US3462572A

US3462572A - Vacuum type circuit interrupter having contacts provided with improved arcpropelling means

Info

Publication number: US3462572A
Application number: US583808A
Authority: US
Inventors: Joseph C Sofianek
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1966-10-03
Filing date: 1966-10-03
Publication date: 1969-08-19
Anticipated expiration: 1986-08-19
Also published as: CH471455A; DE1640256A1; DE1640256B2; SE339258B; FR1540090A; GB1161442A; JPS4529935B1

Description

llg- 19, 1959 J. c. SOFIANEK 3,462,572

VACUUM TYPE CIRCUIT INTERRUPTER HAVING CONTACTS PROVDED WITH IMPROVED AHCPROPELLING MEANS l Filed oct. s, 196e /NvE/vTo/e: JOSEPH C. oF/A/vE/f,

ay Mza@ M ATTORNEY United States Patent O VACUUM TYPE CIRCUIT INTERRUPTER HAVING CONTACTS PROVIDED WITH IMPROVED ARC- PROPELLING MEANS Joseph C. Solianek, Broomall, Pa., assignor to General Electric Company, a corporation of New York Filed Oct. 3, 1966, Ser. No. 583,808 Int. Cl. H0111 9/30, 33/00, 9/44 U.S. Cl. 20G-144 10 Claims ABSTRACT F THE DISCLOSURE Discloses a vacuum-type circuit interrupter comprising a pair of disc-shaped contacts, each having a face confronting the other. The usual arc is rotated on said faces by means comprising slots in the `disc-shaped members extending radially and circum-ferentially thereof. Each contact comprises a centrally-located contact-making button. The slots in each contact extend radially inwardly past the outer periphery of the associated button and are bridged near their inner end by said button.

This invention relates to a vacuum-type circuit interrupter, and, more particularly, to contact structure for such an interrupter that is capable of handling very high currents.

The invention is concerned with the general type of contact structure shown and claimed in U.S. Patent 2,949,520-Schneider, assigned to the assignee of the present invention. The contact structure of the Schneider patent comprises a disc-shaped member having a plurality of slots therein extending both radially and circumferentially of the disc member. These slots are used to produce an arc-rotating effect that `forces arcs having a terminal located on the slotted portion of the disc member to revolve about the central axis of the disc member. Centrally of the disc member there is a contact-making region where arcs are initiated during circuit-interrupting operations. Such an a-rc is magnetically driven radially outward off of the contact-making region; and as it approaches the outer periphery of the disc member, it is rotated by the arc-rotating action produced by the slots in the disc member.

The arc-rotation that results from the slots has been found to increase the amount of current that can be interrupted by contacts of a given diameter.

One Ifactor that seems to limit the amount of current that can be interrupted 'by contacts of the type shown in the Schneider patent is that under certain conditions, not fully understood, the normally rapidly-moving are terminal may stall near the inner end of a slot. This can result in excessive heating and erosion of the contact material in this localized region, and this seems to detract from the interrupting ability, as well as the life span, of the contacts.

An object of the present invention is to materially reduce this tendency of the arc to stall and produce excess erosion at the inner end of a rotation-producing slot in such a contact.

A disc-shaped contact with slots of the general type described above may be thought of as comprising a plurality of radially and circumferentially extending ngers respectively bounded by adjacent pairs of slots. The amount of arc-rotating force that will be developed on an arc located near the outer periphery of a contact varies directly with the effective length of these iingers. The diameter of the disc-shaped contact can be increased to increase the effective length of the ngers, but typically there are other design considerations that limit the maximum permissible diameter of the contacts.

3,462,572 Patented Aug. 19, 1969 lCC Accordingly, another object of the invention is to construct the contacts in such a manner that lingers of increased length can be provided in a contact of limited diameter.

Still another object is to achieve this increased finger length without detracting from the ability of the contact to cause rapid movement of the arc radially youtward off of the arc-initiation region.

