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Sept. 10, 1946. |__ p‘ HART, JR 2,407,493 ELECTRIC APPARATUS Filéd May 16, 1942v Pigl. l2 l a RooM TEMPERATURE! 7” c‘ | %IVNCORLEUAMS %IVNOCLREUAMS Inventor: Lucas F’. Hart J11, b‘y ?Hiséttorney. 2,407,493 Patented Sept. 10, 1946 UNETE STATES PA'E'EQN'E‘ FENCE 2,407,493 ELECTRIC APPARATUS Lucas P. Hart, J12, Pitts?eld, Mass, assignor to General. Electric Company, a corporation of New York Application May 16, 1942, Serial No. 443,217 1i) Claims. (Cl. 174-17) 1 2 My invention relates to electrical apparatus having an insulating ?uid and to a synthetic rub“ 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 coop her-like material for use in the apparatus and in contact with the ?uid. Electrical apparatus, and particularly high ten sion apparatus, such as transformers are gener ally ?lled with an insulating ?uid which has a crate, 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 relatively high insulation strength. However, the liquid and the gasket material are merely mutu insulation strength of conventional insulating ?uids, such as insulating liquids, is susceptible of 10 ally neutral. Further objects and advantages of my inven deterioration when contaminated by minute tion will become apparent from the following de amounts of moisture and other impurities, so scription referring to the accompanying drawing, that joints and openings in the apparatus cas~ and the features of novelty which characterize ing must be maintained relatively tight far be yond that required for ordinary liquid containers lo my invention will be pointed out with particularity in the claims annexed to and forming a part of so as to prevent seepage of the insulating ?uid this speci?cation. or entrance of impurities from the atmosphere In the drawing, Figs. 1 and 2 illustrate curves into the apparatus casing. Gasket materials of‘ which will be used in the description of my in various kinds have been used for apparatus where the susceptibility of contamination of the insulat 20 vention; Fig. 3 is a side elevation, in partial sec tion, of a relatively high-tension transformer ing ?uid is relatively unimportant, such as in low which is provided with an embodiment of my tension devices, but for electrical apparatus such invention; Fig. 4 is an enlarged view of a por as high-tension transformers, common gasket ma tion of the joint between the cover and the eas terials have not proven dependable, particularly ing of the apparatus illustrated in Fig. 3; Figs. when certain high quality insulating liquids are 5 and 6 illustrate gasket constructions which may used in the apparatus casing. Thus, in some cases be employed in the construction illustrated in it has been the practice to weld the cover to the Figs. 3 and 4, and Fig. 7 illustrates a joint be container so as to secure a fluid-tight seal and, tween a bushing and a cover which may be pro therefore, prevent the entrance of deleterious im vided with an embodiment of my invention. purities into the transformer tank and insulating By virtue of its resilience, rubber has made an ?uid. excellent gasket material for many purposes. It is, therefore, an object of my invention to Thus, pasteurized, rubber-gasketed, canned or provide an electrical apparatus having an insu bottled food products keep unspoiled for years, lating ?uid with a relatively high insulation showing that apparently even microscopic con strength, with an improved arrangement for pro- < tamination cannot penetrate such a joint. Rub viding a substantially ?uid-tight seal between a ber, however, has been found to be unsuccessful removable portion and the casing of the appa as a gasket with electric apparatus which contains ratus. mineral oil and‘ particularly other insulating Another object of my invention is to produce ?uids, such as certain halogenated hydrocarbons. a liquid-insulated high-tension transformer with Exposed to these hydrocarbons, rubber swells up a high-quality liquid insulation and a dependably and disintegrates. It therefore, been cus sealed long-life gasketed container superior to tomary to use cork-composition gaskets for elec what has been available heretofore and suitable tric apparatus having an insulating ?uid such as in many cases as a substitute for a, welded joint. halogenated hydrocarbons, an example of such a A further object of my invention is to provide product being a cyclic chlorinated hydrocarbon an electrical apparatus with an improved com including diphenyl, which is described and bination of an insulating ?uid and a rubber-like claimed in Patent 1,931,373, issued to Clark, and material. assigned to the same assignee as this present in In providing a gasket between the casing and cover of an electrical apparatus having an insu 60 vention. Chlorinated hydrocarbons of these types are strong solvents, and materials used in lating ?uid therein, an important requirement is connection with transformers which are resistant to secure a combination of liquid insulation and to mineral oils are easily attacked and disinte gasket material which will be mutually tolerant at grated by chlorinated hydrocarbons. Some of the