CIRCUIT BREAKER

Abstract: A circuit breaker equipped with a mechanism for current limiting by the use of electromagnetic repulsion, aiming at solving a technical problem of improving current-limiting performance by increasing the contact-opening speed of a contact plate of a current-limiting type circuit breaker and realizing the device in a compact size. The current-limiting contact plate is rotatably supported at its central portion, with one end thereof facing a movable contact plate, and with the other end facing a fixed conductor and electrically connected thereto. An electromagnetic repulsive force between the movable contact plate and the current-limiting contact plate and an electromagnetic repulsive force between the fixed conductor and the current-limiting contact plate are used as a couple of forces. It is therefore possible to increase the contact-opening speed and to decrease the distance between the current-limiting contact plate and the fixed conductor. The invention provides a circuit breaker which is small in size and is excellent in breaking performance.

Description: The invention relates to a circuit breaker according to the preamble of claim 1. Such a circuit breaker is known from JP-46-8358. It relates in particular to a circuit breaker, and more particularly, to one which is suitable for improving the current-limiting performance of a current-limiting breaker. A known device of the sort to which this invention pertains comprises a movable contactor on the load side which is connected to a switching mechanism (first movable contact support), a central movable contactor facing it, having contacts at both ends, and capable of rotating about its own middle portion (second movable contact support), and a movable contactor provided on the power source side and facing the central movable contactor, as disclosed in Japanese Utility Model Application laid open under No. 45164/1977. The movable contactor on the load side and the movable contactor on the power source side are also rotatably supported. An electric current flows in opposite directions through the movable contactor on the load side and the central movable contactor. The same is true with the directions in which an electric current flows through the central movable contactor and the movable contactor on the power source side. If a large amount of electric current is caused to flow through the device, a repulsive force is produced between the movable contactor on the load side and the central movable contactor by the flow of current in the opposite directions, and a repulsive force is likewise produced between the central movable contactor and the movable contactor on the power source side. As a result, a couple of forces act upon the central movable contactor about its middle portion defining the axis of its rotation and cause it to rotate in the direction in which the contacts are separated from each other. The contacts are, however, provided between the central movable contactor and the movable contactor on the power source side. Therefore, it is necessary to maintain a sufficiently large distance therebetween to ensure electrical insulation when the contacts are separated from each other. This makes the device undesirably large. The device also has a high temperature due to the heat which is generated by an arc occurring across the contacts when the current is limited, the heat which is generated by an increased current density resulting from a reduction in the area of contact in which wiping is achieved between the contacts, and the heat which is generated by contact resistance at the contacts. When the electromagnetic repulsive force causes the movable contactor on the power source side to move away from the central movable contactor to open or separate the contacts from each other to limit the flow of a large amount of current, the resulting increase in the distance therebetween and decrease in the amount of current flowing therethrough bring about a reduction in repulsive force and disable any satisfactorily high contact-opening speed to be attained. JP-46-8358 discloses a circuit breaker comprising a housing with two terminals. Within this housing there are provided a stationary conductor, a current limiting contact support being rotatably supported, a movable contact support being rotatably supported, a switching mechanism connected to the movable contact support and a tripping device. It is an object of this invention to provide a small circuit breaker having an improved contact-opening speed and an outstanding current-limiting capacity. This object is solved in accordance with the features of Claim 1. Dependent claims 2-12 are directed on preferred embodiments of the invention. Described is a circuit breaker which comprises a housing provided at one end with a power source terminal, and at another end with a load terminal, a stationary conductor having one end connected to the power source terminal and another end provided with conductive connecting means, a current-limiting contact support having one end connected to the conductive connecting means and facing the stationary conductor, another end provided with a current-limiting contact, and a middle portion at which it is rotatably supported, and a movable contact support facing the current-limiting contact support, supported rotatably and carrying a movable contact facing the current-limiting contact. The movable contact support is connected to a switching mechanism for performing a switching and tripping operation. The tripping operation of the switching mechanism is carried out by a tripping device which detects an overcurrent in a