Claims:WE CLAIM:

1. A multi-pole circuit breaker comprising:
a housing comprising top cover (1) and bottom cover (2), said housing houses a first stationary contact (5), a second stationary contact (8) and a shaft (9) comprising a movable contact (6) for each pole (B, Y, R, N);
wherein said movable contact (6) is adapted to couple or uncouple to said first stationary contact (5);
said movable contact (6) comprising a plurality of movable fingers (B1-5, Y1-5, R1-5, N1-5);
said movable fingers (B1-5, Y1-5, R1-5, N1-5) pivotally rotate around a fulcrum pin (12) located in the shaft (9);
a pair of shielding plates (10) for each pole (B, Y, R), said shielding plates are substantially disposed in close proximity to outermost movable fingers (B1,5, Y1,5, R1,5) to barricade the movable fingers (B1-5, Y1-5, R1-5) of one pole from the movable fingers of the adjacent poles;
wherein perpendicular distance between surface (S2) of said shielding plates (10) and edge (E2) of the outermost movable fingers (B1,5, Y1,5, R1,5) is same as the thickness of shielding plates (10); and
wherein thickness of each shielding plate of the shielding plates (10) is half the thickness of each movable finger (B1-5, Y1-5, R1-5).

2. The multi-pole circuit breaker as claimed in claim 1, wherein each movable finger is operably coupled to a compression spring (11) and an/or extension spring (13) to maintain pressure between the movable contact (6) and first stationary contact (5) for good electrical joint.

3. The multi-pole circuit breaker as claimed in claim 1, wherein said movable fingers (B1-5, Y1-5, R1-5, N1-5) are parallel to each other.

4. The multi-pole circuit breaker as claimed in claim 1, wherein the plurality of movable fingers (B1-5, Y1-5, R1-5, N1-5) collectively carry total current in each pole (B, Y, R, N).

5. The multi-pole circuit breaker as claimed in claim 1, wherein a plurality of flexible copper conductors (7) operably couples the movable fingers of the movable contact (6) to the second stationary conductor (8).

6. A multi-pole circuit breaker comprising:
a housing comprising top cover (1) and bottom cover (2), said housing houses a first stationary contact (5), a second stationary contact (8) and a shaft (9) comprising a movable contact (6) for each pole (B, Y, R, N);
wherein said movable contact (6) is adapted to couple or uncouple to said first stationary contact (5);
said movable contact (6) comprising a plurality of movable fingers (B1-5, Y1-5, R1-5, N1-5);
said movable fingers (B1-5, Y1-5, R1-5, N1-5) pivotally rotate around a fulcrum pin (12) located in the shaft (9);
a pair of shielding plates (10) for Y pole, said shielding plates are substantially disposed in close proximity to outermost movable fingers (Y1,5) to barricade the movable fingers (Y1-5) of Y pole from the movable fingers of the adjacent poles;
wherein perpendicular distance between surface (S1) of said shielding plates (10) and edge (E1) of the outermost movable fingers (Y1,5) is same as the thickness of shielding plates (10); and
wherein thickness of each shielding plate of the shielding plates (10) is equal to the thickness of each movable finger.

7. The multi-pole circuit breaker as claimed in claim 6, wherein each movable finger is operably coupled to a compression spring (11) and an/or extension spring (13) to maintain pressure between the movable contact (6) and first stationary contact (5) for good electrical joint.

8. The multi-pole circuit breaker as claimed in claim 6, wherein said movable fingers (B1-5, Y1-5, R1-5, N1-5) are parallel to each other.

9. The multi-pole circuit breaker as claimed in claim 6, wherein the plurality of movable fingers (B1-5, Y1-5, R1-5, N1-5) collectively carry total current in each pole (B, Y, R, N).

10. The multi-pole circuit breaker as claimed in claim 6, wherein a plurality of flexible copper conductors (7) operably couples the movable fingers of the movable contact (6) to the second stationary conductor (8).

Dated this 31st day of March 2018

Abhishek Sen
Of S. MAJUMDAR & CO.
(Applicant’s Agent)
, Description:FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates to protection devices such as circuit breakers and more particularly, pertains to a circuit breaker with enhanced electrodynamic withstand capabilities.

BACKGROUND OF INVENTION

[002] A circuit breaker is an electrical protection device that can make, break and carry current in normal condition. When there is a fault in the system due to overload, short circuit etc. circuit breaker can break and clear the fault.

