FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules,2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A coil and a method of forming a hotspot therein
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
Inventors
Sanas Ashok Haribhau, Pandharkar Anjani Prasad, Joshi Ulhas Nilkanth, Baganikar Umesh Vishnu and Khedkar Parag Prabhakar, all of S3 Division, Crompton Greaves Limited, Nashik, Maharashtra, India, all Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a coil and a method of forming a hotspot therein and more particularly towards a tripping/closing coil in a circuit breaker and a method of forming a hotspot therein.
BACKGROUND OF THE INVENTION
A tripping/closing coil in a circuit breaker, hereafter referred to as coil, facilitates tripping/closing of the circuit breaker through a plunger connected thereto. Upon energizing the coil, the plunger connected thereto is actuated to operate the circuit breaker mechanism which moves the moving contacts of the circuit breaker, also connected thereto, to trip/close the circuit breaker. Usually, the coil is of a short time rating which means that if the coil is energized continuously for longer than its rated period, the temperature within the coil may increase beyond its permissible limits and may get damaged. There is a possibility of such an overheating when the plunger gets jammed or obstructed and the circuit breaker is not tripped/closed. Consequently, the circuit breaker controlling mechanism, since it did not sense the tripping/closing of the circuit breaker, continues to energize the coil for tripping/closing the circuit breaker. However, since the coil is of short time rating, continuous energization thereof may increase the temperature within the coil beyond a permissible limit thereby damaging it. To prevent this, temperature information within the coil at the time of energization thereof is required which would enable the circuit breaker controlling mechanism to stop energization of the coil before the temperature within the coil reaches a threshold limit. Such temperature information from the coil can be obtained by embedding a thermistor within the coil. However, location of the placement of the thermistor within the coil is a problem since it's a possibility that a

location within the coil other than the location at which the thermistor is embedded within the coil may get heated faster. Thus, even in the presence of the thermistor within the coil, the coil may still get burned out. Embedding a plurality of thermistors within the coil at different location is not feasible and practical. Therefore, there is a need to accurately predict which part of the coil will get heated first which would allow a placement of the thermistor there.
OBJECTS OF THE INVENTION
An object of the invention is to provide a method for forming an artificial hotspot within a coil which is adapted to get heated faster than other areas in the coil during the energization of the coil.
Another object of the invention is to provide a coil with an artificial hotspot formed therein which is adapted to get heated faster than other areas in the coil during the energization of the coil.
Another object of the invention is to provide a coil which has a better protection system therein against overheating thus increasing its shelf life.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, there is provided a method of forming an artificial hotspot in a coil, the artificial hotspot being a localized area on the windings of the coil adapted to get heated faster than other areas on said windings during energization thereof, the method comprising the step of compacting the windings on the coil in a select area on the coil such that the area on the coil comprising the compacted windings gets heated faster than other areas on the coil during the energization of the coil.

According to the invention, there is also provided a coil comprising an artificial hotspot which being a localized area on the windings of the coil adapted to get heated faster than other areas on said windings, said artificial hotspot being formed by compacting the windings on the coil in a select area on the coil such that the area on the coil comprising the compacted windings gets heated faster than other areas on the coil during the energization of the coil.
According to a preferred embodiment, the coil is a tripping/closing coil used in a circuit breaker. The selected area on the windings to be formed as artificial hotspot is compacted by means of at least one string wound tightly around the selected windings and knotted thereupon.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is an isometric view of a tripping/closing coil used in a circuit breaker.
Fig 2 is an exploded view of a tripping/closing coil used in a circuit breaker.
A method is described below for forming an artificial hotspot in a coil such as a 110V, 650W tripping/closing coil having a rectangular shape used in a circuit breaker of 6kV to 800 kV or even higher for tripping/closing the circuit breaker upon energization thereof through a plunger connected thereto. However, the method is not limited to such coils and may be employed in any such coil which is energized and faces a prospect of burning out due to overheating during its energization such as windings of motors, transformers, solenoids, ballasts etc. The artificial hotspot in the coil is a localized area on the windings of the coil adapted to get heated faster than other areas on the windings of the coil during the energization of the coil. Such an adaptation is achieved by compacting the windings on the coil at a select location on

