WO2016167176A1 - Electrically insulating oil base oil for oil-filled electrical device, electrically insulating oil containing same, and oil-filled electrical device - Google Patents

Abstract

An electrically insulating oil base oil for an oil-filled electrical device, containing a fatty acid ester (A) represented by the following general formula (I). R¹-COO-R²…(I) In formula (I), R¹ represents a C5-17 straight-chained or a C5-17 branched hydrocarbon group, and R² is a C6-10 aryl alkyl group. In formula (I), R¹ is preferably a C5-17 branched hydrocarbon group.

Description

Electrical insulating oil base oil for oil-filled electrical equipment, electrical insulating oil containing the same, and oil-filled electrical equipment

The present invention relates to an electric insulating oil base oil for oil-filled electric equipment, an electric insulating oil containing the same, and an oil-filled electric equipment.
This application claims priority based on Japanese Patent Application No. 2015-081805 filed in Japan on April 13, 2015, the contents of which are incorporated herein by reference.

Conventionally, in oil-filled electrical devices such as transformers, cables, circuit breakers, capacitors, etc., electrical insulating oil has been used for the purpose of insulation and cooling. Since oil-filled electrical equipment is used under a high electric field, there is a possibility that partial discharge occurs inside. Therefore, the insulating oil used for oil-filled electrical equipment has excellent partial discharge characteristics, that is, partial discharge is difficult to occur under a high electric field (partial discharge starting voltage is high), and even if partial discharge occurs. It must be extinguished quickly (high partial discharge extinction voltage).
Mineral oil, silicone oil, PCB (polychlorinated biphenyl), dibenzyltoluene, and the like have been used as base oils for electrical insulating oils. However, these base oils are generally poor in biodegradability, and the load when leaking into the environment is regarded as a problem. Furthermore, since mineral oil is a limited resource, its use may be limited in the future. Silicone oils generally have high viscosity and low thermal conductivity. Therefore, the cooling effect of the oil-filled electrical device is inferior, and it is difficult to make the oil-filled electrical device compact.
In recent years, the use of vegetable oils and fatty acid esters having excellent biodegradability as base oils for electrical insulating oils has been studied. For example, Patent Document 1 discloses an electrical insulating oil containing vegetable oil. Patent Document 2 discloses that a higher fatty acid ester solvent containing a higher fatty acid ester compound is effective for applications such as electrical insulating oil.
However, the techniques of Patent Document 1 and Patent Document 2 cannot provide sufficient partial discharge characteristics.

JP 2010-287788 A JP 2004-149705 A

The present invention has been made in view of the above circumstances, and an object thereof is an electrically insulating oil base oil for oil-filled electrical equipment having excellent partial discharge characteristics and excellent biodegradability.

As a result of intensive studies, the present inventors have found that the following electric insulating oil base oil for oil-filled electrical equipment can solve the above problems.
That is, the present invention has the following configuration.
[1] An electric insulating oil base oil for oil-filled electrical equipment, which contains a fatty acid ester (A) represented by the following general formula (I).
R ¹ —COO—R ² (I)
In the formula (I), R ¹ is a linear or branched hydrocarbon group having 5 to 17 carbon atoms, and R ² is an arylalkyl having 6 to 10 carbon atoms. It is a group.
[2] The electrical insulating oil base oil for oil-filled electrical equipment according to [1], wherein in the formula (I), R ¹ is a branched hydrocarbon group having 5 to 17 carbon atoms.
[3] For oil-filled electrical equipment according to [1] or [2], comprising at least one compound (B) selected from the group consisting of alkylbenzene, alkylnaphthalene, diarylalkane, triarylalkane and mineral oil Electrical insulating oil base oil.
[4] The electrical insulating oil base oil for oil-filled electrical equipment according to [3], wherein the mass ratio represented by (A) component / (B) component is 90/10 to 20/80.
[5] An electrical insulating oil containing the electrical insulating oil base oil for oil-filled electrical equipment according to any one of [1] to [4].
[6] An oil-filled electrical device comprising the electrical insulating oil according to [5].

The electrical insulating oil base oil for oil-filled electrical equipment of the present invention has excellent partial discharge characteristics and excellent biodegradability.

It is sectional drawing which showed an example of the capacitor | condenser. It is the schematic which shows an example of a cable.

(Electrically insulating oil base oil for oil-filled electrical equipment)
The electrical insulating oil base oil for oil-filled electrical equipment of the present invention (hereinafter also simply referred to as “electrical insulating oil base oil”) contains a specific fatty acid ester (component (A)).
The biodegradability of the electrical insulating base oil is preferably 60% or more, more preferably 70% or more, further preferably 75% or more, particularly preferably 80% or more, and may be 100%. The biodegradability is a measured value after 28 days measured in accordance with the Manometric Respirometry Test (Guideline 301F, 17th July 1992) defined in OECD Guideline for Testing of Chemicals.
Kinematic viscosity at 40 ° C. of the electrically insulating base oil is preferably 0.1 ~ ^8mm 2 / s, more preferably 0.5 ~ ^4mm 2 / s. When the kinematic viscosity of the electrical insulating oil base oil is within the above preferred range, the cooling effect of the oil-filled electrical device can be easily obtained.
In the present specification, the kinematic viscosity can be measured according to JIS K2283: 2000 (crude oil and petroleum products—kinematic viscosity test method and viscosity index calculation method).
The pour point of the electric insulating base oil is preferably −25 ° C. or less, more preferably less than −35 ° C.
When the pour point of the electric insulating oil base oil is not more than the above upper limit value, it becomes easy to obtain an electric insulating oil excellent in versatility that is not restricted in use even in cold regions.
In this specification, the pour point can be measured according to “3. Pour point test method” of JIS K 2269: 1987 (pour point of crude oil and petroleum product and cloud point test method of petroleum product).

In this specification, “insulation” means that the dielectric breakdown voltage is 40 kV or more when measured in accordance with “22. Dielectric breakdown voltage test” of JIS C 2101: 2010 (electrical insulation oil test method). Say.

<(A) component>
The component (A) is a fatty acid ester represented by the following general formula (I). The electrical insulating oil base oil of the present invention contains the component (A), whereby partial discharge characteristics are enhanced and biodegradability is enhanced.
R ¹ —COO—R ² (I)
In the formula (I), R ¹ is a linear or branched hydrocarbon group having 5 to 17 carbon atoms, and R ² is an arylalkyl having 6 to 10 carbon atoms. It is a group.

In the formula (I), R ¹ is a linear hydrocarbon group having 5 to 17 carbon atoms or a branched hydrocarbon group having 5 to 17 carbon atoms. 11 branched-chain hydrocarbon groups are preferable, and straight-chain hydrocarbon groups having 5 to 9 carbon atoms or branched-chain hydrocarbon groups having 5 to 9 carbon atoms are more preferable. When the carbon number of R ¹ is in the above range, partial discharge characteristics are enhanced. Further, if the carbon number of R ¹ is less than 5, the plasticity of the resin member becomes strong and the resin member may be deformed. When the carbon number of R ¹ is more than 17, the kinematic viscosity becomes high, and there is a possibility that the cooling effect for the oil-filled electrical device cannot be sufficiently obtained.

