FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"Arc Quenching Device for Electrical Switching Device"
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
Electrical & Automation North Wing, Gate 7, Level 0, Powai Campus, Saki Vihar Road, Mumbai 400 072, INDIA
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Arc Quenching Device for Electrical Switching Device
Field of invention:
The present invention relates to an arrangement of deion plates used in an arc chute of an electrical switching devices such as a circuit breaker, a motor circuit breaker or contactor.
Background of the invention:
A circuit breaker consists of housing & cover made up of insulating material, pair of separable contacts enclosed within housing, cover and arc quenching device known as an Arc chute. The switching arc in circuit breaker & its motion are determined by the intensity of current, electromagnetic from the arc chute as well as gas-dynamic process within the arc chute. The arc chute consists of stack of de-ionizing plates made up of magnetic material to attract & split-up the arcs. A stack of deion plates is trapped in between two plates known as lining made up of electrically insulating material. Function of deion plates is to split an arc in several series arcs of approximately equal length which result in higher arc voltage & distinctly greater dielectric strength after current zero.
During short circuit, the arc enters inside the deion plate stack assembly and splits in series of small arcs. It is associated with very high temperature, due to which material of the deion plates & conductors erodes. This results into build up of very high temperature and pressure inside an arcing chamber. An arcing product (molten mass) travels along via the deion plates to an arc vent and released outside the switching device.
While the arcing products (molten mass) travels via the deion plates, some part of the molten mass comes in contact with the deion plates. The molten mass gives off its heat energy to the deion plates and solidifies forming small droplets of

metal called a globule. The tendency of the globules is to stick on the extreme end of the deion plate. Due to sticking of the globules on extreme end of the deion plates, the globule may stick between the two adjacent deion plates. Due to this the adjacent deion plates get short circuited (bridged) and thereby the voltage between these adjacent deion plates cannot build up during short circuit. If such multiple adjacent deion plates get short circuited, the voltage build up between the deion plate stack will be lesser and in this manner the arc quenching would be slower. Due to this, the arc re-strikes resulting into damage of the switching device contacts.
In the present invention, the arc chute assembly is improved upon by means of deion plate arrangement wherein the one corner of the deion plate profile is chamfered and the deion plates are arranged in way such that the chamfered profiles will fall in an alternate direction. This results in a zigzag splitting of the arc as it enters the arc chute which lengthens it further and increases the arc resistance along with splitting, which helps in faster quenching of the arc. Faster quenching of the arc results in lower arcing times which limits the fault current and lowers the let through energy/stresses passed on to the downstream devices.
During short circuit fault, after contact separation arc enters inside the arc chute, it splits in number of smaller series of arcs. The fault current flowing through the circuit and produces a magnetic field in deion plates. Magnetic field lines passing through the deion plates produces a pulling force (attraction force) on the arc which drives it further inside the arc chute. The force acting on the arc due to the gas pressure generated inside the arcing chamber also pushes the arc further inside the arc chute.
The deion plates have a chamfer on one side, which results in crowded magnetic flux lines in that region. This result in higher magnetic flux density in that region compared to any other region of the deion plate. The arc thus experiences maximum magnetic force in the direction of chamfered profile of deion plate.

Also, the hot gases produced due to arc plasma experience lesser opposition while escaping out from the chamfered profile which increases the gas flow in that region. Thus the force acting on the arc due to gas dynamics pushes arc towards the chamfered profile of the deion plate.
The deion plates are arranged, such that the chamfered profile of the deion plate falls in an alternate direction, The combined effect of magnetic force and gas dynamic force pushes the arc root towards chamfered profile of the splitter plate and thus causing lengthening of the arc inside the splitter plates in a zig-zag way. This also helps in faster cooling of arc.
In conventional arc chute assembly, there is possibility that the arc can flash over or re-strike at the end of the deion plate stack or else on the side edges, thus preventing current limiting and correct short circuit disconnection. In conventional arc chute assembly during arc interruption, the molten material gets deposited at the side edges of the deion plate and forms a current path by connecting deion plates by bridging the gap between them at side edges. This current path formed due to molten material, results in arc flash over or re-strike.
In the present invention provides an arc quenching device for electrical switching device, which minimizes the possibility of molten material bridge formation between deion plates and thus prevents the possibility of flash over or re-strike.
Objects of the Invention:
Object of the present invention is to provide an arc quenching device, which is capable of preventing damage of switching device contacts occurred due to arc re-strikes.
Another object of the present invention is to provide an arc quenching device, which improve the arc chute assembly by means of deion plate arrangement

wherein the one corner of the deion plate profile is chamfered and the deion plates are arranged in way such that the chamfered profiles will fall in an alternate direction, which results in a zigzag splitting of the arc as it enters the arc chute which lengthens it further and increases the arc resistance along with splitting which helps in faster quenching of the arc.
Yet another object of the present invention is to provide an arc quenching device, which minimizes the possibility of molten material bridge formation between deion plates by the chamfer profile of deion plate and deion plate stack arrangement, which prevents the possibility of flash over or re-strike.
Summary of the invention
According to the present invention there is provided a circuit breaker having housing & cover made up of insulating material, pair of separable contacts enclosed within housing, cover and an arc quenching device, the arc quenching device comprising:
a plurality of deion plates, characterized in that each of the deion plate of the plurality of deion plates is chamfered on a top corner and disposed in the lining, each of the deion plate having top corner chamfered opposite to that of adjacent deion plates enables zid-zag flow of hot gases produced therein faster quenching of the arc.
Brief description of the drawing:
Figure 1 shows the Arc chute assembly whereby the stack of a deion plates is trapped in between two plates known as a lining made up of electrically insulating material;
Figure 2 shows arrangement of a deion plates in arc chute assembly;

