FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
An interlocking mechanism in a switchgear
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra. India, an Indian Company
INVENTORS
Shukla Raghunath, Gosavi Gopal and Kulkarni Shantanu of Crompton Greaves Ltd , S2 Division, Switchgear Complex, Ambad, Nashik, Maharashtra, India, all Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an interlocking mechanism in a Switchgear panel.
BACKGROUND OF THE INVENTION
A switchgear is typically used in a power distribution system for protection against power line fault conditions, irregular loading conditions etc. In the event of a malfunctioning within the switchgear, the operator/maintenance personnel has to perform a series of checks within the switchgear before initiating diagnosing/repair of the Switchgear. For example, whenever there is a malfunctioning within the switchgear, the circuit breaker therein may be required to be removed from the service condition to test condition and removed/racked out of the switchgear panel for further inspection and/or repairs. Before removing out the circuit breaker from the switchgear panel, it is to be ensured that the circuit breaker is properly isolated and the earth switch within the panel is closed. With the increase in the voltage capacity of the switchgear, the gravity of the hazards significantly increases. In the conventional switchgear, the operator while operating on the switchgear for servicing of fault correction has to manually check the above described and other parameters within the switchgear panel before initiating any maintenance related activity. An error in inspecting any of the parameter can be life threatening and dangerous. Such is also laborious, time consuming and risky. It also requires skilled manpower. Therefore, there is a need to have an interlocking mechanism within the switchgear panel which ensures that all safety related functions are performed pre and post any maintenance related activity of circuit breaker within the switchgear panel.

DETAILED DESCRIPTION OF THE INVENTION
According to the invention, an interlocking mechanism in a switchgear enclosed in a switchgear panel having a front and rear door, the switchgear comprising a circuit breaker adapted to be racked in/out of the switchgear panel for toggling thereof between the test and service positions, the interlocking mechanism comprising a rotatabJe shaft held adjacently to the circuit breaker between the front and rear doors of the switchgear panel; a first and second door lock mechanisms being operable by rotation of the shaft for locking/unlocking the front and rear doors of the switchgear panel respectively; a transmission means connected to the shaft and an earth switch within the switchgear such that upon rotating the shaft for unlocking the interlocking mechanism, the earth switch being closed and upon rotating the shaft in reverse for locking the interlocking mechanism, the earth switch being opened; at least one stopper block mounted on the shaft corresponding to a pre-designated position in the switchgear panel such that upon rotation of the shaft for unlocking the interlocking mechanism, the stopper block being brought in front of the circuit breaker in test position for restricting racking in of the circuit breaker to the service position; upon reversing the rotation of the shaft for locking the interlocking mechanism, the stopper block being moved away from the circuit breaker in test position for allowing racking in of the circuit breaker to the service position; wherein the first and second door lock mechanisms, the transmission means and the stopper block being so synchronized that upon rotating the shaft for unlocking the interlocking mechanism: the front and rear door of the switchgear panel being unlocked for opening; the stopper block being brought in front of the circuit breaker in test position for restricting racking in of the circuit breaker to the service position;

and the earth switch within the switchgear panel being closed and upon rotating the shaft in reverse or further rotating the shaft for locking the interlocking mechanism: the front and rear door of the switchgear panel being locked; the stopper block being moved away from the circuit breaker in test position for allowing the racking in of the circuit breaker to the service position; and the earth switch within the switchgear panel being opened.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is an isometric view of a switchgear.
Fig 2 is an isometric view of a shaft of an interlocking mechanism in the switchgear.
Fig 3a and 3b depicts a first door lock mechanism of the interlocking mechanism in the switchgear in unlock/lock positions respectively for unlocking/locking the front door.
Fig 4a and 4b depict a stopper block arrangement on the shaft of the interlocking mechanism in the switchgear in unlock/lock positions respectively.
Fig 5a and 5b depicts a transmission mechanism of the interlocking mechanism in the switchgear in unlock/lock positions respectively.
Fig 6a and 6b depicts a second door lock mechanism of the interlocking mechanism in the switchgear in unlock/lock positions respectively.
Fig 1 is an isometric view of a switchgear. An interlocking mechanism according of a preferred embodiment is provided within the switchgear 1. A circuit breaker 3 and an earth switch 4 among other things are enclosed in a switchgear panel 5 having a front 6 and rear 7 doors. One of the sidewalls of the switchgear panel 5 is

