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:
CHARGING CAM SPEED CONTROL ARRANGEMENT FOR AIR CIRCUIT BREAKER
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 \S TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to circuit breakers and particularly to control the charging operation and closing of contacts in air circuit breakers. The present invention more particularly relates to provide a charging cam speed control arrangement to control the closing and charging operation of contacts in air circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] The switching mechanism, typically a circuit breaker, includes separable contacts and a common spring operated closing and tripping device. This device includes opening springs which separate the contacts and a pair of closing springs which close the contacts and charge the opening spring. The separable contacts are closed by releasing the energy stored in the closing springs. This can be done manually or remotely through a solenoid.
[0001] The closing spring in these switching devices or circuit breakers is incorporated into an operating mechanism which includes a cam mounted on a cam shaft and coupled to the close spring. The close spring is charged either by a manual charging handle or an electric motor which rotates the cam shaft. In a common arrangement, force stored in the close spring is transmitted to the moveable contact carrier of the switch through a drive cam and drive coupling arrangement. The drive cam is rotated by the close spring. The rotation of the cam by the closing spring results in rotation of the pole shaft, which being connected to the moveable contact carriers in each pole, results in closure of the switch
31 MAR 2009

contacts. When the trip latch is released, the drive roller floats allowing the open spring lo rotate the movable contact carriers to open the switch contacts.
[0004] During closing and charging operation of the contacts in air circuit breaker, the main spring is charged and then it is locked against charging cam and closing latch. For contact closing operation, cam is made free and it rotates freely by main spring initial lorce, The main spring energy is transferred to trip links by follower that closes circuit breaker against pole spring force. After closing of breaker, follower rests on cam and mechanism is ready for nexl charging operation.
[0005] In conventional methods the excess energy of main spring is dissipated in the device. It does not include any mechanism to control cam location after contact closing to locate Ihe cam in correct place. None of the prior art methods available provide a method to control the speed of the rotating cam. More over there is need to control the end position of the cam during discharging of main spring.
[0006] Hence there is a need to develop a method to control the speed of the driving shaft or cam and to control the end position of the cam during discharging of main spring.
C) OBJECTS OF THE INVENTION
[0007] The primary object of the present invention is to provide a charging cam speed control arrangement for air circuit breaker.


[0008] Further object of the present invention is to provide a charging cam speed control arrangement for air circuit breaker to absorb excess energy of cam before resetting for next charging operation.
[0009] Yet another object of the present invention is to provide a charging cam speed control arrangement for air circuit breaker which uses a spring loaded energy absorbing device to control the velocity of cam and to coordinate with velocity of follower.
[0010] Yet another object of the present invention is to provide a charging cam speed control arrangement for air circuit breaker which automatically resets during next charging operation.
[0011] 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.
J>) SUMMARY OF THE INVENTION
(0012] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.


[00131 Various embodiments of the present invention provide a method for controlling the speed of charging cam in air circuit breaker. It comprises of a spring loaded energy absorbing device to control the velocity of cam and to coordinate with velocity of follower. The spring loaded arrangement in the present invention controls the closing and charging operation of air circuit breaker.
|0014| According to one embodiment of the present invention, a cam speed control system in air circuit breaker has a base plate provided with a fulcrum link. An extended arm is provided on the fulcrum link. An extension spring is mounted between the base plate and the fulcrum link. The load on the extension spring is adjusted so that the cam comes to rest at desired position for all values of main spring. The extension spring applies resistive load against the rotation of a charging shaft connected to a cam in the air circuit breaker to control the rotation of the cam, when a follower pin in the air circuit breaker contacts the fulcrum link.
10015] According to one embodiment of the present invention, the spring loaded energy absorbing device controls velocity of cam to coordinate with velocity of follower. Tt consists of base plate fixed to mechanism side plate. A fulcrum link pivoted on base plate and an extended arm. The extension spring is mounted between base plate and the fulcrum link. The side plate ratchet includes a pin which is in same plane as that of arm of fulcrum link. The cam speed is controlled in such a way that, after contact closing, the follower rests on required surface of cam. It allows main spring to discharge fully and
3 1 MAR 2009

ensures that no reverse torque is transferred to cam by follower. It allows follower to positively guide links til] pole closing.
[0016] According to an embodiment of the present invention, when main spring is charged, fulcrum link rests on spacer. When closing command is given and cam is made free trom the follower, charging shaft rotates with the cam in anticlockwise direction due to energy possessed. The ratchet mounted on shaft also rotates and pin comes in contact with fulcrum link arm. The extension spring starts applying load from this point onwards and resistive load acts against rotation of shaft. System reaches at point where energy stored in extension spring matches with energy imparted to cam by rotating follower. At that point, cam comes to rest. The value of load of extension spring is adjusted such that, for all values of main spring and pole spring, the cam comes to rest at required location only. During next charging operation device leaves contact with spacer pin again, reset itself and rests again on spacer.
|0017] According to one embodiment of the present invention, when the main spring is charged, it is locked against charging cam and closing latch. For contact closing operation, cam is made free and it rotates freely by main spring initial force. Main spring energy is also transferred to trip links by follower that closes breaker against pole spring force. After closing of circuit breaker, follower rests on cam and mechanism is ready for next charging operation.
31 MAR 2009

