Natural ester insulating oil bifunctional antioxidant as well as preparation and application thereof

Abstract

The invention discloses a natural ester insulating oil bifunctional antioxidant as well as preparation and application thereof, and relates to the technical field of insulating oil. According to the bifunctional antioxidant, hydroxyl (-OH) and tert-butyl (-C (CH3) 3) are introduced on the basis of an N-phenyl-alpha-naphthylamine molecular structure, when the bifunctional antioxidant is added into natural ester insulating oil, the tert-butyl can effectively capture free radicals in the molecular structure, the hydroxyl improves the free radical scavenging efficiency, and the antioxidant effect is further improved; hydroxyl can also effectively absorb high-energy ultraviolet light, the lightning impulse resistance of the insulating oil is enhanced, the oxidation resistance of the insulating oil is improved, meanwhile, the lightning impulse resistance of the insulating oil is improved, a synergistic gain effect is achieved, the service life of the insulating oil is jointly prolonged, and the operation safety of electrical equipment is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating oil, and in particular to a natural ester insulating oil dual-function antioxidant and a preparation method and application thereof. Background Art

[0002] The oil-paper insulation system is the core insulation part of the oil-immersed transformer, and its insulation strength is crucial to the safe operation of the transformer. As an important part of the system, the insulating oil will gradually undergo oxidation reactions during the long-term operation of the transformer due to the influence of external factors such as heat and light, generating acidic substances and moisture. These oxidation products will not only affect the performance of the insulating oil itself, but also react chemically with the insulating paper, accelerating the aging of the entire oil-paper insulation system, thereby reducing the insulation strength and operating life of the transformer.

[0003] At present, deterioration can be delayed by filtering or replacing insulating oil, but these methods cannot reverse the damage of oxidation products to insulating paper, and there are still great safety hazards. Adding antioxidants (such as 2,6-di-tert-butyl-p-cresol, tea polyphenols, rosemary extract and other substances) to insulating oil is commonly used at home and abroad to slow down the oxidation reaction of oil products. These additives have achieved certain results in improving antioxidant properties.

[0004] However, the lightning impulse resistance of transformer insulating oil is also a key indicator for evaluating its electrical strength. Existing improvement methods mostly focus on modifying the molecular structure of insulating oil. This method is complex and time-consuming, and it is difficult to promote it in practical applications in a short period of time. As for the research on improving the lightning impulse resistance of ester insulating oil through additive modification, the existing research results have limitations, and more efficient additives and optimization methods are still a blank area that needs to be solved urgently. Therefore, it is urgent to conduct in-depth research on additives for ester insulating oil and explore new ways to improve its lightning impulse breakdown resistance through modified additives, so as to better ensure the safe operation of transformers and extend their service life. Summary of the invention

[0005] The present invention provides a natural ester insulating oil bifunctional antioxidant and a preparation method and application thereof. The prepared bifunctional antioxidant has good stability in the natural ester insulating oil. Compared with traditional antioxidants, it can not only reduce the generation of free radicals in the oil and improve the antioxidant performance of the oil, but also absorb high-energy ultraviolet light under lightning impulse conditions, reduce the streamer generation rate, and improve the lightning breakdown voltage of the natural ester.

[0006] In order to solve the above technical problems, one of the purposes of the present invention is to provide a natural ester insulating oil bifunctional antioxidant, whose molecular structure is:

[0007] In order to solve the above technical problems, the second object of the present invention provides a method for preparing a natural ester insulating oil bifunctional antioxidant, comprising the following steps:

[0008] (1) dissolving N-phenyl-α-naphthylamine in solvent A, maintaining the water content in the system below 10 ppm, adding phenol and catalyst A, heating for reaction, retaining the organic layer solution after the reaction is completed, evaporating to remove the solvent, and washing to obtain a crude product;

[0009] (2) The crude product is dissolved in solvent B, tert-butyl bromide and catalyst B are added, and the reaction is heated. After the reaction is completed, the organic layer solution is retained, washed, evaporated to remove the solvent, and dried to obtain a two-component antioxidant.

