Claims:1. A hybrid contact structure for molded case circuit breakers, wherein structure having a current limiting contact structure part and a force compensating contact structure part, wherein said current limiting contact structure part comprising:
a first stationary contact means;
a rotatable moving contact bridge pivotally mounted on a rotating shaft at a hinge point, wherein said rotatable moving contact bridge overlap with said first stationary contact means;
wherein said current limiting contact structure part adapted to generate high electrodynamic forces repelling said rotatable moving contact bridge to a repelled open position during a short-circuit condition;
and said force compensating contact structure part comprising:
a flexible conductor means attached to said rotatable moving contact bridge;
a second stationary contact connecting said conductor means;
wherein said conductor means and said second stationary contact displaced at an angle of 90° from each other;
wherein, said force compensating contact structure part adapted to compensate said electrodynamic forces generated under said short circuit conditions allowing a better selectivity with downstream equipments.

2. The current limiting contact structure as claimed in claim 1, wherein said first stationary contact means comprises a U-shaped bending structure to impose said overlap with said rotatable moving contact bridge.

3. The current limiting contact structure as claimed in claim 1, wherein said second stationary contact is an L-shaped stationary copper conductor means.

4. The current limiting contact structure as claimed in claim 1, comprises a compression spring means inside said shaft, to provide contact force to maintain a pressure between said rotatable moving contact bridge and said first stationary contact means.

5. The current limiting contact structure as claimed in claim 4, wherein a supporting pin means guided through said compression spring means.

6. The current limiting contact structure as claimed in claims 1-5, wherein during said short circuit current flow, repulsion forces generated between the flexible conductor means and the second stationary contact means are transferred to the mating surface of said first stationary contact and said rotatable contact bridge compensating forces generated.

7. The current limiting contact structure as claimed in claim 6, wherein said conductor means transfers said repulsion forces to front end of said rotatable moving contact bridge through said hinge point.

8. The current limiting contact structure as claimed in claims 1-7, wherein during said short-circuit condition, said rotatable moving contact bridge reaches repel open position, said supporting pin means slips a mechanism lever, causing rotation of said shaft, and enabling positive isolating between said first stationary contact means and said rotatable contact bridge.
, Description:TECHNICAL FIELD OF THE INVENTION

[0001] The present subject matter described herein, in general, relates to contact arrangements for molded case circuit breakers, and more particularly to a contact arrangement of molded case low voltage circuit breaker with higher short circuit withstand capacity and higher short circuit breaking capacity.

BACKGROUND OF THE INVENTION

[0002] Molded case circuit breakers are basically classified in to two major categories namely ‘Category A’ and ‘Category B’. ‘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 locations detects the faulty branch and isolates the faulty branch from the whole system ensuring continuity of supply to other feeders or branches.

[0003] Circuit breakers are mainly designed based on these requirements either to have high service breaking capacity or to have a short circuit withstand capacity but not both. For example, a ‘Category A’ circuit breaker having high short circuit breaking capacity, the contact configuration is designed to act ultra-fast during the very high fault conditions in order to limit the damage due to the arc and also to limit the mechanical and temperature stresses induced in to the system during fault duration. So by virtue of the contact arrangement the contact configuration have very little ability to retain the contacts in the mating position against high fault current thus having very low withstand capacity.

[0004] For ‘Category B’ breaker, having high current withstand capacity, the contact arrangement is designed to compensate/counteract the electro dynamic 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. As the configuration is specifically designed to compensate the repulsion forces generated, combined with bulkier system these breakers have very low breaking capacity. As the breaker allows the fault currents to flow thru, the other devices in the system are subjected to high amount of stress which deteriorates the life of the devices.

[0005] In prior art document US6018284 A, a circuit breaker pole is disclosed which comprises movable contact means with a support carrier movable with respect to the frame between an open position and a closed position and one or more contact fingers movable with respect to the support carrier between a contact position and a retracted position. Electromagnetic compensation means are which are designed to apply electromagnetic forces on the contact finger or fingers tending to keep the contact finger or fingers in contact with the stationary contact means. Electromagnetic limiting means are designed to apply electromagnetic forces on the contact finger or fingers tending to drive the finger or fingers to their retracted position. The electromagnetic compensation means and the electromagnetic limiting means are such that when the current intensity flowing in the movable contact means is under a threshold called the limiting threshold, the finger or fingers are kept in contact with the stationary contact means, and that above said threshold, the finger or fingers are driven to their retracted position. The resultant of the forces applied by the carrier on the kinematic connecting means when the current intensity flowing in the movable contact means reaches the limiting threshold is under the ultrafast opening threshold. In this document the electromagnetic compensation means is able to apply electromagnetic forces on the contact finger or fingers tending to keep the finger or fingers in contact with the other contact means and the actuating means acts in conjunction with the movable contact means, the opening lock and the kinematic system cause the ultrafast opening.

