JPH0834066B2 - Electrical insulating oil - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electric insulating oil having excellent dielectric breakdown voltage characteristics. More specifically, the present invention relates to an electric insulating oil in which an additive for improving a dielectric breakdown voltage is added to a mineral oil-based insulating oil, a mixed oil of a mineral oil-based insulating oil and an alkylbenzene.

[Prior Art] In recent years, oil-filled electrical devices have tended to have larger capacities and higher voltages, but on the other hand, there is also a demand for smaller size and lighter weight, and there is a demand for more reliable reliability than ever. Therefore, various efforts have been made in terms of insulating properties such as selection of insulating oil having excellent characteristics, improvement of dryness of electric equipment, and removal of dust in oil.

As a method for improving the dielectric breakdown voltage characteristics of insulating oil, a method of adding a certain compound to the insulating oil has already been reported.

For example, in JP-B-63-4286, a derivative of hexafluoropropylene oligomer is added to mineral oil-based insulating oil, and in JP-A-50-86698, triaryldimethane is added to the insulating oil to absorb gas. The improvement of the dielectric breakdown voltage is also accompanied by the improvement of the electrical conductivity.
No. 42478 discloses a condenser oil which has a dielectric breakdown voltage improved by a mixed oil of alkylnaphthalene and polybutene,
JP-A-60-84714 discloses adding a nonionic surfactant to a mixed oil of mineral oil and a phosphoric ester.
JP-A-55-41667 discloses adding a diarylalkane to a mixed oil of paraffinic insulating oil and alkylbenzene.

[Problems to be Solved by the Invention] However, the surfactant disclosed in JP-A-60-84714 brings about a significant decrease in the interfacial tension of insulating oil, for example, and thus is incompatible with the management standard of insulating oil. There is also a problem that the surfactant is adsorbed by the insulating paper and the concentration may change during the operation of the oil-filled electrical device. Further, the fluorine-based compound disclosed in Japanese Patent Laid-Open No. 63-4286 has a problem that it is expensive even if the addition amount is as small as about 1%, and it is difficult to dissolve in mineral oil-based insulating oil. However, these are difficult to use for improving the dielectric breakdown voltage characteristics.

On the other hand, the additives disclosed in JP-A-50-86698, JP-A-52-42478 and JP-A-55-41667 are all compounds having a benzene ring and account for the molecular weight. It is considered that when the double bond ratio is high, improvement of the dielectric breakdown voltage can be expected.

Therefore, the inventors of the present invention tried various polycyclic oils as additives, for example, but did not necessarily improve the dielectric breakdown voltage because the ratio of benzene rings in one molecule was large.

As inferred from the above-mentioned prior art, the reason why the additive is limited to a single product is that the theoretical understanding of the mechanism of dielectric breakdown is not sufficiently obtained. So far, the search for this dielectric breakdown voltage improver has gone through trial and error. Therefore, it is very difficult to estimate an additive that can solve the above problems from the conventional examples.

[Means for Solving the Problem] As a result of intensive studies in view of such a situation, the present inventors have found that a specific substance has good solubility in mineral oil-based insulating oil and the like, is inexpensive, Moreover, they have found that the dielectric breakdown voltage of the insulating oil is improved without impairing the general characteristics of the insulating oil, and have completed the present invention.

That is, the present invention provides a compound represented by (A) general formula (I): CH ₃ CH _{2 m} CH = CH ₂ (I) (wherein m represents an integer of 30 or less) as an additive in insulating oil. (B) an ester of a hydroxy fatty acid in which a hydroxyl group, an acid group or both are esterified, (C) a general formula (II): (D) DL-p-menta-1,8-diene, which is a compound represented by the formula (n represents an integer) or a mixture of the compounds and has a boiling point of 120 to 300 ° C. ) Diphenylcarbazide or (F) p-hydroxyphenylacetamide is added to the electrical insulating oil, and the proportion of the additive in the electrical insulating oil is 0.01 to 10% by weight. %, The same below), the additive of (B) is 0.01 to 1%,
The additive of (C) is 0.01 to 1%, the additive of (D) is 0.01 to 1%.
1%, (E) additive 0.1-0.8%, (F) additive
0.01 to 0.1% electrical insulating oil.