[0010] By adopting the above scheme, the present invention introduces hydroxyl (-OH) and tert-butyl (-C(CH 3 ) 3 ) realizes the dual functions of antioxidants, and the antioxidant performance and lightning strike resistance of insulating oil can be greatly improved, reducing the breakdown risk caused by lightning strikes in insulating oil and extending the service life of insulating oil.

[0011] N-phenyl-α-naphthylamine itself has excellent antioxidant properties. By introducing the tert-butyl group with steric hindrance effect, the tert-butyl group can effectively capture free radicals in the molecular structure, reduce the generation of free radicals in the oil, and delay the oxidative degradation process. At the same time, the introduction of hydroxyl groups with high free radical scavenging efficiency can achieve a multi-effect antioxidant capacity and enhance the ultraviolet absorption function of hydroxyl groups.

[0012] In addition, hydroxyl can also effectively absorb high-energy ultraviolet light, reduce the generation of high-energy charged particles in insulating oil under lightning strikes or strong electric fields, inhibit the generation rate of charged particles in the streamer channel, help weaken the electric field strength of the streamer head, reduce the speed of streamer branch expansion, thereby increasing the breakdown voltage of insulating oil and enhancing the lightning strike resistance of insulating oil. When insulating oil is exposed to ultraviolet light, some oil components may be excited to generate free radicals, intensifying the oxidation reaction. The improved antioxidant molecules absorb ultraviolet light, reduce the photo-induced oxidation reaction in insulating oil, and can also reduce the oxidation rate of insulating oil under ultraviolet light.

[0013] As a preferred embodiment, in step (1), the molar ratio of N-phenyl-α-naphthylamine to phenol is 1:(1-1.2).

[0014] As a preferred embodiment, in step (1), the catalyst A is NaOH, KOH, Na 2 CO 3 At least one of .

[0015] As a preferred embodiment, in step (1), the mass ratio of the catalyst A to N-phenyl-α-naphthylamine is 1:(13-14).

[0016] As a preferred embodiment, in step (1), the heating reaction temperature is 120-130°C, and the reaction time is 1-3h.

[0017] As a preferred embodiment, in step (2), the molar ratio of the crude product to tert-butyl bromide is 1:(1.1-1.3).

[0018] As a preferred embodiment, in step (2), the catalyst B is at least one of trifluoromethanesulfonic acid, p-toluenesulfonic acid or trifluoroacetic acid.

[0019] As a preferred embodiment, in step (2), the mass ratio of the catalyst B to the crude product is 1:(7-8).

[0020] As a preferred embodiment, in step (2), the heating reaction temperature is 130-140°C, and the reaction time is 1-3h.

[0021] As a preferred embodiment, the solvent A and solvent B are independent of each other and are at least one of anhydrous ethanol, dichloromethane and chloroform, the mass ratio of the solvent A to N-phenyl-α-naphthylamine is (3-6):100, and the mass ratio of the solvent B to the crude product is (3-6):100.

[0022] In order to solve the above technical problems, the third object of the present invention provides an application of a natural ester insulating oil bifunctional antioxidant in the preparation of natural ester insulating oil.

[0023] In order to solve the above technical problems, the fourth object of the present invention provides a natural ester insulating oil, comprising 0.1wt%-1wt% of a natural ester insulating oil bifunctional antioxidant.

[0024] As a preferred solution, the natural ester insulating oil further comprises 90wt%-99.9wt% of a natural ester matrix and 1wt%-9wt% of a functional additive.

[0025] As a preferred embodiment, the functional auxiliary agent is at least one of a preservative, an antifoaming agent, an anti-emulsifier, and a detergent.

