Claims:1. An assembly of Thermo-magnetic release (TMR) adapted to be used in a molded case circuit breaker, said assembly comprising:
a housing for receiving plurality of components of said TMR;
at least one top cover coupled to said housing using at least one mechanical linkage, wherein said top cover comprises one or more slots and adapted to hold at least one adjuster, wherein said top cover constrain free rotation of said adjuster using gear teeth;
at least one magnetic tuner rotatably engaged with said assembly and comprises one or more hooking part for hooking at least one biasing spring means, wherein magnetic tuner adapted to provide wide magnetic setting by varying spring force acting on at least one moving core and air gap between said moving core and at least one fixed core;
at least one shaft latch means comprises a combination of at least one overload shaft part, at least one magnetic shaft part and at least one latch part;
said moving core having one end resting on said magnetic tuner, wherein said moving core comprises plurality of slots for hooking said springs means to provide fine magnetic calibration;
at least one heater having one or more slots for providing a surface for attaching a bimetal; and
said adjuster, provided with a gear mechanism to enable locking of said adjuster with said gear teeth of said top cover and thereby locking of said magnetic tuner and said shaft latch in at least one position.
2. The assembly as claimed in claim 1, wherein said top cover comprises one or more limbs projecting outwards to hold said magnetic tuner and said shaft latch.

3. The assembly as claimed in claim 1, wherein said hooking part in said magnetic tuner is preferably provided below the resting part of said moving core.

4. The assembly as claimed in claim 1, wherein wide magnetic setting is achieved due to at least one rotation of said magnetic tuner facilitating increase/decrease in air gap simultaneously increasing/decreasing said spring force.

5. The assembly as claimed in claim 1, wherein said shaft latch comprises one or more profiles to remove under cuts during molding.

6. The assembly as claimed in claim 1, wherein said adjuster is at least one selected from magnetic adjuster or thermal adjuster or any combination thereof.

7. The assembly as claimed in claim 1, wherein said top cover is snap fitted to said housing or said top cover coupled to said housing using plurality of screw and nut arrangement.

8. The improved assembly as claimed in claim 1, wherein said biasing spring means coupled to said shaft latch means at one end and said housing at other end.

9. The assembly as claimed in claim 8, wherein said spring means selectively comprising torsion spring, tension spring, compression spring or the like.
, Description:TECHNICAL FIELD

[001] The present invention described herein, in general, relates to electrical switching devices such as circuit breakers, and more particularly relates to an improved Thermo-Magnetic release (TMR) used in moulded case circuit breakers (MCCBs).

BACKGROUND

[002] Moulded case circuit breaker construction can be classified into 3 modules. They are: Contact system, Mechanism, and Thermo-Magnetic release/Microprocessor Based Release (TMR / MPR. A typical molded case circuit breaker and its module is illustrated in figure 1.

[003] The TMR provides the trip signal to the breaker during two abnormalities which are: Overload condition and Short circuit condition. According to IEC standard 60947 part I, overload condition is defined as current greater than 1.3 times the rated current, while short circuit current is not exactly defined, but colloquially it is usually current greater than 4 times the rated current to 12 times the rated current. Thermo-Magnetic release construction to MCCB in the existing breaker is of 2 types: Integral type and Modular type. The integral type construction of TMR as shown in figure 2, has the advantage of being economical. However, the disadvantages includes no or less features and not replaceable with other TMR / MPR dependent on mechanism for force and sensitive to tolerances from mechanism components. Further, the modular type construction of TMR as shown in figure 3 has the advantage of being rich in features and Replaceable with other TMR / MPR (Microprocessor Based Release). However, it is Costlier because of more number of components.

