Title of Invention

LOCKING ASSEMBLY FOR A CIRCUIT BREAKER

Abstract

The present invention related to a locking assembly for a circuit breaker comprising a first electrical contact; a contact arm having a second electric contact adjacent to one end and said contact arm is pivotally connected to an operating shaft of a circuit breaker for rotating about a -pivot axis between a contacts closed position and at least one contacts open position with respect the "first electrical contact; a slider pin -mounted adjacent to the other end of the contact arm; a cam having a sliding surface in contact with the slider pin; a spring being compressionally adapted between the cam and the -operating shaft of the circuit breaker exerting a force on the contact arm through the cam and slider pin; wherein said cam allowing the slider pin to roll over the sliding surface accelerates opening of the contact arm before the reversal of the opposition force offer by the spring in conjunction with the electromagnetic repulsion force between the contacts and also reverse the spring force direction thereby resulting in the faster opening and locking of the contact arm. The locking assembly improves the performance and reliability of the circuit breaker thereby ensures the maximum protection of downstream equipments.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] A LOCKING ASSEMBLY FOR A 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. 1 FIELD OF THE INVENTION The present invention relates to a contact operation mechanism of a current limiting circuit breaker particularly to a locking assembly for the circuit breaker. PRIOR ART OF THE INVENTION Circuit breakers are commonly used for providing automatic circuit interruption upon detection of undesired over-current conditions on the circuit being monitored. These over-current conditions include overload conditions, ground fault conditions and short circuit conditions. Generally, circuit breaker comprises an electro-dynamically opening contact system for limiting, current. The contact system has a first electrical contact and a contact arm having opposing ends with a second electrical contact adjacent one of the opposing ends, said contact arm moves into an ON and OFF position by an operating shaft. In case of fault current, the contact arm responds to excessive magnitude current by electromagnetic repulsion between first electrical contact and second •electrical contact and rotates independent of the operating shaft. However, during the rotation, the contact arm experiences continuous reduction in the electro-dynamic force results in increase in the contact opening time and arcing time. Further, if it is not locked properly there -is possibility of re-closing of the moving shaft resulting in turn damage of the contacts reducing the performance of the circuit breaker thereby damaging the downstream equipment on which circuit breaker is mounted for safety purpose. 2 US patent No. 5363076 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 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 electromagnetic repulsion force has to overcome two opposition forces. One is spring force and second is the resistive force offer by the first contour area of the contour and therefore contacts takes more time to separate from each other. This results in increases in the arcing time during electromagnetic repulsion and leads to increase in current cut-off values. SUMMERY OF THE INVENTION: An object of the present invention is to provide a locking assembly for a circuit breaker the faster opening of the contacts on occurrence of the fault in current. 3 Another object of the present invention is to provide a locking assembly for a circuit breaker to reduce arching time during -electromagnetic repulsion between the contacts of the circuit breaker Further object of the present invention is to provide a locking assembly for a circuit breaker that open contacts quickly on repulsion between the contacts. According to the first embodiment of the present invention, a locking assembly for a circuit breaker comprises a first electrical contact; a contact arm having a second electrical contact adjacent to one end and other end of said contact arm is pivotally connected to an operating shaft of a circuit breaker for rotating about a pivot axis between a contacts closed position and at least one contacts open position with respect the first electrical contact; a slider pin mounted adjacent to the other end of the contact arm; a cam having a sliding surface in contact with the slider pin; a spring being compressionally adapted between the cam and the operating shaft of the circuit breaker, exerts a force -on the contact arm through the cam and slider pin; wherein said cam allowing the slider pin to roll over the sliding surface accelerates movement of the contact arm before the reversal of the opposition force offer by the spring in conjunction with the electromagnetic -repulsion force between the contacts and also reverse the spring force direction thereby resulting in faster opening and locking of the contact arm. Advantageously, said sliding surface has a concave surface between the straight surfaces allows the slider pin of the contact arm to roll faster over sliding surface along with accumulation -of energy before reversal of the spring force for utilizing faster separation of the contacts. 