An insulating oil and paper insulation system containing superhydrophobic nanoparticles, its preparation method and application

Abstract

This invention relates to an insulating oil and an oil-paper insulation system containing superhydrophobic nanoparticles, as well as their preparation method and application, belonging to the field of electrical equipment insulation technology. This invention provides an insulating oil containing superhydrophobic nanoparticles, wherein the superhydrophobic nanoparticles are silane-modified nanoparticles, and the nanoparticles include at least one of SiO2, TiO2, and h-BN; the insulating oil includes at least one of mineral insulating oil, synthetic insulating oil, and natural ester insulating oil. This invention achieves the superhydrophobicity of the nanoparticles and good compatibility with the oil phase through silane modification. Adding silane-modified nanoparticles to the insulating oil effectively reduces the water content of the insulating oil and optimizes the interfacial performance of the oil-paper. Combined with the low-temperature, high-efficiency, and uniform rapid impregnation process of this invention, the overall electrical performance and service life of the oil-paper insulation system are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment insulation technology, and in particular to an insulating oil and paper insulation system containing superhydrophobic nanoparticles, its preparation method and application. Background Technology

[0002] With societal development, people have placed higher demands on the environmental friendliness and renewability of insulating oils. In recent years, the application of ester-based insulating oils in transformers has been increasing. Currently, the main environmentally friendly ester-based insulating oils used are natural ester insulating oils and synthetic ester insulating oils. As a liquid insulating medium, ester-based oils undergo complex interactions with the oil-paper insulation system composed of cellulose insulating paper during operation. Ester-based oil molecules have high polarity and strong hygroscopicity, enabling them to quickly absorb free moisture from the insulating paper, reducing the water activity of cellulose and thus inhibiting the hydrolysis reaction of cellulose, protecting the insulating paper. However, during long-term operation, ester-based oils undergo oxidative decomposition, and the synergistic effect of oxidation products and acidic substances accelerates the aging of the insulating paper. Common anti-aging technologies currently involve improving the insulating paper, using acid-resistant insulating paper to enhance hydrolysis resistance, or coating the surface of the insulating paper with nanomaterial fillers to block the penetration of acidic substances.

[0003] The traditional oil-paper insulation system currently in widespread use has the following problems: (1) The impregnation speed is slow, especially in low temperature environments where efficiency is even lower. Conventional processes require long-term impregnation at 60~70℃, resulting in high energy consumption and easy thermal degradation of the insulating paper; (2) Degassing is difficult, and micro-bubbles inside the paperboard are difficult to completely eliminate, causing local electric field distortion and reducing the partial discharge initiation voltage; (3) The insulation performance is significantly affected by the moisture content and interfacial tension of the oil-paper. High moisture content or poor interfacial wettability will lead to increased dielectric loss and decreased breakdown strength; (4) Conventional anti-aging additives are difficult to simultaneously optimize the overall performance of insulating oil and insulating paper. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an insulating oil and paper insulation system containing superhydrophobic nanoparticles, as well as its preparation method and application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides an insulating oil containing superhydrophobic nanoparticles, wherein the superhydrophobic nanoparticles are silane-modified nanoparticles, and the nanoparticles include at least one of SiO2, TiO2 and h-BN nanoparticles; the insulating oil includes at least one of mineral insulating oil, synthetic insulating oil and natural ester insulating oil.

[0006] This invention achieves the superhydrophobicity of nanoparticles and good compatibility with the oil phase through silane modification. The addition of silane-modified nanoparticles to insulating oil results in a new insulating oil with excellent comprehensive electrical properties, strong stability, and improved anti-aging performance.

[0007] As a preferred embodiment of the insulating oil containing superhydrophobic nanoparticles described in this invention, the silane-modified nanoparticles are silane-modified nanoparticles containing epoxy groups and / or fluoroalkyl groups.

[0008] As a preferred embodiment of the insulating oil containing superhydrophobic nanoparticles according to the present invention, the content of the superhydrophobic nanoparticles is preferably 0.01 wt% to 0.10 wt%, for example, including but not limited to any point value or any range of any two points from 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, and 0.10 wt%.

[0009] As a preferred embodiment of the insulating oil containing superhydrophobic nanoparticles according to the present invention, the particle size of the nanoparticles is preferably 15~25 nm, for example, including but not limited to any point value or any range of two points from 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 and 25 nm.

[0010] Secondly, the present invention provides a method for preparing the insulating oil containing superhydrophobic nanoparticles, comprising the following steps: S11: Mix the nanoparticles with a surface modifier and a coupling agent, stir and reflux at 60~80℃ for 7~10h to obtain a reaction mixture, and then separate the solid and liquid to obtain superhydrophobic nanoparticles. The surface modifier includes heptadecyltrimethoxysilane and / or tridecafluorooctyltriethoxysilane, and the coupling agent includes γ-aminopropyltriethoxysilane and / or N-β-aminoethyl-γ-aminopropyltrimethoxysilane. S12: Mix the insulating oil, dispersant and the superhydrophobic nanoparticles described in step S11, disperse and degas to obtain the insulating oil containing the superhydrophobic nanoparticles. The dispersant includes a polyimide-based dispersant and / or a polyhydroxystearic acid dispersant.

