FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: EROSION COMPENSATED SHAFT ARRANGEMENT FOR 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 a circuit breaker arrangement. More particularly the present invention relates to an erosion compensated shaft arrangement for circuit breakers.
BACKGROUND AND THE PRIOR ART
The invention can be used in the field of circuit breakers or switches where contact pressure is provided by means of springs. Currently, all molded case circuit breakers have a main shaft/drive shaft which holds spring for providing the necessary contact pressure. Depending on the type of construction of shaft, different spring arrangements are followed by different manufacturers.
Some of the prior arts of the field of invention is provided as follows:
In US5310971 Contact Bridge of a molded case circuit breaker is rotatably mounted in a bar by two springs arranged symmetrically from the rotation axis. Each spring is, on the one hand, anchored to the contact bridge, and, on the other hand, anchored to a rod housed in a notch of the bar. The same springs provide contact pressure and slowing-down of opening of the contact bridge at the end of repulsion travel by electro-dynamic effect. The contact bridge bears on its edge cam surfaces which, at the end of opening travel, engage the anchoring rods to move them in the notches in the elongation direction of the tension springs. The energy of the contact bridge is thus taken up and stored in the springs causing slowing-down of the contact bridge. The profile of the cams can be chosen to enable reclosing of the contact bridge, this reclosing naturally being delayed by the slowing-down effect at the end of travel. The cam profile can also ensure latching of the contact bridge in the open position.

US6870112 provides a low-voltage circuit breaker, comprising a rotating contact supporting shaft, is provided with a seat that accommodates the central body of a moving contact so that the first arm protrudes externally from the seat, at least one first spring and one second spring being furthermore arranged in the contact supporting shaft and being suitable to ensure, when the circuit breaker is closed, an adequate contact pressure between the active surface and the fixed contact; ; the particularity of the circuit breaker consisting of the fact that a first pivot is fixed to the contact supporting shaft and is coupled to a hole formed in the central body, engagement means and at least one second pivot being furthermore arranged on the shaft on mutually opposite sides with respect to the first pivot, the second pivot being movable with respect to the shaft and to the moving contact, the first and second springs being furthermore anchored to the second pivot and to the engagement means and being arranged along two opposite sides of the arm of the moving contact, the second pivot interacting functionally with the first cam-like surface so as to generate a mechanical moment that matches the direction of rotation of the moving contact during at least one portion of the step for separation of the active surface from the fixed contact in a short-circuit condition.
US6262642 provides a rotary contact arrangement for circuit breakers of the type including a pair of contact springs arranged on each side of a rotary contact arm, as the contact springs interconnect between the rotors and the contact arm via a pair of U-shaped levers. The provision of the U-shaped levers provides uniform contact pressure between both pairs of fixed and moveable contacts to prevent contact erosion.
US2005046539 provides an electrically isolated rotor assembly for a cassette assembly of a circuit breaker includes a rotor having a first side and an opposing second side, a first isolation cap disposed on the first side, a second isolation cap disposed on the second side. Each isolation cap preferably includes a centrally located knob with a bushing surrounding each knob, wherein the bushings are sized for securement within apertures within first and second cassette half pieces.

In a conventional system, when contact button wear out due to short circuit or normal switching, the contact springs adjust to push the contact further closing the contact. Due to this adjustment, a part of contact pressure is lost. This decrease in contact pressure causes increased resistance between contacts. This causes problems of higher temperature rise in the breaker. This also increases the burden on other components in the breaker.
Present invention maintains the contact pressure even after wear out of the contacts. This helps the breaker in maintaining the same level of performance even after erosion of contacts.
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 provide an erosion compensated shaft arrangement for circuit breakers.
Another object of the present invention is to provide a spring arrangement that gradually increase contact pressure.
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.
There is provided an erosion compensated shaft arrangement for circuit breakers.
According to one aspect of the present invention, there is provided a spring arrangement that gradually increase contact pressure.
Other aspect of the present invention provides a shaft arrangement using a spring that gradually increase contact pressure with erosion.
Yet other aspect of the present invention provides an improved shaft arrangement for circuit breakers comprising at least one moving contact; a plurality of compression spring means in communication with said moving contact; a pair of opposing side caps, each of said side caps defining a plurality of slots; a pair of contact buttons provided on said moving contact; a plurality of fixed pin means; a plurality of moving pin means; at least one centre pin means; wherein said centre pin means and said moving pin means extending through said side caps and said movable contact; wherein said centre pin integrated with said spring means adapted for shifting in said slot on side cap on erosion of said contact buttons thus compensating for contact pressure thereby nullifying effect of contact button erosion.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF 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.
Fig 1 illustrates the different shaft constructions according to the prior arts.
Fig 2 illustrates the graph for contact pressure vs Erosion for the conventional system.
Fig 3 illustrates the graph for contact pressure vs Erosion in accordance with the present invention.
Fig 4 illustrates the mechanism in accordance with the present invention.
Fig 5 illustrates side view of the shaft arrangement showing different components.
Fig 6 illustrates the shaft arrangement having unequal erosion of fixed contact button.
Fig 7 illustrates the shaft arrangement wherein the centre pin is shifted in the side cap slot to compensate for erosion.
Fig 8 illustrates the shaft arrangement wherein the centre pin is shifted to the extreme end of the side cap slot to compensate for erosion.
Fig 9 illustrates the left side view of shaft arrangement.

