FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
Flip-flop Contact locking mechanism with isolated spring
2. APPLICANT(S)
(a) NAME : Larsen and Toubro Ltd.
(b) NATIONALITY: Indian
(c)ADDRESS : L&T House, Ballard Estate, Mumbai-400 001, India.
3. PREAMBLE TO THE DESCRITION
PROVISIONAL COMPLETE
The following specification describes The following specification particularly describes the
invention invention and the manner in which it is to be performed
4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble -"I/We claim" on separate page)
6. DATE AND SIGNATURE (to be given on the last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on the separate page)
Note:
* Repeat boxes in case of more than one entry
*To be signed by the app!icant(s)or the authorized registered patent agent
*Name of the applicant should be given in full, family name in the beginning
*Complete address of the applicant should be given stating with postal index no. / code, state and
country
*Strike out the column which is/are not applicable

Flip-flop Contact locking mechanism with isolated spring
Field of the invention
The invention generally relates to switching device, capable of making, carrying and breaking currents under normal circuit conditions. More particularly the invention relates to contact locking system using springs in switching devices such as circuit breaker.
Background of the invention
A circuit breaker is a mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short circuit (Short circuit is an accidental or intentional connection, by a relatively low resistance or impedance, of two or more points in a circuit which are normally at different voltages).
The main function of any electrical switching apparatus is to carry the rated current. Therefore the current carrying capacity of any circuit breaker is so important that if the unit fails to carry the rated current it will damage itself as well as to the electrical equipment to which it is protecting.
Circuit breakers have three 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 and Trip position in which the contacts are tripped open.
These circuit breakers or 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.

When a circuit breaker is in ON condition and a short circuit fault condition arises, high amount of fault current flows through the circuit and in response to this the circuit breaker tries to move the separable contacts to open position after sensing the fault condition through short circuit sensing mechanism (such as magnetic arrangement). The time taken from a fault condition initiation and the fault current being interrupted by circuit breaker determines the let through energy / arc energy passed by the circuit breaker to the downstream equipments. A circuit breaker is said to be more efficient when the let through energy is minimal.
Let through energy of circuit breaker depends on many 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 definite time before giving a trip open signal to the contacts thus increasing the let through energy.
Short circuit conditions involves high amount of fault current levels which induces high repulsive forces between suitably arranged current carrying contacts. Thus if the contacts can be locked in the repelled open position, the let through energy can be reduced substantially. This improves life of the equipments and systems connected downstream and greatly reduce the hazardous conditions which can damage the downstream equipments.
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, i.e. when the separable contacts are in closed condition.
In traditional circuit breakers tension springs are used to achieve contact locking. As seen in the figure 1 and figure 2, the springs are exposed to the arcing products.

US 5633483, describes a circuit breaker is provided having a stationary contact, a movable contact and a blade which has a first end and a second end. The movable contact is secured to the first end of the blade. The blade is rotatable about a pin between a BLOWN OPEN position and a CLOSED position, wherein the movable contact is separated from the stationary contact when the blade is in the BLOWN OPEN position and the movable contact engages the stationary contact when the blade is in the CLOSED position. The blade further has a protrusion portion extending from its second end. The circuit breaker further includes a catcher rotatably coupled to a pivot pin and having a nose portion for engagement with the blade protrusion portion. A spring is mounted about the pivot pin and engages the catcher for biasing the catcher towards the blade whereby the nose portion rests against the protrusion portion of the blade when the blade is in the CLOSED position and the nose portion overlaps the protrusion portion when the blade is in the BLOWN OPEN position thereby holding the blade in the BLOWN OPEN position.
US5874699, describes a molded case circuit breaker has a moving conductor assembly which includes a modular carrier assembly incorporating a plurality of spring biased contact cam members each of which engages contact pressure lobes on a pair of contact arm laminations to provide contact pressure. In response to the magnetic repulsion forces generated by a short circuit, the springs compress allowing the cam members to pivot and side step the contact pressure lobes so that the contact arm blows-open with little resistance. The cam members and springs are preassembled in a transverse channel in the carrier body and laterally retained in place by side plates for easier pivotal attachment of the contact arm laminations to the lobes on the side plates. The side plate lobes raise the contact arm relative to the mass of the carrier to reduce eddy current heating and provide a positive off indication for welded contacts by restricting movement of lower toggle links of the operating mechanism which are coplanar with the side plates. A modular crossbar

