US3667871A

US3667871A - Contact structures for vacuum-type circuit interrupters having radially outwardly-extending spokes

Info

Publication number: US3667871A
Application number: US797930A
Authority: US
Inventors: Richard L Hundstad
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-02-10
Filing date: 1969-02-10
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: AT294964B; GB1291045A; DE2003781A1; CH503365A

Abstract

THE CONTACT STRUCTURE OF A VACUUM-TYPE CIRCUIT INTERRUPTER IS PROVIDED WITH RADIALLY-OUTWARDLY EXTENDING SPOKES, OR CONTACT BARS, EXTENDING OUTWARDLY FROM A CENTRAL PRIMARY CONTACT REGION. THE ARC IS INITIATED AT THE PRIMARY CONTACTING SURFACES ADJACENT THE CENTRAL POINT OF THE SEPARABLE CONTACT STRUCTURE, AND, BECAUSE OF THE PROVISION OF THE OUTWARDLY EXTENDING SPOKES, THE ARC IS MOVED OUTWARDLY TO THE ARC-DISSIPATION SURFACES WHICH EXTEND TO THE OUTER PERIPHERY OF THE CONTACTS. THE ARC IS RAPIDLY MOVED OUTWARDLY, AND THE PRIMARY ARCING SURFACES ARE THEREBY PREVENTED FROM BECOMING ERODED.

Description

June 7 R. L. HUNDSTAD 3, 67, 7

CONTACT STRUCTURES FOR VACUUM-TYPE CIRCUIT INTERRUPTERS HAVING RADIALLY OUTWARDLY-EXTENDING SPQKES Filed Feb. 10, 1969 H/JE I FIG.2. 18 I :0 l2 4 l9 /I9 FIG. I. I Z

Q B .9 FIG. 3.

WITNESSES: NVENTOR Richard L. Hundstod 3,667,871 CONTACT STRUCTURES FOR VACUUM-TYPE CIRCUIT INTERRUPTERS HAVING RADIALLY OUTWARDLY-EXTENDING SPOKES Richard L. Hundstad, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa. Filed Feb. 10, 1969, Ser. No. 797,930

Int. Cl. H01h 33/66 US. Cl. 200-144 B 12 Claims ABSTRACT OF THE DISCLOSURE CROSS REFERENCES TO RELATED APPLICATIONS Applicant is not aware of any related applications pertinent to the present invention.

BACKGROUND OF THE INVENTION It has been customary in the design of vacuum-type circuit interrupters to provide a primary arcing region at which the arc is initially established, and a secondary United States Patent "Ice arcing region, or arc-dissipation surface at which the arc is moved until extinction takes place. United States Pat. 3,182,156 issued May 4, 1965 to Lee et a1. illustrates a prior-art construction of this general nature.

The primary electrode contact surfaces of conventional circuit interrupters, i.e., the surfaces which conduct the current from one electrode to another during normal steady state operation, are subjected to very intense heat while performing their function during a current inter ruption. The electrode surface must support the arc from its initiation at the time the electrodes open until its extinction at approximately zero current. This are energy causes melting, erosion and general deterioration of the surfaces. 'The construction set forth in the aforesaid United States patent partially circumvents this problem by providing primary surfaces for conducting the current during normal steady'state operation, and additional surfaces surrounding the primary surfaces for arc-energy dissipation during an interruption. According to the apparent theory of operation, the arc'is driven from the primary surfaces following initiation and then rotates on the energy-dissipation surfaces until extinction takes place. Spiral slots in the energy-dissipation surfaces cause the are to spiral radially outwardly under the influence of the jXB forces. The spiral slots also provide a cusp-type magnetic field, which causes the arc to rotate under the influence of the jXB forces. Many experimental tests of vacuum switches embodying the foregoing construction have shown that the design is only partially successful. It appears that the spiral slots, although quite effective in rotating the arc, do not confine the intense heat release and resulting deterioration to the energy dissipation surfaces. General, deterioration of all adjacent surfaces results.

Electrodes for vacuum-type circuit interrupters of the construction set forth in the aforesaid patent are not very elfective in providing:' the; necessary jxBforces to g 3,667,871 Patented June 6, 1972 move the arc radially outwardly and away from the contact surfaces. The conically-shaped energy dissipation portion of the electrodes, which extend radially outwardly from the contact surfaces, have a large cross-sectional area through which the current may flow radially outwardly. As a result, the current densities are low, and the self-induced magnetic fields are small, distributed, and ineffective in forcing the are from the contact surfaces.

SUMMARY OF THE INVENTION According to the present invention, the contact construction'for a vacuum-type circuit interrupter is provided having primary and secondary, or arc-dissipation surfaces. The are is initially established at the primary contact surfaces, and then is moved radially outwardly to the arcdissipation surfaces, and arc extinction occurs at these latter secondary surfaces.

