Drive mechanism for circuit breaker The present invention generally relates to a drive mechanism suitable for use in electrical switchgear. More specifically, the present invention relates to a drive mechanism suitable for use in a circuit breaker. Switchgear is a combination of electrical switches, fuses and/or circuit breakers for controlling, isolating, and protecting electrical equipment. A circuit breaker, in particular, is designed to protect an electrical circuit from an overload or short-circuit. Typically, the circuit breaker is an automatically operated electrical switch. The circuit breaker responds to a fault condition and immediately

interrupts an electrical current flow there through.

As well known in the state of the art, a circuit breaker uses a drive mechanism to achieve operation of the circuit breaker in a desired manner. Such drive mechanisms used in the circuit breakers should satisfy a number of functional requirements . As per one such functional requirement, the drive mechanism should be such that after an initial energy transfer to the drive mechanism, the circuit breaker should be able to transition from an open to a closed position and then, back to an open position without any additional energy transfer thereto. In order to achieve the above requirement, a circuit breaker typically uses a set of spring assemblies. In

particular, a closing spring assembly and an opening spring assembly are used to achieve transition of the circuit breaker through an open-closed-open switching sequence. The drive mechanism is configured such that the closing spring assembly and the opening spring assembly may independently be in a charged or a discharged state, as required. In accordance with a typical principle of operation,

initially, the drive mechanism charges the closing spring assembly while the opening spring assembly continues to be in the discharged state. When the circuit breaker is required to be transitioned from an open state to a closed state, the closing spring assembly is triggered to be discharged. While discharging, the closing spring assembly causes an operating lever to be operated whereby the circuit breaker is

transitioned from the open state to the closed state thereof and simultaneously, a part of the potential energy stored in the closing spring assembly is transferred through the drive mechanism to the opening spring assembly, thereby

transitioning the opening spring assembly from the discharged state to the charged state. The opening spring assembly, in the charged state, is capable of transitioning the circuit breaker from the closed state to the open state.

One such exemplary drive mechanism used in the state of the art is illustrated in FIGS 1A through 1C. FIGS 1A through 1C illustrate a schematic representation of a circuit breaker

100. The circuit breaker 100 includes a contact assembly 102 and a drive mechanism 104. The drive mechanism 104 includes a charging assembly 106, an operating assembly 108, a closing spring assembly 110, and an opening spring assembly 112.

The charging assembly 106 includes a driving motor (not shown), a set of gears (not shown), a closing wheel 114, a cam wheel 116, a charging shaft 118, a connecting rod 120, and a closing latch 122.

During a charging operation, the driving motor drives the closing wheel 114 through the set of gears (not shown) . The closing wheel 114 operates the cam wheel 116, which is splined to the charging shaft 118. The charging shaft 118 is a crank shaft which is connected to the closing spring assembly 110 through the connecting rod 120. As the charging shaft 118 rotates, the closing spring assembly 110 is charged. At end of the charging operation, the closing wheel 114 is disengaged from the cam wheel 116. Further, the cam wheel 116 is engaged to the closing latch 122. As shown in FIG 1A, the closing spring assembly 110 is now charged for carrying out a closing operation in the circuit breaker 100.

The energy stored in the closing spring assembly 110 is used to trigger the operating assembly 108 and also, charge the opening spring assembly 112 during the closing operation. The operating assembly 108 includes a set of levers 124, 126 pivoted about an operating shaft 128, a connecting rod 130, a tie rod 132, and a trip latch 134.

During the closing operation, the cam wheel 116 operates the lever 124 and accordingly, the operating shaft 128. The operating shaft 128, in turn, causes the lever 126 to operate the connecting rod 130 and the tie-rod 132. At the end of the closing operation, the lever 124 is engaged with the trip latch 134. As shown in FIG IB, the opening spring assembly 112 is now charged for carrying out an opening operation in the circuit breaker 100.

As a standard practice, the closing spring assembly 110 is independently charged almost immediately after being

discharged during the closing operation. The circuit breaker 100 and in particular, the drive mechanism 104, therefore, attains a state as depicted in FIG 1C.

