FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CONTACT SYSTEM FOR CIRCUIT BREAKER;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
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 circuit breakers. More particularly, the invention relates to electrical contacts of a circuit breaker.
BACKGROUND OF THE INVENTION
Generally, Electrical switching apparatus, such as circuit breakers, are employed in diverse 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). The short circuit capacity of any circuit breaker is totally governed by the performance of its arc quenching chamber.
The prior art circuit breakers consist of contact systems which when subjected to a short circuit current of few kilo amperes, the arc is initiated from contact buttons. These circuit breakers take long time to quench the arc as they cannot limit the current after initiation of the arc. These result in erosion of contact buttons and lower the electrical life of the circuit breakers. The eroded contact buttons leads to higher temperature rise even when the circuit breakers carry rated current. The long arcing times lead to severe stresses on the downstream equipments due to large amount of let through energy. This is because of their inability to limit the fault current. These arc chamber assemblies are inefficient in terms of total arcing time and let through energy.
The prior art circuit breakers consist of arc chambers which when subjected to a short circuit current of few kilo amperes, quench the arc with long arcing times and passes a current

with higher peak value. The long arcing times and higher peak value of the current lead to severe stresses on the downstream equipments due to large amount of let through energy. This is because of their inability to limit the current effectively during high fault conditions.
In view of the above there is a need of a simplified contact system for circuit breakers that can overcome the shortcomings associated with above prior arts.
SUMMARY OF THE INVENTION
Accordingly, the present invention a contact system for a circuit breaker, comprising a pair of contacts; a movable runner at one of the contacts, the movable runner being able to move between a first position and a second position, the first position being at level with the contact, the second position protruding above the contact, the movable runner being connected to the contact through a wire braid; and a magnetic base, the movable runner being mounted on the magnetic base, the magnetic base being able to attract an arc formed between the pair of contacts.
In an embodiment the contact system of the invention comprises means for moving the movable runner between the first position and the second position, the means includes means for holding the runner slidably and spring means connected between the magnetic base and the contact.
The primary feature of present invention is the way arc initiates from runners instead of contact buttons and current is limited within a minimum value.

BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Fig. 1 shows a detailed sectional view of contact system showing current path in accordance with an embodiment of the present invention.
Fig. 2a shows an isometric view of the contact system with arc chute, with contacts at open condition in accordance with an embodiment of the present invention.
Fig. 2b shows a sectional view of the contact system with arc chute with contacts at open condition in accordance with an embodiment of the present invention.
Fig. 3 shows an isometric view of the contact system without arc chute with contacts at open condition in accordance with an embodiment of the present invention.
Fig. 4a shows an isometric view of the contact system with arc chute with contacts at closed condition in accordance with an embodiment of the present invention.
Fig. 4b shows sectional view of contact system with arc chute with contacts at closed condition showing current paths in accordance with an embodiment of the present invention.
Fig. 5 shows contact system without arc chute with contacts at closed condition in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
Various embodiments of the present invention provides a contact system comprising a pair of contacts, a movable runner at one of the contacts, the movable runner being able to

move between a first position and a second position, the first position being at level with the contact, the second position protruding above the contact, the movable runner being connected to the contact through a wire braid; and a magnetic base, the movable runner being mounted on the magnetic base, the magnetic base being able to attract an arc formed between the pair of contact.
Fig. 1 shows a contact system 100 in accordance with an embodiment of the invention. Contact system 100 includes a pair of contacts (110,120), a movable runner 130 and a magnetic base 140.
Movable runner 130 is positioned at contact 120 and connected to contact 120 through a wire braid 136. Movable runner 130 is mounted on magnetic base 140. Magnetic base 140 attracts the arc formed between pair of contacts (110,120). Movable runner 130 moves between a first position 130a and a second position 130b. Movable runner 130 at first position 130a is at level with contact 120 as shown in Figs. 4b and 5. At second position 130b movable runner 130 protrudes above contact 120 as shown in Figs. 1, 2a, 2b, 3.
In an embodiment of the invention, contact system 100 includes means for moving movable runner 130 between first position 130a and second position 130b.
In an embodiment, the means for moving the movable runner includes means for holding runner 130 slidably and spring means.
In an embodiment, the means for holding movable runner 130 is a movable runner holder 160.

