FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION: UPPER CONTACT ASSEMBLY IN MOULDED CASE CIRCUIT
BREAKER
APPLICANT: LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to circuit breakers and particularly relates to an arc chute assembly in molded case circuit breakers. More particularly the present invention relates to an improved upper contact assembly with an arc puller.
B) BACK GROUND OF THE INVENTION
[0002] Circuit breakers are the mechanical switching devices capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal conditions. A circuit breaker basically consists of a pair of separable contacts and an interrupting medium. The function of the contacts is to conduct the electrical current when the breaker is closed and withstand the arcs while interrupting. Generally, the electrical contacts have a stationary part and a moving part. By bringing the moving contact to touch the stationary contact, a flow of an electric current is started and the breaker is closed. By driving the moving contact away from the stationary contact an electric arc is developed and by quenching the developed electric arc, the flow of the electric current is stopped and the breaker is opened.
[0003] In the existing technique, the circuit breakers are extensively used in the power distribution systems to provide a protection for an electrical equipment from electrical fault conditions such as current overloads, short circuits and abnormal level voltage conditions. Further the short circuit capacity of any circuit breaker is governed by the performance of an arc quenching chamber in the circuit breakers.
[0004] Further in the existing technique, the circuit breakers consist of the arc chute assembly which when subjected to a short circuit current of few kilo amperes quench the arc with long arcing times. The long arcing times leads to creating a stress on the downstream equipments due to a large amount of let through energy. Further the arcing

time increases due to the inability to cool the arc effectively during high fault conditions in the circuit breakers.
[0005] Further in the existing technique, the insulation surrounding the arc is subjected to a deposition of a carbon material due to the burning of the insulation during the arcing process. Further the carbonaceous material deposited forms a tracking of the insulation which leads to a flashover from one pole to another pole.
[0006] Further in the existing technique, the circuit breakers do not build up a strong magnetic field on the moving contact to enable a faster contact separation. These arc chute assemblies are inefficient in terms of a total arcing time and a let through energy with a circuit breaker passes to the downstream equipments.
[0007] Hence there exists a need to develop a circuit breaker with an improved arc chute assembly with an arc puller to help a faster separation of the contacts, a faster dielectric built up and to reduce the total arcing time and the let through energy.
[0008] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECT OF THE PRESENT INVENTION
[0009] The primary object of the present invention is to provide an arc chute assembly with an arc puller in the molded case circuit breakers.
[0010] Another object of the present invention is to provide an improved arc chute assembly to build a strong magnetic field on the moving contact.
[0011] Yet another object of the present invention is to provide an arc puller in the circuit breaker for a faster separation of the contacts and a faster dielectric built up.

[0012] Yet another object of the present invention is to provide an improved arc chute assembly to reduce an arcing time, let through energy and stresses on the in-line electric system.
(0013} Yet another object of the present invention is to provide an improved arc chute assembly to reduce the erosion of a contact button and to increase the electrical life of a circuit breaker.
[0014] Yet another object of the present invention is to provide an improved arc chute assembly for efficient utilization of the de-ion plates.
D) SUMMARY OF THE INVENTION
[0015] The various embodiments of the present invention provide an arc chute assembly with an arx puller in the circuit breaker. The upper contact assembly of a molded case circuit breaker includes an arc chute assembly, a moving contact, a contact button, a U-shaped slot provided in the moving contact and an arc puller arranged inside the U-shaped slot. The said arc puller includes a pre-set profile such that the arc puller pulls an arc away from the contact button thereby distributing the arc equally to de-ion plates in the arc chute assembly.
[0016] The present invention consists of a magnetic material so placed inside the U slot provided in the upper contact at its tip. The upper contact of a molded case circuit breaker consists of a U shaped slot arranged just above the contact button. A magnetic material, usually mild steel sheet, is inserted in the U shaped slot of the upper contact to act as an arc puller. The magnetic material is fixed using any one of the possible means including press fit, screw fit or riveted from inside etc.
[0017] The arc puller has a characteristic bending part which is bent towards an arc chute assembly. This profile of the arc puller effectively guides an arc during the short

