DE2638656C2 - Dielectric fluid - Google Patents

Description

R ₂ -C COO-CH ₂ -R ₃

IO i
R, -C -COO-CH ₂

(D

in which R, hydrogen or an alkyl group and R ₂ and Ri are alkyl groups, the total number of carbon atoms for R ₁ , R 2 and Rj being between 3 and 20, as a dielectric liquid.

2. Use 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.

20th

The invention relates to a new dielectric liquid, which is wholly or partially from a or several benzyl esters of saturated monocarboxylic acids which are branched in the α-position.

It is known that fluids that are used for insulating electrical switching devices must have a certain number of properties, in addition to a matched for the respective use of a low dielectric constant ^{Anfangsleitfähigk:;} t and conductivities after aging, good resistance to thermal decomposition and hydrolysis, relatively low viscosity, low vapor pressure, low freezing point, etc. are. The known dielectric liquids meet these requirements to various degrees.

Thus, in US Pat. No. 3,855,508, the use of the esters of acids branched in -position with respect to the carboxyl group and of alcohols branched in -position with respect to the hydroxyl group was proposed as dielectric liquids. These components represent a good compromise between the various properties required for a good dielectric and, in particular, have good resistance to hydrolysis. Nevertheless, they have the disadvantage of poor resistance to overvoltage at low temperature. It is known that dielectric apparatus, such as, for. B. capacitors and transformers, created to be exposed to certain so-called nominal voltages under normal application conditions. For various reasons it happens that these devices are frequently exposed to short-term overvoltages. These overvoltages cause partial discharges which can disappear more or less quickly and completely or not at all after the voltage has reached its nominal value again. These partial discharges, which occur particularly at low usage temperatures, ie at temperatures below 25 ° C, are responsible for the premature aging of the devices and their breakdown. Their more or less rapid appearance and disappearance when the voltage falls back to a normal level depends largely on the nature of the dielectric, without knowing the reasons for it. The poor overvoltage resistance at low temperatures of the known dielectric impregnation _{fluids in which Ri is hydrogen or an alkyl group and R 2} and Rj are alkyl groups, the total number of carbon atoms in the radicals Ri, R ₂ and R _{s being} between 3 and 20, preferably between 5 and 11 , as a dielectric liquid.

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

The esters to be used according to the invention can either be obtained by esterification of the corresponding Acids with benzyl alcohol or preferably by reaction of an alkali salt of these acids with benzyl chloride can be obtained. In both cases, the synthesis is carried out in the usual way, which is known to the person skilled in the art is known, performed.

The following is a production example for the as dielectric fluid given usable ester.

example 1

Amount to a fraction section of branched in α-position saturated monocarboxylic acid of the above formula wherein the total number of KcHlenstoffatome for Ri, _R2 and Rj 7, 8 or 9, the acid value 325 mg potassium hydroxide per g of acid, and the refractive index no 1.4425 , is reacted with sodium carbonate to form the salt, then reacted with benzyl chloride and results in a benzyl ester section which, after distillation at temperatures between 120 and 135 ° C under 133 Pa, has a dielectric constant ε of 331 at 90 "C and under 50 Hz.

The esters mentioned can be used as dielectric liquids in capacitors of all types as well as in Transformers, breakers and other electrical devices are used in which a Isolating fluid is required.

The proposed esters actually have all the necessary properties for this type of use.

However, because of their resistance to hydrolysis, they are used in particular as dielectric liquids Suggested impregnation of "mixed" capacitors; H. of capacitors, their solid insulating sheets consist of paper and polyolefins. In fact, on the one hand, the proposed benzyl esters wet from saturated monocarboxylic acids very good polyolefin films, on the other hand they are not sensitive against hydrolysis, which can be caused by the residual water contained in the paper. To the To assess performances of the proposed fluids, 2 series of mixed Capacitors with 2 layers of polypropylene from

2 microns thick with a layer of unchanged 1-inch thick kraft paper of 10 microns thick between them. each with the product of Example 1 and impregnated with a known dielectric, namely lioctylphthalai. These capacitors were aged inter thermal (90 ⁰ C) and electrical (1780V • AC voltage) load. The development of capacitor losses, dip at 90 ° C and below 120 V.

