Preparation method and evaluation method of high-performance mixed insulating oil

Abstract

The invention discloses a preparation method and an evaluation method of high-performance mixed insulating oil, relates to the technical field of preparation of electrical insulating materials, and solves the technical problems of poor oxidation stability of existing insulating oil and insufficiency of an existing insulating oil evaluation system. The preparation method of the high-performance mixed insulating oil comprises the steps of base oil pretreatment, composite nano dispersion liquid preparation, composite antioxidant preparation, modified oil preparation and post-treatment refining, and the high-performance mixed insulating oil is obtained through ternary cooperation of chemical catalytic oxidation resistance of CeO2, physical adsorption stability of SiO2 and the free radical termination effect of the antioxidant. The oxidation stability and the key electrical performance of the mixed oil are remarkably improved, the acid value rise of the mixed oil in the thermal oxidation process can be remarkably inhibited, the oxidation induction period is prolonged, the breakdown voltage and the heat-conducting property of the mixed oil are synchronously improved, and the process is simple and convenient and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrical insulation material preparation, and relates to a preparation method and an evaluation method of high-performance mixed insulation oil. BACKGROUND

[0002] As a key insulating medium in oil-immersed transformers, the oxidation stability of insulation oil is directly related to the long-term operation reliability and service life of the equipment. The widely used mineral insulation oil has excellent electrical properties and low cost advantages, but also has the increasingly prominent problems of poor biodegradability and low flash point. Although natural ester insulation oil (such as soybean oil) has the characteristics of environmental protection and renewable, it is easy to oxidize under high temperature and oxygen environment due to the presence of unsaturated double bonds in the molecule, resulting in an increase in acid value and the generation of precipitates, which affects the insulation performance.

[0003] In order to balance performance and cost, the industry has begun to try the mixed oil scheme of soybean oil and mineral oil, but the mixed oil system still faces the challenge of insufficient oxidation stability. At present, some existing technologies also try to add antioxidants to enhance oxidation stability, such as patent application CN108130176B (a ternary mixed insulation oil and a preparation method thereof), which discloses a ternary mixed insulation oil prepared by using base oil and antioxidants, wherein the base oil includes soybean oil, palm oil, and mineral oil (selected from type 25# mineral oil and / or 45# mineral oil), and the antioxidants are a mixture of 2,6-di-tert-butyl phenol and alkylated phenyl-alpha-naphthylamine. For example, patent application CN119120092A (a low-carbon type multi-component mixed insulation oil resistant to high temperature and strong electric field and application thereof) uses mineral oil, soybean oil, PFAE, isooctyl stearate, and antioxidants to prepare a low-carbon type multi-component mixed insulation oil.

[0004] However, the commonly used single antioxidant (such as BHT) can improve the oxidation stability to a certain extent, but it is easy to volatilize at high temperature and has limited durability. On the other hand, single nanoparticle modification technology (such as adding nano-ZnO and TiO2) can improve the breakdown strength of insulation oil, but it is difficult to fundamentally inhibit the chemical oxidation nature of the oil, and the synergistic effect between different nano materials and between nano materials and antioxidants and the application process still lack systematic research.

[0005] Moreover, the current GB / T12580-1990 evaluation system only gives the 164h end point acid value and precipitates, and cannot evaluate other properties of the insulation oil, so it is also important to develop related evaluation methods. SUMMARY

[0006] In view of the above, the present application provides a kind of, solve the technical problems of poor oxidation stability of existing insulating oil, the deficiency of existing insulating oil evaluation system, by the ternary synergy of chemical catalytic antioxidant of CeO2, physical adsorption stability of SiO2 And the free radical termination effect of antioxidant, significantly improve the oxidation stability and key electrical performance of mixed oil, can significantly inhibit the acid value rise of mixed oil in thermal oxidation process, prolong oxidation induction period, and simultaneously improve its breakdown voltage and heat conduction performance, and process is simple, suitable for industrial production, specific technical scheme is as follows: A preparation method of high-performance mixed insulating oil, comprising the following steps: (1) base oil pretreatment: the refined soybean oil is mixed with mineral insulating oil, heated and stirred to obtain pretreated base oil; (2) preparation of composite nano dispersion liquid: after drying, nano CeO2 and nano SiO2 are weighed and added to the pretreated base oil of step (1), and ultrasonic treatment is performed to obtain a composite nano dispersion liquid; (3) preparation of composite antioxidant: the main antioxidant PG and the auxiliary antioxidant BHT are weighed and mixed uniformly to obtain a composite antioxidant premix; (4) preparation of modified oil: inert gas protection is carried out by continuously introducing high-purity nitrogen into the pretreated base oil of step (1), the composite nano dispersion liquid of step (2) is added first, high-speed shearing stirring is performed, then the composite antioxidant premix of step (3) is added, and stirring is performed uniformly to obtain modified oil; (5) post-treatment refining: the modified oil of step (4) is finely filtered to obtain the high-performance mixed insulating oil.

[0007] Preferably, in step (1), the acid value of the refined soybean oil is less than 0.05 mgKOH / g, and the moisture content is less than 50 ppm; the mass ratio of the refined soybean oil to mineral insulating oil is (3-7):(3-7); the temperature of the heating and stirring is 60-80°C, the rotation speed is 200-400 rpm, and the time is 20-40 min; the mineral insulating oil is 25# transformer oil, the iodine value of the refined soybean oil is 120-140 gI2 / 100g, and the saponification value is 180-200 mgKOH / g.

[0008] Preferably, in step (2), the drying is carried out at 50-70°C for 2-4h; the mass ratio of nano CeO2 to nano SiO2 is 1:(1-3), and the total mass of both accounts for 0.02%-0.08% of the mass of the pretreated base oil; the ultrasonic treatment is carried out at 300-500W ultrasonic power for 40-80min.

[0009] Preferably, in step (2), the surface of the nano-CeO2 and nano-SiO2 is modified by silane coupling agent, wherein the nano-CeO2 is spherical or near-spherical particle with a particle size of 10-30 nm, and the nano-SiO2 is mesoporous spherical or chain-like nano-particle with a particle size of 20-50 nm; the surface modification process of the nano-particle is as follows: the nano-CeO2 and SiO2 are respectively immersed in a silane coupling agent KH-550 ethanol solution with a mass fraction of 5%-8%, and stirred at 40-50°C for 1-2 h; after filtration, drying is performed until a constant weight is obtained.