shown transparent for clearly illustrating the interlocking mechanism with the switchgear panel 5. The circuit breaker 3 is adapted to be racked in and out of the switchgear panel 5, preferably through the front door 6. In the switchgear panel 5, the circuit breaker 3 can be toggled between the service and test positions. In the service position, the circuit breaker 3 is electrically connected to input power supply terminals (not shown). In the test position, the circuit breaker 3 is disconnected from these terminals. In the event of a fault in the circuit breaker 3 or for routine maintenance checks, the circuit breaker 3 is required to be racked out completely from the switchgear panel 5. To do this, the circuit breaker is first brought in the test position (isolated) from the service position by disconnecting it from the input power supply terminals in the switchgear. Such is usually done by pulling the circuit breaker towards the front door 6 to a pre-designated position 8 in the switchgear 1 by a racking mechanism (not shown) provided within the switchgear 1. Thereafter, the interlocking mechanism is unlocked. The construction, features and functioning of the interlocking mechanism is described in detail in the appended description. By way of unlocking the interlocking mechanism, the earth switch 4 (one end of which is connected to input power supply terminal and the other being electrically grounded) is closed, forward movement of the circuit breaker 3 beyond the pre-designated position 8 for connection thereof with the input power supply terminals restricted and the front 6 and rear 7 doors being allowed to be opened for racking out the circuit breaker 3 outside the switchgear panel 5. After the inspection/repairs, the circuit breaker 3 is racked in the switchgear panel 5 upto the pre-designated position 8 through the front door 6. Thereafter, the interlocking mechanism is locked. By locking the interlocking mechanism, the earth switch 4 is opened, forward movement of the circuit breaker 3

beyond the pre-designated position 8 for connection thereof with the input power supply terminals enabled and the front 6 and rear 7 doors locked.
The interlocking mechanism comprises of a shaft 9_, as shown in Fig 2. rotation of which results in unlocking/locking of the interlocking mechanism. The interlocking mechanism also comprises of a first and second door lock mechanism for unlocking/locking the front 6 and rear 7 doors respectively, a stopper block 10 and a transmission means for closing/opening the earth switch 4 whenever the shaft 9 is rotated. According to a preferred embodiment, the transmission means is a bevel gear mechanism (described in detail below), one gear 11 of which is mounted on the shaft 9 as shown in Fig 2. The shaft 9 is held rotatably between the front 6 and rear 7 doors of the switchgear panel 5 adjacent to the circuit breaker 3 parallel to one of the sidewalls 2 (shown transparent in Fig1). The first and second door lock mechanisms, stopper block 10 and transmission means are all explained in detail in the below appended description:
Fig 3a and 3b depicts a first door lock mechanism of the interlocking mechanism in a switchgear in unlock/lock positions for unlocking/locking the front door 6 according to a preferred embodiment. The first door lock mechanism comprises of a handle 12 provided at the front door end 9a of the shaft 9 and a slot 13 on the front door 6 correspondingly to the handle 12 such that when the handle 12 and the slot 13 are aligned by rotating the shaft 9, as shown in Fig 3a, the front door 6 can be moved away from the switchgear panel 5 beyond the handle 12 through the slot 13 thereby unlocking the front door 6. Similarly, when the handle 12 and the slot 13 are misaligned by reversing the rotation of the shaft 9, as shown in Fig 3b, the front door 6 is obstructed to move beyond the handle 12 thereby locking the front door 6. The

handle 12 may either be fixed rigidly or provided integrated to the front door end 9a of the shaft 9 as shown in Fig 2.
As shown in Figs 4a and 4b, a stopper block 10 of preferably of rubber material (can be of any other material) is mounted on the shaft 9 within the switchgear panel 5 proximal to the front door 6 and corresponding to a pre-designated position 8 in the switchgear panel 5. The stopper block 10 is so mounted on the shaft 9 that upon rotating the shaft 9 for unlocking the interlocking mechanism, the stopper block 10 is brought in front of the circuit breaker 3 to restrict the racking in of the circuit breaker 3 beyond the pre-designated position 8 to the service position. Upon reversing the rotation of the shaft 9 for locking the interlocking mechanism, the stopper block 10 is moved away from the circuit breaker 3 to allowing racking in of the circuit breaker 3 beyond the pre-designated position 8 to the service position. The orientation of the stopper block 10 on the shaft 9 is such that upon rotating the shaft 9 for unlocking the interlocking mechanism, the following occurs simultaneously:
the handle 12 and slot 13 on the front door 6 are aligned;
the stopper block 10 is brought in front of the circuit breaker 3 for restricting
the movement of the circuit breaker 3 beyond the pre-designated position 8; Thus the circuit breaker is allowed to be racked out completely from the switchgear panel 5 and not allowed to be moved into service position until the interlocking mechanism is locked. For locking the interlocking mechanism, the circuit breaker 3 is first racked in the switchgear panel 5 upto the pre-designated position 8 therein. Thereafter, to unlock the interlocking mechanism, the shaft 9 is rotated in reverse. Consequently, the following occurs simultaneously:
the handle 12 and slot 13 on the front door 6 are misaligned:

