FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: HIGH SPEED SWITCHING MECHANISM
FOR CIRCUIT PROTECTION DEVICES
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:

FIELD OF THE INVENTION
The present invention relates to an improved high speed switching mechanism used in circuit protection devices. More particularly, the invention is concerned about an improved switching mechanism for protecting electrical circuitry and equipment from damage due to abnormal condition, such as an overload condition or a relatively high level short circuit or fault condition. Some examples of circuit switching devices and circuit interrupters are circuit breakers, contactors, motor starters, motor controllers and other load controllers which are used to protect electrical circuitry and equipments from damage.
BACKGROUND AND THE PRIOR ART
The known switching devices typically have two positions corresponding to the status of the separable contacts. For example, these positions would include an ON position, in which the separable contacts are closed, an OFF position in which the contacts are open. In a few switching devices there could be a third state which would include TRIP position in which the contacts are tripped open.
These switching devices are usually installed in an enclosure so as to have all the control and distribution network laid in form of metallic sheets and or cable wires inside and all operating means from outside so as to prevent access to high voltage and thus a potential hazard.
One such switching device is a moulded case circuit breaker (MCCB) which is generally used to provide over current protection for various types of electrical equipment. MCCBs have three stable positions - ON, OFF and TRIP in which conditions of contacts as described above.

It is known in the art that when a circuit breaker is in ON condition and a short circuit fault condition arises, high amount of current flows through the circuit. When such a situation arises the circuit breaker has to move the contacts to open position by sensing the fault condition through short circuit sensing mechanism such as magnetic arrangement. The time taken from a fault condition appearing and the current being limited by circuit breaker determines the let through energy of the circuit interrupter. A circuit interrupter is more efficient when the let through energy is lesser.
Let through energy of circuit interruption device depends on lot of parameters one among them being the time for opening of the contacts from closed condition. The short circuit sensing mechanism of a circuit breaker involves mechanical elements in between and thus takes a finite time before giving a trip open signal to the contacts thus increasing the let through energy.
The present inventors have found that mechanism with reduced or minimum number of components will therefore reduce the total time taken to separate the contacts. A mechanism which can trip open the contacts faster can drastically reduce the let through energy. Reduction in let through energy improves life of the equipments and systems connected downstream and greatly reduce the hazardous conditions which can damage the downstream equipments.
Circuit protection devices once tripping on fault, should give a proper indication to the operator if the device has cleared the fault. In other words, there should be an indication means to distinguish if the device is in ON condition, OFF condition or TRIP condition on fault. In protection devices having three positions, especially moulded case circuit breakers have operating handle as the indicating means. However it happens that the knob might not indicate the correct position of the contacts. This happens due to variation in components

and assembly. To ensure that the knob indicates the true position of the contacts, standards have imposed a test for true contact position indication, in which the contacts are welded together in the ON condition, and the knob is moved to the OFF condition. If the knob comes back to the ON condition to indicate that the contacts are still together, the device is said to have a positive isolation. Design safety margin for isolation can be provided. However, the variation in components and assembly in actuality make achieving isolation a complicated phenomenon.
An intentional interference or over travel is provided between the two contacts of the circuit breaker. This intentional over travel helps in building up contact force between the two contacts which thereby helps in reducing the contact resistance at the contact buttons. This also helps in maintaining continuity even after the contacts erode either during electrical operations or due to fault clearance. There is however a variation in the over travel achieved across the devices. This is mainly due to the variation in component and assembly. Reduction in the tolerance band will increase the consistency of the over travel achieved across the devices, but this however will increase the manufacturing cost. Thus, the reduction in the overall number of the component which affects the over travel will help in achieving such consistency.
US3992600 describes a mechanism that can be used for switches where variable speeds of the drive shaft are required. Also, the mechanism in this prior art is a 4 bar mechanism and not a two bar mechanism as in the present invention.
US4710738 and US6015959 describe a conventional 5 bar mechanism which are normally used in three position electrical switches as compared to the present invention made of 2 bar.

GB1516153A has only two positions of the switch, and hence can only be used in the 2 position electrical switches such as miniature circuit breakers (MCBs). Unlike the present invention this prior art method cannot be used for three position electrical switches. In this prior art method, when the operating handle is moved, the main latch (or the U component) moves to change the direction of the spring with respect to the moving contact. However, it was not taught in this prior art that the moving contact itself can be moved using the operating handle to achieve the toggling position.
These and other limitations and needs of the conventional switching mechanisms necessitate an improved mechanism. Such a mechanism has been disclosed here which provides improvements and flexibility apart from overcoming the limitations mentioned above.
The invention achieves a reduction in the total time taken by the mechanism to trip open the contacts when a fault occurs, by reducing the number of components comprising the mechanism, which is not possible in the existing mechanisms.
OBJECTS OF THE INVENTION
One of the objects of the present invention is to overcome the disadvantages/drawbacks of the prior art.
A basic object of the present inventions is to provide an improved switching mechanism for protecting electrical circuitry and equipment from damage due to abnormal condition.
Another object of the present invention is to provide a mechanism which would have a reduced tripping time when fault occurs.

