JP7042163B2 - Electrical insulating oil composition - Google Patents

Description

The present invention relates to an electrically insulating oil composition.

The electrically insulating oil composition contains at least a base oil and an antioxidant, and is widely used as an insulating material for oil-filled electrical equipment such as oil-filled capacitors, oil-filled cables, oil-filled transformers, and oil-filled breakers. There is. For example, Patent Document 1 proposes an electrically insulating oil composition containing at least one of mineral oil and synthetic oil as a main component and containing a predetermined amount of a sulfide-type sulfur content and a phenolic compound.

Japanese Unexamined Patent Publication No. 2000-306430

By the way, when an abnormality such as overheating or discharge occurs inside an oil-filled electric device, hydrogen (H ₂ ), methane (CH ₄ ), ethane (C ₂ H ₆ ), which are decomposition products of an electrically insulating oil composition, etc., Combustible gases such as propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), and carbon monoxide (CO) are produced. Utilizing this phenomenon, oil-in-oil gas analysis for diagnosing the presence or absence of internal abnormalities during operation of oil-filled electrical equipment is widely used. As a result of the oil-filled gas analysis, if it is diagnosed that an internal abnormality has occurred in the oil-filled electrical equipment, the oil-filled electrical equipment is stopped and maintenance work or the like is executed.

However, in recent years, phenomena that may mislead the diagnostic results of oil gas analysis have been reported in Europe and the United States. Specifically, it has been reported that a large amount of flammable gas is generated in the oil-filled electric device at a relatively low temperature regardless of overheating or discharge inside the oil-filled electric device. This phenomenon is called the "stray gas phenomenon". The flammable gas generated in the stray gas phenomenon is called "stray gas". The cause of the stray gas phenomenon has not yet been clarified.
When the stray gas phenomenon occurs, flammable gas is generated even though overheating and discharge have not occurred inside the oil-filled electric device. Therefore, flammable gas is detected in the gas analysis in oil, and based on this detection result, it is erroneously determined that overheating, discharge, or the like is occurring inside the oil-filled electric device. Then, based on this erroneous determination, work such as maintenance is unnecessarily executed for the oil-filled electric device that does not actually have a problem such as overheating or discharge.

Therefore, an object of the present invention is to provide an electrically insulating oil composition in which stray gas is less likely to be generated.

As a result of diligent studies, the present inventors have found that an electrically insulating oil composition containing a specific base oil can solve the above-mentioned problems.
That is, the present invention relates to the following [1].
[1] An electrically insulating oil composition containing a base oil (A), a phenolic antioxidant, and an antistatic agent.
The base oil (A) satisfies the following conditions (A1), (A2), and (A3).
Condition (A1):% CA by ring analysis (nd-M method) is less than 5.3% Condition ( _A2 ):% CN by ring analysis (nd- _M method) is 40.0% or more Condition (A3): The pour point is −40 ° C. or less, and the content of the phenolic antioxidant is 0.06% by mass or more and 0.4% by mass or less based on the total amount of the electrically insulating oil composition.
An electrically insulating oil composition in which the content of the antistatic agent is 3% by mass or more and 40% by mass or less based on the total amount of the electrically insulating oil composition.

According to the present invention, there is provided an electrically insulating oil composition that does not easily generate stray gas.

[Electrical insulating oil composition]
The electric insulating oil composition of the present invention contains a base oil (A), a phenolic antioxidant, and an antistatic agent.
The base oil (A) satisfies the following conditions (A1), (A2), and (A3).
Condition (A1):% CA by ring analysis (nd-M method) is less than 5.3% Condition ( _A2 ):% CN by ring analysis (nd- _M method) is 40.0% or more Condition (A3): The pour point is −40 ° C. or less, and the content of the phenolic antioxidant is 0.06% by mass or more and 0.4% by mass or less based on the total amount of the electrically insulating oil composition.
The content of the antistatic agent is 3% by mass or more and 40% by mass or less based on the total amount of the electric insulating oil composition.

