FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - LATCH SYSTEM FOR A CIRCUIT BREAKER MECHANISM
2. Applicant(s)

(a) NAME : LARSEN & TOUBRO 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
The present invention relates generally to Circuit breakers and more particularly, to a latch system for a circuit breaker mechanism for latching in normal operation and de-latching on occurrence of fault.
BACKGROUND AND THE PRIOR ART
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.
Molded Case Circuit Breakers (MCCB) is employed for current interruption. More particularly MCCBs are utilized to protect instruments from damage during adverse conditions prevailing during the operation of the circuit in which molded case circuit breaker is employed. During adverse conditions like short circuit, the current rises to an alarmingly high level. This high current may cause damage to the parts in the electrical system. Hence during these conditions the circuit has to be opened to protect the parts after the breaker.
A circuit breaker can be manually opened and closed, as well as automatically opened to protect conductors or equipment from damage caused by excessive heating due to over current in abnormal conditions such as overload or short-circuit.
The mechanism of the circuit breaker plays a vital role in determining the credibility of the breaker. A good mechanism should ensure quick and manually independent opening and closing of contact system.

Four operations are performed using the mechanism. They are ON, OFF, TRIP and RESET.
The first two operations are initiated by operator whereas the trip signal is given by the release which senses the abnormal conditions and gives TRIP command to the mechanism, so that the latter opens the circuit.
The operator has access to the mechanism through the knob which will be projected outwards from the housing of the breaker. The knob is placed over the fork of the operating mechanism. In conventional type MCCBs, breaker will feature three positions in the top cover near the knob to show ON, OFF and TRIP.
When the knob indicates ON it means the breaker is in ON condition i.e., the current path is closed. Similarly the position of the knob indicates the state of the circuit breaker.
According to standards, the top position of the knob (if the breaker is placed vertically) or the longest distant position of the knob away from the operator (if the breaker is mounted horizontally) should be marked as ON POSITION. The other extreme end in both cases is marked as the OFF POSITION. The knob will be somewhere, near the center (based on the design of the mechanism) to indicate the TRIP POSITION.
As said above, TRIP command is given automatically to the contacts by the release if it senses an abnormal condition like overload and short circuit. If the trip signal is given, the breaker opens the circuit and the knob goes to the trip position to show the operator that a fault has occurred in the system.

If the operator wants to ON the breaker, he cannot do it without resetting the breaker. This is to make sure that the operator shouldn't switch ON the breaker before clearing the fault.
Resetting of the breaker is done by moving the knob (fork) towards the OFF position from the TRIP position. This movement loads the mechanism spring and now it is possible for the operator to ON the breaker. All these mechanisms are called semiautomatic mechanisms since for ON and OFF operation, the knob of the breaker has to be taken from their respective ON or OFF positions to a position called dead center beyond which he mechanism becomes independent of the operator and completes the respective action by its own automatically.
Disadvantages of the existing systems;
• Intricate shape of the component in the latch and trip system, hence processing is complicated.
• More number of pins required for mounting the components.
• For latching the latch link in normal condition, some bend has to be provided (SIEMENS 3VT 160A MCCB).
• Assembly lead time is more.
• Separate pin is required for mounting the biasing spring.
Thus there is a need to provide a latch system for use in MCCB for latching the latch link in normal condition and also to delatch it, when a fault condition occurs.

The inventors have found that a unique latch profile and trip system can be provided which would be able to overcome the drawbacks of the prior art. The profile of the latch bracket is given in such a manner that avoids the usage of hinge pin for mounting on the side plate, without affecting its function. The inventors have designed the profiles of the latch bracket and trip plate such that they themselves act as stoppers on the side plate. The latch system provides the ease of assembling and also reduces the assembling lead time. Biasing springs are mounted directly with the component without using any pins.
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 a latch system for use in MCCB for latching the latch link in normal condition and also to de-latch it, when a fault condition occurs.
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
There is provided a latching system for a circuit breaker.
According to one embodiment of the present invention, there is provided latch system for a circuit breaker mechanism for latching in normal operation and delatching on

occurrence of fault, said system comprising atleast one latch link; atleast one latch bracket; atleast one trip plate; atleast one side plate; atleast one biasing spring; atleast one trip plate hinge pin; atleast one knob; atleast one fork; atleast one reset pin; wherein profile of said latch bracket and said trip plate adapted to act as stoppers on said side plate.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Figure 1 illustrates an isometric view of the mechanism with cassette.
Figure 2 illustrates an isometric view of the mechanism with latch and trip system.
Figure 3 illustrates an isometric view of the latch and trip system only.
Figure 4 (a) shows the latch bracket.
Figure 4 (b) shows the trip plate.
Figure 5 illustrates an isometric view of the latch and trip system in latching position.
Figure 6 illustrates an isometric view of the latch and trip system in tripping position.
Figure 7 illustrates an isometric view of the latch and trip system in resetting position.

DETAILED 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 with the explanations in the following detailed description.
Reference is first invited to Fig 1 where the isometric view of the mechanism with cassette is shown.
Figure 2 shows an isometric view of the mechanism with latch and trip system.
Figure 3 shows an isometric view of the latch and trip system only.
Figure 4 (a) shows the latch bracket.
Figure 4 (b) shows the trip plate.
Figure 5 shows an isometric view of the latch and trip system in latching position. The latch bracket (1) is held in position by the trip plate (2).
Figure 6 shows an isometric view of the latch and trip system in tripping position. The Trip plate (2) and latch bracket (1) themselves act as stoppers for rotation in their respective slots provided in the side plate (7).
Figure 7 shows an isometric view of the latch and trip system in resetting position.