[0010] Preferably, in step (3), the primary antioxidant PG is propyl gallate with a purity of ≥99%, and the secondary antioxidant BHT is dibutylhydroxytoluene with a purity of ≥98%; the mass ratio of the primary antioxidant PG to the secondary antioxidant BHT is 1: (1-3); the mixing is performed at a speed of 20-40 rpm for 10-20 min.

[0011] Preferably, in step (4), before the composite nano-dispersion liquid is added, the base oil is cooled to 20-35°C, and then the composite nano-dispersion liquid is slowly added in batches; the high-speed shearing stirring is performed at a speed of 800-1200 rpm for 20-40 min to uniformly disperse the nano-particles; the total addition amount of the composite nano-dispersion liquid is 0.04%-0.06% of the mass of the pretreated base oil, and the composite antioxidant premix accounts for 0.3%-0.7% of the mass of the pretreated base oil; after the composite antioxidant premix is added, the stirring speed is adjusted to 500-800 rpm for continuous mechanical stirring for 30-60 min.

[0012] Preferably, in step (5), the fine filtration is performed in a vacuum filtration device at a temperature of 50-70°C and a vacuum degree of -0.08 to -0.10 MPa.

[0013] Preferably, in step (4), the total addition amount of the composite nano-particles is 0.05% of the mass of the base oil, and the mass ratio of CeO2 to SiO2 is 1:2; the speed of the high-speed shearing stirring is 1000 rpm, and the stirring time is 30 min; the mechanical stirring speed after the addition of the composite antioxidant is 600 rpm, and the stirring time is 40 min.

[0014] Preferably, an oxidation stability evaluation method of the high-performance mixed insulating oil prepared by the above preparation method based on the GB / T 12580-1990 standard comprises the following steps: P1. Experimental preparation: select standard low-carbon steel coils and copper coils, polish the surface to be bright with a metallographic sandpaper, ultrasonically clean with acetone and anhydrous ethanol for 10 min respectively, and then dry in a 105°C air-drying oven for 1 h, and cool to room temperature for standby; P2. Accelerated thermal oxidation experiment: accurately take 50.0 mL of the oil sample to be tested into a clean and dry oxidation tube, and respectively put one low-carbon steel coil and one copper coil treated in advance into the oxidation tube; place the oxidation tube in a constant-temperature oil bath at 100.0℃±0.5℃, continuously introduce dry air with a dew point of ≤-40℃ into the oxidation tube at a constant flow rate of (1.0±0.1) L / h, start timing and carry out the accelerated aging experiment for 164 h; P3. Sampling analysis at multiple time points: at 0 h, 72 h, 124 h and 164 h after the start of aging, use a special sampler to take out about 5 g of the oil sample from each oxidation tube, and immediately determine the acid value according to the GB / T264 standard to track the oxidation kinetics process; P4. End-point index determination: after the experiment is completed, take out all the remaining oil samples in the oxidation tube, and determine the sediment content according to the method specified in the appendix of GB / T12580-1990 standard to comprehensively evaluate the oxidation stability of the oil sample.

[0015] Preferably, the high-performance mixed insulating oil prepared by the preparation method is applied in 110kV and above oil-immersed transformers and energy storage system transformers.

[0016] Preferably, in step (4), the flow rate of the high-purity nitrogen introduced is 50-60 mL / min, and the nitrogen atmosphere in the reactor is maintained throughout the process to prevent oxidation of the base oil and modified components.

[0017] Preferably, after the mixed insulating oil is subjected to accelerated thermal oxidation at 100℃ for 164 h, the acid value is ≤0.25 mgKOH / g, the sediment content is ≤0.03%, the breakdown voltage is ≥65 kV, the thermal conductivity is ≥0.19 W / (m·K), the oxidation induction period is ≥80 h, the kinematic viscosity (40℃) is 12-18 mm 2 / s, the flash point is ≥180℃, and the pour point is ≤-15℃, meeting the requirements for the use of oil-immersed transformer insulating medium.

[0018] The present application at least achieves the following beneficial effects: 1. The present application significantly improves the oxidation stability and key electrical properties of the mixed oil through the ternary synergy of chemical catalytic oxidation resistance of CeO2, physical adsorption stability of SiO2 and free radical termination effect of the antioxidant, can significantly inhibit the increase of acid value of the mixed oil during thermal oxidation, prolong the oxidation induction period, and simultaneously improve the breakdown voltage and thermal conductivity, and the process is simple and suitable for industrial production.

[0019] 2. The application uses a mixed oil of refined soybean oil and mineral insulating oil as base oil, adopts specific surface modified cerium dioxide (CeO2) and silicon dioxide (SiO2) nanoparticles as functional fillers, and is compounded with main antioxidant PG (propyl gallate) and auxiliary antioxidant BHT (dibutyl hydroxytoluene), through optimization of nanoparticle addition concentration, mass ratio with antioxidant and addition order, realizes uniform dispersion of each component under inert gas protection and controllable process conditions, through organic combination of nanomodification technology and composite antioxidant modification technology, utilizes ternary synergy of chemical catalytic antioxidant of CeO2, physical adsorption stability of SiO2 and free radical termination effect of antioxidant, can significantly inhibit the increase of acid value of the mixed oil in the thermal oxidation process, prolong the oxidation induction period, and simultaneously improve the breakdown voltage and thermal conductivity.

[0020] 3. The application also provides a complete oxidation stability evaluation scheme, a complete oxidation stability evaluation scheme is designed according to GB / T12580-1990 standard, the prepared insulating oil sample is placed in an accelerated thermal oxidation experiment, through acid value monitoring at multiple time points (0h, 72h, 124h, 164h) and end point precipitate content determination, the synergistic effect of nanoparticles and antioxidants is scientifically verified, the oxidation stability is scientifically verified, the kinetic curve of oil oxidation can be drawn, and the synergistic mechanism is more scientifically and intuitively verified. The technical problems of the deficiencies of the existing evaluation system are solved. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0022] Figure 1 The preparation process flow chart of the high-performance mixed insulating oil of the application; Figure 2 The breakdown voltage and thermal conductivity experiment flow chart of the high-performance (high oxidation stability) mixed insulating oil prepared by the application; Figure 3 The TEM photo of cerium dioxide (CeO2) nanoparticles used in the application; Figure 4 The TEM photo of silicon dioxide (SiO2) nanoparticles used in the application. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of the present application is not limited by the specific embodiments. Unless otherwise defined, all technical terms used in the following have the same meaning as commonly understood by one skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or prepared by existing methods.

[0024] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that can vary depending on the intended application. For numerical ranges, the endpoints are included in the ranges, and the ranges between the endpoints are also included in the ranges. The ranges and values should be construed to be approximations that can vary depending on the intended application.

