US3048682A - Shield mounting arrangement for a vacuum circuit interrupter - Google Patents

Description

Aug. 7, 1962 D. J. VERAS 3,048,682

I SHIELD MOUNTING ARRANGEMENT FOR A VACUUM CIRCUIT INTERRUPTER Filed April 11, 1961 ('(IIIIIII.

'IIIIIIIIIIIIIIIIIIIIIII" "I Inventor: Dem ocritos J. \leras,

b3 Attorn e5.

United States Patent 3,048,682 SHIELD MOUNTING ARRANGEMENT FOR A VACUUM CIRCUIT INTERRUPTER Democritos J. Veras, Media, Pa., assignor to General Electric Company, acorporation of New York I Filed Apr. 11, 1961, Ser. No. 102,204 6 Claims. (Cl. 200-144) This invention relates to a vacuum-type circuit interrupter and, more particularly, to an improved shielding arrangement for protecting the insulation ofthe interrupter against the build-up of metallic coatings thereon.

in a vacuum circuit interrupter, the metallic vapors that are produced by arcing tend to condense on the insulating surfaces of the interrupter and, hence, to form metallic coatings which impair the insulating properties of such surfaces. For protecting these surfaces against such metal deposition, a shielding arrangement of the general type disclosed and claimed in U.S. Patent No. 2,892,9llCrouch, assigned to the assignee of the present invention, has been found effective. Such shielding arrangement comprises a generally tubular metallic shield surrounding the arcing gap between the usual electrodes of the interrupter and electrically isolated from both electrodes and from ground. This electrically isolated shield is physically located between the arcing gap and the internal surface of the usual insulating casing for the interrupter and acts to intercept and condense those metalli-c vapors traveling toward the insulating surface from the arcing gap.

The supporting arrangements that have been proposed for such shields have either been unduly expensive and complicated or have been diflicult to assemble. One such arrangement, for example, has required a supporting plate extending radially outward from the shield through the surrounding insulating casing. This has necessitated making the insulating casing in twoparts and hasinvolved two relatively expensive glass-to-metal seals on opposite sides of the supporting plate.

An object of the present invention is to provide a for causing its bight portion to be shifted radially outward into its aligned recess when the legs of the-tab are forced together, as by a suitable screw -threaded through one of the legs and extending through an opening in the other leg. The material of each of the tabs is of such a nature that the tab is permanently set when the bight portion enters the recess, whereby the bight portion remains in its aligned recess when the screw is removed.

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

FIG. 1 is a cross-sectional View of a vacuum switch embodying one form of my invention. I

FIG. 2 is a sectional view taken along the of FIG. 1. 7

FIG. 3 is an enlarged detailed view of a portion of my line 2 2 shield-supporting arrangement taken along the line -3-3 vacuum interrupter with an improved shield-supporting arrangement that is simple and inexpensive, is easily assembled without requiring undue precision, and requires no glass-to-metal sealsfor preventing leakage 'into'the vacuum envelope.

Another object is to construct the shield-supporting arrangement in such a manner-that the metallic shield. can expandand contract in response to temperature changes without unduly stressing the surrounding insulating hous- In carrying out my invention in one form, I provide I a vacuum circuit interrupter comprising a tubular envelope of insulating material having a pair of longitudinally-spaced annular recesses of concave cross-sectional configuration formed in its internal surface. A tubular metallic shield is disposed internally of the envelope in generallyconcentric relationship with respect thereto for protecting the envelope from being coated with metallic particles. A first series of angularly-spaced deformable tabs projecting radially outward from the external surface of the shield in longitudinal alignment with one of the recesses is provided. A second series of angularly spaced deformable tabs projecting radially outward from the external surface of the shield in longitudinal alignment with the other of the recesses is alsoprovided. Each of the tabs is a generally U-shaped metallic member comprising a pair of legs joined together by a bight portion. One leg of each tab'is secured to the shield and the other 'leg is free to move relative to the shield in 'a direction longitudinally thereof when the legs are forced together. At

of FIG. 2.

