JP2000306430A - Insulating oil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high electric characteristics such as a small tan δ max and flow charge max in addition to high oxidative stability by including a specified amount of each of sulfide type sulfur and a phenolic compound with mineral oil and/or synthetic oil as the main component. SOLUTION: Insulating oil contains 50 wt.ppm, preferably more than 100 wt.ppm but 1000 weight ppm or less, preferably 500 wt.ppm or less sulfide type sulfur, and 10 wt.ppm or more but less than 300 wt.ppm phenolic compound. The phenolic compound is preferably selected from formulas I, II, III. The phenolic compound is preferable to be 2,6-tertiary butyl paracresol. In the formulas, R11,13,15,18 are 3-12C branched chain alkyl; R12,16, are methyl, ethyl; R17 is 1-4C alkylene, alkylidene; R18 is H, 1-12C alkyl; R20 is H, methyl; and R12 is direct bonding or same as R17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric insulating oil, and more particularly to an electric insulating oil having excellent oxidative stability, electric insulating properties and fluid charging characteristics.

[0002]

2. Description of the Related Art Electrical insulating oil is filled in high-voltage electrical equipment such as transformers, high-voltage cables, high-voltage circuit breakers, and capacitors, and is required to maintain long-term stable electrical characteristics, oxidation resistance, and metal corrosion resistance. is there. Further, as ultrahigh-voltage power transmission technology of 500,000 to 3,000,000 volts is put to practical use for economical large-capacity power transmission, the problem of flowing electrification has been emphasized. This is because the transformer is designed to circulate the electric insulating oil forcibly or by natural convection to release the heat generated in the coil, and as the amount of circulation of the electric insulating oil increases, the separation of electric charge is performed. This occurs because the electrical insulating oil is charged and this discharge may cause dielectric breakdown. It is said that this flow electrification phenomenon is observed as an increase in the dielectric loss tangent (tan δ, measured by a method specified in JIS C 2101) of the electric insulating oil.

[0003] Also, various methods for measuring the amount of the flow electrification itself have been proposed (for example, see JP-A-52-427).
No. 99, IEEE Transaction on Power Apparatus an
d System, PAS-103, 1923 (1984)), and the applicant of the present application has also proposed an improved method for measuring flow electrification (Japanese Patent Application No. 10-300709). Flow charging can be measured by these methods. The flow charge and tan δ tend to increase rapidly in the early stage of the deterioration (oxidation) of the electrical insulating oil, and the maximum value (hereinafter referred to as “flow charge max” or “tan δ max” as necessary) Small electrical insulating oils are desired.

[0004] The applicant of the present invention can obtain an electric insulating oil having excellent oxidation stability by first controlling the basic nitrogen content, non-basic nitrogen content and sulfide type sulfur content in the oil within a specific range. Patent Application 58-31761 (JP-A-59-160)
906) and Japanese Patent Application No. 58-208247 (Japanese Patent Application Laid-Open No. 60-101804) have proposed an electric insulating oil having excellent oxidation stability or a method for producing the same. However, although the electric insulating oils according to these prior proposals are excellent in terms of oxidation stability, they are not always sufficiently satisfactory in terms of controllability of the above-mentioned tan δ max or flow charging max. That is, improvement of oxidation stability and tan δ max or flow charging max
It was difficult to satisfy both the controls for the increase sufficiently.

[0005] I & EC Product Research & Development
Journal, Vol. 6, p. 61 (1967) states that sulfur and nitrogen in oils are thoroughly removed, while white oil containing a small amount of polycyclic aromatic hydrocarbons prevents abnormal increase of tan δ max. However, oxidation stability and hydrogen gas absorption are not sufficient. In the market, there is no electrical insulating oil which is preferable for both performances. Therefore, oxidation stability, ta
There is a demand for the development of an electric insulating oil having both the suppressing property of n δ max and the hydrogen gas absorbing property.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electric insulating oil having excellent electric characteristics such as a small tan δ max. Or a fluid charging max while maintaining good oxidation stability. Make it an issue.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention comprises a mineral oil and / or a synthetic oil as a main component and a sulfide type sulfur content of 50 to 100.
An electric insulating oil containing 0 ppm by weight and 10 to 300 ppm by weight of a phenolic compound. Preferably, the phenolic compound is one or more selected from the following general formulas (1) to (3). Is an electrical insulating oil.

