Modified natural ester insulating oil for power transformer and preparation method thereof

Abstract

The present invention provides a modified natural ester insulating oil for power transformers and a preparation method thereof, comprising the following steps: (1) preparing soybean oil; (2) adding a modified adsorbent to the soybean oil, stirring the oil at 70-75° C. for 8-10 hours, and filtering the oil to obtain impurity-removed soybean oil; (3) decolorizing the impurity-removed soybean oil, filtering the oil with a pore size of 10 μm, stirring the oil under vacuum at 100° C. for 5-6 hours to remove water, adding an antioxidant and an anticoagulant, dissolving the oil, and stirring the oil to obtain the modified natural ester insulating oil for power transformers. The modified natural ester insulating oil for power transformers prepared by the present invention has excellent performance and meets the index requirements of insulating oil for power transformers.

Description

Technical Field

[0001] The invention belongs to the technical field of insulating oils, and in particular relates to a modified natural ester insulating oil special for power transformers and a preparation method thereof. Background Art

[0002] Insulating oil plays a crucial role in transformers, a core component of power systems. It not only acts as an insulating medium to protect the transformer's internal electrical components from electric shock but also serves as a cooling and heat dissipation mechanism. With growing environmental awareness and the growing popularity of sustainable development concepts, traditional mineral oil-based insulating oils, due to their non-renewable nature and potential environmental pollution, are being gradually replaced by newer, more environmentally friendly insulating oils. Natural ester insulating oils stand out among these, due to their unique advantages.

[0003] While natural ester insulating fluid offers many advantages in power transformers, its application also presents several technical and practical challenges: 1. Viscosity and Temperature Characteristics: Natural ester insulating fluids typically have higher viscosities than mineral oils, especially at low temperatures, which can affect their fluidity. High viscosity can reduce cooling efficiency and require additional heating to ensure fluidity during startup or operation in cold climates. 2. Lower Thermal Conductivity: Natural ester insulating fluids have slightly lower thermal conductivity than mineral oils, meaning they may not be as effective at dissipating heat. This is a potential problem for large transformers or those operating under high loads, where good heat dissipation is critical for maintaining performance and extending life. 3. Compatibility Issues: Natural ester insulating fluids may not be fully compatible with some conventional sealing materials, paints, and other non-metallic components, potentially accelerating aging or degrading their performance. 4. Differences in Electrical Properties: While most natural ester insulating fluids provide adequate electrical insulation, their breakdown voltage is typically slightly lower than that of mineral oils. 5. Oxidation Stability: While natural ester insulating fluids exhibit excellent resistance to oxidation, they can still oxidize under extreme conditions, such as high temperatures or prolonged exposure to air. 6. Due to its molecular composition, the pour point of soybean insulating oil is generally higher than -20℃. However, the lowest ambient temperature in most parts of northern my country is lower than -20℃. When the ambient temperature is lower than its pour point, natural ester insulating oil will gradually change from liquid to solid, which greatly limits the application range of natural ester insulating oil.

[0004] Existing methods use a blended insulating oil composed primarily of soybean oil and an appropriate proportion of mineral oil to lower the pour point to around -20°C. However, research has shown that exceeding 10% mineral oil in a vegetable insulating oil can lead to a sharp drop in its flash point, severely impacting its fire resistance and preventing it from meeting IECK-grade requirements. Furthermore, the breakdown voltage of most commercially available insulating oils is less than 65kV, failing to meet practical requirements.

[0005] Therefore, there is an urgent need for a modified natural ester insulating oil dedicated to power transformers and a preparation method thereof. Summary of the Invention

[0006] The purpose of the present invention is to provide a modified natural ester insulating oil special for power transformers and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing modified natural ester insulating oil for power transformers comprises the following steps:

[0009] (1) soybeans are crushed and passed through a 40-80 mesh sieve, the sieved material is extruded and puffed to obtain puffed soybeans, and the puffed soybeans are mixed with water at a mass ratio of 1:(15-20) to obtain a mixed solution; bromelain is first added to the mixed solution for enzymatic hydrolysis, and after the enzyme is inactivated, cellulase is added for enzymatic hydrolysis, and after the enzyme is inactivated, alkaline protease is added for enzymatic hydrolysis, and after the enzyme is inactivated, mixed bacteria are continuously added to ferment, and after the fermentation is completed, the mixture is sterilized, and centrifuged at a temperature of 4-6°C and a rotation speed of 10000-12000 rpm for 15-20 minutes to remove the hydrolyzate and residue to obtain soybean oil.

