F0RM2
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 CONTACT LOCKING MECHANISM
FOR CIRCUIT BREAKER
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 a contact locking mechanism for circuit breakers. In particular, to a contact locking mechanism for circuit breakers which operate at high speed. More particularly, the invention relates to a high speed contact locking mechanism for circuit breakers being provided with movement of multiple points across which spring is connected. The system is further provided with a lock lever driven by the moving contact resulting in deflection of the spring. It is also related to a contact locking mechanism for circuit breakers capable of giving actuation to external mechanisms such as tripping mechanism of breaker and for external indication.
BACKGROUND OF THE INVENTION
The circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers are used to protect 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.
These 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 device there could be a third state which would include tripped 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 condition of contacts is as described above.

When circuit breaker is in ON condition and a short circuit fault condition arises, high amount of current flows through the circuit and in which case, 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 various parameters one among them being the time for opening of the contacts from closed condition. The short circuit sensing mechanism of 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.
Short circuit conditions involves high amount of current levels which induces repulsion forces between suitably arranged contacts. Thus if the contacts can be locked in the repelled open position, the let through energy can be drastically reduced. This improves life of the equipments and systems connected downstream and greatly reduce the hazardous conditions which can damage the downstream equipments. This will also lead to improved life of the circuit breaker.
Thus many of the circuit breakers use such locking systems for contact locking under short circuit conditions. Further, efficiency of a contact locking system is measured by the velocity it can induce to the contacts once they have repelled open. It is also important to have the desired contact force in the ON condition.
A general locking mechanism is a toggle mechanism, which consists of one or more links and springs. When there is only one link toggling is achieved when link crosses the spring axis or vice versa. When there are two links, the spring can be connected to the links in which case toggling is achieved when both the links are in line with each other. If the spring is connected to the pin connecting the two links, toggling is achieved when the spring crosses one of the link axes.
The above principle is used in most contact locking mechanisms to toggle the movable contacts from a normal closed condition to a lock open position. When the repulsion forces

due to current in the contact is more than the spring force for toggling, the contacts repel open and get locked.
It is desirable to have the toggling position closer to ON condition of the contacts since the repulsion forces become less when the contacts move apart. It is also desirable to make the contacts move faster once it crosses the toggling position. It is also very important to achieve optimum contact force in the ON condition. To achieve this, the spring axis should be perpendicular to the contact axis but this condition will shift the toggling position away from the ON position which is not desired from the locking perspective. Achieving closer toggling position also exposes the breaker to the manufacturing variations by false locking in case of vibration.
Also it happens that the contact repels open and gets locked due to fault condition but the breaker protection system takes a finite time to trip the mechanism when compared to the time taken by the contact to repel open. Some time it also happens that the protection system fails to trip the mechanism. In such case, the knob will be indicating ON position but since the contacts have repelled open, the breaker is not conducting current to the downstream equipment. This condition is a non compliance to the standard and thus has to be eliminated. Thus it is desired to have positive and faster tripping from the protection system.
The actuation can be taken from the contacts once they are locked and can be used to trip the breaker by giving signal to the protection system. The actuation can also be used to give an indication on the breaker (Like ON-OFF) to give the true contact position. So that if the protection system fails to trip then the indication will be actuated and will show to the operator if the contacts have repelled open.
US 5,844,455 discloses a current limiting apparatus for a circuit breaker, and in particular to an improved current limiting apparatus for a circuit breaker which is capable of effectively protecting an electric load element by quickly blocking an electric flow path when an excessive current flows due to a ground, shortage, etc. within an electric flow path and preventing a re-formation of an electric flow path after the electric flow path is blocked.
US 4255732 discloses a circuit breaker includes a high speed releasable operating mechanism for moving the carriage from the closed to the open position. High speed trip means

responsive to current flow through the contacts are provided, an over current condition through the contacts causing the trip means to release the operating mechanism and move the carriage to a tripped position to separate the contacts.
US 6084489 discloses a circuit breaker having rotary contact assembly. The rotary contact system has a locking arrangement for locking the contact arm open under an occurrence of a large over current condition.
In conventional two link type of locking mechanisms, one end of the spring is connected to either moving contact or locking link and the other end is fixed to the driveshaft. This arrangement will not have the advantages given by the present invention.
So there is a need to provide an improved contact locking mechanism to overcome the limitations of the conventional mechanisms. Thus, the present invention provides an improved contact locking mechanism for circuit breaker, which achieves a better repel open speed after toggling and at the same time provide higher contact force with high degree of flexibility to fix the position of toggling which are normally not possible in the existing mechanisms. The present invention can be used to give a signal to the protection system so that it trips as soon as the contacts lock. The invention is an improvement over the existing locking mechanism for circuit breakers.
OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the prior art.
Basic object of the present invention is to provide a high speed contact locking mechanism for circuit breaker which can induce high velocity to moving contacts on occurrence of fault conditions and rapidly lock the moving contacts in open condition.
Another object of the present invention is to provide a high speed contact locking mechanism for circuit breaker which increases the deflection of the spring using lock lever driven by the moving contact.