[0026] As a preferred embodiment, the natural ester matrix is ​​soybean vegetable transformer oil.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The bifunctional antioxidant of the present invention is prepared by introducing hydroxyl (-OH) and tert-butyl (-C(CH 3 ) 3), the tert-butyl group can effectively capture free radicals in the molecular structure, and the hydroxyl group improves the free radical scavenging efficiency and delays the oxidative degradation process; the hydroxyl group can also effectively absorb high-energy ultraviolet light, and under the action of lightning strikes or strong electric fields, it reduces the generation of high-energy charged particles in the insulating oil, thereby increasing the breakdown voltage of the insulating oil and enhancing the insulating oil's lightning strike resistance, achieving dual efficacy improvement, with a synergistic gain effect, jointly extending the service life of the insulating oil and improving the operating safety of electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : A schematic diagram of the synthesis route of a natural ester insulating oil bifunctional antioxidant in Preparation Example 1 of the present invention;

[0030] Figure 2 : is the hydrogen nuclear magnetic resonance spectrum of a natural ester insulating oil bifunctional antioxidant in Preparation Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0035] As used herein:

[0036] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0037] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0038] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically inventing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is invented separately. For example, when a range of "1 to 5" is invented, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0039] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0040] Herein, parts and percentages are all based on mass unless otherwise specified.

[0041] "Parts by mass" refers to the basic unit of measurement that represents the proportional relationship between the masses of multiple components. 1 part can represent any unit mass. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Or, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0042] In the description of the present invention, it is necessary to understand that the terms "up", "down", "left", "right", "top", "bottom", etc., indicating directions or positional relationships, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0043] In order to further illustrate the present invention, the natural ester insulating oil dual-function antioxidant provided by the present invention and its preparation method and application are described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present invention. Unless otherwise specified, the raw materials used can be obtained from the market, and the same raw materials are used in parallel experiments.

[0044] Preparation Example 1

[0045] A method for preparing a natural ester insulating oil dual-function antioxidant, the synthetic route is as follows Figure 1 As shown, the following steps are included:

[0046] (1) 4.1 g of N-phenyl-α-naphthylamine was added to a three-necked flask, and 100 mL of anhydrous ethanol was used to dissolve the mixture, and the water content in the system was maintained below 10 ppm. Phenol was added as a hydroxyl-introducing agent, and the molar ratio of N-phenyl-α-naphthylamine to phenol was 1:1.1. 0.3 g of NaOH was added as a catalyst, and the mixture was heated to 120° C. The reaction was controlled to proceed for 2 hours by a reflux condenser. After the reaction was completed, the reaction solution was separated by a separating funnel, and the organic layer was retained and washed with distilled water. The solvent was removed by a rotary evaporator to obtain a crude product of 3-hydroxy-N-phenyl-α-naphthylamine.

[0047] (2) 3.6 g of the crude product was dissolved in 100 mL of anhydrous ethanol, and tert-butyl bromide was added. The molar ratio of the crude product of 3-hydroxy-N-phenyl-α-naphthylamine to tert-butyl bromide was 1:1.2. Then, 0.5 g of trifluoromethanesulfonic acid was added as a catalyst. The reaction temperature was maintained at 130° C. and the reaction was stirred for 2 h. After the reaction was completed, the mixture was separated using a separatory funnel, the organic solution was retained, and the mixture was washed with water for multiple times to remove inorganic by-products. The solvent was removed using a rotary evaporator, and the mixture was dried under vacuum at 50° C. for 8 h to obtain the final product 3-hydroxy-N-phenyl-α-naphthylamine, whose molecular structure is

[0048]

[0049] Comparative Preparation Example 1

[0050] A method for preparing a natural ester insulating oil antioxidant comprises the following steps:

[0051] (1) Add 4.1 g of N-phenyl-α-naphthylamine to a three-necked flask, dissolve it in 100 mL of anhydrous ethanol, maintain the water content in the system below 10 ppm, add 0.5 g of trifluoromethanesulfonic acid as a catalyst, then add tert-butyl bromide, the molar ratio of N-phenyl-α-naphthylamine to tert-butyl bromide is 1:1.2, heat to 130° C., and control the reaction by a reflux condenser for 2 h;

[0052] (2) After the reaction is completed, the organic solution is separated and retained using a separatory funnel, and the organic layer is washed with distilled water for multiple times to remove inorganic by-products, and the solvent is removed using a rotary evaporator, and vacuum drying is performed to obtain the final product.

