FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
ARC-CHUTE ASSEMBLY IN A CIRCUIT INTERRUPTING DEVICES
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to electrical switching devices and particularly to circuit interrupting devices. The present invention more particularly relates to improvement in de-ion plate design based on surface finish which is used in arc chute assembly of circuit interrupting devices.
B) BACKGROUND OF THE INVENTION
[0002] Circuit interrupting devices such as circuit breakers typically include a set of stationary electrical contacts and a set of movable electrical contacts. The stationary and movable contacts are actuated to be in physical contact with one another when the circuit breaker needs to provide electricity through a load. However when it is desired to interrupt the circuit, the movable contacts are moved away from the stationary contacts thereby creating a space between the stationary contacts and the movable contacts.
[0003] The movement of the movable contacts away from the stationary contacts results in the formation of an electrical arc in the space between the contacts. Such an arc must be extinguished quickly to prevent damage of the electrical wiring and the load, as well as the circuit interrupting device itself. Additionally, the electrical arc between the contacts often results in vaporization or sublimation of the contact material itself, eventually resulting in deformation of the movable and stationary contacts. Hence it is desired to eliminate any such arcs as soon as possible upon their propagation.
[0004] A general requirement of the circuit interrupting devices is that the electric arc has to be split into multiple series arcs for efficient quenching. This is achieved by introducing multiple plates such as de-ion plates in the path transverse to the arc column. The movable electrical contacts typically are mounted on arms that are contained in a pivoting assembly which pivots the movable contacts away from the stationary contacts. An arc chute is provided along the path of each arm to break up and dissipate such arcs. Such arc chutes typically include a plurality of spaced apart

de-ion arc plates. As the movable contact is moved away from the stationary contact; the movable contact moves past the ends of the de-ion arc plates with the arc being magnetically urged towards and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken up and extinguished by the arc plates.
[0005] A formation of an anode root and a cathode root on the de-ion plates determines the status of the arc, as whether the arc is split or not. The formation of the cathode roots is governed by surface temperature, effective work function and electric field at emission spot. Conventionally, high thermal time constant of de-ion plates inhibit the immediate splitting of the arc leading to an increase in total arcing time.
[0006] During electrical faults, high arcing time can be detrimental to the installation. Hence there is a requirement for a method of reducing the arcing time by generating conditions favorable for arc splitting.
[0007] The abovementioned shortcomings, disadvantages and problems are
addressed herein and which will be understood by reading and studying the following
specification.
C) OBJECTS OF THE INVENTION
[0008] The primary object of the present invention is to provide an improved arc chute assembly to enhance the performance of the existing arc guidance for circuit interrupting device.
[0009] Another object of the present invention is to provide a method of reducing the arcing time by generating conditions favourable for arc splitting.
[0010] Yet another object of the present invention is to modify the work function of the de-ion plates.
[0011] Yet another object of the present invention is to provide a predefined surface characteristic to the de-ion plates.

[0012] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0013] The various embodiments of the present invention provide an arc-chute assembly in a circuit interrupting device comprising an arc chute, a plurality of de-ion plates arranged in the arc chute; wherein each de-ion plate has a preset profile to distribute a work function within the arc chute to reduce an arc splitting time and to enhance the arc voltage to reduce the arc quenching time.
[0014] The arc chute assembly consists of de-ion plates arranged in parallel or in a partially divergent assembly to each other with a preset profile, wherein the preset profile on each de-ion plate has a rough surface profile at a first portion (at arc entrance face) followed with a smooth surface profile at a second portion (at arc exit face). The rough surface profile is formed on an upper surface and lower surface of each de-ion plate. The rough surface profile having a corrugated shape. Further the rough surface profile is provided at an arc entering face of each de-ion plate and extended along a direction of propagation of the arc.
[0015] The smooth surface profile portion is formed after the rough surface profile portion on each de-ion plate and extended up to an arc exit face of each de-ion plate. The smooth surface profile is formed on both the upper and lower surface of each de-ion plate wherein the work function of each de-ion plate at the rough surface profile portion is less than the work function of each de-ion plate at the smooth surface profile portion to reduce an arc splitting time and to reduce an arc temperature. Further the work function of each de-ion plate at the smooth surface profile portion is more than the work function of each de-ion plate at the rough surface profile portion to enhance an arcing voltage to reduce arc quenching time.

