FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
A VARIABLE CONTACT LOCKING ARRANGEMENT FOR CIRCUIT BREAKERS
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra,
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to electrical switching
apparatus and particularly to current limiting circuit breakers. The present invention more particularly relates to multiple locking arrangements for contact arm position/rotational locking in current limiting circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] Circuit breakers are the mechanical switching devices 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 conditions, A circuit breaker basically consists of a pair of separable contacts and an interrupting medium. The function of the contacts is to conduct the electrical current when the breaker is closed and withstand the arcs while interrupting. Generally, the electrical contacts have a stationary part and a moving part. By bringing the moving contact to touch the stationary contact, electric current flows and the breaker is closed. By driving the moving contact away from the stationary contact, the electric arc develops and by quenching it the current stops flowing and the breaker is open.
[0003] A circuit breaker typically comprises a spring loaded contact system to carry, make and break the current under normal and abnormal conditions involving very high over-currents. 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 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 a serious damage to the circuit breaker and the installation.
[0004] A current iimiting circuit breaker should clear the fault as fast as possible so that the "let through energy" permitted to the connected downstream devices/equipment of the installation can be minimized thereby inhibiting the high thermal stresses associated with the "let through" current. Simultaneously, a current limiting circuit breaker should also limit the fault current to a value as low as possible so that the connected downstream devices are not subjected to high electro-dynamic stresses set up by the high magnitude fault current.
[0005] Hence there is a need to provide an improved contact system to
prevent the contact from bounce back and to limit the fault current in order to achieve a low value of let through energy. Also there exists a need for an arrangement which causes the moving contact to remain in a locked open position until the breaker is reset.
[0006] There is a need for an arrangement to provide contact pressure
under normal current carrying conditions and also lock the moving contact arm at any one of the multiple positions/rotations subsequent to its repulsion upon exceeding a threshold value of current, depending on breaker requirement for downstream breakers so as to achieve lower let through energy as well as reliable coordination with upstream breakers. [0007] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

C) OBJECT OF THE INVENTION
[0008] The primary object of the present invention is to develop an
improved contact locking arrangement for multiple positions/rotational locking of a moving contact arm in current limiting circuit breakers.
[0009] Another object of the present invention is to develop an
improved contact locking arrangement to prevent a contact bounce.
[0010] Yet another object of the present invention is to develop an
improved contact locking arrangement to limit a fault current,
[0011] Yet another object of the present invention is to develop a
contact locking arrangement to reduce a let through energy in case of fault.
[0012] Yet another object of the present invention is to develop an improved contact locking arrangement to lock the moving contact arm at any of the multiple predetermined positions/rotations.
[0013] Yet another object of the present invention is to develop an
improved contact locking arrangement with minimal components resulting in ease of assembly.
[0014] Yet another object of present invention is develop an improved
contact locking arrangement to achieve coordination between an upstream side circuit breaker and a downstream side circuit breaker wherein the same circuit breaker can work both as upstream side circuit breaker or downstream side circuit breaker to achieve coordination with its counterparts.

[0015] These and other objects and advantages of the present invention
will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0016] The above mentioned shortcomings, disadvantages and
problems are addressed herein and which will be understood by reading and studying the following specification.
[0017] The various embodiments of the present invention provide an improved contact locking arrangement to lock the arms of the moving contact at any of the predetermined positions. The contact locking arrangement for circuit breakers comprising an assembly holder, a moving contact coupled to the assembly holder, a contact pin to connect the moving contact to the assembly holder, a bracket arranged on the assembly holder and a spring mechanism arranged between the bracket and the contact pin. The spring mechanism generates a pressure to lock the moving contact arm at a predetermined locking position during fault conditions.
[0018] The arrangement provides a contact pressure under normal
current carrying conditions to lock the moving contact arm at any of the multiple predetermined positions subsequent to its repulsion upon exceeding a threshold value of current. The lock-out positions can be varied depending on a breaker requirement for the downstream side breakers so as to achieve a lower let through energy as well as reliable coordination with the upstream side breakers.

