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 shock absorber mechanism 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, Vishal Bagade and Parag Khedkar, all of Crompton Greaves Ltd, Switchgear Division, Nashik, Maharashtra, India, all 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 following specification particularly describes the nature of this invention and the manner in which it is to be performed:
BACKGROUND OF THE INVENTION
Circuit breakers are used in electric transmission or distribution systems to protect i.e. isolate faulted sections under fault conditions and to switch on/off i.e. interrupt the flow of current under normal conditions, Switching on/off of the transmission or distribution systems is carried out by a set of fixed and moving contacts in the circuit breaker. In regular operation the fixed contacts and moving contacts are in eJectricaJ contact with each other and during a fault condition (commonly known as a trip event) are isolated from each other. The moving contacts are connected to a drive mechanism comprising a charging mechanism housed in an enclosure located below the contacts of the circuit breaker. As known in the art, the drive mechanism comprises a closing spring and tripping spring connected to the moving contacts of the circuit breaker and mounted in the enclosure and adapted to be releasably latched to a closing spring latch assembly and a tripping spring latch assembly, respectively through closing spring connecting rod, tripping spring connecting rod and mechanical linkages present therein. The closing and tripping springs are compressed or charged by the charging mechanism through the mechanical linkages. A hydraulic shock absorber is usually present within the tripping spring to absorb the impact of the release or expansion of the closing and tripping springs and thereby reducing the wear and tear of the mechanical linkages during the closing and opening of contacts.

In a trip event, the moving contacts are isolated and pulled away from the fixed contacts through a fixed distance by the release action of the trip spring. As the moving contacts get removed away from the fixed contacts an electric arc is caused between them and these electrical arcs over a period of time causes damage to the electrical contacts. A quick retraction of the moving contacts from the fixed contacts can minimize the electric arc and can prevent the damage caused to the electrical contacts over a period of time. The present invention provides shock absorber mechanism in a tripping spring that allows for a faster retraction of moving contacts from the fixed contacts.
OBJECTS OF THE INVENTION
An object of the invention is to provide a shock absorber mechanism within a tripping spring that allows for a faster retraction of the moving contacts from the fixed contacts,
DETAILED DESCRIPTION OF THE INVENTION
According to the invention a shock absorbing mechanism coaxially disposed within a tripping spring of a circuit breaker, to control lably effect an isolation of the moveable contact against a fixed contact of the circuit breaker on the occurrence of a trip event, the tripping spring being firmly secured between a moveable plate and a stationary plate, the moveable plate being coupled to the moveable contacts of the circuit breaker by a series of mechanical linkages, the mechanism comprises of an oblong slotted member having a pre-defined slot length being rigidly connected to the

moveable plate along a central axis of the tripping spring, wherein the oblong slotted member is subjected to an axial displacement along the central axis when the tripping spring retracts from a compressed state to a normal state, and a bar pin located within the oblong slotted member, wherein the bar pin is displaceable along the pre-defined slot length of the oblong slotted member, and a twin tube shock absorber including a piston and a cylinder firmly secured to the stationary plate, the piston being firmly secured to the bar pin and capable of being moveably guided within the cylinder. wherein a movement of the piston is effected subsequent to the axial displacement of the oblong slotted member through the pre-defined slot length, relative to the bar pin.
Preferably, in the shock absorbing mechanism, the tripping spring is triggerable by an actuating mechanism as is commonly known for retracting the trip spring from the compressed state to the expanded state.
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-Ib-lc is a sectional view of the shock absorbing mechanism of a circuit breaker in which the trip spring goes from a compressed state through an intermediary state to a normal state during a trip event in accordance with an embodiment of the present invention;
Figure 2a-2b-2c is a isometric view of a portion of the shock absorbing mechanism of a circuit breaker in which the trip spring goes from a compressed state through an

