FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"Arrangement For High Speed Opening Of Contact System In Electric
Switchgears"
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. 0. 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.

Arrangement For High Speed Opening Of Contact System In Electric
Switchgears
Field of the invention
The present invention relates to electric switchgears, and more particularly, to an arrangement which provides high speed opening of contact system by flipping action of moving contact using repulsion forces generated by electromagnetic fields.
Background of the invention
Electric switchgears are used in electric transmission and distribution networks. Switchgears are used for protection of electric network/circuit and equipments. The switchgear consist of an outer enclosure made of insulating material in which switching (make/break) takes place, a current path which is connected to the main supply line and makes/breaks electric supply, a mechanism which may be a combination of a number of mechanical links and springs or may be any arrangement which stores energy and releases in mechanical form when required. The current path/conductor of the electric switch gears is made of highly electric conductive materials to reduce the losses. The current path has a fixed contact and a moving contact which moves to make/break (close/open) the circuit. Due to the breaking of circuit, an arc generates because of voltage gradient between the fixed and the moving contacts. This generated arc erodes the fixed and the moving contacts and enclosure also. This causes reduced operational life of switchgears.
Accordingly, it is 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. Existing available arrangements use a rotary moving contact system

using torsion springs to maintain adequate contact pressure between the moving and the fixed contacts. In the case of fault due to high current flow, Lorentz forces generated in the contact system. As these forces exceed the spring force, the moving contact repeal opens quickly. In these existing systems there are very high chances that close back (reclose) because of slight drop in Lorentz force below spring force. At the same time the torsion springs are not so reliable and difficult to manufacture to provide specified force within the limits. Further, the spring guide pin in prior art prevents buckling. However, it does not prevent the spring from resting onto the same at an angle. This would result in a normal reaction misaligned with the spring force axis and hence resulting into a drop in effective spring force.
An US patent application 2012/0298489 discloses an arrangement having pivot pin like arrangement instead of double spring holders. The arrangement disclosed in US patent application '489 has higher number of components and higher assembly process time. Further, the arrangement of moving contact is such that the assembly is only possible from the arcing zone side. This poses a danger of arc products entering into the spring and contacts, thereby damaging the same
Accordingly, there exists a need to provide an arrangement which overcomes drawbacks of the prior art.
Objects of the invention
An object of the present invention is to provide high speed opening of contact system in the switchgears.
Another object of the present invention to provide an effective arc-chute utilization during both blow open condition and operation of contact through mechanical means.

Summary of the invention
Accordingly, the present invention provides an arrangement for high speed opening of contact system in electric switchgears. The arrangement comprises an operating mechanism for driving a shaft assembly which rotates a shaft in on, off and trip conditions, a moving contact assembly hinged to a shaft housing of the shaft assembly via a cylindrical pin, a compression spring capable of generating a contact pressure between the moving contact assembly and a fixed contact assembly, a spring holder assembled with the moving contact assembly with a first pin and a second pin with the help of a third pin and a moving contact provided in the moving contact assembly. The moving contact includes a first profile provided for fixing of the contact button thereon, a second profile and a third profile provided for the first pin and the cylindrical pin, the second profile and the third profile having location of holes configured in such a way that after crossing a dead centre, direction of the compression spring force gets reversed to provide a flipping action.
Brief description of the drawings
Figure 1 shows a complete shaft assembly of switchgear, in accordance with the present invention;
Figure 2 shows a sectional view of the complete shaft assembly of switchgear of figure 1;
Figure 3 shows a moving contact assembly used in shaft of the figure 1 and 2;
Figure 4 shows the moving contact used in moving contact assembly of figure
3;

Figure 5 shows spring holders used in shaft assembly of figure 1 and 2;
Figure 6 shows a complete switching arrangement in closed or on condition;
Figure 7 shows a complete switching arrangement in the condition of dead centre.
Figure 8 shows a complete switching arrangement in flipped or repelled condition, in accordance with the present invention; and
Figure 9 shows the complete switching arrangement in opened or off condition.
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.
The present invention provides an cost effective arrangement to be used in switchgears mainly in molded case circuit breakers. The arrangement provides high speed contact opening with negligible chances of reclosing and having improved reliability and operational life. The arrangement works on the phenomenon of dead centre. Dead centre is the critical rotation angle of the moving contact after which direction of spring force reversed across the hinge of a moving contact. As the moving contact crosses or moves above the dead centre the force direction get reversed. Due to this force direction reversal the moving contact rotates in direction of opening and remains there until the resetting force is applied to bring back it below dead centre. The present invention provides an arrangement which uses compression spring to provide contact pressure and has the flip lock arrangement. As the moving contact