includes molded bearings engaged by or made integral with hexagonal metal shaft sections which extend into hex openings in the carrier bodies of adjacent poles.
US7217895, describes a contact assembly for a circuit breaker includes a fixed contact, a movable contact, and a movable contact arm. The movable contact arm includes a first end carrying the movable contact, a second end, and a pivot portion proximate the second end. A moving arm portion extends from the first end toward the pivot portion. The moving arm portion has a width, an upper edge, a lower edge, and a height defined by the distance between the upper edge and the lower edge. In response to a trip condition, the movable contact separates from the fixed contact and the movable contact arm pivots open at an angular opening velocity. The height of the moving arm portion of the movable contact arm is at least four times the width of the moving arm portion, thus minimizing the moment-of-inertia of the movable contact arm, and increasing the angular opening velocity.
US5844455, describes a current-limiting apparatus for a circuit breaker which makes it possible to effectively protect an electric load element by quickly blocking an electric flow path when an excessive current flows due to a ground, shortage, etc. at an electric flow path and preventing a re-formatian of an electric flow path after the electric flow path is blocked. The apparatus includes a guide pin passing through the second pin hole and being extended from both side surfaces of the movable contact member, a holder, a portion of which support both ends of the movable contact member rotation center pin, for rotatably supporting the movable contact member, a current-limiting latch having a curved guide surface formed on one outer circumferential surface of the same on which the guide pin slides, a support groove formed on another outer circumferential surface of the same, and a pin hole for supporting the holder, a rotation center pin inserted into the pin hole of the current-limiting latch, both ends of which rotation center pin are inserted into portions of

the holder, and a contact spring, both ends of which are supported by the support groove of the current-limiting latch and the support surface of the holder, for generating a variable force which prevents the movable contact member from being rotated.
US4539538, describes a molded case circuit breaker includes a movable upper electrical contact having a base portion with a slot formed therein for releasably receiving a portion of an elongated spring biased locking pin disposed in a rotatable cross bar of an operating mechanism of the circuit breaker. The locking pin is biased in the slot by a pair of tension springs secured to the cross bar, enabling the upper electrical contact to move in unison with the cross bar. Upon the occurrence of a high level short circuit or fault current of sufficient magnitude, the pin is displaced from the slot enabling the independent rotational movement of the upper contact arm. During such movement, an elongated leaf spring is downwardly deflected and then released by the base portion. Subsequently, the upper electrical contact is prevented from contacting the lower electrical contact by the engagement of the leaf spring with the base portion. A subsequent trip operation of the operating mechanism removes the latching feature of the leaf spring.
In traditional devices, during fault clearance the arcing products may fall on the spring which deteriorates the spring. The spring then will lose its properties. Sometimes the arcing product will weld the turns of the spring making it useless for the product performance. These springs are also exposed to the heat generated during arc interruption. This heat will in turn change the load value of the spring may lead to reduced contact pressure which will eventually lead to thermal runaway.
It is desirable to make the contact spring as immune as possible to the heat generation within arcing chamber. It is also very important to achieve optimum contact force in the ON condition to keep the potential drop at the contact buttons to

the minimum. These and other limitations and needs of the conventional mechanisms necessitate an improved contact locking mechanism. Such a locking mechanism has been disclosed here which overcomes the limitations over and above the improvements and flexibility provided additionally.
Object of the invention
An object of the invention is to provide contact locking mechanism with spring isolated from arcing products with an inbuilt feature to flip-flop without having any complex component.
Another object of the present invention is to provide higher velocity of moving contact after toggling resulting in faster cut-off of fault current and increasing the current limiting capability of the circuit breaker.
Yet another object of the present invention is to maintain the consistency in the contact force throughout the life of the contact locking mechanism
Summary of the invention
Accordingly the invention provides a contact locking mechanism with spring isolated from arcing products and having an inbuilt flip-flop mechanism, the contact locking mechanism having,
A drive shaft;
An upper contact, the upper contact is pivoted to the said drive shaft by pivot pin and a braid block brazed to the said upper contact;
A compression spring, the said compression spring placed inside the spring holder on one end and other end is engaged to the spring connector through washer
At least one connecting link, the connecting link is connected to the said upper contact on one end by pivot pin and on other end to the said spring connector.

Description of drawings
Figure 1 shows three dimensional view of the spring locking mechanism of the prior art
Figure 2 shows three dimensional view of the spring locking mechanism of the prior art
Figure 3 shows the orthographic view (Top view) of the contact locking mechanism of the present invention
Figure 4 shows the front view in wireframe with contacts in ON condition of the contact locking mechanism
Figure 5 shows the front view in wireframe of the present contact locking mechanism with spring isolated from the arcing and inbuilt flip-flop mechanism with contacts in repelled condition
Figure 6 shows the Isometric view of the present contact locking mechanism with spring isolated from the arcing and inbuilt flip-flop mechanism
Figure 7 shows the Exploded Isometric view of the present contact locking mechanism with spring isolated from the arcing and inbuilt flip-flop mechanism
Detail description of the invention
Various embodiment of the present invention provide an actuation mechanism for coupling a plurality of electrical devices, the mechanism comprising a shaft for each electrical device, the shaft having a variable cross-section, the shaft adapted to reversibly engage with an internal operating system of the electrical devices; and a seat on a casing of each electrical device, the seat providing an access to the internal operating system of the electrical devices.
The contact locking mechanism with spring isolated form arcing products with an inbuilt feature to flip-flop without having any complex component with cam profile

