Vacuum interrupter

Abstract: In a vacuum interrupter comprising a disc-shaped stationary electrode (20) and a disc-shaped movable electrode (30) arranged in an evacuated envelope in opposed relationship, a slot (40,50) or a salient part (80) is formed on the surface of both the electrodes and thereby a path of an arc current in disconnection operation of both the electrodes is formed along the circumference of the disc-shaped electrode. The shape and position of the slot is selected so that the arc current flows uniformly along the entire circumference of both the electrodes.

Description: The present invention relates generally to a vacuum interrupter which is used in a vacuum circuit breaker or the like, and more particularly to a vacuum interrupter having an electrode-structure which generates a magnetic field in the direction parallel to an electric arc generated after disconnection of the vacuum interrupter. In a vacuum interrupter for interrupting a heavy-current in an evacuated envelope, diffusion of an arc generated after disconnection operation of the vacuum interrupter have been studied in order to improve interruption characteristic thereof. The diffusion of the arc is performed by a magnetic field which is generated by an arc current flowing after the disconnection operation. A conventional vacuum interrupter comprising such an arc diffusion means is elucidated hereafter with reference to FIGs. 12 to 14. FIG. 12 is a cross-section of a side view showing schematic structure of the conventional vacuum interrupter. Referring to FIG.12, an evacuated envelope 4 is composed of a cylindrical insulating container 1 and end plates 2 and 3 for sealing both ends of the insulating container 1. A disc-shaped stationary electrode assembly 6 connected to a stationary electrode rod 5 and a disc-shaped movable electrode assembly 7 connected to a movable electrode rod 8 are arranged in opposed relationship in the evacuated envelope 4. The movable electrode assembly 7 is constructed so as to connect or disconnect with respect to the stationary electrode assembly 6 by an operation mechanism (not shown) connected mechanically to the movable electrode rod 8. A bellows 10 is disposed between the end plate 3 and the movable electrode rod 8, and thereby air-tightness of the evacuated envelope 4 is maintained and the movable electrode rod 8 is permitted to move in the axial direction (upward or downward in FIG.12). Moreover, a shield 9 is arranged in a manner of surrounding the stationary electrode assembly 6 and the movable electrode assembly 7 in the evacuated envelope 4. In a conventional vacuum circuit breaker having the vacuum interrupter constructed as mentioned above, when a disconnecting instruction is inputted to the vacuum circuit breaker, the movable electrode assembly 7 is disconnected from the stationary electrode assembly 6 by activation of the operation mechanism. At the instant, an arc A is generated between the stationary electrode assembly 6 and the movable electrode assembly 7, and an arc current flows across the stationary electrode assembly 6 and the movable electrode assembly 7. A magnetic field in the axial direction is generated between the stationary electrode assembly 6 and the movable electrode assembly 7 by controlling a direction of the arc current flowing across the stationary electrode assembly 6 and the movable electrode assembly 7. The magnetic field in the axial direction serves to diffuse a plasma arc produced between both the electrode assemblies onto entire surfaces of the stationary electrode assembly 6 and the movable electrode assembly 7 which are arranged in opposed relationship. An arc voltage across the stationary electrode assembly 6 and the movable electrode assembly 7 is decreased by diffusing the plasma arc during the disconnection operation, and a temperature rise in both the electrode assemblies is significantly suppressed. An example of the conventional vacuum interrupter having the electrode-structure for generating the magnetic field is shown in US-A-4 473 731 and GB-A-2 111 309. FIG.13 is an exploded perspective assembly view of a movable electrode assembly 7 in the vacuum interrupter of US-A-4 473 731 and GB-A-2 111 309, and FIG.14 is a plan view of the movable electrode assembly 7 shown in FIG.13. Referring to FIG.13, a movable electrode 21 is mounted on the top of a movable electrode rod 8 through a short circuit member 22, and is supported at the central part by a support member 23 which is made of high resistance material and fixed on the movable electrode rod 8. Four arms 21a are formed on the peripheral portion of the movable electrode 21 along the circumference thereof. On the other hand, four arms 22a extending in radial directions are formed on the short circuit member 22. The ends of the arms 22a of the short circuit member 22 contact the respective