Title of Invention	BREAKING DEVICE FOR A MOLDED CASE CIRCUIT BREAKER
Abstract	A molded case circuit breaker comprising a pair of fixed contacts arranged in a case, a rotary moving contact rotating about a shaft between an open and closed position of the circuit breaker, a plurality of pairs of springs arranged in a housing of the rotary moving contact, wherein the torque due to the force exerted by the springs on the rotary moving contact reduces as the rotary moving contact moves away from the fixed contact, is provided. The torque reduces to zero and after that becomes negative, i.e., the torque acts in the opposite direction. As the torque acts in the opposite direction, the rotary moving contact is not able to return to the home position after repulsion unless it is reset. The repulsive force is able to overcome the spring force as the torque reduces as the contacts move away from each other.

Title of Invention

BREAKING DEVICE FOR A MOLDED CASE CIRCUIT BREAKER

Abstract

A molded case circuit breaker comprising a pair of fixed contacts arranged in a case, a rotary moving contact rotating about a shaft between an open and closed position of the circuit breaker, a plurality of pairs of springs arranged in a housing of the rotary moving contact, wherein the torque due to the force exerted by the springs on the rotary moving contact reduces as the rotary moving contact moves away from the fixed contact, is provided. The torque reduces to zero and after that becomes negative, i.e., the torque acts in the opposite direction. As the torque acts in the opposite direction, the rotary moving contact is not able to return to the home position after repulsion unless it is reset. The repulsive force is able to overcome the spring force as the torque reduces as the contacts move away from each other.

