FORM 2
THE PATENT ACT 1970
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"An immobility phase improvement mechanism for circuit breakers"
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: Larsen & Toubro Limited
L&T House. Ballard Estate.
P.O Box No. 278, Mumbai 400001. INDIA.
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification
particularly describes the invention and the manner in which it is to be performed.

An immobility phase improvement mechanism for circuit breakers
Field of invention
The present invention relates to circuit breakers, and more particularly to a mechanism adapted for improving contact opening velocity of the circuit breakers under fault conditions.
Background of the invention
Circuit breakers are well-known for their function of providing rapid and reliable protection of electrical systems from overload and/or short-circuit. The circuit breakers normally include protection modules such as an overload protection module and a short-circuit protection module. Generally, the overload protection modules consist of bimetallic elements as an actuator and the shot-circuit protection module consist of coil and armature as an actuator. These modules along with operating mechanism are suitably arranged in the electrical enclosure to assist in making and breaking of the circuit as desired. The trip point of these operating mechanisms is suitably placed such that the trip signal from over current sensing modules is given to the mechanism for opening the contacts, thereby interrupting the circuit during abnormal conditions.
In these circuit breakers, the contacts are opened when the abnormal condition is sensed. During opening of the contacts, an arc is developed between the contacts which need to be quenched as fast as possible for successful breaking of the circuit and to protect downstream electrical apparatuses. The breaking phenomenon includes three different phases of arc namely an immobility phase, a running phase and a splitting phase. The total time required for quenching can be reduced by improving one or all of the above phases.

Attempts are seen in the art towards improving immobility time phase of the arc by optimizing the factors such as contact opening velocity, contact material property, flux density on arc elements, rate of rise of current and the like. The contact opening velocity of the modular devices is mainly contributed by the operating mechanism of the circuit breakers. The velocity attained by the prior art mechanisms is almost limited in practical instances due to mechanical constraints.
Generally, the prior art circuit breakers have simultaneous contact opening and mechanism operations. Particularly, in case of miniature circuit breaker, this is done by transfer of mechanical energy of moving magnetic core directly to the moving contact which opens the contact to certain distance depending upon the stroke of magnetic release. Once the mechanism delay is over mechanism takes away the contact from that position to its full opening with its intended velocity. However, the main drawback of this system is that opening of moving contact is not continuous. In addition, the moving contact opens at mechanism velocity after mechanism delay. Thus, the immobility time increases due to reduced rate of rise in current in response to reduction of the current rating of breakers. Accordingly, the gap attained between the contacts by means of magnetic release may not remain sufficient enough to push the arc into mobile state. In addition, there is possibility of standing arc between the open contacts until the mechanism operates that eventually erodes contact material depending on mechanism delay and rate of rise in current.
Accordingly, there exists a need of an immobility phase improvement mechanism for circuit breakers that overcomes all the drawbacks of the prior art.
Objects of the invention
An object of the present invention is to provide an immobility phase improvement mechanism that improves an operating mechanism velocity of a circuit breaker.

Another object of the present invention is to provide an immobility phase improvement mechanism that maintains continuous movement of contacts of the circuit breaker under fault conditions.
Further object of the present invention is to provide an immobility phase improvement mechanism that improves an immobility period of contacts of the circuit breaker under fault conditions.
Yet another object of the present invention is to provide an immobility phase improvement mechanism that reduces erosion between contacts of the circuit breaker under fault conditions.
Summary of the invention
Accordingly, the present invention provides an immobility phase improvement mechanism adapted for improving immobility phase of a circuit breaker during an electrical fault that comprises a housing including a contact link and a trip link. The contact link hingedly mounts on the housing. The trip link positions above the contact link. The trip link hingedly connects to a moving contact. The housing includes a fixed contact positioned therein. The contact link includes a first surface, a second surface, a third surface and a fourth surface. The contact link includes a first undercut and a second undercut. The trip link includes a first surface, a second surface, a third surface and a fourth surface. The trip link includes a first projected part, a second projected part and a third projected part. The immobility phase improvement mechanism includes a main spring having a first arm and a second arm such that the first arm connects to the moving contact and the second arm connects to the housing. The main spring exerts a contact making force between the fixed contact and the moving contact in an ON position of the moving contact thereby forming a four bar linkage mechanism, The main spring exerts a force on the moving contact and the contact link in an OFF position of the moving contact. The immobility phase improvement mechanism

includes a helical expansion spring connecting between the contact link and the trip link. The helical expansion spring retains the trip link in a predefined position. The helical expansion spring exerts a Force for rotating the trip link by a predefined angle in an anticlockwise direction for de-latching the four bar linkage mechanism.
Brief description of the drawings
FIG. I is a front view of an immobility phase improvement mechanism of a circuit breaker constructed in accordance with the present invention in an OFF position:
FIG. 2 is a front view of the immobility phase improvement mechanism of the circuit breaker of FIG. 1 in an ON position:
FIG. 3 is perspective view of a contact link of the immobility phase improvement mechanism of the circuit breaker of FIG. 1:
FIG. 4 is another perspective view of the contact link of the immobility phase improvement mechanism of the circuit breaker of FIG. I:
FIG. 5 is a perspective view of a trip link of the immobility phase improvement mechanism of the circuit breaker of FIG. 1;
FIG. 6 is another perspective view of the trip link the immobility phase improvement mechanism of the circuit breaker of FIG. 1: and
FIG. 7 is a front view showing an assembly of the contact link and the trip link of the immobility phase improvement mechanism of the circuit breaker of FIG. 1.
Detailed description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art. techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
Accordingly, the presem invention provides an immobility phase improvement mechanism of a circuit breaker that includes a contact iink and a trip link assembled within a body of the circuit breaker to improve an operating mechanism velocity and immobility period of contacts of the circuit thereby maintaining continuous movement of contacts in addition to reducing erosion between contacts of the circuit breaker under fault conditions.
in accordance with a preferred embodiment of the present invention, a surface part of a body of the immobility phase improvement mechanism is referred and abbreviated as 'S' hereinafter. In addition, a projected part of the body of the immobility phase improvement mechanism is referred and abbreviated as lP' hereinafter. Also, a cut in the body of the immobility phase improvement mechanism is referred and abbreviated as 'C' hereinafter.
Referring now to FIGS. 1 and 2. an immobility phase improvement mechanism (100) of a circuit breaker constructed in accordance with the present invention is illustrated. The immobility phase improvement mechanism (100) is enclosed within a housing (I) that preferably includes a contact link (2) and a trip link (3). The contact link (2) is suitably hinged on the housing 1 and the trip link (3) is preferably placed above the contact link (2) in this one embodiment. A moving contact (4) is hinged to the contact link (2) as shown. The moving contact (4) is of low resistivity materia!, such as copper in this one preferred embodiment. The immobility phase improvement mechanism (100) includes a main spring (5). The main spring (5) is having two arms such thai a first arm is connected to the moving contact (4) and second arm is connected to the housing (I). The immobility phase improvement mechanism (100) includes a helical expansion

spring (6) that is connected between the contact link (2) and the trip link (3). The helical expansion spring (6) is adapted to retain the trip link (3) in a predefined position. The immobility phase improvement mechanism (100) is adapted to be operated from an OFF position (see FIG. I) to an ON position (see FIG. 2) thereby forming a four bar linkage mechanism. In the ON position, the moving contact (4) establishes the electrical circuit by making contact with a fixed contact (7). The main spring (5) is configured to exert the contact making force between the moving contact (4) and the fixed contact (7) on forming the complete four bar linkage mechanism. The four bar linkage mechanism is adapted to be weakened when the trip link (3) is rotated in anticlockwise direction against the force exerted by the helical expansion spring (6) wherein the four bar linkage mechanism is not maintained after a predefined degree of rotation and is said to be de-latched. In the OFF position, the main spring (5) exerts a force on the moving contact (4) and the contact link (2) with a norma! velocity of the mechanism to bring back the moving contact (4) to the OFF position.
Referring to FIGS. 3-6, the contact link (2) includes a first surface (2SI). a second surface (2S2). a third surface (2S3) and a fourth surface (2S4). The trip link (3) includes a first surface (3S1). a second surface (3S2). a third surface (3S3) and a fourth surface (3S4). The trip link (3) includes a first projected pan (3PI). a second projected pan (3P2). and a third projected part (3P3). The contact link (2) includes a first undercut (2C1) and a second undercut (2C2).
The first projected part (3PI) and the second projected part (3P2) are respectively engaged with the first undercut (2CI) and the second undercut (2C2). The first surface (2SI) and the third surface (2S3) respectively engage with the first surface (3S1) and the third surface (3S3) of the trip link (3) when the spring (6) connects between the contact link (2) and the trip link (3). The spring (6) is exerts a force on the trip link (3) when the surfaces (2S1. 2S3. 3Sl and 3S3) meet each other respectively under normal working condition of the immobility phase improvement mechanism (100).