the stopper block 10 is moved away from the circuit breaker 3 for allowing the
movement of the circuit breaker 3 beyond the pre-designated position 8; Thus, after the circuit breaker 3 is removed from the switchgear panel 5 and reentered into the switchgear panel 5, it is not allowed to be racked in beyond the pre-designated position 8 and brought in the service mode until the front door 6 is locked by the interlocking mechanism.
It will be obvious to a person skilled in the art that the shape of the stopper block may not necessarily be square and may be of any shape but large enough to block the racking in of the circuit breaker 3 beyond the pre-designated position 8.
Fig 5a and 5b depicts a transmission mechanism of the interlocking mechanism in a switchgear in unlock/lock positions. According to a preferred embodiment, the transmission means is a bevel gear mechanism through which the earth switch 4 is opened or closed upon rotating the shaft 9. One of the gears 11 of the bevel gear mechanism is mounted on the shaft 9 at a distance from the stopper block 10 and proximal to the rear door 7. The other gear 14 in contact with the gear 11 on the shaft 9 is mounted on one end of a lever 15 held perpendicular to the shaft 9 within the switchgear panel 5. On the lever 15, a plurality of moving contacts 16 of the earth switch 4 are mounted one end of which is electrically grounded and other free ends are adapted to be connected/disconnected to the corresponding fixed contacts 17 of the earth switch 4. The other ends of the fixed contact 17 are connected to the input power supply terminals. The orientation of the mounting of the moving contacts 16 on the lever 15 is such that when the shaft 9 is rotated for unlocking the interlocking mechanism, the following occurs simultaneously:
the handle 12 and slot 13 on the front door 6 are aligned as shown in Fig 3a;

the stopper block 10 is brought in front of the circuit breaker 3 as shown in Fig 4a;
the moving contacts 16 of the earth switch 4 are moved to be electrically
connected to the corresponding fixed contacts 17 of the earth switch 4 for
closing the earth switch 4 as shown in Fig 5a. Similarly, when the shaft 9 is rotated in reverse for locking the interlocking mechanism, the following occurs simultaneously:
the handle 12 and slot 13 on the front door 6 are misaligned as shown in Fig 3b;
the stopper block 10 is moved away from the circuit breaker 3 as shown in Fig
4b;
the moving contacts 16 of the earth switch 4 are moved to be electrically
disconnected from the corresponding fixed contacts 17 of the earth switch 4
for opening the earth switch 4 as shown in Fig 5b. Thus, as soon as the circuit breaker 3 is brought in the test position and upon rotating the shaft 9 for unlocking the interlocking mechanism, the earth switch 4 is closed along with the unlocking of the front 6 door and the movement of circuit breaker 3 is restricted by the stopper block 10 for racking it into service position. Upon rotating the shaft 9 in reverse for locking the interlocking mechanism, the earth switch 4 is opened along with locking of the front 6 door and allowing the circuit breaker 3 to be racked into service position.
Fig 6a and 6b depicts a second door lock mechanism of the interlocking mechanism in a switchgear in unlock/lock positions for unlocking/locking the rear door 7. The rear door 7 is held onto the edges 28 & 30 of the switchgear panel 5 by means of screws or such other fastening means. According to a preferred

