FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION

An electromagnetic tripping mechanism of a circuit breaker
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTORS
Bagade Vishal, Joshi Himanshu and Khedkar Parag, all of Crompton Greaves Limited, Technology Cell (S3), A-3 MIDC, Ambad, Nasik, Maharashtra, India, all Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an electromagnetic tripping mechanism of a circuit breaker.
BACKGROUND OF THE INVENTION
Circuit breakers are protective electrical devices used in power supply and power distribution systems in order to clear fault currents under overload conditions and in order to prevent accidents and damage to the other electrical equipments / devices in the power supply and power distribution systems. Electromagnetic tripping mechanisms are generally used to trip circuit breakers and to clear fault currents under overload conditions. An electromagnetic tripping mechanism generally includes a single tripping coil assembly or a double tripping coil assembly. An electromagnetic tripping mechanism including a single tripping coil assembly comprises an electromagnetic coil and a plunger reciprocally disposed within the electromagnetic coil and spring biased inwardly. On energising the coil, owing to the repulsive force of the electromagnetic field generated in the coil, the plunger moves out under compression of the spring to actuate a tripping trigger located in the proximity of the plunger. The tripping trigger is connected to a latching mechanism which in turn is connected to the moving contact of the circuit breaker. On being actuated, the tripping trigger delatches the latching mechanism so as to trip the circuit breaker. On denergising the coil, the plunger moves back to its original position under expansion of the spring. Along with the plunger, the tripping trigger also moves back to its original position. In a single coil electromagnetic tripping mechanism, if the electromagnetic coil fails the tripping mechanism will not operate and clear the fault current, the consequences of which can be disastrous. Therefore, a single coil electromagnetic tripping mechanism is not reliable. An electromagnetic tripping

mechanism including a double tripping coil assembly comprises two tripping coil assemblies co-axially arranged. Each of the coil assemblies comprises an electromagnetic coil and a plunger reciprocally disposed within the coil and spring biased inwardly. The plungers are disposed coaxially describing an air gap between them. One of the coil assemblies is disposed close to the tripping trigger. On energising the said one coil assembly, the respective plunger moves out under the repulsive force of the electromagnetic field generated and compression of the respective spring to actuate the tripping trigger and trip the circuit breaker. On denergising the said one electromagnetic coil, the respective plunger moves in to its original position under expansion of the respective spring and with it the tripping trigger also moves back to its original position. On energising the other electromagnetic coil, namely the backup coil, the respective plunger moves out under the repulsive force of the electromagnetic field generated within the coil and under compression of the respective spring and engages against the plunger of the said one coil assembly and pushes the plunger of the said one coil assembly to trip the tripping trigger and the circuit breaker. On denergising the said other coil assembly, the respective plunger moves back to its original position under expansion of the respective spring and with it, the plunger of the said one coil assembly and the tripping trigger also move back to their original position. In case the said one coil assembly has failed, there is every possibility of the plunger of the said one coil assembly being jammed. In such a case if the said other coil assembly is energised, the plunger of the said other coil assembly will not be in a position to push forward the plunger of the said one coil assembly and trip the tripping trigger and circuit breaker. Failure of the said other coil assembly to operate and clear the fault current can be disastrous and reduces the reliability of the tripping mechanism. Besides,

during tripping by the said other coil assembly, the plunger of the said other coil assembly has to travel through the air gap between the two plungers, engage against the plunger of the said one coil assembly and push the plunger of the said one coil assembly forward to trip the tripping trigger and the circuit breaker. In order to push both the plungers, a greater force is required but both the coil assemblies are of the same capacity. Also the plunger of the said other coil assembly has to describe a larger stroke to trip the tripping trigger. As a result of all this, there is considerable delay in tripping and the tripping time increases. Tripping delay reduces the efficiency of operation and safety of the tripping mechanism and this can have disastrous consequences.
OBJECTS OF THE INVENTION
An object of the invention is to provide an electromagnetic tripping mechanism of a circuit breaker, which tripping mechanism is reliable and is also simple in construction, easy and convenient to operate.
Another object of the invention is to provide an electromagnetic tripping mechanism of a circuit breaker, which tripping mechanism reduces tripping time and tripping delay so as to improve the efficiency of operation and safety of the tripping mechanism and to avoid disastrous consequences of the tripping delay.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an electromagnetic tripping mechanism of a circuit breaker, the tripping mechanism comprising a first tripping coil assembly and a second tripping coil assembly mounted on a frame, the first coil assembly and

the second coil assembly each comprising an electromagnetic coil and a plunger reciprocally disposed within the electromagnetic coil and held inwardly spring biased, the electromagnetic coils of the first tripping coil assembly and the second coil assembly each being configured to push out the respective plungers on being energised under the repulsive force of the electromagnetic field generated and under compression of the respective springs, the first tripping coil assembly being disposed in the proximity of a tripping trigger with the outer end of the plunger of the first tripping coil assembly adapted to trip the tripping trigger, the tripping trigger being mounted on a cross pin which in turn is fixed across the frame, the tripping trigger being connected to the latch mechanism of the circuit breaker and an actuator engaged against the tripping trigger and adapted to be actuated by the outer end of the plunger of the second tripping coil assembly to trip the tripping trigger independently of the plunger of the first tripping coil assembly, the plungers of the first and second coil assemblies describing the same stroke.
The following is a detailed description of the invention with reference to the accompanying drawings in which :
Fig 1 is an isometric view of the electromagnetic tripping mechanism of a circuit breaker according to an embodiment of the invention; and
Fig 2 is an enlarged view of the clamp, tripping trigger and outer end of the plunger of the first tripping coil assembly of the tripping mechanism of Fig 1; and

