FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CIRCUIT BREAKER WITH FLEXIBLE LOWER
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.

BACKGROUND OF THE INVENTION
Field of the invention
This invention relates generally to circuit breakers and, more particularly, to
current carrying components for lower contacts of circuit breakers.
Prior Art
A circuit breaker is a mechanical switching device, 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 circuit conditions such as those of short circuit. Short circuit is an accidental or intentional connection, by a relatively low resistance or impedance, of two or more points in a circuit which are normally at different voltages. The main function of any electrical switching apparatus is to carry the rated current. Therefore the current carrying capacity of any circuit breaker is so important that if the unit fails to carry the rated current it will cause damage to itself as well as to the electrical equipment to which it is protecting. The current carrying capacity is governed by the resistive drop across the circuit breaker. In traditional circuit-breakers, the current limiting principle is used. In order to achieve current reversal, the lower contact is made U-shaped. In order to achieve higher contact gap during short circuit and better over-travel during normal operating condition, the lower contact is made of three components (i.e. a lower contact terminal, a lower contact finger and a hinge, for example a screw made of copper. One of the members, lower contact finger is spring loaded to make the contact flexible and to achieve desired function of rotation.

However, sometimes to achieve better/lower mV (miliVoft) drop, the lower
contact is made of single component as shown in Figure 1. This single
component is either extruded with the desired profile or the developed profile is
cut (blanked) from Copper sheets and then bent to achieve the desired profile.
Further, US Patent 4245203 provides a circuit interrupter which includes
separable contacts, at least one of which is supported upon a movable pivoting
contact arm. The arm includes an axle member rigidly secured to and extending
through one end of the contact arm.
US Patent 4626811 describes circuit interrupter with integral resilient stop means
for contact arm where the gap distance separating the contacts of a low-voltage
circuit breaker in the tripped position is increased by utilizing resilient stop means
which is located at the bottom wall of the breaker housing rather than at the top
wall or on the handle of the breaker.
US Patent 4644121 describes a circuit breaker which has a contact carrying arm
movable about a pivot and a helical torsion spring movable on the arm to and
from the pivot for applying a varying force as the arm moves from closed to open
positions.
The inherent drawback of the prior art listed above is the problem of having either
high contact gap with higher resistive drop or low contact gap with lower resistive
drop since for high contact gap additional component is required to be hinged for
rotational movement to generate separation gap during fault clearance. The
additional component leads to additional voltage drop at hinge/joint of two
components.
In case of contact system shown in Figure 1, the lower mV drop could be
achieved while sacrificing contact gap. The reduction in contact gap leads to poor
arc extinction.
Therefore, there is a need for a flexible current carrying component for a lower
contact of a circuit breaker which overcomes the drawback described above and
provides higher contact gap with lower resistive drop.

SUMMARY OF THE INVENTION
An objective of the invention is to provide a flexible current carrying component for a lower contact of a circuit breaker which enhances the current carrying capacity and the short circuit fault clearance capacity of the circuit breaker by providing higher contact gap during fault clearance.
Accordingly, the present invention provides a circuit breaker comprising an upper contact and lower contact, wherein the current carrying component of the lower contact is formed out of an array of plurality of metallic sheets which are solidified together at selective locations based upon the flexibility requirement of the lower contact.
The invention also provides a method of manufacturing a lower contact for a circuit breaker comprising arranging a plurality of metallic sheets in an array in the shape of the lower contact and solidifying the metallic sheets at selective locations depending upon the flexibility requirement of the lower contact.
As a result, the current carrying component is made in a single piece and has flexibility at selective locations thereby enhancing the current carrying capacity and contact gap in the circuit breaker.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention
can be understood in detail, a more particular description of the invention, briefly
summarized above, may be had by reference to various embodiments, some of
which are illustrated in the appended drawings. It is to be noted, however, that
the appended drawings illustrate only typical embodiments of this invention and
are therefore not to be considered limiting of its scope, for the invention may
admit to other equally effective embodiments.
Fig. 1 and Fig. 2 show circuit breaker arrangements in the prior art.
Fig. 3a and Fig. 3b show front views of the upper and lower contact arrangement
of a circuit breaker in on and off position respectively, in accordance with an
embodiment of the invention.