[0018] According lo one embodiment of the present invention, the charging cam speed is controlled by making the follower to rest on the required surface of the cam after closing of the circuit breaker. It allows main spring to discharge fully and no reverse torque is transferred to cam by follower. Method also allows follower to positively guide links till pole closing. This velocity of follower is coordinated with velocity of cam so that follower pin touches cam in just right place where it exerts no force on cam and the mechanism is ready for next charging operation
[0019] The arrangement in the present invention controls the speed of driving shaft or cam and controls end position of the cam during discharging of main spring. It absorbs excess energy of cam before resetting for next charging operation. It automatically resets during next charging operation,
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0020] 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:
[002 l] FIG. 1 shows a front view of the charging cam speed control arrangement for air circuit breaker when main spring is in discharged position according to one embodiment of the present invention.


[0022| FIG. 2 shows a front view of the charging cam speed control arrangement for air circuit breaker with pawl and ratchet mechanism according to one embodiment of the present invention.
[0023] FIG .3 shows a front view of the charging cam speed control arrangement for air circuit breaker when the main spring is in charging position according to one embodiment of the present invention.
[ 0024] FIG. 4 shows a front view of the charging cam speed control arrangement for air circuit breaker when the main spring in compressed state according to one embodiment of the present invention.
[0025] FIG. 5 shows a front view of the charging cam speed control arrangement using a spring loaded mechanism when the main spring is discharged partially according to one embodiment of the present invention,
[0026] Although specific features of the present invention are shown in some drawings and not in others. This is done lor 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
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[0027] 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.
[0028] Various embodiments of the present invention provide a method for controlling the speed of charging cam in air circuit breaker. It comprises of a spring loaded energy absorbing device to control the velocity of cam and to coordinate with velocity of follower. The spring loaded arrangement in the present invention controls the closing and charging operation of air circuit breaker.
[0020] According to one embodiment of the present invention, a cam speed control system in air circuit breaker has a base plate provided with a fulcrum link. An extended arm is provided on the fulcrum link. An extension spring is mounted between the base plate and the fulcrum link. The load on the extension spring is adjusted so that the cam comes to rest at desired position for all values of main spring. The extension spring applies resistive load against the rotation of a charging shaft connected to a cam in the ait-circuit breaker to control the rotation of the cam, when a follower pin in the air circuit breaker contacts the fulcrum link.
3 1 MAR 2009

[0030] According to one embodiment of the present invention, the spring loaded energy absorbing device controls velocity of cam to coordinate with velocity of follower. It consists of base plate fixed to mechanism side plate. A fulcrum link pivoted on base plate and an extended arm. The extension spring is mounted between base plate and the fulcrum link. The side plate ratchet includes a pin which is in same plane as that of arm of fulcrum link. The cam speed is controlled in such as way that, after contact closing, the follower rests on required surface of cam. It allows main spring to discharge fully and ensures that no reverse torque is transferred to cam by follower. Method also allows follower to positively guide links till pole closing.
[0031] According to embodiment of the present invention, when main spring is charged, fulcrum link rests on spacer. When closing command is given and cam is made free from follower, charging shaft rotates with the cam in anticlockwise direction due to energy possessed. The ratchet mounted on shaft also rotates and pin comes in contact with fulcrum link arm. The extension spring starts applying load from this point onwards and resistive load acts against rotation of shaft. System reaches at point where energy stored in extension spring matches with energy stored in cam. At that point, cam comes to rest. The value of load of extension spring is adjusted such that, for all values of main spring and pole spring, the cam comes to rest at required location only. During next charging operation device leaves contact with spacer pin again, reset itself and rests again on spacer.


[0032] According to one embodiment of the present invention, when the main spring is charged, it is locked against charging cam and closing latch. For closing operation, cam is made free and it rotates freely by main spring initial force. Main spring energy is also transferred to trip links by follower that closes breaker against pole spring force. After closing of circuit breaker, follower rests on cam and mechanism is ready for next charging operation.
[0033] According to one embodiment of the present invention, the charging cam speed is controlled by making the follower to rest on the required surface of the cam after closing of the circuit breaker. It allows main spring to discharge fully and no reverse torque is transferred to cam by follower. Method also allows follower to positively guide links till pole closing.
[0034] FIG. I shows a front view of the charging cam speed control arrangement for air circuit breaker when main spring is in discharged position according to one embodiment of the present invention. With respect to figure 1, the main charging spring 101 is rigidly connected between the fixed frame 109 and the follower 104. The charging cam 103 is mounted on the charging shaft 102, The follower 104 is pivoted 105 with respect to the mechanism side plate 108. The follower 104 includes a roller 106 which operates against cam 103. Initially, the follower 104 rests against fixed pin 107 in spring discharged position. As cam 103 is rotated anticlockwise, it pushes roller 106 of follower 104 which causes anticlockwise rotation of follower 104 against its pivot 105. This further causes compression of main spring 101.