[Example] The insulating oil used in the present invention is not particularly limited, and an insulating oil generally used as an electric insulating oil can be used.

Specific examples of such insulating oil include JIS C
2320 Mineral oil type insulating oil such as 1st type oil 1st oil, 2nd oil, 3rd oil, 4th oil; JIS C 2320 2nd type 1st oil, 2nd oil, 3rd oil,
Alkylbenzene such as No. 4 oil; JIS C 2320 7 type No. 1 oil, No. 2 oil, No. 3 oil, oil mixture of mineral oil type insulating oil such as No. 4 oil and alkylbenzene; for avoiding disasters such as fire and explosion Polyol ether for high flash point, flame retardancy, non-combustibility, etc .; JIS C 2320 6 kinds of silicone oil;
Fluorinated oil; phosphate ester oil and the like.

Among these, from the viewpoint that the solubility of the additives (A) to (F) and the various properties of the insulating oil are not adversely affected,
Mineral oil-based insulating oil or a mixed oil of mineral oil-based insulating oil and alkylbenzene is preferable.

The additive added to the electric insulating oil of the present invention is for increasing the dielectric breakdown voltage of the insulating oil, and the additives (A) to (F) are used as such an additive.

The additive (A) is a compound represented by the general formula (I): CH ₃ CH _{2 m} CH═CH ₂ (I), where m in the general formula (I) is 30.
Below, it is preferably an integer of 10 to 30, and more preferably 10 to 20. When m exceeds 30, the improvement in dielectric breakdown voltage characteristics becomes small. The compound represented by the general formula (I) may be used alone or in combination of two or more kinds.

The ester of hydroxy fatty acid which is the additive (B) is obtained by esterification or acetylation of a hydroxy fatty acid such as ricinoleic acid or 12-hydroxystearic acid with an alcohol component such as methanol, ethanol or butanol. is there. When the hydroxy fatty acid is added to the insulating oil, the interfacial tension and the total acid value of the insulating oil are significantly reduced due to the influence of hydroxyl groups and acid groups.
Either the hydroxyl group or the acid group, and preferably both of them are esterified and used in the present invention. The ester of hydroxy fatty acid may be used alone or in combination of two or more kinds.

Specific examples of such esters of hydroxy fatty acids include methyl ricinoleate, butyl ricinoleate, methyl acetyl ricinoleate, and butyl acetyl ricinoleate.

The ester of hydroxy fatty acid is preferably purified before use from the viewpoints of influence on the interfacial tension and the acid value stability of the insulating oil. From the viewpoint of improving the various properties, particularly the effect of improving the interfacial tension, it is preferable to carry out the purification in the state of being added to the insulating oil rather than the purification of the hydroxy fatty acid ester alone. A method of performing chemical adsorption treatment using clay, activated alumina or the like can be adopted.

The additive (C) has the general formula (II): One of the compounds represented by the formula (wherein n represents an integer) or a mixture of two or more of the compounds having a boiling point of 120.
~ 300 ° C, preferably 123-263 ° C. Boiling point 1
When the temperature is lower than 20 ° C, the influence on the insulating oil becomes large, such as the lowering of the flash point and the increase of the evaporation amount, and when it exceeds 300 ° C, the improvement of the dielectric breakdown voltage characteristic becomes small.

The amount of DL-p-mentha-1,8-diene, which is the additive (D), is small compared to the other additives, and the same effect can be obtained.

 Next, the proportion of the additive in the electric insulating oil will be described.

