US2189621A - Bushing - Google Patents

Description

Feb. 6, 1940. E. E. ARNOLD 2,189,621

BUSHING Filed Jan. 13, 1938 WITNESSES:

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INVENTOR v Patented Feb. 6, 1940 BUB Edwin E. Arnold, Westinghouse El HING Pittsburgh, Pa., assignor to t Manufacturing Oomh. Pa., a corporation of Application January 1:, me, w No. 184.880

.This invention relates to high-tension electrical insulating bushings and particularly an improved construction of the shell or weather-casing thereof of the same general type as disclosed in James 5 G. I'iords copending application, Serial No. 184,832, Med January 13, 1938, and assigned to the same assignee as this invention.

The type of bushing here involved is usually associated with an oil-immersed transformer or circuit breaker and comprises 'a dielectric tubular shell or weather easing fllled with an i ting fluid surrounding th apparatus. In order to provide a visual indication of the level of the insulating fluid within the bushing, a glass cylinder is mounted at one end of the weather casing to constitute an extension thereof; the normal level of the fluid being between the ends oi the cylinder.

Gasketed joints are usually provided between e glass cylinder and the weather casing but these Joints are not entirely satisfactory in that they are not always leak-proof and do not result in a desired unitary assembly. Joints which are considered to be tight become weakened under varying temperature and stress conditions with v the result that such Joints are apt to fail, permitting the insulating fluid to escape from within the bushing or outside air to be drawn into the An object of his invention is the provision of a high-tension insulating bushing having a sealed and leak-proof weather casing with parts substantially integrally united.

Another object of this invention is the pro- I vision of a bushing weather casing having thermoplastically sealed Joints between certain parts thereof.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, the single figure of which is a view in elevation and partly in section of structed in accords tion.

Referring to the drawing, the electrical apparatus with which the bushing is to be associated includes a tubular conductor III which is wrapped with alternate layers of conducting and insulating material to constitute a condenser type of insulator II. The lower portion 01 the condenser bushing i2 and the tank of the immersed apparatus with which the bushing is to be employed are not illustrated since they are of usual construction common in this art.

a The exposed end of the conductor and connce with the present invene conducting lead from such a portion of a bushing condenser wrapping I! are enclosed by a dielectric tubular member or. weather casing ll of suitable material, such as porcelain, disposed in spaced relation'to the conductor. The casing it is provided with a plurality of radial creepage flanges it as is usual practice. I Since the space between the conductor and the weather casing is to be fllled with an insulating fluid, a cylindrical shell II is so proportioned with respect to the upper end of the weather casing that it seats thereon when disposed in spaced relation to the conductor. In order that the height of the insulating liquid within thebushing may be readily ascertained, the cylindrical shell II is made of a transparent material such as glass, and is of a shape suitable for seating on the end of the dielectric weather casing in alignment therewith.

In order to maintal n the insulating liquid within the bushing and to prevent admission of air thereto, it is necessary to so seal the joint between the glass cylinder II and the dielectric weather casing it that it is unatl'ected by the stresses encountered in operation, or the stresses due to the relatively diiierent expansion characand the porcelain. It has been found that a seal embodying a thermoplastic bond is entirely satisfactory in this type of service.

In making the seal a gasket 20 of a suitable thermoplastic material, such as the cellulosic materials, cellulose nitrate, cellulose acetate or cellulose acetobutyrate, is disposed between the ends of the dielectric tube and the glass cylinder. In order to promote adhesion in the surfaces of the gasket and secure a good seal between the members of the weather casing, the surfaces of the gasket and, where desired, the ends oi the porcelain tube and glass cylinder are coated with a thermoplastic bonding material or cement which contains a suitable solvent or plasticizer. In the making of the seal, when the bonding material, usually in the liquid form, is applied to the members of the bushing and/or surfaces 01 the gasket, it is air dried either with or without the application oi heat to render it tacky to prevent flow in the process of assembling the members.

With the gasket and/or surfaces thus coated, the glass cylinder and porcelain tube with the gasket therebetween are securely clamped together under a suitable pressure, such as 200 to 750 lbs. per square inch and subjected to a temperature of the order of to C. for a'sufflcient length of time to cause a chemical and physical change in surface of the cell the bond and the softened ulosic material to eiiect a ll cylinder,

' taining the joint between the glass cylinder and pressures is neglible and permanent tight junction. The assembled glass to room temperature while mainand Upon examinalowed to cool porcelain tube under pressure.

tion it is found that the juncture thus formed is hard, bonding the glass and porcelain tube into an integral, leak-proof structure which is capable of withstanding operating, temperatures and stresses encountered in service.

In making the seal it is found that the plasticity of the thermoplastic material is increased with both a rise in temperature and the applicauntil the gasket reaches the hereinbefore described varies with the type of thin,;stable, wafer-likeform. If the temperature of the treatment is increased over the initial treating temperature, plastic flow again occurs reaches a stable thickness somewhat less than the original thickness of, the

until the gasket gasket.

Advantage enon of the thermoplastic materials a bushing which may be subjected in service to temperatures, up to to 0., the sealis formed at temperaturesabove these values and is thus rendered stable at the temperatures en'- countered in service. The point of stability of these seals is affected by the temperature and pressure at which they are formed and .the initial cross-section of the area of the gasket. These factors bear a definite relationship for a given material, but of course the relationship I material;

*{I he glass cylinder and porcelain weather casing have different expansion and contraction characteristics. By sealing the glass and dielectric tube with a suitable thermoplastic material, stresses set up in the seal under operating condi-- tions of the bushing or by reason of the unequal expansion or contraction of the members are dissipated in the seal of the plastic material. This is because the seal is of a material which has a modulus of elasticity so much lower than the glass cylinder and porcelain tube that it may yield within its workable limits to dissipate the stresses.