[0010] (2) adding the modified adsorbent to the soybean oil, stirring at 70-75° C. for 8-10 hours, and filtering to obtain the impurity-removed soybean oil;

[0011] (3) The impurity-removed soybean oil is decolorized, filtered with a pore size of 10 μm, and then stirred for 5-6 hours in a vacuum environment at 100° C. to remove water. An antioxidant and an anticoagulant are added, dissolved and stirred evenly to obtain a modified natural ester insulating oil specifically for power transformers.

[0012] Furthermore, the decolorization process in step (3) is specifically as follows: the decolorizer is white clay, the amount of which is 2-4% of the mass of the insulating oil, and after adding the decolorizer, the mixture is heated under reduced pressure and stirred at a pressure of 2-5 mmHg, a temperature of 90-100°C, a stirring speed of 40-60 r / min, and a time of 1-1.5 hours.

[0013] The clay particle size was 300-500 mesh and was purchased from Tianjin Yandong Haotian Mineral Products Co., Ltd.

[0014] Furthermore, the enzymatic hydrolysis conditions of bromelain in step (1) are as follows: the enzyme amount is 100-110 U / mL of the mixed solution, the pH is adjusted to 5.5-6.0, the enzymatic hydrolysis temperature is 44-47° C., and the enzymatic hydrolysis time is 2-3 h; the enzymatic hydrolysis conditions of cellulase are as follows: the enzyme amount is 110-120 U / mL of the mixed solution, the pH is adjusted to 4.0-4.5, the enzymatic hydrolysis temperature is 44-47° C., and the enzymatic hydrolysis time is 3-4 h; and the enzymatic hydrolysis conditions of alkaline protease are as follows: the enzyme amount is 120-130 U / mL of the mixed solution, the pH is adjusted to 8.8-9.2, the enzymatic hydrolysis temperature is 50-55° C., and the enzymatic hydrolysis time is 4-5 h.

[0015] The present invention improves the dielectric strength of modified natural ester insulating oil for power transformers by using a gradient enzymatic hydrolysis method, using specific enzymes for sequential enzymatic hydrolysis. Analysis shows that the gradient fermentation method effectively removes polar substances in the natural ester oil, such as glycolipids, sterols, and phospholipids, which are prone to forming partial discharge paths under the action of an electric field. Different components in the oil can be gradually removed or modified, ensuring optimal treatment results at each step.

[0016] Furthermore, the extrusion puffing conditions in step (1) are as follows: the extrusion puffing machine sleeve temperature is 90-100° C., and the screw speed is 100-110 r / min.

[0017] Furthermore, the mixed bacteria in step (1) include Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus; the amount of Bacillus licheniformis is 1×10 8 -3×10 8 CFU / mL mixed solution; the amount of Bacillus subtilis is 1×10 9 -3×10 9 CFU / mL mixed solution; the amount of Bacillus pumilus is 6×10 8 -8×10 8 CFU / mL mixed solution.

[0018] Furthermore, the fermentation conditions of the mixed bacteria in step (1) are: pH 6.0-6.5, aerobic fermentation at 30-35°C for 20-25h.

[0019] The present invention utilizes composite bacteria for fermentation after gradient enzymatic hydrolysis to improve the pour point of modified natural ester insulating oils specifically designed for power transformers. Through the synergistic effects of enzymatic hydrolysis and fermentation, the present invention can more comprehensively optimize the physical and chemical properties of the oil. Enzymatic hydrolysis can specifically remove specific impurities and high-melting-point substances, while fermentation can further optimize the composition and structure of the oil, ensuring maximum improvement in the oil's pour point, further lowering the pour point and improving the oil's low-temperature performance.

[0020] They also unexpectedly discovered that adding specific amounts of enzymes and bacteria can improve the dielectric strength of modified natural ester insulating oil for power transformers after long-term storage, maintaining excellent electrical properties and chemical stability during this period. The complex bacteria used in the fermentation process produce a variety of antioxidants that effectively scavenge free radicals, inhibit oil oxidation reactions, and extend the oil's service life. Specific amounts of enzymes and bacteria can improve the oil's thermal stability by optimizing its fatty acid composition and removing harmful impurities. This helps prevent the oil from decomposing or deteriorating in high-temperature environments, maintaining the stability of its dielectric strength.

