JPH09272891A - Electric-insulating oil and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject oil which comprises a mineral oil as a base oil, specific amounts of a basic nitrogen component, a nonbasic nitrogen component, a sulfide sulfur component and an aromatic hydrocarbon component and is excellent in oxidation stability, electric-insulating property and, hydrogen gas absorbency. SOLUTION: This oil contains a base oil purified by hydrogenation and an antioxidant of a phenol compound and possesses a composition containing a total nitrogen component of less than 15ppm, a sulfide sulfur component of less than 50ppm and 15-40mass% of an aromatic hydrocarbon component. In order to obtain this electric-insulating oil, a mineral oil distillate in the range of a boiling point of 250-500 deg.C separated by initially distilling from a raw oil is treated by hydrogenation at 320-380 deg.C in the presence of a hydrogenation catalyst to obtain an electric-insulating oil base material having a composition containing a total nitrogen component of less than 15ppm, a sulfide sulfur component of less than 50ppm and 15-40mass% of an aromatic hydrocarbon. Then, 0.03-3mass% of an antioxidant of a phenol compound are added to this base material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrically insulating oil using a mineral oil as a base oil and a method for producing the same, and more specifically, to suppress oxidation stability and electrical insulation, particularly increase in dielectric loss tangent at the initial stage of oxidation, and to prevent hydrogen. TECHNICAL FIELD The present invention relates to an electric insulating oil having excellent gas absorption and a method for producing the same.

[0002]

2. Description of the Related Art Electrical insulating oil is used for transformers, high voltage cables,
It is necessary to fill high-voltage electrical equipment such as high-voltage circuit breakers and capacitors, and maintain stable long-term stable oxidation resistance, electrical characteristics, and metal corrosion resistance.

In order to carry out large-capacity power transmission more economically,
With the introduction of ultra-high voltage transmission technology of 500,000 to 1 million volts, the problem of flow electrification is becoming more important.
This is because as the circulation amount of the electrical insulating oil increases, charge separation may occur, which may result in dielectric breakdown due to discharge. This flow charging phenomenon is observed as an increase in the dielectric loss tangent (tan δ, measured by the method specified in JIS C 2101; the same applies hereinafter) of the electrically insulating oil. One of the causes of this is the conductive component generated in oil, and the maximum value is generally observed at the initial stage of oxidation. Therefore, tan δ tends to increase in the initial stage of oxidation (hereinafter, referred to as “tan δ max” if necessary).
There is a demand for an electric insulating oil having a small value.

The present applicant has proposed that such a general deterioration of the dielectric loss tangent can be suppressed by setting the content of the specific component in the electric insulating oil within a specific range (Japanese Patent Laid-Open No. 6-325622). Issue).

[0005]

With the prior art such as Japanese Patent Laid-Open No. 6-325622, the temporary deterioration of the dielectric loss tangent can be suppressed to some extent. However, long-term oxidation stability and tan δ max at the initial stage of oxidation are contradictory phenomena, and the technique described in JP-A-6-325622 is an optimization of these, but both are very excellent. It could not be said that it exhibited the characteristics. Therefore, compared with conventional electrical insulating oils, the oxidation stability and tan δ m are far superior.
There is a demand for an electric insulating oil that can obtain the characteristics of both ax and ax.

Therefore, the present invention provides the oxidative stability, tan δ m
An object of the present invention is to provide an electric insulating oil having both ax suppressing property and hydrogen gas absorbing property and a method for producing the same.
Specifically, in the present invention, in terms of oxidative stability, the oxidative stability is 0.6 mgKOH / g or less (the quality specified in JIS C 2320).
Of course, further satisfy 0.05mgKOH / g or less,
In addition, in terms of suppressing tan δ max, the tan δ max value is 0.3
% And further 0.1% or less, and an object of the present invention is to provide an electrically insulating oil having a high hydrogen gas absorption and a method for producing the same.

[0007]

The inventor of the present invention has reached the present invention as a result of extensive studies to solve the above problems. That is, the electrical insulating oil of the present invention, using a hydrorefined base oil, in an electrical insulating oil containing an antioxidant consisting of a phenol compound, the total nitrogen content is 15ppm or less, sulfide sulfur content is 50ppm or less and aromatic Hydrocarbon content is 15
The present invention relates to an electrically insulating oil, which has a composition of about 40% by mass.

