A CIRCUIT BREAKER

Abstract: The present invention relates to a circuit breaker wherein a pair of rigid conductors (201, 301) which are disposed therein and at least one of which has a movable portion that separates a pair of contacts (202, 302) by an electromagnetic force produced by an excess current flowing through the con­ tacts (202, 302) adapted to come into and out of contact with and from each other, are provided with arc shields (6, 7) in a manner to surround the contacts (202, 302), thereby to bring forth the effects of increasing the arc voltage of an electric arc struck across the contacts (202, 302) and raising the separat­ ing speed of the contacts (202, 302).

Description: The present invention relates to an circuit breaker according to the preamble of claim 1. Prior circuit breakers as known from DE-A-29 28 823; US-A-3 402 273 and DE-C-944 566 have the disadvantage that an electric arc struck across contacts expands its feet (base) to the parts of rigid conductors near the contacts, so that metal particles of the contacts cannot be effectively injected into the arc. With the prior devices, it has been imposssible to achieve a circuit breaker with enhanced current-limiting performance. It is the object of the present invention, to improve the circuit breaker as known from DE-A-29 28 823 in such a way that the feet of an electric arc are prevented from spreading to the parts of the rigid conductors near the contacts, thereby to effectively inject the metal particles of the contacts into the arc and to raise the arc voltage of the electric arc, whereby the pressure of the arc space of the electric arc is increased, thereby to raise the separating speed of the contacts. This object of the invention is obtained by providing the features as stated within claim 1. Further improvements of the invention are obtained by providing the features as stated within the subclaims 2-4. Preferred ways of carrying out the invention are described in detail below with reference to drawings, in which: Fig. 1 is a sectional plan view showing an embodiment of the circuit breaker according to the present invention, Fig. 2 is a sectional side view taken along line b - b in Fig. 1 thereby showing the state in which the contacts of the circuit breaker are disengaged, Fig 3 is a sectional side view showing the state in which the contacts of the circuit breaker in Fig. 1 are engaged, Fig. 4 is a sectional side view showing the state in which the contacts of the circuit breaker in Fig. 1 have started to separate, and Fig. 5 is a perspective view of the second contactor for the circuit breaker of Fig. 1. In the drawings, the same symbols indicate identical or corresponding parts. Fig. 1 shows an embodiment of the invention, in which an enclosure 1 made of an insulator forms the outer frame of a switching device and is provided with an exhaust port 101. A first contactor 2 is constructed of a first rigid conductor 201, and a first contact 202 which is mounted on one end part of the first rigid conductor 201, the other end part of which is turnably supported by a pivot pin 2b on a holder 2a fixed to the enclosure 1. The first rigid conductor 201 is connected to a connection terminal 204 through a flexible conductor 203. A second contactor 3 being movable relative to the first contactor 2 in order to close or open the circuit breaker, is constructed of a second rigid conductor 301 which is operated relative to the first rigid conductor 201 so as to close or open the circuit breaker, and a second contact 302 which is mounted on one end part of the second rigid conductor 301 in a manner to confront the first contact 202. The second rigid conductor 301 is connected to an external conductor (not shown) through a flexible conductor 303, and the intermediate part thereof is turnably supported on one end part of a movable frame member 305 by a pivot pin 304. The other end part of the movable frame member 305 is turnably supported on a supporter 306 by a pivot pin 307. A spring 2A is interposed between the first rigid conductor 201 and the enclosure 1, and a torsion spring 3A is applied to the pivot pin 304 and has its respective end parts held in engagement with the second rigid conductor 301 and the movable frame member 305. These springs bias the first and second contacts 202 and 302, respectively. An operating mechanism 4 for operating the second contactor 3 so as to close or open the circuit breaker, is formed so that one end part of a lower link 401 constituting a linkage is turnably coupled to the pivot pin 304 and that also an operating handle 402 is turnably coupled to the linkage. Arc extinguishing plates 5 extinguish an electric arc struck when the second contact 302 is separated from the first contact 202, and they are supported by a pair of side plates 501 and 502. Arc shields 6 and 7 made of a high resistivity material are respectively mounted on the first and second rigid conductors 201 and 301 in a manner to have the first and second contacts 202 and 302 projecting therethrough and to oppose to the electric arc A. When the operating handle 402 is turned clockwise, the first and second contacts 202 and 302 are engaged as illustrated in Fig. 3. When a high current, such as a short-circuit current flows under these conditions, the first and second rigid conductors 201 and 301 are electromagnetically repelled on account of parallel currents flowing in opposite directions to each other through these rigid conductors. Thus the first and second rigid conductors 201 and 301 are separated from each other, so that the electric arc A develops across the first and second contacts 202 and 302 as illustrated in Fig. 4. Thereafter, the operating mechanism 4 works to completely separate the second rigid conductor 301. In the arc A metal particles are reflected by the arc shields 6 and 7 to render the pressure of the arc space high, with the result that the arc is effectively cooled and extinguished. In the embodiment as described above, the other end part of the second rigid conductor 301 is turnably supported on the movable frame member 305 by the pivot pin 304, the other end part of the first rigid conductor 201 is turnably supported on the supporter 2a by the pivot pin 2b, and the currents flowing through the first and second rigid conductors 201 and 301 are in parallel and opposite in direction to each other. Therefore, when the high current, such as short-circuit current flows, the first and second rigid conductors 201 and 301 are electromagnetically repelled by the currents flowing therethrough, without waiting for the operation of the operating mechanism 4. The electromagnetic repellence separates both the first and second rigid conductors 201 and 301, to generate the arc A. Upon the generation of the arc A, the rigid conductors can be separated at very high speed by the pressure rise of the space Q between the arc shields 6 and 7, in addition to the electromagnetic repellent force. Accordingly, the arc voltage starts rising very quickly. Since both the first and second rigid conductors 201 and 301 separate, the arc length stretches, and this raises the arc voltage very greatly conjointly with the effect of the arc shields 6 and 7, so that the peak value of the current to flow through the circuit can be made very small. Fig. 5 is a perspective view showing the arc shield 7. this arc shield 7 is provided with a groove or arc runway 701 which extends from the second contact 302 toward the arc extinguishing plates 5, so as to expose the second movable rigid conductor 301. Owing to the provision of this groove 701, the arc A runs toward the arc extinguishing plates 5 within this groove, to become effectively extinguished in direct contact with the arc extinguishing plates 5. Due to these arc shields 6 and 7 the arc voltage can be remarkably raised so that a high current-limiting performance can be attained. The circuit breaker of this invention is constructed such that except for a part of the electically contacting surface of either contact of the circuit breaker, the part of a rigid conductor adjacent to the contact as projects to the surrounding space is concealed behind an arc shield (a plate-shaped pressure reflector or a covering such as taping and coating) which is made of a substance of a highly resistive material (called the "high resistivity material" hereinbelow) having a resistivity higher than that of a material forming the rigid conductor, thereby to forcibly inject metal particles into an arc space, and that the electrodes are separated at high speed by a high pressure established owing to the provision of the arc shield. As high resistivity material, there can be used, for example, an organic or inorganic insulator, or a high resistivity metal such as copper-nickel, copper-manganese, manganin, iron-carbon, iron-nickel and iron-chromium. It is also possible to use iron whose resistance increases abruptly in accordance with a temperature rise. In a circuit breaker for alternating current, the polarity of the current on a contact during arcing is not decided, and moreover, the polarity on the same contact changes even during arcing. In this regard, the circuit breaker of the present embodiment can prevent the polarity effect on the current-limiting performance from becoming different depending upon whether the polarity on the contact to be separated by the electromagnetic repellence is a cathode or an anode and it can stabilize the current-limiting performance. That is, such beneficial result is achieved by the measure that both the first rigid conductor 201 and the second rigid conductor 301 on which the first contact 202 and the second contact 302 are respectively mounted are formed of the turnable electromagnetic repulsion type.