Fig 10 illustrates the right side view of the shaft arrangement.
Fig 11 illustrates the arrangement of plurality of compression springs.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Accordingly in the present invention, an improved shaft arrangement for moulded case circuit breaker is provided. Fig. 1 provides shaft arrangement of different prior arts. Fig. 3 shows the variation of contact pressure with erosion in the new compensated system. As shown in Fig. 3, the contact pressure increases with erosion. The system is arranged in such a way so as to increase the contact pressure with erosion.
In ON condition Torque due to spring by moving contact is transferred to contact pressure. As contacts wear, due to adjustment by springs, the spring force reduces. For keeping spring torque at the same value, the perpendicular distance from line of action of spring force to shaft centre should increase with erosion. This increase in length should produce a greater increment in torque than what is lost due to decrease in spring force. This is achieved by keeping the spring rate to the lowest possible value.
The present invention comprises at least one moving contact; a plurality of compression spring means in communication with said moving contact; a pair of opposing side caps, each of said side caps defining a plurality of slots; a pair of contact buttons provided on said moving contact;
a plurality of fixed pin means; a plurality of moving pin means; at least one centre pin means; wherein said centre pin means and said moving pin means extending through said side caps and said movable contact; wherein said centre pin

integrated with said spring means adapted for shifting in said slot on side cap on erosion of said contact buttons thus compensating for contact pressure thereby nullifying effect of contact button erosion.
The said centre pin means, said moving pin means, said moving contact and said spring means move in unison. The spring means is adapted to balance contact pressure on erosion of said contact buttons. The moving contact is arranged proximate to said fixed pin and arranged for opposing said moving contact. Further, the present invention is adapted to compensate for both equal and unequal erosion of said contact buttons.
Main constructional features involved are as follows (illustrated in Fig. 11):
1. Moving contact
2. Moving contact buttons
3. Side caps
4. Spring means
5. Fixed pin means
6. Compression spring means
7. Moving pin means
8. Centre pin means
9. Centre pin slots etc.
This gives the following advantages:
1. Improved thermal performance of the breaker due to improved contact pressure.
2. Higher electrical life of breaker due to the ability to perform after erosion.

3. Improved performance after short circuit due to the ability to perform even after erosion.
4. Chance to use less thick button giving option for material saving.
During Short circuit or Electrical operation in contact system the contact buttons erode. In a single break per pole concept, inter-pole unequal erosion has to be take care. But in double break per pole concept, intra-pole unequal erosion has to be take care. This concept is meant to consider that.
In figure 5 it is shown that the hinge point for moving contact is different in case
of equal and unequal erosion. During Equal erosion the hinge point of the moving
contact coincide with the centre point of shaft where it is assembled. Hence the
basic equation that is implemented for contact pressure in shaft arrangement is as
follow:-
Torque on Contact (Moving contact button 1) = Torque due to Springs Set (1 & 2)
FcXD = FsXd
where, Fc = Contact Pressure in kg
D = Perpendicular distance from hinge point to contact reaction in mm
Fs = Spring forces in kg
d = Perpendicular distance from hinge point to spring axis in mm
During Unequal erosion the hinge point of moving contact is on the other side of
the button which is eroded. Hence the basic equation that is implemented for
contact pressure in shaft arrangement during Unequal Erosion is as follow :-
Torque on Contact (Moving contact button 1) = Torque due to Springs Set (1 & 2)
- Torque due to Springs Set ( 3 & 4 )
FcXD = (FslXdl)-(Fs2Xd2)
where, Fc & D is same as above
Fsl = Forces due to springs 1 & 2 (Figure-1)
dl = perpendicular distance from hinge point to spring axis in mm
Fs2 = Forces due to springs 3 & 4 (Figure-1)

d2 = perpendicular distance from hinge point to spring axis in mm
Illustration:
As shown in figure 5 the value of contact pressure at 0 mm erosion of button is :
At no Erosion position :-
D = 41.9mm
dl = 16.4mm
62 = 8.8mm Fc = 2.98 kg
As shown in figure-4 the value of contact pressure at 3 mm erosion of button is : At full Erosion position :-
D = 38.9mm
dl = 17.7mm
d2 = 0.75mm Fc = 3.50kg
Figure 6 & 7 are the intermediate positions of moving contact during Unequal erosion where the value of contact pressure increases from 1mm to 2mm erosion.
So the contact pressure during unequal erosion is achieved by:
• Peculiar arrangement of fixed pins with respect to the hinge point during Unequal erosion
• Slot given in the Side caps of shaft for movement of centre pin during Unequal erosion
• Keeping the spring constant K of springs as minimum as possible.
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 shaft arrangement for circuit breakers comprising:
at least one moving contact;
a plurality of compression spring means in communication with said moving contact;
a pair of opposing side caps, each of said side caps defining a plurality of slots;
a pair of contact buttons provided on said moving contact;
a plurality of fixed pin means;
a plurality of moving pin means;
at least one centre pin means;
wherein said centre pin means and said moving pin means extending through said side caps and said movable contact;
wherein said centre pin integrated with said spring means adapted for shifting in said slot on side cap on erosion of said contact buttons thus compensating for contact pressure thereby nullifying effect of contact button erosion.
2. Arrangement as claimed in claim 1 wherein said centre pin means, said moving pin means, said moving contact and said spring means move in unison.
3. Arrangement as claimed in claim 1 wherein said spring means adapted to balance contact pressure on erosion of said contact buttons.
4. Arrangement as claimed in claim 1 wherein said spring means having a substantially low spring constant.

5. Arrangement as claimed in claim 1 wherein said moving contact arranged proximate to said fixed pin and arranged for opposing said moving contact.
6. Arrangement as claimed in claim 1 configured to compensate for both equal and unequal erosion of said contact buttons.
7. An improved shaft arrangement for circuit breakers as herein described and illustrated with reference to accompanying drawings.