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 POSITION INDICATION IN DRAW OUT TYPE
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 circuit breakers. More particularly, the present invention relates to an improved draw out type circuit breaker arrangement.
BACKGROUND AND THE PRIOR ART
An electrical circuit breaker may be defined as a unit designed to carry, make & break current and protect the equipments connected in the electrical circuit from abnormal conditions like overload, under-voltage or short circuit etc. A circuit breaker is commonly used as an electrical switching device.
There are two popular versions of circuit breakers namely, Fixed and Draw-Out Type. In the Draw out type, the breaker can be removed without dismantling the terminals, in order to facilitate maintenance and secure stability. Unlike fixed breakers, draw out breakers are housed inside the cradle. They can be racked-in & out inside the cradle. This patent refers to the provision of locking the breaker with respect to cradle at distinct positions followed by acknowledgement from the user for further Racking operation.
In US 2010/0263995 by Jian Sheng Bi et al, a position locking arrangement is made using a screw rod, a catching plate, a positioning plate, a locking plate, and a push rod. The screw rod has key ways. The catching plate has a hole and a protrusion that can be inserted into the keyways. Positioning notches for limiting the positions are framed on the surface of the positioning plate, and corresponding protruding platforms are disposed on the bottom surface. One end of the locking plate bears against the bottom surface of the positioning plate, and the other end is locked to or

unlocked from an outward protruding platform of the catching plate. One end of the push rod passes through the catching plate hole, and has an inclined surface. When the push rod is pushed, the inclined surface makes the catching plate leave the key ways.
CN1402397A discloses a locking arrangement for a draw-out circuit breaker, which provides a arrangement capable of locking under the three different states of off, test, and on. In the patent, this function is achieved through a cooperation of a plurality of members, that is, a fork shaft and an unlocking shaft, a locking sheet and a roller thereon, a slot and a roller slot on a square shaft, and a locking trench on a catching plate.
In patents similar to the above, series of links and transmission members have been used to achieve distinct position locking, making it more complex. Also in such similar patents, the locking is done at the last member of whole racking linkage system. So there is always a chance of force losses in complex mechanical chain of linkages. There may be a lag between the actual breaker position and the intended position of the breaker due to tolerances. Hence, the intended position of the additional member may not correspond to that of the switchgear. This difference may lead to a false intimation of the actual position of the switchgear. This may hinder the safety of the operation. Also, it is not possible to defeat the locking mechanism throughout the racking operation, in case the user needs it.
In a Draw out type of circuit breaker, positions of breaker with respect to cradle are normally defined as 'Disconnected/ Isolated', 'Test' & 'Connected/ Service'. In a Draw out type of breaker, the breaker can be racked in from 'Disconnected' position to 'Test position' and then to 'Connected' position and racked out in the reverse order.

When breaker is completely racked in i.e. in 'Connected' position, breaker terminals are in contact with cradle terminals through jaws. In this condition, both Power (main) circuit & control circuit are connected and the breakers can be switched ON. When the breaker is completely racked out i.e. in 'Disconnected' position, both main circuit and control circuit are disconnected. In the 'Test' position, Power (main) circuit is not connected but control circuit is connected.
In a Draw out type of circuit breaker, the breaker is supported on the rail assembly or any equivalent draw-out assembly, which is an integral part of the Cradle assembly. The Cradle assembly consists of the base plate, Racking assembly, side plates for guiding breaker and rail assembly. Racking operation is accomplished by the racking assembly mounted on the base plate. The rotation of the racking handle causes the driving link to rotate which, in turn moves the rack inside or outside depending upon whether it is a rack-in or rack-out operation. When the racking handle is rotated in the clockwise direction, the breaker is racked in (Disconnected - Test - Connected) & on the other hand, when rotated in counter clock wise direction, the breaker is racked-out (Connected - Test - Disconnected).
While performing rack-in operation, the position of the breaker in the cradle is indicated by the position Indicator. There is a possibility that, the position indication gets neglected by the user, if there is no positive locking. Hence user will be unaware of the positions and their related safety instructions. Also, in case the breaker is not racked in sufficiently and it is switched ON (closing the power circuit), due to insufficient overlap between the breaker terminals and the cradle jaws, the contact area might be less. This can lead to localized overheating at the contact terminals & may result into flashovers.