|0035| FIG. 2 shows a front view of the charging cam speed control arrangement with pawl and ratchet mechanism in discharged position according to one embodiment of the present invention. Charging shaft 102 includes a pawl 204 and ratchet arrangement 202 to avoid reverse rotation of cam 103 due to main spring force 101. One pawl 204 is fitted on mechanism side plate 108 and other pawl on the charging handle. Both pawl 204 and ratchets 202 are mounted on charging shaft 102.
|0036] FIG .3 shows a front view of the charging cam speed control arrangement when main spring is in charging position according to one embodiment of the present invention. During charging operation the spring mechanism in the air circuit breaker provides energy for closing the electrical contacts. Initially, follower 104 rests against fixed pin 107 in spring discharged position. As cam 103 is rotated anticlockwise, it pushes roller 106 of follower 104 which causes anticlockwise rotation of follower 104 against ils pivot 106. This causes compression of main spring 101. The ratchet 202 and pawl 204 arrangement locks reverse rotation of cam 103. At the end of charging, force of main spring 101 acts on cam 103 through follower 104 which tends to rotate cam 103 in anticlockwise direction. Cam 103 is locked in this position by closing latch & close-D shaft (not shown). Cam 103 holds follower 104 and thus main spring 101 in compressed slate..
[0037] FIG. 4 shows a front view of the charging cam speed control arrangement using a spring loaded mechanism when the main spring is in closed state according to one


embodiment of the present invention. To initiate closing, latch is made free by rotating close-D shaft (not shown), it removes restriction on cam 103. Cam 103 rotates due to force component of main spring 101 continues to rotate further. At this point, there is no contact between cam 103 and follower 105 (Fig 5). Cam 103 velocity depends on inertia of cam 103, main spring 101 energy and friction in joints. As follower 104 is now free from cam 103, it pushes trip links (not shown) to close poles. Follower 104 rotates with high velocity because of stored energy in main spring 101. Links have got toggle position alter which poles are held in closed position. Follower 104 guides toggle links till it crosses toggle position and then rests against fixed pin 107. Velocity of follower 104 depends on main spring energy 101, pole spring energy, inertia of poles, and coefficient of friction in various joints. The velocity of the follower 104 is coordinated with velocity of cam 103 in such as way that follower pin 107 touches cam 103 in just right place where it exerts no force on cam 103 and mechanism is ready for next charging operation.
[0038] FIG .5 shows a front view of the charging cam speed control arrangement using a spring loaded mechanism when the main spring is in closed state according to one embodiment of the present invention. The spring loaded energy absorbing device in the present invention controls the velocity of cam 103 to coordinate with velocity of follower 108. It consists of fixed base plate 401 fixed to mechanism side plate 108. The fulcrum link 402 is pivoted on base plate 401 with an extended arm 402. The fulcrum link is pivoted at point 403. The extension spring 404 is mounted between base plate 401 and fulcrum link 402. The side plate ratchet 202 includes pin 203 in the same plane as that of arm of fulcrum link 402.


|0039] When main spring 101 is charged, fulcrum link 402 rests on the spacer 201. When the contact closing command is given and cam 103 is made free from follower 104, charging shaft 102 rotates with cam 103 in anticlockwise direction due to energy possessed. The ratchet 202 mounted on shaft 102 also rotates and pin 203 comes in contact with fulcrum link arm 402. Extension spring 404 starts applying load from this point onwards and resistive load acts against rotation of shaft 102. The system reaches at point where energy stored in extension spring matches with energy stored in cam 103. At this point, the cam 103 comes to rest. The value of load of extension spring 404 is adjusted such that, for all values of main spring 101 and pole spring, cam 103 comes to rest at required location only. During next charging operation device leaves contact with spacer pin 201 again, reset itself and rests again on spacer 201.
G) ADVANTAGES OF THE INVENTION
[0040] Various embodiments of the present mvention provide a method for controlling the speed of charging cam in air circuit breaker. It comprises of a spring loaded energy absorbing device to control the velocity of cam and to coordinate with velocity of follower. The spring loaded arrangement in the present invention controls the closing and charging operation of air circuit breaker. The charging cam speed is controlled by making the follower to rest on the required surface of the cam after closing of the circuit breaker. It allows main spring to discharge fully and no reverse torque is transferred to cam by follower. Method also allows follower to positively guide links till pole closing.
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CLAIMS
What is claimed:
1. A cam speed control system in air circuit breaker comprising:
a base plate;
a fulcrum link provided on the base plate;
an extended arm provided on the fulcrum link; and
an extension spring mounted between the base plate and the fulcrum link;
wherein the load on the extension spring is adjusted so that the cam comes to rest
at desired position for all values of main spring,
2. The system according to claim 1, wherein the extension spring applies resistive
load against the rotation of a charging shaft connected to a cam in the air circuit
breaker to control the rotation of the cam, when a follower pin in the air circuit
breaker contacts the fulcrum link.

RAKESH PRABHU Patent Agent,
ALMT Legal,
#2, Lavelle Road, Bangalore-560 001
To,
The Controller of Patents, The Patent Office, Mumbai
Dated this the 30th day of March 2009