Claims:
1. A moulded case circuit breaker with compact and modular coil for short circuit protection, said circuit breaker comprising:
a resistor coil assembly connected in series with a protection release mechanism of the circuit breaker, the protection release mechanism comprising:
an I core magnetic flapper assembly (4) comprising: a I core magnetic flapper (1) operably coupled to a holder (3) by means of a spring (2);
a C core magnetic coil assembly (11) comprising a magnetic coil (7) engaged with a C core fixed magnet (8), a spacer (9) and a support (10),
wherein the C core magnetic assembly (11) is operably coupled to the I core magnetic flapper assembly (4) and I core gets attracted towards the C core when fault current exceeds the predetermined value,
wherein the resistor coil assembly facilitates reduction in cut-off current and let-through energy.

2. The circuit breaker as claimed in claim 1, wherein the resistor coil assembly is an internal resistor kit/coil (5) placed inside the circuit breaker, and operably coupled to the protection release mechanism in series and further coupled to a flexible conductor (15).

3. The circuit breaker as claimed in claim 1, wherein the resistor coil assembly is an external resistor kit/coil (12) placed outside the circuit breaker, and operably coupled to the protection release mechanism in series and further coupled to a flexible conductor (15).

4. The circuit breaker as claimed in claims 1-3, wherein the circuit breaker comprises both internal resistor kit/coil (5) operably coupled to the protection release mechanism in series and further coupled to a flexible conductor (15), and an external resistor kit/coil (12) operably coupled to the protection release mechanism in series and further coupled to a flexible conductor (15).
, Description:

FIELD OF THE INVENTION

Embodiments of the invention in general relate to an electrical distribution device, such as a circuit breaker, more particularly to a circuit breaker with compact and modular protection module for short circuit protection with provision to install resistor coils in series to reduce the limit the fault current and hence the reduction in let-through energy.

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 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 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 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 is 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.

Reference is being made to US3192338, which teaches a circuit conducting coil spring 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.

Reference is made to US5917390A, disclosing a circuit breaker comprising 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.

Yet other reference is being made to US3505622, disclosing a current limiting circuit breaker device which upon the occurrence of a severe fault condition of a predetermined 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 operating mechanism latch.

Thus, there is a dire need for a moulded case circuit breaker facilitating reduction of a let through energy of the circuit breaker by means of connecting a resistor kit/coils in series with the circuit to limit the short circuit current and hence the let through energy. This makes the 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.

SUMMARY OF THE INVENTION

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.

An object of present invention is to provide a provision in an electrical circuit breaker to provide 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 the present 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.

According to one aspect of the present invention, a moulded case circuit breaker with compact and modular coil for short circuit protection is disclosed. The circuit breaker comprises a resistor coil assembly connected in series with a protection release mechanism of the circuit breaker, the protection release mechanism comprising an I core magnetic flapper assembly comprising: a I core magnetic flapper operably coupled to a holder by means of a spring; and a C core magnetic coil assembly comprising a magnetic coil engaged with a C core fixed magnet, a spacer and a support , wherein the C core magnetic assembly is operably coupled to the I core magnetic flapper assembly and I core gets attracted towards the C core when fault current exceeds the predetermined value, wherein the resistor coil assembly facilitates reduction in cut-off current and let-through energy.

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 illustrates a front view of a moulded case circuit breaker, according to an embodiment of the present invention.

Figures 2 and 3 illustrate a side view of a moulded case circuit breaker without external resistor housing and with external resistor housing respectively, according to embodiments of the present invention.

Figures 4-5 illustrate a current path in a sectional side view of a moulded case circuit breaker without external resistor housing and with external resistor housing respectively, according to embodiments of present invention.

Figures 6-7 illustrate steps to be followed for magnetic flapper assembly and to assemble the magnetic flapper assembly in a moulded case circuit breaker, respectively, according to an embodiment the present invention.

Figure 8 illustrates steps to be followed to assemble filler support in a moulded case circuit breaker, according to an embodiment the present invention.

Figure 9 illustrates steps to be followed to assemble terminal in a moulded case circuit breaker, according to an embodiment the present invention.

Figures 10-11 illustrate steps to be followed to assemble a coil sub-assembly and to assemble the coil sub-assembly in a moulded case circuit breaker, respectively, according to an embodiment the present invention.

Figure 12 illustrates resistor coil to limit the fault current / cut-off current in a moulded case circuit breaker, according to an embodiment the present invention.

Figure 13 illustrates a sectional isometric view of a moulded case circuit breaker corner showing the protection release construction, according to an embodiment the present invention.

Figure 14 illustrates a side view of a moulded case circuit breaker corner showing the protection release construction, according to an embodiment the present invention.

