FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POSITION LOCKING MECHANISM FOR DRAW-OUT TYPE CIRCUIT BREAKERS;
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.

FIELD OF THE INVENTION
The present invention relates to circuit breakers, and more particularly to position locking mechanisms for draw-out type circuit breakers.
BACKGROUND OF THE INVENTION
A draw-out circuit breaker has a breaker (withdraw-able portion) mounted inside a cradle (fixed portion). The circuit breaker can take three positions within the cradle - (i) a disconnected position, wherein main contacts as well as control circuit contacts are disengaged from supply; (ii) a test position, wherein the main contacts are disengaged and control circuit contacts are engaged; (iii) a connected position, wherein the main contacts as well as control circuit contacts are connected to supply. In addition to these positions, there is a maintenance position from which the breaker can be lifted from the cradle for maintenance. It is important for the breaker to lock in an intended position and indicate the correct position.
In a conventional circuit breaker, the circuit breaker position is locked by means of halting the motion of the rack depending upon the motion it has traversed. This creates a possibility of unnecessary loads introduced on a racking screw and the rack. These parts may experience damage, and this is detrimental to the operation of the circuit breaker
One prior art, United States Patent 2010/0263995 by Jian Sheng Bi et al, discloses a position locking device 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 farmed 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,
Another prior art, Chinese Patent CN1402397A discloses a locking device for a draw-out circuit breaker, which provides a device capable of locking under the three different states of off, test, and on. 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.
These prior arts rely on the position of an additional member added to the racking system. 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 circuit breaker. This difference may lead to a false intimation of the actual position of the circuit breaker. This may hinder the safety of the operation and may lead to an inaccurate intimation of the breaker position.
Also, while racking the breaker into a cradle, the position of the breaker needs to be indicated for safety purposes. This is achieved using a position indicator. The position indicator may be neglected by the user, or user may be unaware of the positions and

their related safety instructions. The safety of the operation may thus be jeopardized in case of an unintended motion of the circuit breaker within the drawing space. Further, conventional circuit breaker relies on visual or audio indication of the position of the circuit breaker within the draw-out device. This indication may not be comprehensible at times due to the working environment that the circuit breaker is used in, for example in loud and dusty working environment. In such a condition, the circuit breaker position is not easily intimated to the user.
In view of the above, there is a need for a locking mechanism which eliminates possibility of a mismatch in intended locking position and actual locking position.
SUMMARY OF THE INVENTION
Accordingly, the present invention in one aspect provides a position locking mechanism for a draw-out type circuit breaker, the position locking mechanism comprising: a locking member, the locking member comprising an engagement plate, the engagement plate comprising a fork shaped engagement slot, the engagement slot engages with a racking screw of a racking mechanism of the circuit breaker, the engagement slot capable of moving between a locked position and an unlocked position depending upon the racking screw orientation; and means for restraining the engagement plate; and a receiving plate, the receiving plate having a plurality of receiving slots, the receiving slots capable of engaging with a position indicator of the circuit breaker.

BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may
be illustrated in the accompanying figures. These figures are intended to be illustrative,
not limiting. Although the invention is generally described in the context of these
embodiments, it should be understood that it is not intended to limit the scope of the
invention to these particular embodiments.
Figure 1 shows a position locking mechanism for a draw-out type circuit breaker in
accordance with an embodiment of the invention, where
Figure 1A shows a locking member adapted to a racking mechanism of the circuit breaker in accordance with an embodiment of the invention; and Figure 1B shows the locking member in greater detail in accordance with an embodiment of the invention.
Figure 2 shows the position locking mechanism in detail in accordance with an
embodiment of the invention, where
Figure 2A shows position locking mechanism during a racking operation; and
Figure 2B shows position locking mechanism in a locked position during the racking
operation.
Figure 3 shows position of a handle of the position locking mechanism in accordance
with an embodiment of the invention, where
Figure 3A shows the handle in a locked position; and Figure 3B shows the handle in an unlocked position.

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the present invention provide a position locking mechanism for a draw-out type circuit breaker, the position locking mechanism comprising: a locking member, the locking member comprising an engagement plate, the engagement plate comprising a fork shaped engagement slot, the engagement slot engages with a racking screw of a racking mechanism of the circuit breaker, the engagement slot capable of moving between a locked position and an unlocked position depending upon the racking screw orientation; and means for restraining the engagement plate; and a receiving plate, the receiving plate having a plurality of receiving slots, the receiving slots capable of engaging with a position indicator of the circuit breaker.
The position locking mechanism is capable of locking circuit breaker in three positions - a disconnected position, a test position and a connected position when a circuit breaker is 'racked in' or 'racked out' during a racking operation.
Figure 1 shows a position locking mechanism 100 for a draw-out type circuit breaker in accordance with an embodiment of the invention. Position locking mechanism 100 comprises a locking member 102. Figure 1B shows locking member 102 in greater detail in accordance with an embodiment of the invention. Locking member 102 includes an engagement plate 104, and a receiving plate 106.
Engagement plate 104 includes a fork shaped engagement slot 108 and means for restraining engagement plate 104. Engagement plate 104 is capable of moving linearly between an unlocked position and a locked position (as shown in figure 2A and 2B). Means for restraining engagement plate 104 includes a spring receiving hole 110

