DE2638656A1 - DIELECTRIC LIQUID - Google Patents

Description

The invention relates to a new dielectric liquid, which is wholly or partly composed of one or more Benzyl esters of saturated monocarboxylic acids branched in the © ^ position exist.

It is known that fluids used to insulate electrical switchgear have a certain number of properties must have, in addition to a dielectric constant adapted for the respective use a low initial conductivity and conductivity after aging, good resistance to thermal decomposition and hydrolysis, a relatively low viscosity, low vapor pressure, low freezing point etc. are. The known dielectric liquids meet these requirements to various degrees.

It has now been found, completely surprising, that the esters of the formula below are suitable products for dielectric Represent liquids. The invention is a dielectric liquid, which is characterized is that it consists entirely or in part of at least one ester of the formula

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consists, in R. is hydrogen or alkyl and R ~ and R ₃ are alkyl radicals, the total number of carbon atoms in the radicals R, R and R ₃ between 3 and 20, preferably is 5 to 11

These products are also ideal for shutting down the partial discharges that occur at very low temperatures. The mixtures of benzyl esters of fraction cuts of saturated aliphatic acids of the formula (1) in which the total number of carbon atoms for R 1, R _{2 and R 3 is} 7.8 or 9 are particularly suitable for these purposes.

Those proposed as constituents of dielectric fluids Products can be made either by esterification of the corresponding acids with benzyl alcohol or preferably can be obtained by reacting an alkali salt of these acids with benzyl chloride. In both cases the synthesis carried out in the usual manner known to those skilled in the art.

The following is a production example of the ingredients given esters proposed by dielectric fluids.

example 1

A fraction cut of ^{saturated monocarboxylic acid branched in the 0} ^ -position of the above formula, in which the total number of carbon atoms for R., R ₂ and R _{3 is} 7.8 or 9, the acid index is 325 mg of potassium hydroxide per g of acid and the refractive index n_ 1.4425, is reacted with sodium carbonate to the salt, then reacted with benzyl chloride and gives a benzyl ester cut, which after distillation at

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-S.T Temperatures between 120 and 135 ° C below 1 Torr a dielectric constant £ of 3.31 at 90 ° C and below 50 Hz.

The products proposed according to the invention can be used as dielectric Liquids in capacitors of all types as well as in transformers, breakers and other electrical devices can be used in which an · insulating liquid is required will. The proposed esters actually have all the necessary properties for this type of use.

Because of their resistance to hydrolysis, however, they are used in particular as dielectric liquids for impregnating "mixed" Capacitors proposed, i.e., capacitors whose solid insulating sheets are made of paper and polyolefins. In fact, on the one hand, the proposed benzyl esters of saturated monocarboxylic acids wet polyolefin films very well, on the other hand they are not sensitive to hydrolysis caused by the residual water contained in the paper can. In order to assess the performance of the proposed fluids, 2 series of mixed condensers were created with 2 polypropylene layers of 12 / U thickness, between which a layer of unchanged Kraft paper of density 1 of 10, u-strength was attached, each with the product of the example 1 and impregnated with a known dielectric, namely dioctylphthalate. These capacitors were under thermal (90 ° C) and electrical (1780 V AC) load aged. The development of the capacitor losses, which were measured at 90 ° C. and below 120 V and 1500 V, is shown in the following Table reproduced. Each number is the arithmetic mean of a range of values.

After 5000 hours, the capacitors according to the invention were soaked with the product of Example 1, no breakdown was detected, while the capacitors that. were soaked with dioctyl phthalate, only 30% worked.

