A) TECHNICAL FIELD
[0001] The present invention generally relates to switchgear applications and particularly to moving contact assembly in circuit breakers. The present invention more particularly relates to rotary contact assembly for current limiting type Moulded Case Circuit Breakers (MCCB) to increase the velocity of opening of the contacts during a short circuit fault condition.
B) BACKGROUND OF THE INVENTION
[0002] Circuit breakers are widely used in domestic, commercial and light industrial installations. The circuit breakers protect circuits from overload and short circuit faults. Generally contact assembly in current limiting type moulded case circuit breaker has a moving contact which is suspended with a contact shaft with the help of one or more springs and moves along with the contact shaft during normal ON/OFF/TRIP operations. The moving contact opens rapidly on its own, when the fault current exceeds the threshold limit. The contact separation happens due to the electro-dynamic repulsion force generated between the moving contacts and the fixed contacts. As the moving contact moves away from the fixed contact, the electro-dynamic repulsion force is gradually reduced with respect to the opening gap between the contacts. Further, the torque due to the electro-dynamic force goes below a torque due to a contact spring force, depending on the design. Hence the moving contact is closed. Thus it becomes necessary to retain the moving contact in open position with help of a separate latching arrangement or inbuilt arrangement to avoid the reclosing of a contact.
[0003] During a short circuit fault, an electric arc is drawn between the opening contacts. The arc generated while contact separation is elongated and pushed into arc quenching plates to quench the arc. However, the whole arc quenching

cycle, from the opening time of the moving contact, through arc initiation to arc quenching, should be less in order to minimize the let-through energy.
[0004] In current limiting type circuit breakers, the moving contact opening time depends on the magnitude of the electro-dynamic force generated. It is necessary to maintain enough contact pressure to ensure proper contact between the moving contact and the fixed contact to avoid an effect caused to the contact life of the contacts and to maintain a temperature rise within an acceptable limit. Usually springs are used to generate the contact pressure between the contacts. The torque, at the contact pivot point, due to electro-dynamic force has to overcome the torque due to the contact pressure to ensure a contact separation. In the currently available rotary contact assemblies, as the moving contacts starts opening, the electro-dynamic force due to constriction is vanished and only repulsion force continues to exist. However, later the repulsion force also gets reduced as distance between the moving and the fixed contact increases. Thus, due to reduction of the electro-dynamic force, the opening velocity of the moving contact is significantly reduced.
[0005] Hence, there exists a need to provide an efficient rotary contact assembly for low voltage circuit breakers to increase the contact opening velocity and to latch the contact in opened position with minimum bouncing. Also there exists a need to reduce the contact opening time significantly.
[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 provide a rotary contact assembly for low voltage circuit breakers to increase the contact opening velocity.
[0008] Another object of the present invention is to provide a rotary contact assembly to latch the contact in an opened position with minimum bouncing effect.
[0009] Another object of the present invention is to provide a rotary contact assembly for low voltage circuit breakers to reduce the contact opening time significantly.
[0010] Another object of the present invention is to develop a rotary contact assembly to reduce the let-through energy of the breaker significantly.
[0011] Yet another object of the present invention is to provide a rotary contact assembly for low voltage circuit breakers to avoid re-striking of arc between the moving contact and the fixed contact during a fault condition.
[0012] Yet another object of the present invention is to provide a rotary contact assembly for low voltage circuit breakers to eliminate the need for an additional latching arrangement to keep the moving contact in open condition during fault condition.
[0013] These and other objects and advantages of the present invention will become readily apparent fi-om the following detailed description taken in conjunction with the accompanying drawings.