4 The slider pin is mounted between the pivot pin and the other end of the contact arm. The cam is guided in the operating shaft mounted perpendicular to the central axis of the slider pins and free to move to and fro inside operating shaft. Preferably, said cam and slider pin are adapted -on either side of the contact arm. According to the second embodiment of the present invention, single-phase circuit breaker comprises a locking assembly according to the first embodiment. According to the third embodiment of the present invention, a poly-phase circuit breaker comprises a locking assembly according to the first embodiment-of the present invention for each phase. BRIEF DESCRIPTION OF THE DRAWINGS OF THE PRESENT INVENTION Fig 1 is a side view of a locking assembly of a circuit breaker in ON position. Fig 2 is a side view of a locking assembly of a circuit breaker in OFF position. Fig 3 is a side view of a locking assembly of a circuit breaker in blown -open position. Fig 4 is a side view of the cam according to the present invention 5 DETAILED DESCRIPTION OF THE INVENTION A locking assembly (109) for circuit breaker according to the present invention in the 'ON or closed ', 'OFF or open' and tripped position is shown in Fig 1 to 3. The locking assembly (100) according to the present invention comprises a first electrical contact (10) mounted on a fixed arm (12); a contact arm (22) having a second electric contact (20) adjacent to one end (hereinafter referred as first end) (22a) and other end (22b) (hereinafter referred as second end) of said contact arm (22) is pivotally connected to an operating shaft (40) of a circuit breaker (not shown) for -rotating about a pivot axis (26) between a contacts (10, 20) closed position shown in Fig 1 and at least one contacts open position with respect the first electrical contact (10); a slider pin (24) mounted adjacent to the other end of the contact arm "(22); a cam (30) having a sliding surface (32) in contact with the slider pin (24); a spring (38) being compressionally adapted between the cam (30) and a operating shaft (40) exerts a force on the contact arm (22) through the cam (30) and slider pin (24). The contact arm (22) via a pivot pin (26) and the cam (30) via the spring (38) are secured in the operating shaft (40). This operating shaft (40) pivotally connected to the operating mechanism (46) of the circuit breaker to rotate about a second pivotal axis (44). The first electrical contact (10) can be mounted pivotally on an arm along with a spring to absorb the vibrations during normal closing and opening and electromagnetic repulsion. The slider pins (24) are mounted on both sides of the contact arm (22) between the second end (22b) and the pivot pin (26) of the contact arm (22) is in contact with the sliding surface (32) of the cam (30). 6 The sliding surface (32) of the cam (30) as shown in Figures 1-4 according to the present invention has a concave surface (33) between the straight surfaces (34). The linkage (35) between the concave surface (33) and the straight surface (34) is chamfered round for smooth rolling of the slider pin (24) over the sliding surface (32). Alternatively, the sliding surface can -be a plane or straight surface. The cam ,(30) provided with two supporting legs (36) that are inserted in the slots (44) provided on the operating shaft (40) for mounting cam (30) perpendicular to the central axis of the slider pin (24) in the operating shaft (40). The springs (38) are adapted on the supporting legs (36) before inserting the supporting legs (36) in the slots (42) and then contact arm (22) is pivotally mounted on the operating shaft (40) such that the slider pin (24) compresses the spring (38) via cam (30) and the cam (30) is free to make to and -fro movement in the operating shaft (40). In this way, the cam (30) is mounted oh either sides of the contact arm (22) and the sliding surface (32) is in the contact with the slider pin (24). Alternatively, the slider pin (24) in contact with a cam (30) may be mounted on one of the side of the contact arm (22). The compressionaily mounted springs (38) generate a spring force that is transmitted to the contact arm (22) for its every position through the cam (30) and slider pin (24). Due to the spring biasing, the contact arm (22) moves in conjunction with the operating shaft (40) of the circuit breaker in normal ON positions as shown in Fig 1 or OFF position as shown in Fig 2 whereas in case of fault current condition, it enables independent •movement of the contact arm (22) about the first axis. 7 In the 'ON' position as shown in Fig 1 the compressed spring (38) exerts a force on the cam (30) which in turn generates enough contact pressure (x) in a direction as shown in Fig 1 on the contact arm (22) through the top straight surface of the sliding surface of the contact to keep contacts in 'ON' position. The contact arm (30) moves from ON position to the blown-open position as shown in Fig 3 by rotating around a pivot pin (26) in response to an electromagnetic repulsive force, which develops between the electrical contacts 20 and 10 during over-current condition or fault current condition. As distance between the contacts (10, 20) increases the electromagnetic repulsive force between the contacts (10, 20) start decreasing. Simultaneously, the .slider .pins (24) of the contact arm (22) start rolling over the sliding surface (32) of the cam (30) leaving upper straight surface (34a) moves in the concave surface (33) of the sliding surface (32). The downhill (33a) of the concave surface (3) accelerates the contact arm -(30) in conjunction with the decreasing electromagnetic repulsive force by allowing faster rolling of the slider pins (24) of the contact arm (22) before the reversal of the opposite force of the spring (38) and further slider pins (24) applies force on the cam (30) while rolling over the sliding surface (32) thereby compressing the spring (38). As the slider pin (24) moves from the downhill portion (33a) to the uphill portion (33b) of the concave surface (32) of the cam (30), the slider pin (24) gains energy while sliding over the downhill portion (33a) and the spring force are about to reverse. The combined effect of the spring force reversal and energy gained helps quick/nimble opening of the contact arm (22) to move to its final blown open position as shown in Fig 3. 