JP2514005B2 - Electrical insulating oil composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel electrical insulating oil composition. More specifically, it relates to an electrical insulating oil composition having suitable electrical properties for impregnating a capacitor and having excellent low temperature properties.

[Prior art and its problems] Benzyltoluene has a high ratio of aromatic carbons in the molecule, high hydrogen gas absorption, and excellent withstand voltage characteristics.
It has been widely used as an electric insulating oil.

Benzyltoluenes have a viscosity of 200 cSt or less at −50 ° C. in a supercooled state before crystal precipitation. Generally, the viscosity at the temperature corresponding to the pour point is tens of thousands to 100,000 cS.
Since it is t, benzyltoluene has a low viscosity at low temperature unless crystals are precipitated, and thus it can be said that it is extremely excellent as an insulating oil for low temperature.

However, according to the literature, the three regioisomers of benzyltoluene are o-form + 6.6 ° C., m-form 27.8 ° C. and p-form + 4.6 ° C., which cannot be said to have low melting points, and thus benzyltoluene. It is also related to the fact that it has a low viscosity, and rather it must be said that crystals are likely to occur at low temperatures.

In order to solve such a problem, in JP-A-60-87231, benzyltoluene obtained by reacting toluene and benzyl chloride with an iron chloride catalyst is mixed with a coproduct, dibenzyltoluene. Is proposed. As a product having the same technical content as the proposal of the publication, there are electric insulating oil compositions commercialized by Prodelec Co. of France under the trade names of JARYLEC C-100 and C-101. . The above publication discloses an oligomer mixture of triarylmethane, which is essentially a mixture of benzyltoluene and dibenzyltoluene.

On page 3 of the above publication, monobenzyltoluene is described as "having a defect that it crystallizes at -20 ° C after supercooling",
In order to suppress this crystallization, the composition is formed by mixing dibenzyltoluene.

However, adding a compound such as dibenzyltoluene is not advisable for the following two reasons.

That is, even if the freezing point depressing phenomenon is expected by the addition of dibenzyltoluene, the freezing point does not drop as much as the added weight because benzyltoluene has a high molecular weight. The freezing point depression phenomenon is proportional to the molar concentration of the added substance, but in the case of about 20% by weight of dibenzyltoluene added to the above-mentioned product JARYLEC C-100, the decrease of the crystallization temperature is 6 to 6 when calculated from the molar concentration. Only about 8 ° C.

On the other hand, benzyltoluene merely increases the viscosity of the insulating oil and lowers the mobility of liquid molecules to apparently suppress the precipitation of crystals. Therefore, with careful cooling, precipitation of crystals can be seen.

In order to prove this phenomenon, the present inventors reacted benzyl chloride and toluene in the same manner as in the above publication using iron chloride as a catalyst and obtained benzyltoluene and dibenzyltoluene by distillation, respectively. By mixing this benzyltoluene and dibenzyltoluene at a weight ratio of 80:20, the content of benzyltoluene isomers in the resulting insulating oil composition was o-form 39.1 wt% and m-form 5.4 wt. % And p-form 35.5 wt%. This value is based on the JARYLEC C
Insulation oil value of -100 o-body 36.2 wt%, m-body 5.9 wt%
% And p-form 37.8 wt%.

In a freezer with a temperature programmable viewing window, the benzyltoluene obtained above, the benzyltoluene / dibenzyltoluene mixture above and JARYLEC C-1 above.
00 was placed in a test tube with a lid, and the state of crystal precipitation was observed. The temperature was programmed to be between -40 ° C and -50 ° C for one cycle over 12 hours. According to this observation result, in the case of benzyltoluene, crystals were precipitated in 1 to 3 days and the whole liquid was solidified. On the other hand, in the benzyltoluene / dibenzyltoluene mixture and JARYLEC C-100, precipitation of crystals started in 4 to 7 days, and crystal growth was gradually observed, and after 2 weeks, crystals were observed almost on the entire surface of the test tube. .

As is clear from this, the mixing of dibenzyltoluene does not prevent the formation of crystals of benzyltoluene, it does not merely prevent the formation of crystals thereof, it merely reduces the growth rate of the crystals. However, it is unavoidable that the formation of crystals is actually observed even if dibenzyltoluene is added.