R ¹ may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.
Examples of R ¹ include a linear or branched alkyl group having 5 to 17 carbon atoms, an alkenyl group, and an alkynyl group. Examples of R ¹ include pentyl, hexyl, heptyl, isoheptyl, octyl, isooctyl, nonyl, isononyl, decyl, undecyl, dodecyl, tridecyl, tridecenyl, tetradecyl, pentadecyl Group, pentadecenyl group, hexadecyl group, heptadecyl group, heptadecenyl group, heptadecadienyl group, heptadecatrienyl group, heptadecatetraenyl group and the like.
R ¹ is preferably a branched hydrocarbon group. When R ¹ is a branched hydrocarbon group, the low temperature fluidity is more likely to be improved. The branched hydrocarbon group in the present invention includes those in which the carbon atom bonded to the carbon atom of the carbonyl group in the formula (I) such as 1-ethylpentyl group is a secondary carbon atom. It is.

In the formula (I), R ² is an arylalkyl group having 6 to 10 carbon atoms. Examples of R ² include benzyl group, 2-phenylethyl group, 1-phenylethyl group, 2-phenyl-1-propyl group, 3-phenyl-1-propyl group, 1-phenyl-1-butyl group and the like. Can be mentioned. Among these, benzyl group, 2-phenylethyl group, and 1-phenylethyl group are preferable as R ² from the viewpoint that good partial discharge characteristics are easily obtained.

Component (A) includes benzyl caproate, 2-phenylethyl caproate, 1-phenylethyl caproate, 2-phenyl-1-propyl caproate, caproic acid 3 because the partial discharge extinction voltage is further improved. -Phenyl-1-propyl, 1-phenyl-1-butyl caproate, benzyl enanthate, 2-phenylethyl enanthate, 1-phenylethyl enanthate, 2-phenyl-1-propyl enanthate, 3-phenyl enanthate -1-propyl, 1-phenyl-1-butyl enanthate, benzyl caprylate, 2-phenylethyl caprylate, 1-phenylethyl caprylate, 2-phenyl-1-propyl caprylate, 3-phenyl-1 caprylate -Propyl, 1-phenyl-1-butyl caprylate, benzyl isooctylate, iso 2-phenylethyl octylate, 1-phenylethyl isooctylate, 2-phenyl-1-propyl isooctylate, 3-phenyl-1-propyl isooctylate, 1-phenyl-1-butyl isooctylate, benzyl isononanoate, isononanoic acid 2-phenylethyl, 1-phenylethyl isononanoate, 2-phenyl-1-propyl isononanoate, 3-phenyl-1-propyl isononanoate, 1-phenyl-1-butyl isononanoate, benzyl caprate, 2-caprate Phenylethyl, 1-phenylethyl caprate, 2-phenyl-1-propyl caprate, 3-phenyl-1-propyl caprate, 1-phenyl-1-butyl caprate, benzyl isodecanoate, 2-phenylethyl isodecanoate 1-phenylethyl isodecanoate 2-phenyl-1-propyl isodecanoate, 3-phenyl-1-propyl isodecanoate, 1-phenyl-1-butyl isodecanoate, benzyl myristate, 2-phenylethyl myristoleate, 1-phenyl myristoleate Ethyl, 2-phenyl-1-propyl myristoleate, 3-phenyl-1-propyl myristoleate, 1-phenyl-1-butyl myristoleate, benzyl palmitoleate, 2-phenylethyl palmitate, 1-palmitoleate Phenylethyl, 2-phenyl-1-propyl palmitate, 3-phenyl-1-propyl palmitolate, 1-phenyl-1-butyl palmitate, benzyl oleate, 2-phenylethyl oleate, 1-phenylethyl oleate ,oleic acid 2-phenyl-1-propyl, 3-phenyl-1-propyl oleate, 1-phenyl-1-butyl oleate, benzyl linoleate, 2-phenylethyl linoleate, 1-phenylethyl linoleate, 2-linoleate Phenyl-1-propyl, 3-phenyl-1-propyl linoleate, 1-phenyl-1-butyl linoleate, benzyl linolenate, 2-phenylethyl linolenate, 1-phenylethyl linolenate, 2-phenyl linolenic acid 1-propyl, 3-phenyl-1-propyl linolenate, 1-phenyl-1-butyl linolenate, benzyl elaidate, 2-phenylethyl elaidate, 1-phenylethyl elaidate, 2-phenyl-1-elaidate Propyl, 3-phenyl-1-propyl elaidate, elaidic acid 1 Phenyl-1-butyl, benzyl vaccenate, 2-phenylethyl vaccenate, 1-phenylethyl vaccenate, 2-phenyl-1-propyl vacsenate, 3-phenyl-1-propyl vaccenate, 1-phenyl-vaccenate 1-butyl, benzyl stearidate, 2-phenylethyl stearidate, 1-phenylethyl stearidate, 2-phenyl-1-propyl stearidate, 3-phenyl-1-propyl stearidate, 1-phenyl-1-stearidonate Butyl is preferred.

Of these, benzyl caproate, 2-phenylethyl caproate, 1-phenylethyl caproate, 2-phenyl caproate, and the like, are improved in partial discharge extinction voltage and good low-temperature fluidity. 1-propyl, 3-phenyl-1-propyl caproate, 1-phenyl-1-butyl caproate, benzyl enanthate, 2-phenylethyl enanthate, 1-phenylethyl enanthate, 2-phenyl-1-enanthate Propyl, 3-phenyl-1-propyl enanthate, 1-phenyl-1-butyl enanthate, benzyl caprylate, 2-phenylethyl caprylate, 1-phenylethyl caprylate, 2-phenyl-1-propyl caprylate, 3-phenyl-1-propyl caprylate, 1-phenyl-1-butyl caprylate, iso Benzyl octylate, 2-phenylethyl isooctylate, 1-phenylethyl isooctylate, 2-phenyl-1-propyl isooctylate, 3-phenyl-1-propyl isooctylate, 1-phenyl-1-butyl isooctylate, isononanoic acid Benzyl, 2-phenylethyl isononanoate, 1-phenylethyl isononanoate, 2-phenyl-1-propyl isononanoate, 3-phenyl-1-propyl isononanoate, 1-phenyl-1-butyl isononanoate, benzyl caprate, More preferred are 2-phenylethyl caprate, 1-phenylethyl caprate, 2-phenyl-1-propyl caprate, 3-phenyl-1-propyl caprate, and 1-phenyl-1-butyl caprate.
As the component (A), any one type may be used alone, or two or more types may be used in combination.

[Production method of component (A)]
Examples of the method for producing the component (A) include: (i) a method by transesterification between an oil and fat and an alcohol having an arylalkyl group having 6 to 10 carbon atoms; and (ii) an aliphatic alkyl group having 6 to 10 carbon atoms. And (iii) a method by transesterification between a fatty acid ester and an alcohol having an arylalkyl group having 6 to 10 carbon atoms.