least to the extent of avoiding deleterious effect on each other. rubber-like arti?cial compositions which have 2,407,493 3 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 hydrocar 4 than rubber in chlorinated hydrocarbons, and in spite of the characteristics described above which show that this material is unacceptable as a gas ket material in such chlorinated hydrocarbons as carbon tetrachloride, I have found that rubber_ bons, such as the group described in the above like or synthetic elastomer compositions such as mentioned Clark patent. Thus, in “Product Engi neering” for March, 1941, at page 152, it is stated that certain types of synthetic rubber-like ma terials including copolymerized butadiene and 10 those including butadiene, and particularly those which include a copolymer of acrylonitrile with in the range of approximately 25 .to 40%, and butadiene within the range of approximately 60 to 75% when in contact with hydrocarbons of the halogenated cyclic or aromatic hydrocarbon type, such as chlorinated aromatic hydrocarbons in cluding chlorinated diphenyl, not only swell up much less than rubber but that the plasticity thereof is maintained and substantially no acrylic nitrile or styrene swell up more than rub ber in the presence of chlorinated hydrocarbons and organic bases. I have veri?ed 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, di shrinkage, after initial expansion, occurs. Thus, chloroethylene and chloroform. It was also found by curve [4, in Fig. 2 I have illustrated such char that not only did the rubber-like materials show acteristics of a material having approximately a much greater swelling than rubber in these 20 40% acrylonitrile and 60% butadiene as the base chlorinated hydrocarbons but that their tensile ingredients, the days that the material was im strength decayed considerably. mersed in the liquid being plotted as abscissa and In spite of the general tendency of such syn the per cent volume increase being plotted as or thetic rubber-like compositions of swelling con dinate. Curve l5 indicates the characteristics of siderably and deteriorating in the presence of natural rubber, and curve I6 indicates the char chlorinated hydrocarbons, it is known that nat acteristics of a rubber-like material having chlor ural rubber swells considerably more than cer oprene as the base polymer. Such relative char tain synthetic rubber-like materials, such as acteristics were determined with the liquid at a chlorobutadiene in carbon tetrachloride. Such temperature of approximately 100° C. It is ap~ characteristics of these rubber-like materials are 30 parent that such a characteristic as curve M for described in the “India Rubber Journal” for Sep rubber-like compositions in a chlorinated cyclic tember 23, 1939, at page 12. It was determined, hydrocarbon was quite unexpected since the prior however, that when synthetic rubber-like com knowledge of the behavior of these materials positions which contain a copolymer of acrylo showed them to be unacceptable as a gasket ma nitrile and butadiene were placed in carbon tetra terial in chlorinated hydrocarbons. chloride at elevated temperatures the swelling Although it appears that a rubber-like com was not maintained constant but after the mate~ position including butadiene and particularly rials were in the carbon tetrachloride at around butadiene copolymerized with acrylonitrile loses 70 degrees C. for a few days they shrank about its plasticizer in the chlorinated aromatic hydro 40 per cent of the amount they had previously 40 carbons also, such as those including chlorinated expanded or swelled when they were ?rst placed diphenyl (as it was observed that the solvent into the carbon tetrachloride. Such a charac turned the same brownish color as did the carbon teristic would, of course, be undesirable if the tetrachloride), the unexpected property of the material were being used as a fluid-tight gasket maintenance of the plasticity of the synthetic material of the type necessary for high-tension rubber-like material in the case of the chlori electrical apparatus referred to above. This nated aromatic hydrocarbons appears to result shrinkage after a swelling may be accounted for from the fact that this particular family of halo by the plasticizer in the rubber-like composition genated hydrocarbons has the characteristics of being dissolved by the chlorinated hydrocarbon. displacing the dissolved plasticizer and function 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 de ing as a plasticizer itself, and thereby substan creases as it remains in the hot carbon tetra chloride. Another indication that the plasticizer is removed is that it was noticed that the carbon tetrachloride took on a brownish color as the tially 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 e?iciently employed in an electrical apparatus rubber-like material began to shrink. The relative changes in volume for rubber and which has such a chlorinated hydrocarbon as a certain types of synthetic rubber-like composi 60 ?uid insulating material. Referring, therefore, tions in carbon tetrachloride are illustrated in Fig. 1 in which the number