[0019] The present invention also provides an arrangement to achieve
coordination between an upstream side breaker and a downstream side breaker wherein the same circuit breaker is able to work both as upstream side circuit breaker and downstream side circuit breaker to achieve coordination with other counterparts.
[0020] The arrangement includes an assembly holder which holds at
least one arm of the moving contact. The moving contact is engaged through the opening on the peripheral surface of the assembly holder by aligning a hole on the contact arm with a hole on the assembly holder. The location of the contact arm is completed through the insertion of the center pin through the aligned holes. A floating contact pin is inserted through the hole in the contact structure. The holder is fixed on the surface of the assembly holder with the fixing screws. The bracket is fixed in either of its two positions X or Y by a screw and the guiding surface of the assembly holder. The spring is secured by the bracket pin and the floating contact pin.
[0021] The spring held between the bracket and the floating contact
pin generates a force F on one side of an imaginary plane. The imaginary plane, herein after, is referred to as the locking position plane. The locking position plane is a plane defined by the center portion of the center pin, contact pin and the spring assembled portion of the bracket pin tracing a single straight line. The force F generates a torque on the moving contact 1 about its axis of the rotation and also imparts the required contact force Fl to the contact.
[0022] The electrodynamics force F2 exerted on the moving contact 1 consequent to the flow of high fault currents through the current limiting contact tends to cause the moving contact to rotate against the contact force Fl. When the force F2 exceeds the threshold value, the contact starts rotating

about the center pin. If the force F3 is in excess of the opposing component of force F corresponding to the position of the spring in the locking plane, the moving contact is compelled by the net force to cross the locking position. The moving contact is locked out after crossing the locking position as both the floating contact pin and the extension spring will cross the locking position plane and exert a force F2 on the moving contact. The forces F2 exerted on the moving contact is suffice to hold the moving contact in the OFF position and precludes any possibility of a bounce back to the ON position.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0024] FIG. 1 illustrates a front view of the assembly holder
employing locking arrangement of moving contact in ON condition according to one embodiment of the present invention.
[0025] FIG. 2 illustrates the front view of the assembly holder
employing locking arrangement of moving contact in OFF condition according to one embodiment of the present invention.
[0026] FIG. 3 illustrates the assembly holder locking arrangement of moving contact in the locked condition according to one embodiment of the present invention.

[0027] FIG. 4 illustrates an isometric view of the moving contact locking assembly according to one embodiment of the present invention.
[0028] FIG. 5 illustrates the assembly holder employing locking arrangement of the moving contact in ON condition corresponding to another locking position according to one embodiment of the present invention.
[0029] FIG. 6 illustrates the assembly holder employing locking arrangement of moving contact in OFF condition corresponding to another locking position according to one embodiment of the present invention.
[0030] FIG. 7 illustrates the assembly holder employing locking
arrangement of moving contact in LOCKED condition corresponding to another locking position according to one embodiment of the present invention.
[0031] FIG. 8 illustrates an exploded view of the assembly holder employing locking arrangement of moving contact in ON condition according to one embodiment of the present invention.
[0032] FIG. 9 illustrates the double break concept of the assembly holder according to one embodiment of the present invention.
[0033] FIG. 10 illustrates the assembly holder employing locking arrangement of moving contact for higher efficiency according to one embodiment of the present invention.
[0034] FIG. 11 illustrates the perspective view of the assembly holder according to one embodiment of the present invention..