[0011] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the mass ratio of the nanoparticles to the surface modifier is preferably 1:(1~2), for example, including but not limited to any point value or any range value composed of any two points such as 1:1, 1:1.2, 1:1.5, 1:1.8 and 1:2; And / or, the mass ratio of the nanoparticles to the coupling agent is preferably 1:(1~3), for example, including but not limited to any point value or any range of two points from 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8 and 1:3.

[0012] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the nanoparticles are dispersed in ethanol, and a suspension is obtained by sonication. The suspension is then mixed with a surface modifier and a coupling agent.

[0013] As a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the ratio of nanoparticles to ethanol is: nanoparticles: ethanol = 1 g: (40~60) mL, preferably 1 g: 50 mL.

[0014] As a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the ultrasonic parameters are 30~50 kHz for 20~40 min, preferably 40 kHz for 30 min, so that the nanoparticles are initially deagglomerated.

[0015] As a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the mixture is stirred and refluxed at 80°C for 8 h.

[0016] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the stirring speed is 400~800 r / min, preferably 600 r / min.

[0017] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S11, the reaction mixture is centrifuged, the precipitate is retained, washed, vacuum dried at 70~90℃ for 10~15 h, ground and sieved to obtain superhydrophobic nanoparticles; preferably, vacuum dried at 80℃ for 12 h.

[0018] As a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, the reaction mixture is centrifuged at 8000~12000 r / min for 5~15 min; preferably at 10000 r / min for 10 min.

[0019] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the mass ratio of the nanoparticles to the dispersant is preferably 1:(1~3), for example, including but not limited to any point value or any range value composed of any two points from 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8 and 1:3.

[0020] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the content of the superhydrophobic nanoparticles is preferably 0.01 wt% to 0.10 wt%, for example, including but not limited to any point value or any range of any two points from 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, and 0.10 wt%.

[0021] In a preferred embodiment of the preparation method of the insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the insulating oil is first dried and degassed at 80~90℃ and -0.08~0.10 MPa vacuum for 20~25 h to obtain pretreated insulating oil, and then mixed with dispersant and the superhydrophobic nanoparticles described in step S11.

[0022] As a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the oil is dried and degassed for 24 h under vacuum conditions of 90°C and -0.09 MPa.

[0023] In a preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the pretreated insulating oil, dispersant and superhydrophobic nanoparticles described in step S11 are sheared and mixed for 15 to 20 minutes at a rotation speed of 3000 to 5000 rpm, and then subjected to pulsed ultrasonic treatment at a power of 300 to 500 W for 30 to 60 minutes.

[0024] As a more preferred embodiment of the preparation method of insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the pretreated insulating oil, dispersant and superhydrophobic nanoparticles described in step S11 are sheared and mixed at 4000 rpm for 20 min, and then subjected to pulsed ultrasonic treatment at 400 W power for 40 min.

[0025] In a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the pulsed ultrasonic working mode is 1~3 s working and 1~3 s intermittent, preferably 2 s working and 2 s intermittent.

[0026] In a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the oil is allowed to stand and degas for 10 to 15 hours at 50 to 70°C and -0.08 to -0.10 MPa.

[0027] In a more preferred embodiment of the method for preparing insulating oil containing superhydrophobic nanoparticles according to the present invention, in step S12, the oil is allowed to stand for degassing at 60°C and -0.09 MPa for 12 h.

[0028] Thirdly, the present invention provides an oil-paper insulation system comprising insulating oil containing superhydrophobic nanoparticles and insulating paper.

[0029] Fourthly, the present invention provides a method for preparing the oil-paper insulation system, comprising the following steps: S21: Impregnate the insulating paper in the insulating oil containing superhydrophobic nanoparticles, and sonicate at 30~70℃ and 30~50 kHz for 8~12 h; S22: The oil-paper insulation system processed in step S21 is ultrasonically impregnated under vacuum conditions of -0.03~-0.10 MPa, 30~70℃, and 30~50 kHz for 3~24 h to obtain the oil-paper insulation system.

[0030] In a preferred embodiment of the preparation method of the oil-paper insulation system of the present invention, in step S21, the insulating paper is pretreated insulating paper, which is dried and degassed at 80~90℃ and under vacuum conditions of -0.08~0.10 MPa for 20~25 h to obtain pretreated insulating paper.

[0031] As a more preferred embodiment of the preparation method of the oil-paper insulation system of the present invention, in step S21, the paper is dried and degassed for 24 h under a vacuum of 90°C and -0.09 MPa to obtain pretreated insulation paper.

[0032] As a more preferred embodiment of the preparation method of the oil-paper insulation system of the present invention, in step S21, the paper is ultrasonicated at 40°C and 40 kHz for 10 h.

