COMPETE AFTER PROVISIONAL LEFT ON
7 DEC 2005
FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENS RULES, 2003
COMPLETE SPECIFICATION [See section 10, Rule 13]
A SLIDER-CRANK MECHANISM FOR CIRCUIT BREAKER;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAl - 400 001, MAHARASHTRA, INDIA.

THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE NATURE OF THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFOMED.

FIELD OF INVENTION:
The present invention relates to circuit breakers and particularly to the contact holding arrangement of the current limiting circuit breaker.
BACKGROUND ART / PRIOR ARTS:
Isolation of electrical circuits is necessary to protect downstream equipments or apparatus against high currents/voltage arising during short circuit, overload current. 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, earlier inventions in this field of the circuit breakers overcame this problem, a need arose to minimize the response time of circuit breakers to surge currents.
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 oh a movable arm that are further drawn by mechanisms.
There are prior arts depicting mechanisms used in circuit breakers as for example, US Patent No. US5363076 discloses a blade suspension assembly for a circuit breaker including a first electrical contact, an elongated contact arm having a second electrical contact adjacent a first
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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 Patent No. US4841266 describes a circuit breaker comprising 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
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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 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. Further, the moving contact of the circuit breaker disclosed in US5363076 or US4841266 has to overcome one more opposing force offered by the contoured support surface described in the US5363076 patent or a rounded corner described in the US4841266 patent along with the spring force thereby increasing the arcing time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simple and compact slider crank mechanism for holding a contact of circuit breaker.
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Another object of the present invention is to provide a slider crank mechanism to obviate the problem of the prior art as discussed above.
According to the present invention, a slider mechanism for locking a contact of the circuit breaker comprises a first electrical contact; an operating shaft having a guide recess for adapting a slider pin; a contact arm having a second electric contact adjacent to one end and a pivot pin at other end; said contact arm is pivotally connected to the operating shaft of a circuit breaker for rotating about a second pivot axis between a contacts closed position and contacts open positions with respect to the first electrical contact; a connecting link connected pivotally to the contact arm linking to the operating shaft by means of the slider pin; a spring connected to the slider pin biasing the connecting link; such that said connecting link in conjunction with spring generates required contact pressure during normal operation of the circuit breaker and changes the spring force during electromagnetic repulsion resulting in faster separations of the contacts and locking the contact arm.
According to the present invention, said guide recess is straight, inclined concave or convex. Said slider pin is adapted fixedly on the connecting link. According to the present invention, the spring is a tension spring or a compression spring.
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DETAILED DESCRIPTION OF THE DRAWINGS
Now the invention will be described with reference to accompanying drawings wherein
Fig. 1 is a cross sectional view of slider crank mechanism according to the present invention in 'ON' position.
Fig. 2 is a cross sectional view of the slider crank mechanism according to the present invention in 'OFF' or tripped position.
Fig. 3 is a cross sectional view of the slider crank mechanism according to the present invention in blown open position.
Fig 4 is an exploded view of the slider crank mechanism of the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
Turning now to the drawings, Fig 1 through 3 show cross sectional views of a slider crank mechanism (100) according to the present invention, in the 'ON' or closed position (Fig 1), the 'OFF' or open or a tripped position (Fig 2) in which entire cictuating mechanism of the circuit breaker rotates away from the first electrical contact mounted on the fixed contact arm (1) and a blown-open position (Fig 3) in which the moving contact arm (3) is rotated away from the fixed contact arm (1).
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More specifically, Fig 1 to 4 depicts the primary components of the slider crank mechanism (100) of the present invention mounted in a circuit breaker comprising an elongated contact arm (3) (hereinafter referred to as moving contact arm) having second electrical contact (2b) at one end and a pivotal pin (7) on other end of the moving contact arm (3), a connecting link (5), a spring (10) and a longitudinal guide recess (12) provided on operating shaft (4) and a first electrical contact (2a) on a fixed contact arm (1). One end of the connecting link (5) is firmly connected to the slider pin (8) and other end is connected pivotally to the pivotal pin (7) of the moving contact arm (3). The slider pin (8) is adapted in the longitudinal guide recess (12) of the operating shaft (4) to slide therein and is biased by the spring. For biasing, the spring is connected tensionally between the slider pin (8) and mounting pin (9) provided over the operating shaft (4). Accordingly, the operating shaft (4) with the guide recess (12) acts as a guide member for the slider pin (8) permitting limited pivot motion of the moving contact arm (3) independently.
The operating shaft (4) is also connected to the conventional actuating mechanism (6) for mechanically opening and closing of the contacts (2a) and (2b) which is known per se. This actuating mechanism (6) may be electro-magnetically and/or thermally tripped in a manner known per se. It is thus possible to open the contacts (2a) and (2b) by the conventionally actuating mechanism (6) via operating shaft (4) actuating moving contact (3) via one of the edges of the guide recess (12) and the slider pin (8).
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Independently, it is also possible to open the contacts independently due to the toggle-like action of spring (10) with slider pin (8) traveling in the guide recess (12).
As per the modification, the guide recess can be convex/straight inclined anticlockwise.
