FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - AN ARC CHUTE ASSEMBLY HAVING
IMPROVED ARC QUENCHING AND A CIRCUIT INTERRUPTING DEIVCE COMPRISING SAID ARC CHUTE ASSEMBLY
2. Applicant
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY : An Indian company
(c) ADDRESS : L&T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
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 arc chute assembly in circuit breaker. More particularly, the invention is concerned about arc chute assembly having de-ion plates comprising different material coatings with different work functions so as to facilitate reduction in the arcing time thereby resulting in fast quenching of the arc by means of enhancing cathode root formation aiding in faster travel of the arc into the arc chutes. The invention further relates to a circuit interrupting device comprising the arc chute assembly.
BACKGROUND OF THE INVENTION
A general requirement of circuit interrupting device is that the arc has to be split in to multiple series arcs for efficient quenching. This is achieved by introducing multiple plates (here after referred as de-ion plates) in the path transverse to the arc column. Whether the arc is split or not is decided by formation of anode and cathode roots on these de-ion plates. The formation of cathode roots is governed by surface temperature, effective work function and electric field at emission spot. High thermal time constant of de-ion plates inhibit the immediate splitting of the arc leading to an increase in total arcing time. During electrical faults, high arcing time can be detrimental to the installation.
US document 3483343 discloses that use of magnetic field to pull the arc in to arc chutes for fast arc quenching unlike the present invention. US document 4143256 discloses that coating of arc chutes with arc resistance ceramic material to get thermal resistivity for the arc chutes unlike the present invention.
Thus, there is a need to overcome the disadvantages in the prior art. So, the present invention provided an improved arc quenching in arc chute assembly to overcome the disadvantages in the prior art.

The present inventors have found that coating the de-ion plates in an arc chute assembly using materials having different work functions enhances the arc quenching process in the assembly by way of facilitating faster cathode root formation thus aiding in faster arc travel into the assembly.
OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the prior art.
Another object of the present invention is to provide an improved arc quenching in arc chute assembly.
Another object of the present invention is to provide by the assembly to reduce arcing time.
Further object of the present invention is to provide fast splitting of arc.
Yet, another object of the present invention is to provide high arc voltage.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an arc chute assembly having improved arc quenching , said assembly comprising: plurality of material coated de-ion plates;
wherein each of the said de-ion plates being coated with plurality of different materials having different predetermined work functions whereby each of the said de-ion plates being coated with materials having less work function at its bottom portion and high work function at its top portion adapted to provide fast cathode root formation aiding in faster arc travel into the assembly.
According to another aspect of the present invention there is provided a circuit interrupting device having an arc chute assembly having improved arc quenching, said assembly comprising: plurality of material coated de-ion plates;

wherein each of the said de-ion plates being coated with plurality of different materials having different predetermined work functions whereby each of the said de-ion plates being coated with materials having less work function at its bottom portion and high work function at its top portion adapted to provide fast cathode root formation aiding in faster arc travel into the assembly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates the arc in its final position in an arc chute.
Fig 2 illustrates schematic diagram of the de-ion plate having different work function coatings.
Fig 3 illustrates schematic isometric view of the arc chute assembly.
Fig 4 illustrates schematic isometric view of circuit breaker comprising the arc chute assembly of the present invention.
Fig 5 illustrates a graph of variation of cathode voltage drop with different work function values.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention there is provided an improved arc quenching in an arc chute assembly. Electrical arcs between the contacts extinguish when a sufficient arc voltage appears across the two contacts. Especially at near current zero the value of arc voltage plays major part in arc extinguishing. Faster the buildup of arc voltage, lesser would be the time taken to extinguish the arc. As shown in figure 1, the de-ion plates (4) have the significant role in the arc extinguishing part. As the circuit breaker contacts open, the arc chute (de-ion plates) segments, cools, and move the arc away from the contacts. Moving the arc away preserves the Integrity of the contacts for a longer service life.

