FORM 2
THE PATENTS ACT, 1970 COMPLETE SPECIFICATION
(See Section 10)
ARC CHUTE WITH TRIMETAL ARC PLATES FOR ARC CHAMBER IN CIRCUIT BREAKER DEVICE
Numbered as dated
INVENTORS:
a) PRAVEEN. P. KURVEY
b) DINESH. R. KANNADKAR
c) MAYURS. HORE
APPLICANT:
M/s. LARSEN & TOUBRO LIMITED
L&T House, BaUard Estate, P.O. Box No 278,
Mumbai, 400 001, Maharashtra,
INDIA
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THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION

ARC CHUTE WITH TRIMETAL ARC PLATES FOR ARC CHAMBER IN CIRCUIT BREAKER DEVICE
A) TECHNICAL FIELD
[0001] The present invention generally relates to a circuit breaker device and more particularly to the arc splitter plates in an arc chute at an arc chamber or an arc extinguishing device in a circuit breaker device such as a molded case circuit breaker device, to provide high breaking capacity to the molded case circuit breaker.
B) BACKGROUND OF THE INVENTION
[0002] Generally a circuit breaker device is a mechanical switching device which is capable of making, carrying and breaking currents under normal circuit conditions. The circuit breaker is also capable of making and carrying currents for a specified time and breaking currents under specified abnormal circuit conditions, such as a short circuit condition. The circuit breaker device can control and protect an electrical circuit and people operating an electrical device. The circuit breaker has contact which are made to contact or separate from each other to supply or to cut off electrical current supply to a device. An arc drawn between the circuit interrupting contacts is very violent and has very
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high energy. The extinction of such an arc to interrupt the flow of large fault currents is an extremely challenging task. The arc must be extinguished quickly to prevent damaging consequences to the electrical wiring, a load and also to the circuit interrupting device itself. Hence the current breaking capacities must be increased while keeping the size of interrupting device in compact.
[0003] Normally a protective equipment on high-voltage transmission lines prevents the formation of an unwanted arc, or ensures that it is de-energized within tens of milliseconds. The electrical apparatus arranged to interrupt high-voltage circuits is designed to safely direct the resulting arc so that it dissipates without damage. The high voltage circuit breakers often use a blast of high pressure air, a special dielectric gas (such as SF6 under pressure), or immersion in mineral oil to quench the arc when the high voltage circuit is broken.
[0004] The arc extinguishing device or an arc quenching device has an arc chamber in which the arc drawn between the two contacts in a breaker contact system is extinguished or quenched. Hence the design of an arc chamber is very important in this manner. The arc chamber consists of a pair of contacts and an arc chute. The arc chute includes a stack of closely spaced metallic plates called splitter plates and two side walls. The metallic plates are generally made up of mild steel and have a groove on the contact side to pull an arc inside the arc chute. The mild steel is used for a splitter plate to pull an arc inside the arc chute due to its ferromagnetic properties. The arc pulled inside the arc chute is split by the splitter plates and extinguished. It is very important to cool the arc and to drag it away from contacts, to quench or extinguish an arc effectively. The cooling of arc is done by the splitter plates.
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[0005] The splitter plates are generally coated with the material having good arc mobility such as Copper or Nickel. But the main drawback in this type coated splitter plates is that the coating on the splitter plates gets vanished resulting into inferior performance for the next short circuit condition, after clearing the first or maximum a second shot during the short circuit conditions, The erosion of the coating layer on the splitter plates after two short circuit conditions results into the higher energy dissipation and higher thermal and mechanical stresses on the system.
[0006] Hence there is a need to choose a suitable material and coating layer for the splitter plates in an arc chute to improve the arc quenching efficiency, to maintain the arc quenching efficiency for a long period of time and to enhance the life of the splitter plates in an arc chute.
[0007] The US patent No.4143256, discloses the arc plates coated with a welding retardant material. An arc chute used for assisting the extinction of an arc drawn between circuit interrupting contacts, in the air includes a stack of closely spaced metallic plates. These metallic plates (splitter plates) are coated with a weld deterrent material such as silicone varnish. The varnish coating gets evaporated after a first shot, during a short circuit condition and the steel arc plates are exposed to the arc. Further due to lesser arc mobility, the steel arc plates would erode to a higher extent, reducing the breaking capacity for next short circuit condition.
[0008] The US patent No. 4 375 021 discloses a rapid arc extinguishing assembly for an electrical circuit breaker provided with an arc chute containing
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several de-ionizing plates arranged in parallel and bent in U - shape. The plates are made up of magnetically permeable and electrically conductive plates.
[0009] Thus none of the prior art devices provide a splitter plate that does not require a plating layer. Also none of the splitter plates of the prior art devices reduces the erosion of the arc plates and achieves a uniform distribution of heat during high fault currents.
