FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF INVENTION
A drive mechanism for a switching device
INVENTORS
Massimiliano Lissandrin, an Italian National, of Enercom s.r.l, Via Chioggia 2 A, 35142 Padova, Italy and Srinivas Gopa, an Indian National, of Crompton Greaves Limited, Technology Cell, Switch Gear Division, A3 MIDC, Ambad, Nashik 422010, Maharashtra, India
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality ; Indian Company
Address : CG House, Dr. Annie Besant Road, Worli, Mumbai -400025, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to a drive mechanism for a switching device.
This invention relates to, in particular, a drive mechanism for a switching device which is used to protect and to switch on/off high voltage electric transmission or distribution systems.
BACKGROUND OF INVENTION
Switching devices are used in electric transmission or distribution systems to protect ie isolate faulted sections under fault conditions and to switch on/off ie interrupt the flow of current under normal conditions. Switching on/off of the transmission or distribution systems is carried out by a set of fixed and moving contacts in the switching device. The moving contacts are connected to a drive mechanism comprising a charging mechanism housed in an enclosure located below the contacts of the switching device. The charging mechanism includes an electric motor, bevel gears, pawls and ratchet wheel. Instead of the bevel gears, pawls and ratchet wheel the charging mechanism may comprise a chain and sprocket arrangement or a belt drive. The drive mechanism further comprises a closing spring and tripping spring connected to the moving contacts of the switching device and mounted in the enclosure and adapted to be releasably latched to a closing spring latch assembly and a tripping spring latch assembly, respectively through closing spring connecting rod, tripping spring connecting rod and mechanical linkages comprising a main lever, crank and cam and their respective shafts. The closing and tripping springs are compressed or charged by the charging mechanism through the mechanical linkages. Hydraulic shock absorbers is/are associated with the
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mechanical linkages for absorbing the impact of the release or expansion of the closing and tripping springs. The size of the closing and tripping springs increases with increase in the rating of the switching devices. Therefore, the closing and tripping springs of the drive mechanism for switching devices of high voltages are heavy and bulky. Heavy torque generating electric motors are required for compression of heavy and bulky springs. During compression of heavy and bulky springs, there are also chances of the mechanical linkages breaking as the high torque generated by the electric motor is transmitted to the springs through the mechanical linkages thereby reducing the reliability and life of the drive mechanism. The size of the enclosure for the drive mechanism also increases owing to the increase in the size of the drive mechanism. Heavy torque generating motors also draw high electric currents _for their operation and require frequent maintenance thereby increasing the running cost. The torque generated by the motor is transmitted to the springs through the mechanical bevel gears, pawl and ratchet wheel. In such a configuration substantial losses in the torque (force) during transmission from the motor to the springs is inevitable. Therefore, the entire torque (force) developed by the electric motor is not directly applied to the springs and is not available for compression of the springs.
US 4968861 describes a hydraulic drive mechanism comprising a spring energy accumulator connected to a fluid pressure operated motor for charging the spring energy accumulator through a flow regulator means. The drive mechanism also comprises transmission means for converting released energy of the spring energy accumulator into operation of the circuit breaker. The fluid operated motor comprises a high pressure motor connection, low pressure motor connection and a fluid supply
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means comprising a fluid pressure accumulator having an energy capacity corresponding to the energy requirement for charging the spring energy accumulator at least one time. The fluid operated motor uses pressurized gas which is delivered into the fluid pressure accumulator through a check valve. The fluid pressure accumulator is connected to the high pressure motor connection. The switching mechanism also comprises a control valve for controlling the flow of fluid from the fluid pressure accumulator to the motor. The control valve is opened by control means operated by the spring energy accumulator. The fluid operated motor is operatively connected to the spring energy accumulator through gear means. The switching mechanism also comprises a pump for delivering fluid from a low pressure source into the fluid pressure accumulator. The hydraulic switching mechanism described in US 4968861 is complex and complicated in construction and operation. It makes use of a hydraulic pressure accumulator which is expensive. As very high pressures are involved, the switching mechanism requires periodic maintenance.
OBJECTS OF INVENTION
An object of the invention is to provide a drive mechanism for a switching device
especially high voltage switching device, which eliminates the electric motor
operated charging mechanism, consumes reduced electricity for its operation, is
simple in construction and operation and is compact requiring reduced space for
occupation.
