US3522399A - Vacuum-type circuit interrupter with contacts having particularly shaped circumferentially spaced slots - Google Patents

Description

July 28, 1970 I D. w. CROUCH 3,522,399

VACUUM-TYPE CRCUIT INTERRUPTER WITH CONTACTS HAVING PARTICULARLY SHAPED CIRCUMFERBNTIALLY SPACED SLOTS Filed March 8, 1968 INVENTOR. DONALD W. CROUCH A TTORNEY Patented July 28, 1970 r 3,522,399 VACUUM-TYPE CIRCUIT INTERRUPTER WITH CONTACTS HAVING PARTICULARLY SHAPED CIRCUMFERENTIALLY SPACED SLOTS Donald W. Crouch, Newtown Square, Pa., assignor to General Electric Company, a corporation of New York 1 Filed Mar. 8, 1968, Ser. No. 711,613 Int. Cl. H01h 33/6'4 Us. Cl. 200-444 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a vacuum-type circuit interrupter and, more particularly, to contact structure for such an interrupter that is capable of interrupting very high currents for a small diameter of contact.

The invention is concerned with the general type of contact structure shown and claimed in US. Patent 2,949,- S20Schneider, assigned to the assignee of the present invention. The contact 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 potrion 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 arc is magnetically driven radially outward ofii 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.

While the slot configuration disclosed in the Schneider patent has been found effective in increasing the amount of current that can be interrupted by contacts of a given diameter, there is an upper current limit beyond which thesecontacts will not successfully interrupt.

An object of my invention is to construct the contacts in such a manner that currents above this current limit can be successfully interrupted with a contact of equal diameter.

In carrying out my invention in one form, I provide a pair of disc-shaped contacts having a substantially circular outer periphery and a pair of contact-making buttons respectively secured to said contacts, each having a substantially circular outer periphery concentric with the outer periphery of its associated contact. The contact-making buttons have a diameter greater than onehalf that of the disc-shaped contacts. Each contact is provided with circumferentially-spaced slots extending from a starting point at the outer periphery of the contact substantially tangent to the outer periphery of the but ton to provide circumferentially-extending finger portions between the slots and the outer contact periphery. The slots have an average width of at least substantially half of the average widht of the fingers. Each slot extends away from its starting point at the outer periphery of the contact for a substantial distance past the point at which the slot first touches the outer periphery of the button.

At its innermost end, the slot has a portion extending transversely of the tangential portion of the slot past the outer periphery of said button to a point spaced radiallyinwardly from said button periphery.

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

FIG. 1 is a sectional side elevational view of vacuum interrupter embodying one form of the invention.

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

FIG. 3 is a perspective view of the contact structure of FIG. 2 with a portion thereof removed for clarity.

Referring now to FIG. 1, there is shown a vacuumtype circuit interrupter comprising a sealed envelope 10 evacuated to a pressure of 10 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 vacuumtight 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, portion. 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. 1, 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 substantially circular 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 the 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 flowing through the closed contacts follows a radially-outwardly bowing loop-shaped path L, as is indicated by the dotted 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 arc radially outward. To make the loop in the loop-shaped path sufficiently pronounced so as to provide the desired high radially-outwardly acting force, the outer diameter of the contact-making button 25 is made greater than half that of the disc-shaped contact.

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 are 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. Each slot 32 extends from a starting point at the outer periphery of its disc 17 or 18 substantially tangent to the outer periphery of the button 25, first touching the outer periphery of the button at a point 34, and continuing tangentially of the button periphery for a substantial distance past point 34. At its innermost end, each slot has an inwardly-extending portion 35 that is substantially perpendicular to the tangential portion of the slot. This inwardly extending portion 35 extends from the outer periphery of the button to a point 36 spaced radially inward from the outer periphery of the button. As seen in FIG. 2, the button extends across, or bridges, the inwardly-extending slot portion 35.

These slots 32 force the current flowing to or from an arc terminal on a finger 33 to follow a path through the finger that extends circumferentially of the disc in the vicinity of the are. For example, if the arc terminal is at a position 40 in FIG. 2, the effective path of the current flowing through the finger 33 to the arc will be as shown at 41, extending circumferentially of the disc. This circumferential component of the current path causes the current flowing through the loop L to develop a net circumferentially-acting force component which revolves 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 at the free end of fingers 33, thus producing a continuous rotational movement of the arc n the contact surface. It is now generally recognized that such continuous rotational movement of the arc enables higher currents to be interrupted, apparently because it reduces the quantity of metal vapors generated by the arc, thus permitting more complete condensation of the metal vapor at current zero.

Heretofore, the slot configuration most widely used for effecting arc-rotation in vacuum interrupters is substantially that shown in FIG. 2 of the aforesaid Schneider patent. While that slot configuration is quite effective, I have been able with the slot configuration disclosed and claimed in the present application to interrupt considerably higher currents with contacts of a given diameter. For example, with contacts having a diameter of 1% inches, I have been able under corresponding voltage conditions to interrupt 10,000 amperes R.M.S., as compared to 7500 R.M.S. with contacts of the same diameter slotted in substantially the same manner as illustrated in FIG. 2 of the aforesaid Schneider patent. For larger diameter contacts, an increase in interrupting capacity by approximately was also noted.