The construction according to the present invention has spokes, or radially-outwardly-extending contact bars which extend from the primary contact surfaces, and these spokes are purposely made smallv in cross-sectional area adjacent to the primary contact button so as to concentrate the self-induced magnetic fields as well as the arc columns and, thereby, effectively provide the necessary j B forces to move the arc radially outwardly and away from the primary contact surfaces.

Accordingly, it is a general object of the present invention to provide an improved contact construction for a vacuum-type circuit interrupter.

A morespecific object of the present invention is to provide an improved contact, or electrode construction for a vacuum-type circuit interrupter utilizing primary contact surfaces and outwardly-extending spokes, or contact bars, which move the initially established are outwardly away from the primary contact surfaces.

Still a further object of the present invention is the provision of an improved electrode or contact construction for a vacuum-type circuit interrupter in which primary contact surfaces are provided of one material, and the secondary orarc-dissipation surfaces are provided utilizing another contact material. 7

According to a preferred embodiment of the invention, a vacuum-type circuit interrupter has separable contacts, at least one of which uses, preferably, a generallydiscshaped primary contact surface of one material, such as a copper-bismuth alloy, and spokes or contact bars, which extend radially outwardly from the primary contact surfaces, and the secondary contact surfaces are preferably formed of a difierent contact material, such as pure copper, for example.

Further objects and advantages will readily become apparent upon reading the following specification taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of a vacuum-type circuit interrupter embodying the contact construction of the present invention the contacts being shown in full lines in the open-circuit position;

FIG. 2 is a detailed side elevational view taken of the contact structure of FIG. 1 in an initial stage of the opening operation;

FIG. 3 is a view similar to that of FIG. 2, but illustrating the arc position at a later point of time during the opening operation;

FIG. 4 is a plan view of one of the contacts drawn to an enlarged scale;

FIG. 5 is a sectional view taken along the line VV of FIG. IV; and, I

FIG. 6 is a plan view of the primary contact button prior to assembly.

When the electrodes of a vacuum switch are opened at the beginning of a given interruption, a metallic arc initiates between the separating electrodes, and serves as a vehicle for current conduction until the normal alternating current cyclic variation of current drops the magnitude of the current below the chopping current. At this value of current, the mechanisms which cause the arc to extinguish predominate over those, which sustain the arc, and it goes out. Because of the high-power density impressed upon the electrodes during the conduction interval, substantial erosion takes place, and it is, therefore, desirable to move the established arc outwardly away from the primary contacting surfaces.

Referring now to the vacuum interrupter of FIG. 1, there is shown a highly-evacuated envelope 1 comprising a casing 2 of suitable insulating material, and a pair of metallic end caps 3 and 4 closing off the ends of the casing. Suitable seals 5 are provided between the end caps and the casing to render the envelope vacuum-tight. The normal pressure within the envelope 1 under static conditions is lower than torr; so that reasonable assurance is had that the mean free path for electrons will be longer than the potential breakdown paths within the envelope.

Located within the envelope 2 is a pair of relatively movable disk-shaped contacts or

electrodes

7 and 8 shown in full lines in their separated or open-circuit position. When the contacts are separated, there is an arcing gap 9 located therebetween. The upper contact 7 is a stationary contact suitably secured to a conductive rod 10, which at its upper end is united to the upper end cap 3. The lower contact 8 is a movable contact joined to a conductive operating rod 11, which is suitably mounted for movement. The operating rod 11 projects through an opening 12 in the lower end cap 4, and a flexible metallic bellows 13 provides a seal about the rod 11 to allow for movement of the rod without impairing the vacuum inside the envelope 2. As shown in FIG. 1, the bellows 13 is secured in sealing relationship at its respective opposite ends to the operating rod 11 and to the end cap 4.

Coupled to the lower end of the operating rod 11, suitable actuating means (not shown) is provided for driving the movable contact 8 upwardly into engagement with the stationary contact 7 so as to close the interrupter. The closed position of the movable contact is indicated by the dotted line 14. The actuating means is also capable of returning the contact 8 to its illustrated solid-line open position so as to open the interrupter. A circuit-opening operation will, for example, entail a typical gap length, when the contacts are fully separated, of perhaps /2 inch.

The are (indicated at 15) that is established across the gap 9 between the electrodes, as the electrodes are opened and also when they are closed, vaporizes some of the contact material, and these vapors are dispersed from the arcing gap 9 toward the envelope 2. In the illustrated interrupter, the internal insulating surfaces of the casing 2 are protected from the condensation of arc-generated metallic vapor and particles thereon by means of a tubular metallic shield 16 suitably supported on the casing 2 and preferably isolated from both end caps 3 and 4. This shield 16 acts to intercept and to condense arc-generated metallic vapors before they can reach the casing 2. To reduce the chances for vapor bypassing the shield16, a pair of end shields 17 and 18 are provided at opposite ends of the central shield 16.

With particular attention being directed to FIG. 4 of the drawing, it will be observed that there is provided a contact, or electrode 8 which has radially-outwardlyextending spokes, or contact bars 19. With attention being area of the spoke, or contact bar at its outward periphery 19b. Although only six spokes or contact bars 19 are shown, there may be more or less depending on the current rating of the vacuum-interrupting device.