E) BRIEF DESCRIPTION OF THE DRAWINGS:
[0016] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0017] FIG. 1 illustrates a sectional view of a circuit interrupting device according to one embodiment of the present invention.
[0018] FIG. 2 illustrates a schematic diagram of the rough surface profile of a de-ion plate according to one embodiment of the present invention.
[0019] FIG. 3 illustrates a schematic diagram of the smooth surface profile of the de-ion plate according to one embodiment of the present invention.
[0020] FIG. 4 is a schematic diagram illustrating an arc splitting according to one embodiment of the present invention.
[0021] FIG. 5 illustrates a schematic representation of the Smoluchowski effect on the de-ion plates according to one embodiment of the present invention.
[0022] FIG. 6 illustrates a block diagram depicting the characteristics of the smooth surface and the rough surface of the de-ion plate according to one embodiment of the present invention.
[0023] FIG. 7 illustrates a graph comparing work function of the de-ion plates against cathode voltage drop according to one embodiment of the present invention.
[0024] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be

combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0025] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0026] The various embodiments of the present invention provide an arc-chute assembly in a circuit interrupting device comprising an arc chute, a plurality of de-ion plates arranged in the arc chute; wherein each de-ion plate has a preset profile to distribute a work function within the arc chute to reduce arc splitting time and to enhance the arc voltage to reduce the arc quenching time.
[0027] A general requirement of a circuit interrupting device is that the arc has to be split into multiple series arcs for efficient quenching. This is achieved by the arc chute assembly which consists of multiple de-ion plates arranged in parallel to each other in the path traverse to the arc column. The splitting of arc is decided by the formation of the anode roots and the cathode roots on the de-ion plates. Here the formation of cathode roots is governed by surface temperature, effective work function and electric field at emission spot.
[0028] The electrical arcs between the contacts extinguish when a required arc voltage appears across the two contacts, especially at near current zero the value of arc voltage plays a major part in extinguishing the arc. Faster the buildup of the arc voltage the lesser would be the time taken to extinguish the arc. Hence the de-ion plates has significant role in extinguishing the arc. As circuit breaker contacts open, the arc chute (de-ion plates) segments, gets cooled and move the arc away from the

contacts. Moving the arc away preserves the integrity of the contacts for a longer service life where the movement of arc is governed by the gas dynamics and the magnetic pull imposed on the arc by the arcing chamber.
[0029] The arc chutes primarily comprises a plurality of metal plates which are de-ion plates arranged at right angles to the length of the arc chute with spacers between the plates to allow the arc to be split up into a series of smaller arc, increasing its resistance and extracting heat. This in turn affects the sustainability of the arc by itself. In DC (direct current) circuit breakers, if adequate plates are used in series, the arc voltage across the chute can be greater than the system voltage, forcing the current down to zero in a short time and thereby interrupting the current.
[0030] The movement of the movable contacts away from the fixed contacts results in the formation of an electrical arc in the space between the contacts beginning at the time the contacts are initially separated (FIG.l). The electromagnetic and thermal blowout forces cause the arc to move away from the contacts thereby transferring the arc to the arc chutes. An important factor in the arcing period is the time taken by the arc to enter into the arc chutes and the series of anode cathode voltage drops on the de-ion plates across the arc chute. The time delay for the arc to enter into arc chutes depends on the work function of the material used in making de-ion plates. Further the work function of the de-ion plates depends on the material characteristics and its surface finish. The work function of the de-ion plates can be fixed on use of a suitable metal. Thus the work function of the de-ion plates can be varied based on the selection of suitable metal through Smoluchowski effect.
[0031] According to Smoluchowski effect, a metallic material having a closed packed surface (FIG. 3) and an open surface (FIG. 2) is selected. Here the closed packed surface is a smooth surface whereas the open surface has a rough surface characteristic. On the open surface, it is observed that the Smoluchowski effect of charge smoothing and the surface corrugation is represented by the zigzag profile line (FIG. 5). Further a higher gradient in the charge density leads to a higher kinetic

energy. Thus to lower the kinetic energy, the charge distribution is smoothed out. Further the charge redistributes from the maximum peak (501) into the minimum peak (502) formed by the surface atoms there by a net positive charge on the maximum peak (501) and a negative charge in the minimum peak 502 arises. For a close-packed surface, the smoothing mechanism has no big effect, whereas the surface charge distribution of an open surface or a stepped surface is effected strongly by the smoothing mechanism. The work function of a closed packed surface will be higher than that of an open surface. The Smoluchowski effect optimizes that the work function of a closed packed surface is higher than the open surface. [0032] Further, the formation of cathode roots across the de-ion plates at a fast pace caters a quick dissipation of the arc into the arc chutes. At lower work function values, cathode root can be formed at lower temperatures on base material. The rough surface profile (FIG.2) of the de-ion plates facing the arc used herein the arc chute provides for a low work function The terminal thermal time delay can be reduced by using lower work function value plates at the arc entering surface of de-ion plates.
Further number of electrons emitting per second per unit area from the cathode body is given by:
Jem = A.. 7",;,. exp - , "
* " \ fc«7",v /
Where
Ac=Richardson constant.
Tw=surface temperature (k).
e = electron charge (coulombs).
k=Boltzmann constant.
q>eff= effective work function
Ec = electric field intensity (V/m). From the above, equation effective work function value is a function of the electric field intensity. The electric field intensity is high for rough surface and further, the high electric field reduces the effective work function of the material. The reduction