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

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, reference to “a component surface” includes 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 subject invention lies in a moulded case circuit breaker with compact and modular coil for short circuit protection with a provision to install resistor coils in series to reduce the cut-off current. The provision helps to connect resistor coils in series either internally inside the circuit breaker or externally outside the circuit breaker. The reduction in cut-off current in turn reduces the let-through energy. With the use of resistor coils to reduce the let-through energy, lower ratings of contactors can be used which will reduce the total cost of the combination used for motor protection. These resistor coils (kit) add resistance to circuit through which the current flowing via the circuit breaker. Hence, during short circuit condition the resistor(s) is in series with the circuit leading to overall reduction of the fault current. 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.

The protection module consists of a C core assembly and a I core assembly fixed inside the relevant cavity of the circuit breaker. The resistors in the present invention, restricts the fault current flowing through the circuit breaker resulting in reduction in let-through energy passed on to the equipment under protection e.g. Motor and other products connected in series in downstream. The resistor block can be placed either inside the circuit breaker or externally or both ways.

An embodiment of the present invention provides short circuit protection by means of a coil assembly wound over simple C core component which is fixed with the I core component by means of spring. The I core gets attracted towards the C core when fault current exceeds the predetermined value. The wound coil on C core and I core connected by means of spring assembly also called as protection module is assembled outside the circuit breaker. This protection module is assembled inside the cavity provided within the housing of the circuit breaker. The resistor coil can be assembled either internal or external to circuit breaker. This would not have been possible in conventional circuit breaker. The present invention requires minimum changes in the circuit breaker for installing the resistor kits either internally or externally. So maximum number of standard components can be reused.

The circuit breaker in present invention consists of mechanism, contact assembly and protection release. The resistor coil assembly is connected in series with the protection release either outside the circuit breaker or inside the circuit breaker or both ways.

As illustrated in Figure 12, an external resistor coil assembly (12) is connected to protection release outside the circuit breaker. Figure 3 shows the side view of circuit breaker where the resistor coil assembly is connected to protection release externally/outside the circuit breaker.

Figure 4 illustrates the sectional view of circuit breaker where protection module (4) is connected in series with the internal resistor kit (5) inside the circuit breaker. The other end of the internal resistor kit is connected to the flexible conductor. The internal resistor kit is wire wound assembly potted to form suitable shape so that it can be fixed inside the circuit breaker cavity of the standard circuit breaker.

The path of current flow as shown in the Figure 5, current passage is highlighted on sectional side view of circuit breaker without external resistor housing. Current flows from fixed contact assembly to moving contact assembly to flexible conductor. The flexible conductor is connected to resistor coil assembly that is in series of coil assembly, which is a part of protection release. In this configuration, the resistor coil assembly that is used to limit the fault current is placed outside the circuit breaker.

Figure 6 shows the I core (1) and spring (2) connected by means of a connecting component (3). This assembly is called as I core assembly (4). Figure 4 shows the assembly (4) of I core assembly inside the circuit breaker housing. Figure 10 shows coil (7), C Core (8) and connecting components (9) and (10). This assembly is called as C core assembly (11). Figure 11 shows the C Core assembly (11) inside the circuit breaker housing.

According to an embodiment, a moulded case circuit breaker with a provision to install resistor coils in series inside the circuit breaker or outside the circuit breakers or both ways has been disclosed. The moulded case circuit breaker comprises compact and modular coil for short circuit protection with provision to install resistor coils in series to reduce the let-through energy. The short circuit protection is achieved by means of I core assembly (4) and C core assembly (11) which is fixed inside the circuit breaker housing. The said C core assembly and I core assembly when fixed inside the housing is called as protection module. The I core gets attracted towards the C core when fault current exceeds the predetermined value. With the use of resistor coils to reduce the let-through energy, lower ratings of contactors can be used which will reduce the total cost of the combination used for motor protection.

Some of the non-limiting advantages of the moulded case circuit breaker with fault limiter coils are:

1. Resistor coils in series places either internally inside the circuit breaker or externally outside the circuit breaker, to reduce the let-through energy.
2. With the use of resistor coils to reduce the let-through energy, lower ratings of contactors can be used which will reduce the total cost of the combination used for motor protection.
3. The size of the panel board / switch board panel can be reduced based on the lower depth / lower rating contactors. This will further reduce the entire cost of the switchboard panel.
4. The resistor kit can be coil wound on suitable material of very high thermal withstand type. The assembly can be potted for giving it a particular shape especially for assembly within the circuit breaker.

Although a moulded case circuit breaker with fault limiter coils thereof has been described in language specific to structural features, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific methods or devices described herein. Rather, the specific features are disclosed as examples of implementations of a moulded case circuit breaker with fault limiter coils.

Nomenclature

1. Magnetic flapper
2. Spring
3. Holder
5. Magnetic flapper assembly
6. Internal Resistor kit
7. Terminal
8. Magnetic coil
9. Fixed Magnet
10. Spacer
11. Support
12. Magnetic coil assembly
13. External Resistor kit
14. Fixed contact assembly
15. Moving contact assembly
16. Flexible conductor