When the additive is a compound represented by the general formula (I), the proportion is 0.01 to 10%, preferably 0.1 to 2%,
Further, it is preferably 0.3 to 1%, and if it is less than 0.01%, the effect due to the addition is not sufficiently obtained, and if it exceeds 10%, the improvement of the dielectric breakdown voltage becomes small.

When the additive is an ester of hydroxy fatty acid in which hydroxyl groups, acid groups or both are esterified, the ratio is 0.01 to 1%, preferably 0.05 to 0.8%, more preferably 0.1 to 0.5%, If it is less than 0.01%, the effect of the addition is not sufficiently obtained, and if it exceeds 1%, the oxidation stability and the interfacial tension are lowered.

When the additive is a compound represented by the general formula (II) or a mixture thereof and has a boiling point of 120 to 300 ° C., the ratio is 0.01 to 1%, preferably 0.05 to 0.8%, more preferably It is 0.4 to 0.5%, and if it is less than 0.01%, the effect due to addition is not sufficiently obtained, and if it exceeds 1%, the flash point is lowered and the evaporation amount is increased.

When the additive is DL-p-mentha-1,8-diene, the ratio is 0.01 to 1%, preferably 0.02 to 0.5%, more preferably 0.04 to 0.3%. The effect is not sufficiently obtained, and if it exceeds 1%, the flash point is significantly lowered and the evaporation amount is increased.

When the additive is diphenylcarbazide, the ratio is 0.1 to 0.8%, preferably 0.2 to 0.6%, more preferably 0.3 to 0.6%, if less than 0.1%, the effect due to the addition is not sufficiently obtained, Even if it exceeds 0.8%, the dielectric breakdown voltage does not improve so much.

When the additive is p-hydroxyphenylacetamide, the ratio is 001 to 0.1%, and if it is less than 0.01%, the effect due to the addition is not sufficiently obtained, and even if it exceeds 0.1%, the dielectric breakdown voltage is much improved. Disappear.

The electric insulating oil of the present invention can be obtained by mixing the insulating oil as described above and an additive (by a conventional method).

Next, the electrical insulating oil of the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

Example 1 and Comparative Example 1 Insulating oil consisting only of mineral oil (JIS C 2320 Type 1 No. 2 oil (hereinafter referred to as JIS Type 1 No. 2 oil)) and α-olefin (where m in the general formula (I) is 16) ) In the electric insulating oil obtained are 0.005%, 0.05%, 0.1%, 0.5% and 1.0, respectively.
%, 3.0%, 5.0%, 10% were added and mixed to obtain 9 kinds of electrical insulating oil including a blank (0%).
The number of particles in the obtained electrical insulating oil is approximately 5000 / oil
100 ml, water content in oil is 7-9 ppm.

The breakdown voltage of the obtained electric insulating oil was measured by the method described below, and the dependency of the additive (α-olefin) concentration on the breakdown voltage was examined. The results are shown in Fig. 1.

(Dielectric breakdown voltage) An AC voltage is applied at a boosting rate of 3 kV / s to an electrode gap of 2.5 mm in diameter of a 12.5 mm spherical electrode. When oil has a dielectric breakdown, carbon is generated and the number of particles such as carbon in the oil increases. Since the particles in oil influence the dielectric breakdown voltage as shown in FIG. 3 described later, the breakdown voltage value was measured only once for each sample oil.

Example 2 and Comparative Example 2 A mixed oil of mineral oil and alkylbenzene (JIS C 2320 No. 7 oil No. 2 (hereinafter referred to as JIS No. 2 oil)) was obtained with the electrical insulation of the α-olefin used in Example No. 1. The proportion in oil is 0.05%, 0.1%, 0.5%, 1.0%, 3.0%, 5.0
%, 10% so that they are mixed and mixed with blank (0
%), And 8 types of electrical insulating oils were prepared, and the breakdown voltage was measured in the same manner as in Example 1. The results are shown in Fig. 1.

As can be seen from FIG. 1, the dielectric breakdown voltage increases with the concentration of the additive, and tends to decrease with a peak at about 0.5%. Moreover, the same effect was obtained even if the oil type was different.