The invented system is thus a latch system for a circuit breaker mechanism for latching in normal operation and de-latching on occurrence of fault.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention the profile of the latch bracket is given in such a manner that avoids the usage of hinge pin for mounting on the side plate, without affecting its function. The profiles of the latch bracket and trip plate are so designed that they themselves act as stoppers on the side plate. The latch system provides the ease of assembling and also reduces the assembling lead time. Biasing springs are mounted directly with the component without using any pins.
Latch system (Fig 2 & Fig 3) in the mechanism is used for latching the latch link in normal (On & Off) conditions and tripping when release gives signal during abnormal (Trip) condition. The Latch System comprises of Latch Bracket(l), Trip plate (2), Trip plate hinge pin (3), Biasing spring-1 (4) and Biasing Spring-2 (5) which are intended to perform its function.
LATCHED POSITION:
The term Latched refers to the condition where the latch link is locked by the latch system. At this condition the circuit breaker is only intended to perform either ON-OFF or OFF-ON operation. While the latch system is in this position, the latch bracket(l) is held in position by the trip plate(2) as shown in the Fig(5). The trip plate (2) is L-shaped and mounted in the trip plate hinge pin(3). The Biasing spring-2(5) is also mounted in the trip plate hinge pin (3) to give enough force for trip plate (2) to latch the latch bracket (1) in normal condition. The profile of latch bracket (1) which is made to mount in the side plate rotates to latch the latch link (6). The latch bracket (1) is substantially u-shaped having a hook profile (11) at one of its side edges which gets engaged into one of the slots provided in the side plate. The biasing spring-1(4)

is mounted on the side plate (7) is used to give enough force to latch bracket (I) to latch the latch link (6).
TRIPPING POSITION:
If a fault occurs, the signal from FSD is given at the bottom surface of trip plate (2) which makes the trip plate (2) to rotate in counter-clockwise direction, at this instant the biasing spring (2) starts to energize and which can be used to bring the trip plate (2) to its original position while resetting (4th operation). Trip plate(2) starts rotating, the latch bracket (1) is forced by the operating mechanism spring to rotate in counter-clockwise direction, at this instant the biasing spring-1 (4) starts energizing to give enough force to bring the latch bracket(2) to its original position while resetting (4th operation) .The Trip plate (2) and latch bracket (I) themselves act as stoppers for rotation in their respective slots provided in the side plate(7) as shown in the Fig (6).
RESETTING POSITION:
While resetting, the knob (8) mounted onto the fork (9) is moved manually from trip to off position. At this instant the position of latch bracket (1) and trip plate (2) is as shown in the Fig (5). While we reset, the fork (9) makes the latch link to rotate in counter-clockwise direction as the reset pin (10) is mounted in the latch link (6). The profile of latch link (6) is given in such a manner that the counter-clockwise rotation of latch link (6) makes the latch bracket (1) to rotate in counter-clockwise direction, at this time biasing spring-1 (4) is energized which makes the latch bracket (1) to rotate in clockwise direction. It is latched by the trip plate (2) as shown in the Fig (7).
Advantages:
1. Optimized and effective latching
2. Reliability in operation
3. Space occupied by the Latch is reduced

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. A latch system for a circuit breaker mechanism for latching in normal operation and delatching on occurrence of fault, said system comprising:
atleast one side plate;
atleast one latch bracket (1);
atleast one trip plate (2);
wherein said latch bracket and trip plate being mounted in the said side plate;
atleast one biasing spring (4);
atleast one biasing spring (5);
atleast one trip plate hinge pin (3);
wherein said latch bracket (1) is substantially u-shape and trip plate (2) is substantially L-shape, both having a provision to act as a stopper on said side plate and also provision for mounting said biasing spring (4) and biasing spring (5) in the said side plate and trip plate hinge pin (3) to give enough force at the time of operations.
2. System as claimed in claim 1 wherein said trip plate (2) is being offset on one side.
3. System as claimed in claiml wherein said trip plate (2) mounted on said trip plate hinge pin (3).

4. System as claim in claim 1 wherein said biasing spring (5) mounted on said trip plate hinge pin (3) adapted to provide force for said trip plate (2) to latch said latch bracket (1).
5. System as claimed in claim 1 further comprising a latch link (6).
6. System as claimed in claim 1 wherein said latch bracket comprising hook profile (11) adapted to movably engage said latch bracket with said side plate for latching said latch link (6).
7. System as claimed in claim 1 wherein said biasing spring (4) mounted on said side plate adapted to provide force to said latch bracket to latch said latch link.
8. System as claimed in claim 1 wherein said side plate further comprising a plurality of slots providing for rotation of said trip plate and said latch bracket.
9. System as claimed in claim 1 wherein said circuit breaker is substantially a moulded case circuit breaker.
10. A latch system for a circuit breaker mechanism for latching in normal operation and delatching on occurrence of fault as herein described and illustrated with reference to the accompanying drawings.