Compound antioxidant for natural ester insulating oil, insulating oil and preparation method

Abstract

The invention discloses a compound antioxidant for natural ester insulating oil, the insulating oil and a preparation method, and relates to the field of insulating oil. The compound antioxidant is prepared from the following components in parts by weight: 0.3 to 1.4 parts of 2, 6-di-tert-butyl-p (dimethylaminomethyl) phenol; 0.1 part to 0.9 part of tetraethylenepentamine; 0.1 part to 0.9 part of an auxiliary antioxidant; and the auxiliary antioxidant is at least one of 2, 6-butylated hydroxytoluene, tert-butylhydroquinone and 2, 4, 6-tri-tert-butylphenol. According to the invention, a plurality of antioxidant active components are matched with each other to serve as the compound antioxidant, and the addition proportion of each component is controlled, so that the adaptation degree of the compound antioxidant with the natural ester insulating oil is improved, the electrical insulation performance of the insulating oil is not influenced, the oxidation resistance of the natural ester insulating oil can be improved to the greatest extent, the required addition amount of the antioxidant is small, and the service life of the natural ester insulating oil is prolonged. The material has the advantages of good thermal stability, good anti-oxidation effect, high volume resistivity, low cost and the like.

Description

Technical Field

[0001] The invention relates to the field of insulating oil, in particular to a compound antioxidant for natural ester insulating oil, the insulating oil and a preparation method thereof. Background Art

[0002] As an important liquid insulating medium, insulating oil plays a role in improving the electrical insulation strength and heat dissipation performance of oil-immersed insulated high-voltage power transmission and transformation equipment such as transformers, circuit breakers, current and voltage transformers, and bushings. Traditional mineral insulating oil is widely used for its excellent dielectric and cooling properties, but in fact, the specific fractions are mainly composed of hydrocarbons, with low ignition point (usually below 160°C), low flash point, and non-renewable. Therefore, it is not suitable for some special occasions, such as densely populated areas, so it is necessary to find a new liquid insulating medium with high ignition point, biodegradable, renewable, and environmentally friendly.

[0003] Compared with mineral insulating oil, natural ester insulating oil is derived from oil crops such as soybeans and rapeseed. It has the advantages of high flash point, natural degradation, and renewability. It has good environmental protection characteristics and fire resistance, filling the specific application scenarios of fire safety and environmental protection standards that mineral insulating oil cannot meet.

[0004] However, due to the complex sources of natural ester insulating oil, there are more unsaturated carbon-carbon double bonds and carbon-carbon triple bonds in the oil, which significantly reduces the oxidation stability of natural ester insulating oil. The most intuitive manifestation of this property is the short oil change cycle of natural ester insulating oil. At present, the most commonly used method to improve the oxidation stability of natural ester insulating oil is to add antioxidants, but the antioxidant effect is still insufficient, the antioxidant time is short, and although the purpose of improving the antioxidant performance can be achieved by increasing the amount of antioxidants, it reduces the electrical insulation performance of natural ester insulating oil. Summary of the invention

[0005] The invention provides a compound antioxidant for natural ester insulating oil, the insulating oil and a preparation method thereof. Aiming at the problem that the natural ester insulating oil is easily oxidized, a plurality of antioxidant active ingredients are compounded to effectively improve the antioxidant property of the insulating oil. Meanwhile, the compound antioxidant can be adapted to the natural ester insulating oil and effectively improve the volume resistivity of the insulating oil.

[0006] In order to solve the above technical problems, one of the objects of the present invention is to provide a compound antioxidant for natural ester insulating oil, comprising the following components in parts by weight:

[0007] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol: 0.3-1.3 parts;

[0008] Tetraethylenepentamine: 0.1-0.5 parts;

[0009] Auxiliary antioxidant: 0.1-0.9 parts;

[0010] The auxiliary antioxidant is at least one of 2,6-di-tert-butyl-p-cresol, tert-butylhydroquinone and 2,4,6-tri-tert-butylphenol.