Example 3 In JIS type 1 No. 2 insulating oil, m in general formula (I) is 10, 16, 1
The α-olefin of 8, 20 or 30 was added so that the ratio in the obtained electric insulating oil was about 0.5%, and mixed to obtain 5 kinds of electric insulating oil.

The breakdown voltage of the obtained electric insulating oil was measured in the same manner as in Example 1 to examine the carbon number (m) dependency of the breakdown voltage when the content of α-olefin was 0.5%. Results are shown in FIG.

As can be seen from Fig. 2, when the carbon number (m) is 30 or less, α
-The significant effect of adding olefins was seen.

As can be seen from FIG. 1 and FIG. 2, the dielectric breakdown voltage is maximum at a specific addition concentration or a specific carbon number (m).

Example 4 The α-olefin concentration at which the effect of the additive on the dielectric breakdown voltage was the largest was determined as in Example 1 for new oil, deteriorated oil, oil taken from oil-filled electrical equipment and insulating oil having a large number of particles in oil. When examined in the same manner, the same results as in Example 1 were obtained. Therefore, it was found that the duality of the phenomenon that the dielectric breakdown voltage is improved by the addition of α-olefin is good.

From the results of Examples 1 to 4 and Comparative Examples 1 and 2, the α-olefin represented by the general formula (I) is most suitable for improving the dielectric breakdown voltage when m is 18 and the concentration in the electric insulating oil is 0.5%. Then, the effect of addition under these conditions was investigated.

Example 5 and Comparative Example 3 The number of particles in oil is 750 to 9,000 / 100 ml of oil and the water content in oil is 7
To 9 ppm of insulating oil (JIS Class 1 No. 2 oil), α-olefin (a compound of m in the general formula (I) of 18) was added so that the ratio of the obtained electrical insulating oil was 0.5%. (Example 5), and the number of particles in oil is 750 to 10000/100 ml of oil
Then, the dielectric breakdown voltage of the insulating oil (JIS type 1 No. 2 oil) (Comparative Example 3) having a water content in the oil of 7 to 9 ppm was examined in the same manner as in Example 1. Results are shown in FIG.

As can be seen from FIG. 3, the dielectric breakdown voltage increased as the number of particles in the oil decreased, but the difference between the added oil and the non-added oil was maintained. This phenomenon was also observed for degraded oil.

Example 6 and Comparative Example 4 JIS 1 type 2 oil and JIS 7 type 2 oil were mixed with α-olefin (compound of m in the general formula (I) is 18) in the obtained electric insulating oil to 0.5%. The properties of the added oil and the additive-free oil that were added and mixed as described above were examined according to JIS C 2101. The results are shown in Table 1.

The α-olefin used here has almost the same molecular weight as the insulating oil (α-olefin: 252, JIS Class 1 No. 2 oil: about 250, JIS
Since it is a hydrocarbon liquid of 7 type 2 oil: approx. 250), no adverse effect on the insulating oil properties was observed by the addition.

Example 7 and Comparative Example 5 Methyl ricinoleate, butyl ricinoleate, and methyl acetyl ricinoleate as esters of hydroxy fatty acid were added to mineral oil type insulating oil (JIS type 1 No. 2 oil) in a proportion of 0.01% in the electric insulating oil. , 0.05%, 0.1%, 0.5%,
Twenty-four types of insulating oil including blanks (0%) were prepared by adding 1.0%, 5% and 10% and mixing, and a dielectric breakdown voltage test was performed in the same manner as in Example 1. Since the dielectric breakdown voltage at this time is affected by the water content in oil, the water content in oil was adjusted to 8 to 11 ppm. Results are shown in FIG. In Figure 4, MR is methylricinolate, BR
Indicates butyl ricinoleate, and MAR indicates methyl acetyl ricinoleate.

