US3869589A

US3869589A - Vacuum interrupter including contacts having improved weld break characteristics

Info

Publication number: US3869589A
Application number: US416470A
Authority: US
Inventors: Richard L Hundstad
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1972-05-03
Filing date: 1973-11-16
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04

Abstract

A vacuum type circuit interrupter is provided having separable contacts. Each separable contact comprises multiple contact surfaces which are resiliently attached to the main body of the contact by contact surface supporting means. The contact surface supporting means are constructed so that if contact surfaces are welded and if force is applied to separate the contacts, a nonuniform stress distribution is set up in any weld at the contact surfaces. This stress concentration, due to the elastic bending of the contact surface supporting means, aids in breaking the weld and allowing the contacts to separate.

Description

United States Patent [1 1 Hundstad I 1 Mar. 4, 1975 i541 VACUUM INTERRUPTER INCLUDING CONTACTS HAVING IMPROVED WELD BREAK CHARACTERISTICS [75] Inventor: Richard L. Hundstad, Pittsburgh,

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Nov. 16, 1973 [21] Appl No.: 416,470

Related US. Application Data 1 nuat on of Sen Q- 9199211 1 1 12.

[52] US. Cl..., 200/144 B [51] Int. Cl. H0lh 33/66 [58] Field of Search 200/144 8 [56] References Cited UNITED STATES PATENTS 3.275.777 9/1966 Pflanz et a1. ZOO/144 B FORElGN PATENTS OR APPLICATIONS 1.143.829 2/1969 Great Britain 200/144 B 3/1966 Japan ZOO/144 B 9/1968 Switzerland 200/144 B Primary ExaminerRobert S. Macon Attorney, Agent, or FirmH. G. Massung [57] ABSTRACT A vacuum type Circuit interrupter is provided having separable contacts. Each separable contact comprises multiple contact surfaces which are resiliently attached to the main body of the contact by contact surface supporting means. The contact surface supporting means are constructed so that if contact surfaces are welded and if force is applied to separate the contacts, a non-uniform stress distribution is set up in any weld at the contact surfaces. This stress concentration, due to the elastic bending of the contact surface supporting means, aids in breaking the weld and allowing the contacts to separate.

4 Claims, 8 Drawing Figures 1 VACUUM INTERRUPTER INCLUDING CONTACTS I-IAVINGIMPROVED WELD lBREAK CHARACTERISTICS CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION The present invention relates to vacuum type circuit interrupters, and more particularly to the contact assembly which is a part of such vacuum interrupter. The

- contact assemblies disclosed utilize stress concentration to aid in breaking welds which might form when the vacuum interrupter is closed.

Vacuum type circuit interrupters generally comprise an evacuated insulating envelope with separable contacts disposed within the insulating envelope. The contacts are movable between a closed position in which the contacts are engaged and an open position where the contacts are separated and an arcing gap is established therebetween. An arc is initiated between the contact surfaces when the contacts move into or out of engagement while the circuit in which the interrupter is used is energized. When the contacts are brought together the arc that is formed melts some of the metallic contact material. After the contacts are brought into high pressure engagement welds may be formed between the contact surfaces due to the melted contact material formed during arcing. The magnitude of the force required to break the welds so that the contacts can be opened depend upon many factors including the arc voltage, the current, the contact area and the contact material. These welds are objectionable since they interfere with the easy movement of the separable contacts and may result in the vacuum interrupter failing to open.

It is felt that the present invention has significant advantages over prior art methods of weld breaking such as disclosed in US. Pat. No. 3,591,742 issued July 6, 1971 in which an asymmetrical contact support means was disclosed and US. Pat. No. 3,591,743 in which the contact surface was located adjacent the outer periphery of the contact in order to obtain the maximum lever arm to pry the contacts apart.