[0011] Since natural ester insulating oil has a complex source and contains a large number of unsaturated carbon-carbon double bonds and carbon-carbon triple bonds, its electrical insulation performance is easily affected by antioxidant components. In the compound antioxidant of the present application, a variety of antioxidant active components are selected to cooperate with each other, and the addition amount of each component and the ratio between the components are strictly controlled to improve the compatibility of the compound antioxidant with the natural ester insulating oil. When added to the natural ester insulating oil, it is evenly dispersed after dissolution, and does not affect the volume resistivity of the insulating oil. At the same time, the antioxidant performance of the natural ester insulating oil can be maximized, and the required amount of antioxidant added is reduced. It has the advantages of good thermal stability, good antioxidant effect and low cost.

[0012] As a preferred embodiment, the invention comprises the following components in parts by weight:

[0013] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol: 0.6-1.2 parts;

[0014] Tetraethylenepentamine: 0.1-0.5 parts;

[0015] Auxiliary antioxidant: 0.2-0.7 parts;

[0016] As a preferred embodiment, the auxiliary antioxidant includes 2,6-di-tert-butyl-p-cresol and tert-butylhydroquinone in a mass ratio of (1-2):(1-2).

[0017] As a preferred embodiment, the auxiliary antioxidant includes 2,6-di-tert-butyl-p-cresol and tert-butylhydroquinone in a mass ratio of 1:1.

[0018] As a preferred embodiment, the mass ratio of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and auxiliary antioxidant is (7-9): (2-4): (3-5).

[0019] As a preferred embodiment, the mass ratio of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and auxiliary antioxidant is 8:3:4.

[0020] The composite additive of the present application controls the auxiliary antioxidant to be 2,6-di-tert-butyl-p-cresol and tert-butylhydroquinone in a ratio of 1:1, and at the same time controls the mass ratio of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and the auxiliary antioxidant to be 8:3:4. The proportion of each component is better, the antioxidant performance of the prepared natural ester insulating oil is optimal, and the composite antioxidant has the lowest effect on the electrical insulation performance of the natural ester insulating oil, and the comprehensive performance of the insulating oil is good.

[0021] In order to solve the above technical problems, the second object of the present invention is to provide an application of a compound antioxidant for natural ester insulating oil in the field of preparing natural ester insulating oil.

[0022] In order to solve the above technical problems, the third object of the present invention is to provide an insulating oil with high oxidation resistance and resistivity, comprising a compound antioxidant with a mass fraction of 0.5wt%-5wt% and the remainder of natural ester insulating oil, wherein the compound antioxidant is a compound antioxidant for natural ester insulating oil.

[0023] As a preferred solution, the mass fraction of the compound antioxidant is 1wt%-3wt%.

[0024] As a preferred embodiment, the mass fraction of the compound antioxidant is 1.2wt%-2.1wt%.

[0025] As a preferred embodiment, the natural ester insulating oil is at least one of soybean oil, rapeseed oil, camellia oil and sunflower oil.

[0026] As a preferred solution, the insulating oil further comprises 0.1-5wt% of a metal passivator, and the metal passivator is at least one of benzotriazole, methylbenzotriazole, and Irgamet 39.

[0027] In order to solve the above technical problems, the fourth object of the present invention is to provide a method for preparing insulating oil with high oxidation resistance and resistivity, comprising the following steps:

[0028] The compound antioxidant and other additives are added into the natural ester insulating oil, mixed and stirred for 0.5-5h, the stirring temperature is 40-80°C, and the stirring speed is 100-1000r / min to obtain the insulating oil.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present application selects a variety of antioxidant active ingredients to cooperate with each other as a compound antioxidant to improve its compatibility with natural ester insulating oil, does not affect the electrical insulation performance of the insulating oil, ensures the normal use of the insulating oil, and at the same time can maximize the antioxidant performance of the natural ester insulating oil. Adding a small amount of compound antioxidant can meet the antioxidant requirements of the natural ester insulating oil, and has the advantages of good thermal stability, good antioxidant effect, high volume resistivity, low cost, etc. DETAILED DESCRIPTION

[0031] The following will be combined with 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] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with the examples, but they should not be construed as limiting the scope of protection of the present invention. Raw materials used in the following examples and comparative examples of the present application, unless otherwise specified, can be obtained from commercial sources, and the same raw materials are used in parallel experiments.

