FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: AN IMPROVED THERMAL OVERLOAD
RELAY MECHANISM
2. Applicant(s):
(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 THE NVENTION
The present invention relates to a thermal overload relay mechanism. More particularly, the invention is concerned about an improved thermal overload relay mechanism comprises a rotary NC mechanism relieved from NO/NC (Normally open/Normally closed) contacts load for independent actuation of mechanism
BACKGROUND OF THE INVENTION
Relay is a device which causes a mechanical switching device (i.e. contactor) to open with or without time delay when the current in the relay exceeds a predetermined value. Thermal overload relay is an inverse time-delay overload relay which for its operation (including time-delay) depends on the thermal action of the current flowing in the relay.
Bimetallic thermal overload relay works on the principle of conversion of electrical energy in to heat energy along with phenomenon of differential thermal expansion of thermostatic bimetal. In bimetallic thermal overload relay the main input current causes the heating of bimetal. The deflection resulted because of differential thermal expansion of bimetal is sensed by a mechanism. The mechanism after certain predefined deflection of bimetal, changes its state thus the control contacts actuated by the mechanism give the trip command to the associated switching device (contactor).
A thermal overload relay comprises of three parts, sensing part, coupling part and actuation mechanism. The sensing part is basically a thermal element which comprises of bimetal and the heater, the heater produces heat in response to current flowing through them and which is the cause for bimetallic strips to actuate in the form of deflection, hence thermal part converts the electrical energy in to mechanical output. The other part is coupling part which transfers the mechanical output of thermal system to the mechanism, which in turn actuates control contact to cause the

switching device to open. Mechanism is responsible for the actuation of control contacts by sensibly following the deflection produced by bimetals.
JP10214401 (A) teaches a signal relay mechanism to prevent an invasion of a foreign matter from the outside and a scatter of a wear particle, etc., caused in a signal relay part to the outside and to eliminate the occurrence of an operation failure by covering the whole periphery of the signal relay part provided with a connection part electrically and mechanically connected to a rotary body and rotating integrally with it, a rotary contact provided on this connection part and a fixed contact being in contact with this with a cover body.
In the prior art, there is an instability in actuation system and thus ultimate load on the bimetals can be increased significantly. Thus, there is a need to overcome the problems of the prior art. Therefore, inventors have developed a rotary NC mechanism relieved from NO/NC (Normally open/Normally closed) contacts load for independent actuation of mechanism.
OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the prior art.
Another object of the present invention is to provide an improved thermal overload relay mechanism
Another object of the present invention is to provide a rotary NC contact mechanism for use in thermal overload relays.
Yet, another object of the present invention is to provide independent function of Mechanism spring.

SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an improved
thermal overload relay mechanism comprising:
actuating means;
plurality of normally open contact means;
plurality of normally closed contact means operatively connected to said actuating
means;
wherein said normally closed contact means having a rotary profile adapted to allow
said normally closed contact means to rotate about a predetermined axis when
actuated by said actuating means;
wherein said rotary profile of said normally closed contact means is such that it gets
double break at normally closed terminals eliminating any possibility of re-striking or
leakage currents.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures 1&2 illustrate operation of relay mechanism. Figures 3&4 illustrate auto mode of relay mechanism. Figures 5&6 illustrate manual mode of relay mechanism.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention there is provided an improved thermal overload relay mechanism, in which a rotary NC contact profile and a double actuated slider profile is used to achieve dead center actuation of the mechanism.
Figures 1&2 show the operation of relay mechanism. The mechanism is a combination of functionally interdependent components. The function of each component is determined by its previous component's function. The function of mechanism starts from the component called actuatorl which receives the deflection through primary lever (a link which transfers the deflection of bimetals to the

mechanism) generated by bimetals. This actuator is located on component called pivot 2 which has a degree of freedom for its rotation about a particular axis. This pivot takes reaction from a current setting knob 3 which allows relay to operate at different current values. Receiving the bimetallic deflection the actuator lpushes a component called the trip lever 4 which is coupled with trip indicator 5 with the help of a spring called mechanism spring 6. Trip indicator 5 rests at an angular position which is basis for relay's intentional delayed operation. The trip indicator 5 drives a component called slider 9 which actuates the normally open 7 / normally closed contacts 8. The NC contact has a rotary profile 12 and it can rotate about an axis. The contact pressure on the fixed contact by rotary NC 12 is achieved by using one torsion spring 10. As the actuator 1 pushes the trip lever 4, the mechanism spring 6 tends to align the trip indicator 5 which rests at an angular position, the mechanism spring 6 is extended till the time spring gets aligned with the trip indicator 5, the moment spring gets aligned the state is called as dead center, just at this dead center one arm of slider 9 pushes the rotary NC 12 to open it and the other arm of slider 9 pushes the NO leaf 11 to give an alarm contact continuity. The actuation of both NO and NC takes place just at the dead center so that mechanism spring 6 is not counter loaded with NO 7 and NC 8 contact force. There are two possible ways the relay can show trip behavior such as auto mode and/or manual mode.
In auto mode as shown in figures 3&4, the relay is suppose to reset back after a predetermined delay, and in this case the trip indicator doesn't drive slider to its full extent as the trip indicator 5 is stopped intentionally at the dead center so that once load from bimetal side is removed (as the cool down) the trip indicator 5 can take the slider 9 back to its initial state. In this case the angular opening of NC contact 12 is quite less but by actuating it bit closer to the fulcrum point, so that at the contact level substantial contact gap can be achieved.