Embedded image (In the formula, R ₁₁ and R ₁₃ represent a branched alkyl group having 3 to 12 carbon atoms, and R ₁₂ represents a methyl group or ethyl.)

Embedded image (In the formula, R ₁₅ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group, and R ₁₇ represents 1 carbon atom.
Represents an alkylene group or an alkylidene group. )

Embedded image (Wherein, R ₁₈ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₉ represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R ₂₀ represents a methyl group when R ₁₉ is hydrogen. And R
_{When 19} is an alkyl group having 1 to 12 carbon atoms, it represents hydrogen, and R ₂₁ represents a direct bond, an alkylene group having 1 to 4 carbon atoms or an alkylidene group. )

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, terms used in the present specification will be described. [Sulfide-type sulfur (Sf)]: The following general formula (4)
Or it is the total amount of sulfur constituting the organic sulfur compounds represented by the general formulas (5a) to (5e). That is, those originally contained in mineral oil, those generated by nuclear hydrogenation of thiophene-type organic sulfur compounds during hydrotreating,
Alternatively, any of those newly added may be used.

R ₁ -SR ₂ (4) (wherein R ₁ and R ₂ represent an alkyl group having 10 to 15 carbon atoms or an aromatic hydrocarbon group)

Embedded image (In the formula, R ₃ and R ₄ represent a hydrogen atom or an alkyl group.)

The sulfide-type sulfur content is a value that is separated and quantified by the method described below. Spraying 0.5 wt% palladium chloride hydrochloric acid-acetone-acetone-water mixture onto a thin-layer plate for thin-layer chromatography (eg, a glass plate coated with silica gel to a thickness of about 0.25 mm) After air-drying, 2 to 4 μl of the sample oil is spot-dried, developed about 10 cm from the spotting position with a carbon tetrachloride solution, and further developed about 5 cm with a chloroform / methanol (volume ratio of 9/1) mixed solution. . By this operation, the sulfide-type sulfur compound is separated from hydrocarbons and other organic sulfur compounds, and shows a yellow colored spot. Visible light of 380 nm is applied to the colored spot portion with a densitometer (for example, a two-wavelength chromatoscanner CS-910 manufactured by Shimadzu Corporation) to determine the absorbance. When measuring the sample oil, a sample having a known sulfide-type sulfur compound concentration is simultaneously developed and the same measurement is performed. Thereby, the sulfide-type sulfur content (Sf) contained in the sample is determined.

[Total Sulfur Content (St)]: The total sulfur content of the organic sulfur compound present in the oil. Such organic sulfur compounds include the above-mentioned sulfide-type sulfur (Sf).
And thiophenes and the like. St is JIS K 25
It is measured by the method specified in 41.

[Total nitrogen content (Nt)]: JIS K 2609 (198
0) It is a value measured by the method specified in "Normal test method for crude oil and petroleum products", and refers to the total amount of nitrogen contained in oil as an organic nitrogen compound.

[Basic nitrogen content (Nb)]: UOP Method, U.S.A., No. 313-70, "Nitrogen Bases in
Distillates by Indicator Titration ”. In this measurement method, a sample oil is dissolved in glacial acetic acid, and crystal violet is used as an internal indicator, and titration is performed with perchloric acid in glacial acetic acid.

Next, the electric insulating oil of the present invention will be described. As the base oil of the electric insulating oil of the present invention, a mineral oil having a kinematic viscosity at 40 ° C. of 4 to 13 cSt, a synthetic oil such as a long-chain alkylbenzene, an alkylene polymer, or a mixture thereof can be used. As the mineral oil, it is preferable to use a base oil obtained by subjecting a mineral oil fraction having a boiling point of 250 to 500 ° C., which has been distilled and separated from crude oil, to hydrogenation at a temperature of 250 to 500 ° C. using a hydrorefining catalyst. The long-chain alkylbenzene is known as an electric insulating oil, and specifically, an alkylbenzene having a substituent of a linear or branched alkyl group having 9 to 36 carbon atoms is preferable. In particular, a mineral oil or a mixed oil of a mineral oil and a long-chain alkylbenzene is preferable, and a sulfide-type sulfur compound contained in the mineral oil can be effectively used.

