FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: IMPROVED CONTACT SYSTEM FOR CURRENT LIMITATION DURING SHORT CIRCUIT FAULTS FOR USE IN CIRCUIT BREAKERS
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 assembly for current limitation during short circuit faults for use in circuit breakers.
BACKGROUND AND THE PRIOR ART
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. ON time is the time elapsed between the instant of occurrence of an electrical fault to the instant the breakers comes to final isolation state. In a typical MCB, the contact running time is one of the main constituent of total ON Time. The contact running time is the time for which arc runs on the arc during its travel from contact region to the splitter plates. The present invention mainly relates to the reduction in arc running time by providing higher blow out force on the arc.
This invention deals with the arcing behavior in Miniature 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.
Some of the prior arts of the present field of invention are as follows:

EP 0009156 (Al) discloses a line protection relay with contact arrangement forming a blow out loop formed from a conductor piece which enhances the magnetic force on the arc and hence the arc movement is accelerated towards the arc chute. The blow out loop is formed by a rearward prolongation of the arc guide rail.
Limitation: Although the magnetic blow out loop present in this prior art tends to increase the magnetic blow out force, but due to conventional flat profile of slot motor the force on arc cannot be maximized. This problem is solved in the present invention by using a split L-I construction of the slot motor assembly which covers both the current carrying lengths and maximize the blow out force on the arc.
In US005185590, a circuit breaker is presented where the arc extinction is improved by utilizing a booster loop that extends parallel to the arc runner. The booster loop and the arc runner are formed from a single piece of rigid conductor material. The current does not flow through the booster loop during normal operation. Booster loop only comes into the circuit when the arc transfers from one of the contacts to the arc runner at the time of short circuit and thus reducing the short circuit current.
Limitation: Although the magnetic blow out loop present in this prior art, tends to increase the magnetic blow out force, but due to conventional flat profile of slot motor the force on arc cannot be maximized. This problem is solved in the present invention by using a split L-I construction of the slot motor assembly which covers both the current carrying lengths and maximize the blow out force on the arc.
In US4614928, an automatic switch is presented with a ferromagnetic contact strip (26) (or blow plate) on the contact element that facilitates a faster commutation of arc from contact region to the de ion plates.

Limitation: Although the ferromagnetic strip tries to enhance the magnetic field on the arc and facilitates a faster commutation of arc from contact region to the de ion plates, but the force produced in not maximized as there is only one current carrying length on the other side and the blow out loop is absent. This problem is solved in the present invention by using a split L-I construction of the slot motor assembly along with a blow out loop.
In EP 0649155B1, a uni-polar heavy duty circuit breaker is presented having a primary arc conduction plates and the secondary arc conduction plates which forms a loop (C) .The flow of current in both the conduction plates is in the same direction giving high magnetic force on the arc.
Limitation: Although the magnetic blow out loop present in this prior art, tends to increase the magnetic blow out force, but due to conventional flat profile of slot motor the force on arc cannot be maximized. This problem is solved in the present invention by using a split L-I construction of the slot motor assembly which covers both the current carrying lengths and maximize the blow out force on the arc.
General design of MCBs as seen in cited prior arts utilize different methods to increase the blow out force on the arc. It is generally achieved by placing two ferromagnetic material plates along the walls of arc chamber in arc running zone. Some designs also utilize reverse current loop (see prior art) to increase the blow out force.
Thus there is a need to overcome the limitations of the prior arts. In MCBs it is desirable to minimize the let through energy that 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 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 blow out forces (caused by flow of current through arc runners) and pressure dynamics forces .
The present invention therefore provides an improved design of slot motor and arc runner has been presented here which helps to achieve higher blow out force on arc to facilitate faster arc transition from contact region to the splitter plates and thereby achieving effective current limiting and minimizes let through energy. This also ensures minimum damage to the circuit breaker because of reduction in thermal and mechanical stresses inside the breaker and hence increasing life of the MCB. This invention can be used in Single Break and Double Break constructions of the MCB with equal ease.
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 improved short circuit performance.
Another object of the present invention is to achieve effective current limiting in circuit breakers.
Another object of the present invention is to achieve an improvement in the breaking capacity for a given design of MCB.
Yet other object of the present invention is to provide an assembly equally suitable for both single break and double break contact system designs.

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.
According to one embodiment of the present invention, there is provided an improved assembly for current limitation during short circuit faults, said assembly comprising atleast one slot motor; atleast one blow out loop assembly; atleast one arc chute; atleast one arc runner, said arc runner forming a blow out loop assembly providing magnetic blow out force on arc in direction of said arc chute; a plurality of splitter plates; a plurality of ablation plates; atleast one slot motor plate of substantially L shape; atleast one slot motor plate of substantially I shape; atleast one moving contact; and atleast one connector means.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
So that those having ordinary skill in the art will more readily understand how to construct an improved assembly for current limitation during short circuit faults for use in circuit breakers in accordance with the present disclosure, exemplary

embodiments are described in details herein below with reference the accompanying drawings wherein:
Fig 1 illustrates the complete contact assembly.
Fig 2 illustrates the contact assembly internal view with the details of current path.
Fig 3 illustrates the exploded view of the slot motor, ablation plate and arc runner assembly.
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 improved assembly for current limitation during short circuit faults is shown.
Fig 2 shows the contact assembly internal view with the details of current path.
Fig 3 shows the exploded view of the slot motor, ablation plate and arc runner assembly.

