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: AN IMPROVED CONTACT SYSTEM 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:


FIELD OF THE NVENTION

The present invention relates to a circuit breaker. Particularly, the invention is concerned about a contact system of a moulded case circuit breaker. More particularly, the invention is concerned about an improved contact system of moulded case circuit breaker having a unique diverging magnetic arc runners profile.

BACKGROUND OF THE INVENTION

US 4,295,022 discloses a relatively high current capacity molded case circuit breaker having arcing and main contacts and an arc chute to receive and extinguish arcs drawn between the arcing contacts is provided with a trifurcated magnetic arc runner extending from the stationary arcing contact well into the arc chute. The outer sections or legs of the arc runner extend generally parallel to the forward surface of the terminal strap on which the stationary contacts are mounted, and the center leg of the arc runner is curved forward so that the free end of the center leg extends forward of a substantial number of plates in the arc chute. The center leg is shaped so that during opening of the circuit breaker the movable arcing contact moves in close proximity to the center leg and in so doing encourages arcs which may form between the main contacts to extinguish rapidly.

US 4,276,526 discloses a miniature current limiting circuit breaker incorporates double break circuit interrupting contacts capable of being abruptly separated by a high fault current responsive solenoid acting to first trip the breaker mechanism and then forcibly effect contact separation. The arc chamber is constructed to achieve enhanced blowout of the arc into the arc chute and to develop gas pressures acting to accelerate contact separation. The circuit breaker is trip-free and includes both thermal tripping and internal common tripping capabilities

The disadvantages of the prior art circuit breakers are such that breakers consist of an arc chamber 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. This is because of their inability to attract the arc towards arcing chamber and cool it effectively during high fault conditions. These arc chamber assemblies are inefficient in terms of total arcing time and let through energy passed on to the downstream devices.

Thus, there is a need to overcome the problems of the prior art. Therefore, present inventors have developed an improved contact system of moulded case circuit breaker having a unique diverging magnetic arc runners profile. The improved contact system would enhance the blow out force on arc for rapid separation of arc away from the contact buttons.

OBJECTS OF THE INVENTION

An object of the present invention is to overcome the problems/disadvantages of the prior art.

Another object of the present invention is to provide an improved contact system of moulded case circuit breaker having a unique diverging magnetic arc runners profile

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 an improved contact system for use in circuit breakers, said system comprising:
a moving contact means;
a fixed contact means;
plurality of arc runner means comprising a moving contact runner means, a fixed contact runner means;
wherein said arc runners being operatively located on said moving contact means and said fixed contact means such that a predetermined angle being formed between said arc runners so as to enhance blow out force on the arc.

DETAILED DESCRIPTION OF THE INVENTION

According to a preferred embodiment of the invention, there is provided an improved contact system of moulded case circuit breaker. The improved contact system comprises diverging magnetic arc runners on fixed and moving contacts of a moulded case circuit breaker. This invention enhances the circuit breaker’s breaking capacity by faster arc movement from contact buttons, thereby increasing electrical life of circuit breaker as well as enhancing its performance during fault conditions.

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). Therefore the short circuit capacity of any circuit breaker is totally governed by the performance of its arc quenching chamber

In the present invention, Conventional contact system is improved upon by addition of diverging magnetic arc runners by means of a surface treated magnetic material attached to fixed and moving contact of a moulded case circuit breaker. The assembly of the arc runners on fixed and moving contacts is done close to the contact buttons in such a way that it creates a divergent angle towards the arc chute. The angle made is such that it enhances the blow out force on the arc driving it faster towards the arc chute. Also, due to the divergent angle, the arc is spread in a larger angle when contacts are in open condition. The greater spread facilitates accommodation of higher no of deion plates which increases the arc voltage rapidly thereby quenching the arc faster.