FIG. 4 is an end view of the part illustrated in FIG. 3 taken along the line 44;

Referring now to the interrupter of FIG. 1, there is shown a highly-evacuated envelope 10 comprising a tubul ar casing 11 of insulating material, such as a suitable glass, and a pair of metallic end caps 12 and 13 closing off the ends of the casing. Suitable seals 14 are provided between the end caps and the casing to render the envelope 10 vacuum-tight.

Located within the envelope is a pair of separable electrodes, or rod contacts, 17 and 18 shown by solid lines in the closed-circuit position. The electrode 17 is a stationary electrode suitably united to the upper end cap 12, whereas the electrode 18 is a movable electrode suitably mounted for vertical movement and projecting through an opening in the lower end cap 13. A flexible metallic bellows 20 interposed between the end cap 13 and the movable electrode 18 provides a seal about the movable electrode and allows for vertical movement thereof without impairing the vacuum inside the interrupter. As shown on the drawing, the bellows 20* is sealingly secured at its respective opposite ends to the electrode 18 and the end cap 13.

Soupled to the lower end of the movable electrode 18, I provide suitable actuating means (not shown) which is capable of driving the elect-rode rapidly downwardly from its solid-line position of FIG. 1 to its dotted-line position to open the interrupter and which is also capable of releast one weakened region is provided in each of the tabs r turning the electrode to the solid-line position to close the interrupter. V

When the electrode is driven downwardly to open the interrupter; a circuit-interrupting, or arcing, gap is established between the adjacent ends of the electrodes, and the resulting arc,-though quickly extinguished, vaporiz'es some of the metal of the electrodes; 1 In order to prevent this metallic vapor from condensing on the internal insulating surfaces of the casing 11, there is provided a metallic shield 25 which corresponds in certain respects to a similarly designated shield in the aforesaid Crouch patent. This metallic shield 25 is of a generally tubular configuration and extends along the length of the casing 11 for substantial distances on oppositesides of the gap between the electrodes. The shield 25 is electrically isolated from both of the electrodes 17 and 18 and, preferably, is also isolated from ground, or .in other words, is at a floating potential relative to the two electrodes. I This'electrical isolation between the shield 25 and the electrodes 17 and 18 is achieved by mounting the shield 25 'on the insulating casing adjacent the central region Essentially all straight line paths extending from the general region of the arcing gap to the insulating casing 11 are intercepted by the floating central shield 25. As a result of this relationship, substantially all metallic particles that are liberated from the electrodes by arcing are intercepted and captured either by the shield 25 or the end caps 12 and 13 before they can reach the internal surfaces of the casing 1'1.

The shield-supporting arrangement comprises two groups of metallic tabs 30 longitudinally-spaced from each other on the outer periphery of the shield 25. As shown in FIG. 2, the tabs 30 of each group are angularly-spaced from each other about the periphery of the shield 25. Also in FIG. 2, the tabs of one group are shown angularly offset from the tabs of the other group. The tabs of the upper group are received within an annular dimple or recess 32 of concave cross-section formed in the inner wall of the insulating housing in longitudinal alignment with these tabs. A similar dimple or recess 34 is provided in longitudinal-spaced relationship to the first recess 32 and in longitudinal alignment with the tabs of the lower group for receiving these lower tabs.

