F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention:
IMPROVED ARC CHUTE ASSEMBLY FOR ELECTRICAL SWITCHING DEVICES

2. Applicant(s):

(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:

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to switching devices. More particularly present invention relates to an improved arc chute assembly for electrical switching devices.

BACKGROUND AND THE PRIOR ART

Electrical switching apparatus, such a switch disconnector provides safety isolation for any low voltage circuits and suitable for diverse applications in motor control centers, switchboards and as main switches in various equipment and machines. These switches are ideal for breaking stalled motor current, switching highly inductive loads, capacitor banks, DC loads etc.

The electrical contact system assembly of low-voltage switches, for example generally comprise a conductor assembly including a movable contact assembly having a plurality of movable contacts, and a stationary contact assembly having a plurality of corresponding stationary contacts. The contact mechanism is knife/blade type with self cleaning action during operation. The fixed contact terminals in each phase have separate main and arcing contacts. There are four breaks per pole (two series, two parallel) resulting into easy quenching of arcs. The contact is first made with the main contact area and thereafter with the arcing contact area. During breaking, the arc formation is across the arcing contacts thereby protecting the main contacts which results into enhanced life of the switch. The arc is effectively quenched & confined by the set of arc chutes (arc quenching media).

A general requirement of arc quenching medium is that the arc has to be split into multiple series arcs for efficient quenching. This is achieved by introducing multiple de-ion plates at multi locations in the path transverse to the arc column. During electrical faults, high arcing can be observed, where the arcing time is very high, which can be reduced by splitting the arc into multiple arcs quickly and de-ionizes the arc particles, by this the total arcing time can be reduced and increases the life of the contacts.

The gas flow in arc quenching media has an important effect on the interruption capacity of low voltage circuit breakers. The smaller vent size is, the higher pressure and better the interruption performance will be, but when the vent size smaller than a certain proportion, the arc will re-ignite and when the vent size larger than a certain proportion, the arc will also re-ignite. If the venting size is comparatively bigger, then the gas pressure rise inside the arc quenching chamber is lower, and the pressure gradient is less. In this case arc cannot enter into the de ion plates (splitter plates) so the interruption performance is lower. In addition, the dielectric recovery strength is reduced and re-ignition occurs.

If the venting size is extremely small, then the gas pressure rise and the pressure gradient inside the arc quenching chamber are all higher. Therefore, the gas-driven force acting on arc is stronger, and the interruption performance is better during the first half cycle. However, due to the smaller venting size, it is difficult for the metallic vapor to escape from the arc quenching chamber, and the heat exchange between the high temperature gas and the environmental atmosphere is not sufficient. Therefore, the re-ignition occurs either. In addition, the smaller venting size is the shorter current less period.

US 3483343 disclose use of magnetic field to pull the arc in to arc chutes for fast arc quenching unlike the present invention.

US 7674996 disclose that, a gassing insulator for the arc chute assembly of a circuit breaker includes a number of insulating members.

US 7186941 B2 discloses an arc extinguisher assembly provided for a mould cased circuit breaker capable of reducing time for arc extinguishing and preventing contacts from being damaged due to a back flow of an arc.

US 7091438 B2 discloses an arc extinction system having one or more insulators that generates a desirable gas in the presence of an arc. The presence of the gas can reduce the concentration of ions and electrons within the interior of the circuit breaker and can increase the pressure within the circuit breaker, and these also facilitate extinction of the arc.
US 3662133 titled “Space-Plate arc chute for an air-break circuit breaker” discloses an arc-chute of the space-plate type providing for an air break circuit breaker in which a molded insulating casing is provided with grooves for supporting the spaced magnetisable conducting plates. The casing has an enlarged lower opening communicating with a laterally disposed restricted opening. Additionally, the insulating casing has flange, or shelf means integrally formed therewith to prevent downward movement or blasting of the arcing gases, which are heated during the arcing interrupting operation. In this the space metallic magnetisable plates are provided a plurality of spaced expansion chambers, which are partitioned from each other by vertically extending solid insulating plate portions interspersed lengthwise of the arc-chute along the upper portion thereof. Arc chute assembly having effective de-ion plates structure, which will de-ionizes the gas particles by which the arc will travel very fast into de-ion plates and split into multiple arcs, by which length of arc increases and then the arc voltage increases, thereby total arcing time reduces.

