CIRCUIT BREAKER

Abstract

 To provide a circuit breaker that is capable of appropriately moving an arc, which is generated between contact points, toward an arc-extinguishing device, even in a relatively small current region, without enlarging equipment having the circuit breaker. The circuit breaker includes, in each of poles, a pair of front/rear fixed contacts (2, 3) disposed facing each other, a movable contact (4) formed as a bridge between the fixed contacts (2, 3), and a pair of front/rear magnetic drive yokes (10) made from permanent magnets and disposed so as to hold side surface parts on both ends of the movable contact (4) therebetween. In a closed state, the movable contact (4) closes a current feed path of each pole by being pressed against the fixed contacts (2, 3) by a contact spring (5). In an open state, the movable contact (4) opens the current feed paths by being pressed back toward the contact spring (5) by an opening/closing mechanism to separate from the fixed contacts (2, 3).

Description

TECHNICAL FIELD

[0001] The present invention relates to a circuit breaker used for wiring protection, and more particularly to a circuit breaker having a linear-motion two-contact point structure.

BACKGROUND ART

[0002] A technology described in, for example, Patent Document 1 exists as a conventional circuit breaker. In this technology, a U-shaped magnetic body is provided outside a movable contact and fixed contact of different current paths. Such a configuration can generate electromagnetic repulsive force (Lorentz force) in a repulsive direction between contact points when a large current such as a short-circuit current is applied, and can improve interruption performance by operating the movable contact to move away from the fixed contact. The configuration can also move an arc, generated between the contact points after the contact points are opened, to an arc-extinguishing device disposed on either end side of the movable contact.

[0003] 

Patent Document 1: Japanese Patent Publication No. 3859053

[0004] Incidentally, electromagnetic force that is generated by a magnetic body is proportional to a current. Therefore, in case of the circuit breaker described above, a current region in which a relatively small current such as a rated current flows cannot generate large electromagnetic force.
For this reason, the low-current region lacks in power to move the arc to the arc-extinguishing device, the arc being generated when the contact points are opened. At the time of current interruption (at the time of contact point opening operation), interruption needs to take place when the arc generated between the contact points is stagnated in the short distance between the contact points. The opening distance between the contact points needs to be increased in order to deal with a high voltage in a DC circuit that does not have current zero. This results in enlargement of the arc-extinguishing device and equipment having the circuit breaker.
An object of the present invention, therefore, is to provide a circuit breaker that is capable of appropriately moving an arc, generated between contact points, to an arc-extinguishing device, even in a relatively small current region, without causing enlargement of the arc-extinguishing device.

[0005] In order to achieve the object described above, a first aspect of a circuit breaker according to the present invention is a circuit breaker including, in each of poles, a pair of front/rear fixed contacts disposed facing each other, a linear-motion type movable contact formed as a bridge between the fixed contacts, and a pair of front/rear magnetic drive yokes that is disposed so as to hold side surface parts on both ends of the movable contact therebetween, wherein the movable contact closes a current feed path of each pole by being pressed against the fixed contacts by a contact spring, and opens the current feed paths by being pressed back toward the contact spring by an opening/closing mechanism to separate from the fixed contacts, and the magnetic drive yokes are made from permanent magnets.

[0006] According to this configuration, when a current flows to the movable contact in the closed state, the current is interlinked with a magnetic flux converged by the magnetic drive yokes, and the movable contact is driven to separate from the fixed contacts in response to a strong electromagnetic repulsive force (Lorentz force). At the time of a contact point opening operation, an arc is generated between each fixed contact point and the movable contact point. The generated arcs are driven by being interlinked with the magnetic flux reinforced by the magnetic drive yokes, moved to arc-extinguishing devices disposed in front of and behind the movable contact, and then extinguished.

[0007] Because the magnetic drive yokes are made from permanent magnets, a constant magnetic flux can be obtained regardless of the level of the current. Therefore, even in a relatively small current region, each of the arcs generated between the contact points at the time of the contact point opening operation can efficiently be driven to move to the arc-extinguishing device.