After the glass cylinder and weather casing are integrally united by the thermoplastic seal, the integral structure is disposed in spaced rela-' tion about the conductor and condenser bushing l2. In order to maintain the sealed weather casing in position with respect to the conductor and to provide an expansion chamber, a hollow chamber 22 is disposed about the end of the conductor and secured thereto for seating on the end of the glass cylinder. A gasket 24 of any suitable materials, for example, a gasket compounded from cork and synthetic rubber, is disposed between the end of the glass cylinder and the bottom of the hollow chamber for effecting a sealed joint there between.

In practice, the hollow chamber may be of any suitable form so maintained in position about the conductor as to apply a compressive force to the gasket between the glass cylinder and the ho]- low chamber, and maintain the glass cylinder, thermoplastic seal, and weather casing under is taken of the stabilizing phenomgasket and'porcelain tube are then 9.1-

in that forcompression. A hollow chamber sealingcap of this type is illustrated in issued April 2'7, 1937, to G. 'A. ternately, the type of cap may closed. in copending application Serial No. 168,216, filed October 9, 1937, by Lingal and Arnold.

Bushings embodying this invention are satis- Burr et 0.1. or, al-

factory under all operating conditions encountered in practice; Under abnormal mechanical and thermal shock tests the thermoplastic seal has been found to be stronger than the glass cylinder and the porcelain weather casing; the seal remaining intact under tests in which the glass cylinder and the porcelain failed.

I Although this invention has been described with reference to a particular embodiment thereof, it is of course 'not to be limited thereto except insofar as is necessitated by the prior art and the scope of the appended claims.

I claim as my invention:

1. A bushing comprising, in combination, a conductor, a tubular member of dielectric ma terial disposed around the conductor substantially concentric therewith and in spaced relation'thereto, a cylinder of transparent dielectric material having a coefficient of expansion different from that of the tubular member disposed in end to end relation therewith and in spaced relation about the conductor, a thermoplastic cellulosic material disposed betweenthe confronting ends of the tubular member and the cylinder and intimately unitedtherewith, means associated with the end of the cylinder opposite its united end and the conductor for closing the space therebetween, and means associated with the end of the tubular member opposite its united end and the conductor for closing the space therebetween, the thermoplastic cellulosic material cooperating with the cylinder and the tubular member to provide a leak-proof structure about the conductor;

2. A bushing comprising, in combination, a conductor, a tubular member of dielectric material disposed aroundthe conductor substantially concentric therewith and in spaced relation thereto, a glass cylinder having a coefllcient of expansion different from that of the tubular member disposed in end to end relation therewith and in spaced relation about the conductor, a gasket of thermoplastic cellulosic material disposed between the confronting ends of the glass cylinder and the tubular member, a binder material associated with the surfaces of the gasket whereby the glass cylinder, gasket and tubular members are flrmly and intimately united, means associated with the end of the glass cylinder opposite 'itsunited end and the conductor for closing the space therebetween, and means associated with the end of the tubular member opposite its united end and the conductor for closing the space therebetween, the binder and gasket cooperating with the glass cylinder 'andthe tubular member to provide a leak-proof structure about the conductor.

3. A bushing comprising, in combination, a conductor; a tubular member of dielectric material disposed around the conductor substantially concentric therewith and in spaced relation thereto, a glass cylinder having a coefficient of expansion different from that of the tubular member disposed in end to end relation therewith and in spaced relation about the conductor, a seal oi cellulosic material disposed between the adjacent ends of the glass cylinder and the tubular member uniting them into an integral structure, the cellulosic material comprising cellulose nitrate, means associated with the unsealed end of the glass cylinder and the conductor for closing the Patent No. 2,078,219,

take the form disspace therebetween, and means associated with the unsealed end of the tubular member and the conductor for closing the space therebetween, the seal of cellulosic material cooperating with the glass cylinder and the tubular member to provide a leak-proof structure about the conductor.

4. A bushing comprising, in combination, a conduotor, a tubular member of dielectric material disposed around the conductor substantially concentric therewith and in spaced relation thereto, a glass cylinder having a coeillcient of expansion different from that or the tubular member disposed in end to end relation therewith and in spaced relation about the conductor, a seal of cellulosic material disposed between the adjacent ends of the glass cylinder and the tubular member uniting them into an integral structure. the cellulosic material comprising cellulose acetate, means associated with the end 01 the glass cylinder opposite its sealed end and the conductor tor closing the space therebetween, and means associated with the end oi the tubular member opposite its sealed end tor closing the space therebetween,

the seal of cellulosic material cooperating with 25 the glass cylinder and the tubular member to the conductor, a seal 01' provide a leak-proof structure about the conductor.

5. A bushing comprising, in combination, a conduotor, a tubular member 01' dielectric material disposed around the conductor substantially concentric therewith and in spaced relation thereto, a cylinder of transparent dielectric material having a comcient of expansion diii'erent from that of the tubular member disposed in end to end relation therewith and in spaced relation about thermoplastic material comprising a gasket oi cellulosic material disposed between the adjacent ends oi the tubular member and the cylinder uniting them into an integral structure, a cap secured to the conductor and bearing upon the unsealed end of the cylinder for maintaining the integrally united cylinder and tubular member under compression and closing the space between the cylinder and the conductor, and means associated with the unsealed end of the tubular member and the conductor for clodng the space therebetween, the seal cooperating with the cylinder and tubular member to provide a leak-proof structure about the conductor.

E. ARNOLD.

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