The IEC standard (IEC60296), which is an example of the standard for electrically insulating oil, includes "small amount of additive oil" and "added oil" as classifications of electrically insulating oil. The electrically insulating oil classified into "trace amount added oil" and "added oil" contains a predetermined amount of antioxidant. The antioxidant is usually a phenolic antioxidant. Further, in order to satisfy various standards for electrically insulating oil, a predetermined amount of antistatic agent is usually added.
The "IEC standard" is an international standard established by the International Electrotechnical Commission.
As a result of various studies in consideration of various standards of electrically insulating oil, the present inventors have come to find out the following.
In general, the oxidation stability of an electrically insulating oil composition containing an antioxidant is improved as the degree of purification of the base oil is higher. That is, the smaller the aromatic content, sulfur content, nitrogen content, etc. of the base oil, the less the consumption of the antioxidant, the better the antioxidant effect of the antioxidant, and the higher the oxidation stability of the electric insulating oil. The composition is obtained.
However, as a result of diligent studies by the present inventors, it has been found that the electrically insulating oil composition using a highly refined base oil tends to generate stray gas rapidly after the antioxidant is consumed. ..
To solve this problem, the present inventors have consumed the antioxidant by using the base oil used in the electrically insulating oil composition as the base oil satisfying the above conditions (A1), (A2), and (A3). It was found that an electrically insulating oil composition in which the rapid generation of stray gas was suppressed can be obtained even after the above. Based on this finding, in the electric insulating oil composition to which a predetermined amount of a phenolic antioxidant and a predetermined amount of an antioxidant are added in order to satisfy various specifications of the electric insulating oil, the above conditions (A1) and (A2) , And (A3), it was found that the problem of the present invention can be solved by using the base oil.

Hereinafter, the electric insulating oil composition of the present invention will be described in detail, and the properties of the electric insulating oil composition, the method for producing the electric insulating oil composition, the method of using the electric insulating oil composition, and the electric insulation thereof. An oil-filled electrical device having an oil composition will be described in detail.

<Base oil (A)>
The base oil (A) contained in the electrically insulating oil composition of the present invention satisfies the following conditions (A1), (A2), and (A3).
Condition (A1):% CA by ring analysis (nd-M method) is less than 5.3% Condition ( _A2 ):% CN by ring analysis (nd- _M method) is 40.0% or more Condition (A3): Pour point is -40 ° C or less

In the present invention,% CA and% CN are values obtained by ring analysis (nd- _M method) according to ASTM _D3238-95 .
% _CA is a value indicating the mass ratio (percentage) of the amount of aromatic carbon to the total amount of carbon.
% CN is a value indicating the mass ratio (percentage) of the _naphthenic carbon amount to the total carbon amount.

Further, in the present invention, the pour point is a value measured according to JIS K 2269: 1987.

In the present invention, as the condition (A1) of the base oil ( _A ), it is stipulated that% CA by the ring analysis (nd-M method) is less than 5.3%. When the% CA of the base oil ( _A ) is 5.3% or more, the antioxidant in the electrically insulating oil composition is consumed quickly, and the antioxidant ability of the electrically insulating oil composition cannot be sufficiently maintained. Therefore, it does not pass the IEC standard oxidation stability test or JIS standard oxidation stability test.
The IEC standard oxidation stability test and the JIS standard oxidation stability test are carried out by the methods described in Examples described later.

Here, in one aspect of the present invention, from the viewpoint of facilitating the suppression of the amount of hydrogen generated in the stray gas, the consumption of the antioxidant in the electrically insulating oil composition, which is the starting point of the rapid generation of the stray gas, is further suppressed. The% CA of the base oil ( _A ) is preferably 5.2% or less, more preferably 5.0% or less, still more preferably, from the viewpoint of facilitating the process and further improving the antioxidant ability of the antioxidant. Is 4.8% or less, more preferably 4.6% or less, even more preferably 4.4% or less, still more preferably 4.2% or less, even more preferably 4.0% or less, even more preferably. It is 3.8% or less, and even more preferably 3.5% or less. Further, it is preferably 0.01% or more, more preferably 0.1% or more, still more preferably 0.5% or more, still more preferably 1.0% or more, still more preferably 1.5% or more, still more preferable. Is 2.0% or more, more preferably 2.5% or more.