of days that the ma terial was in the solvent is plotted as abscissa and the per cent volume increase is plotted as ordi nate. The curve indicated by the numeral i 0 in~ dicates the characteristic of a synthetic rubber like composition including approximately 40% acrylonitrile and 60% butadiene for its base in gradients. vCurve 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 in cluding butadiene swell up considerably more to Fig. 3, I have illustrated a high-tension trans former 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 con traction a conventional conservator or expansion chamber 24 is provided, and the casing may be completely ?lled with any suitable insulating ?uid including a halogenated aromatic hydrocar bon, such as a mixture of said halogenated hy drocarbon that also includes halogenated di phenyl. 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. 2,407,493 6 Referring to Fig. 4, the tank and cover are sealed together so as to provide a relatively ?uid tight seal through a structure including a shoul ticizer for said copolymer being dissolvable in said ?uid at operating temperatures of said ap paratus, said fluid having the characteristic of der 28 which may be attached to the outer sur face of the tank cover around the top. The replacing the dissolved plasticizer so as to main tain substantially the plasticity of said gasket material, whereby a ?uid-tight seal is main tained between said adjoining portions of said tank. shoulder is provided with an outwardly extend ing ?ange 23 against which the cover 2! is adapt ed to be tightly secured in any suitable manner such as by means of bolts 30. The shoulder 29 2. In an electrical apparatus having a tank, a is .provided with a peripheral recess 3| which is 10 cover for said tank, an insulating ?uid and an adapted to receive a gasket ‘J2 composed of any electrical conductor within said tank, said ?uid suitable material having the improved charac including a halogenated aromatic hydrocarbon teristics of having its plasticity maintained with and being susceptible of contamination with im purities from the atmosphere, and means in cluding a gasket between said cover and tank providing a substantially ?uid-tight seal, said gasket being formed of a material comprising a plasticized copolymer of butadiene and acrylo nitrile, the plasticizer for said copolymer being dissolvable in said ?uid at operating tempera tures of said apparatus, said fluid having the characteristic of replacing the dissolved plasti cizer so as to maintain substantially the plastic ity of said .gasket material, whereby a substan tially fluid-tight seal is maintained between said a halogenated aromatic hydrocarbon, as de» scribed above. With the cover bolted tightly in place against the upper surface of the ?ange 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 dimen~ sion of the gasket 32. In this manner the gasket will be compressed between the adjacent surface of the cover 2| and the surface de?ning the recess 3 I. In Fig. 5 I have illustrated a gasket construc tion 33 which has a slanted joint 34 in a plane tank and cover. parallel to the axis of the ring but not passing 3. A high-tension electrical apparatus com 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 tu bular form. An alternative form of seam is il lustrated 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 com prising in combination a container, a cover on said container, a high-tension electrical conduc tor and a high-quality liquid insulation within said container, said insulation including a chlo rinated 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 acrylo pression due to the bolts 38 and the tendency nitrile and butadiene, and compression means to to swell due to any seepage of the enclosed liquid compress and maintain in compression said gas into the seam. 40 ket means in said joint, said gasket means and In Fig. '7 I have illustrated a portion of a bush compression means providing and maintaining a ing having a flange 31 which may be attached to substantially ?uid-tight seal between said con a cover 38 of any suitable apparatus, such as a transformer or capacitor in any suitable manner tainer and cover. such as through bolts 39. A peripheral recess i’ 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 prising in combination a container, a cover on described above. By tightening the bolts 39 the gasket 33 will be compressed to the dimensions 4. A high~tension electrical apparatus com 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, me chanical means to make fast said cover to said container and compress said gasket means, said gasket means and mechanical means providing of the recess as. It will be apparent that rubber-like materials, such as those copolymers including butadiene, and maintaining a substantially ?uid-tight seal which have characteristics as described above, when in contact with halogenated aromatic hy between said tank and cover, a high-tension electrical conductor in said container, and an insulating liquid including a chlorinated aro drocarbons are suitable not only as a gasket ma terial but for other uses in an electric