Each of the tabs is expanded radially outward into its aligned recess after the shield 25 has been inserted into the surrounding envelope 11 and the tabs longitudinally aligned with their cor-responding recesses. Preferably, a suitable fixture (not shown) is provided to hold the shield 25 rigidly with respect to the envelope 11 during the step of radially expanding the tabs 30. Before the tabs are so expanded, each is of the generally U-shaped form shown in FIG. 3. More specifically, each tab as shown in FIG. 3 comprises a pair of spaced-apart legs 40 and 41 projecting radially outward from the shield 25 and joined together by a bight portion 43. One of the legs 40 is provided with a foot portion 44 that is secured, as by spot welding, to the outer periphery of the shield 25. The other leg 41 is provided with a foot portion 45 that is unattached to the shield 25 and is free to move relative to the shield in a direction longitudinal thereof when the legs 40 and 41 are forced together during the tab-expansion step soon to be described. The foot 45 is preferably provided with an L-shaped extension that is bent back on the leg 41 and serves to provide a double thickness for the leg 41. The tabs 30 do not interfere with the above-described step of inserting the shield 25 into the envelope inasmuch as, before deformation, they project radially outward to only a limited extent, sufficiently small to locate their bight portions 43 radially inward of the inner periphery of the envelope 11.

*For drawing the legs 40 and 41 together to produce radial expansion of the tabs, I prefer to utilize a screw 47 that extends through aligned openings 48 and 49 in the legs of the tab. The opening 49 in the lower leg is provided with internal threads that mesh with the threads of screw 47 so that when the screw is rotated in the proper direction, it forces the leg 41 upwardly toward engagement with the leg 40. A relative heavy washer 46 disposed between the head of the screw 47 and the upper leg 40 prevents the upper leg from being distorted by the forces applied thereto when the legs 40 and 41 are being forced together. As the legs 40 and 41 approach each other, the bight portion 43 of the tab deforms radially outward and ultimately assumes a shape such as shown in dotted lines in FIG. 3.

To facilitate deformation of the bight 43 into the shape shown by the dotted lines of FIG. 3, the tab is provided With suitable notches 50 to produce weakened regions, preferably at the center of the bight 43 and at the junction of the bight 43 and the legs 40 and 41. These notches 50 are best seen in FIG. 4. In addition, the bight is preferably predeformed slightly outward in its central region to increase its tendency to expand radially outward when the legs 40 and 41 are forced together with the screw 47.

When the tab has been deformed radially outward into 4 its dotted line position of FIG. 3, the screw 47 can be removed simply by rotating it in an opposite direction to that required for forcing the legs 40 and 41 together. The tab remains in its deformed position during and after removal of the screw 47 inasmuch as the tab has then acquired a permanent set as a result of the prior deformation step. When all of the tabs have thus been deformed radially outward, they are seated in the recesses 32 and 34 and thus support the shield 25 within the envelope 11, anchoring it against appreciable axial movement relative to the envelope.

During the above described deformation process, the foot 45 of the tab acts as a bearing for slidably supporting the free end of leg 41 on the shield. The presence of this bearing advantageously serves to prevent the tab from being bent in an undesired manner during the deformation process. In this regard, when a screw driver is applied to the head of the screw 47 and a downward force is applied while the screw is being rotated, there is a tendency to bend the leg 40 of the tab in a clockwise direction about the region 52. If such bending were permitted, the axis of the screw 47 would tip and the free end of the screw could dig into the outer surface of the shield 25, thereby producing needless chips of metal and possible damage to the threads of the screw which could later prevent removal of the screw. The chips of metal could be a possible source of trouble in subsequent switch operation.

Referring to FIG. 1, where the tabs 30 are shown after having been deformed as described hereinabove, it will be observed that although the tabs 30 project into the corresponding recesses 32 and 34, there is still some radial clearance between the radially outermost surface of the tab and the maximum internal diameter portion of the envelope (which, for the respective recesses, is located along the reference planes 60 and 61). It will also be observed that the bight of each tab is in alignment with that surface of the recess which is disposed on the longitudinally-inner side of the maximum diameter region of the recess. In other words, referring to the upper recess 32 of FIG. 1, the bight 43 of the tab 30 aligns with the surface of recess 32 disposed below the reference plane 60, which marks the maximum diameter portion of the recess. Each of the upper tabs 30 is longitudinallyspaced from that surface of recess 32 which is disposed above the reference plane 60. The lower tabs are similarly positioned with reference to their recess in that the bight of each tab 30 aligns with that surface of its recess 34 which is disposed on the longitudinally inner, or upper side of the maximum diameter region 61 of the lower recess. At normal room temperatures, there is preferably a slight amount of longitudinal clearance between the tab and this upper surface of the recess 34, and there is also clearance between the tab and the lower surface of recess 34.