[003] A circuit breaker typically consists of at least one stationary contact and at least one movable contact in each pole. When the circuit breaker is switched ON by means of an operating mechanism, its movable contact mates with the stationary contact. To hold the movable contact at the mating position, high contact pressure is applied on the movable contact using springs. Current flowing through the stationary contact and movable contact generated electrodynamic and constriction forces, which are repulsive in nature and acts against the applied contact pressure.

[004] Significantly, the magnitude of both electrodynamic and constriction forces are directly proportional to the square of the current flowing through the contacts. Accordingly, when there is a fault in the system, both electrodynamic and constriction forces increase rapidly. When the combined electrodynamic and constriction forces are higher than the applied contact pressure, the movable contact repels open.

[005] Notably, moulded case circuit breakers are basically classified into two major categories namely ‘Category A’ and ‘Category B’. The ‘Category A’ breakers are designed to have a high short circuit breaking capacity to clear higher faults levels while the ‘Category B’ breakers are designed to have a capability to withstand faults current allowing the selectivity of the breakers, where breaker immediate upstream to the fault location detects the faulty branch and isolates the faulty branch from the whole system ensuring continuity of supply to other feeders or branches

[006] For ‘Category B’ breaker, having high current withstand capacity, the contact arrangement is designed to compensate/counteract the electrodynamic forces generated during the flow of short circuit current allowing the stationary and movable contacts mating with each other. The contact configuration should be designed efficiently to sustain mechanical and thermal stresses built up during the passage of the fault current, making the system bulkier and heavier.

[007] ‘Category B’ circuit breakers generally consist of plurality of movable contacts in each pole. These movable contacts are parallel to each other. Due to dimensional limitations of a circuit breaker, the movable contacts are very close to each other. Similarly, each pole of the circuit breaker is also at very close proximity to each other to ensure compact size of circuit breakers. The current flowing in the individual movable contacts is not uniformly distributed in density due to proximity effect. Any one of the outermost movable contact in any of the poles carry higher current. In case of a pole consisting of five movable contacts, generally any one of the outermost movable contacts in a certain pole carries 35% higher current than the normal current in the absence of proximity effect, resulting in higher electrodynamic and constriction forces. As a result, movable contact repels open, thereby decreasing the fault current withstand capacity of the breaker.

[008] For some existing technology in this field, reference is made to US Patent Number 7989721 B2, wherein a single-pole or multi-pole device for low-voltage systems is disclosed. In particular, the circuit breaker or disconnector comprises an outer casing containing for each pole at least one fixed contact and at least one mobile contact that can be coupled to/uncoupled from one another; a rotating element that comprises a shaped body made of insulating material comprising at least one seat for each pole of said switch, said seat being designed to house at least one mobile contact of a corresponding pole; a control mechanism operatively connected to the rotating element for enabling movement thereof; and one or more elements made of ferromagnetic material set in a position corresponding to at least one portion of the inner surface of said at least one seat of the mobile contact.

[009] Reference is also made to US Patent Number 7935902 B2, wherein a contact arm assembly including a plurality of substantially parallel plates is disclosed. These parallel plates have a space between each of the plurality of substantially parallel plates and a plurality of finger assemblies, at least one of the plurality of finger assemblies being pivotally attached to the plurality of substantially parallel plates and being located in the space between each of the plurality of substantially parallel plates, each of the plurality of finger assemblies having a body and an arc runner, the arc runner being locked against the body in at least two locations. The exemplary embodiments provide a rigid and robust contact movement arrangement that can withstand and account for large electrodynamic repulsion forces created by current flowing in the circuit breaker.

[0010] The drawbacks associated with these existing technologies is that they require the use of a plurality of parallel plates in shaft assembly that results in increasing the overall number of components present therein. This makes the assembly more complex, bulky and large.

[0011] Accordingly, there is a need to limit the phenomena of non-uniform distribution of current in the movable contacts to enhance the fault current withstanding capacity of a circuit breaker. Moreover, it is necessary to provide a circuit breaker that assures high reliability while also being cost-effective.

[0012] The above-described need to limit the phenomena of non-uniform distribution of current in the movable contacts to provide enhanced electrodynamic withstand capabilities 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 circuit breaker with enhanced electrodynamic withstand capabilities.