[0010] So, there is a need to develop the arc plates with a suitable material and coated with a suitable plating layer to reduce the erosion of the plating layer during short circuit conditions to maintain the efficiency of the quenching process over a long period of time, to improve the heat distribution uniformly to improve the cooling of the arc, to maintain the dielectric strength of the arc chamber, to improve the arc mobility and to permit the passage of lesser energy.
C) OBJECT OF THE INVENTION
[0011] The primary object of the present invention is to provide a splitter plate with a suitable material and a coating layer to reduce the erosion of the plating layer during a short circuit condition to maintain the efficiency of the arc quenching process.
[0012] Another object of the present invention is to provide a splitter plate of suitable material and structure to improve the heat distribution and conduction uniformly to improve the cooling efficiency of the arc.
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[0013] Another object of the present invention is to provide a splitter plate of suitable material to maintain the dielectric strength of the arc chamber.
[0014] Another object of the present invention is to provide a splitter plate of suitable material to improve the mobility of the arc in the arc chamber.
[0015] These and other objects and advantages of the present invention will become readily apparent.from the following summary and detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE PRESENT INVENTION
[0016] The above mentioned shortcomings, disadvantages, problems, objectives and advantages are addressed herein, which will be understood by reading and studying the following specification.
[0017] According to one embodiment of the present invention, a tri-metal structure is used for a splitter plate to take care of the problems mentioned above. The splitter plate is made up of mild steel which is sandwiched between two copper plates. The copper has high thermal and electrical conductivity properties so that the heat of arc is uniformly distributed over the entire splitter plate thereby improving the cooling of the arc quickly. Moreover the arc mobility is increased due to the use of copper metal plates so that arc is rapidly
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taken away from the circuit breaker contacts to reduce the erosion of the contacts.
[0018] The arc-chute consists of number of arc plates or an arc plate stack. The arc plates are made up of magnetic material like steel. They are mounted in parallel to each other between two side walls. The arc plates have projections which extend through the openings provided in the side walls. Each arc plate is provided with a dip notch through which the breaker contacts are moved. The side walls are generally made up of insulating material like glass polyester so that all the plates are kept insulated from each other. The splitter plates are made up of a tri-metal structure. A mild steel plate is interposed between two copper plates to form a tri metal structure. The tri-metal plates are used to provide a significant improvement in the breaking capacity because the tri-metal plates improve the cooling efficiency of the arc and the arc mobility. The mild steel is a magnetic material. A groove is provided on the arc plate to pull an arc inside the arc plates. A small dip is given on the back of arc plate to enable the cooling and quenching gases to flow out easily.
[0019] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiments and the accompanying drawings.
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E) BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG.l shows a perspective view of an arc chute provided in an arc extinguishing device in a molded circuit breaker according to one embodiment of the present invention.
[0021] FIG.2 shows a cross sectional view of an arc chute provided in an arc extinguishing device in a molded circuit breaker according to one embodiment of the present invention.
[0022] FIG.3 shows a perspective view and a cross sectional view of an arc plate used in an arc chute provided in an arc extinguishing device in a molded circuit breaker according to one embodiment of the present invention.
[0023] Although the 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
[0024] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof and in which the specific embodiments that may be practiced are shown by way of illustration. These
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embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that 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.
[0025] Various embodiments of the present invention relates to material used for arc splitter plates so as to provide high breaking capacity to the molded case circuit breaker. However, the embodiments are not limited and may be implemented in connection with other circuit breaker or switch gear devices.
[0026] According to one embodiment of the present invention, a molded case circuit breaker device is provided with an arc chute having splitter plates made up of suitable material and structure to achieve high breaking capacity and to improve the cooling efficiency of an arc in an arc chamber to quench the arc quickly and efficiendy. The splitter plates are formed with a tri-metal structure. The tri-metal structure is formed by sandwiching a mild steel plate between two copper plates. The tri- metal structure distributes the heat of arc more uniformly to cool the arc efficiently, improves the arc mobility and maintains the dielectric strength of the arc chamber effectively.
[0027] According to one embodiment of the present invention, an arc chamber is provided in an arc extinguishing device arranged in a circuit breaker device such as a molded case circuit breaker. The arc chamber has an arc chute and a pair of contacts and arc chute. The arc chute has a stack of closely spaced metallic plates called arc splitter plates and two side walls. The metallic arc splitter plates are formed with a tri-metal structure. The tri-metal structure is
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formed by sandwiching a mild steel plate two copper plates. The arc splitter plates are arranged in parallel between the two side wall plates. The arc splitter plates have projections which are extended through the openings in the side walls of the arc chute. The splitter plates have a groove on the contact side to pull an arc inside the arc chute. Each arc splitter plate has a dip notch at the back so that the arc plates are aligned easily and the quenching gases are passed through easily. The side walls are generally made up of insulating material like glass polyester so that all the arc splitter plates are insulated from each other. The arc plates are provided with a slight upward gradient as the natural movement of the gas is generally along the upward direction.