Present invention can be used in any electrical switching apparatus, such as Miniature Circuit Breaker (MCB), Moulded Case Circuit Breaker (MCCB), Air Circuit Breaker (ACB) and Switch Dis connector with Fuse (SDF) etc. More particularly this invention is implemented in electrical switching apparatus, such as switch dis connector (SD).

OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another object of the present invention is to provide means for interrupting the flow of electricity through an arc quenching medium.

Yet another object of the present invention is to provide an improved arc chute assembly having different types of arc plates facilitating arc quenching.

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

There is provided an improved arc chute assembly for electrical switching devices.

According to one embodiment of the present invention, there is provided An improved arc chute assembly for electrical switching devices comprising a plurality of substantially bent de-ion plates; a plurality of substantially slotted de ion plates; a plurality of substantially serrated de ion plates for increasing arc length; atleast one insulation sheet attached to said serrated de ion plate; atleast one substantially perforated sheet, said perforated sheet acting as a coolant; atleast one arc chute support; and atleast one venting block.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

So that those having ordinary skill in the art will more readily understand how to construct an improved arc chute assembly for electrical switching devices in accordance with the present disclosure, exemplary embodiments are described in details herein below with reference the accompanying drawings wherein:

Fig 1 illustrates the general view of switch disconnector comprising of all conducting parts, non conducting parts and arc quenching media which embodies Top housing (1), bottom housing (2), terminal (3), arc chute (4) and phase barrier (5).

Fig. 2 illustrates the general view of single pole switch disconnector comprises of terminal (3), arc chute (4), movable bridge (6), moving contact (7) and magnetic cladding (8).

Fig.3 illustrates general view of arc chute (4) comprises of de-ionization plates (de-ion plate1 (10), de-ion plate2 (11), de-ion plate3 (12), de-ion plate4 (13) and de-ion plate5 (14)), insulated sheet/ insulator (15), perforated sheet (16) and venting block (17) which embodies this invention.

Fig. 4 illustrates exploded view of different elements that embodies this invention.

Fig. 5 illustrates detailed cross-sectional of the present invention.

Fig. 6, 7 and 8 illustrates the clear views of arc (18) travel in arc chute.

Fig. 9 illustrates a front view of de-ion plate 2 (11).

Fig. 10 illustrates a general view of de-ion plate2 (11), which indicates the aerodynamic shape 11(a)).

Fig. 11 is a general view of de-ion plate2 (11), which indicates the sharp corners (11(b)).

Fig. 12 is a general view of de-ion plate3 (11), which shows the arc (18) and magnetic flux density (19).

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.

Reference is first invited to Fig 1 where the general view of switch dis-connector comprising of all conducting parts, non conducting parts and arc quenching media is shown.

Fig 2 shows single pole switch dis-connector comprising of terminal (3), arc chute (4), movable bridge (6), moving contact (7) and magnetic cladding (8).

Fig 3 shows arc chute (4) comprising of de-ionization plates (de-ion plate1 (10), de-ion plate2 (11), de-ion plate3 (12), de-ion plate4 (13) and de-ion plate5 (14)), insulated sheet/ insulator (15), perforated sheet (16) and venting block (17).

Fig 4 shows an exploded view of an arc chute assembly.

Fig 5 shows detailed inner view of arc chute assembly.

Fig 6, 7 and 8 shows movement of arc in an arc chute.

Fig. 9, 10 and 11 shows different types of de ion plates used in the present invention.