line from the movable contact support to the load terminal and causes the switching mechanism to perform the tripping operation. The current-limiting contact support is provided at one end thereof with a repulsing portion, so that a repulsive force may be produced between the current-limiting contact support and the stationary conductor by the currents flowing in the opposite directions, and so that, if a large amount of current has flown as a result of e.g. shortcircuiting, the current-limiting contact support may be rotated by a couple of forces, i.e. the repulsive force produced between the movable contact support and the current-limiting contact support and the repulsive force produced between the stationary conductor and the current-limiting contact support, and thereby separate the current-limiting contact from the movable contact. The one end and the middle portion of the current limiting contact support are enclosed in an insulating case. The repulsive force produced between the repulsing portion and the stationary conductor can wholly be used as the force for rotating the current-limiting contact support, so that a high contact-opening speed can be achieved. The current-limiting contact support and the stationary conductor have only a small distance therebetween, since no arc is likely to form therebetween, insofar as the former is conductively connected to the latter. This invention provides a small circuit breaker having a high contact-opening speed and an outstanding current-limiting efficiency, as the current-limiting contact support is rotated by a couple of forces, i.e. not only the repulsive force produced between the movable and current-limiting contact supports, but also the repulsive force produced between the stationary conductor and the current-limiting contact support. FIGURE 1 is a side elevational view, partly in section, of a circuit breaker according to a first embodiment of this invention; FIGURE 2 is a side elevational view showing the repulsive position of the main portion of the circuit breaker shown in FIGURE 1; FIGURE 3 is a view similar to FIGURE 2, but showing its trip position; FIGURE 4 is a side elevational view of the main portion of a circuit breaker according to a second embodiment of this invention; FIGURE 5 is a side elevational view of the main portion of a circuit breaker according to a third embodiment of this invention; FIGURE 6 is a side elevational view of the main portion of a circuit breaker according to a fourth embodiment of this invention; FIGURE 7(a) is a side elevational view, partly in section, of the main portion of a circuit breaker according to a fifth embodiment of this invention; FIGURE 7(b) is a perspective view of the current-limiting contact support in the circuit breaker shown in FIGURE 7(a); FIGURE 7(c) is a cross sectional view of the current-limiting contact support shown in FIGURE 7(b); FIGURE 8(a) is a side elevational view of the main portion of a modified form of the device shown in FIGURE 7(a); FIGURE 8(b) is a cross sectional view of the current-limiting contact support in the device shown in FIGURE 8(a); FIGURE 9(a) is a side elevational view, partly in section, of a circuit breaker according to a sixth embodiment of this invention; FIGURE 9(b) is a cross sectional view of a sliding portion in the device shown in FIGURE 9(a); FIGURE 10 is a side elevational view of the main portion of a circuit breaker according to a seventh embodiment of this invention; FIGURE 11 is a perspective view of the device shown in FIGURE 10; FIGURE 12(a) is a bottom plan view of the main portion of a circuit breaker according to an eighth embodiment of this invention; FIGURE 12(b) is a bottom plan view showing the displacement of a part in the device shown in FIGURE 12(a); FIGURE 12(c) is an enlarged view of the displacement shown in FIGURE 12(b); FIGURE 13 is a bottom plan view of a modified form of the device shown in FIGURE 12(a); FIGURE 14 is a side elevational view, partly in section, of a circuit breaker according to a ninth embodiment of this invention; FIGURE 15 is a side elevational view showing in its repulsive position the main portion of the device shown in FIGURE 14; FIGURE 16 is a side elevational view showing the trip position of the portion shown in FIGURE 15; FIGURE 17(a) is a side elevational view, partly in section, of a circuit breaker according to a tenth embodiment of this invention; FIGURE 17(b) is a cross sectional view of the magnetic drive shown at 80 in FIGURE 17(a); FIGURE 17(c) is a cross sectional view of the magnetic drive shown at 80 a in FIGURE 17(a); FIGURE 17(d) is a cross sectional view of a modified form of the magnetic drive 80; FIGURE 18 is a side elevational view, partly in section, of a circuit breaker according to an eleventh embodiment of this invention; and FIGURE 19 is a side elevational view of the main portion of a circuit breaker according to a twelfth embodiment of this invention. The invention will now be described in detail with reference to the drawings showing a variety of preferred embodiments thereof. Referring first to FIGURES 1 to 3, the circuit breaker according to a first embodiment of this invention includes a case 1 as a housing which is provided at one end with a power source terminal 18, and at another end with a load terminal 28. The case 1 contains at its bottom a stationary conductor 15 connected to the power source terminal 18. A current-limiting contact support 12 is rotatably supported by a pin 17 above the stationary conductor 15. The current-limiting contact support 12 has one end 12 b carrying a current-limiting contact 11, and another end defining a