Examples of the fats and oils in the method (i) include olive oil, cacao oil, perilla oil, camellia oil, peanut oil, soybean oil, rapeseed oil, mustard oil, dehydrated castor oil, tung oil, safflower oil, linseed oil, corn oil, sunflower oil Corn oil, cottonseed oil, sesame oil, rice bran oil, cannabis oil, evening primrose oil, palm oil, palm kernel oil, coconut oil and the like. Moreover, the fats and oils made edible etc. may be reused as the said fats and oils. Among these, palm oil, palm kernel oil, and coconut oil are preferable from the viewpoint of excellent oxidation stability. (A) Palm kernel oil and palm oil are more preferable from the point which the partial discharge characteristic of a component is easy to be improved.
The method (i) can be performed by a conventionally known method.

As the fatty acid in the method (ii), caproic acid, enanthic acid, caprylic acid, isooctylic acid, isononanoic acid, capric acid, isodecanoic acid, undecyl acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, myristoleic acid , Palmitic acid, palmitoleic acid, heptadecanoic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, vaccenic acid, stearidonic acid and the like. Moreover, as the fatty acid, a fatty acid made edible or the like may be reused.
Examples of the fatty acid include caproic acid, enanthic acid, caprylic acid, isooctylic acid, isononanoic acid, capric acid, isodecanoic acid, myristoleic acid, palmitoleic acid, olein because the partial discharge characteristics of the component (A) are more easily improved. Acid, linoleic acid, linolenic acid, elaidic acid, vaccenic acid and stearidonic acid are preferred. Among these, caproic acid, enanthic acid, caprylic acid, isooctylic acid, isononanoic acid, capric acid are preferred because the partial discharge characteristics of component (A) are easily enhanced and good low-temperature fluidity is easily obtained. More preferred.

The method (ii) can be carried out by a known method. For example, while gradually raising the temperature from room temperature to 200 ° C., the pressure is gradually reduced from normal pressure to 0.7 KPa, and water produced as a by-product is removed. This can be done by removing.
The catalyst used in the method (ii) is not particularly limited, and examples thereof include acid catalysts such as sulfuric acid, p-toluenesulfonic acid (p-TS), benzenesulfonic acid (BS), and methanesulfonic acid; ZrO ₂ , TiO ₂ , SiO ₂ , PO ₄ , Al ₂ O ₃ , ZnO, and other inorganic oxide catalysts; lithium, cesium, sodium, potassium, magnesium, barium, calcium, and other hydroxides, bicarbonates, carbonates, sodium Basic catalysts such as methoxide, potassium methoxide; organotitanium compound catalysts such as tetraisopropyl titanate, tetra n-butyl titanate, tetraethanolamine titanate, tetrastearyl titanate; normal propyl zirconate, normal butyl zirconate, zirconium tetraacetyl Acetonate The organic zirconium compound catalysts such as zirconium mono acetylacetonate.

Examples of the fatty acid ester in the method (iii) include fatty acid ester compounds in the method (ii). As said ester compound, the ester compound comprised from the same fatty acid as a preferable fatty acid in the method of (ii) is preferable.

The method (iii) can be carried out by a known method. For example, alcohols produced as a by-product by gradually reducing the pressure from normal pressure to 0.7 KPa while gradually raising the temperature from room temperature to 200 ° C. This can be done by removing.
The catalyst used in the method (iii) is not particularly limited, and examples thereof include hydroxides such as lithium, cesium, sodium, potassium, magnesium, barium, and calcium; hydrogen carbonate, carbonate, sodium methoxide, Basic catalysts such as potassium methoxide; organotitanium compound catalysts such as tetraisopropyl titanate, tetra n-butyl titanate, tetraethanolamine titanate, tetrastearyl titanate; normal propyl zirconate, normal butyl zirconate, zirconium tetraacetylacetonate, Examples include organic zirconium compound catalysts such as zirconium monoacetylacetonate.

(A) As a manufacturing method of component, from the point which electrical characteristics, such as a partial discharge characteristic, are improved, refinement | purification, such as alcohol removal, glycerol separation, inorganic component removal, neutralization, water washing, distillation, adsorption treatment, deaeration treatment, etc. Is preferably performed. Among these, it is preferable that an adsorption process and / or a deaeration process are performed. When the adsorption treatment is performed, the acid value of the electrically insulating oil base oil is reduced, and the electrical characteristics are easily improved. When the deaeration process is performed, the moisture content of the electric insulating oil base oil is reduced and the electric characteristics are easily improved.

The adsorption treatment is performed by adding an adsorbent such as activated clay or activated alumina to the reaction solution after completion of the reaction, adsorbing a free fatty acid, an acid catalyst or the like, and then removing the adsorbent by filtration.
As the adsorbent, Kyowa Chemical Industry Co., Ltd. Kyoward 100, 200, 300, 400, 500, 600, 700, 1000, 2000 (inorganic synthetic adsorbent mainly composed of Mg, Al, Si, etc.) Kyodo Mug series such as Kyowa Chemical Industry Co., Ltd., Kyowa Mug series such as Kyowa Chemical Industry Co., Ltd., and Tomita AD100, 500, 600 and 700 (Tomita Pharmaceutical Co., Ltd.) , Product name) and the like.
The adsorbent is preferably added in an amount of 0.01 to 5 parts by mass with respect to 100 parts by mass of the ester compound obtained by the reaction. Further, the adsorption treatment is preferably performed at a temperature of 20 to 160 ° C. for 10 minutes to 5 hours in the air, in an inert gas atmosphere such as nitrogen or argon, or under reduced pressure conditions.
By such adsorption treatment, the acid value of the component (A) can be preferably reduced to 0.0001 to 0.01 mg KOH / g, more preferably 0.0001 to 0.005 mg KOH / g, and the electrical characteristics can be further enhanced.
The acid value can be measured by the method of “16. Acid value test” of JIS C 2101: 2010 (electrical insulation oil test method).

In the deaeration treatment, the inside of the reactor is purged with nitrogen, depressurized at 20 to 160 ° C. and a vacuum degree of 0.1 kPa to 80 kPa for 10 minutes to 5 hours, and water and air are distilled off from the reaction solution after the reaction. Done. At this time, a compound azeotropically with water such as toluene, isopropyl alcohol, ethanol, pyridine or the like may be added in an amount of 0.1 to 3 mol with respect to the water in the reaction solution to carry out azeotropy.
By such degassing treatment, the water content in the component (A) can be reduced to preferably 0.1 to 100 ppm, more preferably 0.1 to 50 ppm.
The amount of moisture can be measured by the method of “20. Moisture test” of JIS C 2101: 2010 (electrical insulation oil test method).
After the deaeration treatment is performed, the component (A) is preferably stored under a nitrogen atmosphere or dry air so as not to absorb moisture again. The component (A) is stored by adding 0.1 to 30 parts by mass of a dehydrating agent such as Molecular Sieves 4A (trade name, manufactured by Junsei Chemical Co., Ltd.) to 100 parts by mass of the component (A). Also good. Thereby, a moisture content can be maintained in said preferable range for a long period of time.