Next, in the present invention, as the condition (A2) of the base oil (A), it is stipulated that the% CN by the ring analysis (nd- _M method) is 40% or more. When the% CN of the base oil (A) is less than 40%, _abrupt generation of stray gas is likely to occur after the antioxidant is consumed.

Here, in one aspect of the present invention, the% CN of the base oil (A) is preferably _41.0 % or more, from the viewpoint of making it easier to suppress the generation of stray gas after the antioxidant is consumed. More preferably 41.2% or more, further preferably 41.4% or more, still more preferably 41.6% or more, still more preferably 41.8% or more, still more preferably 42.0% or more, still more preferable. Is 42.2%, and even more preferably 42.4% or more.
In one aspect of the present invention, the% _CN of the base oil (A) is usually 52% or less from the viewpoint of suppressing the consumption of the antioxidant and improving the antioxidant effect of the antioxidant. It is preferably 51% or less, more preferably 50% or less.

In the present invention, the% _Cp of the base oil (A) is less than 60%. Here, in one aspect of the present invention, the% Cp of the base oil (A) is preferably _57.5 % or less, from the viewpoint of making it easier to suppress the generation of stray gas after the antioxidant is consumed. More preferably 57.2% or less, still more preferably 57.0% or less, still more preferably 56.8% or less, still more preferably 56.6% or less, still more preferably 56.4% or less, even more preferably. Is 56.2% or less, and even more preferably 56.0% or less. From the same viewpoint, the% Cp of the base oil (A) is preferably _53.6 % or more, more preferably 53.8% or more, still more preferably 54.0% or more, still more preferably 54. It is 2% or more, more preferably 54.4% or more, still more preferably 54.6% or more.
% C _p is a value indicating the mass ratio (percentage) to the amount of paraffin carbon.

Next, in the present invention, it is stipulated that the pour point is −40 ° C. or lower as the condition (A3) of the base oil (A). If the pour point of the base oil (A) is higher than −40 ° C., the fluidity of the electrically insulating oil composition may deteriorate when used in a low temperature environment.
From the viewpoint of preparing an electrically insulating oil composition that satisfies the fluidity under lower temperature conditions, the pour point of the base oil (A) is preferably less than -40 ° C, more preferably -42.5 ° C or less. More preferably, it is -45.0 ° C. or lower. The pour point of the base oil (A) is usually −65.0 ° C. or higher.

Here, in one aspect of the present invention, from the viewpoint of further improving practical safety, the flash point of the base oil (A) is preferably 135 ° C. or higher, more preferably 140 ° C. or higher, still more preferably 145 ° C. or higher. That is all.
In the present invention, the flash point is a value measured by the Penske Martens sealing method in accordance with JIS K 2265-3: 2007.

Further, in one aspect of the present invention, the density of the base oil (A) is preferably 0.8400 g / cm ³ or more, more preferably 0.8450 g / cm ³ or more, still more preferably 0.8500 g / cm ³ or more. be. The density of the base oil (A) is preferably 0.8950 g / cm ³ or less, more preferably 0.8800 g / cm ³ or less, and further preferably 0.8650 g / cm ³ or less.
In the present invention, the density is a value measured according to JIS K 2249.

The base oil (A) satisfying the conditions (A1), (A2), and (A3), and further the above-mentioned ignition point and density requirements in addition to the conditions (A1), (A2), and (A3). Examples of the base oil (A) to be satisfied include refined paraffin-based mineral oil.
In the refined paraffinic mineral oil, for example, the residual oil after atmospheric distillation of the paraffinic crude oil is distilled under reduced pressure, and the obtained vacuum distilled oil is hydrorefined at least once, preferably once, and then hydrogen is produced. After the dewaxing treatment, a distillate having an appropriate viscosity as a base oil used in the electrically insulating oil composition is recovered and prepared.

