US3783182A

US3783182A - Electrical bushing assembly having a direct cable to conductor rod terminal assembly

Info

Publication number: US3783182A
Application number: US00289403A
Authority: US
Inventors: W Horton
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1972-09-15
Filing date: 1972-09-15
Publication date: 1974-01-01
Anticipated expiration: 1991-01-01

Abstract

Bushing apparatus including a terminal assembly suitable for use with large currents. The terminal assembly clamps an electrical cable directly to the conductor rod of the bushing. The conductor rod extends through an opening in the terminal assembly with the end of the conductor rod positioned flush with the inside of the terminal assembly. Current flowing from the cable to the conductor rod does not appreciably flow through the terminal assembly.

Description

Jan. 1, 1974 United States Patent [191 Horton, III

2,370,288 2/1945 Brolinson.................... 174/152 R X ELECTRICAL BUSHING ASSEMBLY FOREIGN PATENTS OR APPLICATIONS mmm nl. m W Mn m 0a mmm 0 CGL 306 566 999 mmw 563 8002 O OQ 425 223 HAVING A DIRECT CABLE TO CONDUCTOR ROD TERMINAL ASSEMBLY [75] Inventor: William E. Horton, III, Bogart, Ga.

783,796 4/1935 France.............................. 174/75 R Primary Examiner-Laramie E. Askin Att0rney-A. T. Stratton et a].

[22] Filed:

n -Se- H... C Hm w m m xn mn .WIa Xflt bflc w u u m edyuuw eiho w fim fb fl aro m m i o u a t n ne ma m m wm T r wnmn C mmhdw fm. A wh efi mw R rbht Tmmw e m e m s A cw mmm nr. n. ml atsg a S Un n hh u te m 3 6 r. MmWn D- e atomw wmm mm m m hlhtt .mmmm m lh w 7 S] d 5 [Babttes R MD R 2 2 2 522 7%7 ,7W 2 22 b 991R0 3 25 3 5 3 H7 3 m6 W R2 n 4 R 9 3 ./33 3 4.,6 "NR 5 u a .3 M UN "14 4 mm m mm "m C m m m.U4 r a m wu mSl 1.. n C G M7l 2 m U hr. 2 N 5 55 [5 References Ci the cable to the conductor rod does not appreciably UNITED STATES PATENTS flow through the terminal assembly.

498,407 5/1893 Rich.............. 339/272 A X 1 Claim, 3 Drawing Figures ELECTRICAL BUSHING ASSEMBLY HAVING A DIRECT CABLE TO CONDUCTOR ROD TERMINAL ASSEMBLY BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates, in general, to electrical bushing assemblies and, more specifically, to connector terminals for electrical bushing assemblies.

2. Description of the Prior Art Connector terminals are mounted on top of electrical bushings to provide means for connecting an electrical cable to the bushing. Generally, the terminal conducts current from the cable to a conductor rod or lead which extends through the bushing. To prevent possible destructive power losses in the connector terminal, the resistance of the portion of the connector terminal through which the current passes must be low enough to safely carry the rated current. I

Connector terminals also provide a fixture in which the electrical cable is suitably clamped into position. Tosatisfactorily provide this function, the connector terminal must be constructed of a material having mechanical properties suitable to provide sufficient rigidity to the connector terminal when the cable is clamped. Copper is generally used as the material for the conductor rod. An alloy of copper is generally used as the material for the connector terminal to enhance the mechanical properties thereof.

Typical copper alloys have a conductivity of approximately 20 percent that of pure copper. In some applications, the difference in resistance of the conductor rod and the connector terminal does not present significant problems. Heat sink effects and design safety factors have permitted the use of conventional connector terminals in bushings for moderately rated apparatus, such as distribution transformers. However, when the rating of the transformer becomes relatively large, such as 500 KVA at 2,400 volts, conventional connector terminals are unsatisfactory. At the large power ratings, the portion of the connector terminal which conducts the current disintegrates upon the application of power. During short circuit conditions when the current is approximately 30 times the rated current, de struction occurs within a few 'cycles after being energized, thus heat sink effects are not effective in protecting the connector terminal from overheating.

Therefore, it is desirable, and it is a first object of this invention, to provide an electrical bushing assembly wherein the connector terminal thereof does not present a region of relatively high resistance in the path of the current flowing through the bushing. It is also desirable, and it is a second object of this invention, to provide a connector terminal which provides the first objective without decreasing the mechanical strength of the connector terminal.

