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 specification describes novel arrangements of the magnet and a novel design of the nozzle, for enhancing the arc-extinguishing capability.

Description: BACKGROUND OF THE INVENTION 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 teen 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, piston (12) and the bottom face of the stationary outer cylinder (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, in the conventional device constructed as described above, 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 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 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 insulating nozzle defines a smoothly tapered inner transition surface convergent from said gas storage chamber to said opening for permitting a smooth flow of the pressurized arc extinguishing gas through said opening, and said magnet means is made of an electrically insulating material. Preferably the inner transition surface is conically tapered. Preferably the magnet is mounted to the nozzle and is an annular magnet magnetized in the radial direction. Alternatively the switchgear according to the present invention may have, as a magnet for generating a magnetic flux in the radial direction at the gas storage chamber opening, a combined magnet composed of an outer permanent magnet disposed outside of the gas storage chamber and surrounding the gas storage chamber, an annular or cylindrical inner magnet disposed inside of the gas storage chamber, and a magnetic material for short-circuiting the outer and the inner magnets in their magnetic path. A cylindrical arc contact made of a good electrically conductive material may be disposed around the first contact. A non-magnetic holder may be mounted outside or inside the first contact, and an annular second magnet is mounted to the holder. According to another embodiment of the switchgear of the present invention, the magnet is mounted to the nozzle and has 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. According to another embodiment of the present invention, the magnet is mounted to the nozzle and is circumferentially divided into a plurality of sections, and a non-magnetic material is circumferentially interposed between each of the magnet sections. BRIEF DESCRIPTION OF THE DRAWINGS 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 magnet arrangement; Fig. 5 is a view similar to Fig.3 but illustrating still another magnet arrangement; Fig. 6 is a view similar to Fig.3 but illustrating a further embodiment of the present invention; Fig. 7 is a view similar to Fig.3 but illustrating still another magnet arrangement; and Fig. 8 is a view similar to Fig.3 but illustrating a further magnet arrangement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in conjunction with Fig.3 in which one embodiment of the invention is illustrated. In the figure, except for the magnet (21), the insulating nozzle (22) and the gas storage chamber opening (23), the components designated by the reference numerals (1) - (10) are similar to those of the conventional device described in conjunction with Figs. 1 and 2, so that their descriptions are not repeated here. The reference numeral (21) designates a permanent magnet disposed outside of the gas storage chamber (9) or the insulating nozzle (22), the permanent magnet being made of an electrically insulating material and having a magnetic flux component in the radial direction in the vicinity of the storage chamber opening (23). Therefore, the arc (10) is generated across the contacts (2) and (3) is driven in the direction of rotation, and the arc (10) is driven outwards in the radial direction by centrifugal force. Further, since the gas storage chamber opening (23) defined by the lower portion of the stationary outer cylinder (6) and the upper portion of the insulating nozzle (22) is 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 (23) 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 electrically conductive Alnico magnet, the magnet is heated by an eddy current and degraded. However, according to the present invention, the magnet (21) is made of an electrically insulating material such as a rare earth metal magnet material, so that no eddy current generates 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 as a puffer mechanism or a negative pressure puffer mechanism for assisting the self-extinguishing characteristics are not required. As for the material for the magnet, ferrites, samarium-rare earth metals and neodymium-iron-boron materials may be used, the arc extinguishing effect is greater with an electrically insulating, magnetically strong magnet. As has been described, according to the embodiment of the present invention shown in Fig. 3, the permanent magnet is a magnet made of an electrically insulating material, and the gas storage chamber opening is configured in a conical shape, so that no eddy current is generated for cases ranging from a small current to a large current and no heating occurs and the driving of the arc can be effectively achieved, so that there is no need for an additional arc extinguishing mechanism, resulting in a simple structure, and therefore providing a reliable switchgear having a stable interrupting capability. Figures 4 to 8 show further magnet arrangements. Fig. 4 shows an annular magnet (24) mounted to the nozzle (7) and magnetized in the radial direction. Since the magnet (24) 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 by the arc. Therefore, the pressure 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 as explained above 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. As has been described, with the magnet illustrated in Fig. 4, 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. 5 shows a combined magnet (25) which 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 and 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), 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. 6 in which another embodiment of the present invention is illustrated, the reference numeral (33) is a combined magnet as in Fig. 5, 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. As has been described, according to the embodiment of the present invention shown in Fig. 6, the magnet for driving the arc is a combined magnet composed of an outer permanent magnet disposed outside of the gas 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. Fig. 7 shows a rod-shaped or tubular holder (44) of a non-magnetic material disposed outside of 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) generates 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. In Fig. 8 a rod-shaped holder (46) made of a non-magnetic material is disposed inside the stationary contact (2) and the holder (46) is provided with a second magnet (47). An advantageous effect and operation which are similar to those in the above embodiment described in conjunction with Fig.7 can be obtained. In Figs. 7 and 8, the first magnet (8) mounted on the nozzle 7 and the second magnets (45) and (47) are arranged to have the N pole on the gas storage chamber opening (9a) and the S pole on the opposite side. However, the first magnet and the second magnet can be magnetized in the radial direction. Alternatively, the first magnet (8) may be magnetized in the axial direction and the second magnet (45) and (47) may be magnetized in the radial direction, or the magnetization may be combined oppositely. In summary, the magnets may be arranged in any manner as long as they function so that the radial magnetic flux generated by the first and the second magnets may be intensified at the gas storage chamber opening (9a). Further, the holder (44) or (46) may be made of an electrically insulating material or a metal as long as it is non-magnetic. As has been described, with a second magnet mounted on the tip of the holder in the vicinity of the first contact, the magnetic flux in the radial direction at the gas storage chamber opening generated by the first magnet disposed on the nozzle and the second magnet is intensified. Therefore, the arc driving force is increased to expand the arc and the heating effect of the insulating arc extinguishing gas is increased, resulting in an advantageous effect that arc extinguishing capability of the switchgear is increased even upon the interruption of a small current.