[0028] The mild steel is used for splitter plate due to it is ferromagnetic properties, to pull the arc inside the arc chute. The arc drawn inside an arc chute is split by the splitter plates so that the split arc is cooled and extinguished. Actually it is very important to cool the arc and drag it away from the contacts, to quench an arc inside an arc chute. The cooling of arc is also done by splitter plates. The splitter plates are generally coated with the material having good arc mobility like copper or Nickel. According to one embodiment of the present invention, the splitter plate is formed by interposing a mild steel plate between two copper plates, thereby eliminating the need for any outer coating layer. The outer copper layer is thick enough to withstand three shots during a short circuit condition so the efficiency of the splitter plates in cooling and quenching the arcs is maintained for a long period of time. The copper is very good conductor of heat and electricity, so that the heat produced due to the arc is uniformly distributed over an entire arc plate and the arc is cooled quickly and efficiently. In the present invention, a major thermal mass is provided by the mild steel layer. When an arc is split, the arc root should move
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away from the breaker contacts quickly to keep the breaker contacts in good condition. The copper metal layer gives the good arc mobility so that the arc is pulled away from the breaker contacts quickly.
[0029] Thus the present invention provides a tri-metal plate structure for the metal arc splitter plates to eliminate the need for a plating layer on the splitter plate thereby reducing the erosion of the arc plates over a longer period of use. The tri-metal arc splitter plate increases the arc mobility to reduce the energy passed through the plates. The tri-metal arc splitter plates also ensure uniform heat distribution in high fault current conditions.
[0030] According to another embodiment of the present invention, a molded case circuit breaker is provided with an arc extinguishing device having an arc chute provided with tri-metal arc splitter plates to quench the arc column produced between the breaker contacts quickly.
[0031] The Fig.l shows a perspective view of an arc-chute used in a molded case circuit breaker which is used for interrupting the short circuit currents in electrical equipment. The arc-chute consists of number of arc plates 5 or an arc plate stack 3. The arc plates 5 are made up of magnetic material like steel. The arc plates 5 are mounted in parallel to each other between the two side walls 1. The arc plates 5 have projections 4 which extend through the openings 2 provided in the side walls 1. Each arc plate 5 is provided with a dip notch through which the breaker contacts move. The side walls 1 are generally made up of insulating material like glass polyester so that it keeps all plates insulated from each other. According to the present invention, the tri-metal arc plates 5 are used for the metallic splitter plates. The tri-metal arc plates 5 provide
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significant improvement in breaking capacity, as the tri-metal provides better cooling of arc and high arc mobility. The maximum let through energy of all phases was seen to be 0.8 million whereas in case of regular arc plates the let through energy was above 1 million.
[0032] The Fig.2 shows a cross sectional view of an arc-chute provided in a molded case circuit breaker and installed with tri-metal arc plates 5 as metal arc splitter plates. The arc plates 5 are arranged in parallel to each other. A minimum gap is maintained between the arc plates 5 for preventing the shorting of the arc plates 5 and for allowing the quenching and cooling gases to escape. The arc plates 5 are provided with a slight gradient as the natural movement of the gas is generally along the upward direction.
[0033] The Fig.3 shows a perspective view and a side view of an arc plate 5 according to one embodiment of the present invention. The arc plates 5 are formed with a tri-metal structure containing three metallic layers 6,7,8 that are laminated successively. The upper and the lower layers 6 and 8 are copper metal layers and the middle layer 7 is a mild steel metal layer. The mild steel is a magnetic material. The upper and the lower metal layers 6, 8 can be formed with any metal such as nickel, etc, providing good arc mobility. Each arc plate 5 is provided with a groove 10 to pull an arc inside an arc plate 5. The flux produced by the arc reduces the path reluctance so that the arc is pulled inside an arc plate 5. A small dip like notch 9 is formed at the back of the arc plate 5 so as to help the quenching and cooling gases to flow out easily.
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[0034] Generally, it is common practice to use mild steel arc plates to split and extinguish the arc. To extinguish a high energy arc, the arc plates execute the following operations. For low fault currents, the arc plates split the arc forming cathode and anode on the arc plate, to increase the arc voltage. For very high fault currents, the arc is not split but it travels around the front edges of the arc plates and follows a serpentine path, there by increasing the arc resistance and hence an arc voltage. In such cases, the arc deionization is done by cooling the arc.