In carrying out the invention in one form, I construct at least one of the two contacts of the vacuum interrupter of a disc-shape having a face confronting the other contact on which an arc is adapted to be located during circuit interruption. The arc is rotated on the face of the disc-shaped member by means comprising a plurality of slots in said disc-shaped member extending radially and circumferentially thereof. The contact also comprises a contact-making button joined to said face for engaging the other contact when the interrupter is closed. The contact-making button is generally centrally located with respect to its associated contact and has an outer periphery radially spaced from the outer periphery of the discshaped member. The slots respectively extend from an outer end location located radially outward of said contact-making button to an inner end location disposed radially inwardly of the outer periphery of and under the button. The contact-making button bridges over the slots near said inner end locations.

For a better understanding of the invention, reference may be had to the following `description taken in conjunction with the accompanying drawings, wherein:

FIG. l is a sectional side elevational view of a vacuum interrupter embodying 4one form of the invention.

FIG. 2 is a plan view taken along the line 2-2 of FIG. 1.

FIG. 3 is a sectional view similar to FIG. 1 showing a modified form of the invention.

Referring now to FIG. l, there is shown a vacuumtype circuit interrupter comprising a sealed envelope 10 evacuated to a pressure of 10d4 millimeters of mercury or lower. This envelope comprises a tubular casing 11 of insulating material and a pair of

end caps

12 and 13 joined to opposite ends of the casing 11 by suitable vacuum-tight seals 14.

Located within the envelope 10 is a pair of relatively movable contacts 17 and 18, shown by the solid lines of FIG. 1 in their `disengaged or open position. The upper Contact 17 is a stationary contact suitably attached to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower contact 18 is a movable contact attached to a conductive operating rod 18a, which is suitably mounted for vertical movement. Upward movement of the -contact 18 from its solid line position to its dotted line position engages the contacts and thus closes the interrupter, whereas return movement in a downward direction separates the contacts and opens the interrupter.

The operating rod 18a projects freely through an opening in the lower end cap 13, and a flexible metallic bellows 20 provides a seal about rod 18a to allow -for vertical movement of the rod without impairing the vacuum inside envelope 10. As shown in FIG. l, the bellows is secured in sealed relationship at its respective opposite ends to the operating rod 18a and the lower end cap 13.

Each of the contacts 17 and 18 is of a disc-shape and has one major surface facing the other contact. Each contact comprises a centrally located contact-making button 25 suitably brazed to the remainder of the contact. Each of these contact-making buttons is provided with a centrally located recess 27 so that contact between the buttons occurs on an annular contact-making area 30 when the contacts are in their dotted-line engaged position of FIG. 1. These annular contact-making regions 30 are of such a diameter that current owing through the closed contacts follows a radially outwardly bowing loopshaped path L, as is indicated by the dot-dash line of FIG. 1. The magnetic effect of current flowing through this loop-shaped path L tends in a well-known manner to lengthen the loop. As a result, when the contacts are separated to form an arc between the areas 30, the magnetic effect of the current through the loop will impel the a-rc radially outward.

As the terminals of the arc move toward the outer periphery of the discs 17 and 18, the arc is subjected to a circumferentially-acting magnetic force that rotates the arc about the central axis of the discs. This circumferentially-acting magnetic force is produced by a plurality of slots 32 provided in each of the discs and dividing the discs into a plurality of fingers 33 bounded `by adjacent pairs of slots. The slots extend from the outer periphery of the discs radially inward by paths that extend both circumferentially and radially of the discs, as is shown in FIG. 2. These slots 32 correspond to similarly designated slots in the aforementioned Schneider patent and, thus, force the current flowing to or from an arc terminal on the slotted portion of the contact to follow a path that has a component extending circumferentially of the disc in the vicinity of the arc. This circumferential component of the current path causes the current flowing through the loop L to develop a net circumferentiallyacting force component which tends to rotate the arc about the central axis of the disc.

This circumferentially-acting force component is high enough to drive each terminal of the arc across slots 32, thus producing a continuous rotational movement of the arcon the contact surface. This continuous rotational movement of the arc enables higher currents to be interrupted, apparently because it reduces contact-erosion by the arc, thus reducing the quantity of metal vapors generated and thereby permitting more complete condensation of the metal vapors at current zero.

One factor that seems to limit the amount of current that can be interrupted by contacts of the type shown in the aforementioned Schneider patent is that under certain high current conditions the normally rapidly-moving arc may stall near the .inner end of a slot. This can result in excessive heating and erosion of thc contact material in this localized region, and this seems to detract from the interrupting ability of the contacts.