arms 21a of the movable electrode 21, and the movable electrode 21 is electrically connected to the short circuit member 22. The movable electrode assembly 7 comprising the movable electrode 21, the movable electrode rod 8, the short circuit member 22 and the support member 23 shown in FIG.13 is arranged in the evacuated envelope 4 in opposed relationship to the stationary electrode assembly 6 as shown in FIG.12. Referring to FIG.14, current paths of the arc current are illustrated by arrows. The arc current flows from the central part P of the movable electrode 21 to the connection parts of the arms 21a in the radial direction as shown by arrows X, and passes through the arms 21a along the circumference of the movable electrode 21 as shown by arrows Y. Subsequently, the arc current flows to the movable electrode rod 8 through the arms 22a of the short circuit member 22 in the radial directions as shown by arrows Z. Consequently, four fan-shaped current paths are formed as shown in the plan view of FIG.14, and magnetic fields in the axial direction are generated in these fan-shaped regions by the known right-handed screw rule. The plasma arc produced between the stationary electrode assembly 6 and the movable electrode assembly 7 is diffused by the magnetic field. The intensity of the magnetic field in the fan-shaped region is larger than that in the region between neighboring two fan-shaped regions. Therefore, the intensity of the magnetic field is not uniform between the stationary electrode assembly 6 and the movable electrode assembly 7, and the plasma arc is not effectively diffused owing to the lack of uniformity of the magnetic field. A vacuum interrupter according to the preamble of claim 1 is known from EP-A-0 113 961. An object of the present invention is to provide a vacuum interrupter in which a uniform magnetic field is generated between a stationary electrode and a movable electrode by guiding an arc current along full circumference of the stationary electrode and the movable electrode. This object is solved by the subject matter of claim 1. Further advantageous modifications of the present invention are subject matter of the dependent claims. According to the configuration of the vacuum interrupter of claim 1, the coil part arranged along the circumference of the coil electrode is protruded to the back surface of the main electrode and contacts the main electrode Therefore, the magnetic field in the axial direction of the coil electrode is enhanced, and leak of magnetic flux decreases. Consequently, suitable distribution of the magnetic field is realizable, and the arc in disconnection operation is effectively diffused. And thereby the vacuum interrupter having superior disconnection characteristic can be provided. Moreover, the vacuum interrupter which is superior in mechanical strength of the coil electrode can be provided. In the drawings: FIG.1 is an exploded perspective assembly view of an electrode assembly of the vacuum interrupter in a first embodiment in accordance with the present invention; FIG.2(a) is a perspective view of the electrode assemblies in the first embodiment; FIG.2(b) is a cross-section of the electrode assembly in the first embodiment; FIG.3(a) is an exploded perspective assembly view of an electrode assembly in the first embodiment; FIG.3(b) is a perspective view of an electrical conducting member in the first embodiment; FIG.3(c) is a cross-section of the electrode assembly in the first embodiment; FIG.4(a) is a perspective view of electrode assemblies of a second embodiment in accordance with the present invention; FIG.4(b) is a cross-section of the electrode assembly of the second embodiment; FIG.5(a) is a perspective view of electrode assemblies of an example of the second embodiment; FIG.5(b) is a cross-section of the example of the electrode assembly in the second embodiment; FIG.6 is a perspective view of electrode assemblies of another example of the second embodiment; FIG.7 is a perspective view of electrode assemblies of a vacuum interrupter for elucidating the subject matter of the present invention, which is, however, not part of the present invention; FIG.8 is an exploded perspective assembly view of the electrode assemblies shown in FIG.7; FIG.9 is a cross-section of relevant parts of the movable electrode assembly shown in FIG.7; FIG.10 is a perspective view of electrode assemblies of the vacuum interrupter in a third embodiment in accordance with the present invention; FIG.11 is a cross-section of the movable electrode assembly shown in FIG.10; FIG.12 is the cross-section of the vacuum interrupter of the prior art; FIG.13 is the exploded perspective assembly view of the movable electrode assembly of the vacuum interrupter of the prior art; FIG.14 is the plan view of the movable electrode of the vacuum interrupter shown in FIG.58. FIG.1 