in the work function value of the material at the arc entrance causes less temperature and less time for splitting the arc.
[0033] Another embodiment of the present invention is to improve the arcing voltage by developing higher value of work function at the exit end of on the de-ion plates. According to Smoluchowski effect, we know that variation of work function can be achieved by modifying the surface profile of de-ion plates. Thus when the arc enters into de-ion plates, the higher work function of de-ion plates (7 of fig.2) cause rapid buildup of arc voltage, leading to a fast arc quenching. The analysis results of variation of cathode voltage drop with different work function values have been depicted in the gra^h. From the graph analysis results, it is evident that with the increase in work function, the cathode voltage drop is also increased. For example, by increasing the 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 de-ion plates are 10, then there is a voltage boost of (10*2=20V). This additional 20V arc voltage helps in faster arc quenching.
[0034] Thus fast Splitting of arc is achievable by low work function and higher voltage drop is achievable by high work function. The low work function and the high work function in turn provides for lower arcing time and lower energy dissipation. The de-ion plates with the surface having a rough surface profile ttmstiwsted £} the 3?c entrance of the de-ton pJate and smooth surface profile for the remaining section of the de-ion plates renders the low work function and high work function to a single c[e-ion plate.
[0035] FIG.l illustrates a sectional view of a circuit interrupting device according to one embodiment of the present invention. With respect to FIG. 1, the circuit interrupting device includes an arc chute assembly (105) comprising of a plurality of de-ion plates (101) arranged parallel to each other. Each of the de-ion plate has rough profile surface (102) at the first position followed by a smooth surface profile (103). The first position can be defined as the section of arc entry. When the electric source (106) is interrupted V>y separating the movable contact from a fixed contact (104), an

arc (107) is generated between the movable and fixed contacts (104). Further the arc (107) is transferred into the arc chute (105) by electromagnetic and thermal blowout forces causing the arc to move away from the contacts along the arc runners. The arc entering the arc chute assembly, at the beginning of the arc chute traverses through the rough surface profile area (102). Due to the low work function of the rough surface on de-ion plates, arcs are split rapidly. After the arcs are split, the residual arc enters the smooth surface profile area (103) which is of high work function. When the arc is in the smooth surface area (103) high voltage drop occurs due to high work function of the smooth surface on the de-ion plates. Thus lower arcing time and lower let through energy dissipation is achieved by integrating low work function (rough surface profile) and high work function (smooth surface profile) on a single de-ion arc plate.
[0036] FfG. 2 illustrates a schematic diagram of the rough surface profile of a de-ion plate according to one embodiment of the present invention. With respect to FIG. 2, each de-ion plates has a preset profile, wherein the preset profile on each de-ion plate has a rough surface profile (102) at a first portion followed with a smooth surface profile at a second portion. The rough surface profile (102) is formed on an upper surface and lower surface of each de-ion plate with the rough surface profile having a corrugated shape. The rough surface profile (102) is provided at an arc entering face of each de-ion plate and extended along a direction of propagation of the arc.
[0037] FIG. 3 illustrates a schematic diagram of the smooth surface profile of the de-ion plate according to one embodiment of the present invention. With respect to FIG. 3, the smooth surface profile (103) portion is formed after the rough surface profile portion on each de-ion plate and extended up to an arc exit face of each de-ion plate. The smooth surface profile is formed on both the upper and lower surface of each de-ion plate. The work function of each de-ion plate at the rough surface profile portion (102) is less than the work function of each de-ion plate at the smooth surface profile portion to reduce an arc splitting time and to reduce an arc temperature. Further the work function of each de-ion plate at the smooth surface profile portion is

