FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A CONTACT MECHANISM FOR CIRCUIT BREAKER;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
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FIELD OF INVENTION
The present invention relates to circuit breakers and more particularly to the contact arrangement of the current limiting circuit breaker.
PRIOR ARTS
Usually electrical and electronic appliances require quick isolation from current sources to protect them during high currents/voltage arising due to short circuit, overload current or other abnormal current situations. Various isolation devices may be used based on current levels, place of application etc. Devices used to accomplish electrical isolation during fault have evolved from early fuse elements with obvious need of replacement of fuse to reenergize the circuit. Although, invent of circuit breakers overcame this problem a need arose to minimize the response time of circuit breakers to abnormal situations.
Current limiting circuit breakers utilizing electro-magnetic repulsion to respond to sudden high currents overcame the drawback of high response time by providing clipping operation in less than half wave cycle. Typically, current limiting circuit breakers consist of at least two electrical contacts either or both of which are mounted on a movable arm. The circuit breaker may be brought into a contact closed condition by actuating mechanisms allowing the flow of current through the circuit breaker.
Arrangements are generally provided to facilitate opening of contacts. The arrangements or assemblies may be provided in form of contact mechanism that helps in holding and maintaining the contact arms in open condition.
There are prior arts depicting mechanisms used in circuit breakers, US Patent No. US5363076 discloses A blade suspension assembly for a circuit breaker includes a first electrical contact, an elongated contact arm having a second
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electrical contact adjacent a first end of the contact arm, a compression spring, and an elongated lever. The second electrical contact is movable about a first pivot axis between a contacts-closed position and at least one contacts-open position with respect to the first electrical contact. The lever has a first end adjacent a second pivot axis, a second end supported by the compression spring, and a contoured support surface between the first and second ends which supports a second end of the contact arm. The compression spring exerts a force against the second end of the lever so that the contoured support surface biases the second end of the contact arm about the first pivot axis in the contacts-closed position during normal operation and in the contacts-open position in response to the contact arm moving to the contacts-open position. However, the intricateness involved in the placement and manufacturing of parts makes it a complex arrangement. Moreover, the contoured surfaces involved are liable to worn-out thereby threatening the reliability of the circuit breaker.
The US paten No.US4841266 describes a circuit breaker comprises a housing; a stationary contact mounted in the housing; an operating shaft disposed in the housing and rotatable about a first axis of rotation; and a movable contact including a contact arm pivotally held in the operating shaft for rotation about a second axis of rotation from an on position into a tripped position. By rotating the operating shaft about the first axis of rotation, the contact arm is movable into and out of the on position and an off position. The contact arm further has a terminus including a rounded corner and an adjoining rounded engagement face. There is further provided a structural unit stationarily supported in the housing and comprising a spring having a stationarily supported first end and a second end and a transfer lever having an end pivotally supported for rotation about a third axis of rotation. The lever is disposed between the second end of the spring
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and the terminus of the contact arm and engages the rounded corner or the rounded engagement face dependent on the position of the contact arm for transmitting a torque from the spring to the contact arm about the second rotary axis.
As described above, circuit breakers attempting to achieve quickness and reliability using various mechanisms are substantially complex, in that they achieve the quickness and reliability at the cost of high part count, intricate positioning drive pins, usage of special shaped parts and numerous biasing springs. These complications further entangle the troubleshooting and repairing operations.
SUMMARY OF THE INVENTION
A contact mechanism for a circuit breaker is described. The mechanism provides for current limiting characteristics and avoids re-striking of contacts of a circuit breaker by providing a reliable locking mechanism by using a slider crank arrangement of various parts of the circuit breaker.
In one embodiment of the present invention a recess is provided at one end of a moving contact arm. A slider pin is rotatably engaged with the recess allowing rotation therein during transition between various conditions of the circuit breaker. A sliding path on the operating shaft is provided for guiding a biasing means and the other end of the slider pin resulting in desired force characteristics.
The contact mechanism described may be applied to various types of circuit breakers such as for example single phase or multiphase circuit breaker. Also, the circuit breakers employing single break/pole or multi-break/pole system may implement the invention. The contact mechanism may be applied to a single or
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multiple contact arms of a circuit breaker. The contact mechanism of the present invention is compact, simple in construction thereby making it easier to manufacture. Moreover, it is very easy to dismantle, as all parts are separable and not permanently fixed to the operating shaft of the circuit breaker. This enables easier troubleshooting operations on the circuit breaker.
Further, easier replacement of individual parts is made possible, reducing the overall repair cost. According to the present invention, the spring is a tension spring or a compression spring. The contact mechanism of the present invention ensures an early and quick opening of the contacts and safety extinguishes the electric arc between the contacts.
