FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)


TITLE OF THE INVENTION: CONTACT BOUNCE CONTROL SYSTEM FOR CONTACTORS
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. BoxNo. 278,
Mumbai- 400 001, Maharashtra. INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to switching system and particularly to contactors such as capacitor duty switching contactor used for electric motor, capacitor bank, resistance furnace etc. The present invention more particularly relates to an auxiliary contactor system in the capacitor duty contactor.
B) BACKGROUND OF THE INVENTION
[0002] A contactor is an electrically controlled switch that is used generally to control or remotely switch the power to any electric power driven circuit like electric motor, capacitor bank, resistance furnace etc. The contactor is used to make and break the flow of current in the electric power driven circuit and carries the rated current under the closed condition. The current under switching conditions, i.e. during making or breaking, is higher than the rated current. The magnitude of this switching current depends upon the type of device being switched. For example, in induction motors the magnitude of the switching current is 12 times the rated current during making operation and 10 times the rated current during the breaking operation. In the capacitor switching duty contactor, the capacitor draws very high current of the magnitude of 180 - 200 times the rated current during switching operation, which is pretty high. Thus the making current is of the order of 180 - 200 times the rated current of capacitor during switching of capacitors.
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[0003] The contactor is basically composed of three different systems namely a contact system that carries current, an electromagnet system that generates the driving force to close the contact system for carrying current and an enclosure system comprising of housings moulded from engineering plastics.
[0004] The contactor system includes moving contacts situated in a contact carrier, called as contact bridge, which are movable under the action of electromagnetic force. The fixed contacts are secured in a plastic moulded housing. The contact bridge also carries contact springs to generate contact pressure thereby generating low resistance path for an electric current to flow.
[0005] In addition to the main contact, the contactor has an auxiliary contact system which is enclosed separately in an auxiliary contact block and engaged to main contact bridge of a contactor. As similar to the main contact system, the auxiliary contacts also comprise of moving contacts which are housed in the auxiliary bridge and fixed contacts that are secured in the housing of an auxiliary contact block. The auxiliary contact bridge is directly engaged with the main contact bridge so that the moving contacts of the auxiliary contacts also move, when the main contact bridge moves. The distance between the moving contact tip and fixed contact tip is known as "contact gap". The contact gap in the auxiliary contacts is kept lower than the main contact gap so that the auxiliary contacts will first close first to establish the current path before the main contacts close at a later instant.
[0006] For Capacitor switching duty, the capacitor during switching draws very high current, of the magnitude of 180 - 200 times the rated current, which is pretty high.
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Hence during switching of capacitors the making current is of the order of 180 - 200 times the rated current of capacitor.
[0007] In applications where the initial current drawn is very high like that in a capacitor switching contactor, the auxiliary contacts are connected in series with the current limiting resistors. Thus the auxiliary contacts close first when the contactor is being switched on (being closed) and the initial current in the circuit is limited to a lower value since the current limiting resistors are connected in series with auxiliary contacts. Then the main contacts close at a later instance. As the main contacts are in parallel to the auxiliary contacts and the resistance of the path containing the main contacts is less than that of the path containing auxiliary contacts, the current is diverted to the main contacts. The value of the current is also reduced to nearly rated current.
[0008] When the contactor is switched off (being opened) , the main contacts of the contactor open first to make the entire current to flow through the auxiliary contacts thereby enabling the auxiliary contacts to break the current. However the auxiliary contacts are not designed to break the high current. Further, the auxiliary contacts are burnt and the premature failures of the contacts are occurred due to the current conduction and heating generated during the arcing process.
[0009] But there are two issues that are generally faced in this kind of a system. Firstly as the contact gap of the auxiliary contacts is kept low during the touching of both the main contacts, there is a high tendency for the early make auxiliary contacts to bounce, due to lower contact gap thereby causing the circuit to make and break
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repeatedly at a high current. This is detrimental to the auxiliary contacts as these are not designed to break the currents of such high magnitude. This reduces the life of the contactor and hence poses a danger to the system.
