CLIAMS:1. A rack for withdrawable switching devices comprising:
a L-shaped base having a short arm and a long arm, wherein the long arm is configured as bottom member, and wherein the short arm is configured as power screw engaging member; and
at least one side member welded on at least one side of the base, wherein the side member is configured to have at least one surface that engages with a base plate of the withdrawable switching device and prevents the bottom member from coming in contact with the base plate.
2. The rack of claim 1, wherein the L-shaped base and the side member are made of sheet metal.
3. The rack of claim 1 wherein the rack is manufactured by any or a combination of cutting bending, punching, and welding operations.
4. The rack of claim 1, wherein the rack further comprises a nut that is configured on the power screw engaging member.
5. The rack of claim 4, wherein the nut is a forged nut.
6. The rack of claim 4, wherein the nut is welded to the power screw engaging member of the L-shaped base.
7. The rack of claim 1, wherein the bottom member incorporates at least one slot that is configured to engage with teeth of a pinion of a racking shaft of the withdrawable switching device.
8. The rack assembly of claim 7, wherein the at least one slot has chamfered edges for entry and exit of the pinion teeth.
,TagSPECI:TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of low voltage power equipment. In particular, it relates to a rack assembly for withdrawable switching devices and method of manufacture thereof.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art
[0003] Switching devices such as electrical circuit breakers and disconnectors include essential functional modules of a distribution board for control and protection of electrical power systems. The modular design provides much needed flexibility of design and also enables combining and integrating numerous functions within a distribution board. Low voltage switchgear are generally available in two broad categories viz., withdrawable or drawout type and fixed type.
[0004] Simplicity and compactness are the main advantages of fixed type LV switchgear modules. However, these modules cannot be isolated from the power supply for maintenance or replacement, if needed, without necessitating a general shutdown. The withdrawable or drawout type LV switchgear however minimizes downtime and although complex, offers advantages of being completely withdrawable and permitting isolation of the particular module for maintenance or replacement without the need for de-energizing the entire switchboard.
[0005] Withdrawable or drawout switchgear devices basically include a fixed module or a cradle into which a movable module can be inserted. The fixed module is connected to the power supply. The movable module is completely inserted into the fixed module to establish connection with the power supply during normal operating conditions. Alternatively the movable module can be drawn out and removed from the fixed module for maintenance and/or replacement. Accordingly, withdrawable or drawout switchgear devices can be designed for different operative positions including connected, test, stand by, disconnected and removed position to satisfy operation requirements.
[0006] The translational motion of the moving module into and out of the fixed module is generally referred to as racking in and racking out of the switchgear device. Rack assembly provides means to perform the racking in and racking out operation and enable mechanical /electrical connection of the moving module within the switchboard. The rack assembly works on the rack and pinion principle such that pinion teeth of racking shaft engage with slots defined in a rack component. The rack is connected to a power screw that engages with threads provided in the rack. The rotation of the power screw results in linear motion of the rack. Because of the insertion of the pinion teeth into the slots of the rack, the linear motion of the rack causes rotational motion of the racking shaft which further enables linear motion of a rail arrangement. The moving module rests on the rail arrangement and thus moves linearly into and out of the fixed module.
[0007] The rack is a critical component of the rack assembly and is manufactured in the art by casting process which involves large process time, is complex and expensive and also necessitates further machining operation post the casting process. Low voltage switchgear devices are subject to frequent racking in and racking out operations for maintenance or inspection. With performance characteristics of switchgear devices becoming superior, it is imperative that performance characteristics of the rack assembly also remain consistent throughout its life with minimal racking torque variations. Any wear and tear of the slots in the rack will cause an increase in the vertical components of force applied by the pinion teeth on the rack slots in comparison to the horizontal component thereby causing damage to the rack base plate and degeneration in the performance and life of the rack assembly.
[0008] Again, performance of the rack is also dependent on the thread engagement of the power screw and the rack. Rack assemblies known in the art provide threads in the cast rack which have a tendency to wear out when high racking torque is applied which again is detrimental to the life of the rack assembly. Presence of dust or foreign particles between the rack and base plate can also increase friction during translational motion of the rack adding to the deterioration of the rack assembly.
[0009] There is therefore a need for an improved rack assembly that at least overcomes some of the aforementioned drawbacks of the prior art.