The content of the component (A) is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 40% by mass or more, and 100% by mass, ie, electric, based on the total mass of the electric insulating oil base oil. An insulating oil base oil may be comprised only from (A) component. When the content of the component (A) is equal to or higher than the lower limit, partial discharge characteristics and biodegradability are easily improved.
The content of the component (A) is preferably 10 to 100% by mass, more preferably 20 to 90% by mass, and still more preferably 40 to 80% by mass with respect to the total mass of the electric insulating oil base oil.

<(B) component>
The component (B) is at least one compound selected from the group consisting of alkylbenzene, alkylnaphthalene, diarylalkane, triarylalkane and mineral oil.
By using the component (B), the partial discharge extinction voltage can be easily increased. Furthermore, the low temperature fluidity is easily increased.

Alkylbenzene is an aromatic hydrocarbon having an alkyl group bonded to one benzene ring. The alkyl group may be linear or branched. One alkyl group or a plurality of alkyl groups may be bonded to the benzene ring. Examples of the alkyl benzene include monoalkyl benzene, dialkyl benzene, trialkyl benzene, and tetraalkyl benzene.
The alkyl group of the alkylbenzene preferably has 1 to 30 carbon atoms, more preferably 3 to 30 carbon atoms, still more preferably 4 to 24 carbon atoms, and particularly preferably 10 to 20 carbon atoms.
As the alkylbenzene, those having 1 to 4 alkyl groups bonded to the benzene ring are preferable. The alkylbenzene is preferably one having a total carbon number of 3 to 30 alkyl groups bonded to the benzene ring, more preferably a total carbon number of 4 to 24 alkyl groups, and a total carbon number of alkyl groups of 10 to 10. More preferred are those of ˜20. When alkylbenzene is blended with the electric insulating oil base oil, the low-temperature fluidity is easily improved.
Examples of the alkyl group include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, heptadecyl group. , Octadecyl group, nonadecyl group, icosyl group, heicosyl group, docosyl group, tricosyl group, tetracosyl group, pentacosyl group, hexacosyl group, heptacosyl group, octacosyl group, nonacosyl group, triancotyl group and the like. These alkyl groups may be linear or branched.

As the alkylbenzene, those in which the total number of carbon atoms of the alkyl group bonded to the benzene ring is 10 to 20 are preferable from the viewpoint that the partial discharge extinction voltage is easily increased. The alkyl group is preferably a linear or branched decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, heptadecyl group, octadecyl group, nonadecyl group or icosyl group.
Any one of alkylbenzenes may be used alone, or two or more thereof may be used in combination.

Specific examples of alkylbenzene include decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene, heptadecylbenzene, octadecylbenzene, nonadecylbenzene, icosylbenzene and the like.

The method for producing alkylbenzene is not particularly limited, and includes known methods. Examples of the production method include a method of alkylating a raw material such as benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene and a mixture thereof with an alkylating agent. Examples of the alkylating agent include linear or branched olefins obtained by polymerization of lower monoolefins such as ethylene, propylene, butene, and isobutylene, waxes, heavy oils, petroleum fractions, polyethylene, polypropylene, and the like. Linear or branched olefins obtained by cracking, or linear olefins obtained by separating n-paraffins from petroleum fractions such as kerosene and light oil and olefinating them with a catalyst, as well as these A mixture etc. are mentioned.

Alkylnaphthalene is an aromatic hydrocarbon in which an alkyl group is bonded to one naphthalene ring.
Examples of the alkyl group include the same alkyl groups bonded to the above alkylbenzene. One or more alkyl groups may be bonded to the naphthalene ring.
The alkyl group of the alkylnaphthalene preferably has 1 to 30 carbon atoms, more preferably 3 to 30 carbon atoms, still more preferably 10 to 25 carbon atoms, and particularly preferably 14 to 20 carbon atoms. As the alkylnaphthalene, those having 1 to 4 alkyl groups bonded to the naphthalene ring are preferable. The alkylnaphthalene is preferably one having a total carbon number of 3 to 30 alkyl groups bonded to the naphthalene ring from the viewpoint of easily increasing the partial discharge extinction voltage, and having a total carbon number of 6 to 24 alkyl groups. More preferred are those having an alkyl group with a total carbon number of 14-20.
One kind of alkylnaphthalene may be used alone, or two or more kinds thereof may be used in combination.

Specific examples of the alkylnaphthalene include decylnaphthalene, undecylnaphthalene, dodecylnaphthalene, tridecylnaphthalene, tetradecylnaphthalene, heptadecylnaphthalene, octadecylnaphthalene, nonadecylnaphthalene, icosylnaphthalene and the like.

The production method of alkylnaphthalene is not particularly limited, and can be produced by various known methods. For example, hydrocarbons having 14 to 20 carbon atoms, olefins having 14 to 20 carbon atoms, solid acids such as sulfuric acid, phosphoric acid, silicotungstic acid, hydrofluoric acid, etc., acidic clay, activated clay, etc. Examples thereof include a method of adding to naphthalene in the presence of an acid catalyst such as a Friedel-Crafts catalyst which is an acidic substance or a metal halide such as aluminum chloride and zinc chloride.

Examples of the diarylalkane include alkane compounds having two aromatic hydrocarbon groups in the molecule. For example, diphenylmethane, benzyltoluene, benzylxylene, phenyl-sec-butylphenylmethane, di-sec-butyldiphenylmethane, diphenylethane , Phenylethylphenylethane, phenylcumylethane, diisopropylphenylethane, phenyltolylethane, di-sec-butylphenylethane, di-tert-butylphenylethane, phenylxylylethane, phenyl-sec-butylphenylethane, diphenylpropane , Diphenylbutane, ditolylethane, dixylyloctane, dixylyldecane and the like.
Of these, phenylethylphenylethane and phenylxylylethane are preferred.
Examples of phenylethylphenylethane include 1-phenyl-1- (2-ethylphenyl) ethane, 1-phenyl-1- (3-ethylphenyl) ethane, 1-phenyl-1- (4-ethylphenyl) ethane, -Phenyl-2- (2-ethylphenyl) ethane and the like. Examples of phenylxylylethane include 1-phenyl-1- (2,3-dimethylphenyl) ethane, 1-phenyl-1- (2,4-dimethylphenyl) ethane, 1-phenyl-1- (2,5- Dimethylphenyl) ethane, 1-phenyl-1- (2,6-dimethylphenyl) ethane, 1-phenyl-1- (3,4-dimethylphenyl) ethane, 1-phenyl-1- (3,5-dimethylphenyl) ) Ethane, 1-phenyl-2- (2,3-dimethylphenyl) ethane and the like.
The total number of carbon atoms in the diarylalkane is preferably 13 to 30, and more preferably 13 to 20.
One kind of diarylalkane may be used alone, or two or more kinds thereof may be used in combination.

Examples of the triarylalkane include alkane compounds having three aromatic hydrocarbon groups in the molecule. For example, dibenzylbenzene, dibenzyltoluene, dibenzylxylene, and alkyl group substitution products thereof can be used.
The total number of carbon atoms of the triarylalkane is preferably 19 to 30, and more preferably 19 to 26.
One triarylalkane may be used alone, or two or more triarylalkanes may be used in combination.

