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. -
ARC RESISTANCE ARRANGEMENT FOR SWITCHING DEVICES AND A METHOD THEREOF
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
The present invention relates generally to a switching device and more particularly, to an arc resistant arrangement for use in switching devices facilitating cooling and reduction in arc gas pressure and a method thereof.
BACKGROUND AND THE PRIOR ART
A switching apparatus like a circuit breaker is used in a switchgear assembly to carry, make 8B break the circuit in power distribution systems. An arc is generated in the switching contacts, of the switching apparatus, when the contacts open on a fault current or even on normal current. The heat generated by switching arc produces gases from the material in its vicinity.
These gases generate a high pressure. Hence, the arc gases need to be cooled down and channelized through proper venting so as to protect the enclosure/cabinet of the switchgear assembly in which the switching apparatus is mounted. Also the control circuit wirings are taken from top or from the sides of the switching apparatus which also need to be protected from the arc gases.
Thus there is a requirement for arc resistant arrangement in switchgear assemblies which can withstand the intense internal temperature and pressure of the arc gases and protect the enclosure/cabinet of the switchgear assembly and the control circuit or secondary wiring.

Generally, the design of switching apparatus is such that an Arc chute, which contains several number of deionizing plates stacked with a certain space between them and placed so as to split the switching arc, is placed above the switching contacts.
Barriers, provided with vents, are placed above the deionizing plates. Thus, when an arc is produced, the arc gases are sufficiently cooled down and are released from vents in the barriers at the top of the switching apparatus. This arrangement provides protection, up to a certain level, to the enclosure in which the switching apparatus is being placed.
Still, there are chances that during high current faults, when the switching contacts get opened, the arc gases may reach the enclosure as well as control circuit/secondary circuit/ auxiliary wiring at the top and damage it.
A switching apparatus like a circuit breaker which is placed in a cabinet/enclosure in a switchgear assembly has switching contacts, which are connected to a set of terminals, either of which can be line/supply or load terminal. The terminals and the switching contacts arc mounted in a withdrawable unit of assembly called as the "Breaker" part. The terminals of the Breaker part are on the rear side of Breaker.
This withdrawable unit (Breaker) is, in turn, mounted on a fixed structure made up of metallic components known as "Cradle" part.

The "Breaker" can be racked-in/plugged-in into the Cradle from the front so that the terminals of the breaker part get connected to "disconnecting contacts" on the "Cradle" part. The "disconnecting contacts" are connected to the bus-bars. The bus-bars are connected to the line and load terminals of the switchgear assembly.
The disconnecting contacts, mentioned above, need to be shielded from top side so as to prevent falling of any unwanted material like a metallic object or hardware like bolts, nuts, etc. which are commonly used in switchgear assembly. These metallic objects can cause a flash-over by shorting the disconnecting contacts/breaker terminals between phase-to-phase or between incoming and outgoing terminals/contacts.
In existing design, the arc shield provided does not cover/shield the area above the disconnecting contacts/ breaker terminals.
The switching apparatus have a certain current carrying capacity (typically upto 6300 A) at certain voltage ratings (upto 1000 V). Typically, these capacities are claimed, by the manufacturers, when the apparatus is placed in open air. When placed in enclosures/cabinets in the switchgear assembly, manufacturers suggest derating i.e. use of the same switching device at a reduced current.
This is because, when placed in an enclosure/cabinet, the flow of air around the switching apparatus is restricted. This reduces the heat flow from switching apparatus to the environment through