is an exploded perspective assembly view of the electrode assembly of the vacuum interrupter in a first embodiment. Referring to FIG.1, coil electrodes 43 made of conductive material are provided with ring-shaped holding parts 43a at the central parts which are put on the bosses 5a and 8a of the electrode rods 5 and 8. Four arms 43b are extended from the holding part 43a to the radial direction. Arc-shaped coil parts 43c are connected to the ends of the respective arms 43b and are arranged on a circular. The coil parts 43c are protruded in the axial direction and contact with the back surface of the respective disc-shaped main electrodes 41 at the entire circumferential surfaces 43d. Support members 42 mechanically support the back surfaces of the respective main electrodes 41. The support members 42 are made of high resistance material such as stainless steel, and rod parts 42a are inserted in a supporting hole 8b of the electrode rods 8 and are fixed thereby. A disc-shaped supporting part 42b supports the central part of the main electrodes 41. Operation of the vacuum interrupter in the first embodiment is elucidated with reference to FIG.2(a). FIG.2(a) is a perspective view showing disconnection state of the electrode assemblies. Currents flow from an arc spot P generated on the main electrode 41a to the circumference of the main electrode in radial direction as shown by dotted lines. When the currents reach the coil part 43c of the coil electrode 43, the current flows in the coil part 43c which is lower in resistance than the main electrode 41a, and reaches the electrode rod 8 through the arm parts 43b and the holding part 43a of the coil electrode 43 shown in FIG.2(b). The current flows in the directions shown by dotted lines with arrow in the other main electrode 41b. Consequently, the magnetic field in the axial direction is generated between both the main electrodes and thereby the arc is diffused. According to the first embodiment, (1) First, since the upper surfaces 43d of the coil parts 43c are closely contacted with the respective main electrodes 41a and 41b, respectively, distances from the coil parts 43c of the coil electrodes to the surfaces of the main electrodes are reduced. Consequently, the intensity of the magnetic field in the axial direction between both the electrodes is enhanced with respect to the prior art. Moreover, leak of the magnetic flux is reduced by the above-mentioned structure, and thereby the distribution of the magnetic field is improved. Since the magnetic field in the axial direction having a high intensity and an improved distribution can be generated, effect for diffusing the arc to the entire surfaces is enhanced, and disconnecting ability is also improved. (2) Additionally, since the entire upper surfaces of the coil parts 43c are contacted with the back surfaces of the main electrodes 41a and 41b, there is an effect to be enhanced in mechanical strength. A cross-shaped good conductivity member 44, for example, is formed on the upper surface 44b of the support member 42 as shown in FIG.3a in the first embodiment such that the main part of the current from the arc spot P flows to the ends of the coil parts 43c through the cross-shaped good conductive member 44 formed on the upper surface of the support member 42. Subsequently, the current flows to the electrode rod 8 through the arm parts 43b of the coil electrode 43 and the holding part 43a. The good conductivity member 44 formed on the upper surface of the support member 42 serves to lead the arc current generated on the main electrode 41 to the end of the coil part 43c as much as possible. Consequently, the current flowing the coil part 43c is increased, and the intensity of the magnetic field is increased. The good conductivity member 44 may be formed to other shape which can effectively flows the current to the coil part 43c other than the cross, for example may be formed to a disk-shape as shown in FIG.3(b). The good conductivity member 44 serves to reduce the resistance between both the electrode assemblies and to suppress the current which leaks to the electrode rod 8 through the main electrodes 41 and the support members 42. FIG.3(c) is a partial cross-section of assembled movable electrode assembly 43. FIG.4(a) is a perspective view of the electrode assemblies of the vacuum interrupter in a second embodiment. Referring to FIG.4(a), high resistance parts 45 are slots or fillers made of high resistance material such as stainless steel filled in the slots and are disposed inward from the circumference of the main electrode 41 along the circumference. The high resistance parts 45 are formed along the arm parts 43b of the coil electrodes 43 extending to the radial directions and the arm parts 43c extending along the circumference, and are terminated at the positions which are shorter than the arm