on engagement plate 104 and a spring 112 on the circuit breaker. Spring 112 is a tensile spring. Spring 112 at a first end engages with a casing of the circuit breaker and at a second end engages with engagement plate 104 through spring receiving hole 110, restraining movement of engagement plate 104 at all times. Receiving plate 106 of locking member 102 as shown in figure 1B is perpendicular to engagement plate 104 and has a plurality of receiving slots 114.
In an embodiment of the invention, locking member 102 includes a handle 116. Handle 116 is connected to engagement plate 104, and handle 116 is capable of being used to move locking member 102 between the locked position and the unlocked position (as shown in figure 3A and 3B).
In an embodiment of the invention, when locking member 102 is adapted to a racking mechanism of the circuit breaker as shown in figure 1A, engagement plate 104 engages with a racking screw 118, receiving plate 106 engages with a position indicator 120 and handle 116 protrudes out of the circuit breaker through a first slot 122 and is accessible from outside the circuit breaker.
In an embodiment of the invention, engagement slot 108 of engagement plate 104 engages with a nut 124 on racking screw 118. In an embodiment of the invention, nut 124 is a hex nut. Engagement slot 108 engages with nut 124 on racking screw 118. In this regard engagement slot 108 has a predetermined width proportional to distance between opposite sides of nut 124 such that when nut 124 engages with engagement slot 108 with its opposite sides between engagement slot 108, movement of nut 124 is restricted.

In an embodiment of the invention one of receiving slots 114 of receiving plate 106 are capable of engaging with position indicator 120. Position indicator 120 has a first end and a second end and is mounted on a pivot 126 between the first end and the second end. Pivot 126 enables position indicator 120 to have a pivotal movement along a vertical axis. Position indicator 120 has a pip 128 near the first end which engages with one of receiving slots 114. At the second end position indicator 120 engages with the racking mechanism of the circuit breaker. Also at the first end, position indicator 120 protrudes out of the circuit breaker through a second slot 130. Advantageously, position of position indicator 120 outside circuit breaker gives physical indication of position of circuit breaker.
In an embodiment of the invention, during the racking operation, racking screw 118 is rotated. Rotation of racking screw 118 rotates nut 124, and locking member 102 moves linearly depending upon the movement of racking screw 118 as shown in figure 2A and 2B, and pre-determined locking position is achieved when nut 124 of racking screw 118 is coupled to engagement slot 108 as shown in figure 2B. As shown in figure 2B, nut 124 cannot be rotated further and racking of the circuit breaker is halted thereby locking position of the circuit breaker. Advantageously, motion of racking screw 118 is locked and thus no unnecessary load is transferred to the circuit breaker and possibility of damage is minimized considerably. Also, during the racking operation, pip 128 at first end of position indicator 120 engages with one of receiving slots 114 depending on position of circuit breaker, and remains engaged till next racking operation.
Further, during the racking operation as locking member 102 moves, handle 116 of locking member 102 also moves from an unlocked condition to a locked position as shown in figure 3A and 3B respectively. In this regard, to further rack the circuit breaker,

handle 116 can be moved from locked position shown in figure 3B to unlocked position shown in figure 3A, wherein handle 116 is pulled, the movement of handle 116 defeats spring force acting on locking member 102 and engagement slot 108 disengages with nut 124, and one of receiving slot 114 disengages with pip 128 enabling locking member 102 to be moved to a position to continue the racking operation of the circuit breaker till next locked position of handle 116.
In an embodiment of the invention, position locking mechanism 100 provides physical indication of positions of circuit breaker. During the racking operation, pip 128 at first end of position indicator 120 engages with one of receiving slots 114 depending upon position of circuit breaker, and position of position indicator 120 protruding out of circuit breaker will be relative to engagement of position indicator 120 with one of receiving slots 114. Position indicator 120 protruding out of circuit breaker as shown in figure 3A and 3B thus provides a physical indication of position of circuit breaker.
Advantageously the present invention provides a position locking mechanism which eliminates the possibility of a mismatch in an intended locking position of the circuit breaker and also provides physical indication of physical position of the circuit breaker.
While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

We Claim :
1. A position locking mechanism for a draw-out type circuit breaker, the position locking
mechanism comprising a locking member, the locking member comprising:
a) an engagement plate, the engagement plate comprising:
i) a fork shaped engagement slot, the engagement slot engages with a racking screw of a racking mechanism of the circuit breaker, the engagement slot capable of moving between a locked position and an unlocked position depending upon the racking screw orientation; and
ii) means for restraining the engagement plate; and
b) a receiving plate, the receiving plate having a plurality of receiving slots, the
receiving slots capable of engaging with a position indicator of the circuit breaker,
2. The position locking mechanism as claimed in claim 1, wherein the engagement slot engages with a nut on the racking screw of the racking mechanism.
3. The position locking mechanism as claimed in claim 2, wherein the nut is a hex nut.
4. The position locking mechanism as claimed in claim 2, wherein the engagement slot has a predetermined width proportional to distance between opposite sides of the nut.
5. The position locking mechanism as claimed in claim 1, wherein the engagement slot is capable of moving linearly between the locked position and the unlocked position.
6. The position locking mechanism as claimed in claim 1, wherein at least one of the receiving slots engages with the position indicator using a pip.
7. The position locking mechanism as claimed in claim 1, wherein the position indicator protrudes out of the circuit breaker through a second slot to indicate position of the circuit breaker.
8. The position locking mechanism as claimed in claim 1, wherein the means for restraining comprises a spring receiving hole on the engagement plate and a spring on the circuit

breaker, the spring engages with the spring receiving hole.
9. The position locking mechanism as claimed in claim 1, wherein the locking member further comprises a handle connected to the engagement plate, the handle being used to move the locking member between the locked and unlocked position.