JP2000164034A - Electric insulating oil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an excellent heat/oxidation stability, a flow electrification characteristic and higher safety by using a mineral oil with the aromatic percentage of a specific value or below as a base oil, and containing a benzotriazole compound and alcohol. SOLUTION: The aromatic percentage in a mineral oil must be 10% or below, preferably 5% or below, more preferably 3% or below, and further more preferably 2% or below. A compound expressed by formula I or formula II is used for the benzotriazole compound, where R1, R2 are each an alkyl group of C1-4, R3 is methylene group or ethylene group, R4, R5 are each H, or an alkyl group of C1-18, and (a), (b) are integers of 0-3. The content of this compound is set to 1000 mass ppm or below in the electric insulating oil total quantity standard. Monohydric or polyhydric alcohol of C1-24 such as methanol, ethanol, ethylene glycol, or trimethylol ethane is used for alcohol, and its content is most preferably set to 0.5 mass % or below in the electric insulating oil total quantity standard.

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 which is excellent in heat / oxidation stability, flow charging characteristics and safety.

[0002]

2. Description of the Related Art Since so-called impurities such as heterocyclic compounds impair the electrical properties and long-term stability of an electric insulating oil, the production of a base oil of the electric insulating oil is difficult. In doing so, it is necessary to remove these substances. In addition, among the polycyclic aromatic compounds, compounds that have been pointed out as having a possibility of carcinogenicity are also included, and a more safe electric insulating oil has been required. These heterocyclic compounds and polycyclic aromatic compounds can be removed by advanced hydrorefining. On the other hand, when the electric insulating oil circulates inside the transformer, charge separation occurs at an interface with a solid insulator such as a press board, so that the electric insulating oil is positively charged and the insulator is negatively charged. This flow-charging phenomenon accumulates electric charges inside the tank or on the surface of the insulator, and in some cases, causes discharge in oil or on the surface of the insulator, which may lead to an accident. From the viewpoint of preventing such disasters, among the performances required for the electric insulating oil, particularly improvement of the flow electrification property is required, and addition of a flow antistatic agent such as benzotriazole has been proposed. However, the base oil obtained by advanced hydrorefining has poor solubility of benzotriazole, and is difficult to add in an effective amount. Therefore,
In view of such circumstances, the present invention is excellent in various properties required for electric insulating oils such as heat / oxidation stability and flow electrification characteristics, and has higher safety than electric insulating oils conventionally used. The purpose is to obtain electrical insulating oil.

[0003]

In order to achieve the above object, the electric insulating oil of the present invention comprises a mineral oil having an aroma content of not more than 10% as a base oil and a benzotriazole compound and an alcohol. It is a feature.