repulsing portion 12 a and carrying a flexible conductor 14 as means for conductive connection to the stationary conductor 15. A movable contact support 9 is provided above the current-limiting contact support 12 and is connected to a switching machanism 4. The switching mechanism 4 performs the switching or tripping operation of the movable contact support 9 as a result of either manual operation by a handle 3, or the operation of an overcurrent detecting relay as a tripping device which comprises an oil dashpot relay 5 and a movable iron piece 19 which is thereby attracted. The ON and OFF operation of the device as hereinabove described is performed by the handle 3 projecting from a molded cover 2. If the handle 3 is turned toward a power source, two links in the switching mechanism 4 including a toggle link mechanism function to rotate an interlocking shaft 7 provided at one end of the switching mechanism 4 for rotating the movable contact support 9. If the shaft 7 is rotated counterclockwise, the movable contact support 9 is rotated about a pin 16 and a movable contact 10 carried on one end of the movable contact support 9 and facing the current-limiting contact 11 is, therefore-moved until it abuts on the current-limiting contact 11. The current-limiting contact support 12 is located below the switching mechanism 4 and faces the movable contact support 9. The pin 17 about which the current-limiting contact support 12 is rotatable is provided with a return spring 13 urging the current-limiting contact support 12 clockwise. The spring 13 has one end engaging the molded case 1, and another end engaging the repulsing portion 12 a of the current-limiting contact support 12. The flexible conductor 14 comprises a flexible twisted wire of copper and is connected to one end of the repulsing portion 12 a for supplying an electric current from the stationary conductor 15 to the current-limiting contact support 12. The stationary conductor 15 has an extension 15 a lying below the repulsing portion 12 a of the current-limiting contact support 12 in parallel thereto. Thus, the electric current flows through the current-limiting contact support 12 in the direction opposite that in which it flows through the stationary conductor 15 and the movable contact support 9. A contact spring 8 is provided coaxially with the pin 16 about which the movable contact support 9 is rotatable, and supplies contact pressure between the movable contact 10 and the current-limiting contact 11. The movable contact support 9 is connected to the load terminal 28 by a line 88 which comprises a flexible conductor 88 a connected to the movable contact support 9, and a coil 88 b . The oil dashpot relay 5 comprises a cylinder 5 a containing a plunger not shown, the coil 88 b of the line 88, and the movable iron piece 19 which is attracted by the cylinder 5 a . If an overcurrent flows through the line 88, the plunger in the oil dashpot relay 5 rises to attract and thereby rotate the movable iron piece 19. This movement of the movable iron piece 19 is transmitted to the mechanism for performing a tripping operation. If the formation of a short circuit results in the flow of a large amount of electric current through the circuit breaker, a shortcircuit current flows in opposite directions between the extension 15 a of the stationary conductor 15 and the repulsing portion 12 a of the current-limiting contact support 12, and between the end 12 b of the current-limiting contact support 12 on which the current-limiting contact 11 is carried, and the movable contact support 9, whereby an electromagnetic repulsive force is produced. A couple of forces are, thus, produced to rotate the current-limiting contact support 12 counterclockwise about the pin 17 rapidly to thereby separate the contacts, as shown in FIGURE 2. If the circuit is broken, the current-limiting contact support 12 is returned by the return spring 13 to its original position, as shown in FIGURE 3. As the extension 15 a is stationary, the repulsive force which is produced between the repulsing portion 12 a and the extension 15 a is wholly used as a force for rotating the current-limiting contact support 12. As the current-limiting contact support 12 and the stationary conductor 15 are connected by the flexible conductor 14, no arc causing the loss of electric current occurs therebetween, but the repulsing portion 12 a and the extension 15 a produce a high repulsive force therebetween. Therefore, the current-limiting contact support 12 enables a contact-opening speed which is higher than has hitherto been possible. Moreover, the circuit breaker of this invention is smaller, as the current-limiting contact support 12 and the stationary conductor 15 can be positioned closer to each other. Referring now to FIGURE 4, the circuit breaker according to a second embodiment of this invention is characterized by including an extension 12 c connected to the repulsing portion 12 a to prolong the distance along which the parallel conductors extend and an electric current flows in the opposite directions to produce an electromagnetic repulsive force, and thereby to increase to a further extent the speed at which the current-limiting contact 11 can be opened. The extension 12 c is connected to the repulsing portion 12 a by a hinge 22 and a flexible conductor 24 so as to form a joint which can be bent to permit the opening of the the contact. Referring to FIGURE 5, the circuit breaker according to a third embodiment of this invention is characterized by having an opening 20 formed in the extension 15 a of the stationary conductor 15 to receive therein a part of the repulsing