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:
PROFILE BASED CONTACT LOCKING ARRANGEMENT 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 the contact profile to provide flipping of contact arm.
B) BACKGROUND OF THE INVENTION
[0002] 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 to touch the stationary contact, an electric current flows and the breaker is closed. By driving the moving contact away from the stationary contact, the electric arc is developed and by quenching it the current stops flowing and the breaker is opened.
[0003] A circuit breaker typically comprises a spring loaded contact system to carry, make and break the current under normal and abnormal conditions involving very high over-currents. A typical 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 stationary and moving contacts. The inherent nature of any spring loaded contact system introduces the probability of

"contact bounce-back," even after the successful opening. This phenomenon, if unchecked, may eventually result in a violent re strike of the arc between the contacts and consequently, serious damage to the circuit breaker and the installation.
[0004] A current limiting circuit breaker should clear the fault as fast
as possible so that the "let through energy" permitted to the connected downstream devices/equipment of the installation can be minimized thereby inhibiting the high thermal stresses associated with the "let through" current. Simultaneously, a current limiting circuit breaker should also limit the fault current to a value as low as possible so that the connected downstream devices are not subjected to high electro-dynamic stresses set up by the high magnitude fault current.
[0005] Hence there is a need to provide an improved contact
arrangement to provide for contact pressure sufficient to ensure a temperature rise. Also there exists a need for a contact arrangement to ensure the minimal value of let through energy and positive isolation.
[0006] 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
[0007] The primary object of the present invention is to develop a moving contact locking arrangement with enough contact pressure so as to ensure the permissible level of temperature.

[0008] Another object of the present invention is to develop an improved contact system to flip the contact arm when the fault current reaches the threshold value of contact arrangement.
[0009] Another object of the present invention is to develop an
improved contact system to prevent a contact bounce.
[0010] Yet another object of the present invention is to develop an improved contact arrangement to limit a fault current.
[0011] Yet another object of the present invention is to develop an
improved contact arrangement to reduce a let through energy in case of a fault.
[0012] Yet another object of the present invention is to develop an
improved contact locking arrangement, relevant for both single break and double break contact arrangements.
[0013] Yet another object of the present invention is to develop an
improved contact arrangement with fewer components resulting in the ease of an assembly process.
[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 for a current limiting circuit breaker. The arrangement comprising a drive shaft assembly, a moving contact arranged in the drive shaft assembly, at least one guide plate arranged in the drive shaft assembly and a contact spring. The moving contact and the at least one guide which includes a predefined profile such that the contact spring generates a force on each side of the moving contact thereby creating a contact pressure to maintain a circuit continuity during an operation. The arrangement includes a driveshaft with two the halves carrying a moving contact and two guide plates. The contact arm is allowed to rotate within a predetermined locus about the central anchor pin. The spacers are fitted between two guide plates. The spacers provide a necessary gap between the two guide plates. The floating anchor pins are inserted to the assembly through a profile on the contact arm and a profile on a guide plate.
[0017] The contact spring is secured by the driveshaft anchor pin and
the floating anchor pin. The spring is held tight between the two anchor pins on both side of the contact arm which generates force on each side of the contact arm. This force generates a torque on the moving contact about its axis of rotation and also imparts the required contact pressure. The contact arm and guide plate profiles are designed in such a way that during an operating condition, the floating anchor pin rests on the contact profile of the

moving arm and should be isolated from the profile on the guide plate. The force generated through contact spring assists the contact arm to maintain circuit continuity under normal operating conditions.
[0018] The electrodynamic forces exerted on the moving contact consequent to the flow of high fault currents through the unique current limiting contact profile tends to cause the moving contact to rotate against the generated force. When the electrodynamics force exceeds the threshold value, the contact arm starts rotating about the central anchor pin. As the rotation of a contact arm continues, the floating anchor pin is transferred to the profile on a guide plate from the profile on contact. The motion of a contact arm is governed by the profile on the guide plate and the profile on the contact.
[0019] With incremental travel, a contact spring is extended through
the contact and the guide plate profiles reaching a maximum extended position called 'Dead center'. The dead center is defined as the collective or unique position of drive shaft pin, floating anchor pin and contact spring up to which the energy is getting stored in the system and released afterwards making it a fast acting mechanism. The transitory position for the assembly is referred to as the dead center. In transitory position, the contact spring endures maximum extension.
[0020] After the dead center, the stored energy is released while
traveling to a lock-out position. The floating anchor pin follows the conjunction of the contact profile and guide plate profile. After being locked out, the moving arm cannot be bounced back. Generally, high impact forces due to current and inherent nature of spring will introduce bounce-back of contacts. The contact arm is locked out for avoiding a re-striking.