Another object of the invention is to provide a drive mechanism for a switching device especially high voltage switching device, which minimizes chances of
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breakage of the mechanical linkages during operation of the tripping and closing springs thereby increasing the reliability and life of the drive mechanism.
Another object of the invention is to provide a drive mechanism for a switching device especially high voltage switching device, which is very efficient in closing and opening of the contacts of the switching device and ensures proper working of the switching device.
Another object of the invention is to provide a drive mechanism for a switching device especially high voltage switching device, which is economical.
Another object of the invention is to provide a drive mechanism for a switching device especially high voltage switching device, which does not require frequent maintenance.
DETAILED DESCRIPTION OF INVENTION
According to the invention, there is provided a drive mechanism for a switching device, the drive mechanism comprising a closing spring and a tripping spring disposed in an enclosure with their one ends pressed against a retainer plate extending across the enclosure; a closing spring connecting rod and a tripping spring connecting rod passing through openings in the retainer plate and through the closing spring and tripping spring, respectively; one end of the closing spring connecting rod being releasably latched to a closing spring latch assembly through a crank and a cam mounted on a cam shaft and one end of the tripping spring connecting rod being releasably latched to a tripping spring latch assembly through a main lever mounted
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on a main lever shaft; the cam being operatively in contact with the main lever and a hydraulic charging and shock absorbing means connected to the other end of the closing spring connecting rod, the hydraulic charging and shock absorbing means being operated by the control unit of the switching device .
The following is a detailed description of the invention with reference to the accompanying drawings, in which:
Fig 1 is an exploded view of a conventional electric motor operated drive mechanism for a high voltage switching device;
Fig 2 is an exploded view of the drive mechanism according to an embodiment of the invention; and
Fig 3 is an enlarged crosssection at X in Fig 2.
The drive mechanism 1A as illustrated in Fig 1 of the accompanying drawings comprises a closing spring 2a and tripping spring 2b positioned in an enclosure ( not shown) with their one ends pressed against a retainer plate 3 extending across the enclosure. The enclosure is located below the contacts (not shown) of a switching device 3a. 4 and 5 are a closing spring connecting rod and tripping spring connecting rod passing through openings 6a, 6b in the retainer plate and through the closing spring and tripping spring and retainer members 6c and 6d fixed at the other ends of the closing spring and tripping spring respectively. The closing spring connecting rod and tripping spring connecting rod are fixed to the one ends of the respective
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retainer members 6c and 6d. The drive mechanism also comprises a charging mechanism including a electric motor 7 whose shaft 7a is coupled to one end of an eccentric shaft 10 through bevel gears 9a and 9b. 10a is a set of two pawls mounted at the other end of the eccentric shaft. The pawls are in mesh with a ratchet wheel 11 mounted on a cam shaft 12 and is provided with a roller 1 la supported thereon. The electric motor is also connected to the control unit 13 of the switching device. The other end of the closing spring connecting rod is connected to a crank 14 mounted on the cam shaft. 15 is a closing spring latch assembly located in the proximity of the ratchet wheel. The latch assembly 15 is connected to a solenoid 17 which in turn is connected to the control unit 13 of the switching device. The latch assembly 15 comprises an arm 15a adapted to latch onto the roller on the ratchet wheel. 18 is a main lever comprising three limbs marked 19a, 19b and 19c. The main lever is mounted on the main lever shaft 18d with the tripping spring connecting rod connected to limb 19a of the main lever. The limb 19a of the main lever is provided with a roller 20. 2lis a tripping spring latch assembly located in the proximity of the main lever. The latch assembly 21 is connected to a solenoid 22 which in turn is connected to the control unit of the switching device. The latch assembly 21 comprises an arm 21a adapted to latch on to the roller 20 on the limb 19a of the main lever. 23 is a cam mounted on the cam shaft and held operatively in contact with the main lever. A hydraulic shock absorber 24 is connected to the limb 19c of the main lever. The moving contacts (not shown) of the switching device 3a are connected to the limb 19c of the main lever through a connector 25a.