portion 12 a of the current-limiting contact support 12. The repulsive force which is produced between the opposite edges of the opening 20 and the opposite sides of the repulsing portion 12 a makes it possible to maintain a low contact jump when a medium amount of electric current flows, while not allowing for any rise in contact pressure between the movable contact 10 and the current-limiting contact 11, and a couple of forces work to cause electromagnetic repulsion only when a large amount of current flows. As long as only a small amount of current flows through a short circuit, the repulsive force which is produced by the concentration of the current to the movable contact 10 and the current-limiting contact 11 is sufficient for breaking the circuit. Hardly any electromagnetic repulsion by a couple of forces is required. If a large amount of current flows, the current-limiting contact support 12 is somewhat rotated to have its repulsing portion 12 a rise to some extent from the opening 20 of the stationary conductor 15 and the repulsive force, therefore, changes its direction to cause repulsion by a couple of forces. Attention is now drawn to FIGURE 6 showing the circuit breaker according to a fourth embodiment of this invention. The electric current flowing through that portion of the stationary conductor 15 which is close to the power source terminal 18 differs in direction from the current flowing through the end 12 b of the current-limiting contact support 12. This difference produces a force acting against the electromagnetic repulsive forces produced in the form of a couple of forces. The device shown in FIGURE 6 is, therefore, characterized by including a magnetic force absorbing plate 25 provided on the stationary conductor 15 for absorbing the magnetic force producing any such contrary effect. That portion of the stationary conductor 15 which is closer to the power source terminal 18 has an opening 23 in which the end 12 b of the current-limiting contact support 12 can be received, so that the magnetic force absorbing plate 25 may retain a magnetic force when the contact support 12 stays in its repulsive position. When the end 12 b of the current-limiting contact support 12 stays below the opening 23 of the stationary conductor 15 and the corresponding hole 23 of the magnetic force absorbing plate 25, as shown in FIGURE 6, the shortcircuit current which is already flowing produces a magnetic repulsive force between the side faces of the current-limiting contact support 12 and the stationary conductor 15. The repulsive force acting against the force urging the current-limiting contact support 12 to return works as an electromagnetic retaining force and thereby produces a magnetic locking effect. Reference is now made to FIGURES 7(a) to 7(c) showing a circuit breaker according to a fifth embodiment of this invention. It is characterized by the current-limiting contact support 12 which is formed from a flat plate to acquire an increased repulsive force, and is reinforced so as not to be deformed by the repulsive force. The construction of the main part of the circuit breaker is shown in FIGURE 7(a), and the current-limiting contact support 12 in FIGURE 7(b), while FIGURE 7(c) is a sectional view taken along the line A-A of FIGURE 7(a). The current-limiting contact support 12 is formed from a flat plate, and is reinforced by a reinforcing member 30 secured to it at right angles thereto, as shown in FIGURE 7(b). The current-limiting contact support 12 has a width which is equal to that of the stationary conductor 15, as shown in FIGURE 7(c), so that the repulsing portion 12 a may receive a greatly increased repulsive force from the extension 15 a of the stationary conductor 15. All the other features of the device are identical to their counterparts in the device according to the first embodiment of this invention. A modified form of the device shown in FIGURES 7(a) to 7(c) is shown in FIGURES 8(a) and 8(b). The modified device is characterized by a modified current-limiting contact support 12 which does not have any reinforcing member of the type shown at 30 in FIGURES 7(a) to 7(c), but has a pair of reinforcing portions 12 d upstanding from its longitudinal edges, respectively, as shown in FIGURE 8(a). The current-limiting contact support 12 has a U-shaped cross section, as shown in FIGURE 8(b). This type of reinforcement can be made merely by bending and can, therefore, reduce the time and labor required for the preparation of the parts of the circuit breaker. Referring to FIGURES 9(a) and 9(b), the circuit breaker according to a sixth embodiment of this invention is characterized by including a sliding member 36 connected as means for conductive connection to the stationary conductor 15, and a contact portion 12 e extending from the repulsing portion 12 a of the current-limiting contact support 12 and contacting the sliding member 36 to maintain electrical connection between the stationary conductor 15 and the current-limiting contact support 12. The ON position of the current-limiting contact support 12 and the repulsive position thereof are shown by solid and two-dot chain lines, respectively. When the current-limiting contact support 12 is rotated to its repulsive position, its contact portion 12 e slides along the sliding member 36, while maintaining its electrical connection therewith. All the other features of the device are identical to their counterparts in the device according to the first embodiment of this invention. The device can be held at a satisfactorily low temperature, since the heat which is generated in the current-limiting contact support 12 