The arc runners in the present invention are made up of magnetic material. Being a magnetic material, the arc runner pulls the arc rapidly from the contact buttons towards itself decreasing the arc immobility time i.e time for which the arc remains immobile on the contact buttons. The surface treatment of the arc runners is of a material which has higher arc mobility. This further enhances faster running of arc on the arc runners and moves it rapidly towards the arc chute. This reduces the contact button erosion and improves the electrical life of MCCB.

Further, at the time of fault, due to current repulsion, the contacts start separating. The magnetic nature of the arc runner on moving contact separates it faster by enhancing the magnetic field surrounding it. This helps in faster contact separation & thereby faster dielectric built up. In case where slot motor is used for making the moving contact repel faster, and is placed close in line with the opening locus of the moving contact arc runner, the effect of the slot motor is enhanced further by magnetic field linkages of arc runner and slot motor moving the moving contact faster. The faster contact separation consequently reduces total arcing time and the let through energy of the circuit breaker.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:

Fig 1 illustrates RHS view of MCCB
Fig 2 illustrates front view of MCCB
Fig 3 illustrates sectional view of MCCB showing contact assembly
Fig 4 illustrates moving (upper) contact assembly
Fig 5 illustrates fixed (lower) contact assembly
Fig 6 illustrates sectional view of MCCB showing contact assembly in closed condition
Fig 7 illustrates detailed sectional view of MCCB showing contact assembly in closed condition
Fig 8 illustrates detailed sectional view of MCCB showing contact assembly in initial instances of separation during fault conditions.
Fig 9 illustrates flux linkages in Moving (upper) contact assembly under arcing.
Fig 10 illustrates flux linkages in Fixed (lower) contact assembly under arcing.
Fig 11 illustrates sectional view of MCCB showing contact assembly in open condition without arc chute.
Fig 12 illustrates detailed Sectional view of MCCB showing contact assembly in open condition without arc chute.
Fig 13 illustrates flux linkages of moving contact assembly and slot motor during opening on fault conditions.

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 system has been discussed below to describe the way the system 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.

According to a preferred embodiment of the invention, there is provided an improved contact system of moulded case circuit breaker. The improved contact system comprises diverging magnetic arc runners (4, 6) on fixed contact (7) and moving contact (5) of a moulded case circuit breaker. The prime feature of present invention is the way arc is blown away then pulled and run up by a magnetic material placed near the upper contact (5) and lower contact (7).

The present invention comprises of improved contact system by addition of diverging arc runners of a magnetic material so placed near the upper contact button (8) and lower contact button (9) near its tip as shown in figure 6 and figure 7. The upper (5) and lower contact (7) of a moulded case circuit breaker consists of slot just after the contact button. A magnetic material (usually mild steel) sheet (called as magnetic arc runner) is attached in this slot. This can be done by any of the possible means e.g. screw fit, riveted from inside, Brazing etc. The assembly of upper and lower contact with runners is shown in figure 4 and figure 5.

The assembly of the arc runners on fixed and moving contacts (7, 5) is done in such a way that it creates a particular divergent angle towards the arc chute (α). The particular angle made is such that it enhances the blow out force on the arc (10) driving it faster towards the arc chute (2). Also, due to the divergent angle, the arc (10) is spread in a larger angle when contacts are in open condition. The greater spread, as shown in figures 11 and12, facilitates accommodation of higher no of deion plates. Higher no of deion plates effectively increases the magnitude of the arc voltage build up when the arc (10) is spilt in the arc chute, quenching the arc faster. Also, the magnetic nature of arc runner enables full utilization of all the deion plates thereby increasing the arc length. Rapid built up of arc voltage reduces cut off current and let through energy on the downstream equipments.