D) SUMMARY OF THE INVENTION
[0014] The various embodiments of the present invention provide a rotary contact assembly for low voltage circuit breakers to increase the contact opening velocity during repel opening of the electrical contacts in the circuit breakers. The contact assembly includes a contact shaft, at least one moving contact, at least one fixed contact, a cam profile, at least two extension springs, a copper braid, a plurality of fixed cylindrical pins and a plurality of moving cylindrical pins (follower pin).
[0015] According to one embodiment of the present invention, the moving contact assembly includes a moving contact with a cam profile, a follower pin, two extension springs and a supporting shaft with a follower slot. At least one moving contact with both the ends is arranged to have separation with respect to the fixed contacts. Alternatively, one moving contact includes one end arranged to have separation with respect to the fixed contfKSt and the other end connected to the fixed terminal through copper braids.
[0016] In one embodiment of the present invention, one end of the at least two extension springs is connected to a movably arranged cylindrical pin and the other end is connected to the fixed cylindrical pin. At least one moving cylindrical pin is movably arranged in the slots provided in the contact shaft and at least one fixed cylindrical pin is placed in the suitable profile provided in contact shaft. The rotary contact assembly includes at least one cylindrical pin which acts as pivotal guide for the moving contact. The contact shaft in the contact assembly rotates with respect to its own centre.
[0017] The moving contact is suspended with the contact shaft with the help of extension springs and a pin. When the contact shaft is rotated by the mechanism during ON position, the moving contact rotates along vdth the contact shaft and
touches the fixed contacts. After touching the fixed contacts, the torque at the contact pivot point due to springs is transferred to the contact points and there by the contact pressure is established based on further rotation or over travel of the contact shaft.
[0018] During short circuit or fault condition, if the torque due to electro-dynamic force reaches the threshold level of the contact, the moving contact starts moving away from the fixed contact. As the contact moves, the follower pin slides over the cam profile of the moving contact and the springs are stretched due to increasing distance between the pins 4 and 5. When the follower pin crosses the peak point of the cam profile, the spring length starts reducing rapidly and fiirther movement of the follower pin causes acceleration of the moving contact. This eliminates the need of an electro-dynamic force to rotate the moving contact. Thus the opening time is significantly reduced by utilizing the spring torque in addition to the electro-dynamic force to open the moving contact.
[0019] When the moving contact reaches the maximum opening position, the torque due to a spring force gradually reaches zero and hence the contact bouncing is minimized. By utilizing the spring torque in addition to electro-dynamic force to open the contact, the contact opening time is reduced significantly. The opened contact is brought to the home position, when the contact shaft returns to OFF position by the main mechanism.
[0020] The contact opening velocity is increased by providing a cam profile on the moving contacts and the follower pin with which one end of the each extension spring is connected. The spring force is utilized to deliver the contact pressure when the contacts are in closed position. This helps to accelerate the contact opening after pre-determined opening stroke or dead centre, while the contact repels to reduce the total contact separation time. The springs bring the contact to the maximum opening position irrespective of the electro-dynamic

force. The contact is retained in its opened position by the spring to minimize the contact bouncing and to avoid the re-striking of arc between the moving and the fixed contacts. The contact spring torque is used to generate the contact pressure between the moving contact and the fixed contact. The contact spring torque is utilized to increase the contact opening velocity and to latch the contact in opened position with minimum bouncing. This is achieved by a special cam profile on the moving contact, follower pin and suitable orientation and the arrangement of the spring and suitable slot in the contact shaft. Hence it eliminates the need of additional latching arrangement required to keep the moving contact in open condition during fault.
[0021] The springs are arranged in such a way that the maximum spring force is converted into useful torque to generate contact pressure between moving and fixed contacts when the breaker is in ON condition. Hence the spring size would be less and effective and either the contact shaft size could be reduced or spring size is increased significantly as required by the design. As the electro-dynamic force is gradually reduced while the moving contact moves away from the fixed contact, the positive opening of a contact is ensured by gradually reducing the spring torques while the moving contact is opening. This is achieved by a suitable orientation of the spring with resj^ct to a cam profile on the moving contact. The springs are arranged on the outer portion of the contact shaft, which leads to the ease of an assembly and simple design of contact shaft.
[0022] The rotary assembly increases electro-dynamic force between the contacts of the circuit breaker, thereby increasing the opening velocity of the moving contact. The springs and the contact shaft provided in the contact assembly leads to ease of assembly and simple design. The contact assembly provides a contact pressure between the fixed contact and the moving contact of the rotary contact assembly when the circuit breaker is in ON condition. The contact assembly avoids the re-striking of an arc between the moving and the fixed contacts during a fault condition. The design of the contact assembly eliminates the need for an additional latching arrangement required to keep the moving contact in open condition during fault condition.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0023] 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:
[0024] FIG. 1 shows an isometric view of a rotary type contact assembly according to one embodiment of the present invention.
[0025] FIG. 2 shows a front view of the double break rotary type contact assembly showing the moving contact in ON position according to one embodiment of the present invention.
[0026] FIG. 3 shows a front view of the double break rotary type contact assembly with the moving contact in open position and the contact shaft in ON position, according to one embodiment of the present invention.
[0027] FIG. 4 shows a front view of the double l»eak rotary type contact assembly with the moving contact in ftiUy open position and the contact shaft is in ON position, according to one embodiment of the present invention.
[0028] FIG. 5 shows an isometric view of a single break rotary type contact assembly, according to one embodiment of the present invention.
[0029] FIG. 6 shows a front view of the single break rotary type contact assembly, according to one embodiment of the present invention.