In manual mode as shown in figures 5 and 6 once the relay trips it has to be reset manually. In this operation by virtue of trip indicator 5 moving to its final resting condition after tripping, then gets sufficient contact gap at NC contacts 8.
Generally because of NO 7/NC 8 contacts and their contact pressures (which is essential to make/break current) the load comes on the slider 9 hence the mechanism force as seen by the actuator 1 becomes low. In this case to obtain a dead center tripping mechanism, compensate that reduction in final load values by increasing the absolute value of mechanism spring, and this load is ultimately seen by the bimetals, for a nuisance free operation bimetals are loaded suitably so that the operate well within their stress limits, but because of "NO/NC compensation the spring values are kept high and it may so happen that bimetals are stressed because of force on to them beyond permissible limits and this may cause a permanent change/damage in bimetal's physical/electrical properties hence malfunctioning may occur at the time of tripping. Also at the dead center the force component of mechanism spring 6 along the slider 9 axis is zero, (because of the axis alignment of mechanism spring 6 and trip indicator 5) the NC 8/NO 7 contact force are dominant and may cause a nuisance tripping before the dead center is reached, so this instability is also compensated by means of increasing the absolute load values of mechanism spring 6. But using this concept the NO/NC loads can be eliminated and mechanism can be operated at lower value of mechanism spring and without stressing the bimetals.
Another advantage that using this NC contact 12 profile provides a double break at NC terminals so that there is no possibility of any re-striking or leakage current that usually occur in case of low contact gaps.
One more advantage of using this concept is that the absolute value at which mechanism works can be reduced substantially so that bimetals require lesser energy to overcome that resistance (mechanism force) and finally the watt loss of thermal

assembly can be reduced, so same relay can now operate for existing current range at lower energy consumption, hence cost and energy savings.
This invention is concerned to a mechanism, in which a rotary NC contact profile and a double actuated slider profile is used to achieve dead center actuation of the mechanism. This facilitates the mechanism relieved from NO/NC contact load and no compensation is required in main mechanism spring to overcome the NO/NC contact loads. It also increases the stability of actuation system as NO and NC actuation takes places accurately at the dead center. This way mechanism spring works independently, and the load on the actuating bimetals can be reduced to a significantly lower value.
ADVANTAGES OF THE INVENTION
1. Increases the stability of actuation system
2. Mechanism relieved from NO/NC contact load.
3. Load on the actuating bimetals can be reduced.
4. Independent function of mechanism spring and a significant reduction in its load values.
5. Double break at NC contact
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 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.

WE CLAIM:
1. An improved thermal overload relay mechanism comprising:
actuating means;
plurality of normally open contact means;
plurality of normally closed contact means operatively connected to said
actuating means;
wherein said normally closed contact means having a rotary profile adapted to
allow said normally closed contact means to rotate about a predetermined axis
when actuated by said actuating means;
wherein said rotary profile of said normally closed contact means is such that
it gets double break at normally closed terminals eliminating any possibility
of re-striking or leakage currents.
2. Mechanism as claimed in claim 1 wherein said actuating means comprising a slider having plural arms for actuating said normally closed contact means and normally open contact means.
3. Mechanism as claimed in claim 1 wherein said normally closed contact means comprising a fulcrum point allowing said contact means to rotate about its axis with the application of force by the slider.
4. Mechanism as claimed in claims 1 and 2 wherein said slider is proximally located to said fulcrum point such that substantial contact gap is achieved at contact level.
5. Mechanism as claimed in claims 1 to 4 wherein said normally closed contact means comprises a torsion spring.

6. Mechanism as claimed in any of the preceding claims comprising operating in automatic mode.
7. Mechanism as claimed in any of the preceding claims comprising operating in manual mode.
8. An improved thermal overload relay mechanism as herein substantially described and illustrated with the accompanying drawings.