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'Product of the
Example 1 0 120 Dielectric losses: daily 493 556 949 988 S X 10 ' 1 1817 2402 3519 4348 4832 5664 ) except in hours Dioctyl
phthalate 241 8.1 1573 6.2 9.8 11.3 10.9 120 V Product of the
Example 1 12.1 19.2 19.3 25.1 26.3 17.9 1500 V Dioctyl
phthalate 4.1 • 4.1 3.8 17.1 3.5 3.6 3.7 3.5 5.4, .10.5 4.1 13.9 20.3 11.0 9.9 14.7

CD CO CO

In practice, depending on the particular applications envisaged, the benzyl esters of saturated monocarboxylic acids are used alone or in a mixture with other known dielectric liquids, such as chlorobiphenyls, alkylchlorobiphenyls, Chlorobenzenes such as trichlorobenzene, benzene or biphenyl alkylate are used. The advantage of such mixtures lies in the fact that they have one or more properties, such as the relative dielectric constant, viscosity, Can adjust density, etc. at will. The respective proportions of the components of the mixture are not critical and obviously depend on the property change desired; however, those inherent in the proposed esters To obtain advantages, it is generally favorable that these at least 10%, based on the total weight the mixture. The dielectric constant of the esters according to the invention or those containing them can also be used Mixtures by adding compatible solid or liquid compounds with a high dielectric constant raise. For this purpose, the use of the monocyanophenoxybenzenes described in French patent application 74/25 788, the monocyanobiphenyls described in French patent application 74/40 725 and in the monocyanoterphenyls described in French patent application 75/17 209 are particularly advantageous.

In general, the amount of the high dielectric constant compound added, which is a function of the for the total dielectric constant of the desired value and the compatibility - solubility or miscibility - of the Product with the base liquid is 5 to 50 wt .-%

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- 6 of the total mix.

The proposed esters or the liquids containing them are recommended prior to using any for dielectrics usual treatment, for example with activated earth, subjected.

One can use the dielectric liquids according to the invention also known stabilizers, such as epoxy compounds, incorporate.

The following description, which refers to the figures, illustrates some forms of application of those defined above Liquids.

FIG. 1 shows a wound capacitor which consists of sheets 1 and 2 made of aluminum or another suitable metal contains existing electrodes, which are separated by the insulating layers (3 and 4). The latter consist of sheets of paper, but can also consist of foils of plastic material or of composite foils known to the person skilled in the art and e.g. 2 polyolefin foils have, between which a layer of paper has been placed. Parts 5 and 6 are contacts for power consumption .

Figure 2 shows a cross section through a capacitor, a metallic container (1) and a cover (2), the ensures a tight seal, a capacitor element (3) of the winding capacitor type corresponding to that of Figure 1, as well as connecting lines (4 and 5) which conduct the contacts of the coil with the outer terminals (6) and (7) connect, contains. The condenser tank is with the

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- 7 liquid according to the invention (8) according to Example 1 filled.

The liquid wets the dielectric material and fills the voids and spaces throughout the apparatus.

In Figure 3, a transformer is shown, which has a low-voltage terminal (2), the transformer housing (3), the mounting flanges (4), insulating parts (5) and (6), which the Low-voltage winding (8) from the magnetic core (10) on the one hand and the high-voltage winding (9) from the transformer housing on the other hand separates, contains. The parts (7) serve as insulating spacers. The heads of the Nieder- and high voltage windings are insulated with a strong insulating material such as paper.

The transformer housing is filled with a dielectric liquid according to the invention, which completely from the Ester according to Example 1 consists. The liquid fills all cavities and wets the windings and other parts of the apparatus, which are wettable.

It is emphasized that the invention can also be used in other known apparatus constructions.

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Claims (2)

Claims ily dielectric fluid, characterized in that they are wholly or partly composed of at least one ester of the formula C- COO - CH ₂ - / '\ R ₂ -C- COO - CH _{2 2} C COO CH ₂ ^R 3 in which R. is hydrogen or an alkyl group and R ₉ and R 1 are alkyl groups, the total number of carbon atoms for R., R ₂ and R _{3 being} between 3 and 20. 2. Dielectric fluid according to claim 1, characterized in that the total number of carbon atoms for R 1, R ₂ and R _{3 is} between 5 and 11. 709810/1176 L e r s e i t e