[0008] In a second aspect, the magnetic drive yokes are made from U-shaped permanent magnets and disposed such that leg parts of each of the magnetic drive yokes hold the side surface parts of the movable contact therebetween.
Because the magnetic drive yokes are made from U-shaped permanent magnets, the leg parts of the U-shaped magnetic drive yokes can securely hold the side surface parts on both ends of the movable contact therebetween. In addition, the magnetic drive yokes can be disposed in any desired positions. This increases the degree of freedom for disposing the magnetic drive yokes.

[0009] Moreover, a third aspect of the present invention is a circuit breaker that has a pair of arc-extinguishing devices disposed in front of and behind the movable contact, and an arc commutation plate that is disposed under the movable contact so as to extend over the arc-extinguishing devices and commutates feet of arcs on the movable contact side, the arcs being generated between the movable contact and the fixed contacts at the time of current interruption, wherein the arc commutation plate has a pair of U-shaped magnetic bodies bent toward the movable contact, and the magnetic drive yokes are made from rectangular permanent magnets and are disposed such that lower surfaces thereof are fixed to upper surfaces of both leg parts of the U-shaped magnetic bodies in order to hold the side surfaces of the movable contacts therebetween.

[0010] Due to the configuration in which the magnetic drive yokes are made from rectangular permanent magnets, the permanent magnets can be made smaller than when the magnetic drive yokes are made from U-shaped permanent magnets, accomplishing cost reduction. Furthermore, because the magnetic drive yokes are configured integrally with the arc commutation plate, the number of components of the circuit breaker can be reduced, thereby simplifying the assembly of the circuit breaker.

[0011] A fourth aspect of the present invention is a circuit breaker that has a pair of arc-extinguishing devices disposed in front of and behind the movable contact, and an arc commutation plate that is disposed so as to extend over the arc-extinguishing devices and commutates feet of arcs on the movable contact side, the arcs being generated between the movable contact and the fixed contacts at the time of current interruption, wherein the arc commutation plate has a pair of U-shaped magnetic bodies bent toward the movable contact, and the magnetic drive yokes are made from rectangular permanent magnets and are disposed so as to hold the side surface parts of the movable contact therebetween by being fixed to inner surfaces of leg parts of the U-shaped magnetic bodies.

[0012] Due to the configuration in which the rectangular permanent magnets are fixed to the inner surfaces of the leg parts of the U-shaped magnetic bodies that are bent in the arc commutation plate, leakage flux of the permanent magnets can be reduced more than when the permanent magnets are fixed to the tips of the leg parts of the U-shaped magnetic bodies. As a result, the arcs generated between the contact points at the time of the contact point opening operation can efficiently be driven to move to the arc-extinguishing devices.

DISCLOSURE OF THE INVENTION

[0013] According to the present invention, because the magnetic drive yokes are made from permanent magnets, even in a relatively small current region each of the arcs generated around each current feed path at the time of the contact point opening operation can efficiently be driven to move to the arc-extinguishing devices. Therefore, the present invention can provide a small circuit breaker suitable for a DC circuit and contribute to reduction in size of equipment having the circuit breaker. In addition, the parts of the circuit breaker can be replaced with parts exclusive to an AC circuit. Thus, a low cost circuit breaker can be provided by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 

Fig. 1 is a cross-sectional diagram showing a structure of a current interrupting part of a circuit breaker according to an embodiment of the present invention;

Fig. 2 is an exploded perspective view showing a structure of a magnetic drive yoke part according to a first embodiment;

Fig. 3 is a cross-sectional diagram showing a structure of the current interrupting part in a contact point closing position;

Fig. 4 is a cross-sectional diagram showing the vicinity of a contact point according to the first embodiment, showing vectors of a current, magnetic flux, and electromagnetic repulsive force;

Fig. 5 is a top view showing the vicinity of a contact point according to the first embodiment, showing vectors of a current, magnetic flux, and electromagnetic repulsive force;