[002 1 ] The circuit breaker functionality can a)so be enhanced by
implementing a series of double arc breaking arrangement resulting in a lower let through energy by faster arc quenching and enabling the same to operate at very high voltage applications. The present invention is relevant for both single break and double break contact arrangements.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0022] 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:
[0023] FIG. 1 illustrates an exploded view of the driveshaft assembly employing a locking arrangement for a moving contact according to one embodiment of the present invention.
[0024] FIG. 2 illustrates a perspective f ront view of the driveshaft assembly with the moving contact in ON condition according to one embodiment of the present invention.
[0025] FIG. 3 illustrates another perspective view of the driveshaft
assembly for moving contact in ON condition according to one embodiment of the present invention.
[0026] FIG. 4 illustrates a perspective front view of the driveshaft
assembly with the moving contact in TOGGLING condition according to one embodiment of the present invention.

[0027] FIG. 5 illustrates a perspective view of the driveshaft assembly with the moving contact in TOGGLING condition according to one embodiment of the present invention.
[0028] FIG. 6 illustrates the sectional view of the driveshaft assembly
with the moving contact in LOCKED condition according to one embodiment of the present invention.
[0029] FIG. 7 illustrates the perspective view of the driveshaft assembly with the moving contact in LOCKED condition according to one embodiment of the present invention.
[0030] Although the 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
[0031] 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.

[0032] The various embodiments of the present invention provide a
contact locking arrangement for circuit breakers. The present invention describes an arrangement to provide a contact pressure under normal current carrying conditions and also lock the moving contact arm upon exceeding a threshold value of current.
[0033] FIG. 1 illustrates an exploded view of the driveshaft assembly
employing a locking arrangement for moving contact according to one embodiment of the present invention. The assembly includes a drive shaft 1 and 2comprising of at least two halves, fixed through drive shaft anchor pins
5 and supporting nuts 10 or any suitable fixing means. Alternatively, the two
halves can also be a single component. The drive shaft 1 and 2 includes a
moving contact/contact arm 3 which forms a rotary actuating structure and
guide plates 9. The guide plates 9 are structured to the drive shaft 1 and 2 by
aligning a hole on drive shaft 1 and 2with a corresponding hole on guide
plate B through drive shaft anchor pins 5. The moving contact 3 is engaged
to the drive shaft 1 and 2 through the opening on the peripheral surface of
the drive shaft by aligning a hole E on the moving contact 3 with a slot D on
the guide plate 9 by central anchor pin 4.This permits the moving contact 3
to rotate within a predetermined locus about the central anchor pin 4. The
drive shaft assembly further includes spacers 8 provided between two guide
plates 9 using pins 5. The spacers 8 are provided to create necessary gap
between two guide plates 9. The same spacers 8 can be integrated
structurally with the driveshaft 1 and 2.
[0034] Floating anchor pins 6 are inserted to the drive shaft assembly
through a profile on the moving contact A and profile on guide plate C. The contact spring 7 is secured by the driveshaft anchor pin 5 and the floating anchor pin 6. The spring is thus held tight between the two anchor pins 5 and
6 on both sides of the contact arm 3 presenting a double arc break
arrangement.

[0035] FIG. 2 illustrates a perspective front view of the driveshaft
assembly with the moving contact in ON condition according to one embodiment of the present invention. FIG. 3 illustrates another perspective view of the driveshaft assembly with moving contact in ON condition according to one embodiment of the present invention. The contact spring 7 extended between the drive shaft anchor pin 5 and the floating anchor pin 6 generates a force on each side of the moving contact 3. The force generates a torque on the moving contact 3 about its axis of the rotation and also imparts the required contact pressure. The relative locations of the slot A, slot C, the driveshaft anchor pin 5 and the floating anchor pin 6 can be varied depending upon the ease of assembly, the functional requirements and the contact pressure required. The profiles A and C are designed in such a way that during an operating condition, the floating anchor pin 6 rests on profile A of the moving contact 3 and should be isolated from the profile on the guide plate C. This mode generates a highly efficient arrangement for generating a contact pressure. The force generated through a contact spring 7 assists the moving contact 3 to maintain circuitry continuity under normal operating conditions.
[0036] FIG. 4 illustrates a perspective view of the driveshaft assembly
with the moving contact in TOGGLING condition according to one embodiment of the present invention. FIG. 5 illustrates the perspective view of the driveshaft assembly with the moving contact in TOGGLING condition according to one embodiment of the present invention. The electrodynamic forces exerted on the moving contact 3 consequent to the flow of high fault currents through the unique current limiting contact profile tends to cause the moving contact to rotate against the generated force. When the electrodynamic forces exceed the threshold value, the contact arm 3 starts rotating about the central anchor pin 4. The continued rotation of the