Another object of the present invention is to provide a high speed contact locking mechanism for circuit breaker which can give actuation to external mechanisms by using either lock lever or pin means or moving contact.
Yet, another object of the present invention is to provide a high speed contact locking mechanism for circuit breaker in which toggling position is closer to the circuit breaker ON condition without affecting other parameters such as contact force.
Yet, another object of the present invention is to provide a high speed contact locking mechanism for circuit breaker with reduced let through energy.
Yet another object of the present invention is to provide a high speed contact locking mechanism for circuit breaker to improve the life of the breaker by reducing the erosion of contacts due to arcing.
It is yet another object of the present invention to provide a high speed contact locking mechanism for circuit breaker which facilitates positive tripping of the circuit breaker.
It is yet another object of the present invention to provide a high speed contact locking mechanism for circuit breaker which gives positive indication of the state of circuit breaker such as ON, OFF /TRIP.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a high speed contact
locking mechanism for use in circuit breakers, said mechanism comprising:
drive shaft means;
movable contact means;
plurality of lock member means;
plurality of spring means;
plurality of pin means;
slot means;
wherein said movable contact means having a predetermined degree of freedom being
pivoted by said pin means to said drive shaft means,

wherein said lock member means being co-pivoted with said movable contact means and having a predetermined degree of freedom for its movement along said slot means, said lock member means being suspended and supported by pin means whereby one of said pin means being journal led in said slot means aiding in the movement of said lock member means ; wherein said spring means being operatively connected at its one end with said pin means connected to the movable contact means and on its other end with another pin means connected to one end of lock member means
such that movement of said movable contact means co-operatively extends said spring means correspondingly moving the said lock member means wlereby said movement of lock member being guided by pin means journalled in the said slot means and whereby said slot means being such that sufficient degree of freedom is provided to said lock member means so as to rotate to a position establishing a predetermined angle with said movable contact means at the same time when there is a fault,
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates 3D view of the arrangement for a single pole of the circuit breaker.
Fig 2 illustrates the 3D view from the rear end of the drives haft
Fig 3 illustrates the top view of the arrangement
Fig 4 illustrates an exploded view of the internal arrangement i.e. excluding the springs.
Fig 5A illustrates the front view of arrangement in the normal or assembled condition
Fig 5B illustrates the sectional view of arrangement in the normal or assembled condition
Fig 6A illustrates the front view of arrangement in its ON condition when assembled in the
circuit breaker
Fig 6B illustrates the sectional view of arrangement in its ON condition when assembled in
the circuit breaker
Fig 7A illustrates the front view of the toggling or the locking position
Fig 7B illustrates the sectional view the toggling or the locking position
Fig 8A illustrates the front view of the toggling or the locking position of arrangement
beyond its normal locking position during fault condition.
Fig 8B illustrates the sectional view the toggling or the locking position of arrangement
beyond its normal locking position during fault condition.
Fig 9 illustrates an alternate arrangement with gear profile

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention, there is provided a high speed contact locking mechanism for circuit breaker. Locking system disclosed herein is shown in fig 1. It consists of a movable contact 2 pivoted at pin 6 to the driveshaft 1. Two lock levers 3 are suspended on the driveshaft 1. Two springs 4 are connected between the pin 5 on the moving contact 2 and the pin 8 on the lock lever 3. Springs are arranged one each on either side of the driveshaft as shown in the top view of the arrangement, fig 3. Moving contact 2 and lock lever 3 are pivoted to each other with pin 9 in fig 5B. Pin 7 suspended from lock levers 3 moves in the slot provided in the driveshaft 1.
Fig ] shows the 3D view of the arrangement for a single pole of the circuit breaker. For multiple poles multiple such assemblies will be used side by side using a common connecting driveshaft across ail the poles. The driveshaft is connected in turn to the circuit breaker mechanism. Movement of the mechanism to different positions makes the driveshaft rotate and thereby making moving contacts open or close the circuit. Fig 2 shows the 3D view from the rear end of the driveshaft. Fig. 3 is the top view of the arrangement and fig 4 shows an exploded view of the internal arrangement i.e. excluding the springs.
The working of the invention is shown in Fig 5, 6, 7 & 8 with different positions. The same is explained below. In the figs mentioned, sub-figure A refers to the front view of the invention and B refers to the sectional view of the invention in which the changes in internal components can be observed.
Fig 5 shows the arrangement in the normal or assembled condition. This is the position in which the moving contact cannot go further down since it stops on the driveshaft.
When the contact locking mechanism is assembled in the circuit breaker along with the mechanism and operated, in ON condition, the moving contact will be slightly upward when compared to the normal position (fig 5). This is due to the intended over travel provided in the circuit breaker mechanism to achieve a certain minimum contact force. This position is shown in fig 6.