[0035] Example 1

[0036] An insulating oil with high oxidation resistance and resistivity comprises 98.2wt% of soybean insulating oil, 1wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.3wt% of tetraethylenepentamine and 0.5wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0037] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and 2,6-di-tert-butyl-p-cresol were added to soybean insulating oil in sequence, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0038] Example 2

[0039] An insulating oil with high oxidation resistance and resistivity comprises 98.8wt% of soybean insulating oil, 0.6wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.1wt% of tetraethylenepentamine and 0.5wt% of tert-butylhydroquinone, and a preparation method thereof comprises the following steps:

[0040] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and tert-butylhydroquinone-p-cresol are sequentially added to soybean insulating oil, and the mixture is stirred for 1 hour at a stirring temperature of 60° C. and a stirring rate of 400 r / min to obtain insulating oil.

[0041] Example 3

[0042] An insulating oil with high oxidation resistance and resistivity comprises 97.9wt% of soybean insulating oil, 1.2wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.2wt% of tetraethylenepentamine and 0.7wt% of 2,4,6-tri-tert-butylphenol, and a preparation method thereof comprises the following steps:

[0043] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and 2,4,6-tri-tert-butylphenol were added to soybean insulating oil in sequence, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 500 r / min to obtain insulating oil.

[0044] Example 4

[0045] An insulating oil with high oxidation resistance and resistivity comprises 98.5wt% of soybean insulating oil, 0.8wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.3wt% of tetraethylenepentamine, 0.2wt% of tert-butylhydroquinone and 0.2wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0046] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine, tert-butylhydroquinone and 2,6-di-tert-butyl-p-cresol were added to soybean insulating oil in sequence, and the mixture was stirred for 1 hour at a stirring temperature of 60° C. and a stirring rate of 400 r / min to obtain insulating oil.

[0047] Example 5

[0048] An insulating oil with high oxidation resistance and resistivity comprises 98.4wt% of soybean insulating oil, 0.5wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.5wt% of tetraethylenepentamine and 0.6wt% of 2,4,6-tri-tert-butylphenol, and a preparation method thereof comprises the following steps:

[0049] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and 2,4,6-tri-tert-butylphenol were added to soybean insulating oil in sequence, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 500 r / min to obtain insulating oil.

[0050] Comparative Example 1

[0051] An insulating oil comprises 98.2 wt% of soybean insulating oil, 1 wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol and 0.8 wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0052] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol and 2,6-di-tert-butyl-p-cresol were sequentially added into soybean insulating oil, and the mixture was mixed and stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0053] Comparative Example 2

[0054] An insulating oil comprises 98.2 wt% of soybean insulating oil, 0.8 wt% of tetraethylene pentamine and 1 wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0055] Tetraethylenepentamine and 2,6-di-tert-butyl-p-cresol were sequentially added to the soybean insulating oil, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0056] Comparative Example 3

[0057] An insulating oil comprises 98.2 wt% of soybean insulating oil, 1 wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol and 0.8 wt% of tetraethylenepentamine, and a preparation method thereof comprises the following steps:

[0058] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol and tetraethylenepentamine were added to soybean insulating oil in sequence, and the mixture was mixed and stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0059] Comparative Example 4

[0060] An insulating oil comprises 98.2wt% of soybean insulating oil and 1.8wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0061] 2,6-di-tert-butyl-p-cresol was added to the soybean insulating oil, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0062] Comparative Example 5

[0063] An insulating oil comprises 97.7 wt% of soybean insulating oil, 1.4 wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.1 wt% of tetraethylenepentamine and 0.3 wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0064] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and 2,6-di-tert-butyl-p-cresol were added to soybean insulating oil in sequence, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0065] Comparative Example 6

[0066] An insulating oil with high oxidation resistance and resistivity comprises 98.2wt% of soybean insulating oil, 0.5wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 1wt% of tetraethylenepentamine and 0.3wt% of 2,6-di-tert-butyl-p-cresol, and a preparation method thereof comprises the following steps:

[0067] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and 2,6-di-tert-butyl-p-cresol were added to soybean insulating oil in sequence, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0068] Comparative Example 7

[0069] An insulating oil comprises 98.2 wt% of synthetic ester insulating oil, 1 wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.3 wt% of tetraethylenepentamine and 0.5 wt% of 2,6-di-tert-butyl-p-cresol, wherein the synthetic ester insulating oil is pentaerythritol ester, and a preparation method thereof comprises the following steps:

[0070] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and 2,6-di-tert-butyl-p-cresol were sequentially added to the synthetic ester insulating oil, and the mixture was stirred for 0.5 h at a stirring temperature of 60° C. and a stirring rate of 300 r / min to obtain insulating oil.

[0071] Comparative Example 8

[0072] An insulating oil comprises 98.8 wt% of synthetic ester insulating oil, 0.6 wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.1 wt% of tetraethylenepentamine and 0.5 wt% of tert-butylhydroquinone, wherein the synthetic ester insulating oil is pentaerythritol ester. The preparation method comprises the following steps:

[0073] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and tert-butylhydroquinone-p-cresol are sequentially added to the synthetic ester insulating oil, and the mixture is stirred for 1 hour at a stirring temperature of 60° C. and a stirring rate of 400 r / min to obtain insulating oil.

[0074] Comparative Example 9

[0075] An insulating oil comprises 98.5wt% of synthetic ester insulating oil, 0.8wt% of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, 0.3wt% of tetraethylenepentamine, 0.2wt% of tert-butylhydroquinone and 0.2wt% of 2,6-di-tert-butyl-p-cresol, wherein the synthetic ester insulating oil is pentaerythritol ester. The preparation method comprises the following steps:

[0076] 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine, tert-butylhydroquinone and 2,6-di-tert-butyl-p-cresol are sequentially added to the synthetic ester insulating oil, mixed and stirred for 1 hour at a stirring temperature of 60° C. and a stirring rate of 400 r / min to obtain insulating oil.

[0077] Performance testing

[0078] (1) Antioxidation Test: The insulating oil samples prepared in the embodiments of the present invention and the comparative examples were subjected to oxidation stability tests using Shanghai Shenkai Company's SKY3021-Ⅱ automatic lubricating oil oxidation stability tester. Pure soybean insulating oil and synthetic ester insulating oil were used as blank samples. The test results of the oxidation induction time of the insulating oil are shown in Table 1.

[0079] (2) Volume resistivity test: The volume resistivity of the insulating oil samples prepared in the embodiments of the present invention and the comparative examples was tested using an Austrian BAUR DTL C insulating oil dielectric loss tester. Pure soybean insulating oil and synthetic ester insulating oil were used as blank samples. The test results are shown in Table 1.

[0080] Table 1 - Antioxidation and resistivity test results of insulating oil samples of the present application examples and comparative examples

[0081]

[0082]

[0083]

[0084] As shown in Table 1, the total amount of compound additives in Examples 1-5 is 1.8wt%, 1.2wt%, 2.1wt%, 1.5wt% and 1.6wt%, respectively, among which the content of compound additives in Example 2 is the lowest, and the content of compound additives in Example 3 is the highest. However, the test results show that the insulating oil of Example 4 has the highest antioxidant capacity and volume resistivity, followed by Example 1, and the content of compound additives in the insulating oil of Example 4 is lower than that of Examples 1 and 3. This shows that by controlling the components and the proportions of the components in the compound additives within the range of Example 4, the antioxidant capacity and volume resistivity of the natural ester insulation can be maximized.