Even more inconvenient is the addition of high molecular weight compounds such as dibenzyltoluene, which results in a very high viscosity of the insulating oil composition. In this case, the low viscosity of benzyltoluene is offset, and the formation of crystals is unavoidable. Therefore, mixing dibenzyltoluene with benzyltoluene does not have any advantage, but rather has an adverse effect. Obviously, it is not preferable.

That is, the object of the present invention is to improve the ease of crystallization of benzyltoluene while maintaining good electrical properties such as hydrogen gas absorption inherent to benzyltoluene and low viscosity. Another object of the present invention is to provide an electric insulating oil composition having much lower temperature characteristics.

[Means for Solving Problems] That is, according to the present invention, as a component for lowering the crystallization temperature of benzyltoluene, ditolylmethanes having a low viscosity and a low crystallization temperature of 20 to 20% relative to the composition are used.
It is a mixture of 80% by weight.

Further, in order to further increase the effect of lowering the crystal precipitation temperature of ditolylmethanes, ditolylmethanes containing 30% by weight or more of ditolylmethane in which at least one of the methyl groups is substituted in the meta position is used as the ditolylmethanes. By doing so, an electrically insulating oil composition having a low viscosity and excellent low-temperature characteristics in which crystals are less likely to precipitate can be obtained.

 Hereinafter, the present invention will be further described.

To the benzyltoluene, 20 to 80% by weight of the ditolylmethanes are added, based on the mixture with the benzyltoluene. When it is less than 20% by weight, the effect of adding ditolylmethanes, that is, the effect of suppressing the precipitation of benzyltoluene crystals cannot be expected, which is not preferable. On the other hand, if the amount exceeds 80% by weight, the electrical properties of the obtained insulating oil composition deteriorate, which is not preferable.

Ditolylmethane has two nuclear-substituted methyl groups, and six types of positional isomers exist depending on the substitution position. In the present invention, it is necessary to use ditolylmethanes containing at least 30% by weight or more of the positional isomer of ditolylmethane substituted at the meta-position with respect to the benzene nucleus, at least one of the nucleus-substituted methyl groups. . When the content of ditolylmethanes is less than 30% by weight, the ditolylmethanes themselves are liable to crystallize, and the insulating oil composition itself containing the ditolylmethanes is also liable to crystallize, which is not preferable. . A more preferable content is 50% by weight or more.

Benzyltoluene used in the present invention also has positional isomers, but if the mixing ratio of ditolylmethanes and the content of the positional isomers are in the above-mentioned ranges, the type and ratio of the positional isomers of benzyltoluene are It can be used without particular limitation. Therefore, benzyltoluene produced by any method such as benzyltoluene produced by reacting benzyl chloride and toluene with aluminum chloride or iron chloride as a catalyst can be used.

Several examples of the method for producing m-isomer-rich ditolylmethanes of the present invention can be exemplified.

For example, ditolylmethanes can be produced by benzylating toluene with methylbenzyl chloride. A Lewis acid such as a metal halide such as iron chloride or aluminum chloride is used as the catalyst. However, when the catalyst is iron chloride, the amount of the meta-substitution of the methyl group contained in the obtained ditolylmethanes should be increased by using methylbenzyl chloride containing a large amount of m-methylbenzyl chloride as a raw material. You can

Also, ditolylmethane having a large amount of meta-position substitution can be produced by reacting toluene with benzyl chloride using aluminum chloride as a catalyst.

When the electric insulating oil composition of the present invention is used, other known electric insulating oils can be added at an arbitrary ratio and used within the scope of the object of the present invention. Examples of such other insulating oil include phenylxylylethane and diisopropylnaphthalene.

A suitable capacitor impregnated with the electrically insulating oil composition of the present invention is a so-called foil wound capacitor. This capacitor is obtained by impregnating a capacitor element, which is obtained by stacking and winding a metal foil such as an aluminum foil as an electrode, and a plastic film as a dielectric or an insulator, with electrically insulating oil. Insulating paper can be used together with the plastic film, but preferably all plastic films are used. As the plastic film, a polyolefin film such as a biaxially oriented polypropylene film is preferable. Impregnation of the capacitor element with the electrically insulating oil composition can be carried out by a conventional method.