Claims: Circuit breaker comprising an operating mechanism (4) to close or open an electric circuit by engaging or disengaging a pair of contacts (202, 302), said pair of contacts (202, 302) being disposed on rigid current conductors (201, 301) of contactors (2, 3) said contactors (2, 3) being pivotally supported in order to be able to move to and from the opposite contact (202, 302) whereby the second contactor (3) is pivotally mounted on the circuit breaker's enclosure (1) realizing a contactor (3) in form of a toggle element connected with the operating mechanism (4), whereby the first contactor (2) is pivotally supported on the enclosure (1) and provided with a spring (2A) forcing the first contactor (2) into the direction towards the second contactor (3), and whereby these contactors (2, 3) are arranged with respect to each other in parallel and symmetric way, so that a current loop is formed in the closed state, characterized in that the second contactor (3) is additionally provided with a further spring (3A) loaded pivot (304) in its intermediate part, that on said contactors (2, 3) there are disposed arc shields (6, 7) in a way as to surround the respective contacts (202, 302), that the arc shields (6, 7) are made of high resistivity material and that each of these arc shields (6, 7) is provided with an arc runway (701) which extends from the contacts (202, 302) in the direction of arc extinguishing plates (5), thereby exposing the conductors (201, 301) of the contactors (2, 3). Circuit breaker according to claim 1, characterized in that the two contactors (2, 3) are connected via flexible conductors (203, 303) to external terminals (204). Circuit breaker according to claim 1 or 2, characterized in that the material of the arc shields (6, 7) is an organic or inorganic insulator. Circuit breaker according to claim 1 or 2, characterized in that the material of the arc shields (6, 7) is a high resistivity metal such as copper-nickel, copper-manganese, iron-carbon, iron-nickel, iron-chromium or iron.

Inventors: HISATSUNE, FUMIYUKI, TERACHI, JUNICHI, YAMAGATA, SHINJI, YOSHIYASU, HAJIMU
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1982
Main classification: H01H73
IPC codes: H01H73, H01H77