[0010] Secondly at the time of breaking of the circuit by the main contacts, high voltage is generated across the main contacts. Since the main contacts are in parallel to the auxiliary contacts, this high voltage appears across the very low contact gaps of auxiliary contacts and increases the severity of arcing.
[0011] At present a delatching type contactor is used to overcome the above stated problems. However the delatching type contactor could not provide sufficient higher contact gap for early make auxiliary contacts after the delatching process, when the main contacts are closed, to prevent the arcing and damage to the contactor. The currently available systems include an electronic auxiliary contact and the operation of the contactor can be monitored. The auxiliary contact has a switch and a switch-activating element is connected to the contact bridge to activate the switch. However the auxiliary contacts can bounce due to lower contact gap when the main contacts touch to establish the high voltage circuit.
[0012] Thus none of the currently available contactor systems provide higher contact gap for the auxiliary contacts after the closing of the main contacts and restores back the lower contact gap for inserting the current limiting resistors in the circuit on de-energization of the contactor. At present none of the currently available contactor systems have different contact gaps for early make auxiliary contacts.
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[0013] Hence there is a need to provide a system and method to reduce bouncing of auxiliary contacts in the contactor system, when the main contacts are closed. Also there is a need to increase the contact gap in auxiliary contacts to reduce contact bounce in the contactors after the closing of the main contacts. Also there is a need to reduce the contact gap in auxiliary contact system for pre-insertion of resistors to limit the current. Also there is a need to develop a contactor system provided with two different contact gaps to prevent the bounce of the auxiliary contacts and to prevent damage to the contactor system.
C) OBJECT OF THE INVENTION
[0014] The primary object of the present invention is to develop a contact bounce control system for the contactors to reduce the bouncing of the auxiliary contacts to prevent damage to contactor system.
[0015] Another object of the present invention is to develop a contact bounce control system for the auxiliary contacts in the contactors to provide a higher contact gap for the auxiliary contacts after the closing of the main contacts.
[0016] Yet another object of the present invention is to develop a contact bounce control system for the auxiliary contacts in the auxiliary contacts to provide a lower contact gap for the auxiliary contacts for inserting the resistors to limit the current.
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[0017] Yet another object of the present invention is to develop a contact bounce control system for the auxiliary contacts to provide two different types of contact gaps for the auxiliary contacts to prevent the damage to the auxiliary contacts.
[0018] Yet another object of the present invention is to develop a contact bounce control system to provide two different types of contact gaps for the auxiliary contacts to prevent the severity of the arcing.
[0019] Yet another object of the present invention is to develop a contact bounce control system to provide two different types of contact gaps for the auxiliary contacts to prevent the damage to the auxiliary contacts thereby increasing the life of the contactor system.
[0020] Yet another object of the present invention is to develop a contact bounce control system for the auxiliary contacts to provide two different types of contact gaps to prevent the damage to the auxiliary contacts to prevent the damage to the equipments.
[0021] Yet another object of the present invention is to develop a contact bounce control system for the auxiliary contacts to provide a two different type of contact gaps to improve the performance of the contactors.
[0022] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
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D) SUMMARY OF THE INVENTION
[0023] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[0024] The various embodiments of the present invention provide a system and method to reduce the bouncing of the contacts to prevent the damage to the auxiliary contacts due to the arcing thereby improving the reliability and performance of the contactors. According to one embodiment of the present invention, a lever provided with two arms is pivotally mounted in the cover area of the housing of the contactor system. The lever is moved to provide a low value of auxiliary contact gap initially and a larger value of auxiliary contact gap at the time delatching and after the switching off of the contactor system. The lever is arranged above the auxiliary contact block provided with an upper portion and a lower portion. The lower portion of the auxiliary contact block is coupled to the main contactor bridge. A latch having two arms is pivotally mounted in the lower portion of the auxiliary contact block. The upper portion of the auxiliary bridge comprises auxiliary return spring and a slot to receive the latch to secure the position of the latch.