When user performs racking operation, distinct positions (Connected / Test / Disconnected) cannot be accurately determined, by observing the continuous position indication through the position Indicator. For instance, if the user wants to rack in the breaker from Disconnected position to Test position, he has to constantly observe the continuous position indication. Even after careful observation at the position indication, due to the parallax error, there is strong possibility of mismatch between actual distinct position and position seen on the indication. It gives rise to a requirement of distinct position indication which can eliminate such errors.
Absence of acknowledgement or locking arrangement in distinct positions could result in over racking of breaker, which can further damage the racking arrangement. Hence it is needed that, when breaker reaches to the Connected / Test /Disconnected position, it should get locked. Acknowledgement is necessary for defeating the locking mechanism. Until then, further racking will should not be possible.
The additional arrangement for locking and latching should not affect the functionality of existing Racking arrangement in switchgear and must have minimal lag.
Thus, it becomes very important to have a locking arrangement at distinct positions with no lag, which can prevent further Rack-in/ Rack-out operations, unless acknowledged by the user. Such an arrangement needs to be very economical; also it should adhere to the space limitations of the breaker. The disclosed invention thus provides indication in all the distinct positions, and ensures breaker locking in these positions with its physical acknowledgement.

OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known prior art.
Another object of the present invention is to provide a Locking arrangement to arrest the breaker in three distinct positions namely 'Disconnected', 'Test' & 'Connected', both in Rack-in and Rack-out operations,
Yet another object of the present invention is to provide a mechanism to defeat the locking system during complete racking operation, such that it doesn't affect any other functionality.
Yet another object of the present invention is that after being acknowledged by the customer, said locking arrangement should reset automatically before breaker reaches the next distinct position.
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
According to one embodiment of the present invention, there is provided an improved draw out type circuit breaker arrangement wherein said arrangement comprising a locking arrangement preventing a driving link (racking screw) from rotating, said arrangement comprising a nut connected to said driving link7 a guiding link mounted on a racking arrangement adapted to provide minimum lag during locking at distinct positions. Said locking arrangement is spring loaded and having a substantially

polygonal profile for locking said driving link and an arm with a protrusion sliding along said guiding link. A latching arrangement comprising a latching link supported on said locking arrangement guided by surface of a guiding link adapted to prevent said locking arrangement from moving towards said driving link.
Other embodiment of the present invention provides an arrangement wherein a guiding link further comprising a slot through which arm of locking arrangement travel, a triplet of slots corresponding to three distinct positions and a bottom slot to release said latching link in between any two distinct positions.
Yet other embodiment of the present invention provides an arrangement wherein arm adapted to align with said triplet of slots to provide for three distinct positions namely, connected, test and disconnected positions.
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 Draw out Breaker and Cradle Assembly.
Fig 2 illustrates Cradle assembly. It includes the side plate (11), rails (12) on which the breaker is mounted. The rack -pinion (17-18) arrangement guides the shaft (13), to which a cam (14) is mounted, which in turn causes the rail to move.

Fig 3 illustrates a Racking mechanism mounted on the plate. When driving link (16) is rotated by a racking handle, it drives the rack (17). Guiding link (19) is attached to the rack (17).
Fig 4 illustrates spring loaded locking arrangement (21) shows the polygonal locking profile (23) used to Jock the driving link (16). Latching link (25) is a rotary part driven by a torsion spring. It is used to latch the locking arrangement. Arm (24) travels inside the Guiding link (19) where link (15) is used as user interface link.
Fig 5 illustrates Guiding link (19) is provided with a slot (29), through which one arm (24) of the locking arrangement travels. Three distinct slots (26s 27, 28) corresponding to three distinct positions are provided inside the guiding link (19). Bottom slots (31) are provided to release the latching link (25) in between any two distinct positions.
Fig 6 illustrates a Cross sectional view of the locking arrangement (21) & nut (22) on the driving link. Latching link (25) latches the locking arrangement (21) when it is pulled back by the user.
Fig 7 illustrates the driving link (16) locked by the locking arrangement (21).
Fig 8 illustrates the locking arrangement that has been pulled back by the user via the user interface (15) & is now latched.

Fig 9 illustrates the locking arrangement is in the intermediate position, where its arm (24) rests against guiding link (19).
DETAILED DESCRIPTION OF THE INVENTION
According to the embodiment of the present invention, the locking and latching arrangement of a circuit breaker are described below:
• Locking arrangement: This arrangement prevents the driving link (racking
screw (16)) from rotating. It consists of a locking element like nut (22) which is connected to the driving link (16) and a spring loaded locking arrangement (21) shown in Fig 4, and a guiding link (19), which is positively mounted on racking arrangement, to have minimum possible lag during locking at distinct positions. The locking arrangement (21), consists of a polygonal profile for locking the nut (23), an arm (24) with a protrusion which will slide along the guiding link (19) shown in Fig 5 and a latching link (25). The user interface (15) is attached to the locking arrangement (21).
• Latching arrangement: The latching link (25), which is supported on the
locking arrangement (21), is also a spring loaded member. Its profile is such that it can be guided by the surface of guiding link (19). When it is taken to the other side of the guiding link (19), against the spring force, it rests against the guiding link (19) & prevents the locking arrangement (21) from moving towards the driving link (16).
The spring loaded locking arrangement which slides on the base of the driving link support, locks the driving link (16) by arresting the nut connected to it, in three distinct positions of the breaker. By this locking of the breaker movement at three distinct positions can be achieved.

