FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: IMPROVED THERMAL MAGNETIC
OVER- CURRENT RELEASE ASSEMBLY FOR A CIRCUIT BREAKER
2. Applicant(s):
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company
(c) ADDRESS : L & T House, Ballard Estate, Mumbai
400001, 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:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to circuit breakers. More particularly the present invention relates to an improved thermal magnetic over-current release assembly for a circuit breaker.
BACKGROUND AND THE PRIOR ART
Conventional thermal overload releases use cantilever type bimetal strips which bend on heating due to differential expansion. One end of these bimetal is connected to the current carrying conductor through which the heat is transferred. The other end is free to move and it hits actuating device after bending to trip the circuit breaker. The force required for actuating comes from the bimetal itself. It imposes many constraints on design. Similar is the case with the magnetic trip unit. The I-core which moves due to the attraction force of the current hits the actuator (which is generally mechanism trip plate), delivers the force required for actuating.
Some of the prior arts are illustrates in figures 1 to 6. Fig. 1 shows the different bending conditions of the bimetal at different temperatures. Similarly Fig. 2 shows the application of the bimetal as switch. When bimetal gets heated it bends and previously closed contacts at the free end are opened. The top figure shows the closed condition and the bottom figure shows the open condition. Fig.3 and Fig.4 shows the application with respect to circuit breaker release. The bimetal bends and hits the actuating device. Fig.4 shows general arrangement and fig. 5 shows adjustment of spring force for variable thermal release.
US5381120 provides a thermal-magnetic trip unit for molded case circuit breakers comprising a load strap having means for attachment to a circuit breaker load terminal at one end and joined to a bimetal element at an opposite end; a support

plate arranged on said load strap intermediate said bimetal and said attachment means; a magnet having support tabs extending from a top thereof and magnetic means extending from a front for concentrating magnet forces in a forward direction; an armature on said support tabs and arranged for rotation toward said magnetic means upon transport of overcurrent through said bimetal; means on said armature biasing said armature away from said magnetic means during transport of quiescent current through said bimetal, said biasing means comprises a spring arranged on a slotted tab extending from a top of said armature; a trip tab projecting from said armature and arranged for contacting a circuit breaker trip bar; and a calibration tab extending from said top of said armature and a calibration screw extending through said calibration tab, an end of said screw contacting a part of said trip tab for setting overcurrent response to said armature.
US6087914 provides a trip mechanism, including two trip actuators, namely a bimetal trip actuator and a magnetic trip actuator that act on a plunger. A plunger guide guides motion of the plunger along a straight line path of travel. Each trip actuator is capable of moving the plunger independently of the other trip actuator to cause the circuit breaker to trip in response to detection of either a thermal fault or a magnetic fault.
US6222433 provides a thermal-magnetic trip unit, suitable for use in a circuit breaker, for eliminating the requirement for latching surfaces while still providing the additional force and motion required to trip the breaker during a short circuit or an overcurrent trip event. The trip unit comprises a link that is biased based on the position of a trip bar. A spring biases the link in a first direction when the trip unit is in a reset condition and biases the link in a second direction when the trip bar is rotated about a pivot point. A trip unit further including an improved indication-of-trip system comprising a two-piece trip bar mechanism and flag system is described to discriminate between overcurrent and short circuit faults. In this embodiment of the invention, visual confirmation of the cause of the trip is provided. The case of the circuit breaker includes a window disposed therein in a

location conducive to a user viewing an identification flag thus enabling the rapid determination of the type of trip which has occurred. To identify a trip caused by an overcurrent condition, a first flag is employed. To identify a trip caused by a short circuit condition, a second flag is employed. If an overcurrent event occurs then the first slide of the two piece trip bar mechanism moves to expose the first flag. If a short circuit event occurs, only the second slide of the two-piece trip bar system moves to expose the second flag.
Some thermal releases use snap disc which flips on heating (the concave disc becomes convex). Thermal releases using the snap disc bimetal use single spring loading concept. The spring force is varied to get adjustable thermal protection. While using low spring force the heat conduction is affected and accuracy is poor. It uses metal parts to apply load on the disc which causes some heat loss.
In the present invention, a latch to actuate the actuator (to hit the trip plate) is provided. It gives some benefits as the actuation force does not depend on the force given by bimetal or I-core. The bimetal or I-core just need to give the force required to de-latch the latch. This force depends on the design of the latch & the latch can be designed for very low actuation force.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Another object of the present invention is to provide an improved thermal magnetic over-current release assembly for a circuit breaker.
Another object of the present invention is to provide a latch pin for tripping and resetting of the disc

Another object of the present invention is to provide a Single action resetting of all discs and the latch
Yet another object of the present invention is to provide an actuating force independent of the thermal & magnetic trip units
These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the
accompanying drawings.
SUMMARY OF THE INVENTION
There is provided an improved thermal magnetic over-current release assembly for a circuit breaker.
According to one embodiment of the present invention, there is provided An improved over-current release assembly for a circuit breaker comprising atleast one latch means to actuate an actuator; atleast one trip plate; atleast one bimetallic disc; atlest one disc pin; atleast one fixed magnetic core; atleast one moving magnetic core; atleast one pin means; atlest one compression spring means; atlest one spring holder; atlest one centre pin; atleast one tripping pin; and atleast one link means.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale

(unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
FIG. 1 illustrates US Patent No. 3670283
FIG. 2 illustrates US Patent No. 3670283
FIG. 3 illustrates US Patent No. 20100164676 Al
FIG. 4 illustrates another prior art.
FIG. 5 illustrates another prior art.
FIG. 6 illustrates another prior at.
FIG. 7 illustrates Complete Release with enclosures
FIG. 8 illustrates Complete Release without enclosures
FIG. 9 illustrates Latch with mechanism trip plate
FIG. 10 illustrates Single Pole with Thermal & Magnetic trip units
FIG. 11 illustrates Single Pole with only thermal trip unit complete and section
view
FIG. 12 illustrates Thermal trip unit when latched
FIG. 13 illustrates Thermal trip unit when de-latched
FIG. 14 illustrates Single Pole with Magnetic trip unit Complete and Section view
FIG. 15 illustrates Magnetic trip unit latched and de-latched
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention, release assembly provides the overload protection by the bimetal disc and the short circuit protection is achieved with the fixed (C-core) & moving (I-core) magnetic cores. Both thermal & magnetic units actuates same latch which in turn hits the trip plate of the release to trip the breaker.
Parts mentioned in the drawings:
1. Release Box A

2. Release Box B
3. Conductor
4. Mechanism Trip Plate
5. Tripping Pin
6. Latch Pin
7. Extension Spring - Tripping Pin
8. Centre Pin
9. Spring Holder
10. Bimetal Disc
11. Disc Pin
12. Compression Spring - Thermal Unit 13.1-Core

14. C-Core
15. Compression Spring - Magnetic unit
The thermal and magnetic units are separate for each pole of the breaker, but the latch will be only one per breaker which will be actuated by a single pin common for all the poles. The latch consists of a latch pin and tripping pin. Tripping pin is loaded with springs. Latch pin holds the tripping pin at its normal position at all normal conditions. The latch pin when hit by actuator from any pole's thermal or magnetic units it de-latches the tripping pin. The tripping pin then travels under spring force to hit the trip plate of the mechanism to trip the breaker.
Each single pole consists of a thermal unit and a magnetic unit. The thermal unit and the magnetic unit are similar for each pole. The thermal unit of each pole unit will consist of one bimetal disc, one disc loading component, one compression spring, one spring holder and one centre pin. The disc pin is made up of plastic to avoid any heat loss. The bimetal disc is primarily convex and it will become concave after attaining predetermined temperature. When current exceeds the maximum operating value for the breaker, excess heat is produced in the link carrying the current. The link can be made up of copper, brass or any other

material. The heat is transferred to the bimetal disc through the touching surface between the disc and the current carrying link. The touching surface may be plane or any profile like ring. The compression spring applies contact pressure at the joint through the disc pin. The contact pressure is same throughout and ensures good heat transfer between current carrying link and the bimetal disc. When disc become concave from convex it pushes the centre pin. The centre pin then hits the latch pin of latch to trip the breaker.
For resetting the disc the tripping pin is pushed back
against the spring force. The tripping pin hits the latch pin which pushes back the centre pin of the thermal trip unit to flip back the bimetal disc. Single latch pin is used to flip back all the bimetal discs.
The magnetic trip unit consists of one C-core (fixed), one I-Core (moving) and one compression spring. The C- core rests in contact with the I-core and it encircles the conductor over three of its sides. The I-core is hinged at one of the ends in the C-core and the other end is free to rotate about the hinge. The compression spring acts on the I-core in such a way that it tries to push I-core from the C-core. When current passes through the conductor flux is set up. The C & I core material being of very low reluctance like mild steel, channelizes the flux through it. The air gap between the C & I core forms major reluctance section in the path of the flux. As flux tries to get low reluctance path the C & I cores experience a force of attraction. As C core is fixed the force tries to attract the I-core towards C-core but it has to act against the spring force acting on the I-core. As the current flowing through the conductor increases the force also increases. The attraction force is balanced against the spring force. The spring force is adjusted such that the attraction force will not exceed the spring force below predetermined current value (this current value is generally 8 to 10 times of the maximum operating value). When current exceeds this predetermined current value the attraction force overpowers the spring force moving the I-core to hit the

latch pin of the latch to de-latch the tripping pin. When current reduces the spring force overpowers the attraction force bringing it to its normal position.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM:
1. An improved over-current release assembly for a circuit breaker
comprising:
atleast one latch means to actuate an actuator;
atleast one trip plate;
atleast one conducting heater element
atleast one fixed magnetic core means of substantially c shape;
atleast one moving magnetic core means of substantially I shape;
atlest one spring means being connected to said fixed and moving magnetic core means such that in operation said spring means pushes the said core means from each other upto a predetermined limit of spring force;
atlest one spring holder;
atlest one centre pin; the said pin means captures disc displacement after flipping of the disc to hit the pin
atleast one bimetallic disc; the said disc is in contact with heater for heat transfer
atlest one disc loading component (disc pin); the said disc loading component maintains contact pressure between disc and heater
atleast one pin means (6) the disc on movement de-latches the
wherein tripping pin means being spring loaded such that under spring action in operation said pin means hits said trip plate means for tripping the breaker; and

wherein the said bimetal disc spring loaded against conducting heater element with the help of disc loading element; the disc upon heating flips to give displacement to centre pin (8) which hits the pin (6) of the latch
2. Assembly as claimed in claim 1 wherein said spring means adapted to balance attraction force between said fixed magnetic core and said moving magnetic core by spring force.
3. Assembly as clamed in claim 1 wherein said spring means having spring force adjusted such that said spring force is adapted to overpower said magnetic force of attraction upto predetermined current value.
4. Assembly as claimed in claim 1 wherein said pin means common to all poles adapted to actuate said latch means.
5. An improved over-current release assembly for a circuit breaker as herein described and illustrated with reference to accompanying drawings.