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: AN IMPROVED MECHANICAL
LOCKING MECHANISM FOR USE IN CONTACT SYSTEMS
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:

Field of the invention
The present invention relates to an improved mechanical locking mechanism for use in contact systems. Particularly, the invention relates to mechanical compensation for the electrodynamic forces on the moving contacts in a contact system. More particularly, the invention is concerned about a mechanism which could withstand high electrodynamic forces without repulsion which requires a significant amount of compensation to offset ensuing mechanical stresses.
Background and the prior art
Circuit breaker is a device employed to protect the equipments in an installation/power transmission or distribution system in case of over currents arising out of fault conditions. An electric circuit breaker contact locking mechanism is provided including at least one stationary contact member and at least one movable contact member and biasing means between the movable contact member and a normally stationary support member to provide contact closing pressure during normal condition. It is also required to interrupt the fault current rapidly in one or more circuit’s paths upon the occurrence of an over current in any one circuit path so as to minimize damage to the installation resulting from thermal and mechanical stresses.
In the power system the circuit breakers are connected in series. During any fault condition both the downstream and the upstream breakers see the fault current. Even though in most case the downstream breaker clears the fault, the upstream breaker opens to some extent and then closes due to the high electrodynamics forces of the current it carries for a short duration of time. Even-if the contacts of the upstream breaker opens by a small amount an arc is observed due to which there occurs a disturbance in the system and also the life of the breaker decreases. To avoid this, there is a need to provide a mechanism by which the upstream breaker will wait and not open till the downstream breaker clears the fault or if the downstream breaker fails to clear the fault then the

upstream breaker will open. In the present invention this is achieved with mechanical compensation for the electrodynamics forces on the moving contact.
US 6,084,489 discloses the circuit breaker is characterized by separable contacts operable between a closed and an open position a contact arm having a latching surface and a latch arranged to engage the latching surface when the contacts are blown-open under short-circuit conditions. The arrangement of the latch allows for a positive lock under high magnitude short circuit levels while minimizing the force required by a mechanism to unlock the arm. This prior art does not teach cam engagement at both closed and open (after reset) position. It was not knonw from the prior art that arms can be unlocked by self triggering mechanism.
In US 6015959, cam mechanism is used for switching in Normal conditions, however, no reference have been found in this prior art about operation of cam arrangement in abnormal (short circuit) condition. Further cam mechanism used in US 6015959 is manually operated.
US 6,448,522 disclose a motor operator mechanism is disclosed for moving a breaker handle of a circuit breaker between off and on positions. The motor operator mechanism comprises of a first pin biased to engage the breaker handle in a direction to close the circuit breaker, a pin latch configured to releasable engage the first pin when the breaker handle is in a position intermediate to the off and on positions, wherein releasing the pin latch allows the first pin to move the breaker handle to the on position. In US 6,448,522 locking of moving contact till particular threshold value and self triggered unlocking beyond threshold value was not taught.
US 6,590,482 discloses a circuit breaker operating mechanism for separating a pair of electrical contacts within an electrical circuit breaker includes a lower link operatively connected to one of the electrical contacts. An upper link includes first and second legs extending from a central portion. The first leg is pivotally secured to the lower link, and the second leg includes a cam surface formed thereon. A roller is in intimate contact with the cam surface, and the cam surface is configured such that movement of the upper link

relative to the roller causes the upper link to pivot about the central portion. Pivoting of the upper link about the central portion moves the lower link causing the second contact to move away from the first contact. An operating spring is configured to provide a force for separating the electrical contacts when the operating mechanism is tripped. An operating handle includes a void disposed therein, and an end of the spring is secured to the operating handle within the void. It was not known from US 6,590,482 that cam action can be used for locking moving contact till particular threshold value and self triggered unlocking beyond threshold value.
The inventors have found that to provide comprehensive coordination with downstream protection devices, the device in consideration is required to withstand the maximum through fault current. Whilst it should respond instantaneously if the fault current is higher than the pre-set current value designated for withstand. Withstanding such high electrodynamics forces without repulsion requires a significant amount of compensation to offset ensuing mechanical stresses. Compensation of these forces can be done either through special current path configurations or from the combination of both such configurations and mechanical locking arrangements. These types of compensation require higher space to accommodate the same and require an external actuation or impetus for operation/de-latching. The inventors have found that a uniquely designed locking mechanism can be provided within the limited space of the rotor assembly of the contact system by which high electrodynamic force compensation can be done.
Objects of the invention
A basic object of the present invention is to overcome the drawbacks/disadvantages of the prior art.
One of the main objects of the invention is to improve the life of the contact system and to provide enhanced discrimination among the circuit breakers.