Fig. 6 is a diagram showing a structure of the current interrupting part and a direction of travel of an arc, in a contact point opening position according to the first embodiment;

Fig. 7 is a cross-sectional diagram showing a structure of a current interrupting part according to a second embodiment;

Fig. 8 is an exploded perspective view showing a structure of a magnetic drive yoke part according to the second embodiment;

Fig. 9 is a top view showing the vicinity of a contact point according to the second embodiment, showing vectors of a current, magnetic flux, and electromagnetic repulsive force;

Fig. 10 is an exploded perspective view showing a structure of a magnetic drive yoke part according to a third embodiment;

Fig. 11 is a top view showing the vicinity of a contact point according to the third embodiment, showing vectors of a current, magnetic flux, and electromagnetic repulsive force;

Fig. 12 is a diagram showing a leakage flux of the magnetic drive yoke; and

Fig. 13 is a diagram showing a structure of a current interrupting part of a conventional circuit breaker.

BEST MODE FOR CURRYING OUT THE INTENTION

[0015] Embodiments of the present invention are described hereinafter with reference to the drawings.

(First Embodiment)

(Configuration)

[0016] Fig. 1 is a cross-sectional diagram showing a current interrupting part of a circuit breaker according to an embodiment of the present invention. The circuit breaker according to the present embodiment is a circuit breaker with linear-motion two-contact point structure.

[0017] In the diagram, reference numeral 1 represents a current interrupting part. In each phase current feed path, U-shaped fixed contacts 2, 3 formed from straight angle conductors are disposed in front and rear parts of the current interrupting part so as to face each other. Fixed contact points 2a, 3a are attached to the fixed contacts 2, 3 respectively. A rectangular movable contact 4, either end of which is bent downward, has a pair of movable contact points 4a and 4b capable of coming into contact with the fixed contact points 2a and 3a respectively. In a closed state in which each current feed path is closed, the movable contact 4 serves as a bridge between the fixed contacts 2, 3 by being pressed against the fixed contacts 2, 3 by a contact spring 5 of a compression spring so that the movable contact points 4a and 4b come into contact with the fixed contact points 2a and 3a respectively. In an open state in which the current feed path is opened as shown in the diagram, the movable contact 4 separates from the fixed contacts 2, 3 by being pushed down toward the contact spring 5 by an opening/closing mechanism, which is not shown.

[0018] A pair of arc-extinguishing devices 6 is disposed in front of and behind the movable contact 4. A plurality of grids 7 of the arc-extinguishing device 6 surround the ends of the movable contact 4. The grids 7 are each made from a U-shaped magnetic plate and supported by a pair of left/right insulator side walls 8 as viewed in a top view. An arc commutation plate 9 made from a high-resistance material such as a steel plate is provided under the arc-extinguishing devices 6 so as to extend over the front and rear arc-extinguishing devices 6. This arc commutation plate 9 functions as a backing plate for the contact spring 5.

[0019] Reference numeral 10 in the diagram represents a pair of front/rear magnetic drive yokes made from U-shaped permanent magnets. The magnetic drive yokes 10 are disposed such that left and right leg parts of each of the magnetic drive yokes hold the side surface parts on the ends of the movable contact 4 therebetween. One of the leg parts is constituted as a south pole and the other as a north pole. Each of the magnetic drive yokes is disposed so as to obtain the polarity shown in Fig. 5. The left and right leg parts of the magnetic drive yokes 10 are covered with an insulation cover 11.

[0020] Fig. 2 is an exploded perspective view showing a structure of a magnetic drive yoke part configured by the arc commutation plate 9, the magnetic drive yokes 10, and the insulation cover 11.
The insulation cover 11 is formed by resin molding into a U-shape and has a pair of left/right side walls 11a, 11b, wherein the movable contact 4 is held so as to be able to move in an opening/closing direction (a vertical direction in Fig. 1) between the side walls 11a, 11b. A lower surface of each of the side walls 11a, 11b of the insulation cover 11 is opened to form a pouch-like part. The pouch-like parts cover the leg parts 10a, 10b of the magnetic drive yokes 10 when assembling the circuit breaker. The arc commutation plate 9 is disposed between the leg parts 10a, 10b of the magnetic drive yokes 10 and outside the lower surface parts of the insulation cover 11, when assembling the circuit breaker.