[0030] FIG. 7 shows a front view of the smgle break rotary type contact assembly with the moving contact in open position and the contact shaft in ON position, according to one embodiment of the present invention.
[0031] FIG. 8 shows a front of single break rotary type contact assembly with moving contact in fully open position and the contact shaft in ON position, according to one embodiment of the present invention,
[0032] 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 DES CRIPTION OF THE INVENTION
[0033] 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.
[0034] The various embodiments of the present invention is to provide a rotary contact assembly for low voltage circuit breakers to increase the contact opening velocity during repel opening of the electrical contacts in the circuit breakers. FI G. 1 shows an isometric view of rotary type contact assembly according to one embodiment of the present invention. With reference to FIG. 1, the double break rotary type contact assembly includes a contact shaft 1, at least one moving contact 2, at least one fixed contact, a cam profile, at least two extension springs 3, a copper braid, a plurality of fixed cylindrical pins 5, a pin 6 and a plurality of moving cylindrical pins (follower pin) 4. The moving contact assembly includes a moving contact with cam profile, follower pin, extension springs, and supporting shaft with follower slot. At least one moving contact (2) with both the ends is arranged to have separation with respect to the fixed contacts (7). Alternatively, at least one moving contact includes one end connected to the fixed contact and the other end connected to the fixed terminal (8) through copper braids (9) (as shown in FIG.4).
[0035] FIG. 2 shows a front view of the double break rotary type contact assembly showing the moving contact in ON position according to one embodiment of the present invention. The moving contact (2) is suspended with the contact shaft (1) with help of extension springs (3) and a pin (6). When the contact shaft is rotated by mechanism during ON position, the moving contact also rotates along with the contact shaft until it touches the fixed contacts (7 & 8). Immediately after touching the fixed contacts, the tOTque at the contact pivot point due to springs is transferred to the contact points and there by the contact pressure is established based on further rotation or over travel of the contact shaft.
[0036] During a short circuit or fault condition, if the torque due to electro-dynamic force reaches the threshold level of the contact, the moving contact(2) starts moving away firom the fixed contact. As the contact moves, the follower pin (4) slides over the cam profile (10) of the moving contact and the springs (3) are stretched due to an increase in distance between the pins 4 and 5. When the pin (4) crosses the peak point of cam profile, the spring length starts reducing rapidly and fiirther movement of follower pin (4) causes acceleration of moving contact(2). From this point onwards, there is no need of electro-dynamic force to rotate the contact (2) further. However the presence of torque due to such force also aids contact rotation in addition to the spring torque

[0037] When the contact reaches the maximum opening position, the torque due to spring force gradually reaches zero and hence the contact bouncing due to sudden stop is minimized. Hence, by utilizing the spring torque in addition to electro-dynamic force to open the moving contact, the contact opening time is reduced significantly. The opened contact is brought to its home position, when the contact shaft returns to OFF position by main mechanism.
[0038] According to one embodiment, one end of the two extension springs is connected to a movably arranged cylindrical pin (4) and the other end is connected to the fixed cylindrical pin (5). At least one moving cylindrical pin 4 is movably arranged in the slots provided in the contact shaft (1) and the at least one fixed cylindrical pin (5) is placed in the suitable profile provided in contact shaft (1). The rotary contact assembly includes at least one cylindrical pin (6) which acts as pivotal guide for moving contact. The contact shaft in the contact assembly rotates with respect to its own centre.
[0039] The contact opening velocity is increased by providing a cam profile on the moving contacts and the follower pin with which one ends of the each extension spring is connected. The spring force is utilized to deliver the contact pressure when the contacts are in closed position. Further, the spring force helps in accelerating the moving contact opening once the moving contact 2 reaches dead centre position. Thus, the moving contact repels away fi-om the fixed contact during fault to reduce the total contact separation time. Irrespective of the electro-dynamic force the contact is taken to its maximum opening position by these springs. The contact is retained in opened position by the spring to minimize the contact bouncing and to avoid the re-striking of arc between the moving and the fixed contacts. The contact spring torque is used to generate the contact pressure between the moving and the fixed contact. The contact spring torque is utilized to increase the contact opening velocity and to latch the contact in opened position with minimum bouncing. This is achieved by a special cam profile on the moving contact, follower pin and suitable

