FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
LINK ARRANGEMENT FOR CONTACT LOCKING;
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
This invention relates to the field of circuit breakers and more particularly to the field of current limiting circuit breaker with contact locking arrangement.
BACKGROUND
The current limiting circuit breakers are aimed at mitigating fault current flow in a circuit by quickly reacting to such surge currents. They are based on the principal of electromagnetic repulsion between elements carrying current in opposite directions. The agility of a circuit breaker to respond to a fault current decides its efficacy in protecting downstream equipments.
In addition to the quickness of the circuit breaker to react to the fault currents factors like re-striking contribute to the effective time taken by the circuit breaker to break a circuit. Usually, contact re-striking occurs as a result of reduced electromagnetic force of repulsion between the contacts, as the distance between the contacts increases. The extended arc time thus created may harm the downstream equipments and also the circuit breaker itself. Arc extinguishing methods are thus used to suppress arc soon after its creation.
In order to overcome the problem of contact reclosure contact locking arrangements are designed. These contact locking arrangements aim to lock a moving contact in an open condition after the parting of the contact elements. After the fault clearance the circuit breaker may be switched to normal operating condition either manually or by an automatic means.
During the normal working of the circuit breaker the contact elements are required to be kept in constant contact by optimum contact pressure, allowing a continuous current path between the contact elements. An
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optimum value of contact pressure ensures that during normal condition at rated currents temperature rise of circuit breaker does not go high.
Generally, means for applying optimum contact pressure during normal working of the circuit breaker is integrated with contact locking arrangement, which acts during fault-open conditions. Inclusion of such assembly in the circuit breaker usually requires complex arrangements and intricate positioning of the elements. Further to effect working of two functionalities, such assemblies may need specially designed or profiled elements.
This causes complications in the design of the circuit breaker leading to increase in overall size and manufacturing cost associated. Additionally, this causes extra overhead during troubleshooting and replacement of parts.
Moreover, the position and arrangement of contact locking assembly usually exposes the assembly to ionized gases. Therefore, there is a need for a circuit breaker incorporating simple elements and their positioning, which is compact in size yet effective in working.
SUMMARY
The present invention provides a contact locking assembly for a circuit breaker. In one of the embodiments, the contact locking assembly is attached to a contact arm of the circuit breaker. A housing for the contact locking assembly provides for grooves enabling motion of biasing means. The housing and the contact locking assembly provide for a compact assembly which acts as the driving part of the contact arm it links to.
The contact locking assembly described can be applied to various types of circuit breakers such as for example single phase or multiphase circuit breaker. Futher this contact locking assembly can be implemented in single
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break/pole or multi-break/pole system. Also, the assembly may be applied to a single or multiple contact arms.
Additionally, the arrangement of the parts in the housing is such that exposure of the biasing means to harmful ionized gases is minimized. Further, using a strong material for the driving part may reduce the size of the entire circuit breaker. This makes possible accommodating other assemblies required in the circuit breaker.
In another embodiment two contact locking assemblies may be provided acting on a common contact arm. The assembly provided ensures reliable contact locking soon after contact arms part as a result of electromagnetic repulsion.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a circuit breaker as per one embodiment of the present invention.
Fig. 2. is the contact locking assembly as per one embodiment of the
present invention.
Fig.3. shows the circuit breaker in closed condition as per one embodiment
of the present invention.
Fig. 4. shows the circuit breaker in open condition as per one embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A contact locking assembly for circuit breaker is described. The contact locking assembly provides for current limiting characteristics and avoids re-striking of contacts of a circuit breaker by providing a reliable locking mechanism.
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The contact locking assembly described can be applied to various types of circuit breakers such as for example single phase or multiphase circuit breaker. Futher this contact locking assembly can be implemented in single break/pole or multi-break/pole system. Also, the assembly may be applied to a single or multiple contact arms.
Fig. 1 shows a circuit breaker comprising a contact locking assembly as per one embodiment of the invention. The contact locking assembly is covered in a housing (10). The housing along with the contact locking assembly forms the driving part (20) of the circuit breaker. The driving part (20) acts on the contact arm (30) during various conditions of the circuit breaker. Groove (22) may be provided in the housing (10) for allowing motion of inner locking assembly.
The contact arm (30) of the circuit breaker may be pivoted about a first axis (40). Accordingly, ends of the pivot may be hinged to the housing (10) allowing rotation of the contact arm in response to a force applied by the contact locking assembly. Contact element/s(32) may be provided at ends of the contact arm (30) for engaging with the other contact elements of other contact arm. The contact element/s of the contact arm to which the contact locking assembly is attached may engage to contact element/s of the other stationary or moving contact arm.