[0004]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in detail. The mineral oil used as the base oil of the electric insulating oil of the present invention needs to have an aroma content of 10% or less, preferably 5% or less, more preferably 3% or less, and still more preferably 2% or less. When the aroma content exceeds 10%, there is a possibility that a problem may occur in safety due to the remaining polycyclic aromatic compound, and when an antioxidant is added, the effect of addition may be reduced, which is not preferable. . Also,
The mineral oil used as the base oil of the electric insulating oil of the present invention has a naphthene content of 5% or more, preferably 10% or more, more preferably 15% or more, and 65% or less, preferably 50% or less.
%, More preferably 40% or less. If the naphthene content exceeds 65%, the effect of adding an antioxidant may be reduced. The mineral oil used as the base oil of the electric insulating oil of the present invention has a paraffin content of 25% or more, preferably 40% or more, more preferably 50% or more, and 95% or less, preferably 9% or less.
Desirably, it is 0% or less, more preferably 85% or less. The values of the aroma, naphthene, and paraffin components described above are all specified in ASTM-D-3238-90 as "Standar
d Test Method for Carbon Distributionand Structura
l Group Analysis of Petroleum Oils by the ndM Me
The mineral oil used as a base oil of the electric insulating oil of the present invention may have an aroma content of 10% or less as described above, and there are no restrictions on other properties. No, however, DM
It is preferable that the amount of the SO extract is 3.0% by mass or less. Here, the amount of the DMSO extract refers to IP (The The
(Institute of Petoleum) 346 (PCA standard test) means the weight percentage of the polycyclic aromatic compound relative to the total amount of mineral oil. The mineral oil used as the base oil of the electric insulating oil of the present invention preferably has a mutagenicity index MI of less than 1.0. MI
Is 1.0 or more, there is a case where the possibility of causing a problem in safety increases. The mutagenicity index MI here is the "Standard Test Method" defined in ASTM-E-1687-95.
for Determining Carcinogenic Potential of VirginBa
se Oils in Metalworking Fluids ". The mineral oil used as the base oil of the electric insulating oil of the present invention has a sulfur content of 500 mass ppm or less,
Preferably 100 ppm by mass or less, more preferably 50 ppm by mass.
Mass ppm or less, still more preferably 10 mass ppm
It is most desirable that the content be 5 ppm by mass or less. If the sulfur content exceeds 500 ppm by mass, the effect of adding an antioxidant may be reduced. The sulfur content here indicates a value measured in accordance with JIS K 2541 "Crude oil and petroleum products-Sulfur content test method". The kinematic viscosity of the mineral oil used as the base oil of the electric insulating oil of the present invention is not particularly limited, but is 5 to 50 m at 40 ° C.
It is preferably at least m ² / s. The mineral oil used as the base oil of the electric insulating oil of the present invention is JIS K226.
5 It is preferable that the flash point specified in accordance with “Crude oil and petroleum product flash point test method” is 130 ° C. or higher. The mineral oil used as the base oil of the electric insulating oil of the present invention is JI
Preferably, the pour point specified in accordance with SK 2269 “Testing methods for pour point and cloud point of petroleum products of petroleum products and petroleum products” is −27.5 ° C. or less.

[0005] A method for producing a base oil of an electric insulating oil according to the present invention is described.
Is not particularly limited, but preferably the raw material is hydrocracked.
Total pressure 150 kg / cm in the presence of a catalyst^TwoBelow, temperature 3
60-440 ° C, LHSV 0.5 hr^-1The following reaction conditions
Hydrocracking so that the decomposition rate is 40% by mass or more
The product as it is, and a lubricating fraction is separated from the product.
Dewaxed and then dearomatized
Or after dearomatization, followed by dewaxing
It is desirable to be manufactured. In this case,
Is a vacuum distillation distillate (WVGO), mild of WVGO
Hydrocracking (MHC) treated oil (HIX)
Grain oil (DAO), DAO MHC treated oil or these
Any of the above mixed oils can be used. WVGO is crude oil
Of residual oil from the atmospheric distillation unit was vacuum distilled
The distillate obtained at this time, preferably at 360 to 530 ° C
Those with a boiling point are good. HIX means WVGO is MHC
Treated oil (total pressure 100kg / cm^TwoBelow, preferably
60-90kg / cm^TwoTemperature is 370-450 ° C, good
Preferably, 400-430 ° C, LHSV is 0.5-4.0.
hr^-1, Preferably 1.0 to 2.0 hr ^-1Reaction conditions
Below, 360 ° C⁺The decomposition rate of the fraction is in the range of 20 to 30% by mass.
Relatively mild hydrogen decomposition. By)
It is a heavy vacuum gas oil produced. As a catalyst for MHC treatment
Is a compound of alumina, silica alumina, alumina boria, etc.
Group VI metal and Group VIII metal on the composite oxide support
What carried and sulfided can be used. Compare to alumina
If a promoter such as a phosphorus compound is added,
is there. The amount of the metal supported is a Group VI metal on an oxide basis.
In the case of, for example, molybdenum, tungsten and chromium are 5
In the range of 10 to 30% by mass, preferably 10 to 25% by mass.
In the case of Group VIII metals, for example, cobalt, nickel
Is in the range of 1 to 10% by mass, preferably 2 to 10% by mass.
It is. When mixing WVGO and HIX, use WVGO
It is preferable to mix 50% by mass or more of HIX. Previous
De-oiling oil refers to the reduction of residual oil from atmospheric distillation units for crude oil.
Distillation is carried out using a pressure distillation apparatus.
Do not contain real asphaltenes treated by
Oil.