[0035] FIG. 12 illustrates an isometric view of the assembly holder for
adjusting the brackets in the circuit breaker according to one embodiment of the present invention.
[0036] Although the specific features of the present invention are
shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0037] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0038] The various embodiments of the present invention provide a variable contact locking arrangement for circuit breakers. The present invention discloses an arrangement to provide a contact pressure under normal current carrying conditions and also to lock the moving contact arm at any of the multiple predetermined positions/rotations subsequent to the repulsion of the arm from the normal position upon exceeding a threshold value of current. The lock-out positions can be varied depending on the circuit breaker requirement for downstream side breakers so as to achieve a

lower let through energy as well as a reliable coordination with the upstream side breakers. This invention is an arrangement to achieve a coordination between an upstream side circuit breaker and a downstream side circuit breaker wherein the same breaker can work both as upstream or downstream breaker to achieve coordination with different counterparts.
[0039] FIG. 1 illustrates a front view of the assembly holder employing a locking arrangement of a moving contact in ON condition corresponding to a locking position X according to one embodiment of the present invention. FIG. 2 illustrates the assembly holder employing locking arrangement of moving contact in an OFF condition according to one embodiment of the present invention. Referring to FIG. 1 and FIG. 2, an assembly hoider 5, which carries a minimum of one contact arm i, forms a rotary actuating structure. The contact arm is alternately called as a pole or a moving member or a moving contact, The moving contact 1 is engaged through an opening on the peripheral surface of the assembly holder by aligning a hole B on the moving contact 1 with a hole A inside the assembly holder, as shown in the FIG. 8. The location of the moving contact 1 is completed by the insertion of the center pin 9 through the aligned holes A and B. This provides the moving contact 1 a freedom to rotate within a predetermined locus about the center pin 9. A floating contact pin 8 is inserted through the hole C in the contact structure. The bracket 2 is structured on the surface of the assembly holder so that the center of the bracket 2 is aligned with the center of the contact arm 1. The holder 3 is fixed on the surface of the assembly holder 5 with fixing screws 7 such that it restricts the motion of the bracket 2 beyond a certain rotation. The bracket 2 is fixed in either of the two positions X or Y by screwl and the guiding surface of the assembly holder 5. The spring 4 is secured by the bracket pin 10 and the floating contact pin 8.

[0040] Referring to FIG. 1, the spring 4 extended between the bracket
2 and the floating contact pin 8, generates force F on one side of an imaginary plane. The imaginary plane is referred as the locking position plane, wherein the locking position plane is defined by the centers of the center pin 9, the contact pin 8 and the spring assembled portion of the bracket pin 10 tracing a single straight line. The force F generates a torque on the moving contact 1 about its axis of the rotation and also imparts the required contact force Fl to the contact. The cumulative locations of the contact pin 8, than bracket pin 10 and the spring 4 force is adjusted so as to give equal contact pressure during ON position at hoth the locking positions X and Y.
[004 i] FfG. 1 shows the unique arrangements having different lockout positions. Typically these arrangements are evolved through positional variation of bracket pin 10 via bracket handle 11 of integrated bracket 2. FIG. 1 shows the arrangement for X-position locking. The locking position can be varied to Y by moving the bracket 2 via peripheral of assembly holder 5 with bracket handle 11.
[0042] FIG. 3 illustrates the assembly holder locking arrangement of moving contact in the locked condition according to one embodiment of the present invention. The electrodynamics force F2 exerted on the moving contact 1 consequent to the flow of high fault currents through the current limiting contact causes the moving contact to rotate against the contact force Fl. When the force F2 exceeds the threshold value, the contact starts rotating about the center pin 9. If the force F3 is in excess of the opposing component of force F corresponding to the position of the spring 4 in the locking plane, the moving contact 1 is compelled by the net force to cross the locking position. The moving contact 1 is locked out after crossing the locking position as both the floating contact pin 8 and the extension spring 4 will cross the locking position plane and exert a force F2 on the moving contact 1