[0010] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0011] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0012] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0013] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0014] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0015] An object of the present disclosure is to mitigate short comings of the rack assemblies of conventional withdrawable switchgear devices.
[0016] Another object of the present disclosure is to provide a method of manufacture of rack assembly that is simple.
[0017] Another object of the present disclosure is to provide a method of manufacture of rack assembly that is cost effective.
[0018] Another object of the present disclosure is to provide a method of manufacture of rack assembly that does not consume time.
[0019] Another object of the present disclosure is to provide a rack assembly for withdrawable switchgear devices that is reliable.
[0020] Another object of the present disclosure is to provide a rack assembly for withdrawable switchgear devices that has a long life with consistent performance characteristics.

SUMMARY
[0021] Aspects of present disclosure relate to rack assemblies for withdrawable switchgear devices. In an aspect, the disclosure provides a rack assembly that can include a rack made of sheet metal. In an embodiment, the rack assembly can further include a moving module that can be inserted into or withdrawn from a fixed module wherein the rack can be configured to slide on a base plate for facilitating racking in or racking out of the moving module from the fixed module.
[0022] In an embodiment, the rack can be provided with a side member welded on either side such that the side member has at least one surface that can slide on a base plate with minimum contact surface area to minimize presence of dust and foreign particles that increase friction between the surfaces.
[0023] In an embodiment, the rack assembly can further include a power screw that engages with the rack at one end and with a racking handle at another end for initiating the racking in and racking out of the moving module such that rotation of the racking handle and corresponding rotation of the power screw results in linear motion of the rack.
[0024] In an embodiment, the rack assembly can further include a racking shaft that can be configured to rotate as a result of the linear motion of the rack. The racking shaft can be further configured with racking cams at either end to cause linear motion of rails configured on the fixed module and accordingly cause linear motion of the moving module that rests on the rails.
[0025] In an embodiment, the power screw can include a stopper nut that can be configured to stop the moving module from being further inserted into the fixed module once the moving module is completely racked in.
[0026] In an embodiment, the rack is substantially L-shaped and can include a bottom member forming a long arm of the substantially L-shaped rack. The bottom member can be configured with at least one slot for engaging with pinion teeth of the racking shaft. The L-shaped rack can further include a power screw engaging member forming a short arm of the substantially L-shaped rack. The power screw engaging member can be configured with at least one welded nut for engaging with threads of the power screw.
[0027] In an embodiment, at least one slot in the rack can be configured with chamfered edges for easy and smooth entry and exit of pinion teeth.
[0028] In another aspect, the disclosure provides a method of manufacturing a rack assembly wherein a rack is formed by one or more combinations of bending, punching and welding of sheet metal.
[0029] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0031] FIG. 1A illustrates an exemplary isometric view of a sheet metal rack in accordance with an embodiment of the present disclosure.
[0032] FIG. 1B illustrates an exemplary exploded view of a sheet metal rack in accordance with an embodiment of the present disclosure.
[0033] FIG. 2 illustrates an exemplary isometric view of a sheet metal rack with a position indicator in accordance with an embodiment of the present disclosure.
[0034] FIG. 3 illustrates an exemplary isometric view of a rack assembly with power screw in accordance with an embodiment of the present disclosure.
[0035] FIG. 4 illustrates an exemplary partial isometric view of a withdrawable switchgear device with a moving module and a fixed module in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0036] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0037] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0038] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0039] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0040] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0041] Embodiments of the present disclosure relate to rack assemblies for withdrawable switchgear devices. In an aspect, the disclosure provides a rack assembly that can include a rack made of sheet metal. In an embodiment, the rack assembly can further include a moving module that can be inserted into or withdrawn from a fixed module wherein the rack can be configured to slide on a base plate for facilitating racking in or racking out of the moving module from the fixed module.
[0042] In an embodiment, the rack can be provided with a side member welded on either side such that the side member has at least one surface that can slide on a base plate with minimum contact surface area to minimize presence of dust and foreign particles that increase friction between the surfaces.
[0043] In an embodiment, the rack assembly can further include a power screw that engages with the rack at one end and with a racking handle at another end for initiating the racking in and racking out of the moving module such that rotation of the racking handle and corresponding rotation of the power screw results in linear motion of the rack.
[0044] In an embodiment, the rack assembly can further include a racking shaft that can be configured to rotate as a result of the linear motion of the rack. The racking shaft can be further configured with racking cams at either end to cause linear motion of rails configured on the fixed module and accordingly cause linear motion of the moving module that rests on the rails.
