Claims:1. A molded case circuit breaker (MCCB) with resistor coils in series to reduce the let-through energy, the MCCB comprising
a mechanism contact assembly (1) mounted over an electronic protection release (2) to offer multiple ratings with multiple magnetic threshold from a single circuit breaker; and
a resistor coil assembly (6) electrically connected to the protection release (2);
wherein a conductive shorting rod (5) is used to change the effective resistance value of resistor coil assembly (6) by inserting the shorting rod (5) in inner diameter of resistor coil and connecting the coil thereby controlling the current flow through the circuit breaker.

2. The MCCB as claimed in claim 1, wherein a base housing (3) positioned over the mechanism contact assembly (1) to cover and support the resistor coils connected in series to reduce the let-though energy of the protection release.

3. The MCCB as claimed in claim 1, wherein the shorting rod (5) is supported by the base housing (3).

4. The MCCB as claimed in claim 1, wherein the resistor coil assembly (6) is connected to protection release (2) with the connecting wires (7).
, Description:TECHNICAL FIELD OF THE INVENTION

The present subject matter described herein, in general, relates to circuit breakers. Particularly, the invention relates to a circuit breaker with built-in resistors to limit the fault current.

BACKGROUND OF THE INVENTION

A circuit breaker is a mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short circuit (Short circuit is an accidental or intentional connection, by a relatively low resistance or impedance, of two or more points in a circuit which are normally at different voltages).

The main function of any electrical switching apparatus is to carry the rated current. Therefore the current carrying capacity of any circuit breaker is so important that if the unit fails to carry the rated current it will cause damage to itself as well as to the electrical equipment to which it is protecting.

Circuit breakers have three positions corresponding to the status of the separable contacts. For example, these positions would include an ON position, in which the separable contacts are closed, an OFF position in which the contacts are open and Trip position in which the contacts are tripped open.

These circuit breakers / switching devices are usually installed in an enclosure so as to have all the control and distribution network laid in form of metallic sheets and or cable wires inside and all operating means from outside so as to prevent access to high voltage and thus a potential hazard.

When a circuit breaker is in ON condition and a short circuit fault condition arises, high amount of fault current flows through the circuit and in response to this the circuit breaker tries to move the separable contacts to open position after sensing the fault condition through short circuit sensing mechanism (such as magnetic arrangement). The time taken from a fault condition initiation and the fault current being interrupted by circuit breaker determines the let through energy / arc energy passed by the circuit breaker to the downstream equipment. A circuit breaker is said to be more efficient when the let through energy is minimal.

Let through energy of circuit breaker depends on many parameters, one among them being the amplitude of cut-off current. (Cut off current is the maximum instantaneous value of current attained during the breaking operation of a switching device) This cut off current depends primarily on the resistance of the current path. Higher the resistance lower would be its cut-off current and thus lower would be let-through energy. Hence, during fault clearance the amplitude of the cut-off current flowing through the circuit breaker gets reduced to a lower value. The let-though energy generated at the lower cut-off current would also be lower than the let-though energy without resistor coils.

There are several prior art technologies dealing with circuit breaker with current limiter. Reference has been made to patent document US3192338. In US ‘338 document, the circuit conducting coil spring (refer Figure 1A) is tapering in shape from one coil turn to the next coil turn, resulting in each coil turn being slightly thinner in thickness than the coil turn just ahead of it. In a maximum fault current limiting electrical circuit breaker, the combination of breaker contact points attached to and in series with one end of a flexible coil spring, lever means for compressing the flexible coil spring and holding said breaker contact points closed, means for opening the breaker contact points under overload, said means releasing the levers holding said compressed flexible coil spring, whereby the instant release and expansion of the flexible coil spring causes a high impedance path to the flow of electrical current in the flexible coil spring, thereby instantly limiting the maximum fault current at the breaker contact points.

In this prior art, the coil is compressed with the help of some mechanism lever. During normal working this coil remains closed offering low resistance to the flow of current. During fault clearance, the mechanism lever releases the coil and the coil expands while offering higher resistance path to the flow of fault current. This arrangement requires a special mechanism to act accordingly. Such mechanism is not required in our present invention.

