FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: CONTACT LOCKING SYSTEM HAVING AN INBUILT SIMPLE CAM PROFILE TO FLIP-FLOP
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 to a contact system in circuit breaker. More particularly, the present invention relates to contact locking mechanism with minimum components with an inbuilt feature simple cam profile to flip-flop instead of complex cam profile for flip-flop
BACKGROUND AND THE PRIOR ART
A circuit breaker is a mechanical switching device capable of carrying current under normal circuit condition and also carrying for a specified time and breaking currents under abnormal circuit conditions such as those of short circuit (Short circuit is an accidental or intentional connection, by a relatively low resistance or impedance, of two or more points in a circuit which are normally at different voltages). The main function of any electrical switching apparatus is to carry the rated current. Therefore the current carrying capacity of any circuit breaker is so important that if the unit fails to carry the rated current it will cause damage to itself as well as to the electrical equipment to which it is protecting. Circuit breakers have three positions corresponding to the status of the separable contacts. For example, these positions would include an ON position, in which the separable contacts are closed, an OFF position in which the contacts are open and Trip position in which the contacts are tripped open. These circuit breakers / switching devices are usually installed in an enclosure so as to have all the control and distribution network laid in form of metallic sheets and or cable wires inside and all operating means from outside so as to prevent access to high voltage and thus a potential hazard. When a circuit breaker is in ON condition and a short circuit fault condition arises, high amount of fault current flows through the circuit and in response to this the circuit breaker tries to move the separable contacts to open position after sensing the fault condition through short circuit sensing mechanism (such as magnetic arrangement). The time taken from a fault condition initiation and the fault current being interrupted by circuit breaker determines the let through energy / arc energy passed by the circuit breaker to the downstream equipments.
A circuit breaker is said to be more efficient when the let through energy is minimal. Let through energy of circuit breaker depends on many parameters, one among them being the

time for opening of the contacts from closed condition. The short circuit sensing mechanism of circuit breaker involves mechanical elements in between and thus takes a definite time before giving a trip open signal to the contacts thus increasing the let through energy. Short circuit conditions involves high amount of fault current levels which induces high repulsive forces between suitably arranged current carrying contacts. Thus if the contacts can be locked in the repelled open position, the let through energy can be reduced substantially. This improves life of the equipments and systems connected downstream and greatly reduce the hazardous conditions which can damage the downstream equipments. Thus many of the circuit breakers use such locking systems for contact locking under short circuit conditions. Further, efficiency of a contact locking system is measured by the velocity it can induce to the contacts once they have repelled open. It is also important to have the desired contact force in the ON condition, i.e. when the separable contacts are in closed condition.
US 5,633,483 disclose a circuit breaker having a stationary contact, a movable contact and a blade which has a first end and a second end. The movable contact is secured to the first end of the blade. The blade is rotatable about a pin between a BLOWN OPEN position and a CLOSED position, wherein the movable contact is separated from the stationary contact when the blade is in the BLOWN OPEN position and the movable contact engages the stationary contact when the blade is in the CLOSED position.
US 5,874,699 disclose a molded case circuit breaker has a moving conductor assembly which includes a modular carrier assembly incorporating a plurality of spring biased contact cam members each of which engages contact pressure lobes on a pair of contact arm laminations to provide contact pressure. In response to the magnetic repulsion forces generated by a short circuit, the springs compress allowing the cam members to pivot and side step the contact pressure lobes so that the contact arm blows-open with little resistance. The cam members and springs are preassembled in a transverse channel in the carrier body and laterally retained in place by side plates for easier pivotal attachment of the contact arm laminations to the lobes on the side plates.

US 7,217,895 disclose a contact assembly for a circuit breaker includes a fixed contact, a movable contact, and a movable contact arm. The movable contact arm includes a first end carrying the movable contact, a second end, and a pivot portion proximate the second end. A moving arm portion extends from the first end toward the pivot portion. The moving arm portion has a width, an upper edge, a lower edge, and a height defined by the distance between the upper edge and the lower edge.
US 5844455 disclose a current-limiting apparatus for a circuit breaker which makes it possible to effectively protect an electric load element by quickly blocking an electric flow path when an excessive current flows due to a ground, shortage, etc. at an electric flow path and preventing a re-formation of an electric flow path after the electric flow path is blocked.
US 4539538 disclose a molded case circuit breaker includes a movable upper electrical contact having a base portion with a slot formed therein for releasably receiving a portion of an elongated spring biased locking pin disposed in a rotatable cross bar of an operating mechanism of the circuit breaker. The locking pin is biased in the slot by a pair of tension springs secured to the cross bar, enabling the upper electrical contact to move in unison with the cross bar. Upon the occurrence of a high level short circuit or fault current of sufficient magnitude, the pin is displaced from the slot enabling the independent rotational movement of the upper contact arm.
All the above mentioned prior art relates on mechanism that discloses Contact Locking. All the locking mechanisms disclosed here are of only single point moving type.
The disadvantages of the above mentioned prior art is that circuit breakers having additional moving components and having complex cam profile is used to achieve contact locking. This reduces the efficiency of the locking mechanism as there is some amount of energy lost in overcoming friction. Friction also results in added amount of heat generated at the surface of the contacts. It also increases wear and tear of the parts, thereby reducing the overall life of

the system. Also due to such wear and tear there will be variation in the contact force over a period of time.
These and other limitations and needs of the conventional mechanisms necessitate an improved contact locking mechanism. It is also desirable to make the contacts move faster once it crosses the toggling position resulting in faster cut-off of fault current increasing the current limiting capability of the circuit breaker and reduction in let through energy of the circuit breaker during short circuit fault condition. It is also very important to achieve optimum contact force in the ON condition to keep the potential drop at the contact buttons to the minimum. However, in the prior art cases the contacts do not move after toggling due to friction between sliding component and drive shaft.
The present invention provides for a contact locking mechanism with optimum components with an inbuilt feature to flip-flop without having any component with complex cam profile for flip-flop. Thus enhances the velocity of contact system after toggling during fault clearance by circuit breaker while reducing let through energy. Hence the life of circuit breaker against short circuit fault clearance is improved.
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 an improved contact locking mechanism with simple cam profile to flip-flop thus reducing friction for movement.
Another object of the present invention is to provide for an improved contact locking mechanism adapted to generate higher velocity of moving contact after toggling.
Another object of the present invention is to provide for faster cut-off of fault current thus increasing the current limiting capability of the circuit breaker.

Another object of the present invention is to enhance the life of circuit breaker against short circuit fault clearance.
Another object of the present system is to provide for contact locking mechanism with minimum components.
Another object of the present invention is reduction in Jet through energy of the circuit breaker during short circuit fault condition.
Another object of the present invention is to achieve optimum contact force in the ON condition to keep the potential drop at the contact buttons to the minimum.
Yet another object of the present invention is to provide greater flexibility than the known art.
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 contact locking mechanism with minimum components and an inbuilt simple cam profile to flip-flop instead of complex cam profile for flip-flop.
According to one embodiment of the present invention, there is provided an improved contact locking mechanism with simple cam profile to flip-flop thus reducing friction for movement.
Other embodiment of the present system provides for an improved contact locking mechanism adapted to generate higher velocity of moving contact after toggling.
Other embodiment of the present system provides for faster cut-off of fault current thus increasing the current limiting capability of the circuit breaker.
Other embodiment of the present system provides for enhancement of the life of circuit breaker against short circuit fault clearance.

Other embodiment of the present system provides for contact locking mechanism with minimum components.
Other embodiment of the present system provides for reduction in let through energy of the circuit breaker during short circuit fault condition.
Other embodiment of the present system provides for optimum contact force in the ON condition to keep the potential drop at the contact buttons to the minimum.
Yet other embodiment of the present system provides for greater flexibility than the known art.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Figure 1 illustrates the orthographic views.
Figure 2 illustrates sectional view of fig-1.
Figure 3 illustrates the front view in repelled condition.
Figure 4 illustrates the front sectional view of fig-3.
Figure 5 illustrates the Exploded Isometric view.
Figure 6 illustrates the view of moving contact.
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 orthographic view of locking system is shown. It shows driveshaft (1) to which the upper contact (2) is pivoted at pin (3). Rotation of this driveshaft will cause upper moving contacts to come in contact with the lower contacts and thereby complete the electrical circuit.
Fig 2 shows the sectional view of the locking system comprising driveshaft (1), upper contact (2), pin (3), spacer (4) and a compression spring (5).
Fig 3 shows the front view in repelled condition. This is the position in which the moving contact cannot go further down or up since it stops on the driveshaft.
Fig 4 shows the sectional view of the locked position. Once the moving contact gets locked, it is brought back to the normal condition when the circuit breaker protection system subsequently trips the mechanism due to fault.
Fig 5 shows the exploded isometric view wherein each parts of the locking system is shown separately.
Fig 6 shows the moving contact. The orientation of the contacts can be changed by changing the angle A shown.
The invented system is thus a contact locking mechanism with minimum components and an inbuilt simple cam profile to flip-flop instead of complex cam profile for flip-flop.
DETAILED DESCRIPTION OF INVENTION
Accordingly the present invention discloses a contact locking mechanism with minimum components and an inbuilt simple cam profile to flip-flop instead of complex cam profile for flip-flop. This feature enhances the velocity of contact system after toggling during fault clearance by circuit breaker as the friction required for additional component is reduced, thus the contact opening time of the circuit breaker is reduced and therefore the let through energy while clearing short circuit is minimized.

Locking system disclosed herein is shown in Figure 1. Referring exploded view of locking system in Figure 5, it consists of a rotating member of the circuit breaker mechanism. driveshaft (1) to which the upper contact (2) is pivoted at pin (3). Rotation of this driveshaft will cause upper moving contacts to come in contact with the lower contacts and thereby complete the electrical circuit. Compression spring (5) is placed inside the cavity of drive shaft, over the compression spring a spacer (4). The spacer is placed in such a way that spacer touches the upper contact and pull is provided by the spring placed in the driveshaft to get contact pressure. The motion of moving contact and spacer is inter-related due to their connection and spring force. Movement of either of them will result in the change in direction of the force on the other component and thus result in moving the other component.
All Figures show the arrangement of the driveshaft for a single pole of the circuit breaker. For multiple poles, multiple such assemblies will be used side by side using a common connecting driveshaft across all the poles while the other components/parts remaining the same. Figure 2 is the sectional view of figure-1. The working of the invention is shown in Figure-1 & figure-3 with different positions. This is the position in which the moving contact cannot go further down or up since it stops on the driveshaft.
When the contact locking mechanism is assembled in the circuit breaker along with the mechanism and operated, in ON condition, the moving contact will move slightly upward when compared to the normal position. This is due to the intended over travel provided in the circuit breaker mechanism to achieve a certain minimum contact force this position is shown in fig-1.
When the fault occurs, there is an upward force on the moving contact (2) thereby it will rotate about the pivot (3). This movement of the contact will cause the spacer (4) to move. Thereby increase in the spring (5) pressure. As soon as the toggling point is crossed, the spring will exert force in another direction on upper contact, thus the spring which is compressed to its maximum deflection reaches an equilibrium state by releasing the length and releasing energy in the process to move the moving contact and it will rotate the moving contact in upward direction till it stops over mechanism. If the repulsion force on the upper contact is less than that offered by compression spring on upper contact, then the contact will

not get locked and the moving contact will again come to it ON position. The locked position is shown in figure-3 and the sectional view of this position is shown in figure-4.
Once the moving contact gets locked, it is brought back to the normal condition when the circuit breaker protection system subsequently trips the mechanism due to fault. When the signal is given, the driveshaft rotates in the upward direction. The moving contact then comes in contact with the cover / top portion of the circuit breaker and experiences a reaction force in the downward direction in a way as to make the moving contact cross the toggling position. Once the moving contact crosses the toggling position, it goes to the normal position by virtue of the force exerted by the spring. Therefore, process of unlocking of moving contact is just the opposite of the locking process.
Since moving contact moves after toggling without repulsive force, there is faster energy release by the spring after toggling, resulting in higher velocity of moving contact. This results in faster cut-off of fault current increasing the current limiting capability of the circuit breaker. Toggling position is that instant at which the hinge pivot 3, the orientation of the contacts can be changed by changing the angle A shown in fig-6. Thus the contact position and toggling point can be varied.
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 contact locking mechanism for use in circuit breakers comprising:
a rotating member (1) having a predetermined cavity;
a spring means (5) accommodated inside said cavity of the said rotating member (1);
a duality of contacts wherein the upper contact (2) is pivoted at pin (3);
a spacer (4) placed such that it touches the upper contact and pull is provided by the spring placed in the driveshaft to get the contact pressure.
2. A system as claimed in claim 1 wherein rotation of driveshaft results in contact between upper moving contact and the lower contact.
3. A system as claimed in claim 1 wherein moving contact and spacer is connected such that motion of moving contact and spacer gets inter-related due to spring force.
4. A system as claimed in claim 1 wherein movement of moving contact or spacer result in the change in direction of the force on the other component resulting in moving the other component.
5. A system as claimed in claim 1 wherein the contact opening time of the circuit breaker is reduced after toggling during fault clearance and therefore let through energy while clearing short circuit is minimized.

6. A system as claimed in claim 1 wherein an intended over travel is provided in the circuit breaker mechanism to move the moving contact slightly upward for achieving a certain minimum contact force.
7. A system as claimed in claim 1 wherein contact position and toggling point can be varied by changing the angle A of the drive shaft.
8. A system as claimed in claim 1 wherein moving contact moves after toggling without repulsive force providing for faster energy release by the spring resulting in higher velocity of moving contact.
9. A method of contact locking using an inbuilt simple cam profile to flip flop assembled in the circuit breaker enhancing the velocity of the contact system as herein substantially described and illustrated with reference to the accompanying drawings.