[0033] In a more preferred embodiment of the preparation method of the oil-paper insulation system of the present invention, in step S22, ultrasound is performed at 40°C and 40 kHz.

[0034] In a preferred embodiment of the preparation method of the oil-paper insulation system of the present invention, in step S22, the oil-paper insulation system treated in step S21 is impregnated under a vacuum of -0.03 to -0.06 MPa for 3 to 5 hours, then impregnated under a vacuum of -0.07 to -0.08 MPa for 5 to 7 hours, and then impregnated under a vacuum of -0.085 to -0.10 MPa for 4 to 12 hours.

[0035] In a preferred embodiment of the preparation method of the oil-paper insulation system of the present invention, in step S22, the oil-paper insulation system treated in step S21 is impregnated under a vacuum of -0.05 MPa for 4 h, then impregnated under a vacuum of -0.075 MPa for 6 h, and then impregnated under a vacuum of -0.09 MPa for 10 h.

[0036] Fifthly, the present invention provides a method for improving the anti-aging performance of an oil-paper insulation system, wherein the oil-paper insulation system is prepared using the insulating oil containing superhydrophobic nanoparticles.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Significantly improved impregnation efficiency: The low-temperature, high-efficiency, uniform and rapid impregnation process developed in this invention can achieve efficient impregnation at a low temperature of 40℃, shortening the time by 40%~70% compared with the traditional 65℃ process, reducing energy consumption and avoiding heat damage to the cardboard.

[0038] (2) Effectively reduce the moisture content of insulating oil: Superhydrophobic nanoparticles inhibit moisture adsorption and diffusion, reducing the moisture content of the oil-paper system by 20%~40%.

[0039] (3) Optimize the interfacial properties of oil paper: Superhydrophobic nanoparticles reduce the interfacial tension of oil paper, improve wettability, make impregnation more uniform and bubble removal more thorough.

[0040] (4) Excellent long-term stability: The modified nanoparticles are stably dispersed in oil for more than 6 months without sedimentation or agglomeration, making them suitable for long-term operation equipment and significantly improving the overall electrical performance and service life of the oil-paper insulation system. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the dyeing process for a common synthetic ester paper insulation system.

[0042] Figure 2 This is a schematic diagram of the dyeing process for the oil-paper insulation system in Example 5. Detailed Implementation

[0043] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Unless otherwise specified, other materials and reagents used in the embodiments are commercially available.

[0044] Example 1: Preparation of Insulating Oil 1. Surface modification and activation of SiO2 superhydrophobic nanoparticles.

[0045] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0046] (2) Chemical grafting reaction: Surface modifiers FAS-17 (heptadecyltrimethoxysilane) and KH-550 (γ-aminopropyltriethoxysilane) were added to the suspension. The mass of FAS-17 was twice that of the SiO2 nanoparticles, and the mass of KH-550 was once that of the SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) and refluxed for 8 h at 80 °C to obtain the reaction mixture.

[0047] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0048] 2. Blending and dispersion of insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles.

[0049] (1) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0050] (2) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles were added to the pretreated synthetic ester insulating oil, and polyimide dispersant (Lubrizol, Solsperse 13940) was added at the same time. The mass of polyimide dispersant was 1 times that of SiO2 nanoparticles to obtain a compound insulating oil composition.

[0051] (3) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0052] (4) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to degas, eliminating the bubbles introduced during the dispersion process, and obtaining the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles.

[0053] Example 2: Effect of SiO2 superhydrophobic nanoparticle addition on insulating oil I. Experimental Methods 1. Preparation of insulating oil containing 0.01 wt% SiO2 superhydrophobic nanoparticles.

[0054] (1) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0055] (2) Compounding: 0.01 wt% of the SiO2 superhydrophobic nanoparticles prepared in Example 1 were added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant was added at the same time. The mass of the polyimide-based dispersant was 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0056] (3) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0057] (4) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.01 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0058] 2. Preparation of insulating oil containing 0.03 wt% SiO2 superhydrophobic nanoparticles.

[0059] (1) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0060] (2) Compounding: 0.03 wt% of the SiO2 superhydrophobic nanoparticles prepared in Example 1 were added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant was added at the same time. The mass of the polyimide-based dispersant was 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0061] (3) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0062] (4) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to degas, eliminating the bubbles introduced during the dispersion process, and obtaining the finished insulating oil containing 0.03 wt% SiO2 superhydrophobic nanoparticles.

[0063] 3. Prepare insulating oil containing 0.08 wt% SiO2 superhydrophobic nanoparticles.

[0064] (1) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0065] (2) Compounding: 0.08 wt% of the SiO2 superhydrophobic nanoparticles prepared in Example 1 were added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant was added at the same time. The mass of the polyimide-based dispersant was 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0066] (3) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0067] (4) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.08 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0068] 4. Prepare insulating oil containing 0.10 wt% SiO2 superhydrophobic nanoparticles.

