FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
OVERLOAD INDICATION IN THERMAL OVERLOAD RELAYS

APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate. P.O. Box No. 278.
Mumbai, 400 001. Maharashtra .
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to overload protection devices and particularly to thermal overload relays. The present invention more particularly relates to overload indication system in a thermal overload relay.
B) BACKGROUND OF THE INVENTION
[0002] A thermal overload relay comprises of a switching mechanism to switch contacts to on or off state according to transferred power. The relay protects the electrical load from overload or over-current when current flowing through the load exceeds a predetermined current value. The thermal overload relay protects the connected motor from overload or phase failure.
[0003] The relay comprises of a plurality of heating members connected to power source. Flow of current through the heating members produces heat proportional to the current in the member. An actuation mechanism with plurality of bimetals is provided in the relay. The heating of the members deflects the bimetals actuating the motion of differential levers and primary lever.
[0004] The thermal overload relay comprises of a current setting knob to set the required current value. The base of the current setting knob in the relay has a cam shape. The compensation bimetal is aligned to the cam surface of current setting knob. The rotation of the current setting knob moves the cam surface away from the compensation bimetal


to create a gap between the compensation bimetal and the cam surface. The movement of primary lever is actuated to bridge the gap between the compensation bimetal and the cam surface.
[0005] Currently, the thermal overload rely detects an abnormal condition and gives a trip command to the switching device. However the relays do not provide any warning of the abnormal conditions. The system is completely shutdown in the event of an abnormal condition without the operator's intervention. Hence there is a need to provide an indication to the operator of an abnormal condition to take preventive steps to avoid complete shutdown of the system.
C) OBJECTS OF THE INVENTION
[0006] The primary object of the present invention is to provide a system and method to indicate the overload in a thermal overload relay.
[0007] Another object of the present invention is to activate the indication device by sensing the movement of a pivot using a modular device.
[0008] Yet another object of the present invention is to provide the calibration to the device at desired current level and the method of doing so.
[0009] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.


D) SUMMARY OF THE INVENTION
[0010] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[0011] The various embodiments provide an overload indication in a thermal overload relay. According to an embodiment of the present invention, An overload indication system in thermal over load relays for switching device has a modular switch provided with a fixed contact and a moving contact. This modular switch is mounted on the internal wall of the housing of thermal overload relay. A shaft is connected to the moving contact. An indication device connected to the modular switch. The shaft senses the condition in the relay to move the moving contact in the modular switch to activate the indication device to provide an indication with respect to an over load condition. The shaft senses the motion of pivot and moves the moving contact and bridges the gap between fixed contact and moving contact to close a circuit outside the modular switch to provide an indication. The modular switch activates the indication device to provide an indication with respect to an overload condition, till the relay is reset / working. The indication device gives overload indication and indicates to reduce the load connected to the contactor in the switching device. The modular switch further comprises a calibration screw. The calibration screw is adjusted such that the moving contact and the fixed contact gap in the modular switch can be adjusted to activate an indication device to provide an indication with respect to any desired overload condition. The indication device can provide an audio/visual/electrical indication.


[0012] The current settings in a relay may be adjusted by a current setting knob. The rotation of the knob is translated to the motion of the cam surface at the base of the knob in the relay. The movement of the cam surface away from the compensation bimetal creates a gap between the compensation bimetal and cam surface. The movement of primary lever is actuated to bridge the gap between the cam surface and the compensation bimetal. The motion of the pivot is actuated after the completion of motion of the primary lever.
[0013] The movement of the pivot actuate the tripping of the relay. The pivot movement is sensed in a pre defined position to detect the tripping of the relay. A shaft is used to sense the position of the pivot. The shaft actuates the motion of a moving contact in a modular switch.
[0014] For the calibration of this device, The rated current is passed through the thermal element for pre defined duration to bring the relay assembly to its final steady state temperature and cause steady the bimetal deflection. The actuator moves the pivot to the intermediate position. The calibration screw of the modular switch is adjusted to establish contact between fixed and moving contacts for a prolonged duration of time. The calibrated contact pair is used to provide the required indication of the tripping of the relay.
[0015] According to one embodiment of the invention a source is connected to one terminal of the modular switch. An indication device is connected to the other terminal of the modular switch. The connection of the source to the modular switch provides the
- 1 APR 2009

indication signal which can include electric, audio or visual indication even after the relay is tripped.
[0016] According to another embodiment a wire is connected to one terminal of the modular switch and normally closed (NC) terminal. The high potential point is connected to a specific point in the relay to derive the required power for the indication device from the coil supply circuit of the contactor.
[0017] The pivot reaches the threshold deflection point when the relay is overloaded. The threshold deflection of the pivot closes the contact of the modular device to give the indication signal. If the overload persists, the relay trips that makes the moving contact of the relay to move away from the fixed contact. The terminal connected to the terminal of the modular switch separated form high potential terminal of the mechanism. The current in the indication switch is stopped. The indication signal is active until the pivot reaches the threshold deflection and the relay mechanism is in reset condition.
[0018] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. E) BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:


[0020] FIG. 1A illustrates the minimal current settings in the thermal overload relay according to an embodiment of the present invention.
[0021] FIG. IB illustrates the maximum current setting in the thermal overload relay according to an embodiment of the present invention.
[0022] FIG. 2 illustrates the position of the moving contact and fixed contact in thermal overload relay according to one embodiment of the present invention.
[0023] FIG. 3 illustrates the sectional view of thermal overload relay mounted with an indication system according to one embodiment of the present invention,
[0024] FIG. 4 illustrates the top perspective view of an overload indication system in a thermal overload relay according to one embodiment of the present invention.
[0025] FIG. 5 illustrates the block circuit diagram an overload indication system in a thermal overload relay according to one embodiment of the present invention.
[0026] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF INVENTION
[0027] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be


practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0028] The various embodiments provide an overload indication in a thermal overload relay. According to an embodiment of the present invention, An overload indication system in thermal over load relays has a modular switch provided with a fixed contact and a moving contact. A shaft is connected to the moving contact. An indication device connected to the modular switch. The shaft senses the position of pivot in the relay to move the moving contact of the modular switch to activate the indication device to provide an indication with respect to an over load condition. The shaft senses the position of pivot and moves the moving contact to be in contact with a fixed contact to close a circuit connected with the modular switch to provide an indication. The modular switch activates the indication device to provide an indication with respect to an overload condition, till the relay is reset. The indication device is connected to the contactor coil in the switching device to draw power supply. The modular switch further comprises a calibration screw. The calibration screw is adjusted such that the moving contact and the fixed contact in the modular switch contact each other to activate an indication device to provide an indication with respect to an overload condition. The indication device can provide an audio/visual/electrical indication.
[0029] Thus the various embodiments provide an overload indication in a thermal overload relay. The current settings in a relay may be adjusted by a current setting knob.


The rotation of the knob is translated to the motion of the cam surface at the base of the knob in the relay. The movement of the cam surface away from the bimetal creates a gap between the bimetal and cam surface. The movement of primary lever is actuated to bridge the gap between the cam surface and the bimetal. The motion of the pivot is actuated after the completion of motion of the primary lever.
[0030] The movement of the pivot is actuated by the tripping of the relay. The pivot position is sensed in a pre defined position to detect the tripping of the relay. A shaft is used to sense the position of the pivot. The shaft actuates the motion of a moving contact in a modular switch.
[0031] The rated current is passed through the thermal element for pre defined duration to bring the relay assembly to its final steady state temperature and cause the bimetal deflection. The actuator moves the pivot to the intermediate position. The calibration screw of the modular switch is adjusted to establish contact between fixed and moving contacts for a prolonged duration of time. The calibrated contact pair is used to provide the required indication of the tripping of the relay.
[0032] According to one embodiment of the invention a source is connected to one terminal of the modular switch. An indication device is connected to the other terminal of the modular switch. The connection of the source to the modular switch provides the indication signal which can include electric, audio or visual indication even after the relay is tripped.
[0033] According to another embodiment a wire is connected to one terminal of the modular switch and normally closed (NC) terminal. The high potential point is connected


to a specific point in the relay to derive the required power for the indication device from the coil supply circuit of the contactor.
[0034] The pivot reaches the threshold deflection point when the relay is overloaded. The threshold deflection of the pivot closes the contact of the modular device to give the indication signal. The moving contact of the relay is moved away from the fixed contact. The terminal connected to the terminal of the modular switch separated form high potential terminal of the mechanism. The current in the indication switch is stopped. The indication signal is active until the pivot reaches the threshold deflection and the relay mechanism is in reset condition.
[0035] FfG. 1A illustrates the minimal current settings in the thermal overload relay according to an embodiment of the present invention. The compensation bimetal lis connected to the cam surface2 at the base of the current setting knob 2 . The current settings in a relay may be adjusted by rotating a current setting knob 2. [0036] FIG. IB illustrates the maximum current setting in the thermal overload relay according to an embodiment of the present invention. The rotation of the current setting knob 2 for the maximum current setting actuates the motion of the cam surface 2 at the base to its extreme position away from the compensation bimetal I. A gap is created between the bimetal 1 and the cam surface 2 which ultimately results in gap3 between differential lever & primary lever as shown in the figure.
[0037] FIG. 1 illustrates the movement of the moving contact in thermal overload relay according to one embodiment of the present invention. The current setting knob is rotated to introduce a gap between the bimetal and cam surface. The pivot 7 is moved to bridge