is transmitted to the stationary conductor 15 through the contact portion 12 e and the sliding member 36. Attention is now directed to FIGURES 10 and 11 showing the circuit breaker according to a seventh embodiment of this invention. The device is particularly intended for making and breaking a DC circuit and maintaining the necessary breaking distance. It is small and yet maintains the necessary breaking distance between the contacts having the current-limiting and repulsing construction. It also provides a switching mechanism which is effective for an AC circuit, too. Moreover, it has an improved current-limiting and breaking capacity. The electromagnetically repulsed contact supports are held in their repulsed positions until the circuit is completely broken. The current-limiting switching mechanism is enclosed in a molded insulating case 58 and is of the doubly insulated construction. The mechanism is not damaged by any arc occurring when the circuit is broken, nor does any molten matter adhere to it. Therefore, it is a highly reliable mechanism. When the handle is turned for a switching operation, the current-limiting contact supports which are moved by electromagnetic repulsion are moved to maintain the breaking distance. In other words, they are moved by repulsion not only when a large amount of electric current, such as a shortcircuit current, has flowed, but also when the switching operation is made. One electromagnetically repulsive contact support is provided for each phase. The contact supports are all moved together to maintain the breaking distance for a DC power source and provide a simultaneous three-phase repulsion mechanism for an AC power source to thereby achieve an improved current-limiting performance. The three movable contact supports 12 are connected together by two insulating shafts 17 and 54 and are rotatable together about the pin 17. A movable frame 57 secured to the interlocking shaft 7 in the switching mechanism 4 is provided for each movable contact support and a metal fixture 56 is connected to the frame 57 by the pin 16 about which the movable contact support is rotatable. The metal fixture 56 as a connecting member has another end engaging the insulating shaft 54 connecting the three contact supports 12 which are movable together by repulsion. If the movable frames 57 are rotated clockwise, the insulating shaft 54 is raised to rotate the three current-limiting contact supports 12 counterclockwise about the shaft 17, so that they may maintain the breaking distance by moving to nearly the same position as when they are moved by repulsion. The contact supports 12 are returned together to their original positions by the return spring 13 fastened to the middle support 12 and supported on a shaft 55. The ON operation of the current-limiting contact supports 12 is performed by the counterclockwise rotation of the movable frames 57, as opposed to the OFF (opening) operation thereof, whereupon the supports 12 are moved up to have the contacts 11 abut on the movable contacts 9. The three movable contact supports are connected by the shafts 17 and 54 to form an integral structure and when they are moved by electromagnetic repulsion, they are moved by the total amount of the electromagnetic force produced by the electric current flowing therethrough. The movable frames 57 are engaged with the shaft 54 to allow for a large breaking distance between the movable contacts and the current-limiting contacts to break a DC circuit and the breaking operation of the mechanism 4 causes the three current-limiting contact supports 12 to rotate counterclockwise about the pin 17. Therefore, it is possible to maintain the same breaking distance when they are in the OFF position, as when they are moved by electromagnetic repulsion. Referring to FIGURES 12(a) to 12(c), the circuit breaker according to an eighth embodiment of this invention is characterized by including means for preventing the lateral displacement of the current-limiting contact support which might otherwise be caused by the gap, if any, between it and the pin, and result in the failure of the contacts to make proper contact. The pin 17 is held by a frame 62 having projections 62 a and 62 b between which the pin 17 is located, and which are provided for restraining the movement of the current-limiting contact support 12 in the direction perpendicular to the plane in which it is rotatable, as shown in FIGURE 12(a). The current-limiting contact support 12 which has been laterally displaced, or rotated about the pin 17 in the plane thereof, is shown by one-dot chain lines in FIGURE 12(b). No further displacement of the support 12, however, occurs, as it abuts on the projections 62 a and 62 b of the frame 62. FIGURE 12(c) is an enlarged view of a portion of the support 12 close to the pin 17. When the current-limiting contact support 12 is in its normal position, it and the pin 17 have a gap A therebetween, but if it is displaced as shown by one-dot chain lines, they have a smaller gap B. The projections on both sides of the pin 17 prevent any further displacement of the support 12, irrespective of the gap B. Although the gap A is shown as being larger than the gap B, they are of the same width if the distance between the opposite projections 62 a and the distance between the opposite projections 62 b are both equal to the thickness of the current-limiting contact support 12. The projections 62 a and 62 b can be provided at any desired distances from the pin 17 to prevent the displacement of the support 12 and thereby any insulation failure by the formation of an arc, even if the projections 62 b may not