[0069] (1) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0070] (2) Compounding: 0.10 wt% of the SiO2 superhydrophobic nanoparticles prepared in Example 1 were added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant was added at the same time. The mass of the polyimide-based dispersant was 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0071] (3) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0072] (4) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.10 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0073] II. Detection Methods According to GB / T 507-2002 "Determination of Breakdown Voltage of Insulating Oil", an automated insulating oil dielectric strength tester was used to test the insulating oil containing SiO2 superhydrophobic nanoparticles. A spherical cap electrode with a spacing of 2.5 mm and a voltage ramp rate of 2.0 kV / s was used. Each sample was tested six times, and the average value was taken to obtain the breakdown voltage of the insulating oil containing SiO2 superhydrophobic nanoparticles.

[0074] According to GB / T 5654-2007 "Measurement of Relative Permittivity, Dielectric Loss Factor and DC Resistivity of Liquid Insulating Materials", the dielectric loss of insulating oil containing SiO2 superhydrophobic nanoparticles was obtained by using an oil dielectric loss tester.

[0075] III. Experimental Results Table 1 The results are shown in Table 1. When the SiO2 superhydrophobic nanoparticles were added at a content of 0.05 wt%, they were most evenly distributed in the insulating oil. This not only exerted the electron trapping effect to improve the breakdown voltage, but also avoided the increase in dielectric loss caused by agglomeration.

[0076] Example 3: Effect of different nanoparticles on insulating oil I. Experimental Methods 1. Insulating oil containing 0.05 wt% TiO2 superhydrophobic nanoparticles was prepared by replacing SiO2 nanoparticles with TiO2 nanoparticles.

[0077] (1) TiO2 nanoparticles with an average particle size of 20 nm were dispersed in anhydrous ethanol at a ratio of 1 g to 50 mL. The mixture was sonicated at 40 kHz for 30 min to allow it to initially deagglomerate and obtain a suspension.

[0078] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of TiO2 nanoparticles, and the mass of KH-550 was once that of TiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0079] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain TiO2 superhydrophobic nanoparticles.

[0080] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0081] (5) Compounding: 0.05 wt% TiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the TiO2 nanoparticles to obtain a compound insulating oil composition.

[0082] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0083] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% TiO2 superhydrophobic nanoparticles is obtained.

[0084] 2. Replace SiO2 nanoparticles with h-BN (hexagonal boron nitride) nanoparticles to prepare insulating oil containing 0.05 wt% h-BN superhydrophobic nanoparticles.

[0085] (1) h-BN nanoparticles with an average particle size of 20 nm were dispersed in anhydrous ethanol at a ratio of 1 g to 50 mL. The mixture was sonicated at 40 kHz for 30 min to allow it to initially deagglomerate and obtain a suspension.

[0086] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of h-BN nanoparticles, and the mass of KH-550 was once that of h-BN nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0087] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain h-BN superhydrophobic nanoparticles.

[0088] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0089] (5) Compounding: 0.05 wt% h-BN superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the h-BN nanoparticles to obtain a compound insulating oil composition.

[0090] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0091] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to degas, eliminating the bubbles introduced during the dispersion process, and obtaining the finished insulating oil containing 0.05 wt% h-BN superhydrophobic nanoparticles.

[0092] 3. Replace SiO2 nanoparticles with Al2O3 nanoparticles to prepare insulating oil containing 0.05 wt% Al2O3 superhydrophobic nanoparticles.

[0093] (1) Al2O3 nanoparticles with an average particle size of 20 nm were dispersed in anhydrous ethanol at a ratio of 1 g to 50 mL. The mixture was sonicated at 40 kHz for 30 min to allow it to initially deagglomerate and obtain a suspension.

[0094] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of Al2O3 nanoparticles, and the mass of KH-550 was once that of Al2O3 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0095] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200 mesh (75 μm pore size) sieve to obtain Al2O3 superhydrophobic nanoparticles.

[0096] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0097] (5) Compounding: 0.05 wt% Al2O3 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the Al2O3 nanoparticles to obtain a compound insulating oil composition.

[0098] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0099] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to degas, eliminating the bubbles introduced during the dispersion process, and obtaining the finished insulating oil containing 0.05 wt% Al2O3 superhydrophobic nanoparticles.

[0100] II. Detection Methods According to GB / T 30693-2014 "Measurement of Contact Angle between Plastic Films and Water", the seated drop method was used for testing. Four types of modified nanoparticles (SiO2 superhydrophobic nanoparticles, TiO2 superhydrophobic nanoparticles, h-BN superhydrophobic nanoparticles, and Al2O3 superhydrophobic nanoparticles) were pressed into tablets, and 3 μL of deionized water was added using an optical contact angle meter to measure the static contact angle between the water droplet and the sample surface.

