Claims:1. A racking mechanism for a draw-out circuit breaker or draw-out electrical switching devices, said mechanism comprising:
at least one racking screw means rotatably disposed in an enclosure of the circuit breaker, wherein rotation of said racking screw means being converted into a translational motion of plurality of rails provided on an enclosure cradle assembly and thereby enabling insertion of said circuit breaker; and
at least two split bearing means adapted to hold the racking screw means,
Characterized in that said bearing means having diametrical configuration so as to reduce the collar friction torque thereby producing substantial reduction in the final torque produced during racking operation.

2. The mechanism as claimed in claim 1, wherein said split bearing means mounted on a racking bracket.

3. The mechanism as claimed in claim 2, wherein split bearing means comprising upper split bearing means and lower split bearing means.

4. The mechanism as claimed in claim 1, assembled on a base plate of said enclosure cradle assembly.

5. A circuit breaker assembly comprising:
an enclosure;
a draw out circuit breaker insertable in said enclosure; and
a racking mechanism for enable racking of said draw out circuit breaker into said enclosure, said racking mechanism comprising:
at least one racking screw means rotatably disposed in an enclosure of the circuit breaker, wherein rotation of said racking screw means being converted into a translational motion of plurality of rails provided on an enclosure cradle assembly and thereby enabling insertion of said circuit breaker; and
at least two split bearing means adapted to hold the racking screw means,
Characterized in that said bearing means having diametrical configuration so as to reduce the collar friction torque thereby producing substantial reduction in the final torque produced during racking operation.
, Description:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to switch gears and circuit breakers. More particularly, the subject invention relates to racking mechanisms for draw out air circuit breakers (ACB)

BACKGROUND

[002] A Circuit breakers are used to safeguard the electrical equipment from over current situations caused or short current situations in equipment. On flow of fault current conditions, the electrical contacts within the circuit breaker will open and it stops the flow of electrical current through the circuit breaker to the equipment.

[003] Switchgear systems can be either fixed to the bus bar systems or removable type known as Draw-out circuit breakers with an enclosure Cradle arrangement provided for establishing and removing connection with the bus bar system.

[004] As per international standards, depending upon construction, air circuit breakers are classified as fixed and draw-out type circuit breakers. Draw-out type circuit breakers comprises of two major parts cradle and breaker. Cradle is fixed part and breaker is moving part. Inside cradle arrangement is there to put breaker and move it in and out to achieve different positions such as isolated, test and service. Cradle consists of the racking mechanism, rail system along with locking system and contact system.

[005] To move breaker in and out of the cradle, arrangement is provided called rack-in arrangement. In the arrangement rotating motion of the screw is converted into oscillating motion of rack. A pinion is engaged with rack and is welded on the cradle shaft. Breaker is mounted on rails of cradle and thus rotating motion of screw is finally converted to translational motion of rails and the breaker is inserted. The rack-in or rack-out is cranking operation and is to be performed manually. As manual efforts are required to move breaker in or out of the cradle, the force limits should be within ergonomically specified limits.

[006] Existing breakers as shown in figure 3, have a racking mechanism assembly which consists of a rack, racking screw, support bracket (5) lock nuts (7, 9, 11) and brass washer (8, 10). Existing racking screw (6) is mounted on existing support bracket (5) with the help of Lock Nuts 7, 9 and 11 and washers (8) and (10). As the screw (6) rotates in racking operation, due to larger diameter of washers (8) and (10) a high collar friction torque is being generated which adds to the total racking torque resulting in higher force required to perform the racking operation. The design is such that the collar friction torque is more and this adds to the total torque required to rack-in the breaker. There are more no of components and so assembly time is more and complicated.

[007] Reference is made to US patent number US7821775 B2, which discloses 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. 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.

[008] Reference is made to US patent number US 5278722 A, which discloses switchgear cubicle racking mechanisms; and in particular hand-operated cranking mechanisms which accomplish racking movement of switchgear draw-out units and mechanical displays which indicate position of draw-out units within cubicles.

[009] Reference is also made to application number US3019309 A, wherein improved mechanism for mounting a circuit breaker structure in a cubicle and controlling its arcing contacts is provided. This mechanism integrates the action for both racking and circuit breaker contact controlling movement in single sequential operations. A driving shaft is utilized for actuating the racking means and the arcing contacts upon rotation thereof. This driving shaft is sequentially detachably connected to two driven shafts for rotation thereof. One of the driven shafts actuates the racking means while the other of the driven means charges a contact closing spring load means.

[0010] However, following are the drawbacks of the existing racking mechanism which is addressed by the present invention:
• The existing mechanism uses a cross shaft (Racking Screw) in an enclosure and input links connecting to the cradle shaft for performing the racking operation. This adds to the total racking torque resulting in higher force required to perform the racking operation.
• Racking Operation is more complex.
• More number of components in racking mechanism assembly.
• Increased assembly time.
• Less efficient and reliable.

[0011] Thus, in view of the drawbacks of the existing racking mechanism for draw-out of circuit breaker, there is a necessity to provide an improved mechanism for mounting a circuit breaker structure in a cubicle and controlling the total racking torque and the force required to perform the racking operation.

