Claims:1. A racking arrangement for a draw-out circuit breaker, said circuit breaker being mounted on a racking assembly (14), said racking assembly (14) being operably coupled to a cradle shaft arrangement (15) of a cradle assembly (10) for moving said circuit breaker between 'Disconnected’, 'Test' and 'Connected’ positions,
said cradle shaft arrangement (15) 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 assembly (14) being mounted on said a cradle base plate (13);
a cradle cam shaft (152) operably fitted thereon to a cradle cam (151), said cradle cam shaft (152) receives racking operation input from the racking assembly (14);
a drop plate assembly (121) operably coupled to the rail assembly (12) and the cradle cam (151);
wherein the racking assembly (14) being operably coupled to the cradle cam shaft (152) and cradle cam (151) to transfer rotational force of the cradle cam shaft (152) to the drop plate assembly (121) thereby resulting in linear movement of the rail assembly (12) on the cradle side plate (11);
characterized in that by the racking assembly (14) comprising:
a racking support plate (143) mounted on the cradle base plate (13) of the cradle shaft arrangement (15);
a connector link (141) having two ends, said connector link (141) being pivotally coupled to a racking block (142) at one end and operably coupled to a pivot link (144) on the opposite end, wherein said connector link (141) transfers motion to said pivot link (144);
said pivot link (144) rotates the cradle shaft arrangement (15) to drive the drop plate assembly (121) to linearly move the rail assembly (12);
a racking screw (145) operably coupled to a racking block (142), said racking screw (145) being capable of undergoing rotation about an axis thereof upon application of an input torque thereon, wherein rotational movement of said racking screw (145) is converted into linear translation of the racking support plate (143);
wherein linear translation of said racking support plate (143) moves the cradle cam (151) of the cradle shaft arrangement (15) in a gradual upward movement to connect with the drop plate assembly (121), said drop plate assembly (121) being operably coupled to the rail assembly (12), thereby resulting in linear movement of the rail assembly (12) to the desired circuit breaker position.

2. The racking arrangement as claimed in claim 1, wherein, the pivot link (144) converts the linear motion of the racking support plate (143) into the rotational motion of the cradle cam (151) fitted on the cradle shaft arrangement (15) thereby moving the drop plate assembly (121) and eventually the rail assembly (12) on the cradle side plate (11).

3. The racking arrangement as claimed in claim 2, wherein, the pivot link (144) converts the linear motion of the racking support plate (143) into the rotational motion of the cradle cam (151) fitted on the cradle shaft arrangement (15), thereby moving the circuit breaker mounted on the racking assembly (14) to any of the 'Disconnected' position, the 'Test' position and the 'Connected’ position.

4. The racking arrangement as claimed in claim 1, wherein application of a clockwise input torque to the racking screw (145) results in achieving the ‘Connected’ position of the circuit breaker.

5. The racking arrangement as claimed in claim 1, wherein application of a counter clockwise input torque to the racking screw (145) results in achieving the ‘Disconnected’ position of the circuit breaker.

6. The racking arrangement 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).

7. The racking arrangement as claimed in claim 1, wherein a locking pin (146) pivotally connects one end of said connector link (141) to the racking block (142).

8. The racking arrangement as claimed in claim 1, wherein the pivot link (144) is welded on the cradle cam shaft (152) of the cradle shaft arrangement (15).
, 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 assembly arrangement in a cradle assembly 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 of the draw-out circuit breaker 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] The existing mechanisms employ the rack and pinion arrangement for racking where the circuit breaker is mounted on a rail assembly that slides on cradle side plate. A power screw transmits the force to the sliding rack. The rack and pinion arrangement transforms the translational motion of the rack to rotational motion of the pinion which is rigidly coupled to the cradle cam shaft, which in turn is responsible for racking the circuit breaker. During rack-in operation, the rack-in handle is engaged with the power screw head and rotated clockwise. The rotary motion of the screw is converted into linear motion of the rack. As the 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 draw-out circuit breaker is mounted on rails, the breaker moves to the desired position in the cradle.

[007] For some existing technology in this field, reference is made to US Patent Number 7821775 B2, wherein a racking mechanism for a draw-out circuit breaker including a cross shaft movably positioned in an enclosure and at least one input link in operable communication with the cross shaft via at least one connecting link is disclosed. At least one racking cam is movably positioned in the enclosure and is in operable communication with the input link. Each racking cam has at least one cam slot receptive of a portion of the circuit breaker. Movement of the cross shaft about an axis of the cross shaft is capable of moving the at least one racking cam from an open position toward a closed position with the portion of the circuit breaker disposed in the at least one cam slot, thereby securing the circuit breaker in the enclosure and the at least one racking cam is in the closed position. This document discloses a racking mechanism that employs links for racking with a cradle shaft and cradle cam in non-axial movement. Additional links are used for connecting cradle shaft with cradle cam and movement of cradle shaft and cradle cam are opposite in nature.