Figure 3 shows magnetic flux distribution in deion plate; and
Figure 4 shows gas flow in deion plate.
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.
Accordingly, in the present invention the Circuit Breaker consists of housing (not shown) & cover made up of insulating material (not shown), a pair of separable contacts (not shown) enclosed within the housing, cover and arc quenching device known as Arc chute. The switching arc in circuit breaker & its motion are determined by the intensity of current, electromagnetic from arc chute as well as the gas-dynamic process within the arc chute. The arc chute consists of stack of de-ionizing plates (2) made up of magnetic material to attract & split-up the arcs. The function of deion plates is to split the arc in several series arcs of approximately equal length which will result in higher arc voltage & distinctly greater dielectric strength after current zero.
In the present invention, the arc chute assembly is improved upon by means of deion plate arrangement, as shown in figure 2, a top corner of the deion plate profile is chamfered (3) and the deion plates are arranged in way such that the chamfered profiles will fall in an alternate direction (each of the deion plate (2) having top corner chamfered (3) opposite to that of adjacent deion plates). This results in a zig-zag splitting of the arc as it enters the arc chute which lengthens it further and increases the arc resistance along with splitting, which helps in faster quenching of the arc. Faster quenching of the arc results in lower arcing times,

which limits the fault current and lowers the let through energy/stresses passed on to the downstream devices.
During short circuit fault, after contact separation arc enters inside the arc chute, it splits in number of smaller series arcs. The fault current flowing through the circuit produces a magnetic field in deion plates. Magnetic field lines passing through deion plates produces a pulling force (attraction force) on the arc which drives it further inside the arc chute. The magnitude and direction of the pulling force acting on the arc depends on the magnetic flux density and its distribution in the deion plates. The force acting on arc due to the gas pressure generated inside the arcing chamber also pushes the arc further inside the arc chute.
As shown in figure 3, the deion plates have a chamfer (3) on one side which results in crowded magnetic flux lines in that region. This result in higher magnetic flux density in that region compared to any other region of the deion plate. The arc thus experiences maximum magnetic force in the direction of chamfered profile of deion plate. Also the hot gases produced due to arc plasma experience lesser opposition while escaping out from the chamfered profile which increases the gas flow in that region as shown in figure-4. Thus the force acting on the arc due to gas dynamics pushes arc towards the chamfered profile of the deion plate.
As shown in figure 2, the deion plates are arranged such that the chamfered profile of the deion plate falls in an alternate direction. The combined effect of magnetic force and gas dynamic force pushes the arc root towards chamfered profile of the splitter plate and thus causing lengthening of the arc inside the splitter plates in a zig-zag way. This also helps in faster cooling of arc.
The deion plates are arranged such that the chamfered profile (3) of the deion plate falls in an alternate direction. The chamfer profile of deion plate and deion plate stack arrangement minimizes the possibility of molten material bridge

formation between deion plates and thus prevents the possibility of flash over or re-strike.
Following features are included in Arc quenching device
1. The construction of the deion plate (2) which have chamfer at one corner.
2. The construction of the deion plate (2) having chamfer at one corner which produces high magnetic flux density thus very high magnetic force on arc.
3. The construction of the deion plate (2) assembly wherein the deion plates (2) having chamfered profile at one corner are arranged such that the chamfered profile of the deion plate falls in an alternate direction. The profile of deion plate & the arrangement of deion plate assembly generates high magnetic field which drives the arc inside the arc chute, generates gas pressure which pushes the arc towards the chamfered corner causing lengthening of the arc in a zig zag way leading to faster quenching of arc.
4. The unique construction of deion plate assembly wherein the deion plates having chamfered profile at one corner are arranged such that the chamfered profile of the deion plate falls in an alternate direction which minimizes the formation of bridge between deion plates due to molten material & thus reducing the possibility of flash over or restrike.
Advantages of the present invention:
1) Rapid penetration of arc inside the arc chute because of magnetic blast effect generated due to current flow in parallel deion plates.
2) Zig zag movement of arc within deion plates, this results into higher arc voltage which leads to faster arc quenching.
3) Rapid buildup of dielectric medium within contact gap.
4) The chances of restrike are minimized.

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 circuit breaker having housing & cover made up of insulating material, pair of separable contacts enclosed within housing, cover and an arc quenching device, the arc quenching device comprising:
a plurality of deion plates, wherein the improvement comprises each of the deion plate of the plurality of deion plates is chamfered on a top corner and disposed in the lining, each of the deion plate having top corner chamfered opposite to that of adjacent deion plates enables zig-zag flow of hot gases produced therein faster quenching of the arc.