(Operations)

[0021] Next, operations of the first embodiment are described with reference to Fig. 3 to Fig. 6.
Fig. 3 is a cross-sectional diagram showing a structure of a current interrupting part in a contact point closing position. Fig. 4 is a cross-sectional diagram showing the vicinity of each contact point. Fig. 5 is a top view showing the vicinity of each contact point. Fig. 6 is a diagram showing the structure of the contact point interrupting part in a contact point opening position and a direction of travel of an arc.

[0022] In the closed state shown in Fig. 3, suppose that a large current I such as a short-circuit current flows as shown by arrows in the diagram. At this moment, as shown in Fig. 4, suppose that the current I flows from top to bottom in the movable contact 4, in a direction perpendicular to the page space of Fig. 4. A magnetic flux Φ based on the current I is focused by the magnetic drive yokes 10 and passes through the movable contact 4 and the magnetic drive yokes 10 in a clockwise direction. In such a state, because the magnetic flux Φ passing through the movable contact 4 from the left to the right in Fig. 4 intersects with the current I flowing through the movable contact 4, a downward electromagnetic repulsive force (Lorentz force) F1 acts in the movable contact 4, as shown in Fig. 4, based on the Fleming's left-hand rule.

[0023] At the same time, an overcurrent detector, not shown, detects an overcurrent and outputs a tripping signal, in response to which the opening/closing mechanism pushes the movable contact 4 downward as shown in Fig. 3. As a result, the fixed contact points 2a and 3a of the respective fixed contacts 2 and 3 are pulled away from the movable contact points 4a and 4b of the movable contact 4.
Thus, the movable contact 4 is driven to separate from the fixed contacts at a speed higher than that of driving the movable contact by using the electromagnetic repulsive force alone or the opening/closing mechanism alone. Consequently, interruption performance of the circuit breaker can be improved.

[0024] At the time of the contact point opening operation in which the fixed contact points 2a and 3a are separated from the movable contact points 4a and 4b, an arc is generated between the movable contact 4 and the fixed contacts 2 and 3. Because this arc A intersects with the magnetic flux (the magnetic flux from the left to the right in Fig. 4) Φ reinforced by the magnetic drive yokes 10 as shown in Fig. 5, force F2 acts on the arc A outwardly in a front/rear direction of the movable contact 4, based on the Fleming's left-hand rule. Therefore, the arc A that is generated between the contact points shifts from arc A1 -> arc A2 -> arc A3 -> arc A4, towards each of the arc-extinguishing devices 6 disposed outwardly in the front/rear direction of the movable contact 4 as shown in Fig. 6. The arc A drawn to each of the arc-extinguishing devices 6 is analyzed, cooled, and extinguished. As a result, a short-circuit interruption operation is completed.
In so doing, due to the arc commutation plate 9 provided in the circuit breaker, feet of the arcs A on the movable contact 4 side move to the arc commutation plate 9 and extinguished such that a current does not flow through the movable contact 4, preventing the movable contact 4 from being damaged by a large current.

[0025] In a prior art, a magnetic body is used as a magnetic drive yoke.
Fig. 13 is a diagram showing a structure of a current interrupting part of a conventional circuit breaker. Fig. 13 (a) is a top view of the current interrupting part, and Fig. 13(b) a front view of the current interrupting part. Fig. 13 shows an example in which magnetic drive yokes 110 configured by magnetic bodies are integrated with an arc commutation plate 109. In other words, the pair of front/rear magnetic drive yokes 110 is bent integrally with the arc commutation plate 109 and extends upright in a direction in which a movable contact 104 moves to separate from a fixed contact.

