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: A CIRCUIT BREAKER WITH AN IMPROVED ARC QUENCHING SYSTEM

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:

Field of the invention

The present invention relates to an arc quenching system for use in switching devices likes circuit breakers, contactors and the like. More particularly, the invention is concerned about an arc quenching mechanism for use in switching devices likes circuit breakers, contactors and the like, more specifically circuit breakers which prevents backward flow of gases (from arc chamber towards mechanism) produced during arcing by means of a unique bellow arrangement. This invention enhances the circuit breakers breaking capacity by faster movement of arc towards arc chute because of high pressure generation behind the arc. Also it protects the operating mechanism and other parts of the switching device from hot gases and globules generated in the arcing chamber thereby reducing the chances of potential failure due to the same.

Background of the prior art

Electrical switching apparatus, such as circuit breakers, are employed in high range of capacities in power distribution systems such as, for example, to provide protection for electrical equipment from electrical fault conditions (e.g. without limitation, current overloads, short circuits, abnormal level voltage conditions). Therefore the breaking capacity of any circuit breaker is totally governed by the performance of its arc quenching chamber.

US3985988 discloses a circuit breaker assembly is provided with a pair of contact elements defining therebetween an arc site across which an arc is struck upon separation of the contacts to break the circuit within which the breaker is connected. A compressed gas contained within a quenching chamber is caused to flow across the quenching site to quench the arc upon breaking of the contact. A pair of electrodes located within an auxilliary gas chamber operate to strike a second arc simultaneously with the circuit breaking operation in order to increase pressure in the auxiliary chamber thereby providing auxiliary power to enhance the circuit breaking operation and quenching of the main arc.

US4650940 discloses a circuit breaker having a flap or barrier, which is disposed within a terminal compartment and over the inner side of an opening for a screwdriver. The ionized gases flowing into the terminal compartment are stopped from flowing through the opening by the flap extending thereacross. The flap is preferably composed of a sheet of fiber or fiber type material, which is chemically and electrically impervious to hot ionized gases. The fiber sheet is folded into a configuration including a central wall portion, an upper foldable flap portion and a lower T-shaped portion. The central wall portion and the lower T-shaped portion are adapted to fit snugly against a compartment wall and an opening from the circuit breaker arc chute. A suitable adhesive is provided between the wall surfaces and the corresponding central wall portion and lower T-shaped portion to retain the folded sheet in place. However, because the fiber sheet is not coupled to the wall or to the terminal collar assembly, it can easily be accidentally removed, thereby allowing a path for ionized gases to reach ground through the screwdriver opening.

US7679020 discloses an electrical service switching device, in particular a circuit breaker, motor circuit breaker or the like, having a housing which has two housing halves and connecting means for electrical connection to busbars and/or power lines, having at least one electrical switching contact on which an arc is struck in an initial arcing chamber on disconnection of the electrical contact, with an arc quenching unit being provided adjacent to this, in order to quench the arc. An AC blowout device which comprises two iron plates adjacent to the initial chamber area in the lateral direction and guides the arc into the arc quenching device by magnetic interaction during AC operation, is provided. The housing wall has an opening in the area of the iron plates, through which a permanent magnet can be inserted in order to create an AC/DC blowout device, which guides the arc into the arc quenching device in both AC and DC operation, when the housing is assembled.

It has been found that the prior art circuit breakers consist of an arc chamber assembly which when subjected to a short circuit current of few kilo amperes quench the arc with long arcing times. The long arcing times lead to severe stresses on the downstream equipments due to large amount of let through energy.

The prior art circuit breakers do not consist of any equipments attached to the moving contact which increases the pressure produced behind the arc and also prevents backward flow of gases during arcing resulting in slower movement of arc and long arching time.

Thus there is a need to provide for an arc quenching system for use in switching devices likes circuit breakers, contactors and the like, more specifically circuit breakers which prevents backward flow of gases (from arc chamber towards mechanism) produced during arcing by means of a unique flapping mechanism.

The present inventors have found that a circuit breaker having an improved arc quenching mechanism can be achieved by means of a unique bellow arrangement which attaches and moves corresponding to the movement of the moving contact. This mechanism increases the pressure to a great extent build up behind the arc compared to the pressure in front of it and moves it faster towards the arc chute reducing the total arcing time. Also, it protects the mechanism and other parts of the electrical switching device from hot gases and globules produced during arcing. Further it has been found that the improved arc quenching system improves the breaking capacity of the circuit breaker.

Objects of the invention

One object of the present invention is to overcome the drawbacks/disadvantages of the prior art.

A basic object of the present invention is to provide a circuit breaker having improved breaking capacity.

Another object of the present invention is to provide an improved arc quenching mechanism for use in circuit breakers.

Another object of the present invention is to provide reduction in the arcing time.

Another objective is to avoid hot gasses and globules formed during short circuit reaching the mechanism of the circuit breaker.