I have been able to materially reduce this tendency of the arc to stall or hang at the inner end of the slots by extending the slots 32 radially inwardly past the outer periphery of and under the contact-making button 25. This is best illustrated in FIG. 2, where it can be seen that the button 25 extends across, or lbridges over, each of the slots 32 near its inner end. The extreme inner end of a slot 32 is designated 32a. When an arc terminal on the major surface of the contact approaches the intersection of a slot 32 and the outer periphery of 'button 25, there is a repulsive magnetic effect, not fully understood, which forcesthe arc to continue moving, preventing it from stalling in this localized region. Numerous contacts of the design shown in FIG. 2 have been examined after repeated high current interruptions; and these examinations have revealed 'far less erosion in this localized region than has been typical with similar contacts having their slots terminating at the outer periphery of the button. This has been the case even though higher currents, e.g. 25,000 amperes, had been interrupted with the contacts of the design shown in FIG. 2 than with those having their slots terminating at the outer periphery of the button.

The amount of arc-rotating force that will be developed on an arc located near the outer periphery of a contact 17 or 18 varies directly with the effective length of the fingers 33. The diameter of the contact can be increased to increase the effective length of the fingers, but usually there are other vdesign considerations that limit the maximum permissible diameter of the contacts. 'I am able to obtain fingers of increased length in my contact without increasing the diameter of the contact inasmuch as I extend the slots radially-inward past the outer periphery of the contact button 25.

Prior to arriving at the design of FIG. 2, I considered using a smaller diameter contact-making button (25) in contacts of the design shown in the Schneider patent to provide for longer fingers 33, but it was found that this smaller diameter significantly detracted from the speed at which the arc was driven radially outward off the button following its initiation. By extending the slots radially inwardly 'beyond the outer periphery of the button 25 and, more specifically, radially inward ybeyond the outermost periphery of the actual contact-making region 30, I can still utilize a button of the large diameter needed to obtain the desired high speed radially-outward arc motion, yet without shortening the finger length.

For accentuating the radially-outward bow in the current path L, a sleeve of high resistance metal such as stainless steel is provided about each of the contact rods 17a and 18a where they are joined to the contact structure. The presence of the sleeve forces most of the current to enter the contact through its central region, thus forcing it to flow radially outward to reach the contact-making area 30.

Another advantage of the contact structure of FIG. 2 is that the central button 25 imparts added mechanil strength to the relatively long and slender fingers 33. Since the button 25 is brazed to all the fingers and to the central region of the disc-shaped contact, it resists any tendency of the fingers to bend in response to mechanical forces incident to an interruption operation.

In a preferred form of the invention, the button 25 is made of material that has a high resistance to contact welding, e.g., the copper-bismuth or copper-lead alloys disclosed and claimed in Patent 3,246,979-Laierty et al. assigned to they assignee of the present invention. The remainder of the contact is preferably made of a dissimilar metal which is easy to process, e.g., pure copper. Although it is preferred to make the button of a different material from the rest of the contact, it is satisfactory in certain applications to use the same material for the entire contact so that the button is integral with the remainder of the contact.

In a preferred form of the invention, the slots 32, in the region outside button 25, extend through the entire thickness of their associated discs and also extend to the outermost periphery of the discs, thereby rendering the :fingers almost completely separate from each other. This separateness results in a stronger arc-rotating force being available since the current flowing to an arc terminal is confined to a path especially shaped to produce arcrotation.

For condensing the metallic vapors generated by arcing, suitable vapor condensing shields 50, 54, 56 and 58 are provided. The main shield comprises a tubular member 50 surrounding the arcing gap 52 and located between the insulating casing 11 and the arcing gap. This shield is preferably maintained at a potential substantially midway that of the two electrodes when the circuit interrupter is opened. Auxiliary shields 54 of tubular form connected to the end caps 12 and 13, respectively, surround opposite ends of the main shield 50. Additional auxiliary shields 56 of tubular form are also connected to the end caps and are surrounded by the main shield 50. A suitable shield 50a of cup-shaped configuration is disposed about the bellows 20 to protect it from arcing products. This shielding arrangement is described in greater detail and claimed in my copending application S.N. 583,893, filed Oct. 3, 1966 and assigned to the assignee of the present invention.

