FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"Rotary Contact Arrangement for Low Voltage Circuit Breakers"
2. APPLICANT;
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: LARSEN & TOUBRO LIMITED,
L&T House, Ballard Estate, P. O. Box: 278, Mumbai 400 001, India
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Rotary Contact Arrangement for Low Voltage Circuit Breakers Field of invention
The present invention relates to moulded case circuit breakers, and more particularly, to a contact pressure improvement mechanism of the circuit breakers.
Background of the invention
In any current limiting type moulded case circuit breaker (MCCB, hereinafter), the moving contacts are suspended with the rotary contact shaft with the help of springs such that the spring force is converted into a contact pressure between the moving contact and the fixed contact buttons. The moving contact moves along the contact shaft during the ON/OFF/TRIP operation of the circuit breaker. In case of short circuit or fault conditions, the moving contact opens rapidly on its own when the fault current exceeds the designed threshold current limit. This contact separation happens due to the electro-dynamic repulsion force that is generated between the moving and fixed contacts due to the effect of current flow in opposite direction.
In general, faster separation of moving contact is preferred to help minimize the cut¬off current value which in turn leads to reduced let-through in the circuit. In some designs, the contacts are arranged in such a way that the springs used to deliver contact pressure in the ON condition of the circuit breaker are utilized to achieve a flipping action that accelerates the moving contact during aforesaid separation during short circuit fault.
It is necessary to maintain good contact pressure to ensure proper contact between the moving contact and the fixed contact to maximize contact life and control

temperature rise in the system. However, achieving desired contact pressure is a challenge in prior art systems as they use either heavy springs or alternatively more number of springs thereby occupying lot of space thereby making the design costly and complex.
For example, U.S. Patent No, 6326868 discloses a circuit breaker rotary contact arm that is used within a plurality of single pole circuit breakers ganged together to form a single multi-pole circuit breaker. To provide uniform contact wear among the associated circuit breaker contacts, the rotor carrying the rotary contact arm pivot is slotted to automatically position the rotary contact arm to allow for changes in the contact geometry while maintaining constant contact compressive forces. The individual circuit breakers connect with the central operation mechanism by means of a single pin.
Also, Patent No: U.S. Patent No. 6259048 teaches a circuit breaker rotary contact assembly that employs a common pivot between the rotor assembly and the rotary contact arm wherein a pair of off-center expansion springs directly engage the rotor at one end and engage the rotary contact arm via a linkage arrangement at an opposite end thereof. The circuit breaker includes a first spring on a one side of said rotor and a first pair of pins attaching said first contact arm to said rotor on said one side. The circuit breaker includes a second spring on a opposite side of said rotor, said first pair of pins attaching said first contact arm to said rotor on said opposite side. The circuit breaker includes a a third spring on said one side of said rotor and a second pair of pins attaching said first contact arm to said rotor on said one side. The circuit breaker includes a fourth spring on said opposite side of said rotor, said second pair of pins attaching said first contact arm to said rotor on said opposite side.

Accordingly, there exists a need of a contact assembly that is compact. Also, there exists a need of a contact assembly having minimum number of springs for achieving flipping action and facilitating desired contact pressure with relatively less spring force.
Object of the invention
An object of the present invention is to provide a single-break type flipping contact arrangement having least number of springs.
Another object of the present invention is to provide a contact arrangement having a flexible conductor with a reduced effective length.
Yet another object of the present invention is to provide a contact arrangement having a drastically reduced effective width.
Summary of the invention
Accordingly, the present invention provides a rotary contact arrangement for low voltage circuit breakers. The rotary contact arrangement comprises a contact shaft (2) adapted to rotate with respect to its own center. The contact shaft (2) is rotated by the circuit breakers mechanism during normal ON, OFF and TRIP operation. The rotary contact arrangement further includes at least one moving contact (1) pivoted to the contact shaft (2), at least one first cylindrical pin (4) movably arranged in a slot provided in the contact shaft (2), at least one fixed/ stationary cylindrical pin (5) arranged on the contact shaft (2), at least one second cylindrical pin (6) attached to the second end of the moving contact (1), at least one connecting

link (3) having a first end connecting to the first cylindrical pin (4) and a second end connecting to the second cylindrical pin (6), at least one pivotal pin (10) for suspending the moving contact (1) with the contact shaft (2), and at least one contact spring (11) having a first end connected to the first cylindrical pin (4) and a second end connected to the fixed/ stationary cylindrical pin (5). The torque on the moving contact (1) due to electro-dynamic force exceeds the torque offered by the contact spring (11), the moving contact (1) starts moving away from the fixed contact (8) whereby the first cylindrical pin (4) slides along the slot in the contact shaft (2) and causes the perpendicular distance between the line of force acting on the moving contact (1) due to the spring (11) which helps to open moving contact (1) with relatively less electro-dynamic force, and when the torque offered by the contact spring (11) becomes zero, any further movement of moving contact (1) leads to flipping of moving contacts.(l) by contact spring (11).
Brief description of the drawings
FIG. 1 is an isometric view of a preferred embodiment of a rotary contact arrangement constructed in accordance with the present invention;
FIG. 2 is a cross sectional view of the preferred embodiment of the rotary contact arrangement of FIG. 1 showing a plurality of structural components configured in conjunction with a fixed contact;
FIG. 3 is a cross sectional view of the preferred embodiment of the rotary contact arrangement of FIG. 1 in an ON position of a moving contact;

