FORM2THE PATENTS ACT, 1970(39 of 1970)&The Patents Rules, 2003COMPLETE SPECIFICATION(See section 10; rule 13)
Title of the invention - MODULAR STRUCTURE FOR THERMALLYACTUATED CIRCUIT BREAKER
2. Applicant(a) NAME : LARSEN & TOUBRO LIMITED(b) NATIONALITY : An Indian Company(c) ADDRESS : L&T House, Ballard Estate, Mumbai 400 001,State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF INVENTION
The present invention relates to a modular thermal structure adapted to actuate tripping motion in moulded case circuit breakers (MCCBs). The invention, particularly, relates to a site convertible thermal structure for actuating tripping motion in circuit breakers and providing flexibility in operation over a wide current range, wherein transfer of heat generated by resistance in the structure to a bimetal, is sensed to trip circuit breakers for protection against overload faults in power distribution system to which it is connected.
BACKGROUND AND PRIOR ART
The function of a circuit breaker is to carry normal currents and to interrupt higher currents. Circuit breakers are normally employed for protection of distribution system devices against various overload conditions. The part of the breaker that senses higher current and generates the tripping signal is the "Release". For overload faults thermal actuation is used to trip the circuit breaker leading to protection of downstream equipments. The bimetal element which is important part of thermal structure actuates the trip bar which in turn actuates the mechanism on which moving contact is held rigidly; thereby separating moving and fixed contact and in turn resulting in circuit interruption.
The thermal structure of circuit breaker includes bimetal
element, heater element, use of heater depends on current
rating of the circuit breaker. In most of low current
applications where current magnitude is less than 100 amp
heater is avoided and load current flows through bimetal
2

element. For higher current application heater element is used such that load current flows through heater and generates heat which is in turn transferred to bimetal element. This arrangement of indirect heating bimetal used to avoid excessive heating of bimetal. This whole arrangement holds good for one rating of current, for range of current another method of technique must be used. Most preferred is changing trip bar location and trip bar with varying slope at bimetal actuation point. Certain patents discusses about changing heater such that heaters can be arranged in series or parallel thereby giving current range as desired. The major disadvantage with this kind of arrangement is various heaters for different kind of range and assembly problems. The other problem associated with this is little control over current range for user as such arrangements are not site convertible.
US4570143 describes a molded case circuit breakers of the residential and commercial frame type. Residential and commercial frame circuit breakers are utilized in panel boards and load centers for protecting branch lighting and appliance circuits. The invention deals with operating the release at different current values and comprises two parallel paths in its heater element, one of which is selected over the other to change the resistance of the heater and thus control the heat produced and in turn the bending performance of the bimetal. Circuit breakers of this type are available in various ampere ratings, the most common being 15 and 20 ampere rated breakers. Commonly, breakers of the two ratings are structurally the same but utilize thermal trip elements having different operating characteristics. Accordingly, the manufacturer provides and the distributor stocks two distinct
3

breakers to accommodate both the 15 amp and 20 amp ratings, which results in a substantial inventory for both.
US5872495 describes a thermal and magnetic trip unit for a multi-pole circuit breaker includes a thermal structure having a bimetallic element and one or more U heater elements. The heater elements and bimetallic element may be configured in parallel or in series. In this configuration, the thermal structure defines a coil having one turns for each heater element and the bimetallic element. This coil may be used to implement a magnetic trip structure by inserting one or two magnetically permeable yokes, each yoke surrounding one leg of the combined thermal structure.
In none of the above documents, simple way of selection of current flowing part by adjusting the heat in the bimetal has been found. In most of the cases the total heat produced in the plates is transferred to the bimetal leading to malfunctioning of the tripping actuators, which may cause serious damage to the connected power distribution system and its equipments during any overload fault condition.
In some cases heater material is changed to give desired heat generation. Despite all these efforts current range gets restricted to (0.65-1) In (where In is the rated current of the circuit breaker), thus there should be heater and bimetal combination such that it should cater to current range of (0.4-1) In, with minimal number of heater and bimetal combination. In addition this combination should be user friendly that means user should be in position to change the current rating from 1 In to 0.4 In and in between as per his convenience. The heat generated by this heater will be
4

transferred to bimetal, and is accurately sensed to trip the circuit breaker in turn protecting downstream equipments from faults.
The present inventors have surprisingly found that by way of their modular thermal structure flexibility in actuating tripping operation over a wide range of amperes can be provided by controlling / limiting / adjusting the heat generated in the bimetal which minimizes the risk of malfunctioning of the tripping actuators, which may cause serious damage to the connected power distribution system and its equipments during any overload fault condition. Also for desired heat generation one would not have to change the whole heater material, only by some adjustments the heat can be varied as desired by the user.
OBJECTS OF INVENTION
Thus, one object of present invention is to provide controls / adjustments thereby offering flexibility in operation to user for changing current range at site without recalibration efforts.
Another object of the present invention is to constitute the
interaction between the heater and bimetal in order to
increase the range of currents at which the release can be set
to generate the tripping command.
Yet another object of the present invention is to provide flexibility in the variation of resistance of thereby varying the amount of heat in the thermal structure.
5