[008] Reference is also made to US Publication Number 3019309 A, wherein a circuit breaker structure for mounting in a cubicle is disclosed. It comprises a frame, a pair of cooperating movable arcing contacts mounted on said frame, means for causing relative movement between said contacts, a racking means mounted on said frame for cooperating with the cubicle for varying the position of said frame within the cubicle upon actuation thereof, a dual purpose driving means for actuating said racking means and said contact movement means, and means for selectively connecting said driving means to said racking means and said contact movement means. This document discloses an integrated geared racking mechanism for a draw-out circuit breaker.

[009] The drawbacks associated with the existing technology that employs the rack and pinion arrangement for racking are probe to backlash error and misalignment of rack and pinion. Notably, the backlash, also called as lash or play, is a clearance or lost motion in a mechanism caused by gaps between the parts. It is the clearance between two mating gears. If the clearance is more misalignment of gears takes place which leads to improper transmission of torque. Backlash error in rack and pinion causes mating issue of rack and pinion and thus racking operation is affected as force transmission is improper. Further, the force required to rotate the cam through rack and pinion arrangement is considerable and dependent on the distance between drop pin and rack-in shaft axis. Still further, the complex and considerably bulky rack and pinion type arrangement adds up the transmission losses. 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.

[0010] Therefore, there is a need for reducing the backlash and misalignment of rack and pinion by doing away with the conventional rack and pinion type arrangement racking the breaker into the cradle of the draw-out air circuit breaker. There is also a need to reduce the transmission losses and long term wear and tear between the rack and pinion.

[0011] 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

[0012] 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.

[0013] An object of the present invention is to provide a racking arrangement for draw-out circuit breakers.

[0014] Another object of the present invention is to provide a translation type effective racking arrangement for a draw-out circuit breaker.

[0015] Another object of the present invention is to eliminate the rack and pinion type arrangement for racking the draw-out circuit breaker.

[0016] Yet another object of the present invention is to eliminate the backlash and misalignment of rack and pinion issues associated with the rack and pinion type arrangement of the draw-out circuit breaker.

[0017] Yet another object of the present invention is to eliminate the use of less efficient power screws from the racking assembly arrangement of the draw-out circuit breaker.

[0018] According to an aspect of the present invention, there is provided a racking arrangement for a draw-out circuit breaker, said circuit breaker being mounted on a racking assembly, said racking assembly being operably coupled to a cradle shaft assembly of a cradle assembly for moving said circuit breaker between 'Disconnected’, 'Test' and 'Connected’ positions. The cradle shaft 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 assembly being mounted on said a cradle base plate; a cradle cam shaft operably fitted thereon to a cradle cam, said cradle cam shaft receives racking operation input from the racking assembly; a drop plate assembly operably coupled to the rail assembly and the cradle cam; wherein the racking assembly being operably coupled to the cradle cam shaft and cradle cam to transfer rotational force of the cradle cam shaft to the drop plate assembly thereby resulting in linear movement of the rail assembly on the cradle side plate. The racking assembly comprising: a racking support plate mounted on the cradle base plate of the cradle shaft assembly; a connector link having two ends, said connector link being pivotally coupled to a racking block at one end and operably coupled to a pivot link on the opposite end, wherein said connector link transfers motion to said pivot link; said pivot link rotates the cradle shaft assembly to drive the drop plate assembly to linearly move the rail assembly; a racking screw operably coupled to a racking block, 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 racking support plate; wherein linear translation of said racking support plate moves the cradle cam of the cradle shaft assembly in a gradual upward movement to connect with the drop plate assembly, said drop plate assembly being operably coupled to the rail assembly, thereby resulting in linear movement of the rail assembly to the desired circuit breaker position.

[0019] In a possible implementation of the racking arrangement according to the first aspect, the pivot link (144) converts the linear motion of the racking support plate (143) into the rotational motion of the cradle cam (151) fitted on the cradle shaft assembly (15) thereby moving the drop plate assembly (121) and eventually the rail assembly (12) on the cradle side plate (11). This moves the circuit breaker mounted on the racking assembly (14) to any of the 'Disconnected' position, the 'Test' position and the 'Connected’ position.

[0020] In another possible implementation of the racking arrangement according to the first aspect, application of a clockwise input torque to the racking screw (145) results in achieving the ‘Connected’ position of the circuit breaker while application of a counter clockwise input torque to the racking screw (145) results in achieving the ‘Disconnected’ position of the circuit breaker.

[0021] In yet another possible implementation of the racking arrangement according to the first aspect, 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.

[0022] In yet another possible implementation of the racking arrangement according to the first aspect, a locking pin pivotally connects one end of said connector link to the racking block. This pivot link is welded on the cradle cam shaft of the cradle shaft assembly.

[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 disconnected position according to one implementation of an embodiment of the present invention.

[0026] Figure 2 illustrates the cradle assembly in the connected position according to another implementation the embodiment of the present invention.

[0027] Figure 3 illustrates the racking assembly according to an 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 an efficient racking arrangement that integrates a unique linkage arrangement for racking the circuit breaker on draw-out rails along with minimal user effort.

