Vacuum interrupter

Abstract: A cylindrical coil conductor (20) incorporated in a vacuum interrupter comprises a cylindrical body with a plurality of inclined slits (26) therein defining a plurality of current paths (55). The coil conductor is uniformly cylindrical to reduce radial magnetic fields, which tend to cancel the axial magnetic field generated by the coil conductor. The cylindrical coil conductor electrically connects to a conductor disk (19) and to a main electrode (17) and the conductor disk electrically connects to a conductor rod (35). A support rod (23) is attached to the main electrode and extends through the coil conductor disk to reduce mechanical stress on the coil conductor. A second cylindrical coil conductor (60) is mounted in an opposing manner with inclined slits (27) defining current paths (56) in parallel to the slits in the first coil conductor. The current paths in the two coil conductors comprise one-turn current flow generating a uniform axial magnetic field to permit uniform distribution of the arc current between the main electrodes.

Description: The present invention relates to a vacuum interrupter and more particularly to an improved electrode structure for a vacuum interrupter. Still more particularly, the invention relates to an improved tubular coil conductor forming a part of the electrodes for a vacuum interrupter. A vacuum interrupter for handling a high current generally includes (for example see EP0062186A) a pair of main electrodes disposed in a vacuum vessel so that at least one of the pair is movable toward and way from the other, coil conductors mounted on the rear surfaces of the main electrodes, and conductor rods extending to the exterior of the vacuum vessel from the rear surfaces of the coil conductors. Current flows from one of the conductor rods to the other through the coil conductors and main electrodes. When one of the conductor rods is urged by an actuator for the purpose of interrupting the current, at least one of the main electrodes is moved away from the other, and an arc current is caused to flow between the spaced electrodes. This arc current is dispersed into a plurality of filament-like arc currents by a magnetic field created by the flow current through the coil conductors. U.S. Patent No. 3,946,179 discloses a coil conductor that comprises a plurality of conductive arms connected to arcuate sections. The arms connect at one end to a conductor rod and diverge in a generally radial direction therefrom to connect to an arcuate section at the other end. The arcuate sections extend circumferentially from the arms and connect to a main electrode. A plurality of arms and associated arcuate sections with clearances formed between adjacent arcuate sections, form an imaginary coil of one turn. Current flows from the rod to the main electrode through the spaced arms and associated arcuate sections. The one-turn current produces a uniform axial magnetic field that produces the diffuse, filamentary arc currents between the main electrodes. The use of the clearance in U.S. Patent 3,946,179 to produce the coil effect in the coil conductor results in a weak axial magnetic field in the region of the clearances. Arc currents have a tendency to migrate from a low intensity region toward a high intensity region of an axial magnetic field. Thus, the arc current flowing into the main electrode migrates away from the region of the clearances, causing localized overheating of the main electrode. In addition, because the entire area of the main electrode cannot be utilized effectively for the current interruption, it becomes necessary to increase the size of the main electrode. In our European Patent Application No. 89301436.5 (Publication No. 0329410A) a uniform axial magnetic field is produced by providing parallel slits in the coil conductors. However, the configuration of the coil conductors still provide certain limitations in the size of the axial magnetic field that may be generated. The axial magnetic field is partially cancelled by a radial magnetic field, which is generated by current flow through the bottom of the diverging coil conductors. Furthermore, the structure of the coil conductors may be susceptible to mechanical fatigue. In accordance with the present invention there is provided a vacuum interrupter as set forth in claim 1. Accordingly, there is provided herein a small, compact vacuum interrupter that operates with an improved current interruption performance. The electrode structure has a tubular coil conductor for increasing the axial magnetic field within the vacuum vessel. The coil conductor has a generally uniform cylindrical configuration enclosed at one end thereof by a conductor disk, which adjoins an external conductor rod. The generally uniform cylindrical configuration reduces the radial magnetic field generated by prior art coil conductors and thereby eliminates undesirable cancellation of the axial magnetic field. A number of electrical connectors extend from the opposing end of the tubular electrode structure for providing current to the main electrode. The coil conductor includes a plurality of inclined slits, at least two, formed on a cylindrical body, defining separate current paths of