As mineral oil, what was distilled and refined from heavy oil is mentioned. Examples of the mineral oil include, for example, solvent removal, solvent extraction, and hydrogenation of a lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of paraffinic crude oil, intermediate crude oil, or naphthenic crude oil. Examples thereof include paraffinic mineral oil or naphthenic mineral oil that has been subjected to one or more purification methods such as decomposition, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment. Among these, highly refined mineral oil is preferable because it is more excellent in thermal stability. As the mineral oil, a distillate obtained by subjecting paraffin-based crude oil, intermediate-based crude oil or naphthenic-based crude oil to atmospheric distillation or vacuum distillation residual oil is purified according to a conventional method. Refined oil obtained by further deep dewaxing after purification, hydrotreated oil obtained by hydrotreatment, and the like.
The mineral oil preferably has a kinematic viscosity at 40 ° C. of 0.1 to 100 mm ² / s, more preferably 0.1 to 50 mm ² / s, and still more preferably 0.1 to 10 mm ² / s. . The kinematic viscosity may be adjusted with one kind of mineral oil, or may be adjusted by mixing two or more kinds of mineral oils having different kinematic viscosities.

As the component (B), alkylbenzene and alkylnaphthalene are preferable, and alkylbenzene is more preferable from the viewpoint of excellent balance between partial discharge characteristics and biodegradability when used in combination with the component (A). Among the alkylbenzenes, monoalkylbenzene having a linear alkyl group having 10 to 20 carbon atoms is particularly preferable.
As the component (B), any one type may be used alone, or two or more types may be used in combination.
The content of the component (B) is preferably 0 to 80% by mass, more preferably 10 to 80% by mass, still more preferably 20 to 70% by mass, and more preferably 35 to 65% with respect to the total mass of the electric insulating oil base oil. Mass% is particularly preferred.
When the content of the component (B) is equal to or higher than the lower limit, the partial discharge extinction voltage can be easily increased and the low temperature fluidity can be easily increased.

When component (B) is included in the electrical insulating oil base oil, the mass ratio represented by component (A) / component (B) [mass ratio of component (A) to component (B)] is 90/10 to 20/80 is preferable, 80/20 to 30/70 is more preferable, and 65/35 to 35/65 is still more preferable.
When the mass ratio represented by the component (A) / component (B) is within the above range, an electrically insulating oil base oil excellent in partial discharge characteristics and biodegradability is easily obtained.

The total content of the component (A) and the component (B) is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, based on the total mass of the electrical insulating oil base oil. 100% by mass, that is, the electric insulating oil base oil may be composed only of the component (A) and the component (B). When the total content of the component (A) and the component (B) is in the preferred range, partial discharge characteristics and biodegradability are easily improved.

The electrical insulating oil base oil of the present invention comprises benzyl caproate, 2-phenylethyl caproate, 1-phenylethyl caproate, 2-phenyl-1-propyl caproate, 3-phenyl-1-propyl caproate, caproic acid. 1-phenyl-1-butyl, benzyl enanthate, 2-phenylethyl enanthate, 1-phenylethyl enanthate, 2-phenyl-1-propyl enanthate, 3-phenyl-1-propyl enanthate, 1-enanthate Phenyl-1-butyl, benzyl caprylate, 2-phenylethyl caprylate, 1-phenylethyl caprylate, 2-phenyl-1-propyl caprylate, 3-phenyl-1-propyl caprylate, 1-phenyl caprylate 1-butyl, benzyl isooctylate, 2-phenylethyl isooctylate, iso 1-phenylethyl octylate, 2-phenyl-1-propyl isooctylate, 3-phenyl-1-propyl isooctylate, 1-phenyl-1-butyl isooctylate, benzyl isononanoate, 2-phenylethyl isononanoate, isononanoic acid 1-phenylethyl, 2-phenyl-1-propyl isononanoate, 3-phenyl-1-propyl isononanoate, 1-phenyl-1-butyl isononanoate, benzyl caprate, 2-phenylethyl caprate, 1-caprate At least one fatty acid ester (A) selected from the group consisting of phenylethyl, 2-phenyl-1-propyl caprate, 3-phenyl-1-propyl caprate, and 1-phenyl-1-butyl caprate, And alkylbenzene, alkylnaphthalene, diaryl Glucan preferably contains at least one compound selected from the group consisting of triaryl alkanes and mineral oil (B).

The electrically insulating oil base oil of the present invention includes at least one fatty acid ester (A) selected from the group consisting of benzyl caprylate, benzyl caprate, benzyl palm oil fatty acid, and benzyl isooctylate, and alkylbenzene, alkylnaphthalene, It is preferable to include at least one compound (B) selected from the group consisting of dibenzyltoluene and phenylxylylethane.

The electrically insulating oil base oil of the present invention includes at least one fatty acid ester (A) selected from the group consisting of benzyl caprylate, benzyl caprate, benzyl palm oil fatty acid, and benzyl isooctylate, and alkylbenzene, alkylnaphthalene, Including at least one compound (B) selected from the group consisting of dibenzyltoluene and phenylxylylethane;
The content of the component (A) is 20 to 100% by mass with respect to the total mass of the electric insulating base oil,
The content of the component (B) is 0 to 80% by mass with respect to the total mass of the electric insulating base oil,
The total amount of component (A) and component (B) is preferably not more than 100% by mass.

The electrically insulating oil base oil of the present invention is composed of at least one fatty acid ester (A) selected from the group consisting of benzyl caprylate, benzyl caprate, benzyl palm oil fatty acid, and benzyl isooctylate. preferable.

The electrically insulating oil base oil of the present invention includes at least one fatty acid ester (A) selected from the group consisting of benzyl caprylate, benzyl caprate, benzyl palm oil fatty acid, and benzyl isooctylate, and alkylbenzene, alkylnaphthalene, Including at least one compound (B) selected from the group consisting of dibenzyltoluene and phenylxylylethane;
The content of the component (A) is 20 to 90% by mass with respect to the total mass of the electric insulating base oil,
The content of the component (B) is 10 to 80% by mass with respect to the total mass of the electric insulating base oil,
The total amount of component (A) and component (B) is preferably not more than 100% by mass.

(Electric insulating oil for oil-filled electrical equipment)
The electrical insulating oil for oil-filled electrical equipment of the present invention (hereinafter also simply referred to as “electrical insulating oil”) contains the above-described electrical insulating oil base oil.
The content of the electric insulating oil base oil is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and 100% by mass with respect to the total mass of the electric insulating oil. Good. When the content of the electric insulating oil base oil is equal to or higher than the lower limit value, the partial discharge characteristics and biodegradability of the electric insulating oil are easily improved.
The biodegradability of the electrical insulating oil is preferably 60% or more, more preferably 70% or more, further preferably 75% or more, particularly preferably 80% or more, and may be 100%. The biodegradability is measured in the same manner as the method for measuring the biodegradability of an electrically insulating oil base oil.
Kinematic viscosity at 40 ° C. of the electrical insulating oil is preferably 0.1 ~ ^8mm 2 / s, more preferably 0.5 ~ ^4mm 2 / s. When the kinematic viscosity of the electrical insulating oil is within the above preferred range, a cooling effect on the oil-filled electrical device is easily obtained.
The pour point of the electrical insulating oil is preferably −25 ° C. or less, more preferably less than −35 ° C. When the pour point of the electrical insulating oil is not more than the above upper limit value, good usability can be obtained even in cold districts and the versatility of the electrical insulating oil is enhanced.

