DESC:TECHNICAL FIELD
[0001] The present disclosure generally relates to low voltage switchgear applications and more specifically to molded case circuit breakers and circuit breakers where thermo-magnetic release is used. The present disclosure also relates to a short-circuit protection device that has adjustable magnetic settings used for generator protection and special applications in the switchgear industry.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] In low voltage distribution system, circuit breakers provide rapid and reliable protection against both overload and short-circuit currents. These circuit breakers typically contain two different switching mechanisms, a thermal part having a bimetal switch and a magnetic part having an electromagnet switch and therefore are known as thermo magnetic circuit breakers. The electromagnet switch responds instantaneously to large surges in current such as a short circuit current and the bimetallic switch responds to less extreme but longer-term over-current conditions. The thermal portion of the circuit breaker provides an "inverse time" response feature, which trips the circuit breaker sooner for larger over currents but allows smaller overloads to persist for a longer time. On occurrence of very large over-currents such as during a short circuit, the magnetic switch trips the circuit breaker with no intentional additional delay.
[0004] The bimetal typically sits behind a trip bar and may be part of the current carrying path or may be located close to a current carrying member that acts as a heater. Electrical current exceeding the breaker-overload rating heats the bimetal enough to bend it toward the trip bar. As the bimetal bends, it touches and rotates the trip bar to open the circuit. The time the bimetal needs to bend and trip the circuit varies inversely with the current.
[0005] The magnetic portion of the breaker uses magnetic effect of current wherein a high-level of current makes the electromagnet generate enough field strength to attract a nearby current carrying member. It typically consists of a set of fixed and movable current carrying members and as movable member moves under the magnetic force generated due to high current, it rotates a trip bar to trip the breaker and open the current path.
[0006] A typical arrangement of overload protection module and short circuit module in a Thermo-magnetic Release (TMR) in a circuit breaker is illustrated in FIG. 1. As shown, the overload protection module includes a heater 102 and a bimetallic element 104 as an actuator for tripping the circuit during overload conditions. As overload current flows through the heater 102, it gets heated which in turn heats the bimetallic element 104 causing it to bend and actuate the trip mechanism.
[0007] Magnetic switch (short circuit module) uses arrangement of fixed core (C Core) 106 and moving core (I core) 108as an actuator to provide signal during short-circuit condition. The C Core 106 is connected to the heater 102 by means of riveting or screwing in the traditional methods. When the breaker is switched ON, current flows through the heater 102 and thereafter to C Core 106. Magnetic effect of high short circuit current flowing through the C core 106 causes the I core 108 to get attracted to the C Core 106. The attraction force on the I core 108 is directly proportional to the amount of current passing through the heater 106. This movement of I core 108 is used as a means of actuation to trip the breaker by hitting the magnetic shaft, which opens the latching mechanism to give the output to the mechanism of the breaker. The movement of I core 108 varies depending upon the opposing force of a spring holding the I core. The difference in movement between non-trip and trip current is usually achieved by maintaining a stringent tolerance on the spring force holding the I core.
[0008] Molded case circuit breakers (MCCB) call for compliance to IEC 60947-2 standard, wherein the short circuit protection is verified at 80 % and 120 % of short-circuit current setting of the release. At 80% of the current-setting, the circuit breaker should not trip within a time period of 0.2 seconds and at 120%, the circuit breaker should trip within a time interval of 0.2 seconds. Most of MCCBs available in the market offer short-circuit protection with adjustability of settings. By providing settings, it enables the customer to change the short-circuit current setting of the MCCB according to the requirement.
[0009] MCCBs in the current market usually have different range of short-circuit protection settings. The highest setting is around 10 In, while the lowest setting is what usually determines the range. When customers look for protection of sensitive equipments for lower ratings, with the existing product portfolio, existing vendors provide the micro processor release, which costs higher than a thermo-magnetic release option. As users buyan MCCB with a long term plan, they are likely to buy a breaker that is capable of breaking a range of short-circuit current than a single value. For instance, if there is a short-circuit tripping current requirement of 300 A, a user would prefer a MCCB with a tripping current capacity higher than 300 A, say 600 A and change the setting to 300 A, so that he does not replace the protective device if his short-circuit current requirement goes up. Thus, it becomes logical for MCCB manufacturers to provide a range of settings for short-circuit protection currents. In the existing designs this range of settings is typically achieved in a TMR by means of air gap adjustment and variation of spring force.