[0015] The electric insulating oil of the present invention comprises:
It contains sulfide-type sulfur Sf in a specific amount.
Sf is 50 ppm by weight to improve oxidation stability.
, Preferably at least 100 ppm by weight. On the other hand, if present in excess, the oxidation stability is reduced, so Sf is 1000 ppm by weight or less, preferably 50 ppm by weight.
0 ppm by weight or less. As Sf, what is originally contained in a mineral oil fraction separated from crude oil as a raw material can be effectively used.

In terms of oxidation stability, the acid value is 0.6 m
In order to obtain an electrical insulating oil having improved oxidation stability satisfying gKOH / g or less (quality specified in JIS K 2320), preferably 0.3 mgKOH / g or less, the basic nitrogen content Nb is 1 wt ppm. And the total nitrogen content Nt is preferably 1 ppm by weight or less. Further, it is preferable that an appropriate amount of aromatic hydrocarbon is contained in the electric insulating oil in order to sufficiently impart corona resistance, that is, hydrogen gas absorption. Specifically, the content of the aromatic hydrocarbon is 1
It is at least 5% by weight, more preferably at least 20% by weight.
However, when the content of the aromatic hydrocarbon is increased, the light stability performance may be reduced.
It is preferable that the content be not more than weight%.

[Phenol compound]: In the present invention, the phenol compound added as an antioxidant is
Each phenolic compound represented by the following general formulas (1) to (3) is preferable, and among them, a compound represented by the general formula (1) is preferable.

[0018]

Embedded image In the general formula (1), R ₁₁ and R ₁₃ represent a branched alkyl group having 3 to 12 carbon atoms, and R ₁₂ represents a methyl group or an ethyl group. Preferred examples thereof include 2,6-di-tert-butylparacresol, 2,4-di-methyl-5-tert-butylphenol, and 2,6-di-tert-butyl-4-ethylphenol. .

[0019]

Embedded image In the general formula (2), R ₁₅ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group,
R ₁₇ represents an alkylene group having 1 to 4 carbon atoms or an alkylidene group (preferably a methylene group). As a preferred example of this,
2,2'-methylenebis (6-tert-butyl-4
-Methylphenol), 2,2'-methylenebis (6-
Tert-butyl-4-ethylphenol) and the like.

[0020]

Embedded imageIn the general formula (3), R₁₈Is a branched chain having 3 to 12 carbon atoms
Represents an alkyl group;₁₉Is hydrogen or an atom having 1 to 12 carbon atoms.
Represents a alkyl group;₂₀Is R₁₉If is hydrogen, methyl
R represents a group₁₉Is an alkyl group having 1 to 12 carbon atoms
Represents hydrogen, and R _{twenty one}Is a direct bond, methylene group or carbon
An alkylene group or an alkylidene group of Formulas 1 to 4 (preferably
Represents a methylene group). A preferred example of this is 4,4'-
Methylene bis (2,6-di-tert-butylpheno)
Can be exemplified.

Among these phenolic compounds, compounds of the general formula (1) are preferred, and 2,6-di-tert-butylparacresol is more preferred. The amount of the phenolic compound added is 1 to the total weight of the electric insulating oil.
0 to 300 ppm. If this is less than 10 ppm, the effect of suppressing tan δ max is small, while 300 p
However, the effect of suppressing tan δ max corresponding to the increase in the amount of addition exceeding pm cannot be obtained.

Other additives: The electrical insulating oil according to the present invention contains benzotriazole or its derivative as a metal deactivator, polyalkyl methacrylate as a pour point depressant, ethylene propylene copolymer, or alkylated naphthalene. Condensates and the like can also be added.