Yet another object of present invention is to achieve whole current range with one heater and bimetal combination.
Another abject of present invention is to avoid recalibration after changing from one current range to another current range, in between available current range.
Yet another object of present invention is to make thermal structure modular in nature and to reduce assembly time.
The other object of present invention is to reduce number of components and thereby reducing inventory and making it economical.
SUMMARY OF INVENTION
Thus according to one aspect of the present invention there is provided a site convertible thermal structure in a circuit breaker, said thermal structure being adapted to sense thermal health of the circuit breaker components for actuating tripping operation in the circuit breaker, said thermal structure comprising :
heater section;
wherein said heater section comprises plurality of sub section including section 1 and section 2 in a manner that both the sections 1 and 2 are operatively connected to each other adopting connecting means;
said connecting means connecting said section 1 and section 2 in a co-operative manner ; and
6

bimetallic element in operative connection with one of the said sections in a manner that heat from the section is transmitted causing bend of the bimetallic element in a predetermined direction.
DETAILED DESCRIPTION OF INVENTION
The present invention relates to variable site convertible modular thermal structure for moulded case circuit breakers. The thermal structure of the present invention being part of release system comprises plurality of heater section, bimetal; other part of release system is magnetic tripping device to protect downstream equipments from short circuit faults. The heater section is operatively connected to the bimetal. The release structure gives tripping signals to trip bar which is cylindrical member. The rotation of trip bar in predetermined manner releases latch bracket which is in turn holding latch, thereby trips mechanism and ensures there is separation of moving and fixed contacts resulting in interruption of current flow. This mechanism of tripping is followed, when release detects overload or short circuit condition.
When current flows through heater, heat is generated. Bimetal element is connected to the heater thereby receiving heat produced in heater due to effect of current flow through heater. On receiving heat, bimetal bends towards predetermined direction, which is towards trip bar and mechanism side in this case.
In one embodiment of the present invention the heater section of the present invention comprises two parts hereafter referred as section 1 and section 2 of heater. The bimetallic element (also referred above as bimetal) is attached to heater
7

section 1 and section 2 of heater acts as shunt for the current path. One end of section 1 of heater is firmly connected to outgoing terminal. The section 2 of heater is electrically connected to outgoing terminal. The sections are attached by connecting means which includes spacer but this does not restricts scope of the invention to spacer. Other means such as spring loaded claps can be used to make this flexible electrical connection.
In another embodiment of the present invention section 1 and section 2 being connected to outgoing terminal forms the parallel path for current, of which bimetal is attached to section 1 of heater. Whether to add shunt in current path of section 1 or not is decided by the connection provided at end of section 2, this means adding spacer in section 2 to outgoing terminal adds parallel path for section 1 current, if spacer is removed then this path is broken and section 1 alone is in circuit.
The major advantage of this invention is just by electrically connecting section 2 adds path parallel to section 1 and disconnecting this joint eliminates this parallel path in circuit leaving behind only current path of section 1. When current is set to flow through heater section 1 and section 2 it generates heat and heat generated from section 1 is transferred to the bimetal.
Distance between two sections, section 1 and section 2 is maintained in such as that heat generated by section 2 will not cause any problem with working of bimetal and section 1 combination. Selection of heater material and bimetal depends on current range requirement, properties of bimetal element and corresponding best matching heater material.
8

For 250 Amp circuit breaker general current range available for user is 200Amp- 250 Amp, which is 0.8-1 In where In is rated current of circuit breaker. The present invention offers customer / user range from lOOAmp to 250 amp where 100-250 ampere. Whole release is site convertible, so circuit breaker with 200-250 amp is converted to 160-200 amp circuit breaker by elimination of section 2 spacer, circuit breaker is converted to 125-160 amp circuit breaker by adding same spacer and by eliminating same spacer circuit breaker is converted to 100-125 amp circuit breaker. Section 2 and the outgoing terminal is connected to each other by means of a screw with desired engaging torque so as to achieve flexibility of operation in the wide ampere range between 100 and 250 amps.
Material used for section 1 and for section 2 is copper, this material is used through out current range. The selection of heater material depends on required amount of heat generation which in turn is decided deflection of bimetal, bimetal properties. Once distance and required heat generation is calculated required resistance is determined and heater geometry is decided.
For 250 Amp for deflection of 5mm heater section 1 and section 2 is copper, based on heat requirements current division is achieved. From section 1 out of 250 amps, 200 amps will flow while for section 2 remaining 50 amps will flow. Once this circuit breaker is calibrated for 250 amps this thermal structure will generate trip command for 5% and 30% overload from set reference which is 250 amps in this case. Section 2 spacer is in tight position means section 1 is shunted by section 2 thereby achieving current division.
9