One feature which contributes to the improved performance of my slotted construction is the relatively great width of the slots 32 in comparison to the width of fingers 33. In this regard, I make the average Width W of the slots at least substantially one-half the average width Y of fingers 33, considered in the region where the fingers extend parallel to the circumference of the disc. This will be apparent from FIG. 2, where these widths in contact 17 are shown as they would be viewed from the other contact. This enlarged slot width contributes to a number of important advantages. First of all, it results in reduced width of the fingers and thus confines the current path through the finger to a direction more effectively cir cumferential in the vicinity of the arc terminal. By concentrating the current path in this manner, the magnetic force on the arc is directed more effectively circumferential and is thus more effective in rotating the arc about the disc periphery. Secondly, the enlarged slot Width reduces the chance that molten metal resulting from high current arcs will fill the slots and thus decrease their effectiveness by forming metal bridges thereacross. Such metal bridges are undesirable in that they form current paths across the slots which interfere with confining the current to the desired circumferentially-extending path.

Another feature which contributes to improved performance of my slot configuration is that the finger 33 formed by each slot between the outer edge of the slot and the contact-periphery extends over most of its length substantially parallel to the disc periphery. This contributes to making the current path 41 more effectively circumferential than would be the case with a slot that was more effectively radial. My slot, over its entire length except at its innermost end 35, extends approximately parallel to the outer periphery of the disc. This is a result of making the slot substantially tangential to the periphery of contact-making button 25, which has a diameter greater than half the disc diameter.

It appears that the arc terminal, in moving radially-outward from the contact-making button after its initiation, frequently jumps across a slot 32. This immediately places the arc terminal on finger 33 in a position where there is a strong circumferential acting force on it, thus commencing rotation of the are at an exceptionally early point following its initiation. The position of the slot immediately adjacent the periphery of contact-making button and extending tangential thereto encourages the arc terminal to follow this short path onto a portion of finger 33- where there is a high circumferentially-acting force on the arc.

Another feature which contributes to improved performance is that the end of each finger is rounded, being radiused or arcuate over its entire width, as indicated at 45. Previous contact designs have had sharp points at the end of the fingers, and there seems to have been a tendency for the arc terminal to hang on such points, hesitatoing before moving across the solt 32. By removing these sharp points, this tendency for the arc to hang at the end of a finger is reduced and the arc moves more freely across slot 32.

It is to be noted that my slot 32, except for its inner end portions 35, is of a substantially straight-line configuration. This straight-line configuration permits the slots to be easily formed by a milling process. A rotating milling-tool, driven about an axis perpendicular to the disc 17 and having a diameter equal to the slot width, is simply fed from the outer periphery of the disc into a position near the inner end of the slot along a straight line path. Thereafter, the direction of feed is changed by approximately degrees to form the short inwardly-extending portion 35 of the slot.

The inwardly extending portion 35 of each of the slots 32, which is bridged by contact-making button 25, serves to discourage the are from stalling near the inner end of a slot, as is explained in application Ser. No. 583,808, now Pat. No. 3,462,572-Sofianek, filed Oct. 3, 1966, and assigned to the assignee of the present invention.

For accentuating the radially-outward bow in the current path L, a sleeve 43 of high resistance metal such as stainless steel is provided about each of the contact rods 17a and 18a where it is 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.

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 Pat. 3,246,979-Lafferty et al., assigned to the 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 arc-rotation.

For condensing the metallic vapors generated by arcing, suitable vapor-condensing shields 50 and 54 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 sihelds 54 of tubular form connected to the end caps 12 and 13, respectively, surround opposite ends of the main shield 50.

While I have shown and described a particular embodiment of my invention, it will be obivous 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. A vacuum-type circuit interrupter comprising:

(a) a highly evacuated envelope,

(b) a pair of relatively movable disc-shaped contacts within said envelope having a generally circular outer periphery,

(c) contact-making buttons respectively secured to said disc-shaped contacts and each having a substantially circular outer periphery substantially concentric with the outer periphery of its associated disc-shaped contact, the diameter of said button being greater than half the diameter of said disc,

(d) each of said contacts having circumferentiallyspaced slots therein extending from a starting point at the outer periphery of said contact substantially tangent to the outer periphery of said button to provide circumferentially-extending finger portions between said slots and the outer periphery of said contact,

(e) each of said slots having an average width of at least substantially half of the average width of the circumferentially-extending finger portion bounding its outer edge, said widths in each contact being measured as viewed from the other contact,

(f) each of said slots extending away from its starting point at the outer periphery of said contact for a substantial distance past the point at which the slot first touches the outer periphery of said button,

(g) said slot having a portion at its innermost end extending transversely of the tangential portion of said slot across the outer periphery of said button to a point spaced radially inwardly of the button periphery.

2. The structure of claim 1 in which the portion of said slot at the innermost end thereof extends beneath said button and is bridged by said button.

3. The structure of claim 1 in which each of said finger portions has a rounded free end, being arcuate over its entire width.

4. The structure of claim 1 in which each of said slots follows a substantially straight line path from the outer contact periphery to said portion at its innermost end.

5. The structure of claim 4 in which said slot portion at the innermost end of each slot follows a straight line path.

References Cited UNITED STATES PATENTS 3,182,l56 5/19-65 Lee et al 200144 3,345,484 10/1967 Polinko et al. 200-144 3,441,698 4/ 1969 Sofianek 200l44 FOREIGN PATENTS 1,505,699 12/1966 France.

ROBERT K. SCHAEFER, Primary Examiner -R. A. VANDERHYE, Assistant Examiner US. Cl. X.R. 200166

Images