[004] As shown in figure 4 and 5, a typical modular type construction of said TMR consists of the following components:
1. Housing
2. Calibration Cover
3. Closing cover
4. Top cover
5. Transparent cover
6. Popper
7. Latch
8. Overload shaft
9. Magnetic shaft
10. Magnetic tuner / Slider
11. Heater
12. Bimetal
13. Moving core
14. Fixed core
15. Hardware for fixing
16. Springs
17. U strip
18. Trip spring holder
19. Adjuster
20. ring

[005] The housing component (1) houses all the components. Calibration cover is required to fix Latch, Magnetic shaft and overload shaft in its place. This facilitates access to magnetic calibration. Closing cover completely closes the housing to provide immunity from the external environment. Calibration cover and closing cover are fixed in housing using screw and nuts. Top cover is fixed with the housing using snap fit arrangement. Top cover provides visibility and accessibility of Thermal calibration screw.

[006] Modular TMR has an independent trip system inside. It comprises of Latch (7), Popper (6), trip spring and Latch spring. During overload and short circuit conditions, the latch opens up de-latching the popper. The stored energy of the trip spring is released through popper. The popper during its travel enables tripping of the breaker. This trip system will be accessed by 2 components Overload shaft for thermal trip and Magnetic shaft for Magnetic trip system.

[007] In a typical, thermal trip system as shown in figure 7, heater is the conductor which provides the current path. It connects contact system of breaker to the termination. Its function is to generate localized heat and conduct to bimetal which is welded or can be bound to it by any other means too. Bimetal has a tapping at its head and secures a grub screw which is termed as calibration screw. This screw serves as a single point hitting of bimetal on the overload shaft and it also allow us to vary the gap between the screw tip to the overload shaft. An illustration of a heater bimetal assembly is shown in figure 6. According to IEC – 60947 part I, the breaker should not trip for 1.05 times the rated current for 2 hours and it should definitely trip within 2 hours, when 1.3 times the rated current is passed. When higher current flows, higher heat is generated in the heater which is conducted to the bimetal. This bimetal deflects more as a result and hence pushes the overload shaft.

[008] While, a typical Magnetic trip / Short circuit trip system as shown in figure 8, uses the principle, that when current is passed through a conductor, magnetic field is produced around it. This magnetic field is made use of by 2 steel components – Fixed core and moving core. The fixed core is firmly fixed with heater using screw and the moving core rotates towards and away from the fixed core. A tensile spring is hooked on the moving core to the magnetic tuner. This spring offers opposing force if the moving core rotate towards the fixed core. The other end of the moving core rests on the magnetic tuner / Slider. The slider has a slope on which the Moving core rests. When an operator adjusts the magnetic adjuster the slider slides over the housing. The moving core also rest on different points of the slope of Slider. This varies air gap as well the spring force. When high current passes through heater, strong magnetic field is produced around it. This magnetic field exerts attraction force of moving core towards the fixed core. When the magnetic force exceeds the opposing spring force, moving core rotates and during its travel it hits the magnetic shaft. The magnetic shaft in turns de-latches the internal trip system.

[009] However, in the conventional arrangement, the following drawbacks are existed which are as follows:
• Costlier or feature less were the options;
• For modular construction, the number of components is high hence posing problems in assembly, manufacturing, storing and productivity;
• Magnetic air gap between moving core and fixed core cannot be measured due to lack of accessibility.

[0010] Reference is made to a patent application with application number 1079/MUM/2010, wherein an improved thermo magnetic release assembly for use in multi-pole moulded case circuit breaker is provided. However, this application comprises the drawbacks of involving higher cost, higher assembly time and a potential bottleneck for MCCB assembly, and higher rejection of MCCB due to failure of Magnetic tests.

[0011] Thus, in view of the drawbacks of the prior art as stated above, there exist a dire need to an improved assembly of TMR for moulded case circuit breakers (MCCB).

SUMMARY OF THE INVENTION

[0012] 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.

[0013] An object of the present invention is to provide an improved assembly of TMR for moulded case circuit breakers (MCCB) that overcomes the drawbacks of the prior art mentioned above to provide TMR with enhanced productivity.

[0014] Another object of the present invention is to provide an improved assembly of TMR for moulded case circuit breakers (MCCB) with lesser number of components such as to make the TMR cheaper with respect to the material cost, labour and assembly cost, manufacturing cost and inspection cost.