The above-described disposition of the tabs relative to their corresponding recess is advantageous in permitting the shield 25 to expand from its condition of FIG. 1 in response to temperature (rises without stressing the surrounding housing 11 In this regard, when the shield expands in a longitudinal direction the longitudinal spacing between the two groups of tabs 30 increases, and the radially-outermost portions of the tabs are thus shifted into larger diameter regions of the envelope more in alignment with the maximum diameter regions 60 and 61. In these larger diameter regions of the envelope, there is additional radial clearance available to allow radially outward expansion of the shield to occur without driving the tabs radially into the glass. Thus, the glass envelope is protected from the stresses that would otherwise be produced by radial expansion of the shield 25.

When the shield contracts in response to a temperature drop, the tabs of the longitudinally spaced groups move slightly closer together, but the effective diameter of the shield also decreases, thus preventing the tabs from being driven into the walls of the envelope by longitudinal contraction. In effect then, the particular disposition of the tags relative to their aligned recess causes longitudinal expansion of the shield to compensate for radial expansion and radial contraction to compensate for longitudinal contraction.

Another way of describing the disposition of the tabs relative to their recesses is: the longitudinal spacing between the radially-outermost portions of the tabs of the two groups is less than the spacing between reference planes 60 and 61. FIG. 1 illustrates the position of the tabs in their recesses at normal room temperature. During interrupting operations, the temperature of the shield could temporarily rise considerably above that of the envelope, but the above-described compensating action would prevent such unequal temperature conditions from causing overstress-ing of the envelope.

It will be apparent that the tabs of my shield supporting arrangement need have no significant resilience and can therefore be made of a relatively inexpensive metal. In an arrangement that relies upon springs for supporting the shield of a vacuum switch, one must employ a relatively expensive spring material inasmuch as vacuum switches require high temperature bake-outs that would dam-age most spring materials. The usual procedure for baking-out a vacuum switch such as shown in FIG. 1 involves first baking the shield 25 while still removed from the envelope 1-1 at temperatures on the order of 1200 C. and then baking the vacuum switch after complete assembly at temperatures on the order of 400 C. Conventional spring materials could be impaired by either of these temperatures. With my arrangement, I am able to attach the tabs to the shield even before the first bakeout. The first bake-out not only cleans up on the interior of the shield the portion of the spot weld that is used for attaching each tab but also aneals the tabs, thus permitting them subsequently to be deformed more easily and with less chance of fracture.

It will therefore be apparent that my shield supporting arrangement lends itself particularly well to use in a device such as a vacuum interrupter where high temperature bake-outs are involved.

By supporting the shield at longitudinally spaced-apart locations, it will be apparent that a more stable mounting has been provided than could ordinarily have been achieved by supporting the shield at a single location along the shield length. Moreover, the use of spa-cedapart supporting locations permits the shield to be assemblied within its envelope without requiring as much precision as v'here a single supporting location is relied upon. In this regard, where supports at two spacedapart locations are utilized, it is possible to rely upon one of the supports to counteract looseness in the other support.