As can be seen from FIG. 4, the effect of improving the dielectric breakdown voltage of any of the additives was remarkably recognized from the content rate of 0.01%, peaked at 0.5%, and the addition effect was clear even at 10%. Above all, the effect of adding methylacetylricinoleate was remarkable.

Example 8 and Comparative Example 6 The ester of hydroxy fatty acid improves the dielectric breakdown voltage characteristics of insulating oil, but if the amount of addition is large, there is a concern that various characteristics required for insulating oil may be adversely affected. Therefore, Example 7
Methyl ricinoleate, butyl ricinoleate, and methyl acetyl ricinoleate were added to the insulating oil used in the above so that the ratio in the obtained electric insulating oil would be the ratios shown in Tables 2 to 4, respectively. Solubility, interfacial tension and oxidation stability were measured for insulating oil samples having a water content in oil of 8 to 11 ppm. The results are shown in Tables 2-4.

The interfacial tension was measured for the purified and unpurified ones after the ester of hydroxy fatty acid was added to the insulating oil, followed by chemical adsorption treatment with a 1: 2 mixture of activated clay and activated alumina.

It can be seen from Tables 2 to 4 that the insulating oil to which the ester of hydroxy fatty acid is added has no adverse effect on the solubility.

Further, as a result of the above-mentioned purification, various properties were improved, and especially the interfacial tension was greatly improved. It should be noted that those obtained by purifying only the ester of hydroxy fatty acid by the above-described refining method and then adding it to the insulating oil could not significantly improve those characteristics.

By this purification, the ester of hydroxy fatty acid can be used up to a content rate of 1% in this example.

Example 9 and Comparative Example 7 An electrical insulating oil was obtained by adding a mixture of polybutene (average molecular weight 212) having a boiling point of 123 to 263 ° C. with a compound represented by the general formula (II) to a mineral oil type insulating oil (JIS type 1 No. 2 oil). 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%,
Eight kinds of electrical insulating oils including blank (0%) were prepared by adding so as to be 10% and mixed, and a dielectric breakdown voltage test was conducted in the same manner as in Example 1. Since the dielectric breakdown voltage at this time is affected by the water content in the oil, the water content in the oil was adjusted to 7 to 10 ppm. Results are shown in FIG.

As can be seen from FIG. 5, the effect of improving the dielectric breakdown voltage was remarkably recognized from the content rate of 0.01%, and showed a peak at 0.5%, and the effect was large even at 5%.

Example 10 and Comparative Example 8 The mixture of polybutene used in Example 9 improves the dielectric breakdown voltage characteristics of insulating oil, but the solubility, interfacial tension, flash point, and evaporation required for insulating oil increase with increasing addition amount. There is concern about the effects on various properties such as the amount and oxidation stability. Therefore, the polybutene was added to the insulating oil used in Example 9 so that the ratio in the obtained electric insulating oil was the ratio shown in Table 5, and the water content in the oil obtained by mixing was 7 to 10 ppm. These characteristics tests were also conducted on the insulating oil sample of No. 1. The results are shown in Table 5.

Of the polybutene used here, compounds with a large average molecular weight (average molecular weight of about 300 or more) are insulating oils (JIS
It is used as a type 3 insulating oil) and is a liquid consisting of hydrocarbons, and when mixed with a hydrocarbon mineral oil type insulating oil, adverse effects on solubility, interfacial tension and oxidation stability were not observed.

However, the mixture of polybutene used had a flash point of 87 ° C.
When the content rate is 5%, the flash point deviates from the standard value of JIS C 2320 (130 ° C or higher). The amount of evaporation shows an increasing tendency as the amount of addition increases, but it complies with the JI standard value.

From the above, in consideration of the flash point in this example, the maximum content of the polybutene mixture was 2%.