[0035] The copper plate has a high thermal and electrical conductivity so the heat of an arc is uniformly distributed over an entire splitter plate, thereby cooling the arc quickly. Moreover the arc mobility is increased due to the use of copper metal layers so that the arc is rapidly removed from the breaker contacts to reduce the erosion of the breaker contacts in a circuit breaker device.
[0036] Thus various embodiments of the present invention provide an arc chute with an arc plate formed with a tri- metal structure.
[0037] It will be obvious for a person of skilled in the art to practice the present invention with several modifications. However, all those modifications will be deemed to be covered within the scope of the present invention as covered in the claims mentioned hereunder.
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G) ADVANTAGES OF THE PRESENT INVENTION
[0038] According to the present invention, the arc splitter plate is formed with a tri-metal structure in which a mild steel plate is sandwiched between two outer copper metal plates. The copper has a high thermal and electrical conductivity so that the heat of arc is uniformly distributed over the entire splitter plate, to cool an arc quickly. Moreover the arc mobility is increased due to copper so that arc is rapidly removed from the breaker contacts thereby reducing the erosion of the contacts. The tri-metal plates provide a high breaking capacity to the molded case circuit breaker because the tri-metal arc splitter plates cool an arc efficiently and quickly and increase the arc mobility. The copper layer is thick enough to withstand three shots during a short circuit condition so that the efficiency of the arc splitter plates in cooling and quenching the arc is maintained uniformly over a long period of time. The dielectric strength of an arc chamber is maintained for a long period of time. The copper layer also ensures uniform distribution of heat in case of high faulty currents.
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CLAIMS
What is claimed is:
1. An arc chute in an arc extinguishing device at a circuit breaker,
comprising
a) arc plate stack containing number of arc splitter plates arranged in parallel between two side plates;
b) Wherein each arc plate is formed with a tri-metal structure obtained by interposing a mild steel plate between two copper metal plates.

2. An arc chute according to claim. 1 wherein the said arc splitter plates are provided with a groove at front side to pull an arc inside.
3. An arc chute according to claim. 1 wherein the each said arc splitter plate is formed with a notch at the back side.
4. An arc chute according to claim.1 wherein the each said arc splitter plate is formed with a dip at the back side.
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5. An arc chute according to claim.l wherein the each said arc splitter plate is provided with a projection extended out from each side edge.
6. An arc chute according to claim.l wherein the each said side wall of the said arc stack has several openings through which the projections of each arc splitter plate are extended out.
7. An arc chute according to claim.l wherein the each said arc plate is separated from an adjacent arc plate by a predetermined distance to prevent shorting and to permit the quenching gases to escape.
8. An arc chute according to claim.l wherein the each said arc splitter plate is provided with an upward gradient to enable free movement of gases.
9. An arc chute according to claim.l wherein the said side walls of the said arc plate stack are made up of insulating materials.
10. An arc chute according to claim.l wherein the said side walls of the arc plate stack are made up of glass polyester.
11. An arc chute according to claim.l wherein the outer metal plates in the tri-metal structure is a conductive material providing arc mobility.
12. An arc chute according to claim.l wherein the outer metal plate in the said tri-metal structure is nickel.
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13. An arc metal plate for an arc chute in an arc extinguishing device in a
circuit breaker, comprising:
a tri- metal structure formed by interposing a mild steel metal between two copper metals.
14. An arc metal plate according to claim. 13, further comprising a groove at the front side.
15. An arc metal plate according to claim. 13 further comprising a projection extended from the side walls.
16. An arc metal plate according to claim. 13 further comprising a notch at the back side.
17. An arc metal plate according to claim.16 wherein a dip is formed at the back side.
18. An arc metal plate according to claim. 13 wherein the outer metal layer in the said tri-metal structure is formed with a conductive metal providing arc mobility.
19. An arc metal plate according to claim. 18 wherein the outer metal layer in the said tri- metal structure is nickel.
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20. A circuit breaker device having an arc extinguishing device including an arc chute consisting of arc splitter plates formed with a tri- metal structure.
Dated this the 13™ day of March, 2007

Rakesh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA
To,
The Controller of Patents, The Patent office, At Mumbai
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ABSTRACT
According to one embodiment of the present invention, an arc chute is provided with a stack of arc plates consisting of number of arc splitter plates arranged in parallel between two side walls made up of insulating material. The arc splitter plate is formed with a tri-metal structure obtained by interposing a mild steel plate between two copper plates. Each arc splitter plate has a groove at the front side to pull an arc inside and a notch at the back side to permit the flow of gases. Each plate has a projection which is extended out from the side edges through the openings in the side walls of the stack.
20 claims, 3 drawing sheets
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