[0015] Another object of the present invention is to limit the non-uniform distribution of current in the movable contacts of the circuit breaker to increase the fault current withstand capacity of the circuit breaker.

[0016] Yet another object of the present invention is to provide an arrangement of shielding plates in a circuit breaker to enhance the circuit breakers withstanding capacity.

[0017] According to a first aspect of the present invention, there is provided a multi-pole circuit breaker. The circuit breaker comprising a housing comprising top cover and bottom cover, said housing houses a first stationary contact, a second stationary contact and a shaft comprising a movable contact for each pole (B, Y, R, N); wherein said movable contact is adapted to couple or uncouple to said first stationary contact; said movable contact comprising a plurality of movable fingers; said movable fingers pivotally rotate around a fulcrum pin located in the shaft; a pair of shielding plates for each pole (B, Y, R), said shielding plates are substantially disposed in close proximity to outermost movable fingers to barricade the movable fingers of one pole from the movable fingers of the adjacent poles; wherein perpendicular distance between surface (S2) of said shielding plates and edge (E2) of the outermost movable fingers is same as the thickness of shielding plates; and wherein thickness of each shielding plate of the shielding plates is half the thickness of each movable finger.

[0018] In a possible implementation of the circuit breaker according to the first aspect, each movable finger is operably coupled to a compression spring and/or an extension spring to maintain pressure between the movable contact and first stationary contact for good electrical joint.

[0019] In another possible implementation of the circuit breaker according to the first aspect, the plurality of movable fingers is parallel to each other.

[0020] In yet another possible implementation of the circuit breaker according to the first aspect, the plurality of movable fingers collectively carry the total current in each pole (B, Y, R, N).

[0021] In yet another possible implementation of the circuit breaker according to the first aspect, a plurality of flexible copper conductors operably couples the movable contact to the second stationary conductor.

[0022] According to a second aspect of the present invention, there is provided a multi-pole circuit breaker. This multi-pole circuit breaker comprises: The circuit breaker comprising: a housing comprising top cover and bottom cover, said housing houses a first stationary contact, a second stationary contact and a shaft comprising a movable contact for each pole (B, Y, R, N); wherein said movable contact is adapted to couple or uncouple to said first stationary contact; said movable contact comprising a plurality of movable fingers; said movable fingers pivotally rotate around a fulcrum pin located in the shaft; a pair of shielding plates for Y pole, said shielding plates are substantially disposed in close proximity to outermost movable fingers to barricade the movable fingers of Y pole from the movable fingers of the adjacent poles; wherein perpendicular distance between surface (S1) of said shielding plates and edge (E1) of the outermost movable fingers is same as the thickness of shielding plates; and wherein thickness of each shielding plate of the shielding plates is equal to the thickness of each movable finger.

[0023] In a possible implementation of the circuit breaker according to the second aspect, each movable finger is operably coupled to a compression spring and/or an extension spring to maintain pressure between the movable contact and first stationary contact for good electrical joint.

[0024] In another possible implementation of the circuit breaker according to the second aspect, the plurality of movable fingers is parallel to each other.

[0025] In yet another possible implementation of the circuit breaker according to the second aspect, the plurality of movable fingers collectively carry the total current in each pole (B, Y, R, N).

[0026] In yet another possible implementation of the circuit breaker according to the second aspect, a plurality of flexible copper conductors operably couples the movable contact to the second stationary conductor.

[0027] 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

[0028] 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:

[0029] Figure 1 illustrates the 4-pole configuration of a moulded case circuit breaker according to an embodiment of the present invention.

[0030] Figure 2 illustrates the cross section view of the circuit breaker in ON condition according to an implementation of the present invention.

[0031] Figure 3 illustrates the isometric view of the stationary and movable contacts assembly according to an implementation of the present invention.

[0032] Figure 4 illustrates the isometric view of the shaft assembly according to an implementation of the present invention.

[0033] Figure 5 illustrates the current distribution per movable finger due to proximity effect.

[0034] Figure 6 illustrates the arrangement of shielding plates in Y pole compensating proximity effect according to an implementation of the first embodiment of the present invention.

[0035] Figure 7 illustrates the current distribution per movable finger for the arrangement of shielding plates in Y pole according to an implementation of the first embodiment of the present invention.