Both the closing spring 2a and tripping spring 2b are initially in the released and expanded condition and the contacts (not shown) of the switching device are open ie
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the switching device is in the non-operative condition. On receiving a signal from the control unit 13, the electric motor 7 operates and rotates the cam 23 in the anticlockwise direction through rotation of the bevel gears 9a, 9b, eccentric shaft 10, pawls 10a the ratchet wheel 11 and cam shaft 12. The crank 14 rotates with the cam shaft in the anti clockwise direction. The rotation of the cam in the anti clockwise direction does not, however, cause rotation of the main lever 18 due to the cam positioning on the main lever. During rotation of the crank in the anti clockwise direction, the closing spring connecting rod 4 is moved in the direction of the crank causing compression of the closing spring 2a against the retainer plate. When the closing spring is fully compressed or charged, the arm 15a of the closing spring latch assembly 15 latches onto the roller 1 la on the ratchet wheel and stops the further rotation of the ratchet wheel in the anticlockwise direction and thereby further rotation of the cam and the crank and the closing spring is held compressed against the retainer plate. When the contacts of the switching device are to be closed and current is to be allowed to flow through the switching device, the control unit 13 of the switching device energizes the solenoid 17 of the closing spring latch assembly. As a result, the closing spring latch assembly disengages the arm 15a thereof from the roller 1 la on the ratchet wheel and the ratchet wheel is free to rotate in the anti clockwise direction. The crank 14 is also free to rotate with the ratchet wheel and cam shaft 12 in the anti clockwise direction. This causes release and expansion of the compressed closing spring 2a. The closing spring connecting rod moves in the opposite direction into its original position. During rotation of the cam shaft in the anti clockwise direction, the cam rotates in the anti clockwise direction against the main lever thereby causing rotation of the main lever in the clockwise direction. During rotation of the main lever in the clockwise direction, the
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moving contacts (not shown) of the switching device connected to the limb 19c of the main lever move downwards and close against the fixed contacts (not shown) of the switching device thereby allowing the current to flow through the switching device. Simultaneously, the tripping spring connecting rod 5 connected to the limb 19a of the main lever moves up and causes compression of the tripping spring 2b. When the tripping spring is fully compressed or charged, the arm 21a of the tripping spring latch assembly 21 latches onto the roller 20 in the limb 19a of the main lever and stops the further rotation of the main lever in the anti clockwise direction and the tripping spring is held compressed against the retainer plate. When the contacts of the switching device are to be opened and current flow through the switching device is to be interrupted, the control unit 13 energizes the solenoid 22 connected to the tripping spring latch assembly. The tripping spring latch assembly disengages its arm 21a from the roller 20 on the main lever and the main lever is free to rotate. This causes release and expansion of the compressed tripping spring. The main lever rotates in the anti clock wise direction and the moving contacts of the switching device connected to the limb 19c of the main lever are moved upwards thereby opening the contacts and interrupting the current flow through the switching device. The closing spring gets compressed as explained above and is ready to close the contacts of the switching device to allow current to flow through the switching device when the control unit gives a signal to the electric motor. The impact of the force of release or expansion of both the closing and tripping springs is absorbed by the hydraulic cylinder 24.
The drive mechanism IB of the invention as illustrated in Fig 2 of the accompanying drawings comprises a closing spring 2a and a tripping spring 2b
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which are disposed in an enclosure ( not shown) with their one ends pressed against a retainer plate 3 extending across the enclosure. The enclosure is located below the contacts (not shown) of a switching device 3a. 4 and 5 are a closing spring connecting rod and tripping spring connecting rod passing through openings 6a, 6b in the retainer plate and through the closing spring and tripping spring and retainer members 6c and 6d fixed at the other ends of the closing spring and tripping spring, respectively. 25 is a hydraulic cylinder with pump whose piston rod 26 is coupled to the one end of the closing spring connecting rod by coupling 27 which comprises a cup shaped element 28 whose closed end is fixed to the piston rod. The coupling also comprises an open ended cylindrical element 29 whose one end is disposed against the cup shaped element. The retainer member 6c at the other end of the closing spring connecting rod abuts against the other end of the cylindrical element 29. The other end of the closing spring connecting rod extends into the cylindrical element through an aperture 30 in the retainer member 6c and is provided with a flange 29c. 32 is a compression spring disposed over the piston rod and located between the hydraulic cylinder and the closed end of the cup shaped element. 33 is a compression spring located in the cup shaped element and the open ended cylindrical element between the bottom of the cup shaped element and the flange 29c. The hydraulic cylinder is operated by the control circuit 35 of the switching device. The other end of the closing spring connecting rod is releasably latched to a closing spring latch assembly 15 through a crank 14 and a cam 23 mounted on a camshaft 12. The closing spring latch assembly is located in the proximity of the cam and comprises an arm 15a adapted to releasably latch onto a roller 36 provided on the cam. The latch assembly 15 is also connected to a solenoid 37, which in turn is connected to the control unit 35 of the switching device. The
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tripping spring connecting rod is releasably latched to a tripping spring latch assembly 38 through a main lever 39 comprising limbs 39a, 39b and 39c. 40 is the shaft of the main lever. Limb 39a of the main lever is connected to the tripping spring connecting rod. The tripping spring latch assembly is located in the proximity of the main lever and comprises an arm 42 adapted to latch onto the roller 41 provided on the limb 39c of the main lever. The latch assembly is also connected to a solenoid 43 which in turn is connected to the control unit of the switching device. The cam is operatively in contact with the main lever. The moving contacts (not shown) of the switching device are connected to the limb 39a of the main lever through connector 44.
