Patent Publication Number: US-4547638-A

Title: Vacuum interrupter

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a vacuum interrupter, particularly to a vacuum interrupter including a vacuum envelope a major portion of which consists of a generally cylindrical (including bottom-cylindrical) metallic housing and a disc-shaped insulating end plate, made of insulating ceramics, hermetically brazed to an opening end of the metallic housing. 
     For the purpose of size-down and production cost-down, a vacuum envelope of a vacuum interrupter which, as described above, includes in the main a metallic housing and insulating end plate has replaced one which includes in the main an insulating cylinder made of insulating ceramics or crystallized glass and a metallic end plate hermetically sealed to the opposite opening ends of the insulating cylinder (See U.S. patent application No. 276,862). 
     Since the insulating surface distance of an insulating end plate is shorter than that of an insulating cylinder if vacuum interrupters of the two types described above are equal in interruption capacity, dielectric strength per unit length of the insulating end plate must be greater than that of the insulating cylinder. Therefore, voltage distribution per unit length for the insulating end plate, i.e., electric field intensity therein, is necessarily greater than that in the insulating cylinder. 
     Moreover, in case of a vacuum envelope as described above including in the main a metallic housing and an insulating end plate, both the members are conventionally united with each other by hermetic-brazing the surface of an opening edge of the metallic housing in the surface-to-surface manner to an extremely thin metallized layer which covers the outer peripheral region of the sealing surface of the insulating end plate. In view of the shape, the metallized layer, the inner edge region of the surface and the extremely narrow side surface thereof caused to appear within the vacuum envelope, has a capability of electric field concentration. 
     Moreover, where the insulating end plate centrally has an aperture through which an electrode lead rod extends, and where metallized layers cover the inner peripheral region as well as the outer peripheral region in the sealing surface of the insulating end plate, the electric field concentration which is effected at the respective extremely thin edge surfaces of both the metallized layers, opposed to each other, is ready to trigger insulation breakdown between the metallized layers. 
     Moreover, since the metallized layer microscopically has small protrusions thinly spread over the surface, which causes electric field concentration, the layer is capable of triggering the internal insulation breakdown of the vacuum envelope. 
     Moreover, the metallized layer is made of Mn, W, Mo or the like which has a pronounced tendency to effect electron emission. This feature also leads to the internal insulation breakdown of the vacuum envelope. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a vacuum interrupter having a vacuum envelope of which is much improved in the internal dielectric strength. According to the inventive vacuum interrupter, two spaced edges, appearing within the envelope, of extremely thin metallized layers which are formed in a hermetic-sealing surface of insulating end plate and to which a cylindrical metallic housing and other members of the envelope are brazed are shielded from electric field concentration by an electrically conductive shield for a metallized layer edge. 
     Dielectric strength of a vacuum envelope having the metallized-layer edge shield is about between 1.5 and 2 times that of another vacuum envelope having no metallized-layer-edge shield. 
    
    
     Other objects and advantages of the present invention will be apparent from the following description, claims and attached drawings. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a longitudinally fragmented sectioned view of a vacuum interrupter in accordance with a first embodiment of the present invention; 
     FIG. 2 is an enlarged view of the encircled portion A of FIG. 1; 
     FIG. 3 is an enlarged view as FIG. 2, of a vacuum interrupter in accordance with a second embodiment of the present invention; 
     FIG. 4 is an enlarged view as FIG. 2, in a vacuum interrupter in accordance with a third embodiment of the present invention; 
     FIG. 5 is an enlarged view as FIG. 2, in a vacuum interrupter in accordance with a fourth embodiment of the present invention; 
     FIG. 6 is an enlarged view as FIG. 2, in a vacuum interrupter in accordance with a fifth embodiment of the present invention; and 
     FIG. 7 is an enlarged view as FIG. 2, in a vacuum interrupter in accordance with a sixth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The vacuum interrupter, shown in FIG. 1, in accordance with the first embodiment of the present invention, includes a vacuum envelope 1 comprising the following listed members. The members consist of: a generally cylindrical metallic housing 4 consisting of a metallic cylinder 2 and the first sealing members 3 which are in the form of a substantially short metallic cylinder and hermetically brazed in the compression seal manner to the opposite ends of the metallic cylinder 2; disc-shaped insulating end plates 5a and 5b hermetically brazed in the surface-to-surface manner to outer edge surfaces 3d of the first sealing members 3; a stationary electrode lead rod 6; the second sealing member 7 which is in the form of a substantially metallic cylinder and serves to hermetically unite the stationary lead rod 6 and the insulating end plate 5a; a movable electrode lead rod 8 in alignment with and near or away from the stationary lead rod 6; a bellows 9 located around the movable lead rod 8 within the metallic housing 4; the third sealing member 10 which is in the form of a substantially short metallic cylinder and serves to hermetically unite the outer end of the bellows 9 and the insulating end plate 5b and; an enlarged-diameter portion 11 integrally of the movable lead rod 8 which serves as an aid for hermetic-brazing the inner end of the bellows 9 to the movable lead rod 8. 
