SWITCH

Abstract: A switch comprising: a fixed contact attached to a fixed contactor; a movable contact attached to a movable contactor so as to face to the fixed contact; a first metal arc-­ extinguishing plate constituted by a U-shaped upright wall surrounding the fixed contact with an open portion thereof directed toward the end of the fixed contactor; and a second metal arc-extinguishing plate provided parallel to the first metal arc-extinguishing plate on the side thereof further from the contacts, wherein each of the first and second metal arc-­ extinguishing plates is positioned at predetermined distances from the fixed contactor.

Description: This invention relates to switches for interrupting or allowing an electric current to flow, particularly to arc extinguishing mechanisms for such switches. Switches to which the present invention is applicable include electromagnetic contactors and circuit breakers. First, one example of a conventional electromagnetic contactor will be described with reference to Fig. 1. In Fig. 1, (1) is a mount bed molded of plastics material, (2) is a stationary iron core having silicon steel laminations disposed on the mount bed, (3) is a movable core disposed in a facing relationship with the stationary core (2) and made of silicon steel laminations, (4) is an operating coil for providing a driving force which attracts the movable core (3) to the stationary core (2) against the force of a trip spring (not shown), and (5) is a cross bar made of a plastics material and having a rectangular window, the bottom end of which has attached thereto the movable core (3). (6) is a movable contact inserted within the rectangular window of the cross bar (5) and held under pressure by a compression spring (7), (6A) is a movable contact element disposed on the movable contact, (8) is a stationary contact facingly disposed with respect to the movable contact (6) for conducting a current, (8A) is a stationary contact element disposed on the stationary contact (8), and (8C) is a terminal portion for the stationary contact (8). Also, (9) is a terminal screw for connecting the electromagnetic contactor main body to an external circuit, (10) is a base for mounting the stationary contact (8), and (11) is a cover for covering the upper portion of the electromagnetic contactor. In the conventional electromagnetic contactor which has the above-described structure, when the operating coil (4) is de-energized, an unillustrated trip spring causes the movable core (3) to separate from the stationary core (2) and the cross bar (5) occupies the position shown in Fig. 1, and the movable contact element (6A) and the stationary contact element (8A) are separated to generate an electric arc (12), the arc (12) being extinguished at the zero current point to interrupt the electric current. In the conventional electromagnetic contactor, as shown in Fig. 2, the arc (12) is subjected to a driving force F₂ due to a magnetic field formed by a current I flowing through the movable contact (6) and a driving force F₁ due to a magnetic field formed by a current I flowing through the stationary contact (8). Since the driving forces F₁ and F₂ are substantially equal in intensity and opposite in direction, the arc (12) stays on the movable contact element (6A) and the stationary contact element (8A). Thus, since the arc (12) is not driven, the legs of the arc do not move outside of the contact elements and the disadvantage of large contact element wear arises. GB-A-1 121 012 discloses a switch comprising a stationary contact element joined to a stationary contact, a movable contact element joined to a movable contact in a facing relationship to said stationary contact element, an arc gap being defined extending between the movable and stationary contact elements when the contacts are opened, said movable contact and an arc-carrying portion of the stationary contact extending respectively in opposite directions away from their respective contact elements, a first sheet metallic arc extinguishing plate formed of a U-shaped vertical wall and disposed with the U extending around the tip of said movable contact, and a second metallic plate disposed at the side of the base of the U of said first metallic arc extinguishing plate that is remote from said contact elements, the said first plate being disposed so that at the base of the U the lower edge of the first plate overlies the stationary contact with a predetermined gap, extending generally in the same direction as the said arc gap, between the arc-carrying portion of the stationary contact and the said lower edge, the second plate being disposed with a predetermined gap between its lower edge and the said arc-carrying portion