Under normal operating conditions, the contacts (2a) and (2b) are closed as shown in Fig 1. This closed position as shown in Fig 1 is achieved by conventional actuating mechanism (6) rotating the operating shaft (4) about the first axis (not shown). The moving contact arm (3) being coherent with the operating shaft (4) rotates with the operating shaft (4) about the first axis and touches the second electrical contact (2b) to the first electrical contact (2a) of the fixed contact arm (1). To avoid hotspots at contact, contact pressure is required between the contacts (2a) and (2b). This necessary pressure between the electrical contacts (2a) and (2b) is generated by force F2 produced by the spring (10) mounted tensionally via the slider pin (8) and connecting link (5) on the moving contact arm (3). The flow of current is shown in Fig 1 by line (x) over the fixed contact arm (1), electrical contacts (2a, 2b) through the movable contact arm (3), thus forming a narrow loop.
Fig.2 shows the OFF condition of the circuit breaker comprising slider crank mechanism. This condition of circuit breaker is achieved when the operating mechanism (6) is pulled back to the OFF position and
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mechanism spring pulls the operating shaft (4) rotating it to the OFF position. In this condition, the moving contact (3) being coherent to operating shaft (4) rotates with the operating shaft (4).
As soon as a predetermined over load current occurs, for example in case of short circuit, the current loop and the narrow current passage and the contacts produce an electro-dynamic force due to electromagnetic repulsion between the contacts (2a, 2b), based on the well-known fact that the current loop tends to widen itself thereby magnetic field, which tends pushing the contacts (2a, 2b) apart causing the moving contact arm (3) to rotate independently about second axis (11). Here moving contact arm (3) has to overcome the force F2 offered by the spring (10) only and not any other force/s as discussed in the prior art. This causes traveling of the slider pin (8) inside the guide recess (12) from one edge to the other edge of the guide recess (12) in the operating shaft (4). Therefore, as distance between the moving contact and fixed contact increases, the force F1 decreases gradually passing through zero and then becomes negative as shown in Fig 3 due to the connecting link pivotal pin (7) and second axis (11) about which the movable contact rotates (3). This negative force F2 pulls the moving contact (3) further away from the fixed contact arm (1) in conjunction with the decreasing electromagnetic force instead of pressing the moving contact (3) against the fixed contact (1) thereby resulting in faster separation of the contacts (2a, 2b). Further, the negative force (F2) stops the moving contact (3) as soon as moving contact come to rest from
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returning back towards the fixed contact (1) thereby locks the moving contact (3).
The slider crank mechanism of the present invention is compact, simple and can be easily mounted in the single-phase circuit breaker and multiphase circuit breaker. Moreover, it is very easy to dismantle, as all parts are separable and not permanently fixed to the operating shaft of the circuit breaker. The circuit breaker comprising slider crank mechanism of the present invention ensures an early and quick opening of the contacts and safely extinguishes the electric arc between the contacts. The operation of the circuit breaker comprising the slider crank mechanism according to the present invention under normal conditions is in the manner known per se and in predetermined critical conditions such as short circuit; the slider crank mechanism of the present invention operates as described above. Further, the drawings illustrate a particular embodiment of the present invention and modifications can be made without departing from the scope of the invention, which is specifically claimed through the appended claims.
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WE CLAIM
1. A slider-crank mechanism for locking contact of a circuit breaker
comprising
a first electrical contact;
an operating shaft having a guide recess for adapting a slider pin;
a contact arm having a second electric contact adjacent to one end and a pivot pin at other end; said contact arm is pivotally connected to the operating shaft of a circuit breaker for rotating about a second pivot axis between a contacts closed position and contacts open positions with respect to the first electrical contact;
a connecting link connected pivotally to the contact arm linking to the operating shaft by means of the slider pin;
a spring connected to the slider pin biasing the connecting link;
such that said connecting link in conjunction with spring generates required contact pressure during normal operation of the circuit breaker and changes the spring force during electromagnetic repulsion resulting in faster separations of the contacts and locking the contact arm.
2. A slider-crank mechanism for locking contact of a circuit breaker as
claimed in claim 1 wherein said slider pin is adapted fixedly on the
connecting link.
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3. A slider-crank mechanism for locking contact of a circuit breaker as claimed in claim 1 wherein said guide recess is straight, concave or convex.
4. A slider-crank mechanism for locking contact of a circuit breaker as claimed in claim 1 wherein said spring is a tension spring .
5. A slider-crank mechanism for locking contact of a circuit breaker as hereinbefore described with reference to the drawings.
Dated this 16th day of June, 2005

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ABSTRACT
The present invention relates to a locking contact arrangement for a circuit breaker. According to the present invention, a slider mechanism for locking a contact of the circuit breaker comprises a first electrical contact; an operating shaft having a guide recess for adapting a slider pin; a contact arm having a second electric contact adjacent to one end and a pivot pin at other end; said contact arm is pivotally connected to the operating shaft of a circuit breaker for rotating about a second pivot axis between a contacts closed position and contacts open positions with respect to the first electrical contact; a connecting link connected pivotally to the contact arm linking to the operating shaft by means of the slider pin; a spring connected to the slider pin biasing the connecting link; such that said connecting link in conjunction with spring generates required contact pressure during normal operation of the circuit breaker and changes the spring force during electromagnetic repulsion resulting in faster separations of the contacts and locking the contact arm.
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7 DEC 2005