[0036] Figure 8 illustrates the arrangement of shielding plates in all the three poles – R, Y, B to compensate the proximity effect according to an implementation of the second embodiment of the present invention.

[0037] Figure 9 illustrates the current distribution per movable finger for arrangement of shielding plates in all the three poles according to an implementation of second embodiment of the present invention.

[0038] 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

[0039] 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.

[0040] 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.

[0041] 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.

[0042] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The present invention lies in providing a circuit breaker with enhanced electrodynamic withstand capabilities.

[0047] In particular, the present invention describes the construction of a circuit breaker that is capable of limiting the non-uniform distribution of current in a plurality of movable contacts so that the fault current withstand capacity of the circuit breaker can be increased. This circuit breaker assures high reliability and cost-effectiveness.

[0048] In the existing prior art, the ferromagnetic material is caged inside shaft whereas in present invention, a pair of shielding plates is positioned outside shaft. Moreover, the ferromagnetic material is not related to mobile contact dimensionally while in the present invention, the thickness of the shielding plates as well as the distance of the shielding plates with respect to movable finger is related to the thickness of movable finger. Further, the plurality of parallel plates used in shaft assembly of the prior art increase the overall number of components while in the present invention, the shielding plates are a part of the circuit breaker assembly and not a part of the shaft assembly. The thickness of the parallel plates has no bearing on the fingers while in the present invention, the thickness of the shielding plates as well as distance of shielding plates with respect to movable finger is related to the thickness of movable finger

[0049] According to a first embodiment of the present invention, a multi-pole circuit breaker with enhanced electrodynamic withstand capabilities is disclosed. The circuit breaker comprising: The circuit breaker comprising a housing comprising top cover (1) and bottom cover (2), said housing houses a first stationary contact (5), a second stationary contact (8) and a shaft (9) comprising a movable contact (6) for each pole (B, Y, R, N); wherein said movable contact (6) is adapted to couple or uncouple to said first stationary contact (5); said movable contact (6) comprising a plurality of movable fingers (B1-5, Y1-5, R1-5, N1-5); said movable fingers (B1-5, Y1-5, R1-5, N1-5) pivotally rotate around a fulcrum pin (12) located in the shaft (9); a pair of shielding plates (10) for each pole (B, Y, R), said shielding plates are substantially disposed in close proximity to outermost movable fingers (B1,5, Y1,5, R1,5) to barricade the movable fingers (B1-5, Y1-5, R1-5) of one pole from the movable fingers of the adjacent poles; wherein perpendicular distance between surface (S2) of said shielding plates (10) and edge (E2) of the outermost movable fingers (B1,5, Y1,5, R1,5) is same as the thickness of shielding plates (10); and wherein thickness of each shielding plate of the shielding plates (10) is half the thickness of each movable finger (B1-5, Y1-5, R1-5).

[0050] According to a second embodiment of the present invention, a multi-pole circuit breaker with enhanced electrodynamic withstand capabilities is disclosed. The circuit breaker comprising: a housing comprising top cover (1) and bottom cover (2), said housing houses a first stationary contact (5), a second stationary contact (8) and a shaft (9) comprising a movable contact (6) for each pole (B, Y, R, N); wherein said movable contact (6) is adapted to couple or uncouple to said first stationary contact (5); said movable contact (6) comprising a plurality of movable fingers (B1-5, Y1-5, R1-5, N1-5); said movable fingers (B1-5, Y1-5, R1-5, N1-5) pivotally rotate around a fulcrum pin (12) located in the shaft (9); a pair of shielding plates (10) for Y pole, said shielding plates are substantially disposed in close proximity to outermost movable fingers (Y1,5) to barricade the movable fingers (Y1-5) of Y pole from the movable fingers of the adjacent poles; wherein perpendicular distance between surface (S1) of said shielding plates (10) and edge (E1) of the outermost movable fingers (Y1,5) is same as the thickness of shielding plates (10); and wherein thickness of each shielding plate of the shielding plates (10) is equal to the thickness of each movable finger.

[0051] Figure 1 illustrates the 4-pole configuration of a moulded case circuit breaker. A top cover (1) and a bottom cover (2) make the moulded case housing. A plurality of current carrying conductors is operated by a mechanism (3) through an operating lever (4).