[0021] Furthermore, the preparation method of the modified adsorbent in step (2) comprises the following steps:

[0022] S1: mixing diatomaceous earth, silicon dioxide and kaolin in a mass ratio of 1: (1.2-1.5): (0.4-0.7) to obtain a mixed adsorbent;

[0023] S2: Place the mixed adsorbent with a mass ratio of 1:(10-15) in a 0.4-0.6 mol / L sodium hydroxide aqueous solution, ultrasonically vibrate for 0.5-1 h, magnetically stir at 120-150 r / min in a 40-45°C water bath for 1-2 h, filter, wash with deionized water until neutral, and vacuum dry at a constant temperature of 80-85°C for 4-6 h;

[0024] S3: Slowly add 20-22 parts by mass of polyvinyl alcohol to 20 parts by mass of deionized water under stirring conditions of 600-800 rpm / min, increase the speed to 1500-1700 rpm / min, stir for 20-30 minutes, continue to add 1-1.3 parts by mass of emulsifier, and reduce the speed to 600-800 rpm / min, stir for 10-15 minutes, slowly add 20-22 parts by mass of dodecyltriethoxysilane, and stir at a speed of 600-800 rpm / min for 30-40 minutes to fully emulsify the dodecyltriethoxysilane to obtain an alkylsilane emulsion;

[0025] S4: slowly adding 80 parts by mass of the mixed adsorbent to the alkylsilane emulsion, increasing the rotation speed to 1300-1500 rpm / min, stirring for 30-40 minutes, centrifuging, drying and crushing the solid to obtain a modified adsorbent.

[0026] The median particle size D50 of the diatomite is 50 μm; it was purchased from Linjiang Dayuan Diatomite New Material Ecological Environmental Protection Technology Co., Ltd., model DZ300N.

[0027] The average particle size of silicon dioxide is 15 nm and the specific surface area is 250 m 2 / g; purchased from Beijing Dekedao Gold Technology Co., Ltd., model: DK-SiO2-15.

[0028] Kaolin with a particle size of 325-500 mesh was purchased from Shandong Qiyi Chemical Technology Co., Ltd.

[0029] In existing techniques, direct addition of an adsorbent for adsorption can hinder adsorption due to the adsorbent's inherent oleophobicity. The present invention, by modifying the adsorbent, can improve the dielectric loss of modified natural ester insulating oils used in power transformers. Analysis indicates that the oleophilic modification of the adsorbent has a stronger affinity for polar impurities in the oil, allowing it to adsorb more impurities and increasing adsorption capacity.

[0030] Furthermore, the emulsifier in S3 includes octylphenol polyoxyethylene ether OP-10, Tween 80 and glyceryl monostearate in a mass ratio of 1: (1.3-1.5): (0.6-0.8).

[0031] And when the present invention uses an emulsifier with a specific ratio, the prepared lipophilic modified adsorbent can improve the thermal stability and oxidation resistance of the insulating oil by removing polar impurities and oxidation products. This helps to prevent the oil from decomposing or deteriorating in a high-temperature environment and maintain the stability of its dielectric strength. The present invention uses alkylsilane to perform hydrophobic treatment on the mixed adsorbent to prepare a super-hydrophobic mixed adsorbent, forming a core-shell structure with the hydrophobic group exposed, which has good hydrophobicity. The use of an emulsifier with a specific ratio is more conducive to the alkylsilane completely wrapping the adsorbent, and is more conducive to forming a core-shell structure with the hydrophilic group facing inward and the hydrophobic group facing outward on the surface of the alkylsilane, which has better system compatibility and stronger adsorption strength, thereby improving the thermal stability and oxidation resistance of the insulating oil.

[0032] Furthermore, in step (2), the modified adsorbent accounts for 10-12 wt% of the soybean oil.

[0033] Furthermore, the antioxidant in step (3) includes at least one of benzoquinone, methyl benzoquinone, p-dimethylquinone, tetramethyl-1,4-benzoquinone, and anthraquinone.

[0034] Furthermore, in step (3), the antioxidant accounts for 1.3-1.8% by mass of the soybean oil.

[0035] Furthermore, the pour point depressant in step (3) is one or more of hexylnaphthalene, octylnaphthalene, and polyacrylate.

[0036] Furthermore, in step (3), the mass percentage of the pour point depressant to the soybean oil is 1.0-1.5%.

[0037] The invention provides a modified natural ester insulating oil specially used for power transformers, which is prepared by the preparation method.

[0038] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0039] 1. The present invention improves the dielectric strength of modified natural ester insulating oil for power transformers by using a gradient enzymatic hydrolysis method and sequentially performing enzymatic hydrolysis with specific enzymes.

[0040] 2. The present invention uses composite bacteria for fermentation after gradient enzymatic hydrolysis, which can improve the pour point of the modified natural ester insulating oil specially used for power transformers.

[0041] 3. When a specific amount of enzymes and bacteria are added, the dielectric strength of modified natural ester insulating oil for power transformers can be improved after long-term storage, and excellent electrical properties and chemical stability can be maintained during long-term storage.