In the method for producing an electrically insulating oil of the present invention, a mineral oil fraction having a boiling point range of 250 to 500 ° C. which is distilled and separated from crude oil is hydrolyzed at a temperature of 320 to 380 ° C. using a hydrorefining catalyst. Treated to produce an electric insulating oil base material having a composition of total nitrogen content of 15 ppm or less, sulfide sulfur content of 50 ppm or less, and aromatic hydrocarbon of 15 to 40% by mass. Antioxidant consisting of 0.03-3
It is characterized by containing mass%.

After the hydrogenation treatment, if necessary, a solvent for selectively extracting aromatic hydrocarbons is used to carry out solvent extraction and purification under the conditions of a raffinate yield of 60 to 90% by volume to obtain a total nitrogen content. Is 15ppm or less, sulfide type sulfur content is
An electrically insulating oil base material having a composition of 50 ppm or less and an aromatic nitrogen carbon content of 15 to 40 mass% can be produced.

In the method for producing an electric insulating oil of the present invention, the basic nitrogen content is 1 ppm or less, the non-basic nitrogen content is 15 ppm or less, the sulfide-type sulfur content is 50 ppm or less, and the aromatic group by the following steps. Hydrocarbon content 15-40% by mass
An electric insulating oil having the composition of can be produced.

(I) Boiling point range of 250-
The mineral oil fraction at 500 ° C was heated to 32 ° C using a hydrorefining catalyst.
Hydrotreating in the range of 0 to 380 ℃, if necessary, (ii)
After the hydrogenation treatment, with a solvent that selectively extracts aromatic hydrocarbons, by performing solvent extraction purification under the conditions of a raffinate yield of 60 to 90% by volume, the total nitrogen content is 15 ppm or less, and the sulfide-type sulfur content is An electrically insulating oil base material having a composition of 50 ppm or less and an aromatic hydrocarbon content of 15 to 40 mass% is produced. Further, if necessary, (iii) a dewaxing treatment is performed before or after the hydrotreating treatment to perform a step of obtaining a predetermined pour point.
This dewaxing may be solvent dewaxing or hydrodewaxing. Further, if necessary, (iv) alkylbenzene, antioxidant is treated with a solid adsorbent before or after mixing with the electric insulating oil base material, and (v) 100 parts by weight of the mixed electric insulating oil base material is added. On the other hand, 10 to 40 parts by weight of long-chain alkylbenzene is mixed, and (vi) an antioxidant consisting of a phenol compound is added in an amount of 0.03 to 3% by mass based on the electric insulating oil base material.

The contents of the present invention will be described in detail below. First, terms used in the present specification will be described.

Total nitrogen content (Nt); value measured by the method specified in JIS K 2609 (1980) "Test method for nitrogen content of crude oil and petroleum products". Nitrogen content contained in oil as organic nitrogen compound The total amount of

Basic Nitrogen Content (Nb); UOP Method No.313-70 "Nitrogen Bases in Petr"
oleum Distillates by Color 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.

Non-basic nitrogen content (Nn); determined from the above Nt and Nb by the following formula. Nn = Nt-Nb Total nitrogen is a constituent element of organic nitrogen compounds that have been naturally present in crude oil and have been modified by nuclear hydrogenation and dealkylation in the hydrorefining process. Typical nitrogen compounds in the fraction are quinoline, acridine, indole, pyrrole and carbazole derivatives.
The basic nitrogen component is a constituent element of a nitrogen compound having basicity that can be detected by titration with perchloric acid as described above,
The difference between Nt and Nb is the non-basic nitrogen content.

Total sulfur content (St): The total amount of sulfur content that constitutes an organic sulfur compound present in oil. Such organic sulfur compounds include sulfides and thiophenes. St is measured by the method specified in JIS K 2541.

Sulfide type sulfur (Sf); the following general formula
It is the total amount of sulfur constituting the organic sulfur compound shown in (i) or (ii). That is, it may be either one originally contained in the mineral, one obtained by purifying the thiophene type organic sulfur compound by nuclear hydrogenation during the hydrogenation treatment, or one newly added. In the formula, R ₁ and R ₂ are carbon numbers
It represents an alkyl group of 10 to 15 or an aromatic hydrocarbon.
R ₃ and R ₄ represent a hydrogen atom or an alkyl group.

