Circuit breaker

Abstract: In a circuit breaker of double break type, a first moving contact arm (4) and a second moving contact arm (5) are pivoted on a common pin shaft (10) in a manner to move mechanically independent from each other and are electrically connected at the parts near the pivoted ends by a flexible conductor (16), such as the braided wires (16c), so that stable and reliable contacts of the moving contacts (3, 6) on the stationary contacts are assured thereby.

Description: The present invention relates to an improvement in a circuit breaker of double break type which has serially connected two sets of contacts for each phase. The invention relates particularly to the configuration of moving contact arm in the circuit breaker of the double break type. DESCRIPTION OF THE RELATED ART A circuit breaker of the double break type has been disclosed, for instance, in the Japanese published examined patent application JP-A-50-118260, which is considered to represent the most relevant prior art and comprises the features of the preamble of claim 1, essential part thereof is shown herein by Fig. 5 and Fig. 6. As shown in these drawings, first stationary contact holder 1 having a first stationary contact 2 and a second stationary contact holder 8 having a second stationary contact 7 are disposed parallel and in opposite directions to each other. An integral U-shaped moving contact arm is formed by a first moving contact arm 4, a second moving contact arm 5 and a connecting part 9 there-between integrally connecting the first and the second moving contact arms 4, 5, and has a first moving contact 3 and a second moving contact 6, respectively. The first and second moving contact arms 4, 5 are provided movably above the first stationary contact holder 1 and the second stationary contact holder 8, in such a manner that the first moving contact 3 and the second moving contact 6 contact the first stationary contact 2 and the second stationary contact 7, respectively, when the moving contact arms 4, 5 are driven downward by a conventional driving member (not shown). The moving contact arms 4, 5 are pivotally mounted by a pin 10. A torsion spring 11 is provided being coupled at one end thereof to a part of the first moving contact arm 4, at the other end to an arm 121 of a driving member 120 and at its middle wound part to the pin 10, thereby to urge the first and the second moving contact arms 4, 5 downward to the stationary contacts 2, 7, respectively. The above-mentioned components are assembled on a base casing 12 which is made of an insulating plastic material. The base casing 12 has a partition wall 15 thereon for defining a first arc extinguishing space 13 on one side thereof and a second arc extinguishing space 14 on the other side thereof. The driving member 120 is linked to a conventional driving mechanism, such as a tripping mechanism or a remote driving electromagnet through a known cross bar 123 in a usual manner, and the cross bar 123 usually links similar driving members of three similar circuit breakers of three phases. The above-mentioned general double break type circuit breaker operates as follows. When the moving contact arms 4, 5 are in the closing state wherein the first moving contact 3 and the second moving contact 6 are in contact with the first stationary contact 2 and the second stationary contact 7, respectively, the current flows from the first stationary contact holder 1, through the first stationary contact 2, the first moving contact 3, the first moving contact arm 4, the connecting part 9, the second moving contact arm 5, the second moving contact 6, the second stationary contact 7 and to the second stationary contact holder 8, or in the opposite direction as indicated above. In order to break the circuit, the moving contact arms 4, 5 are driven in clockwise direction in the situation shown in the drawings by a usual driving mechanism (not shown). Then, the moving contacts 3 and 6 separate from the stationary contacts 2, 7, respectively, and arcs are generated between the parting contacts 3 and 2 as well as the other parting contacts 6 and 7. Since the two contact pairs 3-2 and 6-7 are isolated from each other by the partition wall 15, two arcs generated between each contact pairs are in series-connected relation. And therefore, the total length of the arc column is twice as long as that of the single contact type circuit breaker. Thus, the configuration of such a double break type circuit breaker can raise the arc voltage at a rate (or speed) twice as high as that of a single contact type breaker. Therefore, its current is quickly suppressed and the breaking time is sufficiently short, and there are only little damages in the double break type circuit breaker. However, the above-mentioned conventional double break type circuit breaker has a problem in that contact pressures in the two contact pairs, namely the first contact pair 2 and 3 and the second contact pair 6 and 7 are likely to have different contact pressure, for some reason. The reason may be, for instance, a certain initial difference of the faces of the contacts, or a difference of surface consumption of the contacts, etc.. Of course, any such difference of the contact pressure is substantially not adjustable, because the moving contact arms 4 and 5 are rigidly and integrally connected with each other by the connecting part 9 therebetween, and thereby the contact is liable to become unstable. OBJECT AND SUMMARY OF THE INVENTION In order to solve the above-mentioned problem, the present invention is intended to provide an improved circuit breaker to achieve a more stable contact by both pairs of contacts of the double break type circuit breaker. The above-mentioned problem is achieved by the circuit breaker comprising the features of claim 1. Such circuit