Switchgear

Abstract: A switchgear comprises, in a housing containing an arc extinguishing gas, a pair of separable contacts 2, 3 defining therebetween an arcing region in which an electric arc is generated when the contacts are separated. A cylindrical wall 6 and an insulating nozzle 22 are provided for defining a gas storage chamber 9 around the stationary contact, communicating with the arcing region, for storing the arc extinguishing gas to be increased in pressure by heat from the arc. The insulating nozzle defines an opening through which the movable contact 3 movably extends and through which the pressurized arc extinguishing gas flows. Around the arcing region a magnet system is disposed for generating a magnetic field in the opening of the gas storage chamber for rotating and elongating the electric arc generated in the arcing region upon current interruption. The magnet system is an annular magnet 8 at the nozzle and an annular magnet 45 around the stationary contact. A novel design of the nozzle enhances the arc-extinguishing capability.

Description: This invention relates to a switchgear for an electric circuit and, more particularly, to a self-extinguishing type switchgear having a magnet for generating alternating magnetic flux against an electric arc for driving the arc upon separation of the contacts. Fig 1 is a fragmental vertical sectional view of the separated state of a conventional switchgear disclosed in Japanese Utility Model Laid-Open No. 59-77742, and Fig. 2 is a sectional view taken along line II - II of Fig. 1. In the figures, the reference numeral (1) designates a first terminal plate, (2) designates a stationary contact which is one of a pair of contacts attached to the first terminal plate (1), (3) designates a movable contact which is the other contact for engaging and separating the stationary contact (2), (4) designates a collector which is in sliding contact with the movable contact (3), (5) designates a second terminal plate attached to the collector (4), (6) designates a stationary outer cylinder secured to the first terminal plate (1) at one end and having an opening at the other end, and (7) designates an insulating nozzle secured to the opening of the stationary outer cylinder (6) and made of an insulating material, the insulating nozzle having a through hole (7a) formed so that the movable contact (3) is inserted and slidable therealong. The reference numeral (8) designates an annular magnet disposed in the insulating nozzle (7), (9) designates a storage chamber defined by the stationary outer cylinder (6) for storing an electrically insulating, arc extinguishing gas, (9a) designates a storage chamber opening through which the insulating arc extinguishing gas flows into and from the storage chamber, (10) designates an electric arc which is generated when the movable contact (3) separates from the stationary contact (2), (11) designates a cylinder attached at one end to the outer surface of the stationary outer cylinder (6), (12) designates a piston mounted to the movable contact (3) and in sliding contact with the inner surface of the cylinder (11), and (13) designates a negative pressure chamber defined between the cylinder (12) and the bottom face of the stationary outer piston (6) that is formed when the movable contact (3) moves in the direction of an arrow A. Next, the operation will be described. With this switchgear in its closed state in which the current flows from the first terminal plate (1) to the stationary contact (2) and from the movable contact (3) to the second terminal plate (5) through the collector (4), when the movable contact (3) is driven in the direction of the arrow A by the operating mechanism (not shown), the movable contact (3) separates from the stationary contact (2) and an electric arc is generated between the two contacts. On the other hand, the annular magnet (8) provides a driving force proportional to the product of the intensity of the magnetic field generated by the magnet and the magnitude of the arc current against the arc (10). The arc (10) is rotated by this driving force and elongated into the storage chamber (9) by centrifugal force. When the current phase of the arc generated upon the interruption is in the vicinity of the current peak, the surrounding insulating arc extinguishing gas heated by the arc (10) flows into the storage chamber (9) through the storage chamber opening (9a) and is stored therein, increasing the temperature and the pressure of the insulating arc extinguishing gas within the storage chamber (9). Further, when the current phase is in the vicinity of current zero, the pressure of the arc (10) is low and, conversely the insulating arc extinguishing gas is blown or puffed from the storage chamber (9) to the arc (10), leading to extinction of the