FIG. 4 is a cross sectional view of the preferred embodiment of the rotary contact arrangement of FIG. 1 wherein the moving contact is in partially open position and a contact shaft is in an ON position;
FIG. 5 is a cross sectional view of the preferred embodiment of the rotary contact arrangement of FIG. 1 wherein the moving contact is in a fully opened position and the contact shaft is in the ON position;
FIG. 6 is an isometric view of an alternative embodiment of a rotary contact arrangement constructed in accordance the present invention;
FIG. 7 is a cross sectional view of the alternative embodiment of the rotary contact arrangement of FIG. 6 having a plurality of structural components configured in conjunction with a fixed contact;
FIG. 8 is a cross sectional view of the alternative embodiment of the rotary contact arrangement of FIG. 6 in an ON position of a moving contact; FIG. 9 is a top view of the alternative embodiment of the rotary contact arrangement of FIG. 6in an ON position of the moving contact;
FIG. 10 is a cross sectional view of the alternative embodiment of the rotary contact arrangement of FIG. 6 wherein the moving contact is in partially open position and a contact shaft is in an ON position; and
FIG. 11 is a cross sectional view of the alternative embodiment of the rotary contact arrangement of FIG. 6 wherein the moving contact is in a fully opened position and the contact shaft is in the ON position.

Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
Referring to FIGS. 1-2, a rotary contact arrangement (100) in accordance with the present invention is shown. In this one preferred embodiment, the rotary contact arrangement (100) is a single break type rotary contact arrangement. The rotary contact arrangement (100) includes at least one moving contact (1) that is pivoted to a contact shaft (2). The contact shaft (2) is connected with a MCCB mechanism (not shown) and is adapted to rotate with respect to its own center. The moving contact (1) is preferably pivoted along a center portion of rotation of the contact shaft (2). However, it is understood that the moving contact (1) can be mounted along an offset position from the center of the contact shaft (2) in other alternative embodiment of the rotary contact arrangement (100).
The rotary contact arrangement (100) includes a connecting link (3). The connecting link (3) is having a first end that connects to a first cylindrical pin (4). The rotary contact arrangement (100) includes a fixed/ stationary cylindrical pin (5). The rotary contact arrangement (100) includes a second cylindrical pin (6) that is attached to the moving contact (1). The connecting link (3) is having a second end that connects to the third cylindrical pin (6).
The moving contact (1) includes a first end that includes a contact button (7) adapted to meet with a fixed contact (8). However, it is understood that the moving contact (2) may include the contact button (7) on both the ends of the moving contact (1) in other alternative embodiment of the rotary contact arrangement (100).

The moving contact (1) includes a second end that is connected with a fixed terminal (not shown) through a flexible conductor (12) in this one embodiment.
The moving contact (1) is suspended with the contact shaft (2) with a pivotal pin (10) and at least one extension type contact spring (11). The extension type contact spring (11) is having a first end that is connected to the first movable cylindrical pin (4). The extension type contact spring (11) is having a second end that is connected to the fixed/ stationary cylindrical pin (5). The first movable cylindrical pin (4) is movable within a slot (13) defined on the contact shaft (1). The rotary contact arrangement (100) includes a second cylindrical pin (10) which acts as a pivotal guide for the moving contact (1).
Referring to FIGS. 3-5, the moving contact (1) is respectively shown in an ON position, a partially open position and a fully open position. In this one preferred embodiment, the contact shaft (2) constantly remains in an ON position. The moving contact (1) is configured to remain in the fully open position until a main mechanism (not shown) brings the contact shaft (2) to a home position. In the ON position, the moving contact (1) rotates along with contact shaft (2) until contact button (7) touches the fixed contact button (9). In operation, the contact shaft (2) is configured to rotate by a MCCB mechanism (not shown) during normal ON, OFF and TRIP operation of the moving contact (1).
When the contact shaft (2) is rotated by MCCB mechanism (not shown) during normal ON, OFF and TRIP operation, the moving contact (1) also rotates along with the contact shaft (2). During ON operation, Immediately after that the torque at the contact pivot point due to contact spring (11) is transferred to the contact points and there by the contact pressure is established between contact buttons (7&9) corresponding to further rotation of the contact shaft(2).