In one aspect of the present invention, the appropriate viscosity as the base oil used in the electrically insulating oil composition is that the kinematic viscosity of the base oil (A) at 40 ° C. is preferably 5 mm ² / s or more and 12 mm ² / s or less. It means that it is more preferably 6 mm ² / s or more and 11 mm ² / s or less, and further preferably 7 mm ² / s or more and 10 mm ² / s or less.
Further, in one aspect of the present invention, when the viscosity suitable for the base oil used in the electrically insulating oil composition is defined by the kinematic viscosity at 100 ° C., the kinematic viscosity of the base oil (A) at 100 ° C. is preferably 1 mm. It is ² / s or more and 10 mm ² / s or less, more preferably 1.4 mm ² / s or more and 8 mm ² / s or less, and further preferably 1.8 mm ² / s or more and 6 mm ² / s or less.

In one aspect of the present invention, the content of the base oil (A) in the electrically insulating oil composition is preferably 95% by mass or more, more preferably 97% by mass or more, and further, based on the total amount of the electrically insulating oil composition. It is preferably 99% by mass or more.
By using the base oil (A) satisfying the above requirements as a base oil for an electrically insulating oil composition, it is possible to suppress the generation of stray gas after consumption of the antioxidant. Therefore, in one aspect of the present invention, the base oil (A) satisfying the above requirements provides a base oil for an electrically insulating oil composition capable of suppressing the generation of stray gas after consumption of the antioxidant.

<Phenolic antioxidant>
The electric insulating oil composition of the present invention contains a phenolic antioxidant in an amount of 0.06% by mass or more and 0.4% by mass or less based on the total amount of the electric insulating oil composition.
In the electrically insulating oil composition of one aspect of the present invention, the content of the phenolic antioxidant sufficiently exerts the antioxidant effect of the electrically insulating oil composition, while sufficiently exhibiting the insulating performance of the electrically insulating oil composition. From the viewpoint of ensuring the above, it is preferably 0.06% by mass or more and 0.35% by mass or less, and more preferably 0.06% by mass or more and 0.30% by mass or less based on the total amount of the electrically insulating oil composition.

Here, when it is assumed that the electrically insulating oil composition of one aspect of the present invention is used as "tracely added oil (T)" in the IEC standard (IEC60296), the content of the phenolic antioxidant is electric. Based on the total amount of the insulating oil composition, it is preferably 0.06% by mass or more and less than 0.08% by mass, and more preferably 0.065% by mass or more and 0.075% by mass or less.
Further, when it is assumed that the electrically insulating oil composition of one aspect of the present invention is used as "additional oil (I)" in the IEC standard (IEC60296), the content of the phenolic antioxidant is the electric insulating oil. Based on the total amount of the composition, it is preferably 0.08% by mass or more and 0.4% by mass or less, more preferably 0.15% by mass or more and 0.4% by mass or less, and further preferably 0.2% by mass. It is 0.35% by mass or less.

Examples of the phenolic antioxidant include 2,6-di-t-butyl-p-cresol, 2,6-di-t-butyl-4-ethylphenol, and 2,4-dimethyl-6-t-butylphenol. , 2,6-di-t-amyl-p-cresol, n-octyl-3- (4-hydroxy-3,5-di-t-butylphenyl) propionate, 6-methylheptyl-3- (3,5) Examples thereof include monophenolic antioxidants such as -di-t-butyl-4-hydroxyphenyl) propionate and n-octadecyl-3- (4-hydroxy-3,5-di-t-butylphenyl) propionate.
In addition, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-bis (2,6-di-t-butylphenol), 4,4'-bis (2-methyl-6). -T-butylphenol), 2,2'-methylenebis (4-ethyl-6-t-butylphenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-butylidenebis (3) -Methyl-6-t-butylphenol), 4,4'-isopropylidenebis (2,6-di-t-butylphenol), 2,2'-methylenebis (4-methyl-6-nonylphenol), 2,2' -Isobutylidenebis (4,6-dimethylphenol), 2,2'-methylenebis (4-methyl-6-cyclohexylphenol), 4,4'-thiobis (2-methyl-6-t-butylphenol), 4 , 4'-thiobis (3-methyl-6-t-butylphenol), 2,2'-thiobis (4-methyl-6-t-butylphenol), bis (3-methyl-4-hydroxy-5-t-butyl) Bisphenols such as benzyl) sulfide, bis (3,5-di-t-butyl-4-hydroxybenzyl) sulfide, thiodiethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] Examples include system antioxidants.
Among these, monophenolic antioxidants are preferable, and 2,6-di-t-butyl-p-cresol is even more preferable.
The antioxidant may be used alone or in combination of two or more.