[0006] Accordingly, there is a dire need for a circuit breaker with adequate fault current withstand capacity and high breaking capacity to offer selectivity with the downstream breakers when needed and reduce the stress on the system during fault clearing.

SUMMARY OF THE INVENTION

[0007] 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.

[0008] An object of the present invention is to provide a contact arrangement of molded case low voltage circuit breaker with higher Short circuit withstand capacity and higher Short circuit breaking capacity.

[0009] Another object of the present invention to provide a contact structure with two halves, the first half namely current limiting contact structure and the second half namely compensating contact structure.

[0010] Accordingly, in one aspect, the present invention provides a hybrid contact structure for molded case circuit breakers, wherein structure having a current limiting contact structure part and a force compensating contact structure part, wherein said current limiting contact structure part comprising:
a first stationary contact means;
a rotatable moving contact bridge pivotally mounted on a rotating shaft at a hinge point, wherein said rotatable moving contact bridge overlap with said first stationary contact means;
wherein said current limiting contact structure part adapted to generate high electrodynamic forces repelling said rotatable moving contact bridge to a repelled open position during a short-circuit condition;
and said force compensating contact structure part comprising:
a flexible conductor means attached to said rotatable moving contact bridge;
a second stationary contact connecting said conductor means;
wherein said conductor means and said second stationary contact displaced at an angle of 90° from each other;
wherein, said force compensating contact structure part adapted to compensate said electrodynamic forces generated under said short circuit conditions allowing a better selectivity with downstream equipments.

[0011] 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

[0012] 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:

[0013] Figure 1 shows the 4 pole configuration of molded case circuit breaker, in accordance with an embodiment of the present invention.

[0014] Figure 2 shows the cross sectional view of the contact system of circuit breaker in ON condition, in accordance with an embodiment of the present invention.

[0015] Figure 3 illustrates the rotatable moving contact bridge inside a shaft, in accordance with the present invention.

[0016] Figure 4 illustrates the contact structure with current limiting and compensating structures ,in accordance with an embodiment of the present invention

[0017] 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

[0018] 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.

[0019] 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.

[0020] 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.

[0021] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The present invention relates to a contact structural arrangement of molded case low voltage circuit breakers with higher short-circuit withstand capacity and higher short–circuit breaking capacity. The present invention includes a contact structure with two halves, the first half namely current limiting contact structure and the second half namely compensating contact structure.

[0026] In one implementation, the contact structure comprising of a rotary contact bridge; a first stationary contact cooperating with the rotatable contact bridge; a secondary contact connected to the rotary bridge through a flexible current carrying conductor. The flexible current carrying conductor allows the contacts to be separated smoothly under fault conditions.

[0027] In one implementation, the present invention includes a rotatable contact bridge pivotally mounted on a rotating shaft wherein the pivot of the rotatable contact bridge divides the contact structures in to two equal halves.

[0028] In one implementation, the present invention includes a current limiting contact structure which generates high electrodynamic forces repelling the contact bridge to a repelled open position when a short circuit occurs, limiting the fault current to the minimum and limiting the stresses to the downstream equipment.

[0029] In one implementation, the present invention includes a force compensating contact structure, to compensate high forces generated under short circuit conditions allowing better selectivity with the downstream equipment.

[0030] In one implementation, the limiting contact structure consist of first stationary contact means and a rotatable contact bridge wherein the first stationary contact can have a U-shaped bend structure to impose an overlap with the contact bridge. This overlapping develops high electro dynamic forces when high short circuit current flows through the contact structure and repels the rotatable contact bridge in order to break the circuit.

[0031] In one implementation, the second half of the contact arrangement, force compensating structure consist of flexible copper conductors connecting the rotatable contact bridge and the L shaped stationary copper contact means, during short circuit current flow the repulsion forces generated between the flexible copper conductors and the second secondary conductors are transferred to the mating surface of the first stationary conductor and rotatable contact bridge compensating any forces generated.

[0032] In one implementation, the repulsion forces, the compensating forces along with the contact spring force acting on the mating surface of the rotatable contact bridge and the first stationary conductor helps the contact to withstand the fault current up to a threshold value set by the force balance. Beyond this threshold value the contact repels very fast and breaks the circuit with a minimum arcing and limit the stresses developed in the system.

[0033] In one implementation, reference made to figure 1, which shows the 4 pole configuration of a molded case circuit breaker, wherein Top cover (1) and bottom cover (2) make the molded case housing the current carrying conductors operated by a mechanism (3) through the operating lever (4).