the windings of the coil. As a result of compacting, the density of windings is increased in the hotspot vis-a-vis the density of windings in the area selected to be the hotspot before compacting. Also, the shape of the windings of the coil around the hotspot changes from rectangular to shapes such as circular, almost circular, ellipse or squarish. For example, if the size of the rectangular windings of the coil is 15 mm long and 8 mm wide, upon compacting the selected area on the windings, the shape of that area may become circular or almost circular with a diameter of 12.5 mm or elliptical of a size 12.2 x 15.5 mm (12.2 minor axis, 15.5 major axis) or squarish of a size llxl 1mm. Shape of the compacted windings may depend upon the compressing strength applied on the windings at the time of compacting. As a result of the formation of the artificial hotspot, during the energization the coil, the hotspot gets heated relatively faster compared to other areas on the windings of the coil since the rate of heating of an area on the windings of the coil is directly proportional to the number of windings in that area. In a hotspot formed by compacting the windings, number of windings in the area selected to be the hotspot on the windings of the coil is more compared to other areas on the windings of the coil since compacting stuffs in more number of windings (conductors) in a given area. Thus, the hotspot gets heated faster than other areas on the windings of the coil, more particularly the central area of the hotspot which gets heated the fast.
According to a preferred embodiment, in a tripping/closing coil as described above, the compaction of the windings on the coil to form the artificial hotspot may be achieved by the following method:
(a) Before initiating the winding process of the coil, a middle portion of a string made up of polyester or any such high temperature insulation material and approximately 10 cms of length is placed across the width of the coil former

on which the windings are to be winded. The length of the thread is provided sufficiently long enough such that the ends of the thread extend well beyond the coil former.
(b) The windings of the coil are wind over the coil former such that the middle portion of the string placed across the width of the coil former remains disposed beneath the windings.
(c) Upon completing the winding process of the coil, the string is tightened on the windings by pulling the ends of the string against each other and knotting the string on the windings to bring the windings in the vicinity of the knot in close proximity with each other thereby compacting the windings in the viscinity of the knot thereby forming the artificial hotspot
Preferably and optionally, after a partial winding of the coil, say 50 turns out of a total 100 turns of the coil, a thermistor is placed at a predetermined spot on the windings winded over the bobbin surface. This is to have the thermistor at the central area of the artificial spot which gets heated fastest within the artificial hotspot. The thermistor is usually a NTC or PTC (negative temperature coefficient or positive temperature coefficient) thermistor such as thermistor such as DMP 11 MP series which is connected to the circuit breaker control mechanism or any other warning mechanism through wires or wirelessly. Next, the coil is continued to be winded such that the thermistor is buried beneath the remaining windings.
However, there may be other methods available for compacting a selected portion of the windings such as changing the cross-section of the bobbin itself from rectangular to circular at the hotspot. Similarly, the thermistor may not necessarily be embedded within the windings and there can be other place in/around the hotspot from where as an accurate measurement of temperature of the hotspot can be measured. Also, there

may be other means/method of measuring temperature in/around the hotspot which is not necessarily restricted to using the thermistor.
According to the invention, when the coil is energized, the artificial hotspot gets heated considerably faster than other areas in the winding coil. Since the temperature at the hotspot is always higher than the other areas of the coil, at the current rate of energization of the coil, the temperature at the hotspot is most likely to be the temperature at the other areas of the coil a little while later. This delay gives the operator/circuit breaker control mechanism to take a decision regarding stopping any further energization of the coil thereby preventing the burning out of the coil: The temperature data in/around the hotspot is picked up by the thermistor or such other means/method employed and transmitted to the circuit breaker control mechanism or other warning mechanism/systems.
Figs 1 and 2 are respectively an isometric and exploded views of a tripping/closing coil used in a circuit breaker. The tripping/closing coil is a 110V, 650W coil, windings 1 of which are winded on a rectangular shaped coil former 2. Such a tripping/closing coil is used in a circuit breaker of 6kV to 800 kV or even higher for tripping/closing the circuit breaker upon energization thereof through a plunger connected thereto. The coil comprises an artificial hotspot 3 which is a localized area on the windings 1 of the coil adapted to get heated faster than other areas on the windings of the coil. The artificial hotspot 3 is an area on the winding coil 1 compacted by force. As a result of compaction, more numbers of windings I are present in the area as compared to the number of windings 1 in that area before compaction. Also, compaction results in the change of shape of the windings 1, say from rectangular to circular, almost circular, elliptical or squarish For example, if the size of the rectangular windings 1 of the coil is 15 mm long and 8 mm wide, upon