[0006] Hydrocracking of a feedstock is carried out by using a hydrocracking catalyst.
In the presence, the total pressure is 150 kg / cm ^TwoBelow, preferably
100-130kg / cm^TwoMedium to low pressure, temperature 3
60-440 ° C, preferably 370-430 ° C, LHSV
Is 0.5 hr^-1Or less, preferably 0.2 to 0.3 hr^-1
Low LHSV and a hydrogen to feed oil ratio of 1000 to 60
00s. c. f / bbl feedstock, preferably 2500
~ 5000s. c. f / bbl—reaction conditions that are feed oil
It is preferable to carry out in. For hydrocracking of feedstock
Means that the decomposition rate of 360 ° C + fraction in the feed oil is 40% by mass or less.
Above, preferably at least 45% by mass, more preferably at least 50% by mass.
It is preferred that the reaction conditions be adjusted so as to be at least
New When HIX is used as a feedstock oil, MHC
The total decomposition rate of the treatment and hydrocracking is 60% by mass or more,
It is preferably at least 70% by mass. In addition, uncracked oil
When recycling parts, the decomposition rate referred to here is
Per fresh field, not decomposition rate with oil
Decomposition rate. Catalysts used for hydrocracking are particularly limited
However, those having a dual function are preferred.
Is, for example, a Group VIb metal and a Group VIII iron group metal
A hydrogenation point consisting of groups III, IV and
Having a decomposition point composed of a complex oxide of a group V element
A catalyst is used. Tungste as a Group VIb metal
And molybdenum, which are group VIII iron group metals.
Include nickel, cobalt and iron, which are complex
After being supported on an oxide carrier, it is eventually used as sulfide
You. As the composite oxide used for the carrier, silica aluminum
Na, silica zirconia, silica titania, silica magne
Shea, silica alumina zirconia, silica alumina tita
Near, silica alumina magnesia, crystalline silica aluminum
Na (zeolite), crystalline alumina phosphate (AL
PO), crystalline silica alumina phosphate (SAP)
O) and the like. Amount of the metal supported on the composite oxide
Is 5 to 30% by mass of Group VIb metal on an oxide basis
%, Preferably in the range of 10 to 25% by mass.
For group II iron group metals, 1 to 20% by mass, preferably 5 to 1% by mass.
The range is 5% by mass. Just to make sure, you can
In hydrocracking, the bed packed with hydrocracking catalyst
On the upstream side, a pretreatment touch with excellent desulfurization and / or denitrification ability
The medium may be filled. This kind of pretreatment catalyst
For example, carriers such as alumina and alumina boria
Group VI metal and Group VIII metal supported and sulfurized
Things can be used. Professional for alumina and alumina boria
A motor, such as a phosphorus compound, may be added.