General formula (i): [R ₁ -S-R ₂ ] General formula (ii)

Embedded image

The sulfide type sulfur content in the present invention is a value which is separated and quantified by the method described below. Spraying a 0.5 wt% hydrochloric acid-acidified acetone-water mixture of palladium chloride onto a commonly used thin-layer chromatography thin-layer plate (for example, a glass plate coated with silica gel to a thickness of about 0.25 mm) Then, after air-drying, 2-4 μl of the sample oil is spotted, and carbon tetrachloride solution is used for about 10 minutes from the spotting position.
cm, and then chloroform / methanol (volume ratio 9
/ 1) Develop about 5 cm with the mixed solution.

By this operation, sulfide type sulfur compounds, hydrocarbons and other organic sulfur compounds are separated, and yellow colored spots are shown. A densitometer (such as Shimadzu 2-wavelength chromatograph OS
Apply 380 nm visible light with a −910 type) and obtain the absorbance.
When measuring a sample oil, a sample with a known sulfide concentration is developed at the same time, and the same measurement is performed. Thereby, the sulfide type sulfur content contained in the sample is quantified.

In the present invention, the amount of aromatic hydrocarbon is
It is a value determined by a method according to ASTM D2549-84. Similar results can be obtained by measuring with supercritical fluid chromatography (SFC) according to ASTM D5186-91.

Next, the electric insulating oil of the present invention will be described. The base oil used in the present invention has a viscosity of 5 to 30 cST (40
C)) or a mixture of mineral oil and long-chain alkylbenzene. The long-chain alkylbenzene is known as an electrically insulating oil, and specifically, an alkylbenzene substituted with a linear or branched alkyl group having 9 to 36 carbon atoms is preferable.

The electrical insulating oil of the present invention comprises the above base oil,
Basic nitrogen content Nb, non-basic nitrogen content Nn, sulfide sulfur content
Sf and the aromatic hydrocarbon content contain a specific amount or a specific range amount.

That is, in terms of oxidative stability, the acid value is 0.6 m.
In order to improve the oxidation stability so as to satisfy g KOH / g or less (the quality specified in JIS C 2320), the basic nitrogen content Nb is controlled to 1 ppm or less, preferably 0. . Nn has no problem in increasing the acid value, but since it causes hue deterioration, it is preferably 15 ppm or less, further 7 ppm.
The following is preferred.

Since Sf interferes with the effect of addition of the phenolic antioxidant, it is desirable that the Sf be small. However, it is 150 ppm or less, and there is no problem if the acid value is 0.05 mg KOH / g. However, to keep tan δ max below 0.1%, Sf should be 50
It should be below ppm, and more preferably below 10 ppm.

Further, in order to sufficiently impart the corona resistance that the electric insulating oil must have, that is, the hydrogen gas absorption, an appropriate amount of aromatic hydrocarbon is required, and specifically, 1
It is necessary to make it 5 mass% or more, and it is preferable to contain 20 mass% or more. If the aromatic hydrocarbon exceeds 40% by mass, the photostability is deteriorated.

Summarizing the above, the basic nitrogen content Nb
Is 1 ppm or less, preferably zero, and the non-basic nitrogen content Nn is 15
ppm or less, preferably 7 ppm or less, sulfide type sulfur content
Sf is 50 ppm or less, preferably 10 ppm or less, and aromatic hydrocarbon content is 15 to 40% by mass, preferably 20 to 40% by mass.

Next, a preferred embodiment of the hydrorefining treatment will be described. The mineral oil fraction was converted into a hydrorefining catalyst using
Hydrotreating in the range of 320 ° C. to 380 ° C., and optionally, after the hydrotreating, with a solvent for selectively extracting aromatic hydrocarbons, solvent extraction purification under conditions of a rafnate yield of 60 to 90% by volume. To produce a refined mineral oil. As the hydrorefining catalyst, a catalyst in which one or more metals such as Ni, Co, Mo and W are supported on a carrier such as silica, alumina or silica-alumina can be used.

