US2859271A

US2859271A - High voltage bushing

Info

Publication number: US2859271A
Application number: US501845A
Authority: US
Inventors: Donald L Johnston; William A Wooldridge
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1955-04-18
Filing date: 1955-04-18
Publication date: 1958-11-04
Anticipated expiration: 1975-11-04

Description

United States Patent O HIGH VOLTAGE RUSHING Donald- L. Johnston and William A.y Wooldridge, Pittsfield, Mass., asslgnors to General Electric Company, a corporation of New York Application April 18, 195s, serial No. 501,845

9 Claims. (Cl. 174-31) This invention relates to bushings, and more in partlcular to an improved high voltage bushing for electrical apparatus of the dielectric liuid filled type and a method for making the same.

High voltage bushings of the type used for handling potentials greater than about 69 kilovolts are generally comprised of a central axial conductor surrounded by a core of dielectric fluid impregnated insulating material immersed in a dielectric uid insulating medium. A top and bottom ceramic shell separated by a metallic mounting flange surround the core and central conductor, and provide means for retaining the dielectric uid. A terminal is provided at the top end of the bushing, and the terminal may be connected to the central axial conductor, or to a cable passing through the conductor if the latter is in tubular form.

Since it is not readily possible to manufacture ceramic shells to close tolerances, the shells must be made suiciently large that a space exists between them and the insulating core they surround. This of course results in increased size of the bushing. The shells must be provided with gaskets where they join the metal parts of the bushing, and caution must be taken during assembly that the various parts and gaskets are accurately aligned. Although such bushings are satisfactory from the standpoint of the function they serve, they are extremely costly to manufacture.

In `order to reduce costs, bushings for use at voltages less than about 69 kilovolts generally omit the bottom ceramic shell and dielectric fluid filled core and employ instead a solid insulating material surrounding the central conductor. The solid insulating material generally extends for a considerable `distance upward through the top ceramic shell. A dielectric fluid may surround the insulating material in the upper portion of the bushing, but in this type of bushing the full benefit is not derived from the insulating tiuid, and the solid insulating material provides the majority of the insulation. Thus, although this type of bushing is much less costly than the type having a bottom porcelain shell, the insulating characteristics are decreased since optimum use is not made of the dielectric fluid insulating material.

It is therefore an object of this invention to provide an improved high voltage bushing for electrical apparatus.

It is also an object to provide an improved dielectric fluid illed high voltage bushing without a bottom ceramic shell.

A further object of this invention is to eliminate the necessity for bottom ceramic shells in high voltage bushings -of the type employing a dielectric lluid impregnated core surrounding a central conductor.

Still another object is to provide an improved method for fabricating high voltage bushings of the type employing a dielectric fluid filled core surrounding a central` conductor.

Briefly stated, in accordance with one embodiment of this invention, a high voltage bushing is provided com- 2,859,271 Patented Nov. 4, 1958 prising a central axial conductor which may be solid or tubular. A secondary tubular electrode electrically connected to the central conductor radially surrounds the conductor and provides an annular dielectric fluid lled chamber surrounding the conductor. A dielectric fluid permeable core surrounds the secondary electrode, which is in turn surrounded by a tube of solid insulating material to be more fully described in the following paragraphs.l The top half `of the solid insulating tube is surrounded by a ceramic shell, while the bottom half of the insulating tube serves as an external surface of the bushing, Means are provided so that dielectric lluid may circulate by way of the annular chamber surrounding the central conductor to an annular chamber betweenv the insulating tube and the ceramic shell and also to an annular chamber inside of the insulating tube below the bottom end of the core.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing:

Fig. l is a partial cross-sectional view of a high voltage bushing illustrating one embodiment of this invention, and

Fig. 2 is an enlarged cross-sectional view of a portion of the high voltage bushing of Fig. l.

Referring now to the drawing, a high voltage bushing is therein illustrated having a conducting cable 10 extending from a top terminal assembly' 11 downwardly through a central conductor 12, and thence emerging from the bottom end of the bushing. Although the central conductor 12 is herein illustrated as being hollow, in some applications of the bushing, for example on circuit breakers, it may be desirable that the cable be eliminated and the conductor be a solid member extending from the top terminal through the bushing to a bottom terminal.

Por all except the top portion of its length the central conduct-or is surrounded by a unitary structure comprised of a secondary tubular electrode 13, a dielectric uid permeable core 14, a solid electrical insulating tube 15, and ground sleeve 16. The secondary electrode 13 has an inside diameter larger than outside diameter of the central conductor 12, so that an annular space 17 is provided between the electrode 13 and the conductor. The electrode 13 is electrically connected and firmly held to the central conductor by means of a set screw 18 extending through the thickened top end of the electrode and also by an end plate 19 threaded to the bottom ends of the electrode and the conductor. A plurality of holes 20 are drilled through the top and bottom ends of the electrode for a purpose to be described later.

