Preparation method of mixed insulating oil based on surface modified nanoparticles

Abstract

The invention discloses a preparation method of mixed insulating oil based on surface modified nanoparticles, relates to the technical field of insulating material production and processing, and solves the problems of poor heat-conducting property and insufficient dielectric strength of the existing vegetable insulating oil. Comprising the steps of preparation of nano ZnO, surface modification of nano ZnO, surface modification of nano SiC powder, preparation of mixed oil and preparation of mixed insulating oil, the dispersion stability of nano particles in the mixed insulating oil is improved, a large number of electron traps can be formed in the mixed insulating oil, migration of charged particles is reduced, and the dielectric property of the insulating oil is improved; the preparation method has the advantages of simple steps and good modification effect, is beneficial to industrial production and large-scale application of the mixed insulating oil, can meet the requirements of transformers on the heat-conducting property, insulating property and nanoparticle dispersion stability of the insulating oil, and solves the problem of poor dispersion stability of binary nanoparticles in the insulating oil.

Description

Technical Field

[0001] This invention relates to the field of insulating material production and processing technology, and to a method for preparing a mixed insulating oil based on surface-modified nanoparticles. Background Technology

[0002] Oil-immersed power transformers, as core equipment and operational hubs for power system energy conversion, directly determine the safety and stability of the power system and are a crucial link in ensuring reliable power supply from the grid. The insulation performance of this type of transformer is primarily determined by the internal insulation system composed of insulating oil and insulating paper. In this system, the insulating oil mainly undertakes the dual core functions of heat dissipation and insulation. Therefore, the breakdown voltage and thermal conductivity of the insulating oil are key indicators for evaluating its performance, directly affecting the operational reliability of the transformer.

[0003] With the continuous advancement of the construction of a robust and green power grid and the widespread application of environmentally friendly materials, traditional mineral insulating oils, due to their inherent limitations in environmental friendliness and resource sustainability, are no longer able to meet the technical requirements of new high-voltage and high-efficiency transformers. Against this backdrop, plant-based insulating oils, represented by soybean oil, rapeseed oil, and coconut oil, have become ideal alternatives to mineral insulating oils due to their core environmental advantages of being non-toxic and highly biodegradable. Furthermore, plant-based insulating oils possess outstanding characteristics such as high ignition point, high flash point, and a wide range of raw material sources that are recyclable, further highlighting their application potential.

[0004] However, the main component of vegetable insulating oil is triglycerides, which causes its viscosity to be significantly higher than that of mineral insulating oil. This high viscosity severely hinders the oil's heat exchange efficiency and significantly weakens its heat dissipation performance—this not only easily leads to excessive temperature rise during transformer operation but may also trigger internal transformer faults, ultimately threatening the stable operation of the entire power system. Currently, some publicly available literature in the industry reduces the viscosity of mixed insulating oils by adding a certain proportion of mineral oil. For example, patent application CN108130176B (a ternary mixed insulating oil and its preparation method) adds mineral oil as a base oil to soybean oil and palm oil; another example is patent application CN104450037B (a novel transformer anti-aging mixed insulating oil and its preparation method), which prepares a novel transformer anti-aging mixed insulating oil by mixing refined rapeseed oil and 25# mineral oil at a mass ratio of 15% and 85% at room temperature. However, these technical solutions sacrifice the environmental advantages of vegetable insulating oil to some extent, making it difficult to balance performance and environmental requirements. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a method for preparing a mixed insulating oil based on surface-modified nanoparticles. This method solves the problems of poor thermal conductivity and insufficient dielectric strength in existing plant-based insulating oils. Using mixed insulating oil as the base sample, binary nanoparticles of surface-modified KH550 surface-modified ZnO and SiC powders are used as modifying materials. This improves the dispersion stability of nanoparticles in the mixed insulating oil and also forms numerous electron traps within the oil, reducing the migration of charged particles and enhancing the dielectric properties of the insulating oil. The method is simple, has good modification effects, and facilitates the industrial production and large-scale application of this type of mixed insulating oil. It can meet the requirements of transformers for thermal conductivity, insulation performance, and nanoparticle dispersion stability, while simultaneously solving the problem of poor dispersion stability of binary nanoparticles in insulating oil. The specific technical solution is as follows: A method for preparing a mixed insulating oil based on surface-modified nanoparticles includes the following steps: (1) Preparation of nano ZnO: Zn(NO3)2 was added to deionized water under stirring, heated and stirred, and NaOH solution was slowly added dropwise. The reaction was continued to be heated and stirred. After cooling, the filter cake was collected by suction filtration. The filter cake was baked at high temperature and then ground to obtain nano ZnO powder. (2) Surface-modified nano-ZnO: First, n-butanol is added to the reactor, and then silane coupling agent KH550 and nano-ZnO powder from step (1) are added respectively. The mixture is ultrasonically treated, heated and stirred for reflux reaction. The product solution is centrifuged, washed, extracted, dried and ground to obtain KH550 surface-modified nano-ZnO powder. (3) Surface-modified nano-SiC powder: The nano-SiC powder was dried, mixed with silane coupling agent KH550, and then toluene was added. After heating and stirring, the mixture was reacted. After the reaction was complete, it was ultrasonically cleaned while hot. After filtration, grinding and washing, it was ultrasonically dispersed in acetone, centrifuged and dried to obtain KH550 surface-modified nano-SiC powder. (4) Preparation of mixed oil: Coconut insulating oil and Karamay transformer oil are vacuum filtered separately, mixed at a volume ratio of 5:1, heated and stirred to obtain mixed oil; (5) Preparation of mixed insulating oil: The KH550 surface-modified nano ZnO powder from step (2) and the KH550 surface-modified nano SiC powder from step (3) are added to the mixed oil from step (4). After ultrasonic treatment and vacuum drying, the mixed insulating oil based on surface-modified nanoparticles is obtained.