of the stationary contact, the said gap between said second plate and said stationary contact being smaller than the said gap between said first plate and said stationary contact, and the side walls of the said U-shaped first plate extending around the longitudinal sides of the movable contact and embracing the movable contact element between them. In this document the outer second plate is provided as a protective baffle plate, and is placed further from the arc gap than is the free end of the arc-carrying portion of the stationary contact, so that the gap between the stationary contact and the baffle plate extends away from the arc gap and, so far as can be determined from the document, cannot assist arc interruption to any significant extent. The arc is said to extend between the stationary contact, the U-shaped arc extinguishing plate, and the movable contact, in two portions. FR-A-1108488 discloses a switch with a U-shaped suction electrode behind which is a vertical arc extinction screen closer to the fixed contact. The switching arc is drawn onto the side flanges of the suction electrode, which do not extend below the stationary contact and do not extend around the contact position. The arc extinction screen is L-shaped and extends between the suction electrode and the fixed contact. Because the arc is drawn onto the side flanges of the suction electrode, there is a risk of damage to the interior of the switch case, and the configuration of electrodes and arc extinction screens described does not provide the rapid and reliable arc extinction achieved in the present invention. The present invention has as its object to provide an arc extinguishing mechanism promoting the arc extinction by a quick transfer of the arc, thereby to reduce the contact element wear and to improve the interrupting capability. The present invention resides in a switch comprising a stationary contact element joined to a stationary contact, a movable contact element joined to a movable contact in a facing relationship to said stationary contact element, an arc gap being defined extending between the movable and stationary contact elements when the contacts are opened, said movable contact and an arc-carrying portion of the stationary contact extending respectively in opposite directions away from their respective contact elements, a first sheet metallic arc extinguishing plate formed of a U-shaped vertical wall and disposed with the U extending around the tip of said movable contact, and a second metallic plate disposed at the side of the base of the U of said first metallic arc extinguishing plate that is remote from said contact element, the said first plate being disposed so that at the base of the U the lower edge of the first plate overlies the stationary contact with a predetermined gap, extending generally in the same direction as the said arc gap, between the arc-carrying portion of the stationary contact and the said lower edge, the second plate being disposed with a predetermined gap between its lower edge and the arc-carrying portion of the stationary contact, the said gap between said second plate and said stationary contact being smaller than the said gap between said first plate and said stationary contact, and the side walls of the said U-shaped first plate extending around the longitudinal sides of the movable contact and embracing the movable contact element between them, characterized in that the said second plate is a second arc extinguishing plate arranged parallel to the first arc extinguishing plate, and the said arc-carrying portion of the stationary contact extends longitudinally from its contact element to a distance greater than the distance of the second plate from the contact elements, such that the lower edge of the second plate overlies the arc-carrying portion of the stationary contact and that the said gap between the arc-carrying portion of the stationary contact and the lower edge of the second plate extends generally in the same direction as the said arc gap. The switch according to the present invention has the advantage of significantly improving the interrupting capability, by dividing the arc into three portions extending between the stationary contact, the second plate, the first plate and the movable contact. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial sectional view of a switch of a conventional design; Fig. 2 is an explanatory view showing the contact element arrangement; Fig. 3 is a partial sectional view of a switch of an embodiment of the present invention; Fig. 4 is an enlarged view of a main portion of the arc extinguishing chamber shown in Fig. 3; Fig. 5 is a view for explaining the arc extinguishing function of the chamber shown in Fig. 4; Fig. 6 is a perspective view showing the second metallic arc extinguishing plate of another embodiment of the present invention; Fig. 7 is an explanatory view showing the arc extinguishing operation of the arc extinguishing plate shown in Fig. 6; Fig. 8 is an overall explanatory view of the arc extinguishing chamber shown in Fig. 3; Fig. 9 is a partial perspective view showing a modification of the arc extinguishing plate; Fig.10 is an explanatory view showing the arc extinguishing operation of another embodiment of the present invention; Fig. 11 is an overall schematic view showing the arc extinguishing chamber of still another embodiment; Fig. 12 is a perspective view showing a partially modified embodiment of the arc extinguishing chamber; Fig. 13 is a view for explaining the arc extinguishing operation of the embodiment shown in Fig. 11; Fig. 14 is an enlarged view of the arc extinguishing chamber of the embodiment shown in Fig. 11; Fig. 15 is an enlarged view of the arc extinguishing chamber of another embodiment; Fig. 16 is a perspective view showing a partially modified embodiment of the embodiment shown in Fig. 15; Figs. 17 and 18 are enlarged views showing the manner in which the arc moves in the arc extinguishing chamber; Fig. 19 is a perspective view showing the metallic arc extinguishing plate of another embodiment; Fig. 20 is an explanatory view showing the arc extinguishing operation of the embodiment shown in Fig. 19; Figs. 21, 22, 23 and 24 are perspective views showing the metallic arc extinguishing plates of still another embodiments; Fig. 25 is a perspective view showing the metallic arc extinguishing plate of a still further embodiment; and Fig. 26 is a perspective view showing the metallic arc extinguishing plate of another embodiment. BEST MODE FOR WORKING THE INVENTION The present invention will now be described in conjunction with an embodiment shown in Figs. 3 to 5. As clearly seen from Fig. 3, the switch of this embodiment is different from the conventional switch of Figs 1 and 2 primarily in the arc extinguishing mechanism and this mechanism is shown in an enlarged view in Fig. 4. As shown in Fig. 4, within an arc extinguishing chamber shown in Fig. 3 are disposed a first metallic arc extinguishing plate (13) and a second metallic arc extinguishing plate (14) made of a magnetic material for extinguishing an electric arc (12) established between a stationary contact element (8A) and a movable contact element (6A). The stationary contact (8) has a free end portion (8D) which extends from the contact element (8A) longitudinally away from the arc gap between the contact elements (6A, 8A) to a distance further than plates (13) and (14). The free end portion (8D) acts as an arc-carrying portion or arc runner when the contact elements are opened, as will be described below. The first metallic arc extinguishing plate (13) is constructed in the form of a U-shaped frame bridging across the stationary contact (8) to cover the stationary contact element (8A) so that the lower edge (13A) of the plate (13) overlies the upper surface of the contact (8), and the second metallic arc extinguishing plate (14) is a single plate similarly positioned parallel to and outside the base of the first metallic arc extinguishing plate (13) such that the lower edge (14A) of the plate (14) overlies the upper surface of the contact (8). The first metallic arc extinguishing plate (13) and the second metallic arc extinguishing plate (14) are positioned with predetermined gaps between their lower edges and the free end portion (8D) of the stationary contact (8), these gaps extending in the same direction as the arc gap between the contact elements, and the gap (d) formed between the lower edge (14A) of the second metallic arc extinguishing plate (14) and the stationary contact (8) is selected to be smaller than the gap (D) formed between the lower edge (13A) of the first metallic arc extinguishing plate (13) and the stationary contact (8) as seen from Fig. 8. Also, the first metallic arc extinguishing plate (13) is constructed in order that its three sides surrounding each contact element promote the drawing of the arc while shielding the surrounding insulating material from being damaged by the arc, and the first metallic arc extinguishing plate (13) may be selected to have a suitable U-shape taking heat dissipating effect into consideration as shown in Fig. 9, for example. With the above arrangement, when the operating coil (4) of this electromagnetic contactor is de-energized, the unillustrated trip spring separates the movable core (3) from the stationary core (2) and the cross bar (5) occupies the position shown in Fig. 3 to separate the