Fig. 4a and Fig. 4b depict the process of manufacturing of a lower contact of
circuit breaker, in accordance with an embodiment of the invention.
Fig. 4a and 4b shows the details of a lower contact, in accordance with an
embodiment of the invention.
Fig. 5 is an isometric view of a lower contact, in accordance with an embodiment
of the invention.
DETAILED DESCRIPTION OF INVENTION
Various embodiments of the invention provide a circuit breaker comprising an
upper contact and lower contact, wherein the current carrying component of the
lower contact is formed out of an array of plurality of metallic sheets which are
solidified together at selective locations based upon the flexibility requirement of
the fower contact.
Fig. 3 shows a circuit breaker 100 including a lower contact 102 and upper
contact 104, in accordance with an embodiment of the invention.
Lower contact 102 is described in details with reference to figure 4. Figure 4a
shows a front view and an isometric view of lower contact 102. In accordance
with an embodiment of the invention, lower contact 102 includes an array of a
plurality of metallic sheets 402a, 402b, 402c and so on. The number of metallic
sheets 402 depends upon the thickness of lower contact 102. For example, if
thickness of metallic sheets 402 is 0.05 mm, hundred such sheets will be
required to make a 5 mm thick lower contact 102. It may be apparent to a person
skilled in the art that the flexibility of a hundred 0.05 mm thick sheets is much
more than that of single 5 mm thick sheet.
Metallic sheets 402 are made of metals such as copper which are known good
conductor of electricity.
In accordance with an embodiment of the invention, metailic sheets 402 are
solidified together at selective locations using solidifying means based upon the
flexibility requirement of the lower contact. Referring to Figure 4b, the locations
solidified have been identified as 404a, 404b, and 404c. Sheets 402 may be
solidified using known methods of solidifying such as welding, brazing, soldering

and the like. For example, the locations 404a-c where solidification is required is kept under brazing tool under pressure. The brazing fixture has two electrodes under which this portion is kept for solidification. Due to high pressure and temperature the thin sheets under electrodes melts at hot spots and generates micro welding and thus the solidified portions 404a-c are formed.
Holes on solidified portions 404a-d are drilled after the process of solidification as shown in figure 5. In figure 5, termination area 502 is a space for termination of cable/link, part 504 is a space used for assembly with housing using hardware, part 506 provides a flexible area for rotational movement to generate gap during fault clearance, and part 508 provides a solid space for brazing of contact button used for having least contact resistive.
In various embodiments, the process of drilling and solidification may be carried out simultaneously.
The portion of the lower contact which is not solidified is flexible and bends on application of force. The present invention therefore provides a current carrying component called lower/bottom contact for a circuit breaker which is flexible and does not have any additional part for rotation/movement, thereby enhancing the current carrying capacity of circuit breaker by reducing resistive voltage drop across it as the number of joints gets reduced and at the same time enhancing the short circuit fault clearance capacity by providing higher contact gap during fault clearance.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

We Claim :
1. A circuit breaker for electric devices comprising:
a. an upper contact; and
b. a lower contact, wherein the lower contact is formed out of an array
of a plurality of metallic sheets, the metallic sheets being solidified
together at selective locations using solidifying means, the locations
being selected based upon the flexibility requirement of the lower
contact.
2. A method for manufacturing a lower contact for a circuit breaker, the
method comprises:
a. arranging a plurality of metallic sheets in an array, the array being
in the shape of the lower contact; and
b. solidifying the metallic sheets at selective locations depending upon
the flexibility requirement of the lower contact.
3. The method according to claim 2 further comprising drilling holes in the solidified portion of the lower contact.
4. The method according to claim 2 further comprising shaping the array in the form of the lower contact using tools and fixtures.