FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
BREAKER SERVICE POSITION LATCHING MECHANISM FOR DRAW OUT TYPE CIRCUIT BREAKER

APPLICANT:

LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra . INDIA.

PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED



A) TECHNICAL FIELD
[0001] The present invention generally relates to switching devices and particularly to circuit breakers like draw out type circuit breakers. The present invention more particularly relates to a latching mechanism for locking the breakers during service condition.
B) BACKGROUND OF THE INVENTION
[0002] A Circuit breaker is a switching device used to interrupt the fault currents which occur in a circuit. It is mainly required to prevent the electrical system from the faults occurring in the system like over voltage, over current, short circuit etc. The circuit breakers found in switchgear, distribution centers, and service entrance equipment are generally of three types such as molded case circuit breakers, insulated case circuit breakers, fixed and draw-out type circuit breakers.
[0003] In the electrical power distribution systems, the draw-out type voltage circuit breakers are quite large and are usually housed in corresponding circuit breaker cells of switchgear. Some mechanical means, such as racking devices, are employed to rack-in or withdraw these large circuit breakers. Usually the Circuit breakers are removed from the service by taking out their moving part from their fixed or stationary part during maintenance.
[0004] A draw out type air circuit breaker comprises of a basic multi phase interrupting unit called breaker. It consists of poles enclosed in housing capable of making and breaking the main circuit, and cradle on which basic interrupting unit is


mounted. This basic interrupting unit can be disconnected from the main circuit, which is connected to cradle, by means of a rack and pinion type mechanism.
[0005] The circuit breaker shall be isolated by horizontal racking and positively fixing the unit into any one of the following positions such as a Service position in which main and auxiliary circuits connected, a Test position in which main circuits disconnected auxiliary circuits connected and an isolated position shall be completely contained in the apparatus. Generally the locking of the machinery and equipment when they are being serviced or maintained is accomplished with a number of devices that attempt, for example, to lock-out switches of circuit breaker boxes. These devices are intended to prevent the switches from being switched from the "OFF" position to the "ON" position and possibly injuring someone during service or maintenance of equipment associated with the circuit breaker.
[0006] The circuit breakers are locked generally to prevent the unauthorized person from accessing it. The locking mechanism prevents its access during service position. But during abnormal conditions due to the high short circuit forces acting upon the circuit breaker the circuit beaker assembly may move causing automatic closing of the circuit breaker. Hence there is a need to develop a system and method to prevent the movement of the circuit breaker in service position. So there is a need to develop a system and method to lock the circuit breaker movement in service position to prevent the immense short circuit forces acting upon it during abnormal conditions.


C) OBJECTS OF THE INVENTION
[0007] The primary object of the present invention is to develop a latching mechanism to lock the circuit breaker under service to prevent the movement of the circuit breaker under service.
[0008] Another object of the present invention is to develop a latching mechanism to lock the circuit breaker under service to prevent the movement of the circuit breaker under service to counter the short circuit forces acting on the circuit breaker during abnormal conditions in the main circuit loads.
[0009] Yet another object of the present invention is to develop a latching mechanism to lock the circuit breaker and to generate a locking sound to ensure that the circuit breaker is fully racked into service position.
[0010] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0011] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
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[0012] The various embodiments of the present invention provide a service latch mechanism to lock the circuit breaker under service to prevent the movement of the circuit breaker under service. According to one embodiment of the present invention, the latch is actuated by a simple link mechanism to engage or disengage the breaker from the cradle. The link mechanism is in turn operated by a rack in mechanism. A cam surface is used to push the link forward to rotate it in the clock wise direction to enable the latch to operate and lock the breaker. The latching mechanism is mounted on the side plates of circuit breaker. The latching mechanism is operated or actuated with the help of a unique profile of the cam which ensures the locking sound, when the breaker is fully racked in to the service position. The whole latching mechanism includes four links. The self actuating mechanism is driven by a cradle cam which is formed integrally with the breaker racking system. The cam contact profile synchronises the breaker movement with the actuation of the link mechanism accurately. A mild click sound is generated to indicate the actuation of the latch, when the breaker is moved to the service position.
[0013] According to on embodiment of the present invention, the latch mechanism has a main link and a support link. The support link is pivotally connected to the main link. A latch is engaged to the support link. The latch has protrusions to engage with the slots provided in the side plate of a cradle installed to mount the circuit breaker. The protrusions in the latch are engaged with slots in the side plate to permit only the vertical movement of the latch. The side plate is fixed with two parallelly arranged grooved guides through rivets. The symmetric rails mounted with circuit breaker are slidably moved on the grooved guides. A cam is provided to move the symmetric rails. The cam is rotated in anticlockwise direction to push the rail in the forward
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direction to move the circuit breaker mounted on the rails. The cam is further moved to contact the protrusions in the main link to move the main link to the rest position to make the latch to move vertically to engage with slots in the symmetric rails to prevent the movement of the rails thereby avoiding the horizontal movement of the circuit breaker.
[0014] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0016] FIGURE. 1 illustrates a side sectional view of a service latch mechanism with rack and pinion arrangement used to engage or disengage breaker from cradle, according to one embodiment of the present invention.
[0017] FIGURE. 2 illustrates a side sectional view of a service latch mechanism in the initial position, according to one embodiment of the present invention.
[0018] FIGURE. 3 illustrates a side sectional view of a service latch mechanism operated by the cam rotation, according to one embodiment of the present invention. .
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[0019] FIGURE. 4 illustrates a side sectional view of a service latch mechanism indicating the final position of the latch locking the movement of symmetric rails used for sliding, according to one embodiment of the present invention.
[0020] FIGURE.5 illustrates a side sectional view of a service latch mechanism indicating the de-latching of rails by means of cam rotation, according to one embodiment of the present invention.
[0021] FIGURE. 6 illustrates an exploded perspective view of latching mechanism, according to one embodiment of the present invention.
[0022] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0023] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.