arc. However, when the arc current effective value is small, the pressure rise within the storage chamber (9) is not sufficient, so that the pressure of the insulating arc extinguishing gas within the storage chamber (9) is small and, accordingly, the arc extinguishing capability is insufficient. In order to cope with this, according to the conventional device, a negative pressure chamber (13) in which pressure decreases upon the interrupting operation of the movable contact (3) is provided, thereby generating a forced gas flow from the storage chamber (9) to the negative pressure chamber (13) through the arc (10) and the insulating nozzle (7), and a magnetic field is applied to the arc (10) to rotate it, thereby generating a relative flow movement between the insulating arc extinguishing gas and the arc, thus extinguishing the arc (10) upon a small current interruption. Since the conventional device is constructed as described above, a proper arc driving cannot be achieved in response to the arc current value, the effect of the permanent magnet being insufficient, a problem is posed wherein a negative pressure generating device must be added. Also, since the magnet is made annular, and since the conventional cast magnet such as an alnico magnet is high in electrical conductivity, the magnet is heated and degraded quickly by the eddy current resulting from the current flowing through the switchgear. However, in the conventional switchgear which is constructed and operates as described above, since the magnet (8) is magnetized in the axial direction, the radial component of the magnetic flux () at the gas storage chamber opening (9a) is small and the magnetic force in that direction is weak. Therefore, the arc driving force in the circumferential direction acting on the arc (10) at the gas storage chamber opening (9a) is small, so that the heating effect of the insulating arc extinguishing gas within the gas storage chamber opening (9a) is small. Therefore, the pressure increase of the insulating arc extinguishing gas within the storage chamber (9) is small, and the blasting of the insulating arc extinguishing gas to the arc (10) is weak, posing a problem that sufficient arc extinguishing effect cannot be obtained. Also, in the conventional switchgear which is constructed as described above, the gas heating effect by the arc is small upon a small current interruption, so that the gas pressure increase within the gas storage chamber (9) is small. Also, since the first contact composed of a finger contact has a plurality of slits axially extending from its tip, it is difficult for the leg of the arc (10) on the first contact (2) to be moved by the magnetic flux () generated by the magnet 8, posing a problem that the flow of the gas relative to the leg of the arc 10 is weak, providing only insufficient arc extinguishing effect. An object of the present invention is to provide a reliable switchgear of a simple structure in which no eddy current flows through the magnet and accordingly the magnet does not become heated, and in which the arc is driven properly in accordance with the arc current value. Another object of the present invention is to provide a switch gear improved in arc extinguishing capability at a small current interruption. Still another object of the present invention is to provide a switchgear which provides a stable interrupting capability even during a small current interruption. A further object of the present invention is to provide a switchgear improved in arc extinguishing capability at a small current interruption which is free from thermal degradation of the magnet even during large current arc generation. Another object of the present invention is to provide a switchgear in which the eddy current loss in the magnet is reduced to decrease the heating of the magnet, improving the stability and the operating life of the magnet. The present invention resides in a switchgear comprising, in a housing containing an arc extinguishing gas: - a stationary contact; a movable contact capable of contacting with and separating from said stationary contact, said movable contact and said stationary contact defining therebetween an arcing region in which an electric arc is generated when said contacts are separated; means defining a gas storage chamber around said stationary contact communicating with said arcing region for storing the arc extinguishing gas increased in pressure by heat from the arc; an insulating nozzle attached to said gas storage chamber defining an opening through which said movable contact movably extends and through which said arc extinguishing gas flows; and magnet means for generating a magnetic field in said opening of said gas storage chamber for rotating and elongating the electric arc generated between said stationary contact and said