While I have shown and described a particular embodiment 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. A vacuum switch .comprising a tubular envelope of insulating material, said envelope having a pair of longitudinally-spaced annular recesses of concave crosssectional configuration formed in its internal surface, a tubular metallic shield disposed internally of said envelope in generally concentric relationship with respect to said envelope for protecting said envelope from being coated with metallic particles, a first series of annularly-spaced deformable tabs projecting radially outward from the external surface of said shield in longitudinal alignment with one of said recesses, a second series of angularlyspaced deformable tabs projecting radially outward from the external surface of said shield in longitudinal alignment with the other of said recesses, each of said tabs being a generally U-shaped metallic member comprising a pair of legs joined together by a bight portion, means for securing one leg of each of said tabs to said shield, the other leg being free to move relative to said shield longitudinally thereof when said legs are forced together, aligned openings one of which is threaded provided in the legs of each tab for receiving a screw for forcing said legs together, at least one weakened region provided in each of said tabs for causing its bight portion to be shifted radially outward into its aligned recess when said legs are forced together, the material of each of said tabs being of such a nature that said tab is permanently set when said bight portion enters said recess whereby said bight portion remains in its aligned recess when said screw is removed.

2. A vacuum switch comprising a tubular envelope of insulating material, said envelope having a pair of longitudinally-spaced annular recesses of concave crosssectional configuration formed in its internal surface, a tubular metallic shield disposed internally of said envelope in generally concentric relationship with respect to said envelope for protecting said envelope from being coated with metallic particles, a first series of annularlyspaced deformable tabs projecting radially outward from the external surface of said shield in longitudinal alignment with one of said recesses, a second series of angularly spaced deformable tabs projecting radially outward from the external surface of said shield in longitudinal alignment vwith the other of said recesses, each of said tabs being a generally U-shaped metallic member comprising a pair of legs joined together by a bight portion, means for securing one leg of each tab to said shield, the other leg being free to move relative to said shield longitudinal-1y thereof when said legs are forced together, forcing together of said legs causing said tab to deform into a permanently set condition in which said bight portion is shifted radially outward into its aligned recess, said legs being sufficiently spaced during positioning of said shield in said envelope to locate said bight portion radially inward of the inner wall of said envelope whereby to permit positioning of the shield without interference from said tabs.

3. The vacuum switch of claim 2 in which each of said recesses includes a maximum internal diameter region for the recessed portion of said envelope which is sufficiently large to provide radial clearance between said maximum internal diameter region and the outermost radial surface of the tabs disposed in said recess at normal temperatures of said shield, the bight of said tabs being disposed in alignment with that surface of the recess located on the longitudinally inner side of said maximum internal diameter region at normal temperatures of said shield, the tabs being further located in such a manner that at normal temperatures clearance in a direction longitudinal of the shield is provided between the tab and the surface of the recess located on the longitudinally outer side of said maximum internal diameter region.

4. The vacuum switch of claim 2 in which said recesses are so shaped and located relative to said tabs that longitudinal expansion of said shield in response to a temperature rise shifts said tabs longitudinally relative to said envelope into positions where the effective internal diameter of said envelope is larger so as to permit radially outward expansion of said shield in response to said temperature rise without stressing said envelope.

5. The vacuum switch of claim 2 in which each of said recesses includes a maximum internal diameter region for the recessed portion of said envelope which is suf ficien-tly large to provide radial clearance between said maximum internal diameter region and the outermost radial surface of the tabs disposed in said recess at normal temperatures of said shield; the longitudinal spacing at normal temperatures between said recesses, measured between the regions of maximum internal diameter of said recesses, being greater than the longitudinal spacing between said two groups of tabs, measured between the radially outermost points on the tabs of the two groups; said recesses being so shaped that longitudinal clearance is provided at normal temperatures between the walls of said recesses and the longitudinally-outwardly disposed surfaces of said tabs.

6. The interrupter of claim 1 in which said movable leg is provided with a foot portion that extends longitudinally of said shield in a direction away from said stationary leg to provide a slide bearing for supporting said movable leg on said shield during movement toward said stationary leg.

References Cited in the file of this patent UNITED STATES PATENTS 2,491,742 Lein Dec. 20, 1949 2,516,663 Zunic July 25, 1950 2,745,981 S-anabria et al May 15, 1956 2,892,911 Crouch June 30, 1959 FOREIGN PATENTS 379,342 Great Britain Aug. 29, 19,32

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