Another object of the present invention is to provide an improved mechanism to compensate the electrodynamic force by auto de latching of the contact defined by a biased cam arrangement.
Yet another object of the present invention is to provide an improved cam based contact mechanism where the threshold value can be can be tuned to address various threshold requirements to provide flexibility to the function by varying various constructional parameters with very less change in restraining force of energy device.
Yet another object of the present invention is to provide an improved circuit breaker which is easily adapted to any type of contact system such as single break, double break, and multiple finger system.
Yet another object of the present invention is to provide an intelligent auto de-latching mechanical contact locking arrangement that will ensure contact stability to a pre-defined threshold force calibrated to a pre defined threshold current.
Yet another object of the present invention is to provide an improved mechanism to cause rapid rotation of the contacts, which will ensure fast arc quenching and subsequent clearance of fault.
Summary of the invention
According to one aspect of the present invention there is provided an improved locking
mechanism for use in contact systems, said mechanism comprising:
rotor means;
plurality of fixed contact means and moving contact means, said fixed contact means
being proximally located to said moving contact means such that said moving contacts
get contacted to said fixed contacts at ON condition; said moving contacts being coupled
to said rotor means;
wherein said rotor means comprises a slot profile substantially at its centre so as to define
rotary locus of said moving contact means;

plate means having a cam profile being riveted or screwed or connected together by any
other means to said moving contact means;
locking link element;
wherein said element has a cam profile adapted to restrict rotary motion of said movable
contact means up to a predetermined threshold force value;
plural link means operatively integrated to said locking link element;
one or more energy storing elements engaged to said link means adapted to provide
anticlockwise torque to locking link element at locked position; and
contact pressure assembly operatively connected to said plate means and locking link
element so as to provide contact pressure.
Brief Description of the accompanying drawings
Figure 1 illustrates an isometric view of mechanical locking mechanism for contact system in the present invention.
Figure 2 illustrates an isometric view (without fixed contact assembly) of mechanical locking mechanism for contact system in the present invention.
Figure 3 illustrates an isometric view of contact pressure arrangement for contact system at ON Position in the present invention.
Figure 4 illustrates an isometric view (without locking spring) of mechanical locking arrangement for contact system at ON Position i.e. Locked Position.
Figure 5 illustrates an isometric view (without locking spring) of mechanical locking mechanism for contact system at TRIP i.e. Unlocked Position.
Figure 6 illustrates an isometric view (without locking spring) of mechanical locking arrangement for contact system at OFF Position.

Detailed description of the accompanying drawings
As shown in figure 1 the mechanism of the present invention comprises fixed contact (1) which is a current carrying element of the circuit. moving contact (2) is connected to side plate which has cam profile to engage with cam profile of contact pressure link (6) to facilitate locking and give contact pressure till predefined threshold value of force and unlocking beyond the same threshold value.
Rotor (4) is connected to contact through centre pin (not shown here in the figures) and accommodates anchor pin (not shown here in the figures) for contact pressure spring (7) (shown in figure 2). The centre pin connects moving contact to the rotor to allow rotary motion of contact about Z axis and also determines dead centre of the contact system. Rotor (4) is operatively connected to an operating mechanism (not shown in the figures), which provides energy to rotor to achieve rotary motion of contact arms. The rotor has slot in the centre to define two positions of contact arm and also define rotary locus of contact from one position to another. It facilitates assembly of contact pressure link (6) (shown in figure 2) and locking link element (8) (shown in figure 2) through contact pressure link pivot pin and locking link pivot pin respectively and has provision to couple with operating mechanism of breaker through coupler (3) (shown in figure 1). Also one end of contact pressure spring (7) is mounted on rotor (4) (as shown in figure 2). It can be manufactured as single component or two halves connected by any joining arrangement. In the present invention, it is made up of two halves and joined together by coupling screw. The coupler (3) connects operating mechanism of circuit breaker to moving contact through rotor. It acts as coupling element between different poles. In the present invention coupling screws have been used. However, any other joining elements can be used and coupling screws should not be considered to be restricting scope of the present invention.
As shown in figure 3 side plate (5) is connected to moving contact (2) through joining arrangement such as riveting, screwing to make it integral part of moving contact. It has cam profile which is engaged with contact pressure cam pin to exert contact pressure.