[0025] The present inventors have been exploring the field of insulating oil and have made many creative designs and countless failed experiments to solve the technical problems in the background art. The present inventors have unexpectedly found that cerium dioxide (CeO2) nanoparticles exhibit intrinsic antioxidant catalytic ability due to their unique Ce 3+ / Ce 4+ Redox properties, and silicon dioxide (SiO2) nanoparticles have high specific surface area and surface silicon hydroxyl groups, which can act as physical barriers and free radical adsorption sites. The combination of the two and the compounding with chemical antioxidants are expected to form a synergistic protection mechanism in mixed oils, but the optimal ratio and addition process are still current technical difficulties.

[0026] More importantly, the current GB / T 12580-1990 evaluation system only evaluates the end point acid value and precipitate after 164 hours, which cannot reflect the oxidation kinetics process, is difficult to distinguish the respective action weights of the nanomaterials and antioxidants, and cannot clearly determine the time period and degree of synergistic effect, resulting in a lack of effective data support for formula optimization and equipment operation and maintenance.

[0027] Therefore, it is urgent to establish a synergistic modification technology that can achieve the triple goals of "oxidation inhibition-electrical improvement-heat conduction enhancement", and a scientific evaluation method that can track the oxidation dynamic process throughout the process, to fill the gap in the existing technology in this field. The present inventors are committed to developing a synergistic modification scheme that is simple in process, suitable for industrialization, and can achieve multiple effects with one dose, and overcoming the defects of the existing standard that can only give end point results and cannot reveal the synergistic mechanism, to achieve the following goals: 1. Acid value ≤0.25 mgKOH / g (reduced by ≥75% compared with the blank oil) after 100℃, 164h accelerated oxidation; 2. Oxidation induction time (OIT) ≥ 80 h (extended by ≥ 160% over the blank oil); 3. Breakdown voltage ≥ 65 kV (improved by ≥ 44%); 4. Thermal conductivity ≥ 0.19 W / (m·K) (improved by ≥ 12%); 5. A "multi-time point sampling-kinetics curve-end point precipitate" evaluation system is provided to match the above performance verification, which is used for rapid determination of synergistic effectiveness in scientific research and engineering field.

[0028] The inventors finally obtained the technical solution of the present application through creative design.

[0029] A preparation method of high-performance mixed insulating oil, comprising the following steps: (1) Base oil pretreatment: refined soybean oil with an acid value of less than 0.05 mgKOH / g, a moisture content of less than 50 ppm, an iodine value of 120-140 gI2 / 100 g, and a saponification value of 180-200 mgKOH / g, and mineral insulating oil (25# transformer oil) are mixed to obtain base oil in a mass ratio of (3-7):(3-7), and the base oil is placed in a clean reactor that can be heated, slowly heated to 60-80°C, and continuously stirred at a speed of 200-400 rpm for 20-40 min at this temperature to reduce the viscosity of the base oil and remove dissolved gas, thereby creating conditions for uniform dispersion of subsequent components, and obtaining pretreated base oil; (2) Preparation of composite nano dispersion liquid: in a dry environment, nanometer cerium dioxide (CeO2) and nanometer silicon dioxide (SiO2) with surface modified by silane coupling agent KH-550 are selected, wherein the CeO2 is spherical or near-spherical particles with a particle size of 10-30 nm, and the SiO2 is mesoporous spherical or chain-shaped nanoparticles with a particle size of 20-50 nm, the two kinds of nanoparticles are first dried at 50-70°C for 2-4 h, then weighed in a mass ratio of nanometer CeO2 to nanometer SiO2 of 1:(1-3), so that the total mass of the two accounts for 0.02%-0.08% of the mass of the pretreated base oil, and the weighed composite nanoparticles (nanometer CeO2 and nanometer SiO2) are dispersed in 5-10 times the mass of the light step (1) pretreated base oil, treated under a ultrasonic power of 300-500 W for 40-80 min to prepare a uniform and stable composite nano dispersion liquid; The surface modification process of the nanoparticles is as follows: the nanometer CeO2 and nanometer SiO2 are respectively soaked in a 5%-8% KH-550 ethanol solution, stirred and reacted at 40-50°C for 1-2 h, filtered and dried to constant weight to obtain; (3) Preparation of composite antioxidant premix: In a dry environment, accurately weigh the main antioxidant PG (propyl gallate) with a purity of ≥99% and the auxiliary antioxidant BHT (butylated hydroxytoluene) with a purity of ≥98% respectively, mix them according to the mass ratio of 1: (1-3), and then place them in a mixer for mixing at a speed of 20-40 rpm for 10-20 min to obtain a uniform composite antioxidant premix; (4) Preparation of modified oil: continuously introduce high-purity nitrogen into the pretreated base oil obtained in step (1) at a flow rate of 50-60 mL / min to protect it under inert gas, maintain the nitrogen atmosphere in the reactor throughout the process to prevent oxidation of the base oil and modified components, cool the base oil to 20-35℃, then slowly add the composite nanodispersion obtained in step (2) in batches, immediately stir at a high speed of 800-1200 rpm for 20-40 min to ensure uniform dispersion of the nanoparticles; then add 0.3%-0.7% of the composite antioxidant premix obtained in step (3) based on the mass of the base oil, adjust the stirring speed to 500-800 rpm, and continue mechanical stirring for 30-60 min; (5) Post-treatment and refining: transfer the modified oil obtained in step (4) to a vacuum filtration device, and perform fine filtration at 50-70℃ and a vacuum degree of -0.08 to -0.10 MPa to obtain a clear and transparent high-performance mixed insulating oil product.

[0030] More specifically, in step (2), the total amount of the composite nanoparticles added is 0.05% of the mass of the base oil, and the mass ratio of CeO2 to SiO2 is 1:2.

[0031] More specifically, in step (4), the stirring speed of the high-speed shearing is 1000 rpm, and the stirring time is 30 min; after adding the composite antioxidant, the mechanical stirring speed is 600 rpm, and the stirring time is 40 min.

[0032] More specifically, after the mixed insulating oil is accelerated to heat oxidation at 100℃ for 164 h, the acid value is ≤0.25 mgKOH / g, the precipitate content is ≤0.03%, the breakdown voltage is ≥65 kV, the thermal conductivity is ≥0.19 W / (m·K), the oxidation induction period is ≥80 h, the kinematic viscosity (40℃) is 12-18 mm² / s, the flash point is ≥180℃, and the pour point is ≤-15℃, meeting the requirements for the use of insulating medium in oil-immersed transformers.

