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THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: IMPROVED MECHANISM FOR CIRCUIT BREAKERS

2. Applicant(s):
(a) NAME : LARSEN & TOUBR0 LIMITED
(b) NATIONALITY : An Indian Company
(c) ADDRESS : L & T House, Ballard Estate, Mumbai 400 001, > State
of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to circuit breakers. More particularly the present invention relates to an improved mechanism for circuit breakers.
BACKGROUND AND THE PRIOR ART
A circuit breaker is a mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short circuit. Short circuit is an accidental or intentional connection, by a relatively low resistance or impedance, of two or more points in a circuit which are normally at different voltages. The main function of any electrical switching apparatus is to carry the rated current. Therefore the current carrying capacity of any circuit breaker is so important that if the unit fails to carry the rated current it will cause damage to itself as well as to the electrical equipment to which it is protecting.
Circuit breakers have three positions corresponding to the status of the separable contacts. For example, these positions would include an ON position, in which the separable contacts are closed, an OFF position in which the contacts are open and Trip position in which the contacts are tripped open.
These circuit breakers / switching devices are usually installed in an enclosure so as to have all the control and distribution network laid in form of metallic sheets and or cable wires inside and all operating means from outside so as to prevent access to high voltage and thus a potential hazard.
When a circuit breaker is in ON condition and a short circuit fault condition arises, high amount of fault current flows through the circuit and in response to this the circuit breaker tries to move the separable contacts to open position after sensing the fault condition through short circuit sensing mechanism (such as magnetic arrangement). The time taken from a fault condition initiation and the fault current being interrupted by circuit breaker determines the

let through energy / arc energy passed by the circuit breaker to the downstream equipments. A circuit breaker is said to be more efficient when the let through energy is minimal.
It is required for any circuit breaker to carry current up to its rated value. However, sometimes the circuit breakers are found tripped even when the electric system is healthy. It was observed that the circuit breaker trips due to vibration generated by tripping of circuit breaker installed nearby.
In case of control panel, when the control panel receives any undesired / unwanted / nuisance impact on external surface (i.e. Earth quake, vibration due to hitting etc) the vibrations generated due to these unwanted impacts gets transferred to the circuit breaker and in response to these vibrations circuit breaker trips. It was therefore necessary to device a circuit breaker which is immune to the vibrations generated due to unwanted impacts.
In circuit breakers, generally mechanism assembly is of 4/5 bar type where in main latch, lower plate, upper plate and drive-shaft constitutes four bar of the system whereas fork works as fifth bar of the system. Mechanism side plates (2nos) encompass the total mechanism assembly. Main latch is pivoted at one end on mechanism side plates. One end of upper link is pivoted on the other end of main latch. One end of lower link is pivoted on the other end of upper link. Drive shaft is placed below^mechanism plates and it is hinged such a way that the other end is free to rotate in available space. The other end of lower link is attached to this end of driveshaft which is free to rotate Fork is pivoted on mechanism plate so that the other end is free to rotate. One end of tension springs are attached toihe free end of fork and the other end are attached to the pins having upper link and lower link joined together. This pin is generally galled floating pin.
The mechanism has three stable states ON, OFF & Trip.
OPERATING PROCEDURE:
1. In tripped condition of circuit-breaker, the main latch is rotated at pivot point using fork till latching surface on main latch goes below latch bracket. Once the latching surface of main latch goes below the latch bracket, it holds the main latch in the rotated position. During this process the upper link is pushed below extending the tension spring with the help of floating pin, hence the spring attached to fork is

extended increasing the spring energy. As soon as the fork axis crosses the spring axis, toggling of mechanism takes place and fork moves to OFF condition keeping tension spring in energized condition. This position of mechanism is called as OFF condition.
2. From OFF condition, when the fork is rotated toward contacts side, as soon as the
fork axis crosses the spring axis the floating pin moves forward. During this the
tension spring is extended and then the spring energy is released and the lower link
pushes the drive shaft having contact system and contacts are closed. Since main latch
is held by latch bracket, it does not rotate. Upper link rotates with the help of pivot
*
point on main latch. This position of mechanism is called as ON condition.
3. In ON condition, when the protection system of circuit-breaker responds to overload
or short circuit condition it initiates signal to de-latch the mechanism and separate the
contact system. When the signals are received by the mechanism, latch bracket
releases the main latch. The main latch then rotates to the other side as the tension
spring releases the energy moving the main latch upward. This upward movement
pulls the upper link upward and hence the lower link also moves upwards, while
pulling the free to rotate point of drive shaft. In this way the contacts get separated.
There are various parameters which determine the performance of the mechanism of circuit breaker. One of them is ability to withstand the vibrations at installed locations which enables the circuit breaker to perform its intended functions at rated current. When the vibrations are received by the housing, these are transferred to mechanisms system and then to the latching zone. If the latching zone gets disturbed during operation
Some of the prior arts in the related field of invention are as follows:
US6727788 discloses a latch mechanism comprising a latch frame mounted in the circuit breaker housing. A latch roller is mounted on the cradle. A latch member is configured to selectively engage the latch roller and the latch member is rotatably coupled to the latch frame. A latch shaft assembly is rotatably mounted in the latch frame and selectively engaged by the latch member. Upon rotation of the latch shaft assembly, the latch shaft assembly will disengage from the latch member and cause the movable contact to move.