breaker may comprise: a first stationary contact holder which has a first stationary contact at one end thereof, a second stationary contact holder which has a second stationary contact at one end thereof and is disposed substantially in parallel and in opposite direction to the first stationary contact holder, a first moving contact arm which has a first moving contact at the moving end part thereof, a second moving contact arm which has a second moving contact at the moving end part thereof and is disposed substantially parallel and in the same direction as the first moving contact arm, and a flexible conductor for electrically connecting parts of ends of the first moving contact arm and the second moving contact arm, opposite to the moving ends thereof, in a manner to allow mechanically independent motions thereof from the other. By provision of the flexible conductor for electrically connecting parts of opposite ends to the moving ends of the first moving contact arm and the second moving contact arm, the first moving contact arm and the second moving contact arm can move mechanically free from each other, and thereby, appropriate contact pressures are provided for respective contact points pair in the double break type circuit breaker. Other aspects, features and advantages of embodiments of the invention will become readily apparent from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of an essential part of a circuit breaker embodying the present invention. Fig. 2 is a perspective view for showing the detailed configuration of the mechanically free and electrically connected parts of the embodiment shown in Fig. 1. Fig. 3 is a partly cut off perspective view of the circuit breaker of the embodiment of Fig. 1 shown with its cover plate removed. Fig. 4 is a partly cut off perspective view of the circuit breaker of the embodiment shown with its partition wall and driving member partly removed. Fig. 5 is the perspective view of the essential parts of a prior art circuit breaker. Fig. 6 is the perspective view for showing the detailed configuration of the integral rigid mechanical connection parts of the moving contact arms. It will be recognized that some or all of the Figures are schematic representations for purposes of illustration only and do not necessarily depict the actual relative sizes or locations of the elements shown. DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention is described in detail with reference to the accompanying drawings of Fig. 1, Fig. 2, Fig. 3 and Fig. 4. As shown in these drawings, a first stationary contact holder 1 having a first stationary contact 2 and a second stationary contact holder 8 having a second stationary contact 7 are disposed parallel and in opposite directions to each other. A pair of moving contact arms disposed in parallel, namely a first moving contact arm 4 and a second moving contact arm 5 are pivotally connected by a pin 10 to a driving member 120. The first moving contact arm 4 and the second moving contact arm 5 are electrically connected by a flexible conductor 16, for instance braided wires 16c whose both ends are hardened by, for instance, high temperature heating and pressing, to form hard end parts 16a and 16b. Alternatively, the hardened parts 16a and 16b may be hardened by silver-soldering. The hardened ends of the braided wires are electrically and mechanically fixed by welding or silver-soldering to the upper edge parts near the pivoted ends of the first moving contact arm 4 and the second moving contact arm 5, respectively. Thus, the first and second moving contact arms 4, 5 are held movably above the first stationary contact holder 1 and the second stationary contact holder 8, in such a manner that the first moving contact 3 and the second moving contact 6 make contact with the first stationary contact 2 and the second stationary contact 7, respectively, when the moving contact arms 4, 5 are driven downwards by a conventional driving member (not shown). The moving contact arms 4, 5 are pivotally mounted by the pin 10. A first torsion spring 11 is provided being coupled at one end thereof to a part of the first moving contact arm 4, at the other end to an arm 121 of a driving member 120, and at its middle wound part to the pin 10, thereby to urge the first moving contact arm 4 downward to the first stationary contact 2 so as to make a contact pressure therebetween. Similarly, another torsion spring 17 is provided being coupled to a part of the second moving contact arm 5, the other arm 121′ of the driving member 120, and the wound medium part around the pin 10, thereby to urge the second moving contact arm 5 downward to the second stationary contact 7 so as to make another contact pressure therebetween. The above-mentioned components are assembled on a base casing 12 which is made of an insulating plastic material. The base casing 12 has a partition wall 15 thereon to define a first arc extinguishing space 13 on one side thereof and a second arc extinguishing space 14 on the other side thereof. The driving member 120 is linked to a conventional driving mechanism, such as, a tripping mechanism or a remote driving electromagnet through a cross bar 123. Usually, the cross bar 123 links similar driving members of three similar circuit breakers for three phases with each other. The above-mentioned general double break type circuit breaker operates as follows. In order to close the circuit breaker, the moving contact arms 4, 5 as shown are driven counter-clockwise by the driving member 120 to the closing state, wherein the first moving contact 3 and the second moving contact 6 come in contact with the first stationary contact 2 and the second stationary contact 7, respectively. Then, the current can flow from the first stationary contact holder 1, through the first