Claims:WE CLAIM:

1. A spring based double break contact system for circuit breakers, said contact system comprising:
a shaft (1);
a moving contact (2) comprising a plurality of holes (10, 11, 12);
wherein said moving contact (2) is pivotally mounted over said shaft (2) by a center pin (9) such that said moving contact (2) rotates with respect to the movement of said shaft (1); and
a pair of spring assemblies (4) rotatably anchored over said shaft (1) and said moving contact (2) such that said assemblies rotate with respect to the movement of said shaft (1) and moving contact (2);
wherein each assembly (4) comprises one contact spring (5) and one spring holder (3); and
wherein each spring assembly (4) is anchored by a pair of moving pin (6) and fixed pin (7).

2. The contact system as claimed in claim 1, wherein each contact spring (5) is secured over the shaft (1) by one spring holder (3); and wherein said spring holder (3) is adapted to accommodate one contact spring (5) .

3. The contact system as claimed in claim 1, wherein said contact springs (5) are adapted to provide a force opposing the electromagnetic force and the force aiding said electromagnetic force.

4. The contact system as claimed in claim 1, wherein position of said moving pin (6) changes dynamically as the moving contact (2) and shaft (1) rotates; and wherein positions of the fixed pin (7) and the center pin (9) remains constant.

5. The contact system as claimed in claim 3, wherein said contact spring (5) is a compression spring channelizing the spring force exactly in the requisite direction.

6. The contact system as claimed in claim 1, further comprising a shaft cover (8) to secure the shaft (1), said shaft cover (8) further comprising a plurality of shaft cover flaps.

7. The contact system as claimed in claim 1, wherein said shaft cover (8) comprises a pair of slots to allow the moving contact (2) to protrude outside said shaft cover (8).

8. The contact system as claimed in claim 4, wherein the pair of fixed pins (7), the pair of moving pins (6) and the center pin (9) align to form a straight line when the moving contact is in open condition.

9. The contact system as claimed in claim 5, wherein electromagnetic forces repel the moving contact (2) against the direction of the contact spring (5) force.

Dated this 29th day of March 2019

Abhishek Sen
IN/PA Reg No: 980
Of S. MAJUMDAR & CO.
(Applicant’s Agent)
, Description:F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention –

A SPRING BASED DOUBLE BREAK CONTACT SYSTEM FOR CIRCUIT BREAKERS

2. Applicant(s)

(a) NAME : LARSEN & TOUBRO LIMITED

(b) NATIONALITY: An Indian Company.

(c) ADDRESS: L & T House, Ballard Estate, P.O. Box: 278,
Mumbai 400 001, State of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates to circuit breakers and more particularly, pertains to a spring based double break contact system for circuit breakers.

BACKGROUND OF INVENTION

[002] During operation of power systems, it is often desirable and necessary to switch on or off the various circuits (e.g., transmission lines, distributors, generating plants etc.) under both normal and abnormal conditions. Switching devices are instruments employed for opening and closing an electric circuit. A switching device comprises at least one pole and a control device adapted to open and close said pole. Examples of switching devices include switches and switch-fuses. With advancement of power systems, the lines and other equipment’s operate at very high voltages and carry large currents. The traditional arrangement of switches with fuses cannot serve the desired function in such high capacity circuits.

[003] A circuit breaker can make or break a circuit either manually or automatically under all conditions viz., no-load, full load and short-circuit conditions. They are used for switching and protection of electrical equipment. The use of circuit breakers is widespread in modern-day residential, commercial and industrial electric systems, and they constitute an indispensable component of such systems toward providing protection against over-current conditions. Various circuit breaker mechanisms have evolved and have been perfected over time on the basis of application-specific factors such as current capacity, response time, and the type of reset (manual or remote) function desired of the breaker.

[004] Switching devices like, Moulded Case Circuit Breakers (MCCBs) operating on the current limiting principle typically have a pair of solid stationary electrical contacts joined by a solid moving electrical contact, which provides a path to carry the electrical current in the network. They are typically installed in a distribution load center with other like breakers. Usually multiple MCCBs have a single load center which consists of a sheet metal enclosure with a hinged door that allows access to the face of the enclosed MCCBs. The circuit breakers are secured within an inner sheet metal panel. Electrical busses and conductor raceways are located beneath this inner panel. The MCCBs generally include a moulded case main breaker supplying at least one common bus located within the load center.