stationary contact element (8A) and the movable contact element (6A) to generate the electric arc (12) between the stationary contact element (8A) and the movable contact element (6A). This arc, (12) is extinguished at the current zero point by the first metallic arc extinguishing plate (13) and the second metallic arc extinguishing plate (14), thereby interrupting the electric current. This extinguishing process of the arc (12) will now be described in more detail in conjunction with Fig. 5 in which a section of the arc extinguishing chamber is shown. The arc (12) drawn between the movable contact element (6A) and the stationary contact element (8A) is attracted by the first metallic arc extinguishing plate (13) made of a magnetic material and is expanded as shown by an electric arc (12A). At this time, since the stationary contact (8) is in the form of a U-shaped cross-section as shown in Fig. 4, the arc (12) is rapidly attracted and driven by a magnetic field formed by a current flowing through the stationary contact (8), whereby the arc (12) is further elongated. When the arc (12) is thus elongated, the arcing voltage increases. Therefore, dielectric breakdown occurs between the stationary contact (8) and the first metallic arc extinguishing plate (13), and between the first metallic arc extinguishing plate (13) and the movable contact element (6A), so that the arc (12A) is divided into two arcs (12B) and (12C). One of the divided arcs (12C) is attracted by the second metallic arc extinguishing plate (14) and driven by the magnetic field formed by the current through the stationary contact (8), whereby the arc is expanded as shown by an arc (12D). When the arcing voltage is increased due to this expansion of the arc (12D), the arc (12D) is further divided into two arcs (12E) and (12F) and is ultimately divided into three arcs (12B), (12E) and (12F) which are extinguished at the current zero point, thus interrupting the electric current. Thus, according to the above-described switch, since the first metallic arc extinguishing plate (13) is constructed as a vertically disposed U-shaped frame surrounding the movable contact element (6A), a magnetic field due to the surrounding three walls promotes the magnetic driving of the arc, and the damage to the surrounding insulating material is minimized. Further, since the first metallic arc extinguishing plate (13) and the second metallic arc extinguishing plate (14) are disposed in parallel, the arc is divided as described above, thereby increasing the arc extinguishing capability. When the gap (d) between the second metallic arc extinguishing plate (14) and the stationary contact (8) is selected to be smaller than the gap (D) between the first metallic arc extinguishing plate (13) and the stationary contact (8), the arc is prevented from remaining on the first metallic arc extinguishing plate (13), enabling further promotion of the arc dividing effect previously described. As shown in Figs. 6 and 7, a lower edge of the second metallic arc extinguishing plate (14) may be folded toward the arc driving direction to form an arc lead portion (14B). With this arrangement, since an arc (12F) moves along the arc lead portion (14B) as shown in Fig. 7, an electric field concentration on the second metallic arc extinguishing plate (14) due to the stay of one end of the arc (12F) seldom occurs, and since the arc extinction is achieved on the arc lead portion (14B) which is a flat surface portion having a good thermal conductivity, burning is prevented, providing a superior interrupting capacity. A further embodiment of the present invention will be described in conjunction with Fig. 10, in which a lower edge (13A) of the first metallic arc extinguishing plate (13) opposing to the stationary contact (8) is positioned on substantially the same plane as that in which the contact surface of the movable contact element (6A) lies in the open position, and the lower edge (14A) of the second metallic arc extinguishing plate (14) is positioned so that the gap between the lower edge (14A) and the stationary contact (8) is less than one half of the gap between the lower edge (13A) and the stationary contact (8), and is preferably about 1 to 2 mm. In the arc extinguishing mechanism constructed as described above, the arc (12) generated between the movable contact element (6A) and the stationary contact element (8A) is drawn toward the first metallic arc extinguishing plate (13) made of a magnetic material to be elongated as shown by the arc (12A). The arc (12A) is then driven by a magnetic field formed by the electric current flowing through the stationary contact (8) which is U-shaped as shown, and the leg of the arc (12A) is moved to the