In case of short circuit fault in the system, electro-dynamic force is generated between fixed contact (8&9) and moving contact (1&7) due to current flow in opposite directions, which is the basic design feature of current limiting type circuit breakers. The magnitude of this electro-dynamic force depends on the construction of contact system and the fault current level.
When the torque experienced by the moving contact (1) due to the said electro-dynamic force exceeds the torque offered by contact spring (11), the moving contact (1) starts moving away from fixed contact (8 &9). As the contact (1) moves, the moving pin (4) slides along the slot in the shaft which causes the perpendicular distance between the line of force acting on the moving contact due to springs (11) and contact rotating center to reduce gradually and thus the effective torque offered by contact springs reduces rapidly though the spring (11) is stretched, and hence it helps to open moving contact (1) with relatively less electro-dynamic force.
At the point where the center of moving pins (4& 6) coincides with the moving contact(l) rotating center the torque offered by contact spring becomes zero and any further movement of moving contact (1) beyond this point leads to flipping of moving contacts (1) by contact spring (11). This flipping action helps to further accelerate the moving contact (l)in addition to electro-dynamic force and thus moving contact opening time is reduced significantly which in turn helps to limit the cut-off current.
Once the moving contact (1) is flipped, it is retained in the open position by contact springs (11). Subsequent tripping of operating mechanism brings the moving contact (1) to home position.

Referring now to FIG. 6 to 11, there is shown an alternative embodiment of a rotary contact arrangement (200) constructed in accordance the present invention for a double break, construction of the rotary contact arrangement (200), The rotary contact arrangement (200) includes a second fixed contact (9). The components used for the rotary contact arrangement (200) are similar to the rotary contact arrangement (100). Specifically, to achieve the double break construction, a similar set of elements of the rotary contact arrangement (100) is used in opposite direction of the contact shaft (2) where the other fixed contact (9) is located. More specifically, the moving contact (2) includes the contact button (7) on both the ends of the moving contact (1). Other elements of the rotary contact arrangement (200) are similar to the elements of the rotary contact arrangement (100) and are not described herein in detail for the sake of brevity of the description.
Fig. 8 shows the sectional view of the rotary contact arrangement (200) having double break type construction, wherein the moving contact (1) is in ON position, Fig. 10 shows the sectional view of the rotary contact arrangement (200). Here, the moving contact (1) is in partially open position but the contact shaft (2) is in same ON position, and Fig. 11 shows the sectional view of the rotary contact arrangement (200), wherein the moving contact (1) is in fully opened position but the contact shaft (2) is still in ON position. The moving contact (1) is retained in this position till the main mechanism (not shown) brings the contact shaft (2) to its home position.
Advantages of the present invention
1. The rotary contact arrangement (100) uses only one extension type contact spring to achieve flipping action in a single break type contact configuration.

2. . The rotary contact arrangement (100) design can be used in both single break type and double break type contact configuration.
3. The rotary contact arrangement (100) includes an arrangement of a contact spring and connecting links away from center of rotation of the moving contact which helps to achieve higher contact pressure between moving contact button and fixed contact button with relatively less spring force.
4. In the rotary contact arrangement (100),flipping action of moving contact can be achieved at desired angle with help of a connecting link arrangement without compromising on required spring torque on moving contact
5. The rotary contact arrangement (100) design can be used in both modular construction and normal construction type of contact arrangements.
6. The contact springs and flexible conductors in the rotary contact arrangement (100) are arranged on the rear side of the moving contact, away from arcing zone, which eliminates the possibility of electrical break down between flexible conductor and fixed contact, and protects spring from exposure to high temperature.
7. The rotary contact arrangement (100) provides possibility of drastic reduction in pole width of breaker.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various

embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We claim:
1. A rotary contact arrangement for low voltage circuit breakers, the rotary contact arrangement comprising:
a contact shaft (2) adapted to rotate with respect to its own center, the contact shaft (2) rotated by the circuit breakers mechanism during normal ON, OFF and TRIP operation;
at least one moving contact (1) pivoted to the contact shaft (2), the moving contact (1) a having,
a first end having a contact button (7) adapted to meet with a
fixed contact (8),
a second end connected with a fixed terminal through a flexible conductor (12);
at least one first cylindrical pin (4) movably arranged in a slot provided in the contact shaft (2);
at least one fixed/ stationary cylindrical pin (5) arranged on the contact shaft (2);
at least one second cylindrical pin (6) attached to the second end of the moving contact (1);
at least one connecting link (3) having a first end connecting to the first cylindrical pin (4) and a second end connecting to the second cylindrical pin (6);
at least one pivotal pin (10) for suspending the moving contact (1) with the contact shaft (2); and
at least one contact spring (11) having a first end connected to the first cylindrical pin (4) and a second end connected to the fixed/ stationary cylindrical pin (5),
wherein torque on the moving contact (1) by electro-dynamic repulsion force generated between the moving contact (1) and fixed contact (8) due to the

effect of current flow in opposite direction exceeds the torque offered by the contact spring (11), the moving contact (1) starts moving away from the fixed contact (8) whereby the first cylindrical pin (4) slides along the slot in the contact shaft (2) and causes the perpendicular distance between the line of force acting on the moving contact (1) due to the spring (11) which helps to open moving contact (1) with relatively less electro-dynamic force, and when the torque offered by the contact spring (11) becomes zero, any further movement of moving contact (1) leads to flipping of moving contacts (1) by contact spring (11).
2. The rotary contact arrangement as claimed in claim 1, wherein the moving contact (1) is preferably pivoted along a center portion of rotation of the contact shaft (2).
3. The rotary contact arrangement as claimed in claim 1, wherein the contact spring (11) is extension type contact spring.