The electric insulating oil of the present invention is produced by appropriately using various known oil or lubricating oil refining steps, that is, by adjusting the processing conditions in each step and appropriately combining various steps. it can. For example, a lubricating oil fraction having a boiling point of 250 to 500 ° C. is separated from crude oil by atmospheric distillation and then vacuum distillation. (2) Hydrotreating the lubricating oil fraction using a hydrorefining catalyst at a reaction temperature of 300 to 400 ° C. (4) After the hydrogenation treatment, a raffinate yield of 6 was obtained using a solvent for selectively extracting aromatic hydrocarbons.
Solvent extraction purification is performed under the condition of 0 to 90% by volume. () A dewaxing process is performed before or after the hydrogenation process. This dewaxing treatment may be solvent dewaxing or hydrodewaxing. () Perform solid adsorbent treatment using activated clay or the like. () A base material such as long-chain alkylbenzene and an additive such as an antioxidant are mixed. Not all of these steps are necessary, and the point is that it is only necessary to obtain a base oil or an electrical insulating oil that satisfies the above physical properties, and in some cases, some processing steps can be omitted, and Change the order or perform a certain processing step multiple times (in some cases, change the processing conditions)
You can also. Further, an electrical insulating oil having satisfactory physical properties may be obtained by appropriately combining intermediate base materials generated in the above-described steps.

[0024]

Hereinafter, the contents of the present invention will be described in more detail with reference to examples. Note that the present invention is not limited by these examples. (Example 1) [Mineral oil fraction] A lubricating oil fraction was separated from a crude oil by a normal method under normal pressure distillation and reduced pressure distillation, and a raw material base material (kinematic viscosity at 40 ° C: 7.96 cSt, total sulfur content: 2.2) Wt%, total nitrogen content 230 wtppm).

[Production of First Refined Mineral Oil] Using a catalyst in which the above-mentioned raw material base material supported nickel alumina and molybdenum 12.0 weight% on a silica alumina carrier, hydrogen partial pressure was 8.
9 × 10 ⁶ Pa, temperature 350 ° C., liquid hourly space velocity (LHS
V) Hydrotreating treatment under the condition of 0.6 hr ^-1 to obtain a first hydrorefined mineral oil. At this time, both the desulfurization rate and the denitrification rate were 99%. The first refined mineral oil shown in Table 1 was obtained.

[Production of Second Refined Mineral Oil] The above-mentioned base oil was extracted at a raffinate yield of 70% by volume by contacting 250 parts by volume of furfural per 100 parts by volume of the base oil with a rotary disc extractor at 70 ° C. Thus, a second refined mineral oil (raffinate) was obtained.

[Production of Electric Insulating Oil] The first refined mineral oil and the second refined mineral oil obtained by the above method were mixed at a ratio of 96: 4 (weight ratio) to prepare a mixed oil, and methyl ethyl ketone was prepared. / Toluene mixed solvent (volume ratio 1/1) was added 2.5 times with respect to the mixed oil, and after cooling to -32.5 ° C, a dewaxed oil having a pour point of -30 ° C was obtained. . Further, 1.5 parts by weight of activated clay was added to 100 parts by weight of dewaxed oil, and the mixture was stirred at 60 ° C. for 20 minutes, and then filtered to obtain an insulating oil base material 1. 2,6-di-tert-butylparacresol (DBPC) was added to the insulating oil base material 1 at a weight ratio of 50 p.
pm so as to obtain an electric insulating oil A.

Comparative Example 1 Same insulating oil base material 1 as in Example 1.
The substance itself (that is, one to which DBPC was not added) was used as the electric insulating oil B.

(Comparative Example 2) Sulfide type sulfur content is 20 p
pm as the base oil and the DBP
The electric insulating oil C was added by adding C so as to be 50 ppm.

(Comparative Examples 3 and 4) Commercially available electric insulating oils containing no phenolic antioxidant were used as commercial oils A and B. Commercial oil B contains a large amount of both total sulfur and sulfide-type sulfur. For each of the thus prepared electric insulating oils A to C and the procured commercial oils A and B, the dielectric loss tangent, volume resistivity, flow electrification, tan δ
An evaluation test for max and oxidation stability was performed.