[0006] Preferably, in step (1), the concentration of the Zn(NO3)2 solution is 0.25 mol / L; the concentration of the NaOH solution is 1 mol / L, and the addition is completed within 58 to 62 minutes, and the reaction continues for 58 to 63 minutes after the addition is completed.

[0007] Preferably, in step (1), the heating and stirring temperature is controlled at 58-65℃, and the stirring rate is controlled at 200-250 r / min; the high-temperature baking temperature is controlled at 148-155℃, and the baking time is 3.8-4.2 h; the particle size of the nano ZnO powder is ≤1 mm.

[0008] Preferably, in step (2), the ultrasonic frequency of the ultrasonic treatment is 35-40 kHz, the ultrasonic time is 1.1-1.7 h, the temperature of the reflux reaction is controlled at 99-101 °C, the reaction time is 7.8-8.1 h, and the stirring rate is 150-200 r / min.

[0009] Preferably, in step (2), the washing is performed by washing the centrifuged material with anhydrous ethanol of 99.99% purity; the particle size of the KH550 surface-modified nano ZnO powder is ≤1mm.

[0010] Preferably, in step (3), the drying temperature of the nano-SiC powder is controlled at 95-105℃, the pressure is 58-63pa, and the drying time is 11.8-12.3h; the weight ratio of the silane coupling agent KH550 to the nano-SiC powder is 1:20; and the volume ratio of the amount of toluene added to KH550 is 350:1.

[0011] Preferably, in step (3), the reaction is carried out in a nitrogen atmosphere for 6-8 hours; the particle size of the KH550 surface-modified nano-SiC powder is ≤1mm; and the washing is performed by washing twice with deionized water and acetone respectively.

[0012] Preferably, in step (4), the mixing involves mixing the filtered coconut insulating oil and the filtered Karamay transformer oil at a volume ratio of 5:1; the heating and stirring temperature is 70-75°C, the stirring rate is 150-200 r / min, and the stirring time is 50-60 min.

[0013] Preferably, in step (5), the weight ratio of the KH550 surface-modified nano-ZnO powder to the KH550 surface-modified nano-SiC powder is 3:1, and the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.06–0.3 g / L. More preferably, the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.12–0.24 g / L. Even more preferably, the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.18 g / L.

[0014] Preferably, in step (5), the frequency of the ultrasonic treatment is 35-40 kHz, and it is performed twice, with each treatment lasting 25-30 min. After each ultrasonic treatment, the mixture is stirred at a rate of 150-200 rpm.