The conditions for the hydrorefining treatment are that the temperature is 3
In addition to the range of 20 ℃ ~ 380 ℃, hydrogen partial pressure 45
It is preferable to set in the range of 120 to 120 kg / cm ² , and more preferably in the range of 60 to 100 kg / cm ² . Other conditions include liquid space velocity (LHS
The V) 0.2~2.0Hr ^{- 1} to. Further, the conditions may be set so that the desulfurization rate is preferably 95% or more, more preferably 98% or more, and the denitrification rate is preferably 95% or more, more preferably 98% or more. It is preferable to set the conditions so that the decomposition rate is 5% or less.

[Phenol Compound] As the phenol compound serving as an antioxidant, the phenol compounds represented by the following chemical formulas 2, 3, and 4 are preferable, and the phenol compound represented by the chemical formula 2 is most preferable.

[0031]

Embedded image In Chemical Formula 2, R ₁₁ and R ₁₃ represents a branched alkyl group having 3 to 12 carbon atoms, R _{1 2} denotes a -CH ₂ CH ₂ COOR ₁₄ methyl group or an ethyl group or a group. R ₁₄ has 1 carbon atom
Represents up to 20 alkyl groups. The preferred example is 2,6
Examples thereof include di-tert-butyl para-cresol and stearyl-β- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

[0032]

Embedded image In Chemical Formula 3, R ₁₅ represents a branched chain alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group, and R ₁₇ represents an alkylidene group having 1 to 4 carbon atoms or a methylene group. Represent Preferred examples of this include 2,2'-methylenebis (6-tert-butyl-4-methylphenol) and 2-2'-methylenebis (6-tert-butyl-4-ethylphenol).

[0033]

Embedded image In Chemical Formula 4, R ₁₈ represents a branched chain alkyl group having 3 to 12 carbon atoms, and R ₁₉ represents hydrogen or an alkyl group having 1 to 12 carbon atoms. R ₂₀ represents a methyl group when R ₁₉ represents hydrogen, and represents hydrogen when R ₁₉ represents an alkyl group having 1 to 12 carbon atoms. R ₂₁ represents a direct bond, a methylene group, or an alkylidene group having 1 to 4 carbon atoms. As a preferred example of this, 4,4'-methylenebis (2,6-di-tert-butylphenol) can be exemplified.

The amount of the phenol compound added is 0.03 to 3% by mass based on the total weight of the electric insulating oil. If it is less than 0.03% by mass, the oxidation stability of the electrical insulating oil is low, and if it exceeds 3% by mass, not only the oxidation stability commensurate with the cost cannot be obtained, but also the oxidation may be accelerated. From this viewpoint, the addition amount of the phenol compound is preferably 0.1 to 1% by weight based on the total weight of the electric insulating oil,
It is particularly preferable that the content is 0.2 to 0.5% by mass.

[Other Additives] The electrically insulating oil according to the present invention includes benzotriazole which is a metal deactivator, a derivative thereof, polyalkyl methacrylate which is a pour point depressant, ethylene-propylene copolymer, and the like. It is also possible to add an alkylated naphthalene polycondensate or the like.

[0036]

Hereinafter, the contents of the present invention will be described in more detail based on examples of the present invention, and the effects of the present invention will be illustrated. It should be noted that the present invention is not limited to the embodiments.

(Example 1) [Mineral oil fraction] From Arabian light crude oil by a conventional method,
Separated by atmospheric distillation and vacuum distillation, raw base oil (40 ° C viscosity:
9.4 mm ² / g, total sulfur content: 2.54% by mass, total nitrogen content:
357 ppm, boiling point range 250 ° C to 400 ° C) was obtained.

(Production of Insulating Oil Base Material 1) The raw material base oil was hydrorefined under the following conditions to obtain a desulfurization rate of 99% and a denitrification rate.
Refined mineral oil was obtained with 97% and a decomposition rate of 2%. Hydrorefining
1.0 mass% nickel on silica-alumina carrier as catalyst,
Using one carrying 12.0 mass% molybdenum, hydrogen partial pressure: 90 kg / cm ² G, reaction temperature 350 ° C, liquid hourly space velocity (LHSV)
It was conducted under the condition of 1.0 hr ^-1 .

