VACUUM INTERRUPTER

Abstract: A cylindrical coil electrode (10) incorporated in a vacuum interrupter comprises a cylindrical body (12) having an opening at one end thereof, three electrical connectors (16) provided between the edge surface (15) of the opening of the cylindrical body and a main electrode (11). A second cylindrical coil electrode having slits parallel to the first cylindrical coil electrode is mounted in an opposing manner. Because of the above structure, one-turn current flow throughout the current paths so that a uniform axial magnetic field is applied to the main electrode, and an arc current can be uniformly distributed over the entire surface of the main electrode, thereby improving the current interruption performance of the vacuum interrupter.

Description: A vacuum interrupter for interrupting a large current generally includes a pair of main electrodes disposed in a vacuum vessel so as to be movable relatively towards and away from each other, coil electrodes mounted on the rear surfaces of the main electrodes, and rods extending to the exterior of the vacuum vessel from the rear surfaces of the coil electrodes. Current flows from one of the rods to the other through the coil electrodes and main electrodes. When one of the rods is urged by an actuator for interrupting the current, one of the main electrodes moves away from the other main electrode, and an arc current is generated to flow across the two main electrodes. This arc current is dispersed into filament-like arc currents by a magnetic field. Such a coil electrode is disclosed in, for example, US-A-3946179. In that coil electrode, arms, connected at one end to a rod, extend in a radial direction to connect at the other end thereof to one end of respective arcuate sections, and the arcuate sections extend in a circumferential direction to be electrically connected at the other end thereof to a main electrode. Thus, an arm and an assoicated arcuate section constitute a so-called L-shaped conductive member. Four L-shaped conductive members are mounted to the rod, and a clearance is formed between the adjacent ones of the four arcuate sections arranged in a circular pattern. Current flows throught the coil electrode via the route of the rod-arms-arcuate sections to the main electrode. Because of the presence of the clearances, the current flows through the four arcuate sections in the same direction, that is, the current flows substantially through an imaginary coil of one turn. This one-turn current produces a uniform axial magnetic field which acts to produce diffuse arc current flowing across the main electrodes. DE-A-2527319 discloses a somewhat similar disk-like electrode having part spiral arms and formed with a central raised portion or recess. Thus, the clearances present in the known coil electrode play an important role for generation of a uniform axial magnetic field in the arcuate sections. In spite of such a great effect exhibited by the clearances, the known coil electrode is defective in that the axial magnetic field is weak in the vicinity of the clearances. Generally, an arc current has such a tendency that it migrates from a low intensity portion towards a high intensity portion of an axial magnetic field. Therefore, the arc current flowing through the portions of the main electrode near the clearances migrates toward the central area of the main electrode where the intensity of the axial magnetic field is high, and concentration of the arc current to the central area of the main electrode having the high field intensity results in localized overheating of the main electrode, thereby degrading the capability of current interruption. Since, also, the entire area of the main electrode cannot be effectively utilized for the current interruption, it becomes necessary to increase the size of the main electrode. DE-A-3227482 discloses a vacuum interrupter comprising a pair of electrode assemblies disposed in a vacuum vessel so as to be relatively movable towards and away from each other; and rods extending out of the vacuum vessel from the rear of respective ones of the electrode assemblies; each electrode assembly comprising a substantially disk-shaped main electrode, a cylindrical coil electrode means electrically connected between the rear surface of each of the main electrodes and the respective rod, the electrode means including a hollow cylindrical body with an annular portion adjacent to the main electrode and a base portion at the end of the annular portion remote from the main electrode and with at least two substantially part helical high resistance paths extending along the body from its end adjacent to the main electrode through the annular portion and continuing into the base portion, and a plurality of electrical connections between an end edge surface of the annular portion and the respective main electrode; the cylindrical coil electrode means of the two electrode assemblies being similar and symmetrically arranged so that their electrical connections are opposite to one another and corresponding opposed ones of their part helical high resistance paths are substantially parallel to one another, and, according to the invention, such an interrupter is characterised in that the base portion contains a depression with a radially inwardly facing wall surface; and in that the paths continue so far into the base portion as to intersect and be exposed at and partly around the wall surface. With this structure, one-turn current flows throughout current paths separated by the high resistance paths so that a uniform axial magnetic field is applied to the main electrode, and an arc current can be uniformly distributed over the entire surface of the main electrode, thereby providing good current interruption performance of the vacuum interrupter. In the accompanying drawings:- Figure 1 is a partly sectional, schematic side elevation view of a vacuum interrupter according to the present invention; Figure 2 is a perspective exploded view of on electrode assembly incorporated in the vacuum interrupter shown in Figure 1; Figure 3 is a side view partially in phantom of two opposed electrode assemblies; and, Figure 4 is a top view partially in phantom of a cylindrical electrode of one of the electrode assemblies. As shown in Figure 1, a vacuum vessel 3 is formed by mounting a pair of end plates 2 one on each end of a cylindrical member 1 of an electrical insulating material. A stationary electrode assembly 4 and a movable electrode assembly 5 are disposed opposite to each other in the vacuum vessel 3, and a pair of rods 6 and 7 extend to the exterior of the vacuum vessel 3 from the rear surfaces of respective ones of the electrode assemblies 4 and 5. A bellows 8 is mounted between one of the rod 7 and the associated end plate 2. The bellows 8 acts to drive an actuator, not shown, mounted on the rod 7 in its axial direction. When the rod 7 is urged in its axial direction, the movable electrode assembly 5 is electrically moved away from the stationary electrode assembly 4, and an arc current 9 generated between these two electrode assemblies 4 and 5 produces metal vapour. The metal vapour attaches to an intermediate shield 1A supported in the insulating cylindrical member 1, and the arc is extinguished by being dispersed by a magnetic field generated in the axial direction of cylindrical coil electrodes 10. One of the cylindrical coil electrodes 10 is provided in each of the stationary and movable electrode assemblies 4 and 5. The cylindrical coil electrode 10 provided in the movable electrode assembly 5 will be explained with reference to Figure 2. The cylindrical coil electrode 10 is essentially identical in both the electrode assemblies 4 and 5. Referring to Figures 2-4, the cylindrical coil electrode 10 is mounted to the rear surface of a disk-shaped main electrode which is imperforate, i.e. has a continuous surface from edge to edge. The coil electrode 10 includes a cylindrical body 12 having an opening at one end and a closed flat base portion 13, with a central cup-shaped depression 29, at the other end. The body 12 is formed in one piece with the rod 7. A spacer 14 made of a high resistance material, for example, a stainless steel, is disposed between the main electrode 11 and the bottom 13 of the cylindrical body 12. Projections 16 are formed on an annular end edge surface 15 around the opening of the cylindrical body 12, and the main electrode 11 is electrically connected to the projections 16. The projections 16 could alternatively be formed on the main electrode. Inclined slits 26 are formed at positions of the cylindrical body 12. One end of each of the inclined slits 26 extends from the end surface 15 of the opening of the cylindrical body, adjacent to a projection 16. Each inclined slit 26 may be replaced by a stepped slit or by a member of a high resistance material, for example, a stainless steel. The requirements is that current flowing from the input end toward the output end of one of the part helical current paths can be separated from current flowing from the input end toward the output end of an adjacent current path, so that current of one turn of an imaginary coil can flow throughout the current paths. An electrical coil such as described above is mounted on both main electrical contacts. An essential feature of the invention is that opposed portions of the inclined slits 26 are approximately parallel to each other. As shown in Figure 3, opposed cylindrical coil electrodes 10 are mounted opposed to each other so that projections 16 of opposite electrodes will be directly opposite one another. In this position, it is seen that inclined slits 26 for the opposed electrodes will be angularly offset but overlap one another as seen in side elevation (Figures 3). Thus, functionally, current flowing in one direction, for example, from the bottom coil electrode on the left, will flow up, as indicated by arrows, through the projections 16, both main electrodes 11, and through the projections 16 for the top coil electrode. In operation, when the movable electrode assembly 5 is parted away from the stationary electrode assembly 4 to interrupt the current flow, an arc current 9 flows across the two electrode assemblies 4 and 5. As shown by the arrows, the arc current 9 flows through the projections 16 and flows then into the rod 7 through the bottom 13 of the cylindrical body 12. It will be seen from the above description of the present invention that current flowing into and flowing out is equivalent to current flowing through one turn of an imaginary coil. Thus, an axial magnetic field H produced by such a current is uniformly applied over the entire surfaces of the main electrodes 11, and the arc current 9 is uniformly distributed over the entire surface of the main electrodes 11. Therefore, the current interrution performance can be good, and the vacuum interrupter can be small in its overall size because of the capability of effective utilization surface of the main electrode for current interruption. In the illustrated example, three projections 16 are provided on the cylindrical body 12. However, provision of more than three projections, for example four, six or more projections can further reduce the overall size of the vacuum interrupter, because current is further dispersed to prevent localized overheating at the projections. Further, the intensity of an eddy current generated by a magnetic field produced by current flowing through the bottom 13 of the cylindrical body 12 is limited by the presence of slits 28 which are continuations of the slits 26 into the base portion 13 of the body 12. These base slits 28 are oriented to have a component tangential to the cup-shaped depression in the base portion. The resultant magnetic flux is not strong enough to cancel the axial magnet field H. Therefore, an undesirable intensity reduction of the axial magnetic field H can be prevented. In this connection, provision of more slits 28 can further prevent an undesirable reduction of the intensity of the axial magnetic field H.