[0015] The present invention has at least the following beneficial effects: 1. This invention uses mixed insulating oil as the base oil sample and employs binary nanoparticles of surface-modified KH550 surface-modified nano-ZnO powder and KH550 surface-modified nano-SiC powder as modifying materials. This improves the dispersion stability of nanoparticles in the mixed insulating oil and also forms a large number of electron traps in the mixed insulating oil, reducing the migration of charged particles and improving the dielectric properties of the insulating oil. The modification effect is good, which is conducive to the industrial production and large-scale application of this type of mixed insulating oil and can meet the requirements of transformers for the thermal conductivity, insulation performance and nanoparticle dispersion stability of insulating oil.

[0016] 2. The surface modification of nanoparticles with KH550 in this invention replaces the hydrophilic hydroxyl groups on the nanoparticle surface with lipophilic groups, significantly improving their dispersion stability in mixed insulating oils. The addition of KH550-modified binary nanoparticles to mixed insulating oils creates numerous electron traps, reducing the migration of charged particles and improving the dielectric properties of the mixed insulating oil. Simultaneously, the addition of KH550-modified binary nanoparticles results in a thicker and more compact interface between the nanoparticles and the mixed insulating oil, which increases the contact area between the nanoparticles and the insulating oil, reduces thermal resistance, improves the system's heat transfer efficiency, and enhances thermal conductivity. The preparation method of this invention is simple, has good performance, and is environmentally friendly, making it suitable for widespread application.

[0017] 3. This invention utilizes the silane coupling agent KH550 to modify the surface of nano-ZnO and nano-SiC. KH550-modified binary nanoparticles are then used as modifying materials to prepare a mixed insulating oil. The resulting surface-modified binary nanoparticle-modified mixed insulating oil exhibits a higher breakdown voltage, lower dielectric loss, higher thermal conductivity (improved thermal conductivity), and enhanced dispersion stability (slow and uniform increase in transmittance). Furthermore, the mixing of coconut oil and Karamay transformer oil significantly reduces the viscosity of the insulating oil, lowering the kinematic viscosity of the mixed oil to 28.06 mm. 2 / s, compared to coconut insulating oil, the kinematic viscosity is reduced; the kinematic viscosity of the mixed insulating oil after adding surface-modified binary nanoparticles decreased to 26.79 mm. 2 / s. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the preparation process of KH550 surface-modified nano-ZnO powder according to the present invention; Figure 2 This is a schematic diagram of the preparation process of KH550 surface-modified nano-SiC powder according to the present invention; Figure 3 This is a schematic diagram of the preparation process of the mixed insulating oil based on surface-modified nanoparticles according to the present invention; Figure 4 This is a schematic diagram of the microscopic mechanism of the KH550 modified nanoparticles of the present invention; Figure 5 This is a schematic diagram of the interface mechanism of the surface-modified nanoparticles of the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] To address the existing technical problems mentioned in the background section, the inventors of this application have continuously explored and researched in this field. To overcome the performance bottlenecks of plant-based insulating oils and promote their large-scale application, the inventors turned their attention to nanoparticle modification technology. Due to their excellent thermal conductivity, nanoparticles have been widely used to improve the thermal and electrical properties of insulating materials.

[0023] During their research and development, the inventors unexpectedly discovered that the binary nanoparticle modification scheme significantly improved the insulation strength of insulating oil compared to single nanoparticle modification. However, further in-depth research revealed that the binary nanoparticle-modified insulating oil technology faces the following core bottleneck: the binary nanoparticles exhibit poor dispersion stability in plant-based insulating oils, easily leading to aggregation, which significantly reduces the modification effect and may even introduce new insulation hazards.

[0024] Therefore, how to achieve long-term stable dispersion of binary nanoparticles in plant-based insulating oils and simultaneously improve the oil's overall insulation and heat dissipation performance remains a key technical problem that urgently needs to be solved in the field of electrical insulation materials. Based on this, the inventors of this application have developed the following technical solution after inventive design.

