F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention: PARTIAL ATTRACTION TYPE LOCKING MECHANISM FOR CONTACT SYSTEM

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 locking mechanism for use in contact systems. More particularly, the present invention relates to a system in 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.

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. These types of compensation require higher space to accommodate the same and require an external actuation or impetus for operation/de-latching. In this invention we have provider locking within the limited space using electromechanical compensation.

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.

In US6084489 Latch engages when contact is in open position while in present invention cam engagement is at both closed and open (after reset) position. In US6084489 arm is unlocked by operating mechanism whereas present invention is self triggering mechanism.

US 6015959 discloses cam mechanism used for switching in Normal conditions where as present invention cam arrangement is used to operate only in abnormal (short circuit) condition. US 6015959 cam mechanism used is manually operated whereas present invention is self triggering mechanism.

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 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 purpose is to operate the breaker however in present invention mechanical arrangement is used for locking moving contact till particular threshold value and self triggered unlocking beyond threshold value.

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.

In US 6,590,482 cam action is utilized to increase space available for operating mechanism for more powerful operating spring while in present invention cam action is used for locking moving contact till particular threshold value and self triggered unlocking beyond threshold value.

The disadvantages of the above mentioned prior art is that in the power system the circuit breakers are connected in series. During any fault condition both the downstream and the upstream breaker experience 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.

Thus there is a need to provide a system in 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. Here this is achieved with electro-mechanical compensation for the electrodynamics forces on the moving contact.

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 objective of the invention is to use the electro-mechanical forces available in the system for withstanding high repulsive forces during high currents for the time the downstream breaker clears the fault.

Yet another object of the present invention is to provide an improved electro-mechanical means where the threshold value (the current corresponding to initiation of contact separation) 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 up to a preset value by auto de latching of the contact arrangement beyond the preset value.

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 opening of the contacts, which will ensure fast arc quenching and subsequent clearance of fault.

Another objective of the invention is to achieve linear opening for clearing the fault.

These and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided an improved locking mechanism in circuit breakers, said mechanism comprising:
a contact system , said system comprising a right half and a left half;
said contact system comprising :
a pair of fixed contact means, said each fixed contact means substantially flanked on the right half and the left half of said contact system;
a pair of moving contact means ,said each moving contact means substantially flanked on the right half and the left half of said contact system, said each moving contact means comprising :
a moving button means operatively connected with said moving contact means;
a moving contact pin means operatively connected with said moving contact means;
a pair of pivot pin means ;
a guide link means having a slotted profile comprising:
a first profile means and a second profile means substantially perpendicular to said first profile means ;
said first profile means comprising a pair of slot means, said each slot means adapted to accommodate the moving contact pin means ;
said second profile means compressing a slot means, said slot means adapted to accommodate a pivot pin means ;
a pair of slider link means comprising a right slider link means substantially placed at the right half of said contact system and a left slider means substantially placed at the left half of said contact having define a modular V-shaped profile ;
wherein said right slider means and left slider means is operatively connected to said moving contact means at the first profile means of said guide link means by moving contact pin means at the slot means provide in said first profile means of guide link means adapted to slide the moving contact means from on –off, off-on positions ;
a linear slider link means operatively connected with said slider link means by pivot pin means at the slot provided in said second profile means of said guide link means adapted to operate said moving contact simultaneously;
an operating handle operatively connected with said linear slider link means adapted to perform on off operations and
an energy storing element operatively connected with said handle means adapted to exert force on moving contacts to perform on off operations.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:
Fig. 1 illustrates the Isometric view of the contact arrangement along with the operating mechanism in ON condition
Fig. 2 illustrates the Isometric view of the contact arrangement along with the operating mechanism in ON condition with hidden lines.
Fig. 3 illustrates the Isometric view of the contact arrangement along with the operating mechanism in OFF condition.
Fig. 4 illustrates the Isometric view of the contact arrangement along with the operating mechanism in OFF condition with hidden lines.
Fig. 5 illustrates Isometric view of the contact arrangement.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWING

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and illustrate the best mode presently contemplated for carrying out the invention. Further functioning of the mechanism has been discussed below to describe the way the mechanism operates. However, such description should not be considered as any limitation of scope of the present unit. 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.