[0010] As I core movement is directly proportional to the current and inversely proportional to the air gap between the C and I core, it becomes important to have higher air gap for higher setting and lower air gap for lower setting. This variation of air gap and spring force ensures that the mandated standard requirement (80 % of short-circuit setting – no trip & 120 % of short-circuit setting – trip) is met at every setting. The air gap compensation for different setting is usually provided by having a ‘Slope/ Intermediate slant’ on the magnetic slider 200 of FIG. 2 or on the projection of the magnetic shaft. When the user adjusts the setting outside, internally, the air gap and the spring force increases or decreases accordingly.
[0011] With the existing construction of fixed and moving core, achieving lower settings of short-circuit protection is not possible since the magnetic attraction force is low. This is because of single current path and hence the number of Ampere Turns for producing attraction force is only one. Any attempt to increase the number of ampere turns by flexible conductor on a single core affects the productivity because of high amount of time required for winding over existing solid core.
[0012] There is therefore a need in the art for an improved overload protection module for circuit breakers that increases the number of Ampere turns and effectively the magnetic attraction force for the same amount of current, thus avoiding limitations of the existing construction, where lower current ratings cannot be used for magnetic protection.
[0013] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0014] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0015] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0016] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0017] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0018] An object of the present disclosure is to overcome problems associated with short circuit modules of conventional circuit breakers employing thermo-magnetic release for cover current and short circuit current protection.
[0019] Another object of the present disclosure is to provide a magnetic release that helps in achieving lower settings of short-circuit protection.
[0020] Another object of the present disclosure is to provide a magnetic release that is more sensitive to low short circuit currents.
[0021] Another object of the present disclosure is to provide a magnetic release that has higher magnetic force even at low short circuit currents.
[0022] Another object of the present disclosure is to improve sensitivity of the magnetic release to low short circuit currents by increasing ampere turns of the magnetic release of the circuit breaker.
[0023] Another object of the present disclosure is to increase the ampere turns of the magnetic release of the circuit breaker without adversely affecting productivity.

SUMMARY
[0024] The present disclosure relates to thermo-magnetic release of molded case circuit breakers/circuit breakers used in low voltage switchgear applications. In particular it pertains to a short-circuit protection magnetic switch that has adjustable magnetic settings for adjusting the rated short circuit current of the circuit breaker.
[0025] In an aspect, the present disclosure provides for a magnetic release that is more sensitive to low short circuit currents therefore does not need reduction of air gap between the moving and fixed core to unacceptably small values. Thus the disclosure provides a solution for enabling use of existing circuit breakers for low short circuit currents that were not feasible earlier.
[0026] In an embodiment, the increased sensitivity of magnetic switch to low short circuit currents is achieved by increasing ampere turns of the magnetic cores. In an aspect the increase in ampere turns is achieved without affecting productivity.
[0027] In an embodiment, the present disclosure uses a coil to increase the ampere turn of the fixed core so as to increase the magnetic force even at low short circuit currents. In an aspect the coil is pre-wound and inserted over a cylindrical core and two ends of the cylindrical core are riveted to two limbs of the thermo-magnetic release. Such an arrangement increases the number of ampere turns, and effectively increases the magnetic attraction force for the same amount of current, thus avoiding limitations of the existing construction, where lower current ratings cannot be achieved for short circuit protection. In another aspect, pre-wound coil prevents effect on productivity as it can be prepared separately and has to be merely inserted over the cylindrical core.
[0028] In another embodiment, the heater of the thermal switch is replaced by a heating element to facilitate use of coil that provides multiple current paths instead of a single path thus increasing the ampere turn over those available with earlier C core.
[0029] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0031] FIG. 1 illustrates an exemplary arrangement of bimetallic switch and magnetic switch in a typical thermo-magnetic release of a circuit breaker.
[0032] FIG. 2 illustrates an exemplary arrangement of a magnetic slider with a slope that is used to vary air gap between fixed and moving magnetic cores in a typical thermo-magnetic release of a circuit breaker.