which suffices to hold the moving contact in the OFF position and precludes any possibility of a bounce back to the ON position.
[0043] FIG. 4 illustrates the perspective view of the moving contact
locking assembly comprising assembly holder 5, which carries a minimum of one contact arm 1. The moving contact 1 is engaged through the opening on the peripheral surface of the assembly holder by aligning hole B on the contact arm with hole A on the inside the assembly holder, as shown in the FIG. 8. The location of the contact arm is completed through insertion of the center pin 9 through the aligned holes A and B thereby providing the contact arm 1 a freedom of rotation within a predetermined locus about the center pin 9. A floating contact pin 8 is inserted through the hole C in the contact structure. The bracket 2 is structured on the surface of the assembly holder so that the center of the bracket aligns itself with the center of the contact arm 1. The holder 3 is fixed on the surface of the assembly holder 5 with fixing screws 7 such that it restricts the motion of the bracket beyond a certain rotation. The bracket is fixed in either of its two positions X or Y by screwl and the guiding surface of the assembly holder 5. The assembly holder profile D is visible in the FIG. 4. The spring 4 is secured by the bracket pin 10 and the floating contact pin 8.
[0044] FIG. 5 illustrates the assembly holder employing locking arrangement of moving contact in ON condition corresponding to a locking position Y according to one embodiment of the present invention. FIG. 6 illustrates the assembly holder employing locking arrangement of moving contact in OFF condition corresponding to a locking position Y according to one embodiment of the present invention. FIG. 7 illustrates the assembly holder employing locking arrangement of moving contact in LOCKED condition corresponding to a locking position Y according to one embodiment of the present invention. Referring to FIG. 5, the spring 4 held between the bracket 2 and the floating contact pin 8 generates a force F on

one side of an imaginary plane, herein after referred to as the locking position plane. The locking position plane is defined by the centers of the center pin 9, contact pin 8 and the spring assembled portion of the bracket pin 10 tracing a single straight line. The force F generates a torque on the moving contact 1 about its axis of rotation and also imparts the required contact force Fl to the contact. The cumulative locations of the contact pin 8, the bracket pin 10 and the spring 4 force can be adjusted to give equal contact pressure during ON position at the locking position Y. Referring to FIG. 5, the assembly holder employing locking arrangement of moving contact is in OFF condition corresponding to a locking position Y. Referring to FIG. 7, the assembly holder employing locking arrangement of moving contact is in LOCKED condition corresponding to a locking position Y.
[0045] The locking position of the contact 1 is reached when the center of contact pin 8, the center of the center pin 9 and the center of the bracket pin 10 align themselves. In this position the contact spring endures maximum extension. The locking position is a transitory position as the contact toggles at the position due to its momentum caused by the force F2. The force F2 generated is due to electrodynamics repulsion between the contacts which in turn depends on the current. The energy required to cross the locking position depends on electrodynamics force F3. By changing the locking position of the contact arm, the energy required to toggle the contact can be varied. The methodology is applied for achieving the coordination where in the same breaker is used to coordinate with is counterparts depending on the specific needs.
[0046] FIG. 8 illustrates the exploded perspective view of the assembly
holder employing a locking arrangement of moving contact in ON condition according to one embodiment of the present invention. The assembly comprising an assembly holder 5, which carries a minimum of one moving

contact. The moving contact 1 includes at least two moving contact arms. The moving contact 1 is engaged through the opening on the peripheral surface of the assembly holder by aligning hole B on the contact arm with hole A on the inside the assembly holder, as shown in the FIG. 8. The location of the moving contact is completed by the insertion of the center pin 9 through the aligned holes A and B thereby providing the contact arm 1 freedom to rotate within a predetermined locus about the center pin 9. A floating contact pin 8 is inserted through the hole C in the contact structure. The bracket 2 is structured on the surface of the assembly holder so that the center of the bracket aligns itself with the center of the contact arm 1. The holder 3 is fixed on the surface of the assembly holder 5 with fixing screws 7 such that it restricts the motion of the bracket beyond a certain rotation. The bracket is fixed in either of the two positions X or Y by screwl and the guiding surface of the assembly holder 5. The spring 4 is secured by the bracket pin 10 and the floating contact pin 8.
[0047] FIG. 9 illustrates a double break concept of the assembly holder
according to one embodiment of the present invention. The assembly is applied for double break contacts as shown in FIG. 9. According to the figure 9, only two locking positions of the moving contacts is taken into consideration. The same methodology can also be extended to different unique locking positions. The bracket is positioned between the assembly holder profile and the screwl 6. The bracket is not restricted to its shape provided the purpose is achieved. The springs used here is extension springs. Alternatively other kind of springs such as compression springs, conical springs or the like can also be used provided the purpose of using it remains same.
[0048] FIG. 10 illustrates the assembly holder employing locking
arrangement of the moving contact for higher efficiency according to one