A further object of the present invention is to reduce the number of components in the mechanism making it cost effective.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an improved high speed
switching mechanism for use in circuit protection devices, said mechanism comprising:
plurality of mechanism plates;
driveshaft means secured between the mechanism plates with some portion of the
driveshaft means hinged on both sides with said plate means;
pivot means;
movable contact means pivotally engaged to the driveshaft;
fork means is hinged with the said plates on its outside surface, and connected to the said
driveshaft with a slot means provided in the fork;
a latch bracket means being hinged to the said plates and resting on an interfacing
component forming an interface between magnetic and thermal protection;
a latching component being latched to the latch bracket means when the circuit protection
device is in either OFF or ON condition; and
spring means for toggling of the mechanism between ON and OFF.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates a side view of the mechanism of the present invention in TRIP condition
Fig. 2 illustrates a side view of the mechanism of the present invention in OFF condition
Fig. 3 illustrates a side view of the mechanism of the present invention in toggling condition

Fig. 4 illustrates a side view of the mechanism of the present invention in ON condition
Fig. 5 illustrates a side view of the mechanism of the present invention in ON condition with upper contact locked upon fault
Fig. 6 illustrates a 3D view of the mechanism with a 3 pole driveshaft (without springs) in the present invention.
Fig. 7 illustrates a cut out 3D view of the mechanism in the present invention
Fig. 8 illustrates an exploded view of the mechanism in the present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Mechanism disclosed herein is shown in fig 1 is a two bar mechanism. It consists of a movable contact 1 pivoted at pin 10 to the driveshaft 2 which itself is hinged at 17. The operating handle 7 is connected to the mechanism fork 3 using screws at holes 14, Fork 3 is hinged at 12 on side plates 17 (fig. 6) and is connected to the driveshaft using pivot pin 10 which slides in the slot provided in the fork. Main latch 4 is the latching component in the mechanism. Main latch is pivoted at 12 using a pin and it latches to the latch bracket 5 when the breaker is in either OFF or ON condition. Latch bracket 5 is hinged using pin 15 which is fixed to the mechanism plate 17. Latch bracket 5 in turn rests on the trip plate 6 in OFF and ON condition of the mechanism, which is the component forming an interface between the protection i.e. magnetic and thermal. Trip plate 6 receives a trip signal from the protection system in case a fault occurs. A set of mechanism springs 8 are connected across the pins 10 and 13. These springs 8 are responsible for the toggling of mechanism between

OFF and ON conditions. Trip spring 9 is connected between main latch and the ground body or housing of the breaker (Names of the spring means "Mechanism" and "Trip" are used here for defining the components and such names are not to be considered as restriction of scope for the present invention). Pin 11 which is fixed in the fork 3 is utilized for engaging the main latch 4 with the latch bracket 5. The mechanism is also provided with a return spring (not shown here) which is responsible for bringing back the trip plate back to its initial position once it has been rotated by trip signal given from the protection system.
Fig.l shows the mechanism in TRIP condition. Main latch is in the disengaged condition. Fork and thereby knob is in an intermediate position between OFF and ON, Contacts I and 16 are not in contact with each other i. e, they are open circuited. In this condition, the mechanism spring is in a non-stretched condition and the direction of force application is in such a way as to pull the main latch and the driveshaft towards each other but away from lower contact. Fork pin 11 stops on the main latch and cannot move further since it requires trip spring to be compressed. This is intentionally made not possible by making the spring rate of the mechanism spring lesser when compared to the tripping spring.
Fig. 2 shows the mechanism in OFF condition. When the operating handle is moved to the right of the fig. 1 from TRIP condition towards OFF, the main latch is rotated by the fork pin through the handle. During this process, trip spring gets compressed as the main latch is moving downward and the driveshaft rotates backward with the fork due to the coupling between slot in fork and driveshaft pin. The distance between the two contacts in this case increases in comparison to that in the TRIP condition. However, the mechanism springs are not deflected during this process. When the main latch travels to the extreme position towards OFF, it engages with the slot provided in the latch bracket. This result in an upward force on the latch bracket by virtue of the upward force exerted on the main latch

