US2407493A - Electric apparatus - Google Patents

Description

Sept. 10, 1946. p HART, JR 2,407,493

ELECTRIC APPARATUS Fild May 16, 1942 Pigl.

l a RooM TEMPERATURE! VOLUME INCREASE VOLUME INCREASE Inventor: Lucas F. Hart J11,

b Histtorney.

Patented Sept. 10, 1946 ELECTRIC APPARATUS Lucas P. Hart, J12, Pittsfield, Mass, assignor to General. Electric Company, a corporation of New York Application May 16, 1942, Serial No. 443,217

1i) Claims. 1

My invention relates to electrical apparatus having an insulating fluid and to a synthetic rub her-like material for use in the apparatus and in contact with the fluid.

Electrical apparatus, and particularly high tension apparatus, such as transformers are generally filled with an insulating fluid which has a relatively high insulation strength. However, the insulation strength of conventional insulating fluids, such as insulating liquids, is susceptible of deterioration when contaminated by minute amounts of moisture and other impurities, so that joints and openings in the apparatus casing must be maintained relatively tight far beyond that required for ordinary liquid containers so as to prevent seepage of the insulating fluid or entrance of impurities from the atmosphere into the apparatus casing. Gasket materials of various kinds have been used for apparatus where the susceptibility of contamination of the insulating fluid is relatively unimportant, such as in lowtension devices, but for electrical apparatus such as high-tension transformers, common gasket materials have not proven dependable, particularly when certain high quality insulating liquids are used in the apparatus casing. Thus, in some cases it has been the practice to weld the cover to the container so as to secure a fluid-tight seal and, therefore, prevent the entrance of deleterious impurities into the transformer tank and insulating fluid.

It is, therefore, an object of my invention to provide an electrical apparatus having an insulating fluid with a relatively high insulation strength, with an improved arrangement for providing a substantially fluid-tight seal between a removable portion and the casing of the apparatus.

Another object of my invention is to produce a liquid-insulated high-tension transformer with a high-quality liquid insulation and a dependably sealed long-life gasketed container superior to what has been available heretofore and suitable in many cases as a substitute for a, welded joint.

A further object of my invention is to provide an electrical apparatus with an improved combination of an insulating fluid and a rubber-like material.

In providing a gasket between the casing and cover of an electrical apparatus having an insulating fluid therein, an important requirement is to secure a combination of liquid insulation and gasket material which will b mutually tolerant at least to the extent of avoiding deleterious effect on each other.

It is, therefore, another object of my invention to not only satisfy the above requirement but to go beyond it and provide a combination in which the insulating liquid and gasket material coopcrate, beyond mere tolerance of each other, so as to produce a joint that is tighter and otherwise also more dependable than that which could be secured by a combination in which the insulating liquid and the gasket material are merely mutually neutral.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing, Figs. 1 and 2 illustrate curves which will be used in the description of my invention; Fig. 3 is a side elevation, in partial section, of a relatively high-tension transformer which is provided with an embodiment of my invention; Fig. 4 is an enlarged view of a portion of the joint between the cover and the easing of the apparatus illustrated in Fig. 3; Figs. 5 and 6 illustrate gasket constructions which may be employed in the construction illustrated in Figs. 3 and 4, and Fig. 7 illustrates a joint between a bushing and a cover which may be provided with an embodiment of my invention.

By virtue of its resilience, rubber has made an excellent gasket material for many purposes. Thus, pasteurized, rubber-gasketed, canned or bottled food products keep unspoiled for years, showing that apparently even microscopic contamination cannot penetrate such a joint. Rubber, however, has been found to be unsuccessful as a gasket with electric apparatus which contains mineral oil and particularly other insulating fluids, such as certain halogenated hydrocarbons. Exposed to these hydrocarbons, rubber swells up and disintegrates. It therefore, been customary to use cork-composition gaskets for electric apparatus having an insulating fluid such as halogenated hydrocarbons, an example of such a product being a cyclic chlorinated hydrocarbon including diphenyl, which is described and claimed in Patent 1,931,373, issued to Clark, and assigned to the same assignee as this present invention. Chlorinated hydrocarbons of these types are strong solvents, and materials used in connection with transformers which are resistant to mineral oils are easily attacked and disintegrated by chlorinated hydrocarbons. Some of the rubber-like artificial compositions which have been developed in recent years and which show excellent resistance to some hydrocarbons, such as gasoline, have also been found to swell up even more than rubber and to deteriorate rapidly when exposed to various halogenated hydrocarbons, such as the group described in the above mentioned Clark patent. Thus, in Product Engineering for March, 1941, at page 152, it is stated that certain types of synthetic rubber-like materials including copolymerized butadiene and acrylic nitrile or styrene swell up more than rubber in the presence of chlorinated hydrocarbons and organic bases. I have verified this and found that synthetic rubber-like materials of the general types described in this publication swell up to a much higher degree than rubber in such chlorinated hydrocarbons as benzyl chloride, dichloroethylene and chloroform. It was also found that not only did the rubber-like materials show a much greater swelling than rubber in these chlorinated hydrocarbons but that their tensile strength decayed considerably.

