FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: A CONTACT SYSTEM ASSEMBLY WITH CONTACT BARRIER FOR CURRENT LIMITATION DURING SHORT CIRCUIT FAULTS
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 circuit breakers. More particularly the present invention relates to an improved contact assembly for limiting current during short circuit faults in a circuit breaker. A contact system assembly with contact barrier for current limitation during short circuit faults is provided.
BACKGROUND AND THE PRIOR ART
This invention deals with the arcing behavior in Circuit Breakers during short circuit fault clearing. Miniature circuit breakers (MCBs) are used in industrial and domestic applications to provide the protection against overload and short circuit currents .MCB works on the concept of current limiting which means limiting the value of current in case of short circuit fault to a lower value as compared to its prospective value.
In MCBs it is desirable to minimize the let through energy and it can be achieved by developing the arc voltage in opposition to the system voltage in minimum elapsed time. The arc is initiated in the contact region at the time of contact separation and it is important to transfer the arc from contact region to the splitter plates in minimum time to avoid the excessive contact erosion as well as to minimize the on time. This rapid movement of arc from contact region to splitter plates generally takes place under the effect of pressure dynamics forces and magnetic blow out forces.
In this design a contact barrier in terms of flexible thermoplastic material sheet is provided, having flame retardant characteristics and high temperature withstand property ?that moves with the movement of the moving contact and closes the opening in the region of movement of moving contact. It creates high pressure on

back side of arc and thus accelerates the arc towards the arc chute due to higher differential pressure across the arc.
In an electrical installation, miniature circuit breakers are installed to provide the protection against overload and short circuit fault conditions. From system safety point of view, the effective current limiting achieved and let through energy delivered by MCB to downstream devices shall be maintained as low as possible which calls for reduction in the total ON Time. The present invention relates to the faster transition of arc from contact region to the arc chute due to increase in higher differential pressure on arc body.
US 5796061 presents a breaker where the region behind the arc chamber is open and the pressure behind the arc is not developed fully as the gases escape from the openings available behind the arc chamber. This results in the slower movement of arc from the contact region to the arc plates (40) and hence results in higher let through energy.
US 7247808 B2 shows a circuit breaker where the region in the contact region behind the arc chamber is open . The hot gases escape towards the mechanism and thereby the pressure drops behind the arc, resulting in slower arc movement towards the arc quenching device (12).
Conventionally, circuit breakers do not have any means to close the arc chamber from back side. So at the time of short circuit, the pressure generated by the hot gases is relieved from this opening which results in lower pressure on back side of arc resulting in slower movement of arc towards the arc chute. The present invention solves this issue by providing a barrier (preferably flexible) on the moving contact and thereby maintaining high pressure on back side of arc as compared to the front side of the arc.

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 achieve a faster transition of arc from contact system to the deion plates (arc chute).
Another object of the present invention is to achieve improved short circuit
performance.
Another object of the present invention is to achieve effective current limiting.
Another object of the present invention is to achieve an improvement in the breaking capacity for a given design of MCB.
Another object of this invention is to make this invention equally suitable for both single break and multi break contact system designs.
Yet another objective of this invention is to protect the mechanism components form hot gases and products of arcing.
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 improved contact assembly for limiting current during short
circuit faults.
According to one embodiment of the present invention, there is provided an improved contact assembly for limiting current during short circuit faults in a circuit breaker, said assembly comprising atleast one moving contact; atleast one fixed contact; atleast one arc runner; a pair of contact breaks; atleast one contact barrier means assembled with said moving contact; a plurality of guide means provided on middle separator, housing and cover walls of said circuit breakers; Wherein said barrier means is adapted to move with said moving contact thereby closing an arc chamber behind the arc of said contact system thus creating high differential pressure across the arc resulting in faster transition of arc from contact region to an arc chute.
BRIEF 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.
Fig 1 illustrates the contact system assembly with contact barrier when contacts are in closed condition.
Fig 2 illustrates the contact system assembly with contact barrier when contacts are in fully open condition.