[0024] The various embodiments of the present invention provide a service latch mechanism to lock the circuit breaker under service to prevent the movement of the circuit breaker under service. According to one embodiment of the present invention, the latch is actuated by a simple link mechanism to engage or disengage the breaker from the cradle. The link mechanism is in turn operated by a rack in mechanism. A cam surface is used to push the link forward to rotate it in the clock wise direction to enable the latch to operate and lock the breaker. The latching mechanism is mounted on the side plates of circuit breaker. The latching mechanism is operated or actuated with the help of a unique profile of the cam which ensures the locking sound, when the breaker is fully racked in to the service position. The whole latching mechanism includes four links. The self actuating mechanism is driven by a cradle cam which is formed integrally with the breaker racking system. The cam contact profile synchronises the breaker movement with the actuation of the link mechanism accurately. A mild click sound is generated to indicate the actuation of the latch, when the breaker is moved to the service position.
[0025] A draw out type air circuit breaker comprises of a basic multi phase interrupting unit called breaker. The breaker consists of poles enclosed in housing to make and break electrical connection/contacts in a main circuit. The basic interrupting unit is mounted on a cradle. This basic interrupting unit can be disconnected from the main circuit and is connected to the cradle by means of a rack and pinion type mechanism. A service latch device is used to lock the breaker movement while the breaker is under service. The immobility of the breaker in service condition helps to counter the immense short circuit forces acting upon the breaker during abnormal
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conditions in the main circuit loads. The latch is actuated by a simple link mechanism which is operated by the rack in mechanism used to engage or disengage the breaker from cradle. The cam surface pushes the link forward to rotate it in the clockwise direction causing the latch to operate and lock the breaker.
[0026] According to on embodiment of the present invention, the latch mechanism has a main link and a support link. The support link is pivotally connected to the main link. A latch is engaged to the support link. The latch has protrusions to engage with the slots provided in the side plate of a cradle installed to mount the circuit breaker. The protrusions in the latch are engaged with slots in the side plate to permit only the vertical movement of the latch. The side plate is fixed with two parallelly arranged grooved guides through rivets. The symmetric rails mounted with circuit breaker are slidably moved on the grooved guides. A cam is provided to move the symmetric rails. The cam is rotated in anticlockwise direction to push the rail in the forward direction to move the circuit breaker mounted on the rails. The cam is further moved to contact the protrusions in the main link to move the main link to the rest position to make the latch to move vertically to engage with slots in the symmetric rails to prevent the movement of the rails to avoid the horizontal movement of the circuit breaker.
[0027] FIGURE. 1 illustrates a side sectional view of a service latch mechanism with rack and pinion arrangement used to engage or disengage breaker from cradle, according to one embodiment of the present invention. With respect to FIG.l, the cradle consists of parallel side plates 1 which are connected by the base plate 2 and other cross pieces (not shown the fig). A shaft 3 is provided between the parallel side
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plates land is connected to cam 60. The shaft is rotated freely in the clockwise or anticlockwise directions. The shaft 3 is operated via a rack 5 and pinion 4 arrangement attached to the base plate 2. The Cradle side plates 1 are fixed with two parallel grooved guides 53 by means of rivets. The symmetric rails 50 used for mounting the circuit breaker are moved between the grooved guides 53. These rails are put into motion when the cam surface 61 or 62 pushes the rivet 52, attached to the rail, in the forward or backward direction in lieu of its clockwise or anticlockwise rotation.
[0028] FIGURES. 2-5 illustrate a side sectional view of a service latch, according to
one embodiment of the present invention. The FIG.2 illustrates a side sectional view
of a latch mechanism in the initial position,while FIGURE. 3 illustrates a side
? sectional view of a service latch mechanism operated by the cam rotation. The
FIGURE. 4 illustrates a side sectional view of a service latch mechanism indicating the final position of the latch locking the movement of symmetric rails used for sliding while FIGURE.5 illustrates a side sectional view of a service latch mechanism indicating the de-latching of rails by means of cam rotation.
[0029] With respect to the FIGS 2-5, The latching mechanism consists of latch 10,
*v. support link 20 and main link 30.The whole mechanism is pivoted around the axis 31
on the main link and axis 21 on the support link. Protrusions 12 in the latch are engaged in the slot 14 (as shown in the fig 6) in the side plate allowing only the vertical motion of the latch. Main link 30 is pivoted around axis 31 and linked to the support link through a slot 32 in which the pin 23 attached to support link 20 is received. A round protrusion 33 is pivoted on the main link to come into direct