[0101] According to GB / T 507-2002 "Determination of Breakdown Voltage of Insulating Oil", a fully automatic insulating oil dielectric strength tester was used for testing. Spherical electrodes with a spacing of 2.5 mm and a voltage ramp rate of 2.0 kV / s were employed. Each sample was tested six times, and the average value was taken to obtain the breakdown voltage of the insulating oil under test.

[0102] The sedimentation stability was determined by measuring the rate of change of absorbance of the insulating oil sample after standing for different periods using ultraviolet-visible spectrophotometry (absorbance At of the upper oil sample after standing for a period of time / absorbance A0 of the freshly prepared sample).

[0103] III. Experimental Results Table 2 The results are shown in Table 2. When the nanoparticles are Al2O3, the contact angle and breakdown voltage are low, and the sedimentation stability is only 3 months. The effect is better when the nanoparticles are SiO2, TiO2 or h-BN.

[0104] Example 4: Effects of different modifiers on contact angle and stability I. Experimental Methods Different modifier systems and their mass ratios to SiO2 nanoparticles were set up, as follows: 1. The mass ratio of FAS-17 to SiO2 nanoparticles is 2:1, the mass ratio of KH-550 to SiO2 nanoparticles is 1:1, and the mass ratio of polyimide dispersant to SiO2 nanoparticles is 1:1.

[0105] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0106] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of SiO2 nanoparticles, and the mass of KH-550 was once that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0107] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0108] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0109] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0110] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0111] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0112] 2. The mass ratio of FAS-17 to SiO2 nanoparticles is 1:1, the mass ratio of KH-550 to SiO2 nanoparticles is 1:1, and the mass ratio of polyimide dispersant to SiO2 nanoparticles is 1:1.

[0113] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0114] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was 1 times that of SiO2 nanoparticles, and the mass of KH-550 was 1 times that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0115] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0116] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0117] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0118] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0119] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0120] 3. The mass ratio of FAS-17 to SiO2 nanoparticles is 2:1, the mass ratio of KH-550 to SiO2 nanoparticles is 3:1, and the mass ratio of polyimide dispersant to SiO2 nanoparticles is 1:1.

[0121] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0122] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of SiO2 nanoparticles, and the mass of KH-550 was three times that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0123] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0124] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0125] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0126] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0127] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0128] 4. The mass ratio of FAS-17 to SiO2 nanoparticles is 2:1, the mass ratio of KH-550 to SiO2 nanoparticles is 1:1, and the mass ratio of polyimide dispersant to SiO2 nanoparticles is 3:1.

[0129] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0130] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of SiO2 nanoparticles, and the mass of KH-550 was once that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0131] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0132] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0133] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and polyimide dispersant is added at the same time. The mass of polyimide dispersant is 3 times that of SiO2 nanoparticles to obtain a compound insulating oil composition.

[0134] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0135] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0136] 5. The mass ratio of PFOTES (tridecylfluorooctyltriethoxysilane) to SiO2 nanoparticles is 2:1, the mass ratio of KH-550 to SiO2 nanoparticles is 1:1, and the mass ratio of polyimide dispersant to SiO2 nanoparticles is 1:1.

[0137] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0138] (2) Chemical grafting reaction: PFOTES and KH-550 surface modifiers were added to the suspension. The mass of PFOTES was twice that of SiO2 nanoparticles, and the mass of KH-550 was once that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0139] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0140] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0141] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0142] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0143] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0144] 6. The mass ratio of FAS-17 to SiO2 nanoparticles is 2:1, the mass ratio of KH-792 (N-β-aminoethyl-γ-aminopropyltrimethoxysilane) to SiO2 nanoparticles is 1:1, and the mass ratio of polyimide dispersant to SiO2 nanoparticles is 1:1.

[0145] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0146] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-792 were added to the suspension. The mass of FAS-17 was twice that of SiO2 nanoparticles, and the mass of KH-792 was once that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0147] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0148] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0149] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and a polyimide-based dispersant is added at the same time. The mass of the polyimide-based dispersant is 1 times that of the SiO2 nanoparticles to obtain a compound insulating oil composition.

[0150] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0151] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0152] 7. The mass ratio of FAS-17 to SiO2 nanoparticles is 2:1, the mass ratio of KH-550 to SiO2 nanoparticles is 1:1, and the mass ratio of polyhydroxystearic acid dispersant to SiO2 nanoparticles is 1:1.

[0153] (1) Disperse SiO2 nanoparticles with an average particle size of 20 nm in anhydrous ethanol at a ratio of 1 g to 50 mL and sonicate at 40 kHz for 30 min to initially deagglomerate them and obtain a suspension.

[0154] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of SiO2 nanoparticles, and the mass of KH-550 was once that of SiO2 nanoparticles. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0155] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain SiO2 superhydrophobic nanoparticles.

[0156] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0157] (5) Compounding: 0.05 wt% SiO2 superhydrophobic nanoparticles are added to the pretreated synthetic ester insulating oil, and polyhydroxystearic acid dispersant is added at the same time. The mass of polyhydroxystearic acid dispersant is 1 times that of SiO2 nanoparticles to obtain a compound insulating oil composition.

