FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A mechanical linkage in a circuit breaker
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Rajgopal Desale and Vishai Bagade of Crompton Greaves Ltd, Switchgear Division. Nasik, Maharashtra. India, both Indian Nationals.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
The present invention relates to mechanical linkage for a circuit breaker. More specifically, the present invention relates to a mechanical linkage that is disposed between the operating mechanism and a moveable shaft which further drives the moveable contacts of the circuit breaker.
BACKGROUND OF THE INVENTION
A contact set in a circuit breaker includes fixed and moveable contacts. The fixed contacts have a stationary position while the moveable contacts travel towards the fixed contacts or traveJ away from the fixed contacts, to close (make) or open (break or isoJate) the circuit. Circuit breakers have an operating mechanism that controls the travelling of the moveable contacts to perform the opening and closing of the contacts. As commonly known to one skilled in the art, the operating mechanism includes a closing spring that acts upon a series of mechanical linkages connected to the moveable contacts to travel during the opening and closing of the circuit. Additionally, the operating mechanism is designed to operate and control the velocity with which the moveable contacts travel towards the fixed contacts to complete the operation of closing and opening in a stipulated time,
Often due to aging of components and other malfunctions in the circuit breakers, the operating mechanism tends to deviate from the specifications for which they are designed. For e.g., in the closing operation the moveable contacts can over travel towards the fixed contacts with a greater momentum than desired, and this may result in a

collision between the contacts. The contact set in the circuit breaker is an expensive component and is usually difficult to replace,
It is desired that the contact set in a circuit breaker be protected from damage caused during the closing and opening actions. More particularly, it is desired that the contacts do not break over a period of time due to an over travel of the moveable contacts towards the fixed contacts and a subsequent collision between them.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a low cost and mechanical linkage in a circuit breaker to reduce the chances of a collision between the moveable contact and the fixed contact during a closing operation.
DETAILED DESCRIPTION OF THE INVENTION
According to an embodiment of the present invention there is provided a mechanical linkage securely engaged between a shaft and a link rod of a circuit breaker, the link rod being driven by an operating mechanism to cause an opening or closing operation in the circuit breaker, the shaft driving a main moveable contact of the circuit breaker away from a main fixed contact during the opening operation and towards the main fixed contacts during the closing operation, the mechanical linkage member comprising of a coupling means to elastically engage the shaft in the event of an over travel of the shaft during the closing operation; and a connecting member that operatively engages the coupling means and the link rod.

Preferably, the coupling means comprises of a cylindrical hollow member longitudinally extending between a first end and a second end, the first end being open and the second end sealed, the hollow member receiving a portion of the shaft therein from the first end; and
a spring operatively interposed there between the shaft and the second end of the cylindrical hollow member, whereby movement of the shaft is transferred through the spring, the spring allowing for a dampened movement of the main moveable contact towards the main fixed contact during the over travel.
Preferably, the connecting member is firmly secured to the second end of the cylindrical hollow member and is pivotally connected to the link rod.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Figure la is a front view that depicts a portion of a circuit breaker that includes a mechanical linkage and an operating mechanism according to an embodiment of the present invention.
Figure lb is the close-up front view of the mechanical linkage as illustrated in Figure I.
Figure 2 is an isometric view of the mechanical linkage according to the embodiment of the present invention.

Figure 3 is a sectional front view of the mechanical linkage according to the embodiment of the present invention.
Figure la-lb illustrate a mechanical linkage 100 according to an embodiment of the present invention and the manner in which it is connected to an operating mechanism 101 that controls the closing and opening of contacts of the circuit breaker. As is commonly known, the operating mechanism that effects the closing and opening of contacts generally includes a tripping coil and an opening coil that are connected to the moveable contacts through a series of mechanical linkages. A contraction and retraction of the closing coil and the tripping coil respectively causes a transfer of momentum though the series of mechanical linkages to the moveable shaft, that results in a shaft movement, thereby causing closing and opening of the contacts. As shown in Figure lb, one end of mechanical linkage 100 is connected to the operating mechanism 100 by means of a link rod 11. while the other end is connected to the moveable shaft 10. The contraction and retraction of the closing coil and the tripping coil result in a downward or an upward movement to the link rod 11. The downward movement of the link rod 11 results in the moveable contacts (not shown) moving away from the fixed contacts (not shown) and opening of the contacts; whereas the upward movement results in the moveable contacts moving towards the fixed contacts resulting in the closing of contacts. The moveable contacts travel a fixed distance that is pre-designed for the circuit breaker to close or open the electrical contacts. Over a period of time some components of the operating mechanism tend to wear out and this leads to the moveable contacts travelling a distance that is more than prescribed to close the contacts. Such a malfunction leads to a collision between the moveable contacts and the fixed contacts during the closing of the contacts. The mechanical linkage 100, as proposed overcomes this problem. The manner in which

mechanical linkage 100 functions to overcome the problem can be better understood in the following paragraphs that describe Figure 2 and Figure 3.
Referring to Figure 2, the mechanical linkage 100 according to the embodiment of the invention is shown having a cylindrical hollow member 5 that has a circular opening 6 at one end and other end sealed. The moveable shaft 10 (as in Figure 1) is inserted in to hollow recess 6 provided in the cylindrical hollow member 5 though the circular opening 6. The cylindrical hollow member 5 is securely welded to a circular plate 1. A spring (not shown) is disposed within the hollow recess 6 between the moveable shaft and the sealed end of the cylindrical hollow member 5. The circular plate 1 is secured to a connecting member 2 using nut and bolt arrangement 4. The connecting member 2 can be pivotally connected through the holes 3 to the link rod 11 as shown in Figure 1.
Referring to Figure 3, in which the cross section of the mechanical linkage 100 is shown, it may be noticed that the positioning of the spring 5 below the moveable shaft 10 that is disposed within the cylindrical hollow member 5 through the circular opening 6. During the closing operation the moveable shaft 10 travels a fixed distance with a controlled velocity and allows the moveable contacts to engage with the fixed contacts. However due to malfunctions in the operating mechanism the moveable shaft 10 may over travel and collide with the fixed contacts. In such an event, the spring 5 absorbs the impact of the collision and reduces the force of impact between the moveable contacts and the fixed contacts. Over travel of the moveable contacts is a common issue in circuit breakers , and using the mechanical linkage 100 the impact of the collision between the contacts can be significantly reduced. Thus, any damage to the electrical contacts (moveable and fixed) can be avoided.

Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as vveli as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We Claim:
1. A mechanical linkage securely engaged between a shaft and a link rod of a circuit
breaker, the link rod being driven by an operating mechanism to cause an opening or
closing operation in the circuit breaker, the shaft driving a main moveable contact of the
circuit breaker away from a main fixed contact during the opening operation and towards
the main fixed contacts during the closing operation, the mechanical linkage member
comprising of:
a coupling means to elastically engage the shaft in the event of an over travel of the shaft
during the closing operation; and
a connecting member that operatively engages the coupling means and the link rod.
2. The mechanical linkage of claim 1, wherein the coupling means comprises of:
a cylindrical hollow member longitudinally extending between a first end and a second
end, the first end being open and the second end sealed, the hollow member receiving a
portion of the shaft therein from the first end; and
a spring operatively interposed there between the shaft and the second end of the -
cylindrical hollow member, whereby movement of the shaft is transferred through the
spring, the spring allowing for a dampened movement of the main moveable contact
towards the main fixed contact during the over travel; and
wherein the connecting member is firmly secured to the second end of the cylindrical
hollow member and is pivotally connected to the link rod.