embodiment of the present invention. Here, the axis of rotation of the assembly holder and the axis of rotation of the bracket is the same. The same arrangement is realized for getting higher spring efficiency by making the different axis of rotation of assembly holder 5 and the holder 3 as shown in FIG. 10. This is so arranged that lower value springs are used to generate same contact pressure as in FIG. 1. The rest of the arrangement is same as that in FIG. 1.
[0049] FIG. 12 illustrates an isometric view of the assembly holder for
adjusting the bracket according to one embodiment of the present invention. Referring to FIG. 12, the bracket handle 11 is moved for getting unique positions X and Y of bracket 2 by loosening the screwl6, fitted in the holder 3. The position stability of the bracket 2 is achieved by tightening the screwl6. The bracket 2 is located between the profile on the periphery of the assembly holder 5 and the screwl 6 such that the motion of bracket 2 is hindered during the operation of the contact arml.
G) ADVANTAGES OF THE INVENTION
[0050] The present methodology can be applied for achieving the coordination where in the same circuit breaker can be used to coordinate with the counterparts depending on the specific needs.
[0051] A variable contact locking arrangement of the present invention does not require any sensing unit to sense the fault for providing coordination. The methodology is made intelligent such that the moving contact itself senses the fault and trips depending on the energy. The energy utilization can be varied by varying the locking position. Further, no extra module is required for co-coordinating between circuit breakers. Also there is no need for additional components, which results in ease of assembly.

[0052] With the present invention, the energy characteristic of the
circuit breaker can be varied over a range. The cumulative locations of the contact pin, bracket pin and spring force is adjusted to give equal contact pressure during ON position for several locking positions according to the requirements.
[0053] Although the invention is described with various specific
embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0054] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. A contact locking arrangement for circuit breakers, the arrangement
comprising:
an assembly holder;
a moving contact coupled to the assembly holder;
a contact pin to connect the moving contact to the assembly holder;
a bracket arranged on the assembly holder; and
a spring mechanism arranged between the bracket and the contact pin;
Wherein the spring mechanism generates a pressure to lock the moving
contact arm at any of the predetermined locking positions during fault
conditions.
2. The contact locking arrangement according to claim 1, wherein the predetermined position includes at least one of an ON position, OFF position and locked position of the moving contact.
3. The contact locking arrangement according to claim 1, further the moving contact is engaged through an opening on the surface of the assembly holder by aligning a hole on the moving contact with a

corresponding hole on the assembly holder and fastening using a center pin.
4. The contact locking arrangement according to claim 1, wherein the bracket is arranged on a surface of the assembly holder such that the center of the bracket aligns with the center of the moving contact.
5. The contact locking arrangement according to claim 1, further comprising a bracket pin to attach the bracket on the assembly holder.
6. The contact locking arrangement according to claim 1, wherein a locking position of the moving contact is achieved when the contact pin, the bracket pin, and the center pin aligns in a single straight line.
7. The contact locking arrangement according to claim 1, wherein the pressure exerted by the spring generates a torque on the moving contact about an axis of rotation.
8. The contact locking arrangement according to claim 1, wherein the position of the contact pin, the bracket pin and the spring is adjusted to provide equal contact pressure at all the predetermined locking positions during an ON condition.

9, The contact locking arrangement according to claim 1, wherein the
locking position is varied depending on a circuit breaker requirement for
the downstream side circuit breakers to achieve a lower let through
energy and coordination with the upstream side circuit breakers so that a
circuit breaker functions like both as an upstream side circuit breaker
and as a downstream side circuit breaker to coordinate with the
counterparts depending on the specific needs.
10. The contact locking arrangement according to claim 6, wherein a shift in
position of the contact pin and the spring from the straight line exerts an
additional force on the moving contact so as to hold the moving contact
in an OFF position.