[0025] A method for preparing a mixed insulating oil based on surface-modified nanoparticles, comprising: S1. Add Zn(NO3)2 to deionized water to prepare a Zn(NO3)2 solution with a molar concentration of 0.25 mol / L. Heat and stir, controlling the temperature at 58-65℃ and the stirring rate at 200-250 r / min. Slowly add a NaOH solution with a molar concentration of 1 mol / L, and complete the addition within 58-62 min. After the addition is completed, continue the reaction for 58-63 min. After constant temperature and stirring, a mixed reaction solution is obtained. S2. After heating the mixed reactant solution obtained in step S1, stir until the reaction is complete. The temperature is controlled at 58-65℃ and the stirring rate is controlled at 200-250r / min. Cool to room temperature under natural conditions and filter to obtain filter cake. S3. The filter cake obtained in step S2 is baked at high temperature, with the temperature controlled at 148-155℃ and the baking time being 3.8-4.2h. After being removed, it is ground to obtain nano ZnO powder with a particle size ≤1mm. S4. Add n-butanol to the reactor, and add the silane coupling agent KH550 and the nano ZnO powder obtained in step S3 respectively. Mix to obtain a mixture. Sonicate the mixture at a frequency of 35-40 kHz for 1.1-1.7 h. Heat and stir to carry out reflux reaction at a temperature of 99-101℃ for 7.8-8.1 h and a stirring rate of 150-200 r / min to obtain a product solution. After centrifuging the product solution, wash the precipitate obtained by centrifugation with anhydrous ethanol of 99.99% purity. Place the washed precipitate in a vacuum drying oven for drying and grind it into powder to obtain KH550 surface-modified nano ZnO powder with a particle size ≤1 mm. S5. Place the finished nano-SiC powder in a vacuum drying oven for drying treatment. The temperature is controlled at 95-105℃, the pressure is 58-63pa, and the drying time is 11.8-12.3h. Mix the silane coupling agent KH550 with the nano-SiC powder at a weight ratio of 1:20. Add toluene, and the volume ratio of toluene to KH550 is 350:1. Heat under nitrogen and stir for 6-8h. After the reaction is complete, perform ultrasonic cleaning while hot, filter, and grind to obtain preliminary modified nano-SiC powder with a particle size ≤1mm. S6. The preliminarily modified nano-SiC powder obtained in step S5 is washed twice with deionized water and acetone respectively, ultrasonically dispersed in acetone, centrifuged, and the washed powder is dried to obtain KH550 surface modified nano-SiC powder. S7. Vacuum filter the coconut insulating oil and Karamay transformer oil separately, heat and stir them. Heat to 70-75℃, stir at 150-200 r / min for 50-60 min to obtain filtered coconut insulating oil and filtered Karamay transformer oil. Mix the filtered coconut insulating oil and filtered Karamay transformer oil at a volume ratio of 5:1, heat and stir to obtain mixed oil. S8. The KH550 surface-modified nano-ZnO powder obtained in step S4 and the KH550 surface-modified nano-SiC powder obtained in step S6 are added to the mixed oil in S7 at a weight ratio of 3:1. The mixture is ultrasonically treated at a frequency of 35-40kHz in two separate processes, each lasting 25-30 minutes. After each ultrasonic treatment, the mixture is stirred at a stirring rate of 150-200 rpm and then vacuum dried to obtain the mixed insulating oil based on surface-modified nanoparticles.

[0026] Specifically, the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.06–0.3 g / L.

[0027] More specifically, the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.12–0.24 g / L.

[0028] More specifically, the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.18 g / L.