Full Text	BREAKING DEVICE FOR A MOLDED CASE CIRCUIT BREAKER Field of the invention [0001] The present invention relates to molded case circuit breakers (MCCB) and more particularly to breaking devices in low voltage molded case double-break rotary circuit breaker. Prior Art [0002] Conventional molded case low-voltage circuit breaker comprising a rotary moving contact and a pair of fixed contacts cooperating with the rotary moving contact have been described in US Patent Number 5313180 (hereinafter referred to as patent 1) and 4910485 (herein after referred to as patent2). The current limiting effect by a circuit breaker of the kind referred to depends on the speed of opening of the contacts. Regardless of the operating mechanism, speed of opening depends on the intensity of the electro-dynamic repelling forces and on the weight of the moving contact. To limit the duration and the intensity of short circuit currents, a circuit breaker must separate its contacts within the shortest possible time. [0003] Generally, springs are used in molded case circuit breakers to overcome the magnetic repulsion forces generated by a reverse electrical current loop formed between the contact arms. In case of molded case low-voltage circuit breaker described in patent 1 and patent2, the contact pressure force due to the springs exists even after the rotary moving contact disconnects from the fixed contacts during a short circuit. Further, force due to the springs keeps on increasing as the rotary moving contact moves away from the fixed contact. The electro-dynamic repulsion force reduces as the contacts move away from each other. However, as the contacts become separated when the circuit blows open due to occurrence of opposing electro-dynamic repulsion fields between the rotary moving contact and the fixed contact, it is desired that the force due to the springs must be overcome by the electro-dynamic repulsion force. [0004] In patentl, after repelling fully if the moving contact is released, it will come to the home position, whereas in patent2, the moving contact is locked. The moving contact should not return to the home position after repulsion unless it is reset. Also, it is desirable that the current limiting circuit breakers are able to produce higher braking capacity with efficient arc quenching to ensure longer life. [0005] In the light of foregoing discussion, there is a need for a molded case circuit breaker with a breaking device which overcomes the force due to the springs and does not allow the moving contact to return to the home position after repulsion unless it is reset. Further, the current limiting circuit breaker should be able to produce higher braking capacity with efficient arc quenching in order to ensure a longer life. SUMMARY OF THE INVENTION [0006] An objective of the invention is to provide a molded case circuit breaker with a breaking device, which overcomes the force due to the springs. [0007] Another objective of the invention is to provide a molded case circuit breaker with a breaking device, which does not allow the moving contact to return to the home position after repulsion unless it is reset. [0008] Yet another objective of the invention is to provide a molded case circuit breaker, which produces higher braking capacity with efficient arc quenching in order to ensure a longer life. [0009] Still yet another objective of the invention is to provide a molded case circuit breaker which eliminates the use of a locking device for the moving contact. [0010] Accordingly, the present invention provides a molded case circuit breaker comprising a pair of fixed contacts arranged in a case, a rotary moving contact rotating about a shaft between an open and closed position of the circuit breaker, a plurality of pairs of springs arranged in a housing of the rotary moving contact, wherein the torque due to the force exerted by the springs on the rotary moving contact reduces as the rotary moving contact moves away from the fixed contact. The torque due to the springs reduces as the rotary moving contact moves away from the fixed contact until it becomes zero and after that the torque becomes negative, i.e., the torque acts in the opposite direction. As the torque acts in the opposite direction, the rotary moving contact is not able to return to the home position after repulsion unless it is reset. [0011] The present invention, therefore, provides a molded case circuit breaker with a breaking device where the repulsive force is able to overcome the spring force as the torque due to the springs on the rotary moving contact reduces as the contacts move away from each other. BRIEF DESCRIPTION OF THE DRAWINGS [0012] 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, [0013] FIG, 1 shows a low voltage molded case circuit breaker, in accordance with an embodiment of the invention. [0014] FIG. 2A represents the low voltage molded case circuit breaker in a closed position, in accordance with an embodiment of the invention. [0015] FIG. 2B represents the low voltage molded case circuit breaker in a partly open position, in accordance with an embodiment of the invention. [0016] FIG. 2C represents the low voltage molded case circuit breaker in an open position, in accordance with an embodiment. [0017] FIG. 3 is an isometric view of the low voltage molded case circuit breaker, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF INVENTION [0018] Various embodiments of the present invention provide a molded case circuit breaker with a breaking device where the electro-dynamic repulsive force overcomes the spring force as the torque due to the springs' force on the rotary moving contact reduces as the contacts move away from each other. [0019] FIG. 1 shows a Molded Case Circuit Breaker (MCCB) 100, in accordance with an embodiment of the invention. MCCB 100 includes a pair of fixed contacts 102a and 102b; a rotary moving contact 104; a shaft 106; a case 108; two pairs of springs 110a and 110b, and 110c and 1 lOd; arc chutes 112a and 112b; slot motors 114a and 114b; and a housing 116. Rotary moving contact 104 rotates about the shaft 106 between an open (shown in FIG. 2C) and a closed position (shown in FIG. 2A) of MCCB 100. Shaft 106 is mounted on case 108. Case 108 also houses arc chutes 112a and 112b, and slot motors 114a and 114b. Springs 110 are arranged in housing 116. Housing 116 includes a rotating bar section 118. [0020] In accordance with an embodiment of the invention, shaft 106 consists of two symmetrical halves, which are riveted together to form a single piece. Slot motors 116 provide an easier path for the repulsive flux produced and the electro-dynamic repelling force. Arc chutes 112 cool the arc, and magnetic blowout coils deflect the arc into arc chutes 112. The magnetic field produced by the blowout coils force the electric arc to lengthen and move away from the contact buttons towards the arc chute. FIG, 1 also shows an input fixed conductor 120a and an output fixed conductor 120b. [0021] In the closed position of MCCB 100 (shown in FIG. 2A), the current input at any moment through input fixed conductor 120a, closed moving conductor (rotary moving contact 104 in closed position as depicted by FIG. 2A), and output fixed conductor 120b forms a closed loop. The current flowing through the fixed conductors and the moving conductors are of opposite polarity, which produces a repelling force. The current movement in fixed contacts 102 and rotary moving contact 104 is shaped to form a looped trajectory to generate electro-dynamic repelling forces. Whenever this repelling force goes higher than the contact pressure, rotary moving contact 104 starts opening. Rotary moving contact 104 has the freedom of rotation about shaft 106 in the opening direction. [0022] In accordance with an embodiment of the invention, at one end spring 110a is pinned to rotary moving contact 104 at a point away from the fulcrum and at the other end spring 110a is fixed to rotating bar section 118. Similarly, springs 110c, 110b, and 1 lOd are fixed at one end to rotating bar section 118 and pinned at the other end on rotary moving contact 104. Springs 110 are compressive springs which exert force on rotary moving contact 104 and provide the contact pressure force. In an embodiment, springs 110 are arranged appreciably symmetrically and may be initially compressed to generate a predetermined contact pressure force. [0023] It may be apparent to a person skilled in the art, that only a part of the compressive spring force due to each springs 110 is available as the contact pressure force. The force due to springs 110 can be resolved in to two components in the plane of axes of springs and rotary moving contact 104: one along the axis of rotary moving contact 104 and the other perpendicular to the axis of rotary moving contact 104. The components perpendicular to the axis of rotary moving contact 104 provides the contact pressure force or the torque. [0024] Referring to FIGs 2A, 2B, and 2C, it can be seen as rotary moving contact 104 moves away from fixed contacts 102, the component of force perpendicular to the axis of rotary moving contact 104 and therefore the torque due to springs 110 on rotary moving contact 104 decreases. The torque keeps on decreasing as rotary moving contact 104 moves from the position depicted by FIG. 2A to that depicted by FIG. 2B. The torque becomes zero in the position depicted by FIG. 2B. As rotary moving contact 104 moves further away from the position depicted by FIG. 2B to that depicted by FIG, 2C, the torque becomes negative (acts in the opposite direction) and increases in magnitude. [0025] FIG. 3 shows an isometric view of the molded case circuit breaker, in accordance with an embodiment of the invention. [0026] Thus, the braking device of the molded case circuit breaker of the present invention enables reduction in the spring force as the contacts move away and therefore enables the electro-dynamic repulsive force to over come the spring force during short circuiting. Further, as the torque becomes negative and acts in the opposite direction, the rotary moving contact is not allowed to return to the home position due to the spring force unless the moving contact is reset.. As a result, the need of locking means to hold the moving contact in the open position is eliminated. [0027] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. We claim: 1. A low voltage molded case circuit breaker comprising: a. a pair of fixed contacts, the pair of fixed contacts being arranged in a case; b. a rotary moving contact, the rotary moving contact being capable of rotating about a shaft, the rotation being between an open and a closed position of the circuit breaker, the shaft being mounted on the case; and c. a plurality of pairs of springs, the plurality of pairs of springs being arranged in a housing of the rotary moving contact, each spring exerting force on the rotary moving contact, wherein the torque due to the force exerted decreases as the rotary moving contact moves away from the fixed contact. 2. The low voltage molded case circuit breaker according to claim 1, wherein the rotary moving contact and the fixed are shaped to form a looped trajectory of electric current to generate an electro-dynamic repulsive force; 3. The low voltage molded case circuit breaker according to claim 1 further comprising a plurality of arc chutes. 4. The low voltage molded case circuit breaker according to claim 1 further comprising a plurality of slot motors. 5. The low voltage molded case circuit breaker according to claim 1, wherein the direction of torque changes as the rotary moving contact moves away from the fixed contact. 6. The low voltage molded case circuit breaker according to claim 1, wherein the torque increases as the rotary moving contact moves away from the fixed contact. 7. The low voltage molded case circuit breaker according to claim 1, wherein the torque increases as the rotary moving contact moves away from the fixed contact after the torque has reduced to zero. 8. An apparatus substantially as herein above described in the specification with reference to the accompanying drawing.