According to the present invention, said sliding path is straight, inclined concave or convex. Various sliding path profiles may provide for different force characteristics during transition of the circuit breaker from one condition or stage to another.
DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross sectional view of slider crank mechanism according to one embodiment of the present invention in blown open condition in closed condition.
Fig. 2 is a cross sectional view of the slider crank mechanism according to one embodiment of the present invention in blown open condition in an open condition.
Fig. 3 is a cross sectional view of the slider crank mechanism according to one embodiment of the present invention in blown open condition.
Fig. 4 is an isometric view of the present invention according to one embodiment of the present invention.
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Fig. 5 is a cross sectional view of the slider crank mechanism according to one embodiment of the present embodying a concave sliding path.
Fig. 6 is a cross sectional view of the slider crank mechanism according to one embodiment of the present embodying a convex sliding path.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
A contact mechanism for a circuit breaker is described. The mechanism provides for current limiting characteristics and avoids re-striking of contacts of a circuit breaker by providing a reliable locking mechanism by using a slider crank arrangement of various parts of the circuit breaker.
The contact mechanism described may be applied to various types of circuit breakers such as for example single phase or multiphase circuit breaker. Also, the circuit breakers employing single break/pole or multi-break/pole system may implement the invention. The contact mechanism may be applied to a single or multiple contact arms of a circuit breaker.
Fig. 1 shows a contact mechanism as per one embodiment of the present invention. An operating shaft (11) may be provided rotatably connected to a housing (9). The operating shaft may be rotatable about first axis (14) of rotation. The rotation of the operating shaft may cause the circuit breaker to achieve a closed condition in which current is allowed to flow through the circuit breaker. Various actuating mechanisms may be used in rotating the operating shaft about the first axis.
In one embodiment of the present invention a first contact button (22) may be provide on a stationary arm (20) of the circuit breaker. A moving contact arm (30) may be provided rotatably connected to the operating shaft (11). A second contact button (32) may be mounted on one end of the moving contact arm (30).
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The moving contact arm may rotate about a second axis (19) independent of the operating shaft in transition between various stages of the circuit breaker.
A biasing means is provided, one end (52) of which is connected to a connecting edge (12) of the operating shaft (11). A slider pin (40) facilitates the transfer of biasing force from the biasing means to the moving contact arm. A recess (36) is provided at an other end (34) of the moving contact arm (30). One end (42) of the slider pin may be allowed to rotate in the recess (36) at another end (34) of the moving contact arm (30). Another end (44) of the slider pin may be pivotally connected to another end (54) of the biasing means (50). During closed condition of the circuit breaker necessary contact pressure is maintained between the first contact button (22) and the second contact button (32). The force F1 80 acting on the recess (36) of the moving contact arm maintains the contact buttons in contact.
Biasing means may use a tension spring. Alternatively a leaf spring may be used. A person skilled in the art shall recognize that a compression spring may be used as a biasing means to produce similar force characteristics.
Fig.2 shows the open condition of the circuit breaker as per one embodiment of the present invention. The circuit breaker may be brought to an open condition wherein the moving contact arm (30) moves coherently with the operating shaft (11). In this condition the first contact button (22) and the second contact button (32) are away from each other.
No current flow from the circuit breaker is maintained in this condition. The circuit breaker may be brought back to the closed condition by rotating the operating shaft. This causes the moving contact arm to rotate coherently with the operating shaft to bring the contact buttons in contact.
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While operating in the closed condition the circuit breaker allows flow of the intended amount of current allowing the downside equipments to operate. On occurrence of short circuit the electromagnetic repulsion between the contacts arms increases. This leads to the parting of the contact arms leading to a blown open condition of the circuit breaker. The value of the predetermined load current causing automatic opening of the circuit breaker may be decided. The biasing means (50) may be designed accordingly to cause the intended force characteristics in the circuit breaker.
A repulsive force caused between two contact arms tends to push the contacts apart causing the moving contact arm to rotate independently about the second axis. In transiting from the closed condition to the open condition the force exerted initially by the biasing means needs to be overcome.
The movement of the moving contact arm under repulsive force causes the other end (44) of the slider pin to slide along a sliding path (15) of the operating shaft (11). The one end (42) of the slider pin is rotatable in the recess of the moving contact arm. The application of force by the biasing means is at a point where the one end of the slider pin (42) engages with the recess of the moving contact arm. The recess may comprise of two flat surfaces and a circular portion (36a) between said flat surfaces (36b), thereby forming a "U" shape recess. During transition of the circuit breaker from closed condition to the blown open condition, the one end of the slider pin engages with the circular portion (36a) of the recess. The provision of the recess reduces the manufacturing cost since no welding may be required for the recess as compared to a closed joint.
