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 pair of tripping coil assemblies mounted on a frame, one tripping coil assembly comprising a first

electromagnetic coil and a first plunger reciprocally disposed within the first electromagnetic coil and inwardly spring biased, the first electromagnetic coil being disposed in the proximity of a tripping trigger with the outer end of the first plunger adapted to actuate the tripping trigger, the tripping trigger being rotatably mounted on a crosspin which in turn is fixed across the frame, the said one electromagnetic coil being configured to push the first plunger out on being energised and actuate the tripping trigger under the repulsive force of the electromagnetic field generated and under compression of the respective spring and the other tripping coil assembly comprising a second electromagnetic coil and a second plunger reciprocally disposed within the second electromagnetic coil and held outwardly spring biased, the said other electromagnetic coil being configured to pull the second plunger in on being energised under the attractive force of the electromagnetic field generated and under compression of the respective spring and an actuator engaged against the tripping trigger and connected to the outer end of the second plunger adapted to actuate the tripping trigger independently of the first plunger when the second magnetic coil is energised, the plungers being adapted to describe 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 an electromagnetic tripping mechanism of a circuit breaker according to an embodiment of the invention;
Fig 2 is a scrap view of the L-shaped clamp, tripping trigger and outer end of the first plunger of the tripping mechanism of Fig 1;

Fig 3 is a crosssectional view of the first tripping coil assembly of the tripping mechanism of Fig 1;
Fig 4 is a crosssectional view of the second tripping coil assembly of the tripping mechanism of Fig 1;
Fig 5 is an isometric view of the electromagnetic tripping mechanism of a circuit breaker according to another embodiment of the invention; and
Fig 6 is front view of the tripping mechanism of Fig 5.
The electromagnetic tripping mechanism 1 as illustrated in Figs 1 to 4 of the accompanying drawings comprises a first tripping coil assembly 2 and a second tripping coil assembly 3 mounted on a frame 4 and on a subframe 4a respectively. Subframe 4a is mounted on frame 4. The first coil assembly 2 is disposed below the second coil assembly 3 in spaced apart relationship. The first coil assembly comprises a first electromagnetic coil 5 disposed within a housing 5a and a first plunger 6 reciprocally disposed within the first electromagnetic coil. The first plunger is inwardly biased by a first spring 7 located in the housing against the head 6a of the plunger (Fig 3). The first coil assembly is disposed in the proximity of a tripping trigger 8 rotatably mounted on a crosspin 9 which in turn is fixed across the frame. The first electromagnetic coil is configured to push the first plunger out on being energised under the repulsive force of the magnetic field generated in the coil and under compression of the first spring 7 and actuate the tripping trigger which is

connected to a latch mechanism 10 which in turn is connected to the moving contact (not shown) of a circuit breaker (not shown). The second coil assembly comprises a second electromagnetic coil 11 disposed within a housing 11a and a second plunger 12 reciprocally disposed within the second electromagnetic coil. The second plunger is held outwardly biased by a second spring 13 located in the housing against the head 12a of the plunger (Fig 4). The second electromagnetic coil is configured to pull the second plunger in on being energised under the attractive force of the magnetic field generated in the coil and under compression of the second spring 13. 14 is an L-shaped clamp, one limb 15 of which is slotted (slot marked 16) and is engaged against the tripping trigger with the outer end of the first plunger disposed to pass freely through the slot 16 in the said one limb. The other limb 17 of the L-shaped clamp is connected to the outer end of the second plunger by a wire rope 18 engaged over a pair of vertically spaced apart pulleys 19, 19 which are rotatably mounted in the lateral arms 20 of an upright member 21 which in turn is mounted on the frame. Both the plungers are adapted to describe the same stroke. When the electromagnetic coil of the first coil assembly is energised, the first plunger moves out under the repulsive force of the electromagnetic field generated and under compression of the first spring 7. The first plunger passes freely through the slot 16 in the said one limb of the re¬shaped clamp and actuates the tripping trigger. The tripping trigger rotates on the cross pin anticlockwise and delatches the latching mechanism. As a result, the moving contact of the circuit breaker moves away from the fixed contact thereof and trips the circuit breaker. On deenergising the electromagnetic coil of the first coil assembly, the spring 7 expands and brings the first plunger to its original position and with the first plunger, the tripping trigger also moves back to its original position. On energising the electromagnetic coil of the second coil assembly, the second plunger is pulled in