The measurement test methods used in these evaluations are as follows. "Aromatic hydrocarbon content" was measured by supercritical fluid chromatography. “Dielectric loss tangent” and “volume resistivity” were measured in accordance with JIS C 2101.

The "fluid charge max" is the maximum value of the fluid charge in an accelerated test measured under specific conditions assuming actual use conditions in order to measure the practical performance of the transformer oil. The specific measuring method is described in Japanese Patent Application No. 10-300709 previously filed by the applicant of the present invention, so please refer to it for details. The outline is briefly described below: a cell in which a test oil is forcibly circulated is provided with a cell loaded with filter paper, and a charge amount for charging the oil during circulation is measured by a flow charge measurement electrode terminal provided on the cell. This is a method of measuring with an ammeter connected between the ground and the ground. At this time, since the gas injection pipe and the discharge pipe are provided in the test oil container provided in the circulation system, the test oil can be placed in an oxygen-free atmosphere by blowing nitrogen gas, and air Can be placed in an aerobic atmosphere. The temperature of the test oil can be controlled by a heater surrounding the container.

FIGS. 1 and 2 show charts of actual measurement of the flow electrification of the electric insulating oil A (Example 1) and the electric insulating oil B (Comparative Example 1). In both figures, the horizontal axis indicates time, and the vertical axis indicates the dielectric loss tangent (tan δ), flow electrification, and temperature from the left. Also, in the figure, the chain line indicates the temperature, the solid line indicates the flow electrification, and the dotted line indicates the change in the dielectric loss tangent. The left half of the figure is temperature-dependent, that is, the temperature of the test oil is raised from room temperature and kept at 95 ° C. under anoxic condition by blowing nitrogen gas (0 to 600 minutes), and then the temperature is lowered to room temperature and increased ( (After 600 minutes) shows changes in dielectric loss tangent and flow electrification under the conditions. The right half is affected by oxidative degradation, that is, the temperature is raised to 95 ° C. (-130 to 0 minutes) while blowing nitrogen gas (under no oxygen), and the nitrogen gas is switched to air while maintaining the temperature at a constant level. Shown below are the changes in dielectric loss tangent and flow charge. From this figure, the flow electrification under anoxic and aerobic conditions can be determined, and the maximum value of the dielectric loss tangent (tan δ max) can also be determined. For example, from FIG. 2, the flowing electrification max of the electric insulating oil B (Comparative Example 1) under anoxic condition takes the highest value at 600 minutes on the horizontal axis from the left side diagram of FIG. 2, and the value shows 400 pA (picoamps). In addition, the flow charging max under aerobic conditions takes the highest value at about 35 minutes on the horizontal axis from the right side of FIG.
00pA (picoamps) is shown.

"Oxidation stability" conforms to JIS C 2101,
The test oil was kept at 120 ° C. for 75 hours for deterioration, and the total acid value and the amount of sludge of the deteriorated oil were measured. The “sulfide-type sulfur content”, “total sulfur content”, “total nitrogen content” and “basic nitrogen content” were measured according to the method described in the text.

The results of the tests performed in this way are summarized in Table 1.

[Table 1] From Table 1, the electric insulating oil A of the present invention shown as an example,
It can be seen that the oxidation stability and various electrical properties are excellent in a well-balanced manner. On the other hand, the electric insulating oil B to which DBPC is not added
(Comparative Example 1) and Commercial Oil A (Comparative Example 3) are inferior in tan δ max, and Electrical Insulating Oil C (Comparative Example 2) having a low sulfide type sulfur content is inferior in oxidation stability (total acid value). , DBP
It can be seen that the commercial oil B (Comparative Example 4) to which C was not added and which had a high sulfide-type sulfur content was inferior in oxidation stability and almost all electric properties.

[0036]

The electrical insulating oil according to the present invention contains a specific amount of sulfide-type sulfur and a specific amount of a phenolic compound.
Since it is excellent in practical performance such as electrical characteristics such as δ max and oxidation stability, it is expected that it will not be easily deteriorated by long-term use. Thus, according to the present invention,
It can provide an electric insulating oil having excellent practical performance.

[Brief description of the drawings]

FIG. 1 is a chart showing changes in flow electrification and dielectric loss tangent of an electrical insulating oil A (Example 1) under oxygen-free and oxygen-free conditions.