[0007] After hydrocracking the feed oil, a lubricating oil fraction may be recovered from the cracked product by ordinary distillation if necessary. The lubricating oil fraction that can be recovered includes a 70-pale fraction having a boiling point range of 343 ° C. to 390 ° C., 390 ° C. to 44 ° C.
SAE-10 fraction at 5 ° C, SAE at 445 ° C to 500 ° C
-20 fractions, SAE-30 fraction at 500 ° C to 565 ° C, and the like. If necessary, the hydrocracked product from which the lubricating oil fraction has been separated and recovered is then dewaxed and then dearomatized, or dewaxed and then dewaxed. As the dewaxing treatment, a solvent dewaxing treatment or a contact dewaxing treatment can be employed. The solvent dewaxing process is, for example, ME
It can be performed by a usual method such as the K method. The MEK method uses benzene, toluene, acetone or benzene as a solvent,
A mixed solvent such as toluene and methyl ethyl ketone (MEK) is used. The processing conditions adjust the cooling temperature so that the dewaxed oil has a predetermined pour point. Solvent / oil volume ratio is 0.5
~ 5.0, preferably 1.0 ~ 4.5, temperature is -5 ~-
The temperature is 45C, preferably -10C to -40C. The contact dewaxing treatment can be performed by a usual method. For example, using a pentasil-type zeolite as a catalyst, the reaction temperature is adjusted so that the dewaxed oil has a predetermined pour point under hydrogen flow, and the reaction conditions are generally such that the total pressure is 10 to 70 kg / c.
m ² , preferably 20-50 kg / cm ² , temperature of 240
To 400 ° C, preferably 260 to 380 ° C. LH
SV is 0.1 to 3.0 hr ^-1 , preferably 0.5 to 2.0 hr ^-1 .
It is in the range of ⁰ hr ^-1 . As the dearomatization treatment, any of a solvent dearomatization treatment and a high-pressure hydrogenation dearomatization treatment can be adopted, but a solvent dearomatization treatment is preferable. The solvent dearomatization treatment is usually performed using a solvent such as furfural and phenol, but in the present invention, it is preferable to use furfural as the solvent. As conditions for the solvent dearomatization treatment, the solvent / oil volume ratio is 4 or less, preferably 3 or less, more preferably 2 or less, and the temperature 90 to 1
50 ° C., and the raffinate yield is at least 60% by volume, preferably at least 70% by volume, more preferably at least 85% by volume.
It is desirable that the volume be equal to or more than the volume%. The dearomatization treatment by high-pressure hydrogenation is usually carried out by adding V
In the presence of a sulfided catalyst supporting a Group Ib metal and a Group VIII iron group metal, a total pressure of 150 to 200 kg / cm ² ,
Preferably 70-200 kg / cm ² , temperature 280-3
50 ° C, preferably 300-330 ° C, LHSV 0.2
The reaction is preferably performed under the conditions of -2.0 hr ^-1 , preferably 0.5-1.0 hr ^-1 . The amount of metal supported on the catalyst is, for example, molybdenum,
5-30% by mass of tungsten and chromium, preferably 1%
In the case of a Group VIII iron group metal, for example, cobalt and nickel are preferably in the range of 1 to 10% by mass, preferably 2 to 10% by mass.
When a solvent dearomatization treatment is used as the dearomatization treatment, a hydrogenation treatment can be performed after this treatment if necessary. In this hydrogenation treatment, the solvent-removed aromatic treated oil is subjected to a total reaction pressure of 50 kg / cm ² or less, preferably 25 to 40 kg.
/ Cm ² hydrogenation reaction conditions at low pressure, V
It is carried out by contacting a hydrogenation catalyst which carries a group Ib metal and a group VIII iron group metal and is sulfided. In the case of a Group VIb metal on an oxide basis, for example, molybdenum, tungsten, and chromium are in the range of 5 to 30% by mass, preferably 10 to 25% by mass, and the amount of the metal supported is a Group VIII iron group metal, for example, The content of cobalt and nickel is preferably in the range of 1 to 10% by mass, preferably 2 to 10% by mass. Such hydrotreatment under a relatively low pressure contributes to dramatically improving the photostability of the solvent-free aromatic oil.

The above is an example of a method for producing an oil used as a base oil in the electric insulating oil of the present invention. When the lubricating oil fraction is not recovered, the lubricating oil fraction can be recovered by a usual distillation operation after the dearomatic treatment, dewaxing treatment or hydrogenation treatment. The lubricating oil fraction collected here is, similarly to the previous case, a 70-pale fraction having a boiling range of 343 ° C to 390 ° C,
SAE-10 fraction at 445 ° C, S at 445 ° C to 800 ° C
AE-20 fraction, SAE-30 fraction at 500 ° C to 565 ° C, and the like.

In the present invention, the above-mentioned hydrocracked base oil is preferably used alone as the base oil, but it is also possible to use a mixture of known mineral and / or synthetic oil-based lubricating base oils. . As a mineral base oil, for example, a lubricating oil fraction obtained by atmospheric distillation and decompression distillation of crude oil is subjected to solvent removal, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrogenation. Base oils such as paraffinic and naphthenic oils which are purified by appropriately combining purification treatments such as purification, washing with sulfuric acid, and clay treatment are exemplified. In addition, as a synthetic oil base oil,
For example, poly-α-olefin (polybutene, 1-octene oligomer, 1-decene oligomer, etc.), alkylbenzene, alkylnaphthalene, diester (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di3
-Ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropaneperargonate, pentaerythritol 2-
Ethylhexanoate, pentaerythritol pelargonate), polyoxyalkylene glycol, polyphenyl ether, silicone oil, perfluoroalkyl ether, or a mixture of two or more of these. When a mineral oil-based and / or synthetic oil-based lubricating base oil is mixed, the above-mentioned hydrocracked base oil is added to the base oil in an amount of 5%.
It is desirable that the content is 0% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more.