[0042] 4. The present invention can improve the dielectric loss of modified natural ester insulating oil used for power transformers by modifying the adsorbent.

[0043] 5. When the present invention uses an emulsifier with a specific ratio, the prepared oleophilic modified adsorbent can improve the thermal stability and oxidation resistance of insulating oil by removing polar impurities and oxidation products, and maintain the stability of its dielectric strength. DETAILED DESCRIPTION

[0044] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0045] The raw materials used in the following examples of the present invention are all commercially available commodities:

[0046] The enzyme used in the present invention was purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0047] Bacillus licheniformis was purchased from Shanghai Baocang Microorganism Co., Ltd., product number: SHMCC D10742.

[0048] Bacillus subtilis was purchased from Shanghai Preservation Microorganism Co., Ltd., product number: SHMCC D15537.

[0049] Bacillus pumilus was purchased from Shanghai Baocang Microorganism Co., Ltd., product number: SHMCC D10474.

[0050] Bacillus megaterium was purchased from Shanghai Collection Microorganisms Co., Ltd., product number: SHMCC D11374.

[0051] Bacillus amyloliquefaciens was purchased from Shanghai Preservation Microorganism Co., Ltd., product number: SHMCC D10877.

[0052] Bacillus coagulans was purchased from Shanghai Preservative Microorganism Co., Ltd., product number: SHMCC D10638.

[0053] Dodecyltriethoxysilane, CAS: 18536-91-9.

[0054] Polyvinyl alcohol, Anhui Wanwei High-tech Materials Co., Ltd., polyvinyl alcohol PVA 17-99(H).

[0055] Example 1

[0056] This embodiment provides a method for preparing a modified natural ester insulating oil for power transformers, comprising the following steps:

[0057] (1) Soybeans are crushed and passed through a 40-mesh sieve, and the sieved material is extruded and puffed, with the sleeve temperature of the extruder being 95° C. and the screw speed being 105 r / min; puffed soybeans are obtained, and the puffed soybeans are mixed with water at a mass ratio of 1:17 to obtain a mixed solution; bromelain is first added to the mixed solution for enzymolysis, and after the enzyme is inactivated, cellulase is added for enzymolysis, and after the enzyme is inactivated, alkaline protease is added for enzymolysis, and after the enzyme is inactivated, mixed bacteria are continuously added for fermentation, and after the fermentation is completed, the mixture is sterilized, and centrifuged at a temperature of 4° C. and a speed of 10,000 rpm for 15 min to remove the hydrolyzate and residue to obtain soybean oil.

[0058] The enzymatic hydrolysis conditions of bromelain are as follows: the enzyme amount is 105U / mL of the mixed solution, the pH is adjusted to 5.5, the enzymatic hydrolysis temperature is 45℃, and the enzymatic hydrolysis time is 2.5h; the enzymatic hydrolysis conditions of cellulase are as follows: the enzyme amount is 115U / mL of the mixed solution, the pH is adjusted to 4.5, the enzymatic hydrolysis temperature is 45℃, and the enzymatic hydrolysis time is 3.5h; the enzymatic hydrolysis conditions of alkaline protease are as follows: the enzyme amount is 125U / mL of the mixed solution, the pH is adjusted to 9, the enzymatic hydrolysis temperature is 50℃, and the enzymatic hydrolysis time is 4.5h.

[0059] The mixed bacteria include Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus; the amount of Bacillus licheniformis is 2×10 8 CFU / mL mixed solution; the amount of Bacillus subtilis is 2×10 9 CFU / mL mixed solution; the amount of Bacillus pumilus is 7×10 8 CFU / mL mixed solution. The fermentation conditions of the mixed bacteria were: pH 6.0, 35℃ aerobic fermentation for 23h.

[0060] (2) adding the modified adsorbent to the soybean oil (the modified adsorbent accounts for 11 wt % of the soybean oil), stirring at 75° C. for 9 h, and filtering to obtain the impurity-removed soybean oil;

[0061] The preparation method of the modified adsorbent comprises the following steps:

[0062] S1: mixing diatomaceous earth, silicon dioxide and kaolin in a mass ratio of 1:1.3:0.5 to obtain a mixed adsorbent;

[0063] S2: Place the mixed adsorbent with a mass ratio of 1:12 into a 0.5 mol / L sodium hydroxide aqueous solution, ultrasonically vibrate for 0.7 h, magnetically stir at 130 rpm in a 45°C water bath for 1.5 h, filter, wash with deionized water until neutral, and vacuum dry at 82°C for 5 h.