Example 11 and Comparative Example 9 Mineral oil type insulating oil (JIS type 1 No. 2 oil) was added with DL-p-mentor-1,
The proportion of 8-diene in the obtained electric insulating oil is
0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 5%, 10% were added and mixed to prepare 8 kinds of electrical insulating oil including blank (0%). A dielectric breakdown voltage test was conducted in the same manner as in 1. Since the breakdown voltage at this time is affected by the water content in oil, the water content in oil was adjusted to 7 to 9 ppm. Results are shown in FIG.

From FIG. 6, the effect of improving the dielectric breakdown voltage is the content rate.
Remarkably recognized from 0.01%, peaking at 0.05%, 5
It can be seen that the effect is clear up to%.

Thus, the optimum content of DL-p-mentha-1,8-diene is 0.5 to 0.5% for the other additives used in the present invention.
It is characteristic that the effect is recognized at a very small ratio of 0.05% compared to 1%.

Example 12 and Comparative Example 10 The flash point of DL-p-menta-1,8-diene was as low as 45 ° C., and by adding DL-p-menta-1,8-diene, the flash point of electrically insulating oil was obtained. And the amount of evaporation is expected to be adversely affected. Therefore, DL-p-mentor-1,8-diene was added to JIS Class 1 No. 2 oil, and the ratio of the obtained electrical insulating oil was 6th.
An insulating oil sample with a water content of 7 to 9 ppm obtained by adding and mixing it in the proportions shown in the table was subjected to a characteristic test and an oxidation stability test as an effect evaluation during long-term use. It was The results are shown in Table 6.

It can be seen from Table 6 that when the amount of DL-p-mentha-1,8-diene added is more than 1%, the flash point decreases remarkably and the amount of evaporation also tends to increase. However, no effect on oxidative stability was observed, and DL-p-
It is considered that there is no problem with long-term use of insulating oil containing mentha-1,8-diene. This addition effect was confirmed in the same manner for JIS 7 type 2 oil.

Example 13 and Comparative Example 11 Diphenylcarbazide was added to JIS No. 1 No. 2 oil and JIS No. 7 No. 2 oil, and the ratio in the obtained electric insulating oil was 0.1, respectively.
%, 0.4%, 0.5%, 0.7%, 0.8%, 1.0% were added and mixed to prepare 14 kinds of electrical insulating oil including blank (0%) with water content of 7 to 11 ppm. The dielectric breakdown voltage was measured in the same manner as in Example 1. The results are shown in Fig. 7.
These results show the dependency of the additive concentration on the dielectric breakdown voltage for JIS 1 type 2 oil and JIS 7 type 2 oil, as in FIG.

As can be seen from FIG. 7, the dielectric breakdown voltage increases with the concentration of the additive added, and shows a decreasing tendency after peaking at about 0.4%. Even if the oil types of JIS Type 1 No. 2 oil and JIS No. 7 type 2 oil are different, the addition effect is similar. Seventh
From the figure, in the present example, the diphenylcarbazide content is 0.
It can be seen that 1 to 0.5% is preferable.

Example 14 and Comparative Example 12 The characteristics of the additive oil and the additive-free oil in which diphenylcarbazide was added to JIS Type 1 No. 2 oil so that the ratio in the electrically insulating oil was 0.4% were investigated. The results are shown in Table 7.

As can be seen from Table 7, no adverse effect of the addition on the insulating oil characteristics was observed. Table 7 shows the results for JIS Class 1 and 2 oils, but also for JIS Class 7 and 2 oils.
Good results similar to those in the table were obtained.

Example 15 and Comparative Example 13 JIS Type 1 No. 2 oil was added with p-hydroxyphenylacetamide, and the ratio in the obtained electric insulating oil was 0.01%, 0.05%, 0.
Add 1% and 1.0%, mix and add blank (0
%) Was prepared and five types of electrical insulating oils were prepared, and the dielectric breakdown voltage was measured in the same manner as in Example 1. The results are shown in Fig. 8.

As shown in Fig. 8, the breakdown voltage is 0.05 when the added concentration is
There is a peak around 10%, and the effect of addition is clearly seen. From FIG. 8, the addition amount in this example is 0.01 to 0.1.
It turns out that% is preferable.