right as viewed in the figure on the surface of the stationary contact (8). Since the lower edge (13A) of the first metallic arc extinguishing plate (13) is at substantially the same level as the surface of the movable contact element (6A), and since the lower edge (14A) of the second metallic arc extinguishing plate (14) is positioned at a distance from the stationary contact (8) less than one half of the gap between the lower edge (13A) and the stationary contact (8), a circularly bent portion of an arc (12G), which is an arc formed with the legs of the lower arc (12A) moved to the right and elongated, substantially simultaneously contacts at two points with the first metallic arc extinguishing plate (13) and the second metallic arc extinguishing plate (14), the arc (12G) being divided into three arcs (12B), (12E) and (12F), resulting in a high arcing voltage which causes the interruption at the current zero point. Thus, since the phenomenon in which the arc (12C) stays at the lower edge (13A) of the first metallic arc extinguishing plate (13) as in the arrangement shown in Fig. 5 is prevented, the interrupting operation of the just above described arrangement is very stable and the arrangement provides a very high interrupting capacity. As above described, with this arrangement, the distances of the first metallic arc extinguishing plate and the second metallic arc extinguishing plate from the stationary contact are selected in a particular relationship, and the interrupting capacity is significantly advantageously improved. Fig. 11 shows still another embodiment of the present invention, in which the lower edge of the first metallic arc extinguishing plate (13) facing the stationary contact (8) is positioned above a line (P) connecting between the tip of the movable contact (6) in the open position and the tip of an arc runner formed by the free end portion (8D), on which the contact element is carried, of the stationary contact (8), and in which the lower edge of the second metallic arc extinguishing plate (14) is positioned below the above line (P), both facing the stationary contact (8). Also, the first metallic arc extinguishing plate (13) is arranged to increase the attractive force on the arc due to the three sides of the plate (13) surrounding the respective contact elements and to protect the surrounding insulations, and a U-shape as shown in Fig. 12 may be selected taking the heat dissipation into consideration. The process of the arc extinction will be described in more detail in conjunction with Fig. 13. The arc (12) generated between the movable contact element (6A) and the stationary contact element (8A) is drawn by the first metallic arc extinguishing plate (13) made of a magnetic material to be extended to become the elongated arc (12A). Since the stationary contact (8) has a U-shaped cross-section as shown in Fig. 14, the arc (12) is rapidly attracted and driven by the magnetic field formed by a current flowing through the stationary contact (8) to be further extended. Since the arcing voltage increases as the arc (12) expands, dielectric breakdowns occur between the stationary contact (8) and the first metallic arc extinguishing plate (13), and between the first metallic arc extinguishing plate (13) and the movable contact element (6A), and the arc (12A) is divided into two arcs (12B) and (12C). One of the divided arcs (12C) is attracted by the second metallic arc extinguishing plate (14) and driven by the magnetic field formed by a current flowing through the stationary contact (8) to be expanded as shown by an electric arc (12D). As the arc (12D) is expanded the arcing voltage increases and the arc (12D) is further divided into two arcs (12E) and (12F). Thus, the arc (12) is ultimately divided into three arcs (12B), (12E) and (12F) and extinguished at the current zero point, thereby interrupting the current. According to the above described switch, since the first metallic arc extinguishing plate (13) is a U-shaped frame vertically disposed around the movable contact element (6A), the driving and attraction of the arc is promoted by the magnetic field formed by the surrounding three side walls and damage to the surrounding insulations is minimized. Also, since the first metallic arc extinguishing plate (13) and the second metallic arc extinguishing plate (14) are disposed in parallel, the arc is divided as previously described and the arc extinguishing capacity is further increased. Moreover, since the lower edges of the first metallic arc extinguishing plate (13) and the second metallic arc extinguishing plate (14) are positioned above and below the previously-mentioned line (P), the arc is prevented from staying at the lower edge of the