[0029] Example 1 A method for preparing a mixed insulating oil based on surface-modified nanoparticles, comprising: S1. Add Zn(NO3)2 to deionized water to prepare a Zn(NO3)2 solution with a molar concentration of 0.25 mol / L. Heat and stir at 58℃ and 200 r / min. Slowly add a NaOH solution with a molar concentration of 1 mol / L over 58 min. After the addition is complete, continue the reaction for another 58 min. Stir at a constant temperature to obtain a mixed reaction solution. S2. After heating the mixed reactant solution obtained in step S1, stir until the reaction is complete. The temperature is controlled at 58℃ and the stirring rate is controlled at 200r / min. Cool to room temperature under natural conditions and filter to obtain filter cake. S3. The filter cake obtained in step S2 is baked at a high temperature of 148°C for 3.8 hours. After baking, it is ground to obtain nano ZnO powder with a particle size ≤1mm. S4. Add n-butanol to the reactor, and add the silane coupling agent KH550 and the nano ZnO powder obtained in step S3 respectively. Mix to obtain a mixture. Sonicate the mixture at a frequency of 35 kHz for 1.1 h. Heat and stir to carry out reflux reaction at a temperature of 99 ℃ for 7.8 h and a stirring rate of 150 r / min to obtain a product solution. After centrifuging the product solution, wash the precipitate obtained by centrifugation with anhydrous ethanol with a purity of 99.99%. Place the washed precipitate in a vacuum drying oven for drying and grind it into powder to obtain KH550 surface-modified nano ZnO powder with a particle size ≤1 mm. S5. The finished nano-SiC powder was placed in a vacuum drying oven for drying at 95℃ and 58 Pa for 11.8 h. Silane coupling agent KH550 was mixed with the nano-SiC powder at a weight ratio of 1:20, and toluene was added at a volume ratio of 350:1 to KH550. The mixture was heated under nitrogen atmosphere and stirred for 6 h. After complete reaction, it was ultrasonically cleaned while hot, filtered, and ground to obtain preliminary modified nano-SiC powder with a particle size ≤1 mm. S6. The preliminarily modified nano-SiC powder obtained in step S5 is washed twice with deionized water and acetone respectively, ultrasonically dispersed in acetone, centrifuged, and the washed powder is dried to obtain KH550 surface modified nano-SiC powder. S7. Vacuum filter the coconut insulating oil and Karamay transformer oil separately, heat and stir them. Heat to 70℃, stir at 150r / min for 50min to obtain filtered coconut insulating oil and filtered Karamay transformer oil. Mix the filtered coconut insulating oil and filtered Karamay transformer oil at a volume ratio of 5:1, heat and stir to obtain mixed oil. S8. The KH550 surface-modified nano-ZnO powder obtained in step S4 and the KH550 surface-modified nano-SiC powder obtained in step S6 are added to the mixed oil in S7 at a weight ratio of 3:1. The concentration of surface-modified nanoparticles in the mixed insulating oil is 0.06 g / L. The mixture is ultrasonically treated at a frequency of 35 kHz in two separate processes, each lasting 25 min. After each ultrasonic treatment, the mixture is stirred at a stirring rate of 150 r / min and then vacuum dried to obtain the mixed insulating oil based on surface-modified nanoparticles.

[0030] Example 2 A method for preparing a mixed insulating oil based on surface-modified nanoparticles, comprising: S1. Add Zn(NO3)2 to deionized water to prepare a Zn(NO3)2 solution with a molar concentration of 0.25 mol / L. Heat and stir at 65℃ and 250 r / min. Slowly add a NaOH solution with a molar concentration of 1 mol / L over 62 min. After the addition is complete, continue the reaction for 63 min. Stir at a constant temperature to obtain a mixed reaction solution. S2. After heating the mixed reactant solution obtained in step S1, stir until the reaction is complete. The temperature is controlled at 65℃ and the stirring rate is controlled at 250r / min. Cool to room temperature under natural conditions and filter to obtain filter cake. S3. The filter cake obtained in step S2 is baked at a high temperature of 155℃ for 4.2 hours. After baking, it is ground to obtain nano ZnO powder with a particle size ≤1mm. S4. Add n-butanol to the reactor, and add the silane coupling agent KH550 and the nano ZnO powder obtained in step S3 respectively. Mix to obtain a mixture. Sonicate the mixture at a frequency of 40 kHz for 1.7 h. Heat and stir to carry out reflux reaction at a temperature of 101 ℃ for 8.1 h and a stirring rate of 200 r / min to obtain a product solution. After centrifuging the product solution, wash the precipitate obtained by centrifugation with anhydrous ethanol with a purity of 99.99% and extract it. Place the washed precipitate in a vacuum drying oven for drying and grind it into powder to obtain KH550 surface-modified nano ZnO powder with a particle size ≤1 mm. S5. The finished nano-SiC powder was placed in a vacuum drying oven for drying at 105℃ and 63 Pa for 12.3 h. Silane coupling agent KH550 was mixed with the nano-SiC powder at a ratio of 1:20, and toluene was added at a volume ratio of 350:1 to KH550. The mixture was heated under nitrogen atmosphere and stirred for 8 h. After complete reaction, it was ultrasonically cleaned while hot, filtered, and ground to obtain preliminary modified nano-SiC powder with a particle size ≤1 mm. S6. The preliminarily modified nano-SiC powder obtained in step S5 is washed twice with deionized water and acetone respectively, ultrasonically dispersed in acetone, centrifuged, and the washed powder is dried to obtain KH550 surface modified nano-SiC powder. S7. Vacuum filter the coconut insulating oil and Karamay transformer oil separately, heat and stir them. Heat to 75℃, stir at 200r / min for 60min to obtain filtered coconut insulating oil and filtered Karamay transformer oil. Mix the filtered coconut insulating oil and filtered Karamay transformer oil in a 5:1 ratio, heat and stir to obtain mixed oil. S8. The KH550 surface-modified nano-ZnO powder obtained in step S4 and the KH550 surface-modified nano-SiC powder obtained in step S6 are added to the mixed oil in S7 in a ratio of 3:1. The concentration of surface-modified nanoparticles in the mixed insulating oil is 0.3 g / L. The mixture is ultrasonically treated at a frequency of 40 kHz in two separate processes, each lasting 30 min. After each ultrasonic treatment, the mixture is stirred at a stirring rate of 200 r / min and then vacuum dried to obtain the mixed insulating oil based on surface-modified nanoparticles.