[0064] S3: slowly adding 20 parts by mass of polyvinyl alcohol to 20 parts by mass of deionized water under stirring at 700 rpm / min, increasing the speed to 1600 rpm / min, stirring for 25 minutes, and continuing to add 1 part by mass of an emulsifier, the emulsifier comprising octylphenol polyoxyethylene ether OP-10, Tween 80 and glyceryl monostearate in a mass ratio of 1:1.4:0.7; and reducing the speed to 700 rpm / min, stirring for 15 minutes, slowly adding 20 parts by mass of dodecyltriethoxysilane, stirring at 700 rpm / min for 35 minutes to fully emulsify the dodecyltriethoxysilane to obtain an alkylsilane emulsion;

[0065] S4: 80 parts by mass of the mixed adsorbent was slowly added to the alkylsilane emulsion, the rotation speed was increased to 1400 rpm / min, the mixture was stirred for 35 minutes, and the mixture was centrifuged. The solid was dried and crushed to obtain a modified adsorbent.

[0066] The median particle size D50 of the diatomite is 50 μm; it was purchased from Linjiang Dayuan Diatomite New Material Ecological Environmental Protection Technology Co., Ltd., model DZ300N. The average particle size of silicon dioxide is 15 nm, and the specific surface area is 250 m 2 / g; purchased from Beijing Dekedao Gold Technology Co., Ltd., model: DK-SiO2-15. Kaolin particle size of 325-500 mesh, purchased from Shandong Qiyi Chemical Technology Co., Ltd.

[0067] (3) The impurity-removed soybean oil is decolorized, filtered with a pore size of 10 μm, and then stirred for 5.5 hours in a vacuum environment at 100° C. to remove water. An antioxidant and an anticoagulant are added, dissolved and stirred evenly to obtain a modified natural ester insulating oil specifically for power transformers.

[0068] The antioxidant is benzoquinone, and the weight percentage of the antioxidant in the soybean oil is 1.5%. The pour point depressant is hexylnaphthalene, and the weight percentage of the pour point depressant in the soybean oil is 1.2%.

[0069] The decolorization process specifically involves using white clay as the decolorizer, at a rate of 3% of the insulating oil's mass. After adding the decolorizer, the mixture is heated and stirred under reduced pressure at a pressure of 4 mmHg, a temperature of 95°C, a stirring speed of 50 rpm, and a time of 1.2 hours. The white clay particle size is 300-500 mesh and was purchased from Tianjin Yandong Haotian Mineral Products Co., Ltd.

[0070] Example 2

[0071] This embodiment provides a modified natural ester insulating oil for power transformers, the preparation method of which includes the following steps:

[0072] (1) Soybeans are crushed and passed through an 80-mesh sieve, and the sieved material is extruded and puffed, with the sleeve temperature of the extruder being 90° C. and the screw speed being 110 r / min; puffed soybeans are obtained, and the puffed soybeans are mixed with water at a mass ratio of 1:20 to obtain a mixed solution; bromelain is first added to the mixed solution for enzymolysis, and after the enzyme is inactivated, cellulase is added for enzymolysis, and after the enzyme is inactivated, alkaline protease is added for enzymolysis, and after the enzyme is inactivated, mixed bacteria are continuously added for fermentation, and after the fermentation is completed, the mixture is sterilized, and the mixture is centrifuged at a temperature of 4° C. and a speed of 12000 rpm for 15 min to remove the hydrolyzate and residue to obtain soybean oil.

[0073] The enzymatic hydrolysis conditions of bromelain are as follows: the enzyme amount is 110U / mL of the mixed solution, the pH is adjusted to 6.0, the enzymatic hydrolysis temperature is 44°C, and the enzymatic hydrolysis time is 3h; the enzymatic hydrolysis conditions of cellulase are as follows: the enzyme amount is 120U / mL of the mixed solution, the pH is adjusted to 4.0, the enzymatic hydrolysis temperature is 47°C, and the enzymatic hydrolysis time is 3h; the enzymatic hydrolysis conditions of alkaline protease are as follows: the enzyme amount is 130U / mL of the mixed solution, the pH is adjusted to 8.8, the enzymatic hydrolysis temperature is 55°C, and the enzymatic hydrolysis time is 4h.

[0074] The mixed bacteria include Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus; the amount of Bacillus licheniformis is 3×10 8 CFU / mL mixed solution; the amount of Bacillus subtilis was 1×10 9 CFU / mL mixed solution; the amount of Bacillus pumilus is 8×10 8 CFU / mL mixed solution. The fermentation conditions of the mixed bacteria were: pH 6.0, aerobic fermentation at 35℃ for 25h.