[0158] (6) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0159] (7) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to eliminate the bubbles introduced during the dispersion process, and the finished insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles is obtained.

[0160] II. Detection Methods According to GB / T 30693-2014 "Measurement of Contact Angle between Plastic Film and Water", the seated drop method was used for testing. Seven groups of modified SiO2 superhydrophobic nanoparticles were pressed into tablets, and 3 μL of deionized water was added to each tablet using an optical contact angle meter to measure the static contact angle between the water droplet and the sample surface.

[0161] The sedimentation stability was determined by measuring the rate of change of absorbance of the insulating oil sample after standing for different periods using ultraviolet-visible spectrophotometry (absorbance At of the upper oil sample after standing for a period of time / absorbance A0 of the freshly prepared sample).

[0162] III. Experimental Results Table 3 The results are shown in Table 3. The superhydrophobic nano-insulating oil prepared by the modifier system in Example 1 and the mass ratio of the modifier system to SiO2 nanoparticles has a higher contact angle and better sedimentation stability.

[0163] Example 5: Impregnation Method for Preparing an Oil-Paper Insulation System 1. Pretreatment: Select cellulose insulating paper that meets the technical requirements of the international standard IEC60641-2 for electrical paper, and dry the insulating paper at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0164] 2. Low-temperature impregnation: The pretreated insulating paper was impregnated in the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles prepared in Example 1 for 10 h at 40°C, and ultrasonication was performed at 40 kHz during the impregnation process. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles was 1:10.

[0165] 3. Staged vacuum impregnation: Perform three vacuum procedures sequentially: Stage I: -0.05 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h; Stage II: -0.075 MPa, 40℃, 40 kHz ultrasonic immersion for 6 h; Phase III: -0.09 MPa, 40℃, 40 kHz ultrasonic immersion for 10 h.

[0166] Example 6: Effects of Impregnation Temperature and Ultrasonic Assistance on Oil-Paper Insulation Systems I. Experimental Methods 1. Conventional impregnation method (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0167] (2) The pretreated insulating paper was immersed in the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles prepared in Example 1 at 70°C. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles was 1:10.

[0168] 2. Low-temperature impregnation method (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0169] (2) The pretreated insulating paper was immersed in the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles prepared in Example 1 at 40°C. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles was 1:10.

[0170] 3. High-temperature ultrasonic impregnation method (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0171] (2) The pretreated insulating paper was immersed in the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles prepared in Example 1 at 70°C. During the immersion process, 40 kHz ultrasound was performed. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles was 1:10.

[0172] II. Detection Methods The impregnation time (time required for 2 mm thick insulating paper to be completely impregnated) and the decrease rate of the degree of polymerization of the insulating paper were statistically analyzed in the conventional impregnation method, the low temperature impregnation method, the high temperature ultrasonic impregnation method and the impregnation method of Example 5.

[0173] III. Experimental Results Table 4 The results are shown in Table 4. 40℃ combined with ultrasound (Example 5) is the optimal point for balancing impregnation efficiency and insulation paper protection.

[0174] Example 7: The Influence of Different Insulating Oils on Paper Insulation Systems I. Experimental Methods Group A: Ordinary synthetic ester paper insulation system.

[0175] (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0176] (2) The pretreated insulating paper was immersed in Midle7131 synthetic ester insulating oil at 70°C for 24 h. The mass ratio of the pretreated insulating paper to the Midle7131 synthetic ester insulating oil was 1:10.

[0177] Group B: The impregnation method of Example 5, wherein the impregnation time in stage III is 4 h.

[0178] Group C: Impregnated with insulating oil containing 0.05 wt% TiO2 superhydrophobic nanoparticles.

[0179] (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0180] (2) Low-temperature impregnation: The pretreated insulating paper was impregnated at 40°C in the insulating oil containing 0.05 wt% TiO2 superhydrophobic nanoparticles prepared in Example 3 for 10 h, and ultrasonication was performed at 40 kHz during the impregnation process. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% TiO2 superhydrophobic nanoparticles was 1:10.

[0181] (3) Staged vacuum impregnation: Three vacuum procedures are performed sequentially: Stage I: -0.05 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h; Stage II: -0.075 MPa, 40℃, 40 kHz ultrasonic immersion for 6 h; Phase III: -0.09 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h.

[0182] Group D: Impregnated with insulating oil containing 0.05 wt% h-BN superhydrophobic nanoparticles.

[0183] (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0184] (2) Low-temperature impregnation: The pretreated insulating paper was impregnated in the insulating oil containing 0.05 wt% h-BN superhydrophobic nanoparticles prepared in Example 3 for 10 h at 40 °C, and ultrasonication was performed at 40 kHz during the impregnation process. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% h-BN superhydrophobic nanoparticles was 1:10.