[0033] The application of a high-performance mixed insulating oil prepared by the above-mentioned preparation method in 110 kV and above oil-immersed transformers and energy storage system transformers.

[0034] An oxidation stability evaluation method for a high-performance mixed insulating oil prepared by the above-mentioned preparation method based on the GB / T12580-1990 standard, comprising the following steps: P1. Experimental preparation: Select standard low carbon steel coil and copper coil, polish to the surface bright with metallographic sandpaper, ultrasonic cleaning with acetone, anhydrous ethanol for 10 min respectively, then dry in 105℃ air drying oven for 1h, cool to room temperature for standby; P2. Accelerated thermal oxidation experiment: accurately take 50.0mL of the oil sample to be tested into a clean and dry oxidation tube, and put one low carbon steel coil and one copper coil into it respectively; place the oxidation tube in a constant temperature oil bath stabilized at 100.0℃±0.5℃, and continuously introduce dry air with dew point ≤-40℃ into the oxidation tube at a constant flow rate of (1.0±0.1) L / h, start the timer and conduct a 164h accelerated aging experiment; P3. Sampling analysis at multiple time points: In order to accurately track the oxidation kinetics process, at 0h, 72h, 124h and 164h after the start of aging, about 5g of oil sample was taken from each oxidation tube with a special sampler, and the acid value was immediately determined according to GB / T264 standard to track the oxidation kinetics process; P4. End point index determination: After the experiment, the remaining oil sample in the oxidation tube was taken out, and the sediment content was determined according to the method specified in the appendix of GB / T12580-1990 standard, and the oxidation stability of the prepared high performance mixed insulating oil sample was comprehensively evaluated.

[0035] Example 1 A method for preparing a high performance mixed insulating oil, comprising the following steps: (1) Base oil pretreatment: refine soybean oil with acid value less than 0.05mgKOH / g, moisture content less than 50ppm, iodine value of 120gI2 / 100g, and saponification value of 180mgKOH / g, and mineral insulating oil (25# transformer oil) are mixed according to the mass ratio of 3:7, heated and stirred, the temperature is 60℃, the rotation speed is 200rpm, and the time is 20min, to obtain pretreated base oil; (2) Preparation of composite nano dispersion liquid: according to the mass ratio of 1:1, respectively take nano CeO2 and nano SiO2 dried at 50℃ for 2h, add the pretreated base oil of step (1), the total mass of nano CeO2 and nano SiO2 accounts for 0.02% of the mass of the pretreated base oil, ultrasonic treatment for 40min under the power of 300W, to obtain the composite nano dispersion liquid; the surface of nano CeO2 and nano SiO2 is modified by silane coupling agent, wherein the nano CeO2 is spherical or near-spherical particle with particle size of 10nm, the nano SiO2 is mesoporous spherical or chain-like nano particle with particle size of 20nm, and the surface modification process of nano particles is: immerse nano CeO2 and SiO2 in 5% silane coupling agent KH-550 ethanol solution, stir at 40℃ for 1h, filter and dry to constant weight; (3) Composite antioxidant preparation: according to the mass ratio of 1:1, the main antioxidant PG (propyl gallate) with purity ≥99% and the auxiliary antioxidant BHT (dibutyl hydroxytoluene) with purity ≥98% are weighed respectively, and the materials are mixed uniformly at a speed of 20 rpm for 10 min to obtain a composite antioxidant premix; (4) Modified oil preparation: inert gas protection is carried out by continuously introducing high-purity nitrogen into the pretreated base oil of step (1), and the base oil is cooled to 20°C. First, the composite nanodispersion of step (2) is slowly added in batches. The total amount of the composite nanodispersion is 0.04% of the mass of the pretreated base oil. High-speed shearing stirring is carried out at a speed of 800 rpm for 20 min to uniformly disperse the nanoparticles. Then, the composite antioxidant premix of step (3) is added, which accounts for 0.3% of the mass of the pretreated base oil. After adding the composite antioxidant premix, the stirring speed is adjusted to 500 rpm for continuous mechanical stirring for 30 min to uniformly stir the materials. The modified oil is obtained. (5) Post-treatment refining: the modified oil of step (4) is placed in a vacuum filtration device with a temperature of 50°C and a vacuum degree of -0.08 MPa for fine filtration. The high-performance mixed insulating oil is obtained.

[0036] Specifically, the high-performance mixed insulating oil prepared by the above preparation method is applied in 110 kV and above oil-immersed transformers and energy storage system transformers.

[0037] Specifically, the oxidation stability evaluation method of the high-performance mixed insulating oil prepared by the above preparation method based on the GB / T12580-1990 standard includes the following steps: P1. Experimental preparation: select standard low-carbon steel coils and copper coils, polish the surface to be bright with a metallographic sandpaper, ultrasonically clean with acetone and anhydrous ethanol for 10 min respectively, then dry in a 105°C air-drying oven for 1 h, and cool to room temperature for standby; P2. Accelerated thermal oxidation experiment: accurately measure 50.0 mL of the oil sample to be tested and inject it into a clean and dry oxidation tube, and place one low-carbon steel coil and one copper coil in the oxidation tube respectively; place the oxidation tube in a constant-temperature oil bath at 100.0°C±0.5°C, continuously introduce dry air with a dew point ≤-40°C into the oxidation tube at a constant flow rate of (1.0±0.1) L / h, start the timer and conduct a 164 h accelerated aging experiment; P3. Sampling analysis at multiple time points: at 0 h, 72 h, 124 h and 164 h after the start of aging, about 5 g of oil sample is taken from each oxidation tube with a special sampler, and the acid value is immediately determined according to the GB / T264 standard to track the oxidation kinetics process; P4. Terminal index determination: After the end of the experiment, the remaining oil sample in the oxidation tube was taken out in whole, the content of precipitate was determined according to the method specified in the appendix of GB / T12580-1990 standard, and the oxidation stability of the prepared high-performance mixed insulating oil sample was comprehensively evaluated.