<Antistatic agent>
The electric insulating oil composition of the present invention contains an antistatic agent in an amount of 3% by mass or more and 40% by mass or less based on the total amount of the electric insulating oil composition.
In the electrically insulating oil composition of one aspect of the present invention, from the viewpoint of effectively suppressing the flow charging phenomenon of the electrically insulating oil composition, it is preferably 4 mass ppm or more and 38 mass ppm based on the total amount of the electrically insulating oil composition. Hereinafter, it is more preferably 5 mass ppm or more and 35 mass ppm or less, and further preferably 7 mass ppm or more and 30 mass ppm or less.

The type of antistatic agent used in the electrically insulating oil composition of one aspect of the present invention is not particularly limited, and one or more selected from the antistatic agents generally used in the electrically insulating oil composition may be appropriately used. can.
Here, it is preferable to use a benzotriazole-based compound as the antistatic agent used in the electrically insulating oil composition of one aspect of the present invention. Benzotriazole compounds are compounds that function as metal inactivating agents. Therefore, the antioxidative ability of the electrically insulating oil composition can be further improved.
Examples of the benzotriazole-based compound include benzotriazole and its derivatives. Among these, benzotriazole is preferable, and 1,2,3-benzotriazole is more preferable.
The antistatic agent may be used alone or in combination of two or more.

<Metal inactivating agent>
The electrically insulating oil composition according to one aspect of the present invention may further contain a metal deactivating agent.
The type of the metal inactivating agent used in the electrically insulating oil composition of one aspect of the present invention is not particularly limited, and one or more selected from the metal inactivating agents generally used in the electrically insulating oil composition may be used. It can be used as appropriate.
Examples of such a metal inactivating agent include benzotriazole-based compounds and thiadiazole-based compounds.
Examples of the benzotriazole-based compound include benzotriazole and its derivatives.
Examples of the thiadiazole-based compound include thiadiazole and its derivatives.
As described above, the benzotriazole compound also functions as an antistatic agent. Therefore, when the benzotriazole-based compound is used as the metal inactivating agent, the effect of effectively suppressing the flow charging phenomenon can be exhibited.
Further, in the case of containing the benzotriazole-based compound as the antistatic agent in the electrically insulating oil composition of one aspect of the present invention, the metal inactivating agent other than the benzotriazole-based compound is further contained as the metal inactivating agent. You may.
The metal inactivating agent may be used alone or in combination of two or more.

<Other additives>
The electrically insulating oil composition according to one aspect of the present invention may contain additives other than the above components as long as the effects of the present invention are not impaired. Examples of additives other than the above components include pour point lowering agents and the like.

[Characteristics of electrically insulating oil composition]
The electrically insulating oil composition according to one aspect of the present invention has the following properties.

<Acid value and amount of sludge generated>
(Acid value and sludge generation amount according to JIS C2101 standard method)
In the evaluation test based on JIS C2101 standard, the acid value of the electrically insulating oil composition of one aspect of the present invention after the oxidation test is 0.6 mgKOH / g or less, preferably 0.5 mgKOH / g or less, more preferably 0.5 mgKOH / g or less. It is 0.4 mgKOH / g or less, more preferably 0.3 mgKOH / g or less.
Further, in the evaluation test based on the JIS C2101 standard, the amount of sludge generated after the oxidation test of the electrically insulating oil composition according to one aspect of the present invention is 0.4% or less, preferably 0.3% or less, more preferably. Is 0.2% or less, more preferably 0.1% or less.