The electrical insulating oil may contain other components usually used for the electrical insulating oil in addition to the electrical insulating oil base oil. Examples of other components include base oils other than the above components (A) and (B), and additives such as antioxidants, pour point depressants, metal deactivators, and decomposition inhibitors. However, the content of the base oil other than the component (A) and the component (B) is 20% by mass or less with respect to the total mass of the electrical insulating oil, because better partial discharge characteristics and biodegradability can be obtained. Is preferably 10% by mass or less, more preferably 5% by mass or less, and may be 0% by mass.

Examples of the antioxidant include phenolic antioxidants such as dibutylhydroxytoluene and butylhydroxyanisole; amine-based oxidations such as phenyl-α-naphthylamine and N, N-di (2-naphthyl) -p-phenylenediamine. Inhibitors; Vitamin E such as tocopherol, d-tocopherol, dl-α-tocopherol, acetic acid-α-tocopherol, dl-α-tocopherol, tocopherol acetate, α-tocopherol; ascorbic acid, ascorbates, stearic ascorbate Vitamin Cs such as acid esters; green tea extract; fresh coffee extract; sesamol; sesaminol and the like. Among these, a phenol-based antioxidant is preferable from the viewpoint of excellent solubility in an electric insulating oil base oil. When antioxidant is mix | blended with electrical insulation oil, the oxidation stability at the time of a preservation | save and a long-term use will become easy to be improved.
One type of antioxidant may be used alone, or two or more types may be used in combination.
When the electrical insulating oil of the present invention contains an antioxidant, the content of the antioxidant is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the electrical insulating oil base oil.

Examples of the pour point depressant include acrylic polymers such as sucrose fatty acid ester, polyalkyl methacrylate, and polyalkyl acrylate. The acrylic polymer preferably has a weight average molecular weight of about 5,000 to 500,000. Examples of the acrylic polymer include polymers having a linear or branched alkyl group having 1 to 20 carbon atoms, such as polymethyl acrylate, polymethyl methacrylate, polypropyl acrylate, polypropyl methacrylate, polyheptyl. Acrylate, polyheptyl methacrylate, polynonyl acrylate, polynonyl methacrylate, polyundecyl acrylate, polyundecyl methacrylate, polytridecyl acrylate, polytridecyl methacrylate, polypentadecyl acrylate, polypentadecyl methacrylate, polyheptadecyl acrylate, poly Examples include heptadecyl methacrylate. A commercial item may be used as the acrylate polymer. As said commercial item, the point which is excellent in the fall effect of a pour point, and the handleability, from the Sanyo Kasei Kogyo Co., Ltd. 100 series of accruals (accomputing 132, 133, 136, 137, 138, 146, 160, the above-mentioned brand name). preferable.
When the electrical insulating oil of the present invention contains a pour point depressant, the content of the pour point depressant is preferably 0.01 to 5 parts by weight, more preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the electrical insulating oil base oil. 3 parts by mass is more preferred. When the content of the pour point depressant is equal to or more than the lower limit, the low temperature fluidity can be easily improved. When the content of the pour point depressant is equal to or lower than the upper limit, the increase in viscosity of the electrical insulating oil is easily suppressed.

Examples of the metal deactivator include 4-alkyl-benzotriazoles such as benzotriazole, 4-methyl-benzotriazole, 4-ethyl-benzotriazole; 5-methyl-benzotriazole, 5-ethyl-benzotriazole 5-alkyl-benzotriazoles such as 1-dioctylaminomethyl-2,3-benzotriazole and the like; 1-alkyl-benzotriazoles such as 1-dioctylaminomethyl-2,3-toltriazole and the like Benzotriazole derivatives such as toltriazoles; 2- (alkyldithio) -benzos such as benzimidazole, 2- (octyldithio) -benzimidazole, 2- (decyldithio) -benzimidazole, 2- (dodecyldithio) -benzimidazole Imidazole Benzoimidazole derivatives such as 2- (alkyldithio) -toluimidazoles such as 2- (octyldithio) -toluimidazole, 2- (decyldithio) -toluimidazole, 2- (dodecyldithio) -toluimidazole; 2- (alkyldithio) benzothiazoles such as thiazole, 2-mercaptobenzothiazole derivatives, 2- (hexyldithio) benzothiazole, 2- (octyldithio) benzothiazole; 2- (hexyldithio) tolthiazole, 2- ( 2- (alkyldithio) torthiazoles such as octyldithio) tolthiazole; 2- (N, N-diethyldithiocarbamyl) benzothiazole, 2- (N, N-dibutyldithiocarbamyl) -benzothiazole, 2- (N, N-dihexyl dithiocarba 2-) (N, N-dialkyldithiocarbamyl) benzothiazoles such as 2-benzothiazole; 2- (N, N-diethyldithiocarbamyl) tolthiazole, 2- (N, N-dibutyldithiocarbamyl) And benzothiazole derivatives such as 2- (N, N-dialkyldithiocarbamyl) -torzothiazoles such as tolthiazole and 2- (N, N-dihexyldithiocarbamyl) tolthiazole. Among these, a benzotriazole derivative is preferable from the viewpoint of obtaining an action as a fluid antistatic agent.
A metal deactivator may be used individually by 1 type and may be used in combination of 2 or more type.
When the electrical insulating oil of the present invention contains a metal deactivator, the content of the metal deactivator is preferably 0.0001 to 0.5 parts by mass with respect to 100 parts by mass of the electrical insulating oil base oil. More preferred is 0.0005 to 0.1 parts by mass.

Examples of the decomposition inhibitor include carbodiimide compounds such as bis (alkylphenyl) carbodiimide such as diphenylcarbodiimide, ditolylcarbodiimide, bis (isopropylphenyl) carbodiimide, and bis (butylphenyl) carbodiimide; phenylglycidyl ether, phenylglycidyl ester, alkylglycidyl Ether, alkyl glycidyl ester, 3,4-epoxycyclohexylmethyl (3,4-epoxycyclohexane) carboxylate, vinylcyclohexylene epoxide, 3,4-epoxy-6-methylcyclohexylmethyl (3,4-epoxy-6-methyl) Hexane) carboxylate, a phenol novolac epoxy compound which is a diglycidyl ether type epoxy compound of bisphenol A; Seo cresol novolak type epoxy compound such as epoxy compound, and the like. When the electrical insulating oil of the present invention contains a decomposition inhibitor, deterioration due to heat, oxygen and the like is easily suppressed.

The electrical insulating oil of the present invention is produced by a conventionally known production method. Examples of the method for producing the electrical insulating oil of the present invention include a method of adding other components to the electrical insulating oil base oil and mixing them.
The electrical insulating oil of the present invention can be used as an insulating oil for oil-filled electrical equipment.