first metallic arc extinguishing plate (13) and obstructing the proper functioning of the second metallic arc extinguishing plate (14), thereby promoting the previously-described arc dividing function. As shown in Fig. 6, the second metallic arc extinguishing plate (14) may be provided with an arc lead portion (14B) formed by folding the lower edge thereof toward the arc driving direction. As has been described, according to this embodiment, the U-shaped first metallic arc extinguishing plate (13) and the parallel second metallic arc extinguishing plate (14) are disposed in a facing relationship to the movable contact element and in a particular lower edge position, and the advantage of significantly increasing the interrupting capacity is obtained. Fig. 15 illustrates still another embodiment of the present invention. In the figure, the first metallic arc extinguishing plate (13) is provided with shield tongues (13B) facing the back side of the movable contact element (6A). The U-shape of the first metallic arc extinguishing plate (13) may be selected with the heat dissipation taken into consideration as shown in Fig. 16. The gap (d) between the lower edge of the second metallic arc extinguishing plate (14) and the stationary contact (8) of this embodiment is selected to be smaller than the gap (D) between the lower edge of the first metallic arc extinguishing plate (13) and the stationary contact (8). In this embodiment, the first metallic arc extinguishing plate (13) is provided with the shield tongues (13B) in facing relationship with the back face of the movable contact element (6A), so that the insulating wall in an upper position or at the back side of the movable contact element (6A) is prevented from being damaged by the heat of the arced gas. As in the embodiment shown in Fig. 6, the lower edge of the second metallic arc extinguishing plate (14) may be folded toward the arc driving direction to form the arc lead portion (14B). In the switch shown in Figs. 4 and 5, since a magnetic flux shown in a dash line in Fig. 17 is generated around the arc (12) on the stationary contact element (8A) due to the presence of the first metallic arc extinguishing plate (13) made of a magnetic material, the arc (12) is subjected to a force F shown in Fig. 17 to be driven toward the corner portion (13D) of the U-shaped first metallic arc extinguishing plate (13). However, because the spacing between the first metallic arc extinguishing plate (13) and the stationary contact (8) is small, the arc (12C) tends to stay between the corner portion (13D) of the first metallic arc extinguishing plate (13) and the stationary contact (8) as shown in Fig. 18 particularly during small current interruption, and therefore the interrupting capacity is not sufficient for interrupting a high voltage circuit. The description will be made as to still another embodiment of the present invention for solving the above problem. As shown in Fig. 19, the corner portion (13D) of the first metallic arc extinguishing plate (13) facing the stationary contact is provided with notches (13E), and this embodiment is different from the first embodiment in this respect. The description will now be made with reference to Fig. 20 as to the arc extinguishing process in terms of the arc (12) for the embodiment having the first metallic arc extinguishing plate (13) of the above structure. The arc (12) generated between the movable contact element (6A) and the stationary contact element (8A) is attracted by the first metallic arc extinguishing plate (13) to be elongated as shown by the arc (12A). At this time, since the arc (12A) is drawn into the deepest portion of the notches (13E) of the first metallic arc extinguishing plate (13), the arc (12A) becomes longer than that in the embodiment shown in Fig. 5. Therefore, the arcing voltage is correspondingly increased and the dielectric breakdown occurs more quickly than that in the embodiment shown in Fig. 5 between the stationary contact (8) and the first metallic arc extinguishing plate (13) and between the first metallic arc extinguishing plate (13) and the movable contact element (6A), thus dividing the arc (12A) into two arcs (12B) and (12C). One of the divided arcs (12C) is attracted to the second metallic arc extinguishing plate (14) and driven by a magnetic field formed by a current flowing through the stationary contact (8), and is thus elongated as shown by the arc (12D) which is longer than the corresponding arc shown in the embodiment of in Fig. 5. This longer elongation of the arc (12D) causes the increase of the arcing voltage to divide the arc (12D) into two arcs (12E) and (12F). Thus, the arc (12) is ultimately divided into three arc (12B), (12E) and (12F), the arc (12F) being extinguished between the arc lead portion (14B) of the second metallic arc extinguishing plate (14) and the stationary contact. According to this embodiment, since the arc extinguishing operation is as described above, the arc (12A) is drawn into the deepest portion of the notches (13E) of the first metallic arc extinguishing plate (13) and the arcing voltage is increased, whereby the arc (12A) can be more easily divided into two arcs (12B) and (12C). Also, since the corner portions of the folded portion (13A) on the stationary contact side of the first metallic arc extinguishing plate (13), at which the arc tends to stay, are provided with the notches (13E), the length of the arc (12C) is increased and the arcing voltage of the arc (12C) is correspondingly increased. Therefore the arc (12C) is quickly divided into two arcs. As a result, the arc (12C) is prevented from staying at the first metallic arc extinguishing plate (13) and the quick dividing and extinction of the arc (12C) is promoted, thereby providing a superior interrupting capacity. The position and the shape of the notches (13E) are not limited to those shown in Fig. 19. As shown in Fig. 21, wedge-shaped notches 13E may be formed in the first metallic arc extinguishing plate (13) on lines extending from the respective side faces (8B) of the stationary contact (8). With this embodiment, since the arc is drawn into the deepest portion of the notches of the first metallic arc extinguishing plate (13), the arcing voltage is increased and the arc is easily divided into two arcs. Also, since the length of the arc between the stationary contact (8) and the first metallic arc extinguishing plate (13) increases because of the presence of the notches, which further increases the arcing voltage, the arc is further more easily divided into two arcs. That is, the arc is prevented from staying on the first metallic arc extinguishing plate (13) and is divided into two arcs, ensuring a superior interrupting capacity. The shape of the notches is not limited to the wedge-shape and a superior interrupting capacity similar to those of the wedge-shape can be obtained even with the notches as shown in Figs. 22 and 23. Fig. 24 illustrates a further embodiment of the notches. In the vicinity of the lower edge center of the first metallic arc extinguishing plate (13) are formed projections (13C) (13C), which form notches along their sides. The U-shape of the first metallic arc extinguishing plate (13) may be selected to be the one shown in Fig. 25 when considering heat dissipation. Similarly to the embodiment shown in Fig. 8, the gap (d) between the second metallic arc extinguishing plate (14) and the stationary contact (8) is selected to be smaller than the gap (D) between the first metallic arc extinguishing plate (13) and the stationary contact (8). In this embodiment, since wave-shaped projections (13C) are formed on the lower edge of the first metallic arc extinguishing plate (13), the arc is drawn toward the center by the arc drawing function of the wave-shaped projections (13C) to be extinguished, thus preventing the damaging of the insulating side walls and the reduction of the arc extinguishing capacity due to the the arc remaining at the arc extinguishing plate side portions, resulting in a more efficient arc dividing and extinguishing operation. Fig. 26 illustrates a modification of the second metallic arc extinguishing plate (14). The second metallic arc extinguishing plate (14) has formed on its lower edge of the portion bridging over the stationary contact an arc lead portion (14B) folded to form a U-shaped cross section and facing the stationary contact. With this embodiment, when the arc is divided into two by the second metallic arc extinguishing plate (14), a concentration of an electric field on the second metallic arc extinguishing plate (14) is prevented by the presence of the U-shaped arc lead portion (14B), and the arc is quickly extinguished on the bottom planar surface of the U of the arc lead portion (14B). Also, since the above bottom planar surface is effectively provided with a heat dissipation due to a vertical leg portion of the U, there is no risk of burning, thereby providing a superior interrupting capacity. Although the stationary contact (8) in all of the above-described embodiments has a U-shape, a similar effect can be obtained with a straight shape rather than the U-shape. Although the description has been made in terms of the embodiments of the present invention applied to switches in which the contacts are operated by a magnet, i.e., electromagnetic contactors, the present invention may equally be applicable to other switches such as circuit breakers.

