Claims:1. A racking mechanism (14) for a circuit breaker, said circuit breaker being mounted on a cradle assembly for moving said circuit breaker between 'Disconnected’, 'Test' and 'Connected’ positions,
said cradle assembly comprising:
a pair of rail assemblies (12);
a pair of cradle side plates (11) having flanges to guide and constrain the rail assembly (12);
a cradle base plate (13) being coupled to located between said pair of cradle side plates (11); said racking mechanism (14) being mounted on said a cradle base plate (13);
a cradle shaft cam (18) fitted on a cradle shaft assembly (17), said cradle shaft assembly (17) having a cradle shaft guide (21) and a cradle shaft slider (20) fitted thereon, wherein said cradle shaft assembly (17) receives racking operation input from the racking mechanism assembly (14) through movement on the cradle shaft slider (20);
a drop plate assembly (16) having a drop plate pin (23), said drop plate assembly (16) being rigidly coupled to the rail assembly (12), and said cradle shaft cam (18) being welded onto the cradle shaft assembly (17);
wherein the cradle shaft slider (20) and the guide cam (24) are operably coupled to the cradle shaft assembly (17) to transfer rotational force to the drop plate pin (23) of the drop plate assembly (16) thereby resulting in linear movement of the rail assembly (12) on the cradle side plate (11);
characterized in that by said racking mechanism (14) comprising:
a rack (19) mounted on the cradle base plate (13) and said cradle shaft guide (21) being mounted on said rack (19);
a racking screw (15) operably coupled to the cradle shaft guide (21), said racking screw (15) being capable of undergoing rotation about an axis thereof upon application of an input torque thereon, wherein rotational movement of said racking screw (15) is converted into linear translation of the rack (19);
wherein linear translation of said rack (19) moves the cradle shaft assembly (17) over cradle shaft slider (20) in a gradual upward movement to connect with the drop plate assembly (16) thereby resulting in linear movement of the rail assembly (12) to the desired breaker position.

2. The racking mechanism (14) as claimed in claim 1, wherein said circuit breaker is a draw-out circuit breaker.

3. The racking mechanism (14) as claimed in claim 1, wherein a racking handle (22) is operably coupled to the free end of the racking screw (15) to rotate said racking screw (15) on application of an input torque thereon.

4. The racking mechanism (14) as claimed in claim 1, wherein each of said cradle shaft slider (20) and said guide cam (24) has a profile thereon for receiving cradle shaft assembly (17).

5. The racking mechanism (14) as claimed in claim 1, wherein, the cradle shaft guide (21) along with cradle shaft slider (20) converts the linear motion of the rack (19) into the translation motion of the cradle shaft cam (18) fitted on the cradle shaft assembly (17) thereby moving the drop plate assembly (16) and eventually the rail assembly (12) on the cradle side plate (11).

6. The racking mechanism (14) as claimed in claim 5, wherein, the cradle shaft guide (21) converts the linear motion of the rack (19) into the translation motion of the cradle shaft cam (18) fitted on the cradle shaft assembly (17), thereby moving the circuit breaker mounted on the cradle assembly to any of the 'Disconnected' position, the 'Test' position and the 'Connected’ position.

7. The racking mechanism (14) as claimed in claim 1, wherein application of a clockwise input torque to the racking screw (15) results in achieving the ‘Connected’ position of the circuit breaker.

8. The racking mechanism (14) as claimed in claim 1, wherein application of a counter clockwise input torque to the racking screw (15) results in achieving the ‘Disconnected’ position of the circuit breaker.

9. The racking mechanism (14) as claimed in claim 1, wherein the circuit breaker comprises a housing having a plurality of projections, said projections being operably coupled to a plurality of slots of the rail assembly (12).
, Description:FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates protection devices such as circuit breakers and more particularly, pertains to a racking mechanism in a cradle arrangement for a draw-out circuit breaker.

BACKGROUND OF INVENTION

[002] Electrical transmission and distribution systems employ a circuit breaker, which is an automatically operated electrical switch, to protect an electrical circuit from damage caused by overcurrent, typically resulting from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected and can be reset either manually or automatically to resume normal operation. Air Circuit Breaker (ACB) is type of circuit breaker used to provide overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps and are used in low voltage power distribution systems. The ACB is used to carry, make and break current in low-voltage and high current applications.

[003] There are two types of ACB’s where one is fixed ACB and other is a draw- out ACB. The draw-out type ACB’s comprises of a cradle assembly which used to carry breaker and can move and hold the breaker in four critical positions of any circuit breaker that is “connected”, “test”, “disconnect” and “maintenance”. A typical advantage of the draw out ACB is that it helps in frequent maintenance of circuit breaker and one can provide interlocked earthling and testing of breaker; it also helps in easy replacement of circuit breaker.