Further racking operation (Either Rack-in or Rack-out) is possible only when acknowledged by the user, i.e. when the locking arrangement is pulled back by user to its original position. Once acknowledged by the user and till the next distinct position is reached, locking arrangement should not hinder the breaker movement.
The disclosed invention consists of rack (17) and guiding link (19) actuated mechanism which locks the breaker in three distinct positions namely 'Disconnected', 'Test' & 'Connected' positions. The invention includes a spring loaded locking arrangement (Fig 4) and a latching arrangement (Fig 5) as new parts in the switchgear.
On arrival of distinct position, the locking arrangement (21) slides over the base & locks the driving link (16). Further racking is possible only upon acknowledgement from the user, for which it is required to defeat the locking by pulling the locking arrangement (21) back to. Now, it gets latched and the driving link (16) is now free to operate rotate. The latching action is achieved by latching link (25), which rests against the guiding link (19). The unlatching action takes place in between any two distinct positions via the two slots provided at the bottom of link (31). Once unlatched, the protrusion on the arm (24) of locking arrangement (21) rests against the guiding link (19). When this protrusion gets aligned with any of the slots (26, 27, 28), corresponding to the distinct positions, it is free to slide due to spring action & hence locks the nut profile (22) again in the subsequent distinct position. As the slots (26, 27, 28) are derived from switchgear travel and guiding link (19) is attached to the rack (17), there is minimal «e lag between actual distinct position & its indication.

ADVANTAGES;
1. The disclosed invention resolves the problem of lag between the actual breaker position and the intended position of the breaker by introducing a spring loaded locking member, by which, racking is stopped exactly in each of the three distinct positions. Since it takes reference directly from the rack, it gives an accurate indication when each of the three positions namely Connected, Test & Disconnected is reached. Since the driving link is locked, the locking is achieved at the very first member of complete mechanical chain of linkages conforming minimal force losses.
2. When the breaker gets locked in the distinct positions, without acknowledgement, which is used to unlock the driving link, further racking is not possible. This solves problem of over racking as the user will know when the desired position is reached. There is no need to hold the locking arrangement when it is acknowledged. When locking arrangement is pulled back, it gets latched on its own and doesn't need to be held by the user till further racking is started.
3. There is no need for the constant observation of the existing visual continuous indication, acknowledgement is mandatory for further racking operation.
4. It gives positive locking at the distinct positions irrespective of the sequence of Racking (i.e. either Rack-in or Rack-out operation) For e.g. If the user does the rack-in operation, halfway between two distinct positions, and then decides to rack-out the breaker, the locking action will still be achieved, as it is not dependant on the sequence of racking.

5. The system has single degree of freedom. Also to avoid overstressing of components during over-racking operation, component arrangement is done in such a manner to have uniform distribution of load. So, bending stresses are not developed on single component.
6. The invention ensures proper contact surface overlap between the cradle jaws and the breaker terminals in connected position.
7. The locking and latching arrangement are a combination of links, which take reference of the Racking arrangement of the switchgear, without actually affecting the functionality of Racking.
8. In case the user doesn't wish to use Distinct Position Locking (for a few operations), this arrangement can be defeated, by holding back the user interface link throughout the racking operation.
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. A draw out type circuit breaker arrangement wherein said arrangement
comprising:
a locking arrangement for arresting driving link (16); said arrangement (21) comprising element to be locked (a polygonal profile nut 22) connected to said driving link (16); a guiding link (19) is mounted on the said racking arrangement so that there is minimum lag during locking at distinct positions; said locking arrangement being flexibly loaded and having a substantially polygonal profile (23) for locking said driving link and a means to hold the arrangement away from the driving link, here an arm (24) with a protrusion; and
a latching arrangement comprising a latching link supported on said locking arrangement (21), said latching arrangement guided by surface of said guiding link adapted to prevent said locking arrangement from moving towards said driving link.
2. An arrangement as claimed in claim 1 wherein said locking arrangement is adapted for pull back using a user interface link.
3. Arrangement as claimed in claim 1 wherein said latching link acting as a latch and driven using a flexible means, like spring.
4. Arrangement as claimed in claim 1 wherein said guiding link having a slot through which said arm of said locking arrangement travels, having at least

one slot corresponding to the distinct positions and a means to unlatch said latching link in between any two distinct positions.
5. Arrangement as claimed in claim 1 and 4 wherein said arm adapted to align with said number of slots to provide for the distinct positions namely, connected, test and disconnected positions.
6. A draw out type circuit breaker arrangement as herein described and illustrated with reference to accompanying drawings.