SUMMARY OF THE INVENTION This invention discloses contact constructions which effectively use stress concentration to aid in weld breaking. In the present invention contact surfaces are supported by contact surface support means which are resiliently attached to the body of the contacts. The contact surface support means are constructed so that, if the contact surfaces are welded, as the contacts are pulled to sepparate a non-uniform stress distribution is set up in any weld at the contact surfaces. This stress concentration results from the elastic bending of the contact surface support means. The method of weld breaking taught in the present invention is applicable for all contact materials but is most effective on relatively brittle contact materials.

In one embodiment of the invention the main contact body is disc-shaped and multiple contact surfaces are attached to the disc-shaped contact body. The contact surfaces extend generally radially with respect to the center of the disc-shaped contact. The contact surfaces are generally shaped like a rectangular bar and are attached to the main contact body at an angle so that the contact surface support means are sloped from the disc-shaped contact .body. If a weld is present as contacts are separated the sloped contact surface support means tends to straighten out and as a result a nonuniform stress distribution is set up in any weld formed at the contact surfaces. The stress concentration results from the elastic bending of the sloped contact surface support means. Since each sloped contactsurface support means is independently able to flex the total number of contact points is increased. This increase in the number of contact points reduces the overall contact resistance. This embodiment of the invention has a large effective area for arc interaction, and it is known that current interruption ability increases with increased electrode area. Electrode area, however, is effective in the arc interruption process only if it is in intimate contact with the arc plasma. For this reason this embodiment of the invention is quite open to permit the desired interaction. The volumetric space between the sloped contact surface support means is greater than the volume occupied by the sloped contact support means. Increased contact area is known to be beneficial in arc interruption even though the extended contact area is somewhat removed from the contact surfaces. This beneficial effect is thought to partially result from the lower mean temperature of the electrode, due to the lower energy density in the contact and electrode. The relatively open construction of this embodiment also permits rapid expansion of the vapors and gases, formed during arc interruption, from the inner electrode space, so as to permit the vacuum to quickly recover its high dielectric strength.

In another embodiment of the present invention a pair of separable cup-shaped contacts are provided. Multiple contact surface support means extend radially inward from the lip of the cup-shaped contact. The contact surface support means extend substantially perpendicular to the sides of the cup-shaped electrode. The contact surfaces are attached to or made integral with the free ends of the contact support means. Although the contact construction of this embodiment looks considerably different from the first embodiment, the construction of the contact surface support means is similar so as to obtain stress concentration from the elastic bending of the contact surface support means. In this embodiment of the invention the angle between the contact surface and the contact surface support means is zero thereby producing the maximum stress concentration from elastic bending of the contact support means. Another advantage of this embodiment of the invention is that any are formed during circuit interruption is formed and contained within the arcing gap. Confining the arc to this inner electrode space is an important advantage since the arc is thereby prevented from interacting with the arc shield. It has been verified experimentally that current interruption limits are reached when the arc interacts with the arc shield. By a partial confinement of the arc, as taught by this embodiment of the invention, the volume of the vacuum interrupter can be used more effectively.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages of the present invention will be readily apparent upon reading the following description taken in conjunction with the drawings in which:

FIG. 1 is a vertical section of a vacuum type circuit interrupter embodying a contact construction of the present invention;

FIG. 2 is an isometric view of a contact embodying the teachings of the present invention;

FIG. 3 is a side view of a pair of contacts of the type shown in FIG. 2 in the closed position;

FIG. 4 is a representation of the portion of the contact structure shown in FIG. 3 with a uniform tensional stress distribution;

FIG. 5 is a view similar to FIG. 4 with a non-uniform tensional stress distribution resulting from bending;

FIG. 6 is a view similar to FIG. 4 showing the combined stress distribution resulting from combining the applied stresses in FIG. 4 and FIG. 5;

FIG. 7 is an isometric view of a contact used in the vacuum interrupter shown in FIG. 1; and

FIG. 8 is a side view, partially in section, of a pair of contacts in the closed position, of the type shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1, there is shown a vacuum type circuit interrupter 10 embodying the teachings of the present invention. The vacuum type circuit interrupter 10 comprises a highly evacuated envelope 12 formed of glass or suitable ceramic material and a pair of metallic end caps 14 and 16 closing off the end of the insulating envelope 12. Suitable seals 18 are provided between the end caps 14 and 16 and the insulating envelope 12 to render the envelope 12 vacuum tight. The vacuum in the envelope 12 under normal operating conditions is lower than 10' torr so that the mean free path of electrons will, be longer than the potential breakdown distance within the tubular envelope l2.