     The metallic cylinder 2 is for instance made of austenitic stainless steel. 
     The first sealing member 3 as mentioned above is made of Fe-Co-Ni or Fe-Ni alloy or copper for instance. Particularly, the first sealing member 3 made of copper serves to neutralize in plastic deformation thereof thermal stress which is to be generated in the metallic cylinder 2, the insulating end plates 5a and 5b and brazed portions between the metallic cylinder 2 and insulating end plates 5a and 5b in a slow-cooling process after a hermetic brazing. 
     Each first sealing member 3 is provided at a part of the outer periphery of the outer end with a first outward flange 3a which is hermetically brazed in the surface-to-surface manner to the insulating end plates 5a and 5b. It is also provided near a part of the outer periphery of the inner end with the second outward flange 3b which is hermetically brazed to the edge surface of the opening end of the metallic cylinder 2. It is still further provided near a part of the inner periphery of the inner end and the opposite second outward flange 3b with an inward flange 3c. 
     The insulating end plates 5a and 5b are made of insulating ceramics as alumina ceramics, steatite ceramics, mullite ceramics, zircon ceramics or the like. The insulating end plates 5a and 5b have at the center thereof respective apertures 5c through which the stationary and movable lead rods 6 and 8 extend into the metallic housing 4. The respective sealing surfaces of the insulating end plates 5a and 5b are provided with annular inner-diameter side and outer-diameter side shoulders 12 and 13. 
     Inner-diameter side and outer-diameter side metallized layers 14 and 15, being extremely thin, are overall formed by conventional methods in the surfaces of the respective inner-diameter side and outer-diameter side shoulders 12 and 13, which are separated from each other by an annular groove 16 therebetween. The groove 16 is about between 0.1 and 3 mm in depth so as to increase surface dielectric strength in the vacuum envelope 1 of each insulating end plate 5a or 5b. 
     The outer edge surface 3d of each first sealing member 3 is hermetically brazed to the outer-diameter side metallized layer 15. Since the outer edge surface 3d of the first sealing member 3 is narrower in width than the outer-diameter side metallized layer 15 and, as apparent from FIG. 2, the first outward flange 3a of the first sealing member 3, in view of a difference between coefficients of thermal expansion of the first sealing member 3 and insulating end plate 5a or 5b, is located so as to overlap neither the inner nor outer edge of the outer-diameter side metallized layer 15, the inner edge region of each outer-diameter side metallized layer 15 is caused to appear within the vacuum envelope 1. 
     An auxiliary arc shield 17 and a first annular metallized-layer-edge-shield 18, which will later be described in detail, are brazed to the inward flange 3c of each first sealing member 3. 
     The stationary lead rod 6 extends into the metallic housing 4 through the aperture 5c of the insulating end plate 5a. Located within the vacuum envelope 1 is the inner end of the stationary lead rod 6 to which a disc-shaped stationary electrode 20 including a stationary contact 19 is secured by brazing. A main arc shield 21 which is in the form of a cylinder with an apertured bottom is secured to the stationary lead rod 6 behind the stationary electrode 20 by brazing via a snap ring 22 at a bottom 21a of the shield 21 to the rounded periphery of the rod 6. The main arc shield 21 will be described in detail later. 
     The second sealing member 7, which is made of the same material as the first sealing member 3, is of a cup shape and provided at the inner end with an apertured bottom 7a which is hermetically brazed to the rounded periphery of the stationary lead rod 6 via a snap ring 23. 
     The outer edge surface 7b of the second sealing member 7 is hermetically brazed to the inner-diameter side metallized layer 14 of the insulating end plate 5a. The relationship between the outer edge surface 7b and the inner-diameter side metallized layer 14 is the same as between the outer edge surface 3d of the first sealing member 3 and the outer-diameter side metallized layer 15. Therefore, the outer edge region of the inner diameter side metallized layer 14 is caused to appear within the vacuum envelope 1. 
     The second sealing member 7 is provided near a part of the outer periphery of the outer edge with an outward flange 7c. 