intermediary state to a normal state during a trip event in accordance with an embodiment of the present invention;
Referring to Figure la, the cross section of the shock absorber mechanism is shown comprising a trip spring 1 firmly disposed between a moveable plate 3 and a stationary plate 4. The trip spring 1 is shown in a compressed state. The moveable plate 3 has a central opening through which an oblong slotted member 5 is disposed axially downward therein. A bar pin 6 is disposed with the oblong slot of the oblong slotted member 5. and is capable of being displaced through the length of the oblong slot. A twin tube shock absorber 2 is firmly mounted on the stationary plate 4 that is further mounted firmly on the body of a circuit breaker (not shown). The twin tube shock absorber 2 operates in co-ordination with a piston 7. The piston 7 is connected to the bar pin 6 via a slot present at one end of the oblong slotted member 5. A change in the position of the moveable plate 3 with respect to the stationary plate 4 results in a proportional displacement of the oblong slotted member 5. Depending upon the current location of the bar pin 6 within the oblong slot, the oblong slotted member 5 travels through a distance through the oblong slot before effecting a motion to the piston 7 that is firmly secured to the bar pin 6.
Referring to Figure la, one can see that the trip spring 1 is in a fully compressed state and the bar pin 6 is located at the top position within the oblong slot represented as 'a'. It may also be observed that the one end of the piston 7 is secured to the bar pin at 'a! in the oblong slot and the other end of the piston 7 is at the bottom dead centre (bdc) within the cylinder in the twin tube shock absorber 2. As the trip spring 1 is released from the compressed state by an actuating mechanism (not

shown), the moveable plate 3 and therefore the oblong slotted member 6 is effected a displacement. Figure 2a represents an equivalent isometric view of the shock absorber mechanism of Figure la. In Figure 2a the trip spring 1 is not shown in order to bring clarity to the figure.
Figure lb and Figure 2b shows the shock absorbing mechanism in which the trip spring 1 retracts to an intermediary release position. In figure 1 b, one can observe that the oblong slotted member 5 is displaced by a finite distance as compared to Figure la. The bar pin 6 is displaced within the oblong slot to the position represented by 'b:, but however no displacement is extended to the piston 7. One may notice that the other end of the piston 7 continues to be at the bottom dead centre (bdc) within the cylinder o f the twin tube shock absorber 2.
In Figure lc and 2c, the trip spring 1 expands from the compressed state to the normal state. Further, the trip spring 1 extends a further displacement to the moveable plate 3 and this causes a further displacement to the oblong slotted member 5. The bar pin 6 that was already in a position 'b' cannot proceed further in the oblong slot. As can be seen, the piston 7 is displaced by a certain distance. As known well in the art, the twin tube shock absorber 2 resists any motion that is incident on the piston 7.
As can be appreciated by one skilled in the art, the shock absorbing action is delayed by introducing the oblong slotted member 5. The oblong slotted member inhibits the shock absorption by traveling from position 'a' to position 'b' unrestrictedly. Any displacement more than the oblong slotted length is transmitted to the piston 7 and this displacement is opposed by the twin tube shock absorber 2.

The moveable plate 3 is connected to the moving contacts of the circuit breaker by a series of mechanical linkages. On an occurrence of the trip event, the trip spring 1 releases from the compressed state to an expanded state. For an initial distance as decided by the length of the oblong slotted member 5 (i.e. the distance between 'b' and 'a') the release of the trip spring is not restricted by the twin tube shock absorber 2 and thereby delaying the shock absorbing action of the twin tube shock absorber 2. The expansion of the trip spring 1 results in the retraction of the moving contacts from the fixed contacts. For an initial displacement (as decided by the oblong slot length) the trip spring 1 is allowed for an unrestricted expansion and thereafter the opposing forces of the twin tube shock absorber 2 opposes further expansion of the trip spring 1. In this manner, shock absorber mechanism in a tripping spring 1 allows for a faster retraction of moving contacts from the fixed contacts for the initial distance. As the moving contacts retract away faster (for the initial displacement only) from the fixed contacts the formation of the electrical arc is minimized to an extent.
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 well 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 shock absorbing mechanism coaxiaJiy disposed within a tripping spring of a circuit breaker, to controllably effect an isolation of the moveable contact against a fixed contact of the circuit breaker on the occurrence of a trip event, the tripping spring being firmly secured between a moveable plate and a stationary plate, the moveable plate being coupled to the moveable contacts of the circuit breaker by a series of mechanical linkages, the mechanism comprising of:
an oblong slotted member having a pre-defined slot length being rigidly connected to the moveable plate along a central axis of the tripping spring, wherein the oblong slotted member is subjected to an axial displacement along the central axis when the tripping spring retracts from a compressed state to a normal state,
a bar pin located within the oblong slotted member, wherein the bar pin is displaceable along the pre-defined slot length of the oblong slotted member, and
a twin tube shock absorber including a piston and a cylinder firmly secured to the stationary plate ,
the piston being firmly secured to the bar pin and capable of being moveably guided within the cylinder, wherein a movement of the piston is effected subsequent to the axial displacement of the oblong slotted member through the pre-defined slot length, relative to the bar pin.

2. The shock absorbing mechanism of claim 1, wherein the tripping spring is triggerable by an actuating mechanism for retracting the trip spring from the compressed state to the expanded state.