[005] It is the rotor construction of the double-break arrangement that helps in the better make and break, under normal and abnormal conditions involving very high over-currents. The switching device needs to interrupt an over current arising due to abnormal conditions in the network, as rapidly as possible to minimize damage caused by thermal and mechanical stresses to the equipment installed downstream. It is necessary that the rotor or shaft of the moulded case circuit breaker is robust as high electro dynamic repulsive forces are generated between the stationary and moving contacts in the over current conditions.

[006] A circuit breaker mainly consists of current sensing means, mechanism and contact system. The contact system consists of a set of fixed contacts and a moving contact. During any fault (short circuit) in the line, the moving contact is opens and clears the fault. During ON condition, a set of springs provide contact force to maintain the moving contact in ON condition. Different arrangements of springs are followed currently for maintaining contact pressure. Significantly, the construction of contact system is such that the moving contact repels open during any fault in line due to electromagnetic forces. During this movement, the electromagnetic force acts against the springs providing contact pressure initially. As the moving contact moves further in its trajectory, the spring force aids the electromagnetic force. Once the dead center is crossed, the moving contact is flip-locked in the open position. This aids with lower let-through energy and lower fault clearing time.

[007] For some state of the art technology, reference is made to Indian Patent application number 911/MUM/2012. It discloses an improved double break contact system for moulded case circuit breakers. In particular, it teaches a suitable shift in the position of the hole in the moving contact carrier of the existing compression spring based double break contact system with flip-locking mechanism. The position of the hole on the moving contact carrier decides the position of dead center or the no-return point of the moving contact assembly.

[008] The drawbacks associated with the existing contact assembly arrangements are due to the limitations associated with their construction that result in the low fault clearing time applications requiring discrimination. In particular, the multitude of drawbacks associated with the existing construction of the shaft assemblies of MCCB’s are listed hereinbelow:

a) nuisance tripping of up-stream MCCB when used in applications requiring selectivity;
b) re-closure of up-stream breaker does not happen when the fault current is limited and cleared by the downstream breaker;
c) total discrimination cannot be achieved due to low fault clearing time since the fault clearing time of MCCB remains constant irrespective of its position in the power system hierarchy, therefore, when such MCCB is used as an up-steam protection device, discrimination is not achieved; and
d) energy discrimination is possible only when the difference between the rating upstream and downstream breakers is substantially high.

[009] Accordingly, there is a need to overcome the drawbacks associated with the existing construction of moulded case circuit breakers by providing a spring based double break contact system for use in moulded case circuit breakers. In particular, there is a need for a compression spring based double break contact system with defeated flip-locking mechanism for moulded case circuit breakers.

[0010] The above-described need for a spring based double break contact system for moulded case circuit breakers 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

[0011] 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.

[0012] An object of the present invention is to alleviate the drawbacks associated with the existing construction of shaft assemblies of moulded case circuit breakers.

[0013] Another object of the present invention is to suggest minimal changes to the existing construction of the shaft assembly, with no compromise on the contact gap, to resolve the limitations associated with the existing design of moulded case circuit breakers.

[0014] Yet another object of the present invention is to provide a compression spring based double break contact system with defeated flip-locking mechanism for moulded case circuit breakers.

[0015] According to a first aspect of the present invention, there is provided a spring based double break contact system for circuit breakers. The contact system comprising: a shaft, a moving contact, a center pin and a pair of spring assemblies. The moving contact comprises a plurality of holes where said moving contact is pivotally mounted over said shaft by the center pin such that said moving contact rotates with respect to the movement of said shaft. The pair of spring assemblies is rotatably anchored over said shaft and said moving contact such that said assemblies rotate with respect to the movement of said shaft and moving contact, where each assembly comprises one contact spring and one spring holder and where each spring assembly is anchored by a pair of moving pin and fixed pin.

[0016] In one possible implementation of the contact system according to the first aspect, each contact spring is secured over the shaft by one spring holder; and wherein said spring holder is adapted to accommodate one contact spring.

[0017] In another possible implementation of the contact system according to the first aspect, said contact springs are adapted to provide a force opposing the electromagnetic force and the force aiding said electromagnetic force.

[0018] In yet another possible implementation of the contact system according to the first aspect, position of said moving pin changes dynamically as the moving contact and shaft rotates; and wherein positions of the fixed pin and the center pin remains constant.