US2005/0140479 Al discloses a latching mechanism that prevents circuit breaker nuisance tripping due to shock or vibration forces without impeding the intended circuit trip function.
US6552637 teaches a mechanism for operating a plurality of circuit interruption mechanisms of a circuit breaker, the mechanism applies a uniform force to the circuit interruption mechanisms. The mechanism applies a force to an elongated member for manipulating the circuit interruption mechanisms. The mechanism applies a force to the elongated member at a first position and a second position, the first position and the second position being intermediate to a center of the elongated member and the plurality of circuit interruption mechanisms.
US 5444423 teaches a latch mechanism for a circuit breaker comprises a pair of longitudinal legs, a lateral section bridging the pair of longitudinal legs, and a longitudinal section extending from the lateral section in an opposite direction relative to the pair of legs.- The lateral section includes a lower bearing surface for releasably engaging a cradle of the circuit breaker. The lower bearing surface includes a coined radius for facilitating engagement and disengagement of the cradle. The longitudinal section includes a protrusion for supporting a latch spring. The latch mechanism is manufactured in •& single stamping operation, during which the protrusion is formed by cold extrusion.
US5844188 teaches a trip mechanism for a circuit breaker. The mechanism relates to a construction for a contact arm and its arrangement with a spring pin whereby the direction of force applied by the swinging-open contact arm to the spring pin is controlled to cause the force to be applied along a particular direction that changes as the contact arm acts on the spring pin to collapse the toggle mechanism.
US2008/0122563 Al teaches an instantaneous trip mechanism for a mould cased circuit breaker which is capable of adjusting a trip current sensitivity using a simple mechanism and of fabricating a reliable mould cased circuit breaker supplying a constant trip current sensitivity according to products.

In conventional circuit breaker, mechanism components are arranged to achieve the intended function. In ON & OFF condition of circuit breaker, the latching overlap between latch bracket and trip bracket plays a crucial role. In the latching zone of the mechanism it can be seen that the net resultant force transferred on the trip bracket by latch bracket is passing above the centre of the trip bracket. The net force will then exert torque on the trip bracket in de-latching direction by arrow rotating in clockwise direction. To avoid disengagement due to this force, an additional spring is attached to the trip bracket which holds it in the desired position / location. This additional spring used for trip bracket in turn increases the force required to rotate the trip bracket to disengage the latching overlap and trip the circuit breaker. The trip force governs the design of the bimetal used for thermal overload protection. During thermal overload this bimetal gets deflected by the heat generated due to fault current. More the force required to rotate the trip bracket bigger is the size of the bimetal and hence more is the cost of the bimetal and in turn more is the cost of circuit breaker.
Therefore there is a need to overcome the above cited disadvantages of the prior arts. The present invention therefore provides an improved mechanism for circuit breakers. It relates to the profile engagement of latch bracket and trip bracket of mechanism of circuit breaker, which governs the ability to withstand the vibrations.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Another object of the present invention is to provide an improved mechanism for circuit breakers.
Other object of the present invention is to provide an arrangement that is adapted to withstand vibrations.

Yet other object of the present invention is to reduce the tripping force so as to reduce the size of bimetal.
These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a'prelude to a more detailed description of the invention presented later.
There is provided an improved mechanism for circuit breakers.
According to one embodiment of the present invention, there is provided an improved mechanism for circuit breakers comprising atleast one main latch (1) pivoted to a mechanism plate (7); atleast one upper link (2) pivoted to said main latch (1); atleast one lower link (6) pivoted to said upper link (2); atleast one drive shaft (12) placed below said mechanism plate (7), said drive shaft hinged and adapted to rotate; atleast one tension spring means (13) having one end attached to said fork and other end attached to a pin (11); atleast one resetting pin (3) attached to a fork (4) and adapted to rotate during resetting, said fork having one end pivoted on said mechanism plate (7); atleast one trip bracket having a flange bend, said bend having substantially round surface providing resting surface for a latch bracket, wherein arrangement of said trip plate and said latch bracket is adapted to withstand vibrations.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the