circuit conditions. Also the upward bent profile helps to pull the arc towards the upper de-ion plates so that they are efficiently utilized for a faster arc voltage built up and an arc quenching. The arc puller can also be arranged with a straight part instead of acharacteristic bent part. The straight arc puller is easy to manufacture as it avoids bending operation.
[0018] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0020] FIG. 1 illustrates the front view of the molded case circuit breaker with a cover according to one embodiment of the present invention.
[0021] FIG. 2 illustrates the front view of the molded case circuit breaker without a cover according to one embodiment of the present invention.
[0022] FIG.3 illustrates the sectional view of the molded case circuit breaker (Y Pole) according to one embodiment of the present invention.
[0023] FIG.4 illustrates a front perspective view of the upper contact assembly (with an arc puller bent upwardly) of the molded case circuit breaker according to one embodiment of the present invention.

[0024] FIG.5 illustrates a front perspective view of the upper contact assembly (with a straight arc puller) of the molded case circuit breaker according to one embodiment of the present invention.
[0025] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0026] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0027] The various embodiments of the present invention provide an arc chute assembly with an arc puller in the circuit breaker. The upper contact assembly of a molded case circuit breaker includes an arc chute assembly, an upper contact, a contact button, a U-shaped slot provided in the upper contact and an arc puller arranged inside the U-shaped slot. The upper contact of a molded case circuit breaker consists of the U shaped slot arranged just above the contact button. The present invention consists of a magnetic material placed inside the U shaped slot provided in the upper contact at its tip. A magnetic material is a mild steel sheet and is inserted in the U shaped slot provided in the upper contact to act as an arc puller. The magnetic material is fixed by using any one of the possible means such as a press fit, a screw fit or riveted from inside etc. The said arc puller includes a pre-set profile such that the arc puller pulls an arc away from the contact button thereby distributing the arc equally to de-ion plates in the arc chute assembly.

[0028] FIG. 1 illustrates the front view of the molded case circuit breaker with a cover according to one embodiment of the present invention, while FIG. 2 illustrates the front view of the molded case circuit breaker without a cover according to one embodiment of the present invention. With respect to the FIG.l and FIG.2, the molded case circuit breaker includes an arc chute assembly 1, an upper contact assembly 2, a housing 6, a knob 8, a release 9 and a cover 7. The said arc chute assembly 1 is provided with an improved arc puller 4 to pull the arc efficiently from the contact buttons 5 as shown in FIG. 4 and FIG. 5.
[0029] FIG. 3 illustrates the sectional view of the molded case circuit breaker (Y Pole) according to one embodiment of the present invention. With respect to FIG. 3 the assembly includes a lower contact assembly 10. The upper contact assembly 2 is provided with the U slot at its tip and just above the contact button 5. The arc puller 4 is placed inside the U slot provided in the upper contact assembly 2 by any of the possible means e.g, press fit; screw fit or riveted from inside etc. The said arc puller 4 is a magnetic material usually made of mild steel sheet.
[0030] The conventional moving conductor is improved upon by an addition of an arc puller 4 by means of a magnetic material attached to the upper contact 2. At the time of fault, due to a current repulsion, the upper contact 2 and the lower contact 10 start separating. The arc puller 4 being a magnetic material pulls the upper contact 2 by enhancing the magnetic field surrounding it. This helps in faster separation of the contacts and thereby a faster dielectric built up. This consequently.reduces the total arcing time and the let through energy
[0031] FIG.4 illustrates a perspective view of the upper contact assembly (with an upwardly bent arc puller) while FIG.5 illustrates a front perspective view of the upper contact assembly (with a straight arc puller) of the molded case circuit breaker according to one embodiment of the present invention. With respect to FIG. 4 and FIG. 5 the upper contact assembly 2 includes the upper contact 3, the arc puller 4 and the upper contact