[0075] (2) adding the modified adsorbent to the soybean oil (the modified adsorbent accounts for 10 wt % of the soybean oil), stirring at 75° C. for 8 h, and filtering to obtain the impurity-removed soybean oil;

[0076] The preparation method of the modified adsorbent comprises the following steps:

[0077] S1: diatomaceous earth, silicon dioxide and kaolin are mixed in a mass ratio of 1:1.2:0.4 to obtain a mixed adsorbent;

[0078] S2: Place the mixed adsorbent with a mass ratio of 1:15 into a 0.4 mol / L sodium hydroxide aqueous solution, ultrasonically vibrate for 1 hour, magnetically stir at 150 rpm in a 40°C water bath for 1 hour, filter, wash with deionized water until neutral, and vacuum dry at 85°C for 4 hours;

[0079] S3: slowly adding 20 parts by mass of polyvinyl alcohol to 20 parts by mass of deionized water under stirring at 800 rpm / min, increasing the speed to 1500 rpm / min, stirring for 30 minutes, and continuing to add 1 part by mass of an emulsifier, the emulsifier comprising octylphenol polyoxyethylene ether OP-10, Tween 80 and glyceryl monostearate in a mass ratio of 1:1.3:0.6; and reducing the speed to 800 rpm / min, stirring for 15 minutes, slowly adding 20 parts by mass of dodecyltriethoxysilane, stirring at 600 rpm / min for 40 minutes to fully emulsify the dodecyltriethoxysilane to obtain an alkylsilane emulsion;

[0080] S4: 80 parts by mass of the mixed adsorbent was slowly added to the alkylsilane emulsion, the rotation speed was increased to 1300 rpm / min, the mixture was stirred for 30 minutes, and the mixture was centrifuged. The solid was dried and crushed to obtain a modified adsorbent.

[0081] The median particle size D50 of the diatomite is 50 μm; it was purchased from Linjiang Dayuan Diatomite New Material Ecological Environmental Protection Technology Co., Ltd., model DZ300N. The average particle size of silicon dioxide is 15 nm, and the specific surface area is 250 m 2 / g; purchased from Beijing Dekedao Gold Technology Co., Ltd., model: DK-SiO2-15. Kaolin particle size of 325-500 mesh, purchased from Shandong Qiyi Chemical Technology Co., Ltd.

[0082] (3) The impurity-removed soybean oil is decolorized, filtered with a pore size of 10 μm, and then stirred for 6 hours in a vacuum environment at 100° C. to remove water. An antioxidant and an anticoagulant are added, dissolved and stirred evenly to obtain a modified natural ester insulating oil specifically for power transformers.

[0083] The antioxidant is methyl benzoquinone, and the weight percentage of the antioxidant in the soybean oil is 1.3%. The pour point depressant is octyl naphthalene, and the weight percentage of the pour point depressant in the soybean oil is 1.5%.

[0084] The decolorization process specifically involves using white clay as the decolorizer, at a rate of 4% by weight of the insulating oil. After adding the decolorizer, the mixture is heated and stirred under reduced pressure at a pressure of 5 mmHg, a temperature of 90°C, and a stirring speed of 60 rpm for one hour. The white clay particle size is 300-500 mesh and was purchased from Tianjin Yandong Haotian Mineral Products Co., Ltd.

[0085] Comparative Example 1

[0086] The difference between this comparative example and Example 1 is that the soybean oil is a commercially available product, Yihai Jiali Xiangmanyuan first-grade soybean oil.

[0087] Comparative Example 2

[0088] The difference between this comparative example and Example 1 is that the enzymatic hydrolysis conditions of bromelain are as follows: the enzyme amount is 125 U / mL of the mixed solution, the pH is adjusted to 5.5, the enzymatic hydrolysis temperature is 45°C, and the enzymatic hydrolysis time is 4.5 h; the enzymatic hydrolysis conditions of cellulase are as follows: the enzyme amount is 105 U / mL of the mixed solution, the pH is adjusted to 4.5, the enzymatic hydrolysis temperature is 45°C, and the enzymatic hydrolysis time is 2.5 h; the enzymatic hydrolysis conditions of alkaline protease are as follows: the enzyme amount is 115 U / mL of the mixed solution, the pH is adjusted to 9, the enzymatic hydrolysis temperature is 50°C, and the enzymatic hydrolysis time is 3.5 h.