FIG. 2 is a chart showing changes in flow electrification and dielectric loss tangent of an electrical insulating oil B (Comparative Example 1) under oxygen-free and oxygen-containing conditions.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission Date] January 14, 2000 (2000.1.1)
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

The electric insulating oil of the present invention is produced by appropriately using various known oil or lubricating oil refining steps, that is, by adjusting the processing conditions in each step and appropriately combining various steps. it can. For example, ( i ) a lubricating oil fraction having a boiling point of 250-500 ° C. is separated from crude oil by atmospheric distillation and then vacuum distillation. ( ii ) hydrotreating the lubricating oil fraction using a hydrorefining catalyst at a reaction temperature of 300 to 400 ° C. ( iii ) After the hydrogenation treatment, solvent extraction and purification are carried out with a solvent that selectively extracts aromatic hydrocarbons at a raffinate yield of 60 to 90% by volume. ( iv ) Dewaxing treatment is performed before or after the hydrogenation treatment. This dewaxing treatment may be solvent dewaxing or hydrodewaxing. ( v ) Perform solid adsorbent treatment using activated clay. ( vi ) A base material such as long-chain alkylbenzene is mixed with an additive such as an antioxidant. Not all of these steps are necessary,
The point is that it is only necessary to obtain a base oil or an electrical insulating oil that satisfies the above physical properties, and in some cases, a certain processing step can be omitted, the order of the processing steps can be changed, or a certain processing step can be performed several times. Can be performed (in some cases, by changing the processing conditions). Further, an electrical insulating oil having satisfactory physical properties may be obtained by appropriately combining intermediate base materials generated in the above-described steps. ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 10, 2000 (2007.1.
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Embedded image (In the formula, R ₁₁ and R ₁₃ represent a branched alkyl group having 3 to 12 carbon atoms, and R ₁₂ represents a methyl group or ethyl.)

Embedded image (In the formula, R ₁₅ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group, and R ₁₇ represents 1 carbon atom.
Represents an alkylene group or an alkylidene group. )

Embedded image (Wherein, R ₁₈ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₉ represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R ₂₀ represents a methyl group when R ₁₉ is hydrogen. And R
_{When 19} is an alkyl group having 1 to 12 carbon atoms, it represents hydrogen, and R ₂₁ represents a direct bond, an alkylene group having 1 to 4 carbon atoms or an alkylidene group. )

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention comprises a mineral oil and / or a synthetic oil as a main component, and a sulfide-type sulfur content of 50% by weight.
Beyond pm an electrical insulating oil of the following and phenolic compounds 1000 ppm by weight containing less than 10 ppm by weight to 300 ppm by weight, preferably selected, the phenolic compound is of the following general formula (1) to (3) Or two or more types of electrical insulating oils.

Embedded image (In the formula, R ₁₁ and R ₁₃ represent a branched alkyl group having 3 to 12 carbon atoms, and R ₁₂ represents a methyl group or ethyl.)

Embedded image (In the formula, R ₁₅ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group, and R ₁₇ represents 1 carbon atom.
Represents an alkylene group or an alkylidene group. )

Embedded image (Wherein, R ₁₈ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₉ represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R ₂₀ represents a methyl group when R ₁₉ is hydrogen. And R
_{When 19} is an alkyl group having 1 to 12 carbon atoms, it represents hydrogen, and R ₂₁ represents a direct bond, an alkylene group having 1 to 4 carbon atoms or an alkylidene group. )

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

[0015] The electric insulating oil of the present invention comprises:
It contains sulfide-type sulfur Sf in a specific amount.
Sf is 50 ppm by weight to improve oxidation stability.
More than 100% by weight
pm or more. On the other hand, if present in excess, the oxidation stability decreases, so Sf is 1000 ppm by weight.
Or less, preferably 500 ppm by weight or less. Sf
Can effectively utilize what is originally contained in a mineral oil fraction separated from crude oil as a raw material.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

[0020]

