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: A CAM BASED CONTACT MECHANISM FOR LOW
VOLTAGE MOLDED CASE CIRCUIT BREAKER
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 a contact mechanism in a low voltage molded case circuit breaker comprising contact arm with cam profile adapted to provide enhanced contact stability up to a pre-defined threshold force. More particularly the invention relates to a cam based contact mechanism, said mechanism is used to lock the contacts till a predefined threshold value of current and opening the contact beyond the predefined threshold value.
BACKGROUND OF THE INVENTION
Circuit breaker is a device employed to protect the equipments in an installation 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.
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, as have been illustrated in various prior arts. These types of

compensation require higher space to accommodate the same and require an external actuation or impetus for operation/de-latching.
US 5,424,701 discloses an operating mechanism is disclosed which is capable of meeting electrical code requirements in the world market. The operating springs controlling the OPEN and CLOSED states of the circuit breaker contacts are charged both before and after the contacts are in their CLOSED conditions. The mechanism is both latched and unlatched by operation of a rotating cradle operator.
US 5,994,988 discloses a circuit breaker (10) has a housing (12). A crossbar (114) is pivotally connected to the housing to pivot about an axis (117) between open and closed positions. A load contact arm (110) is pivotally connected to the crossbar (114). The load contact arm (110) is capable of pivoting about the axis (117). A cam mechanism (140) is mechanically coupled to the load contact arm (110). The cam mechanism (140) is slideably mounted within the crossbar (114) for movement between first and second positions. In the first position of the cam mechanism (140), the load contact arm (110) pivots through an angle (β) about the axis, relative to the crossbar (114) between the "touch" and closed positions, and the load contact arm (110) pivots together with the crossbar (114) through an angle (.alpha.) about the axis (117) between the open and "touch" positions. (2) In the second position of the cam mechanism (140), the load contact arm (110) is free to pivot about the axis (117) through the angle .alpha, to the open position while the crossbar (114) is in the closed position. A biasing spring (160) applies a biasing force to bias the cam mechanism (140) towards the first position.
US 6,018,284 discloses the circuit breaker pole or poles comprise a movable contact means with a support carrier movable with respect to the frame between an open position and a closed position and one or more contact fingers movable with respect to the support carrier between a contact position and a retracted position. Electromagnetic compensation means are designed to apply electromagnetic forces

on the contact finger or fingers tending to keep the contact finger or fingers in contact with the stationary contact means. Electromagnetic limiting means are designed to apply electromagnetic forces on the contact finger or fingers tending to drive the finger or fingers to their retracted position. The electromagnetic compensation means and the electromagnetic limiting means are such that when the current intensity flowing in the movable contact means is under a threshold called the limiting threshold, the finger or fingers are kept in contact with the stationary contact means, and that above said threshold, the finger or fingers are driven to their retracted position. The resultant of the forces applied by the carrier on the kinematic connecting means when the current intensity flowing in the movable contact means reaches the limiting threshold is under the ultrafast opening threshold.
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.
US 6,448,522 discloses 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 releasably 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.
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.
The disadvantage of the above mentioned prior art is that to compensate the electro dynamic forces that are generated by the low voltage molded circuit breaker adapted to have contact stability of the circuit breaker requires higher space to accommodate the special current path configurations or the mechanical locking arrangements . Further the breaker requires an external actuating or impetus for operation/de latching.
The mechanical locking disclosed in the prior art are not compact, requires higher space and cumbersome. Moreover it does not provide an intelligent auto de-latching mechanical contact locking arrangement that will ensure contact stability to a predefined threshold force calibrated to a pre defined threshold current.
Thus there is a need to provide an improved mechanism of a tow voltage molded case circuit breaker that will easily adapt to any type of contact system. Further the threshold value can be tuned to address various threshold requirements, to provide flexibility to the function. Moreover where few number of components are required so that the assembly time line is considerably reduced.
Further the improved mechanism is adapted to compensate the electrodynamic force by auto de latching mechanical contact locking arrangement and thus maintain an