Example 16 and Comparative Example 14 The characteristics of added oil and non-added oil in which p-hydroxyacetamide was added to JIS No. 1 No. 2 oil so that the ratio in the obtained electric insulating oil was 0.05% were examined. The results are shown in Table 8.

As can be seen from Table 8, p-hydroxyphenylacetamide is recognized as a useful additive for insulating oil without adverse effects due to the addition of p-hydroxyphenylacetamide.

In Examples 1 to 16 described above, the case where the additive was added to the mineral oil-based insulating oil and the mixed oil of the mineral oil-based insulating oil and the alkylbenzene was described, but alkylbenzene, polyol, silicone oil, fluorinated oil, phosphate ester, etc. The same effect can be obtained with this insulating oil.

[Effects of the Invention] The electrically insulating oil of the present invention comprises a compound represented by the general formula (I), an ester of hydroxy fatty acid, a compound represented by the general formula (II), and DL-p-menta-1,8-. Diene, diphenylcarbazide or p-hydroxyphenylacetamide is added to the insulating oil in a fixed amount, and the addition of them has the effect of improving the dielectric breakdown voltage without deteriorating the various characteristics required of the insulating oil. Play.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the content rate of α-olefin and the breakdown voltage, FIG. 2 is a graph showing the relationship between the carbon number (m) of α-olefin and the breakdown voltage, and FIG. 3 is electric. A graph showing the relationship between the number of particles in oil in the insulating oil and the dielectric breakdown voltage, FIG. 4 is a graph showing the relationship between the content ratio of the ester of hydroxy fatty acid and the dielectric breakdown voltage, and FIG. 5 is the content of the mixture of polybutene. 6 is a graph showing the relationship between the breakdown rate and the breakdown voltage, FIG. 6 is a graph showing the relationship between the content rate of DL-p-menta-1,8-diene and the breakdown voltage, and FIG. 7 is the content of diphenylcarbazide. FIG. 8 is a graph showing the relationship between the rate and the breakdown voltage, and FIG. 8 is a graph showing the relationship between the content rate of p-hydroxyphenylacetamide and the breakdown voltage.

Front Page Continuation (72) Inventor Motoo Doe 651 Tenwa, Awa City, Ako City, Hyogo Prefecture Inside the Ako Works, Mitsubishi Electric Corporation (56) Reference JP-A-59-128708 (JP, A)

Claims (6)

[Claims] 1. A compound represented by the general formula (A): CH ₃ CH _{2 m} CH═CH (I) (wherein m represents an integer of 30 or less) as an additive in insulating oil. An electrically insulating oil which is added, wherein the ratio of the additive in the electrically insulating oil is 0.01 to 10% by weight. 2. An electrical insulating oil comprising an insulating oil to which (B) an ester of a hydroxy fatty acid in which a hydroxyl group, an acid group or both are esterified is added as an additive. Electrical insulating oil whose content is 0.01-1% by weight. 3. Insulating oil containing (C) general formula (I) as an additive.
I): An electrically insulating oil comprising a compound represented by the formula (n is an integer) or a mixture of the compounds and having a boiling point of 120 to 300 ° C. Electrical insulating oil whose ratio in oil is 0.01 to 1% by weight. 4. An electric insulating oil comprising (D) DL-p-mentha-1,8-diene as an additive added to an insulating oil, wherein the ratio of the additive to the electric insulating oil is 0.01. ~ 1% by weight
Electrical insulating oil that is. 5. An electric insulating oil comprising (E) diphenylcarbazide as an additive added to the insulating oil, wherein the ratio of the additive to the electric insulating oil is 0.1 to 0.8% by weight. oil. 6. An electrical insulating oil comprising (F) p-hydroxyphenylacetamide as an additive added to the insulating oil, wherein the ratio of the additive to the electrical insulating oil is 0.01-0.
Electrical insulating oil that is 1% by weight.