FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: IMPROVED ROTOR ASSEMBLY FOR A MOULDED CASE CIRCUIT BREAKER
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. More particularly the present invention relates to an improved rotor assembly for a moulded case circuit breaker.
BACKGROUND AND THE PRIOR ART
The present invention relates to low Voltage current limiting circuit breaker. Switching devices like, molded case circuit breaker operating on the current limiting principle typically have a pair of solid stationary Electrical contacts joined by a solid moving Electrical contact, which provides a path to carry the electrical current in the network.
Rotor construction enables the design of double break arrangement that helps in the better make & break under normal and abnormal conditions involving very high over-currents. The Switching device should interrupt the over current arising due to abnormal conditions in the network, as rapidly as possible to minimize damage caused by thermal and mechanical stresses to the equipment installed downstream. The rotor or shaft of the molded case circuit breaker has to be robust as high electro dynamic repulsive forces are generated between the stationary and moving contacts in the over current conditions.
The rotor should have provisions for providing contact pressure so as to provide the intended repulsion threshold as well as to keep the temperature rise within allowable limit set by the relevant product standards under normal working condition. The moving contact is rotated by a certain angle or distance which is termed as over-travel for attaining the contact pressure. The springs that provide the contact pressure should not be exposed to the arcing, a phenomenon of electrical breakdown of gases which enables the passage of current during contact separation, to prevent the drop in spring force and ensure contact pressure.

During the separation of contacts due to repulsion, very high energy is released due to arcing which results in the erosion of the buttons on both moving contact as well as fixed contact. Rotor should have the provisions for compensating for the erosion so as to maintain the contact
pressure even after the erosion of buttons.
Some of the prior arts in the present field of invention are as follows:
US 5310971 provide the 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,
US 6870112 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.
US 6262642 provides a circuit breaker rotary contact arrangement comprising a pair of opposing circular rotor plates, each of said rotor plates defining a carrier slot on a perimeter thereof; a movable contact arm intermediate said rotor plates, said contact arm defining a first movable contact at one end arranged opposite an opposing first fixed contact and a second movable contact at an end opposite said one end arranged proximate a second fixed contact; a pivot pin extending through said rotor plates and said movable contact arm, whereby said rotor plates and said movable contact arm rotate in unison; a pair of first contact springs, one of said first contact springs arranged on one side of said movable contact arm and another of said first contact springs arranged on an opposite side thereof; and a U-shaped lever intermediate said rotor plates, said U-shaped lever defining a pair of side arms joined at one end by a bight, said bight arranged proximate a first shaped surface formed on said contact arm for providing a constant spring force between said first and second fixed and movable contacts.
US 6965292 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.
The prior arts posses the following disadvantages:
1. During arcing, hot gases and arc products are produced which can enter inside the shaft damaging the components like springs and pins inside the shaft.
2. An open construction leads to lesser differential pressure on arc, i.e. the pressure difference between the front and rear of arc will be lesser. Increased differential pressure is required for efficient driving of arc into the extinguishing zone.

3. An open shaft construction increases the chance of standing arc because of lesser insulation between the contacts.
4. Slot on the moving contact causes increase in the current density and leads to unnecessary temperature rise.
The present invention describes a robust rotor construction to provide double break, ensure contact pressure under normal and abnormal working conditions and enhance current breaking. Currently, all molded case circuit breaker have a rotor/drive shaft which rotates and switches the electrical circuit. The present technology for shaft construction uses an open shaft construction or partially closed construction.
The present invention therefore provides an enclosed single shaft construction, the components are secluded from damage and the contact pressure is ensured in normal and abnormal conditions. By giving provision for erosion compensation in the rotor cover, current density on the moving contact is reduced and the temperature rise is kept under control.
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 improved rotor assembly for a moulded case circuit breaker.
Another object of the present invention is to prevent hot gases and arc products from entering inside the shaft and therefore prevent damaging of the components like springs and pins present
inside the shaft.
Yet another object of the present invention is to prevent high temperature rise in the breaker.

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
There is provided an improved rotor assembly for a moulded case circuit breaker.
According to one embodiment of the present invention, there is provided an improved rotor assembly for a moulded case circuit breaker, said assembly comprising atleast one contact arm (2) anchored at the centre of said assembly; atleast one cover means (3) enclosing said rotor assembly; atleast one slot (12) adapted to block circular motion of said cover means; a plurality of spring means placed in spring holders (5) for providing contact pressure, said holder supported by a pin; atleast one hole (9) enabling the passage of a through pin for coupling; atleast one oblong slot (21) adapted to provide movement of a center pin and a moving contact thereby compensating for erosion.
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 new MCCB contact system in ON condition. It shows fixed contact, rotor assembly, arc quenching chamber, vent and fixed contact etc.
Fig 2 illustrates the repelled position of circuit breaker.
Fig 3 illustrates the improved rotor assembly in accordance with the present invention.
Fig 4 illustrates another view of rotor assembly.