[0038] Example 2 A preparation method of a high-performance mixed insulating oil, comprising the following steps: (1) Base oil pretreatment: refined soybean oil with an acid value less than 0.05 mgKOH / g, a moisture content less than 50 ppm, an iodine value of 140 gI2 / 100g, and a saponification value of 200 mgKOH / g is mixed with mineral insulating oil (25# transformer oil) at a mass ratio of 7:3, heated and stirred, the temperature is 80℃, the rotating speed is 400 rpm, and the time is 40 min, to obtain pretreated base oil; (2) Preparation of composite nano dispersion liquid: nano CeO2 and nano SiO2 dried at 70℃ for 4h are respectively taken at a mass ratio of 1:3, and added into the pretreated base oil of step (1), the total mass of nano CeO2 and nano SiO2 accounts for 0.08% of the mass of the pretreated base oil, and ultrasonic treatment is carried out at 500W ultrasonic power for 80 min to obtain a composite nano dispersion liquid; the surfaces of nano CeO2 and nano SiO2 are both modified by silane coupling agent, wherein the nano CeO2 is spherical or near-spherical particles with a particle size of 30 nm, and the nano SiO2 is mesoporous spherical or chain-like nanoparticles with a particle size of 50 nm, and the surface modification process of the nanoparticles is as follows: the nano CeO2 and SiO2 are respectively immersed in an ethanol solution of silane coupling agent KH-550 with a mass fraction of 8%, and stirred at 50℃ for 2h, then filtered and dried to constant weight to obtain; (3) Preparation of composite antioxidant: a main antioxidant PG (propyl gallate) with a purity of ≥99% and a secondary antioxidant BHT (dibutyl hydroxytoluene) with a purity of ≥98% are respectively taken at a mass ratio of 1:3, and mixed at a rotating speed of 40 rpm for 20 min to make the materials uniformly mixed, to obtain a composite antioxidant premix; (4) Preparation of modified oil: inert gas protection is carried out by continuously introducing high-purity nitrogen into the pretreated base oil of step (1), the base oil is cooled to 35℃, the composite nano dispersion liquid of step (2) is slowly added in batches, the total addition amount of the composite nano dispersion liquid accounts for 0.06% of the mass of the pretreated base oil, high-speed shearing stirring is carried out at a rotating speed of 1200 rpm for 40 min to make the nanoparticles uniformly dispersed, then the composite antioxidant premix of step (3) is added, the composite antioxidant premix accounts for 0.7% of the mass of the pretreated base oil, after the addition of the composite antioxidant premix, the stirring rotating speed is adjusted to 800 rpm for continuous mechanical stirring for 60 min to make the materials uniformly stirred, to obtain modified oil; (5) Post-treatment refining: the modified oil of step (4) is placed in a vacuum filtration device with a temperature of 70°C and a vacuum degree of -0.10 MPa for fine filtration to obtain the high-performance mixed insulating oil.

[0039] Other conditions are the same as in Example 1.

[0040] Example 3 A method for preparing a high-performance mixed insulating oil, comprising the following steps: (1) Base oil pretreatment: refined soybean oil with an acid value of less than 0.05 mgKOH / g, a moisture content of less than 50 ppm, an iodine value of 130 gI2 / 100g, and a saponification value of 190 mgKOH / g is mixed with mineral insulating oil (25# transformer oil) at a mass ratio of 5:5, heated and stirred, the temperature is 70°C, the rotation speed is 300 rpm, and the time is 30 min to obtain pretreated base oil; (2) Preparation of composite nano dispersion liquid: nano CeO2 and nano SiO2 dried at 60°C for 3h are respectively weighed at a mass ratio of 1:2 and added to the pretreated base oil of step (1), the total mass of nano CeO2 and nano SiO2 accounts for 0.05% of the mass of the pretreated base oil, and ultrasonic treatment is performed for 60 min under a ultrasonic power of 400 W to obtain a composite nano dispersion liquid; the surfaces of nano CeO2 and nano SiO2 are both modified by silane coupling agent, wherein nano CeO2 is spherical or near-spherical particles with a particle size of 20 nm, and nano SiO2 is mesoporous spherical or chain-like nanoparticles with a particle size of 35 nm, and the surface modification process of the nanoparticles is as follows: nano CeO2 and SiO2 are respectively immersed in a silane coupling agent KH-550 ethanol solution with a mass fraction of 6.5%, stirred and reacted at 45°C for 1.5h, filtered and dried to constant weight; (3) Preparation of composite antioxidant: main antioxidant PG (propyl gallate) with a purity of ≥99% and auxiliary antioxidant BHT (dibutyl hydroxytoluene) with a purity of ≥98% are respectively weighed at a mass ratio of 1:2, mixed at a rotation speed of 30 rpm for 15 min to uniformly mix the materials, and a composite antioxidant premix is obtained; (4) Modified oil preparation: inert gas protection is performed on the pretreated base oil of step (1) by continuously introducing high-purity nitrogen, the base oil is cooled to 33°C, the composite nano dispersion liquid of step (2) is slowly added in batches, the total addition amount of the composite nano dispersion liquid is 0.05% of the mass of the pretreated base oil, high-speed shearing stirring is performed at a rotation speed of 1000 rpm for 30 min to uniformly disperse the nanoparticles, the composite antioxidant premix of step (3) is then added, the composite antioxidant premix accounts for 0.5% of the mass of the pretreated base oil, the stirring rotation speed is adjusted to 600 rpm after the addition of the composite antioxidant premix, and mechanical stirring is continuously performed for 40 min to uniformly stir the materials, and a modified oil is obtained; (5) Post-treatment refining: the modified oil of step (4) is placed in a vacuum filtration device with a temperature of 60°C and a vacuum degree of -0.09 MPa for fine filtration, to obtain the high-performance mixed insulating oil.

[0041] Other conditions are the same as in Example 1.