Full Text

BREAKING DEVICE FOR A MOLDED CASE CIRCUIT BREAKER
Field of the invention
[0001] The present invention relates to molded case circuit breakers (MCCB) and more particularly to breaking devices in low voltage molded case double-break rotary circuit breaker.
Prior Art [0002] Conventional molded case low-voltage circuit breaker comprising a rotary moving contact and a pair of fixed contacts cooperating with the rotary moving contact have been described in US Patent Number 5313180 (hereinafter referred to as patent 1) and 4910485 (herein after referred to as patent2). The current limiting effect by a circuit breaker of the kind referred to depends on the speed of opening of the contacts. Regardless of the operating mechanism, speed of opening depends on the intensity of the electro-dynamic repelling forces and on the weight of the moving contact. To limit the duration and the intensity of short circuit currents, a circuit breaker must separate its contacts within the shortest possible time.
[0003] Generally, springs are used in molded case circuit breakers to overcome the magnetic repulsion forces generated by a reverse electrical current loop formed between the contact arms. In case of molded case low-voltage circuit breaker described in patent 1 and patent2, the contact pressure force due to the springs exists even after the rotary moving contact disconnects from the fixed contacts during a short circuit. Further, force due to the springs keeps on increasing as the rotary moving contact moves away from the fixed contact. The electro-dynamic repulsion force reduces as the contacts move away from each other. However, as the contacts become separated when the circuit blows open due to occurrence of opposing electro-dynamic repulsion fields between the rotary moving contact and

