US2315666A

US2315666A - Transformer bushing

Info

Publication number: US2315666A
Application number: US348718A
Authority: US
Inventors: Alexander A Skvortzoff
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1938-10-18
Filing date: 1940-07-31
Publication date: 1943-04-06
Anticipated expiration: 1960-04-06

Description

April 6, l1943. A.. A. sKvoRTzol-'F -TRANSFORMER BUSHING Original Filed Oct. 18, 1938 WITNESSES:

ATTO

Patented Apr. 6, 1943 TRANSFORMER RUSHING Alexander A. Skvortzof, Sharon, Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Original application October 18, 1938i, Serial No. 235,611. Divided and this application July 31, 1940, Serial No. 348,718

2 Claims.

This application is a division of .my copending application Serial No. 235,611, le-d October 18, 1938 (Patent No. 2,228,089), and the invention, as in the parent case, relates to bushings for insulating the conducting leads of high-tension electrical apparatus, such as transformers and circuit breakers, and has particular reference to an im* proved cap for closing the exposed end of such bushings.

Bushings of the type contemplated usually comprise an elongated cylindrical member of insulating material, such as porcelain, through which the conductor or lead from the apparatus extends to be connected at the upper end of the casing to a terminal which, in turn, is to be connected to an electrical circuit. The conducting lead in many cases is surrounded by a hollow metallic stud or the stud itself may be used as the conductor. In either event, by reason of the difference in the coeicient of expansion between the metallic and porcelain parts, it is diicult to maintain the bushing fluid tight and to prevent breathing upon change in temperature. rlhe bushing is usually filled with a dielectric uid, which may be oil or a gum, and upon breathing cycles moisture may be drawn into the bushing with resultant damage. l

It is usually undesirable to have communication between the hollow stud and the interior of the bushing, and this is particularly diicult to prevent because the thermalexpansion and contraction of the hollow stud longitudinally thereof makes it necessary to terminate the stud within the bushing'and allow space to permit such expension and contraction.

Itis an object of the present invention to provide a bushing terminal cap, in conjunction with a bushing having a hollow metallic stud, in Which means is provided to prevent communication between the interior of the stud and the interior of the bushing in spite of contraction and elongation of the stud under the influence of temperature changes, and at the same time to provide a simple construction, which facilitates assembly of the bushing for accomplishing this result.

Other objects of the invention will be apparent from the following description in conjunction with the accompanying drawing in which the single gure' of the drawing is a view in vertical section of the cap i a bushing of the type contemplated, including a part of the bushing, a part of the bushing being broken away.

Referring to the drawing, the bushing may comprise a cylindrical casing 2 of dielectric ma terial, such as porcelain, usually having a plurality of flanges 4, only one oi which is shown. The upper end of the bushing casing 2 is surmounted by a cap E, which rests upon the end face of the porcelain casing 2, being spaced therefromby gaskets 'I and 8 of different compressibility so that one acts as a compression stop for the other. rIhe top of the cap 6 is surmounted by a terminal I0 to which the external electrical circuit is to be connected.

By way of example the present invention may be used with a bushing of the condenser type in which alternate layers of conducting and insulating material are wound upon a hollow metallic stud I2. In the drawing, the condenser wrapping is indicated at I4, the construction and assembly being substantially the same, as shown in the patent to E. E. Arnold et al. No. 2,088,502, issued July 27, 1937. It is intended, however, that the invention is applicable to bushings of other than the condenser type. f

The cap 6 comprises a main body portion of substantially cup-shape having a base portion proportioned to rest upon the end face of the insulating shell or casing 2. The body portion is provided with a central aperture through which loosely extends the upper end of the metallic stud I2, the latter terminating within the confines of the cap. The cap is provided with a cover IG suitably bolted thereto to effect a fluidtight joint and has a central extension I8 surmounted by the terminal I0 secured to the extension I8 in a iiuidtight manner.

The conducting lead 2l] from the electrical apparatus with which the bushing is to be associated, is drawn up through the stud I2 and is suitably secured to a block 22 threaded to the interiorl of the cover extension I8 by means of a nut 2,4.

Upon variations in temperature, relative movement between the porcelain shell 2 and the stud I2 will occur. The relative movement is quite small, but unless provision is made for it, the destructive forces resulting will, upon contraction of the stud, tend to crush the porcelain or crack the metallic parts of the bushing, and upon elongation, the various gasket joints may open, destroying the fluid-tight character of the bushing. In order to take care of this situation, a fitting 26 is threaded to the upper end of the stud I2, and then preferably brazed to it, and is provided with a plurality of apertures through which bolts 28 extend, terminating at their lower ends in sockets 30 cast into the base of the cap 6. It is intended that the fitting 26 is preferably in the form of a spider and that the bolts 28 will extend loosely through their respective apertures. The number of bolts and springs required must be determined by the size of the bushing, four being indicated, by way of example in the drawing.