The base oil of the electric insulating oil includes volume resistivity,
In order to improve electrical properties such as dielectric loss tangent, clay treatment has been indispensable in the final stage of refining. However, the waste clay left after the white clay treatment requires a large processing cost, and there is a concern that the waste may be imposed on the natural environment. From such a background, it is desired to produce an electrical insulating oil that does not require clay treatment, but in the present invention, particularly when the hydrocracking is used as a base oil, clay treatment is not necessarily required, An electric insulating oil having excellent electric properties can be obtained, and the influence on the natural environment can be reduced while reducing the production cost.

The electric insulating oil of the present invention uses a base oil that satisfies the above properties and contains a benzotriazole compound and an alcohol. The benzotriazole-based compound in the present invention is a compound represented by the following general formula (1) or (2).

Embedded image (In the formula (1), R ¹ represents a linear or branched alkyl group having 1 to 4 carbon atoms, and a represents an integer of 0 to 3.)

Embedded image (In the above formula (2), R ² represents a linear or branched alkyl group having 1 to 4 carbon atoms, R ³ represents a methylene group or an ethylene group, and R ⁴ and R ⁵ are each independently Represents a hydrogen atom or a linear or branched alkyl group having 1 to 18 carbon atoms, and b represents an integer of 0 to 3). In the formula (1), 1 to 1 carbon atoms represented by R ¹ . Specific examples of the linear or branched alkyl group of 4 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group and a tert- A butyl group. Among them, a methyl group and an ethyl group are preferred. A represents an integer of 0 to 3, preferably an integer of 0 to 2. In the formula (2), examples of the linear or branched alkyl group having 1 to 4 carbon atoms represented by R ² include, for example,
Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group,
A tert-butyl group is exemplified. Among them, a methyl group and an ethyl group are preferred. R ³ represents a methylene group or an ethylene group. R ⁴ and R ⁵ each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 18 carbon atoms. As the alkyl group having 1 to 18 carbon atoms, specifically, for example, a methyl group, an ethyl group, n
-Propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl, linear or branched pentyl group, linear or branched hexyl group, linear or branched heptyl group, linear or branched octyl Group, straight or branched nonyl group, straight or branched decyl group, straight or branched undecyl group, straight or branched dodecyl group,
Examples include a linear or branched tridecyl group, a linear or branched tetradecyl group, a linear or branched pentadecyl group, a linear or branched hexadecyl group, a linear or branched heptadecyl group, a linear or branched octadecyl group, and the like. Among them, those having 1 to 12 carbon atoms are preferable. B is 0 to 3
And preferably an integer of 0 to 2. The content of the benzotriazole-based compound in the present invention is not particularly limited, but if the content is large, the electrical properties may be reduced.
m or less, more preferably 500 ppm by mass or less, and most preferably 50 ppm by mass or less. In addition, since the effect of the addition cannot be expected, the content is preferably 5 ppm by mass or more based on the total amount of the electric insulating oil.

