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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: CO-AXIAL EXTENSION SPRINGS ARRANGEMENT
FOR CIRCUIT BREAKER MECHANISM
2. Applicant:
(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:

FIELD OF THE INVENTION
The present invention relates to a circuit breaker mechanism. More particularly. the invention is concerned about co-axial extension springs arrangement for circuit breaker mechanism.
BACKGROUND OF THE INVENTION
Circuit Breaker is a mechanical switching device, capable of making (i.e. switching ON), carrying and breaking (i.e. switching OFF) current under normal circuit conditions and more specifically breaking current (Tripping) during abnormal circuit conditions such as short-circuit. Quit often, the short circuit current is sensed automatically and the signal is given to the mechanism as a TRIP command which leads to opening of the contacts by means of mechanism. However, during normal ON-OFF and OFF-ON operation, input to mechanism is given through the rotation of knob by manual means. The rotation of knob leads to storing potential energy (spring charging) in the spring member while restricting the contact movement during the charging operation. At a specified instance the potential energy of spring is released in form of Kinetic energy through Mechanical Linkages leading rotation of the contacts at high velocity. Circuit breaker mechanisms use dead centre based Extension spring arrangements.
Conventionally the mechanisms used in Circuit Breakers use single extension spring per side of the mechanism as energy means. The velocity of the contact depends on the spring potential energy which again depends on the spring force. Higher spring force in the same space increases the potential energy which leads to increase the contact velocity.
US 6479774 discloses a circuit breaker operating mechanism comprises a movable handle yoke, a mechanism spring extending in tension from the handle yoke to a pin, and a lower link extending from the pin to a crank operatively connected to a contact arm bearing a movable contact. The crank is positionable in open and closed positions, being in an open position when the movable contact

is separated from an associated fixed contact and being in a closed position when the movable contact is mated to said associated fixed contact. The circuit breaker further comprises an interface formed on said crank and a blocking prop having a first surface that engages said interface, the first surface preventing the crank from rotating towards the closed position.
US 6590172 discloses Circuit breaker mechanism for a rotary contact system comprises a linkage assembly defined by a lower link and an upper link. The lower link is secured to the crank member by a connecting pin. The opposite end of the lower link is secured to the upper link by a spring spindle. The upper link in turn is connected to a cradle by an upper link pivot pin. A spring is secured between the spring spindle and a handle pin wherein the handle pin is disposed in a handle.
US 5369384 discloses the new breaker mechanism reliably opens the contact system and consists of fewer and technologically simpler individual parts. It is inserted between two symmetrical breaker plates held in a die cast housing, and in which a connecting piece is mounted. Two toggle levers are connected at a distance from one another by means of a connecting shaft engaged in crossbar cam slots. A toggle lever spring is engaged between the connecting piece and the connecting shaft. A bracing lever which can be driven by the connecting piece is friction locked in the breaker plates, and the toggle levers in the bracing lever. A latch lever and a latch holding the latter in the locked position are friction locked by means of a latch spring in recesses of the breaker plates.
The cited documents disclose circuit breaker mechanisms with single extension springs and these mechanisms use extension springs with hook or an external element is attached to the end of the springs. There is no disclosure from the prior art which suggests use of two parallel extension springs with hook. It has been found that an extra element is used at the end of springs such that springs work as extension springs. Such use of extra elements and its fixation cause problem of

assembling of the springs. Because of the extra element being fixed to the springs externally, sometimes during high stress condition in circuit breaker mechanism there are chances of failure of the extra element. Such failure in withstanding high stressed condition affects mechanical health of the springs which may create variation in spring working and as spring plays important role in mechanism it may affect on the working of the whole mechanism.
Thus, there is a need to overcome the problem of assembly of the springs for circuit breaker mechanism. The inventors have now developed Co-axial extension springs arrangement for circuit breaker mechanism having unique integrated hook profiles which would give higher spring force resulting in high circuit breaker contact velocity and ease of assembling the springs into the breaker mechanism, Further, elimination of the use of extra elements at the end of the springs for their engagement with the breaker mechanism has substantially reduced the complexity of assembling and has made the co-axial spring arrangement of the present invention cost effective.
OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the prior art.
Another object of the present invention is to provide a co-axiai extension springs arrangement for circuit breaker mechanism.
Yet, another object of the present invention is to provide high spring force for same deflection to result in high circuit breaker contact velocity.

SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a co-axial
extension spring arrangement for circuit breaker mechanism, said arrangement
comprising:
atleast one co-axial spring means comprising an outer spring means and an inner
spring means;
wherein said outer spring means having predetermined number of turns being less
than the number of turns of said inner spring means such that said outer spring
means covers a predetermined length of said inner spring means;
wherein said outer spring means comprises at its ends unique integrated hook
profile adapted to engage said spring means to plurality of pin means provided in
said circuit breaker mechanism;
wherein said inner spring means comprises at its ends unique integrated hook
profile adapted to engage said spring means to plurality of pin means provided in
said circuit breaker mechanism;
such that said unique hook profiles of the outer spring means and inner spring
means are placed substantially equidistant on the said pin means at both ends
thereby enabling both outer spring means and inner spring means to work
substantially parallel to each other thus providing high spring force for same
deflection resulting in high circuit breaker constant velocity.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The co-axial spring arrangement of present invention comprises knob, Co-axial extension spring means, and Rotor. The knob is the spring actuating device facilitating the ON-OFF operation of the circuit breaker. Input to mechanism is given through the rotation of Knob by manual means. The co-axial extension spring arrangement comprises at least one co-axial spring means comprising an outer spring means and an inner spring means, Upper pin means, and Lower pin means. The outer spring means have predetermined number of turns which is less

than the number of turns of the inner spring means. The outer spring means covers a predetermined length of the inner spring means.
One embodiment of the present invention describes the outer spring means having unique integrated hook profiles at its both ends adapted to engage the spring means to the pin means provided in the circuit breaker mechanism. The inner spring means also comprises unique integrated hook profiles at its both ends adapted to engage the spring means to the pin means. The unique hook profiles of the outer spring means and inner spring means are placed substantially equidistant on the said pin means at both ends which enables both outer spring means and inner spring means to work substantially parallel to each other. Such arrangement provides high spring force for same deflection resulting in high circuit breaker constant velocity. The upper and the lower pins are parts of the circuit breaker mechanism the springs are engaged to the pins on their both ends.
Another embodiment of the present invention describes a rotor housed in moving contact assembly of circuit breaker mechanism.
In another embodiment of the present invention the unique integrated hook profiles of the outer spring are substantially C-shaped and have symmetrical curvatures. The hook profiles of the outer springs are adapted to be engaged with the pins means having the symmetrical curvatures facing in the same direction. Further the hook profiles of the inner springs are substantially J-shaped and have symmetrical curvatures and are adapted to be engaged with the pins means having the symmetrical curvatures facing in the opposite direction.
One embodiment of the present invention describes the circuit breaker mechanism in its ON position. Input to the mechanism is given through the rotation of Knob by manual means. When knob is rotated the extension springs which are connected to upper and the lower pin means get extended up to dead centre. When springs are extended potential energy is stored in the springs. Stored potential

energy gets converted into kinetic energy and contact is rotated from ON to OFF position.
Similarly when breaker is in OFF condition to make breaker ON, knob is rotated in opposite direction. Again springs get extended up to dead centre and potential energy is stored in the springs which get converted to kinetic energy and contact gets rotated from OFF to ON condition.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates Isometric view of the Circuit Breaker cassette
Fig. 2 illustrates Isometric view of Mechanism in ON condition with mechanism
cassette hidden
Fig. 3 illustrates Isometric view of Mechanism in OFF condition
Fig. 4 illustrates Isometric view of Mechanism in TRIP condition
Fig. 5 illustrates assembly of co-axial extension springs
Fig. 6 illustrates exploded view of co-axial extension springs
Fig. 7 illustrates Force - Deflection characteristics for co-axial extension springs.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the spring arrangement comprising knob (1), Co-axial extension spring arrangement (2), and Rotor (3). Knob (1) is the spring actuating device facilitating the ON-OFF operation of the circuit breaker. The spring arrangement (2) comprises an outer spring means and an inner spring means (2b, 2a), Upper pin means (2c), and Lower pin means (2d) as shown in figures 5 and 6. The outer spring means (2b) as shown in figures 5 and 6 comprises unique integrated hook profiles (H2b) at its both ends. The inner spring means (2a) also comprises unique integrated hook profiles (H2a) at its both ends. The unique hook profiles (H2b, H2a)

of the outer spring means (2b) and inner spring means (2a) are placed substantially equidistant on the said pin means (2c,2d) at both ends. Rotor (3) is a part which is housed in moving contact assembly of circuit breaker mechanism.
As shown in the Fig.2 circuit breaker is in at ON position. Input to the mechanism is given through the rotation of Knob (I) by manual means. When knob (1) is rotated extension springs (2a, 2b) which are connected to upper pin means (2c) and lower pin means (2d) get extended up to dead centre. When springs are extended potential energy is stored in the springs. Stored potential energy gets converted into kinetic energy and contact is rotated from ON to OFF position.
When breaker is in OFF condition as shown in Fig. 3 to make breaker ON knob 1 is rotated in opposite direction. Again springs get extended up to dead centre and potential energy is stored in the springs which get converted to kinetic energy and contact gets rotated from OFF to ON condition.
Figure 7 shows the force - deflection characteristics of the spring-2a and spring-2b. It also shows the force - deflection characteristics of co-axial spring's arrangement. As co-axial springs work parallel to each other for the same deflection of the two springs combined force is more than the individual springs force. As force is increased more potential energy is stored in the springs. As this potential energy gets converted into kinetic energy more potential energy increases circuit breaker contact velocity.
ADVANTAGES OF THE INVENTION
1. Co-axial extension spring arrangement gives more spring force in less
space.
2. Higher spring force results in more circuit breaker contact velocity.
The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The

invention is not limited to the details cited above. The extension spring arrangement with knob, rotor and pins as stated do not limit the scope of the present invention. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.

We Claim
1. A co-axial extension spring arrangement for circuit breaker mechanism, said arrangement comprising:
atleast one co-axial spring means comprising an outer spring means and an inner spring means;
wherein said outer spring means having predetermined number of turns being less than the number of turns of said inner spring means such that said outer spring means covers a predetermined length of said inner spring means;
wherein said outer spring means comprises at its ends unique integrated hook profile adapted to engage said spring means to plurality of pin means provided in said circuit breaker mechanism;
wherein said inner spring means comprises at its ends unique integrated hook profile adapted to engage said spring means to plurality of pin means provided in said circuit breaker mechanism;
such that said unique hook profiles of the outer spring means and inner spring means are placed substantially equidistant on the said pin means at both ends thereby enabling both outer spring means and inner spring means to work substantially parallel to each other thus providing high spring force for same deflection resulting in high circuit breaker constant velocity.
2. Arrangement as claimed in claim 1, wherein said unique integrated hook profiles of the outer spring is substantially C-shaped.
3. Arrangement as claimed in claims 1 and 2, wherein said unique integrated hook profiles of the outer spring comprises symmetrical curvatures at both
ends.
4. Arrangement as claimed in claims 1 to 3, wherein said unique integrated
hook profiles of the outer spring is adapted to be engaged with the said

pins means having the symmetrical curvatures facing in the same direction.
5. Arrangement as claimed in claim 1, wherein said unique integrated hook profiles of the inner spring is substantially J-shaped.
6. Arrangement as claimed in claims 1 and 5, wherein said unique integrated hook profiles of the inner spring comprises symmetrical curvatures at both ends.
7. Arrangement as claimed in claims 1, 5 and 6, wherein said unique integrated hook profiles of the inner spring is adapted to be engaged with the said pins means having the symmetrical curvatures facing in the opposite direction.
8. Arrangement as claimed in claim I, wherein said pin means comprises a lo'wer pin.
9. Arrangement as claimed in claim 1, wherein said pin means comprises an upper pin.
10. A co-axial extension spring arrangement for circuit breaker mechanism as herein substantially described and illustrated with the accompanying drawings.