[0026] In such a configuration, when a large current such as a short-circuit current flows, electromagnetic repulsive force is generated between contact points, as with the present embodiment, whereby the movable contact 104 can be operated to separate from the fixed contact. Furthermore, after the contact point opening operation, electromagnetic force for moving an arc, which is generated between the contact points, toward an arc-extinguishing device can be generated.

[0027] However, because the electromagnetic force generated by the magnetic bodies is proportional to the current, a current region in which a relatively small current such as a rated current flows cannot generate large electromagnetic force, when the magnetic bodies are used as the magnetic drive yokes. For this reason, the arc generated at the time of the contact point opening operation cannot be moved appropriately toward each arc-extinguishing device. When an arc is generated between the contact points at the time of current interruption (at the time of the contact point opening operation), interruption needs to performed when the arc is stagnated in the short distance between the contact points. The opening distance between the contact points needs to be increased in order to deal with a high voltage in a DC circuit that does not have current zero. This results in enlargement of the arc-extinguishing device and equipment having the circuit breaker.

[0028] However, in the present embodiment, because the magnetic drive yokes are made from permanent magnets, a constant electromagnetic force can be generated regardless of the level of the current. Therefore, even in a current region in which a current is as small as a rated current, sufficient electromagnetic force can be generated, and the arc that is generated between the contact points at the time of the contact point opening operation can be moved appropriately to each arc-extinguishing device.
As described above, this embodiment can accomplish current interruption by efficiently using the arc-extinguishing devices of the circuit breaker in a wider range of current regions.

(Effects)

[0029] In the first embodiment, as described above, because the pair of front/rear magnetic drive yokes is disposed so as to hold the side surface parts of the ends of the movable contact therebetween, a strong electromagnetic repulsive force (Lorentz force) can be generated between the movable contact and the fixed contacts when a current flows to the movable contact in the closed state, whereby the movable contact can be driven to separate from the fixed contacts. Moreover, at the time of the contact point opening operation, the arc generated between the contact points can be driven by the Lorentz force to move in towards each arc-extinguishing device.

[0030] Because the magnetic drive yokes are made from permanent magnets, a constant magnetic flux can be obtained regardless of the level of the current. Therefore, even in a relatively small current region, the arc generated between the contact points at the time of the contact point opening operation can efficiently be driven to move to each arc-extinguishing device.
Therefore, although it is difficult to perform DC interruption in a low-current region in the conventional structure, wide range of current interruption can be accomplished by using the arc-extinguishing devices securely. The present invention, therefore, can provide a small arc-extinguishing device suitable for a DC circuit and contribute to reduction in size of the entire equipment having the circuit breaker of the present invention. In addition, the parts of the circuit breaker can be replaced with parts exclusive to an AC circuit. Thus, a low cost circuit breaker can be realized by the present invention.

[0031] The magnetic drive yokes are made from U-shaped permanent magnets. Thus, the U-shaped leg parts of each magnetic drive yoke can securely hold the side surface parts of the ends of the movable contact. Because the magnetic drive yokes are provided as independent members, not only is it possible to shape the arc commutation plate into a belt, but also the arc commutation plate can be molded more easily than when the magnetic drive yokes are integrated with the arc commutation plate, increasing the degree of freedom for disposing the magnetic drive yokes.
Additionally, in the course of the contact point opening operation, sections in the vicinity of the contact points are filled with high-pressure conductive gas that is generated by the arcs. However, covering the entire leg parts of the magnetic drive yokes with the insulation cover can prevent the occurrence of phase-to-phase short circuit between the magnetic drive yokes.

(Second Embodiment)

[0032] A second embodiment of the present invention is described next.
While the U-shaped magnetic drive yokes 10 are applied in the first embodiment described above, the magnetic drive yokes 10 are integrally configured with the arc commutation plate 9 in the second embodiment.