This cam profile can also be on moving contact directly. Contact pressure (CP) Link (6) transmits CP spring force to moving contact (2) through cam engagement with side plate profile. It is engaged with cam profile of locking link element (8). It has stopper cam profile to engage with reset pin. Stopper cam profile (not shown in the figure) can be integral part of CP link or separate component joined to CP link by any arrangement. Contact pressure cam pin (13) is connected to CP link (6) with joining arrangement to make it integral part of CP link and engaged with side plate cam profile to exert contact pressure. Contact pressure spring (7) is connected between rotor (4) and CP link (6). It can be any energy storing element such as extension, compression, torsion spring etc. In the present invention, torsion spring is used for effective utilization of volume.
As shown in figure 4 locking link (8) restricts rotary motion of contact assembly till predefined threshold force value and allows rotary motion of contact assembly beyond the same threshold value. In this case, symmetrical locking arrangement is used to achieve the function but same function can be achieved by nonsymmetrical arrangement as well. Locking spring (9) (as shown in figure 2) are the energy storing elements which are used to apply anticlockwise(direction opposite to torque applied due to contact arm forces) torque on locking link at locked position and to restore locking link at unlocked position. In this case locking spring used is extension spring. It can be conventional extension spring with any type of hook arrangements. Also by appropriate modifications, Compression and torsion spring can also be used for this application. In addition, Operating threshold of the invention mentioned can be adjusted by varying restrain force values associated with springs. As shown in figure 2 spring link (11) is connected to locking link element (8) by any joining arrangement to make it integral part of locking link. Locking spring (9) is connected between two opposite spring links. It also supports reset pin which is engaged with stopper cam on CP link at OFF position and allows operating mechanism to rotate rotor till over travel position.
ON-OFF Operation:

Referring to figures 4 and 6 at ON Position, moving contact arm 2 is at first stable position with side plate 11 cam profile engaged with respective CP cam pin 13. During ON-OFF operation, input to the rotor 4 is given through the operating mechanism connected to rotor 4 through coupler 3. When extension springs of the operating mechanism get extended up to dead centre, potential energy is stored in the springs. This Stored potential energy gets converted into kinetic energy after dead centre of the operating mechanism and rotor 4 is rotated along with moving contact arm 2 from ON to OFF position.
OFF-ON Operation:
At OFF Position, moving contact arm 2 is at second stable position with side plate 11 cam profile engaged with respective CP cam pin 13.During OFF-ON operation also, Input to the rotor 4 is given through the operating mechanism connected to rotor 4 through coupler 3. Extension springs of the operating mechanism get extended up to dead centre to store potential energy in the springs. This Stored potential energy gets converted into kinetic energy after dead centre of the operating mechanism and rotor 4 is rotated along with Contact arm 2 from OFF to ON position.
ON-TRIP Operation:
Referring to figures 4 and 5 during ON-TRIP Operation, contact arm 2 is not displaced till the predefined threshold force value of stated arrangement is reached. Threshold value is the mechanical compensation force essential to withstand the electro-dynamic forces exerted on the moving contact arm 2 because of high flow of current through contact elements. When Electro-dynamic forces go beyond the pre-defined threshold force, locking link 8 will rotate in opposite direction of locking spring torque to allow rotary motion of contact arm 2. Hence contact arm 2 will move to the OFF Position independently. Operating mechanism is still at ON position.
Resetting Operation:

When Operating mechanism drives the rotor 4, locking link 8 and contact arm 2 are resettled to locking position. Now, breaker is ready for next OFF-ON operation.
Threshold point of contact arm displacement and Slope of contact arm displacement can be changed by varying various constructional parameters such as locking link length, perpendicular distances of cam force from contact arm pivot point and locking link pivot.
Definitions of some technical terms
Threshold value:
It is the mechanical compensation force essential to withstand the electro-dynamic forces exerted on the moving contact because of the high fault current. Electro-dynamic forces generated beyond the pre-set value will enable moving contact to rise over the threshold value thereby operating the same. Compensation mechanism can be tuned to achieve desired threshold value by changing the constructional parameters.
Dead centre:
Dead centre is an equilibrium condition of actuating mechanism. In this condition the mechanism spring is fully charged and beyond this point mechanism flips & operates independently due to energy discharged by mechanism spring.
Advantages:
1. Intelligent Auto triggering Mechanism
2. Easily adapted to any type of contact system such as single break, double break, and multiple finger system.
3. Threshold value can be can be tuned to address various threshold requirements to provide flexibility to the function by varying various constructional parameters with very less change in restraining force of energy device.
4. Negligible resistance during opening of contact arms and assisting torque on moving contact after dead centre rotation of contact.

5. Life of the breaker increases. Because during fault condition, upstream breaker only opens if downstream breaker fails to clear the fault. This significantly reduces occurrence of arcing at button which in turn reduces contact button erosion.
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 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. An improved locking mechanism for use in contact systems, said mechanism
comprising :
rotor means;
plurality of fixed contact means and moving contact means, said fixed contact
means being proximally located to said moving contact means such that said
moving contacts get contacted to said fixed contacts at ON condition; said moving
contacts being coupled to said rotor means;
wherein said rotor means comprises a slot profile substantially at its centre so as
to define rotary locus of said moving contact means;
plate means having a cam profile being riveted or screwed or connected together
by any other means to said moving contact means;
locking link element;
wherein said element has a cam profile adapted to restrict rotary motion of said
movable contact means up to a predetermined threshold force value;
plural link means operatively integrated to said locking link element;
one or more energy storing elements engaged to said link means adapted to
provide anticlockwise torque to locking link element at locked position; and
contact pressure assembly operatively connected to said plate means and locking
link element so as to provide contact pressure.
2. Mechanism as claimed in claim 1 wherein said contact pressure assembly comprises contact pressure spring means.
3. Mechanism as claimed in claim 2 wherein said contact pressure spring means is a torsion spring adapted for effective utilization of volume.

4. Mechanism as claimed in claim 2 and 3 where said contact pressure spring means is optionally an extension spring or a compression spring or any other energy storing device.
5. Mechanism as claimed in claim 1 wherein said contact pressure assembly comprises contact pressure link means adapted to transmit contact pressure spring force to moving contact means.
6. Mechanism as claimed in claim 1 wherein said contact pressure assembly comprises contact pressure cam pin means operatively engaged to said plate means cam profile for exerting contact pressure.
7. Mechanism as claimed in claim 1 wherein said locking link element comprises symmetrical locking arrangement.
8. Mechanism as claimed in claim 7 wherein said locking link element optionally comprises symmetrical locking arrangement.
9. Mechanism as claimed in claim 1 wherein said energy storing elements comprise locking springs.
10. Mechanism as claimed in claim 9 wherein said locking spring is an extension spring.
11. Mechanism as claimed in claims 9 and 10 wherein said locking spring is optionally a compression spring or a torsion spring.
12. Mechanism as claimed in claim 1 wherein said link means are spring links.
13. Mechanism as claimed in claim 1 wherein said rotor comprises two halves coupled by a coupling screw.

14. Mechanism as claimed in claim 1 wherein said rotor is optionally one single component.
15. Mechanism as claimed in claim 1 wherein said moving contact means optionally comprises a cam profile.
16. Mechanism as claimed in any of the preceding claims further comprising a centre pin adapted to operatively connect said moving contact to said rotor so as to allow rotation of said moving contacts.
17. An improved locking mechanism for use in contact systems as herein substantially described and illustrated with reference to the accompanying drawings.