Disposed within the envelope 12 are a pair of relatively movable electrodes or

contacts

20 and 22 embodying the teachings of the present invention. As shown in FIG. 1 when these

contacts

20 and 22 are separated there is an arcing gap 24 formed therebetween. The upper contact 20 is stationary and is secured to a conducting rod 26 by a suitable means, such as welding or brazing. The conducting rod 26 is secured at its upper end to the stationary end cap 14 by suitable means, such as welding or brazing. The lower contact 22 is movable and is joined to a conducting operating rod 28. The conducting operating rod 28 is suitably mounted for movement along the longitudinal axis of the tubular insulating envelope 12. The movable operating rod 28 projects through an opening 30 in the bellows end cap 16. As shown in FIG. 1 a flexible metal bellows 32 is secured in sealing relationship at its respective opposite end to movable operating rod 28 and the opening 30 in the bellows end cap 16. The flexible metal bellows 32 provides a seal about the rod 28 to allow for movement of the rod 28 without impairing the vacuum inside the insulating envelope 12.

Coupled to the lower end of the operating rod 28 suitable actuating means (not shown) is provided for driving the movable contact 22 upward into engagement with the stationary contact 20 so as to close the interrupter 10. The actuating means is also capable of returning the contact 22 to its open position as as to open the interrupter 10. The circuit opening operation will for example entail a typical gap length when the contacts are fully separated of approximately k inch.

When

contacts

20 and 22 of a vacuum interrupter 10 are opened at the beginning of circuit interruption a metallic arc initiates between the separated

contacts

20 and 22 and serves as a vehicle for current conduction until the arc is extinguished. In an alternating current circuit the arc is usually extinguished near the first current zero of the alternating current wave. The are thatis established across the arcing gap 24 between the

contacts

20 and 22. when they are opened and also when they are closed vaporizes and melts some of the contact material. The vapors are dispersed from the arcing gap 24 towards the inside of the insulating envelope 12. The internal surfaces of the insulating envelope 12 are protected from the condensation of the are generated metallic vapor and particles thereon by means of a tubular metallic shield 36. The tubular metallic shield 36 is supported on the insulating envelope l2 and preferably electrically isolated from both end caps 16 and 14. This shield 36 acts to intercept and condense are generated metallic vapors before they can reach the insulating envelope 12. To reduce the chances of metallic vapor or particles bypassing the main shield 36 a pair of end shields 38 and 40 are provided at opposite ends of the central shield 36. A cupshaped shield 42 is attached to the movable operating rod 28 and surrounds the flexible metal bellows 32 to prevent the bellows 32 from being bombarded by the are generated metallic vapors or particles.

As previously discussed when the

contacts

20 and 22 are closed an arc is formed therebetween. This are may cause melting of the contact surfaces and upon high pressure engagement of the

contacts

20 and 22 contact welding can result.

Referring now to FIG. 2 of the drawings there is shown a vacuum interrupter contact 86. The vacuum interrupter contact 86 comprises a main body portion 88, multiple contact surfaces 90, and contact surface support means 92. The contact 86 is disposed within the insulating envelope 12 of a vacuum interrupter 10 with a mating contact 96 as shown in FIG. 2. The mating contact 96 is a mirror image of contact 86, through the plane in which the contact surfaces lie.

In the

contacts

86 and 96 shown in FIG. 3 the contact surface support means 92 are rectangular rod shaped portions which are attached to the main body portion 88 in a sloping relationship. If a weld is present at the contact surfaces 90 as the contacts are pulled to separate the sloped contact surface support means 92 tends to straighten out and asa result a non-uniform stress distribution is set up in the weld. This stress concentration results from the elastic bending of the contact surface support means 92 and aids in weld breaking.

