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 25 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 outer annular magnet 26, an inner annular magnet 27, and a yoke 28. 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 switchgear 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 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 said magnet means is an annular outer magnet disposed around said gas storage chamber, an inner magnet disposed within said gas storage chamber, and a magnetic material connecting said inner magnet to said outer magnet for short-circuiting the magnetic path therebetween. The gas storage chamber opening may be formed in a conical shape divergent toward the 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 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 previously described except for a combined magnet (25). The combined magnet (25) comprises an annular outer permanent magnet (26) magnetized in the axial direction, a rod-shaped inner permanent magnet (27) magnetized in the opposite axial direction, and a magnetic material such as an iron plate (28) short-circuiting the magnetic paths for the magnetic flux generated by the inner and the outer permanent magnets 26 and 27 on the gas storage chamber opening an the opposite side, the magnetic material (28) having formed therein a communication hole (29) for allowing the insulating arc extinguishing gas to flow into the gas storage chamber (9) and a discharge port (30) for discharging a high temperature gas from the arc (10) to the exterior of the arc extinguishing chamber through the stationary contact (2). In the first terminal plate (1), an exhaust port (31) is provided through which a high temperature gas heated by the arc (10) and discharged from the discharge port (30) is exhausted to the exterior of the arc extinguishing chamber. When the movable contact (3) is pulled down in the direction of the arrow A by an interruption command with a current flowing through the closed contacts (2) and (3), an electric arc is generated across the contacts (2) and (3), and the insulating arc extinguishing gas heated by the arc (10) is discharged downwardly in the figure through the insulating nozzle (7) and also to the exterior of the arc extinguishing chamber through the exhaust port (31), a part of the arc extinguishing gas entering into the gas storage chamber (9) through the gas storage chamber opening (9a). The insulating arc extinguishing gas within the gas storage chamber (9) is heated by the gas entering into the gas storage chamber (9) and the pressure is also increased. On the other hand, when the arc current reaches close to the zero crossing point, the pressure in the arcing region is decreased and the pressurized insulating arc extinguishing gas within the gas storage chamber (9) is blasted against the arc (10), thereby cooling the arc to achieve interruption. The pressure of the insulating arc extinguishing gas stored within the gas storage chamber (9) becomes smaller as the arc current becomes smaller, making the arc extinguishing capability insufficient. The magnetic field in the radial direction in the vicinity of the gas storage chamber opening (9a) generated by the combined magnet (25) of the present invention drives the arc (10) into the circumferential direction, and if this drive force is strong enough the arc is expanded into the interior of the gas storage chamber (9) by centrifugal force. Thus, the energy of the arc (10) is effectively stored within the gas storage chamber (9), so that a sufficient pressure rise is obtained even with a small arc current and therefore a stable interrupting capability can be obtained. In this case, the rotating force for the arc (10) and therefore the centrifugal force therefor is provided only by the radial component of the magnetic field. Therefore, with the magnet arranged to generate a magnetic field in the radial direction mainly in the vicinity of the gas storage chamber opening (9a) as in the present invention, the magnetic field can be efficiently utilized in the extinction of the arc (10) even if the absolute magnitude of the magnetic field is small. In Fig. 4 in which another embodiment of the present invention is illustrated, the reference numeral (33) is a combined magnet as in the previous embodiment, but the annular outer permanent magnet (34) is also used as a stationary outer cylinder defining the gas storage chamber (9), and the iron plate (35) which is a magnetic material is also used as one of the walls of the gas storage chamber (9). In other respects, the construction is similar to the previous embodiment. With such an arrangement, the number of parts are reduced and the flow of the gas within the gas storage chamber (9) is not impeded, so that a switchgear of a simpler structure exhibiting a stable arc extinguishing capability can be obtained. 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 shown in Fig. 4, the magnet for driving the arc is a combined magnet composed of an outer permanent magnet disposed outside of the gas storage chamber to annularly surround the gas storage chamber, an inner permanent magnet of an annular or a cylindrical shape and disposed inside of the gas storage chamber, and a magnetic material short-circuiting a magnetic path between the magnets. Therefore, the magnetic flux in the radial direction effectively acts on the arc, advantageously providing a switchgear exhibiting a stable small current interrupting capability. As described in EP-A-248677, the gas storage chamber opening defined by the lower portion of the stationary outer cylinder (6) and the upper portion of the insulating nozzle (7) may be formed in a conical shape divergent toward 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 convention design, providing a stable ar 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 an 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.

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 defining an opening through which said movable contact movably extends and through which said arc extinguishing gas flows; and magnet means (25) 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 said magnet means (25) is an annular outer magnet (26; 33) disposed around said gas storage chamber, an inner magnet (27) disposed within said gas storage chamber, and a magnetic material (28) connecting said inner magnet to said outer magnet for short-circuiting the magnetic path therebetween. Switchgear as claimed in claim 1, wherein said outer magnet (26) is mounted to the outer surface of said means defining said gas storage chamber. Switchgear as claimed in claim 1, wherein said outer magnet (33) forms said means defining said gas storage chamber. Switchgear as claimed in claim 1, 2 or 3, wherein said stationary contact is tubular and has a gas exhaust port. Switchgear as claimed in claim 1, 2, 3 or 4 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 5, 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: 1992
Main classification: H01H33
IPC codes: H01H33