Fig 3 illustrates the contact system assembly with arc between the runners. Fig 4 illustrates the assembly of moving contact with the contact barrier.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Accordingly in the present invention an improved contact assembly for limiting current during short circuit faults in a circuit breaker is provided.
Elements and Construction:
The present invention consists of following parts:
1. Moving Contact
2. Fixed Contact
3. Contact Barrier
4. Arc Running Chamber
5. Arc Chamber Wall
6. Arc Runner
7. Fixed Contact Runner
8. Magnetic Release
9. Arc Chute
10. Contact Barrier Guide
11. Arc
At the time of short circuit fault, arc is produced between the fixed and moving contact of miniature circuit breaker. Arc roots are formed on the arc runners and arc

starts elongating under the effect of magnetic blow out forces and pressure dynamic forces. It is important to transfer the arc from contact region to the arc chute as fast as possible so as to reduce the let through energy. In this invention, fast arc movement is achieved by increasing the differential pressure across the arc.
In this new concept, a double break contact system is presented, where the two breaks are present side by side. In the figures only on side contact break is visible .The other break is exact replica of the visible break. The two arc chambers are separated by a component called middle support. Here, the contact system assembly with a barrier is presented where the barrier is made up of a flexible thermoplastic material having flame retardant characteristics and high temperature withstand property. This barrier is assembled with moving contact. A guide is provided on the middle separator to guide the movement of contact barrier. Similar guide is also present in the housing and cover walls of the circuit breaker where the region behind the arc chamber is closed .When the arc is produced between the two runners, the volume behind the arc is closed by the barrier, resulting in more pressure build up on the back side in comparison to the pressure at the front of arc.
Fig. ] shows the contact system in when breaker is in ON condition. At the time of short circuit fault, the moving contact starts separating from the fixed contact and an arc is established between the contacts. As the moving contact moves it takes the barrier along with it. Barrier movement is supported by the corresponding guides in middle support, housing and cover. The barrier is a thermoplastic material plate having slots for insertion of moving contact arms.
Fig 2 shows the contact system with contacts fully opened.
Fig 3 shows the contact system when the arc is transferred to the runners and the contact is in full open condition .At this instant the contact barrier closes the arc

chamber from the backside . Also the arc chamber is closed by housing wall (5) from one side and by walls from middle support from the other side. The only side available for release of pressure is vent side on the front side of arc chute. This construction helps in achieving high pressure on back of arc as compared to the front pressure, which results in higher force on arc towards of arc chute and subsequently in faster quenching.
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 contact assembly for limiting current during short circuit faults in a circuit breaker, said assembly comprising:
atleast one moving contact;
atleast one fixed contact;
atleast one arc runner;
a pair of contact breaks;
atleast one contact barrier means assembled with said moving contact;
a plurality of guide means provided on middle separator, housing and cover walls of said circuit breakers;
Wherein said barrier means is adapted to move with said moving contact thereby closing an arc chamber behind the arc of said contact system thus creating high differential pressure across the arc resulting in faster transition of arc from contact region to an arc chute.
2. Assembly as claimed in claim 1 wherein said contact barrier is substantially flexible thermoplastic material sheet having flame retardant characteristics and high temperature withstanding property.
3. Assembly as claimed in claim 1 adapted for use in both the single and double break construction of circuit breaker.

4. Assembly as claimed in claim 1 wherein said guide means adapted to support said barrier during movement.
5. Assembly as claimed in claim 1 wherein said barrier plate further comprising a plurality of slots, said slots having moving contact arms inserted therein.
6. Assembly as claimed in claim 1 wherein said arc barrier is adapted to create high pressure on back of arc compared to front resulting in higher force on arc towards an arc chute and subsequently in faster quenching.
7. An improved contact assembly for limiting current during short circuit faults in a circuit breaker as herein described and illustrated with reference to
accompanying drawings.