Fig 12 shows the arc (18) and magnetic flux density (19).

The invented system is thus an improved arc chute assembly for electrical switching devices.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly the present invention provides means for interrupting the flow of electricity through arc quenching media. A switch disconnector with arc quenching device is capable of opening high voltages, large current arcs in arcing chamber by using arc quenching media. The principle field for immediate application of this invention is in connection with alternating current (ac) and direct current (dc) switch disconnector and therefore describing an embodiment of this invention as applied to such switch disconnector, without in any way intending to restrict the scope of this invention, except as indicated in the appended claims.

The arc incident to the opening of a circuit is driven into a de-ionizing structure comprising a series of spaced metallic plates having multi level of cooling arrangement, which is perpendicular to the motion of arc. When forced into this arrangement, there is a large de-ionizing action, and the arc is extinguished as the current passes through zero. By thus rapidly eliminating the ionization that would otherwise maintain the electrical conductivity of the path until the line voltage had risen sufficiently to reignite the arc, current flow through the switch dis-connector is effectively stopped.

The principle object of this invention is different arc chute arrangements to quench the arc in faster way by means of faster heat dissipation. All de-ion plates (splitter plates) placed in such a way that, they have to maintain the distance between them has to more than the thickness of them. First de-ion plate (10) (arc runner) has to positively attach with the terminal (3a) for smooth moment of arc. And these all de-ion plates maintain their distances between them has to be more than thickness. Maintain the distance between slotted de-ion plate (11) and serrated de-ion plate (14) should be more than the thickness, which should help in increase the length of arc and increases the power dissipation. The serrated de-ion plates should be placed such that, the serrated portion should be exposed to air and by means of serration which will increasing the heat absorption area, by thus sudden increase in arc voltage and reduction in arc current, which will help in quickly quenching the arc.

Attach the insulation sheet (15) to serrated de-ion plate (14) positively, which will help in increasing the length of arc, by which increase in arc voltage. Assembly of insulation sheet (15) such that the gap between this sheet and de-ion plate (arc runner) (10) should be maintained. This can allow the hot gases to flow out from this gap, by this there is possibility of increase the length of arc and arc voltage. Perforated sheet placed in such a way that, it will cover entire venting area and should not allow the arc particles (arc members) outside the cassette, which can make external flash over between other poles. The venting area can be decided by number hole and their dimension in this perforated sheet. This venting area should be 25% - 50 % of arc chute front open area by which the high temperature gas escape from the arc quenching media. To maintain the flow of high temperature gas in intended direction, one insulating material (venting block) is needed to cover-up entire de-ion plates and in order to give proposed direction for hot gases. And the perforated sheet is fixed in this insulating material (venting block) with sufficient distance from de-ion plates, in order to avoid jumping arc roots on to it.

These all components are set of one assembly block. Which consisting of bent de-ion plates, slotted de-ion plates, serrated de-ion plates, insulation sheet, perforated sheet, arc chute support and venting block.

When arc ignites between moving contact (7) and fixed contact (3) at the time of breaking abnormal currents (6 to 10 times rated current) at higher voltages (415 V and above up to 1000V). At Initial stages arc strengthens itself up to the distance between the moving contact (7) and fixed contact (3) is more than the arc root radius; this total time period up to the mobility of arc is known to be immobile period (time). As arc root radius crosses the distance between the moving contact (7) and fixed contact (3) arc start move, While arc moves (travels) on terminal (3) it will suddenly jump on to the first de-ion plate (arc runner), because which is positively attached to terminal and very nearer to breaking point, due to low reluctance path the arc jump on it. The effect of this will results in reduction in contact erosion and increasing the life of contacts. It will move (travels) further, due to gas dynamics and magnetic blow-out force. This phase is known as running phase, during this phase arc will rapidly accelerate to reach a velocity where the gas dynamic force on the arc is equal to the magnetic force (which is known as mass balance equation). Mass balance equation: “If the mass of the arc column is small, it will accelerate to certain velocity and where the pressure drop across the arc is equal to magnetic driving force.”