(Configuration)

[0033] Fig. 7 is a cross-sectional diagram showing a structure of a current interrupting part 1 according to the second embodiment.
As shown in Fig. 7, the configuration of the current interrupting part 1 of the present embodiment is same as that of the current interrupting part 1 shown in Fig. 1, except for the configurations of the magnetic drive yoke parts. Therefore, the same reference numerals are applied to the parts having the configurations same as those shown in Fig. 1, and parts of different configurations are mainly described in this embodiment.
In the present embodiment, an arc commutation plate 19 is used in place of the arc commutation plate 9, and rectangular magnetic drive yokes 20 are used in place of the magnetic drive yokes 10.

[0034] Fig. 8 is an exploded perspective view showing a structure of magnetic drive yoke parts according to the second embodiment.
As shown in Fig. 8, U-shaped magnetic bodies 19a, 19b bent toward the movable contact 4, are formed, respectively, at the positions of the ends of the movable contact 4 in a front/rear direction of the arc commutation plate 19.
Furthermore, the magnetic drive yokes 20 are made from rectangular permanent magnets. Lower surfaces of the magnetic drive yokes 20 are fixed to upper surfaces of both leg parts of the U-shaped magnetic bodies 19a, 19b of the arc commutation plate 19 and thereby integrated with the arc commutation plate 19. In so doing, the magnetic drive yokes 20 are disposed so as to obtain the polarity shown in Fig. 9 in a width direction (lateral direction) of the movable contact 4, wherein poles of different magnetism face each other.

[0035] When assembling the circuit breaker, while the magnetic drive yokes 20 are fixed to the upper surfaces of the leg parts of the U-shaped magnetic bodies 19a, 19b of the arc commutation plate 19, the insulation cover 11 that has the same configuration as that of the first embodiment is placed on the U-shaped magnetic bodies 19a, 19b and the magnetic drive yokes 20.
In this manner, the side surface parts of the movable contact 4 are held by the magnetic drive yokes 20 that are fixed to the leg parts of the U-shaped magnetic bodies 19a, 19b. Specifically, the leg parts of the U-shaped magnetic bodies 19a, 19b are made short to realize the placement of the magnetic drive yokes 20 within a range of movement of the movable contact 4.

(Operations)

[0036] Operations of the second embodiment are described next.
In the closed state, when a large current I such as a short-circuit current flows and the fixed contact points 2a and 3a of the fixed contacts 2 and 3 are pulled away from the movable contact points 4a and 4b of the movable contact 4, an arc is generated between the movable contact 4 and the fixed contacts 2 and 3.
This arc A is interlinked with a magnetic flux Φ reinforced by the magnetic drive yokes 20, as shown in Fig. 9. Thus, the force F2 acts on the arc A outwardly in the front/rear direction of the movable contact 4. As a result, the arc A moves to each arc-extinguishing device 6 disposed in each end of the movable contact 4.
As with the first embodiment, the arc that is generated around each current feed path at the time of the contact point opening operation can appropriately be moved to each arc-extinguishing device.

(Effects)

[0037] As described above, the magnetic drive yokes are integrally configured with the arc commutation plate in the second embodiment. Therefore, assembly of the circuit breaker and management of the components thereof can be achieved easily.
Also, due to the rectangular shape of the magnetic drive yokes, the size of each permanent magnet can be made smaller than those of the U-shaped magnetic drive yokes of the first embodiment described above, accomplishing cost reduction.

(Third Embodiment)

[0038] A third embodiment of the present invention is described next.
While the magnetic drive yokes are fixed to the upper surfaces of the leg parts of the U-shaped magnetic bodies formed in the arc commutation plate in the second embodiment, in the third embodiment the magnetic drive yokes are fixed to inner surfaces of the leg parts of the U-shaped magnetic bodies.

