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 21 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 is magnetized radially. 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. Accordingly, 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 and 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 is annular and is magnetized in the radial direction. The magnet mounted to the nozzle may have a magnetic material secured on at least one of the magnetic poles and the magnetic material is positioned close to the arc in the gas storage chamber. 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 view similar to Fig. 3 but illustrating another embodiment of the present invention; Fig. 5 is a cross-sectional view similar to Fig. 2 but illustrating the cross-section of the magnet of an embodiment of the present invention; and Fig. 6 is a view similar to Fig. 5 but illustrating still another embodiment of the present invention. In Fig. 3, in which an embodiment of the present invention is illustrated, the reference numerals 1-10 designate the same or similar components as those in the conventional device except for the magnet 21. An annular magnet 21 mounted to the nozzle 7 is a magnet magnetized in the radial direction. Since the magnet 21 of this embodiment is magnetized in the radial direction as described above, the magnetic field at the gas storage chamber opening 9a mainly forms a magnetic flux distributed in the radial direction. Therefore, the magnetic flux that crosses the arc 10 generated between the stationary contact 2 and the movable contact 3 is increased in number and intensity, so that the circumferential driving force acting on the arc 10 is increased and the arc 10 is rotated and elongated in the radial direction, increasing the heating of the insulating arc extinguishing gas within the gas storage chamber 9 is increased and the blasting of the insulating arc extinguishing gas against the arc 10 is intensified, thereby providing a sufficient arc extinguishing capability. On the other hand, the radial magnetic field generated by the magnet 24 magnetized in the radial direction exists in the vicinity of the nozzle outlet, and therefore the arc 10 in the vicinity of the nozzle 7 is rotated to contact with the relative flow of the surrounding low temperature gas, whereby the arc 10 in the vicinity of the nozzle outlet 7 is further cooled to provide a greater arc extinguishing effect. While the inner side of the magnet 24 is magnetized. as an N pole and the outer side is magnetized as an S pole in the above embodiment, the polarity may be reversed, and a plurality of magnets magnetized in the radial direction may be combined into an annular shape, providing effects similar to those in the above embodiment. 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 has been described, according to the embodiment of the present invention illustrated in Fig. 3, since the nozzle has mounted thereon an annular magnet magnetized in the radial direction, the radial component of the magnetic flux is greater and, therefore the arc-rotary driving force is intensified to further expand the arc, thereby increasing the gas pressure within the gas storage chamber even during a small current interruption, resulting in an advantageous switchgear in which the arc extinguishing capability is increased. Fig. 4 is a fragmental vertical cross-sectional view showing the state of the magnet disposed in a switchgear of another embodiment of the present invention. In Fig. 4, at least one of the magnetic poles of a magnet 52 of or arranged in an annular shape and magnetized in the radial direction has a magnetic material 53 of or arranged in an annular shape secured thereto, the magnetic material being secured on both of the magnetic poles in this embodiment. Although the magnetic material for the magnet 52 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. Since at least one of the magnetic poles of the magnet disposed in the nozzle is provided with a magnetic material, the magnetic field can be intensified at the chamber opening and the thermal effects of the arc on the magnet can be decreased by the magnetic material, so that a reliable, inexpensive switchgear exhibiting superior small current interruption capability and free from the thermal degradation of the magnet can be advantageously obtained. This magnetic material 53 is disposed close to the gas storage chamber opening 9a through the nozzle 7, thereby strengthening the magnetic field () in the gas storage chamber opening. In this embodiment, since the switchgear is constructed as described above and the magnetic field () is intensified at the gas storage chamber opening 9a, a sufficient interrupting capability is obtained even during a small current interruption by the interaction of the magnetic field and the arc. During a large current interruption, the arc energy increases and the tip portion of the magnetic material is heated through the nozzle 7 by the thermal or radiation energy generated by the arc. However, the magnetic materials is made of a heat resistant material such as iron, so that the magnet 51 is prevented from being thermally degraded. As set out in EP-A-248677 from which this application was divided, 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 field 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 a conventional Alnico magnet, the magnet is heated by an eddy current and degraded. However, when the magnet 21 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. 5 and 6, 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. 5 and 6, 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. 6, also providing an advantageous effect similar to that in the embodiment shown in Fig. 5. 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. As has been described, according to the present invention, since the magnet mounted on the nozzle is divided into a plurality of magnet sections and a non-magnetic material is interposed between the divided magnet segments the magnetic reluctance in the circumferential direction is increased, and the amount of the magnetic flux passing through the magnet is reduced. Therefore, the eddy current loss and the heating of the magnet are reduced, resulting in an advantageous switchgear in which the magnetic force is stable and the life of the magnet is long.

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 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 (7) attached to said gas storage chamber and defining an opening through which said movable contact movably extends and through which said arc extinguishing gas flows; and magnet means (21; 52, 53) 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 (21; 52, 53) is annular and is magnetized in the radial direction. A switchgear as claimed in claim 1, wherein said stationary contact is tubular and has a gas exhaust port. 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. A 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. A switchgear as claimed in claim 1, 2, 3 or 4 wherein said magnet means is an annular magnet embedded in said nozzle.

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 MITSUB. DENKI, HASEGAWA, HIROSI, C/O MARUGAME SEISAKUSHO, MARUYAMA, TOSIMASA, C/O MARUGAME SEISAKUSHO, MURAI, YUTAKA, C/O CHUO KENKYUSHO MITSUB. DENKI, SASAO, HIROYUKI, C/O CHUO KENKYUSHO MITSUB. DENKI, WADA, YUICHI, C/O CHUO KENKYUSHO MITSUB. DENKI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: H01H33
IPC codes: H01H33