[0052] Figure 2 illustrates the cross section view of circuit breaker in on condition. The current conducts through a first stationary contact (5) and a movable finger (6), a second stationary conductor (8), a plurality of flexible copper conductors (7) connect to a plurality of the movable fingers (6) to a second stationary conductor (8) and vice-versa. The movable fingers (6) rotate around a fulcrum pin (12) located in a shaft (9). Compression springs (11) and extension springs (13) are attached to each movable finger inside the shaft (9) to provide the contact force required to maintain the pressure between movable finger (6) and first stationary contact (5) for good electrical joint. The torque due to the contact springs act against the electrodynamic and constriction forces during overload and short circuit conditions.

[0053] Figure 3 illustrates an isometric view of the stationary and movable contacts assembly. As illustrated in the figure, there are four poles: N, R, Y and B. The shaft (9) houses a plurality of movable fingers (6).

[0054] Figure 4 illustrates an isometric view of the shaft assembly (9). Five movable fingers (6) are housed in each pole. All the five parallel movable fingers (6) together carry the total current in each pole. These movable fingers (6) rotate around the fulcrum pin (12) located at pivotal hole (12). In ON operation, the contact pressure between stationary and movable contact is applied due to the torque on movable fingers (6) around the fulcrum pin (12). The movable fingers (6) in R pole are designated as R1, R2, R3, R4 & R5. Similar is the case in Y and B pole.

[0055] Figure 5 illustrates the current distribution per movable finger due to proximity effect. The alternating magnetic field in the adjacent movable fingers alters the current density of the movable fingers depending on their position due to proximity effect. The graph illustrates the current distribution of respective movable finger as percentage of the normal current in the absence of proximity effect. As depicted in the graph, movable finger (Y1) and (B1) carries 35% & 21% respectively higher current than the normal current.

[0056] Figure 6 illustrates the arrangement of MS plate in Y pole compensating the proximity effect. To limit the non-uniform distribution of current in respective movable fingers, the shielding plates (10) is placed adjacent to movable fingers (Y1) and (Y5). The thickness of the said shielding plates (10) is equal to the thickness of each movable contact (6). This shielding plates (10) has to be placed in close proximity to the movable fingers (Y1) and (Y5), and preferably the perpendicular distance between surface (S1) of shielding plates (10) and edge (E1) of Y1, 5 should be the thickness of the shielding plates (10).

[0057] Figure 7 illustrates the current distribution per movable finger for arrangement illustrated in Figure 6. Here the graph depicts that with the arrangement discussed hereinabove, the current in the movable fingers (Y1) and (B1) has been reduced by 19% and 5%, respectively.

[0058] Figure 8 illustrates the arrangement of shielding plates (10) in all the three poles – R, Y, B to compensate the proximity effect. To limit the non-uniform distribution of current in respective movable fingers, the shielding plates (10) is placed adjacent to movable fingers (R1), (R5), (Y1), (Y5), (B1) and (B5). For this particular arrangement of the shielding plates (10), the thickness of the said shielding plates (10) should be half the thickness of each movable contact (6). The shielding plates (10) has to be placed in close proximity to the extreme movable fingers (R1), (R5), (Y1), (Y5), (B1) and (B5) in each pole, preferably the perpendicular distance between surface (S2) of shielding plates (10) and edge (E2) of R5 should be same as the thickness of shielding plates (10), i.e., same distance is maintained in case of placement of shielding plate w.r.t. R1, Y1, Y5, B1, B5. This shielding plates (10) is preferably made from mild steel.

[0059] Figure 9 illustrates the current distribution per movable finger for arrangement illustrated in Figure 8. The graph depicts that with above said arrangement, current in movable fingers (Y1) and (B1) has been reduced by 19% and 9%, respectively.

[0060] Some of the non-limiting advantages of the present invention are mentioned hereinbelow:
1. It limits the non-uniform distribution of current in the movable contacts of the circuit breaker to increase the fault current withstand capacity;
2. It provides a cost effective circuit breaker with low manufacturing cost and high reliability;
3. It provides higher electrodynamic withstanding capacity when compared to prior art; and
4. It employs lesser number of components thereby reducing the assembly time significantly.

[0061] Although a circuit breaker with enhanced electrodynamic withstand capabilities 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 to limit the non-uniform distribution of current in the movable contacts to increase the fault current withstand capacity of the circuit breaker.