[0045] In an embodiment, the power screw can include a stopper nut that can be configured to stop the moving module from being further inserted into the fixed module once the moving module is completely racked in.
[0046] In an embodiment, the rack is substantially L-shaped and can include a bottom member forming a long arm of the substantially L-shaped rack. The bottom member can be configured with at least one slot for engaging with pinion teeth of the racking shaft. The L-shaped rack can further include a power screw engaging member forming a short arm of the substantially L-shaped rack. The power screw engaging member can be configured with at least one welded nut for engaging with threads of the power screw.
[0047] In an embodiment, at least one slot in the rack can be configured with chamfered edges for easy and smooth entry and exit of pinion teeth.
[0048] In another aspect, the disclosure provides a method of manufacturing a rack assembly (also referred to as rack interchangeably hereinafter) wherein a rack is formed by one or more combinations of bending, punching and welding of sheet metal.
[0049] FIG. 1A illustrates an exemplary isometric view of sheet metal rack 100 in accordance with an embodiment of the present disclosure. Rack such as the Rack 100 is one of the most critical components of a rack assembly for efficient and smooth racking operation in withdrawable switchgear devices. A rack is typically made of a casting by a process such as investment casting which is an expensive and time consuming process. In an embodiment, the disclosed rack 100 is made of sheet metal by fabrication process involving sheet metal cutting, pressing, bending and welding. The disclosed process is inexpensive and requires short lead time. In accordance with the present disclosure the rack 100 can be configured to slide on a base plate for facilitating racking in or racking out of the moving module from the fixed module of the withdrawable switchgear devices. The strength of sheet metal rack of the present disclosure supersedes the strength of cast rack known in the art. This ensures minimal wear and tear of slots 104 during the racking in and racking out process of the withdrawable switchgear device. In an embodiment, rack 100 can be substantially L-shaped comprising base 102 that is substantially L-shaped and can include a bottom member forming a long arm of the substantially L-shaped base 102 and a power screw engaging member forming a short arm of the substantially L-shaped base 102. Slots 104 are configured on the bottom member for engaging with pinion teeth (406 of FIG. 4) of racking shaft (404 of FIG. 4). Nut 106 can be configured on the power screw engaging member of the base 102 for engaging with threads of power screw (302 of FIG.3). In an embodiment, nut 106 can be configured on the power screw engaging member of the base 102 by a process such as but not limited to welding.
[0050] Referring to FIG. 1B wherein an exploded view 150 of the exemplary sheet metal rack 100 in accordance with an embodiment of the present disclosure is illustrated, it can be noted that there is a side member that can be welded on either side of base 102. For instance, left side member 110 and right side member 112 are welded on both sides of base 102 respectively.
[0051] In an embodiment, both the side members have at least one surface that can be in contact with base plate (402 of FIG. 4) and preventing bottom member of the base 102 coming in contact with the base plate (402 of FIG. 4). Thus the rack 100 of the present disclosure ensures that minimum contact surface area is maintained between base plate (402 of FIG. 4) and rack 100 such that dust and other undesired foreign elements do not accumulate and cause friction losses affecting the performance of the rack assembly.
[0052] In accordance with an embodiment, slots 104 configured in rack 100 can be provided with chamfered edges 108 for easy and smooth entry and exit of pinion teeth (406 of FIG. 4). Chamfered edges 108 ensure forces applied by pinion teeth (406 of FIG. 4) provides maximum horizontal component which enables linear motion of rack 100 and reduces vertical components which can damage slots 104 and correspondingly rack 100 and base plate (402 of FIG. 4) thereby compromising life of the rack assembly.
[0053] FIG. 2 illustrates an exemplary isometric view 200 of sheet metal rack 100 with position indicator 202 in accordance with an embodiment of the present disclosure. Withdrawable or drawout modules are advantageous for the ability to withdraw the moving module to various operative positions including test position, isolated position, and the like. In an embodiment, position indicators 202 can be coupled to rack 100 through fixing screws 204 via side members 110 and 112 (of FIG. 1B) at positions 114 (of FIG. 1B). In an embodiment, positions of the moving module can be further configured to be displayable by visual means such as flags or color coded tags for enhanced user experience. In an embodiment, position indicators 202 coupled to side member 110 and 112 also serve to enable actuation of interlocks of the switchgear device that can be utilized for other purposes.