Surrounding the secondary electrode 13 is a dielectric uid impregnated core 14 `of the type conventionally ernployed in fluid filled bushings. This core may consist of a plurality of layers of paper wrapped around the electrode 13. The core may have a plurality of electrostatic shield members Wrapped integrally therewith according to the usual practice, as well as an external shield 21.

Radially surrounding the core 14 is a tube 15 of solid insulating material. The insulating tube 15 extends from the top end of the core downwardly to the end plate 19, thereby enclosing a chamber 22 below the bottom of the core, and is preferably formed by wrapping a plurality of layers of resin impregnated laminar 'insulating material tightly around the core 14 and then A ground sleeve 16 is shrunk iit over a machined portion on the outside of the insulating tube with its bottom edge against a machined shoulder 23 on the insulating tube.

The top outside surface of the bushing is comprised of a ceramic insulator 25 and a metallic mounting flange 26. .The ceramic insulator extends between the top terminal assembly and the mounting flange, and the mounting iiange surrounds the central portion of the insulating tube 15. In order to hold the ceramic insulator and mounting ange in place, the flange is provided with a shoulder 27, and tightening of the terminal assembly 1l against the ceramic insulator forces the flange shoulder 27 against the top edge of the ground sleeve. If desired the diameter of the insulating tube may be reduced above the top edge of the ground sleeve in order to provide a shoulder on the insulating tube engaging with the shoulder 27 on the liange. The ceramic insulator encloses a top chamber 2S surrounding the top end of the insulating tube.

Therentire bushing is filled with a dielectric insulating fluid to a level 29 above the top of the core, and the iiuid is free to circulate between the top chamber l28 and the bottom chamber 22 by way of holes 20 and the annular space 17 surrounding the central conductor. Gaskets are provided at the joints between the ceramic insulator, the top terminal assembly, and the mounting ange in order to prevent escape of the dielectric uid. A gasket may also be inserted between the top edge of the ground sleeve and the mounting flange.

The top terminal may be of any suitable conventional type, and will not be further described herein other than to say that it should be provided with a plug 30 to facilitate lling the bushing with dielectric uid and to measure the quantity of fluid in the bushing. It is also preferred that a plug 33 be inserted in the bottom plate 19 to facilitate emptying of the bushing.

According to usual practice in such bushings, an electrical connection is made between the shield 21 and the mounting flange by means of a conductor 31, and electrical connection between the ground sleeve and the mounting flange is assured by means of a screw 32 threaded in the mounting flange and contacting the sleeve.

As has been previously stated, the lower end of the bushing is a unitary structure comprised of the secondary tubular electrode 13, core 14, insulating tube 15, and ground sleeve 16. This assembly may be readily fabricated by first wrapping the core tightly around the tubular electrode, then wrapping layers of resin impregnated laminar material tightly around the outside of the core. The structure is then heated to allow the resin impregnated material to form a solid insulating material. After cooling the insulating material is machined to the desired dimensions, and the ground sleeve is shrunk lit over the central portion thereof. This method produces a unitary structure that requires a minimum of handling in the fabrication of the bushing. The assembly of the remaining portions of the bushing will be obvious to one skilled in the art.,

From the above description it is readily seen that the bushing of this invention provides means for reducing the electrical stress between the bushing conductor and ground metal by providing an increase in the diameter of the insulating core surrounding the central conductor without increasing the bottom end diameter of the bushing as would be required in the case of a bushing having a bottom ceramic shell.

The present invention is an improvement over the invention of the copending application of E. F. Cronin and D. L. Johnston, Serial No. 501,846, iiled April 18, 1955, and assigned to the present assignee.

It will be understood, of course, that while the form of the invention herein shown and described constitutes a preferred embodiment of the invention, it is not in tended herein to illustrate all of the possible equivalent forms or ramifications thereof. It will also be understood that the words used are words of description rather than of limitation, and that various changes may be made without departing from the spirit or scope of the invention herein disclosed.

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

l. In a high Voltage bushing for electrical apparatus, an axial central conductor extending through said bushing, a secondary tubular electrode coaxial with said conductor and separated therefrom providing an annular chamber surrounding said conductor, a dielectric uid impregnated insulating core surrounding at least a portion of said secondary electrode, solid insulating tubular means surrounding said core and defining a lower dielectric fluid lled chamber, ceramic shell means surrounding Vthe upper portion of said tubular insulating means and defining an upper dielectric fluid filled chamber, and means including said annular chamber providing circulation of dielectric fluid between said upper and lower chambers.

2. In a high voltage bushing for electrical apparatus, an axial central conductor extending through said bushing, a secondary tubular electrode coaxial with said conductor and electrically connected thereto, said conductor and electrode deiining an annular dielectric iluid lled chamber surrounding said conductor, coaxial dielectric uid impregnated insulation core means wrapped around at least a portion of said electrode, coaxial solid insulating means surrounding said core means and in contact therewith, ceramic shell means surrounding the upper portion of said bushing and deiining an Lipper dielectric fluid lilled chamber, said solid insulating means extending from the lower end of said bushing into said upper chamber and defining a lower dielectric fluid lled chamber below the bottom of said core, and means including said annular chamber providing circulation of dielectric fluid between said upper chamber and said lower chamber.