the fixed contact, it is desired that the force due to the springs must be overcome by the electro-dynamic repulsion force.
[0004] In patentl, after repelling fully if the moving contact is released, it will come to the home position, whereas in patent2, the moving contact is locked. The moving contact should not return to the home position after repulsion unless it is reset. Also, it is desirable that the current limiting circuit breakers are able to produce higher braking capacity with efficient arc quenching to ensure longer life. [0005] In the light of foregoing discussion, there is a need for a molded case circuit breaker with a breaking device which overcomes the force due to the springs and does not allow the moving contact to return to the home position after repulsion unless it is reset. Further, the current limiting circuit breaker should be able to produce higher braking capacity with efficient arc quenching in order to ensure a longer life.
SUMMARY OF THE INVENTION [0006] An objective of the invention is to provide a molded case circuit breaker with a breaking device, which overcomes the force due to the springs. [0007] Another objective of the invention is to provide a molded case circuit breaker with a breaking device, which does not allow the moving contact to return to the home position after repulsion unless it is reset.
[0008] Yet another objective of the invention is to provide a molded case circuit breaker, which produces higher braking capacity with efficient arc quenching in order to ensure a longer life.
[0009] Still yet another objective of the invention is to provide a molded case circuit breaker which eliminates the use of a locking device for the moving contact. [0010] Accordingly, the present invention provides a molded case circuit breaker comprising a pair of fixed contacts arranged in a case, a rotary moving contact rotating about a shaft between an open and closed position of the circuit breaker, a plurality of pairs of springs arranged in a housing of the rotary moving contact, wherein the torque due to the force exerted by the springs on the rotary moving contact reduces as the rotary moving contact moves away from the fixed contact. The torque due to the springs reduces as the rotary moving contact moves away

from the fixed contact until it becomes zero and after that the torque becomes negative, i.e., the torque acts in the opposite direction. As the torque acts in the opposite direction, the rotary moving contact is not able to return to the home position after repulsion unless it is reset.
[0011] The present invention, therefore, provides a molded case circuit breaker with a breaking device where the repulsive force is able to overcome the spring force as the torque due to the springs on the rotary moving contact reduces as the contacts move away from each other.
BRIEF DESCRIPTION OF THE DRAWINGS [0012] 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, [0013] FIG, 1 shows a low voltage molded case circuit breaker, in accordance with an embodiment of the invention.
[0014] FIG. 2A represents the low voltage molded case circuit breaker in a closed position, in accordance with an embodiment of the invention. [0015] FIG. 2B represents the low voltage molded case circuit breaker in a partly open position, in accordance with an embodiment of the invention. [0016] FIG. 2C represents the low voltage molded case circuit breaker in an open position, in accordance with an embodiment.
[0017] FIG. 3 is an isometric view of the low voltage molded case circuit breaker, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF INVENTION [0018] Various embodiments of the present invention provide a molded case circuit breaker with a breaking device where the electro-dynamic repulsive force overcomes the spring force as the torque due to the springs' force on the rotary moving contact reduces as the contacts move away from each other.

[0019] FIG. 1 shows a Molded Case Circuit Breaker (MCCB) 100, in accordance with an embodiment of the invention. MCCB 100 includes a pair of fixed contacts 102a and 102b; a rotary moving contact 104; a shaft 106; a case 108; two pairs of springs 110a and 110b, and 110c and 1 lOd; arc chutes 112a and 112b; slot motors 114a and 114b; and a housing 116. Rotary moving contact 104 rotates about the shaft 106 between an open (shown in FIG. 2C) and a closed position (shown in FIG. 2A) of MCCB 100. Shaft 106 is mounted on case 108. Case 108 also houses arc chutes 112a and 112b, and slot motors 114a and 114b. Springs 110 are arranged in housing 116. Housing 116 includes a rotating bar section 118. [0020] In accordance with an embodiment of the invention, shaft 106 consists of two symmetrical halves, which are riveted together to form a single piece. Slot motors 116 provide an easier path for the repulsive flux produced and the electro-dynamic repelling force. Arc chutes 112 cool the arc, and magnetic blowout coils deflect the arc into arc chutes 112. The magnetic field produced by the blowout coils force the electric arc to lengthen and move away from the contact buttons towards the arc chute. FIG, 1 also shows an input fixed conductor 120a and an output fixed conductor 120b.
[0021] In the closed position of MCCB 100 (shown in FIG. 2A), the current input at any moment through input fixed conductor 120a, closed moving conductor (rotary moving contact 104 in closed position as depicted by FIG. 2A), and output fixed conductor 120b forms a closed loop. The current flowing through the fixed conductors and the moving conductors are of opposite polarity, which produces a repelling force. The current movement in fixed contacts 102 and rotary moving contact 104 is shaped to form a looped trajectory to generate electro-dynamic repelling forces. Whenever this repelling force goes higher than the contact pressure, rotary moving contact 104 starts opening. Rotary moving contact 104 has the freedom of rotation about shaft 106 in the opening direction. [0022] In accordance with an embodiment of the invention, at one end spring 110a is pinned to rotary moving contact 104 at a point away from the fulcrum and at the other end spring 110a is fixed to rotating bar section 118. Similarly, springs 110c, 110b, and 1 lOd are fixed at one end to rotating bar section 118 and pinned at the