(Oil-filled electrical equipment)
The oil-filled electrical device of the present invention includes the above-described electrical insulating oil. Examples of the oil-filled electrical device include a transformer, a reactor, a tap changer, a cable, a bushing, a transformer, a capacitor, and a current transformer.
1 is a capacitor element 1 wound in a configuration using a polypropylene film or the like as a dielectric and a metal foil or the like as an electrode; a lead piece 2 formed of a copper foil or the like derived from the capacitor element 1; a capacitor Metal case 3 having an opening for accommodating element 1; Insulating material 4 disposed between metal case and capacitor element 1; Filled inside of metal case to insulate metal case 3 and capacitor element 1 Insulating medium (electrical insulating oil) 5; metal lid 6 that seals the metal case 3; an external lead terminal 7 that is arranged on the top of the metal lid 6 and used for connection to an external power source; a metal lid 6 and an external lead terminal 7; A terminal plate 8 made of a thermosetting resin or the like for insulating the terminals; a terminal bar 9 disposed under the metal lid 6 and electrically connecting the lead piece 2 and the external lead terminal 7; and a metal lid Arranged under 6 5 insulated and insulated medium (electrical insulating oil) and a metal cover 6 and the terminal rod 9 is having a packing rubber 10 for preventing the leakage from the metal case.
The cable of FIG. 2 includes a conductor 16, a first semiconductive layer 17 disposed around the conductor 16, a layer impregnated with the electric insulating oil 12 disposed outside the first semiconductive layer, and the electric insulating oil 12. A second semiconductive layer disposed outside the impregnated layer; a metal screen disposed outside the second semiconductive layer; and a protective sheath 15 disposed outside the metal screen.

As described above, since the electrically insulating oil base oil of the present invention contains the component (A), it has excellent partial discharge characteristics and excellent biodegradability.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. In this example, “%” indicates “% by mass” unless otherwise specified.
The raw materials used in this example are as follows.

<(A) component>
A-1: Benzyl caprylate, prepared as follows.
A-2: Benzyl caprate, prepared as follows.
A-3: Palm oil fatty acid benzyl, prepared as follows.
A-4: Benzyl isooctylate, prepared as follows.

<(B) component>
B-1: Alkylbenzene (monoalkylbenzene having an alkyl group having 10 to 13 carbon atoms, trade name “Alken L” manufactured by JX Nippon Mining & Energy Corporation).
B-2: Alkylnaphthalene (monoalkylnaphthalene having an alkyl group having 16 to 18 carbon atoms, manufactured by Lion Corporation, trade name “Diffusion Pump Oil A”).
B-3: Dibenzyltoluene (trade name “NeoSK-OIL” manufactured by Soken Techniques Co., Ltd.).
B-4: Phenylxylylethane (JIS C2320, Type 5 No. 2 insulating oil).

<(A ′) Component: Comparative Component of (A) Component>
A′-1: Methyl caprylate (product name “Pastel M-8” manufactured by Lion Corporation).
A′-2: methyl palm oil fatty acid (product name “Pastel M-182”, manufactured by Lion Corporation).
A′-3: 2-ethylhexyl caprylate (manufactured by Lion Corporation, trade name “Pastel 2H-08”).
A'-4: Rape seed oil (manufactured by Kanden Engineering Co., Ltd., trade name "Sunohm ECO").

[Preparation example of benzyl caprylate]
In a 5 L four-necked flask equipped with a stirrer, thermometer, partial tube and total tube, 2100 g of caprylic acid (manufactured by Kanto Chemical Co., Ltd.) and 1653 g of benzyl alcohol (manufactured by Kanto Chemical Co., Ltd.) (molar ratio 1) : 1.05) and 0.5 g of p-toluenesulfonic acid monohydrate (manufactured by Tokyo Kasei Kogyo Co., Ltd.) were added to perform nitrogen substitution. Then, while flowing nitrogen at a flow rate of 1 mL / min, the liquid temperature was raised to 140 ° C. to carry out an esterification reaction, and water produced by the reaction was removed by distillation. After removing water, the temperature was raised to 200 ° C. while gradually reducing the pressure to 0.6 kPa, thereby obtaining a crude product containing unreacted caprylic acid and benzyl alcohol in an amount of 1% by mass or less. Next, 33.1 g of Hyflo Supercell (manufactured by Junsei Chemical Co., Ltd.) was added as a filter aid to 3310 g of the crude product, and the mixture was stirred and dispersed uniformly for 10 minutes, followed by pressure filtration at 80 ° C. To obtain benzyl caprylate.

[Preparation example of benzyl caprate]
The above except that capric acid (manufactured by Kanto Chemical Co., Inc.) was used instead of caprylic acid and the molar ratio of capric acid to benzyl alcohol was charged so that capric acid: benzyl alcohol = 1: 1.2. In the same manner as in the preparation example of benzyl caprylate, benzyl caprate was obtained.

[Preparation example of benzyl palm oil fatty acid]
Palm oil fatty acid methyl (trade name “Pastel M-182”, manufactured by Lion Corporation) was used instead of caprylic acid, and the molar ratio of palm oil fatty acid methyl to benzyl alcohol was palm oil fatty acid methyl: benzyl alcohol = 1: A palm oil fatty acid benzyl was obtained in the same manner as in the preparation example of benzyl caprylate except that the amount was adjusted to 1.2.

[Preparation example of benzyl isooctylate]
The above, except that isooctylic acid (manufactured by KH Neochem) was used instead of caprylic acid and the molar ratio of isooctylic acid to benzyl alcohol was such that isooctylic acid: benzyl alcohol = 1: 1.2. In the same manner as in the preparation of benzyl caprylate, benzyl isooctylate was obtained.

(Examples 1 to 10, Comparative Examples 1 to 9)
The above (A-1) was used as the electrical insulating oil base oil of Example 1. Further, according to the compositions shown in Tables 1 and 2, the components (A) and (B) were mixed to produce the electric insulating oil base oils of Examples 2 to 10.
The above (B-4), (B-1), (B-3), (A′-1), (A′-2), and (A′-3) are electrically insulated from Comparative Examples 1 to 6, respectively. Oil base oil was used. Electrically insulating oil base oils of Comparative Examples 7 to 9 were produced in the same manner as in Example 2 except that the component (A ′) was used instead of the component (A).
Tables 1 and 2 show the compositions (blending components, content (mass%)) of the obtained electrical insulating oil base oil of each example.
In the table, when there is a blank blending component, the blending component is not blended.

For the electrical insulating oil base oil of each example, the partial discharge characteristics (partial discharge start voltage, partial discharge extinction voltage) and biodegradability were evaluated as follows. The evaluation results are shown in Tables 1 and 2.
Moreover, the pour point and kinematic viscosity of the electrical insulating oil base oil of each example were measured as follows. The measurement results are shown in Tables 1 and 2.