3. In a high voltage bushing for electrical apparatus, an axial conductor extending through said Vbushing from a top terminal means, a ceramic shell surrounding the top portion of said bushing and dening an upper chamber surrounding said central conductor, and a unitary'structure extending from the bottom of said bushing into said upper chamber and surrounding said central conductor comprising a central tubular electrode, a dielectric fluid iilled insulating core wrapped on said electrode, and a solid tubular insulation means coaxially surrounding said core and dening a lower chamber below the bottom of said core between said solid insulation means and said central electrode, said central electrode surrounding said central conductor and being electrically connected thereto and defining an annular chamber surrounding said central conductor, saidy annular chamber communicating with said upper and lower chambers.

4. A high voltage bushing for electrical apparatus comprising axial conducting means connected to a top terminal means and extending through said bushing, upper external insulating means defining an upper chamber surrounding said conducting means, lower external insulating means extending into said upper chamber, said lower external insulating means comprising a central dielectric uid permeable insulating means and an outer solid insulation means and defining a lower chamber below said permeable insulating means, and an annular chamber between said conducting means and said lower external insulating means and communicating with said upper and lower chambers.

5. The bushing of claim 4 wherein said outer solid insulating means is a resin impregnated laminar material.`

6. A high voltage bushing for electrical apparatus com- I prising axial conducting means connected to top terminal means and extending through said bushing, upper ceramic shell means adjacent said top terminal means providing an upper external surface for said bushing and defining an upper chamber surrounding said conducting means, and a lower external insulating means surrounding the lower portion of said conducting means and extending into said upper chamber, secondary tubular electrode means surrounding said conducting means and electrically connected thereto, said lower insulating means comprising a dielectric uid permeable insulating core means wrapped around said electrode means, and a solid insulating means surrounding said core means and defining a lower chamber surrounding said electrode means below said core means, Said electrode means being spaced from said conducting means to provide an annular chamber therebetween communicating with said upper and lower chambers.

7. A high voltage bushing for electrical apparatus comprising axial conducting means connected to top terminal means and extending through said bushing, upper ceramic shell means adjacent said top terminal means providing an upper external surface for said bushing and defining an upper chamber surrounding said conducting means, a lower external insulating means surrounding the lower portion of said conducting means and extending into said upper chamber, and flanged mounting means lpositioned at the lower end of said ceramic shell means and separating said ceramic shell means from said lower external insulating means, secondary tubular electrode means surrounding said conducting means and electrically connected thereto, said lower insulating means comprising a dielectric fluid permeable insulating core means wrapped around said electrode means, and a solid insulating resin impregnated laminar means surrounding said core means and defining a lower chamber surrounding said electrode means -below said core means, said electrode means being spaced from said conducting means to provide an annular chamber therebetween communicating with said upper and lower chambers.

8. A high voltage bushing for electrical apparatus comprising axial conducting means connected to top terminal means and extending through said bushing, upper ceramic shell means having a top edge adjacent said top terminal means and a bottom edge adjacent a anged metallic mounting means, said ceramic shell means providing an upper external surface for said bushing and defining an upper chamber surrounding said `conducting means, and a lower external insulating means surrounding the lower portion of said conducting means and extending through said flanged mounting means into said upper chamber,

secondary tubular electrode means surrounding said conducting means and being electrically connected thereto, said lower insulating means comprising a dielectric fluid permeable insulating core means spirally wrapped around said electrode means, a solid insulating resin impregnated laminar means surrounding said core means and dening a lower chamber surrounding said electrode means below said core means, and an annular ground sleeve means surrounding a portion of said solid insulating means and being electrically connected to said anged mounting means, said electrode means being spaced from said conducting means to provide an annular chamber surrounding said conducting means and communicating with said upper and lower chambers.

9. A lower external insulating member for a high voltage bushing comprising a secondary axial tubular electrode means through which a central conductor of said bushing extends, the inside diameter of said electrode being greater than the outside diameter of said central conductor to provide an annular space surrounding said conductor, a dielectric uid impregnated insulating core spirally wrapped `around said electrode means, a solid insulating resin impregnated laminar means surrounding said core means and extending below the lower end of said core means to provide an annular chamber surrounding the lower end of said electrode means, and an annular ground sleeve means surrounding a portion of said solid insulating means, said electrode means extending beyond the ends of said core means and having holes drilled through the top and bottom ends of said e1ectrode means beyond the extremities of said core means.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES New Apparatus Bushing, Anderson and Johnson,

Trans. A. I. E. E., vol. 71, part III, 1952. Copy in 174-31.1.