(Configuration)

[0039] The configuration of a current interrupting part 1 of the present embodiment is same as that of the current interrupting part 1 shown in Fig. 8, except for the configurations of the magnetic drive yoke parts. Therefore, parts of different configurations are mainly described in this embodiment.
Fig. 10 is an exploded perspective view showing a structure of magnetic drive yoke parts according to the third embodiment.
As shown in Fig. 10, U-shaped magnetic bodies 29a, 29b bent toward the movable contact 4, are formed, respectively, at the positions of the ends of the movable contact 4 in a front/rear direction of the arc commutation plate 29. Step parts 29c to which magnetic drive yokes 30 are fixed are formed on the inside of both leg parts of the U-shaped magnetic bodies 29a, 29b.

[0040] The magnetic drive yokes 30 are made from rectangular permanent magnets that are as thick as the step parts 29c, and are integrally configured with the arc commutation plate 29 by being fixed to the step parts 29c formed in the arc commutation plate 29. In other words, the magnetic drive yokes 30 are fixed to inner surfaces of the leg parts of the U-shaped magnetic bodies 29a, 29b. At this moment, the magnetic drive yokes 30 are disposed so as to obtain the polarity shown in Fig. 11 in the width direction (lateral direction) of the movable contact 4, wherein poles of different magnetism face each other.

[0041] When assembling the circuit breaker, while the magnetic drive yokes 30 are fixed to the step parts 29c of the arc commutation plate 29, the insulation cover 11 that has the same configuration as those of the first and second embodiments is placed on the U-shaped magnetic bodies 29a, 29b and the magnetic drive yokes 30.
In this manner, the side surface parts of the movable contact 4 are held by between the magnetic drive yokes 30 that are fixed to the leg parts of the U-shaped magnetic bodies 29a, 29b. Specifically, the leg parts of the U-shaped magnetic bodies 29a, 29b are made long to realize the placement of the magnetic drive yokes 30 within the range of movement of the movable contact 4.

(Operations)

[0042] Operations of the third embodiment are described next.
In the closed state, when a large current I such as a short-circuit current flows and the fixed contact points 2a and 3a of the fixed contacts 2 and 3 are pulled away from the movable contact points 4a and 4b of the movable contact 4, an arc is generated between the movable contact 4 and the fixed contacts 2 and 3.
This arc A is interlinked with a magnetic flux Φ reinforced by the magnetic drive yokes 30, as shown in Fig. 11. Thus, the force F2 acts on the arc A outwardly in the front/rear direction of the movable contact 4. As a result, the arc A moves to each arc-extinguishing device 6 disposed in each end of the movable contact 4.

[0043] As with the first and second embodiments, the arc that is generated around each current feed path at the time of the contact point opening operation can appropriately be moved to each arc-extinguishing device.
Incidentally, when fixing the magnetic drive yokes 30 to the upper surfaces of the leg parts of the U-shaped magnetic bodies 19a, 19b of the arc commutation plate 19 in the same manner as described in the second embodiment, a leakage flux Φ' of the permanent magnets is generated. This configuration cannot generate electromagnetic force for driving the arc A, which is generated between the contact points, toward each arc-extinguishing device 6.

[0044] In the present embodiment, on the other hand, the magnetic drive yokes 30 of permanent magnets are fixed to the inner surfaces of the leg parts of the U-shaped magnetic bodies 29a, 29b. In other words, the U-shaped magnetic bodies 29a, 29b are located outside the magnetic drive yokes 30 of permanent magnets. Therefore, the leakage flux Φ' of the permanent magnets shown in Fig. 12 can be reduced, efficiently generating the electromagnetic force for driving the arc A, which is generated between the contact points, toward each arc-extinguishing device 6.

(Effects)

[0045] As described above, the magnetic drive yokes are integrally configured with the arc commutation plate in the third embodiment. Therefore, assembly of the circuit breaker and management of the components thereof can be achieved easily.
Also, due to the rectangular shape of the magnetic drive yokes, the size of each permanent magnet can be made smaller than those of the U-shaped magnetic drive yokes of the first embodiment described above, accomplishing cost reduction.
Further, fixing the magnetic drive yokes to the inner surfaces of the leg parts of the U-shaped magnetic bodies of the arc commutation plate can reduce the leak flux of the permanent magnets. Consequently, the arc generated between the contact points can efficiently moved to each arc-extinguishing device.