Both the closing spring and tripping spring are initially in the released and expanded condition and the contacts of the switching device are open ie the switching device is in the non-operative condition. On receiving a signal from the control unit, the hydraulic pump and cylinder operates and the piston rod moves out in the hydraulic cylinder. The closing spring connecting rod 4 moves in the direction of the crank along with the piston rod compressing the closing spring 2a against the retained plate 3. As the closing spring is compressed the spring 33 is also compressed . The outward movement of the piston rod causes spring 32 to expand. The movement of the closing spring connecting rod in the direction of the crank 14 causes the crank 14 to rotate in the clockwise direction. The cam shaft 12 and cam 23 rotate with the crank in the clockwise direction. The rotation of the cam in the clockwise direction does not, however, cause rotation of the main lever 39 in contact with the cam due to the position of the cam on the main lever. When the closing spring is fully compressed or charged, the arm 15a of the closing spring latch assembly latches onto
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the roller 36 on the cam and stops further rotation of the cam in the clockwise direction and thereby the rotation of the cam shaft and the crank. The closing spring is held compressed against the retainer plate. While the closing spring is held compressed against the retainer plate, the spring 33 tends to expand causing the piston rod to travel into the hydraulic cylinder to a preset distance. The spring 32 gets compressed by the movement of the cup shaped element 28. This prevents expansion of the spring 33 and further movement of the piston rod in the hydraulic cylinder beyond this preset limit. When the contacts of the switching device are to be closed ie current is allowed to flow through the switching device, the control unit of the switching device energizes the solenoid 37 of the closing spring latch assembly. The closing spring latch assembly disengages the arm 15a from the roller 36 and the cam 23 is free to rotate. This causes release and expansion of the compressed closing spring. As the closing spring is released and expanded the crank and cam shaft rotates in the clockwise direction. During rotation of the cam shaft in the clockwise direction, the cam rotates in the clockwise direction against the main lever because of the position of the cam on the main lever as shown in continuous lines thereby causing rotation of the main lever in the clockwise direction. During rotation of the main lever in the clockwise direction, the moving contacts of the switching device connected to the limb 39a of the main lever through connector 44 move upwards and close the contacts thereby allowing the current to flow through the switching device. The impact of the release or expansion of the closing spring is absorbed by the piston rod in the hydraulic cylinder and by spring 32 and spring 33 getting compressed. During rotation of the main lever in the clockwise direction, the tripping spring connecting rod connected to the limb 39a of the main lever moves in the direction of the main lever causing compression of the tripping spring 2b. When
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the tripping spring is fully compressed against the retainer plate, the arm 42 of the tripping spring latch assembly latches onto the roller 41 in the main lever and stops the further rotation of the main lever and the tripping spring is held compressed against the retainer plate. When the contacts of the switching device are to be opened ie current flow through the switching device is to be interrupted, the control unit energizes the solenoid 43 connected to the tripping spring latch assembly. The tripping spring latch assembly disengages the arm 42 from the roller 41 on the main lever and the main lever is free to rotate in the anticlockwise direction. This causes release or expansion of the compressed tripping spring. As the tripping spring is released or expanded, the main lever rotates in the anti clockwise direction and the moving contacts connected to the limb 39a of the main lever through the connector are moved down thereby opening the contacts of the switching device and interrupting the current flow through the switching device. The closing tripping spring gets compressed as explained above and is ready to close the contacts of the switching device when the control unit gives a signal to the solenoid 37. The switching device and its details have not been illustrated and described as such are not necessary for understanding the invention.