convection. This increases the temperature rise at the terminals of the switching apparatus. Standards for the switching apparatus impose certain limits on this temperature rise. e.g. IEC-60947 part-2, which is a standard for low voltage circuit breakers, suggests a maximum temperature rise of 80°C at the terminals.
Use of an arc shield, as mentioned above, without proper venting can result in further increase in the temperature rise at the terminals of switching apparatus, and hence more derating. Hence there is need to provide an arc shield which will not only maintain but improve the current carrying capability of the switching apparatus.
One more requirement for such switching apparatus is that, the arc resistant arrangement should have flexibility to be mounted during assembly of the switchgear or, in the field where switchgear assembly is already installed. This flexibility helps users to improve the arc resistant properties of the existing switchgear. This flexibility demands minimum number of components to be used, so that the user can install the arrangement easily and the cost of doing so is also lower.
US 3621169 relates to electric circuit interrupters of current limiting type including means for minimizing of hot arc gases and the magnitude of noise and shock wave emerging therefrom.
An electric circuit interrupter including arc establishing and interrupting means having an arc-gas venting portion and an arc-gas filter and muffle portion in juxtaposed relation to the arc-gas venting

portion, combined with sleeve including a circumferentially extending inwardly directed rib positioned between the muffle portion and the arc establishing and interrupting means is provided.
US 6410844 relates to switchgear used in low voltage power distribution systems and more particularly to an arrangement for channeling arc gases generated by an electrical switching apparatus such as circuit breaker incorporated into the switchgear and also for guiding and protecting from the arc gases control and instrumentation wiring.
It provides an arc shield/wire tray for secondary wiring terminations for electrical switching apparatus having arc chute vents in an upper surface thereof and mounted in a switchgear cabinet.
US 7391597 relates generally to field of switchgear for electrical power distribution and more particularly to an arrangement and method for improving the arc resistant features and capabilities of switchgear that is applicable either during fabrication or as a retrofit to existing equipment in the field.
The disadvantages of the above mentioned prior art is that there is a reduction in the current carrying capability due to reduction in the heat transfer due to reduced air flow, because of blocking of the gases during normal operation, to carry normal current, of circuit breaker .

Another disadvantage is the use of large number of components, which makes the retrofitting difficult even if possible that too with much added cost.
Hence there is a need to provide an arc resistant arrangement for a switching apparatus using a multi-purpose arc shield which provides arc shield that is extended to shield the area above terminals and disconnecting contacts, improvement in current carrying capability by use of efficient arc shield, suitability for field retrofitting and with minimum number of components, easy to manufacture with low cost.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
A basic object of the present invention is to provide an arc resistant system using an arc shield which is placed on the top of the switching apparatus to cool down, channelize and reduce the pressure of arc gases and protect the enclosure/cabinet as well as control circuit/secondary circuit/ auxiliary wiring of the switchgear assembly from damage.
Another object of the present invention is to extend the function of arc shield and provide shielding to the disconnecting contacts and breaker terminals such that falling of any unwanted object on these regions and hence flash-over is avoided.

Yet another object of the present invention is to provide an arc shield which will not only maintain but improve the current carrying capability of the switching apparatus without sacrificing on the arc resistant and shielding properties.
Yet another object of the present invention is to provide an arc shield which requires minimum components and is suitable for field retrofitting purpose with minimum cost.
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
There is provided an arc resistance arrangement for use in switching devices facilitating cooling and reduction in arc gas pressure.
According to one embodiment of the present invention there is provided an arc resistance arrangement for use in switching devices facilitating cooling and reduction in arc gas pressure, said arrangement comprising an arc shield fixed on each cradle side plate with plurality of screws and nuts, said arc shield having plurality of horizontal and vertical vents for release of arc gases, said arc shield having an extended portion extending from top of an arc chute to end of said cradle side plate and covering disconnecting contact.

Other embodiment of the present invention provides a zone between a barrier and arc shield for cooling of said arc gases.
Other embodiment of the present invention provides A method of providing an arc resistance for use in switching devices facilitating cooling and reduction in arc gas pressure, said method comprising the steps of allowing arc gases to enter zone between a barrier and an arc shield; cooling down of said arc gases in said zone due to convection, reduction in pressure of arc gases due to assembly of plurality of vertical and horizontal vents.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Fig. 1 illustrates a side view of the Breaker installed in Cradle.
Fig.2 illustrates the isometric view of the Breaker installed in Cradle with the Cradle side plate hidden.
Fig.3 illustrates the isometric view of the Breaker installed in Cradle with the Cradle side plate hidden.
Fig.4 illustrates the isometric view of assembly which gives overview of the Rear side of Circuit breaker with the Cradle terminals hidden.