8 The sliding of the contact arm over the downhill portion and accumulating energy while sliding over the downhill portion and further utilizing the same while moving over the uphill portion separates the contacts very fast and thereby achieves reduction in the arcing time and current cut-off values of the circuit breaker. Further, the cam of the present invention offers a negligible resistance to the contact arm during electromagnetic repulsion between the contacts and therefore the contact arm of the present invention has to over come the spring force only whereas the contact arms of the circuit breaker of the available prior art has to overcome the spring force and the repulsive force offer by the locking arrangements. In this way, the locking assembly of the present invention improves the performance and reliability of the circuit breaker .thereby ensures the maximum protection of downstream equipments. Further, the locking assembly of the present invention is easy to assemble 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. Moreover, the cam of the locking arrangement of the present invention moves freely in slots provided in the operating shaft of the circuit breaker thereby reducing the frictional -losses during independent movement of the contact arm. 9 WE CLAIM A locking assembly for a circuit breaker comprising : a first electrical contact; a contact arm having a second electric contact adjacent to one end and said contact arm is pivotally connected ,to an operating shaft of a circuit breaker for rotating about a pivot axis between a contacts closed position and at least one contacts open position with respect the first electrical contact; a slider pin mounted adjacent to the other end of the-contact arm; a cam having a sliding surface in contact with the slider pin; a spring being compressionally adapted between the cam and the operating shaft of the circuit breaker exerting a force on the contact arm through the cam and slider pin; wherein said cam allowing the slider pin to roll -over the sliding surface accelerates opening of the contact arm before the reversal of the opposition force offer by the spring in conjunction with the electromagnetic repulsion force between the contacts and also reverse the spring force direction thereby resulting in the faster opening and locking of the contact arm. 2. A locking assembly for a circuit breaker as claimed -in claim 1 wherein said sliding surface has a concave surface between the straight surfaces allows faster rolling of the slider pin of the -contact arm over sliding surface along with accumulation of energy before reversal of the spring force for utilizing faster separation of the contacts. 10 3. A locking assembly for a circuit breaker claimed in claim 1 wherein said slider pin is mounted between the pivot pin and the other end of the contact arm. 4. A locking assembly for a circuit breaker as claimed in claim 1 wherein the cam is guided in the operating shaft mounted perpendicular to the central a is of the slider pins and free to move to and fro inside operating shaft. 5. A locking assembly for a circuit breaker as claimed in claims 1 and 2 wherein said cam and slider pin are adapted on either side of the contact arm. 6. A single-phase circuit breaker comprising a locking assembly as claimed in claims 1-5. 7. A poly-phase circuit breaker comprising a locking assembly as claimed in claims 1 to 5 for each pole. 8. A locking assembly for a circuit breaker hereinbefore described with reference to the drawings. Dated this 27th day of September, 2005. 11 ABSTRACT The present invention related to a locking assembly for a circuit breaker comprising a first electrical contact; a contact arm having a second electric contact adjacent to one end and said contact arm is pivotally connected to an operating shaft of a circuit breaker for rotating about a -pivot axis between a contacts closed position and at least one contacts open position with respect the "first electrical contact; a slider pin -mounted adjacent to the other end of the contact arm; a cam having a sliding surface in contact with the slider pin; a spring being compressionally adapted between the cam and the -operating shaft of the circuit breaker exerting a force on the contact arm through the cam and slider pin; wherein said cam allowing the slider pin to roll over the sliding surface accelerates opening of the contact arm before the reversal of the opposition force offer by the spring in conjunction with the electromagnetic repulsion force between the contacts and also reverse the spring force direction thereby resulting in the faster opening and locking of the contact arm. The locking assembly improves the performance and reliability of the circuit breaker thereby ensures the maximum protection of downstream equipments. 12

