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. - ELECTRONIC MODULE FOR SWITCHING DEVICE TO PREVENT WELDING AND A METHOD THEREOF
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:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to switching devices. More particularly, the present invention relates to an electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts and a method thereof.
BACKGROUND AND THE PRIOR ART
Switching devices such as contactors are intended to withstand the short circuit current until any protection device clears the fault. However, in contactors, in some applications, particularly in motor controllers, a short circuit fault current generates repulsion force between moving and fixed contacts due to constriction force. Because of this repulsion force, moving contact moves in the upward direction and arcing takes place. When the contacts depart from each other, constriction force reduces to zero and during this condition actuator force tries to keep moving contact in ON condition biased by means on spring force. This condition forces moving contact to close in molten condition and at this point welding occurs.
Weld free coordination can be achieved by electronic circuitry which is present in conjunction with the contactor's circuitry. Such a condition is disclosed in US 6377143. In '143 contactor's coil is energized which engages the contact and creates an electric path for the current to flow. Pulse Width Modulation is then used to lower the power to the coil and maintain the contacts in closed condition.
The disadvantage of the above mentioned prior art is that the method requires additional electronic circuitry so as to achieve the weld-free co-ordination.

Separate provisions will have to be made for low, intermediate and high fault current conditions. After the occurrence of high fault current i.e. after the contacts are blown open and the armature and the movable contact carrier are shifted away from the electromagnetic coil, until and unless the first energy source is reapplied. Thus there is a need to provide a method in which the supply to the contactor's coil is restored on its own, after the short circuit current subsidies without any manual interference. The present invention therefore provides an electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts.
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 electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts.
Another object of the present invention is to provide weld free configuration by making use of an electronic circuit, without affecting the arcing time and the electrical life of the product.
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 electronic module for a switching device to prevent welding of
contacts.
According to one embodiment of the present invention, there is provided an electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts, said circuitry comprising a timer providing for actual time and pick up time; a comparator sensing short circuit on comparing terminal voltage to a prefixed voltage, said comparator passing signal to a relay on sensing short circuit.
Other embodiment of the present invention provides method for preventing contact closure of a switching device in molten condition thus preventing welding of contacts, said method comprising the steps of switching ON a comparator circuit when actual time is greater than pick up time; comparing terminal voltage to a prefixed voltage to sense short circuit using a comparator, on sensing short circuit passing signal to a relay, said signal energizing a relay coil.
Yet other embodiment of the present invention provides time lag before restoring the supply to said contactor coil.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Figure 1 illustrates a switching device.

Figure 2 illustrates the method steps for the weld free feature in switching devices.
DETAILED 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.
Reference is first invited to Fig 1 where a switching device is shown.
Fig. 2 shows different method steps followed to prevent welding during the short circuit condition.
The invented system is thus an electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention a method and device adapted to solve the problem of welding at the time of short circuit by opening the contacts during fault current condition is provided. The object is achieved by providing an electronic module which works in conjunction with the contactor's coil circuit and issues the necessary commands whenever a short circuit occurs.
A series of events is followed in which the contactor is maintained in its open condition for a time period in which the molten metal solidifies which reduces the

probability of welding. The electronic circuit consists of a timer which bring the electronic circuit into picture only after the time equal to the pick-up time of the contactor has elapsed. Having fulfilled this condition, the comparator circuit comes into picture.
One input of the comparator circuit is the voltage across the terminal of switching devices (6) while the other input is the internally generated fixed voltage of 20 Volts. During normal operating condition, when switching devices is turn ON (after pick up) the voltage developed across the terminal of switching devices is less than 20 Volts. Hence, the output of the comparator is zero and the electronic circuit for weld free is bypassed. Relays NC which is connected in series with coil (9) supply maintained normal uninterrupted supply to the coil. However during short circuit, the electronic circuit comes into picture.
During short circuit, due to constriction force, the moving (2)and the fixed contacts(5) repel open and the voltage developed across them is around 25- 80 Volts. The comparator circuit senses this voltage and compares it with the other input which is kept fixed at 20 Volts (internally generated). The output being positive, the electronic circuit senses it as short circuit and provides the necessary command to the relay which is connected in series with coil (9) supply.
As a result, the relay's coil is energized and it changes its state from NC to NO. Thus, the supply to the contactor coil is switched off. As soon as the supply is cut-off, the input to the comparator, which is obtained internally, is reduced to zero. As a result, the relay again changes its state from NO to NC, but an internal circuit is used to provide a time lag of around 80 milliseconds in this transition. After the stipulated time is over, regular supply is restored across the contactor's coil.
Thus, during short circuit, the contactor's moving (2) and fixed(5) contacts are kept open and reclosure occurs only after the fault current subsidies. This prevents the

contact closure in molten condition and helps in preventing the welding of the contacts. The current through the contacts is also limited during a fault current condition due to relatively quick opening of the contacts.
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 electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts, said module comprising a timer providing for actual time and pick up time; a comparator sensing short circuit on comparing terminal voltage to a prefixed voltage, said comparator passing signal to a relay on sensing short circuit.
2. Module as claimed in claim 1 further interfaced with a contactor coil circuit issuing command during short circuit.
3. Module as claimed in claim 1 wherein said relay coil is further connected in series to a contactor coil.
4. A method for preventing contact closure of a switching device in molten condition thus preventing welding of contacts, said method comprising the steps of:
switching ON a comparator circuit when actual time is greater than pick up time; comparing terminal voltage to a prefixed voltage to sense short circuit using a comparator, on sensing short circuit passing signal to a relay, said signal energizing a relay coil.
5. Method as claimed in claim 4 further comprising the step of changing the
state after energizing said relay coil.

6. Method as claimed in claim 5 further comprising the step of switching off supply to contactor coil.
7. Method as claimed in claim 6 wherein after switching off supply to said contactor coil input to said comparator reducing to zero.
8. Method as claimed in claim 6 further comprising step of providing time lag before restoring the supply to said contactor coil.
9. An electronic module for switching device to prevent a contact closure in molten condition thus preventing welding of contacts as herein described and illustrated with reference to the accompanying drawings.
10. A method for preventing contact closure of a switching device in molten condition thus preventing welding of contacts as herein described and illustrated with reference to the accompanying drawings.