FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention. - SITE CONVERTIBLE THERMAL STRUCTURE
FOR CIRCUIT BREAKER
2. Applicant
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY : 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 thermal structure adapted to actuate tripping motion in moulded case circuit breakers (MCCBs). The invention particularly relates to a site convertible thermal structure 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 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
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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 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.
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Thus there is a need to provide for a site convertible thermal structure wherein transfer of heat generated by resistance in the structure to a bimetal, is accurately sensed to trip circuit breakers for protection against overload faults.
OBJECTS OF INVENTION
One object of present invention is to provide controls 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.
Another object of the present invention is to provide flexibility in the variation of resistance of the heater and thereby varying the amount of heat in the thermal structure.
Another object of present invention is to reduce the number of heaters to cover range of current.
Another abject of present invention is to avoid recalibration after changing from one current range to another current range.
Yet another object of present invention is to make thermal structure modular in nature and to reduce assembly time.
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 tripping the circuit breaker, said thermal structure comprising:
heater section
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wherein said heater section comprises plurality of sub sections which include section 1 and section 2;
wherein both sections 1 and 2 are operatively held to each other maintaining desirable distance of separation between sections adopting connecting element; and
bimetallic element in operative connection with one of said sections such that heat from section is transmitted causing deflection of the bimetallic element in a predetermined direction,
DETAILED DESCRIPTION OF INVENTION
The present invention relates to a variable site convertible 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 heater thereby receiving heat produced in heater due to effect of current flow through heater. On receiving heat bimetal bends toward predetermined direction, which is towards trip bar and mechanism side in this case.
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 section 1 and section 2 of heater acts as shunt for the current path. At
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end, 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 element comprising screw arrangement but this does not restrict scope of the invention to screw. Other means such as spring loaded clamps can be used to make this flexible electrical connection.
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 tightening screw of section 2 to outgoing terminal adds parallel path for section 1 current, if screw 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, heat generated from section 1 transferred to 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.
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 range from 160Amp to 250 amp where 160-200 amp section is site convertible, so circuit breaker with 200-250 amp is converted to 160-200 amp circuit breaker by elimination of section 2 screw.
Material used for section 1 is copper and for section 2 is phosphor bronze. These two sections are brazed. The selection of heater material depends on required amount of heat
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generation which in turn decides deflection of bimetal where bimetal properties are also important. 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 is copper and section 2 is phosphor bronze, 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 screw is in tight position means section 1 is shunted by section 2 thereby achieving current division as per law of current division.
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 screw has to be removed in 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 heater section 1 dimension is changed, and section 2 material is changed to brass, this thermal structure will work exactly as per thermal structure mentioned above.
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.
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BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates the cut section view of circuit breaker.
Figure 2 illustrates the release system of the circuit breaker.
Figure 3 illustrates the release system and the bimetal in bent condition.
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 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). 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 screw (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 (3) gives the release structure with bimetal in bent condition.
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. The connecting element herein describes as screw or spring loaded clamp can be replaced by its technical equivalence and yet the invention can be performed. The 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.
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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
tripping the circuit breaker, said thermal structure comprising :
heater section
wherein said heater section comprises plurality of sub sections , which include section 1 and section 2;
wherein both sections 1 and 2 are operatively held to each other maintaining desirable distance of separation between sections adopting connecting element; and
bimetallic element in operative connection with one of said sections such that heat from section is transmitted causing deflection of the bimetallic element in a predetermined direction.
2. A site convertible thermal structure as claimed in claim 1, wherein connecting element comprises a screw means adapted to connect section 1 and section 2 parallely such that loosening and tightening of said screw operatively connects or disconnects the sections to/from circuit of the thermal structure.
3. A site convertible thermal structure as claimed in claim 1, wherein bimetallic element is connected electrically to section 1 so as to receive heat from section 1.
4. A site convertible thermal structure as claimed in claims 1 and 2, wherein section 1 is of copper material.
5. A site convertible thermal structure as claimed in claims 1 and 2, wherein section 2 is of phosphor bronze.
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6. A site convertible thermal structure as claimed in claims 1 to 5, wherein section
1 provides conducting path for 0 to 200 amps.
7. A site convertible thermal structure as claimed in claims 1 to 5, wherein section
2 provides conducting path for 0 to 50 amps.
8. A site convertible thermal structure as claimed in claims 1 to 5, wherein site convertible ampere ranges from 160 amps to 200 amps.
9. A site convertible thermal structure as herein substantially described and illustrated with reference to the accompanying figures.
Dated this 5th day of December 2006
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ABSTRACT
TITLE : SITE CONVERTIBLE THERMAL STRUCTURE FOR CIRCUIT BREAKER
The present invention relates to a site convertible thermal structure in a circuit breaker. The thermal structure comprises heater section wherein said heater section comprises plurality of sub sections which include section 1 (20) and section 2 (21); wherein both sections 1 and 2 are operatively held to each other maintaining desirable distance of separation between sections adopting connecting element and bimetallic element (23) in operative connection with one of said sections such that heat from section is transmitted causing deflection of the bimetallic element in a predetermined direction.
Figure 2
7 DEC 2006