In spite of the general tendency of such synthetic rubber-like compositions of swelling considerably and deteriorating in the presence of chlorinated hydrocarbons, it is known that natural rubber swells considerably more than certain synthetic rubber-like materials, such as chlorobutadiene in carbon tetrachloride. Such characteristics of these rubber-like materials are described in the India Rubber Journal for September 23, 1939, at page 12. It was determined, however, that when synthetic rubber-like compositions which contain a copolymer of acrylonitrile and butadiene were placed in carbon tetrachloride at elevated temperatures the swelling was not maintained constant but after the materials were in the carbon tetrachloride at around 70 degrees C. for a few days they shrank about 40 per cent of the amount they had previously expanded or swelled when they were first placed into the carbon tetrachloride. Such a characteristic would, of course, be undesirable if the material were being used as a fluid-tight gasket material of the type necessary for high-tension electrical apparatus referred to above. This shrinkage after a swelling may be accounted for by the plasticizer in the rubber-like composition being dissolved by the chlorinated hydrocarbon. This conclusion is verified by the fact that the durometer hardness during this shrinkage after the previous swelling increased considerably, thus indicating that the plasticity of the material decreases as it remains in the hot carbon tetrachloride. Another indication that the plasticizer is removed is that it was noticed that the carbon tetrachloride took on a brownish color as the rubber-like material began to shrink.

The relative changes in volume for rubber and certain types of synthetic rubber-like compositions in carbon tetrachloride are illustrated in Fig. 1 in which the number of days that the material was in the solvent is plotted as abscissa and the per cent volume increase is plotted as ordinate. The curve indicated by the numeral i indicates the characteristic of a synthetic rubberlike composition including approximately 40% acrylonitrile and 60% butadiene for its base inradients. Curve ll illustrates the increase in volume for a synthetic rubber of a composition including chloroprene, while curve 12 shows the characteristic of rubber.

However, contrary to this prior knowledge that synthetic rubber-like materials such as those including butadiene swell up considerably more than rubber in chlorinated hydrocarbons, and in spite of the characteristics described above which show that this material is unacceptable as a gasket material in such chlorinated hydrocarbons as carbon tetrachloride, I have found that rubber like or synthetic elastomer compositions such as those including butadiene, and particularly those which include a copolymer of acrylonitrile within the range of approximately 25 .to 40%, and butadiene within the range of approximately 60 to when in contact with hydrocarbons of the halogenated cyclic or aromatic hydrocarbon type, such as chlorinated aromatic hydrocarbons including chlorinated diphenyl, not only swell up much less than rubber but that the plasticity thereof is maintained and substantially no shrinkage, after initial expansion, occurs. Thus, by curve [4, in Fig. 2 I have illustrated such characteristics of a material having approximately 40% acrylonitrile and 60% butadiene as the base ingredients, the days that the material was immersed in the liquid being plotted as abscissa and the per cent volume increase being plotted as ordinate. Curve l5 indicates the characteristics of natural rubber, and curve I6 indicates the characteristics of a rubber-like material having chloroprene as the base polymer. Such relative characteristics were determined with the liquid at a temperature of approximately C. It is apparent that such a characteristic as curve M for rubber-like compositions in a chlorinated cyclic hydrocarbon was quite unexpected since the prior knowledge of the behavior of these materials showed them to be unacceptable as a gasket material in chlorinated hydrocarbons.

Although it appears that a rubber-like composition including butadiene and particularly butadiene copolymerized with acrylonitrile loses its plasticizer in the chlorinated aromatic hydrocarbons also, such as those including chlorinated diphenyl (as it was observed that the solvent turned the same brownish color as did the carbon tetrachloride), the unexpected property of the maintenance of the plasticity of the synthetic rubber-like material in the case of the chlorinated aromatic hydrocarbons appears to result from the fact that this particular family of halogenated hydrocarbons has the characteristics of displacing the dissolved plasticizer and functioning as a plasticizer itself, and thereby substantially maintaining the plasticity and preventing shrinkage of the synthetic rubber material after its initial expansion when placed in the solvent.