movable contact upon current interruption; characterized in that the said magnet means include a first annular magnet mounted to said nozzle and a second annular magnet disposed outside said stationary contact within said gas storage chamber. The gas storage chamber opening may be formed in a conical shape divergent toward the storage chamber. According to another aspect of the present invention, the magnet mounted to the nozzle is an annular magnet magnetized in the radial direction. The magnet mounted to the nozzle may be circumferentially divided into a plurality of sections and a non-magnetic material is circumferentially interposed between each of the magnet sections. The present invention will become more readily apparent from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: Fig. 1 is a fragmental vertical sectional view of the conventional switchgear; Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1; Fig. 3 is a fragmental vertical sectional view of a switchgear of the present invention in the contact open state; Fig. 4 is a cross-sectional view similar to Fig. 2 but illustrating the section of the magnet of an embodiment of the present invention; and Fig. 5 is a view similar to Fig. 4 but illustrating still another embodiment of the present invention. In Fig. 3 the reference numerals 1-10 designate the same or similar components as those in the conventional device. The reference numeral 44 designates a rod-shaped or tubular holder of a non-magnetic material disposed outside the stationary contact 2 and mounted at its one end to the first terminal plate, 45 designates a second magnet mounted on the tip portion of the holder 44, (1) designates a first magnetic field generated by the first magnet 8, and (2) designates a second magnetic flux generated by the second magnet 45. The first magnetic flux (1), generated by the annular first magnet 8 magnetized in the axial direction and mounted on the nozzle 7, and the second magnetic flux (2) generated by the annular second magnet 45 magnetized in the axial direction and mounted on the holder 44, act to strengthen the magnetic flux in the radial direction at the gas storage chamber opening 9a. When the arc 10 is generated across the stationary contact 2 and the movable contact 3, the arc 10 crosses the above magnetic flux (1 + 2) which is intensified by the two components thereof. Therefore, the arc is subjected to a large, driving force in the circumferential direction by the intensified magnetic flux (1 + 2) to be elongated in the radial direction, so that the gas pressure within the gas storage chamber 9 is increased by the heating effect of the arc or the insulating arc extinguishing gas, and the blasting effect of the thereby pressure-increased insulating arc extinguishing gas against the arc is increased to improve the arc extinguishing capability. Further, a similar advantageous effect can be obtained by magnetizing the first and the second magnets 8 and 45 in the radial direction. Although the magnetic material for the magnet may for example be ferrite metals, Alnico metals, samarium rare earth metals and neodymium-iron-boron magnetic materials, a magnet of a strong magnetic force provides a greater arc extinguishing effect. As set out in EP-A-248677, the gas storage chamber opening defined by the lower portion of the insulating nozzle 7 may be formed in a conical shape divergent towards the storage chamber 9 with an angle equal to or less than 80° relative to its axis. Therefore, even when the current is large, there is no stagnation point as in the conventional design, and when the arc is driven deep into the radial direction, the arc becomes even further removed from the permanent magnet to reduce the driving force and the arc does not intrude unnecessarily deep into the storage chamber 9, so that a localized heating of the gas is prevented, and further upon the blasting of the gas from the storage chamber 9, the flow of the gas can be guided with no drag, resulting in stable arc extinguishing performance for the large current. Also, when the current value is small, while the driving force is equal to that of the conventional design since the storage chamber opening is conical, the arc is driven into the interior of the gas storage chamber 9. Therefore, the effect of increasing the gas pressure within the storage chamber 9 is greater than that of the conventional design, providing a stable arc extinguishing performance. When the permanent magnet is annular, an alternating magnetic filed is generated in the permanent magnet by the current flowing through the contacts 2 and 3 when the contacts are closed, and in an electrically conductive magnet such as an Alnico magnet, the magnet is heated by an eddy current and degraded. However, when the magnet is made of an electrically resistive