compacting the selected area on the windings, the shape of that area may become circular or almost circular with a diameter of 12.5 mm or elliptical of a size 12.2 x 15.5 mm (12.2 minor axis, 15.5 major axis) or squarish of a size llx 11mm. Shape of the compacted windings 3 may depend upon the compressing strength applied on the windings 1 at the time of compacting. According to a preferred embodiment, the compacting may be achieved by means of two strings 4 & 5 tightened and knotted around the windings 1 at a location on the windings selected to be the artiflcal hotspot 3. However, only one string may also be used. A thermistor (not shown) is embedded within the windings 1 in the artificial hotspot 3, preferably at the central area of the artificial hotspot 3, for transmitting the temperature in/around the artificial hotspot 3 at the time of energization of the coil and connected to a circuit breaker control mechanism or any other warning mechanism through wires or wirelessly. The thermistor is usually NTC or PTC (negative temperature coefficient or positive temperature coefficient) thermistor such as DMP 11 MP series.
It will be appreciated by a person skilled in the art that the above description of the coils is not limited tripping/closing coils used in a circuit breaker and such is mentioned only for illustration purposes. Similarly, there may be other means available for compacting other than using strings such as changing the cross-section of the bobbin itself from rectangular to circular at the hotspot Also, the thermistor may not necessarily be embedded within the windings and there can be other place in/around the hotspot from where as an accurate measurement of temperature of the hotspot can be measured. There may be other means/method of measuring temperature in/around the hotspot which is not necessarily restricted to using the thermistor.

According to the invention, when the coil is energized, the artificial hotspot gets heated considerably faster than other areas in the winding coil. Since the temperature at the hotspot is always higher than the other areas of the coil, at the current rate of energization of the coil, the temperature at the hotspot is most likely to be the temperature at the other areas of the coil a little while later. This delay gives the operator/circuit breaker control mechanism to take a decision regarding stopping any further energization of the coil thereby preventing the burning out of the coil. The temperature data in/around the hotspot is picked up by the thermistor or such other means/method employed and transmitted to the circuit breaker control mechanism or other warning mechanism/systems.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim:
I. A method of forming an artificial hotspot in a coil, the artificial hotspot being a localized area on the windings of the coil adapted to get heated faster than other areas on said windings during energization thereof, the method comprising the step of compacting the windings on the coil in a select area on the coil such that the area on the coil comprising the compacted windings gets heated faster than other areas on the coil during the energization of the coil.
2. The method as claimed in claim I, wherein the method of compacting the
windings comprises the steps of:
a. placing a middle portion of at least one string across the width of a coil
former of the coil on which the windings are to be wound;
b. winding the windings on the coil former such that the middle portion
of the string remains disposed below the windings;
c. tightening the string around the windings such that the windings
around the thread are compacted to form the hotspot.
3. The method as claimed in claim 1, wherein the coil is of a rectangular shape.
4. The method as claimed in claim 1 or 3, wherein the shape of the compacted windings is changed to circular or almost circular or elliptical or squarish.
5. The method as claimed in claim 1 or 3, wherein the ends of the string are tightened by pulling the ends of the strings against each other and knotting thereof.
6. The method as claimed in claim 1 or 3, wherein a thermistor connected to a circuit breaker control mechanism through wires or wirelessly is embedded between the compacted windings at the time of winding the windings on the coil.

7. A coil comprising an artificial hotspot which being a localized area on the windings of the coil adapted to get heated faster than other areas on said windings, said artificial hotspot being formed by compacting the windings on the coil in a select area on the coil such that the area on the coil comprising the compacted windings gets heated faster than other areas on the coil during the energization of the coil.
8. The coil as claimed in claim 1, wherein the selected area on the windings is compacted by means of at least one string wound tightly around the selected windings and knotted thereupon.
9. The coil as claimed in claim7 is of a rectangular shape.
10. The coil as claimed in claim 7, wherein the shape of the compacted windings is circular or almost circular or elliptical or squarish.
11. The coil as claimed in claim 7, wherein the coil comprises a thermistor embedded between.the compacted windings and connected to a circuit breaker control mechanism through wires or wirelessly.
12. The coil as claimed in claim 1 and 7 is a tripping/closing coil used in a circuit breaker.