[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 arrangement for circuit breakers. The racking assembly of said arrangement employs a four bar linkage arrangement for racking of the draw-out circuit breaker into the cradle. Figure 1 illustrates the cradle assembly-racking assembly arrangement that employs the four bar linkage arrangement of the present invention. 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 shaft assembly (15).

[0039] A cradle assembly comprises of a cradle shaft arrangement (15). The cradle shaft arrangement (15) consists of a cradle base plate (13), a racking assembly (14), a pair of cradle side plates (11) for guiding the circuit breaker and a 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 assembly (14), responsible for the racking operation of the draw-out breaker. The racking operation is accomplished by the racking assembly (14) mounted on the cradle base plate (13).

[0040] Figure 2 illustrates the cradle assembly in the connected position according to the present invention. A drop plate assembly (121) is rigidly coupled to the rail assembly (12) by means of rivets thereby providing the link between the cradle cam (151) and the circuit breaker sitting on the rail assembly (12). The cradle cam (151) is welded onto the cradle cam shaft (152). This cradle cam shaft (152) takes racking operation input from the racking assembly (14) output.

[0041] The racking assembly (14) transmits required force for racking the circuit breaker by means of linkages. This requires minimal exertion of input energy thereby making the racking assembly to be efficient by avoiding frictional losses. The four bar linkages will transfer the motion to a cradle cam shaft (152) which will rotate and this rotational motion is converted into translation motion by the racking support plate (143) provided on racking assembly (14).

[0042] Figure 3 illustrates the racking assembly (14) of the racking arrangement of the present invention. This racking assembly (14) comprises a connector link (141), a racking block (142), a racking support plate (143), a pivot link (144), a racking screw (145) and a locking pin (146). A user applies torque on the racking screw (145) in clock wise direction that moves the racking block (142) towards the cradle shaft arrangement (15). Since the connector link (141) is coupled to the racking block (142), the connector link (141) transfers the motion to the pivot link (144) which is rotates clockwise to rotate the cradle shaft arrangement (15). This cradle shaft arrangement (15) drives the drop plate assembly (121) and accordingly, translational movement of the rail assembly (12) occurs.

[0043] Racking of the draw-out circuit breaker is achieved when user applies an input torque to the racking screw (145) which is assembled on the racking support plate (143). This racking screw (145) is free to rotate about its own axis and is coupled with the corresponding racking block (142) which is guided on base plate assembly (13). One end of the connector link (141) is pivoted to racking block (142) with help of the locking pin (146) while the other end of the connector link (141) is connected to the pivot link (144). The pivot link (144) is welded on cradle cam shaft (152) of the cradle shaft arrangement (15). The cradle cam shaft (152) moves the cradle cam (151) of cradle shaft arrangement (15) and also the drop plate assembly (121) of the rail assembly (12) linearly to achieve the desired circuit breaker position. 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).

[0044] The racking screw (145) is capable of undergoing rotation about its axis on application of an input torque thereon. The racking screw (145) undergoes a clockwise rotation upon application of a clockwise input torque thereon for achieving the ‘Connected’ position of the draw-out circuit breaker and the racking screw (145) undergoes a counter clockwise rotation upon application of a counter clockwise input torque thereon for achieving the ‘Disconnected’ position of the draw-out circuit breaker.

[0045] The translation type movement of cradle shaft arrangement (15) by the movement of the cradle cam shaft (152) and cradle cam (151) will give the incremental mechanical advantage to the racking arrangement of the present invention. As the cradle shaft arrangement (15) moves and gets connected to the drop plate assembly (121), it will reduce the forces coming on the racking screw (145), thereby resulting in reduction in the racking torque. Thus, the user experience is enhanced by reducing the torque required to operate the racking arrangement.

[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 simplification of transition of movement from racking support plate (143) to drop plate (121) reduces the complexity and losses between the existing arrangements of rack and pinion while also doing away with the backlash and misalignment of rack and pinion.

[0047] Significantly, the translation movement of cradle shaft arrangement (15) with the racking assembly (14) provided on the cradle base plate (13) increases the mechanical advantage as the circuit breaker moves into “Connected” position. The special four bar linkage arrangement of the racking assembly (14) moves the cradle shaft arrangement (15) closer to the drop plate (12) and away from the racking screw (145) thereby reducing the racking torque. Synchronizing the movement of the racking support plate (143) and the drop plate (121) results in smooth transmission of forces.

[0048] Some of the non-limiting advantages of the present invention are mentioned hereinbelow:
1. It employs simple linkages for the racking assembly when compared to the traditional rack and pinion arrangement of the draw-out circuit breakers;
2. It employs lesser number of components thereby improving the overall efficiency of the racking arrangement;
3. It provides a hassle free racking operation;
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 inherent to the rack and pinion type arrangement.

[0049] Although a simple, hassle free, economic and low maintenance linkage arrangement for racking a draw-out 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 arrangement for draw-out circuit breakers.