FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A CONTACT LOCKING ARRANGEMENT FOR A CIRCUIT BREAKER;


LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T
HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA

THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 1


Field of the invention
The present invention relates to current limiting breaker. More particularly to the moving contact position locking in current limiting circuit breakers.
Prior Art
Current limiting circuit interruption devices such as molded case circuit breakers, generally contain a movable contact arranged at one end of a movable contact arm which operates to electrodynamically repel the movable contact arm upon the occurrence of a short circuit overcurrent condition to drive the movable contact away from the fixed contact and interrupts the protected circuit.
A circuit breaker should typically have an arrangement to generate enough contact pressure so that under normal operating conditions (i.e. breaker operated at rated current or the permissible level of overload values), the temperature rise of the current carrying components of the breaker should not exceed the allowable limit set by the relevant product standards whilst simultaneously satisfying the requirements necessitated by the current limiting feature of the circuit breaker..
The circuit breaker is called upon to protect the equipment in an installation in case of over currents arising out of abnormal circuit conditions. A circuit breaker typically comprises a spring loaded contact system to carry, make & break the current under normal and abnormal conditions involving very high over-currents. The circuit breaker is expected to operate to interrupt the fault current rapidly so as to minimize damage to the installations (downstream equipments) resulting from thermal and mechanical stresses.
A typical molded case circuit breaker operates on the current limiting principle where in the over current flowing through the circuit breaker contacts results in electro-dynamic repulsive forces between the stationary and moving contacts. The stationary contact being secured to the base of the molded case,

repulsive forces exerted cause the moving contact to trace a curvilinear locus as the contacts separate. Consequent to this motion of moving contact, incremental resistance is introduced between the stationary and moving contacts and this resistance in turn creates an increasing arc voltage that acts opposite to the system voltage and limits the fault current to quench the arc. The inherent nature of any spring loaded contact system introduces the probability of "contact bounce-back" even after successful opening. This phenomenon, if unchecked, may eventually result in violent re strike of the arc between the contacts and consequently, serious damage to the circuit breaker and the installation.
In the prior art means for controlling the travel of an electrodynamically repulsed movable contact arm is found. Further the attempt to control the operation of an electrodynamically driven movable contact arm is described in prior art which utilizes a spring loaded clip assembly. A cam surface on the movable contact arm cooperates with the spring-clip to prevent the movable contact arm from rebounding back to a closed position. Further in prior art circuit breakers with normal moving contact have been provided with an arrangement to provide protection for electrical system against fault specially overload and short circuit. Prior art circuit breakers have trip mechanism to separate moving contact from fixed contact in case of electrical fault, in such breakers higher 'ON' time leads to higher let through energy. In addition to higher 'ON' time moving contact in prior art circuit breaker has tendency of bouncing back.
Hence there is need for a contact locking arrangement to prevent the contact from bounce back and to limit the fault current in order to achieve a low value of let through energy, a contact locking arrangement is essential. Such an arrangement should cause the moving contact to remain in a "locked open" position till such time that the breaker/mechanism is reset.

OBJECT OF THE INVENTION
An object of invention is to provide a contact locking arrangement for a circuit breaker. More particularly it is the object of the invention to provide a contact arrangement that effectively lock the moving contact.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIGURE 1 shows the contact locking arrangement according to an embodiment of the invention.
FIGURE 2 shows the moving contact according to an embodiment of the invention.
FIGURE 3 shows a drive shaft arrangement according to an embodiment of the invention
FIGURE 4 shows moving contact in ON condition according to an embodiment of the invention.
FIGURE 5 shows a moving contact in LOCKED condition according to an embodiment of the invention.
DETAILED DESCRIPTION OF INVENTION
Various embodiments of the present invention provide a contact locking arrangement for circuit breaker.
Referring to Figure 1 and 2 a contact locking arrangement, according to an embodiment of the invention, includes a drive shaft 2, a moving contact 1 mounted on the drive shaft 2. The moving contact comprises of a front region mounted with a contact button 5, a hinge region 8 and a tail region 10. The hinge region 8 is provided with a hole 8a for inserting a drive shaft pin 4. The hinge region 8