[0033] FIG. 3 illustrates exemplary construction details of a thermo magnetic release showing constructional details of a coil and its arrangement in a magnetic switch in accordance with an embodiment of the present disclosure.
[0034] FIG. 4 illustrates exemplary construction details of a thermo magnetic release showing moving core in accordance with an embodiment of the present disclosure.
[0035] FIG. 5 illustrates an exemplary schematic arrangement of the thermo magnetic release assembly into housing of a MCCB in accordance with an embodiment of the present disclosure.
[0036] FIG. 6illustrates an exemplary assembly of the magnetic protection module in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0037] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0038] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0039] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0040] The present disclosure relates to thermo-magnetic release of molded case circuit breakers/circuit breakers used in low voltage switchgear applications. In particular it pertains to a short-circuit protection magnetic switch that has adjustable magnetic settings for adjusting the rated short circuit current of the circuit breaker.
[0041] In an aspect, the present disclosure provides a solution for enabling use of existing circuit breakers for low short circuit currents that were not feasible earlier. In an aspect, it provides a magnetic release that can be adjusted for low short circuit currents without need of reducing air gap between the moving and fixed core to unacceptably small values.
[0042] In an embodiment, the increased sensitivity of magnetic switch to low short circuit currents is achieved by increasing ampere turns of the magnetic cores. In an aspect the increase in ampere turns is achieved without affecting productivity.
[0043] In an embodiment, the present disclosure uses a coil to increase the ampere turn of the fixed core so as to increase the magnetic force even at low short circuit currents. In an aspect the coil is pre-wound and inserted over a cylindrical core and two ends of the cylindrical core are riveted to two limbs of the thermo-magnetic release. Such an arrangement increases the number of ampere turns, and effectively increases the magnetic attraction force for the same amount of current, thus avoiding limitations of the existing construction, where lower current ratings cannot be achieved for short circuit protection. In another aspect, pre-wound coil prevents effect on productivity as it can be prepared separately and has to be merely inserted over the cylindrical core.
[0044] In another embodiment, the heater of the thermal switch is replaced by a heating element to facilitate use of coil that provides multiple current paths instead of a single path thus increasing the ampere turn over those available with earlier C core.
[0045] Referring to FIG. 3wherein the view 300 shows constructional details of the coil along with details of its installation. As shown the coil 304 can be configured with its one end 312 connected to a terminal 302 and other end 314 connected to a heater element 306.The exemplary coil 304 comprises 3 coil turns to increase ampere turn. The heater element 306 can replace a single heater 102 and can function to heat the bimetallic strip 104 that can provide the thermal switch for overload current protection. The coil 304 can be inserted over a cylindrical core 308 that can be riveted to side limbs 310 (one on either side). In an aspect, the winding 304 on the cylindrical core 308 that provides higher ampere turns can produce a higher magnetic attraction force when compared with the conventional C-core, which attraction force can cause the I-core (which is the same component as used in conventional system) to be attracted to the C-core even at lower short circuit currents. In an aspect this can enable adjustment of the magnetic switch for low rated short circuit currents without having to reduce air gap between the fixed and moving cores below acceptable levels.
[0046] In an aspect, the ends 312 and 314 of the coil 304 can be welded to terminal 302 and heater element 306 respectively and thereafter the coil 306 can be assembled over the cylindrical core 308. The cylindrical core 308can be riveted to the side limbs 310 on either side.
[0047] FIG. 4 illustrates exemplary construction details 400 of a thermo magnetic release showing moving core in accordance with an embodiment of the present disclosure. Shown therein is a moving core (I core) 402 fixed with the side limbs 310-1 and 310-2 on either side. When attracted by the fixed core such as coil 304, the I core 402 can move about a fulcrum 404 and can cause to trip the circuit to provide short circuit current protection.