apparatus such as an insulating material when in contact matic hydrocarbon enveloping said conductor. with the halogenated aromatic hydrocarbon. Although I have shown and described particu prising in combination a container, a cover on lar embodiments of my invention, I do not de sire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modi?cations 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 combina tion a tank having therein an electrical conduc tor and an insulating ?uid comprising a halo genated aromatic hydrocarbon, and a gasket ma terial between adjoining portions of said tank, said gasket material being exposed to the action 5. A high-tension electrical apparatus com GO said container, a high-tension electrical c0nduc— tor and a high-quality liquid insulation within said container, said insulation including a chlo rinated 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 approxi mately 25 to 40% acrylonitrile and approximately 75 to 60% butadiene, and compression means to compress and maintain in compression said gas of said ?uid and comprising a plasticized co ket means in said joint, said gasket means and polymer of butadiene and acrylonitrile, the plas compression means providing and maintaining 2,407,493 7 8 a substantially ?uid-tight seal between said con~ said container, a high-tension electrical conduc tor and a high-quality liquid insulation within said container, said insulation including a chlo rinated aromatic hydrocarbon, a mechanical joint tainer and cover. 6. A high-tension electrical apparatus com prising in combination a container, a cover on said container, a high-tension electrical con ductor and a high-quality liquid insulation with in said container, said insulation including a chlorinated aromatic hydrocarbon, a mechan exposed to said liquid insulation and to an ex ternal medium, gasket means in said joint to maintain the high quality of said insulation free from contamination from said external medium, ical joint exposed to said liquid insulation and said gasket means including a gasket formed of a to an external medium, gasket means in said 10 composition comprising a copolymer of acrylo joint to maintain the high quality of said insu nitrile and butadiene, and compression means lation free from contamination from said ex to compress and ‘maintain in compression said ternal medium, said gasket means including a gasket means in said joint to about two-thirds of gasket formed of a composition comprising a co its normal unswollen volume, said gasket means polymer of acrylonitrile and ‘outadiene, and com and compression means providing and maintain pression means to compress and maintain in ing a substantially ?uid-tight seal between said compression said gasket means in said joint, said container and cover. liquid insulation ?lling said container to a level 9. Electrical apparatus comprising in combi at least as high as the level of said gasket means nation a tank having therein an electrical con so that said gasket means will be exposed thereto 20 ductor and an insulating ?uid comprising a continuously, said gasket means and compression halogenated aromatic hydrocarbon, and a gasket means providing and maintaining a substan between adjoining portions of said tank, said gas tially ?uid-tight seal between said container and ket being in contact with said ?uid and com cover. '7. A high-tension electrical apparatus com prising a copolymer of butadiene and acryloni 25 trile, said copolymer having a halogenated aro prising in combination a container, a cover on said container, a high-tension electrical con matic hydrocarbon as a plasticizer for substan ductor and a high-quality liquid insulation with in 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 of said apparatus, and said gasket providing and maintaining a fluid-tight seal between said ad joining portions of said tank. 10. Electrical apparatus comprising in combi maintain the high quality of said insulation free from contamination from said external medium, electrical conductor and an insulating ?uid 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 ?uid and comprising a copolymer of butadiene and acrylonitrile, said said gasket means including a gasket formed of I tially maintaining its plasticity during operation nation a container, a cover on said container, an a composition comprising a copolymer of buta diene and acrylonitrile, and compression means to compress and maintain in compression said gasket means in said joint, said gasket means copolymer being plasticized with a plasticizer and compression means providing and maintain 40 dissolvable in said ?uid, said fluid having the ing a substantially ?uid-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 ten sion on said means to compress the same. 8. A high~tension electrical apparatus com prising in combination a container, a cover on characteristic of displacing the dissolved plasti cizer and maintaining substantially the plasticity of said copolymer during operation of said ap paratus, and the said means which includes said gasket providing and maintaining a ?uid-tight seal between said container and cover. LUCAS P. HART, JR.