Such a synthetic rubber-like material which has the above desirable characteristics when in contact with a chlorinated aromatic hydrocarbon such as of the chlorinated diphenyl type may be efliciently employed in an electrical apparatus which has such a chlorinated hydrocarbon as a fluid insulating material. Referring, therefore, to Fig. 3, I have illustrated a high-tension transformer which includes a casing 20 having a cover 2|. On the cover are mounted a high tension bushing 22 and a low tension bushing 23. In order to take care of thermal expansion and contraction a conventional conservator or expansion chamber 24 is provided, and the casing may be completely filled with any suitable insulating fluid including a halogenated aromatic hydrocarbon, such as a mixture of said halogenated hydrocarbon that also includes halogenated diphenyl. Within the casing is a magnetic core 25 having a conductor or a relatively high tension winding 26 which is adapted to be connected to a stud 21 of the bushing 22.

Referring to Fig. 4, the tank and cover are sealed together so as to provide a relatively fluid tight seal through a structure including a shoulder 28 which may be attached to the outer surface of the tank cover around the top. The shoulder is provided with an outwardly extending flange 23 against which the cover 2! is adapted to be tightly secured in any suitable manner such as by means of bolts 30. The shoulder 29 is .provided with a peripheral recess 3| which is adapted to receive a gasket J2 composed of any suitable material having the improved characteristics of having it plasticity maintained with a halogenated aromatic hydrocarbon, as de scribed above. With the cover bolted tightly in place against the upper surface of the flange 29 the depth of the recess 3| at the joint may have any suitable size in relation to that of the gasket 32, such as being approximately two-thirds the height or thickness of the unswollen dimension of the gasket 32. In this manner the gasket will be compressed between the adjacent surface of the cover 2| and the surface defining the recess 3 I.

In Fig. I have illustrated a gasket construction 33 which has a slanted joint 34 in a plane parallel to the axis of the ring but not passing through the axis. This manner of providing a seam in the ring makes it easy to manufacture the ring gasket by slicing a thick sheet material having its opposite edges beveled on opposite faces and then having the sheet bent into a tubular form. An alternative form of seam is illustrated in Fig. 6 in which the plane of the same will be seen to be slanting with respect to the axis of the gasket. A slanting seam of either type results in a tighter seal under the compression due to the bolts 38 and the tendency to swell due to any seepage of the enclosed liquid into the seam.

In Fig. '7 I have illustrated a portion of a bushing having a flange 31 which may be attached to a cover 38 of any suitable apparatus, such as a transformer or capacitor in any suitabl manner such as through bolts 39. 4B is provided in the upper surface of the cover 21 to accommodate a gasket of the shape shown in Figs. 5 or 6 and composed of the material as described above. By tightening the bolts 39 the gasket 33 will be compressed to the dimensions of the recess as.

It will b apparent that rubber-like materials, such as those copolymers including butadiene, which have characteristics as described above, when in contact with halogenated aromatic hydrocarbons are suitable not only as a gasket material but for other uses in an electric apparatus such as an insulating material when in contact with the halogenated aromatic hydrocarbon.

Although I have shown and described particular embodiments of my invention, I do not desire to be limited to th particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Electrical apparatus comprising in combination a tank having therein an electrical conductor and an insulating fluid comprising a halogenated aromatic hydrocarbon, and a gasket material between adjoining portions of said tank, said gasket material being exposed to the action of said fluid and comprising a plasticized copolymer of butadiene and acrylonitrile, the plas- A peripheral recess ticizer for said copolymer being dissolvable in said fluid at operating temperatures of said apparatus, said fluid having the characteristic of replacing the dissolved plasticizer so as to maintain substantially the plasticity of said gasket material, whereby a fluid-tight seal is maintained between said adjoinin portions of said tank.

2. In an electrical apparatus having a tank, a cover for said tank, an insulating fluid and an electrical conductor within said tank, said fluid including a halogenated aromatic hydrocarbon and being susceptible of contamination with impurities from the atmosphere, and means including a gasket between said cover and tank providing a substantially fluid-tight seal, said gasket being formed of a material comprising a plasticized copolymer of butadiene and acrylonitrile, the plasticizer for said copolymer being dissolvable in said fluid at operating temperatures of said apparatus, said fluid having the characteristic of replacing the dissolved plasticizer so as to maintain substantially the plasticity of said .gasket material, whereby a substantially fluid-tight seal is maintained between said tank and cover.