[0042] Example 4 A method for preparing a high-performance mixed insulating oil, comprising the following steps: (1) Base oil pretreatment: 250 g of refined soybean oil with an acid value of 0.02 mgKOH / g, a moisture content of 35 ppm, an iodine value of 125 gI2 / 100 g, and a saponification value of 185 mgKOH / g is mixed with 250 g of mineral insulating oil (25# transformer oil), heated and stirred at a temperature of 70°C and a speed of 300 rpm for 30 min to obtain pretreated base oil; (2) Preparation of composite nano dispersion liquid: 0.083 g of spherical nano-CeO2 (average particle size 20 nm) dried at 55°C for 2.5 h and 0.167 g of chain-like nano-SiO2 (average particle size 40 nm) (total mass of the two accounting for 0.05% of the mass of 500 g of the base oil, mass ratio 1:2) are weighed and added to 20 g of the pretreated base oil of step (1), the total mass of nano-CeO2 and nano-SiO2 accounting for 0.03% of the mass of the pretreated base oil, and ultrasonic treatment is performed for 50 min under a ultrasonic power of 350 W to obtain a composite nano dispersion liquid; the surfaces of the nano-CeO2 and nano-SiO2 are modified with silane coupling agent KH-550, and the nano-particle surface modification process is as follows: the nano-CeO2 and SiO2 are respectively immersed in a 6% silane coupling agent KH-550 ethanol solution, stirred and reacted at 50°C for 1 h, filtered and dried to constant weight; (3) Preparation of composite antioxidant: 0.625 g of main antioxidant PG (propyl gallate) with a purity of ≥99% and 1.25 g of auxiliary antioxidant BHT (dibutyl hydroxytoluene) with a purity of ≥98% (mass ratio 1:2) are weighed and mixed at a speed of 25 rpm for 10 min to obtain a composite antioxidant premix; (4) Modified oil preparation: continuously introduce 50 mL / min high-purity nitrogen into the pretreated base oil of step (1) for inert gas protection, slowly add the nano dispersion liquid into the base oil cooled to 25°C using a dropping funnel, the total addition amount of the composite nano dispersion liquid is 0.045% of the mass of the pretreated base oil, immediately after the addition is completed, the mechanical stirring speed is increased to 1000 rpm, and the nano particles are uniformly dispersed by continuously high-speed shearing stirring for 3025 min, then the composite antioxidant premix of step (3) is added, the composite antioxidant premix accounts for 0.4% of the mass of the pretreated base oil, after adding the composite antioxidant premix, the stirring speed is adjusted to 600 rpm for mechanical stirring for 40 min to make the material uniformly stirred, and the modified oil is obtained; (5) Post-treatment refining: the modified oil of step (4) is placed in a vacuum filter device (a Buchner funnel) with a temperature of 55°C and a vacuum degree of -0.085 MPa for fine filtration, a mixed cellulose ester filter membrane with a pore size of 0.22 μm is used, and vacuum filtration is carried out at 60°C and a vacuum degree of -0.09 MPa to obtain the high-performance mixed insulating oil.

[0043] The other conditions are the same as in Example 1.

[0044] Example 5 A method for preparing a high-performance mixed insulating oil, comprising the following steps: (1) Base oil pretreatment: refine soybean oil (350 g) with an acid value of less than 0.05 mgKOH / g, a water content of less than 50 ppm, an iodine value of 135 gI2 / 100 g, and a saponification value of 195 mgKOH / g, and mineral insulating oil (25# transformer oil, 150 g) are mixed in a mass ratio of 7:3, heated and stirred, the temperature is 65°C, the stirring speed is 350 rpm, and the time is 35 min to obtain pretreated base oil; (2) Preparation of composite nano dispersion liquid: nano CeO2 (0.125 g) and nano SiO2 (0.125 g) dried at 65°C for 3.5 h are weighed in a mass ratio of 1:1 and added to pretreated base oil (25 g) of step (1), the total mass of nano CeO2 and nano SiO2 accounts for 0.05% of the mass of the pretreated base oil, and ultrasonic treatment is carried out at 450 W for 70 min to obtain a composite nano dispersion liquid; the surfaces of nano CeO2 and nano SiO2 are modified by silane coupling agent, wherein nano CeO2 is spherical or nearly spherical particles with a particle size of 25 nm, and nano SiO2 is mesoporous spherical or chain-like nanoparticles with a particle size of 40 nm, and the surface modification process of the nanoparticles is as follows: nano CeO2 and SiO2 are respectively immersed in a 7% silane coupling agent KH-550 ethanol solution, stirred and reacted at 48°C for 1.8 h, filtered and dried to constant weight; (3) Compound antioxidant preparation: 1.25 g of main antioxidant PG (propyl gallate) with purity ≥ 99% and 1.25 g of auxiliary antioxidant BHT (butylated hydroxytoluene) with purity ≥ 98% were weighed according to the mass ratio of 1:1, mixed at a speed of 35 rpm for 15 min to make the materials uniformly mixed, and a compound antioxidant premix was obtained; (4) Modified oil preparation: inert gas protection was performed on the pretreated base oil in step (1) by continuously introducing high-purity nitrogen gas at a flow rate of 55 mL / min, the base oil was cooled to 28℃, the compound nanodispersion in step (2) was slowly added in batches, the total amount of the compound nanodispersion was 0.055% of the mass of the pretreated base oil, high-speed shearing stirring was performed at a speed of 900 rpm for 25 min to uniformly disperse the nanoparticles, the compound antioxidant premix in step (3) was then added, the amount of the compound antioxidant premix was 0.3%-0.7% of the mass of the pretreated base oil, the stirring speed was adjusted to 550 rpm after the addition of the compound antioxidant premix, and mechanical stirring was continued for 45 min to uniformly stir the materials, and a modified oil was obtained; (5) Post-treatment and refining: the modified oil in step (4) was placed in a vacuum filtration device with a temperature of 58℃ and a vacuum degree of -0.088 MPa for fine filtration, and a high-performance mixed insulating oil was obtained.

[0045] The other conditions are the same as in Example 1.

[0046] Example 6 A method for preparing a high-performance mixed insulating oil includes the following steps: (1) Base oil pretreatment: 150 g of refined soybean oil with an acid value of less than 0.05 mgKOH / g, a moisture content of less than 50 ppm, an iodine value of 135 gI2 / 100g, and a saponification value of 195 mgKOH / g was mixed with 350 g of mineral insulating oil (25# transformer oil) (mass ratio of 3:7), heated and stirred, the temperature was 75℃, the speed was 250 rpm, and the time was 25 min, and a pretreated base oil was obtained; (2) Preparation of the composite nano-dispersion: 0.0375 g of nano-CeO2 dried at 65 °C for 3.5 h and 0.1125 g of nano-SiO2 dried at 65 °C for 3.5 h were weighed according to a mass ratio of 1:3 and added to 12 g of the pretreated base oil of step (1), the total mass of nano-CeO2 and nano-SiO2 accounting for 0.03% of the mass of the pretreated base oil, and ultrasonic treatment was performed for 80 min under a 500 W ultrasonic power to obtain the composite nano-dispersion; the surfaces of the nano-CeO2 and nano-SiO2 were modified by a silane coupling agent, wherein the nano-CeO2 was a spherical or near-spherical particle with a particle size of 25 nm, and the nano-SiO2 was a mesoporous spherical or chain-shaped nanoparticle with a particle size of 40 nm; the surface modification process of the nanoparticles was as follows: the nano-CeO2 and SiO2 were immersed in a 7% mass fraction of the silane coupling agent KH-550 ethanol solution, and stirring reaction was performed at 48 °C for 1.8 h, and then the nanoparticles were filtered and dried to constant weight; (3) Preparation of the composite antioxidant: 0.5 g of main antioxidant PG (propyl gallate) with a purity of ≥99% and 1.5 g of auxiliary antioxidant BHT (dibutyl hydroxytoluene) with a purity of ≥98% were weighed according to a mass ratio of 1:3, and mixing was performed at a rotation speed of 35 rpm for 20 min to uniformly mix the materials, thereby obtaining a composite antioxidant premix; (4) Preparation of the modified oil: inert gas protection was performed on the pretreated base oil of step (1) by continuously introducing 60 mL / min of high-purity nitrogen, the base oil was cooled to 30 °C, the composite nano-dispersion of step (2) was slowly added in batches, the total addition amount of the composite nano-dispersion accounting for 0.055% of the mass of the pretreated base oil, high-speed shearing stirring was performed at a rotation speed of 800 rpm for 20 min to uniformly disperse the nanoparticles, the composite antioxidant premix of step (3) was then added, the composite antioxidant premix accounting for 0.3%-0.7% of the mass of the pretreated base oil, the rotation speed was adjusted to 700 rpm after the addition of the composite antioxidant premix, and mechanical stirring was continuously performed for 30 min to uniformly mix the materials, thereby obtaining the modified oil; (5) Post-treatment and refinement: the modified oil of step (4) was placed in a vacuum filtration device with a temperature of 65 °C and a vacuum degree of -0.095 MPa for fine filtration, thereby obtaining the high-performance mixed insulating oil.