[0053] Example 1

[0054] A natural ester insulating oil, comprising 0.3 wt % of the two-component antioxidant of Preparation Example 1 and the remainder of soybean plant transformer oil, wherein the soybean plant transformer oil is specifically Cargill Natural ester; the preparation method is: grinding the bifunctional antioxidant of Preparation Example 1, vacuum drying the soybean plant transformer oil for 24 hours, mixing the soybean plant transformer oil and the bifunctional antioxidant of Preparation Example 1 and ultrasonically shaking for 2 hours to obtain.

[0055] Example 2

[0056] A natural ester insulating oil, comprising 0.1wt% of the two-component antioxidant of Preparation Example 1 and the remainder of soybean plant transformer oil, wherein the soybean plant transformer oil is specifically Cargill Natural ester; the preparation method is: grinding the bifunctional antioxidant of Preparation Example 1, vacuum drying the soybean plant transformer oil for 24 hours, mixing the soybean plant transformer oil and the bifunctional antioxidant of Preparation Example 1 and ultrasonically shaking for 2 hours to obtain.

[0057] Example 3

[0058] A natural ester insulating oil, comprising 0.5 wt% of the two-component antioxidant of Preparation Example 1 and the remainder of soybean plant transformer oil, wherein the soybean plant transformer oil is specifically Cargill Natural ester; the preparation method is: grinding the bifunctional antioxidant of Preparation Example 1, vacuum drying the soybean plant transformer oil for 24 hours, mixing the soybean plant transformer oil and the bifunctional antioxidant of Preparation Example 1 and ultrasonically shaking for 2 hours to obtain.

[0059] Comparative Example 1

[0060] A natural ester insulating oil, comprising 0.3wt% N-phenyl-α-naphthylamine antioxidant and the balance soybean plant transformer oil, the soybean plant transformer oil being specifically Cargill Natural ester; the preparation method is: grinding N-phenyl-α-naphthylamine antioxidant, vacuum drying soybean vegetable transformer oil for 24 hours, mixing soybean vegetable transformer oil and N-phenyl-α-naphthylamine antioxidant and ultrasonically shaking for 2 hours to obtain the natural ester.

[0061] Comparative Example 2

[0062] A natural ester insulating oil, comprising 0.3wt% 2,6-di-tert-butyl-p-cresol antioxidant and the balance soybean plant transformer oil, the soybean plant transformer oil being specifically Cargill Natural ester; the preparation method is: grinding 2,6-di-tert-butyl-p-cresol antioxidant, vacuum drying soybean plant transformer oil for 24 hours, mixing soybean plant transformer oil and 2,6-di-tert-butyl-p-cresol antioxidant and ultrasonically shaking for 2 hours to obtain the natural ester.

[0063] Comparative Example 3

[0064] A natural ester insulating oil, comprising 0.5wt% 2,6-di-tert-butyl-p-cresol antioxidant and the balance soybean plant transformer oil, the soybean plant transformer oil being specifically Cargill Natural ester; the preparation method is: grinding 2,6-di-tert-butyl-p-cresol antioxidant, vacuum drying soybean plant transformer oil for 24 hours, mixing soybean plant transformer oil and 2,6-di-tert-butyl-p-cresol antioxidant and ultrasonically shaking for 2 hours to obtain the natural ester.

[0065] Comparative Example 4

[0066] A natural ester insulating oil, comprising 0.3 wt % of the antioxidant of comparative preparation example 1 and the remainder of soybean plant transformer oil, wherein the soybean plant transformer oil is specifically Cargill Natural ester; the preparation method is: grinding the antioxidant of comparative preparation example 1, vacuum drying the soybean vegetable transformer oil for 24 hours, mixing the soybean vegetable transformer oil and the antioxidant of comparative preparation example 1 and ultrasonically vibrating for 2 hours to obtain.