(Acid value and sludge generation amount according to IEC61125 standard C method)
In the evaluation test based on the IEC61125 standard C method, the acid value of the electrically insulating oil composition according to the present invention after the oxidation test is 1.2 mgKOH / g or less, preferably 1.0 mgKOH / g or less, more preferably 1.0 mgKOH / g or less. Is 0.9 mgKOH / g or less, more preferably 0.8 mgKOH / g or less.
Further, in the evaluation test based on the IEC61125 standard C method, the amount of sludge generated after the oxidation test of the electrically insulating oil composition according to one aspect of the present invention is 0.8% or less, preferably 0.7% or less. It is preferably 0.6% or less, more preferably 0.5% or less.

<Dynamic viscosity>
The kinematic viscosity of the electrically insulating oil composition according to one aspect of the present invention at 40 ° C. is preferably 5 mm ² / s or more and 12 mm ² / s or less, more preferably 6 mm ² / s or more and 11 mm ² / s or less, and further. It is preferably 7 mm ² / s or more and 10 mm ² / s or less. If it is 5 mm ² / s or more, the volatility is unlikely to increase, the flash point does not decrease, and the possibility of causing a safety problem is reduced. When it is 12 mm ² / s or less, the fluidity does not decrease and it can be avoided that it becomes difficult to circulate in the apparatus, so that the possibility of affecting the cooling performance required for the electrically insulating oil composition is reduced. ..
The kinematic viscosity at 100 ° C. is preferably 1 mm ² / s or more and 10 mm ² / s or less. When the kinematic viscosity at 100 ° C. is in this range, the volatility becomes appropriate and there is no safety problem. From this point of view, it is more preferably 1.4 mm ² / s or more and 8 mm ² / s or less, and further preferably 1.8 mm ² / s or more and 6 mm ² / s or less.

[Manufacturing method of electrically insulating oil composition]
The method for producing the electrically insulating oil composition of the present invention is not particularly limited, but is produced by, for example, a production method including the following steps.
(Step 1): The residual oil after atmospheric distillation of paraffinic crude oil is distilled under reduced pressure, and the obtained reduced pressure distillate is hydrolyzed and decomposed at least once, and then hydrodewaxed to 40 ° C. A step of preparing a base oil (A) having a kinematic viscosity of 5 mm ² / s or more and 12 mm ² / s or less.
(Step 2): The base oil (A) obtained in Step 1, the phenolic antioxidant, and the antistatic agent, and the content of the phenolic antioxidant is based on the total amount of the electrically insulating oil composition. The step of mixing so that the content of the antistatic agent is 0.06% by mass or more and 0.4% by mass or less and the content of the antistatic agent is 3% by mass or more and 40% by mass or less based on the total amount of the electrically insulating oil composition. , The step 2 is not limited to mixing the base oil (A), the phenolic antioxidant, and the antistatic agent at the same time, and after mixing any two of these, the remaining 1 The seeds may be mixed.
As the phenolic antioxidant and antistatic agent, the above-mentioned exemplary compounds can be used.
Further, in step 2, a metal inactivating agent may be further mixed. As the metal inactivating agent, the above-mentioned exemplary compounds can also be used.

[How to use the electrically insulating oil composition]
The electrically insulating oil composition of the present invention can be used as an insulating material for oil-filled electrical equipment such as oil-filled capacitors, oil-filled cables, oil-filled transformers, and oil-filled breakers.
Therefore, according to the present invention, there is a method of using the electrically insulating oil composition of the present invention as an insulating material for oil-filled electrical equipment such as an oil-filled capacitor, an oil-filled cable, an oil-filled transformer, and an oil-filled circuit breaker. Provided.