Each bolt 28 is provided with a square flat plate 32 adjacent its lower extremity to constitute the seat for a helical spring 34 which surrounds the bolt. The upper end of the spring is in engagement with the under face of the fitting 26. By this means` when the springs 34 are under compression, they will transmit a force from the stud 2Q through the tting 26 and bolt 28 to the base of the cap 6, which will maintain the gaskets 1 and 8 under compression, as well as the gasket 8 at the lower end of the porcelain shell. The desired pressure may be maintained by adjustment of the bolts 28, the plates 32 being square will engage the side wall of the cap and not turn with the bolts. gree of compression of the springs 34 should be so chosen that they will always be under compression in spite of elongation of the stud I2 throughout the normal temperature range encountered in service, and throughout such range the springs are positively retained in operative position by the bolts 28.

In order to prevent communication between the interior of the stud I2 and the cap 6, a tubular flexible member 40 of a fluid-impervious material is secured to the upper end of the stud l2 in fluid-tight manner by means of a clamp 42, and the upper end of the flexible member 40 is clamped between a depending conical flange 44 on the cover I6 and the lower beveled edge of a clamping member 46, which is actuated to clamping position, as indicated, by screwing down block 22 to an extent necessary to obtain a hermetic seal.

The flexible member 40 may be of any desired material so long as it is fluid-impervious, retains its flexibility over a reasonable period, and will not deteriorate under the influence of the oil, gum or other compound with which the bushing is usually lled. There are on the market many types of synthetic rubber, and fabric impregnated therewith which are suitable for this purpose, and I have found that one of such materials which is satisfactory is sold under the trade name Duprene.

By means of the construction described, Iit should be apparent that the invention contemplates an unusually simple construction but at the same time takes care of the many severe conditions encountered inthe normal use of bushings of this character.

Also, the construction results in a simple assembly operation involving no soldered joints and a minimum of parts. In such assembly operation, when the cap 6, with the cover I6 removed, is placed in position, the fitting 26 may readily be screwed into place and the bolts 28 inserted with the springs 34 and plates 32 before the springs are placed under compression. The bolts 28 may then be screwed down to draw up the plates 32 to place the springs 34 under the desired degree of compression. This may be accomplished by a simple wrench rather than having to resort to expensive jigs to place the The delil springs under compression before they are placed in position in the cap. The lower end of the flexible member 40 may then be clamped to the top of the stud l2 by means of the clamp 42, and it is of suliicient length that if the cover I6 were in position, it would extend into the cavity defined by the depending flange 44 on the under-side of the cover. The clamping member 46 is then inserted into the end of the flexible member but not sufficiently to deform such member, and the cover is then placed in proper position and bolted. The flexible member now extends into the cover cavity and the clamping member 46 extends into the cover extension 24. The block 22 is then screwed down to expand the upper end of the flexible member 40 into contact with the flange 44 to complete the clamping and sealing action. The conductor 20 is then shed through and secured to the position shown and the terminal member l0 may then be bolted in position to complete the assembly. The disassembly for inspection or repair is equally simple.

Quite obviously, the design described and shown may be varied to take care of various conditions encountered in service, .and it is intended that the invention is not to be limited except as imposed by the appended claims.

I claim as my invention:

1. In a bushing for high-tension electrical apparatus including a cylindrical casing of dielectric material having a hollow stud extending therethrough and projecting beyond an end thereof, a hollow cap enclosingr the projecting portion of said stud including a cover overlying the end of the stud, a flexible tube of fluid-impervious material having one end embracing the end of said stud and means for securing it thereto, a cylindrical flange integral with said cover and depending adjacent to and extending pe- -ripherally around the other end of said flexible tube, an opening through said cover axially of said cylindrical flange, and means extending through said opening into engagement with said other end of said tube for expanding the latter into intimate peripheral engagement with a wall of said cylindrical flange.

2. In a bushing for high-tension electrical apparatus including a cylindrical casing of dlelectric material having a hollow stud extending therethrough and projecting beyond an end thereof, a hollow cap enclosing the projecting portion of said stud including ,a cover overlying the end of the stud and secured to the cap in fluid-tight relation, a exible tube of fluid-impervious material having one end embracing the end of said stud and means for securing it thereto, a cylindrical flange integral with said cover and depending adjacent to and extending peripherally of the other end of said flexible tube, an opening through said cover axially of said cylindrical flange, and means extending through said opening into engagement with said other end of said tube for forcing the latter into intimate peripheral engagement with a wall of said cylindrical flange and means for closing 'said opening in fluid-tight relation.

ALEXANDER A. SKVORTZOFF.