[0048] FIG. 5 illustrates an exemplary schematic arrangement 500 of the thermo magnetic release assembly into housing of a MCCB in accordance with an embodiment of the present disclosure. The thermo magnetic release assembly can be inserted into housing 502and riveted. When the short-circuit current passes through the current path comprising heater element 306 and the coil 304 the coil 304 can produce a magnetic attraction force, causing the I core 402 to be attracted by the coil 304. The I core movement starts once the magnetic attraction force is higher than the opposing force held by the magnetic spring 504. Since the disclosed coil 304 provides higher magnetic attraction force, the I core can start moving at even lower values of short-circuit current and hence provide short circuit protection as low as 3 times (corresponding to increase in number of current paths i.e. 3 against 1 earlier) the earlier current value.
[0049] FIG. 6illustrates an exemplary assembly of the magnetic protection module in accordance with an embodiment of the present disclosure. In an aspect, once the I core 402 starts moving, it starts an irreversible reaction. The movement of I core 402 results in rotation of a magnetic shaft 602, which moves the latching component 604, causing the latch to de-latch and the pop out component 606 (lever) that can be spring loaded, to give a mechanical load to the tripping mechanism of the molded case circuit breaker.
[0050] According to one embodiment, since the present disclosure uses a three turn copper coil in place of a single current path element as fixed core, the number of ampere turns is increased and hence the magnetic attraction force is increased, helping achieve short-circuit protection for current as low as 3 times the earlier rated current. Furthermore, because the fixed core is split into 3 components, the time required for winding the coil is lower. Also, since the coil has a cylindrical profile, winding can be automated, reducing the variations in winding.
[0051] In another aspect, since the magnetic attraction force between the fixed core and the moving core is increased, tolerances on the spring 502 holding the I core 402 can be relaxed, which can reduce the cost of manufacturing. In another aspect, the improved system can give a competitive edge as it gives an advantage of wider range of short-circuit protection.
[0052] According to one embodiment, use of the present construction/arrangement can increase magnetic attraction force and results in achieving short-circuit protection for currents as low as 3 times the earlier achievable values. Winding of the coil over a cylindrical core 308 can achieve automation and facilitate production of the coil 304separately and assemble over the cylindrical core 308.
[0053] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0054] The present disclosure overcomes problems associated with short circuit modules of conventional circuit breakers employing thermo-magnetic release for cover current and short circuit current protection.
[0055] The present disclosure provides a magnetic release that helps in achieving lower settings of short-circuit protection.
[0056] The present disclosure provides a magnetic release that is more sensitive to low short circuit currents.
[0057] The present disclosure provides a magnetic release that has higher magnetic force even at low short circuit currents.
[0058] The present disclosure improves sensitivity of the magnetic release to low short circuit currents by increasing ampere turns of the magnetic release of the circuit breaker.
[0059] The present disclosure increases the ampere turns of the magnetic release of the circuit breaker without adversely affecting productivity.
,CLAIMS:1. A thermo magnetic release for a circuit breaker comprising:
a thermal release comprising a heater element that is configured to carry current passing through the circuit breaker and a bimetallic strip that is configured to bend under influence of heat from the heater element and trip the circuit breaker on occurrence of an overload current; and
a magnetic release comprising:
a fixed core comprising a coil that is configured between the heater element and a terminal to provide a path to carry current passing through the circuit breaker and a cylindrical core inserted through the coil, wherein two ends of the cylindrical core are riveted to a set of side limbs, and wherein the coil and the cylindrical core are configured to provide a magnetic force when a short circuit current passes through the coil; and
a moving core held between the set of side limbs and configured to rotate under influence of the magnetic force of the fixed core and trip the circuit breaker on occurrence of a short circuit current;
wherein the coil is configured to provide multiple current paths and is pre-formed.

2. The thermo magnetic release of claim 1, wherein the coil is made of copper.
3. The thermo magnetic release of claim 1, wherein the coil comprises three turns.
4. The thermo magnetic release of claim 1, wherein one end of the coil is welded to the heater element.
5. The thermo magnetic release of claim 1, wherein second end of the coil is welded to the terminal.
6. The thermo magnetic release of claim 1, wherein magnetic release further comprises a spring that is configured with the moving core, and provides resistance to movement of the moving core under influence of the magnetic force of the fixed core.
7. The thermo magnetic release of claim 1, wherein magnetic release further comprises a magnetic slider to adjust air gap between the fixed core and the moving core to set rated short circuit current of the circuit breaker.