When the fault occurs, there is an upward force on the moving contact 2 by which it will rotate about the pivot 6. Since lock lever is also pivoted to this moving contact, it also rotates but in the opposite direction of the moving contact motion. Since the two pins at which the spring is connected are moving away from each other, spring gets extended and in the process store energy.
Fig 7 shows the toggling or the locking position. If due to fault the moving contact rotates beyond the position shown in the fig, it will get locked to the position shown in fig 8 due to a net force provided by the spring in that direction. Thus, the spring which is stretched to its maximum deflection reaches an equilibrium state by reducing its length and releasing energy in the process to move the moving contact. If the repulsion force on the moving contact is not enough to move the positions beyond the toggling position, the arrangement will fall back to the positions shown in fig 6 i.e. in their ON condition.
Once the moving contact gets locked, it is brought back to the normal condition when the circuit breaker protection system subsequently trips the mechanism due to fault. When the signal is given, the driveshaft rotates in the upward direction. The moving contact then comes in contact with the cover / top portion of the circuit breaker and experiences a reaction force in the downward direction in a way as to make the moving contact cross the toggling position. Once the moving contact crosses the toggling position, it goes to the normal position by virtue of the force exerted by the spring. Therefore, process of unlocking of moving contact is just the opposite of the locking process.
The ultimate principle is the movement of both the points at which the spring is connected. Due to moving contact and lock lever moving at the same time, there is larger deflection of the spring and thus larger energy release after toggling resulting in higher velocity of moving contact. If the same spring is used in prior methods and in the present invention, since the deflection is more in present invention, due to two moving points in the opposite direction, the force delivered by the spring (after toggling) on to the moving contact is higher than the prior methods and thus gives the advantage of higher repel open speed. This is considering that the spring stresses are within limits.
Toggling position is that instant at which the points or pins 5,6,9,7 & 8 come in the same line. The orientation of the line is fixed on various parameters by design. The effectiveness of the

toggling position is decided by the closeness of the toggling position to the ON position. Since, in such case the amount of rotation required by the moving contact to reach the toggling position and get locked will be lesser. If the pin 8 were fixed, for the given toggling position, the amount of rotation would be higher when compared to that required in the present invention. This can be explained since both the moving contact and lock lever are moving at the same time towards the toggling position, they reach the toggling position earlier and since one of the points / pins in earlier invention is fixed, the amount of travel by the moving contact to achieve the toggling position will be higher. Thus on occurrence of fault, the present invention can get locked faster than in the prior methods. This will reduce the let through energy of the mechanism to the downstream equipments.
Above disadvantage can be removed in the prior methods by keeping toggling position closer to the ON position. This will reduce the amount of rotation of moving contact for getting locked. This however will reduce the contact force between the moving and fixed contacts in the breaker due to lesser angle between spring and moving contact. In order to achieve the same contact force with toggling position closer to the ON position, higher load spring can be used. This however will increase the stress levels in the spring and thus reduce the overall factor of safety in the spring and thus the whole mechanism. Also, since the higher load value spring is greater in size, the cost will be higher and the size of the locking mechanism will increase which is undesirable.
Thus the above disadvantages of the prior methods can be avoided since the toggling position can be as closer to the ON position without having to sacrifice on the position of toggling and at the same time achieving the required contact force with lesser dimensions and weight of the entire system.
Lock lever, Pin 8 or the moving contact can be used to give a trip signal or actuation to the protection system using an intermediate mechanism or arrangement of links. This is possible since the present invention has definite positions in ON and in locked condition. This will ensure that breaker always trips speedily when the contacts repel open. Since the time taken by the contacts to repel open is lesser when compared to trip signal given by the breaker protection system, the fault will be cleared faster when such actuation is given directly from the locking system. This will significantly reduce the let through energy of the system and also result in increased life.