provided with a hole for mounting a guiding pin 7. The guiding pin 7 is mounted at the hinge region 8 of the moving contact and is coupled to a contact spring 9.
Referring to Figure 3, the drive shaft 2 has a pair of drive shaft pin hole 6 provided at the proximal end. A stopper 3 is provided in the groove formed between the pair of drive shaft pin hole 6. Further, the stopper 3 is configured to form a step arrangement having two surfaces SI and S2. The drive shaft 2 is also provided with a slot 10 at the distal end for positioning the guiding pin 7 of the moving contact.
In one embodiment of the invention, the moving contact 1 is assembled with drive shaft 2 by aligning drive shaft pin hole 6 and hole 8a, moving contact 1 is held in this position by inserting drive shaft pin 4 in drive shaft 2. Further, simultaneously contact spring 9 is inserted in guiding pin 7 and is held in position by inserting guiding pin 7 in to the slot 10 of draft shaft 2,
The contact spring 9 generates force F at the dead end of the moving contact 1 which generates torque on the moving contact 1 about the axis of rotation and imparts required contact forces to the contact. The generated force F assists the moving contact 1 to maintain continuity of the electrical circuit until the threshold current limit is exceeded and retains the rotary motion of the moving contact 1.
The locking arrangement during ON position of circuit breaker; when the circuit breaker is ON position, the high electrodynamics force exerted on the moving contact 1 because of the flow of high fault currents through the unique current limiting contact profile tends to cause the moving contact 1 to rotate against the contact force and whenever the electrodynamics force acting on the moving contact exceeds the threshold value, the contact starts rotating about the axis of rotation. The increasing force gradient between the force exerted on moving contact 1 due to current flowing through the contact (electrodynamics forces) and contact spring force acting force acting on moving contact 1 leads to achievement of dead center. At this position the hinge region 8 of moving contact 1 is positioned at surface SI of the stopper 3 provided on the drive shaft 2.
The locking arrangement during LOCKED position of circuit breaker: The increasing force gradient between the force exerted on moving contact 1 due to

current flowing through the contact (electrodynamics forces) and contact spring force acting force acting on moving contact 1 leads to the moving contact 1 cross the dead center. At this instance, there will be rapid transition of angle between the axes of moving contact 1 and guiding pin 7 which makes contact spring 9 ineffective and locks the moving contact 1 at surface S2 of the stopper 3. The contact locking avoids any form of contact bouncing phenomenon during arcing time in arc-chamber assembly, this leads to drastic reduction in let-through energy.
The invention, as described herein and as illustrated by diagrams provide a contact locking arrangement for a circuit breaker.
The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof

WE CLAIM:
1. A contact locking assembly for a circuit breaker comprising of:
a drive shaft,
a moving contact mounted on the drive shaft, a guiding pin coupled to the moving contact, and a contact spring mounted on the guiding pin configured for locking the contact during ON condition of the circuit.
2. A contact locking assembly of claim 1, wherein the drive shaft is provided with a stopper having two distinct surfaces for positioning the moving contact during ON and locked conditions of the circuit breaker.
3. A contact locking assembly of claim 1, wherein the drive shaft is provided with a slot for positioning the guiding pin.
4. A contact locking assembly of claim 1, wherein the contact spring mounted the guiding pin is compressed during locked position of the circuit breaker.
5. A contact locking assembly of claim 1, wherein the contact spring generates force which assists the moving contact to restrains the rotary motion on moving contact.
6. A contact locking assembly of claim 1, wherein the dead center is achieved due to excess threshold value on moving contact through contact and contact spring force.
7. A contact locking assembly of claim 1, wherein the achievement of dead center leads to rapid transition of angle between the axes of moving contact and guiding pin making contact spring ineffective and locks the moving contact..

8. A contact locking assembly of claim 1, wherein the locking of moving contact avoids any form of contact bouncing during arcing time in arcing chamber assembly and lets to reduction in let-through energy.
Dated this 2nd day of January, 2009