moving contact 3 causes the floating anchor pin 6 to transfers to the profile on the guide plate B from profile on contact A. The motion of moving contact is governed by two features, the profile on guide plate C and the profile on contact A. With incremental travel, contact spring 7 is extended through profiles A and C reaching a maximum extended position called dead center. Thus dead center is defined as the collective or unique position of the drive shaft pin 5, the floating anchor pin 6 and the contact spring 7 up to which the energy is getting stored in the system and released afterwards making it a fast acting mechanism. The transitory position for the assembly is referred to as the dead center. In the transitory position, the contact spring endures maximum extension.
[0037] FIG. 6 illustrates a front perspective view of the driveshaft assembly with the moving contact in LOCKED condition according to one embodiment of the present invention. FIG. 7 illustrates another perspective view of the driveshaft assembly with the moving contact locking arrangement in LOCKED condition according to one embodiment of the present invention. The moving contact on crossing the dead center to reach a lock-out position, releases the energy stored in the assembly. The floating anchor pin 6 follows the conjunction profiles A and C. After being locked out, the moving contact 3 cannot be bounced back. Generally, high impact forces due to current and inherent nature of spring may introduce bounce-back of contact. The contact arm needs to be locked out for avoiding re striking. Thus the same contact spring 7 provides the contact pressure and also the locking out of moving contact 3.
[0038] A successful fault interruption may results into uneven contact erosion on both sides of the contact arm 3. Under normal conditions i.e. circuit breaker operated at rated current or the permissible level given by the release settings, the temperature rise of the circuit breaker exceeds the allowable limit set by the relevant product standards. The design of B slot on

the guide plate 9 serves for maintaining the required equal force on either side of the moving contact 3 needed for having electrical continuity and also maintaining the allowable limits set by the relevant product standards.
G) ADVANTAGES OF THE INVENTION
[0039] The profile based contact locking arrangement for circuit breakers of the present invention provides high opening velocity resulting in rapid extinction of arc. The profile design on the guide plates makes easy adjustment for achieving equal contact pressure (in double break arcing contact) even after variations in component and assembly tolerances and thus enhances the tolerance band of the components.
[0040] The assembly includes fewer numbers of components resulting
in ease of assembly and higher reliability. The present invention offers higher efficiency in terms of contact pressure developed from spring force. The assembly of the present invention achieves higher mechanical stability, consistency and optimum utilization of contact spring force.
[0041] The assembly of the present invention offers easy inter-convertibility between single break and double break type of contact system. In a double break arching contact system, an identical contact pressure is maintained even after erosion, through the design of slot of the guide plate.
[0042] 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.

[0043] 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 profile based contact locking arrangement for circuit breakers, the
arrangement comprising:
a drive shaft assembly;
a moving contact arranged in the drive shaft assembly; at least one guide plate arranged in the drive shaft assembly; and a contact spring;
Wherein the moving contact and at least one guide plate include a predefined profile such that the contact spring generates a force on each side of the moving contact thereby creating a contact pressure to maintain circuit continuity during operation.
2. The profile based contact locking arrangement according to claim 1,
wherein the at least one guide plate is arranged on the drive shaft by
aligning an opening on the drive shaft with an opening on the guide plate
through a plurality of anchor pins.
3. The profile based contact locking arrangement according to claim 1, the
moving contact is attached to the drive shaft by aligning a hole on the
moving contact with a slot on the at least one guide plate using an
anchor pin.
4. The profile based contact locking arrangement according to claim 1,
wherein the contact spring is held extended between the drive shaft
anchor pin and the floating anchor pin to generate a force on each side of
the moving contact.

5. The profile based contact locking arrangement according to claim 1, wherein the drive shaft assembly further comprising at least one spacer arranged for placing the guide plate.
6. The profile based contact locking arrangement according to claim 1, wherein the contact spring held tight between the central anchor pin and floating anchor pin on both sides of the moving contact provides a double arc break arrangement.
7. The profile based contact locking arrangement according to claim 1, wherein an electrodynamic force exerted on the moving contact during high fault current through the contact profile cause the moving contact to rotate against the generated contact pressure.
8. The profile based contact locking arrangement according to claim 1, wherein a rotation of the moving contact during a high threshold value of the electrodynamic force rotates the moving arm about the central anchor pin.
9. The profile based contact locking arrangement according to claim 1, wherein the contact profile and the at least one guide plate profile provides for the rotation of the moving contact.
10. The profile based contact locking arrangement according to claim 1, wherein the at least one guide plate includes a slot which serves for maintaining the required equal force on either side of the moving contact before and after erosion, needed for having electrical continuity and also maintaining the allowable limits set by the relevant product standards.

1.1. The profile based contact locking arrangement according to claim 1, wherein the conjunction profiles of moving contact and the guide plate are designed in such a way that the floating anchor pin rests on the profile of the moving contact and is isolated from the profile on the guide plate during an operating condition, to generate a contact pressure.