embodiment, the second door lock mechanism comprises of a locking bar 18 pivoted on the inner surface of the rear door 1, four C-shaped brackets 19, 20, 21, 22 and a locking lever 23. As shown in Fig 2, one end 24 of the locking lever 23 is fixed to the rear door end 9b of the shaft 9 and the other end 29 remains free. When the shaft 9 is rotated from the position as shown in Fig 6b for unlocking the interlocking mechanism, the locking lever 23 is swept backwards thereby resulting in withdrawal of the push to the second end 26 of the locking bar 18 which results in the First end 27 of the locking bar 18 being moved away from the edge 28 of the switchgear panel 5. When the shaft 9 is reversely rotated for locking the interlocking mechanism, the locking lever 23 is swept across inner surface of the rear door 7 to push upwardly the second end 26 of the locking bar 18 as shown in fig 6b. The locking bar 18 is pivoted such that upon pushing its second end 26 upwardly, the First end 27 thereof is pulled downwardly in front of the edge 28 of the switchgear panel 5. Four C-shaped brackets 19, 20. 21, 22 are provided on the inner surface of the front door 7 as shown in the Figs 6a and 6b. The first bracket 19 is mounted to limit the upward movement of the First end 27 of the locking bar 18 when the push to the second end 26 of the locking bar 18 is withdrawn. The second bracket 20 is provided to limit the downward movement of the second end 26 of the locking bar 18 when the push thereto is withdrawn by the other (free) end 29 of the locking lever 23. Similarly, the third bracket 21 is provided to limit the upward movement of the second end 26 of the locking bar 18 when it is pushed by the other (free) end 29 of the locking lever 23. The fourth bracket 22 is provided to limit the upward movement of the locking lever 23 while it is being swept across the inner surface of the front door 7. When the shaft 9 is rotated to unlock the interlocking mechanism the following occurs simultaneously:

the handle 12 and slot 13 of the front door 6 are aligned as shown in Fig 3a; the stopper block 10 is brought in front of the circuit breaker 3 as shown in Fig
4a;
the moving contacts 16 of the earth switch 4 are moved to be electrically connected to the corresponding fixed contacts 17 of the earth switch 4 for closing the earth switch 4 as shown in Fig 5a.
as shown in Fig 6a, the locking lever 23 is swept back from the position as shown in Fig 6b to be brought parallel to the rear door 7 or the edges 30 of the switchgear panel 5 which results in withdrawal of the push to the second end 26 of the locking bar 18 which results in away movement of the first end 27 of locking bar 18 from the edge 28 of the switchgear panel 5 thereby rendering the rear door 7 free to be opened.
When the shaft 9 is rotated in reverse for locking the interlocking mechanism, the
following occurs simultaneously:
the handle 12 and slot 13 of the front door 6 are misaligned as shown in Fig
3b;
the stopper block 10 is moved away from of the circuit breaker 3 as shown in
Fig 4b;
the moving contacts 16 of the earth switch 4 are moved to be electrically disconnected to the corresponding fixed contacts 17; of the earth switch 4 for opening the earth switch 4 as shown in Fig 5b.
as shown in fig 6b, the locking lever 23 is swept across the rear door 7 from the position as shown in Fig 6a to push to the second end 26 of the locking bar 18 upwardly which results in the first end 27 of the locking bar 18 being pulled downwardly in front of the edge 28 of the switchgear panel 5. Thus, the

front door 7 is restricted to be moved away from the edges of the switchgear
panel 5 by the locking bar 18 and the locking lever 23.
It will be obvious to a person skilled in the art that variations are possible in the above described locking mechanism. Moreover, there can be provided different types of locking mechanism other than the ones described above, i.e. the first and second door lock mechanism, which can be operated by just rotating the shaft 9. There is also a possibility that a same kind of door lock mechanism being used for both the front and rear doors. The above embodiment is described with respect to a panel where using the same kinds of locking mechanism for front and rear door is not possible or preferable.
It will be obvious to a person skilled in the art that there may be more than one above described shaft based interlocking mechanism within the switchgear panel depending upon the requirement. The unlocking and locking of the interlocking mechanism may not necessarily be achieved by rotating and reversely rotating the shaft respectively and may also be achieve by rotating and further rotating the shaft respectively.
According to the invention, there is provided an interlocking mechanism in a switchgear panel which is simple, operable by just rotating the shaft of the interlocking mechanism, does not require skilled manpower, allows removal of the circuit breaker 3 in test position from the switchgear panel only after the earth switch is closed and does not allow circuit breaker to be pushed into service position until the front and rear doors are closed and the earth switch is opened. Thus important safety measures are such as opening the earthing switch switch only after the front and rear doors are closed, allowing the circuit breaker to be put into service position only if the earth switch is opened, allowing the opening of the front and rear doors of the