under the force of attraction of the electromagnetic field generated and under compression of the spring 13. When the second plunger moves into the second electromagnetic coil, the L-shaped clamp engaged against the tripping trigger rotates the tripping trigger in the anticlockwise direction about the cross pin so as to delatch the latching mechanism and trip the circuit breaker. On denergising the second electromagnetic coil, the second plunger moves out to its original position under expansion of the second spring 13 and with it the tripping trigger also moves back to its original position. According to the invention the plungers of both the coil assemblies move independently separately and describe the same stroke. Both the tripping coil assemblies trip the tripping trigger and the circuit breaker independently separately on being energised. Therefore, the tripping mechanism of the invention is reliable. It is also simple in construction, easy and convenient to operate. Tripping time and tripping delay are reduced so as to improve the performance efficiency of the tripping mechanism and improve safety in operation and to avoid the disastrous consequences of the delay.
The tripping mechanism 22 as illustrated in Figs 5 and 6 of the accompanying drawings comprises two tripping coil assemblies 2 and 3 mounted on the frame 4 at the same level in spaced apart relationship with each other. The L-shaped clamp 14 has one limb 15 which is slotted (slot marked 16) and is engaged against the tripping trigger with the outer end of the first plunger disposed to pass freely through the slot 16 in the said one limb of the L-shaped clamp. The other limb 17 of the L-shaped clamp is directly coupled to the outer end of the plunger of the second electromagnetic coil. The plungers actuate the tripping trigger to trip the circuit breaker as described earlier.

The above embodiments are by way of examples of the invention and should not be construed and understood to be limitative of the scope of the invention. The actuator comprising the L-shaped clamp can be of a different construction or configuration. Embodiments comprising such variations of the invention 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 pair of tripping coil assemblies mounted on a frame, one tripping coil assembly comprising a first electromagnetic coil and a first plunger reciprocally disposed within the first electromagnetic coil and inwardly spring biased, the first electromagnetic coil being disposed in the proximity of a tripping trigger with the outer end of the first plunger adapted to actuate the tripping trigger, the tripping trigger being rotatably mounted on a crosspin which in turn is fixed across the frame, the said one electromagnetic coil being configured to push the first plunger out on being energised and actuate the tripping trigger under the repulsive force of the electromagnetic Fiekl generated and under compression of the respective spring and the other tripping coil assembly comprising a second electromagnetic coil and a second plunger reciprocally disposed within the second electromagnetic coil and held outwardly spring biased, the said other electromagnetic coil being configured to pull the second plunger in on being energised under the attractive force of the electromagnetic field generated and under compression of the respective spring and an actuator engaged against the tripping trigger and connected to the outer end of the second plunger adapted to actuate the tripping trigger independently of the first plunger when the second magnetic coil is energised, the plungers being adapted to describe the same stroke,
2) The electromagnetic tripping mechanism as claimed in claim 1, wherein the said one tripping coil assembly is disposed below the other tripping coil assembly in spaced apart relationship and the actuator comprises an L-shaped clamp, one of the limbs of the clamp being slotted and engaged against the tripping trigger with the

outer end of the first plunger disposed to freely pass through the slot in the slotted one limb and the other limb of the clamp being connected to the outer end of the second plunger by a wire rope engaged over a pair of vertically spaced apart pulleys rotatably mounted on an upright member mounted on said frame.
3) The electromagnetic tripping mechanism as claimed in claim 1, wherein the said one tripping coil assembly and the other tripping coil assembly are placed at the same level in spaced apart relationship and the actuator comprises an L-shaped clamp, one of the limbs of the clamp being slotted and engaged against the tripping trigger with the outer end of the first plunger disposed to pass freely through the slot in the slotted one limb and the other limb of the clamp being directly connected to the outer end of the second plunger.
Dated this 13th day of January 2009