase 0％ +8％ +5％ +12％ Process complexity Low Medium (need to prevent oxidation) Low Medium Long-term stability General Oxidation failure Excellent Excellent (synergistic protection)

[0060] The present application realizes the synergistic effect of multiple physical and chemical mechanisms such as "constructing efficient heat conduction path", "strengthening dielectric and charge suppression", "optimizing interface and dispersion state" and "synergistic anti-aging" by compounding nano-silicon and nano-silicon dioxide of specific types, particle sizes, proportions and surface states, combined with optimized preparation process, in the XLPE matrix. Finally, the breakthrough improvement of breakdown field strength, thermal conductivity, partial discharge suppression and service life is achieved.

[0061] The above describes the present application and its embodiments, which are not limited, and the examples shown are only one of the embodiments of the present application, and the actual structure is not limited thereto. In general, if a person skilled in the art is inspired thereby, without departing from the spirit of the present application, without creative design, similar structure and embodiments of the technical solution, which should belong to the protection scope of the present application.

Claims

1. A high-voltage cable insulation material, characterized in that, The components include the following percentages by mass: Cross-linked polyethylene matrix 93.0–94.0 wt%; Nano-silicon particles, 1.0–2.0 wt%, with a particle size of 1–10 nm; Nano-sized silica particles, 3.0–5.0 wt%, with a particle size of 20–50 nm; Coupling agent 0.3–0.7 wt%; Antioxidant 0.3–0.7 wt%; The mass ratio of nano-silicon to nano-silica is 1:2 to 1:

4.

2. The high-voltage cable insulation material according to claim 1, characterized in that, The surface of the nano-silicon particles is coated with polyethylene glycol.

3. The high-voltage cable insulation material according to claim 1, characterized in that, The nano-silica particles are modified with a silane coupling agent, namely KH-560.

4. The high-voltage cable insulation material according to claim 1, characterized in that, The antioxidant is a compound system of hindered phenol and phosphite in a mass ratio of 2:

1.

5. The high-voltage cable insulation material according to claim 1, characterized in that, The total mass percentage of nano-silicon and nano-silica in the insulating material does not exceed 6 wt%.

6. The high-voltage cable insulation material according to claim 1, characterized in that, The insulating material also includes 0.1–0.3 wt% MgO nanoparticles.

7. The high-voltage cable insulation material according to claim 1, characterized in that, The surface hydroxyl content of the nano-silica is less than 5%, and the water content is less than 0.05%.

8. The high-voltage cable insulation material according to claim 1, characterized in that, The insulating material has a gradient filler distribution in its structure, wherein the content of nano-silica in the inner layer is higher than that in the outer layer, and the content of nano-silica in the outer layer is higher than that in the inner layer.

9. A method for preparing the high-voltage cable insulation material as described in claim 1, characterized in that, Includes the following steps: S1. The nano-silicon particles are ball-milled under nitrogen protection to control the particle size to less than 10 nm, and then coated with polyethylene glycol. S2. The nano-silica particles were modified by wet process with silane coupling agent and then vacuum dried at 80°C for 4 hours. S3. Dispersion is carried out by a two-step blending method: First, the modified nano-silica is premixed with the cross-linked polyethylene matrix, and then the coated nano-silica particles and antioxidants are added for secondary blending. S4. The mixed material is subjected to irradiation crosslinking with an irradiation dose of 150–200 kGy and a crosslinking degree of not less than 90%. S5. Formed by a three-layer co-extrusion process, the insulation layer thickness is not less than 25mm and the eccentricity is less than 5%.

10. The method according to claim 9, characterized in that, In the two-step blending method, the first premixing temperature is 180–190℃, and the second blending temperature is 200–210℃.

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