A mixed solvent of methyl ethyl ketone / toluene (volume ratio 1/1) was added 2.6 times to this refined mineral oil, cooled to -32.5 ° C., and then filtered to obtain a dewaxed oil having a pour point of −30 ° C. Obtained. Further, add 1.5% by mass of activated clay to 60
After stirring at 0 ° C. for 20 minutes, it was filtered to obtain an insulating oil base material 1. Table 1 shows the properties of the insulating oil base material 1.

The above base material 1 and DBPC (2,6-di-tert-butyl paracresol) were mixed in a mass ratio of 99.7:
Mix at 0.3 to obtain an electrical insulating oil A as an example. The oxidation stability, dielectric loss tangent, maximum value of continuous tan δ, volume resistivity, and hydrogen gas absorbency of this electrical insulating oil A were evaluated and shown in Table 1. Also, the time change of tan δ (continuous tan δ) is shown in the figure. Shown in 1.

[Production of Insulating Oil Base Material 2]
A hydrodewaxed oil was obtained by hydrodewaxing, and after hydrorefining, a light fraction at 240 ° C. or lower was removed to obtain an insulating oil base material 2. The properties of this insulating oil base material 2 are shown in Table 1, and the change with time of tan δ is shown in FIG.

In the hydrodewaxing, ZSM-5 type zeolite was used as a catalyst, hydrogen partial pressure: 90 kg / cm ² G, reaction temperature:
It was carried out under the conditions of 371 ° C. and liquid hourly space velocity (LHSV): 1.5 hr ⁻¹ . The hydrorefining is carried out under the conditions of hydrogen partial pressure: 90 kg / cm ² G, reaction temperature: 339 ℃, liquid hourly space velocity (LHSV): 0.6 hr ^-1 , using a catalyst in which Mo, Ni, etc. are supported on an alumina carrier. I did it in.

[Production of Electrical Insulating Oil B] The above hydrodewaxed base material treated with an alumina-based adsorbent and filtered with a filter paper, and DB.
PC (2,6-di-tert-butyl para-cresol) is mixed in a weight ratio of 99.7: 0.3 to obtain an electrically insulating oil B as an example. The oxidation stability, dielectric loss tangent, maximum value of continuous tan δ, volume resistivity and hydrogen gas absorbency of this electrical insulator B are evaluated and shown in Table 1, and tan δ with time is shown in FIG.

[Evaluation method] "Total sulfur content" is JIS K 2541
Compliant. The "total nitrogen content" was measured according to JIS K 2609. The amount of aromatic hydrocarbon was measured by supercritical fluid chromatography (SFC). "Oxidative stability" is JI
Based on the oxidation stability test of SC 2101, the total acid value and the amount of sludge were evaluated. "Dielectric loss tangent" and "Volume resistivity"
Was measured in accordance with JIS C2101. "Continuous tan δ"
Is "Technical Data of Insulating Oil Subcommittee of Japan Petroleum Institute Product Section" (1985
(March, 2013). In addition, the hydrogen gas absorption is based on the technical data No. 6 of the Insulating Oil Subcommittee of the Electrical Insulation Materials Study Group.
It was measured by the method (section method) described in (1965).

[0045]

[Table 1]

Comparative Example 1 The above-mentioned raw material base oil was subjected to solvent extraction purification using a furfural solvent, and then solvent dewaxing was carried out using a methyl ethyl ketone / toluene mixed solvent,
A base material 3 is obtained by filtering at 32.5 ° C. and treating with activated clay. The insulating oil base material 2 and the base material 3 are mixed at a mass ratio of 97: 3, treated with an alumina-based adsorbent, and filtered to obtain an electric insulating oil C of Comparative Example 1. The properties and evaluation results of this electric insulating oil C are shown in Table 2 and FIG.

Comparative Example 2 Insulating oil base material 1 was furfural
250% of the raffinate was contacted with 80% at a raffinate yield of 55%, then treated with an alumina-based adsorbent and filtered. This and DBPC (2,6-di-tert-butyl paracresol) are mixed at a weight ratio of 99.7: 0.3 to obtain an electrically insulating oil D as Comparative Example 2.