[0025] When the contactor coil is energized, the lower portion of the auxiliary bridge is moved downwards and the latch is released from the slot. The lower portion of the auxiliary contact block is moved downwards further while the upper portion of the auxiliary contact block is separated and moved upwardly due to the action of the auxiliary return springs. Due to the presence of the lever mechanism, the upper portion
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of the bridge moved further upwardly to provide a higher contact gap after delatching operation.
[0026] During the switch off condition, the lower portion of the auxiliary bridge is pushed up by the main contactor bridge and is moved upwardly. When the lower portion of the auxiliary bridge is moved upwardly, the lower portion of the auxiliary bridge pushes one arm of the lever so that the other arm of the lever is moved downwardly to push the upper portion of the auxiliary contact downwardly to reduce the contact gap thereby enabling the contactor to be ready for the next operation.
[0027] According to another embodiment of the present invention, a method is provided to reduce the bouncing of the auxiliary contacts to provide two different types of gaps for the contacts to prevent damage to the auxiliary contacts to improve the reliability, safety and the performance of the contactors. According to the method, the lower portion of the auxiliary bridge is moved downwards and the latch is released from the slot, when the contactor coil is energized. The lower portion of the auxiliary contact block is moved downwards further while the upper portion of the auxiliary contact block is separated and moved upwardly due to the action of the auxiliary return springs. Due to the presence of the lever mechanism, the upper portion of the bridge moved further upwardly to provide a higher contact gap after delatching operation.
[0028] During the switch off condition, the lower portion of the auxiliary bridge is pushed up by the main contactor bridge and is moved upwardly. When the lower portion of the auxiliary bridge is moved upwardly, the lower portion of the auxiliary
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bridge pushes one arm of the lever so that the other arm of the lever is moved downwardly to push the upper portion of the auxiliary contact downwardly to reduce the contact gap thereby enabling the contactor to be ready for the next operation.
[0029] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0031] FIGURE.l illustrates a partial sectional view of the contactor provided with a control system for reducing contact bounce of auxiliary contacts according to one embodiment of the present invention
[0032] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
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F) DETAILED DESCRIPTION OF THE INVENTION
[0033] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0034] The various embodiments of the invention provide a system and method to reduce the bouncing of the auxiliary contacts when the main contacts are closed and to provide two different types of contact gaps for the auxiliary contacts to improve the safety, reliability and the performance of the contactor system. The system and the method provide a low value of auxiliary contact gap initially and a larger value of auxiliary contact gap at the time delatching and after the switching off of the contactor system.
[0035] According to one embodiment of the present invention, the system is provided with a lever at upper side of the auxiliary contact block inside the housing. The lever is provided with two arms and is pivotally mounted in the cover area of the housing of the contactor system. The lever is moved to provide a low value of auxiliary contact gap initially and a larger value of auxiliary contact gap at the time delatching and after the switching off of the contactor system. The lever is arranged above the auxiliary contact block provided with an upper portion and a lower portion. The lower portion
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of the auxiliary contact block is coupled to the main contactor bridge. A latch having two arms is pivotally mounted in the lower portion of the auxiliary contact block. The upper portion of the auxiliary bridge comprises auxiliary return spring and a slot to receive the latch to secure the position of the latch.
[0036] When the contactor coil is energized, the lower portion of the auxiliary bridge is moved downwards and the latch is released from the slot. The lower portion of the auxiliary contact block is moved downwards further while the upper portion of the auxiliary contact block is separated and moved upwardly due to the action of the auxiliary return springs. Due to the presence of the lever mechanism, the upper portion of the bridge moved further upwardly to provide a higher contact gap after delatching operation.
[0037] During the switch off condition, the lower portion of the auxiliary bridge is pushed up by the main contactor bridge and is moved upwardly. When the lower portion of the auxiliary bridge is moved upwardly, the lower portion of the auxiliary bridge pushes one arm of the lever so that the other arm of the lever is moved downwardly to push the upper portion of the auxiliary contact downwardly to reduce the contact gap thereby enabling the contactor to be ready for the next operation.