be located near the contact. The frame 62 can be made of an insulating material to ensure to a further extent that no insulation failure occur. The projections 62 a are sufficient to prevent any insulation failure. Although the eighth embodiment of the invention has been shown as applied to the current-limiting contact support 12, it is equally applicable to the movable contact support 9. It is also applicable to a stationary current-limiting contact support, or a movable contact support in a non-current-limiting circuit breaker. A modified form of the device shown in FIGURE 12(a) is shown in FIGURE 13. The modified device has, instead of the projections 62 a , a guide pin 64 secured to the current-limiting contact support 12 for restraining its lateral displacement. Each end of the guide pin 64 that is engageable with the frame 62 is spherically shaped so as to have a low coefficient of friction. Referring to FIGURES 14 to 16, the circuit breaker according to a ninth embodiment of this invention is characterized by including at least two electromagnetic repulsion mechanisms each for rotating a current-limiting contact support by a couple of electromagnetic repulsive forces produced on both sides of the axis of its rotation. The device includes a first current-limiting contact support 12 and a second current-limiting contact support 72 located below it and rotatably supported on a pin 71. A flexible twisted wire 14 has one end connected to one end of the current-limiting contact support 12, and another end connected to one end of a stationary contact support 73. The stationary contact support 73 has another end carrying a stationary contact 74 and the second current-limiting contact support 72 carries a movable contact 75 facing the stationary contact 74. The pin 71 is provided with a spring 76 urging the second current-limiting contact support 72 counterclockwise. A flexible twisted wire 14 is connected between the end of the second current-limiting contact support 72 remote from the contact 75 and one end of a stationary conductor 15. The current-limiting contact support 12 is rotatable about a pin 17 by a couple of electromagnetic repulsive forces which are produced between the movable contact support 9 and the current-limiting contact support 12, and between the current-limiting contact support 12 and the stationary conductor 15, respectively. The second current-limiting contact support 72 is rotatable about the pin 71 by a couple of electromagnetic repulsive forces which are produced between the stationary conductor 15 and the second current-limiting contact support 72, and between the second current-limiting contact support 72 and the stationary contact support 73, respectively. If a shortcircuit has caused a large amount of electric current to flow into the breaker through the stationary conductor 15, the current-limiting contact support 12 is rotated counterclockwise about the pin 17 to break the circuit rapidly, as is the case with any other device embodying this invention. A couple of electromagnetic repulsive forces are produced between the stationary conductor 15 and the repulsing portion 72 b of the second current-limiting contact support 72, and between the end portion 72 a of the support 72 on the opposite side of the pin 71 from the repulsing portion 72 b and that portion of the second stationary conductor 73 which is close to the stationary contact, respectively, and cause the second current-limiting contact support 72 to rotate clockwise about the pin 71 rapidly. If the circuit is completely broken, the first and second current-limiting contact supports 12 and 72 are returned by the springs 13 and 76, respectively, to their respective original positions, as shown in FIGURE 16. The circuit breaker shown in FIGURES 14 to 16 has not only a greatly improved breaking speed, but also a greatly improved current-limiting efficiency, since the presence of two current-limiting contact supports makes twice as high an arc voltage. The provision of the two electromagnetic repulsion mechanisms which produce a couple of forces to cause the circuit breaker to function enables an increase breaking speed, a prolonged breaking distance, and a greatly improved current-limiting efficiency due to an increased arc voltage. Attention is now drawn to FIGURES 17(a) to 17(d) showing the circuit breaker according to a tenth embodiment of this invention. It includes magnetic flux holding means provided for the extension 15 a of a stationary conductor 15 facing the end portion 12 a of a current-limiting contact support 12 remote from a current-limiting contact 11, as shown in FIGURE 17(a). It is provided for ensuring that the necessary magnetic repulsive force and breaking speed be maintained. Another magnetic flux holding means may be provided in a region remote from an arc-suppressing chamber for improving the reliability in performance of the circuit breaker by protecting it from any influence by molten matter which may be produced when the breaker works. A magnetic drive 80 as magnetic flux holding means is formed from a magnetic material and has a U-shaped cross section, as shown in FIGURE 17(b), which is a sectional view taken along the line A-A of FIGURE 17(a). The extension 15 a and the repulsing portion 12 a facing it extend through the magnetic drive 80 adjacent to its inner bottom surface. The flow of a large amount of current through the repulsing portion 12 a produces a magnetic flux flowing clockwise about it as shown by thin arrow lines in FIGURE 17(b). The repulsion which occurs between the repulsing portion 12 a and the extension 15 a causes the repulsing portion 12 a