present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction w?th the explanations in the following detailed description.
Fig 1 illustrates the front view of the mechanism in wireframe
Figure 2 illustrates the front view of the mechanism with hidden lines
Figure 3 illustrates the front view of the force resolution of mechanism with hidden lines
Figure 4 illustrates the enlarged view of the force resolution of mechanism with hidden lines
Figure 5 illustrates0 front view of Trip bracket with enlarged view of circular profile.
Figure 6 illustrates the dismantled view of mechanism
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Accordingly in the present invention profile engagement of latch bracket and trip bracket of mechanism of circuit breaker which governs the ability to withstand the vibrations is provided. This enhances circuit breaker to 'bear the unwanted vibration & carries current without any unwanted interruption.
Engagement profile of Latch bracket & Trip bracket disclosed herein is shown in Figure 1 to 6. Please refer Figure 6 for dismantled view of complete mechanism. As shown in the Figure, it consists of one end of main latch 1 which is pivoted to mechanism plates 7. One end of upper link 2 is pivoted on the other end of main latch 1. One end of lower link 6 is pivoted on the other end of upper link 2. Drive shaft 12 is placed below mechanism plates 7 and it is

hinged such a way that the other end is free to rotate in available space. The other end of lower link 6 is attached to this end of driveshaft which is free to rotate Resetting pin 3 is attached to fork 4 such a way that it is free to rotate while resetting. Fork 4 is pivoted on mechanism plate 7 so that the other end is free to rotate. One end of tension springs 13 are attached to the free end of fork and the other end are attached to a pin 11 having upper link and lower link joined together. This pin is generally called as a floating pin 11.
The present invention relates to the of profile engagement of latch bracket and trip bracket of. mechanism of circuit breaker, which governs the ability to withstand the vibrations. As explained earlier, in ON or OFF condition of circuit breaker, the latch bracket rests on the trip bracket (Please refer Figure 3 to 7). Trip bracket has a flange bend having circular surface. This circular surface is created by removing material from that particular surface using fixtures keeping pivot point of trip bracket as centre of the circular profile. Latch bracket and trip bracket are assembled in such a way that the flat surface of latch bracket rests on the round surfaces of trip bracket. Force exerted on a circular surface passes through normal to the tangent drawn at the point of intersection. With the same principle, when a flat surface of latch bracket rests on a circular surface of trip bracket, the force transferred by flat surface to circular surface passes through the normal to the tangent drawn at the point of intersection i.e. the force is normal to the flat surface of latch bracket at the point of intersection with circular surface of trip bracket. This net force will then exert torque on the trip bracket in anti de-latching direction as shown in the Figure 5 & 6 by arrow rotating in anti-clockwise direction. So to keep the mechanism in stable ON or OFF condition, spring with high load value is not required. Spring value should be good enough to move the weight of the trip bracket during resetting process. This reduces the trip force required to rotate the trip bracket and trip the circuit breaker. Since the trip force governs the design of the bimetal used for thermal overload protection, less the force required to rotate the trip bracket smaller is the size of the bimetal and hence the cost of the bimetal is comparatively less which in turn reduces the cost of circuit breaker.
The present invention relates to the of profile engagement of latch bracket and trip bracket of mechanism of circuit breaker, which governs the ability to withstand the vibrations. No nuisance tripping of circuit breaker leads to increased life span of the circuit breaker.

Following are the features and benefits of this invention.
1. The latching engagement gets the mechanism the ability to withstand vibrations.
2. Another benefit is the trip force required to trip the mechanism is least as additional load of trip bracket spring is not required to avoid disengagement of latch bracket and trip bracket.
3. Additional benefit is the simple & cost effective design of bimetal as the trip force is minimal.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM:
1. An improved mechanism for circuit breakers comprising:
atleast one main latch (1) pivoted to a mechanism plate (7);
atleast one upper link (2) pivoted to said main latch (1);
atleast one lower link (6) pivoted to said upper link (2);
atleast one drive shaft (12) placed below said mechanism plate (7), said drive shaft hinged and adapted to rotate;
atleast one tension spring means (13) having one end attached to said fork and other end attached to a pin (11);
atleast one resetting pin (3) attached to a fork (4) and adapted to rotate during resetting, said fork having one end pivoted on said mechariism plate (7);
atleast one trip bracket having a flange bend, said bend having substantially round surface providing resting surface for a latch bracket, wherein arrangement of said trip plate and said latch bracket is adapted to withstand vibrations.
2. Mechanism as claimed in claim 1 wherein said pin having upper and lower link joint together.
3. Mechanism as claimed 1 and 2 wherein said pin is substantially a floating pin.
4. Mechanism as claimed 1 wherein said spring means adapted to move said trip bracket during resetting thereby reducing the trip force.

5. An improved mechanism for circuit breakers as herein described and illustrated with reference to accompanying drawings.