length of the arm parts 43c. Moreover, other high resistance parts 46 are formed in the radial directions of the main electrode 41. The high resistance parts 46 are made of high resistance material such as stainless steel or may be substituted with slits. Other configuration in the second embodiment is identical with that of the first embodiment, and therefore elucidation is omitted. In operation of the second embodiment, the high resistance parts 45 formed along the circumference serve to flow the current along the coil part 43c as much as possible. The intensity of the magnetic field generated by the coil electrodes 43 is enhanced, and uniformity of the magnetic field is improved. When the magnetic field in the axial direction is generated by the coil electrodes, an eddy current is generated on the main electrode 41 by the magnetic field. Consequently, a magnetic field having the reverse direction is generated by the eddy current, and the intensity of the magnetic field in the axial direction is reduced. The high resistance parts 46 in the radial directions of the second embodiment serve to prevent the reduction of the magnetic field in the axial direction due to the eddy current which is generated on the main electrode 41. In the vacuum interrupter of other example in the second embodiment, as shown in FIG.5(a), reentrants 47 are formed on the central contact surfaces of the main electrodes 41a and 41b so as to reduce the resistance between both the electrode assemblies and to be easy to move the arc. FIG.5(b) is a partial cross-section of the electrode assembly in the example. Protrusions 48 may be formed on the main electrodes 41a and 41b as shown in FIG.6 to obtain the same effect as the reentrants 47 in FIG.5(b). In the second embodiment, though four arm parts 43b and four coil parts 43c are formed on the coil electrode 43, the number of the arm parts 43b and the coil parts 43c of the coil electrode 43 may be changed in order to vary the intensity of the magnetic field in accordance with the change of operation condition or contact material of the vacuum interrupter. In the above-mentioned case, the same effect is realizable. In the vacuum interrupter, a high withstand voltage characteristic is required to withstand a voltage due to a shock wave other than the voltage in the frequency of an electric utility. For this reason, the vacuum interrupter must be configurated so as to maintain the high withstand voltage characteristic between the stationary electrode and the movable electrode. In the conventional vacuum interrupter having the electrodes for generating the magnetic field in the axial direction, since the outer diameter of the main electrode is substantially equal to the outer diameter of the coil electrode, a radius of curvature in the circumferential part of the main electrode must be increased in order to improve the withstand voltage characteristic. In order to increase the radius of curvature, a thickness of the main electrode must be increased, and thus there is a difficulty to miniaturize the vacuum interrupter. FIG.7 is a perspective view of the electrode assemblies of a vacuum interrupter for elucidating for the subject matter of the present invention, which is, however, not part of the present invention, and FIG.8 is an exploded perspective assembly view of the electrode assemblies in FIG.7. FIG.9 is a cross-section of a movable electrode assembly 330 in FIG.7. Both the electrode assemblies of the vacuum interrupter shown in FIG.7 are arranged in the evacuated envelope, and are configurated to connect or disconnect with each other by the operation mechanism (not shown). The electrode assemblies comprise a stationary electrode assembly 320 fixed on the evacuated envelope through a insulating member and a movable electrode assembly 330 which is connected or disconnected with the stationary electrode assembly 320 by moving upward or downward by activation of the operation mechanism. The configuration of the stationary electrode assembly 320 is substantially identical with that of the movable electrode assembly 330, and one of them is inverted and is arranged in opposed relationship to the other. As shown in the exploded perspective assembly view of FIG.8, the stationary electrode assembly 320 comprises the stationary electrode rod 5, a stationary coil electrode 311, a support member 312 and a stationary main electrode 313, and the movable electrode assembly 330 comprises the movable electrode rod 8, a movable coil electrode 316, a support member 315 and a movable main electrode 314. As shown in FIG.8, the stationary coil electrode 311 comprises a ring-shaped holding part 311a put on the stationary electrode rod 5 at the center part, four arm parts 311b extended from the holding part 311a in the radial directions and coil parts 311c connected to the respective arm parts 