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 pYunger 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 m construction, easy and convenient to operate.
Another object of the invention is to provide an electroniagnetic 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 co-axially disposed and inounted on a frame, each of the tripping coil assemblies comprising an electromagnetic coil and a plunger reciprocally disposed within the electromagnetic coil and held, inwardly spring biased, the electromagnetic coils of both the coil assemblies being configured to push out the

respective plunger under the repulsive force of the electromagnetic field generated and under compression of the respective springs, the plungers of the coil assemblies being adapted to describe the same stroke and configured to actuate a tripping trigger independently of each other when the respective coils are energised, the tripping trigger being rotatably mounted on a cross pin which is fixed across the frame.
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 tripping mechanism according to an embodiment of the
Fig 2 is a front view of the tripping mechanism of Fig 1;
Fig 3 is an enlarged scrap view of the tripping trigger and the outer ends of the plungers of the tripping coil assemblies of the tripping mechanism of Fig 1;
Fig 4 is a cross sectional view of the first tripping coil assembly of the tripping mechanism of Fig 1;
Fig 5 is a crosssectional view of the second tripping coil assembly of the tripping mechanism of Fig 1;
Fig 6 is an isometric view of the plungers of the tripping coil assemblies of the tripping mechanism of Fig 1 when the second coil is energised;

Fig 7 is an isometric view of the plungers of the tripping coil assemblies of the tripping mechanism of Fig 1 when the second coil is deenergised;
The electromagnetic tripping mechanism 1 as illustrated in Figs 1 to 7 of the accompanying drawings comprises a first tripping coil assembly 2 and a second tripping coil assembly 3 disposed co-axially and mounted on a frame 4. Coil assembly 2 comprises an electromagnetic coil 5 located within a housing 5a and a plunger 6 reciprocally disposed within the electromagnetic coil and held inwardly biased by a spring 7 against plunger head 6a. Coil assembly 3 comprises an electromagnetic coil 8 located within a housing 8a and a plunger 9 reciprocally disposed within the electromagnetic coil and held inwardly biased by a spring 10 against plunger head 9a. Both the electromagnetic coils are 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. Coil assembly 2 is disposed in the proximity of a tripping trigger 11 rotatably mounted on a cross pin 12 which in turn is fixed across the frame. The plunger 6 is provided with a through passage 6b and the plunger 9 comprises a narrow extension 13 of reduced dimension slidably extending through the passage in the plunger 6 with its outer end adapted to protrude out of the outer end of the plunger 6 when the electromagnetic coil 8 is energised. 14 is a latching mechanism connected to the tripping trigger. The latching mechanism is connected to the moving contact (not shown) of a circuit breaker (not shown). On energising the electromagnetic coil 5, the plunger 6 moves out under the repulsive force of the electromagnetic field generated within the coil and under compression of the spring 7 and engages against and rotates the tripping trigger anticlockwise about the cross pin.

As a result, the latch mechanism connected to the moving contact of the circuit breaker is detached causing the circuit breaker to trip. On deenergising the electromagnetic coil 5, the plunger 6 is pulled back to its original position under expansion of the spring 7 and the tripping trigger return to its original position. On energising the electromagnetic coil 8, the plunger 9 moves out under the repulsive force of the electromagnetic force generated and under compression of the spring 10 and the narrow extension 13 of the plunger 9 slides out through the passage 6b in the plunger 6 to rotate the tripping trigger in the anticlockwise direction and trip the circuit breaker. On deenergising the electromagnetic coil 8, the plunger 9 returns to its original position along with the tripping trigger under expansion of the spring 10. According to the invention both the plungers move independently of each other and describe the same stroke. The tripping coil assemblies of the tripping mechanism independently separately trips the tripping trigger and circuit breaker. Therefore, the tripping mechanism is reliable and is also simple in construction, easy and convenient to operate. The tripping time and tripping delay are reduced so as to improve the operational efficiency and safety of the tripping mechanism.
The above embodiment of the invention is by way of example and should not be construed to limit the scope of the invention. There can be variations in the configuration of the plungers so as to trip the tripping trigger independent of each other. The plunger of the second coil assembly can be configured to slide over the plunger of the first coil assembly and actuate the tripping trigger independent of the plunger of the first coil assembly. 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 :
1) An electromagnetic tripping mechanism of a circuit breaker, the tripping mechanism comprising a first tripping coil assembly and a second tripping coil assembly co-axially disposed and mounted on a frame, each of the tripping coil assemblies comprising an electromagnetic coil and a plunger reciprocally disposed within the electromagnetic coil and held inwardly spring biased, the electromagnetic coils of both the coil assemblies being configured to push out the respective plunger under the repulsive force of the electromagnetic field generated and under compression 0f the respective springs, the plungers of the coil assemblies being adapted to describe the same stroke and configured to actuate a tripping trigger independently of each other when the respective coils are energised, the tripping trigger being rotetebly mounted on a cross pin which is Fixed across the frame.
2) The tripping mechanism as claimed in claim 1, wherein the first coil assembly is disposed in the proximity of the tripping trigger and the plunger the first tripping coil assembly is provided with a passage therethrough and the plunger of the second coil assembly comprises a narrow extension of reduced dimension slidably extending through the passage of the plunger of the first tripping coil assembly and adapted to protrude out of the outer end of the plunger of the first coil assembly the outer ends of the plungers of the first coil assembly and the second coil assembly being adapted to actuate the tripping trigger independently of each other when the respective coils are energised.

Dated this 13th day of January 2009