Additionally, in prior art the coil has varying thickness / cross section. Manufacturing of such coils would be complex and not be easy. In present invention, a simple coil is used which has cross-section area based on calculations

Reference has also been made to patent document US5917390A. The circuit breaker disclosed in US ‘390 (refer FIG 1B) comprises an upper contact arm having a first contact disposed thereon and a lower contact arm having second and third contacts thereon with the Second contact mating with the first contact. A shunt terminal is provided between the upper contact arm and the lower contact arm. The Shunt terminal includes a fourth contact, which mates with the third contact on the lower contact arm. When the circuit breaker is conducting nominal rated current, the first, second, third and fourth contacts remain closed. When the circuit breaker is under fault conditions which are circuit current conditions above the withstand level, the circuit breaker Switches to a current limiting mode. In this mode, the upper contact arm and the lower contact arm move simultaneously in an upward and downward manner respectively, thereby opening the third and fourth contacts resulting in a blow open loop that opens the first and Second contacts and protect a load coupled to the device from overcurrent conditions.

The above mentioned prior art has dual contact system for carrying current. This arrangement is done to withstand high level of current. The circuit breaker was intended to be used in discrimination along with upstream - downstream circuit breaker.

Reference has also been made to US 3505622. That patent application shows a current limiting circuit breaker device (refer FIG 1C) which upon the occurrence of a severe fault condition of a predator mined magnitude, utilizes the blowoff forces generated at the main contact pair to defeat the latch means of the main circuit breaker mechanism. The release of the latch means under such conditions is obtained by the provision of a collapsible portion of the operating mechanism latch train. Upon the occurrence of a severe fault condition, the contact blowoff forces generated at the contact pair are transmitted to the collapsible portions of the latch in opposition to the latch retention biasing means. The collapse of these latch portions then serves to release the main op.

In the prior art, the toggle knee is operatively connected to the movable contact, as by a hook-like member intermediate the contact carrier arm and the toggle knee. In the event of contact arm movement caused by blowoff, the hook-like lever moves the toggle knee overcenter with respect to its biasing spring, thereby collapsing this latch retention toggle mechanism.

The collapse of the latch retention toggle mechanism is accompanied by the collapse of the cradle. This results in the movement of the cradle portions to effect release of the operating mechanism latch, and hence movement of the main circuit breaker overcenter toggle mechanism to the contact disengaged condition.

This prior art is not discussing any resistor / coils the way it has been used in present patent idea.

Therefore, there remain a dire need to provide an electrical circuit breaker having built-in characteristics capable of limiting the maximum short-circuit fault current to a safe operating level for which the circuit breaker is designed for any given voltage of an electrical power system.

SUMMARY OF THE INVENTION

The following disclosure 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.

The object of present invention is to overcome the problems of prior arts.

The Primary object of the present invention is to an electrical circuit breaker having built-in characteristics capable of limiting the maximum short-circuit fault current to a safe operating level for which the circuit breaker is designed for any given voltage of an electrical power system.

Another object of invention is to provide an electrical circuit breaker capable of being operated by personnel under short-circuit fault current wherein safety of operation will be assured against the circuit breaker blowing up because of extreme heavy inrush of electrical current where such capabilities are present from the source of electrical utility.

One aspect of present invention is a molded case circuit breaker (MCCB) with resistor coils in series to reduce the let-through energy. The MCCB comprising a mechanism contact assembly mounted over an electronic protection release to offer multiple ratings with multiple magnetic threshold from a single circuit breaker; and a resistor coil assembly electrically connected to the protection release; wherein a conductive shorting rod is used to change the effective resistance value of resistor coil assembly by inserting the shorting rod in inner diameter of resistor coil and connecting the coil thereby controlling the current flow through the circuit breaker.

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 ACCOMPANYING DRAWINGS

The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 (A-C) illustrates the circuit breakers with current limiters in prior art technologies.

Figure 2 illustrates circuit breaker of present invention according to one of the embodiments of present invention.

Figure 3 illustrates mechanism and contacts section of Circuit breaker of present invention as disclosed in an embodiment of present invention.

Figure 4 illustrates electronic based protection release of Circuit breaker as disclosed in an embodiment of present invention.