to move in the direction of a thick arrow line to the position shown by two-dot chain lines. As the magnetic flux moves within the magnetic drive 80, it does not undergo any reduction, but retains a high driving force in the direction of the thick arrow line to thereby maintain a high speed for the movement of the repulsing portion 12 a . This enables the current-limiting contact support 12 to maintain a high breaking speed and thereby achieve a high current-limiting efficiency. If the magnetic drive 80 is situated within the space defined by molded walls 40 a to 40 c immediately below the mechanism, it can protect the circuit breaker from any influence of molten matter on its performance and thereby improve its reliability. Another magnetic drive 80 a may be provided between a movable contact support 9 and the current-limiting contact support 12 to achieve a still improved current-limiting efficiency. It is also formed from a magnetic material and has a U-shaped cross section, as shown in FIGURE 17(c), which a sectional view taken along the line B-B of FIGURE 17(a). The magnetic fluxes which are formed by the electric current flowing through the movable contact support 9 and the current-limiting contact support 12, respectively, pass through the magnetic material. Therefore, no reduction in magnetic flux occurs during the movement of the movable contact support 9 and the current-limiting contact support 12, but a satisfactorily high breaking speed can be maintained. A U-shaped magnetic plate 82 may be provided about the repulsing portion 12 a in the magnetic drive 80, so that the core and the magnetic plate 82 may have a small gap a therebetween, as shown in FIGURE 17(d). It contributes to improving the performance of the magnetic drive 80. Referring to FIGURE 18, the circuit breaker according to an eleventh embodiment of this invention is a modified form of the circuit breaker according to the ninth embodiment thereof and includes magnetic drives 80 b and 80 c provided as magnetic flux holding means for the stationary conductor 15 and the stationary contact support 73, respectively. An improved breaking speed is achieved between the contacts 74 and 75 by the magnetic drive 80 c , as well as the electromagnetic repulsive force which is produced between the extension 15 a of the stationary conductor 15 and the portion 72 a of the second current-limiting contact support 72. Referring to FIGURE 19, the circuit breaker according to a twelfth embodiment of this invention is a modified form of the device shown in FIGURE 18. It includes a stationary contact support 78 secured by a screw 97 to one end of the stationary conductor 15, and the magnetic drive 80 b for the stationary conductor 15 is secured to the stationary contact support 78. In the device shown in FIGURE 19, the repulsion of the first current-limiting contact support 12 occurs before the repulsion of the second current-limiting contact support 72, as the breaking speed of the former is increased by the magnetic drive. The current-limiting contact support 12 is still connected electrically to the first stationary conductor 15 through the flexible conductor 14 and the second current-limiting contact support 72. The magnetic drive 80 b is secured to the stationary contact support 78 by a screw 99. The stationary conductor 15, the stationary contact support 78 and the magnetic drive 80 b can be prepared as a unitary assembly to improve the efficiency with which the circuit breaker is assembled. The magnetic drive 80 b can be secured to the stationary conductor 15 directly in a circuit breaker of the type according to the tenth embodiment of this invention which has no stationary contact support as shown at 78 in FIGURE 19. The unitary assembly as hereinabove described contributes to realizing the automatic fabrication of the circuit breaker. All the other features of the device are identical to their counterparts in the device shown in FIGURE 18. Although the circuit breakers embodying this invention have been described as having an electromagnetic tripping device including an oil dashpot relay, it is also possible to employ another type of tripping device, such as an electronic device having an electronic circuit for urging a magnetic tripping device in response to the current flowing in a line as detected by a current transformer, etc., or a thermal device employing a bimetal, etc., or a combination thereof. If an electronic device is employed, the line 88 is formed by a flexible conductor 88 a connected to the movable contact support, and a conductor not shown, but connected to the flexible conductor 88 a and leading through a current transformer to the load terminal. If a thermal device is employed, the line 88 is formed by a flexible conductor 88 a connected to the movable contact support, and a heater not shown, but connected to the flexible conductor 88 a , provided for heating a bimetal, and leading to the load terminal. According to this invention, the current-limiting contact support is rotatably supported in its middle portion, and has one end facing the movable contact support, while the other end thereof faces the stationary conductor and is connected to it by conductive connecting means, so that a couple of electromagnetic repulsive forces are produced between the movable and current-limiting contact supports, and between the stationary conductor and the current-limiting contact support. This invention, therefore, provides a small circuit breaker having a small distance between the current-limiting contact support and the stationary conductor, a high breaking speed, and an outstanding breaking efficiency.