[0067] Comparative Example 5

[0068] A natural ester insulating oil, comprising 2 wt% of the two-component antioxidant of Preparation Example 1 and the remainder of soybean plant transformer oil, wherein the soybean plant transformer oil is specifically Cargill Natural ester; the preparation method is: grinding the bifunctional antioxidant of Preparation Example 1, vacuum drying the soybean plant transformer oil for 24 hours, mixing the soybean plant transformer oil and the bifunctional antioxidant of Preparation Example 1 and ultrasonically shaking for 2 hours to obtain.

[0069] Comparative Example 6

[0070] A natural ester insulating oil, including soybean plant transformer oil; the preparation method is: vacuum drying the soybean plant transformer oil for 24 hours, the soybean plant transformer oil is specifically Cargill The natural ester is then subjected to ultrasonic vibration for 2 hours to obtain.

[0071] Performance testing

[0072] 1. The two-component antioxidant product obtained in Preparation Example 1 was verified by nuclear magnetic resonance (NMR) analysis. The obtained nuclear magnetic resonance hydrogen spectrum results are as follows: Figure 2 shown.

[0073] 2. The natural ester insulating oil prepared in the embodiment and the comparative example was subjected to an accelerated aging test. 100 g of the natural ester insulating oil was weighed and placed in a constant temperature box for heat aging. The heat aging temperature was 120° C. and the heat aging time was 7 d, 14 d, 21 d, and 28 d to accelerate the oxidation rate of the natural ester insulating oil. The acid value of the natural ester insulating oil before and after aging was determined according to GB / T 264-1983 standard. The test results are shown in Table 1 below.

[0074] 3. The natural ester insulating oils prepared in the examples and comparative examples were subjected to lightning impulse tests according to GB-T 21222-2007 standard to measure their positive polarity lightning impulse voltage resistance values. The test results are shown in Table 1 below.

[0075] Table 1 - Performance test results of natural ester insulating oils in the present application examples and comparative examples

[0076]

[0077]

[0078] During the oxidation process of transformer oil, cyclohexane acid and low molecular fatty acids such as formic acid, acetic acid, isopropyl acid, etc. are generated. These acidic products not only cause serious corrosion to the metal materials in the transformer, but also destroy the cellulose macromolecules in the insulating paper. Therefore, the acid value in the oil becomes one of the important indicators for measuring the aging degree of transformer oil. As shown in Table 1, after 28 days of accelerated aging, the acid value of the natural ester insulating oil in Comparative Example 6 without adding an antioxidant increased rapidly. After adding an antioxidant to Examples 1-3, the acid value was lower than that of Comparative Example 6. Among them, the acid value of the natural ester insulating oil in Example 1 with 0.3wt% of a bifunctional antioxidant added had the smallest change, indicating that the antioxidant capacity was good.

[0079] As shown in the aging test results of Example 1 and Comparative Example 4 in Table 1, the N-phenyl-α-naphthylamine in the two-component antioxidant of Example 4 itself has excellent antioxidant properties. By introducing a phenolic hydroxyl group with a strong free radical scavenging ability, the free radical scavenging efficiency can be improved. At the same time, the introduction of a tert-butyl group with a steric hindrance effect can effectively capture free radicals, enhance the thermal stability of the molecule and prevent the propagation of the oxidation process, thereby achieving a multi-effect improvement in antioxidant capacity. However, since the antioxidant of Comparative Example 4 does not have a hydroxyl functional group, its free radical scavenging ability is not as good as that of Example 1, resulting in its inhibition of the acid value of the insulating oil being weaker than that of Example 1.