Referring to the embodiment of FIG. 3, for furthef accentuating the radially-outward bow in the current path L, an annular insert 70 of high resistivity metal, such as stainless steel, can be incorporated in each contact-making button 25 just behind the annular contact-making area 30. This insert is similar to one shown and claimed in U.S. Patent 3,158,719-Polinko et al., assigned to the assignee of the present invention. A small clearance space 72 is provided between the outer periphery of the button 25 and the main body of the contact so that current is substantially prevented from entering the button at its outer periphery and is forced to enter through the central region of the button. The annular insert 70 presents a high resistance to current seeking a vertical path across it, thus further encouraging the current entering the button to do so through its central region. In the modification of FIG. 3, the spiral slots 32 extend radially inwardly well past the outer periphery of the annular insert 70. Thus, the insert 70, as well as the body of button 25, bridges the inner end of slots 32. The outer periphery of the stainless steel insert 70 is preferably spaced slightly radially inwardly from the outer periphery of button 25 to reduce the chance for an arc terminal attaching to the insert 70.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. In a vacuum-type circuit interrupter comprising a highly evacuated envelope,

(a) relatively movable contacts located within said evacuated envelope and movable from an engaged position to a disengaged position to establish an arc therebetween,

(b) one of said contacts comprising a generally discshaped member having a face confronting said other contact on which said arc is adapted to be located during circuit interruption,

(c) means for producing rotation of said are on the face of said disc-shaped member comprising a plurality of spaced-apart slots in said disc-shaped member respectively extending radially and circumferentially thereof,

(d) said one contact further comprising a contactmaking button joined to said face for engaging the other of said contacts when said contacts are eneased,

(e) said contact-making button being generally centrally located with respect to said one contact and having an outer periphery radially spaced from the outer periphery of said disc-shaped member,

(f) said slots respectively extending from an outer end location located radially outward of said contactmaking button to an inner end location disposed radially inwardly of the outer periphery of and under said contact-making button,

(g) said contact-making button bridging over said slots near said inner end locations.

2. The apparatus of claim 1 in which both of said contacts are constructed as specified in claim 1, the buttons of said two contacts being arranged to engage each other when said circuit interrupter is closed.

3. The apparatus of claim 2 in which said buttons have annular portions that engage each other when said interrupter is closed.

4. The apparatus of claim 1 in which said slots extend to the outermost periphery of said disc-shaped member and extend through the entire thickness of said disc member in the region disposed radially outside said contactmaking button.

5. The apparatus of claim 1 in which said contactmaking button and said disc-shaped member are formed of dissimilar metals, said contact-making button being formed of an alloy having a high resistance to contactwelding.

6. The apparatus of claim 1 in which said button includes a generally annular contact-making portion and current-directing means comprising a generally annular insert of high resistivity material compared to that of the surrounding material located behind said contactmaking portion for forcing current entering said button to enter through its central region, said insert also bridging over said slots near said inner end locations.

7. The apparatus of claim 6 in which said insert has an outer periphery spaced radially inward from the outer periphery of said button.

8. The apparatus of claim 1 in which said button has a contact-making region which has an outermost periphery located radially-outward of said inner end locations of said slots, said slots extending under said contact-making region and being bridged over by said contact-makmg reg1on.

9. The apparatus of claim 8 in which both of said contacts are constructed as specified in claim 48, the buttons of said two contacts being arranged to engage each other on said contact-making regions.

10. The apparatus of claim 1 in which said button has an annular contact-making region which has an outermost periphery located radially-outward of said inner end locations of said slots, said slots extending under said contact-making region and being bridged over by said contact-making region.

References Cited UNITED STATES PATENTS 2,949,520 8/ 1960 Schneider.

3,158,719 11/1964 Polinko et al. ZOO-144.2 3,182,156 5/1965 Lee et al. 20G- 144.2 3,185,799 5/ 1965 Greenwood et al. 20G- 144.2

ROBERT S. MACON, Primary Examiner U.S. Cl. XR.