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 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 (21) 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 insulating nozzle defines a smoothly tapered inner transition surface convergent from said gas storage chamber to said opening for permitting a smooth flow of the pressurized arc extinguishing gas through said opening, and said magnet means (21) is made of an electrically insulating material. Switchgear as claimed in claim 1, wherein said inner transition surface of said insulating nozzle is a conically tapered surface convergent from said gas storage chamber to said opening. Switchgear as claimed in claim 2 in which the taper angle is equal to or less than 80°. Switchgear as claimed in claim 1, 2 or 3 wherein said magnet means is annular. Switchgear as claimed in claim 4, wherein said magnet means is an annular magnet mounted on said nozzle. Switchgear as claimed in claim 4 or 5, wherein said magnet means is magnetized in the radial direction. Switchgear as claimed in claim 1 or 2, wherein said magnet means comprises 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. Switchgear as claimed in claim 7, wherein said outer magnet is mounted to the outer surface of said means defining said gas storage chamber. Switchgear as claimed in claim 7, wherein said outer magnet forms said means defining said gas storage chamber. Switchgear as claimed in any of claims 1 to 9, wherein a cylindrical arcing contact is disposed around said stationary contact. Switchgear as claimed in any of claims 1 to 10, wherein said stationary contact is tubular and has a gas exhaust port. 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 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 said stationary contact within said gas storage chamber. Switchgear as claimed in any preceding claim in which the electrically resistive magnet is made of ferrite, samarium-rare earth metal, or neodymium-iron-boron material.

Inventors: HAMANO SUENOBU C O CHUO KENKYU, HASEGAWA HIROSHI C O MARUGAME, 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, HASEGAWA, HIROSHI C/O MARUGAME SEISAKUSHO, MARUYAMA, TOSIMASA C/O MARUGAME SEISAKUSHO, MURAI, YUTAKA C/O CHUO KENKYUSHO, SASAO,  HIROYUKI C/O CHUO KENKYUSHO, WADA, YUICHI C/O CHUO KENKYUSHO, Sasao, Hiroyuki c/o Chuo Kenkyusho
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1987
Main classification: H01H33
IPC codes: H01H33