[0046] Also, by fixing the magnetic drive yokes to the step parts formed in the U-shaped magnetic bodies, the permanent magnets can be made thinner than the magnetic drive yokes of the second embodiment described above, accomplishing cost reduction. In addition, because the magnetic drive yokes can be adhered to the step parts, the magnetic drive yokes can be positioned more easily than when the magnetic drive yokes are fixed to the inner surfaces of the leg parts of the U-shaped magnetic bodies without using any steps. Therefore, the assembly of the circuit breaker can be simplified.

INDUSTRIAL APPLICABILITY

[0047] The present invention can provide a small circuit breaker suitable for a DC circuit and contribute to reduction in size of equipment having the circuit breaker. Further, the parts of the circuit breaker can be replaced with parts exclusive to an AC circuit. Thus, the present invention can provide a low cost circuit breaker and is useful.

EXPLANATION OF REFERENCE NUMERALS

[0048] 1... Current breaker, 2... Fixed contact, 2a... Fixed contact point, 3... Fixed contact, 3a... Fixed contact point, 4... Movable contact, 4a, 4b... Movable contact point, 5... Contact spring, 6... Arc-extinguishing device, 7... Grid, 8... Side wall, 9... Arc commutation plate, 10... Magnetic drive yoke, 10a, 10b... Leg part, 11... Insulation cover, 11a, 11b... Side wall, 19... Arc commutation plate, 19a, 19b... U-shaped magnetic body, 20... Magnetic drive yoke, 29... Arc commutation plate, 29a, 29b... U-shaped magnetic body, 29c... Step part, 30... Magnetic drive yoke

Claims

1. A circuit breaker comprising, in each of poles, a pair of front/rear fixed contacts disposed facing each other; a linear-motion type movable contact formed as a bridge between the fixed contacts; and a pair of front/rear magnetic drive yokes that is disposed so as to hold side surface parts on both ends of the movable contact therebetween,
wherein the movable contact closes a current feed path of each pole by being pressed against the fixed contacts by a contact spring, and opens the current feed paths by being pressed back toward the contact spring by an opening/closing mechanism to separate from the fixed contacts, and
the magnetic drive yokes are made from permanent magnets.

2. The circuit breaker according to claim 1, wherein the magnetic drive yokes are made from U-shaped permanent magnets and disposed such that leg parts of each of the magnetic drive yokes hold the side surface parts of the movable contact therebetween.

3. The circuit breaker according to claim 1, comprising:

a pair of arc-extinguishing devices disposed in front of and behind the movable contact; and

an arc commutation plate that is disposed under the movable contact so as to extend over the arc-extinguishing devices and commutates feet of arcs on the movable contact side, the arcs being generated between the movable contact and the fixed contacts at the time of current interruption,

wherein the arc commutation plate has a pair of U-shaped magnetic bodies bent toward the movable contact, and

the magnetic drive yokes are made from rectangular permanent magnets and are disposed such that lower surfaces thereof are fixed to upper surfaces of both leg parts of the U-shaped magnetic bodies in order to hold the side surfaces of the movable contacts therebetween.

4. The circuit breaker according to claim 1, comprising:

a pair of arc-extinguishing devices disposed in front of and behind the movable contact; and

an arc commutation plate that is disposed under the movable contact so as to extend over the arc-extinguishing devices and commutates feet of arcs on the movable contact side, the arcs being generated between the movable contact and the fixed contacts at the time of current interruption,

wherein the arc commutation plate has a pair of U-shaped magnetic bodies bent toward the movable contact, and

the magnetic drive yokes are made from rectangular permanent magnets and are disposed so as to hold the side surface parts of the movable contact therebetween by being fixed to inner surfaces of leg parts of the U-shaped magnetic bodies.

Drawing