The alcohol in the present invention is preferably an alcohol having 1 to 24 carbon atoms, and the alcohol having 1 to 24 carbon atoms may be a monohydric alcohol or a dihydric or higher polyhydric alcohol. The monohydric alcohol having 1 to 24 carbon atoms may be linear or branched, and specifically, for example, methanol, ethanol, linear or branched propanol, linear Or branched butanol, linear or branched pentanol, linear or branched hexanol, linear or branched heptanol, linear or branched octanol, linear or branched Nonanol, linear or branched decanol, linear or branched undecanol, linear or branched dodecanol, linear or branched tridecanol, linear or branched tetradecanol, straight Linear or branched pentadecanol, linear or branched hexadecanol, linear or branched heptadecanol, linear or branched Octadecanol, linear or branched nonadecanol, linear or branched icosanol, linear or branched henicosanol, linear or branched tricosanol, linear or branched tetracosanol And a mixture thereof. Specific examples of the dihydric alcohol include, for example, ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol, and 2-methyl-1,3-propane. Diol, 1,5-
Pentanediol, neopentyl glycol, 1,6-
Hexanediol, 2-ethyl-2-methyl-1,3-
Propanediol, 1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,
2-diethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-
Decanediol, 1,11-undecanediol, 1,
12-dodecanediol and the like. Specific examples of the trihydric or higher polyhydric alcohol include, for example, trimethylolethane, trimethylolpropane, trimethylolbutane, di- (trimethylolpropane), tri- (trimethylolpropane), pentaerythritol, di-
(Pentaerythritol), tri- (pentaerythritol), glycerin, polyglycerin (glycerin 2)
To 20-mers), 1,3,5-pentanetriol, sorbitol, sorbitan, sorbitol glycerin condensate, polyhydric alcohols such as adonitol, arabitol, xylitol, mannitol, xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose And sugars such as mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose, and melezitose, and partially etherified products thereof, and methylglucoside (glycoside). Among these, from the viewpoint of more excellent heat and oxidation stability, insulation properties and solubility improvement of benzotriazole-based compounds,
A monohydric alcohol having 1 to 24 carbon atoms is preferable, and a monohydric alcohol having 12 to 16 carbon atoms is more preferable. The content of the alcohol in the present invention is not particularly limited, but if it is contained in a large amount, the electric properties may be deteriorated. Therefore, the content is preferably 10% by mass or less, preferably 5% by mass or less based on the total amount of the electric insulating oil. More preferably, it is most preferably 0.5% by mass or less. Further, since the effect of the addition cannot be expected, the content is preferably 0.05% by mass or more based on the total amount of the electric insulating oil.

In producing the electric insulating oil of the present invention, there is no particular limitation on the order in which the base oil, benzotriazole and alcohol are blended. However, since the solubility of benzotriazole in the base oil is improved, benzotriazole and alcohol are first mixed,
It is preferable to mix the obtained mixed liquid with the base oil.

As the electric insulating oil of the present invention, when a base oil which has been subjected to a high degree of hydrorefining or solvent refining to remove a heterocyclic compound or a polycyclic aromatic compound, particularly a hydrocracked base oil is used, At the same time, a trace amount of a sulfur compound, which is a natural antioxidant, may disappear, so it is preferable to add an antioxidant. The effect of adding an antioxidant to the hydrocracked base oil is large. As the antioxidant in the present invention, any one can be used, and specific examples include a phenolic antioxidant and an aromatic amine antioxidant. Examples of the phenolic antioxidant include alkylphenols having one or more alkyl groups having 1 to 18 carbon atoms, and more specifically 2,6-ditert-butyl-p-cresol (DBPC) and 2,6-di-tert-butylphenol and the like. Specific examples of the aromatic amine antioxidant include, for example, diphenylamine, dialkyldiphenylamine (the alkyl group has 1 to 18 carbon atoms), phenyl-α-naphthylamine, and alkylphenyl-α-naphthylamine (the carbon number of the alkyl group. Are 1 to 18), phenothiazine, N-alkylphenothiazine (the alkyl group has 1 to 18 carbon atoms) and the like. Further, the content of the antioxidant is not particularly limited, but is usually in the range of 0.01 to 1% by mass, preferably 0.05 to 0.5% by mass based on the total amount of the electric insulating oil.

In order to further improve the excellent performance of the electric insulating oil of the present invention, it is possible to add a known additive for electric insulating oil. Specifically, for example, a condensate of chlorinated paraffin and naphthalene, polymethacrylate, olefin polymer (including ethylene-propylene copolymer, alkylated polystyrene, etc.)
And pour point depressants. Although the content of each of these additives is not limited at all, it is usually preferably 5% by mass or less, preferably 1% by mass, based on the total amount of the electric insulating oil.
The content is more preferably not more than 0.1 mass%, and most preferably not more than 0.1% by mass (total amount).