[0085] As shown in Table 1, the total amount of the compounded additives in Comparative Examples 1-4 is the same as that in Example 1, except that tetraethylene pentamine is not added in Comparative Example 1, 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol is not added in Comparative Example 2, 2,6-di-tert-butyl-p-cresol is not added in Comparative Example 3, and only 2,6-di-tert-butyl-p-cresol is added in Comparative Example 4. The test results show that although the oxidation induction time of the insulating oils of Comparative Examples 1-4 is higher than that of the pure natural ester insulating oil, the antioxidant capacity of Comparative Examples 2-3 is still not high enough, and the volume resistivity of Comparative Examples 1-2 and 4 is greatly reduced, especially in Comparative Example 4, indicating that the compounded antioxidant combination of Comparative Examples 1-4 is not well compatible with the natural ester insulating oil, which will affect the electrical insulation performance of the insulating oil.

[0086] As shown in Table 1, the total amount of the compounded additives in Comparative Examples 5-6 is the same as that in Example 1, except that the amount of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol added in Comparative Example 5 is too high, while the amount of tetraethylenepentamine added in Example 6 is too high. The antioxidant capacity and volume resistivity of Comparative Examples 5-6 are both reduced, which indicates that the excessively high concentration of 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol and tetraethylenepentamine in the natural ester insulating oil system will affect the electrical insulation performance, and the coordination effect of the antioxidant capacity will also be reduced.

[0087] As shown in Table 1, the compound antioxidants of Comparative Examples 7-9 are completely consistent with Examples 1-2 and 4, respectively, but the compound antioxidants are not highly compatible with synthetic ester insulating oils. When added to synthetic ester insulating oils, although the antioxidant capacity can be improved to a certain extent, the electrical properties of the synthetic ester insulating oils will be affected, thereby reducing the volume resistivity.

[0088] 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 compound antioxidant for natural ester insulating oil, characterized in that: The composition comprises the following components in parts by weight: 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol: 0.3-1.3 parts; Tetraethylenepentamine: 0.1-0.5 parts; Auxiliary antioxidant: 0.1-0.9 parts; The auxiliary antioxidant is at least one of 2,6-di-tert-butyl-p-cresol, tert-butylhydroquinone and 2,4,6-tri-tert-butylphenol.

2. The compound antioxidant for natural ester insulating oil according to claim 1, characterized in that: The composition comprises the following components in parts by weight: 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol: 0.6-1.2 parts; Tetraethylenepentamine: 0.1-0.5 parts; Auxiliary antioxidant: 0.2-0.7 parts; 3. The compound antioxidant for natural ester insulating oil according to claim 1, characterized in that: The auxiliary antioxidant comprises 2,6-di-tert-butyl-p-cresol and tert-butyl-hydroquinone in a mass ratio of (1-2): (1-2).

4. The compound antioxidant for natural ester insulating oil according to claim 1, characterized in that: The mass ratio of the 2,6-di-tert-butyl-p-(dimethylaminomethyl)phenol, tetraethylenepentamine and auxiliary antioxidant is (7-9): (2-4): (3-5).

5. Use of the compound antioxidant for natural ester insulating oil according to any one of claims 1 to 4 in the field of preparing natural ester insulating oil.

6. An insulating oil with high oxidation resistance and resistivity, characterized in that: The invention comprises 0.5wt%-5wt% of a compound antioxidant and the balance of natural ester insulating oil, wherein the compound antioxidant is the compound antioxidant for natural ester insulating oil as claimed in any one of claims 1 to 4.

7. The insulating oil with high oxidation resistance and resistivity as claimed in claim 6, characterized in that The mass fraction of the compound antioxidant is 1wt%-3wt%.

8. The insulating oil with high oxidation resistance and resistivity as claimed in claim 6, characterized in that The natural ester insulating oil is at least one of soybean oil, rapeseed oil, camellia oil and sunflower oil.

9. The insulating oil with high oxidation resistance and resistivity as claimed in claim 8, characterized in that The insulating oil also includes 0.1-5wt% of a metal passivator, and the metal passivator is at least one of benzotriazole, methylbenzotriazole, and Irgamet 39.

10. A method for preparing insulating oil with high oxidation resistance and resistivity as claimed in any one of claims 6 to 9, characterized in that: The following steps are involved: The compound antioxidant and other additives are added into the natural ester insulating oil, mixed and stirred for 0.5-5h, the stirring temperature is 40-80°C, and the stirring speed is 100-1000r / min to obtain the insulating oil.

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