Documents:

1203-MUM-2005-ABSTRACT(4-6-2014).pdf

1203-MUM-2005-ABSTRACT--21-01-2015.pdf

1203-mum-2005-abstract.doc

1203-mum-2005-abstract.pdf

1203-MUM-2005-ANNEXURE(20-9-2013).pdf

1203-MUM-2005-CLAIMS AMENDED--21-01-2015.pdf

1203-MUM-2005-CLAIMS(AMENDED)-(4-6-2014).pdf

1203-mum-2005-claims.doc

1203-mum-2005-claims.pdf

1203-MUM-2005-COPY OF FORM 18-21-01-2015.pdf

1203-MUM-2005-CORRESPONDENCE 1(21-10-2005).pdf

1203-MUM-2005-CORRESPONDENCE(22-11-2005).pdf

1203-MUM-2005-CORRESPONDENCE(27-08-2008).pdf

1203-mum-2005-correspondence-received.pdf

1203-mum-2005-description (complete).pdf

1203-MUM-2005-DRAWING--21-01-2015.pdf

1203-mum-2005-drawings.pdf

1203-MUM-2005-FORM 1(21-11-2005).pdf

1203-MUM-2005-FORM 1(4-6-2014).pdf

1203-MUM-2005-Form 1-210115.pdf

1203-MUM-2005-FORM 13-21-01-2015.pdf

1203-MUM-2005-FORM 18(27-08-2008).pdf

1203-MUM-2005-FORM 2 (TITLE PAGE)--21-01-2015.pdf

1203-MUM-2005-FORM 2(TITLE PAGE)-(27-9-2005).pdf

1203-MUM-2005-FORM 2(TITLE PAGE)-(4-6-2014).pdf

1203-MUM-2005-FORM 3(4-6-2014).pdf

1203-MUM-2005-Form 3-210115.pdf

1203-MUM-2005-FORM 5(4-6-2014).pdf

1203-MUM-2005-Form 5-210115.pdf

1203-MUM-2005-FORM 9(21-10-2005).pdf

1203-mum-2005-form-1.pdf

1203-mum-2005-form-2.doc

1203-mum-2005-form-2.pdf

1203-mum-2005-form-3.pdf

1203-mum-2005-form-5.pdf

1203-MUM-2005-GENERAL POWER OF ATTORNEY(20-9-2013).pdf

1203-MUM-2005-GENERAL POWER OF ATTORNEY(4-6-2014).pdf

1203-MUM-2005-GENERAL POWER OF AUTHORITY-21-01-2015.pdf

1203-MUM-2005-GENERATION POWER OF AUTHORITY-21-01-2015.pdf

1203-MUM-2005-MARKED COPY(4-6-2014).pdf

1203-MUM-2005-OTHERS-210115.pdf

1203-MUM-2005-POWER OF ATTORNEY(22-11-2005).pdf

1203-MUM-2005-REPLY TO EXAMINATION REPORT(4-6-2014).pdf

1203-MUM-2005-SPECIFICATION AMENDED--21-01-2015.pdf

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