In an embodiment the spring means is a compression spring 170.
In an embodiment spring means is a leaf spring.
In an embodiment movable runner 130 is placed at a distance from contact 120 to avoid the arc from jumping to contact 120.
In an embodiment, wire braid 136 is a flexible wire braid. Wire braid 136 allows the movable runner 130 to move between first position 130a and second position 130b while maintaining the connection between magnetic base 140 and contact 120. Magnetic base 140 is placed on compression spring 170. Compression spring 170 is placed in movable runner holder 160 and magnetic base 140 also moves inside the movable runner holder 160.
In an embodiment of the invention, movable runner 130 is at some height with respect to fixed contact button 122 due to spring 170 action. Movable runner 130 is stopped at some height by movable runner holder 160 as shown in Figs. 2a, 2b, and 3.
In an embodiment, as the circuit breaker is closed, movable runner 130 goes to the same level as that of fixed contact button 122 as shown in Fig 5. At closed condition, current flows through movable runner 130 and flexible wire strands 136 in parallel with fixed contact button 122 and fixed contact 120 following current path 180a as shown in Fig. 4b.
In an embodiment, most of the current flows through fixed contact button 122 as the alternate path offer high resistance due to resistive flexible wire strands 136. During short circuit fault condition, contacts (110, 120) experience repulsion force.

In an embodiment, during opening of circuit breaker, moving contact button 112 detaches first from fixed contact button 122 and then moving contact runner 150 detaches from movable runner 130 as shown in the Figs. 2a and 2b. The arc initiates from movable runner 130 and moving contact runner 150 instead of contact buttons (112, 122) as runners (130, 150) detaches after contact buttons (112,122).
In an embodiment, the arc initiates from movable runner 130 and goes to Deion plates 190 to split into a series of small arcs due to magnetic pull on the arc. This leaves contact buttons (112, 122) without erosion and hence increases the electrical life of the circuit breaker. The circuit breaker has a pair of arc chutes 192 (192a, 192b) for confining the arc and preventing damage to the circuit breaker as shown in Figs. 2a and 4a.
In an embodiment, the moment moving contact button 112 detaches from fixed contact button 122 the current starts flowing only through movable runner 130 and flexible stranded wire 130a following current path 180b as shown in Fig. 1. The current experiences a high resistance and is limited within a minimum value.
In an embodiment, high resistance flexible stranded wire 136 provides high voltage drop which helps in quenching the arc rapidly. The reduced current and reduced arcing time reduces the let through energy.
In an advantageous aspect, arc initiates from the moving arc runner as it detaches last hence contact button will not be eroded. The current is limited to a minimum value as the flexible wire strand offer a high resistance to the current. The high voltage drop across the flexible wire strands helps to quench down the arc quickly. The arcing time is reduced and let through energy of the circuit breaker due to faster arc quenching and the current limitation.

Lesser or no erosion of contact buttons leads to lower temperature rise of the circuit breaker and increase in electrical life of circuit breaker.
While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

We Claim:
1. A contact system for a circuit breaker, comprising:
a pair of contacts;
a movable runner at one of the contacts, the movable runner being able to move between a first position and a second position, the first position being at level with the contact, the second position protruding above the contact, the movable runner being connected to the contact through a wire braid; and
a magnetic base, the movable runner being mounted on the magnetic base, the magnetic base being able to attract an arc formed between the pair of contacts.
2. The contact system as claimed in claim 1 further comprising means for moving the movable runner between the first position and the second position, the means includes means for holding the runner slidably and spring means connected between the magnetic base and the contact.
3. The contact system as claimed in claim 2 wherein the spring means is a compression spring.
4. The contact system as claimed in claim 2 wherein the spring means is a leaf spring.

5. The contact system as claimed in claim 1 wherein the movable runner is placed at a distance from the contact to avoid the arc from jumping to the contact.