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

Summary of the invention

According to one aspect of the present invention there is provided a circuit breaker system having enhanced breaking capacity, said system comprising :

housing;
shell means inside said housing, said shell means comprising slot means;
moving contact means;
fixed / lower contact means in proximity to said moving contact means in manner that said moving contact means contacts with said fixed/lower contact means during ON condition;
bellow arrangement for arc quenching being movably accommodated in said slot means of said shell means;
wherein said bellow arrangement being operatively engaged with said moving contact means such that movement said moving contact means correspondingly moves said bellow arrangement in a manner that any vacant volume between said moving contact means and said fixed/lower contact means is operatively sealed thereby increasing pressure differential existing therebetween front and behind the arc whereby velocity of arc towards arc chute conventionally present in said circuit breaker increases reducing total arcing time and the let through energy of the circuit breaker.

According to another aspect of the present invention there is provided an improved arc quenching mechanism for use in circuit breakers, said mechanism comprising :

shell means having plural slot means;
bellow arrangement for arc quenching being movably accommodated in said slot means of said shell means;
wherein said bellow arrangement being operatively engaged with moving contact means of the circuit breaker such that movement said moving contact means correspondingly moves said bellow arrangement in a manner that any vacant volume between said moving contact means and fixed/lower contact means of the circuit breaker is operatively sealed thereby increasing pressure differential existing therebetween front and behind the arc whereby velocity of arc towards arc chute assembly of the said circuit breaker increases reducing total arcing time and the let through energy of the circuit breaker.

Brief description of the accompanying drawings

The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention.

In the drawings:

Fig 1 illustrates RHS view of moulded case circuit breaker.

Fig 2 illustrates a Top view of moulded case circuit breaker.

Fig 3 illustrates a Cross sectional view of arc chamber of moulded case circuit breaker without cover.

Fig 4 illustrates an isometric view of flapper assembly of the present invention.

Fig 5 illustrates a Cross section of the isometric view.

Fig 6 illustrates a Cross sectional view at contact open position.

Fig 7 illustrates a Cross sectional view at contact closed position

Fig. 8 illustrates an exploded view of the flapper assembly of the present invention.

Detailed description of the accompanying drawings

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and illustrate the best mode presently contemplated for carrying out the invention. Further functioning of the mechanism has been discussed below to describe the way the mechanism operates. However, such description should not be considered as any limitation of scope of the present unit. 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.

List of components:

Flap (1)
Moving contact (2)
Shell (3)
Lower contact (4)
Release assembly (5)
Housing (6)
Cover (7)
Lower contact assembly (8)
Moving contact assembly (9)
Slots of shell (10)
Slots of flap (11)

The present invention a circuit breaker and an arc quenching system which prevents reverse flow of gases (from arc chamber towards mechanism) produced during arcing by means of bellow type flapping mechanism attached to the moving contact of an electrical switching device, say a circuit breaker. The prime feature of the present invention is the way arc movement is accelerated by means of high pressure build up behind it. Also, protection from hot gases produced during arcing is ensured to the mechanism and other parts due to the same avoiding any potential failure during arcing.

When the contacts separate in any electrical switching device, say a circuit breaker, arc is struck between fixed and moving contact. An arc basically is a discharge of electric current, which produce plasma between the contacts. Because of arc, there are rapid temperatures changes which develop a very high pressure inside the arcing chamber. Also the splitter plates of the arc chute in the circuit breaker exert a magnetic pull on the arc. The arc is blown towards the arc chute due to force exerted on it which is a balance of magnetic forces and the gas dynamics due to high pressure generated inside the arcing chamber. As the arc enters the arc chute, it is split and cooled and thereby effectively quenched.

The arc velocity during its movement towards the arc chute is dependent on balance of magnetic forces and gas dynamics. The gas flow towards the arc chute is because of the pressure difference between arc front and behind it. It is desirable to have high pressure behind the arc and lower pressure in front of it. Due to this, the gas dynamics aids the magnetic forces on the arc and helps the arc to move towards the arc chute. To achieve this, vents are provided behind the arc chute. However, there is some vacant volume produced between the fixed contact and the moving contact when they separate from each other. Some of the pressure generated gets dissipated in this volume reducing the effective pressure behind the arc thereby lowering the arc velocity towards the arc chute. Also, due to this, hot gases may escape to the operating mechanism which may increase the chances of mechanism failure.

The present invention enhances the pressure build up behind the arc by sealing the vacant volume produced between the moving and fixed contact by means of a flapping mechanism attached to the moving contact as shown in fig. 4. The flap is made up of a flexible material which can flex or bend or fold easily and is able to sustain high pressure and temperatures produced in the arcing chamber. The flap has a slot in which moving contact is inserted. The flap along with the moving contact is then inserted in a slit. The slit can be integrated in the housing or a separate component (named as shell here) assembled with the fixed contact can have this provision as shown here in fig. 4.