the gap. The position of the pivot is sensed by a modular switch 5 consisting of a fixed and moving contact in housing. A shaft 6 actuates the motion of the moving contact. The movement of the shaft is used to sense the movement of the pivot.
[0038] FIG. 2 illustrates the actuating components of the indication device according to one embodiment of the present invention. A wire "B" is connected between the other end of NC terminal of the mechanism and one of the terminals of the modular switch. The high potential point is connected to the "A". Thus the power required for the indication device can be derived from the coil supply circuit of the contactor. In case of overload, when the pivot reaches the threshold deflection at which the contact of the modular device closes, the indicating device gives the signal. When the relay trips the moving contact "C" of relay mechanism apart from the fixed contacts of the relay mechanism. Thus the terminal that is connected to the terminal of the modular switch separates from the high potential terminal of the mechanism. Thus the current in the indication switch ceases to flow and thus the indication signal is active only till when pivot has reached its threshold deflection and the relay mechanism is in reset condition the wire B is connected to one terminal of the modular switch and normally closed (NC) terminal A. The high potential point is connected to a specific point C in the relay to derive the required power for the indication device from the coil supply circuit of the contactor.
[0039] FIG. 3 illustrates the sectional view of thermal overload relay mounted with an indication system according to one embodiment of the present invention. The modular switch consists of a fixed contact D on which a spring contact E is mounted as shown. The moving contact moving spring arm F is attached to the fixed terminal G. The moving spring arm is actuated by the plunger H. The other part of plunger is in contact with pivot


as shown in the figures above. Thus when the pivot moves the moving contact arm also moves along with the pivot and the contact gap between the fixed and moving contacts of the modular switch reduces. After certain predetermined movement of plunger the contacts close and thus the circuit becomes live and gives the signal.
[0040] The assembly is calibrated at the rated current, the rated current (desired current) is passed through the thermal element for the time longer enough to bring the assembly into its final steady state temperature and hence the bimetal deflection. This causes the actuator to actuate the pivot and the pivot moves to the intermediate position between the position of rest and trip. At this point the calibration screw J of the modular switch is adjusted in such a way that the fixed and moving contacts of the switch meet and show continuity. These contact pair is used as the indication (audio/visuai/electric).
[0041] FIG. 4 illustrates the top perspective view of an overload indication system in a thermal overload relay according to one embodiment of the present invention. [0042] FIG. 5 illustrates the block circuit diagram an overload indication system in a thermal overload relay according to one embodiment of the present invention. This is the description of circuit attached: The pivot reaches the threshold deflection point when the relay is overloaded. The threshold deflection of the pivot closes the contact of the modular device to give the indication signal. The moving contact of the relay is moved away from the fixed contact. The terminal connected to the terminal of the modular switch separated form high potential terminal of the mechanism. The current in the indication switch is stopped. The indication signal is active until the pivot reaches the threshold deflection and the relay mechanism is in reset condition.


G) ADVANTAGES OF THE INVENTION

[0043] Thus the various embodiments of the present invention provide a system and method of indication of overload in a thermal overload relay. The current required for the indication device is derived from the coils of the contractor in the thermal overload relay. The indication of an overload provides the operator a warning of the condition of the relay to take measures and avoid complete shutdown of the system connected to the relay.
[0044] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifiations are deemed to be within the scope of the claims.

[0045] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. An overload indication system in thermal over load relays for switching device
comprising:
a modular switch including a fixed contact and a moving contact;
a shaft connected to the moving contact;
an indication device connected to the modular switch
wherein the shaft senses the trip condition in the relay to move the moving contact
in the modular switch to activate the indication device to provide an indication
with respect to an over load condition.
2. The system according to claim 1, the shaft senses the position of pivot in mechanism and moves the moving contact to be in contact with a fixed contact to close a circuit in the modular switch to provide an indication.
3. The system according to claim 1, wherein the modular switch activates the indication device to provide an indication with respect to an overload condition.
4. The system according to claim 1. wherein the indication device is connected with the switching device to draw power supply.
5. The system according to claim I. wherein the modular switch further comprises a calibration screw.


To,
The Controller of Patents,
The Patents office. Mumbai
6. The system according to claim I. wherein the calibration screw is adjusted such that the moving contact and the fixed contact in the modular switch contact each other to activate an indication device to provide an indication with respect to an overload condition.
7. The system according to claim l„ wherein the indication device provides an audio indication.
8. The system according to claim 1, wherein the indication device provides a visual indication.
9. The system according to claim i, wherein the indication device provides an electrical indication.