material such as a rare earth metal magnet material, no eddy current flows and no heating and no degrading occur. Also, the shape can be made at any desired configuration. As explained above, the effect of the permanent magnet is sufficient for cases ranging from a small current to a large current and therefore a switchgear of simple structure can be provided in which additional arc extinguishing mechanisms such a puffer mechanism or a negative pressure puffer mechanism for assisting the self-extinguishing characteristics are not required. In Figs. 4 and 5, the reference numerals 56, 57, 58 and 59 designate a plurality of segments divided from a magnet 60 or 61 and mounted to the nozzle 7, the number of the segments being four in this embodiment, and 62 designates a spacer made of a non-magnetic material and interposed between each of the magnetic segments 56-59. While the circumferential magnetic flux generated by the current of a large current arc or during current carrying concentrates in the magnet which has a small magnetic reluctance and increases the number of the magnetic fluxes since the magnet of the switchgear of the present invention is constructed as described above and since the circumferentially divided magnet segments are disposed in the nozzle made of a non-magnetic material such as polytetrafluoroethylene so that the segments are not in contact with each other as shown in Fig. 4 and 5, the magnetic reluctance in the circumferential direction is increased and, therefore, the amount of the magnetic flux generated by the alternating current and passing through the magnet 61 is reduced. Therefore, eddy current loss is reduced and the heating of the magnet is decreased, whereby a stable arc extinguishing capability can be obtained due to the stable magnetic force and the long life of the magnet. In the embodiment shown in Fig. 5, the circumferentially divided magnet sections 56-59 are embedded within the nozzle 7 so that they do not contact with each other. However, a spacer 62 may be fixedly interposed between each of the circumferentially divided magnet segments 56-59 as in the embodiment shown in Fig. 5, also providing an advantageous effect similar to that in the embodiment shown in Fig. 4. The material for the spacer 62 may may be a solid body of a metal or a gas such as an air gap as long as it is a non-magnetic material. These materials may also be combined.

Claims: A switchgear comprising, in a housing containing an arc extinguishing gas: - a stationary contact (2); a movable contact (3) capable of contacting with and separating from said stationary contact, said movable contact and said stationary contact defining therebetween an arcing region in which an electric arc (10) is generated when said contacts are separated; means defining a gas storage chamber (9) around saidstationary contact communicating with said arcing region for storing the arc extinguishing gas increased in pressure by heat from the arc; an insulating nozzle (7) attached to said gas storage chamber defining an opening through which said movable contact movably extends and through which said arc extinguishing gas flows; and magnet means (8, 45) for generating a magnetic field in said opening of said gas storage chamber for rotating and elongating the electric arc generated between said stationary contact and said movable contact upon current interruption; characterized in that the said magnet means include a first annular magnet (8) mounted to said nozzle and a second annular magnet (45) disposed outside said stationary contact within said gas storage chamber. Switchgear as claimed in claim 1, wherein said magnet means includes a first annular magnet mounted to said nozzle and a second annular magnet disposed inside of said stationary contact within said gas storage chamber. Switchgear as claimed in claim 1 or 2 in which said insulating nozzle defines a smooth inner transition surface connecting said gas storage chamber to said opening for permitting a smooth flow of the pressurized arc extinguishing gas through said opening. Switchgear as claimed in claim 3, wherein said inner transition surface of said insulating nozzle is a tapered surface convergent from said gas storage chamber to said opening.

Inventors: HAMANO SUENOBU C O CHUO KENKYU, HASEGAWA HIROSI C O MARUGAME S, MARUYAMA TOSIMASA C O MARUGAME, MURAI YUTAKA C O CHUO KENKYUSH, SASAO HIROYUKI C O CHUO KENKYU, WADA YUICHI C O CHUO KENKYUSHO, HAMANO, SUENOBU, C/O CHUO KENKYUSHO MITSUBISHI, HASEGAWA, HIROSI, C/O MARUGAME SEISAKUSHO, MARUYAMA, TOSIMASA, C/O MARUGAME SEISAKUSHO, MURAI, YUTAKA, C/O CHUO KENKYUSHO MITSUBISHI, SASAO, HIROYUKI, C/O CHUO KENKYUSHO MITSUBISHI, WADA, YUICHI, C/O CHUO KENKYUSHO MITSUBISHI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1987
Main classification: H01H33
IPC codes: H01H33