Elements and Construction:
1: Fixed contact : It is current carrying element of the circuit which remains fixed during the operation.
2: Braids : These are the flexible part carrying current in the circuit. It can be multi stranded conductors or multiplicity of conducting foils.
3. Moving Contact : It is the moving part of the current carrying circuit. While interrupting the circuit this part moves away from the fixed contact to isolate the system.
4. Fixed Runner : It is connected to the fixed contact for efficient movement of the electric arc formed during fault condition in the circuit breaker
5. Deion Plates : It is magnetic material kept at a distance from the fixed and the moving contact for effective pulling of the arc towards it for quenching.
6. Runner : It is a magnetic material put in for efficient movement of the electric arc formed during fault condition in the circuit breaker.
7. Link : It is used for electrically connecting the braids on either side.
8. Stand : It is used for proving support for the links.
9. Guide Link : It provide guide for the contact pivot pin and the link slider. The guide link means can be of any shape and shape of the guide link shown in the present invention is not to be considered as restricting scope of the present invention. Guide links of any other shape which are technically equivalent to the guide link shown herein can also be used.
10. Link Slider : It is a link used for sliding the moving contact from on to off or vice versa.
11. Fixed Contact Button : It is the button on the fixed contact.
12: Moving Contact Button : It is the button on the moving contact
13. Pivot Pin for Moving contact : It is the pivot pin for the moving contact about which it can rotate. Also the slider link is connected to this pivot for operating the moving contact.
14. Linear Slider Link : This element is connected to the slider links so as to operate the moving contacts simultaneously.
15. Pivot Pins: It is the pivot pin for the links for proper guided motion.
16. Link Handle : It is the operating handle to turn on or off the breaker
17. Springs : It is an extension spring used for exerting force on the moving contact. It can be extension spring, compression springs, torsion springs or any other energy storing device.
Threshold value: It’s the electro-mechanical compensation force corresponding to a particular value of current, 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.

Various Positions are explained below

In Fig.-1 the arrangement is in the ON condition. The fixed contact(1) and the moving contact(3) are held together by a force with the help of the extension springs(17). The operating mechanism consisting of Stand(8), Link Handle(16), Linear Slider Link(14), Link Slider(10), Spring(17) are arranged in a way so that it exerts force on the Link Handle(16) and the link handle pushes the Linear slide link(14). The operating mechanism can be any different mechanism as well consisting of different parts to operate the Linear slider link(14) and hence operating the slider link(10). The linear slide link push(14) the Link Slider(10) with the help of the pivot pins(15). The Link slider(10) holds the moving contact(3) in the on position against the repulsive forces of the contact.

In Fig.-3 the arrangement is in the OFF condition. The fixed contact(1) and the moving contact(3) are held separated by the extension springs(17). The operating mechanism consisting of Stand(8), Link Handle(16), Linear Slider Link(14), Link Slider(10), Spring(17) are arranged in a way so that it exerts force on the Link Handle(16) and the link handle pulls the Linear slide link(14) in opposite direction w.r.t the ON position. The linear slide link(14) pulls the Link Slider(10) with the help of the pivot pins. The Link slider(10) holds the moving contact(3) in the OFF position.

In Fig.-5 shows the contact assembly. The arrows show the direction of the current flow through the contacts. The current flows from the fixed contact(1) to the moving contact(3) and then through the braids(2) to the Link(7) and then to the other half of the contact system entering through the braids(2) to the moving contact(3) and coming out of the fixed contact(1). During normal current the pivot pin for moving contact(13) is held tightly by the Link Slider(10) which in turn is held by the spring(17). When current flows through the contacts it generates electrodynamic forces between the fixed contact(1) and the moving contact(3). As the direction of the current in the fixed contact(1) and the moving contact(3) is opposite the electrodynamic forces will be repulsive in nature. The length of the current carrying path on the right side of the moving contact(3) is more than that at the left side of the pivot pin for the moving contact(13). The magnitude of electrodynamic forces generated depends on the current and the overlap lengths. As same current flows through the entire circuit the electrodynamic force generated at the left side of the Pivot Pin for the moving contact(13) is less than the force generated at the right side depending on there respective lengths. Due to this difference in force a torque acts on the moving contact about the Pivot pin of the moving contact(3) in clockwise direction. Now during normal condition the Pivot pin for moving contact(13) is held tightly, due to this the clockwise torque generated on the moving contact(3) helps to maintain the contact pressure. During short circuit condition as the current rises, the torque also increases, which helps to maintain the moving contact(3) in ON position without using any extra external force. Due to this extra torque the extra pressure required to maintain the contacts in on position is obtained from the electrodynamic forces present in the system. The spring(17) is so adjusted such that beyond the threshold value(18) the force at the Pivot pin for moving contact(13) increase beyond the withstand capacity of the spring and the operating mechanism pulls the moving contacts apart from the fixed contact(1). During ON-OFF operation the operating mechanism is operated with the Link Handle(16).
Threshold point of the contact system can be changed by varying various constructional parameters such as link length, perpendicular distances from contact arm pivot point , locking link pivot and spring force.
In this invention linear opening is achieved by adjusting the slots in the guide link(9). Any form of contact opening can also be achieved such as rotational opening between the contacts by adjusting the slots of the guide link(9).