enhanced stability of the contacts up to a pre-defined threshold force calibrated to a corresponding pre-defined threshold current.
OBJECTS OF THE INVENTION
The main object of the present invention is to overcome the disadvantages of the prior
art.
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 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 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 improved mechanism with few number of components so as to reduce the assembly time line of the circuit breaker.
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 cam based contact mechanism of a low voltage molded circuit breaker adapted to withstand/compensate the electrodynamic forces generated and thereby maintaining contact stability, said mechanism comprising
(1) a housing means ;
(ii) an actuator means located inside said housing means adapted to perform ON-OFF-TRIP operations ;
(iii) biased cam arrangement for applying threshold value to withstand/compensate said electrodynamic force generated and thereby maintaining contact stability; said arrangement comprising contact arm means , and
(iv) an operating mechanism adapted to provide energy to said rotor means to archive rotary motion of said contact arms adapted to initiate ON and OFF operation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates Isometric view of Cam based Contact Mechanism.
Fig. 2 illustrates Isometric view (without Cassette) of Cam based Contact Mechanism at ON Position
Fig. 3 illustrates Front view (without Cassette) of Cam. based Contact Mechanism at ON Position.
Fig. 4 illustrates Front view (without Cassette) of Cam based Contact Mechanism at Unlocked Position during ON-TRIP.

Fig. 5 illustrates Front view (without Cassette) of Cam based Contact Mechanism at TRIP Position.
Fig 6 illustrates Contact Displacement Vs Current graph.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to low Voltage molded circuit breaker, and more particularly to the contact arm position locking to provide enhanced discrimination with the downstream devices.
The present invention describes a compact intelligent auto-de-latching mechanical contact locking arrangement that ensures contact stability up to a pre-defined threshold force calibrated to a corresponding pre-defined threshold current. Beyond this pre-defined threshold, the arrangement automatically de-latches and enables the contact arm to rotate freely without any hindrance.
The compensation mechanism comprises of disengage able actuating means causing self-de latching of the contact in the presence of a very high fault current, exceeding a calibration threshold defined by a biased cam arrangement. This self-de-latching mechanism assists the electro dynamic forces to cause rapid rotation of the contact. This very rapid motion ensures fast arc quenching and subsequent clearance of fault.
The improved cam based contact mechanism of a low voltage molded circuit breaker to withstand/compensate the electrodynamic forces generated and thereby maintaining contact stability where the mechanism comprising a housing means , an actuator means (rotor) located inside housing means to perform ON-OFF-TRIP operations ,a biased cam arrangement for applying threshold value to withstand/compensate electrodynamic force generated and thereby maintaining contact stability.

The biased cam arrangement comprises one or more contact arm means comprising cam profile substantially located inside housing means adapted to carry current, locking link means comprising cam profile mechanically coupled with the cam profile of contact means adapted to control the motion of contact means for sustaining contact stability. The arrangement further comprises one or more contact spring means substantially located inside the actuator means to apply torque on contact means, one or more locking spring means which is placed in-between a fixed pivot and locking link means. The locking spring means apply torque on the locking link means. The arrangement also comprises an operating mechanism to provide energy to rotor means to archive rotary motion of contact arms.
During the stable condition of the circuit breaker the breaker performs ON-OFF operations, OFF-ON operations.
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 contact spring is fully charged and beyond this point contact flips & operates independently due to energy discharged by contact spring. As relative position of rotor contact spring pin, centre pin and contact spring pin determines dead centre position of contact system, dead centre position can be varied.
The operating mechanism of the circuit breaker provides energy to rotor to achieve rotary motion of contact arms.

During ON-OFF operation, input to the rotor is given through the operating mechanism connected to rotor at portion 2a. 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 is rotated along with moving contact arm from ON to OFF position.
During OFF-ON operation also, input to the rotor is given through the operating mechanism connected to rotor at portion 2a. 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 is rotated along with Contact arm from OFF to ON position,
During unstable condition (ON-TRIP OPERATION) contact arm is not displaced till the predefined threshold force value of stated mechanism is reached. Threshold value is the mechanical compensation force essential to withstand the electro-dynamic forces exerted on the moving contact arm because of high flow of current through contact elements. When Electro-dynamic forces go beyond the pre-defined threshold force, locking link will rotate in clockwise direction to allow rotary motion of contact arm. Hence contact arm will move to the OFF Position independently. Operating mechanism is still at ON position.
The contact arm means comprising cam profile on lateral faces mechanically coupled with locking link cam profile to facilitate locking of contact till predefined threshold value during stable condition (ON-OFF operation) and the contact arm means comprising cam profile on lateral faces mechanically coupled with locking link cam profile adapted to facilitate unlocking of contacts beyond the same threshold value during unstable condition (TRIP operation).