According to a preferred embodiment of the invention, arc chutes comprise a number of bare metal plates(de-ion plates) arranged substantially at right angles (or in a partially divergent assembly) to the length of the arc chute with spacers between the plates to allow the arc to be split up into a number of series smaller arcs, increasing itss resistance and extracting heat. Eventually the arc is no longer able to sustain itself. In dc circuit breakers if enough plates are used in series the arc voltage across the chute can be greater than the system voltage, forcing the current down to zero and thereby interrupting the current.
When interrupting high short circuit currents the anode to cathode voltage drop is a function of work function of the material across each pair of plates. This invention relates to an arc chute having surface coating of different work function materials to have different voltage drop values across the arc chute. This work function variation of anode Cathode voltage drop has been given in the analysis results (graph) as shown in figure 5.
The work function of a metal is defined as the smallest energy needed to extract an electron at D K. Faster the formation of cathode roots across the de-ion plates, faster would be the arc enter into arc chutes. This thermal time delay depends on work function of the material. The present invention is provided a phenomenon to reduce this thermal time delay by using lower work function metal coating at the arc entering surface of de-iGn plates. At lower work function values, cathode root can be formed at lower temperatures on base material.
Figure 1 shows the arc in its final position in a typical arc chute. The arc is initiated at the point of contact separation between the fixed and moving contacts and is transferred into the chute by electromagnetic and thermal forces causing the arc to run away from the contacts along the arc runners. Arcing times are dependent upon current and voltage and can be relatively long. In order to withstand the transient recovery voltage at the instant of interruption of an inductive current and also any transient over-voltages the contact separation in air is large. The same electromagnetic forces, which move the arc into the chute at high currents, also act on the contacts attempting to blow them apart.

From the analysis results (graph) as shown in figure 5, it is clear that by increase in work function the cathode voltage drop is also increasing. By increase in work function from 4.9ev to 5.9ev the cathode voltage drop increases by 2V (from the analysis results). This increment in voltage is for one cathode de-ion plate, if the number of cathode de-ion plates are 10 then there is a voltage boost of (10*2=20V). This additional 20V arc voltage helps in quick arc extinction.
Total six materials of different work function values have been taken for analysis purpose. Given analysis results are for lOkA current value. The variation of cathode voltage drop with different work function values at low current is more compare to high current values. Arcing times are dependent upon time taken to enter the arc into arc chutes and the series anode cathode voltage drops of de-ion plates across the arc chute. The thermal time delay for arc to enter into arc chutes depends on the work function of the material. The present invention used four different material coatings selected from group of materials like silver, iron, zinc, copper, tungsten, nickel, osmium and the like. The materials are arranged in the order of less work function material at the bottom of the arc chute and high work function material coating at top portion of the arc chute the gradient in this coating is such that arc entering face of de-ion plate must have less work function and the remain portion of the de-ion plate must have higher work function value, coating to be done on both sides (upper and lower) of each de-ion plate.
Figure 2 shows the schematic diagram of the de-ion plate having different work function coatings . As shown in figure 2, the de-ion plate (4) comprises low work function material coating zone (1), medium work function material coating zone (2) and high work function material coating zone (3). Material having less work function cause fast arc splitting (i.e. fast cathode root formation) and material having high work function leads to high arcing voltage. Figure 2 shows the present invention diagram with different work function coatings on each of the de-ion plates, arc easily enter into arc chutes because low work function at arc entering face of de-ion plates. This invention provides both fast splitting of arc and high arc voltage.
ADVANTAGES OF THE INVENTION
1. Reducing the arcing time or improving arc quenching time
2. Providing both fast splitting of arc and high arc voltage

The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. The de-ion plates and materials as stated do not limit the scope of the present invention. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.

WE CLAIM
1. An arc chute assembly having improved arc quenching, said assembly comprising:
plurality of material coated de-ion plates;
wherein each of the said de-ion plates being coated with plurality of different materials having different predetermined work functions whereby each of the said de-ion plates being coated with materials having less work function at its bottom portion and high work function at its top portion adapted to provide fast cathode root formation aiding in faster arc travel into the assembly.
2. The Arc chute assembly as claimed in claim 1, wherein plurality of de-ion plates being arranged substantially right angles to said assembly length.
3. The Arc chute assembly as claimed in claim 1, wherein said coating materials being selected from silver, iron, zinc, copper, tungsten, nickel, osmium and the like.
4. The Arc chute assembly as claimed in claim 1, wherein said arc being transferred into said assembly by electromagnetic force and/or thermal force.
5. A circuit interrupting device having an arc chute assembly having improved arc quenching, said assembly comprising:
plurality of material coated de-ion plates;
wherein each of the said de-ion plates being coated with plurality of different materials having different predetermined work functions whereby each of the said de-ion plates being coated with materials having less work function at its bottom portion and high work function at its top portion adapted to provide fast cathode root formation aiding in faster arc travel into the assembly.

6. An arc chute assembly having improved arc quenching as herein substantially described and illustrated with the accompanying drawings.
7. A circuit interrupting device comprising arc chute assembly having improved arc quenching as herein substantially described and illustrated with the accompanying drawings.