EP0233322B1

EP0233322B1 - A circuit breaker

Info

Publication number: EP0233322B1
Application number: EP86115269A
Authority: EP
Inventors: Shinji Yamagata; Fumiyuki Hisatsune; Junichi Terachi; Hajimu Yoshiyasu
Original assignee: Mitsubishi Electric Corp
Current assignee: OFFERTA DI LICENZA AL PUBBLICO
Priority date: 1981-03-12
Filing date: 1982-03-12
Publication date: 1991-08-28
Anticipated expiration: 2002-03-12
Also published as: EP0233322A2; EP0233322A3

Description

The present invention relates to a circuit breaker according to the preamble of claim 1.
Prior circuit breakers as known from US-A-3599130, US-A-3402273 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 US-A-3599130 so 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 raising 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 circuit breaker of the invention are obtained by providing the features of 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,
Fig. 5: is a perspective view of the first contactor of the arc shield used for the circuit breaker of Fig. 1, and
Fig. 6: 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 invention wherein an enclosure 1 made of an insulator forms the outer frame of a switching device and is provided with an exhaust port 101. A stationary contactor 2 is constructed of a stationary rigid conductor 201, which is fixed to the enclosure 1, and a stationary-side contact 202 which is mounted on one end part of the stationary rigid conductor 201. A movable contactor 3 being movable relative to the stationary contactor 2 in order to close or open the circuit breaker, is formed of a movable rigid conductor 301 which is operated relative to the stationary contactor 2 so as to close or open the circuit breaker, and a movable-side contact 302 which is mounted on one end part of the movable rigid conductor 301 in a manner to confront the stationary-side contact 202. The movable 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. A cross bar 306 is penetratingly inserted in the other end part of the movable frame member 305 in a direction perpendicular to the plane of the drawing, and it turnably supports the movable frame member 305 in each phase.
An operating mechanism 4 for operating the movable contactor 3 so as to close or open the circuit breaker, is constructed of a lower link 401 one end part of which is turnably mounted on the intermediate part of the movable rigid conductor 301 by the pivot pin 304, an upper link 403 one end part of which is turnably mounted on the other end part of the lower link 401 by a pivot pin 402, an operating handle 404 which is turnably mounted on the other end part of the upper link 403 by a pivot pin (not shown), and a torsion spring 405 which is applied to the pivot pin 304 and has its respective end parts held in engagement with the movable rigid conductor 301 and the movable frame member 305.
Arc extinguishing plates 5 extinguish an electric arc struck when the movable contact 302 is separated from the stationary contact 202, and they are held by a pair of side plates 501 and 502. Arc shields 6 and 7 are made of high resistivity material, and are respectively mounted on the stationary rigid conductor 201 and movable rigid conductor 301 in a manner to have the stationary contact 202 and the movable contact 302 projecting therethrough to oppose to the electric arc A.
When the operating handle 404 is turned clockwise, the movable contact 302 and the stationary contact 202 are engaged as illustrated in Fig. 3. In this state, current flows from a power supply side to a load side via the stationary rigid conductor 201, the stationary contact 202, the movable contact 302 and the movable rigid conductor 301. In this state, the directions of currents flowing through the movable rigid conductor 301 and the stationary rigid conductor 201 are the same. Therefore, even when a comparatively great current flows, the repulsion between the movable rigid conductor 301 and the stationary rigid conductor 201 as caused by the currents flowing therethrough does not take place. That is, even when a comparatively great instantaneous current flows, the repulsion between the stationary-side contact 202 and the movable-side contact 302 does not occur unnecessarily, so that the stationary contact 202 and the movable contact 302 experience little wear and can be prevented from fusing and depositing. Now, when a high current, such as short-circuit current, flows through the circuit, the operating mechanism 4 works to separate the movable contact 302 from the stationary contact 202. At this time, the electric arc A develops across contacts 202 and 302. This state is illustrated in Fig. 4. 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 movable rigid conductor 301 is turnably held on the movable frame member 305 by the pivot pin 304; further, the arc shields 6 and 7 are provided. Accordingly, although the operating mechanism 4 affords a low separating speed of the movable rigid conductor 201 on account of its inertia, the pressure of the space Q between the arc shields 6 and 7 becomes very high, and the movable rigid conductor 201 is therefore separated at very high speed without waiting for the drive of the operating mechanism 4. In consequence, the rise of the arc voltage immediately after the separation is rapid, and this suppresses the peak value of the current to flow through the circuit, conjointly with the effect of narrowing the arc A by the arc shields 6 and 7, so that a high current-limiting effect can be attained.
Fig. 5 and 6 are perspective views showing the arc shields 6 and 7, which are provided with grooves or arc runways 601 and 701 extending from the first and second contacts 202 and 302 toward the arc extinguishing plates 5, so as to expose the first and second movable rigid conductors 201 and 301. Owing to the provision of these grooves 601 and 701, the arc A runs toward the arc extinguishing plates 5 within these grooves, to become effectively extinguished in direct contact with the arc extinguishing plates 5. Due to these 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, so 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) of which one of these contactors (2, 3) is pivotally supported in order to be able to move to and from the opposite contact (202, 302), whereby the first contactor (3) being provided with a spring (405) loaded pivot in its intermediate part in order to form a toggle element is only supported by the operating mechanism (4), while the second contactor (2) is a stationary rigid contactor directly mounted on the circuit breaker's enclosure (1), these contactors (2, 3) being arranged to each other in a such way, that only such portions which are adjacent to the contacts (202, 302) are facing each other in the closed state,
characterized in that
the contactors (2, 3) are provided with arc shields (6, 7) surrounding the respective contacts (202, 302), that the arc shields (6,7) are made of high resistivity material and that at least one of the arc shields (6, 7) is provided with an arc runway (601, 701) extending from the respective contact (202, 302) towards arc extinguishing plates (5) thereby exposing the respective conductor (201, 301) of the respective contactor (2, 3).
Circuit breaker according to claim 1
characterized in that the first contactor (3) is connected by means of a flexible conductor (303) to an external terminal.
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.