[0015] Yet another object of the present invention is to provide an improved assembly of TMR for moulded case circuit breakers (MCCB) with provisions for visible checks for air gap between moving and fixed core and enhance magnetic calibration.

[0016] Accordingly to one aspect, the present invention provides an improved assembly of Thermo-magnetic release (TMR) adapted to be used in a molded case circuit breaker, said assembly comprising: a housing for receiving plurality of components of said TMR; at least one top cover coupled to said housing using at least one mechanical linkage, wherein said top cover comprises one or more slots and adapted to hold at least one adjuster, wherein said top cover constrain free rotation of said adjuster using gear teeth; at least one magnetic tuner rotatably engaged with said assembly and comprises one or more hooking part for hooking at least one spring means, wherein magnetic tuner adapted to provide wide magnetic setting by varying spring force acting on at least one moving core and air gap between said moving core and at least one fixed core; at least one shaft latch means comprises a combination of at least one overload shaft part, at least one magnetic shaft part and at least one latch part; said moving core having one end resting on said magnetic tuner, wherein said moving core comprises plurality of slots for hooking said springs means to provide fine magnetic calibration; at least one heater having one or more slots for providing a surface for attaching a bimetal; and said adjuster, provided with a gear mechanism to enable locking of said adjuster with said gear teeth of said top cover and thereby locking of said magnetic tuner and said shaft latch in at least one position.

[0017] 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

[0018] 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:

[0019] Figure 1 illustrates a typical molded case circuit breaker and its module according to a prior art.
[0020] Figure 2 illustrates an integral type of TMR according to a prior art.
[0021] Figure 3 illustrates a modular type of TMR according to a prior art.
[0022] Figure 4 illustrates an exploded view of TMR with clear representation of outer components according to a prior art.
[0023] Figure 5 illustrates integral view of TMR for clear representation of inner components according to a prior art.
[0024] Figure 6 illustrates heater bimetal assembly according to a prior art.
[0025] Figure 7 illustrates components involved in Thermal trip assembly according to a prior art. The housing is excluded for illustration purpose
[0026] Figure 8 illustrates components involved in Magnetic trip assembly according to a prior art. Housing excluded for illustration purpose.
[0027] Figure 9 illustrates SEMI – MODULAR construction of TMR according to one embodiment of the present invention.
[0028] Figure 10 illustrates shaft latch means with the combination of overload shaft means, magnetic shaft means and latch means, according to one embodiment of the present invention.
[0029] Figure 11 illustrates provisions in housing to view the air gap in magnetic system in R pole, according to one embodiment of the present invention.
[0030] Figure 12(a) illustrates housing of the TMR and the trip spring component according to the prior art. Figure 12(b) illustrates the new housing with provision for holding trip spring means according to one embodiment of the present invention.
[0031] Figure 13 illustrates the top cover according to one embodiment of the present invention.
[0032] Figure 14(a) illustrates magnetic tuner/slider component according to a prior art. Figure 14(b) illustrates magnetic tuner component according to one embodiment of the present invention.
[0033] Figure 15(a) illustrates moving core according to a prior art. Figure 15(b) illustrates new moving core according to one embodiment of the present invention.
[0034] Figure 16(a) illustrates heater according to a prior art. Figure 16(b) illustrates new heater according to one embodiment of the present invention.
[0035] Figure 17(a) an adjuster according to a prior art. Figure 17(b) shows new adjuster according to one embodiment of the present invention

[0036] 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

[0037] 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.

[0038] 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.

[0039] 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.

[0040] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0041] 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.

[0042] 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.

[0043] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0044] The present invention provides an improved assembly for TMR. The working of the TMR is identical to that of the typical TMR known in the prior art. However, due to the improved assembly, the TMR provided by the present invention is more reliable with reduced number of components and other added benefits. Further, the construction can be developed in both integral as well modular type. However, the construction of the TMR is explained herein by the semi-modular type of the TMR as shown in figure 9.