In one embodiment of the present invention the sliding path (15) provided may be flat. Alternatively, a concave surface may be provided as shown in fig.5 to alter
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the opening characteristics of the circuit breaker. The concave surface provided may result in faster opening of the circuit breaker. Also, as shown in fig. 6 a convex surface provided may offer larger resistance to the motion of the sliding pin along the sliding path. This may improve the locking characteristic of the circuit breaker in the blown open condition.
A change in the direction of force caused by the biasing means occurs on transiting from the closed condition to the blown open condition. Initially the direction of the force caused by the biasing means at the moving contact arm tends to keep the contact buttons in contact.
As the repulsive force increases the direction of force on the parting contact arms shifts. When the direction of the force caused by the biasing means goes beyond the direction of line joining the recess (36) and the pivot point (13) as shown in fig. 3 a reversal of force effective on the moving contact arm occurs. The force F3 causes the moving contact arm (30) away from the stationary contact arm (20).
The force F3 facilitates movement of the moving contact arm (30) away from the fixed contact arm (20), thereby avoiding re-striking of the contact buttons. Therefore, a reduction in repulsive force between the two arms caused due to partition of the contact arms does not lead to a re-striking of the contact arms. Therefore, the arc time arising due to re-striking of the contact arms may be reduced considerably.
The blown open condition of the circuit breaker is reached as shown in fig.3. In the blown open condition the biasing means provides a force along a direction D4 locking the moving contact arm in an open position. The embodiment of the present invention providing a convex sliding surface may result in added contact locking characteristics. In the blown-open condition of the circuit breaker the one
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end of the slider pin rests at a flat portion (36b) of the profile of the recess (36). The profile of the recess does not allow further movement of the one end of the slider pin thereby locking the moving contact arm.
The contact mechanism of the present invention is compact, simple in construction thereby making it easier to manufacture. Moreover, it is very easy to dismantle, as all parts are separable and not permanently fixed to the operating shaft of the circuit breaker. This enables easier troubleshooting operations on the circuit breaker.
Further, easier replacement of individual parts is made possible, reducing the overall repair cost. The contact mechanism of the present invention ensures an early and quick opening of the contacts and safety extinguishes the electric arc between the contacts. Dismantling of individual components of the circuit breaker is made easy making the parts accessible. These properties of the circuit breaker greatly improve the troubleshooting operation of the circuit breaker.
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WE CLAIM
1. A contact mechanism for a circuit breaker comprising:
a first contact button;
an operating shaft rotatable about a first axis to bring the circuit breaker into a closed condition;
a moving contact arm pivoted to rotate about a second axis to bring the circuit breaker into a blown open condition;
a second contact button at one end of the said moving contact arm;
a recess at another end of the moving contact arm;
one end of a slider pin rotatable in the recess of the moving contact arm;
a sliding path in the operating shaft;
a biasing means tenaciously connected between another end of said slider pin and a connecting edge in the operating shaft such that on transit between said contact closed condition and said blown open condition another end of the slider pin is guided along said sliding path of the operating shaft to affect the reversal of force about said second axis.
2. The contact mechanism as in claim 1, wherein the biasing means is a tension spring.
3. The contact mechanism as in claim 1, wherein the recess has a profile made of at least a circular portion and a flat portion.
4. The contact mechanism as in claim 1, wherein the operating shaft is mounted on a housing.
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The contact mechanism as in claim 1, wherein the first contact button is mounted on a moving contact arm.
A single-phase circuit breaker comprising the contact mechanism as claimed in claim 1.
A multi-phase circuit breaker comprising the contact mechanism as claimed in claim 1.
The contact mechanism as in claim 1, wherein the sliding path is a flat surface.
The contact mechanism as in claim 1, wherein the sliding path is a concave surface.
The contact mechanism as in claim 1, wherein the sliding path is a convex surface.
Dated this 30th day of October, 2006.
FOR LARSEN & TOUBRO LTD. By their Agent
(GIRISH VIJAYANAND SHETH) KRISHNA & SAURASTRI
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ABSTRACT
A contact mechanism for a circuit breaker is described. In one embodiment of the present invention a recess is provided at one end of a moving contact arm. A slider pin is rotatably engaged with the recess allowing rotation therein during transition between various conditions of the circuit breaker. A sliding path on the operating shaft is provided for guiding a biasing means and the other end of the slider pin resulting in desired force characteristics. The sliding path may be provided to have various profiles.
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