Referring now to FIGS. 4, 5 and 6 there is shown contact surface support means 92 sloped at an angle 0 from the plane in which the contact surfaces 90 lie. In FIGS. 4, 5 and 6 the upward pointing arrows 98 represent tension forces and the downward pointing arrows 99 represent compression forces. FIG. 4 shows a uniform tensional stress distribution due to a force tending to pull the contact surfaces apart. This is the force that would result if the contact surface support means are rigidly attached to the main body portion 88 so that no bending or flexing of the

contacts

86 and 96 was possible. If the contact surface support means 92 can elastically bend a non-uniform tensional stress distribution results, the portion due to the bending moment is shown in FIG. 5. This bending moment portion of the non-uniform tensional stress distribution which results from the elastic bending of the contact surface support means combines with the uniform tensional stress distribution and the actual combined resulting stress distribution on the welded contact surfaces is as shown in FIG. 6. As the

contacts

86 and 96 are pulled to separate the sloped contact surface support means 92 tend to straighten out and as a result the non-uniform stress distribution is set up in any weld at the contact surfaces.

In tending to straighten out the sloped contact surface support means 92 are subjected to a combined axial tension and bending moment both of which are resisted by welds at the contact interface. As shown in FIG. 6 the stresses combine to aid in weld breaking. The contact 86 has several other advantages besides the weld breaking feature, such as increased contact area and an open construction to permit arc plasma interaction with this increased contact area. The open construction also permits rapid diffusion of any metallic vapors produced during arcing. Another advantage of this embodiment is that the resilient contact surface support means 92 allows each contact surface 90 to flex independently thereby permitting an increase in the total number of contact points. This increased number of contact points results in a lower overall contact resistance.

It should be noted that if the angle 0, as shown in FIGS. 4, 5 and 6, is zero the maximum tensile stress concentration is achieved. Another embodiment of the invention is shown in FIGS. 7 and 8 in which the angle 0 between the contact surface support means 50 and the plane in which the contact surfaces 54 lie is zero. The contact 22, as shown in FIG. 7, is generally cupshaped in configuration with multiple contact surface support means 50 extending radially inward from the main body cup-shaped portion 52. Contact surfaces 54 are attached to the free end of the contact surface support means 50, by suitable means such as welding or brazing. The contact surface support means 50 are constructed so that ifa weld is present between the contact surfaces 54 when the contacts and 22 are separated stress-concentration at the weld will result. This stress concentration results from the elastic bending of the contact surface support means 50. Note that

contacts

20 and 22 as shown in FIG. 1 and FIG. 8 are identical.

The embodiment of the invention shown in FIG. 7 has several advantages besides the stress concentration feature discussed hereinbefore in detail. It has the advantage of establishing many contact points due to the resilience of the contact surface support means 50. This embodiment of the invention also has the advantage of containing any are formed during circuit interruption to the arcing gap 24 thereby preventing it from interacting with the arc shield 36. The are is contained within the inner contact space due to the magnetic inward force from the current flow.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A vacuum type circuit interrupter comprising:

a highly evacuated tubular insulating envelope;

a first contact structure disposed within said tubular insulating envelope;

a second contact structure disposed within said tubular insulating envelope being movable between a first position in contact with said first contact structure and a second position spaced from said first contact structure to establish an arcing gap therebetween across which an arc is formed during circuit interruption;

said first contact structure comprising a main body portion having a flat circular cross sectional configuration, a plurality of support means attached to said flat planar main body portion in a spaced apart generally circular configuration each extending radially inward from the circumference of said main body portion, a contact surface formed at the free end of each of said support means being separated from other contact surfaces by a sufficient distance so as to inhibit arc movement therebetween, each of said plurality of support means extending from said flat circular body portion at an acute angle with said flat circular body portion, each of said plurality of support means being separated from every other support means by a circumferential spacing which is dependent on the radial position and decreases as the radial position decreases; and,

said second contact structure being a mirror image of said first contact structure.