by the trip spring and causes it to rotate towards trip plate and rest on it. If the force on the handle is removed in this position, the mechanism will remain in this condition.
The operating handle is moved to the left of fig. 2 i,e. towards ON condition, driveshaft starts moving with the fork and the mechanism starts getting stretched. This process will continue till the position shown in fig. 3 is reached. This is the toggling position. In this condition, the axis of the mechanism spring passes through the driveshaft hinge. Even a slight movement of the handle further towards the ON condition will make the contacts come together and close the circuit. This condition is shown in the fig. 4 which is the ON condition.
In the ON condition shown in fig. 4, there is an intentional over travel provided. Since the lower contact is fixed and thus cannot move, the upper contact is rotates away from the lower contact. Driveshaft however reaches its final position and is unaffected by the rotation of the upper contact since the locking system is independent from the mechanism (not shown here). This rotation of the upper contact is responsible for the generation of contact force between the two contacts. Higher the over travel between the contacts, higher will be the rotation of the upper contact and so higher will be the contact force generated. The position of the main latch and other tripping system will be the same as in the OFF condition.
When fault occurs, the protection system of the breaker applies a force on the trip plate, which makes it to rotate in the clockwise direction. This rotation removes the constraint from the latch bracket and makes it free to rotate. This is by virtue of a net clockwise torque on the latch bracket from main latch. After a certain amount of rotation of the latch bracket, main latch becomes disengaged and since the trip spring is in a compressed state in ON condition, it rotates the main latch in the anti-clockwise direction of the fig. 4. During this

movement of the main latch, mechanism spring again comes in line with the driveshaft hinge and results in change in direction of the force on the driveshaft. This rotates the driveshaft away from the contacts and the mechanism reaches the TRIP condition.
In breakers which utilize contact locking feature, the contact first gets locked due to the repulsive forces between the contacts and then the mechanism gets operated to rotate the driveshaft. The condition of the mechanism in the contact locked condition is shown in fig. 5.
Advantages:
Following are the features and advantages of the invention owing to the reduced no. of mechanism components
1. Reduction in the total time taken by the mechanism to trip open the contacts when a fault occurs
2. Achieving isolation is definite and less complicated and the dependency of isolation on the component and assembly variation is reduced, since the operating handle is directly connected to the driveshaft. This will ensure that the operating handle indicates the true position of the contacts.
3. The variation in over travel across breakers is reduced
4. Variation in trip force across breakers is reduced since the mechanism forces delivered to the tripping system will be consistent. This will result in better performance of the protection system

5. The life of the system is increased since there will be less wear and tear between the components due to less no. of moving parts
6. Mechanism of the present invention uses two bars.
7. The overall cost of the mechanism is reduced due to reduction in the no. of components, ease of manufacturing and ease of assembly
8. Overall size of the mechanism is reduced resulting in design of more compact products than existing constructions.
The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.

WE CLAIM
1. An improved high speed switching mechanism for use in circuit protection devices, said mechanism comprising: plurality of mechanism plates;
driveshaft means secured between the mechanism plates with some portion of the driveshaft means hinged on both sides with said plate means; pivot means;
movable contact means pivotally engaged to the driveshaft;
fork means is hinged with the said plates on its outside surface, and connected to the said driveshaft with a slot means provided in the fork;
a latch bracket means being hinged to the said plates and resting on an interfacing component forming an interface between magnetic and thermal protection; a latching component being latched to the latch bracket means when the circuit protection device is in either OFF or ON condition; and spring means for toggling of the mechanism between ON and OFF.
2. Mechanism as claimed in claim I wherein said interfacing component is a trip plate.
3. Mechanism as claimed in clam 2 wherein said trip plate is adapted to receive trip signal from the protection system in case of a fault.
4. Mechanism as claimed in claims 1 to 3 wherein said is adapted to be rotated in clockwise direction by the protection device such that the latch bracket means is made to rotate so as to disengage the latching component and rotate it in anticlockwise direction.

5. Mechanism as claimed in claim 1 wherein said means for toggling comprises springs connected across pivot pin 10 and pivot pin 13.
6. Mechanism as claimed in claim 6 wherein said spring axis passes through the driveshaft hinge in the toggling position.
7. Mechanism as claimed in claim 1 further comprises trip spring operatively connected between main latch and the housing or any other fixed member of the protection device.
8. Mechanism as claimed in claim 1 wherein said fork means comprises pin means for rotating said latch means during RESET operation of the breaker, in order to latch it with latch bracket.
9. Mechanism as claimed in claim 1 wherein said slot means is adapted to rotate the driveshaft.
10. Mechanism as claimed in any of the preceding claims comprising plurality of pin means adapted to provide pivoting action to the mechanism components.
11. Mechanism as claimed in any of the preceding claims further comprising an operating handle connected to the fork,
12. Mechanism as claimed in any of the preceding claims is a two bar mechanism.

13. An improved high speed switching mechanism for use in circuit protection devices as substantially described hereinbefore with reference to accompanying drawings.