Actuation can also be used to give indication on the circuit breaker which will indicate if the contacts are in ON or locked condition. An example for this can be in the form of a pop up arrangement. If the pop up arrangement is directly mounted above the rear end of the lock lever, there will be two positions for the pop up indicator. Firstly in the ON condition when the rear end of the lock lever is towards the bottom, the popup will be depressed from the outer surface of the breaker. When the contacts get locked, the rear end of the lock lever moves up and thus takes the pop up along with it upward. In this case, the popup would be projecting out from the surface of the breaker giving an indication that the contacts have got locked. Similarly, the invention can be used for tripping the breaker or for completing an electrical circuit once the contacts are in a particular position.
In the prior art methods, the only way of giving such actuation or indication was using the moving contacts which had a distinct position in the ON and in the locked / opened position. However, since the moving contact is among the components of the circuit breaker where there is high temperature, the use of such additional mechanism or arrangement would cause damage to the contacts or to the parts that are in contact with it. Thus, the disclosed invention overcomes the disadvantage by providing an additional component from which such an actuation can be taken.
Since the basic principle behind this invention is the two moving points for the spring, the disclosed arrangement can take several other forms in which case also the points are moving but using a different method or arrangement like using gears, cams, belts, chains etc. instead of pivoting between moving contact and lock lever. One such arrangement is shown in fig 9. Gear profile is provided on both moving contact and lock lever instead of pivoting as in previous cases. Moving contact and lock lever are arranged such that the gear profiles mesh with each other so that lock lever rotates when moving contact repels open due to fault conditions. The energy storage in these inventions has been in an extension spring. However, other types of spring can also be used like compression, torsion, leaf etc.
ADVANTAGES OF THE INVENTION
1. High velocity of moving contact after toggling resulting in faster cut-off of fault current increasing the current limiting capability of the circuit breaker.

2.. Greater degree of flexibility in controlling the toggling angle which can be used in controlling the threshold current after which toggling should occur.
3. Higher spring deflection results in more storage of energy and efficient use of the spring capability.
4. Actuation to circuit breaker tripping system reduces the overall tripping time of the breaker giving a higher degree of protection to the downstream equipments.
5. Actuation can also be used for true contact position indication on the outside of breaker.
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 moving contact, pin, gear, cam, belt, chain, spring, lock lever and driveshaft as stated do not limit the scope of the present invention. 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. A high speed contact locking mechanism for use in circuit breakers, said mechanism
comprising:
drive shaft means; movable contact means; plurality of lock member means; plurality of spring means; plurality of pin means; slot means;
wherein said movable contact means having a predetermined degree of freedom being pivoted by said pin means to said drive shaft means,
wherein said lock member means being co-pivoted with said movable contact means and having a predetermined degree of freedom for its movement along said slot means, said lock member means being suspended and supported by pin means whereby one of said pin means being journalled in said slot means aiding in the movement of said lock member means ;
wherein said spring means being operatively connected at its one end with said pin means connected to the movable contact means and on its other end with another pin means connected to one end of lock member means
such that movement of said movable contact means co-operatively extends said spring means correspondingly moving the said lock member means whereby said movement of lock member being guided by pin means journalled in the said slot means and whereby said slot means being such that sufficient degree of freedom is provided to said lock member means so as to rotate to a position establishing a predetermined angle with said movable contact means at the same time when there is a fault.
2. Mechanism as claimed in claim 1, wherein said lock member means is adapted to provide actuation to external mechanisms such as circuit breaker protection system or to provide indication on the breaker.
3. Mechanism as claimed in claim I, wherein said pin means is adapted to provide actuation to external mechanisms such as circuit breaker protection system or to provide indication on the breaker.

4. Mechanism as claimed in claim 1, wherein said movable contact means is adapted to provide actuation to external mechanisms such as circuit breaker protection system or to provide indication on the breaker.
5. Mechanism as claimed in claim 1, wherein said spring means being selected from compression springs, torsion springs, leaf springs and the like
6. Mechanism as claimed in claim 1 wherein said lock member means is lock lever.
7. Mechanism as claimed in any of the preceding claims wherein said spring means has plural movable loading points interconnecting said moving contact means and lock lever.
8. Mechanism as claimed in any one of the preceding claims optionally comprising gear means adapted to operatively connect said movable contact means with said lock member means.
9. Mechanism as claimed in any one of the preceding claims further optionally comprising cam means adapted to operatively connect said movable contact means with said lock member means.
10. Mechanism as claimed in any one of the preceding claims further optionally comprising belt means adapted to operatively connect said movable contact means with said lock member means.
11. Mechanism as claimed in any one of the preceding claims further optionally comprising chain means adapted to operatively connect said movable contact means with said lock member means.
12. A high speed contact locking mechanism for circuit breaker as herein substantially described and illustrated with the accompanying drawings.