[004] In electrical power distribution systems, individual circuit breakers are housed within a switchgear cabinet and periodically need to be disconnected, tested and re-connected. The disconnection and re-connection of the circuit breakers is accomplished by “racking” or displacing the circuit breakers in the switchgear cabinet via a racking mechanism associated with the circuit breaker. Significantly, the racking mechanism in of the ACB is used to move the breaker in & out from the cradle and eventually achieve the desired position of the breaker. It also holds the breaker in its desired position.

[005] The tool for racking the circuit breakers typically includes a handle that is inserted through an opening in the cabinet and engaged to the racking mechanism within the cabinet. The racking mechanism is then screw-driven by rotating the handle to displace the circuit breaker in the cabinet for disconnection and re-connection of the circuit breaker with conductors in the switchgear cabinet.

[006] In the existing mechanisms, the breaker is mounted on a rail assembly that slides on cradle side plate and during rack-in operation; the rack-in handle is engaged with a screw head and rotated clockwise. The rotary motion of the screw is converted into linear motion of the rack. As pinion on cradle shaft is engaged with rack, cradle shaft gets rotated. There are cams at both ends of cradle shaft that engages with the pin of drop plate that is mounted on cradle rail. Thus, the rotary motion of the screw is converted into linear motion of rails. Since the ACB is mounted on rails, the breaker moves to the desired position in the cradle.

[007] For some existing technology, reference is made to US Publication Number 2017/0063055 A1, wherein systems, devices and methods are disclosed for racking circuit breakers in a switchgear cabinet via a drive mechanism that is flexibly linked to a racking mechanism associated with each circuit breaker. This drive mechanism can be connected for racking multiple circuit breakers without requiring re-positioning of the drive mechanism.

[008] Reference is also made to Indian Patent Application Number 1048/MUM/2015, wherein a racking mechanism for a draw-out circuit breaker is disclosed. This racking mechanism eliminates a back drive by using a pair of the worm gear and the worm wheel that provides better wear characteristics and ease of replacement in case of damage as well as ease of adaptability in case of accommodating different worm pairs to increase / decrease torque as per requirement.

[009] Reference is also made to Indian Patent Application Number 201621010936, wherein a racking mechanism for a draw-out circuit breaker is disclosed. The racking mechanism comprises at least one racking screw means rotably disposed in an enclosure; and at least two split bearing means of at least one diameter, connected to said racking screw means to hold said racking screw means; wherein, said racking screw means enabled to rotate with and said rotating motion of said racking screw means converted into a translational motion of plurality of rails provided on an enclosure cradle assembly and thereby enable insertion of said circuit breaker.

[0010] The drawbacks associated with the existing technology are that they employ a drop plate that is connected to the rail and is driven by a cam provided at both ends of the racking shaft. The force required to rotate the cam through rack and pinion arrangement is significantly dependent on the distance between drop pin and rack-in shaft axis. This distance is constant and large thereby increasing the racking torque required by the user to rotate the cam. Further, the existing mechanisms also uses complex rack and pinion type arrangement that adds up the losses into racking torque, which eventually increases the racking torque required by the user after so many rack-in/out operations. Still further, over the period of time during the high life of racking mechanism, pinion on the cradle shaft has a tendency to wear out and further result in inconsistency in racking torque. Moreover, the racking mechanism being the constant part across a variety of frames, as frame size of breaker increases, the racking torque in such lager frames also increases thereby resulting in large and heavy air circuit breakers.

[0011] Therefore, there is a need for reducing the distance between drop pin and rack-in shaft axis during racking operation to reduce the racking torque required by the user for racking the breaker into the cradle of the draw-out air circuit breaker. There is also a need to eliminate the conventional rack and pinion type arrangement to reduce the transmission losses between said rack and pinion, to reduce the long term wearing out and resulting losses.

[0012] The above-described need for eliminating the rack and pinion type arrangement is merely intended to provide an overview of some of the shortcomings of conventional systems / mechanism / techniques, and is not intended to be exhaustive. Other problems/ shortcomings with conventional systems/mechanism/techniques and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.

SUMMARY OF THE INVENTION

[0013] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0014] An object of the present invention is to provide a racking mechanism for circuit breakers.

[0015] Another object of the present invention is to provide a translation type effective racking mechanism for air circuit breaker.

[0016] Another object of the present invention is to improve the racking torque of the racking mechanism to reduce the effort required by the user for racking the air circuit breaker.

[0017] Yet another object of the present invention is to provide a transmission arrangement that provides incremental mechanical advantage to the racking mechanism in synchronizing with main forces coming from compression of contact jaw spring forces.

[0018] Yet another object of the present invention is to eliminate the rack and pinion type arrangement to reduce the transmission losses and long term wearing out of the air circuit breaker.