2. A vacuum type circuit interrupter as claimed in claim 1 wherein:

each of said support means are separated by a substantial air space; and,

said air space within the confines of said contact structure occupying a volume greater than the volume occupied by said support means.

3. The combination as claimed in claim 2, wherein:

said support means are resilient so that if a weld exists, as the contact surfaces as said second contact is moved from said first position to said second position elastic bending of said support means will occur whereby stress concentration at the weld will result.

4. A vacuum type circuit interrupter comprising:

a highly evacuated tubular insulating envelope;

a first contact structure disposed within said tubular insulating envelope;

said first contact structure comprising a main body portion having a flat circular cross sectional configuration, a plurality of support means attached to said flat planar main body portion in a spaced apart generally circular configuration each extending radially inward from the circumference of said main body portion, a contact surface formed at the free end of each of said support means being separated from other contact surfaces by a sufficient distance so as to inhibit arc movement, each of said plurality of support means extending from said flat circular said support means are resilient so that if a weld exists at the contact surfaces as said second contact is moved from said first position to said second position elastic bending of said support means will occur whereby stress concentration at the weld will result;

said main flat body portion is slotted and said plurality of support means fit in the slots in said main body portion.

Claims

1. A vacuum type circuit interrupter comprising: a highly evacuated tubular insulating envelope; a first contact structure disposed within said tubular insulating envelope; a second contact structure disposed within said tubular insulating envelope being movable between a first position in contact with said first contact structure and a second position spaced from said first contact structure to establish an arcing gap therebetween across which an arc is formed during circuit interruption; said first contact structure comprising a main body portion having a flat circular cross sectional configuration, a plurality of support means attached to said flat planar main body portion in a spaced apart generally circular configuration each extending radially inward from the circumference of said main body portion, a contact surface formed at the free end of each of said support means being separated from other contact surfaces by a sufficient distance so as to inhibit arc movement therebetween, each of said plurality of support means extending from said flat circular body portion at an acute angle with said flat circular body portion, each of said plurality of support means being separated from every other support means by a circumferential spacing which is dependent on the radial position and decreases as the radial position decreases; and, said second contact structure being a mirror image of said first contact structure.

2. A vacuum type circuit interrupter as claimed in claim 1 wherein: each of said support means are separated by a substantial air space; and, said air space within the confines of said contact structure occupying a volume greater than the volume occupied by said sUpport means.

3. The combination as claimed in claim 2, wherein: said support means are resilient so that if a weld exists, as the contact surfaces as said second contact is moved from said first position to said second position elastic bending of said support means will occur whereby stress concentration at the weld will result.

4. A vacuum type circuit interrupter comprising: a highly evacuated tubular insulating envelope; a first contact structure disposed within said tubular insulating envelope; a second contact structure disposed within said tubular insulating envelope being movable between a first position in contact with said first contact structure and a second position spaced from said first contact structure to establish an arcing gap therebetween across which an arc is formed during circuit interruption; said first contact structure comprising a main body portion having a flat circular cross sectional configuration, a plurality of support means attached to said flat planar main body portion in a spaced apart generally circular configuration each extending radially inward from the circumference of said main body portion, a contact surface formed at the free end of each of said support means being separated from other contact surfaces by a sufficient distance so as to inhibit arc movement, each of said plurality of support means extending from said flat circular body portion at an acute angle with said flat circular body portion; said second contact structure being a mirror image of said first contact structure; each of said support means are separated by a substantial air space; said air space within the confines of said contact structure occupying a volume greater than the volume occupied by said support means; said support means are resilient so that if a weld exists at the contact surfaces as said second contact is moved from said first position to said second position elastic bending of said support means will occur whereby stress concentration at the weld will result; said main flat body portion is slotted and said plurality of support means fit in the slots in said main body portion.