Fig.5 illustrates the isometric view of complete assembly which gives overview of the Front side of Circuit breaker.
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 side view of the Breaker installed in Cradle is shown. It shows direction for flow out of arc gases.
Fig. 2 and 3 shows the isometric view of the Breaker installed in Cradle with the Cradle side plate hidden. It shows different vertical and horizontal vents for release of arc gases.
Fig. 4 shows the isometric view of assembly which gives overview of the Rear side of Circuit breaker with the Cradle terminals hidden.
Fig. 5 shows the isometric view of complete assembly which gives overview of the Front side of Circuit breaker.

The invented system is thus an arc resistant arrangement for use in switching devices facilitating cooling and reduction in arc gas pressure.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention an arc resistant arrangement for use in switching devices facilitating cooling and reduction in arc gas pressure is provided.
Constructional elements:
Fixed contact (1)
Moving contact (2)
Arc chute (3)
Deionizing plates (4)
Barrier with vents (5)
(Arc) gases (6)
Breaker upper terminal (7)
Breaker lower terminal (8)
Disconnecting contacts (9) Cradle upper terminal (10) Cradle lower terminal (11) Cradle side plate (12) Arc shield fixing holes (13) Arc shield vents (14) Arc shield extended portion (15) Arc (16)

Arc Shield (17)
Construction and Operation;
As shown in Fig.1 & Fig 5, Breaker (movable part) is installed in Cradle (Fixed frame/Chassis). Breaker can be racked-in and out to connect and disconnect the Breaker terminals (7) and (8) from the disconnecting contacts (9).
The Breaker can take three positions in cradle viz.
• Disconnected position, where the main contacts (Fixed (1) and Moving (2)) as well as the control circuit contact (not shown in the figure) are disengaged from supply
• Test position, where the main contacts are disengaged and control circuit contacts are engaged
• Connected position, where the main contacts as well as control circuit contacts are connected to supply
The multiple functions performed by the Arc shield are explained below.
I. Effective Arc resistant arrangement:
When the Breaker is turned ON in connected position (by a stored energy mechanism (not shown) the moving contacts (2) touch the fixed contacts (1), and current flows through the Main contacts. In

this condition, if the Breaker is turned OFF, the main contacts get opened and an arc (16) is formed.
This high temperature arc produces gases (6) due to heating of material in its vicinity. The arc travels to the Arc chute (3) under the influence of a magnetic self blast field.
In Arc chute (3) the arc is split between the Deionizing plates (4) into large number of smaller arcs. The arc gases also travel through the Deionizing plates.
Above Deionizing plates (4), the Arc gas barrier with vents (5) is placed. This barrier takes some energy out of the gases and cools them slightly. The pressure is also reduced to some extent.
The Arc shield (17), which is made up of a metal sheet, is fixed on the Cradle side plates (12) with three screws and nuts (not shown in the figure) on both side plates. The fixing holes (13) for these screws are provided on both side plates. The placement and construction of Arc shield (17) is such that there is a space available between the barrier (5) and the Arc shield (17).
The arc gases (6) after releasing out of barrier (5), enter the zone between barrier and Arc shield (17). In this zone, the gases are further cooled down due to convection of the air present in the space. The large space available also reduces the pressure of gases (6). Vents (14) are provided in the Arc shield (17).

