FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
THERMAL OVER-CURRENT RELEASE ASSEMBLY;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION
The invention relates to a circuit breaker, and more particularly to thermal over-current release in circuit breaker.
BACKGROUND OF THE INVENTION
Overload protection in a circuit breaker causes the circuit breaker to trip and interrupt power under increased current conditions. Overload protection is provided by a thermal bimetal element which bends when heated by increased current, causing the circuit breaker to trip and interrupt the power.
Typically, devices for thermal overload release use a cantilever type bimetal strip which is connected to a current carrying conductor at one end, and is free at its another end. The bimetal strip when heated to a pre-determined temperature bends and trips the circuit breaker. However, since the cantilever bimetal strip has to be attached to a current carrying conductor at one end and left free at its other end, the cantilever bimetal strip requires alignment. Further, manual calibration is required for each release, and hence a skilled operator needs to calibrate the bimetal strip for every release. Calibration of the bimetal strip is time consuming and hence affects manufacturing efficiency. Also cost of cantilever bimetal strip is high.
Another type of thermal overload release device uses a snap disc which flips on heating. As, shown in figure 1, a snap disc 20 rests on a flat conductor plate 10. Further a single spring 40 is adapted between a centre pin 30 and a conductor plate 10, Spring 40 is varied to get adjustable thermal protection, and centre pin 30 is used to capture disc 20 movement after flipping. Due to a single spring, this type of thermal overload release device has poor heat conduction at low spring force (when the spring force is reduced to get variable tripping time).

In view of the above, there is a need in the art for an improved thermal overload release device, which is more efficient and cost-effective.
SUMMARY OF THE INVENTION
Accordingly, in one aspect, the present invention provides a thermal over-current release assembly comprising a conductor plate having a profile , a bimetal snap disc in contact with the conductor plate, the bimetal snap disc being able to flip its orientation depending upon a predetermined temperature; and a plurality of springs, the springs applying a contact pressure on the bimetal snap disc; wherein the bimetal snap disc rests on the profile in the conductor plate.
In another aspect, the present invention provides a thermal over-current release assembly comprising a conductor plate having a profile, a bimetal snap disc in contact with the conductor plate, the bimetal snap disc being able to flip its orientation depending upon a predetermined temperature, a first spring and second spring, the first and second springs being concentric, a centre pin adapted between the bimetal snap disc and the first spring, and an outer pin adapted between the bimetal snap disc and the second spring, wherein the bimetal snap disc rests on the profile of the conductor plate.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows a thermal overload release device using a snap disc in the prior art.

Figure 2 shows a thermal over-current release assembly in accordance with an embodiment of the invention, where
Figure 2A is an isometric view of the thermal over-current release assembly in accordance with an embodiment of the invention;
Figure 2b is an isometric sectional view of the thermal over-current release assembly in accordance with an embodiment of the invention;
Figure 2C is an exploded isometric view of the thermal over-current release assembly in accordance with an embodiment of the invention. Figure 3 shows a conductor plate of the thermal over-current release assembly in accordance with an embodiment of the invention, where
Figure 3A is a conductor plate having a convex groove profile in accordance with an embodiment of the invention;
Figure 3B is a conductor plate having a profile with a ring shape in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE iNVENTION
Various embodiments of the present invention provide a thermal over-current release assembly for circuit breakers. The thermal over-current release assembly comprises a conductor plate having a profile, a bimetal snap disc in contact with the conductor plate, the bimetal snap disc being able to flip its orientation depending upon a predetermined temperature; and a plurality of springs, the springs maintaining a good contact pressure between the bimetal snap disc & the conductor plate; wherein the bimetal snap disc rests on a profile on the conductor plate.
Figure 2a-c shows various views of a thermal over-current release assembly 200, in accordance with an embodiment of the invention. Thermal over-current assembly 200 comprises of a conductor plate 110 having a profile 105, a bimetal snap disc 120 in contact with