Figure 5 illustrates bottom housing to cover resistor coils as disclosed in an embodiment of present invention.

Figure 6 illustrates Shorting rod assembly as disclosed in an embodiment of present invention.

Figure 7 illustrates Resistor coil to limit the fault current / cut-off current as disclosed in an embodiment of present invention.

Figure 8 illustrates Electronic based protection release of Circuit breaker with connecting arms as disclosed in an embodiment of present invention.

Fig. 9 illustrates Resistor coil connected with electronic based protection release of circuit breaker as disclosed in an embodiment of present invention.

Fig. 10 illustrates Electronic based protection release of Circuit breaker with connecting arms connected to Mech-contacts section of circuit breaker as disclosed in an embodiment of present invention.

Fig. 11 illustrates exploded side view of circuit breaker with resistor coil and bottom housing to cover resistor coil as disclosed in an embodiment of present invention.

Fig. 12 illustrates exploded side view of protection release with resistor coil and housing to cover resistor coil as disclosed in an embodiment of present invention.

Figure 13 illustrates exploded isometric view of protection release with resistor coil and bottom housing to cover resistor coil with shorting rod as disclosed in an embodiment of present invention.

Figure 14 illustrates Cross-sectional side view of circuit breaker with the flow of current shown with grey color when the shorting rod is at top end as disclosed in an embodiment of present invention.

Figure 15 illustrates Cross-sectional side view of circuit breaker with the flow of current shown with grey color when the shorting rod is at bottom end as disclosed in an embodiment of present invention.

Figure 16 illustrates Side view of circuit breaker as disclosed in an embodiment of present invention

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have 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

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

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 present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to "a component surface" includes a reference to one or more of such surfaces.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. Also, Expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout.

The present invention talks about moulded case circuit breaker with resistor coils in series to reduce the let-through energy. The circuit breaker has resistor coils in series. This resistor add resistance to the current flowing through the circuit breaker. Hence, during fault clearance the amplitude of the cut-off current flowing through the circuit breaker gets reduced to a lower value. The let-through energy generated at the lower cut-off current would also be lower than the let-though energy without resistor coils.

The present moulded case circuit breaker with resistor coil also employs electronic circuitry that is used to sense the current and act accordingly. The electronic protection release helps to offer multiple ratings with multiple magnetic threshold from a single circuit breaker. This would not have been possible in conventional circuit breaker without electronic circuitry.

In the present invention, electronic protection release is used to offer multiple ratings. The electronic protection release has CTs (current transformer) for sensing the currents and electronic PCB cards to sense these signals, diagnose them and issue command to the FST (flux shift trip device) to trip the MCCB during unfavorable situation. The PCB card has selector DIP switch box which has selection switches/buttons to select desired current setting and then the MCCB will treat that selected current as the rated current of that particular MCCB and will provide protection with respect to rated current. Using this principle, multiple ratings can be offered using PCB cards.

Figure 2 shows the side view of circuit breaker that consists of Mechanism contact assembly (1) and protection release (2). Resistor coil assembly (6) is connected to protection release (2) with the help of connecting wires (7) as shown in Figure 8. Mechanism contact assembly (1) and base housing (3) are then connected as shown in Figure 10. The complete circuit breaker looks as shown in Figure 16. Conductive shorting rod (5) is used to change the effective resistance value of resistor coil assembly (6). The shorting rod is inserted in inner diameter of resistor coil which connects the coils it touches thereby changing the effective resistance. The current path after changing the location of shorting link is shown in Figure 12 highlighted in grey color in Figure 14 & Figure 15.

The base housing is an integral part of this invention to cover / support the resistor coils connected in series (to reduce the let-though energy / to reduce the cut-off current) of the protection release.

Shorting-rod is in direct connection with resistor coil. It is supported by the base housing. The position/location of the shorting rod decides the resistance/impedance of the resistor coil. The shorting rod is suitably inserted inside resistor coil while shorting the required number of turns. This decides the value of resistance/impedance of the resistor coil. The value of resistance is important while selecting rating of the circuit breaker.

The location of the shorting rod and selection of switch on DIP switch will be done simultaneously at factory. The same information can also be provided to end customers suitably.