[0019] In yet another possible implementation of the contact system according to the first aspect, said contact spring is a compression spring channelizing the spring force exactly in the requisite direction.

[0020] In yet another possible implementation of the contact system according to the first aspect, further comprising a shaft cover to secure the shaft, said shaft cover further comprising a plurality of shaft cover flaps.

[0021] In yet another possible implementation of the contact system according to the first aspect, said shaft cover comprises a pair of slots to allow the moving contact to protrude outside said shaft cover.

[0022] In yet another possible implementation of the contact system according to the first aspect, the pair of fixed pins, the pair of moving pins and the center pin aligns to form a straight line when the moving contact is in open condition.

[0023] In yet another possible implementation of the contact system according to the first aspect, electromagnetic forces repel the moving contact against the direction of the contact spring force.

[0024] 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

[0025] 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:

[0026] Figure 1(a) illustrates the shaft assembly of an MCCB in ‘ON’ condition, as prior art of the present invention.

[0027] Figure 1(b) illustrates the shaft assembly when the moving contact is close to dead center, as prior art of the present invention.

[0028] Figure 1(c) illustrates the shaft assembly in flip-locked condition, as prior art of the present invention.

[0029] Figure 1(d) illustrates the position of holes on moving contact assembly, as prior art of the present invention.

[0030] Figure 2(a) illustrates the shaft assembly of an MCCB in ‘ON’ condition, in accordance with an aspect of the present invention.

[0031] Figure 2(b) illustrates the shaft assembly in contact fully open condition, in accordance with another aspect of the present invention.

[0032] Figure 3 illustrates the position of the pins in the shaft construction, in accordance with another aspect of the present invention.

[0033] Figure 4 illustrates the position of holes on moving contact assembly, in accordance with another aspect of the present invention.

[0034] 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

[0035] 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.

[0036] 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.

[0037] 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.

[0038] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The present invention lies in providing a spring based double break contact system for circuit breakers.

[0043] In particular, the present invention describes a compression spring based double break contact system with defeated flip-locking mechanism for moulded case circuit breakers. It requires minimal changes to the existing construction of the shaft assembly of a circuit breaker to resolve limitations associated with the existing design. In particular, it suggests a shift in the position of the three holes in the moving contact carrier. Significantly, since the position of the holes decides the initial compression of the contact springs, thus, spring redesign is necessary to maintain the contact pressure same as the existing construction. Further, the position of the hole on the moving contact carrier decides the position of dead center or the no-return point of the moving contact assembly.

[0044] The existing construction of shaft assembly exhibit limitations since the low fault clearing time applications require discrimination. In particular, the drawbacks associated with the prior art being: nuisance tripping of up-stream MCCB when used in applications requiring selectivity; re-closure of up-stream breaker does not happen when the fault current is limited and cleared by the downstream breaker; total discrimination cannot be achieved due to low fault clearing time since the fault clearing time of MCCB remains constant irrespective of its position in the power system hierarchy, therefore, when such MCCB is used as an up-steam protection device, discrimination is not achieved; and energy discrimination is possible only when the difference between the rating upstream and downstream breakers is substantially high.

[0045] To understand the construction of the prior art, reference is made to Fig 1a which illustrates the shaft assembly of the compression spring based double break contact system with flip-locking mechanism in MCCB ON condition. Moving contact assembly illustrated in Fig 1d can be seen assembled in Fig 1a.

[0046] Fig 1b illustrates the shaft assembly of the compression spring based double break contact system with flip-locking mechanism during fault clearing action. Moving contact assembly illustrated in 1d can be seen at position close to the dead center. Fig 1c illustrates a shaft assembly of the compression spring based double break contact system with flip-locking mechanism at the end of fault clearing action. Moving contact assembly illustrated in Fig 1d can be seen in flip-locked condition.

[0047] In Fig 1a, the direction of motion of the moving contact assembly is depicted by arrows. In case of fault, the electromagnetic forces repel the moving contact assembly against the direction of the contact spring force. As the moving contact assembly moves, the position of the moving pins changes dynamically while the position of the fixed pins remains constant. Fig 1b illustrates the shaft assembly in the dead center point or the no return point. At this point, all the five pins including the fixed pins and the moving pins align to form a straight line. When the electromagnetic force is strong enough to push the pins further to this point, the moving contact assembly gets flip-locked. Fig 1c illustrates the shaft assembly in stable flip locked condition. After the dead center point mentioned in Fig 1b is crossed, the spring forces aid the moving contact in the opening direction along with the electromagnetic forces generated by the fault currents.