orientation and arrangement of spring and suitable slot in the contact shaft. Hence it eliminates the need of additional latching arrangement required to keep the moving contact in open condition during fault.
[0040] The springs are arranged in such a way that the maximum spring force is converted into usefijl torque to generate contact pressure between moving and fixed contacts when the breaker is in ON condition. Hence the spring size would be less and effective and either the contact shaft size could be reduced or spring size increased significantly as required by the design. As the electro-dynamic force is gradually reduced while the moving contact moves away from the fixed contact, a positive opening of a contact is ensured by gradually reducing the spring torques while the moving contact is opening. This is achieved by a suitable orientation of a spring with respect to a cam profile on the moving contact. The springs are arranged on the outer portion of the contact shaft which leads to ease of assembly and simple design of contact shaft
[0041] FIG. 3 shows a front view of the double break rotary type contact assembly with moving contact in open position and the contact shaft (1) still in ON position, according to one embodiment of the present invention. With respect to FIG. 3, the arrow indicates a direction of torque due to electro-dynamic force. The moving contact is almost reached a dead centre position. Further the spring torque gets reversed and accelerates the moving contact (2) to repel away fi-om the fixed contacts (7, 8 as shown in FIG. 4).
[0042] FIG. 4 shows a fi-ont view of the double break rotary type contact assembly with the moving contact (2) in fiilly opened position and the contact shaft (1) in ON position, according to one embodiment of the present invention. The moving contact (2) is retained in this position till the main mechanism (not shown in FIG.4) brings the contact shaft (1) to its home position. The arrow indicates the direction of the torque due to the springs and an electro-dynamic force. The contact opening velocity between the contact position as shown in

FIG. 3 and FIG. 4 is significantly increased by the springs. At this position of the moving contact, the magnitude of spring torque is brought nearly to zero value.
[0043] FIG. 5 shows an isometric view of a single break rotary type contact assembly, according to one embodiment of the present invention. With reference to FIG. 1, the single break rotary type contact assembly includes a contact shaft 1, one moving contact 2, at least one fixed contact, a cam profile, at least two extension springs 3, a copper braid 10, a plurality of fixed cylindrical pins 5, a pin 6 and a plurality of moving cylindrical pins (follower pin) 4. The moving contact assembly includes a moving contact with cam profile, follower pin, extension springs, and supporting shaft with follower slot. The at least one moving contact (2) with one end arranged to have separation with respect to the fixed contacts and the other end connected to the fixed terminal 7 (as shown in FIG. 6) through copper braids (9) (as shown in FIG.6).
[0044] During short circuit or fault condition, when the torque due to electro-dynamic force reaches the threshold level of the cont^t, the moving contact(2) starts moving away fi"om the fixed contact. As the contact moves, the follower pin (4) slides over the cam profile of the moving contact and the springs (3) are stretched due to increasing distance between the pins 4 and 5. When the pin (4) crosses the peak point of cam profile the spring length starts reducing rapidly and fimher movement of follower pin (4) causes acceleration of moving contact(2). From this point onwards there is no need of electro-dynamic force to rotate the contact (2). The presence of torque due to the electro-dynamic force also aids in contact rotation in addition to spring torque.
[0045] When the contact reaches the maximum opening position, the torque due to a spring force gradually reaches zero and hence the contact bouncing due to sudden stop is minimized. Hence, by utilizing the spring torque in addition to

electro-dynamic force to open the contact, the contact opening time is reduced significantly. The opened contact is brought to its home position when the contact shaft returns to OFF position by a main mechanism.
[0046] According to one embodiment, one end of the two extension spring is connected to a movably arranged cylindrical pin (4) and the other end is connected to the fixed cylindrical pin (5). At least one moving cylindrical pin 4 is movably arranged in the slots provided in the contact shaft (1) and at least one fixed cylindrical pin (5) is placed in the suitable profile provided in contact shaft (1). The rotary contact assembly includes at least one cylindrical pin (6) which acts as pivotal guide for moving contact. The contact shaft in the contact assembly rotates with respect to its own centre.
[0047] The contact opening velocity is increased by providing a cam profile on the moving contacts and the follower pin with which one ends of the each extension spring is connected. The spring force is utilized to deliver the contact pressure when the contacts are in closed position. Furtiier, the spring force helps in accelerating the moving contact opening once the moving contact 2 reaches dead centre position. Thus, the moving contact repels away from the fixed contact during a fault condition to reduce the total contact separation time. Irrespective of the electro-dynamic force, the contact is taken to its maximum opening position by these springs. The contact is retained in opened position by the spring to minimize the contact bouncing and to avoid the re-striking of arc between the moving and the fixed contacts. The contact spring torque is used to generate the contact pressure between the moving and the fixed contacts. The contact spring torque is utilized to increase the contact opening velocity and to latch the contact in opened position with minimum bouncing. This is achieved by a special cam profile on the moving contact, follower pin and suitable orientation and arrangement of spring and suitable slot in the contact shaft. Hence it eliminates the need of additional latching