[0185] (3) Staged vacuum impregnation: Three vacuum procedures are performed sequentially: Stage I: -0.05 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h; Stage II: -0.075 MPa, 40℃, 40 kHz ultrasonic immersion for 6 h; Phase III: -0.09 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h.

[0186] Group E: Replace only the SiO2 superhydrophobic nanoparticles in the insulating oil of Group B with a combination of superhydrophobic nanoparticles to obtain an insulating oil containing a combination of superhydrophobic nanoparticles.

[0187] The preparation method of insulating oil containing superhydrophobic nanoparticles is as follows: (1) A nanoparticle assembly with an average particle size of 20 nm was dispersed in anhydrous ethanol at a ratio of 1 g to 50 mL. The assembly was sonicated at 40 kHz for 30 min to initially deagglomerate the nanoparticles and obtain a suspension. The nanoparticle assembly consisted of SiO2, TiO2 and h-BN nanoparticles in a mass ratio of 1:1:1.

[0188] (2) Chemical grafting reaction: Surface modifiers FAS-17 and KH-550 were added to the suspension. The mass of FAS-17 was twice that of the nanoparticle combination, and the mass of KH-550 was once that of the nanoparticle combination. The mixture was magnetically stirred (600 r / min) at 80°C and refluxed for 8 h to obtain the reaction mixture.

[0189] (3) Cleaning and drying: After the reaction is completed, the reaction mixture is centrifuged at 10000 r / min for 10 min, the precipitate is retained, and the precipitate is washed repeatedly with anhydrous ethanol 3 times to remove unreacted residues. The washed precipitate is dried in a vacuum oven at 80℃ for 12 h, and then ground and sieved through a 200-mesh (75 μm pore size) sieve to obtain a superhydrophobic nanoparticle combination.

[0190] (4) Base oil pretreatment: Take 1000 mL of Midle 7131 synthetic ester insulating oil and dry and degas it at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated synthetic ester insulating oil.

[0191] (5) Compounding: 0.05 wt% of superhydrophobic nanoparticles were added to the pretreated synthetic ester insulating oil, and polyimide dispersant was added at the same time. The mass of polyimide dispersant was 1 times that of the nanoparticles to obtain a compound insulating oil composition.

[0192] (3) Multi-stage dispersion: First, a high-shear emulsifier is used to shear and mix the compound insulating oil composition at 4000 rpm for 20 min to break up the agglomerates. Then, a probe-type ultrasonic disperser is used to perform pulsed ultrasonic treatment at 400 W power for 40 min (working for 2 s, then pausing for 2 s to prevent the oil temperature from getting too high). The nanoparticles are uniformly dispersed to the original particle size scale by utilizing the cavitation effect to obtain the dispersed insulating oil.

[0193] (4) Final degassing: The dispersed insulating oil is placed in a vacuum tank and allowed to stand for 12 h at 60℃ and -0.09 MPa to degas, eliminating the bubbles introduced during the dispersion process, and obtaining the finished insulating oil containing 0.05 wt% superhydrophobic nanoparticles.

[0194] The impregnation method for Group E is as follows: (1) Pretreatment: The insulating paper was dried at 90℃ and -0.09 MPa vacuum for 24 h to obtain pretreated insulating paper.

[0195] (2) Low-temperature impregnation: The pretreated insulating paper was impregnated in insulating oil containing 0.05 wt% superhydrophobic nanoparticles for 10 h at 40℃, and ultrasonication was performed at 40 kHz during the impregnation process. The mass ratio of the pretreated insulating paper to the insulating oil containing 0.05 wt% superhydrophobic nanoparticles was 1:10.

[0196] (3) Staged vacuum impregnation: Three vacuum procedures are performed sequentially: Stage I: -0.05 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h; Stage II: -0.075 MPa, 40℃, 40 kHz ultrasonic immersion for 6 h; Phase III: -0.09 MPa, 40℃, 40 kHz ultrasonic immersion for 4 h.

[0197] II. Detection Methods 1. Impregnation depth and uniformity test Add 0.01 wt% of the oil-soluble dye Sudan Red to the insulating oil to make the oil phase colored, which makes it easier to distinguish the unimpregnated areas. Impregnate according to the impregnation methods in this embodiment. Cut the impregnated insulating paper (2 mm thick) into 4 layers (each layer is 0.5 mm thick) along the thickness direction. Observe under an optical microscope or stereomicroscope whether the gaps between the fibers in each layer are filled with oil.

[0198] 2. Based on GB 11026.1-2014 "Guidelines for Determining the Heat Resistance of Electrical Insulation Materials", an oil-paper insulation environment similar to the internal insulation structure of the transformer on site was designed. The oil-paper insulation system samples were subjected to accelerated thermal aging tests at 130℃. Samples were taken periodically at different aging times (0, 20, 40, 60, 80, and 100 days), and the moisture content of the insulating oil samples at different aging times was determined according to GB / T 7600-2014 "Determination of Moisture Content in Transformer Oil and Turbine Oil in Operation (Coulometric Method)".