The locking spring means are energy storing elements adapted to adjust threshold value by varying restrain force values associated with spring.
The locking spring further adapted to apply anticlockwise torque on locking link to implement/enforce locked/latched position of contacts with locking link till the predefined threshold value during stable condition (ON-OFF operations).
During the TRIP operation the electrodynamic forces go beyond the pre-defined threshold force and the locking link will rotate in clockwise direction to allow rotary motion of contact arm .hence the contact arm will move to the OFF position independently.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS Elements and Construction:
Referring to Figure 1 discloses Housing (1) it supports fixed contact arm and rotor.
Rotor (2) it performs multiple functions. It is connected to contact through centre pin and accommodates anchor pin for contact spring. It 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 locking link through lock link pivot hole and pin and has provision to couple with operating mechanism of breaker. Also one end of locking spring is mounted on rotor.
Moving and Fixed Contact Arm (3) they are current carrying elements. Moving contact arm has cam profile on lateral faces to engage with locking link cam profile to facilitate locking till predefined threshold value of force and unlocking beyond the same threshold value.
Centre Pin (4) this element connects moving contact to the rotor to allow rotary motion of contact about Z axis. Also position of centre pin determine dead centre position of contact system.

Contact Spring Pin(5) - Relative position of contact spring pin with respect to centre pin and rotor contact spring pin determine dead centre position of contact system and one end of contact spring is assembled with this pin ,
Rotor Contact Spring Pin (6) - Relative position of rotor contact spring pin with respect to centre pin and contact spring pin determine dead centre position of contact system. This pin also facilitates assembly of contact spring. 7. Contact Spring (7) — Contact spring is energy storing device which will store energy till dead centre and release energy to contact after dead centre. Relative position of contact spring with respect to centre pin decides dead centre of contact system. In this case two extension springs are used to achieve the function. However same can be achieved through number of springs as required by the function.
Locking Link (8) it 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 Link Pivot Pin (9) It facilitates assembly of locking link with the rotor and constrains axial movement of locking link.
Locking Spring(lO) Locking Springs 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 arrangement. 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. Any energy storage device meeting requirement of arrangement can replace locking spring mentioned in this invention.

Locking Spring Pin (11) It facilitates assembly of locking spring with locking link.
Operating mechanism (12) It is the circuit breaker operating mechanism which provides energy to rotor to achieve rotary motion of contact arms.
Various Positions of Cam Based Contact Mechanism are explained below
Referring to Figure 2 and 3 discloses ON-OFF Operation: At ON Position, moving contact arm 3 is at first stable position with its lateral face cam profile engaged with respective cam profile on locking link 8. During ON-OFF operation, input to the rotor 2 is given through the operating mechanism connected to rotor at portion 2a. 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 2 is rotated along with moving contact arm 3 from ON to OFF position.
OFF-ON Operation: At OFF Position, moving contact arm 3 is at second stable position with its lateral face cam profile engaged with respective cam profile on locking link 8.During OFF-ON operation also, Input to the rotor 2 is given through the operating mechanism connected to rotor at portion 2a.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 rotor2 is rotated along with Contact arm 3 from OFF to ON position.
Referring to Figure 4 and 5 discloses ON-TRIP Operation: During ON-TRIP Operation, contact arm 3 is not displaced till the predefined threshold force value of stated mechanism is reached. Threshold value is the mechanical compensation force essential to withstand the electro-dynamic forces exerted on the moving contact arm 3 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

clockwise direction to allow rotary motion of contact arm 3. Hence contact arm 3 will move to the OFF Position independently. Operating mechanism is still at ON position.
Resetting Operation: When Operating mechanism drives the rotor 2 , locking link 8 and contact arm 3 are resettled to locking position. Now, breaker is ready for next OFF-ON operation.
Referring to figure 6 discloses 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 contact arm pivot point and locking link pivot from line of cam force and the like .
Benefits of present invention:
♦ Intelligent Auto triggering Mechanism
♦ Easily adapted to any type of contact system such as single break, double break, and multiple finger system.
♦ 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.
♦ Few numbers of components thereby reducing assembly time.
♦ Negligible resistance during opening of contact arms