approximately one-half turn each around the circumference of the cylindrical coil conductor. Current flows axially through the external conductor rod, radially through the conductor disk, and then axially through the coil conductor and the several current paths defined thereon. Two substantially identical electrode structures are provided in the vacuum vessel so that the inclined slits on each of the opposing coil conductors are generally parallel. Thus, current flows from a first external conductor rod, through a first conductor disk, and then through the several current paths defined by the coil conductor to an electrical connector. At the connector, the current passes from a first main electrode to the opposing electrode structure, which is, in effect a mirror image of the first electrode structure. The slits and current paths on the two opposing conductor coils are aligned such that the current effectively flows through one full turn as it passes through the vacuum vessel. Consequently, a strong, uniform axial magnetic field is applied to the two main electrodes, and current arcing between the spaced main electrodes can be more uniformly distributed over the entire surfaces of the main electrodes. The electrode structures of the improved vacuum interrupter also include a structure support rod that extends axially from the main electrode, through the tubular coil conductor, and co-axially within the external conductor rod. The support rod reduces mechanical stress on the tubular coil and concentrically aligns the electrode structure, thereby maintaining the integrity of the current paths around the coil conductor. These and various other characteristics and advantages of the present invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawings. For a more detailed description of the preferred embodiment of the invention, reference will now be made to the accompanying drawings, wherein: FIG. 1 is a partly sectional, schematic side elevation view of a vacuum interrupter constructed in accordance with the present invention; FIG. 2 is a perspective view of one of the two electrode structures incorporated in the vacuum interrupter shown in Figure 1. The vacuum interrupter of the present invention comprises an improved design of the interrupter disclosed in EP-A-329 410. Referring now to Figure 1, a vacuum interrupter constructed in accordance with the preferred embodiment of the present invention, includes a vacuum vessel 15, a movable electrode structure 25 displaced along the central axis of vessel 15, a stationary electrode structure 30 disposed along the central axis of the vacuum vessel 15 opposite the movable electrode structure 25, and a bellows 28 for displacing the movable electrode structure 25 axially within the vessel 15. Displacing the movable electrode structure 25 from the stationary electrode structure 30 causes current flowing between the two electrode structures to arc across the gap between the structures, as discussed more fully herein. Referring still to Figure 1, vacuum vessel 15 preferably comprises a pair of end plates 8, 9 mounted on both ends of a cylindrical member 10. End plates 8, 9 have a generally circular configuration with a radius r and a central circular aperture 14 therethrough. Cylindrical member 10 also has a radius r and is constructed of an electrically insulative material. End plates 8, 9 fixedly attach to and enclose both ends of cylindrical member 10 to define a controlled environment within the vessel 15. Referring now to Figures 1 and 2, the stationary electrode structure 30 constructed in accordance with the preferred embodiment comprises an external conductor rod 35 extending through the central aperture 14 of end plate 9, a conductor disk 19, a tubular coil conductor 20 electrically connected at one end to disk 19, a main electrode 17 electrically connected to coil conductor 20 and a structural support rod 23 extending along the central axis of the electrode structure 30. The external conductor rod 35 is constructed of an electrically conductive material and includes an external end 38, an internal end 40 having an outer diameter slightly less than that of the external end, and a circumferential lip 39 defined by the juncture of the external and internal ends 38, 40. The conductor rod 35 also includes a central bore 37 extending axially through the rod 35. Upon assembly, the lip 39 engages the end plate 9 adjacent to the central aperture 14 with the external end 38 of rod 35 extending therefrom externally of the vacuum vessel 15 and the internal end 40 of the rod 35 protruding through aperture 14 into the interior of vacuum vessel 15 along the central axis of the vessel. The central bore 37 receives one end of the structural support rod 23 to concentrically align and mechanically support the electrode structure. The conductor disk 19 comprises a generally cylindrical plate of electrically conductive material having a first outer diameter approximately the same as the outer diameter of the coil conductor 20 and a second outer diameter slightly less than the inner diameter of the coil conductor 20 so as to define a shoulder 53 for engaging one end of the conductor coil 20. Conductor disk 19 also includes an axially extending