[0047] The other conditions were the same as in Example 1.

[0048] Comparative Example 1: blank mixed oil without any modifier The difference from Example 4 was that no nanoparticles and any antioxidant were added, no nanoparticles and antioxidant were added in step (4), the mixed oil was only stirred at 600 rpm for 40 min under nitrogen protection, and the other conditions were unchanged.

[0049] Comparative Example 2: mixed oil without adding nano-particle, only adding composite antioxidant (PG:BHT=1:2) The difference from Example 4 is that no nano-particle is added, the composite nano-dispersion addition and high-speed shearing steps in steps (2) and (4) are omitted, only 0.375% of the composite antioxidant (PG 0.625g, BHT 1.25g) is added, and other conditions remain unchanged.

[0050] Comparative Example 3: mixed oil only adding composite nano-CeO2 / SiO2(1:2, 0.05%), without adding composite antioxidant The difference from Example 4 is that no composite antioxidant is added, the composite antioxidant addition step in steps (3) and (4) is omitted, only 0.05% of the composite nano-particle is added, and other conditions remain unchanged.

[0051] According to the evaluation method provided by the present application, the performance of the mixed insulating oil prepared in Examples 1-6 and Comparative Examples 1-3 is systematically evaluated and tested: Oxidation stability evaluation test method: (1) Catalyst preparation: the standard low-carbon steel coil and copper coil are carefully polished to a mirror-like surface with a metallographic sandpaper, and then sequentially ultrasonically cleaned with acetone and anhydrous ethanol for 10 minutes each to completely remove surface contaminants, and then dried in a 105℃ air-drying oven for 1 hour and cooled to room temperature for standby; (2) Accelerated thermal oxidation experiment: 50.0mL of the sample of each example and the sample of each comparative example is respectively placed in a clean and dry oxidation tube, and each is placed with a treated low-carbon steel coil and a copper coil. The oxidation tube is precisely installed in a constant-temperature oil bath that has been stabilized at 100.0℃±0.2℃. The gas path system is connected, and the dry air flow is accurately adjusted to 1.02L / h. Start timing, and perform a standard accelerated aging experiment for 164 hours continuously; (3) Systematic sampling and testing: at 0h, 72h, 124h, and 164h after the start of aging, about 5g of oil sample is accurately extracted from each oxidation tube with a special clean glass syringe, and immediately the acid value is measured according to the GB / T264 standard. After the 164-hour experiment is completed, the sediment content is measured according to the method specified in Appendix of GB / T12580-1990.

[0052] Breakdown voltage evaluation experiment method: According to the dynamic verification method provided by the present application, a breakdown voltage sampling port is reserved in the same oxidation tube of the accelerated thermal oxidation experiment, and sampling and testing are performed at four key nodes of 0h, 72h, 124h, and 164h: (1) Time point sampling: about 50mL of oil sample is extracted at each node with a clean glass syringe, and immediately transferred to a 60℃ vacuum drying oven for degassing for 1h and cooling to 23℃±2℃; (2) Breakdown voltage measurement: according to GB / T507, in an environment of 23℃±2℃, RH≤50%, using 2.5mm ball-ball electrode cup, 2kV / s uniform speed, recording the first flashover value; continuous test for 6 times at the same time point, taking the geometric mean after the first value as the breakdown voltage at this time; (3) Data connection: the results at each time point are plotted as "breakdown voltage-oxidation time" curve in time sequence, for synchronous verification of the maintaining ability of the nano-antioxidant synergistic effect on electrical strength.

[0053] Thermal conductivity evaluation test method: According to the dynamic verification method provided by the application, the same oxidation pipeline is used for acid value and breakdown voltage, and the thermal conductivity is tracked at 0h, 72h, 124h and 164h four nodes: (1) Time point sampling: about 40mL of oil sample is extracted by a clean syringe at each node, degassed at 50℃, -0.09MPa for 30min, and cooled to 25℃±0.1℃; (2) Thermal conductivity measurement: according to the transient hot wire method of ASTM D7896, insert the platinum hot wire probe, apply 1W pulse, and automatically calculate the thermal conductivity; repeat 3 times at each node, RSD≤2%, and take the arithmetic mean; (3) Dynamic curve: plot the thermal conductivity at each time point into "thermal conductivity-oxidation time" curve, compare with the acid value and breakdown voltage curve, and use it for scientific revelation of the whole protection effect of synergistic modification on the heat transfer performance of oil products.

[0054] Meanwhile, according to the test 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, the key physical and electrical performance parameters of the insulating oil prepared by the method of examples 1-6 and comparative examples 1-3 are tested, and the experimental results are shown in Tables 1 and 2.

