FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CONTACT ARRANGEMENT FOR ELECTRICAL SWITCHING DEVICE;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION
The invention relates to switching devices, and more particularly to a contact arrangement for electrical switching devices. BACKGROUND OF THE INVENTION
Electrical switching devices like circuit breakers, switch dis-connectors, etc protect electrical circuits from damage by isolating the circuit, when there is an electrical overload or fault condition. Typically, switching devices comprises a housing, a contact arrangement including a fixed contact and a moving contact enclosed within the housing, an operating mechanism to operate the contacts, and an arc chute.
The operating mechanism of the switching device during the fault condition will separate the contacts, and at this instant an arc is generated and an arc root is formed between the fixed contact and the moving contact, and the arc is pushed into the arc chute. However, penetration of the arc into the arc chute is dependent on radii of the arc root and isolation distance between the contacts. Typically, the isolation distance between the contacts is less than or equal to radii of arc root which saturates and immobilizes the arc. Hence the arc does not penetrate the arc chute. This leads to contact erosion and decrease life of the contacts.
Due to curved feature in moving contact the isolation distance between fixed contact and moving contact is increased from 10mm to 14mm. i.e., in moving contact if don't providing curved feature (if it is straight), then the isolation distance between fixed contact and moving contact is 10mm, after providing the curved feature in this the isolation distance between them is increased to 14mm.
In view of the above, there is a need in the art to reduce erosion of the contacts and increase life of the contacts.

SUMMARY OF THE INVENTION
Accordingly, the present invention in one aspect provide a contact arrangement for an electrical switching device, wherein at-least one of contacts has a slit, the slit being positioned such that when an arc is formed, angle between the current path of the arc and the current path in the contact is an acute angle.
In another aspect, the present invention provides an electrical switching device, the switching device having a contact arrangement, the contact arrangement comprising at-least a pair of contacts, wherein at-least one of the contacts has a slit, the slit being positioned on the contact to modify the current path in the contact, the modified current path making an acute angle with an arc formed during isolation of contacts. BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows a contact arrangement in accordance with an embodiment of the
invention.
Figure 2 shows a moving contact in detail in accordance with an embodiment of the
invention.
Figure 3 shows an electrical switching device in accordance with an embodiment of the
invention.
Figure 4 shows the contact arrangement in accordance with an embodiment of the
invention. DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention provide a contact arrangement for an electrical switching device, wherein at-least one of contacts has a slit, the slit being positioned such that when an arc is formed, angle between the current path of the arc and the current path in the contact is an acute angle.
Figure 1 shows a contact arrangement 100 in accordance with an embodiment of the invention. Contact arrangement 100 includes a fixed contact 102 and a moving contact 104.
In an embodiment of the invention, at-least one of fixed contact 102 and moving contact 104 has a slit. In an embodiment of the invention, moving contact 104 has a slit 106 as shown in figure 2. Moving contact 104 is shown in detail in figure 2. In an embodiment of the invention, slit 106 is positioned such that when an arc is formed, angle between the current path of the arc and current path of moving contact 104 is an acute angle.
In an embodiment of the invention, slit 106 is positioned on moving contact 104 near edge of moving contact 104. In an embodiment, slit 106 modifies the current path in the contact The angle between the current path of arc and the current path in moving contact 104 elongates the arc.
In an embodiment of the invention, as arc travels further with magnetic blow out force and gas dynamics, the angle between the current path of arc and the current path in moving contact 104 is maintained which increases the blowout force and thereby reduces arcing time.
In an embodiment of the invention, contact with slit has a curved edge. In this regard moving contact 104 has a curved edge 108. Curved edge 108 enables higher/increased isolation distance between fixed contact 102 and moving contact 104. For example, as shown in figure 4 the isolation distance increases from 10 mm to 14 mm due to curved edge 108 enabling receding of the arc i.e. the arc moves away from the contacts thereby reducing immobility time of the arc.

In an embodiment of the invention, at-least one of fixed contact 102 and moving contact 104 has a magnetic cladding. For example, moving contact 104 has a magnetic cladding 110 as shown in figure 2.
Figure 3 shows an electrical switching device 300 in accordance with an embodiment of the invention. Electrical switching device 300 includes a top housing 302, a bottom housing 304, a contact arrangement having at-least a pair of contacts - a fixed contact 306 and a moving contact (not shown in figure 3), an arc chute (308) for each of pair of contacts and a plurality of phase barriers (310).
Contact arrangement of electrical switching device is similar to contact arrangement 100 shown in figure 1. In this regard, at-least one of fixed contact 306 and the moving contact has a slit and a curved edge. In an embodiment of the invention, moving contact has a slit and a curved edge. The slit is positioned such that the slit modifies the current path in the contact, the modified current path making an acute angle with an arc formed during isolation of contacts. The angle between the current path of arc and moving contact elongates the arc. Further the curved edge of the moving contact is near the slit, enabling the arc to move away from the contacts, reducing immobility time of the arc.
In an embodiment of the invention, electrical switching device 300 is capable of interrupting alternating current and direct current at high voltages (more than 415V).
In an embodiment of the invention, contact arrangement can be adapted to electrical switching devices such as switch disconnector (SD), miniature circuit breaker (MCB), moulded case circuit breaker (MCCB), air circuit breaker (ACB) and switch disconnector with fuse (SDF) etc.
In an embodiment of the invention, during a fault condition, contacts (fixed contact and moving contact) are opened and an arc is formed. The moving contact has a slit positioned such that angle between the current direction of the arc and the moving contact is an acute angle. The angle between the current direction of arc and the moving contact elongates the arc

increasing magnetic blow out force on the arc and hence reducing arcing time. Further the moving contact has a curved edge near the slit, the curved edge enables the arc to move away from the contacts, reducing immobility time of the arc. Thus the contact arrangement, increases motion of the arc, increases length of the arc and hence increases arc voltage to quench the arc.
Advantageously, the contact arrangement of the present reduces arc quenching period, reduces erosion rate of contacts thereby increasing life of the contacts.
While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

We Claim:
1. A contact arrangement for an electrical switching device, wherein at-least one of contacts has a slit, the slit being positioned such that when an arc is formed, angle between the current path of the arc and the current path in the contact is an acute angle.
2. The contact arrangement as claimed in claim 1, wherein the slit modifies the current path in the contact.
3. The contact arrangement as claimed in claim 1, wherein the contact arrangement has fixed and moving contacts.
4. The contact arrangement as claimed in claim 1, wherein the contact with the slit has a curved edge near the slit, the curved edge enabling the receding of the arc by elongating the arc.
5. The contact arrangement as claimed in claim 1, wherein the contacts have a magnetic cladding.
6. An electrical switching device, the switching device having a contact arrangement, the contact arrangement comprising at-least a pair of contacts, wherein at-least one of the contacts has a slit, the slit being positioned on the contact to modify the current path in the contact, the modified current path making an acute angle with an arc formed during isolation of contacts.
7. The switching device as claimed in claim 6, wherein the acute angle enables elongation of the arc. .
8. The switching device as claimed in claim 6, wherein the contact with the slit has a curved edge near the slit, the curved edge enabling the arc to move away from the contacts.

9. The switching device as claimed in claim 6 further comprising an arc chute for each of pair of contacts.