(Evaluation of partial discharge characteristics)
<Evaluation of partial discharge start voltage>
The partial discharge starting voltage of the electrical insulating oil base oil of each example was measured according to JEC-0401-1990. Specifically, when a partial discharge measuring device (E.R.A. Discharge Detector Model 5 Type 700, manufactured by Robinson Instruments) is used and the applied voltage is gradually increased under a predetermined voltage, a predetermined magnitude is obtained. The voltage (partial discharge start voltage) at which partial discharge exceeding (the magnitude of discharge pulse, occurrence frequency) was measured was measured. Using the measured value of the partial discharge starting voltage of the electric insulating oil base oil of Comparative Example 1 (phenylxylylethane: JIS C2320, Type 2 No. 2 insulating oil) as a reference (100%), the partial discharge of each example with respect to the measured value The relative value of the measured value of the starting voltage was determined. The relative values were classified into the following evaluation criteria, and the partial discharge start voltage of the electric insulating oil base oil of each example was evaluated. AA and A were regarded as acceptable.
[Evaluation criteria]
AA: More than 100%.
A: 95 to 100%.
B: Less than 95%.

<Evaluation of partial discharge extinction voltage>
The partial discharge extinction voltage of the electrical insulating oil base oil of each example was measured according to JEC-0401-1990. Specifically, when a partial discharge measuring device (E.R.A. Discharge Detector Model 5 Type 700, manufactured by Robinson Instruments) is used and the applied voltage is gradually lowered under a predetermined voltage, a predetermined magnitude ( The voltage (partial discharge extinction voltage) at which the partial discharge exceeding the discharge pulse magnitude (occurrence frequency) disappears was measured.
Using the measured value of the partial discharge start voltage of the electric insulating oil base oil of Comparative Example 1 as a reference (100%), the relative value of the measured value of the partial discharge extinction voltage of the electric insulating oil base oil of each example with respect to the measured value is obtained. It was. The relative values were classified into the following evaluation criteria, and the partial discharge extinction voltage of the electric insulating oil base oil in each example was evaluated. AAA, AA, and A were accepted. In addition, B is evaluated by the following evaluation criteria that partial discharge is not extinguished and cannot be used practically.
[Evaluation criteria]
AAA: More than 50%.
AA: 45-50%.
A: 40% or more and less than 45%.
B: Less than 40%.

(Evaluation of biodegradability)
The biodegradability test of the electric insulating oil base oil of each example was performed in accordance with the Manometric Respirometry Test (Guideline 301F, 17th July 1992) defined in the OECD Guidelines for Testing of Chemicals. The test conditions were as follows.
Test conditions: test substance concentration 100 mg / L, activated sludge concentration 30 mg / L (as suspension substance concentration), test solution volume 300 mL, test solution culture temperature 25 ± 1 ° C., test solution culture period 28 days (under light shielding).
The measurement for calculating the degree of degradation was carried out by biochemical oxygen demand (BOD) using a closed oxygen consumption measuring device. Those with a biodegradability of 60% or more were regarded as acceptable.

(Measure pour point)
The pour point of the electric insulating base oil of each example was measured according to “3. Pour point test method” of JIS K 2269: 1987 (pour point of crude oil and petroleum products and cloud point test method of petroleum products).
The pour points of the electrical insulating base oils in each example were classified into the following evaluation criteria, and the pour points were evaluated. If it is AA and A, it is evaluated that it can be used satisfactorily in cold districts and has excellent versatility.
[Evaluation criteria]
AA: Pour point is less than -35 ° C.
A: Pour point is -35 to -25 ° C.
B: Pour point is over -25 ° C.

(Measurement of kinematic viscosity)
The kinematic viscosity at 40 ° C. of the electric insulating oil base oil of each example was determined using a Canon Fenceke type kinematic viscosity tube in accordance with JIS K2283: 2000 (crude oil and petroleum products-kinematic viscosity test method and viscosity index calculation method). It was measured.
The kinematic viscosity of the electric insulating base oil of each example was classified into the following evaluation criteria, and kinematic viscosity was evaluated. If it is AA and A, it will be evaluated that a favorable cooling effect is easily acquired with respect to an oil-filled electrical apparatus.
[Evaluation criteria]
AA: 4 mm ² / s or less.
A: More than 4 mm ² / s and not more than 8 mm ² / s.
B: Over 8 mm ² / s.

From the results shown in Tables 1 and 2, the electric insulating oil base oils of Examples 1 to 10 to which the present invention is applied are excellent in partial discharge characteristics (partial discharge start voltage, partial discharge extinction voltage) and biodegradable. It was confirmed that it was excellent. Furthermore, the electrically insulating oil base oils of Examples 1 to 10 have low pour points and kinematic viscosities, and are evaluated to be excellent in usability in cold districts and the like and in cooling effects on oil-filled electrical equipment.
On the other hand, the electrical insulating base oil composed of (B-4) (Comparative Example 1) and the electrical insulating base oil composed of (B-3) (Comparative Example 3) were not sufficiently biodegradable.
An electrically insulating oil base oil composed of (B-1) (Comparative Example 2) and an electrically insulating oil base oil (Comparative Example 8 and Comparative Example 9) in which the component (A ′) and (B-1) are used in combination are sufficient. Partial discharge characteristics (partial discharge start voltage, partial discharge extinction voltage) were not obtained.
The electrical insulating base oil composed of the component (A ′) (Comparative Examples 4 to 6) did not have sufficient partial discharge characteristics (partial discharge extinction voltage).
The electric insulating oil base oil (Comparative Example 7) in which the component (A ′) and (B-4) were used in combination did not provide sufficient partial discharge characteristics (partial discharge extinction voltage) and biodegradability.
From the above results, it was confirmed that the electrically insulating oil base oil to which the present invention was applied was excellent in partial discharge characteristics and biodegradability.

An object of the present invention is to provide an electrical insulating oil base oil for oil-filled electrical equipment that has excellent partial discharge characteristics and excellent biodegradability.

1 Capacitor element 2 Lead piece 3 Metal case 4 Insulating material 5 Insulating medium (electrical insulating oil)
6 Metal lid 7 External lead terminal 8 Terminal plate 9 Terminal bar 10 Packing rubber 11 Insulating plate 12 Electrical insulating oil 13 Second semiconductive layer 14 Metal screen 15 Protective sheath 16 Conductor 17 First semiconductive layer

Claims (6)

1. An electrically insulating oil base oil for oil-filled electrical equipment, comprising a fatty acid ester (A) represented by the following general formula (I).
   R ¹ —COO—R ² (I)
   In the formula (I), R ¹ is a linear or branched hydrocarbon group having 5 to 17 carbon atoms, and R ² is an arylalkyl having 6 to 10 carbon atoms. It is a group.
2. The electrically insulating oil base oil for oil-filled electrical equipment according to claim 1, wherein R ¹ in the formula (I) is a branched hydrocarbon group having 5 to 17 carbon atoms.
3. The electrically insulating oil base oil for oil-filled electrical equipment according to claim 1 or 2, comprising at least one compound (B) selected from the group consisting of alkylbenzene, alkylnaphthalene, diarylalkane, triarylalkane and mineral oil. .
4. The electrically insulating oil base oil for oil-filled electrical equipment according to claim 3, wherein the mass ratio represented by (A) component / (B) component is 90/10 to 20/80.
5. An electrical insulating oil for oil-filled electrical equipment, comprising the electrical insulating oil base oil for oil-filled electrical equipment according to any one of claims 1 to 4.
6. Oil-filled electrical equipment comprising the electrical insulating oil for oil-filled electrical equipment according to claim 5.

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