Fig 5 illustrates the rotor cover design.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Accordingly in the present invention, Rotor construction enables the design of double break arrangement that helps in the better make & break under normal and abnormal conditions involving very high over-currents. The Switching device should interrupt the over current arising due to abnormal conditions in the network, as rapidly as possible to minimize damage caused by thermal and mechanical stresses to the equipment installed downstream.
The rotor or shaft of the molded case circuit breaker has to be robust as high electro dynamic repulsive forces are generated between the stationary and moving contacts in the over current conditions. The rotor should have provisions for providing contact pressure so as to provide the intended repulsion threshold as well as to keep the temperature rise within allowable limit set by the relevant product standards under normal working condition. The moving contact is rotated by a certain angle or distance which is termed as over-travel for attaining the contact pressure. The springs that provide the contact pressure should not be exposed to the arcing, a phenomenon of electrical breakdown of gases which enables the passage of current during contact separation, to prevent the drop in spring force and ensure contact pressure.
During the separation of contacts due to repulsion, very high energy is released due to arcing which results in the erosion of the buttons on both moving contact as well as fixed contact. Rotor should have the provisions for compensating for the erosion so as to maintain the contact
pressure even after the erosion of buttons.
The present invention describes a robust rotor construction to provide double break, ensure contact pressure under normal and abnormal working conditions and enhance current breaking.

Fig 1 shows the new MCCB contact system in ON condition. The current conduction happens
through the fixed contact onto the moving contact and again to the second fixed contact.
The compression spring arranged between the holders provide the contact force required to
maintain the pressure between moving and fixed contacts to desired levels.
The contacts are designed (as in most of present MCCBs) in such a way that during short circuit
conditions, an electromagnetic force acts between the moving contact and the fixed contacts.
This force rotates the moving contact and brings it to repelled position as shown in Fig.2
While the moving contact moves to the repelled position, arcing happens as a result of which arc products and hot gases are produced. The moving contact cover provides insulation for moving contact from it. The rotor cover isolates the spring chamber from the arcing zone and the moving contact cover is designed to aid it in the isolation of the spring chamber.
Referring to Fig.3, a drive shaft 1, which carries a minimum of one contact arm 2, alternately called a moving member or moving contact, is shown which forms the rotary actuating structure. The rotor cover 3 gives the rotor a closed assembly. The springs that provide the contact pressure are assembled in the spring holders 5. The moving contact 2 is anchored at centre of the driveshaft. The location of the contact arm is secured through insertion of the central anchor pin 7 through the hole 6 on the moving contact aligned with the centre of the drive shaft thereby allowing the contact arm 2 freedom of rotation within a predetermined locus about the said central anchor pin 7.
Referring to Fig.4 Rotor 1 construction includes a separation wall 4 to isolate the springs from the slot 8 where moving contact 2 rotates and is visible to arcing to seclude it from hot gases and arc products, a hole 9 which gives the provision of coupling with the adjacent poles using a through pin., slots 10 which is used for attaching the rotor cover to the rotor via click fit or similar joints in order to give rotor an enclosed construction, slots 11 to engage the click fit and slots 12 to couple the rotor with the cover to prevent the circular motion of cover with respect to the rotor.

The moving contact 2 consists of two buttons 12 which makes contact with the respective fixed contact buttons. The holes 14 accommodate the pins to support the spring holders 5. An opening is necessary in the rotor to enable the connection of moving contact with the springs. The moving contact cover 13 ensures the insulation of spring chamber by closing the opening in the
rotor.
Referring to Fig.5, Rotor cover design consists of hole 15 to enable the passage of through pin for coupling of rotors. The projection 14 is given to accommodate the oblong slot 21 that enables the movement of center pin and thereby the movement of moving contact for compensating for erosion. The circular dip 19 avoids the interference of spring pin in the rotor with the rotor cover. Click fit 21 is provided to engage the rotor cover to the rotor in order to make the rotor a closed assembly. The projection 20 prevents the circular movement of rotor cover with respect to rotor.
ADVANTAGES:
1. Robust design
2. Isolated spring chamber
3. Moving contact cover that ensures isolation of spring chamber
4. Cover attached to rotor to ensure robustness.
5. Erosion compensation slot on rotor cover
6. Over travel indication on rotor cover to ensure contact pressure
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 rotor assembly for a moulded case circuit breaker, said assembly
comprising:
atleast one contact arm (2) anchored at the centre of said assembly;
atleast one cover means (3) enclosing said rotor assembly;
atleast one slot (12) adapted to block circular motion of said cover means;
a plurality of spring means placed in spring holders (5) for providing contact pressure,
said holder supported by a pin;
atleast one hole (9) enabling the passage of a through pin for coupling;
atleast one oblong slot (21) adapted to provide movement of a center pin and a moving contact thereby compensating for erosion.
2. Assembly as claimed in claim 1 wherein said contact arm secured by inserting a central anchor pin (7) through a hole (6) on a moving contact aligned with the centre of said assembly thereby allowing said contact arm (2) to rotate about said anchor pin (7).
3. Assembly as claimed in claim 1 further comprising a separation wall (4) isolating said spring means from said slot (8).
4. Assembly as claimed in claim 1 further comprising a projection (20) adapted to prevent circular movement of said rotor cover with respect to said rotor.

5. Assembly as claimed in claim 1 further comprising a circular dip (19) adapted to prevent interference of said spring pin with said rotor cover.
6. Assembly as claimed in claim 1 wherein said cover means isolating said spring chamber from the arcing zone.
7. Assembly as claimed in claim 1 further comprising an opening for enabling connection of said moving contact with said spring means.
8. Assembly as claimed in claim 1 further comprising a hole (9) facilitating coupling with the adjacent poles using a through pin.
9. An improved rotor assembly for a moulded case circuit breaker as herein described and illustrated with respect to accompanying drawings.