arrangement required to keep the moving contact in open condition during fault.
[0048] The springs are arranged in such a way that the maximum spring force is converted into useful torque to generate a contact pressure between the moving and the fixed contacts when the breaker is in ON condition. The spring size would be less and effective and either the contact shaft size could be reduced or spring size increased significantly as required by the design. As the electro-dynamic force is reduced while the moving contact moves away from the fixed contact, a positive opening of the contact is ensured by gradually reducing the spring torques while the moving contact is opening. This is achieved by suitable orientation of spring with respect to cam profile on the moving contact. The springs are arranged on the outer portion of the contact shaft, which leads to ease of assembly and simple design of contact shaft
[0049] FIG. 6 shows a fi-ont view of the single break rotary type contact assembly, according to one embodiment of the present invention. With respect to FIG. 6, the moving contact (2) is in closed position i.e. breaker is in ON condition. The moving contact includes one end connected to the fixed contact and the other end connected to the fixed terminal 7 (as shown in FIG. 6) through copper braids (9). The bent arrow indicates the spring torque direction and the straight arrow indicates the direction of the contact pressure.
[0050] FIG. 7 shows a fi"ont view of the single break rotary type contact assembly with the moving contact (2) in open position and the contact shaft in ON position, according to one embodiment of the present invention. With respect to FIG. 7, the arrow indicates the torque direction, due to an electro-dynamic force. The moving contact is almost at dead centre position. Hence the spring torque is reversed and accelerates the moving contact would reverse and accelerate the moving contact (2) to move away from the fixed contact 7.

[0051] FIG. 8 shows a front of single break rotary type contact assembly with moving contact (2) in fully open position and the contact shaft in ON position, according to one embodiment of the present invention. The moving contact (2) is retained in open position until the main electrical mechanism (not shown) brings the contact shaft to a home position. The arrow indicates the torque direction, due to springs and electro-dynamic force. The contact opening velocity between the contact position shown in FIG. 3 and FIG. 4 is significantly increased by the springs and the magnitude of spring torque is brought near to zero value.
G) ADVANTAGES OF THE INVENTION
[0052] The various embodiments of the invention provide a rotary contact assembly for a low voltage circuit breaker to increase the opening velocity of the moving contact. The springs and the contact shaft provided in the contact assembly leads to ease of assembly and simple design. The contact assembly provides a contact pressure between the fixed contact and the moving contact of the rotary contact assembly when the circuit breaker is in ON condition. The contact assembly avoids the re-striking of an arc between the moving and the fixed contacts during a fault condition. The design of the contact assembly eliminates the need for an additional latching arrangement required to keep moving contact in an open condition during a fault condition.
[0053] 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.

[0054] 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 rotary contact assembly in circuit breakers, the assembly comprising: a contact shaft, at least one fixed contact,
at least one moving contact, a cam profile,
at least two extension springs, a copper braid,
a plurality of fixed cylindrical pins; and
a plurality of moving cylindrical pins;
wherein the cam profile and the arrangement of at least two contact springs
generate a contact pressure between at least one moving contact and at least one
fixed contact to increase the contact opening velocity and to latch the moving
contact in an open position with a minimum bouncing.
2. The contact assembly according to claim 1, wherein at least one moving contact includes one end connected to the fixed contact and the other end connected to a fixed terminal through the copper braids.
3. The contact assembly according to claim 1, wherein one end of at least two extension spring is coimected to a movably arranged cylindrical pin and the other end is connected to a fixed cylindrical pin.
4. The contact assembly according to claim 1, wherein the rotary contact assembly includes at least one cylindrical pin which acts as pivotal guide for the moving contact.
5. The contact assembly according to claim 1, wherein at least two extension springs are arranged in a way to convert the spring force to a torque to generate the contact pressure between at least one moving contact and at least one fixed contact when the circuit breaker is in ON condition.

6. The contact assembly according to claim 1, wherein the moving cylindrical pin
slides over the cam profile of the moving contact and at least two extension
springs are stretched due to an increase in distance between the moving cylindrical pin and the fixed cylindrical pin.
7. The contact assembly according to claim 1, wherein at least two extension springs are arranged in a manner with respect to the cam profile for reducing the spring torque to provide for a positive opening of at least one moving contact.
8. The contact assembly according to claim 1, wherein at least two extension springs are arranged on an outer portion of the contact shaft.