[0048] Accordingly, there is a need to overcome the drawbacks associated with the existing construction of moulded case circuit breakers with minimal changes in existing design and no compromise on the contact gap. Thus, the present invention discloses a compression spring based double break contact system with defeated flip-locking mechanism for moulded case circuit breakers.

[0049] In Fig 2a, the direction of motion of the moving contact (2) is depicted by arrows. The alignment of two moving pins (6), two fixed pins (7) and one central pin (9) as illustrated in Fig 3 is also indicated in Fig 2a. In case of fault, the electromagnetic forces repel the moving contact (2) against the direction of the contact spring force. As the moving contact (2) moves, the position of the moving pins (6) changes dynamically while the position of the fixed pins (7) and the center pin (9) remains constant.

[0050] Fig 2b illustrates the shaft assembly in contact fully open condition. At this point, all the five pins including the fixed pins (7) and the moving pins (6) align to form a straight line. As the moving contact (2) has already reached the final position of fully open condition, the moving contact (2) does not get flip-locked as described in the existing construction.

[0051] The contact spring (5) is assembled with the spring holder (3) and this assembly is anchored on the shaft (1) and the moving contact (2) by using moving pins (6) and fixed pins (7). Fig 4 illustrates the position of holes on moving contact (2). From the illustrations, it appears that the position of the three holes on the moving contact assembly is at an angle from the vertical axis of the moving contact; however, the angle can be varied according to the construction of the existing contact system. In one example, the angle is about 16.5º while in another the angle is about 18.2º, however, as indicated; this angle of displacement is not limited to any range.

[0052] According to an embodiment of the present invention, a spring based double break contact system for circuit breakers is disclosed. The contact system comprises a shaft (1), a moving contact (2), a center pin (9) and a pair of spring assemblies (4). The moving contact (2) comprises a plurality of holes (10, 11, 12) where said moving contact (2) is pivotally mounted over said shaft (2) by the center pin (9) such that said moving contact (2) rotates with respect to the movement of said shaft (1). The pair of spring assemblies (4) is rotatably anchored over said shaft (1) and said moving contact (2) such that said assemblies rotate with respect to the movement of said shaft (1) and moving contact (2), where each assembly (4) comprises one contact spring (5) and one spring holder (3) and where each spring assembly (4) is anchored by a pair of moving pin (6) and fixed pin (7).

[0053] Each contact spring (5) is secured over the shaft (1) by one spring holder (3) and said spring holder (3) is adapted to accommodate one contact spring (5). The contact springs (5) are adapted to provide a force opposing the electromagnetic force and the force aiding said electromagnetic force. The position of said moving pin (6) changes dynamically as the moving contact (2) and shaft (1) rotates and positions of the fixed pin (7) and the center pin (9) remains constant. The contact spring (5) is a compression spring channelizing the spring force exactly in the requisite direction. A shaft cover (8) secures the shaft (1) and comprises a plurality of shaft cover flaps. The shaft cover (8) comprises a pair of slots to allow the moving contact (2) to protrude outside said shaft cover (8). The pair of fixed pins (7), the pair of moving pins (6) and the center pin (9) align to form a straight line when the moving contact is in open condition. The electromagnetic forces repel the moving contact (2) against the direction of the contact spring (5) force.

[0054] The present invention finds its application in any industry where spring based double break contact system for moulded case circuit breakers are used.

[0055] Some of the non-limiting advantages of the present invention are mentioned hereinbelow:
a) The flip-lock mechanism is defeated without compromising on the contact gap;
b) Minimal changes to the existing construction to resolve the limitations of the existing design;
c) Avoids nuisance tripping of up-stream MCCB when used in applications requiring selectivity; and
d) Re-closure of up-stream breaker is made possible when the fault current is limited and cleared by the downstream breaker.

[0056] Although a spring based double break contact system for circuit breakers have been described in language specific to structural features and/or methods as indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations of a compression spring based double break contact system with defeated flip-locking mechanism for moulded case circuit breakers.