other end on rotary moving contact 104. Springs 110 are compressive springs which exert force on rotary moving contact 104 and provide the contact pressure force. In an embodiment, springs 110 are arranged appreciably symmetrically and may be initially compressed to generate a predetermined contact pressure force. [0023] It may be apparent to a person skilled in the art, that only a part of the compressive spring force due to each springs 110 is available as the contact pressure force. The force due to springs 110 can be resolved in to two components in the plane of axes of springs and rotary moving contact 104: one along the axis of rotary moving contact 104 and the other perpendicular to the axis of rotary moving contact 104. The components perpendicular to the axis of rotary moving contact 104 provides the contact pressure force or the torque. [0024] Referring to FIGs 2A, 2B, and 2C, it can be seen as rotary moving contact 104 moves away from fixed contacts 102, the component of force perpendicular to the axis of rotary moving contact 104 and therefore the torque due to springs 110 on rotary moving contact 104 decreases. The torque keeps on decreasing as rotary moving contact 104 moves from the position depicted by FIG. 2A to that depicted by FIG. 2B. The torque becomes zero in the position depicted by FIG. 2B. As rotary moving contact 104 moves further away from the position depicted by FIG. 2B to that depicted by FIG, 2C, the torque becomes negative (acts in the opposite direction) and increases in magnitude.
[0025] FIG. 3 shows an isometric view of the molded case circuit breaker, in accordance with an embodiment of the invention.
[0026] Thus, the braking device of the molded case circuit breaker of the present invention enables reduction in the spring force as the contacts move away and therefore enables the electro-dynamic repulsive force to over come the spring force during short circuiting. Further, as the torque becomes negative and acts in the opposite direction, the rotary moving contact is not allowed to return to the home position due to the spring force unless the moving contact is reset.. As a result, the need of locking means to hold the moving contact in the open position is eliminated.

[0027] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

We claim:
1. A low voltage molded case circuit breaker comprising:
a. a pair of fixed contacts, the pair of fixed contacts being arranged in
a case;
b. a rotary moving contact, the rotary moving contact being capable of
rotating about a shaft, the rotation being between an open and a
closed position of the circuit breaker, the shaft being mounted on
the case; and
c. a plurality of pairs of springs, the plurality of pairs of springs being
arranged in a housing of the rotary moving contact, each spring
exerting force on the rotary moving contact, wherein the torque due
to the force exerted decreases as the rotary moving contact moves
away from the fixed contact.
2. The low voltage molded case circuit breaker according to claim 1, wherein the rotary moving contact and the fixed are shaped to form a looped trajectory of electric current to generate an electro-dynamic repulsive force;
3. The low voltage molded case circuit breaker according to claim 1 further comprising a plurality of arc chutes.
4. The low voltage molded case circuit breaker according to claim 1 further comprising a plurality of slot motors.
5. The low voltage molded case circuit breaker according to claim 1, wherein the direction of torque changes as the rotary moving contact moves away from the fixed contact.
6. The low voltage molded case circuit breaker according to claim 1, wherein the torque increases as the rotary moving contact moves away from the fixed contact.
7. The low voltage molded case circuit breaker according to claim 1, wherein the torque increases as the rotary moving contact moves away from the fixed contact after the torque has reduced to zero.

8. An apparatus substantially as herein above described in the specification with reference to the accompanying drawing.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=5+qxMwjYGscnOqubLWZgXg==&loc=egcICQiyoj82NGgGrC5ChA==

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Patent Number

279814

Indian Patent Application Number

524/CHE/2008

PG Journal Number

05/2017

Publication Date

03-Feb-2017

Grant Date

31-Jan-2017

Date of Filing

03-Mar-2008

Name of Patentee

LARSEN & TOUBRO LIMITED

Applicant Address

KIADB INDUSTRIAL AREA HEBBAL-HOOTAGALLI MYSORE 570 018

Inventors:

#	Inventor's Name	Inventor's Address
1	Saminathan Ramasamy	KIADB Industrial Area, HebbalHootagalli, Mysore-570 018, Karnataka, India

PCT International Classification Number

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA