FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION: CONTACT LOCKING ASSEMBLY FOR CIRCUIT BREAKERS
APPLICANT: LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to electrical switching
apparatus and particularly to current limiting circuit breakers. The present invention more particularly relates to a locking assembly for movable contact arms in contact assemblies of circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] Electrical switching apparatuses, such as circuit breakers, are employed in diverse capacities in power distribution systems to provide protection for electrical equipment from electrical fault conditions for instance during current overload's, short circuits, abnormal level voltage conditions or the like.
[0003] Circuit breakers are the mechanical switching devices capable of making, carrying, and breaking currents under normal circuit conditions and also making, carrying for a specified time, and breaking currents under specified abnormal conditions. A circuit breaker basically consists of a pair of separable contacts and an interrupting medium. The function of the contacts is to conduct the electrical current, when the breaker is closed and withstand the arcs while interrupting. Generally, the electrical contacts have a stationary part and a moving part. By bringing the moving contact in touch with the stationary contact, an electric current flow through the circuit and the breaker is closed. By driving the moving contact away from the stationary contact, an electric arc is created and by quenching it, the current stops flowing and the breaker is open.
[0004] A circuit breaker typically consists of a current carrying path, a mechanism and an arc quenching chamber. The movable contact arm is

spring loaded to exert contact pressure on the fixed contact assembly. The circuit breaker is expected to operate to interrupt the fault current rapidly so as to minimize damages to the installations resulting from thermal and mechanical stresses.
[0005] A conventionally used molded case circuit breaker operates on
the current limiting principle wherein the over current flowing through the circuit breaker contacts results in electro-dynamic repulsive forces between the fixed and moving contacts. The stationary contact being secured to the base of the molded case, repulsive forces exerted cause the moving contact to trace a curvilinear locus as the contacts separate. Consequent to this motion of moving contact, an incremental resistance is introduced between the stationary and moving contacts. The incremental in turn creates an increasing arc voltage that acts opposite to the system voltage and limits the fault current to quench the arc.
[0006] The inherent nature of any spring loaded contact system
introduces the probability of "contact bounce-back" even after successful opening. This phenomenon, if unchecked, may eventually result in violent re-strike of the arc between the contacts and consequently, cause serious damage to the circuit breaker and the installation.
[0007] Hence there is a need to provide an improved contact locking
arrangement to prevent the contact from bounce back and to limit the fault current in order to achieve a low value of let through energy.
[0008] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECT OF THE INVENTION

[0009] The primary object of the present invention is to develop an
improved moving contact locking arrangement in circuit breakers to prevent contact bouncing.
[0010] Another object of the present invention is to develop an improved contact locking arrangement to limit fault current.
[0011] Yet another object of the present invention is to develop an improved contact locking arrangement to reduce let through energy in case of fault conditions.
[0012] Yet another object of the present invention is to develop an improved contact locking arrangement which is compact and easy to assembly.
[0013] Yet another object of the present invention is to develop an improved contact locking arrangement which provide high mechanical stability and consistency in contact system.
[0014] These and other objects and advantages of the present invention
will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0015] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

[0016] The various embodiments of the present invention provide an improved moving contact locking arrangement in molded case circuit breaker. A moving contact locking mechanism for switching device comprises a driveshaft, a moving contact, a contact pin, two contact springs and two spring mounting pins. A moving contact is assembled with the drive shaft. The moving contact is held in a position by inserting the contact pin into the U-shaped slot of the drive shaft. One end of each contact spring is hinged onto the first spring mounting pin and the other end of each contact spring is hinged onto the second spring mounting pin. The second spring mounting pin is then pressed against the spring force so that the second spring mounting pin gets locked below the driveshaft support.
[0017] The contact springs generate a force on the moving contact. This force generates a torque on the moving contact about the axis of rotation and imparts a required contact force to the contact. This force assists the moving contact to maintain continuity of the electrical circuit until the threshold current limit is exceeded and restrains the rotary motion of moving contact.
[0018] High electrodynamics forces exerted on the moving contact tend to cause the moving contact to rotate against the contact force. When the electrodynamics forces acting on the moving contact exceed the threshold value, the contact starts rotating about its axis of rotation. The increasing force gradient between the force exerted on the moving contact due to the electrodynamics forces and the contact spring force acting on moving contact leads to the achievement of a dead center. The point at which the roller surface aligns with the tip of the moving contact surface is the dead center or toggling position of the moving contact. The moment the contact assembly achieves its dead center for instance, about 10 ° rotations, there will be rapid transition of a moving contact from a toggle position to locked

position. The movement of the contact stops on the stopper surface of the driveshaft. The contact locking avoids any form of contact bouncing phenomenon during arcing time in an arc-chamber assembly. This in turn leads to drastic reduction in let-through energy.
[0019] During short circuit, the contact locking phenomenon is
immediately followed by the driveshaft movement assisted by the circuit breaker mechanism. The movement of driveshaft facilitates the reset operation of the moving contact arm so that it is ready for next ON operation.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The other objects, features and advantages will occur to those
skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0021] FIG.l illustrates a front view of the driveshaft assembly in ON
position according to one embodiment of the present invention
[0022] FIG.2 illustrates a top view of the driveshaft assembly in ON position according to one embodiment of the present invention.
[0023] FIG.3 illustrates the exploded view of the driveshaft assembly according to one embodiment of the present invention.
[0024] FIG.4 illustrates a front view of the driveshaft assembly in a
TOGGLE position according to one embodiment of the present invention.

[0025] FIG.5 illustrates a front view of a locked position of the driveshaft assembly according to one embodiment of the present invention.
[0026] FIG.6 illustrates a perspective view of a three pole driveshaft
assembly according to one embodiment of the present invention.
[0027] FIG.7 illustrates a driveshaft assembly arranged inside a molded case circuit breaker according to one embodiment of the present invention.
[0028] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0029] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0030] The various embodiments of the present invention provide an improved moving contact locking arrangement in molded case circuit breaker. FIG.l illustrates the front view of the driveshaft assembly having moving contact locking arrangement. The moving contact 1 is assembled with drive shaft 3 by aligning the moving contact hole with drive shaft U slot. The moving contact 1 is held in this position by inserting contact pin 2

in the U slot of the drive shaft. One of the hooks of both the contact springs 5a and 5b are hinged onto the first spring mounting pin 4a, The other end of both the contact springs 5a and 5b are hinged onto the second spring mounting pin 4b. The second spring mounting pin 4b is then forced against the spring force so that it gets locked below the driveshaft support.
[0031] The moving contact is provided with a U-shaped profile 8. The U-shaped profile 8 functions as an arc runner. During short circuit, the arc appears across the contact buttons. To reduce the erosion of contact buttons, arc has to be directed towards arc chute assembly as quickly as possible. To facilitate faster arc movement, a copper profile is provided which extends ahead of the contact button as shown in FIG. 1 so that an arc jumps from the contact button to the copper profile.
[0032] FIG.2 illustrates the top view of the driveshaft assembly having
a moving contact locking arrangement according to one embodiment of the present invention. The moving contact 1 is assembled with the drive shaft 3 by inserting a contact pin 2 in the drive shaft. One of the hooks of both the contact springs 5a and 5b is hinged onto the spring mounting pin 4a. The other end of both the contact springs 5a and 5b is hinged onto the spring mounting pin 4b. The contact springs 5a and 5b generate a force F at the extreme end of the moving contact 1 which generates a torque on the moving contact 1 about the axis of rotation and impart required contact force to the contact. This force assists the moving contact 1 to maintain continuity of the electrical circuit until the threshold current limit is exceeded.
[0033] FIG.3 illustrates an exploded view of the driveshaft assembly
according to one embodiment of the present invention. The FIG. 3 shows a moving contact 1 having a U-shaped profile and a contact pin 2. The moving contact 1 is adapted to be engaged with the drive shaft 3 by inserting the contact pin 2 into the U-slot in the driver shaft 3. The FIG.3 also illustrates two contact springs 5a and 5b. One end of each of the contact

springs 5a and 5b is hinged onto the spring mounting pin 4a. The other end of both the contact springs 5a and 5b is hinged onto the spring mounting pin 4b.
[0034] FIG.4 illustrates the TOGGLING position of the driveshaft
assembly according to one embodiment of the present invention. The flow of high fault currents through the unique current limiting contact profile exerts a high electrodynamics force on the moving contact 1. The electrodynamics force in turn causes the moving contact 1 to rotate against the against the contact force. When the electrodynamics forces acting on the moving contact exceeds the threshold value (the opposing force exerted by contact spring), the contact 1 starts rotating about its axis of rotation. The increasing force gradient between the force exerted on moving contact 1 due to current flowing through the contact (electrodynamics forces) and the contact spring force acting on moving contact 1 leads to achievement of dead center. The point at which the roller surface aligns with tip of the moving contact surface is the dead center or toggling position of the moving contact 1. The toggling occurs when the axis of spring crosses the axis formed by spring mounting pin 4a and contact pin 2.
[003 5] FIG. 5 illustrates the front view of the LOCKED position of the driveshaft assembly according to one embodiment of the present invention. The moment the contact assembly achieves the dead center for instance, at about 10 ° rotations, there will be rapid transition of moving contact from dead center or toggle position to locked position. The moving contact 1 stops on the stopper surface 7 of the driveshaft 3. This arrangement causes the moving contact 1 to remain in the "locked open" position until the circuit breaker is tripped. The contact locking avoids any form of contact bouncing phenomenon during arcing time in arc-chamber assembly, this leads to drastic reduction in let-through energy.

[0036] FIG.6 illustrates the three pole driveshaft assembly according to one embodiment of the present invention. Three drive shaft assemblies are connected and placed parallel to each other as shown in FIG. 6. A projection is provided on both the sides of the each driveshaft assembly to connect adjacent driveshaft assemblies with each other. A trip condition is detected in at least one of the driveshaft assembly, and the contact springs or the compression springs 5a and 5b are energized under the trip condition to displace the moving contacts 1 to simultaneously trip all the driveshaft assemblies.
[0037] FIG.7 illustrates the driveshaft assembly arranged inside a moulded case circuit breaker according to one embodiment of the present invention. The moving contact 1 is assembled with drive shaft 3 by inserting the contact pin 2 in the -slot of the driveshaft 3. One of the hooks of both the contact springs 5a and 5b are hinged onto the spring mounting pin 4a. The other end of both the contact springs 5a and 5b are hinged onto the spring mounting pin 4b. All the components are assembled inside the molded case circuit breaker assembly 9. During short circuit, the contact locking phenomenon is immediately followed by the driveshaft movement assisted by the circuit breaker mechanism. The movement of driveshaft facilitates the moving contact arm to reset so that it is ready for next ON operation.
G) ADVANTAGES OF THE INVENTION
[0038] A moving contact locking mechanism of the present invention has high reliability and ease of assembly because of the lower number of components.
[0039] A moving contact locking mechanism of the present invention offers a fast acting dead center crossing type of locking arrangement. The

fast acting locking arrangement reduces the let through energy through the circuit in case of any fault conditions.
[0040] The present invention provides high dielectric strength across
contact gap and facilitates rapid arc voltage development which limits peak current resulting in low let-through energy.
[0041] The present invention offers robust design to achieve high
mechanical stability and consistency in contact system.
[0042] A design of the moving contact locking arrangement assembly
of the present invention is compact and economical.
[0043] Although the invention is described with various specific
embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0044] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. A contact locking mechanism for switching devices comprising;
A driveshaft with a predefined profile;
A moving contact;
A contact pin;
At least two contact springs;
A first spring mounting pin; and
A second spring mounting pin;
Wherein the contact springs generate a force at a dead end of the moving
contact to generate torque on the moving contact
about the axis of rotation to provide a contact pressure under normal
current carrying conditions and lock the moving contact arm at a preset
angular position, when the electrodynamic forces acting on the moving
contact exceeds a threshold value.
2. The locking mechanism according to claim 1, wherein one end of each of the two contact spring gets engaged with the first spring mounting pin while the other end of each of the two contact spring gets engaged with the second spring mounting pin for locking the moving contact with the drive shaft,
3. The locking mechanism according to claim 1, wherein the predefined profile of the driveshaft includes a U-shaped slot.
4. The locking mechanism according to claim 1, wherein the contact pin is adapted to fasten the moving contact with the driveshaft by aligning the U-shaped slot with the moving contact,

5. The locking mechanism according to claim 1, wherein the second spring mounting pin is provided with a force which acts against the spring force such that the second spring mounting pin is locked below the driveshaft support.
6. A locking mechanism according to claim 1, wherein the contact springs generates a force at the moving contact about the axis of rotation to impart required contact force to the moving contact.
7. A locking mechanism according to claim 1, wherein the contact spring force maintains a pressure on the moving contact to maintain continuity of an electrical circuit until a threshold value of current is exceeded so as to restrain the rotary movement of the moving contact.
8. A locking mechanism according to claim 1, wherein a flow of fault current exerts an electrodynamics forces on the moving contact to cause moving contact to rotate against the contact force.
9. A locking mechanism according to claim 1, wherein an increasing force
gradient between the electrodynamics forces and the contact spring forces
acting on moving contact leads to dead center.
10. A locking mechanism according to claim 1, wherein once the contact assembly achieves the dead center, there will be rapid transition of moving contact from dead center to locked position.
11. A locking mechanism according to claim 1, wherein the rapid transition of moving contact from dead center to locked position is on the principle of toggling on the line of axis.

12. A locking mechanism according to claim 1, wherein the moving contact stops on the stopper surface of the driveshaft in a locked position.