[0199] 3. According to GB / T 507-2002 "Determination of Breakdown Voltage of Insulating Oil", a fully automatic insulating oil dielectric strength tester was used for testing. Spherical electrodes with a spacing of 2.5 mm and a voltage ramp rate of 2.0 kV / s were used. Each sample was tested 6 times, and the average value was taken to obtain the breakdown voltage of the insulating oil.

[0200] According to GB / T 5654-2007 "Measurement of Relative Permittivity, Dielectric Loss Factor and DC Resistivity of Liquid Insulating Materials", an oil dielectric loss tester was used to test and obtain the dielectric loss factors of different groups.

[0201] The partial discharge initiation voltage of different groups was tested in accordance with GB / T 7354-2018 "High Voltage Testing Techniques - Partial Discharge Measurement".

[0202] III. Experimental Results In Table 5, the impregnation time (24 h) of Example 5 of the present invention shows better impregnation effect and is more energy-efficient under the same time. Meanwhile, the impregnation effects of groups C, D and E are similar to those of group B, and they can be completely penetrated after 24 h of impregnation, with no color difference and no bubbles.

[0203] Table 5 As shown in Table 6, the insulating oil containing 0.05 wt% SiO2 superhydrophobic nanoparticles prepared in Example 1 of the present invention has a lower water content and can operate normally for a longer time under the same aging conditions.

[0204] Table 6 As shown in Table 7, the insulating oils of groups B, C, D and E of the present invention have better electrical properties than the insulating oil of group A.

[0205] Table 7 Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An insulating oil containing superhydrophobic nanoparticles, characterized in that, The superhydrophobic nanoparticles are silane-modified nanoparticles, and the nanoparticles include at least one of SiO2, TiO2 and h-BN nanoparticles; the insulating oil includes at least one of mineral insulating oil, synthetic insulating oil and natural ester insulating oil.

2. The insulating oil containing superhydrophobic nanoparticles as described in claim 1, characterized in that, The silane-modified nanoparticles are silane-modified nanoparticles containing epoxy groups and / or fluoroalkyl groups.

3. The insulating oil containing superhydrophobic nanoparticles as described in claim 1, characterized in that, The content of the superhydrophobic nanoparticles is 0.01 wt% to 0.10 wt%.

4. The method for preparing the insulating oil containing superhydrophobic nanoparticles according to any one of claims 1 to 3, characterized in that, Includes the following steps: S11: Mix the nanoparticles described in claim 1 with a surface modifier and a coupling agent, stir and reflux at 60~80℃ for 7~10 h to obtain a reaction mixture, and then separate the solid and liquid to obtain superhydrophobic nanoparticles. The surface modifier includes heptadecyltrimethoxysilane and / or tridecafluorooctyltriethoxysilane, and the coupling agent includes γ-aminopropyltriethoxysilane and / or N-β-aminoethyl-γ-aminopropyltrimethoxysilane. S12: Mix the insulating oil, dispersant and the superhydrophobic nanoparticles described in step S11, disperse and degas to obtain the insulating oil containing the superhydrophobic nanoparticles. The dispersant includes a polyimide-based dispersant and / or a polyhydroxystearic acid dispersant.

5. The preparation method according to claim 4, characterized in that, In step S11, the mass ratio of the nanoparticles to the surface modifier is: nanoparticles: surface modifier = 1: (1~2). And / or, the mass ratio of the nanoparticles to the coupling agent is: nanoparticles: coupling agent = 1: (1~3).

6. The preparation method according to claim 4, characterized in that, In step S12, the mass ratio of the nanoparticles to the dispersant is: nanoparticles: dispersant = 1: (1~3).

7. An oil-paper insulation system, characterized in that, The oil-paper insulation system comprises insulating oil containing superhydrophobic nanoparticles as described in any one of claims 1 to 3 and insulating paper.

8. The method for preparing the oil-paper insulation system according to claim 7, characterized in that, Includes the following steps: S21: Impregnate the insulating paper in the insulating oil containing superhydrophobic nanoparticles as described in any one of claims 1 to 3, and sonicate it at 30 to 70°C and 30 to 50 kHz for 8 to 12 hours. S22: The oil-paper insulation system processed in step S21 is ultrasonically impregnated under vacuum conditions of -0.03~-0.10 MPa, 30~70℃, and 30~50 kHz for 3~24 h to obtain the oil-paper insulation system.

9. The preparation method according to claim 8, characterized in that, In step S22, the oil-paper insulation system processed in step S11 is impregnated under a vacuum of -0.03 to -0.06 MPa for 3 to 5 hours, then under a vacuum of -0.07 to -0.08 MPa for 5 to 7 hours, and then under a vacuum of -0.085 to -0.10 MPa for 4 to 12 hours.

10. A method for improving the anti-aging performance of an oil-paper insulation system, characterized in that, Prepare an oil-paper insulation system using the insulating oil containing superhydrophobic nanoparticles as described in any one of claims 1 to 3.

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