311b. The movable coil electrode 316 comprise a ring-shaped holding part 316a put on the boss 8a of the movable electrode rod 8 at the center part, and four arm parts 316b extended from the holding part 316a to the radial directions. The end surface of each arm part 316b is connected to an end of each arc-shaped coil part 316c, and these coil parts 316c are substantially arranged on the same circumference. As shown in FIG.8, a circular stepped pit is formed on the upper surface (the face opposed to the stationary electrode assembly 320) of the coil parts 316c, and in which the movable main electrode 314 is inserted. The movable main electrode 314 is provided with four arc-shaped circumference parts 314a separated from the movable main electrode 314 by respective slots 390. These circumferential parts 314a of the main electrode 314 is inserted in the stepped pit formed on the upper surface of the coil part 316c of the movable coil electrode 316. Moreover, a salient contact 314b which serves as an arc generation position is formed on the center part of the surface of the movable main electrode 314 opposing to the stationary main electrode 313. FIG.9 is a cross-section of the movable electrode assembly 330, showing the state that the movable main electrode 314 is inserted in the movable coil electrode 316. As shown in FIG.9, the circumferential part of the surface of the movable main electrode 314 opposing to the stationary main electrode 313 is made to a curved surface having a radius of curvature c 1 . Moreover, the circumferential part opposing to stationary main electrode 313 of the coil part 316c of the movable coil electrode 316 is made to a curved surface having a radius of curvature C 2 . In a similar manner, the circumferential edge of the salient contact 314b is made to a curved surface of a radius of curvature C 3 . The radius of curvature c 2 of the circumferential part of the coil parts 316c is made to equal to be the radius of curvature c 1 of the circumferential part of the movable main electrode 314 or to be larger than the radius of curvature c 1 . The stationary coil electrode 311 and the movable coil electrode 316 are made of alloy of Cu or Ag including Cu, Cu+Cr as main material. As shown in FIG.8, the support member 315 is made of high resistance material such as stainless steel and mechanically supports the movable main electrode 314 by contacting the lower surface of the movable main electrode 314. A dot-shaped shaft 315a extending in the axial direction of the support member 315 is inserted in a support hole formed on the boss 8a of the movable electrode rod 8 and is fixed thereby. Subsequently, in the electrode assemblies configurated as mentioned above the current flow in generation of the arc is elucidated with reference to FIG.7. When the movable electrode assembly 330 is disconnected from the stationary electrode assembly 320, an arc A is generated between a salient contact formed on a hidden surface of the stationary main electrode 313 and the salient contact 314b of the movable main electrode 314. At this time, the current flows from the stationary electrode rod 5 to the arc generation point of the stationary main electrode 313 through the stationary coil electrode 311, for example. Subsequently, in the movable electrode assembly 330, the current flows from the arc generation point to the movable electrode rod 8 through the movable main electrode 314 and the movable coil electrode 316. Consequently, since the current flows along the circumference of the coil parts 311c of the stationary electrode assembly 320 and the coil parts 316c of the movable electrode assembly 330, the magnetic field in the axial direction is generated between both the electrodes, and the plasma arc generated in the disconnection operation is diffused and is arcextinguished. In the vacuum interrupter described above, an electric field on the circumferential parts of the electrode assemblies 320 and 330 is relaxed by means of the curved part formed on the circumferential parts of the main electrodes and the coil electrodes. Moreover, since the coil parts 311c and 316c of the respective coil electrodes 311 and 316 are configurated so as to oppose directly, the magnetic field in the axial direction is effectively generated between both the electrodes. Consequently, the vacuum interrupter described above is superior in the withstand voltage characteristic and disconnection characteristic and is usable for a switch in a high voltage circuit. FIG.10 is a perspective view of the electrode assemblies of the vacuum interrupter in a third embodiment, and FIG.11 is a cross-section of a movable electrode assembly 330 in the electrode assemblies of FIG.10. In FIGs.10 and 11, elements having the same structure and function as the elements shown in Figs. 7 to 9 are identified by like numerals and the elucidation