Fig 3 is a crosssectional view of the first or second tripping coil assembly of the tripping mechanism of Fig 1.
The electromagnetic tripping mechanism 1 as illustrated in Figs 1 to 3 of the accompanying drawings comprises a first tripping coil assembly 2 and a second tripping coil assembly 3 mounted on a frame 4 and an upright member 5, respectively. Upright member 5 is supported on frame 4. Each of the coil assemblies comprises an electromagnetic coil 6 located within a housing 6a and a plunger 7 reciprocally disposed within the electromagnetic coil. The plungers are held inwardly biased by a spring 8 disposed in the housing against plunger head 7a. Both the electromagnetic coils are configured to push the plunger out on being energised under the repulsive force of the electromagnetic field generated and under compression of the springs. Coil assembly 2 is disposed offset and at a lower level with respect to coil assembly 3. Coil assembly 2 is disposed in the proximity of a tripping trigger 9 with the outer end of the plunger of coil assembly 2 adapted to actuate the tripping trigger. The tripping trigger is rotatably mounted on a cross pin 10 which in turn is fixed across the frame. The tripping trigger is connected to a latching mechanism 11 which in turn is connected to the moving contact (not shown) of a circuit breaker (not shown). 12 is a vertically disposed lever pivoted (pivot marked 13) in a laterally extending arm 14 of the upright member 5. The lower end of the lever is provided with a buckle shaped slotted clamp 15 (slot in the clamp marked 16) which is engaged over the tripping trigger with the outer end of the plunger of the coil assembly 2 adapted to pass freely through the slot 16 in the clamp 15. The upper end of the lever is disposed in the proximity of the outer end of the plunger of the coil assembly 3. Both the plungers are adapted to describe the same stroke. On energising the electromagnetic coil of the first

coil assembly, the respective plunger moves out under the repulsive force of the magnetic field generated and under compression of the respective spring and actuates the tripping trigger through the slot 16 in the clamp 15. As a result, the tripping trigger rotates in the anticlockwise direction about the cross pin and delatches the latching mechanism so as to trip the circuit breaker. On deenergising the electromagnetic coil of the first coil assembly, the respective plunger moves in under expansion of the respective spring and the tripping trigger returns to its original position. While the tripping trigger rotates anticlockwise, the lower end of the lever is slightly displaced outwardly towards the upright member and the upper end of the lever is slightly displaced outwardly away from the outer end of the plunger of the second coil assembly. When the tripping trigger returns to its original position the lever also regains its original position. On energising the electromagnetic coil of the second coil assembly the respective plunger moves out under the repulsive force of the electromagnetic field generated and under compression of the respective spring and pushes the upper end of the lever outwardly away from the second coil assembly. As a result, the lower end of the lever with the clamp moves outwardly in the direction of the upright member so as to rotate the tripping trigger anticlockwise and detach the latching mechanism and trip the circuit breaker. On deenergising the electromagnetic coil of the second coil assembly, the respective plunger moves into its original position under expansion of the respective spring and the lever and tripping trigger return to their original position. According to the invention both the plungers move independently separately and describe the same stroke. Both the tripping coil assemblies trip the tripping trigger and circuit breaker independently and separately on being energised. The tripping mechanism of the invention is reliable and simple in

construction and easy and convenient to operate. Tripping time and tripping delay are reduced so as to improve operational efficiency and safety of the tripping mechanism.
The above embodiment is by way of example of the invention and should not be construed to limit the scope of the invention. There can be various other embodiments within the scope of the invention. The actuator construction and configuration can be different. Embodiments comprising such variations are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.

We claim :
i
1) An electromagnetic tripping mechanism of a circuit breaker, the tripping mechanism comprising a first tripping coil assembly and a second tripping coil assembly mounted on a frame, the first coil assembly and the second coil assembly each comprising an electromagnetic coil and a plunger reciprocally disposed within the electromagnetic coil and held inwardly spring biased, the electromagnetic coils of the first tripping coil assembly and the second coil assembly each being configured to push out the respective plungers on being energised under the repulsive force of the electromagnetic field generated and under compression of the respective springs, the first tripping coil assembly being disposed in the proximity of a tripping trigger with the outer end of the plunger of the first tripping coil assembly adapted to trip the tripping trigger, the tripping trigger being mounted on a cross pin which in turn is fixed across the frame, the tripping trigger being connected to the latch mechanism of the circuit breaker and an actuator engaged against the tripping trigger and adapted to be actuated by the outer end of the plunger of the second tripping coil assembly to trip the tripping trigger independently of the plunger of the first tripping coil assembly, the plungers of the first and second coil assemblies describing the same stroke.
2) The tripping mechanism as claimed in claim 1, wherein the first tripping coil assembly is disposed offset and at a lower level with respect to the second tripping coil assembly and the actuator comprises a vertically disposed lever pivotally held on an upright member, the lower end of the lever being provided with a slotted buckle shaped clamp engaged over the tripping trigger with the outer end of the plunger of the first tripping coil assembly adapted to pass freely through the slot in the buckle shaped clamp and actuate the tripping trigger and the upper end of the lever being disposed in the proximity

of the outer end of the plunger of the second tripping coil assembly adapted to be actuated by the outer end of the plunger of the second tripping coil assembly to trip the tripping trigger independently of the plunger of the first tripping coil assembly. Dated this 13th day of January 2009