[0019] According to an aspect of the present invention, there is provided a racking mechanism for a circuit breaker, said circuit breaker being mounted on a cradle assembly for moving, said circuit breaker between 'Disconnected’, 'Test' and 'Connected’ positions. The cradle assembly comprising: a pair of rail assemblies; a pair of cradle side plates having flanges to guide and constrain the rail assembly; a cradle base plate being coupled to located between said pair of cradle side plates; said racking mechanism being mounted on said a cradle base plate; a cradle shaft cam fitted on a cradle shaft assembly, said cradle shaft assembly having a cradle shaft guide and a cradle shaft slider fitted thereon, wherein said cradle shaft assembly receives racking operation input from the racking mechanism assembly through movement on the cradle shaft slider; a drop plate assembly having a drop plate pin, said drop plate assembly being rigidly coupled to the rail assembly, and said cradle shaft cam assembly being welded onto the cradle shaft assembly; wherein the cradle shaft slider and the guide cam are operably coupled to the cradle shaft assembly to transfer rotational force to the drop plate pin of the drop plate assembly thereby resulting in linear movement of the rail assembly on the cradle side plate. The racking mechanism comprising: a rack mounted on the cradle base plate and said cradle shaft guide being mounted on said rack; a racking screw operably coupled to the cradle shaft guide, said racking screw being capable of undergoing rotation about an axis thereof upon application of an input torque thereon, wherein rotational movement of said racking screw is converted into linear translation of the rack; wherein linear translation of said rack moves the cradle shaft assembly and cradle shaft slider in a gradual upward movement to connect with the drop plate assembly thereby resulting in linear movement of the rail assembly to the desired breaker position.

[0020] In one possible implementation of the racking mechanism according to the first aspect, there is provided a racking handle that is operably coupled to the free end of the racking screw to rotate said racking screw on application of an input torque thereon. The application of a clockwise input torque to the racking screw (15) results in achieving the ‘Connected’ position of the circuit breaker; and application of a counter clockwise input torque to the racking screw (15) results in achieving the ‘Disconnected’ position of the circuit breaker.

[0021] In another possible implementation of the racking mechanism according to the first aspect, each of said cradle shaft slider and said guide cam have a special profile thereon for receiving cradle shaft assembly.

[0022] In yet another possible implementation of the racking mechanism according to the first aspect, the cradle shaft guide converts the linear motion of the rack into the rotational motion of the cradle shaft cam fitted on the cradle shaft assembly thereby moving the drop plate assembly and eventually the rail assembly on the cradle side plate, thereby moving the circuit breaker mounted on the cradle assembly to any of the 'Disconnected' position, the 'Test' position and the 'Connected’ position.

[0023] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0024] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0025] Figure 1 illustrates the cradle assembly in the connected position according to an embodiment of the present invention.

[0026] Figure 2 illustrates the rack assembly with the cradle shaft according to the embodiment of the present invention.

[0027] Figure 3 illustrates the engagement of the cradle shaft and drop plate according to the embodiment of the present invention.

[0028] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0029] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0030] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0031] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0032] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0033] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0034] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0035] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0036] The present invention lies in providing a translation type effective racking mechanism for air circuit breaker.

[0037] In a draw-out type of circuit breaker, positions of the breaker with respect to the cradle are normally defined as 'Disconnected', 'Test' and 'Connected'. When the breaker is completely racked in i.e., in 'Connected' position, breaker terminals are in contact with cradle terminals through cradle jaws in the 'Connected' position. In this condition, both power (main) circuit and control circuit are connected and the breaker 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. The breaker can also be drawn out to ‘Maintenance’ position where it can be lifted off the cradle for servicing and maintenance activities.

[0038] The present invention pertains to a racking mechanism for circuit breakers. This racking mechanism has a translation type arrangement for racking the circuit breaker into the cradle with reduced effort. Figure 1 illustrates the draw out type of circuit breaker of the present invention whose cradle assembly in the connected position. In this draw out type of circuit breaker, the breaker is supported on the rail assembly (12), which is an integral part of the cradle assembly.

[0039] The cradle assembly consists of the cradle base plate (13), racking assembly (14), cradle side plates (11) for guiding breaker and rail assembly (12). The cradle side plate (11) has flanges which guide and constrain the rail assembly (12), allowing only a single degree of freedom to move to and fro within the cradle assembly. The breaker housing has projections which rest onto slots in the rail assembly (12), thus facilitating the draw-out feature of the air circuit breaker. Bolted rigidly to the cradle side plate (11) is the cradle base plate (13) which provides the base for mounting of the racking mechanism assembly (14), responsible for the racking operation of the draw-out breaker.

