FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION:
Tripping Device for Thermal Overload Relays
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: LARSEN & TOUBRO LIMITED,
L&T House, Ballard Estate, P. 0. Box: 278, Mumbai 400 001, India
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Tripping Device for Thermal Overload Relays Field of the invention
The present invention relates to overload relay devices and more particularly, to a tripping device for thermal overload relays.
Background of the invention
The tripping device functions to trip the circuit breaker in an overload/over current situation. Currently available thermal tripping device comprises a bimetal heater assembly. The tripping mechanism involves resistive heating of the heater to heat and bend the bimetal. Upon bending, the bimetal makes engaging contact with a portion of the trip mechanism to trip the circuit breaker. This opens the electrical contacts thereby opening the protected circuit.
The bimetal heater assembly of the prior art thermal tripping device are costly for higher current. Normally the lower range relay has single heater for heating of the bimetal. However, for higher relay ranges such as above 30A, normally heater strips of suitable material are used by connecting parallel to each other or separate CT is used to increase the range of relays. However, this results in a further increase in the cost of relay.
Accordingly, there is a need to provide a tripping device for thermal overload relays that overcomes the problems in the prior art.
Object of the invention

An object of the present invention is to provide an improved, cost effective heater design for higher current relays.
Summary of the invention
Accordingly, the present invention provides a tripping device for thermal overload relays. The tripping device comprises a bimetal element, a heating element, a coupler/joint, an insulating element, and an incoming terminal and outgoing terminal.
The bimetal element is capable of being bent upon heating to activate a tripping mechanism to trip the circuit breaker an overload situation. The heating element is coiled around the bimetal element to heat and bend the bimetal element in overload condition. The heating element being made up of at least three wires connected in parallel. Typically, the three wires are copper wires. The heating element is coupled to the bimetal element by the coupler/joint. The insulating element is connected between the bimetal element and the heating element. The incoming terminal and the outgoing terminal are connected to the bimetal element and the heating element.
Brief description of the drawing
The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawing wherein.
Figure 1 is a view showing components of a tripping device for thermal overload relays, in accordance with the present invention.

Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.
The present invention provides a tripping device for thermal overload relays. The tripping device of the present invention generates heat in the thermal overload relay through a cost effective and improved heating element that is suitable for higher currents.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various
figures.
Referring now to figure 1, there is shown a tripping device (herein after 'the device (100)') f°r thermal overload relays (not shown), in accordance with the present invention. The device (100) comprises a bimetal element (10), a heating element (20), a coupler/joint (30), an insulating element (40) and an incoming terminal (not shown) and an outgoing terminal (not shown).
The bimetal element (10) is capable of being bent upon heating to activate a tripping mechanism (not shown) to trip a circuit breaker (not shown) in an overload condition. The bimetal element (10) includes the heating element (20) coiled there over and resulting bimetal-heater assembly is kept at a suitable distance from the tripping mechanism. The number of turns of heating element (20) on the bimetal element (10) depends on a rating of relay and heat input required for the bimetal element (10) to trip in case of overload condition. The heating element (20) is

adapted to heat and bend the bimetal element (10) in overload situation. The heating element (20) is made up of three wires that are connected in parallel. In an embodiment, the heating element (20) is made up of three bare copper wires/cables/strips that are connected in parallel. Thus, the combination of three parallel bare copper wires as the heating element (20) contributes to generation of heat inside the relay. Due to internal resistance of the copper wires, the current flows through the copper wires thereby heating the copper wires. Due to heating of the copper wires, the temperature of the bimetal-heater assembly starts increasing. As the temperature increases, the bimetal element (10) starts bending to one side where the tripping mechanism is fixed. As soon as the current level crosses a predefined limit, the bimetal element (10) bends to such an extent to give a command to the trip mechanism for tripping.
The heating element (20) is coupled to the bimetal element (10) through the coupler/joint (30). In an embodiment, the coupler (30) joins the heating element (20) and the bimetal element (10) by a brazing or a spot welding process. Since, the bimetal element (10) and the heating element (20) both carry current; the insulating element (40) is connected between the bimetal element (10) and the heating element (20). In an embodiment, the insulating element (40) is a plastic sleeve.
The incoming terminal and the outgoing terminal are connected to the bimetal element (10) and the heating element (20). The positions on the bimetal element (10) and the heating element (20) where the terminals are connected depend on the amount of heat required for the tripping mechanism. The incoming and outgoing terminals are connected to the bimetal element (10) and the heating element (20) by brazing or spot welding spot process. However, it is understood that any suitable process can be used for connecting the incoming and outgoing terminals.

Advantages of the invention
1. The device (100) is cost effective due to use of copper wires.
2. The device (100) is assembled using least components such as three copper wires as the heating element (20), the insulating element (40) and the bimetal element (10) that are easily available.
3. As the difference between lower and higher range relay is only the copper wires which contributes to very small part of total cost of relay. Hence, there is no significant difference between costs of relay across the range.
4. The device (100) is simple and robust in design.
5. The three wire heating element (20) is capable of being used for higher current/ relay ranges such as above 30A.
6. Being a cost effective and easily available material, use of bare copper strip will reduce the cost of relay. Also the change in relay range can be achieved by modification in dimensions of the heating element (20).
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention.

We Claim:
1. A tripping device (100) for thermal overload relays, the tripping device
(100) comprising:
a bimetal element (10) capable of being bent upon heating to activate a tripping mechanism to trip a circuit breaker in an overload condition;
a heating element (20) coiled around the bimetal element (10), the heating element (20) adapted to heat and bend the bimetal element (10) in overload condition;
a coupler/joint (30) joining the heating element (20) to the bimetal element (10);
an insulating element (40) connected between the bimetal element (10) and the heating element (20); and
an incoming terminal and an outgoing terminal connected to the bimetal element (10) and the heating element (20),
characterized in that, the heating element (20) being made up of at least three wires connected in parallel.
2. The tripping device (100) as claimed in claim 1 characterized in that
the heating element (20) being made up of copper.