[0089] Comparative Example 3

[0090] This comparative example differs from Example 1 in that bromelain was replaced with ficin, and cellulase was replaced with neutral protease. The enzymatic hydrolysis conditions for ficin were as follows: an enzyme amount of 105 U / mL of the mixed solution, an adjustment pH of 5.5, an enzymatic hydrolysis temperature of 45°C, and an enzymatic hydrolysis time of 2.5 hours; the enzymatic hydrolysis conditions for neutral protease were as follows: an enzyme amount of 115 U / mL of the mixed solution, an adjustment pH of 7.0, an enzymatic hydrolysis temperature of 45°C, and an enzymatic hydrolysis time of 3.5 hours.

[0091] Comparative Example 4

[0092] The difference between this comparative example and Example 1 is that the mixed bacteria include Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus; the amount of Bacillus licheniformis is 2×10 9 CFU / mL mixed solution; the amount of Bacillus subtilis is 7×10 8 CFU / mL mixed solution; the amount of Bacillus pumilus is 2×10 8 CFU / mL mixed solution. The fermentation conditions of the mixed bacteria were: pH 6.0, 35℃ aerobic fermentation for 23h.

[0093] Comparative Example 5

[0094] The difference between this comparative example and Example 1 is that the mixed bacteria include Bacillus amyloliquefaciens, Bacillus coagulans and Bacillus megaterium. The amount of Bacillus amyloliquefaciens is 2×108 CFU / mL mixed solution; the amount of Bacillus coagulans is 2×10 9 CFU / mL mixed solution; the amount of Bacillus megaterium is 7×10 8 CFU / mL mixed solution.

[0095] Comparative Example 6

[0096] The difference between this comparative example and Example 1 is that the adsorbent is not modified. The adsorbent comprises diatomaceous earth, silicon dioxide, and kaolin in a mass ratio of 1:1.3:0.5; the median particle size D50 of the diatomaceous earth is 50 μm; it is purchased from Linjiang Dayuan Diatomaceous Earth New Material Ecological Environmental Protection Technology Co., Ltd., model DZ300N. The average particle size of silicon dioxide is 15 nm, and the specific surface area is 250 m 2 / g; purchased from Beijing Dekedao Gold Technology Co., Ltd., model: DK-SiO2-15. Kaolin particle size of 325-500 mesh, purchased from Shandong Qiyi Chemical Technology Co., Ltd.

[0097] Comparative Example 7

[0098] The difference between this comparative example and Example 1 is that the emulsifier includes octylphenol polyoxyethylene ether OP-10, Tween 80 and glyceryl monostearate in a mass ratio of 1:1:1.

[0099] Performance Testing

[0100] The modified natural ester insulating oils for power transformers prepared in Examples 1-2 and Comparative Examples 1-7 were subjected to performance tests.

[0101] 1. Acid value: Refer to IEC62021-3 and use a fully automatic acid titrator to test the acid value of the sample. Test each sample twice and take the average value.

[0102] 2. Dielectric Strength: Refer to GB / T507 and use a fully automatic dielectric strength tester to test the breakdown voltage of the samples. Test each sample three times and take the average value. Also, measure the breakdown voltage after 6 months of storage at 25°C and 6 months of storage at 45°C.

[0103] 3. Dielectric loss: Refer to GB / T5654 and use a dielectric loss tester to test the dielectric loss value of the sample at 90°C. Test each sample twice and take the average value.

[0104] 4. Pour point: Refer to GB / T3535 and use a fully automatic pour point tester to test the pour point of the sample. Test each sample twice and take the average value.

[0105] The results are shown in Table 1.

[0106] Table 1 Performance test results

[0107]

[0108] From the above performance test results, it can be seen that the modified natural ester insulating oils for power transformers of Examples 1-2 have excellent comprehensive performance, especially the comprehensive performance of Example 1 is the most outstanding.

[0109] However, the comparative examples were significantly inferior to the embodiments in the corresponding performance tests because they did not adopt the necessary technical solutions. In Comparative Example 1, commercially available soybean oil was used, and it can be seen that the pour point was higher than -20°C and the breakdown voltage was also reduced. In Comparative Example 2, the enzymatic hydrolysis conditions were different, and the dielectric strength of the insulating oil decreased, and the dielectric strength of the insulating oil decreased after long-term storage; in Comparative Example 3, the types of enzymes were different, and the dielectric strength of the insulating oil decreased; in Comparative Example 4, the amount of bacteria added was different, and in Comparative Example 5, the types of bacteria were different, and the pour point of the insulating oil increased, and the dielectric strength after long-term storage decreased; in Comparative Example 6, the adsorbent was not modified, and the dielectric loss factor became larger; in Comparative Example 7, the ratio of the emulsifier was different, and the dielectric strength at high temperature decreased. The above experimental results further demonstrate the importance of the technical solutions defined in the present invention for its technical effects.