     The second annular metallized-layer-edge-shield 24 which will be in detail described later is brazed to the outward flange 7c. 
     The movable lead rod 8, as the stationary lead rod 6, extends into the metallic housing 4 through the aperture 5c of the insulating end plate 5b. A disc-shaped movable electrode 25a including a movable contact 25 is brazed to the inner end of the rod 8. 
     The bottom 21a of another main arc shield 21 is secured by brazing to the enlarged diameter portion 11 and periphery of the movable lead rod 8. 
     The bellows 9, which is made of austenitic stainless steel for instance, is provided at the outer end with a brazing cylinder 9a. The outer periphery and the outer edge surface 10a of the third sealing member 10 are hermetically brazed in the compression seal or surface-to-surface manner to the respective brazing cylinder 9a of the bellows 9 and to the inner-diameter side metallized layer 14 of the insulating end plate 5b. The relationship between the outer edge surface 10a and inner-diameter side metallized layer 14 is also the same as between the outer edge surface 3d of the first sealing member 3 and the outer-diameter side metallized layer 15. Therefore, the outer edge region of the inner-diameter side metallized layer 14 of the insulating end plate 5b is caused to appear within the vacuum envelope 1. 
     The third sealing member 10 which is made of the same material as the first sealing member 3 is provided near a part of the outer periphery of the outer edge with an outward flange 10b. A third annular metallized-layer-edge-shield 26, which will be described in detail later, is brazed to the outward flange 10b. 
     The bellows 9, the thickness of which is about 0.1 mm, may be brazed directly to the metallized layer in the inner-diameter side surface defining the aperture 5c (see FIG. 5) regardless of a difference between coefficients of thermal expansion of the bellows 9 and insulating end plate 5b. 
     Both of the main and auxiliary arc shields 21 and 17, which are made of iron or austenitic stainless steel for instance, are provided to prevent metallic vapor, generated between the stationary and movable electrodes 20 and 25a in closing or opening of the stationary and movable contacts 19 and 25, from depositing on portions, appearing within the vacuum envelope 1, of the inner surfaces of the insulating end plates 5a and 5b (hereinafter referred to as vacuum-chamber-side surfaces). Particularly, the main arc shield 21 has a shape adapted so as to prevent the metallic vapor from directly depositing on the vacuum-chamber-side surface of the insulating end plate 5a or 5b, while, particularly, the auxiliary arc shield 17 has a position and shape adapted so as to prevent the metallic vapor which is reflected on the inner surface of the metallic cylinder 2, from depositing on the vacuum-chamber-side surface of the insulating end plate 5a or 5b. 
     The inner-diameter of the cylindrical portion of the main arc shield 21 is somewhat greater than the outer-diameter of the cylindrical portion of the auxiliary arc shield 17. Moreover, the edges of the cylindrical portions of the main and auxiliary arc shields 21 and 17 always overlap each other. Bending portions between the cylindrical portion and bottom 21a of the main arc shield 21 and between the cylinderical portion and outward flange 17a of the auxiliary arc shield 17 are both rounded to prevent electric field concentration. 
     Each of the first metallized-layer-edge shields 18 which is in the form of a generally short cylinder is provided at the opposite ends of a cylindrical portion 18c with an electric field concentration preventing outward flange 18a and a fixing outward flange 18b. The roundness which is borne on the extension from the inner surface of the cylindrical portion 18c to the one surface 18d of the electric field concentration preventing outward flange 18a facilitates to prevent the occurrence of electric field concentration. It need not be borne if the voltage grade of the vacuum interrupter is low. 
     As shown in FIGS. 1 and 2, each first metallized-layer-edge shield 18 is located by the first sealing member 3 so that the one surface 18d of the electric field concentration preventing outward flange 18a approaches the bottom of the groove 16 beyond a level of the surface of the outer-diameter side metallized layer 15. Thus, the inner edge region of the outer-diameter side metallized layer 15 will be much lessened in electric field concentration. 
     Both the first metallized-layer-edge shields 18 are made of electrically conductive material as austenitic stainless steel or copper, which causes little electron emission and is relatively great in mechanical strength and still brazable. 
     The second or third metallized-layer-edge shield 24 or 26 which is a ring having a J-shaped cross section is provided with an electric field concentration preventing inward flange 24a or 26a and a fixing inward flange 24b or 26b. The electric field concentration preventing inward flange 24a or 26a, as the electric field concentration preventing inward flange 18a of the first metallized-layer-edge shield 18, is located by the second or third sealing member 7 or 10 so that the outer surface of the inward flange 24a or 26a approaches the bottom of the groove 16 beyond a level of the surface of the inner-diameter side metallized layer 14. Thus, the outer edge region of the inner-diameter side metallized layer 14 will be subjected to a much lessened electric field concentration. The second or third metallized-layer-edge shield 24 or 26 is made of the same material as the first metallized-layer-edge shield 18. 