[Oil-filled electrical equipment]
As described above, the electrically insulating oil composition of the present invention can be used as an insulating material for oil-filled electrical equipment such as oil-filled capacitors, oil-filled cables, oil-filled transformers, and oil-filled breakers.
Therefore, according to the present invention, there is provided an oil-filled electric device such as an oil-filled capacitor, an oil-filled cable, an oil-filled transformer, and an oil-filled breaker having the electrically insulating oil composition of the present invention as an insulating material.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

[Preparation of base oils 1 to 5]
Base oils 1 to 5 were prepared by the methods described below.
<Base oil 1>
The viscosity (60N) equivalent to that of electrically insulating oil, which is obtained by subjecting the vacuum distilled fraction of the atmospheric distillation residue of paraffinic crude oil to a hydrorefining treatment once and then a hydrodewaxing treatment once. The distillate was used as the base oil 1.
<Base oil 2>
The viscosity (60N) equivalent to that of electrically insulating oil, which is obtained by subjecting the vacuum distilled fraction of the atmospheric distillation residue of paraffinic crude oil to a hydrogenation refining treatment twice and then a hydrogenation dewaxing treatment once. The distillate was used as the base oil 2.
<Base oil 3>
A fraction having a viscosity (60 N) equivalent to that of electrically insulating oil, which was obtained by performing a hydrogenation refining treatment once with respect to the reduced pressure distilled fraction of the atmospheric distillation residue of paraffin crude oil, was used as the base oil 3.
<Base oil 4>
A distillate having a viscosity (60N) equivalent to that of an electrically insulating oil, which is obtained by subjecting a vacuum distillation fraction of a normal pressure distillation residue of paraffinic crude oil to a hydrorefining treatment once and then a solvent dewaxing treatment once. Fraction was used as the base oil 4.
<Base oil 5>
A vacuum gas oil obtained by vacuum distillation of paraffin-based crude oil is subjected to a hydrocracking treatment once and then a hydride dewaxing treatment once, and has a viscosity (60N) equivalent to that of an electrically insulating oil. The distillate was used as the base oil 5.

[Measurement of properties of base oils 1 to 5]
The following properties were measured for the base oils 1 to 5.
<% _CA ,% _CN , and% _CP >
% CA,% CN, and% CP were determined by ring analysis (nd _{- M} method) according to ASTM _D3238-95 .
<Pour point>
The pour point was measured according to JIS K 2269: 1987.
<Flash point>
The flash point was measured by the Penske martence sealing method according to JIS K 2265-3: 2007.
<40 ° C kinematic viscosity, 100 ° C kinematic viscosity, and viscosity index>
The 40 ° C. kinematic viscosity, 100 ° C. kinematic viscosity, and viscosity index were measured and calculated according to JIS K2283: 2003.
<Density>
Density was measured according to JIS K 2249.

[Preparation of electrical insulating oil composition]
As an antioxidant, 2,6-di-t-butyl-p-cresol, which is a phenolic antioxidant, is added to each of the base oils 1 to 5 in an amount of 0.07% by mass based on the total amount of the electrically insulating oil composition. Further, as an antistatic agent, 1,2,3-benzotriazole was added in an amount of 10 mass ppm based on the total amount of the electrically insulating oil composition to prepare an electrically insulating oil composition.

[evaluation]
The prepared electrically insulating oil composition was subjected to two kinds of oxidation tests described below.

<JIS oxidation test>
The prepared electrically insulating oil composition was evaluated by an evaluation test based on JIS C2101 standard.
Specifically, in the evaluation test based on the JIS C2101 standard, if both the acid value and the amount of sludge generated after the oxidation test of the electrically insulating oil composition meet the following criteria, a comprehensive evaluation A is given and the acid value and sludge are evaluated. Comprehensive evaluation B was given when at least one of the generated amounts did not meet the following criteria.
(Acid value)
・ 0.6mgKOH / g or less (sludge generation amount)
・ 0.4% or less

<IEC oxidation test>
The prepared electrically insulating oil composition was evaluated by an evaluation test based on the IEC61125 standard C method.
Specifically, in the evaluation test based on the IEC61125 standard C method, if both the acid value and the amount of sludge generated after the oxidation test of the electrically insulating oil composition meet the following criteria, the acid value and the amount of sludge are evaluated as comprehensive evaluation A. When at least one of the sludge generation amount did not meet the following criteria, it was evaluated as Comprehensive Evaluation B.
(Acid value)
-1.2 mgKOH / g or less (sludge generation amount)
・ 0.8% or less

