FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
ARC PLATE AND ARC CHUTE ASSEMBLY THEREOF;
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 present invention relates to electrical switching devices and preferably to an arc chute assembly for the electrical switching devices.
BACKGROUND OF THE INVENTION:
Switching devices like circuit breakers protect electrical circuits from damage by isolating the circuit, in the event of short circuit fault. During the process of isolating, an arc generates between the opening contacts of the circuit. This arc is required to be quenched inside the circuit breaker to prevent damage.
An arc basicalfy is a discharge of electric current, flowing through the circuit in the event of short circuit fault, between contacts of a circuit breaker during the opening of contacts to isolate the electric circuit. Arcs may vary in size and intensity depending on the amount of short circuit fault current, and minimizing the arc is important as the arc can damage the contacts. Arc may further ionize gasses inside the circuit breaker which could damage the circuit breaker casing. Further, Arc can also severely damage the circuit breaker and surrounding equipments. Hence, a circuit breaker must not only isolate electrical circuit but also control and quench the arc.
As a result, various arc control mechanisms like stretching the arc; breaking the arc into smaller segments; cooling the arc; blowing out the arc; vacuum interruption of the arc are used in the art.
Generally, circuit breakers employ an arc chute assembly to control and extinguish the electric arc. Arc chute assembly confines, divides and cools the arc thereby resulting in quenching the arc. Arc chute assembly conventionally have arc dividers in the form of

flat segments stacked one above the other preferably with an air gap between them. When an arc is developed, the arc chute assembly pulls the arc and divides it into smaller arcs which are quenched by the flat segments of the arc chute. These flat segments are thick metal plates. However, the metal plates erode very fast as arc root forms on both sides of the metal plates. This erosion of the plates affects the performance of the arc chute assembly and thereby performance of the circuit breaker.
US Patent No. 4,375,021 discloses an arc plate of U-shaped configuration, wherein the curve of the U-shape plate faces the contacts and the arms of the U insulated from one another by a thin insulating sheet. However, U-shape limits the number of plates in an arc chute assembly that can be physically accommodated in the arc chute. Consequently this also affects the arc quenching capability of the arc chute.
There is, therefore, need for improvement in arc chute assembly and arc members thereof.
SUMMARY OF THE INVENTION:
Accordingly, in one aspect, the present invention provides an arc plate for an arc chute assembly comprising an insulating material sandwiched between two electrically connected ferromagnetic metal plates. The insulating material emits gasses under the influence of an electric arc which helps in faster arc quenching.
In another aspect, the present invention provides an arc chute assembly for extinguishing arc in electrical switching devices, comprising a stack of closely spaced, generally parallel ferromagnetic arc plates, each ferromagnetic arc plate having two metal plates, made up of same metal or different metals, connected electrically and an insulating material layer sandwiched between the said two electrically connected metal plates. The metal plates of the arc plate forms a current loop to produce additional force

on the arc and the sandwiched insulating material produces gasses under the influence of the arc thereby extinguishing the arc.
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 an arc chute assembly;
Figure 2 shows an arc plate according to the present invention;
Figure 3 shows a cross-sectional view of an arc plate according to the present invention; and
Figure 4 shows arc quenching using arc plates of the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.
Hereinafter, the preferred embodiments of the present invention will be described in detail. For clear description of the present invention, known constructions and functions will be omitted.
The present invention provides arc plates for an arc chute assembly for electrical switching devices such as circuit breaker, moulded case circuit breaker, motor protection circuit breaker, contactor, etc. Generally, electrical switching devices comprise of a

housing, contacts enclosed within the housing; operating mechanism to operate the contacts and an arc chute to attract & quench an arc generated at the contacts.
Figure 1 shows an arc chute assembly (100) comprising of a plurality of arc plates (10) arranged in a stack of closely spaced, generally parallel configured in between two plates (20) known as lining made of electrically insulating material. The arc chute assembly (100) is generally adapted in close proximity to the contacts (not shown) of a circuit breaker (not shown) to attract & quench an arc that may be generated at the contacts in response to an overload or short-circuit condition. Those skilled in the art will appreciate that the arrangement of the arc chute assembly in a circuit breaker is very well known in the art and hence is not discussed in detail.
Figure 2 & 3 shows detailed configuration of an arc plate (10) as per a preferred embodiment of the present invention. The arc plate (10) comprises of two metal plates (2A, 2B) electrically connected and an insulating material layer (4). The insulating material layer (4) is sandwiched between the two metal plates (2A, 2B).
In a preferred embodiment the insulating materia! layer (4) is an ablative material. According to the present invention, the insulating material is preferably selected from a group including polyoxymethylene (POM), polytetrafluoroethylene (PTFE), polyamide (Nylon) & melamine formaldehyde (MF).and the like
According to the present invention, the metal plates (2A, 2B) are preferably made up of ferromagnetic metal having same electrical & magnetic properties or two different metals having different electncai & magnetic properties. Alternately, the metal plates (2A, 2B) can be coated with suitable magnetic material for achieving higher magnetic pull on arc or material having low electron affinity to provide higher arc mobility.

