Title of Invention

A SYSTEM AND METHOD FOR ACTIVATING A TRIP

Abstract

A system for activating a trip comprising: a moving contact (12) pivotally mounted to a drive shaft (18) for rotating said moving contact (12), and having a rotation path; the drive shaft (18) pivotally adapted to an operating mechanism (14); said operating mechanism (14) pivotally adapted to an actuator for activating trip; said actuator being connected to a trip plate (20); characterized irj. that the trip plate (20) has a vertically extended portion that intersects with the moving contact (12) in the rotation path to activate the trip, wherein the disengagement of the moving contact from the fixed contact and the activation of the trip takes place simultaneously.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION [See section 10; Rule 13] A SYSTEM AND A METHOD FOR ACTIVATING A TRIP; 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 NATURE OF THIS INVENTION AND THE MANNER INWHICH IT IS TO BE 2. 2 DEC 2004 PERFOMED. FIELD OF INVENTION The present invention relates to circuit breakers, more particularly to a system for activating a trip in circuit breaker in abnormal condition such as for example short circuit. BACKGROUND OF INVENTION The principle of current limitation through contact repulsion is employed in circuit breakers. Basically, the function of circuit breaker is to electrically engage and disengage a selected circuit from an electric power supply. The circuit breaker provides protection against persistent over-current condition and against the very high current produced by short-circuits Typically, circuit breakers have atleast a set of separable contacts, which include a fixed contact, and a movable contact engaged to the fixed contact during normal electrical operation. The movable contact separates from the fixed contact by disengaging from the fixed contact to interrupt the current flow on overload conditions. The movable contact is operated by an operating mechanism that rotates the movable contact away from fixed contact to interrupt the current flow. In a conventional non-current limiting circuit breaker, the tripping signal from the release makes the mechanism to operate and the contact to open. Conventional circuit breaker was based on a natural current zero of arc extinction process. On the appearance of the short circuit, it was unable to clear the fault current until the end of the first half cycle of the waveform, resulting in high let-through energy thereby damaging the downstream equipment as the tripping operation takes at least 20 millisecond. This may result in high let through energy thereby damaging downstream equipments. Further, as the tripping operation is delayed, there is a risk of re-closing of the moving contact. High-speed contact separation in circuit breaker is achieved by closely spaced contact carrying current in opposite direction, which create a strong magnetic repulsion between contacts. High-speed contact separation is actually produced by electromagnetic repulsion forces generated by the fault current itself. The higher the current the greater the force pushing the contacts apart. Although rapid contact opening is important, just opening the contact quickly is not enough. The next concern is to control the arc voltage across the contacts to ensure proper arc extinction. This is accomplished by forcing the arc into the arc chute and stretching the arc. The elongated arc is cooled and broken into segments in the arc chute until it is de-ionized and ceases to conduct current, thus being extinguished. Also a magnetic block around the contacts can accelerate the contact separation. Further during the fault, the contact fingers are blown apart by the electromagnetic repulsion. During this time, the mechanism must trip the breaker before the spring-loaded contacts can re-close and therefore the breaker remains open. The problem of re-closing of the moving contact is solved by various arrangements such as for example by providing a latching arrangement as disclosed in the US Patent No. 5912605. US patent No. US5912605 discloses the outside poles of a three pole circuit breaker are each provided with a blow open latch which includes a latch hook having an open slot forming jaws pivotally mounted on the contact arm. A torsion spring biases the jaws to a cocked position in which they are aligned for engagement with a fixed stop member toward which the contact arm rotates as it blows open in response to the magnetic repulsion forces generated by a short circuit. As the jaws engage the stop member, the latch hook is rotated to mechanically latch the latch hook on the stop member thereby preventing rebound and re-closing of the contacts. A leaf spring mounted on the crossbar holds the latch hook in mechanical engagement with the stop member. As the circuit breaker responds to the overcurrent condition and rotates the crossbar, the leaf spring disengages from the latch hook so that the torsion spring can rotate the latch hook back to the cocked 3 position for disengagement from the stop member upon re-closing of the circuit breaker. However, the main disadvantage of such arrangements is that providing a latching mechanism increases the number of component parts in the circuit breaker. Moreover to reset the circuit breaker the latching arrangement release the moving contact automatically which further necessitates more components inside the circuit breaker. Further the time taken to activate the trip also increases substantially as the tripping mechanism is activated only after the latching takes place. OBJECTS OF THE INVENTION: The principle object of the present invention is to simplify the operation and activation of trip in the current limiting circuit breaker thereby reducing the time taken to activate the trip. It is the further object of the present invention to prevent re-closing of the moving contact by using substantially less number of component parts. SUMMARY OF THE PRESENT INVENTION The present invention provides a system and a method for