[0040] The racking operation is accomplished by the racking assembly mounted on the base plate. The racking handle is connected externally to the front part of racking screw (15) for required rotational movement. Rotational movement of racking screw (15) gets converted into linear movement of rack (19). A cradle shaft guide (21) that is provided on the rack moves the cradle shaft assembly (17) and also cradle shaft slider (20), thereby giving it a gradual upward movement to get connected with drop plate assembly (16). This in turn moves the rail assembly (12) linearly to achieve the desired breaker position.

[0041] Figure 2 illustrates the racking assembly with the cradle shaft of the present invention. The racking handle (22) is inserted into the front part of racking screw (15) which results in rotational movement of the racking screw (15) being converted into linear translation of the rack (19). The cradle shaft guide (21) provided on rack (19) is used to guide the cradle shaft assembly (17). During linear translation of the rack (19), cradle shaft will translate on cradle shaft slider (20) and the guide cam (24) is fixed with cradle side plate (11). The special profile of the cradle shaft slider (20) and guide cam (24) allows the cradle shaft assembly (17) to transfer the forces to drop plate pin (23) which is part of rail assembly (12) and moves it linearly on cradle side plate (11).

[0042] The drop plate assembly (16) is rigidly coupled to the rail assembly (12) by means of rivets. This provides the link between the cradle shaft cam (18) and the breaker sitting on the rail assembly (12). The cradle cam (16) itself is welded onto the cradle shaft assembly (17) which takes racking operation input from the racking mechanism assembly (14) through movement on cradle shaft slider (20). The desired position i.e. 'Disconnected', 'Test' and 'Connected' is achieved by the movement of the air circuit breaker that is mounted on the rail assembly (12).

[0043] The racking screw (15) is capable of undergoing rotation about its axis on application of an input torque thereon. The racking screw (15) undergoes a clockwise rotation upon application of a clockwise input torque thereon for achieving the ‘Connected’ position of the ACB and the racking screw (15) undergoes a counter clockwise rotation upon application of a counter clockwise input torque thereon for achieving the ‘Disconnected’ position of the ACB.

[0044] Figure 3 illustrates the engagement of the cradle shaft and drop plate according to the present invention. The profile of the cradle shaft slider (20) and guide cam (24) is such that it allows the cradle shaft assembly (17) to transfer the rotational force to the drop plate pin (23) of the rail assembly (12) thereby moving it linearly on the cradle side plate (11).

[0045] The translation type movement of cradle shaft assembly (17) by the movement over the racking shaft slider (20) and guide by guide cam (24) will give the incremental mechanical advantage to the racking mechanism of the present invention. Moreover, the profile of both racking shaft slider (20) and guide cam (24) will ensure synchronize force transmission between cradle shaft assembly (17) and rail assembly (12). Notably, the synchronized position changes of the cradle shaft assembly (17) is achieved by the unique profile of cradle shaft slider (20) and guide cam (24). This increases the racking torque consistency over the claimed life of the mechanism. As the cradle shaft assembly (17) moves over the cradle shaft slider (20) and gets connected to the drop plate assembly (16), it will reduce the forces coming on the racking screw (15), thereby resulting in reduction in the racking torque. Thus, the user experience is enhanced by reducing the torque required to operate the racking mechanism.

[0046] This simple slider type force transmission reduces the complexity of the racking system and reduces the chances of long-term wear out and resulted losses due to that. The dual mechanical advantage increases as the breaker moves into the cradle will result in racking torque reduction. This simplification of transition of movement from rack (19) to drop plate (16) reduces the complexity and losses between the existing arrangements of rack and pinion.

[0047] Significantly, the translation movement of cradle shaft with cradle shaft slider provided with a base plate of cradle assembly increases the mechanical advantage as the breaker moves into “Connected” position. The special profile of the cradle shaft slider moves the cradle shaft assembly closer to the drop plate assembly and away from racking screw thereby reducing the racking torque. Synchronizing the movement of the rack and the drop plate assembly results in smooth transmission of forces.

[0048] Some of the non-limiting advantages of the present invention are mentioned hereinbelow:
1. It reduces the torque required by the user for racking the breaker into the cradle of the draw-out air circuit breaker;
2. It eliminates the requirement of pinion of the cradle shaft thereby reducing changes of wear and inconsistency / higher racking torque over the life;
3. The sliding type of mechanism reduces the distance between drop plate and cradle shaft thereby improving the mechanical advantage from racking screw to rail;
4. Its simple slider type joints reduce the complexity of the racking system;
5. It reduces the transmission losses between rack and pinion by eliminating the rack and pinion type arrangement; and
6. It reduces the chances of long-term wear out and resulted losses owing to that.
7. It synchronizes the movement of the rack and the drop plate assembly in a manner that results in smooth transmission of forces.

[0049] Although a simple, economic and low maintenance translation type effective racking mechanism for air circuit breaker has been described in language specific to structural features and/or methods as indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations of a racking mechanism for circuit breakers.