[0110] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing modified natural ester insulating oil for power transformers, characterized in that: The following steps are involved: (1) crushing soybeans and sieving them, extruding and puffing the sieved material to obtain puffed soybeans, and mixing the puffed soybeans with water to obtain a mixed solution; first adding bromelain to the mixed solution for enzymolysis, inactivating the enzyme, adding cellulase for enzymolysis, inactivating the enzyme, and then adding alkaline protease for enzymolysis; after inactivating the enzyme, continuing to add mixed bacteria for fermentation; after the fermentation is completed, sterilizing, centrifuging, removing the hydrolyzate and residue, and obtaining soybean oil; The enzymatic hydrolysis conditions of bromelain are as follows: adding 100-110 U / mL of the mixed solution, adjusting the pH to 5.5-6.0, the enzymatic hydrolysis temperature to 44-47°C, and the enzymatic hydrolysis time to 2-3 hours; the enzymatic hydrolysis conditions of cellulase are as follows: adding 110-120 U / mL of the mixed solution, adjusting the pH to 4.0-4.5, the enzymatic hydrolysis temperature to 44-47°C, and the enzymatic hydrolysis time to 3-4 hours; the enzymatic hydrolysis conditions of alkaline protease are as follows: adding 120-130 U / mL of the mixed solution, adjusting the pH to 8.8-9.2, the enzymatic hydrolysis temperature to 50-55°C, and the enzymatic hydrolysis time to 4-5 hours; The mixed bacteria include Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus; the dosage of Bacillus licheniformis is 1×10 8 -3×10 8 CFU / mL mixed solution; the amount of Bacillus subtilis was 1×10 9 -3×10 9 CFU / mL mixed solution; the amount of Bacillus pumilus is 6×10 8 -8×10 8 CFU / mL mixed solution; (2) adding the modified adsorbent to the soybean oil, stirring at 70-75° C. for 8-10 hours, and filtering to obtain the impurity-removed soybean oil; (3) decolorizing the decontaminated soybean oil, filtering it, and then removing water. Finally, an antioxidant and a pour point depressant are added, dissolved, and stirred to obtain a modified natural ester insulating oil for power transformers; The preparation method of the modified adsorbent comprises: S1: mixing diatomaceous earth, silicon dioxide and kaolin in a mass ratio of 1: (1.2-1.5): (0.4-0.7) to obtain a mixed adsorbent; S2: Place the mixed adsorbent in a mass ratio of 1:(10-15) into a sodium hydroxide aqueous solution, ultrasonically oscillate, stir in a 40-45°C water bath for 1-2 hours, filter, wash with deionized water until neutral, and vacuum dry for 4-6 hours; S3: Slowly add 20-22 parts by mass of polyvinyl alcohol to 20 parts by mass of deionized water, stir for 20-30 minutes, continue to add 1-1.3 parts by mass of emulsifier, stir for 10-15 minutes, slowly add 20-22 parts by mass of dodecyltriethoxysilane, and stir at a speed of 600-800 rpm / min for 30-40 minutes to fully emulsify the dodecyltriethoxysilane to prepare an alkylsilane emulsion; the emulsifier includes octylphenol polyoxyethylene ether, Tween 80 and glyceryl monostearate in a mass ratio of 1: (1.3-1.5): (0.6-0.8); S4: slowly adding 80 parts by mass of the mixed adsorbent to the alkylsilane emulsion, stirring for 30-40 minutes, centrifuging, drying and crushing the solid to obtain a modified adsorbent.

2. The method for preparing modified natural ester insulating oil for power transformer according to claim 1, characterized in that: The extrusion and puffing conditions in step (1) are as follows: the extrusion and puffing machine barrel temperature is 90-100° C., and the screw speed is 100-110 r / min.

3. The method for preparing modified natural ester insulating oil for power transformer according to claim 1, characterized in that: The fermentation conditions of the mixed bacteria in step (1) are: pH 6.0-6.5, aerobic fermentation at 30-35°C for 20-25 hours.

4. The method for preparing modified natural ester insulating oil for power transformer according to claim 1, characterized in that: The modified adsorbent in step (2) accounts for 10-12 wt% of the soybean oil.

5. The method for preparing modified natural ester insulating oil for power transformer according to claim 1, characterized in that: The antioxidant in step (3) includes at least one of benzoquinone, methyl benzoquinone, p-dimethylquinone, tetramethyl-1,4-benzoquinone, and anthraquinone; the pour point depressant in step (3) is one or more of hexylnaphthalene, octylnaphthalene, and polyacrylate.

6. A modified natural ester insulating oil for power transformers prepared according to the preparation method according to any one of claims 1 to 5.

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