activating a trip of the circuit breaker against the high current produced by the short circuit. According to the present invention, the system for activating a trip comprises a moving contact pivotally mounted to a drive shaft for rotating said moving contact, and having a rotation path; the drive shaft pivotally adapted to an operating mechanism; said operating mechanism pivotally adapted to a actuator for activating trip; said actuator being adapted to a trip plate; characterized in that the trip plate has a vertically extended portion that intersects with the moving contact in rotation path and activate the trip. The simultaneous activation of trip triggers the operating mechanism that rotates the drive shaft and prevents the re-closing of the moving contact. According to the present invention, the moving contact engages with a fixed contact at one end and has an extended arm at the opposite end. The movable contact is pivoted in such a way that the extended arm of the opposite end of the moving contact intersects with the extended portion of the trip plate on repulsion in its rotation path. Preferably, the moving contact is pivoted centrally to the said drive shaft. The trip plate according the present invention is vertically extended at an angle of 10°-80° towards the moving contact preferably at an angle of 20°-30°. According to another embodiment of the present invention the method for activation a trip comprising the steps of: (a) disengaging the moving contact from the fixed contact; (b) rotating the moving contact and simultaneously intersecting one end of the moving contact with the extended portion of the trip plate; wherein the trip plate activates the operating mechanism to trip the circuit. The trip plate moves towards the operating mechanism activating a trip simultaneously the operating mechanism rotate the drive shaft upwards thereby rotating the moving contact further away from the fixed contacts thereby preventing the re-closing of the moving contact. As the system according to the present invention disengages the moving contact from the fixed contact and activates trip simultaneously, the circuit breaker trips within 6 to 10 millisecond. The system of the present invention uses substantially less component parts for activating the tripping of the circuit breaker and simultaneously preventing the moving contact to re-close. This substantially reduces the time for activating the trip thereby enhancing the efficiency of the circuit breaker. The circuit breaker according to the present invention is compact and substantially efficient than the existing circuit breakers. DESCRIPTION OF DRAWINGS Fig 1 shows a side elevation view of the pertinent part of a circuit breaker without housing incorporating the present invention in the 'ON' position. Fig 2 shows a side elevation view of the pertinent part of a circuit breaker without housing incorporating the present invention in the 'OFF' position. Fig 3 shows a side elevation view of the pertinent part of a circuit breaker without housing incorporating the present invention in the 'REPEL' position. Fig 4 shows a side elevation view of the pertinent part of a circuit breaker without housing incorporating the present invention in the TRIP' position. Fig 5 shows a Flow diagram for comparison of tripping operation between a circuit breaker incorporating the present invention and conventional circuit breaker. DETAILED DESCRIPTION The system for activating a trip according to the present invention is shown in Fig 1 to 4 mounted in a circuit breaker 10. The system for activating a trip comprising a moving contact (12) pivotally mounted on a drive shaft (18) and having a rotation path (x); the drive shaft (18) pivotally adapted to an operating mechanism (14); said operating mechanism (14) pivotally adapted to a actuator (not shown) for activating trip; said actuator being connected to a trip plate (20); characterized in that the trip plate (20) has a vertically extended portion (22) that intersects with the moving contact (12) in the rotation path (x) on repulsion as shown in Fig 3 and activates the trip. The moving contact (12) is mounted to the drive shaft (18) by a resilient means (not shown) such as for example a spring. The moving contact (12) engages with a fixed contact (50) at one end (12A) and has an extended arm (12B) in the opposite end. The resilient means keeps the moving contact in engaged position with the fixed contact under normal current flow conditions as shown in Fig 1. The moving contact (12) is preferably centrally pivoted on the drive shaft (18) as shown in figures 1 to 4 and the drive shaft (18) is pivotally mounted to the operating mechanism (14) at the opposite end such that the operating mechanism (14) rotates the drive shaft upwards enabling the drive shaft to rotate the moving contact further away from the fixed contact (50) during the activation of trip. The trip plate (20) has a vertically extended portion (22) that intersects with the extended arm (12B) of the moving contact (12) in rotation path (x) as shown in Fig 3. The trip plate is extended at an angle of 20°-30° to enable the extended portion (22) to intersect the moving contact (12) in the rotation path (X). The trip plate (20) is adapted pivotally to the operating mechanism (14) via actuator (not shown) as known in the art. During the abnormal condition such as short circuit, the moving contact (12) experiences electromagnetic repulsion, the extended portion (12B) of the moving contact rotates and touches the extended portion of the trip plate thereby simultaneously rotating the trip plate (20). The trip plate (20) moves towards the operating mechanism activating the trip simultaneously the operating mechanism rotates the drive shaft (18) upward thereby rotating the moving contact (12) further away from the fixed contacts (50) thereby preventing the re-closing of the moving contact (12) as shown in Fig 4. The advantage of the invention is that when the contact experiences the electromagnetic repulsion, the moving contact (12) simultaneously goes on rotating the trip plate (20) and avoids the re-closing of the contact by positively ensuring tripping of the mechanism. In the system of the present invention when the moving contact (12) disengages from the fixed contact (50), arcing and arc quenching occurs simultaneously activating instantaneous release sensing and tripping signal causing the circuit to trip mechanically unlike standard circuit breaker systems where the instant release sensing gives a tripping signal that mechanically trip making the contact open and then arcing and arc quenching takes place. This enhances the effectiveness of the current limiting principle in circuit breaker's as it results in the low-let through energy in the system thereby enhancing the breaking capacity as shown in Fig 5. Further, the circuit breaker's reduces substantially both the peak fault current and energy that reach to the downstream equipment. The system of the present invention substantially reduces the time of tripping to substantially half as compared to the prior art. The system according to the present invention trips the circuit within 6 to 10 milliseconds. According to another embodiment, the present invention provides a method for activating the trip comprising the steps of disengaging the moving contact (12) from the fixed contact (50); rotating the moving contact and simultaneously intersecting one end of the moving contact (12) with the extended portion of the trip plate (20) wherein the trip plate (20) activates the operating mechanism (14) to trip the circuit. The operating mechanism (14) rotates the drive shaft to prevent re-closing of the moving contact as shown in Fig 4. According to another embodiment, the present invention provides a circuit breaker (10) having a system for activating trip according to the present invention. The circuit breaker according to the present invention is compact as less components parts are used for its construction. The circuit breaker according to the present invention trips the circuit in substantially lesser time than the prior art preferably at around 6 to 10 milliseconds. According to further embodiments of the present invention, the system for activating trip is also applicable in devices such as switching devices or the like for protection of electrical appliances, systems or equipments against persistent over-current condition and against the very high current produced by short circuits. The other advantages of the invention are evident from the accompanied drawings. The description as above does not limit the invention to the way in which it is described. Any substitutions or immaterial variations known to a We Claim: 1. A system for activating a trip comprising: a moving contact (12) pivotally mounted to a drive shaft (18) for rotating said moving contact (12), and having a rotation path; the drive shaft (18) pivotally adapted to an operating mechanism (14); said operating mechanism (14) pivotally adapted to an actuator for activating trip; said actuator being connected to a trip plate (20); characterized irj. that the trip plate (20) has a vertically extended portion that intersects with the moving contact (12) in the rotation path to activate the trip, wherein the disengagement of the moving contact from the fixed contact and the activation of the trip takes place simultaneously. 2. The system for activating a trip as claimed in claim 1 wherein the operating mechanism rotates the drive shaft preventing re-closing of the moving contact. 3. The system for activating a trip as claimed in any one of the preceding claims wherein the moving contact engages with a fixed contact at one end and has an extended arm at the opposite end. 4. The system for activating a trip as claimed in claim 3 wherein the extended arm of the moving contact intersects with the extended portion of the trip plate on repulsion during short circuit. 5. The system for activating a trip as claimed in any of the preceding claims wherein the moving contact is centrally pivoted to said drive shaft. 6. The system for activating a trip as claimed in claim 1 wherein the trip plate is vertically extended at an angle of 10°-80° towards the moving contact. 7. The system for activating a trip as claimed in claim 6 wherein the trip plate is extended at an angle of 20° -30° towards the moving contact. 8. The system for activating tripping as claimed in any one of the preceding claims wherein said system trips the circuit breaker in 6 -10 milliseconds. 9. A circuit breaker comprising a system for activating tripping as claimed in claims 1 to 8. 10.A method for activation a trip comprising the steps of: disengaging the moving contact (12) from the fixed contact (50); rotating the moving contact (12) and simultaneously intersecting one end of the moving contact (12) with the extended portion of the trip plate (20); activating the operating mechanism (14) to trip the circuit. 11.A method for activating a trip as claimed in claim 10 wherein the moving contact disengages from the fixed contact for interrupting the current flow. 12. The method as claimed in claim 10 wherein the moving contact is rotated by the drive shaft. 13.The method as claimed in claim 10 wherein the operating mechanism rotates the drive shaft upwards preventing re-closing of the moving contact. 14. A circuit breaker as claimed in claim 9 operating by the method claimed in claims 10 to 12.

Documents:

1394-mum-2004-cancelled pages(29-8-2004).pdf

1394-mum-2004-claims(granted)-(29-8-2007).doc

1394-mum-2004-claims(granted)-(29-8-2007).pdf

1394-mum-2004-correspondence(29-8-2007).pdf

1394-mum-2004-correspondence(ipo)-(17-10-2007).pdf

1394-mum-2004-drawing(22-12-2004).pdf

1394-mum-2004-form 1(22-12-2004).pdf

1394-mum-2004-form 19(22-12-2004).pdf

1394-mum-2004-form 2(granted)-(29-8-2007).doc

1394-mum-2004-form 2(granted)-(29-8-2007).pdf

1394-mum-2004-form 3(22-12-2004).pdf

1394-mum-2004-form 5(22-12-2004).pdf

1394-mum-2004-power of attorney(22-12-2004).pdf

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