DETAILED DESCRIPTION OF THE INVENTION
Accordingly the present invention provides an improved assembly for current limitation during short circuit faults for use in circuit breakers.
Elements and Construction:
The present invention consists of following parts:
Arc Runner (2, 7): These are provided in the assembly to facilitate the arc running
and also to provide the magnetic blow out on the arc in the direction of arc chute.
Ablation plates (3, 5): Ablation plate is used to produce the gases during short circuit and is used for cooling of the arc. The ablation plate is also used to house the slot motor plate.
L -shaped Slot Motor (4): It is the metal plate made of ferromagnetic material and is used to produce the magnetic blowout field on the arc.
I-shaped Slot Motor (9): It is the metal plate made of ferromagnetic material and is used to produce the magnetic blowout field on the arc.
Arc (10): It is the representation of arc that exits between the two runners in the event of short circuit fault.
Arc Chute (8): It is a stack of metal plates placed in a direction normal to the arc length, facilitating the division of arc into number of series arcs.
Moving contact (1): Moving contact is the part responsible for making and breaking of the current path.

Connector (6): Connector connects the arc runner to the next element in the current path.
In miniature circuit breakers, at the time of short circuit fault, arc is produced between the fixed and moving contact. 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. The fast arc movement is achieved by enhancing the magnetic field acting on the arc.
In this new concept, a concept of blow out loop (2 ) and the slot motor assembly is presented . Here, one slot motor plate (4) has a L-shaped profile and the other slot motor plate (9) has a I -shape or flat profile. Both the slot motors are fixed in the respective ablation plates (3, 5). A blow out loop is created by extending and bending the arc runner (2) to get a triangular profile (as shown in figure 2) in a way that the arc runner length 2a becomes parallel to the blow out loop length 2b. The connector (6) is welded to the blow out loop to carry the current to the next element in the circuit. At the time of short circuit the arc (10) transfers from contacts to the arc runners. The direction of current flow is shown in Figure 2.
The current lengths 2a and 2b generates the magnetic lines of flux that add each other as the flow of current in is in same direction in both the lengths. In the earlier embodiments as provided in prior art, a flat plate of ferromagnetic material is used to enhance the strength of magnetic field acting on the arc, which does not provide a completely closed path for the magnetic flux lines. In the presented concept of slot motor assembly both the current lengths (2a and 2b) gets covered and a close path (4a) is provided for the magnetic flux. This increases the strength of the magnetic flux lines and thus produce higher force on the arc which subsequently accelerates the

arc(10) in the direction of arc chute(8). The ablation plate profile (3a) facilitates the isolation among the current carrying parts 2a and 2b of blow out loop.
ADVANTAGES:
A design of slot motor and ablative plate assembly to cover both the arc
runner and the blow out loop length to have high magnetic blow out force on
arc.
Suitable for both single break and double break constructions of contact
system.
Reduction in cut off current and let through energy.
Increase in breaker life due to lower thermal and mechanical stresses.
This invention will be mainly used in miniature circuit breakers and the use can be extended to other modular devices too. The invention may be used for Domestic Application, Industrial application, wherever modular devices are used and Wherever short circuit protection devices are used.
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 system for current limitation during short circuit faults
for use in circuit breakers, said assembly comprising:
atleast one slot motor;
atleast one blow out loop assembly;
atleast one arc chute;
atleast one arc runner, said arc runner forming a blow out loop assembly providing magnetic blow out force on arc in direction of said arc chute;
a plurality of splitter plates;
a plurality of ablation plates defining housing for said slot motor plates;
atleast one slot motor plate wherein said plate is of substantially L shape;
atleast one slot motor plate wherein said plate is of substantially I shape;
atleast one moving contact; and
atleast one connector means
wherein the said L and I shaped slot motor plates cover the said arc runner length and the said blow out loop length so as to produce higher magnetic field on the arc and wherein the isolation between the said arc runner length and the said blow out loop length is achieved by having a special extrusion (3a) from the ablation plate (3).
2. Assembly as claimed in claim 1 wherein said slot motor plates are
substantially of ferromagnetic material producing magnetic blowout field on
arc.

3. Assembly as claimed in claim 1 wherein said arc chute comprising a plurality of metal plates placed normal to arc length.
4. Assembly as claimed in claim 1 wherein connector said means connecting said arc runner to next element in the current path.
5. Assembly as claimed in claim 1 wherein said blow out loop assembly is created by extending and bending said arc runner forming a substantially triangular profile.
6. Assembly as claimed in claim 1 wherein the said blow out loop is manufactured as an integral part of the arc runner.
7. Assembly as claimed in claim 6 or by joining the arc runner with separate piece of blow out loop.
8. An improved assembly for current limitation during short circuit faults as herein described and illustrated with reference to accompanying drawings.