contact with cam surface 64 or 63 making it to rotate in the clockwise or anticlockwise direction. The support link 20 is pivoted around axis 21 and linked to latch 30 through profile 22 where the protruding pin 11 rests.
[0030] As the cam 60 rotates anticlockwise from its initial position, it pushes the rails 50 to move forwards. The breaker rests on the rails so that it also moves forward. As the rails move forward, the horizontal motion of the rails is converted into the vertical motion of latch 10 through surface 54 on the rail and surface 13 on the latch. As the cam rotates further, its surface 63 is in touch with the protrusion 33 of the main link. The Cam surface 63 is designed such that as it rotates further the main link comes to the rest position and the latch gets locked on the slot 52 in the rails thereby preventing any further horizontal movement of the rails (fig 4). The click sound generated during the striking of the latch with the slot gives an indirect indication of service condition. The Spring 40 attached between latch and point 41 gets extended, as the latch moves upward and it provides the necessary force required for the whole mechanism to come to initial position.
[0031] Now the rail can't be moved horizontally until the latch is de latched from the slot 52. This is disengaged through the same mechanism. As the cam rotates clockwise from service condition as shown in fig 4, it surface 64 strikes the protrusion 33 making it to rotate clockwise which in turn rotate the support link in the anticlockwise direction through slot 32 and pin 23 thereby disengaging the latch 10 out of the slot 52 and allowing the horizontal movement of rails. As the cam surface 64 gets disengaged from pin 33, the mechanism is free to come to initial condition and spring 40 provides the requisite force.


[0032] The FIGURE. 6 illustrates an exploded perspective view of latching mechanism, according to one embodiment of the present invention. With respect to FIG.6, The latching mechanism consists of latch 10, support link 20 and main link 30.The whole mechanism is pivoted around the axis 31 (as shown in FIG.l) on the main link and axis 21 (as shown in FIG.2) on the support link. Protrusions 12 in the latch are engaged in the slot 14 in the side plate allowing only the vertical motion of the latch. Main link 30 is pivoted around axis 31 and linked to the support link through a slot 32(as shown in FIG.l) in which the pin 23 (as shown in FIG. 1) attached to support link 20 is received. A round protrusion 33 (as shown in FIG.l) is pivoted on the main link to come into direct contact with cam surface 64 or 63 (as shown in FIG.l) making it to rotate in the clockwise or anticlockwise direction. The support link 20 is pivoted around axis 21 and linked to latch 30 through profile 22 (as shown in FIG.l) where the protruding pin 11 rests. A spring 40 is attached to the main link and is extended as the latch is moved upwardly thereby providing the necessary force required for the whole mechanism to come to the initial position.
[0033] Thus the various embodiments of the present invention provide a service latch mechanism to lock the circuit breaker under service to prevent the movement of the circuit breaker under service.
G) ADVANTAGES OF THE INVENTION
[0034] The various embodiments of the present invention provide a service latch mechanism to lock the circuit breaker under service to prevent the movement of the circuit breaker. The latching mechanism generates a click sound to indicate the


actuation of the latch with the breaker. The breaker under service is immobilised by the latch to counter the immense short circuit forces acting upon the breaker during the abnormal conditions.
[0035] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.

[0036] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
WHAT IS CLAIMED IS:
1. a breaker service position latching mechanism for draw out type circuit
breaker, the mechanism comprising :
a main link;
a support link pivotally moved on the main link;
a latch engaged to the support link;
a cradle provided with side plates having slots to engage with the latch;
grooved guides fixed to the side plates ;
symmetric rails slidably moved on the grooved guides and to support the
circuit breaker;
a cam to move the symmetric rails;
wherein the cam moves the main link to rest position to make the latch to engage the rails mounted with the circuit breaker to prevent the movement of the rails to avoid the movement of the circuit breaker .
2. The mechanism according to claim 1, wherein the main link is provided with protrusion to come into direct contact with the cam surface.
3. The mechanism according to claim I, wherein the cam is rotated in anticlockwise direction to push the rail in forward direction thereby moving the circuit breaker mounted on the rails.


4. The mechanism according to claim 1, wherein the cam is moved to contact the protrusion in the main link to move the main link to the rest position.
5. The mechanism according to claim 1, wherein the rails has slots to receive the latch.
6. The mechanism according to claim 1, wherein the cam is moved to contact the protrusion in the main link to move the main link to make the latch to engage with the slot in the rail to prevent the movement of the rail to avoid the horizontal movement of circuit breaker.
7. The mechanism according to claim 1, wherein the latch has protrusions.
8. The mechanism according to claim 1, wherein the protrusions in the latch are received in the slots provided in the side plates of the cradle to engage the latch to permit only the vertical movement of the latch.