[0038] According to another embodiment of the present invention, a method is provided to reduce the bouncing of the auxiliary contacts to provide two different types of gaps for the contacts to prevent damage to the auxiliary contacts to improve the reliability, safety and the performance of the contactors. According to the method, the lower portion of the auxiliary bridge is moved downwards and the latch is released
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from the slot, when the contactor coil is energized. The lower portion of the auxiliary contact block is moved downwards further while the upper portion of the auxiliary contact block is separated and moved upwardly due to the action of the auxiliary return springs. Due to the presence of the lever mechanism, the upper portion of the bridge moved further upwardly to provide a higher contact gap after delatching operation.
[0039] During the switch off condition, the lower portion of the auxiliary bridge is pushed up by the main contactor bridge and is moved upwardly. When the lower portion of the auxiliary bridge is moved upwardly, the lower portion of the auxiliary bridge pushes one arm of the lever so that the other arm of the lever is moved downwardly to push the upper portion of the auxiliary contact downwardly to reduce the contact gap thereby enabling the contactor to be ready for the next operation.
[0040] According to one embodiment of the present invention, a contactor system comprises of a main contact system including fixed and moving contacts. The moving contacts are located in the moving element called contact bridge. A moving electromagnet is coupled to the moving contact bridge. Further, the contactor comprises of an auxiliary contact system which is enclosed in an auxiliary contact block. The auxiliary contact comprises of moving contacts housed in the auxiliary bridge and the fixed contacts enclosed in the auxiliary contact block housing. Further, the auxiliary contact block is coupled to the main contact bridge. [0041] The auxiliary contact block has an upper portion and a lower portion. The upper portion and the lower portion are held together by a latch mounted pivotally in the lower portion of the auxiliary contact block. The upper portion houses the moving
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contacts and has plurality of returns springs to move the upper portion upwardly when the upper portion is separated from the lower portion. A slot is provided in the upper portion to receive the latch mounted in the lower portion to hold both the upper and the lower portion together. The lower portion of the auxiliary block is coupled to the main contact block.
[0042] A lever is pivotally mounted inside the cover portion of the contactor housing. The lever is arranged above the auxiliary contact block inside the housing to provide a lower contact gap initially and to provide a higher contact gap at the time of delatching and after the switch off operation.
[0043] When the contactor coil is energized, the lower portion of the auxiliary bridge is moved downwards and the latch is rotated and released from the slot as the latch is mated with a projection in the housing. The lower portion of the auxiliary contact block is moved downwards further while the upper portion of the auxiliary contact block is separated and moved upwardly due to the action of the auxiliary return springs. Due to the presence of the lever mechanism, the upper portion of the bridge moved further upwardly to provide a higher contact gap after delatching operation.
[0044] During the switch off condition, the lower portion of the auxiliary bridge is pushed up by the main contactor bridge and is moved upwardly. When the lower portion of the auxiliary bridge is moved upwardly, the lower portion of the auxiliary bridge pushes one arm of the lever so that the other arm of the lever is moved downwardly to push the upper portion of the auxiliary contact downwardly to reduce the contact gap thereby enabling the contactor to be ready for the next operation.
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[0045] Thus, the lever provides a higher contact gap for the auxiliary contacts to eliminate the bounce of the latch during the closing of main contacts. Further, the severity of arching due to high voltage across main contacts which appears across auxiliary contact gap is also reduced. The lever also reduces the contact gap in the auxiliary bridge so that the auxiliary contact is set ready for the next operation.
[0046] FIG. 1 illustrates a partial front sectional view of a contactor main contact housing coupled to auxiliary contact housing according to various embodiments of the invention. With respect to the FIG.l, a contactor system comprises of a main contact system including fixed and moving contacts. The moving contacts are located in the moving element called Contact Bridge 13. A moving electromagnet is coupled to the moving contact bridge 13. Further, the contactor comprises of an auxiliary contact system which is enclosed in an auxiliary contact block. The auxiliary contact comprises of moving contacts 9 housed in the auxiliary bridge and the fixed contacts enclosed in the auxiliary contact block housing 11. Further, the auxiliary contact block is coupled to the main contact bridge 13.