The assembly of the flap (1), moving contact (2), fixed contact (4) (reference to figures 3 and 4), location of the slit is such that it creates a gap between the flap, moving contact and the base of the housing. When the moving contact (2) and fixed contact (4) close, the flap bends and gets accumulated in this gap. As the moving contact separate from the fixed contact, the flap gets stretched and opens up with it. When the moving contact is opened fully, the flap also opens with it fully and seals the vacant volume between the moving contact and the fixed contact which else while would have been produced in absence of the same. This increases the pressure build up behind the arc which increases the difference in pressures between the front of the arc and behind it. The greater pressure differential enhances the gas dynamics inside the arc chamber and the hot gases produced rapidly flow towards the arc chute. This aids the magnetic forces exerted on the arc due to splitter plates of the arc chute to a great extent and thereby increases the arc velocity towards arc chute. The increased arc velocity enhances faster movement of the arc and faster entrance of the arc in the splitter plates where it is split, cooled and effectively quenched reducing total arcing time. The reduction in total arcing time reduces the let through energy of the circuit breaker and thereby the stresses on the downstream devices.
Also, since the flap seals the vacant volume between the moving contact and the fixed contact produced when they separate, it prevents the backward flow of hot gases towards the mechanism and other parts of the switching device preventing them from any potential failure due to the same during arcing.

Referring to figures 4 and 5, shell (3) comprises slot profiles (10) which accommodate the bellow/flap arrangements (1). The flaps are flexible in construction and is engaged to moving contact means (2) and moves with the movement of the moving contact means (2). The flap comprises a slot profile (11) in which the moving contact remains inserted.

The material of the flap can also be of an ablative material, which produces electronegative gases when the material burns. The production of electronegative gases rapidly deionizes the ionized hot gases produced and increases the arc voltage. This helps to quench the arc rapidly and further reduce the arcing time. Also, the production of electronegative gases reduces the possibility of arc re-strike after fault clearance by the arc chute.

Advantages :

• Use of flapping mechanism with the moving contact increases pressure build up behind the arc increasing arc velocity.
• The flapping mechanism avoids back flow of hot gases to mechanism and other parts preventing them from potential failure during arcing.
• Less arcing time due to high arc velocity thus reducing let through energy to the downstream equipments.
• Increase in the breaking capacity of the arc quenching chamber

WE CLAIM:

1. A circuit breaker system having enhanced breaking capacity, said system comprising :

housing;
shell means inside said housing, said shell means comprising slot means;
moving contact means;
fixed / lower contact means in proximity to said moving contact means in manner that said moving contact means contacts with said fixed/lower contact means during ON condition;
bellow arrangement for arc quenching being movably accommodated in said slot means of said shell means;
wherein said bellow arrangement being operatively engaged with said moving contact means such that movement said moving contact means correspondingly moves said bellow arrangement in a manner that any vacant volume between said moving contact means and said fixed/lower contact means is operatively sealed thereby increasing pressure differential existing therebetween front and behind the arc whereby velocity of arc towards arc chute conventionally present in said circuit breaker increases reducing total arcing time and the let through energy of the circuit breaker.

2. A circuit breaker system as claimed in claim 1 wherein said bellow arrangement comprising flap means.

3. A circuit breaker system as claimed in claim 2 wherein said flap means is flexible.

4. A circuit breaker system as claimed in claims 2 and 3 wherein said flap means is optionally foldable.

5. A circuit breaker system as claimed in claims 2 to 4 wherein said flap means is preferably made of material capable of producing gases assisting in arc quenching.

6. A circuit breaker system as claimed in claim 1 wherein further comprising slit means.

7. An improved arc quenching mechanism for use in circuit breakers, said mechanism comprising :

shell means having plural slot means;
bellow arrangement for arc quenching being movably accommodated in said slot means of said shell means;
wherein said bellow arrangement being operatively engaged with moving contact means of the circuit breaker such that movement said moving contact means correspondingly moves said bellow arrangement in a manner that any vacant volume between said moving contact means and fixed/lower contact means of the circuit breaker is operatively sealed thereby increasing pressure differential existing therebetween front and behind the arc whereby velocity of arc towards arc chute assembly of the said circuit breaker increases reducing total arcing time and the let through energy of the circuit breaker.

8. Mechanism as claimed in claim 7 wherein said bellow arrangement comprising flap means.

9. Mechanism as claimed in claim 8 wherein said flap means is flexible.

10. Mechanism as claimed in claims 8 and 9 wherein said flap means is optionally foldable.

11. Mechanism as claimed in claims 8 to 10 wherein said flap means is preferably made of material capable of producing gases assisting in arc quenching.

12. Mechanism as claimed in claim 7 wherein further comprising slit means.

13. A circuit breaker system having enhanced breaking capacity as herein substantially described and illustrated with the accompanying drawings.

14. An improved arc quenching mechanism for use in circuit breakers as herein substantially described and illustrated with the accompanying drawings.