To open the circuit breaker 100, the trip latch 134 is released, and then, the potential energy stored in the opening spring assembly 112 is used to open the circuit breaker 100.

As depicted in FIG 1C, in the closed position of the circuit breaker 100, both the closing spring assembly 110 and the opening spring assembly 112 are in the charged state. Thus, the circuit breaker 100 is enabled to perform the open-close- open switching sequence without any external intervention. As will be evident from the foregoing description, the drive mechanism used in the state of the art employs a number of components thereby leading to increased complexity and high cost of maintenance. Moreover, such drive mechanisms are quite heavy and bulky, thereby requiring a lot of space and elaborate means for mounting within the circuit breaker.

It is therefore an object of the present invention to provide a drive mechanism for switchgear and more particularly, for a circuit breaker which is simple and robust, easy to maintain, and cost effective.

The object of the present invention is achieved by a drive mechanism suitable for use in switchgear according to claim 1, and a circuit breaker comprising such drive mechanism according to claim 10. Further embodiments of the present invention are addressed in the dependent claims.

The present invention provides a drive mechanism suitable for use in a circuit breaker. The circuit breaker is operable in one of an open state and a closed state. The drive mechanism comprises a closing spring assembly, an opening spring assembly, a main shaft, an auxiliary shaft, and an auxiliary driving assembly.

Each of the closing and opening spring assemblies is operable in one of a charged state and a discharged state.

The main shaft has a first end and a second end; and is configured for rotation in a first direction. The main shaft is coupled to the closing spring assembly such that rotation of the main shaft transitions the closing spring assembly between the charged and the discharged states thereof. The auxiliary shaft has a first end and a second end. The auxiliary shaft is arranged substantially along an axial direction of the main shaft. Further, the auxiliary shaft is coupled to the opening spring assembly such that rotation of the auxiliary shaft transitions the opening spring assembly between the charged and the discharged states thereof.

The auxiliary driving assembly is configured for driving the auxiliary shaft in the first direction based on rotation of the main shaft, and further configured for permitting

rotation of the auxiliary shaft in a second direction, the second direction being opposite to the first direction, independent of the main shaft .

The present invention, thus, provides a drive mechanism suitable for use in electrical switchgear, and in particular, a circuit breaker, which is simple and robust, compact, easy to maintain, and cost effective.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the

accompanying drawings, in which: FIGS 1A-1C illustrate schematic view of a drive mechanism in accordance with the state of the art,

FIG 2 illustrates a perspective view of a drive

mechanism in accordance with an embodiment the present invention,

FIG 3 illustrates an exploded view of selected parts of a drive mechanism in accordance with an embodiment of the present invention,

FIG 4 illustrates a schematic view of a drive

mechanism in a discharged-discharged state in accordance with an embodiment of the present invention,

FIG 5 illustrates a schematic view of a drive

mechanism in a charged-discharged state in accordance with an embodiment of the present invention, illustrates a schematic view of a drive

mechanism in a discharged-charged state in accordance with an embodiment of the present invention, and illustrates a schematic view of a drive

mechanism in a charged-charged state in

accordance with an embodiment of the present invention .

Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details.

As mentioned earlier in the present description, a circuit breaker is operable in one of an open state and a closed state. In order to operate the circuit breaker in a desired manner, a drive mechanism is provided. The present invention provides a drive mechanism suitable for use in a circuit breaker, as will now be described. Referring to FIGS 2 and 3, a perspective view of a drive mechanism 200 and an exploded view of selected parts thereof are respectively shown in accordance with an embodiment of the present invention. The drive mechanism 200 includes a closing spring assembly

202, an opening spring assembly 204, a main shaft 206, and an auxiliary shaft 208, a main driving assembly 210, and an auxiliary driving assembly 212. Each of the closing spring assembly 202 and an opening spring assembly 204 are operable in one of a charged state and a discharged state. Each spring assembly 202, 204 includes a compression spring housed in a cylindrical casing with a first end plate and a second end plate. The first end plate is fixedly mounted on the cylindrical casing while the second end plate is configured for displacement within the

cylindrical casing in a piston-like manner between a first and a second position. The compression spring is attached to the first and the second end plates at opposite ends thereof. As will be readily evident, potential energy is stored in the compression spring when the second end plate in each spring assembly 202, 204 is displaced within the cylindrical casing against a biasing force of the compression spring. When the compression spring is in relatively high-energy state, the corresponding spring assembly is said to be in charged state. Similarly, when the compression spring is in relatively low- energy state, the corresponding spring assembly is said to be in discharged state. It should be noted that constructional details of the spring assemblies 202, 204, as described above, are only exemplary in nature and several alternative implementations are possible, as is generally well known in the art. All such variations are intended to be covered within the scope of the present invention.