aperture 49 for receiving therethrough the internal end 40 of the conductor rod 35. The conductor disk 19 fixedly attaches to the end plate 9 with the aperture 49 thereof co-axially aligned with central aperture 14 of end plate 9. The internal portion 40 of rod 35 extends through the aperture 49 of the conductor disk 19 to give the electrode structure 30 structural stability. Referring still to Figures 1 and 2, the tubular coil conductor 20 constructed in accordance with the preferred embodiment comprises a uniform cylindrical structure 44 with an external end 47 engaging the shoulder 53 of the conductor disk 19, an internal end 51, and a plurality of inclined slits 26 machined into the cylindrical structure 44. Cylindrical structure 44 is constructed of an electrically conductive material having a generally fixed radius, and connects electrically to conductor disk 19. Slits 26 extend from the internal end 51 of cylindrical structure 44 and spiral approximately 180° along the circumference of the cylindrical structure 44. The plurality of slits 26 are generally equally spaced along the surface of the cylindrical structure 44 to define a plurality of current paths 55 of approximately one-half turn each about the circumference of the tubular coil conductor 20. In the preferred embodiment of Figure 2, three slits 26 are provided defining three current paths 55. However, any number of slits 26 (greater than two) may be provided. The angle of incidence between each slit 26 and the interior end 51 of coil 20 may be arbitrarily chosen, but in the preferred embodiment, is approximately 20 degrees. The interior end 51 of tubular coil conductor 20 electrically connects to the main electrode 17 through a plurality of electrical connectors 12 associated one each with a respective current path 55. As shown in the preferred embodiment of Figure 2, connectors 12 may comprise electrically conducting clips permanently mounted to the interior end 51 of coil conductor 21 at the end of current path 55 adjacent to slit 26. Alternatively, connectors 12 may comprise integral projections formed on the interior end 51 of coil conductor 20 or on the adjoining surface of the main electrode 17, as described in our earlier Application. Referring still to Figures 1 and 2, the main electrode 17 comprises an electrically conductive circular disk that connects electrically to electrical connectors 12 of coil conductor 20. Main electrode 17 has a diameter approximately equal to the diameter of coil conductor 20 and defines an interior surface 57 facing the main electrode 17 of the opposing electrode structure and a back surface 48 facing the interior end 51 of coil conductor 20 and adjoining electrical connectors 12. Referring still to Figures 1 and 2, structural support rod 23 is constructed of a high dielectric material and includes a cap 42 fixedly attached to the back surface 48 of main electrode 17 and a rod portion 46 extending through the electrode structure 30, along the central axis of vessel 15. Cap 42 has a diameter somewhat less than that of coil conductor 20 and main electrode 17. Rod portion 46 of support rod 23 has a diameter slightly less than the inner diameter of the bore 37 in conductor rod 35. The rod portion 46 extends through coil conductor 20, conductor disk 19, end plate 9 and into bore 37 in external conductor rod 35, thereby co-axially aligning electrode structure 30 and reducing stress on coil conductor 20 and main electrode 17. Referring now to Figure 1, movable electrode structure 25 is constructed in a manner substantially the same as the stationary electrode structure 30 described supra . One difference, however, relates to the structure of the conductor disk and the coil conductor 20. Movable electrode structure 25 comprises an external conductor rod 35′ extending through the central aperture 14 of end plate 8, a conductor disk 21, a tubular coil conductor 60 electrically connected to disk 21, a main electrode 17′ electrically connected to coil conductor 60 and a structural support rod 23′ extending through the central axis of the electrode structure 25. The external conductor rod 35′, main electrode 17′ and structural support rod 23′ are constructed in accordance with the description supra of the stationery electrode structure 30. Referring still to Figure 1, the conductor disk 21 and tubular coil conductor 60 also are constructed in accordance with the description supra of the electrode structure 30, except that the conductor disk 21 is of a uniform diameter (devoid of shoulder 53 on disk 19) and exterior end of the coil conductor 60 includes an inner diameter slightly greater than the outer diameter of the conductor disk 21 and somewhat greater than the inner diameter of the inter end of the conductor 60, thereby defining a circumferential shoulder 58 on the inner surface of the conductor 60 approximately halfway between the exterior and interior ends of the conductor 60. Conductor disk 21 of movable electrode structure 25 further comprises an interior face 64, an exterior face 66, an aperture 59 extending axially therethrough, and a circumferential lip 63 protruding from the exterior face 66 about the aperture 59 for engaging bellows 28. Aperture 59 receives therethrough