Claims: A circuit breaker comprising a housing (1) provided at one end with a power source terminal (18), and at another end with a load terminal (28), a conductor (15, 72-75) having a stationary part (15, 73) and having one end connected to said power source terminal and another end provided with first conductive connecting means (14), a current-limiting contact support (12) having one end (12a) connected to said conductive connecting means and another end (12b) carrying a current-limiting contact (11), said support being rotatably supported by a pin (17), a rotatably supported movable contact support (9) carrying a movable contact (10) facing said current-limiting contact, a switching mechanism (4) connected to said movable contact support for performing a switching and tripping operation, and a tripping device (5, 19) for detecting an overcurrent in a line extending from said movable contact support to said load terminal and causing said switching mechanism to perform a tripping operation, said conductor, supports, mechanism, and device being all enclosed in said housing, characterized in that the pin (17) supports the current-limiting contact support (12) in its middle portion, a return spring (13) rotating the current-limiting contact support (12) toward the movable contact support (9), the housing (1) has an insulating case (58) enclosing the one end (12a) and the middle portion of the current-limiting contact support (12), its other end (12b) protruding out of the insulating case (58), the stationary part of the conductor (15) has an extension (15a) bent slantly toward the bottom of the housing (1), wherein the current-limiting contact support (12) is disposed in parallel to the bent extension (15a) so as to define a repulsing portion. A circuit breaker according to claim 1, characterized in that the repulsing portion includes a hinged extension (12c). A circuit breaker according to claim 1, characterized in that the stationary part (15) of the conductor includes an extension lying along said repulsing portion and having an opening (20) for receiving a part of said repulsing portion therein. A circuit breaker according to claim 1, characterized in that the stationary part (15) of the conductor has an opening (23) located below said current-limiting contact, so that said other end of said current-limiting contact support may be received in said opening when electromagnetic repulsion has resulted from the flow of a large amount of electric current. A circuit breaker according to claim 1, characterized in that the current-limiting contact support (12) is formed from an elongated plate having a width which is substantially equal to that of said stationary conductor, and is provided with a reinforcing member (30). A circuit breaker according to claim 1, characterized in that the conductive connecting means comprises a sliding member connected to said other end of said stationary conductor, and said one end of said current-limiting contact support is slidable along said sliding member, while maintaining electrical connection between said stationary conductor and said current-limiting contact support. A circuit breaker according to claim 1, characterized in that the current-limiting contact support is rotatably supported on a first shaft (17), said breaker further including a second shaft lying in parallel to said first shaft and extending through said current-limiting contact support at right angles thereto on the opposite side of said first shaft from said current-limiting contact, and a member connecting said second shaft to the junction between said movable contact support and said switching mechanism to move said second shaft to rotate said current-limiting contact support in the direction of its rotation by electromagnetic repulsion when said switching mechanism is actuated for a circuit-breaking operation. A circuit breaker according to claim 7, characterized in that a plurality of current-limiting contact supports, including said current-limiting contact support, are provided in a spaced apart and parallel relation to one another, and are joined to one another by said first and second shafts so as to be rotatable together in said direction upon actuation of said switching mechanism for said circuit-breaking operation. A circuit breaker according to claim 1, characterized in further comprising means for restraining the movement of said current-limiting contact support in the direction which is perpendicular to the plane of its rotation. A circuit breaker according to claim 1, characterized in that the conductor (15) has a second current-limiting contact support (72) having one end connected via second conductive connecting means to the stationary part of the connector (15) and facing one side of said stationary part, and another end carrying a second current-limiting contact (75), said support being rotatable supported in its middle portion, and a stationary contact support (73) facing said second current-limiting contact support (72), and having one end carrying a stationary contact (74) facing said second current-limiting contact (75), its other end being provided with the first conductive connecting means (14). A circuit breaker according to claim 1, characterized in further comprising magnetic flux holding means provided close to said repulsing portion and extending in the direction in which said repulsing portion is movable. A circuit breaker according to claim 11, characterized in that the stationary part of the conductor includes an extension lying along said repulsing portion, and said magnetic flux holding means comprises a member having a substantially U-shaped cross section through which said repulsing portion and said extension extend.

Inventors: KATO KAZUHIKO, SAITO TOMOYOSHI, SAKAI KUNIYOSHI, SHIMANO TERUMI, SHIODA KINICHI, SUZUKI HIROSHI, TERAOKA WATARU, KATO, KAZUHIKO, SAITO, TOMOYOSHI, SAKAI, KUNIYOSHI, SHIMANO, TERUMI, SHIODA, KINICHI, SUZUKI, HIROSHI, TERAOKA, WATARU, KATO, KAZUHIKO 8-20, TOUSHIN-CHO 1-CHOME, SAITO, TOMOYOSHI 1782-1, OOAZA OOIDE, SHIMANO, TERUMI 3343-17, OOAZA SAKAMACHI, SHIODA, KINICHI 4-18, TOUSHIN-CHO 4-CHOME, SUZUKI, HIROSHI 3-17, DAIEI-CHO 4-CHOME, TERAOKA, WATARU 12-3, MIDORI-CHO 2-CHOME
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1990
Main classification: H01H71
IPC codes: H01H77