Claims:1. A thermo-magnetic release assembly in a multi-pole electrical switching device, said assembly comprising:
plurality of heaters;
plurality of bimetals coupled with said heater;
plurality of trip shaft means; and
plurality of latching mechanism;
plurality of calibration screw means isolated from said heater and said bimetal, wherein each of said calibration screw means operable by a test set up module according to first and second time period;
wherein said test set up module operable by means of a gear based mechanism, and comprising a tool assembly in each poles of said multi-pole electrical switching device to operate each of said calibration screw means;
wherein, said tool assembly rotably engage with each of said calibration screw simultaneously at said first time period presetting said calibration screw ready for calibration, while at said second time period each of said calibration screw enable to rotate simultaneously by means of said gear based mechanism until said electrical switching device trip.

2. The assembly as claimed in claim 1, wherein said calibration screw positioned on a fixed core and said fixed core coupled with said heater.

3. The assembly as claimed in claims1-2, wherein said tool assembly comprises:
a hex key for accessing said calibration screw means in each poles of said multi-pole electrical switching device, wherein said hex key adapted in a spring loaded arrangement, wherein said spring loaded arrangement coupled to a ball bearing means and thereby coupled to said gear based mechanism by means of a bearing shaft.

4. The assembly as claimed in claims 1-3, wherein said tool assembly adapted to rotate based on at least one input signal transmitted from at least one motor through said gear based mechanism.

5. A method for calibrating a multi-pole electrical switching device by using a thermo-magnetic release assembly as claimed in claims 1-4, said method comprising:

transmitting, by means of a motor, one or more input signals through a gear based mechanism to at least one tool assembly for enabling rotation of said tool assembly at first time period, wherein said tool assembly comprises a hex key adapted in a spring loaded arrangement;
engaging, said tool assembly with calibration screws in each poles of said multi-pole electrical switching device due to said rotation; and thereby
rotating, said calibration screws in each poles of said multi-pole electrical switching device simultaneously, by actuating said motor at second time period until said electrical switching devices enabled to trip.
, Description:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to low voltage switchgear applications, and more particularly, to a hot calibration mechanism for calibrating a circuit breaker bi-metal to a permanent setting with a suitable test set up module.

BACKGROUND

[002] A Circuit Breaker is a manually or automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. The molded case circuit breakers have the subsystems which includes: Mechanism, Contact system, Release. The release in the molded case circuit breaker can be either be an electronic or thermos-magnetic releases.

[003] The thermo-magnetic release uses electromagnetic coils to provide short circuit protection, and bimetal to provide overload protection. The overload condition can be explained in simple terms as higher current (not as high as short circuit) persisting for long time. The thermo-magnetic release will be designed to carry a particular rated current for a period of time based on its duty cycle. If higher current (overload current) flows in the system for longer periods, then the system will not be able to dissipate the excess heat generated because of the overload and ultimately the system will break down.

[004] The thermal part of the thermo-magnetic release usually consists of a heater, a bimetal, a calibration screw, a trip shaft, and latching mechanism. Deflection of bimetal under high temperature is the phenomenon used in thermo-magnetic release to protect the circuit from overload current. A heater element is used, which will carry current and will provide the necessary heat to bimetal either by passing current through the bimetal (direct heating) or by thermally conducting the heat to the bimetal (Indirect heating). The bimetal in turn will deflect and give a signal to the trip shaft and finally to the latch mechanism.

[005] Conventionally, a screw called calibration screw, is placed on the apex of the bimetal for calibration. Due to varied reasons like change in resistance, improper mechanical joints, assembly and component level tolerance the gap between the bimetal and the trip shaft varies and may result in early-trip / late-trip / non-trip. In order to adjust this gap, the calibration screw is adjusted to its correct distance either by screwing or unscrewing it. But this conventional method of calibration takes more number of iterations to reach the correct gap and hence making it very tedious.

[006] Another, method called hot calibration is typically adopted to reduce the number of iterations to one by adjusting the gap between the bimetal and trip shaft in live condition until the circuit breaker trips. Generally hot calibration is being done in MCBs where, the calibration has to be done on single pole only. When the same is adopted in MCCBs where there are multiple poles, it is better than the conventional method but still is time consuming to do it pole by pole. Therefore there is need for a proper set up to do the calibration successfully.

[007] Reference is made to US patent number 5,821,839, which discloses an improved calibration means for a circuit breaker. The teaching provides a remote control circuit breaker having an improved calibration arrangement for calibrating and maintaining the pre-determined current level at which the circuit breaker interrupts the current.