conductor rod 35′, with circumferential lip 63 engaging rod 35′. Conductor disk 21 abuts the inner surface coil conductor 60, with the outer periphery of interior face 64 being fixedly attached to the shoulder 58 of coil conductor 60. The circumferential lip 63 is received within the bellows 28. The bellows 28 is any conventional bellows assembly having an interior end 75 engaging conductor disk 21, an exterior end 77 mounted to end plate 8, and a body portion 80 through which external conductor rod 35′ extends. Interior end 75 receives therein circumferential lip 63 of conductor disk 21. A majority of the body portion 80 lies within the coil conductor 60, thereby shielding the bellows from the electric fields within the vessel 15. The bellows drives an actuator (not shown) mounted on the rod 35′ to move rod 35′ axially. Tubular coil conductor 60 of movable electrode 60, like coil conductor 20, comprises a plurality of slits 27 and electrical connectors 24 defining a plurality of current paths 56. As disclosed in our earlier application the inclined slits 26, 27 are positioned approximately parallel to one another, with electrical connectors 12, 24 directly aligned. In operation, when the movable electrode structure 25 parts from stationary electrode structure 30 to interrupt current flow, an arc current flows across the electrode structures 25, 30. Current flows through one turn by passing through one current path 55, through connector 12, main electrode 17, through connector 24 and through current path 56. Due to the uniformly cylindrical configuration of the tubular coil conductors, the radial magnetic field is reduced, thereby eliminating significant cancellation of the axial magnetic field. In addition, more slits 26, 27 may be provided to further limit the generation of radial magnetic fields by the coil conductors 20, 60.

Claims: A vacuum interrupter comprises a vacuum vessel (15) housing a first electrode structure (30) having a main electrode (17); a second electrode structure (25) having a main electrode (17′); means (80) for moving at least one of the first and second electrode structures (25,30) axially of the other; and means (20,60) for generating an axial magnetic field about the main electrodes (17,17′) of the first and second electrode structures (25,30) and minimizing radial components of the magnetic field to enhance uniformity of distribution of current arcing between the main electrodes (17,17′) when the first and second electrode structures (25,30) are parted, characterised in that at least the first electrode structure (30) includes a support rod (23) attached at one end to the main electrode (17), extending through the generating means (20) and its other end being slidably mounted in a bore (37) formed in a conductor rod (35) mounted on and extending through a wall portion of the vacuum vessel (15), the support rod (23) being made of a dielectric material and the generating means (20) electrically interconnects the main electrode (17) and the conductor rod (35). A vacuum interrupter according to claim 1, characterised in that the field generating means (20,60) comprises for at least the first electrode structure (30), a generally cylindrical conductor (20) having a first end (51) and a second end (47); a plurality of inclined slits (26,27) in the first end (51) of the cylindrical conductor (20), the slits (26,27) being spaced one from the next and extending generally circumferentially from the first (51) end of the cylindrical conductor (20) at an acute angle thereto; and a conductor disk (19) substantially enclosing and electrically connected to the second end (47) of the cylindrical conductor (20), whereby said plurality of slits (26,27) define coil-like current paths (55,56) that generate an axial magnetic field which, because of the cylindrical configuration of the cylindrical conductor (20), has a minimal radial component. A vacuum interrupter according to claim 2, wherein at least the first electrode structure (30) includes a plurality of electrical connectors (12) positioned at the first end (51) of the cylindrical coil conductor (20) with one electrical connector (12) associated with each current path (55,56). A vacuum interrupter according to claim 2 or claim 3, wherein each current path (55,56) defines substantially a half turn on the cylindrical coil conductor (20). A vacuum interrupter according to any one of claims 2 to 4, wherein a plurality of the inclined slits (26) on the first electrode structure (30) are positioned substantially in parallel with a plurality of the inclined slits (27) on the second electrode structure (25). A vacuum interrupter according to any one of claims 2 to 5, wherein the vacuum vessel (15) has first and second end plates (9,8) and the first and second electrode structures (25,30) each has a tubular connector rod (35,55) extending through a respective one of the end plates and a respective conductor disk (19,21) the bore (37) of the respective connector rods (35,55) forming the slidable mounting for the pertaining support rod (23,23).

Inventors: BESTEL ERNEST F, BESTEL, ERNEST F.
Applicants: COOPER IND INC, COOPER INDUSTRIES, INC.
Application year: 1989
Main classification: H01H33
IPC codes: H01H33