Horizontal vents provided in front of Arc shield can be seen in Fig. 5. Vertical vents provided on the Arc shield (17) can be seen in Fig.4. This arrangement provides the release of the arc gases in a structured manner such that, the pressure and temperature are reduced substantially.
Thus the Arc shield (17) provides effective arc resistant properties.
II. Avoid material falling on disconnecting contacts:
The construction of Arc shield (17) is such that it has an extended portion (15). The arc shield extends from top of the Arc chute (3) to the end of the Cradle side plate and covers the Disconnecting contact (9). Thus the area above the disconnecting contacts is effectively shielded. Hence falling of any unwanted material on the disconnecting contacts is avoided.
Thus flashover due to falling of such material and shorting of disconnecting contacts (9) between phases, or between, upper terminal (7) and lower terminal (8), is avoided with use of this Arc shield (17).
III. Improvement in the current carrying capability of Circuit
breaker:
In a condition when the Breaker is in ON condition (not shown) and in Connected position, main contacts are closed and normal current flows through the circuit breaker. In this condition, heating takes

place due to copper loss in the main contacts (1), (2), disconnecting contacts (9) and terminals (7), (8), (10), (11).
This heating causes generation of gases (6) due to vaporization of material in the vicinity of these components. These gases (6) from main contacts again travel through the arc chute to the arc shield and are, finally released through vents in arc shield (14). The gases from disconnecting contacts (9) and the terminals also travel towards the arc shield. The Arc shield which is metallic absorbs the heat from gases.
As the Arc shield (17) is connected to the Cradle side plate (12), which is also metallic, the heat is transferred through conduction to the Cradle side plate (12). Also, the Arc shield extended portion (15) covers the disconnecting contacts (9). Hence more amount of heat is dissipated to cradle side plates through Arc shield. Hence the Temperature rise at the cradle terminals (10), (11) is reduced. The limit for the maximum temperature rise is set to be 80°C at the Cradle terminals according to 1EC-60947 part-2 which is a standard for low voltage circuit breakers.
Thus the same equipment can carry more current as compared to other types of arc resistant arrangements.
Thus, the Arc shield provides improvement in the current carrying capability of the circuit breaker.

IV. Retrofitting in field possible with minimum number of components:
The Arc shield (17) is fixed on each Cradle side plate (12) using 3 screws with spring washers and nuts. Thus fixing of 6 screws is required for assembly of Arc shield (17) on the circuit breaker. This type of fixing requires a small amount of time and, as discussed, requires less number of components. The construction of Arc shield (17) is such that, it is not required to remove any components from the Circuit breaker to assemble the Arc shield. Hence retrofitting of Arc shield in the field where the circuit breaker is already installed is possible with this Arc shield (17).
Thus, the Arc shield provides option of retrofitting in field with minimum number of components.
Features:
• Arc shield extended to shield the area above terminals and disconnecting contacts
• Improvement in current carrying capability by use of efficient arc shield
• Suitability for field retrofitting
• Minimum number of components, easy to manufacture with low cost
Advantages:

• Effective arc resistant arrangement provided using arc shield
• Shielding of the area above terminals and disconnecting contacts
• Improvement in current carrying capability
• Suitable for field retrofitting
• Minimum number of components, easy to manufacture
• Low cost of retrofitting
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 arc resistance arrangement for use in switching devices facilitating cooling and reduction in arc gas pressure, said arrangement comprising an arc shield fixed on each cradle side plate with plurality of screws and nuts, said arc shield having plurality of substantially horizontal and vertical vents for release of arc gases, said arc shield having an extended portion extending from top of an arc chute to end of said cradle side plate and covering disconnecting contact.
2. Arrangement as claimed in claim 1 providing a zone between a barrier and said arc shield for cooling of said arc gases.
3. A method of providing an arc resistance for use in switching devices facilitating cooling and reduction in arc gas pressure, said method comprising the steps of:
allowing arc gases to enter zone between a barrier and an arc shield;
cooling down of said arc gases in said zone due to convection,
reduction in pressure of arc gases due to presence of plurality of vertical and horizontal vents.

4. Method as claimed in claim 3 wherein metallic surface of said arc shield absorbing heat from said arc gases.
5. An arc resistance arrangement for use in switching devices as herein described and illustrated with reference to the accompanying drawings.
6. A method of providing an arc resistance for use in switching devices facilitating cooling and reduction in arc gas pressure as herein described and illustrated with reference to the accompanying drawings.