Comparative Example 3 The above raw material base oil was hydrorefined under the following conditions to obtain a refined mineral oil 2 with a decomposition rate of 15%.
For hydrorefining, a silica-alumina carrier supporting 1.0% by weight of nickel and 12.0% by weight of molybdenum was used as a catalyst. Hydrogen partial pressure: 100 kg / cm ² G, reaction temperature 395 ° C., liquid hourly space velocity (LHSV) 0.5 hr. ^It was performed under the condition of ^-1 .

The above purified mineral oil 2 was mixed with methyl ethyl ketone / toluene mixed solvent (volume ratio 1/1) to the oil to obtain 2.
The mixture was added 6 times, cooled to -32.5 ° C, and then filtered to obtain a dewaxed oil having a pour point of -30 ° C. Furthermore, 1.5% by mass of activated clay was added, and the mixture was stirred at 60 ° C for 20 minutes and then filtered off.
I got This base material 4 and DBPC (2,6-di-tert-butyl para-cresol) are mixed at a weight ratio of 99.7: 0.3 to obtain an electrically insulating oil E as Comparative Example 3. Oxidation stability of these electric insulating oils D and E, dielectric loss tangent, volume resistivity,
The hydrogen gas absorption is evaluated and shown in Table 2.

[Comparative Examples 4 and 5] Commercially available electrical insulating oil containing no phenolic antioxidant was used as electrical insulating oil F (Comparative Example 4). In addition, electric insulating oil F and DBPC (2,
6-di-tert-butyl para-cresol) is mixed in a weight ratio of 99.7: 0.3 to obtain an electrically insulating oil G (Comparative Example 5). Properties of these electric insulating oils F and G and evaluation results are also shown in Table 2 and FIG.

[0051]

[Table 2]

As is clear from the above results, according to the electric insulating oils A and B of this embodiment, the dielectric loss tangent (tan δ) was stably 0.1 without causing the maximum value in the continuous tan δ change with time. It can be less than or equal to%. Further, it can be seen that the volume resistivity, the oxidation stability and the like show sufficient characteristics as an electric insulating oil.

Since the electric insulating oils D and E of the comparative examples have a low aromatic hydrocarbon content (aroma content), the hydrogen gas absorbency is a negative value, that is, hydrogen gas is generated. In the electrical insulating oils C and F of the comparative example, the maximum value occurs with the time change of tan δ, and the oxidation stability is low. In the electric insulating oil F, the dielectric loss tangent reaches 0.5%. In the electrical insulating oil G of the comparative example, the phenol compound was added, but the dielectric loss tangent was also changed with the continuous tan δ change with time.
It deteriorates to 0.3% or more.

[0054]

The electrical insulating oil according to the present invention contains a base material produced from a mineral oil fraction as a main component, contains a phenol compound as an antioxidant in an amount of 0.03 to 3% by mass, and has a total nitrogen content of Nt 15 ppm.
Sulfide sulfur content Sf 50ppm or less, aromatic hydrocarbon
15 to 40% by mass. According to the present invention, the dielectric loss tangent
(tan δ) can be stably lowered, and electrical insulating oil with sufficient electrical properties such as volume resistivity, oxidation stability and corona resistance can be obtained, and the stability of electrical equipment can be obtained. It is effective for easy driving.

[Brief description of drawings]

FIG. 1 is a graph showing changes with time of tan δ of electric insulating oils A and B of examples of the present invention and electric insulating oils C, D and E of comparative examples.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C10M 101: 02 129: 10) C10N 40:16

Claims (2)

[Claims] 1. An electrically insulating oil containing a hydrogenated refined base oil and containing an antioxidant composed of a phenol compound, wherein the total nitrogen content is 15 ppm or less and the sulfide sulfur content is 50 ppm.
An electrically insulating oil characterized in that it has the following composition and an aromatic hydrocarbon content of 15 to 40% by mass. 2. A boiling point range of 250 to 50 obtained by distillation separation from crude oil.
A mineral oil fraction at 0 ° C was heated at a temperature of 320 ° C using a hydrorefining catalyst.
Hydrogenated in the range of ~ 380 ℃, total nitrogen content 15ppm or less, sulfide sulfur content 50ppm or less, aromatic hydrocarbons
Producing an electrically insulating oil base material having a composition of 15-40% by mass,
This electrical insulating oil base material contains an antioxidant consisting of a phenol compound in an amount of 0.03 to 3% by mass.
Method for producing electric insulating oil.