[0016]

EXAMPLES Hereinafter, the content of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

First, base oils (base oils 1 to 8) having properties as shown in each example of Table 1 were produced. The method for producing each base oil is as follows. (Base oil 1) A hydrocracking treatment, a solvent dewaxing treatment, and a solvent dearomatization treatment using furfural were performed on a vacuum distilled distillate obtained from a paraffinic crude oil. (Base oil 2) Base oil 1 was treated with clay. (Base oil 3) A high-pressure hydrorefining treatment was performed on a vacuum distilled distillate obtained from a naphthenic crude oil. (Base oil 4) Base oil 3 was treated with clay. (Base oil 5) A high-pressure solvent refining treatment was performed on a vacuum distilled distillate obtained from a naphthenic crude oil. (Base oil 6) Base oil 5 was treated with clay. (Base oil 7) Medium-pressure hydrorefining treatment was performed on a vacuum distilled distillate obtained from a naphthenic crude oil. (Base oil 8) Base oil 7 was treated with clay.

[0018]

[Table 1]

Next, as shown in each example (Examples 1 to 12 and Comparative Examples 1 to 8) of Table 2, a predetermined amount of the following additives was blended with each base oil to produce various electric insulating oils. With respect to these electric insulating oils, the dissolution state of additives was evaluated by the following method. Table 2 shows the results. Additive 1: 1,2,3-benzotriazole Additive 2: 2-hexyldecanol Additive 3: DBPC test 1 80 ml of the produced electric insulating oil was collected in a 100 ml screw tube with a stopper and stored at 0 ° C. for 1 week. Of the sample oil was visually observed to confirm the presence or absence of insolubles.

[0020]

[Table 2]

Next, as shown in each example (Examples 1 to 12 and Comparative Examples 9 to 14) of Table 3, a predetermined amount of the following additives was blended with each base oil to produce various electric insulating oils. For these electric insulating oils, a thermal / oxidation stability test and evaluation of electric characteristics were performed by the following methods. Table 3 shows the results. Additive 1: 1,2,3-benzotriazole Additive 2: 2-hexyldecanol Additive 3: DBPC test 2 “2” of JIS C 2101 “Test method for electrical insulating oil”
3. The dielectric loss tangent (tan δ) and the volume resistivity were measured according to “Dielectric tangent and relative permittivity test” and “24. Volume resistivity test”. Test 3 “1” of JIS C 2101 “Electric insulation oil test method”
8. According to the "oxidation stability test", sludge and total acid value after the sample was deteriorated were measured. Test 4 "Standard Test Method for Oxi specified in ASTM-D-2112
dation Stability of Inhibited Mineral Insulating Oi
l by Rotating Bomb ", the oxidation life was measured at a test temperature of 140 ° C. Test 5 IEEE Trans.on Power Apparatus and Systems, VOL.PAS-
The flow charge was measured at room temperature (24 ° C.) at a flow rate of 1.2 ml / s by the mini electrostatic tester method described in 103, No. 7, July (1984). In addition, assuming the oxidative degradation of insulating oil due to use in open pole transformers, the standard test specified in ASTM-D1934
Method for OxidativeAging of Electrical Insulatin
8.Proced of "g Petroleum Oils by Open-Beaker Method"
The flow electrification was also measured for the oxidized and degraded oil according to ure B.

[0022]

[Table 3]

As is clear from the results in Tables 2 and 3,
Each of the electrical insulating oils (Examples 1 to 12) according to the present invention has a good dissolution state of the additive and is excellent in the thermal / oxidation stability test and the electrical properties. In contrast, Comparative Examples 1 to 8 in which only benzotriazole was added had poor solubility of the additive. Comparative Example 9 using only the base oil of the present invention
Nos. 14 to 14 are inferior in flow charging characteristics.

[0024]

In summary, according to the present invention, it is possible to obtain an electrical insulating oil which is excellent in heat / oxidation stability and flow electrification characteristics and has high safety.

Claims (1)

[Claims] 1. An electric insulating oil comprising a mineral oil having an aroma content of 10% or less as a base oil and containing a benzotriazole compound and an alcohol.