It is particularly desirable to provide the contact area of a highly efficient conducting material, which has a relatively low weld strength, such as a copper-bismuth alloy, such as set forth in United States patent Lee et al. 2,975,256.

To facilitate the manufacture of a composite-type electrode or

contact structure

7, 8, it is desirable to machine, or otherwise provide a recess 21 (FIG. 5) within the body of the secondary contact 8b to accommodate the primary contact surface 8a, which is shown separately in FIG. 6 of the drawings. The two parts 8a, 8b may be secured together, as by a brazing operation.

With reference to FIG. 2, it will be observed that the arc, which is initially established, is formed at the

primary contact surfaces

7a, 8a, and is designated by the reference numeral 16. Soon thereafter, by virtue of the magnetic forces, the initially-established are 15 is moved outwardly along the spoke, or contact bar surfaces 19 to the outer edges of the secondary contacts, where are extinction takes place.

The construction proposed by the present invention alleviates the problem of general deterioration by effectively confining the arc and resultant melting to the en ergy-dissipation surfaces. The proposed construction has spokes extending from the contact surfaces, and these spokes are purposely made small in cross-sectional area adjacent to the primary contact surface so as to concentrate the self-induced magnetic fields as well as the arc columns, and thereby effectively provide the necessary jXB forces to move the arc radially outwardly and away from the primary contact surfaces.

Experimental tests have conclusively demonstrated that regardless of the phenomena utilized, that the initiallyestablished arc is moved rapidly outwardly to the secondary arc dissipation surfaces because of the self-induced magnetic effects. The result is less erosion of the contact structures, and a greater operational life of the circuitinterrupting device as a whole.

For certain applications, the center primary contact button may be made of a copper-bismuth alloy, such as, for example, 99.7% copper and .3% bismuth by weight. In this event, it is desirable to have the outwardly extending spokes or contact bars made of pure copper.

Although it has been suggested that different materials be used for the primary and secondary contact surfaces, for certain applications this may not be absolutely essential, and, as a cost-reduction feature, the same material may be used for both the primary and secondary contact surfaces.

The spoke portions 19 of the two contacts need not be axially or longitudinally aligned, but better results are achieved if they are in longitudinal alignment as shown directed to the plan view of FIG. 4 of one of the elec- I trodes 8, it will be noticed that the cross-sectional area at the hub portion 19a is less than the cross-sectional in the drawing.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for thepurpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, 'without departing from the spirit and scope of the invention.

I I claim as my invention: 1

1. A vacuum-type circuit interrupter including, in combination: (a) means defining an evacuated envelope; (b) a pair of separable contacts disposed within the I evacuated envelope separable to establish arcing; (0) at least one of the separable contacts including a central primary contact portion and a plurality of circumferentially spaced radially-outwardly-extending conducting spoke portions emanating only radial- 1y outwardly from said central primary contact portion and connected thereto,

(d) whereby upon separation of said contacts current flow through said central contact portion and said spokes, by virture of magnetic forces, moves an are established on said central portion exclusively radially outwardly onto one of said spoke portions whereby vaporized metal will be free to disperse radially and axially of said spoke portion.

2. The combination of claim 1, wherein the confronting surfaces of the spoke portions are displaced rearwardly from the confronting surfaces of the associated primary contact portion.

3. The combination of claim 1, wherein the crosssection of the individual spoke portions are rectangular.

4. The combination of claim 1, wherein the cross-sectional area of the inner portion of the spokes is less than the outer portions of the spoke portions.

6. The combinations of claim 1, wherein the primary contact portion and the spoke portions are made of different contact materials with the primary contact portion having a lower chopping current value.

'6. The combination of claim 1, wherein the primary separable contacts each has a central primary contact portion and a plurality of radially-cutwardly-extending conducting spoke portions emanating radially outwardly from said central primary contact portion and connected thereto.

7. The combination of claim 1, wherein the central primary contact portion is disk-shaped and has a central recessed portion.

8. The combination of claim 3, wherein the cross-sectional area of the inner portion of the spokes is less than the outer portions of the spoke portions.

9. The combination of claim 1, wherein six (6) spoke portions are utilized, and the width of the inner ends of the spoke portions is substantially equal to the spacing between the inner ends of the spoke portions.

10. The combination of claim 1, wherein the length (L) of the spoke portions is substantially equal to the radius (R) of the central primary contact portion.

11. The combination according to claim 6, wherein the spoke portions are in longitudinal alignment.

12. The combination of cl m 1, wherein the central primary contact region has a recess portion.

References Cited UNITED STATES PATENTS 3,218,426 11/1965 Montoya et a1. 200-466 B 3,462,572 8/1969 Sofianek 200-166 B8 X FOREIGN PATENTS 1,456,423 9/1966 France 200144.2

460,122 9/ 1968 Switzerland 200144.2

ROBERT S. MACON, Primary Examiner