WE CLAIM
1. A cam based contact mechanism of a low voltage molded circuit breaker
adapted to withstand/compensate the electrodynamic forces generated and
thereby maintaining contact stability, said mechanism comprising
(i) a housing means ;
(ii) an actuator means located inside said housing means adapted to perform ON-OFF-TRIP operations ;
(iii) biased cam arrangement for applying threshold value to withstand/compensate said electrodynamic force generated and thereby maintaining contact stability; said arrangement comprising contact arm means and
(iv) an operating mechanism adapted to provide energy to said actuator means to achieve rotary motion of said contact arms adapted to initiate ON and OFF operation .
2. Mechanism as claimed in claim I wherein said biased cam arrangement
comprising:
at least one contact arm means comprising cam profile substantially located inside said housing means assisting to perform ON-OFF-TRIP operations;
locking link means having cam profile mechanically coupled with said cam profile of contact arm means adapted to control the rotary motion of said contact means for sustaining contact stability;

at least one contact spring means fixed with contact spring pin at its one end and rotor contact spring pin at its another end with said actuator means adapted to apply torque on said contact means and
at least one locking element operatively connected/associated with locking link pivot pin and said locking link means adapted to apply torque on said locking link means.
3. Mechanism as claimed in claim 2 wherein said contact arm means comprises cam profile on its lateral faces mechanically coupled with said locking link cam profile adapted to facilitate locking/latching of said contacts till predefined threshold value during stable condition (ON-OFF operation).
4. Mechanism as claimed in claim 2 wherein said contact arm means comprises cam profile on its lateral faces mechanically coupled with said locking link cam profile adapted to facilitate unlocking/unlatching of said contacts beyond the same threshold value during unstable condition (TRIP operation).
5. Mechanism as claimed in claims 3 and 4 wherein said threshold value corresponds to the change in constructional parameters selectively locking link length, perpendicular distances of contact arm pivot point and locking link pivot from line of cam force and the like .
6. Mechanism as claimed in claim 2 wherein said locking element comprises energy storing springs adapted to adjust said threshold value by varying restrain force values associated with said spring.
7. Mechanism as claimed in claim 6 wherein said locking element is further adapted to apply anticlockwise torque on said locking link to implement/enforce locked/latched position of said contacts with said locking

link till the pre-defined threshold value during stable condition (ON-OFF operations).
8. Mechanism as claimed in claim 6 wherein said locking element is further adapted to apply clockwise torque on said locking link to implement/enforce unlocked/unlatched position of said contacts with said locking link beyond pre-defined threshold value during unstable conditions(TRIP operation).
9. Mechanism as claimed in any of the preceding claims wherein said threshold value is the mechanical compensation force exerted on said moving contact arm because of high flow of current through said contacts during unstable conditions (TRIP operation).
10. Mechanism as claimed in claim 2 wherein said contact spring is adapted to store potential energy till dead center and release kinetic energy after dead center to the said contacts to perform ON-OFF operations ,OFF -ON operations.
11. Mechanism as claimed in claim 10 wherein said contact spring is further adapted to apply torque on said contact means to perform ON-OFF, OFF-ON operations.
12. Mechanism as claimed in claim 1 wherein said actuator means comprises of a rotor operatively connected with said moving contact with center pin to allow rotary motion of contact about Z axis.

13. An improved cam based contact mechanism of a low voltage molded circuit breaker adapted to withstand/compensate the electrodynamic forces generated and thereby maintaining contact stability as substantially described hereinbefore with reference to accompanying drawings.