The drive mechanism of the invention as illustrated in Fig 2 eliminates the charging mechanism comprising bevel gear, ratchet wheel, pawl and high torque generating electric motor. Instead, it employs the hydraulic cylinder to compress / charge the closing spring. The springs associated with the hydraulic cylinder also absorb the impact of expansion or release of the closing spring. The hydraulic piston rod moves linearly to compress the closing spring and the compressive force is directly transmitted to the closing spring. Therefore, losses in the compressive force are
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reduced. Compressive forces required are also reduced. Breakage of mechanical linkages is also eliminated as the compressive force is not transmitted to the closing spring via the mechanical linkages but directly to the closing spring so as to increase the reliability and life of the drive mechanism. The power requirement for the operation of the switching mechanism is also reduced. The drive mechanism of the invention comprises reduced number of components as compared to the conventional drive mechanisms and is, therefore, compact and requires reduced space for its occupation. Because of the linear movement of the compressive force, the drive mechanism of the invention can effectively and efficiently compress or charge the closing spring and tripping spring to ensure proper closing and opening of the contacts of the switching device. Because of the linear movement of the compressive force and reduction of losses in the compressive force, the drive mechanism of the invention can be advantageously used to effectively and efficiently close and open the contacts of even high voltage switching devices comprising heavy and bulky closing and tripping springs. Besides being economical, the drive mechanism of the invention is also simple in construction and easy and convenient to operate.
The invention is basically in the elimination of the charging mechanism comprising high torque generating electric motor, pawl, bevel gear and ratchet wheel and in the compression of the closing spring linearly directly. The construction and configuration of the closing spring latch assembly and tripping spring latch assembly and the respective crank, cam and main lever can vary. Such variations of the invention obvious to those skilled in the art are to be construed and understood to be within the scope of the invention.
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WE CLAIM:
1. A drive mechanism for a switching device, the drive mechanism comprising a closing spring and a tripping spring disposed in an enclosure with their one ends pressed against a retainer plate extending across the enclosure; a closing spring connecting rod and a tripping spring connecting rod passing through openings in the retainer plate and through the closing spring and tripping spring, respectively; one end of the closing spring connecting rod being releasably latched to a closing spring latch assembly through a crank and a cam mounted on a cam shaft and one end of the tripping spring connecting rod being releasably latched to a tripping spring latch assembly through a main lever mounted on a main lever shaft; the cam being operatively in contact with the main lever and a hydraulic charging and shock absorbing means connected to the other end of the closing spring connecting rod, the hydraulic charging and shock absorbing means being operated by the control unit of the switching device .
2. A drive mechanism as claimed in claim 1, wherein the hydraulic charging and shock absorbing means comprises a hydraulic cylinder whose piston rod is connected to the other end of the closing spring connecting rod through a coupling comprising a cup shaped element whose closed end is fixed to the distal end of the piston rod, a first compression spring disposed over the piston rod and located between the hydraulic cylinder and the closed end of the cup shaped element, the coupling further comprising an open ended cylindrical element whose one end is disposed against the cup shaped element, a retainer member provided at the other end of the closing spring being located against the other end of the
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cylindrical element, the other end of the closing spring connecting rod extending into the cylindrical element through an aperture in the retainer member and being provided with a flange and a second compression spring disposed within the cup shaped element and cylindrical element and located between the closed end of the cup shaped element and the flange at the other end of the closing spring connecting rod.
Dated this 28th day of March 2007

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ABSTRACT
A drive mechanism for a switching device. The drive mechanism comprises a closing spring (2a) and a tripping spring (2b) disposed in an enclosure (not shown) with their one ends pressed against a retainer plate (3) extending across the enclosure. A closing spring connecting rod (4) and a tripping spring connecting rod (5) pass through openings (6a, 6b) in the retainer plate and through the closing spring and tripping spring, respectively. One end of the closing spring connecting rod is releasably latched to a closing spring latch assembly (15) through a crank (14) and a cam (23) mounted on a cam shaft (12). One end of the tripping spring connecting rod is releasably latched to a tripping spring latch assembly (38) through a main lever (39) mounted on a main lever shaft (40). The cam is operatively in contact with the main lever. A hydraulic charging and shock absorbing means (25) is connected to the other end of the closing spring connecting rod and is operated by the control unit (35) of the switching device (Fig 2).