[Effects of the Invention] The electrical insulating oil composition of the present invention contains benzyltoluene, which itself has excellent electrical characteristics, and therefore has excellent electrical characteristics.

By selecting ditolylmethanes having a large number of methyl group meta-substitutions as a substance to be mixed with benzyltoluene, the composition of the present invention is less likely to precipitate crystals, and an electrical insulating oil having excellent low-temperature characteristics can be obtained. Further, as mentioned above,
By mixing with specific ditolylmethanes, it can be used even at a low temperature of −40 ° C. without being limited by the type and composition ratio of positional isomers of benzyltoluene. Therefore, since the benzyltoluene produced by any method can be used, it is an economically practical insulating oil composition.

[Examples] Hereinafter, the present invention will be described in detail with reference to Examples.

Production Example (Production of ditolylmethanes) (1) Reaction temperature of 5 ° C. with an aluminum chloride catalyst,
Toluene was reacted with benzyl chloride under the reaction time of 3 hours, and after the reaction was completed, the mixture was neutralized, washed with water, and dried. Then, by distillation, ditolylmethanes having the composition shown in Table 1 were obtained. This is ditolylmethane A.

(2) Toluene and p-methylbenzyl chloride were reacted with iron chloride as a catalyst under the conditions of a reaction temperature of 5 ° C. and a reaction time of 3 hours. After completion of the reaction, neutralization, washing with water and drying were carried out.
Then, by distillation, ditolylmethanes having the same composition as shown in Table 1 were obtained. This is ditolylmethane B.

(3) Ditolylmethane A and ditolylmethane B were added at 4:10
The ditolylmethanes having the same composition as shown in Table 1 were obtained by mixing at a ratio of. This is ditolylmethane C.

The benzyltoluene used had the following positional isomer composition.

Example (destruction test of capacitor) Two biaxially oriented polypropylene films having a thickness of 14 μ were stacked and wound together with an aluminum foil as an electrode to obtain a capacitance.
A 0.4 μF model capacitor was made. According to a conventional method, an electric insulating oil having the composition shown in Table 2 was impregnated. -40 at noon
After cooling for 1 week at a temperature cycle of -50 ℃ at night,
The sample was left to stand at 40 ° C for one day and then used for measurement. Ten capacitors were prepared and measured for each insulating oil composition.
At −40 ° C., the potential gradient was increased by 10 V / μ and the voltage was applied, and the number of capacitors destroyed was calculated for each potential gradient.

 The results are shown in Table 2.

The following can be seen from the results in Table 2.

Compositions Nos. 1, 2, 4 and 5 are also suitable for the content of ditolylmethanes and the amount of m-form therein, so that most capacitors are destroyed at the highest potential gradient of 110 V / μ. . On the other hand, composition Nos. 3 and 6, which differ from these compositions in that only the content of ditolylmethanes is high, lead to destruction at a lower potential gradient, and data are less reproducible. Or, it tends to exhibit a lower potential gradient. It is considered that this is because the amount of benzyltoluene in these compositions decreases, the viscosity of the composition increases at a low temperature of −40 ° C., and the electrical characteristics such as hydrogen gas absorption decrease. On the other hand, in composition No. 7 containing a large amount of benzyltoluene, it was not sufficient to prevent the precipitation of crystals due to the addition of ditolylmethanes, so that the precipitation of crystals was observed, and as a result, the breakdown occurred with a low potential gradient. It was

In Composition Nos. 8 to 10 in which ditolylmethanes having a small amount of m-position substitution of a methyl group were used, the capacitors were destroyed with a low potential gradient. In addition, composition No. 8 has poor reproducibility of the data, probably because the impregnated oil is in a supercooled state, where the precipitation of crystals is accidental.

Claims (2)

(57) [Claims] 1. An electrical insulating oil composition comprising 20 to 80% by weight of benzyltoluene and 20 to 80% by weight of ditolylmethane containing 30% by weight or more of ditolylmethane in which at least one methyl group is substituted in the meta position. 2. The electrical insulating oil composition according to claim 1, wherein at least one of the methyl groups is ditolylmethane containing 50% by weight or more of ditolylmethane substituted in the meta position.