[0031] Example 3 A method for preparing a mixed insulating oil based on surface-modified nanoparticles, comprising: S1. Add Zn(NO3)2 to deionized water to prepare a Zn(NO3)2 solution with a molar concentration of 0.25 mol / L. Heat and stir at 60℃ and 230 r / min. Slowly add a NaOH solution with a molar concentration of 1 mol / L over 60 min. After the addition is complete, continue the reaction for another 60 min. Stir at a constant temperature to obtain a mixed reaction solution. S2. After heating the mixed reactant solution obtained in step S1, stir until the reaction is complete. The temperature is controlled at 60℃ and the stirring rate is controlled at 230r / min. Cool to room temperature under natural conditions and filter to obtain filter cake. S3. The filter cake obtained in step S2 is baked at high temperature, with the temperature controlled at 150℃ and the baking time being 4.0h. After being taken out, it is ground to obtain nano ZnO powder with a particle size ≤1mm. S4. Add n-butanol to the reactor, and add the silane coupling agent KH550 and the nano ZnO powder obtained in step S3 respectively. Mix to obtain a mixture. Sonicate the mixture at a frequency of 38 kHz for 1.4 h. Heat and stir to carry out reflux reaction at a temperature of 100 ℃ for 8.0 h and a stirring rate of 180 r / min to obtain a product solution. After centrifuging the product solution, wash the precipitate obtained by centrifugation with anhydrous ethanol with a purity of 99.99%. Place the washed precipitate in a vacuum drying oven for drying and grind it into powder to obtain KH550 surface-modified nano ZnO powder with a particle size ≤1 mm. S5. The finished nano-SiC powder was placed in a vacuum drying oven for drying at 100℃ and 60 Pa for 12 hours. Silane coupling agent KH550 was mixed with the nano-SiC powder at a weight ratio of 1:20, and toluene was added at a volume ratio of 350:1 to KH550. The mixture was heated under nitrogen atmosphere and stirred for 7 hours. After complete reaction, it was ultrasonically cleaned while hot, filtered, and ground to obtain preliminary modified nano-SiC powder with a particle size ≤1 mm. S6. The preliminarily modified nano-SiC powder obtained in step S5 is washed twice with deionized water and acetone respectively, ultrasonically dispersed in acetone, centrifuged, and the washed powder is dried to obtain KH550 surface modified nano-SiC powder. S7. Vacuum filter the coconut insulating oil and Karamay transformer oil separately, heat and stir them. Heat to 73℃, stir at 180 r / min for 55 min to obtain filtered coconut insulating oil and filtered Karamay transformer oil. Mix the filtered coconut insulating oil and filtered Karamay transformer oil at a volume ratio of 5:1, heat and stir to obtain mixed oil. S8. The KH550 surface-modified nano-ZnO powder obtained in step S4 and the KH550 surface-modified nano-SiC powder obtained in step S6 are added to the mixed oil in S7 at a weight ratio of 3:1. The concentration of surface-modified nanoparticles in the mixed insulating oil is 0.18 g / L. The mixture is ultrasonically treated at a frequency of 38 kHz in two separate processes, each lasting 28 min. After each ultrasonic treatment, the mixture is stirred at a stirring rate of 170 r / min and then vacuum dried to obtain the mixed insulating oil based on surface-modified nanoparticles.