for flip-flop is provided. One of the advantage of the present invention is to provide better velocity of contacts separation after toggling during fault clearance by circuit breaker reducing let through energy and at the same time it enhances the life of circuit breaker against short circuit fault clearance.
It consists of a rotating member of the circuit breaker mechanism, called as drive-shaft to which the upper contact is pivoted by means of pivot pin. Rotation of this driveshaft will cause upper moving contacts to come in contact with the lower contacts and thereby it completes the electrical circuit. Braid block is brazed to upper contact. One end of compression spring is placed inside the spring holder and the other end is engaged to spring connector through washer. This spring connector holds two links together. These links are connected to upper contact and drive-shaft through pivot pin.
For multiple poles, multiple such assemblies will be used side by side using a common connecting driveshaft across all the poles.
The working of the invention is shown in Fig 2 & 3 with different positions. This is the position in which the moving contact cannot go further down or up since it stops on the driveshaft.
When the fault occurs, there is an upward force on the Upper contact thereby it will rotate about the pivot pin. This movement of the contact will cause the sliding movement of spring connector in forward direction (i.e. towards contact button) while compressing the compression spring. As soon as the toggling point is crossed, the compression spring will release its energy, thus the spring which is compressed to its maximum deflection reaches an equilibrium state by increasing its length and releasing energy in the process to move the moving contact and it will rotate the moving contact in upward direction till it stops over mechanism. If the repulsion force on the upper contact is less than that offered by compression spring, then the contact will not get locked and the moving contact will again come to it ON position.

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.
In the prior methods, extension springs were used to achieve contact pressure and contact locking. In present method, compression spring is used to achieve contact pressure and contact locking. This spring is isolated form arcing products with an inbuilt feature to flip-flop without having any complex component with cam profile for flip-flop. This invention is incorporated with the better velocity of contacts separation after toggling during fault clearance by circuit breaker reducing let through energy and at the same time it enhances the life of circuit breaker against short circuit fault clearance.
Since moving contact moves after toggling without repulsive force, there is faster energy release by the spring after toggling, resulting in higher velocity of moving contact. This results in faster cut-off of fault current increasing the current limiting capability of the circuit breaker.
Toggling position is that instant at which the pivot pins, links and spring holder 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 gets locked will be

lesser. This will reduce the let through energy of the mechanism to the downstream equipments.
However it will reduce the contact force between the moving and fixed contacts in the breaker due to lesser angle between compression spring and moving contact with respect to toggling axis. 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.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We claim:
1) A flip-flop contact locking mechanism with isolated spring in electrical device
comprising;
A drive shaft;
An upper contact, the upper contact is pivoted to the said drive shaft by pivot pin and a braid block brazed to the said upper contact;
A spring connector, the spring connector having plurality of ends for making mechanical connections;
A compression spring, one end of the said compression spring is engaged inside the spring holder and other end is engaged to the said spring connector through washer;
At least one connecting link, one end of the said connecting link is connected to the said upper contact by pivot pin and other end of the connecting link is connected to the said spring connector.
2) A flip-flop contact locking mechanism with isolated spring of the claim 1, wherein, in fault condition, the upper contact rotates about the pivot pin, causing the sliding movement of spring connector towards contact button and compressing the compression spring and after the toggling point is crossed, releasing the compression spring to move the contact till it stops over mechanism.
3) A flip-flop contact locking mechanism with isolated spring of the claim 2,
Wherein, in the toggling position, pivot pins, connecting links and spring holder are in same line.
4) A flip-flop contact locking mechanism with isolated spring of the claim 1,
wherein, the cover or top portion of the circuit breaker provides downward force to
the upper contact after the upper contact reaches cover or top portion and the
upper contact is unlocked after it crosses the toggle point.

5) A flip-flop contact locking mechanism with isolated spring of the claim 1, wherein, the spring is isolated from the arcing products.
6) A flip-flop contact locking mechanism with isolated spring of the claim 1,
wherein, if the repulsion force on the upper contact is less than that offered by compression spring, then the contact will not get locked and the moving contact will again come to ON position.
7) A flip-flop contact locking mechanism with isolated spring of the claim 1,
as described in any of the accompanying drawings.