SUMMARY OF THE INVENTION There is disclosed herein new and useful electrical bushing apparatus suitable for use at high current levels. The bushing includes an insulator with an opening extending therethrough. A conductor rod is positioned within the insulator opening and is attached to a terminal assembly. The terminal assembly is constructed with anopening through its lower portion. The conductor rod extends through the opening in the terminal assembly with the end of the conductor rod positioned in flush relationship with the inside of the terminal assembly. An electrical cable is forced against the end of the conductor rod by a shoe member attached to a rotatable threaded shaft.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will be come more apparent when considered in view of the followinging detailed description and drawing FIG. 1 is an elevational view of an electrical bushing assembly constructed according to this invention with a portion thereof enlarged for clarity;

FIG. 2 is a view of the enlarged portion of FIG. 1 constructed according to a prior art arrangement; and

FIG. 3 is a perspective view showing components of the bushing assembly of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all the figures of the drawing.

Referring now to the drawing, and FIG. 1 in particu lar, there is shown an elevational view of an electrical bushing assembly constructed according to this invention with a portion thereof enlarged for clarity. The bushing assembly includes an insulator 1 which is constructed of an insulating material and which contains a substantially longitudinal opening 12 extending therethrough. The sealing plug 14 is constructed of a rubber material and is compressed within the opening 12. The insulator includes the shoulder region 16 which seats on the mounting surface 18, such as a transformer enclosure, with a sealing gasket 20 positioned therebetween. Bushing retaining or fastening means for securing the bushing to the surface 18 is not illustrated.

A longitudinal conductor rod 22 is positionedin the opening 12 and is constructed of a good electrical conducting material, such as copper. The first end of the conductor rod 22 is attached to the terminal assembly 24. The second end 25 of the conductor rod 22 provides means for connecting the rod 22 to the associated electrical circuit components, either directly or through protective devices such as a protective link.

The cap 26 is attached to the terminal assembly 24 and is formed around the flared projection 28 of the insulator 10. A method of forming the cap 26 is disclosed in US. Pat. No. 3,258,523 which is assigned to the same assignee as is this invention. The terminal assembly 24 also includes a knob 30, a threaded shaft 32 which may be rotated by the knob 30, and a shoe 34 which is attached to the lower end of the shaft 32. The shaft 32 extends through a threaded opening 36 in the terminal assembly 24 and moves the shoe 34 down against the electrical cable 38 when the knob is rotated. Thus, the cable 38 may be forced against the base portion 40 of the terminal assembly 24. A projection 42 from the terminal assembly 24 provides a lightning gap with the grounded rod 44. The terminal assembly 24 is constructed of a suitable material, such as an alloy of copper having a conductivity approximately equal to 20 percent that of pure copper.

The enlarged portion of FIG. 1 shows the connection of the terminal assembly 24 to the conductor rod 22 in greater detail. The base portion 40 of the terminal assembly 24 has an upper surface 46 and a lower surface 48. A threaded opening 50 extends through the base portion 40. The lower surface 48 is secured to the cap 26 by suitable means, such as by the brazing material 52.

The region 54 of the conductor rod 22 which is located adjacent to the first end 56 of the conductor rod 22 is threaded to permit insertion into the opening 50. The conductor rod 22 is positioned with its first end 56 substantially flush with the upper surface 46. This permits current flowing from the cable 38 to enter the conductor rod 22 directly without requiring the conduction of substantial current through the base portion 40 of the terminal assembly 24. Suitable means, such as the brazing material 58, may be used to provide a secure fit between the terminal assembly 24 and the conductor rod 22.

FIG. 2 illustrates the circled portion shown in FIG. 1 as it would be constructed according to the prior art. The terminal assembly 60 includes a lower projection 62 which contains a threaded opening 64. The threaded portion 55 of the conductor rod 22 is positioned within the opening 64. Current flowing from the cable 38 must pass through the walls of the projection 62 to the conductor rod 22. Since the resistivity of the material comprising the projection 62 must be approximately five times as much as that of the conductor rod 22 to provide a mechanically rigid terminal assembly 60, excessive heat is generated in the projection 62 unless the cross-sectional area thereof is increased.

FIG. 3 is an exploded view showing several components of a bushing assembly constructed according to this invention. The lip 66 of the lower surface 48 extends through the opening 68 in the cap 26. Brazing material may be conveniently applied by placing a washer formed from brazing material around the lip 66 prior to insertion of the conductor rod 22.

The novel bushing assembly taught by this invention permits the use of a terminal assembly which does not have a relatively large lower projection for connection to a conductor rod. This permits the use of standard components in bushings suitable for high current ratingsr Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting.

I claim:

1. An electrical bushing assembly comprising an insulator having a substantially longitudinal opening therethrough and a flared projection thereon, terminal means constructed of a first electrically conductive material and having a base portion with an opening extending from an upper surface to a lower surface of said base portion, a cap brazed to said lower surface, said cap being formed around said flared projection, a longitudinal conductor rod having first and second ends and constructed of a second electrically conductive material, said conductor rod being positioned in the opening through said insulator with the first end of said conductor rod extending into the opening in and connected to said base portion, with the first end of said conductor rod substantially flush with said upper surface, and means attached to said terminal means for forcing an electrical cable against the first end of said conductor rod, said first conductive material having a lower conductivity and greater mechanical strength than said second conductive material.