more than the work function of each de-ion plate at the rough surface profile portion to enhance an arcing voltage to reduce an arc quenching time.
[0038] FIG. 4 is a schematic diagram illustrating an arc splitting according to one embodiment of the present invention. With respect to FIG. 4, when the electric source (106) is interrupted by separating the movable contact from a fixed contact, an arc is generated between the movable and fixed contacts. Further the arc is transferred into the chute by electromagnetic and thermal blowout forces causing the arc to move away from the contacts along the arc runners. After the arc has completely entered into de-ion plates, the higher work function of de-ion plates (401) cause rapid buildup of arc voltage, leading to a fast arc quenching.
[0039] FIG. 5 illustrates a schematic representation of the Smoluchowski effect on the de-ion plates according to one embodiment of the present invention. According to Smoluchowski effect, consider a closed packed surface (FIG. 3) and an open surface (FIG. 2) of a metallic material. Here, the closed packed surface is a smooth surface whereas the open surface has a rough surface characteristic. On the open surface we find the Smoluchowski effect of charge smoothing and the surface corrugation is represented by the zigzag profile line (FIG. 5). Further a higher gradient in the charge density leads to a higher kinetic energy. Thus to lower the kinetic energy, the charge distribution is smoothed out. Further the charge redistributes from the maximum peak (501) into the minimum peak (502) formed by the surface atoms there by a net positive charge on the "maximum peak (501) and a negative charge in the minimum peak (502) arises. For a close-packed surface, the smoothing mechanism has no big effect, whereas the surface charge distribution of an open surface or a stepped surface is effected strongly by the smoothing mechanism. The work function of a closed packed surface will be higher than that of an open surface. The Smoluchowski effect optimizes that the work function of a closed packed surface is higher than the open surface.
[0040] FIG. 6 illustrates a block diagram depicting the characteristics of the smooth surface and the rough surface of the de-ion plate according to one embodiment of the present invention. When the electric arc enters the de-ion metal plate having smooth

surface profile (601) due to high work function, faster splitting of arc cannot be achieved. Further in the metallic surface having both the rough profile surface (602) and smooth profile surface (603), faster splitting of arc can be achieved by the low work function of the rough surface profile (602) and further higher voltage drop can be achieved by high work function of the smooth surface profile (603) at a single stretch.
[0041] FIG. 7 illustrates a graph comparing work function of the de-ion plate against cathode voltage drop according to one embodiment of the present invention. The graph (FIG. 7) shows that the cathode voltage drop increases with increase in work function. For example, by increasing the work function from 4.9ev to 5.9ev the cathode voltage drop increases by 2V. This increment in voltage is for one cathode de-ion plate, if the number of de-ion plates are 10, then there is a voltage boost of (10*2=20V). This additional 20V arc voltage helps in faster arc quenching.
G) ADVANTAGES OF THE INVENTION
[0042] The various embodiments of the present invention provide an arc-chute assembly in a circuit interrupting device comprising an arc chute, a plurality of de-ion plates arranged in the arc chute; wherein each de-ion plate has a preset profile to distribute a work function within the arc chute to reduce an arc splitting time and to enhance the arc voltage to reduce the arc quenching time.
[0043] The present invention proposes the method of reducing the arcing time by generating conditions favorable for arc splitting. This is achieved by appropriately modifying the work function of de-ion plates so as to aid cathode spot formation and subsequent strategy to aid in arc voltage build up. A faster build up of arc voltage leads to faster extinction of the electric arc which is beneficial from the perspective of electrical system protection.
[0044] The present invention also provides a means of improving the performance of existing means of arc guidance and improved arc quenching time which leads to

limiting the let through energy in current interrupting devices.
[0045] Further it has been found advantageous that by integrating the two properties such as rough surface profile at arc entrance and smooth surface profile for remaining section on a single de-ion metallic plate surface, fast splitting of arc by low work function (rough surface) and high voltage drop by high work function (smooth surface) can be achieved. Also lower arcing time and lower let through energy dissipation can be achieved by grading of the metallic de-ion plates.
[0046] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0047] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. An arc-chute assembly in a circuit interrupting device comprising:
an arc chute;
a plurality of de-ion plates arranged in the arc chute;
wherein each de-ion plate has a preset profile to distribute a work function within the arc chute to reduce arc splitting time and to enhance an arc voltage to reduce the arc quenching time.
2. The assembly according to claim 1, wherein the preset profile on each de-ion plate has a rough surface profile at a first portion followed with a smooth surface profile at a second portion.
3. The assembly according to claim 1, wherein the rough surface profile is formed on an upper surface and on a lower surface of each de-ion plate.
4. The assembly according to claim 1, wherein the rough surface profile has a corrugated shape.
5. The assembly according to claim 1, wherein the rough surface profile is provided at an arc entering face of each de-ion plate and extended along a direction of propagation of the arc.
6. The assembly according to claim 1, wherein the smooth surface profile portion is formed after the rough surface profile potion on each de-ion plate and extended up to an arc exit face of each de-ion plate.
7. The assembly according to claim 1, wherein the smooth surface profile is formed on an upper surface and on a lower surface of each de-ion plate.

8. The assembly according to claim 1, wherein the work function of each de-ion plate at the rough surface profile portion is less than the work function of each de-ion plate at the smooth surface profile portion to reduce an arc splitting time and to reduce an arc temperature.
9. The assembly according to claim 1, wherein the work function of each de-ion plate at the smooth surface profile portion is more than the work function of each de-ion plate at the rough surface profile portion to enhance an arcing voltage to reduce an arc quenching time.
10.The assembly according to claim 1, wherein the pluralities of de-ion plates are arranged in parallel or in a partially divergent assembly.