Claims: A vacuum interrupter comprising a pair of electrode assemblies (4,5) disposed in a vacuum vessel (3) so as to be relatively movable towards and away from each other; and rods (6,7) extending out of the vacuum vessel from the rear of respective ones of the electrode assemblies; each electrode assembly comprising a substantially disk-shaped main electrode (11), a cylindrical coil electrode means (10) electrically connected between the rear surface of each of the main electrodes and the respective rod, the electrode means (10) including a hollow cylindrical body (12) with an annular portion adjacent to the main electrode and a base portion (13) at the end of the annular portion remote from the main electrode and with at least two substantially part helical high resistance paths (26,28) extending along the body from its end adjacent to the main electrode through the annular portion and continuing into the base portion (13), and a plurality of electrical connections (16) between an end edge surface (15) of the annular portion and the respective main electrode; the cylindrical coil electrode means (10) of the two electrode assemblies being similar and symmetrically arranged so that their electrical connections (16) are opposite to one another and corresponding opposed ones of their part helical high resistance paths are substantially parallel to one another; characterised in that the base portion (13) contains a depression (29) with a radially inwardly facing wall surface; and in that the paths (28) continue so far into the base portion as to intersect and be exposed at and partly around the wall surface. A vacuum interrupter according to claim 1, in which the electrical connections (16) are adjacent to the ends of respective ones of the paths. A vacuum interrupter according to claim 1 or claim 2, in which the high resistance paths are slits (26, 28). A vacuum interrupter according to any one of the preceding claims, wherein each rod (6,7) is formed in one piece with the cylindrical body (12) of the respective electrode assembly (4, 5). A vacuum interrupter according to any one of the preceding claims, wherein each of the main electrodes (11) has a continuous surface from edge to edge. A vacuum interrupter according to any one of the preceeding claims wherein the high resistance paths (26, 28) define a current path of at least one full turn about the combined length of the first and second cylindrical coil electrode means.

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