Embedded imageIn the general formula (3), R₁₈Is a branched chain having 3 to 12 carbon atoms
Represents an alkyl group;₁₉Is hydrogen or an atom having 1 to 12 carbon atoms.
Represents a alkyl group;₂₀Is R₁₉If is hydrogen, methyl
R represents a group₁₉Is an alkyl group having 1 to 12 carbon atoms
Represents hydrogen, and R _{twenty one}Is a direct bond, methylene group or carbon
An alkylene group or an alkylidene group of Formulas 1 to 4 (preferably
Represents a methylene group). A preferred example of this is 4,4'-
Methylene bis (2,6-di-tert-butylpheno)
Can be exemplified.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

Among these phenolic compounds, compounds of the general formula (1) are preferred, and 2,6-di-tert-butylparacresol is more preferred. The amount of the phenolic compound added is 1 to the total weight of the electric insulating oil.
0 ppm or more and less than 300 ppm. This is 10p
If it is less than pm, the effect of suppressing tan δ max is small, but even if it is added at 300 ppm or more, it is commensurate with the increase in the amount added.
The effect of suppressing tan δ max cannot be obtained.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

FIGS. 1 and 2 show charts of actual measurement of the flow electrification of the electric insulating oil A (Example 1) and the electric insulating oil B (Comparative Example 1). In both figures, the horizontal axis indicates time, and the vertical axis indicates the dielectric loss tangent (tan δ), flow electrification, and temperature from the left. Also, in the figure, the chain line indicates the temperature, the solid line indicates the flow electrification, and the dotted line indicates the change in the dielectric loss tangent. The left half of the figure is temperature-dependent, that is, the temperature of the test oil is raised from room temperature and maintained at 95 ° C. (0 to 600 minutes) under oxygen-free and oxygen-free conditions, and then lowered to room temperature (600). Min) and changes in the dielectric loss tangent and the flow electrification under the following conditions. The right half is affected by oxidative degradation, that is, the temperature is raised to 95 ° C. (-130 to 0 minutes) while blowing nitrogen gas (under no oxygen), and the nitrogen gas is switched to air while maintaining the temperature at a constant level. Shown below are the changes in dielectric loss tangent and flow charge. From this figure, the flow electrification under anoxic and aerobic conditions can be determined, and the maximum value of the dielectric loss tangent (tan δmax) can also be determined. For example, from FIG. 2, the flowing electrification max of the electric insulating oil B (Comparative Example 1) under anoxic condition takes the highest value at 600 minutes on the horizontal axis from the left side diagram of FIG. 2, and the value shows 400 pA (picoamps). In addition, the flow charging max under aerobic conditions takes the highest value at about 35 minutes on the horizontal axis from the right side of FIG.
00pA (picoamps) is shown.

Continued on the front page F term (reference) 4H104 BB05C BG12C BG15C BG17C BG18C DA02A EB02 LA05 LA14 LA20 PA12 5G305 AA03 AA05 AA12 AB01 AB24 AB27 AB40 BA04 CB01 CB04 CB11 CB25 CD09

Claims (3)

[Claims] 1. An electric insulating oil comprising a mineral oil and / or a synthetic oil as a main component, and containing 50 to 1000 ppm by weight of a sulfide-type sulfur and 10 to 300 ppm by weight of a phenolic compound. 2. The electric insulating oil according to claim 1, wherein the phenolic compound is one or more selected from the following general formulas (1) to (3). Embedded image (Wherein, R ₁₁ and R ₁₃ represent a branched alkyl group having 3 to 12 carbon atoms, and R ₁₂ represents a methyl group or ethyl.) (In the formula, R ₁₅ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group, and R ₁₇ represents 1 carbon atom.
Represents an alkylene group or an alkylidene group. ) (Wherein, R ₁₈ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₉ represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R ₂₀ represents a methyl group when R ₁₉ is hydrogen. And R
_{When 19} is an alkyl group having 1 to 12 carbon atoms, it represents hydrogen, and R ₂₁ represents a direct bond, an alkylene group having 1 to 4 carbon atoms or an alkylidene group. ) 3. The method according to claim 2, wherein the phenolic compound is 2,6-di-
The electrical insulating oil according to claim 1, which is tertiary butyl paracresol.