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 an improved racking mechanism that overcomes the drawbacks of the existing racking mechanism.

[0014] According to one aspect, the present invention provides a racking mechanism for a draw-out circuit breaker comprising:

at least one racking screw means rotatably disposed in an enclosure of the circuit breaker, wherein rotation of said racking screw means being converted into a translational motion of plurality of rails provided on an enclosure cradle assembly and thereby enabling insertion of said circuit breaker; and
at least two split bearing means adapted to hold the racking screw means,
Characterized in that said bearing means having diametrical configuration so as to reduce the collar friction torque thereby producing substantial reduction in the final torque produced during racking operation.

[0015] In second aspect, the present invention provides a circuit breaker assembly comprising: an enclosure; a draw out circuit breaker insertable in said enclosure; and a racking mechanism for enable racking of said draw out circuit breaker into said enclosure, said racking mechanism comprising:
at least one racking screw means rotatably disposed in an enclosure of the circuit breaker, wherein rotation of said racking screw means being converted into a translational motion of plurality of rails provided on an enclosure cradle assembly and thereby enabling insertion of said circuit breaker; and
at least two split bearing means adapted to hold the racking screw means,
Characterized in that said bearing means having diametrical configuration so as to reduce the collar friction torque thereby producing substantial reduction in the final torque produced during racking operation.

[0016] 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

[0017] 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:

[0018] Figure 1 shows an overview of a cradle of a draw-out air circuit breaker with a modified racking arrangement assembled on a base plate of a cradle, according to the present invention.
[0019] Figure 2 shows Base Plate Assembly with modified racking Arrangement, according to the present invention.
[0020] Figure 3 shows Exploded View of Existing Racking Arrangement according to prior art.
[0021] Figure 4 shows the improved Racking Arrangement, according to the present invention.
[0022] Figure 5 shows the exploded view of the racking arrangement, according to the present invention.

[0023] 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

[0024] 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.

[0025] 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.

[0026] 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.

[0027] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0028] 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.

[0029] 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.

[0030] 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 components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0031] The term “means” when used in the specification is taken to specify the mode by which desired result is achieved.

[0032] The racking mechanism of the present invention can be implemented with electrical switching device that may include but not limited to, circuit breakers or thermo-magnetic breaker, molded case circuit breaker (MCCB) residual circuit breaker (RCB), earth leakage circuit breaker (ELCB) and the like.

[0033] In the present invention, an improved racking mechanism for reducing racking torque in ACBs. It uses two split bearings for reducing the collar friction torque and thus there is overall reduction in racking torque of breaker. This will makes racking operation easier and hassle free. The number of components will be reduced, making the assembly easier and also reduces the assembly time.

[0034] List of the components with reference numerals to explain the figures 1-5 are follows:

1. Bracket for Modified Arrangement
2. Screw for Modified Arrangement
3. Upper split bearing
4. Lower split bearing
5. Bracket for Existing Arrangement
6. Screw for Existing Arrangement
7. Lock nut 1
8. Washer 1
9. Lock nut 2
10. Washer 2
11. Lock nut 3
12. Cradle assembly
13. Cradle base plate assembly.
14. Modified Racking Arrangement.
15. Existing Racking Arrangement.

[0035] In one embodiment, reference is made to figure (1) which shows an overview of a Cradle (12) of a Draw-out Air Circuit Breaker with a Modified Racking Arrangement (14) assembled on base plate (13) of cradle, according to one embodiment of the present invention.

[0036] In one embodiment, reference is made to figure (2) which shows a Base Plate Assembly (13) with the improved racking Arrangement (14).The racking Screw (2) can be mounted on racking bracket (1) held tightly with split bearings (3), (4).

[0037] In one embodiment, reference is made to figure (4) which Shows improved Racking Arrangement (14) comprising of racking Bracket (1), racking Screw (2), Upper split bearing (3) and lower split bearing (4).

[0038] In one embodiment, reference is made to figure (5) which shows Exploded View of Modified Racking Arrangement (14). The racking screw (2) will held tightly with upper split bearing (3) and lower split bearing (4) and will mounted on modified bracket (1).

[0039] In one embodiment, during racking operation of the circuit breaker, racking screw (2) will be enable to rotate. As the diameter of Split bearings (3) and (4) is small, there will be a substantial reduction in collar friction torque, thus giving a reduction in total torque for performing racking operation. As the racking torque will be reduced, force required to insert the breaker will also reduce and racking operation can be performed easily and is hassle-free.

[0040] Some of the noteworthy features of the present invention, are as follows:
• Use of Split Bearing for reducing racking torque.
• Arrangement of Racking with split bearings and racking screw.

[0041] Some of the advantages of the present invention, are as follows:
• Substantial reduction in racking torque.
• Racking Operation has become hassle free.
• Less number of components in racking mechanism assembly.
• Reduced assembly time.
• Efficient Performance.
• Providing sufficient torque reduction for racking the breaker and reducing manual efforts

[0042] Although a racking mechanism for draw-out air circuit breakers have been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the racking mechanism for draw-out air circuit breakers.