[0054] FIG. 3 illustrates an exemplary isometric view 300 of a rack assembly 100 along with a power screw in accordance with an embodiment of the present disclosure. In an embodiment, power screw 302 engages with rack 100 at one end through nut 106. In an embodiment, nut 106 can be a forged nut for good mechanical strength. The strength of threads of a forged nut welded to a sheet metal rack is far better than strength of threads provided in cast rack, thereby mitigating wear of rack on application of higher racking torque and enhancing life of the rack. Hence nut 106 welded to rack 100 can withstand high racking torque with no damage to the threads configured therein. Power screw 302 further engages with a racking handle (not shown) at its other end. Rotation of the racking handle causes rotation of power screw 302 which further causes corresponding rotation of power screw 302. Rotation of power screw 302 results in linear motion of rack 100. In accordance with an embodiment, power screw 302 can be provided with stopper nut 304 to prevent over racking of the switchgear device that can cause damage to the rack assembly. Stopper nut 304 prevents further insertion of the moving module into the fixed module once the moving module is completely racked in.
[0055] FIG. 4 illustrates an exemplary partial isometric view 400 of a withdrawable switchgear device with a moving module (not shown) and a fixed module 412 in accordance with an embodiment of the present disclosure. Slots 104 configured in the bottom member of rack 100 engage with pinion teeth 406 of racking shaft 404. Linear motion of rack 100 thus results in rotational motion of racking shaft 404. Racking cams 410 are configured on either end of racking shaft 404 that correspondingly cause linear motion of rails 408 configured on fixed module 412. The moving module (not shown) rests on rails 408 and is thus capable of linear motion along rails 408.
[0056] In an aspect, the present disclosure provides a method of manufacturing a rack assembly for withdrawable switching devices wherein the method includes performing one or more combinations of bending, punching and welding of sheet metal to form a rack that can slide on a base plate for facilitating racking in or racking out of the moving module from the fixed module. The method of the present disclosure besides reducing manufacturing and lead time considerably also provides a durable and reliable rack that ensures consistency of performance throughout the life of the rack assembly.
[0057] In an embodiment, the method can further include welding of a side member on either side of the rack for coupling position indicators with the rack. Such position indicators enhance user experience by enabling the user to identify whether the switchgear device is in connection position, isolated position, test position, and the like depending on the positions configured based on operational requirements.
[0058] In an embodiment, method of the present disclosure further includes coupling of a power screw to the rack at one end and a racking handle at other end. Rotation of the racking handle causes rotation of the power screw and accordingly linear motion of the rack that is coupled to the power screw via welded nut. The method of the present disclosure further includes co-operatively rotating a racking shaft as a result of the linear motion of the rack. This is achieved by engaging of slots configured on the rack with pinion teeth configured on the racking shaft.
[0059] In an embodiment, method of the present disclosure further includes linearly displacing rails configured on the fixed module on which the moving module rests. This is achieved via racking cams provided on either end of the rotating shaft that convey the rotational motion of the racking shaft and result in linear motion of the rails.
[0060] In an embodiment, method of the present disclosure further includes a stopper nut on the power screw to prevent damage to the rack assembly by over racking of the moving module.
[0061] In an embodiment, step of forming sheet metal rack can include forming of a substantially L-shaped base having a bottom member that forms a long arm of the substantially L-shaped rack and a power screw engaging member that forms a short arm of the substantially L-shaped rack.
[0062] It should be understood that while the embodiments of the present disclosure have been described in a manner wherein certain processes like welding is indicated particularly for assembly of parts, it is possible to configure the rack with one or more combination of other processes on sheet metal and such modification is well within the scope of the present disclosure.
[0063] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0064] The present disclosure mitigates short comings of the rack assemblies of conventional withdrawable switchgear devices.
[0065] The present disclosure provides a method of manufacture of rack assembly that is simple.
[0066] The present disclosure provides a method of manufacture of rack assembly that is cost effective.
[0067] The present disclosure provides a method of manufacture of rack assembly that does not consume time.
[0068] The present disclosure provides a rack assembly for withdrawable switchgear devices that is reliable.
[0069] The present disclosure provides a rack assembly for withdrawable switchgear devices that has a long life with consistent performance characteristics.