[0055] Table 1 Test results of main properties of mixed insulating oil prepared by comparative examples 1-3 Table 2 Test results of main properties of insulating oil prepared by examples 1-6 From the above experiment, the mixed insulating oil prepared by the application has an acid value of less than or equal to 0.25 mgKOH / g, a precipitate content of less than or equal to 0.03%, a breakdown voltage of more than or equal to 65 kV, a thermal conductivity of more than or equal to 0.19 W / (m*K), an oxidation induction period of more than or equal to 80 h, a kinematic viscosity (40 DEG C) of 12-18 mm / s, a flash point of more than or equal to 180 DEG C, and a pour point of less than or equal to -15 DEG C, meeting the use requirements of an oil-immersed transformer insulating medium. 2

[0056] In summary, the application can prepare a high-oxidation-stability mixed insulating oil with excellent comprehensive performance through innovative component design and process, and through the ternary synergy of chemical catalytic oxidation resistance of CeO2, physical adsorption stability of SiO2 and free radical termination effect of the antioxidant, the oxidation stability and key electrical properties of the mixed oil are significantly improved, the acid value rise of the mixed oil in the thermal oxidation process is significantly inhibited, the oxidation induction period is prolonged, and the breakdown voltage and thermal conductivity are simultaneously improved, and the process is simple and suitable for industrial production.

[0057] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The particular exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application. It is intended that the scope of the application be defined by the claims appended hereto and their equivalents.​

Claims

1. A method for preparing a high performance blended insulating oil, characterized by, The method comprises the following steps: (1) Base oil pretreatment: refining soybean oil is mixed with mineral insulating oil, heated and stirred to obtain pretreated base oil; (2) Preparation of composite nano dispersion liquid: dried nano CeO2 and nano SiO2 are weighed and added to the pretreated base oil of step (1), and ultrasonic treatment is performed to obtain a composite nano dispersion liquid; (3) Preparation of composite antioxidant: the main antioxidant PG and the auxiliary antioxidant BHT are weighed and uniformly mixed to obtain a composite antioxidant premix; (4) Preparation of modified oil: inert gas protection is performed on the pretreated base oil of step (1) by continuously introducing high-purity nitrogen, the composite nano dispersion liquid of step (2) is first added, high-speed shearing stirring is performed, then the composite antioxidant premix of step (3) is added, and uniform stirring is performed to obtain modified oil; (5) Post-treatment refining: the modified oil of step (4) is finely filtered to obtain the high-performance mixed insulating oil.

2. The production method according to claim 1, characterized by, In step (1), the acid value of the refined soybean oil is less than 0.05 mgKOH / g, and the moisture content is less than 50 ppm; the mass ratio of the refined soybean oil to the mineral insulating oil is (3-7):(3-7); the temperature of the heating and stirring is 60-80°C, the rotation speed is 200-400 rpm, and the time is 20-40 min; the mineral insulating oil is 25# transformer oil, the iodine value of the refined soybean oil is 120-140 gI2 / 100 g, and the saponification value is 180-200 mgKOH / g.

3. The preparation method according to claim 1, characterized in that, In step (2), the drying is performed at 50-70°C for 2-4 h; the mass ratio of the nano CeO2 to the nano SiO2 is 1:(1-3), and the total mass of the two accounts for 0.02%-0.08% of the mass of the pretreated base oil; the ultrasonic treatment is performed at an ultrasonic power of 300-500 W for 40-80 min.

4. The method of claim 1, wherein, In step (2), the surfaces of the nano CeO2 and the nano SiO2 are modified by a silane coupling agent, wherein the nano CeO2 is spherical or near-spherical particles with a particle size of 10-30 nm, and the nano SiO2 is mesoporous spherical or chain-shaped nanoparticles with a particle size of 20-50 nm; the surface modification process of the nanoparticles is as follows: the nano CeO2 and SiO2 are respectively soaked in a 5%-8% silane coupling agent KH-550 ethanol solution, stirred at 40-50°C for 1-2 h, filtered, and dried to constant weight.

5. The preparation method according to claim 1, characterized in that, In step (3), the main antioxidant PG is propyl gallate with a purity of ≥99%, and the auxiliary antioxidant BHT is dibutylhydroxytoluene with a purity of ≥98%; the mass ratio of the main antioxidant PG to the auxiliary antioxidant BHT is 1:(1-3); the uniform mixing is performed at a rotation speed of 20-40 rpm for 10-20 min.

6. The method of claim 1, wherein, In step (4), the base oil is cooled to 20-35℃ before the composite nano-dispersion is added; the high-speed shearing stirring is at a speed of 800-1200 rpm for 20-40 min; the total amount of the composite nano-dispersion added is 0.04-0.06% of the pretreated base oil; the amount of the composite antioxidant premix is 0.3-0.7% of the pretreated base oil; and the stirring speed is adjusted to 500-800 rpm for 30-60 min of mechanical stirring after the composite antioxidant premix is added.

7. The preparation method according to claim 1, characterized in that, In step (5), the fine filtration is performed in a vacuum filter at a temperature of 50-70℃ and a vacuum degree of -0.08 to -0.10 MPa.

8. The method of claim 1, wherein, In step (4), the total amount of the composite nanoparticles added is 0.05% of the base oil, and the mass ratio of CeO2 to SiO2 is 1:2; the speed of the high-speed shearing stirring is 1000 rpm, and the stirring time is 30 min; the speed of the mechanical stirring after the composite antioxidant is added is 600 rpm, and the stirring time is 40 min.

9. An evaluation method of the high performance compounded insulating oil prepared by the production method according to any one of claims 1 to 8, characterized by, The method comprises the following steps: P1. Experimental preparation: select standard low-carbon steel coils and copper coils, polish the surface to be bright with a metallographic sandpaper, ultrasonically clean with acetone and anhydrous ethanol for 10 min each, then dry in a 105℃ air-drying oven for 1 h, and cool to room temperature for standby; P2. Accelerated thermal oxidation experiment: accurately measure 50.0 mL of the oil sample to be tested, inject into a clean and dry oxidation tube, and place one low-carbon steel coil and one copper coil in the oxidation tube respectively, place the oxidation tube in a constant-temperature oil bath at 100.0℃±0.5℃, continuously pass dry air with a dew point of ≤-40℃ into the oxidation tube at a constant flow rate of (1.0±0.1) L / h, start the timer and perform a 164 h accelerated aging experiment; P3. Sampling analysis at multiple time points: at 0 h, 72 h, 124 h and 164 h after the start of aging, take about 5 g of the oil sample from each oxidation tube with a special sampler, immediately measure the acid value according to the GB / T264 standard, and track the oxidation kinetics process; P4. End-point index determination: after the experiment is completed, take out all the remaining oil sample in the oxidation tube, measure the sediment content according to the method specified in the appendix of GB / T12580-1990 standard, and comprehensively evaluate the oxidation stability of the oil sample.

10. Application of the high-performance mixed insulating oil prepared by the preparation method of any one of claims 1-8 in 110 kV and above oil-immersed transformers and energy storage system transformers.

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