As shown in FIG. 7. the first projected part (31M) and the second projected part (3P2). the first undercut (2C1) and the second undercut (2C2) are designed intentionally to maintain an angle (a) between the surfaces (2S2. 2S4) of the contact link (2) and the surfaces (3S2. 3S4) of the trip link (3) respectively when it is retained in position by the spring (6). The angle (a) is configured to be slightly higher than the maximum degree of rotation required to completely de-latch the immobility phase improvement mechanism (100). The projected part (3P3) of trip link (3). as shown in FIG. 5. acts as a trip point for receiving a signal from an electromagnetic actuator. The electromagnetic actuator in this one particular embodiment has a movable core and a coil wound over a fixed core. The electromagnetic actuator senses short circuit current and gives an output in terms of mechanical energy by movement of the moving core that in turn rotates the trip link (3) in an anticlockwise direction by exerting force on the projected part (3P3). It is understood here that the stroke delivered by the moving core of the electromagnetic actuator is intentionally kept higher than the required rotation angle (a) to de-latch the immobility phase improvement mechanism (100).
Referring to FIGS. 1-7. in operation, the electromagnetic actuator senses fault in case of fault conditions and delivers mechanical energy for rotating the trip link (3) thereby opposing the retaining spring (6). Once the trip link (3) is rotated to a certain angle above which the four bar linkage mechanism cannot be maintained then the immobility phase improvement mechanism (100) gets de-latched. Further on rotation, the rotating trip link (3) facilitates engagement between the surfaces (2S2). (2S4) of the contact link (2) and the surfaces (3S2). (3S4) of the trip link (3). In this position, the entire mechanical energy delivered by the moving core is added as a negative torque to the contact link (2) through the mated surfaces (2S2), (2S4). (3S2) and (3S4) while retaining the contact in the closed condition. Accordingly, there is a delay for the components of the immobility phase improvement mechanism (100) to react and break the linkage mechanism. The delay is usually in order of fractions of millisecond. After the said delay, the main

spring (5) delivering contact pressure turns to apply the negative torque on contact link (2) to move the moving contact (4) to the open position for breaking the circuit. The net negative torque in the contact link (2) is contributed by the main spring (5) and the mechanical energy facilitated by the electromagnetic actuator. Due to high torque acting on the contact link (2). the moving contact (4) opens at a higher velocity. On further rotation of trip link (3). a way for reduction in air gap length of electromagnetic actuator is generated which further increases the torque delivered to the contact link. (2), The said torque delivered to contact link (2) is ramped up until the electromagnetic actuator attains its full stroke after which the velocity of contacts slowly decays as there is very low opposition for motion. In such situation a wall projecting from housing (IP!) stops further motion of the moving contact (4) after reaching a fully opened state. Accordingly, the contact is opened with a higher velocity during abnormal conditions thereby improving immobility time and reducing contact erosion.
Advantages of the present invention arc:
1. The immobility phase improvement mechanism (100) improves contact opening velocity by using (he mechanical energy of the electromagnetic actuator.
2. The surface of the projected part (3PI. 3P2) mates with the undercut (2C1, 2C2) which advantageously transfers the mechanical energy to the contact link as a negative torque.
3. The immobility phase improvement mechanism (100) provides substantially higher contact opening velocity only during short circuit conditions.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.

The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We Claim:
1. An immobility phase improvement mechanism adapted for improving
immobility phase of a circuit breaker during an electrical fault, the immobility
phase improvement mechanism comprising:
a housing including a contact link and a (rip link, the contact link hingedly mounting on the housing, the trip link positioning above the contact link, the trip link having a moving contact hingedly connecting thereto, the housing including a fixed contact positioning therein, the contact link having a first surface, a second surface, a third surface and a fourth surface, the contact link having a first undercut and a second undercut, the trip link having a first surface, a second surface, a third surface and a fourth surface, the trip link having a first projected part, a second projected part and a third projected part:
a main spring having a first arm and a second arm. the first arm connecting to the moving contact, the second arm connecting to the housing, the main spring exerting a contact making force between the fixed contact and the moving contact in an ON position of the moving contact thereby forming a four bar linkage mechanism, the main spring exerting a force on the moving contact and the contact link in an Off position of the moving contact: and
a helical expansion spring connecting between the contact link and the trip
link, the helical expansion spring retaining the trip link in a predefined position.
- the helical expansion spring exerting a force for rotating the trip link by a
predefined angle in an anticlockwise direction for de-hitching the four bar linkage
mechanism.
2. The immobility phase improvement mechanism as claimed in claim 1,
wherein the helical spring facilitates the first projected part and the second
projected part to be respectively engaged with the first undercut and the second
undercut thereby maintaining the predefined angle.

3. The immobility phase improvement mechanism as claimed in claim 1,
wherein the helical spring facilitates the first surface and the third surface of the
contact fink to engage with the first surface and the third surface of the trip link.
4. The immobility phase improvement mechanism as claimed in claim I, wherein the predefined angle is relatively higher than a maximum degree of rotation essential for completely de-latching [he four bar linkage mechanism.
5. The immobility phase improvement mechanism as claimed in claim 1. wherein the third projected part communicates with an electromagnetic actuator by acting as a trip point.
6. The immobility phase improvement mechanism as claimed in claim 5. wherein the electromagnetic actuator includes a movable core, a fixed core and a coil wound over the fixed core.
7. The immobility phase improvement mechanism as claimed in claim 5, wherein the electromagnetic actuator is configured to sense short circuit current and give an output in terms of a mechanical energy thai moves the moving core.
8. The immobility phase improvement mechanism as claimed in claim 1, wherein the movement of the moving core rotates the trip link in the anticlockwise direction by exerting a force on the third projected part of the trip link.
9. The immobility phase improvement mechanism as claimed in claim 1, wherein the movement of the moving core is relatively higher than the predefined angle.