For user the reference current for the circuit breaker is 250 Amp. When user wants to convert this circuit breaker for lower rating, the cover has to be opened and the spacer has to be removed from section 2, with this change the shunting path of section 1 is removed and hence reference current which was 250 amp is changed to 200 amp which will flow through section 1 and maintaining same deflection to trip the circuit breaker.
The major advantage of this arrangement is recalibration of circuit breaker is avoided.
Moving trip bar gives current range from 200-250 amp with reference set at 250 amp when section 2 is in circuit. When section 2 is removed and trip bar is moved this will give 160-200 amp breaker with reference set at 200 amp due to removal of section 2 from circuit.
For further lower range spacer is once again added in section 2. so earlier 160-200 amp circuit breaker is changed to 125-160 amp breaker. The modularity achieved to such that spacer dimension remains same for whole current range. In this converted lower rating circuit breaker section 1 will carry 125 amp and section 2 which is shunting section 1 will carry remaining 35 amp by law of current division. For further lower range once again spacer is removed thereby converting same breaker to 100-125 amp circuit breaker.
The present invention is henceforth illustrated specifically with reference to a thermal structure of moulded case circuit breaker (MCCB). This does not restrict the scope of the embodiment of the invention to MCCBs but also may apply to other protection systems.
10

BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates the cut section layout of a general circuit breaker.
Figure 2 illustrates the plan view of the modular thermal structure of the present invention.
Figure 3 illustrates an isometric view of the modular thermal structure alongwith the bimetal in bent condition.
Figure 4 illustrates an isometric view of the modular thermal structure without spacer means.
DETAILED DESCRIPTION OF ACCOMPANYING FIGURES
As shown in figure 1 the MCCB comprises contact system (10), mechanism (11), and release system (12). For circuit interruption separation of fixed contact (13) and moving contact (14) is an essential condition. The moving contact is housed in drive shaft (15) and is part of mechanism (11) . The actuation of mechanism is through trip bar (16).
Release system (12) which detects overload and short circuit conditions and gives tripping signal to trip bar (16) shown in figure 2 with bimetal (23). Figure 3 indicates the heater section is divided in two parts, section 1(20) and section 2 (21). Section 1(20) is connected to outgoing terminal (22), and section 2 is electrically connected to outgoing terminal, at present with spacer (24) . The bimetal (23) is electrically connected to heater section 1(20). On receiving heat from heater the bimetal bends and actuates the tripping mechanism. Figure (4) gives the release structure without spacer.
11

The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. Section 2 of heater is electrically connected to section 1 by a spacer but this does not restricts scope of the invention to spacer. Other means such as spring loaded claps can be used to make this flexible electrical connection and still the invention can be performed. The improved structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements which will still be comprised within its true spirit.
12

WE CLAIM
1. A site convertible thermal structure in a circuit
breaker, said thermal structure being adapted to sense
thermal health of the circuit breaker components for
actuating tripping operation in the circuit breaker, said
thermal structure comprising :
heater section;
wherein said heater section comprises plurality of sub section including section 1 and section 2 in a manner that both the sections 1 and 2 are operatively connected to each other adopting connecting means;
said connecting means connecting said section 1 and section 2 in a co-operative manner ; and
bimetallic element in operative connection with one of the said sections in a manner that heat from the section is transmitted causing bend of the bimetallic element in a predetermined direction.
2. Thermal structure as claimed in claim 1, wherein the connecting means comprises spacer provided on section 2 so as to provide electrical parallel relationship between section 1 and section 2 thereby making tripping operation flexible over wide range of amperes.
3. Thermal structure as claimed in claims 1 and 2, wherein the spacer being provided at one end of section 2 such that connection and removal of the spacer operatively amounts to connection and disconnection of the sections from the thermal structure.
13

4. Thermal structure as claimed, in claims 2 and 3, wherein the spacer is further adapted to adjust the flow of current in the sections so as to generate variable heat in the bimetallic element.
5. Thermal structure as claimed in claims 2 to 4, wherein spacer comprising desired engaging torque so as to provide flexibility in operation between desired ampere range.
6. Thermal structure as claimed in claims 2 to 5, wherein the ampere ranges from 100 amps to 250 amps.
7. Thermal structure as claimed in any of the preceding claims, wherein rated ampere further ranges from 0.4 In to 1 In-
8. A site convertible thermal structure in a circuit breaker substantially as herein described and illustrated with reference to the accompanying figures.

Dated this 14th day of June 2006.


Abhishek Sen Of S. MAJUMDAR & CO. (Applicant's Agent)

14

ABSTRACT
Title : MODULAR STRUCTURE FOR THERMALLY ACTUATED CIRCUIT BREAKER
The present invention relates to a site convertible thermal structure in circuit breakers. The modular structure is adapted to sense thermal health of the circuit breaker components for actuating tripping operation in the circuit breaker and comprises heater section wherein said heater section includes plurality of sub sections section 1 (20) and section 2 (21), connecting means (24) and bimetallic element (23) in operative connection with one of the said sections (20 & 21) in a manner that heat from the section is transmitted causing bend of the bimetallic element (23) in a predetermined direction.
Figure 3
/ST