<Measurement of flammable gas generation>
In order to confirm the state of generation of stray gas after the antioxidant was exhausted, the amount of combustible gas generated was measured for the base oils 1 to 5 by the following procedure. First, according to ASTM D7150, air bubbling was performed at room temperature for 30 minutes, and then 40 mL of base oil was collected in a glass syringe having a capacity of 50 mL. Next, the glass syringe containing the base oil was heated in a constant temperature bath at 120 ° C. for 164 hours, and then the flammable gas in the base oil was measured by a stripping extraction gas chromatography method. The combustible gases to be measured were hydrogen (H ₂ ), methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), isobutane (i-C ₄ H ₁₀ ), and normal butane (i-C 4 H 10). n-C ₄ H ₁₀ ), and carbon monoxide (CO). The total amount of combustible gas to be measured was defined as the total amount of combustible gas generated (TCG), and the TCG was evaluated according to the following criteria to comprehensively evaluate the amount of combustible gas generated.
・ 1500ppm or less: A
・ Over 1500ppm: B

Table 1 shows the property measurement results of the base oils 1 to 5, the JIS oxidation test results, the IEC oxidation test results, and the combustible gas generation amount measurement results.

From the results shown in Table 1, it can be seen that, as in Comparative Examples 1 and 2, when% _CA is 5.3% or more, the antioxidant effect cannot be sufficiently obtained. Further, as in Comparative Example 3, when% C _N is less than 40% and% C _P is larger than that of Comparative Example 1, in particular,% C _N is less than 40% and% C _P is 60. It can be seen that when the base oil has a high degree of purification of 0% or more, a large amount of flammable gas is generated after the antioxidant is consumed.
On the other hand, the electrically insulating oil compositions of Examples 1 and 2 using the base oils satisfying the above conditions (A1), (A2), and (A3) have a sufficient antioxidant effect and have a sufficient antioxidant effect. It can be seen that the generation of flammable gas after the antioxidant is consumed is suppressed.
Further, from the tendency of the hydrogen generation amount in Examples 1 and 2 and Comparative Examples 1 to 3, it can be seen that the hydrogen generation amount is suppressed when the% _CA is less than 5.3%. Then, in Examples 1 and 2, the amount of combustible gas other than hydrogen is sufficiently suppressed, and the amount of hydrogen and combustible gas other than hydrogen is suppressed as a whole. As a result, the generation of stray gas after the antioxidant is consumed is sufficiently suppressed.
Further, when% _CA is 2.7% or more and less than 5.3%, the amount of hydrogen generated and the amount of flammable gas other than hydrogen generated are particularly small, so that the stray gas after the antioxidant is consumed. Can be suppressed very effectively.

Claims (6)

An electrically insulating oil composition containing a base oil (A), a phenolic antioxidant, and an antistatic agent.
The base oil (A) satisfies the following conditions (A1), (A2), and (A3).
Condition (A1):% CA by ring analysis (nd-M method) is less than 5.3% Condition ( _A2 ):% CN by ring analysis (nd- _M method) is 40.0% or more 52.0% or less
Condition (A3): The pour point is −40 ° C. or less, and the content of the phenolic antioxidant is 0.06% by mass or more and 0.4% by mass or less based on the total amount of the electrically insulating oil composition.
An electrically insulating oil composition in which the content of the antistatic agent is 3% by mass or more and 40% by mass or less based on the total amount of the electrically insulating oil composition. The electrically insulating oil composition according to claim 1, wherein the phenolic antioxidant is 2,6-di-t-butyl-p-cresol. The electrically insulating oil composition according to claim 1 or 2, wherein the antistatic agent is a benzotriazole-based compound. The electrically insulating oil composition according to claim 3, wherein the benzotriazole-based compound is 1,2,3-benzotriazole. The electrically insulating oil composition according to any one of claims 1 to 4, further comprising a metal deactivating agent. The electrically insulating oil composition according to any one of claims 1 to 5, wherein the flash point measured by the Penske martence sealing method of JIS K2265-3-2007 is 135 ° C. or higher.