[0032] Example 4 The difference from Example 3 is that the concentration of surface-modified nanoparticles in the prepared mixed insulating oil is 0.12 g / L, while other conditions remain unchanged.

[0033] Example 5 The difference from Example 3 is that the concentration of surface-modified nanoparticles in the prepared mixed insulating oil is 0.24 g / L, while other conditions remain unchanged.

[0034] Comparative Example 1 The difference from Example 3 is that the nano ZnO powder is not surface modified, and the nano ZnO powder from step S3 is directly added to the mixed oil to prepare the mixed insulating oil, while other conditions remain unchanged.

[0035] Comparative Example 2 The difference from Example 3 is that the nano-SiC powder used was not surface modified. The nano-SiC powder was directly added to the mixed oil to prepare the mixed insulating oil, and other conditions remained unchanged.

[0036] Comparative Example 3 The difference from Example 3 is that the added nano-ZnO powder and nano-SiC powder were not subjected to KH550 surface modification treatment. The unmodified nano-ZnO powder and nano-SiC powder were directly added to the mixed oil to prepare the mixed insulating oil, and other conditions remained unchanged.

[0037] Comparative Example 4 The difference from Example 3 is that KH550 surface-modified nano-ZnO powder was not added, while other conditions remained the same.

[0038] Comparative Example 5 The difference from Example 3 is that KH550 surface-modified nano-SiC powder was not added, while other conditions remained the same.

[0039] Comparative Example 6 The difference from Example 3 is that KH550 surface-modified nano-ZnO powder and KH550 surface-modified nano-SiC powder were not added, while other conditions remained the same.

[0040] Performance testing Key physicochemical and electrical performance parameters of the insulating oils prepared by the methods in Examples 1-3 and Comparative Examples 1-6 were tested according to the testing standards of GB / T 265-1988, GB / T 5654-2007, SN / T 3950-2014, NB / SH / T 0836-2010, GB / T507-2002, GB / T 261-2021 and GB / T 21801-2008, respectively. The experimental results are shown in Tables 1 and 2 below.

[0041] Table 1. Test results of the main properties of the mixed insulating oils prepared in Examples 1-3 Table 2. Test results of the main properties of the insulating oils prepared in Comparative Examples 1-6 The experimental data show that Comparative Examples 1-3, due to the lack of nanoparticle surface modification, exhibited poor dispersibility, resulting in increased dielectric loss, decreased breakdown voltage, and deteriorated oxidation stability. Comparative Examples 4-6, lacking one or two types of nanoparticles, showed decreased insulation strength and thermal stability, while slightly increased kinematic viscosity.

[0042] In summary, this invention improves the dispersion stability of nanoparticles in mixed insulating oil, and also forms a large number of electron traps in the mixed insulating oil, reducing the migration of charged particles, improving the dielectric properties of the insulating oil, increasing the heat transfer efficiency of the system, and enhancing the thermal conductivity. It exhibits good performance and high environmental friendliness, meeting the requirements of transformers for the thermal conductivity, insulation performance, and nanoparticle dispersion stability of insulating oil. The surface-modified binary nanoparticle-modified mixed insulating oil prepared by this invention has a higher breakdown voltage than the unmodified oil sample, lower dielectric loss, higher thermal conductivity (improved thermal conductivity), and enhanced dispersion stability (slow and uniform increase in transmittance). The mixing of coconut insulating oil and Karamay transformer oil significantly reduces the viscosity of the insulating oil, lowering the kinematic viscosity of the mixed oil to 28.06 mm. 2 / s, compared to coconut insulating oil, the kinematic viscosity is reduced; the kinematic viscosity of the mixed insulating oil after adding surface-modified binary nanoparticles decreased to 26.79 mm. 2 / s.