stationary contact 2, the first moving contact 3, the first moving contact arm 4, the flexible conductor 16, the second moving contact arm 5, the second moving contact 6, the second stationary contact 7 and then to the second stationary contact holder 8, or in the opposite direction as described above. In order to break the circuit, the moving contact arms 4, 5 are driven in clockwise direction in the situation shown in the drawings by a conventional driving mechanism. Then, the moving contacts 3 and 6 separate from the stationary contacts 2, 7, respectively, and arcs are generated between the parting contacts 3 and 2 as well as the other parting contacts 6 and 7. Since the two contact pairs 3-2 and 6-7 are isolated from each other by the partition wall 15 and a distance having the double length of the moving contact arms 4, 5, two arcs generated by the contact pairs are isolated from each other and hence are in series-connected relation. Therefore, the total length of the arc columns is twice as long as that of the single contact type breaker. According to the above-mentioned configuration of the present invention, since the first moving contact arm 4 and the second moving contact arm 5 are pivoted separately from each other on the pin 10, urged by resective contact pressure springs 11 and 17, and are connected with each other by the flexible conductor 16 (such as the braided wires 16c), both moving contact arms 4 and 5 are movable freely from each other in a rotation around the pin 10 (or vertically) in a direction to apply a contact pressure to the stationary contacts 3 and 6, respectively, and are movable slightly even in left or right direction and even obliquely slightly from its vertical face of the moving contact arms 4, 5, when a predetermined tolerance is provided between the pin 10 and the respective holes in the moving contact arms 4, 5. Therefore, stable and appropriate impressing of contact pressures from the moving contacts 3 and 6 to the stationary contacts 2 and 7, respectively, is achievable. Furthermore, since the first and the second moving contact arms 4 and 5 are electrically connected by a flexible conductor 16, such as the braided wires 16c, at the opposite end parts to the moving parts where the moving contact points are fixed, namely at the distant part from the contact pairs 3-2 and 6-7, substantially the total length of the moving contact arms 4 and 5 can be utilized as insulation distance between the two arcs. Furthermore, by welding or soldering the hardened end parts 16a, 16b of the flexible conductor 16c to the upper edges of the above-mentioned opposite end parts of the moving contact arms 4 and 5, the flexible conductor 16 is short and straight without forced sharp bending and hence can smoothly follow the movement of the moving contact arms 4, 5. Therefore, the welded part or soldered part has a stable and high strength for long service time. Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form may be changed in the details of its construction and the combination and arrangement of parts may be resorted to without departing from the scope of the invention as defined by claim 1.

Claims: A circuit breaker comprising: a first stationary contact holder (1) having a first stationary contact (2) at one end thereof, a second stationary contact holder (8) having a second stationary contact (7) at one end thereof, the first and second stationary contact holders (1, 8) being disposed substantially parallel and in opposite directions to one another, a first and a second moving contact arm (4, 5) disposed substantially parallel to one another and mounted pivotally about a pin (10), a first and a second moving contact (3, 6) located on moving end portions of the first and second moving contact arms (4, 5) respectively, characterized in that the first and second contact arms are pivoted independently, a flexible connector (16) is provided for electrically connecting the first and second moving contact arms (4, 5) while allowing relative motion of the arms with respect to one another, wherein the flexible conductor is fixed to the moving contact arms at a position along the lengthwise direction corresponding to that of the mounting pin (10) and the flexible conductor is arranged substantially parallel with the axis of the mounting pin (10). The circuit breaker in accordance with claim 1, which further comprises: a first spring (11) for providing a first contact force to the first moving contact arm (4) urging the first moving contact (3) into contact with the first stationary contact (2), and a second spring (17) for providing a second contact force to the second moving contact arm (5) urging the second moving contact (6) into contact with the second stationary contact (7). The circuit breaker in accordance with claim 1 or 2, wherein the flexible conductor (16) comprises braided wires (16c). The circuit breaker in accordance with any of claims 1 to 3, wherein the flexible conductor (16) is provided with hardened ends (16a, 16b) fixed by welding or soldering to the moving contact arms (4, 5). The circuit breaker in accordance with any of claims 1 to 4, wherein the first moving contact arm (4) and the second moving contact arm (5) are pivotally mounted by said pin (10) with a predetermined tolerance for a predetermined limited motion in other directions than the simple rotation around the axis of the pin (10).

Inventors: KOBAYASHI YOSHIAKI, MITSUHASHI TAKAO, TAKAHASHI MITSUGU, YAMAGATA SHINJI, KOBAYASHI, YOSHIAKI, MITSUHASHI, TAKAO, TAKAHASHI, MITSUGU, YAMAGATA, SHINJI, KOBAYASHI, YOSHIAKI, C/O CHUOU KENKYUSHO, MITSUHASHI, TAKAO, C/O CHUOU KENKYUSHO, TAKAHASHI, MITSUGU, C/O CHUOU KENKYUSHO, YAMAGATA, SHINJI, C/O CHUOU KENKYUSHO
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: H01H73
IPC codes: H01H1, H01H33, H01H9, H01H73