is omitted. The stationary electrode assembly 320 and the movable electrode assembly 330 shown in FIG.10 are arranged in the evacuated envelope in opposed relationship and have substantially the same structure. The movable electrode assembly 330 is configurated to connect or disconnect with the stationary electrode assembly 320, and they are arranged in point symmetry. As shown in FIGs. 33 and 34, the movable electrode assembly 330 comprises the movable coil electrode 316 having curved circumferential part and a movable main electrode 324 having plural slots 360 in the radial directions. Furthermore, the movable main electrode 324 is provided with slots 350 along the circumference. The movable main electrode 324 is inserted in the circular stepped pit of the movable coil electrode 316 in a similar manner shown in FIG.10. The plural slots 360 formed on the movable main electrode 324 in the radial directions regulate the direction of the current to desired directions in the movable main electrode 324 in generation of the arc. Consequently, a uniform magnetic field in the axial direction is generated between both the electrodes by the current flowing along the circumference of the coil parts 316c of the movable coil electrode 316. In the cross-section of FIG.11, a cross-shaped conducting member or a disk-shaped conducting member 317 is formed on the upper surface of the support member 315 contacting the movable main electrode 324. The conducting member 317 is made of a good conductor and serves to effectively lead the current flowed in the movable main electrode 324 to the circumferential part 324a of the movable main electrode 324. The current in generation of the arc is effectively led to the circumferential parts of both the electrodes and the coil parts of both the coil electrodes by contacting the conducting member 317 to the back face of the movable main electrode 324. Thereby the intensity of the magnetic field in the axial direction is enhanced between both the electrodes. As shown in FIG.11, the radius of curvature c 2 of the circumferential parts of the coil parts 316c is made to be equal to or more than the radius of curvature c 1 of the circumferential parts 324a of the movable main electrode 324. In the vacuum interrupter of the third embodiment configurated as mentioned above, since concentration of electric field on the opposed surfaces of both the electrode assemblies is relaxed and the coil parts of both the coil electrodes are made to directly oppose with each other, the vacuum interrupter in the third embodiment is superior in the withstand voltage characteristic and the disconnection characteristic.

Claims: Vacuum interrupter having a pair of electrode assemblies arranged in an evacuated envelope in a manner to connect or disconnect with each other by respective electrode rods (5, 8), wherein: at least one of said electrode assemblies comprises a main electrode (41) and a coil electrode (43), and said coil electrode (43) is mounted on the back surface of said main electrode (41) and comprises: arm parts (43b) extended from said electrode rod (5, 8), and coil parts (43c) connected to said respective arm parts (43b), protruded to said main electrode (41) and arranged on a circumference, wherein the upper surfaces of said coil parts (43c) of said coil electrode (43) are connected to the back surface of said main electrode (41) on the entire circumference, and thereby, a magnetic field in an axial direction of said electrode assemblies is generated between said pair of electrode assemblies by a current flowing said main electrode (41) and said coil electrode (43), characterized in that : a support member (42) is disposed to support said main electrode (41) by contacting to the back surface thereof, and said support member (42) comprises a member (44) having high electrical conductivity formed on the upper surface thereof so as to extend from the central part of said support member (42) to the circumference. Vacuum interrupter according to claim 1, characterized in that a high resistance part (45) is disposed on the inner side of said coil part (43c) of said coil electrode (43) along the circumference of said main electrode (41) connected to said coil part (43c). Vacuum interrupter according to claim 1 or 2, characterized in that a high resistance part (46) is disposed on the inner side of said coil part (43c) of said coil electrode (43) in the radial direction of said main electrode (41).

Inventors: HASEGAWA HIROSHI, KOYAMA KENICHI, TOYA HIDEAKI, YORITA MITSUMASA, HASEGAWA, HIROSHI, KOYAMA, KENICHI, TOYA, HIDEAKI, YORITA, MITSUMASA, HASEGAWA, HIROSHI, C/O MITSUBISHI DENKI K.K., KOYAMA, KENICHI, C/O MITSUBISHI DENKI K.K., TOYA, HIDEAKI, C/O MITSUBISHI DENKI K.K., YORITA, MITSUMASA, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1993
Main classification: H01H33
IPC codes: H01H33