[008] Reference is made to US patent number 6,104,273, wherein calibration arrangement and process for use in a circuit protective device are presented. An exemplary calibration assembly for use in the calibration process of the present invention includes a split clamp arm having a first opening for receiving and holding a calibration pin and a second opening for receiving an actuator key.

[009] Reference is also made to application number 974/MUM/2014, titled pole wise hot calibration method for an integral circuit breaker. However, the prior art comprises the limitations that the thread provided in the heater for the calibration screw wears out during calibration especially in case of copper material and that it takes more time to calibrate a circuit breaker pole by pole.

[0010] However, the major limitations of the existing calibration mechanism are:
• The tool accessing the calibration screw loads the bimetal during screwing or unscrewing which will result in improper calibration;
• Calibration screw gets heated and thread wears out in the part (copper in this case) where it is held;
• The screw has to rotate by some angle in order to engage with the accessing tool which might result in improper calibration. Hence it becomes inaccurate and iterative;
• The system lacks the provision for calibrating all poles simultaneously;
• The method is inaccurate as it takes more number of iterations and hence more time and cost.

[0011] Thus, in view of the drawbacks of the existing calibration mechanism in an electrical switching device, there is a necessity to provide an improved calibration procedure in thermal release device for calibrating multiple poles circuit breaker simultaneously with more accuracy.
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 a thermal release for adopting hot calibration for multiple poles simultaneously by means of a test set up module which helps in doing hot calibration with more accuracy.

[0014] Another object of the present invention is to provide an improved calibration mechanism that eliminates the inaccuracy in the existing mechanism using merely tool and screw arrangement.

[0015] Yet another object of the present invention is to provide a calibration method with reduce calibration duration.

[0016] Still another object of the present invention is to eliminate thread worn out in the current carrying part which is adapted to hold the calibration screw.

[0017] According to one aspect, the present invention provides a thermo-magnetic release assembly in a multi-pole electrical switching device, said assembly comprising:
plurality of heaters;
plurality of bimetals coupled with said heater;
plurality of trip shaft means; and
plurality of latching mechanism;
plurality of calibration screw means isolated from said heater and said bimetal, wherein each of said calibration screw means operable by a test set up module according to first and second time period;
wherein said test set up module operable by means of a gear based mechanism, and comprising a tool assembly in each poles of said multi-pole electrical switching device to operate each of said calibration screw means;
wherein, said tool assembly rotably engage with each of said calibration screw simultaneously at said first time period presetting said calibration screw ready for calibration, while at said second time period each of said calibration screw enable to rotate simultaneously by means of said gear based mechanism until said electrical switching device trip.

[0018] In second aspect, the present invention provides a method for calibrating a multi-pole electrical switching device by using a thermo-magnetic release assembly as mentioned above, said method comprising:
• transmitting, by means of a motor, one or more input signals through a gear based mechanism to at least one tool assembly for enabling rotation of said tool assembly at first time period, wherein said tool assembly comprises a hex key adapted in a spring loaded arrangement;
• engaging, said tool assembly with calibration screws in each poles of said multi-pole electrical switching device due to said rotation; and thereby
• rotating, said calibration screws in each poles of said multi-pole electrical switching device simultaneously, by actuating said motor at second time period until said electrical switching devices enabled to trip.

[0019] 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

[0020] 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:

[0021] Figure 1 shows an isometric view of the thermal release assembly with isolated calibration screw, according to one embodiment of the present invention.

[0022] Figure 2 shows a section view of the test set up with MCCB mounted, according to one embodiment of the present invention.

[0023] Figure 3 shows an isometric view of the MCCB mounted on to the test set up, according to one embodiment of the present invention.

[0024] 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

[0025] 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.

[0026] 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.

[0027] 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.

[0028] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] It is also to be understood that the term “module” is used in the specification to indicate an apparatus, unit, component and the like. The term “means” when used in the specification is taken to specify the mode by which desired result is achieved.

[0033] The present invention can be implemented with multi-pole electrical switching device that may include but not limited to, circuit breakers or thermo-magnetic breaker, molded case circuit breaker (MCCB) residual circuit breaker (RCB), earth leakage circuit breaker (ELCB) and the like. This invention specifically relates to the release assembly in the electrical switching device and more specifically to the thermo-magnetic release.

[0034] Figure 1 shows an isometric view of the thermal release assembly with isolated calibration screw, according to one embodiment of the present invention.