[0080] As shown in Table 1, from the lightning impulse test results of Example 1 and Comparative Example 6, compared with Comparative Example 6, after adding the bifunctional antioxidant in Example 1, the positive polarity lightning impulse voltage of the natural ester insulating oil is significantly improved, mainly by introducing hydroxyl and tert-butyl groups with ultraviolet absorption function on the basis of the original N-phenyl-α-naphthylamine structure. The improved antioxidant can effectively absorb high-energy ultraviolet light, reduce the generation of high-energy charged particles in the insulating oil under the action of lightning impulse or strong electric field, and inhibit the generation rate of charged particles in the streamer channel, which helps to weaken the electric field strength of the streamer head and reduce the speed of streamer branch expansion, thereby improving the breakdown voltage of the insulating oil and enhancing the lightning impulse resistance of the insulating oil.

[0081] As shown in the aging test results of Example 1 and Comparative Example 5 in Table 1, the antioxidant content of Comparative Example 5 is doubled. Although it has a more obvious inhibition on the increase of the acid value of the insulating oil in the early stage of aging, the acid value increases significantly in the later stage of aging. This may be due to the decomposition of excessive antioxidants during the aging process to produce free radicals, causing a chain reaction. In addition, the addition of excessive antioxidants will also inhibit the improvement of the lightning impulse resistance of the insulating oil.

[0082] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A natural ester insulating oil dual-function antioxidant, characterized in that: Its molecular structure is:

2. The method for preparing the natural ester insulating oil dual-function antioxidant according to claim 1, characterized in that: The following steps are involved: (1) dissolving N-phenyl-α-naphthylamine in solvent A, maintaining the water content in the system below 10 ppm, adding phenol and catalyst A, heating for reaction, retaining the organic layer solution after the reaction is completed, washing, and evaporating to remove the solvent to obtain a crude product; (2) The crude product is dissolved in solvent B, tert-butyl bromide and catalyst B are added, and the reaction is heated. After the reaction is completed, the organic layer solution is retained, washed, evaporated to remove the solvent, and dried to obtain a two-component antioxidant.

3. The method for preparing the natural ester insulating oil dual-function antioxidant according to claim 2, characterized in that: In step (1): The molar ratio of N-phenyl-α-naphthylamine to phenol is 1:(1-1.2); And / or, the catalyst A is at least one of NaOH, KOH, and Na2CO3; And / or, the mass ratio of the catalyst A to N-phenyl-α-naphthylamine is 1:(13-14); And / or, the heating reaction temperature is 120-130° C., and the reaction time is 1-3 h.

4. The method for preparing the natural ester insulating oil dual-function antioxidant according to claim 2, characterized in that: In step (2): The molar ratio of the crude product to tert-butyl bromide is 1:(1.1-1.3); And / or, the catalyst B is at least one of trifluoromethanesulfonic acid, p-toluenesulfonic acid or trifluoroacetic acid; And / or, the mass ratio of the catalyst B to the crude product is 1:(7-8); And / or, the heating reaction temperature is 130-140° C., and the reaction time is 1-3 h.

5. The method for preparing the natural ester insulating oil dual-function antioxidant according to claim 2, characterized in that: The solvent A and solvent B are independent of each other and are at least one of anhydrous ethanol, dichloromethane and chloroform. The mass ratio of the solvent A to N-phenyl-α-naphthylamine is (3-6):100, and the mass ratio of the solvent B to the crude product is (3-6):

100.

6. Use of the natural ester insulating oil bifunctional antioxidant according to any one of claims 1 to 5 in the preparation of natural ester insulating oil.

7. A natural ester insulating oil, characterized in that: The invention comprises 0.1wt%-1wt% of the natural ester insulating oil bifunctional antioxidant as claimed in any one of claims 1-5.

8. The natural ester insulating oil according to claim 7, characterized in that The natural ester insulating oil further comprises 90 wt % to 99.9 wt % of a natural ester matrix and 1 wt % to 9 wt % of a functional additive.

9. The natural ester insulating oil according to claim 7, characterized in that The functional auxiliary agent is at least one of a preservative, an antifoaming agent, an anti-emulsifier and a detergent.

10. The natural ester insulating oil according to claim 7, characterized in that: The natural ester matrix is ​​soybean vegetable transformer oil.

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