FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - ENCLOSED SHAFT ARRANGEMENT FOR CIRCUIT BREAKER TO PREVENT SHORT CIRCUIT FAILURE
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
The present invention relates to moulded case circuit breakers. More particularly, the present invention relates to an enclosed shaft arrangement for circuit breaker to prevent short circuit failure, mainly moulded case circuit breakers.
BACKGROUND AND THE PRIOR ART
Currently, all moulded case circuit breaker have a shaft/drive shaft which rotates and switches the electrical circuit.
The prior art for shaft construction uses an open shaft construction or partially closed construction.
US 5310971 disclose the contact bridge of a molded case circuit breaker 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 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 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. It is illustrated in fig 1.
US 6870112 discloses 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. It is illustrated in fig 2.
US 6262642 discloses 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. It is illustrated in fig 3.
US 6965292 discloses 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 securing within apertures within first and second cassette half pieces. It is illustrated in fig 4.
During short circuit, the moving contact in the shaft starts rotating due to the repulsion forces produced by electromagnetic interaction during short circuit. Simultaneously, arc is produced between the fixed and moving contacts. For rotation of moving contact with respect to the shaft, there has to be an opening in the shaft with slot length depending on degree of rotation of moving contact.
The drawbacks of the above mentioned prior art is that:
• 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.

• 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.
• An open shaft construction increases the chance of standing arc because of lesser insulation between the contacts.
Thus there is need to provide with an enclosed shaft construction where a movable shaft cover encloses the moving contact. The present invention therefore provides a movable shaft cover rotating along with the moving contact during repulsion on short circuit.
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 enclosed shaft arrangement for a moulded case circuit breaker where a movable shaft cover encloses the moving contact.
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 enclosed shaft arrangement for a circuit breaker to prevent short circuit failure.
According to one embodiment of the present invention, there is provided An enclosed shaft arrangement for a circuit breaker to prevent short circuit failure, said arrangement comprising a shaft cover enclosing moving contacts and rotating along with said moving contacts on repulsion during short circuit, said cover substantially cylindrical having a shaft cover flap to facilitate said rotation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawing:
Fig 1 illustrates the prior art shaft construction followed by MCCB manufacturers worldwide.
Fig 2 illustrates the prior art shaft construction followed by MCCB manufacturers worldwide.
Fig 3 illustrates the prior art shaft construction followed by MCCB manufacturers worldwide.
Fig 4 illustrates the prior art shaft construction followed by MCCB manufacturers worldwide.
Fig 5 illustrates the enclosed shaft as a standalone entity.
Fig 6 illustrates the shaft cover used for enclosing the shaft.
Fig 7 illustrates the inside components of the shaft.

Fig 8 illustrates the MCCB with enclosed shaft.
Fig 9 illustrates the moving contact in repelled condition and the position of shaft cover in that condition.
Fig 10 illustrates the open shaft construction.
DETAILED 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.
Reference is first invited to Fig 1-4 where the prior art in the present field of invention is shown.
Fig. 5 shows moving contact, MCCB shaft and shaft cover.
Fig. 6 shows shaft cover, slot for moving contact and shaft cover flap.
Fig. 7 shows spring arrangement inside the cover.
Fig. 8 shows Point A and B.
Fig. 9 shows Point C and D. it shows closed shaft construction and arc extinguishing region.
Fig. 10 shows open shaft construction.

The invented arrangement is thus an enclosed shaft arrangement for a circuit breaker to prevent short circuit failure.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention during repulsion, the moving contact rotates with respect to the shaft. During this rotation, moving contact touches the shaft cover flap shown in Fig 6, and thus rotates the shaft cover along with it.
When the moving contact opens fully during repulsion as show in Fig 9, the shaft cover completely encloses the shaft.
If shaft cover is not present as shown in Fig 10, the shaft leaves an open slot after the moving contact has repelled.
The construction of the shaft cover is in form of hollow cylinder with slots for insertion of the moving contact. The shaft cover is moulded out of flame retardant thermoplastic materials. Different components used and references assigned are as under:
Moving contact (1)
MCCB shaft (2)
Shaft cover (3)
Slot for moving contact (4)
Shaft cover flap (5)
Spring arrangement (6)
Point B (7)
Point A (8)
Point C (9)
Point D (10)
Closed shaft construction (11)
Arc extinguishing region (12)
Open shaft construction (13)

Advantages
• It protects the inside components like springs and pins from hot gases and arc products during short circuit arcing.
• It helps in developing higher pressure behind the arc due to closed region, thus driving the arc away from the shaft into the arc extinguishing region as shown in Fig 9.
• It acts as an insulation barrier between live parts during short circuit and prevents standing arc, thus helping the breaker in effective arc quenching. In Fig 8, there is a possibility of arcing between Points A and B during short circuit. The shaft cover stands as an insulation medium between the two points and hence nullifies the possibility of this arcing.
• When the moving repels open as shown in Fig 9, there is a chance of breakdown of air between Point C and Point D, which can lead to standing arc and hence short circuit failure. The shaft cover flap shown in Fig 6 acts as an insulation barrier between these two points and hence prevents failure.
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 enclosed shaft arrangement for a circuit breaker to prevent short circuit
failure, said arrangement comprising:
a shaft cover (3) enclosing moving contacts and rotating along with said moving contacts on repulsion during short circuit, said cover substantially cylindrical having a shaft cover flap (5) to facilitate said rotation.
2. Arrangement as claimed in claim 1 wherein said shaft cover (3) completely enclosing a shaft on opening fully of said moving contact during said repulsion.
3. Arrangement as claimed in claim 1 wherein said shaft cover (3) is substantially movable.
4. Arrangement as claimed in claim 1 wherein said shaft cover (3) is substantially hollow.
5. Arrangement as claimed in claim 1 further comprising a plurality of slots (4) for insertion of moving contacts.
6. Arrangement as claimed in claim 1 wherein said shaft cover flap (5) providing insulation barrier thereby preventing arcing.
7. Arrangement as claimed in claim 1 wherein said breaker is substantially a moulded case circuit breaker.

8. An enclosed shaft arrangement for a circuit breaker to prevent short circuit
failure as herein described and illustrated with reference to the accompanying drawings.