Advantageously, the metal plates (2A, 2B) can also be coated with conducting material like copper, nickel etc. to enable faster movement of arc.
In a relative aspect of the present invention, the arc plate may comprise at least one metal plate having low electron affinity, such as rear earth materials that helps in faster arc root formation & have higher arc mobility. Advantageously, the metal plate having low electron affinity is connected to cathode side. This helps in faster arc root formation & faster arc movement inside the arc plates (10) resulting in less splitting time & hence faster quenching of arc.
According to the present invention, the metal plates (2) are electrically connected to each other by welding or some other process. Preferably, the metals plates (2A, 2B) are connected at bottom end as shown in Figure 2 & 3. Advantageously, the metal plates are electrically connected with high resistance material to facilitate rapid voltage build up of the arc, which helps in faster arc quenching.
The arc chute assembly (100) of the present invention attracts the arc generated and split the arc into several series arc and only one side of each metal plate (2A, 2B) of the arc plates (10) is subjected to the arc. As the arc root forms on one side of the arc plate (10), less erosion of arc plate (10) takes place and also ensures faster quenching of arc during the next subsequent fault conditions. Further, the heat energy associated with the arc heats the ablative material layer (4) sandwiched between the plates (2A, 2B) of the arc plate (10) causing the insulating material (4) to release electronegative gasses. These electronegative gasses absorb charged particles from the arc thereby assisting in de-ionization of arcing zone & also cooling of arc. This further increases gap resistance and increases the gas velocity which results in cooling of arc & faster penetration of arc inside the arc chute assembly (100). Furthermore, insulating material (4) generates

gasses exactly near the arc root which results in rapid building of dielectric strength of arcing region and faster cooling of arc. This reduces the severity of arcing and results in faster arc quenching.
Figure 4 shows arc quenching using arc plates (10) of the present invention, wherein the assembly of the two metal plates (2) connected electrically to each other at bottom ends provides high voltage drop across arc plate due to increased length of current path. As illustrated in Figure 4 when an arc (8) splits inside the arc chute (100), current flows through the electrically connected metal plates (2) of the arc plate. The current direction in both the metal plates (2) is opposite to each other forming a current loop. This current loop generates additional force which acts on the arc (8) in upward direction and pushes the arc further inside the arc plates (10). This results in faster penetration of arc (8) and hence less arc splitting time which ultimately results into faster arc quenching thereby preventing the circuit breaker and surrounding equipment from potential damage.
While the present invention has been described with respect to certain preferred 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. An arc plate for an arc chute assembly for electrical switching device comprising: an insulating material sandwiched between two electrically connected ferromagnetic metal plates so as to form an arc root at one side of each metal plate of the arc plate..
2. An arc plate as claimed in claim 2, wherein the two metals plates can be electrically connected by a high resistance material-
3. An arc plate as claimed in claim 1 or 2, wherein the electrical connection between the metal plates of the ferromagnetic arc plate is preferably provided at bottom end.
4. The arc plate as claimed in claim 1, wherein the metal plates of the arc plate can be made up of same metals or different metals.
5. An arc plate as claimed in claim 1or 4, wherein the metal plates can be coated with magnetic material.
6. An arc plate as claimed in one of the claims 1, 4 and 5, wherein the metal plates can be coated with, conducting material like copper, nickel etc. to enable faster movement of arc.
7. An arc plate as claimed in claim 1, wherein atleast one plate can be made of metal having low electron affinity such as all rare earth metals having low electron affinity.
8. An arc plate as claimed in claim 7, wherein the plate having low electron affinity is preferably cathode side.
9. An arc plate as claimed in claim 1, wherein the insulating material is preferably ablative material.

10. An arc plate as claimed in claim 1 or 9, wherein the insulating material is preferably selected from a group including polyoxymethylene (POM), polytetrafluoroethylene (PTFE), polyamide (Nylon) & melamine formaldehyde (MF).and the like.
11. An arc plate as claimed in claim 1, wherein the switching device is circuit breaker, moulded case circuit breaker, motor protection circuit breaker, contactor or any electrical switching device.
12. An arc chute assembly for extinguishing arc in electrical switching devices, comprising:
a stack of closely spaced, generally parallel ferromagnetic arc plates, each ferromagnetic arc plate having two metal plates, made up of same metal or different metals, connected electrically and an insulating material layer sandwiched between the said two electrically connected metal plates; wherein metal plates of the arc plate forms a current loop to produce additional force on the arc and the sandwiched insulating materia! produces gasses under the influence of the arc thereby extinguishing the arc.