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, 203) 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 a 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 these known 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. In accordance with the invention this object is obtained by providing the features as stated in 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 and 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 used 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 circuit breaker according of this invention, in which an enclosure 1 forming the outer frame of a switching device is made of an insulator and is provided with an exhaust port 101. A first contactor 2 is constructed of a first rigid conductor 201, which is turnably supported by a pivot pin 2b on a holder 2a that is fixed to the enclosure 1, and a first contact 202 which is mounted on one end part of the first rigid conductor 201. The first rigid conductor 201 is connected to a connection terminal 204 through a flexible conductor 203. A second contactor 3 moves relative to the first contactor 2 in order to close or open the circuit breaker, and it comprises 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, while the other end part thereof is turnably held by a pivot pin 305 on a holder 304 that is fixed to the enclosure 1. A spring 2A being interposed between the first rigid conductor 201 and the enclosure 1 urges the first contact 202 against the second contact 302. 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 second rigid conductor 301 by a pivot pin 402, that one end part of an upper link 403 is turnably coupled to the other end part of the lower link 401 by a pivot pin 404, and that an operating handle 405 is turnably coupled to the other end part of the upper link 403 by a pivot pin (not shown). 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 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. Next, the operation of this embodiment will be described. When the operating handle 405 is turned clockwise, the first and second contacts 202 and 302 are engaged as illustrated in Fig. 3. When in this state a high current, such as short-circuit current flows, the first and second rigid conductors 201 and 301 are electromagnetically repelled on account of parallel currents which flow through these rigid conductors in senses opposite to each other, and the first rigid conductor 201 is separated as shown in Fig. 4, so that the electric arc A develops across the first and second contacts 202 and 302. Subsequently, 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 first rigid conductor 201 it turnably held on the holder 2a by the pivot pin 2b. Therefore, when the high current, such as a short-circuit current flows, the first and second rigid conductors 201 and 202 are electromagnetically repelled by the currents flowing therethrough, without waiting for the operation of the operating mechanism 4, so that the first rigid conductor 201 is separated to generate the arc A. Upon the generation of the arc A, the pressure of the space Q between the arc shields 6 and 7 becomes very high, and hence, the first and second rigid conductors 201 and 301 can be separated at very high speed by the effect of the arc shields 6 and 7 in addition to the electromagnetic repellent force, so that the arc voltage starts rising very quickly and rises very greatly. Accordingly, the peak value of the current to flow through the circuit can be made very small, the arc voltage can be made remarkably higher than in the prior circuit breaker, and a very high current-limiting performance can be attained. Fig. 5 is a perspective view showing an arc shield, which is provided with a groove or arc runway 701 extending 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 the arc shields 6 and 7 the first movable rigid conductor 201 separates at high speed, so that the arc voltage can be remarkably raised far beyond the limit thereof in the prior circuit breaker, and so that a high current-limiting preformance can be attained. The circuit breaker of this invention is formed in such a way that, except for a part of the electrically 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), the first contactor (3) being pivotally mounted on the circuit breaker's enclosure (1) and additionally pivotally connected with the operating mechanism (4), while the second contactor (2) is also pivotally mounted on the enclosure (1), and provided with a spring (2 A) urging the contactor (2) towards the first contactor (3), whereby these contactors (2, 3) are arranged with respect to each other in a parallel and symmetric way so that a current loop is formed in the closed state, characterized in 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 at least one of said arc shields (6,7) is provided with an arc runway (701) extending from the respective contact (202,302) towards arc extinguishing plates (5) thereby exposing the rigid conductor (201, 301) of the respective contactor (2, 3). Circuit breaker according to claim 1, characterized in that the contactors (2, 3) are connected be means of flexible conductors (203, 303) to external connection terminals (e.g. 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, manganin, 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: H01H77, H01H73