[0045] In one embodiment, the components of the semi-modular type TMR consists of the following components:
1. Housing
2. Top cover
3. Shaft Latch means/shaft_latch
4. Magnetic tuner
5. Popper
6. Adjusters
7. Heater
8. Moving core
9. Fixed core
10. Springs
11. Hardware for fixing

[0046] Reference is made to figures 1-8 illustrating the MCCB with conventional assembly of TMR according to prior art. Reference is made to figures 9-17 illustrating the new arrangement of the components of the TMR for MCCB along with comparison to the existing components of the typical TMR.

[0047] In one embodiment, reference is made to figure 12(a), figure 12(b) and figure 13 which shows the housing component and the top cover of the TMR assembly. This component houses all the components of TMR. The features in housing to hold the Magnetic Tuner and Shaft_Latch component enables the top cover to hold those components. This avoids the usage of 2 critical components namely, Calibration cover and Closing cover used in Modular TMR. Also, the side walls of the housing is left partially open which enables visibility of air gap in magnetic circuit in R and B poles. In existing design, a separate component, spring holder, will be used to hold the trip spring. That is provided as an inherent feature in this model thus eliminating the need of that component.

[0048] In one embodiment, as shown in figure 11, the side walls of said housing remains partially open to enable visibility of air gap in a magnetic circuit in R pole.

[0049] In one embodiment, as shown in figure 13, the top cover can be detachable and it can be fixed to Housing using snap fit mechanism, for initial tests, if required. Then it can screwed with the housing using a self-tapping screw. This top cover can be provided with plurality of slots for the operator to see and access the calibration screw. It can also holds the magnetic and thermal adjuster in its place. Also it has gear teeth to constrain the free rotation of adjuster. This feature enables to hold the internal component in its place once after the operator has adjusted it for his/ her requirements. Top cover also has limbs projecting outwards to hold the Shaft_Latch and Magnetic Tuner in its place. The top cover is snap fitted to housing, enabling easy removal and fixing of it as and when required. Once the tests are completed, the top cover can be screwed to the housing. This eliminates the flying of top cover during breakers short circuit test as high pressure gases escapes out in all possible directions

[0050] It is to be understood that the mechanical linkages mentioned herein is only to demonstrate the construction of the assembly according to one embodiment and therefore not limited to it. Other mechanical linkages may also be applicable to the present TMR assembly.

[0051] In the present invention the housing and the top cover is modified in a manner such that these components can be sufficient to arrest the undesired degree of freedom of shafts and magnetic tuners. This eradicates the use of calibration cover and closing cover and hence provides access for magnetic calibration. Due to the removal of calibration cover, the access for magnetic calibration is increased

[0052] In one embodiment, reference is made to figure 14(a) and figure 14(b) which shows the existing magnetic tuner and the new magnetic tuner. The improved magnetic tuner of the present invention enables wider magnetic setting by controlling both spring force (Opposing force) acting on the moving core as well as the air gap between the moving core and the fixed core. In other existing designs, same is achieved by linearly translating (Sliding) the component. This sliding against force rubs the plastic Magnetic tuner against the sharp corners of Moving core which results worn out of tuner. This changes the air gap with several operations. However, the magnetic tuner as shown in figure 14(b) eliminates the need of sliding and hence the problem. When adjuster is rotated, it in turn rotates the magnetic tuner. Moreover, a slope is provided in the existing concept on which the Individual pole moving core will rest. So when the slider is moved, the air gap between the moving and fixed core varies as the moving core is held against an opposing tensile spring force which will always attract the moving core towards the tuner. This slope in all 3 poles will have tolerances and hence more deviations from ideal situation. While in the magnetic tuner of the present invention, such slopes are avoided by making the tuner to rotate. The spring hooking point may be provided below the moving core resting point so that when the tuner will rotate, with increase in air gap, the spring extension will also increase. And when the air gap is decreased spring extension may also decrease. This combined variation helps in providing the wider range of magnetic setting.