[0035] Figure 2 shows a section view of the test set up with MCCB mounted, according to one embodiment of the present invention.

[0036] Figure 3 shows an isometric view of the MCCB mounted on to the test set up, according to one embodiment of the present invention.

[0037] The components of the thermo-magnetic release assembly as shown in figures 1-3 comprises of the following component:
1. Heater
2. Bimetal
3. Calibration screw
4. A trip shaft
5. Latching mechanism
6. Hex key
7. Tool holder
8. Spring means
9. Spring holder
10. Ball bearing
11. Main gear mechanism
12. Bearing shaft
13. Motor
14. Two idle gears

[0038] In one embodiment, the calibration screw (3) is held rigidly and also isolated from the current carrying part thereby avoiding the thread wear out during calibration. The calibration screw (3) head usually consists of hex slot and a hex key (6) will be used for rotating it. In the prior art, while the hex key will get engage with the calibration screw (3), it rotates the calibration screw by some angle till both the hex gets aligned. But this additional rotation is not part of the actual calibration which in turn leads to improper calibration. However, in the present invention, this will be taken care by a test set up module developed for the hot calibration.

[0039] In one embodiment, the test set up module consists of a gear based mechanism in which there is a hex key (6) in each pole for accessing the calibration screw (3). All the hex keys will be operated simultaneously by means a common motor (13) and the signals are transmitted through a gear arrangement. The hex key will be held in a spring loaded arrangement so that it does not mechanically disturb the heater or bimetal assembly during calibration.

[0040] In one embodiment, the calibration method will consists of two time periods. In the first time period the tool will get engage with the calibration screw, and so the rotating angle required by the calibration screw to engage with the tool assembly will not be the part of the actual calibration turns required. Only after this, in the second time period, the calibration screw will start rotating until the circuit breaker trips in desired band. Hence it becomes accurate and at the same time, the duration is very less. This way all the poles will be calibrated simultaneously.

[0041] In one embodiment, the present invention can be implemented by means of a three pole MCCB. The thermal release of the circuit breaker of the present invention suit the hot calibration method. The calibration screw (3) will be placed on a rigid part called fixed core which may be made up of mild steel (15). It can be fixed firmly with the heater (1) and the heater can be welded with the Bimetal (2). The heater, bimetal and fixed core together will make a single assembly and the profile of these will facilitate proper access to the calibration screw as shown in Figure 1. The calibration screw will be isolated from the current carrying parts, which are heater and bimetal.

[0042] In one embodiment, the tool assembly for accessing the calibration screw (3) which will be normally hex key. The hex key (6) is held in a tool-holder (7) and both will be loaded with a spring means (8). The spring means in turn is held in a spring holder (9). The above said parts will be coupled with a ball bearing (10) and then connected to a main gear (11) through a bearing shaft (12). All these together will act as a single assembly and will be enable to rotate when the gear is given input from the motor (13). There can be one such tool assembly for each pole in multi-pole circuit breaker. The figure 3, shows a three pole breaker and hence there are three tool assemblies. It consists of two idle gears (14) as the three main gear assemblies need to rotate in the same direction. In one embodiment, the gear assembly may be adapted to rotate in a clockwise direction as the calibration screw in the circuit breaker need to be rotated so. The set up will have a provision for mounting/de-mounting on the circuit breaker.

[0043] In one embodiment, the calibration time band will predetermined from various experiments, say T1 – T2 seconds. First the circuit breaker will get mounted on the set up. For the time 0 – T1, the motor will give input to the gears based mechanism and rotates the calibration screw of all the poles till the hex key gets engaged properly and presetting it ready for calibration. Therefore, this will not affect the actual calibration turns required by the breaker. Next, for the time T1 – T2, the motor gets ON and rotates the calibration screw further during which the breaker trips. Thereby it is ensured that the circuit breaker always trip in the desired time band, whether the breaker is tripped in T1 – T2. The motor can be controlled either manually or by a control circuit.

[0044] Some of the advantages of the present invention, are as follows:
• The present invention allows the user to calibrate multiple poles of the circuit breaker simultaneously.
• The heater-bimetal-fixed core thermo-magnetic assembly design facilitates the access for calibration screw.
• The tool engagement with the screw does not affect the accuracy of calibration
• Very less duration is required with this set up compared to the conventional calibration mechanism
• automation friendly
• simple in design and cost effective
• elimination of thread worn out in current carrying part which holds the calibration screw

[0045] Although a calibration mechanism in thermal release assembly and a method thereof 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 calibration mechanism in thermal release assembly and a method thereof.