     According to the above embodiment, the dielectric strength of the vacuum envelope 1 is about between 1.5 and 2 times that of a vacuum envelope lacking in a metallized-layer-edge shield. 
     Were either the first metallized-layer-edge shield 18 or the second or third metallized-layer-edge shield 24 or 26 opposing thereto is provided, the one will prevent the occurrence of electric field concentration at either metallized layer 14 or 15. Thus, the dielectric strength between the metallized layer 14 and 15 is greater than that between metallized layers of a vacuum interrupter lacking in a metallized-layer-edge shield. 
     According to the second embodiment of the present invention, the first metallized-layer-edge shields 30, as shown in FIG. 3, are formed for electric field concentration preventing inside flange 30a thereof to curl inward. In this case, each first metallized-layer-edge shield 30 is located by the first sealing member 3 so that the center of a bending portion 30b which is formed between the outer periphery of the cylindrical portion of the first metallized-layer-edge shield 30 and the inner surface of the electric field concentration preventing inside flange 30a, approaches the bottom of the groove 16 beyond the level of the surface of the outer-diameter side metallized layer 15. 
     While the third metallized-layer-edge shield 31 is formed for an electric field concentration preventing outside flange 31a to curl inward. In this case too, a bending portion 31b between the inner periphery of the cylindrical portion of the third metallized edge shield 31 and the outer surface of an electric field concentration preventing outside flange 31a is formed similarly to the bending portion 30b of the first metallized-layer-edge shield 30. 
     The second metallized-layer-edge shield is not shown. A shape thereof and relationship to the inner-diameter side metallized layer 14, however, are substantially the same as those of the third metalllized-layer-edge shield 31. Advantages of the second embodiment are substantially the same as those of the first embodiment. 
     According to the third embodiment, the first and third metallized-layer-edge shields 32 and 33, as shown in FIG. 4, are integrally formed to the respective first and third sealing member 34 and 35. Consequently, both the first and third metallized-layer-edge shields 32 and 33 are necessarily made of metal as copper if the first and third sealing members 34 and 35 made of copper. The second metallized-layer-edge shield is not shown. However, it is substantially as same as the third metallized-layer-edge shield 33. Advantages of the third embodiment are substantially as same as those of the first embodiment. 
     According to the fourth embodiment, the bellows 9, as shown in FIG. 5, is directly brazed in the surface-to-surface seal manner to the inner edge surface defining the aperture 5c of the insulating end plate 5b via a metallized layer 14a so that the element 9b at the outer end of the bellows 9 replaces the third metallized-layer-edge shield according the previously described embodiments. Advantages of the fourth embodiment are substantially as same as those of the first embodiment. 
     According to the fifth embodiment, the inner-diameter side and outer-diameter side metallized layers 14 and 15 of each insulating end plate 36, as shown in FIG. 6, are separated from each other by an annular barrier 37 protruded therebetween. The first or third metallized-layer-edge shield 18 or 26 is located by the first or third sealing members 3 or 10 so that the electric field concentration preventing outward or inward flange 18a or 26a closely approaches the surface of the annular barrier 37, curling outwardly or inwardly. The second metallized-layer-edge shield is not shown. The shape and function thereof are substantially as same as those of the third metallized-layer-edge shield 26. The outer and inner edge regions of the respective inner-diameter side and outer-diameter side metallized layers 14 and 15 are shielded from electric field concentration. 
     According to the sixth embodiment, the inner surface of each insulating end plate 38, as shown in FIG. 7, is flat and the respective outer and inner edge regions of the respective inner-diameter side and outer-diameter side metallized layers 14 and 15 are shielded from electric field concentration by the first and third metallized-layer-edge shields 18 and 26. 
     The above descriptions all direct to a vacuum envelope comprising a cylindrical metallic housing including opposite opening ends and consisting of a metallic cylinder with the opposite ends and with opening sealing members. However, they are also applicable to a vacuum envelope including only a metallic cylinder with the opposite ends opening, to a vacuum envelope comprising a cylindrical metallic housing including the one opening end and consisting of one-bottomed metallic cylinder and sealing member located at the opening end of the cylinder and to a vacuum envelope comprising a metallic bottomed cylinder as a metallic housing.