Due to the gas dynamics and magnetic blow-out force, which is created by arc chute arrangement the arc moves further and further, and arc roots form between de-ion plates and moving contact. As a slot provided in the centre of de-ion plates (11, 12, 13),which will help when arc moves (travels) towards this slot, a maximum amount of blowout force will generated and which will pull the arc towards the arc chute further. As space provided in intermediate de-ion plates, i.e., between de-ion plate (11) and de-ion plate (14) (the air gap), which will result in increase in length of arc, and thus, increase in arc voltage. Which will avoid the continuous root formation in de-ion plates, with the space provided over here the arc root forms between de-ion plates 10, 11, 12, 13 and moving contact (7), due to gas dynamics arc roots of de-ion plates 10, 11 & de-ion plate (13) are try to move further, by this the length of arc increases further, which will help in increase in arc voltage in this phase, this phase called as splitter phase. By this arrangement the arc splitting time will reduce further.

The insulation sheet (15) is provided here to attach to the serrated de-ion plate (14), which will try to avoid the continuous root formation between serrated de-ion plate (14) and de-ion plates (10 & 13), by this arrangement there is a possibility of arc moves further and arc root forms between de-ion plates 10, 11, 14, 12, 14, 13 and moving contact 7, Which will increases the length of arc and this will help in sudden increase in arc voltage. The serrated de-ion plate (14) will help in heat dissipation, this increase the length of arc, thus increase in arc voltage and arc quenching takes place. And also by using this type of serrated de-ion plates (14) can reduce the arc splitting time. The perforated sheet (16) will help in de-ionization of hot gases flow through it. Due to the material composition it acts like a coolant.

Parallel placed de-ion plate is divided into two parts in defined pattern so as to:
a. Increase in length of arc path by creating wide gap.
b. Increase the number of arc roots.
c. Parabolic pattern of arc changes to zig-zag pattern which increased arc length.

All these will result into arc lengthening, increase in arc resistance and arc voltage by arc can be extinguish early.

Typical aerodynamic shape of de-ion plates (11, 12 and 13) reduces back pressure on arc in the arc chamber. Reduction in back pressure is around 50% as compare to contribution of back pressure due to standard rectangular de-ion plate. Typical aerodynamic shape of de-ion plates (11, 12 and 13) increases flux density in de-ion plates which increases the blow out force. This typical shape of de-ion plate (11, 12 and 13) has different sharp corners (ref.fig.6(c)). Sharp corners increases arc commutation towards de-ion plates more effectively.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM

1. An improved arc chute assembly for electrical switching devices comprising:
a plurality of substantially bent de-ion plates whereby said de-ion plates having plurality of slot profiles;
wherein said de-ion plates being serrated for increasing arc length;
atleast one insulation sheet attached to said serrated de ion plate;
atleast one perforated sheet, said perforated sheet acting as a coolant;
atleast one arc chute support; and
atleast one venting block.

2. Assembly as claimed in claim 1 wherein said plates spaced apart at a distance greater than thickness of said plates.

3. Assembly as claimed in claim 1 wherein said de-ion plates having substantially aerodynamic shape reducing back pressure on arc in arc chamber.

4. Assembly as claimed in claim 1 wherein said de ion plates having substantially sharp corners thereby increasing arc commutation.

5. Assembly as claimed in claim 1 wherein said serrated de ion plates having insulation sheets attached thereto thereby increasing arc voltage.

6. Assembly as claimed in claim 1 wherein air gaps provided between said de ion plates facilitating in increasing the arc length.

7. Assembly as claimed in claim 1 wherein said de ion plates having slots thereto, said slots generating substantially high blowout force.

8. An improved arc chute assembly for electrical switching devices as herein described and illustrated with reference to accompanying drawings.