Fig. 2 shows the contact locking assembly embodied in a circuit breaker. The contact locking assembly comprises a biasing means (20) for generating an initial force (30) in a first direction (40). The biasing means may be provided using various forms of springs. In one of the embodiments of the invention a biasing means comprises a compression spring (24 )
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attached to a sliding block(26) for providing a hinge point(28). A link (50) is used to connect the hinge point (28) to the contact arm (10) providing for transfer of force from the biasing means to the contact arm (10). One end (54) of the link pivotally attaches to the biasing means at the hinge point (28). The other end (56) of the link pivots at the contact arm (10) allowing motion of the link in a first plane (65). The pivoting of the link to the contact arm may be done by providing oblong holes in the link(50). Transfer of force along the link causes motion of the contact arm in second plane(60).
In one of the embodiments of the invention the two biasing means each at either side of the second plane (60) are provided. The direction of initial forces (30 and 32) generated by each of the biasing means is towards the second plane (60). The links (50 and 52) are pivotally attached to the contact arm (10). The combined effect of the two biasing means act at the same contact arm(10). Alternatively, a single contact holding assembly may be provided. Contact can also be locked with one biasing means provided a proper support to the contact arm is given on the other side of the contact arm.
During the normal condition of the circuit breaker as shown in fig. 3, the forces( 30 and 32 initially produced by biasing means(20 and 22) causes to produce a corresponding forces (70 and 72) at the contact arm. A force results from the forces (70 and 72) applying an effective force(80) along the second plane and acts to keep the contact elements of the contact arm(10) in engagement with the corresponding other contact elements of the other arm. The optimum pressure on the contact arm of the circuit breaker
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ensures uninterrupted current flow thereby maintaining the temperature within intended limits.
During the fault conditions such as for example excessive current flows, the contact arm gets electromagnetically repelled from the other contact arm. As shown in fig. 4 this effect causes the contact arm (10) to rotate about the first axis (40) against the contact pressure provided by the biasing means during normal working. The initial forces (30 and 32 ) acting towards the second plane results in corresponding forces(70 and 72) to be produced at the contact arm. The initial force(30 and 32) during change of condition of circuit breaker continue to exert force towards second plane , but the effective force(80) direction changes by effect of electromagnetic repulsion force caused due to electromagnetic repulsion. The direction of effective force (80) thus reverses and is in a direction keeping contact arm in open condition. The effect of forces (70 and 72) is such that the contact arm(10) gets locked in the open condition, thereby avoiding occurrence of contact reclosure.
Additionally, the arrangement of the parts in the housing is such that exposure of the biasing means to harmful ionized gases is minimized. Further, using a strong material for the housing may reduce the size of the entire circuit breaker. This makes possible accommodating other assemblies required in the circuit breaker.
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WE CLAIM
1. A contact locking assembly for a circuit breaker comprising
a biasing means for applying initial force in first direction;
a link pivoted to move in first plane having one end pivotally attached to said biasing means and another end pivotally attached at a contact arm pivoted to move about a first axis in second plane such that the first plane is perpendicular to said second plane.
2. The contact locking assembly of claim 1 wherein, direction of effective force experienced at the contact arm due to said initial force exerted by the biasing means is perpendicular to said first direction.
3. The contact locking assembly of claim 1, further comprising a housing supporting movement of said biasing means.
4. The circuit breaker comprising a contact locking assembly of claim 1, wherein two of said contacts locking assemblies are positioned on either side of said first plane such that said another end of each link are pivoted to each other at the contact arm.
5. The contact locking assembly of claim 1, wherein a sliding block in biasing means pivots to said one end of the link.
6. The contact locking assembly of claim 1, wherein the said another end of the link is pivoted to the said contact arm between an end of the contact arm and said first axis.
7. The circuit breaker as in claim 4, wherein an other contact arm for engaging with said contact arm is stationary.
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8. The circuit breaker as in claim 4, wherein the other contact arm for
engaging with said contact arm is moving.
Dated this 31st day of March, 2006.

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ABSTRACT
A locking assembly for contact locking in a circuit breaker is provided. The locking assembly is provided with help of links and biasing means. In one embodiment the plane of motion of the parts of the locking assembly and the plane of motion of the contact arm are provided to be perpendicular to each other. In another embodiment two locking assemblies are arranged opposite to each other to act on a same contact arm.
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