Dielectric loss: tg <5X 10 ⁴

as well as 1500 V are measured in the following Table reproduced. Each number is the arithmetic mean of a range of values.

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

Duration in hours
0 120 241

556 949 988 1573 1817 2402 3519 4348 4832 5664

Product of the
Example 1
Dioctyl phthalate 12.1 19.2

8.1 6.2 9.8 11.3 10.9

19.3 25.1 17.1 26.3 17.9

1500V
Product of the
Example 1
Dioctyl phthalate 5.4 10.5

4.1 4.1 4.1 3.8 3.5 3.6 3.7 3.5

13.9 20.3 14.7 11.0 9.9

In practice, the benzyl esters are saturated by the particular intended uses Monocarboxylic acids alone or in a mixture with other known dielectric liquids, such as. B. the Chlorobiphenylene, alkylchlorobiphenylene, chlorobenzenes such as trichlorobenzene. Benzene or biphenyl alkylate used. The advantage of such mixtures is that they have one or more properties, such as z. B. the relative dielectric constant, viscosity. Can adjust density, etc. at will. the respective proportions of the mixture ingredients are not critical and obviously depend on the desired Property change away; however, to the inherent advantages of the esters to be used obtained, it is generally favorable that this is at least 10%, based on the total weight the mixture. One can also use the dielectric constant the ester or the mixtures containing them by adding compatible solid or increase liquid compounds with a high dielectric constant. For this purpose is the use the monocyanophenoxybenzenes described in French patent 22 79 208, which see in the French Patent 22 93 270 described monocyanobiphenyls and that in French patent 23 12 840 Described monocyanoterphenyls are particularly advantageous.

In general, the amount of the high dielectric constant compound added may be the one Function of the desired value for the total dielectric constant and the compatibility - solubility or miscibility - of the product with the basic liquid. 5 to 50% by weight of the sanitary mixture be.

The proposed esters or the liquids that These contain, before the use of a customary treatment for dielectrics, for example with activated earth.

Known stabilizers, such as / .. B. Epoxy compounds, ei · 'work.

The following description referring to the figures takes, illustrates some forms of application of the liquids defined above.

Fig. 1 shows a wound condenser. the one from the Sheets 1 and 2 made of aluminum or another suitable metal contains electrodes that 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 those skilled in the art and, for. B. 2 polyolefin films have, between which a layer of paper has been placed. Parts 5 and 6 are contacts for the Power consumption.

F i g. 2 shows a cross section through a capacitor, a metallic container (1) and a Cover (2) which ensures a tight seal, a capacitor element (3) of the wound capacitor type corresponding to that of Fig. 1, so / ie connecting lines (4 and 5), which the contacts of the coil with the outer terminals (6) and (7) conductively connect, contains. The condenser container is with the invention Liquid (8) according to Example I filled.

The liquid wets the dielectric material and fills the voids and spaces in it entire apparatus.

In Fig. 3, a transformer is shown, the one Low-voltage terminal (2), the transformer housing (3), the mounting flanges (4), insulating parts (5) and (6), the low-voltage winding (8) from the magnetic Ken, (10) on the one hand and the high-voltage winding (9) Trermt from the transformer housing on the other hand, contains. The parts (7) serve as insulating spacers. The conductors of the low and high voltage windings are fixed to one another Insulating material, such as paper, insulated,

The transformer housing is filled with a 'dielectric liquid according to the invention, the consists entirely of the ester according to Example 1. The liquid fills all cavities and wets them Windings and other parts of the apparatus that can be wetted.

For this purpose 2 sheets of drawings

Claims (1)

Patent claims:
1. Use of esters of the formula Therefore, the problem is a problem that needs to be solved had to. It has now surprisingly been found that the esters of the formula below are suitable products for represent dielectric liquids. The invention relates to the use of esters of the formula