[0043] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a mixed insulating oil based on surface-modified nanoparticles, characterized in that, Includes the following steps: (1) Preparation of nano ZnO: Zn(NO3)2 was added to deionized water under stirring, heated and stirred, and NaOH solution was slowly added dropwise. The reaction was continued to be heated and stirred. After cooling, the filter cake was collected by suction filtration. The filter cake was baked at high temperature and then ground to obtain nano ZnO powder. (2) Surface-modified nano-ZnO: First, n-butanol is added to the reactor, and then silane coupling agent KH550 and nano-ZnO powder from step (1) are added respectively. The mixture is ultrasonically treated, heated and stirred for reflux reaction. The product solution is centrifuged, washed, extracted, dried and ground to obtain KH550 surface-modified nano-ZnO powder. (3) Surface-modified nano-SiC powder: The nano-SiC powder was dried, mixed with silane coupling agent KH550, and then toluene was added. After heating and stirring, the mixture was reacted. After the reaction was complete, it was ultrasonically cleaned while hot. After filtration, grinding and washing, it was ultrasonically dispersed in acetone, centrifuged and dried to obtain KH550 surface-modified nano-SiC powder. (4) Preparation of mixed oil: Coconut insulating oil and Karamay transformer oil are vacuum filtered separately, mixed at a volume ratio of 5:1, heated and stirred to obtain mixed oil; (5) Preparation of mixed insulating oil: The KH550 surface-modified nano ZnO powder from step (2) and the KH550 surface-modified nano SiC powder from step (3) are added to the mixed oil from step (4). After ultrasonic treatment and vacuum drying, the mixed insulating oil based on surface-modified nanoparticles is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the Zn(NO3)2 solution is 0.25 mol / L; the concentration of the NaOH solution is 1 mol / L, and the addition is completed within 58 to 62 minutes. After the addition is completed, the reaction continues for 58 to 63 minutes.

3. The preparation method according to claim 1, characterized in that, In step (1), the heating and stirring temperature is controlled at 58-65℃, and the stirring rate is controlled at 200-250 r / min; the high-temperature baking temperature is controlled at 148-155℃, and the baking time is 3.8-4.2 h; the particle size of the nano ZnO powder is ≤1 mm.

4. The preparation method according to claim 1, characterized in that, In step (2), the ultrasonic frequency of the ultrasonic treatment is 35-40 kHz, the ultrasonic time is 1.1-1.7 h, the temperature of the reflux reaction is controlled at 99-101 °C, the reaction time is 7.8-8.1 h, and the stirring rate is 150-200 r / min.

5. The preparation method according to claim 1, characterized in that, In step (2), the washing is performed by washing the centrifuged material with anhydrous ethanol of 99.99% purity; the particle size of the KH550 surface-modified nano ZnO powder is ≤1mm.

6. The preparation method according to claim 1, characterized in that, In step (3), the drying temperature of the nano SiC powder is controlled at 95-105℃, the pressure is 58-63pa, and the drying time is 11.8-12.3h; the weight ratio of the silane coupling agent KH550 to the nano SiC powder is 1:20; and the volume ratio of the toluene to KH550 is 350:

1.

7. The preparation method according to claim 1, characterized in that, In step (3), the reaction is carried out under nitrogen atmosphere for 6-8 hours; the particle size of the KH550 surface-modified nano-SiC powder is ≤1mm; the washing is carried out by washing twice with deionized water and acetone respectively.

8. The preparation method according to claim 1, characterized in that, In step (4), the mixing involves mixing the filtered coconut insulating oil and the filtered Karamay transformer oil at a volume ratio of 5:1; the heating and stirring temperature is 70-75℃, the stirring rate is 150-200r / min, and the stirring time is 50-60min.

9. The preparation method according to claim 1, characterized in that, In step (5), the weight ratio of KH550 surface-modified nano-ZnO powder and KH550 surface-modified nano-SiC powder is 3:1, and the concentration of surface-modified nanoparticles in the mixed insulating oil is 0.06 to 0.3 g / L.

10. The preparation method according to claim 1, characterized in that, In step (5), the ultrasonic treatment is performed at a frequency of 35-40 kHz, in two sessions, each lasting 25-30 minutes. After each ultrasonic treatment, the mixture is stirred at a rate of 150-200 rpm.

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