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.
 Without any external force arrangement we are able to provide proper contact pressure even if the current increases to a high value below the threshold value set using the springs.
 Negligible resistance during opening of contact arms and assisting torque on moving contact after dead centre rotation of contact.
 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.

WE CLAIM:

1. An improved locking mechanism in circuit breakers , said mechanism comprising :
a contact system , said system comprising a right half and a left half;
said contact system comprising :

a pair of fixed contact means , said each fixed contact means substantially flanked on the right half and the left half of said contact system;

a pair of moving contact means ,said each moving contact means substantially flanked on the right half and the left half of said contact system, said each moving contact means comprising :
a moving button means operatively connected with said moving contact means;
a moving contact pin means operatively connected with said moving contact means;
a pair of pivot pin means ;
a guide link means having a slotted profile comprising:
a first profile means and a second profile means substantially perpendicular to said first profile means ;
said first profile means comprising a pair of slot means , said each slot means adapted to accommodate the moving contact pin means ;
said second profile means compressing a slot means, said slot means adapted to accommodate a pivot pin means ;
a pair of slider link means comprising a right slider link means substantially placed at the right half of said contact system and a left slider means substantially placed at the left half of said contact having define a modular V-shaped profile ;
wherein said right slider means and left slider means is operatively connected to said moving contact means at the first profile means of said guide link means by moving contact pin means at the slot means provide in said first profile means of guide link means adapted to slide the moving contact means from on –off, off-on positions ;
a linear slider link means operatively connected with said slider link means by pivot pin means at the slot provided in said second profile means of said guide link means adapted to operate said moving contact simultaneously;
an operating handle operatively connected with said linear slider link means adapted to perform on off operations;
an energy storing element operatively connected with said handle means adapted to exert force on moving contacts to perform on off operations.

2. Mechanism as claimed in claim 1 wherein said fixed contact means comprising a fixed button means operatively connected with said fixed contact means .

3. Mechanism as claimed in claim 1 wherein said energy storing element is an extension spring.

4. Mechanism as claimed in claim 3 wherein said energy storing element is optionally an torsion spring or a compression spring or any other energy storing device.

5. Mechanism as claimed in claim 2 wherein said fixed button means is operatively connected with said moving button means when in ON position.

6. Mechanism as claimed in claim 1 further comprising a pair of flexible means operatively said moving contact adapted to carry current within the circuit.

7. Mechanism as claimed in claim 6 wherein said flexible means is a multi standard conductors.

8. Mechanism as claimed in claim 7 wherein said flexible means is optionally multiplicity of conducting foils.

9. Mechanism as claimed in claim 8 wherein said flexible means comprises of a link means placed in between said flexible means adapted to electrically connect said flexible means on either side.

10. Mechanism as claimed in claim 1 further comprising a pair of fixed runner means operatively connected with said fixed contact means adapted efficient movement of the electric arc formed during fault condition in the circuit breaker.

11. Mechanism as claimed in claim 1 further comprising a pair of plate means configured substantially away from said fixed contact means and moving contact means adapted for effective pulling of the arc towards it for quenching.

12. Mechanism as claimed in claim 11 wherein said plate means is magnetic material.

13. Mechanism as claimed in claim 1 further comprising a runner means substantially placed in between said pair of plate means adapted for efficient movement of the electric arc formed during fault condition in the circuit breaker.

14. Mechanism as claimed in any of the preceding claims wherein said fixed contact means having current flow in the opposite direction of moving contact means.

15. Mechanism as claimed in claim 14 wherein said fixed contact means and moving contact means generates electrodynamic forces that is repulsive in nature.

16. Mechanism as claimed in claim 1 wherein said guide link means adapted to provide guide for the contact pin and link slider

17. Mechanism as claimed in claim 1 further comprising a stand means adapted for providing support to the operating handle means and said linear slider link means.

18. Mechanism as claimed in claim 1 wherein said right half of contact system is having more length than the left half of contact system.

19. Mechanism as claimed in claim 18 wherein said right half of contact system generates more electro dynamic force than the left side of contact system.

20. Mechanism as claimed in claim 1 wherein said operating handle pulls said linear slider clockwise and anticlockwise direction adapted perform on and off operations.

21. Mechanism as claimed in claim 1 wherein said linear slider link adapted to push said link slider in clockwise and anticlockwise direction adapted to perform on and off operations.

22. Mechanism as claimed in claim 1 wherein said right half and left half are similar.

23. An improved locking Mechanism in circuit breakers as herein substantially described and illustrated with the accompanying drawings.