3. A high-tension electrical apparatus comprising in combination a container, a cover on said container, a high-tension electrical conductor and a high-quality liquid insulation within said container, said insulation including a chlorinated aromatic hydrocarbon, a mechanical joint exposed to said liquid and to an external medium, gasket means in said joint to maintain the high quality of said insulation free from contamination from said external medium, said gasket means including a copolymer of acrylonitrile and butadiene, and compression means to compress and maintain in compression said gasket means in said joint, said gasket means and compression means providing and maintaining a substantially fluid-tight seal between said container and cover.

4. A high-tension electrical apparatus comprising in combination a container, a cover on said container, gasket means between said cover and said container, said gasket means including a gasket formed of a composition comprising a copolymer of acrylonitrile and butadiene, mechanical means to make fast said cover to said container and compress said gasket means, said gasket means and mechanical means providing and maintaining a substantially fluid-tight seal between said tank and cover, a high-t nsion electrical conductor in said container, and an insulating liquid including a chlorinated aromatic hydrocarbon enveloping said conductor.

5. A high-tension electrical apparatus comprising in combination a container, a cover on said container, a high-tension electrical c0nduc tor and a high-quality liquid insulation within said container, said insulation including a chlorinated aromatic hydrocarbon, a mechanical joint exposed to said liquid and to an external medium, gasket means in said joint to maintain the high quality of said insulation free from contamination from said external medium, said gasket means including a gasket formed of a composition comprising a copolymer of approximately to acrylonitrile and approximately 75 to butadiene, and compression means to compress and maintain in compression said gasket means in said joint, said gasket means and compression means providing and maintaining a substantially fluid-tight seal between said container and cover.

6. A high-tension electrical apparatus comprising in combination a container, a cover on said container, a high-tension electrical conductor and a high-quality liquid insulation within said container, said insulation including a chlorinated aromatic hydrocarbon, a mechanical joint exposed to said liquid insulation and to an external medium, gasket means in said joint to maintain the high quality of said insulation free from contamination from said external medium, said gasket means including a gasket formed of a composition comprising a copolymer of acrylonitrile and outadiene, and compression means to compress and maintain in compression said gasket means in said joint, said liquid insulation filling said container to a level at least as high as the level of said gasket means so that said gasket means will be exposed thereto continuously, said gasket means and compression means providing and maintaining a substantially fluid-tight seal between said container and cover.

'7. A high-tension electrical apparatus comprising in combination a container, a cover on said container, a high-tension electrical conductor and a high-quality liquid insulation within said container, said insulation including a chlorinated aromatic hydrocarbon, a mechanical joint exposed to said liquid insulation and to an external medium, gasket means in said joint to maintain the high quality of said insulation free from contamination from said external medium,

said gasket means including a gasket formed of I a composition comprising a copolymer of butadiene and acrylonitrile, and compression means to compress and maintain in compression said gasket means in said joint, said gasket means and compression means providing and maintaining a substantiall fluid-tight seal between said container and cover, and said joint having a groove in which said gasket is placed so as to limit the compression of said gasket means to a predetermined value irrespective of the tension on said means to compress the same.

8. A high-tension electrical apparatus comprising in combination a container, a cover on said container, a high-tension electrical conductor and a high-quality liquid insulation within said container, said insulation including a chlorinated aromatic hydrocarbon, a mechanical joint exposed to said liquid insulation and to an external medium, gasket means in said joint to maintain the high quality of said insulation free from contamination from said external medium, said gasket means including a gasket formed of a composition comprising a copolymer of acrylonitrile and butadiene, and compression means to compress and maintain in compression said gasket means in said joint to about two-thirds of its normal unswollen volume, said gasket means and compression means providing and maintaining a substantially fluid-tight seal between said container and cover.

9. Electrical apparatus comprising in combination a tank having therein an electrical conductor and an insulating fluid comprising a halogenated aromatic hydrocarbon, and a gasket between adjoining portions of said tank, said gasket being in contact with said fluid and comprising a copolymer of butadiene and acrylonitrile, said copolymer having a halogenated aromatic hydrocarbon as a plasticizer for substantially maintaining its plasticity during operation of said apparatus, and said gasket providing and maintaining a fluid-tight seal between said adjoining portions of said tank.

10. Electrical apparatus comprising in combination a container, a cover on said container, an electrical conductor and an insulating fluid in? cluding a chlorinated aromatic hydrocarbon within said container, means including a gasket between said container and cover, said gasket being in contact with said fluid and comprising a copolymer of butadiene and acrylonitrile, said copolymer being plasticized with a plasticizer dissolvable in said fluid, said fluid having the characteristic of displacing the dissolved plasticizer and maintaining substantially the plasticity of said copolymer during operation of said apparatus, and the said means which includes said gasket providing and maintaining a fluid-tight seal between said container and cover.

LUCAS P. HART, JR.

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