[0053] In one embodiment, reference is made to figure 10, which shows the shaft latch means for the improved TMR assembly. This component is a combination of 3 components (Overload shaft, Magnetic Shaft and Latch). It will help in reducing the number of critical components in TMR, thereby reducing the overall cost for manufacturing. This also reduces the stacking up of tolerances. To make manufacturing simpler, under cuts are avoided hence eliminating the need of side cores during moulding. A spring means is hooked to the shaft latch means at one end while the other end is connected with the housing. This serves the function of latch spring. The spring means selectively comprising biasing spring, torsion spring, tension spring, compression spring or any combination thereof.

[0054] In one embodiment, reference is made to figure 15(a) and figure 15(b) which shows the moving core of the prior art and the moving core of the improved TMR assembly. The new moving core avoid complex bending which introduces bending tolerances. It comprises at least 3 holes instead of conventional 1 hole for hooking spring. This gives rise to finer magnetic calibration as different combination of holes leads to finer adjustments of spring force. “Poka-Yoke” mechanism can be introduced in the hinging point of moving core by varying the height of the hinges.

[0055] In one embodiment, reference is made to figure 16(a) and figure 16(b) which shows the heater component of the existing TMR assembly and new TMR assembly. In the existing concept as shown in figure 16(a), a complex Z bend will be provided in heater. This is to provide a defined surface for welding with bimetal. Otherwise the overlap between heater and bimetal will become inconsistent for different samples leading to reliability issues. But this bending is difficult from manufacturing point of view and also it adds on tolerance to the system. However, in the present invention, instead of providing Z bend isolation for bimetal, the heater component will be provided with at least one slot above the defined surface meant for welding with the bimetal as shown in figure 16(b). This provides isolation and is also easier to manufacture, takes lesser time to produce and also avoids the tolerances it brings to the system. In addition, this increases the heat generated in the localized area of heater bimetal junction, which could help in deflection of bimetal.

[0056] In one embodiment, reference is made to figure 17(a) and figure 17(b) which shows adjuster component of the existing TMR assembly and new TMR assembly. In conventional TMR assembly, the adjuster is provided by using O ring around the adjuster. This O ring gives away its properties at high temperatures and hence not reliable. As shown in figure 17(b) the adjuster in the improved TMR assembly will provided with gear teeth so that it gets locked with top cover, which also has gear teeth. This enables the adjuster and hence the Shaft_Latch and Magnetic tuner to get locked in its set position and can be changed by turning the adjuster by the operator.

[0057] Due to an improved assembly of the TMR, the operator can check the air gap between the moving and fixed core in R and B pole before inserting the breaker into the bottom housing. The housing will provide access for viewing the air gap. For minute variations in air gap, the system will be robust enough to trip the breaker within the band allowed by IEC standard which is no trip at 80% of the set current and definite trip at 120% of the set current. But if there is a visible deviation in air gap, then it will definitely trip outside the band. If there is deviation, the spring can be alternately hooked in the provisions provided in Moving core or in tuner. Conventionally, these provisions are either given in tuner or in moving core. But in the present invention, the provisions are provided in both moving core as well as in the tuner which could provide more probability to vary and hence reduce rejections.

[0058] Some of the advantages of the present invention, are as follows:
• The present invention provides a more reliable TMR assembly using reduced number of components. Besides, due to reduction in component numbers, the stack up tolerances will be reduced.
• Visible checks and open magnetic calibration. Visual inspection of air gap in magnetic circuit of R & B pole is enabled by providing window in housing.
• Finer magnetic calibration. Fine tuning of magnetic calibration is possible by providing increased number of options to hook spring to vary force in finer steps.
• Reliable and synchronized air gap and spring force change.
• Distinct profiles to remove under cuts in molding, thus reducing cost of tools and increasing productivity.
• Increase in productivity due to lesser assembly time and Inspection time.
• Consistent and reliable working of magnetic setting due to minimal motion and lesser wear and tear.
• Reduction in cost of manufacturing due to 46% reduction in number of components.
• Lesser assembly time
• Volume w.r.t. dimensions of moulded components is reduced.

[0059] Although an improved assembly of thermo-magnetic release in moulded case circuit breakers have been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the improved assembly of thermo-magnetic release in moulded case circuit breakers.