Claims: A switch comprising a stationary contact element (8A) joined to a stationary contact (8), a movable contact element (6A) joined to a movable contact (6) in a facing relationship to said stationary contact element (8A), an arc gap being defined extending between the movable and stationary contact elements (6A, 8A) when the contacts (6, 8) are opened, said movable contact and an arc-carrying portion (8D) of the stationary contact (8) extending respectively in opposite directions away from their respective contact elements (6A,8A), a first sheet metallic arc extinguishing plate (13) formed of a U-shaped vertical wall and disposed with the U extending around the tip of said movable contact (6), and a second metallic plate (14) disposed at the side of the base of the U of said first metallic arc extinguishing plate (13) that is remote from said contact elements (6A,8A), the said first plate (13) being disposed so that at the base of the U the lower edge (13A) of the first plate (13) overlies the stationary contact with a predetermined gap (D), extending generally in the same direction as the said arc gap, between the arc-carrying portion (8D) of the stationary contact (8) and the said lower edge (13A), the second plate (14) being disposed with a predetermined gap (d) between its lower edge (14A) and the arc-carrying portion (8D) of the stationary contact (8), the said gap (d) between said second plate (14) and said stationary contact (8) being smaller than the said gap (D) between said first plate (13) and said stationary contact (8), and the side walls of the said U-shaped first plate (13) extending around the longitudinal sides of the movable contact (6) and embracing the movable contact element (6A) between them, characterized in that the said second plate (14) is a second arc extinguishing plate arranged parallel to the first arc extinguishing plate (13), and the said arc-carrying portion (8D) of the stationary contact (8) extends longitudinally from its contact element (8A) to a distance greater than the distance of the second plate (14) from the contact elements (6A, 8A), such that the lower edge (14A) of the second plate (14) overlies the arc-carrying portion (8D) of the stationary contact (8) and that the said gap (d) between the arc-carrying portion (8D) of the stationary contact (8) and the lower edge (14A) of the second plate (14) extends generally in the same direction as the said arc gap. A switch as claimed in claim 1, characterized in that said second metallic arc extinguishing plate (14) is provided, on a portion close to the said arc-carrying portion (8D) of said stationary contact (8), with a folded-back arc lead portion (14B) that extends away from the stationary contact element (8A) generally parallel to the said stationary contact. A switch as claimed in claim 2, characterized in that said arc lead portion (14B) is U-shaped. A switch as claimed in claim 1, characterized in that the lower edge (13A) of said first metallic arc extinguishing plate (13) facing the arc-carrying portion (8D) of said stationary contact (8) is positioned in the vicinity of the open position of the movable contact element (6A), and the gap distance (d) between the lower edge (14A) of said second metallic arc extinguishing plate (14) and the arc-carrying portion (8D) of the stationary contact (8) is selected to be less than one half of the gap distance (D) between the lower edge (13A) of the said first metallic arc extinguishing plate (13) and the arc-carrying portion (8D) of said stationary contact (8). A switch as claimed in claim 1, characterized in that the lower edge (13A) of said first metallic arc extinguishing plate (13) facing the arc-carrying portion (8D) of said stationary contact (8) is positioned above an imaginary line connecting the tip of the movable contact (6) in the open position and the tip of the arc-carrying portion (8D) of said stationary contact (8), and the lower edge (14A) of said second metallic arc extinguishing plate (14) is positioned below said imaginary line. A switch as claimed in claim 1, characterized in that the lower edge (13A) of said first metallic arc extinguishing plate (13) facing the arc-carrying portion (8D) of said stationary contact (8) is provided with a notch (13E). A switch as claimed in claim 6, characterized in that corners (13D) of said first metallic arc extinguishing plate (13) facing the arc-carrying portion of said stationary contact (8) are provided with notches (13E). A switch as claimed in claim 6, characterized in that said first metallic arc extinguishing plate (13) is provided with notches (13E) aligned with both side faces of said stationary contact (8). A switch as claimed in claim 6, characterized in that said first metallic arc extinguishing plate (13) has a projection (13C) formed at the central portion of the lower edge (13A) thereof, thereby forming notches on both sides of the projection. A switch as claimed in claim 1, characterized in that said first metallic arc extinguishing plate (13) is provided with wave-shaped projections (13C) at the lower edge (13A) thereof facing the arc-carrying portion (8D) of said stationary contact (8). A switch as claimed in claim 1, characterized in that said first metallic arc extinguishing plate (13) is provided with a shielding tongue portion (13B) facing that surface of said movable contact (6) that faces away from the stationary contact (8).

Inventors: MORI, TEIJIRO MITSUBISHI DENKI CHUO KENKYUSHO, OKADO, HIROYUKI MITSUBISHI DENKI, SAKO, YUJI MITSUBISHI DENKI NAGOYA SEISAKUSHO, TAZAWA, HIROAKI MITSUBISHI DENKI, WADA, YUICHI MITSUBISHI DENKI CHUO KENKYUSHO
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1983
Main classification: H01H9
IPC codes: H01H9