When the contacts start separating during fault conditions, arc is struck between contact buttons as shown in figure 8. The arc runners in the present invention are made up of magnetic material. Being a magnetic material, flux produced by the arc links with the arc runners as shown in figure 9 and figure 10. Due to these flux linkages, the arc runners pull the arc towards themselves and the arc roots move from contact buttons (8,9) and shifts their roots to the arc runners, thereby reducing erosion of contact buttons (8,9). The rapid separation of arc from the contact buttons (8, 9) decreases the arc immobility time i.e. time for which the arc (10) remains immobile on the contact buttons (8, 9). Also, the surface treatment of the arc runners is of a material which has higher arc mobility. This further enhances faster running of arc on the arc runners and moves it rapidly towards the arc chute (2). This effectively reduces the total arcing time and improves the electrical life of the MCCB.

At the time of fault, the moving contact (5) separates from the lower contact (7) due to repulsive forces acting on them. The repulsive forces are produced by the fault current flowing through the lower contact (7) and upper contact (5). The magnetic nature of the arc runner on the moving contact (5) separates it faster during current repulsion by enhancing the magnetic field surrounding it. This helps in faster contact separation and thereby faster dielectric built up.

According to another preferred embodiment of the invention, there is provided an improved contact system of moulded case circuit breaker. In this embodiment where slot motor (11) is used for making the moving contact (5) repel faster and is placed close in line with the opening locus of the moving contact arc runner (4) , the magnetic field linkages are enhanced due to the magnetic nature of the arc runner placed on the moving contact (5) as shown in figure 13. Due to this, the effect of the slot motor (11) is enhanced, thereby moving the moving contact (5) faster. The faster contact separation consequently reduces total arcing time and the let through energy of the circuit breaker.

ADVANTAGES OF THE INVENTION
1. Reduction in arcing time
2. Increasing electrical life of circuit breaker
3. Faster contact separation

Components/structural elements of the invnetion:
1. Moving (upper) contact assembly
2. Arc chute assembly
3. Fixed (lower) contact assembly
4. Moving (upper) contact runner
5. Moving (upper) contact
6. Fixed (lower) contact runner
7. Fixed (lower) contact
8. Moving (upper) contact button
9. Fixed (lower) contact button
10. Arc
11. Slot motor

WE CLAIM
1. An improved contact system for use in circuit breakers, said system comprising:
a moving contact means;
a fixed contact means;
plurality of arc runner means comprising a moving contact runner means, a fixed contact runner means;
wherein said arc runners being operatively located on said moving contact means and said fixed contact means such that a predetermined angle being formed between said arc runners so as to enhance blow out force on the arc.

2. System as claimed in claim 1, wherein said moving contact runner means being operatively located on said moving contact means.

3. System as claimed in claim 1, wherein said fixed contact runner means being operatively located on said fixed contact means.

4. System as claimed in claim 1, wherein said contact means comprising a slot means.

5. System as claimed in claims 1 to 4, wherein said arc runner means is operatively attached with said slot means by means of fasteners, brazing means and the like.

6. System as claimed in claim 1 further comprising a plurality of contact button means.

7. System as claimed in claim 6 wherein said contact button means comprising a moving contact button means.

8. System as claimed in claim 6 wherein said contact button means comprising a fixed contact button means.

9. System as claimed in any claim 4, wherein said slot means being proximate to said contact button means.

10. System as claimed in claim 1, wherein said moving contact runner means being located proximate to said moving contact button means.

11. System as claimed in claim 1, wherein said fixed contact runner means being located proximate to said fixed contact button means.

12. System as claimed in claim 1, wherein said arc runners being made up of magnetic material and the like.

13. System as claimed in claim 1 wherein said angle between said moving contact arc runner means and fixed contact arc runner means is diverging angle.

14. System as claimed in claim 1 further comprising a plurality of deion plate means.

15. System as claimed in claim 1 optionally comprising a slot motor means adapted to making said moving contact means repel faster.

16. System as claimed in claim 15, wherein said slot motor means being operatively located in line with opening locus of said moving contact arc runner means.

17. An improved contact system of moulded case circuit breaker as herein substantially described and illustrated with the accompanying drawings.