switchgear panel only if the earth switch is closed are ensured to be taken by the interlocking mechanism thus leaving no scope of forgetting of taking such precautions by the operator.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim;
1. An interlocking mechanism in a switchgear enclosed in a switchgear panel having a front and rear door, the switchgear comprising a circuit breaker adapted to be racked in/out of the switchgear panel for toggling thereof between the test and service positions, the interlocking mechanism comprising
a. a rotatable shaft held adjacently to the circuit breaker between the front
and rear doors of the switchgear panel;
b. a first and second door lock mechanisms being operable by rotation of
the shaft for locking/unlocking the front and rear doors of the
switchgear panel respectively;
c. a transmission means connected to the shaft and an earth switch within
the switchgear such that upon rotating the shaft for unlocking the
interlocking mechanism, the earth switch being closed and upon
rotating the shaft in reverse for locking the interlocking mechanism,
the earth switch being opened;
d. at least one stopper block mounted on the shaft corresponding to a
pre-designated position in the switchgear panel such that
i. upon rotation of the shaft for unlocking the interlocking mechanism, the stopper block being brought in front of the circuit breaker in test position for restricting racking in of the circuit breaker to the service position:
ii. upon reversing the rotation of the shaft for locking the interlocking mechanism, the stopper block being moved away from the circuit breaker in test position for allowing racking in

of the circuit breaker to the service position; wherein the first and second door lock mechanisms, the transmission means and the stopper block being so synchronized that upon rotating the shaft for unlocking the interlocking mechanism:
a. the front and rear door of the switchgear panel
being unlocked for opening;
b. the stopper block being brought in front of the
circuit breaker in test position for restricting
racking in of the circuit breaker to the service
position; and
c. the earth switch being closed;
and upon rotating the shaft in reverse for locking the interjocking mechanism;
a. the front and rear doors of the switchgear panel
being locked for opening;
b. the stopper block being moved away from the
circuit breaker in test position for allowing the
racking in of the circuit breaker to the service
position; and
c. the earth switch being opened.
2. The interlocking mechanism as claimed in claim 1, wherein the first and second door lock mechanisms are the same.
3. The interlocking mechanism as claimed in claim 1, wherein the first door lock mechanism comprises of

a. a handle attached to the front door end of the shaft and remaining
disposed outside the switchgear panel;
b. a slot on the front door corresponding to the handle such that upon
rotating the shaft by means of the handle the handle and the slot being
aligned for allowing the front door to move away from the switchgear
panel beyond the handle through the slot thereby allowing the front
door to be opened and upon reversing the rotation of the shaft, the
handle and slot being misaligned thus adapting the handle to obstruct
the front door from moving away from the switchgear panel beyond
the handle thereby locking the front door.
4. The interlocking mechanism as claimed in claim 3, wherein the handle is L-shaped or T-shaped provided either integrated or joined to the front door end of the shaft.
5. The interlocking mechanism as claimed in claim 1. wherein the second door lock mechanism comprises of
a. a locking bar having a first end remaining disposed within a first
bracket and a second end remaining disposed within a second and third
bracket, the brackets being provided on the inner surface of the rear
door held onto the edges of the switchgear panel the second and third
bracket being adjacent to each other, the locking bar being pivoted on
the inner surface of the rear door within the switchgear panel such that
i. upon pushing the second end upwardly, the first end being
pulled downwardly in front of the corresponding edge of the
switchgear panel thereby locking the rear door from being
pulled outwardly against the edges of the switchgear panel;

ii. upon withdrawing said upward push to the second end. the first end being pulled upwardly away from the corresponding edge of the switchgear panel thereby unlocking the rear door; wherein the first bracket being provided for limiting the upward movement of the first end, second bracket being provided for limiting the downward movement of the second end and the third bracket being provided for limiting the upward movement of the second end; b. a locking lever connected to the rear door end of the shaft such that
i. upon rotating the shaft, the locking lever being swept across the inner surface of the rear door within a fourth bracket provided adjacent to the third bracket such that the second end of the locking bar within the second and third brackets is pushed upwardly by the free end of the locking lever thereby locking the rear door from being pulled outwardly; ii. upon reversing the rotation of the shaft, the free end of the locking lever being adapted to roll back to its original position thereby unlocking the rear door:
6. The interlocking mechanism as claimed in claim 5. wherein the rear door is held onto the edges of the switchgear panel by means of screws.
7. The interlocking mechanism as claimed in claim 1. wherein the transmission means is a bevel gear mechanism comprising of a first gear mounted on the shaft 9 at a distance from the stopper block and proximal to the rear door, a second gear in contact with the first gear and mounted on a lever held

perpendicularly to the shaft within the switchgear panel, the moving contacts of the earth switch being mounted on the lever such that when the shaft is rotated for unlocking the interlocking mechanism, the moving contacts being moved to be electrically connected to the corresponding fixed contacts of the earth switch and when the shaft is rotated in reverse for locking the interlocking mechanism, the moving contacts being moved to be electrically disconnected from the corresponding fixed contacts of the earth switch.