button. The arc puller 4a has a characteristic bent part which is bent towards the arc chute assembly 1 as shown in FIG. 3 and FIG. 4. This profile of the arc puller 4a effectively guides an arc during the short circuit conditions. Also the upwardly bent profile helps to pull the arc towards upper de-ion plates so that they are efficiently utilized for a faster arc voltage built up and arc quenching. The arc puller 4b can also have a straight part instead of the characteristic bent part as shown in FIG. 5. However in this case the effectiveness of arc puller 4b is slightly less than that of the former type.
[0032] The faster arc movement from the upper contact buttons 5 reduces the let through energy of the circuit breakers. The reduction of the let through energy in turn reduces the stresses on the one or more equipments in the electric system.
[0033] During the short circuit condition, an arcing is initiated across two contact buttons 5. The arc stays across these two buttons 5 for some time until the upper contact 3 starts opening. Because of an electromagnetic pull on the arc by the de-ion plates and pressure differentials across the arc, the arc starts moving towards the de-ion plates. By virtue of the arc puller 4, the arc root moves from the upper contact button 5 and shifts its root to the arc puller 4, thereby reducing the erosion of the contact button 5. Thus the arc puller 4 enables a full utilization of all the de-ion plates thereby increasing an arc length. The rapid built up of an arc voltage reduces a cut-off current and a let through energy on the downstream equipments.
G) ADVANTAGES OF THE INVENTION
[0034] The arc chute assembly of the present invention builds up a strong magnetic field on the moving contact to enable a faster contact separation. The faster contact separation reduces the arcing time and the let through energy of the circuit breaker thereby reducing the stresses on the electric system in-line. The present invention enables an efficient utilization of the de-ion plates placed at the top region due to a higher pull on the arc. The arc chute assembly of the present invention minimizes the erosion of the contact button and increases the electrical life of a circuit breaker. The area inside the arc

chute is completely de-ionized and a dielectric strength is built up rapidly to enhance a post short circuit performance. The present invention substantially reduces the burden on the downstream equipments by virtue of the low let through energy.
[0035] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0036] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. A contact assembly of a molded case circuit breaker comprising:
an arc chute assembly;
an upper contact;
a contact button;
a U-shaped slot provided in the upper contact; and
an arc puller arranged inside the U-shaped slot;
wherein the arc puller includes a pre-set profile such that the arc puller pulls an
arc away from the contact button thereby distributing the arc equally to de-ion
plates in the arc chute assembly.
2. The contact assembly according to claim 1, wherein the preset profile of the arc puller is an upwardly bent portion which is bent towards the arc chute assembly.
3. The contact assembly according to claim 1, wherein the preset profile of the arc puller includes a straight profile.
4. The contact assembly of a molded case circuit breaker of claim 1, wherein the arc puller is made of magnetic material.
5. The contact assembly of a molded case circuit breaker of claim 1, wherein the magnetic material is a mild steel material.
6. The contact assembly of a molded case circuit breaker of claim 1, wherein the arc puller is inserted into the U-shaped slot in the upper contact by at least one of press fit, screw fit or rivet means.
7. The contact assembly of a molded case circuit breaker of claim 1, wherein the arc puller is adapted to pull the upper contact thereby enhancing a separation of the contacts during a short circuit condition,
8. The contact assembly of a molded case circuit breaker of claim 1, wherein the arc puller exerts a magnetic pull on the arc to displace the arc towards the de-ion plates.

9. The contact assembly of a molded case circuit breaker of claim 1, wherein the arc puller displaces an arc root from the contact button and shifts the arc root to the arc puller thereby reducing an erosion of the contact button during the short circuit conditions.
l0.The contact assembly of a molded case circuit breaker of claim 1, wherein the arc puller is adapted to distribute the arc to the de-ion plates to increase the arc length.