[0034] In one implementation, figure 2 shows a cross-section view of the circuit breaker in ON condition. The current conducts through the first stationary contact (5) and the rotatable contact bridge (6); a second stationary conductor (7) and a flexible copper conductor (8), connecting the rotatable contact bridge (6) to a second stationary conductor (7) and vice versa. The compression spring means (9) can be arranged inside the shaft means (10) to provide the contact force required to maintain the pressure between the rotatable contact bridge 6 and first stationary contact 5 for good electrical joint. A supporting pin means (11) can be guided through the compression spring means (9) to avoid buckling and loss of spring force. Alternately, the said supporting pin means (11) can be used to slip the trip mechanism lever (12) when the rotatable contact bridge (6) repels under short circuit fault conditions.

[0035] In one implementation, figure 3 shows the rotatable moving contact bridge (6) which can be hinged inside the shaft means (10). The shaft means (10) can be designed to accommodate multi finger assembly (13) in each pole (14).

[0036] In one implementation, figures 4 shows the contact arrangement of the present invention which is divided into exactly two equal halves along the dotted line AA. The first half namely H1 is the limiting contact structure consist of first stationary contact (5) with a U shaped bend and a rotatable moving contact bridge (6) hinged at P1 inside shaft 10. The first stationary contact means (5) and rotatable Contact Bridge (6) can be arranged to have an overlap between them. When high short circuit current flows through the first stationary contact (5) and rotatable contact bridge (6), constriction and electromagnetic forces are generated in the system which repels the rotatable contact bridge (6) to interrupt the flow of current.

[0037] In the implementation, the second half H2 of the contact structure as shown in figure 4, namely compensating contact structure comprising a flexible copper conductor (8) and a second stationary contact (7). Both the flexible copper conductor (8) and a second stationary contact (7) can be displaced at an angle of 90deg from each other. The height H of the second stationary contact (7) can be preferably chosen in such a way that it is similar to the overlap length in the limiting structure H1 generating less amount of repulsion forces in the compensating structure. When short circuit current flows through flexible copper conductor (8) and second stationary contact (7) repulsion forces are generated making the flexible copper conductor 8 move upwards. As the flexible copper conductor (8) is attached to the rotatable contact bridge (6), the force exerted on the flexible conductor (8) will be transferred to the front end (13) of the rotatable contact bridge (6) via the hinge point P1. The forces transmitted about the hinge point P1 will compensate a portion of the repulsion forces and constriction forces allowing the rotatable contact bridge (6) to remain in mating position allowing the flow of fault current thru the system to achieve selectivity, allowing the downstream breaker (immediate upstream to fault location) clear the fault and maintain continuity of supply for the rest of the healthy system.

[0038] In the implementation, this equilibrium in the system will be disturbed by the fast rising constriction forces increase in value beyond the compensating forces developed because of the flexible copper conductor (8) and a second stationary contact 7. The constriction forces will give a knee jerk force to the rotatable contact bridge (6) to repel open with high velocity. The electromagnetic repulsion forces assist the rotatable contact bridge (6) to reach repel open position. These repel open forces helps the contact bridge to break the current flow, quench the electric arc fast enough to limit the stresses in the system.

[0039] In the implementation, when the contact bridge begins to repel open , the supporting pin means (11) will slip the trip mechanism lever (12) causing the mechanism (3) to rotate the shaft means (10) ensuring positive isolation between the first stationary contact means (5) and the rotatable contact bridge (6).

[0040] Some of the important features of the present invention, considered to be noteworthy are mentioned below:
1) The present invention provides a hybrid contact arrangement with current limiting and current breaking capacity.
2) The current withstand structure of the present invention helps in achieving selectivity with downstream devices.
3) The current limiting structure develops enough forces during repel opening to limit the stresses in the system.
4) The contact springs exert enough pressure to maintain good contact between the first stationary contact and the contact bridge for the circuit current to flow under normal conditions.
5) In the present invention the springs pin means slips the trip mechanism to rotate the shaft and positively break the circuit.
6) The flexible smooth conductors allow smooth repel opening of the contact bridge under fault condition.
7) The force exerted on the flexible conductors transfers on to the moving contact to compensate the repulsion forces at the mating surface.

[0041] Some of the non-limiting advantages of the present invention are mentioned below:
1) The present invention provides both current limiting and current compensating structures without the requirement of additional systems.
2) In the present invention no additional actuating means are required to keep the contacts in locked position as compared to the prior arts which require additional actuating means for ultrafast opening.
3) In the present invention no additional actuating means is required to unlock the movable contact bridge and clear the fault.
4) The electromagnetic forces of the present invention is directly acting up on the movable contact bridge during fault clearing.
5) The mechanism (kinetic energy system) in the present invention ensures a positive isolation of the contacts after the fault is cleared .Thus, the fault clearing is not dependent on the mechanism.

[0042] Although a hybrid contact arrangement with both current limiting and current withstanding capacity 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 herein. Rather, the specific features are disclosed as examples of implementations of the hybrid contact arrangement system without the requirement of additional systems