crosses a limit called dead centre the moving contact flipped in opposite direction remains locked because of reversed direction of force provided by compression spring. Thus the chances of reclosing can be neglected.
Referring now to 1-9, there is shown an arrangement for an arrangement for
high speed opening of contact system in electric switchgears/circuit breaker
(100). The electric switchgear includes a rotating shaft assembly (50) as shown
in figure 1 and 2. The rotating shaft assembly (50) includes a shaft housing (1),
a moving contact assembly (2), a shaft cover (3), a compression spring (9), and
two spring holders (6 and 7). in an embodiment, the'shaft housing (1) is made
of any insulating material to reduce the electromagnetic stresses therein The
rotating shaft assembly (50) is assembled in an enclosure called cassettes or
housing of the circuit hreaker (100) The rotating shaft assembly (50) is driven
by an operating mechanism which rotates the shaft in on, off and trip
conditions.
As shown in figure 3, the moving contact assembly (2) includes current carrying elements such as a moving contact (10), a contact button (11), a flexible conductor like braids (12 and 13), an outer terminal (14), The shaft cover (3) provides protection for braids (12 and 13) from an arc. The moving contact assembly (2) is hinged at a cylindrical pin (5). The cylindrical pin (5) with the moving contact assembly (2) engages in the profile provided on the shaft housing.
The spring holder (6) is assembled with the moving contact assembly (2) with the first pin (4) and a second pin (7) with the-, help of third pin (8). The cylindrical pins (5) and the third pin (8) are fixed with shaft housing (i) while the first pin (4) is free to move with the moving contact (10). The cylindrical pin (5) and the spring holders (6 and 7) are free to rotate on their respective axis. Specifically, the shaft assembly (50) is screw less arrangement and doesn't require any special tool for assembly process.

As shown in figure 4, the moving contact (10) is specially designed for providing the flipping action. A first profile (17) on the moving contact (10) is provided for the proper fixing of the contact button (11) thereon. A second profile (15) and a third profile (16) are provided for the first pins (4) and the cylindrical pin (5). To provide flipping action, the location of the holes of the second profile (15) and the third profile (16) is designed in such a way that after crossing the dead centre the direction of spring force gets reversed.
Figure 6 shows a closed position of the circuit breaker (100). The fixed contact assembly (18) having contact button, terminal and arc runner is shown. In this condition the mechanism locks the shaft in closed condition by rotating the shaft anticlockwise and compress the spring (9), wherein the contact pressure is generated by compression spring (9). In closed condition, as shown in figure 6, direction of the spring (9) force is above the cylindrical pin (5) of the moving contact (10). Accordingly, the resultant force is tries to aid contact pressure. As the circuit breaker (100) faces any fault, current starts increasing in the system thus increasing the repulsion Lorentz force between the fixed contact (18) and the moving contact (10). As the repulsion force overcomes the spring force, the moving contact (10) starts opening. At the time, the moving contact (10) reaches dead centre as shown in figure 7, the direction of the spring force is through axis of the cylindrical pin (5) of the moving contact (10). After this point or as the moving contact (10) crosses the dead centre, the resultant force of the spring (9) is applied below the hinge (5) of the moving contact ()0) as shown in figure 8. Thus, the spring force now acts in opposite direction and rotates the moving contact (10) towards the open condition or flipped it in open condition while the shaft remains in the same condition. At this time the resultant spring force aids the Lorentz force and help the moving contact (10) open very quickly. After completely open the moving contact (10) is locked in this condition as the further rotation is obstructed by the shaft housing (1).

There are no chances or the re-closing of the moving contact after it crosses the dead centre.
For the next operation cycle, the moving contact (10) is reset in original condition. For resetting, the moving contact (10) has to come before dead centre as it was. To achieve this, the shaft is rotated in the clockwise direction by the mechanism as shown in figure (9). For closing the circuit breaker (100) again after clearing the fault shaft will be rotated to anticlockwise direction till the condition shown in the figure 6 reaches.
Advantages of the invention
1. The arrangement can be used in all kind transmission and distribution switchgears/circuit breakers having various size, shapes and current carrying capacities.
2. The unique phenomenon of moving contact flipping is achieved by novel moving contact profile design.
3. The arrangement can be used for switchgears having any number of poles/phases.
4. The arrangement works with the single compression based spring.
5. The angle of flipping can easily be changed by changing the profile of moving contact and shaft housing.
6. High speed contact opening can be achieved with negligible chances of reclosing.

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. An arrangement for high speed opening of contact system in
electric switchgears comprising:
an operating mechanism for driving a rotating shaft assembly which rotates a shaft in on, off and trip conditions;
a moving contact assembly hinged to a shaft housing of the shaft assembly via a cylindrical pin;
a compression spring capable of generating a contact pressure between the moving contact assembly and a fixed contact assembly;
a spring holder assembled with the moving contact assembly with a first pin and a second pin with the help of a third pin; and
a moving contact provided in the moving contact assembly, the moving contact having a first profile provided for fixing of the contact button thereon, a second profile and a third profile provided for the first pin and the cylindrical pin, the second profile and the third profile having location of holes configured in such a way that after crossing a dead centre, direction of the compression spring force gets reversed to provide a flipping action.
2, The arrangement as claimed in claim 1, wherein the fixed contact
assembly includes a contact button, terminal and arc runner.