the conductor plate 110, a first spring 130, and a second spring 140. Bimetal snap disc 120 rests on the profile 105 on conductor plate 110 and bimetal snap disc 120 flips its orientation depending upon a predetermined temperature.
In an embodiment of the invention, profile 105 of a conductor plate 110 is a depression as shown in figure 3. As shown in figure 3A, profile 105 of conductor plate 110 allows one full surface of bimetal snap disc 120 to be in contact with conductor plate 110. In this regard, depression 105 has a conduction area whose curvature matches with curvature of bimetal snap disc 120, in accordance with an embodiment of the invention.
In an optional embodiment of the invention, profile 107 of conductor plate 110 further has a ring shape as shown in figure 3B to allow bimetal snap disc 120 to be in contact with conductor plate 110.
Bimetal snap disc 120 thus rests on edges of ring profile 107. During an over-current condition, at a pre-determined temperature bimetal snap disc 120 flips its orientation. As a result of which, total displacement of the spring after flipping will be the sum of the curvature displacement of bimetal snap disc 120 and profile curvature 105 or 107 of conductor plate 110. Advantageously, resultant displacement due to profile in conductor plate 110 and curvature of bimetal snap disc 120 is more than what would have been achieved had it been a flat conductor plate.
Further, again with reference to figures 2a-c, in accordance with an embodiment of the invention, first spring 130 applies pressure at centre on bimetal snap disc 120 and second spring 140 applies contact pressure at periphery of bimetal snap disc 120, the first spring 130 and second spring 140 being concentric.
Advantageously, springs of the present invention provide higher spring forces at all release settings and thus better heat conduction. Further, first spring 130 has greater effect on flipping temperature of bimetal snap disc 120, whereas second spring 140 has very low effect on flipping temperature of the bimetal snap disc 120 as displacement at periphery is very small

after flipping. Spring force of second spring 140 is maintained constant to insure good contact pressure at all conditions, and spring force of the first spring 130 is varied to allow release to be adjusted.
In accordance with an embodiment of the invention, assembly 200 further comprises a centre pin 125 and an outer pin 135. In various embodiments of the invention, center pin 125 and outer pin 135 are made of insulating material including plastic, fiberglass, and the like to reduce/minimize heat loss. Centre pin 125 is adapted between bimetal snap disc 120 and first spring 130, and outer pin 135 is adapted between bimetal snap disc 120 and second spring 140. Centre pin 125 is concentric with outer pin 135, and outer pin 135 rests on bimetal snap disc 120 outside of centre pin 125.
In an embodiment of the invention, the thermal over-current release assembly comprises of a conductor plate having a profile; a bimetal snap disc in contact with the conductor plate, the bimetal snap disc being able to flip its orientation depending upon a predetermined temperature; a first spring and second spring, the first and second springs being concentric; a centre pin adapted between the bimetal snap disc and the first spring, and an outer pin adapted between the bimetal snap disc and the second spring, wherein the bimetal snap disc rests on the profile of the conductor plate, and when the bimetal snap disc flips its orientation at a predetermined temperature, total displacement of the spring after flipping will be the disc displacement and profile curvature of the conductor.
While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

WE CLAIM:
1. A thermal over-current release assembly comprising:
a. a conductor plate having a profile;
b. a bimetal snap disc in contact with the conductor plate, the bimetal snap disc
being able to flip its orientation depending upon a predetermined temperature;
and
c. a plurality of springs, the springs applying a force on the bimetal snap disc;
wherein the bimetal snap disc rests on the profile on the conductor plate.
2. The thermal over-current release assembly as claimed in claim 1, wherein the profile is a conduction area, the curvature of the conduction area could be matching with the curvature of the bimetal snap disc.
3. The thermal over-current release assembly as claimed in claim 1, wherein the predetermined temperature depends upon the nature of metals in the bimetal snap disc & construction of the disc.
4. The thermal over-current release assembly as claimed in claim 1 or 2, wherein the thermal over-current assembly has a first spring and a second spring, the first and second springs being concentric.
5. The thermal over-current release assembly as claimed in claim 4, wherein the assembly further comprises a centre pin adapted between the bimetal snap disc and the first spring.

6. The thermal over-current release assembly as claimed in claim 4, wherein the assembly further comprises an outer pin adapted between the bimetal snap disc and the second spring.
7. The thermal over-current release assembly as claimed in claim 5 or 6, wherein the centre pin is concentric with the outer pin, the outer pin resting on the bimetal snap disc outside of the centre pin.
8. The thermal over-current release assembly as claimed in claim 7, wherein the pins are made of insulating material.
9. A thermal over-current release assembly comprising:
a. a conductor plate having a profile;
b. a bimetal snap disc in contact with the conductor plate, the bjmetal snap disc
rests on the profile of the conductor plate, the bimetal snap disc being able to flip
its orientation depending upon a predetermined temperature;
c. a first spring and a second spring, the first and the second springs being
concentric;
d. a centre pin adapted between the bimetal snap disc and the first spring; and
e. an outer pin adapted between the bimetal snap disc and the second spring.