[0047] The auxiliary contact block has an upper portion 3 and a lower portion 10. The upper portion 3 and the lower portion 10 are held together by a latch 5 mounted pivotally in the lower portion 10 of the auxiliary contact block. The upper portion 3 houses the moving contacts 9 and has plurality of returns springs 15 to move the upper portion 3 upwardly when the upper portion 3 is separated from the lower portion 10. A slot 4 is provided in the upper portion 3 to receive the latch 5 mounted in the lower portion 10 to hold both the upper portion 3 and the lower portion 10
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together. The lower portion 10 of the auxiliary block is coupled to the main contact block.
[0048] A lever 18 is pivotally mounted inside the cover portion of the contactor housing. The lever 18 is arranged above the auxiliary contact block inside the housing to provide a lower contact gap initially and to provide a higher contact gap at the time of delatching and after the switch off operation.
[0049] When the contactor coil is energized, the lower portion 10 of the auxiliary bridge is moved downwards and the latch 5 is rotated and released from the slot 4 as the latch 5 is mated with a projection 6 in the housing. The lower portion 10 of the auxiliary contact block is moved downwards further while the upper portion 3 of the auxiliary contact block is separated and moved upwardly due to the action of the auxiliary return springs 15. Due to the presence of the lever mechanism, the upper portion 3 of the bridge moved further upwardly to provide a higher contact gap after delatching operation.
[0050] During the switch off condition, the lower portion 10 of the auxiliary bridge is pushed up by the main contactor bridge and is moved upwardly. When the lower portion 10 of the auxiliary bridge is moved upwardly, the lower portion 3 of the auxiliary bridge pushes one arm 8 of the lever 18so that the other arm 2 of the lever 18
is moved downwardly to push the upper portion 16 of the auxiliary contact downwardly to reduce the contact gap thereby enabling the contactor to be ready for the next operation.
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[0051] Thus, the lever provides a higher contact gap for the auxiliary contacts to eliminate the bounce of the latch during the closing of main contacts. Further, the severity of arching due to high voltage across main contacts which appears across auxiliary contact gap is also reduced. The lever also reduces the contact gap in the auxiliary bridge so that the auxiliary contact is set ready for the next operation.
G) ADVANTAGES OF THE INVENTION
[0052] Thus the various embodiments of the present invention provide a lever system to reduce the contact bounce in auxiliary contact in capacitor duty conductor. The contact gap between the auxiliary bridges is increased to reduce the contact bounce and arching. The contact gap is between the auxiliary bridges is decreased to pre-insert resistors to limit current.
[0053] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0054] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

Date: October 28, 2008. Place: Bangalore.

RAKESH PRABHU
Patent Attorney

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CLAIMS
What is claimed is:
1. A contact bounce control system for contactor including main contact
blocks and auxiliary contact blocks, the system comprising:
a lever pivotally mounted above the auxiliary contact blocks including lower portion and upper portion to provide two different types of contact gaps for the auxiliary contacts.
2. The system according to claim 1, wherein the upper portion of the auxiliary contact block is moved further upwardly due to the lever during the de-latching of the upper and the lower contacts to increase the contact gap.
3. The system according to claim 1, wherein the lever is pushed by the lower portion of the auxiliary contact block to push down the upper portion of the auxiliary contact block to reduce the contact gap.
4. The system according to claim 1, wherein the lever has two arms.
5. The system according to claim 1, wherein the lower portion of the auxiliary contact block pushes up one arm of the lever during the upward movement of the lower portion when the contactor is switched off, to push
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down another arm of the lever to move the upper contact block downwardly.
Dated this 28th of October, 2008
Rakesh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA
To,
The Controller of Patents,
The Patent office,
Mumbai
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