In various exemplary embodiments of the present invention, the drive mechanism 200 is configured such that when the closing spring assembly 202 transfers from the charged state to the discharged state, the circuit breaker transitions from the open state to the closed state. Further, when the opening spring assembly 204 transfers from the charged state to the discharged state, the circuit breaker transitions from the open state to the closed state. As shown in the adjoining figures, the main shaft 206 has a first end 206a and a second end 206b. The main shaft is coupled to the closing spring assembly 202 and is configured for rotation in a first direction (I) . As will be evident from the adjoining figure, the rotation of the main shaft 206 transitions the closing spring assembly 202 between the charged and the discharged states thereof. Similarly, the auxiliary shaft 208 has a first end 208a and a second end 208b. The auxiliary shaft 208 is arranged

substantially along an axial direction (X) of the main shaft 206, and is coupled to the opening spring assembly 204. The rotation of the auxiliary shaft 208 transitions the opening spring assembly 204 between the charged and the discharged states thereof.

The main driving assembly 210 includes a main cam wheel 214, a main driving wheel 216, and main controlling means 218. The main controlling means 218 include a main engaging lever 220, a spacer wheel 222, and a main disengaging flange 224.

The main cam wheel 214 is fixedly mounted on the main shaft 206 substantially near the first end 206a, as depicted in the adjoining figures. In an exemplary embodiment of the present invention, the main shaft 206 and the main cam wheel 214 are provided with splines which facilitate fixed mounting of the main cam wheel 214 on the main shaft 206. The term 'fixedly mounted' and variations thereof, are intended to express that a coupling between two components such that no relative motion is permitted there between.

The main driving wheel 216 is mounted on the main shaft 206 in a free-wheeling manner substantially adjacent to the main cam wheel 214. In an exemplary embodiment of the present invention, in order to mount the main driving wheel 216 in a 'free-wheeling manner', a bearing is used, as will be readily apparent to one ordinarily skilled in the art. The main driving wheel 216 is driven using an electrical motor coupled to the main driving wheel 216 through a set of gears. This is achieved using techniques well known in the art and hence, it is not being described herein for the sake of brevity. The main controlling means 218 are configured for selectively engaging/disengaging the main driving wheel 216 to/from the main cam wheel 214 based on respective angular positions in a longitudinal plane (Y-Z) perpendicular to the axial direction (X) .

In an exemplary embodiment of the present invention, the main controlling means 218 include the main engaging lever 220 and the main disengaging flange 224. The main engaging lever 220 is arranged in a fixed spaced relationship relative to the main driving wheel 216. This is achieved using the spacer wheel 222, as depicted in the adjoining figures. The spacer wheel 222 is fixedly attached to the main driving wheel 216. In addition to being fixedly attached to the main driving wheel 216, the spacer wheel 222 may also be supported on the main shaft 206 using a bearing. The main engaging lever 220 is biased towards an engaging position permitting the main engaging lever 220 to engage to the main cam wheel 214. In one example, the desired biasing of the main engaging lever 220 towards the main cam wheel 214 may be achieved using a spring. The main disengaging flange 224 is configured for displacing the main engaging lever 220 towards a disengaging position permitting the main engaging lever 220 to disengage from the main cam wheel 214.

In an exemplary embodiment of the present invention, the main shaft 206 is a crank shaft. In this example, the main shaft 206 is coupled at the crank-end thereof to the closing spring assembly 202.

The auxiliary driving assembly 212 includes an auxiliary cam wheel 226, an auxiliary driving wheel 228, and auxiliary controlling means 230. The auxiliary controlling means 230 include an auxiliary engaging lever 232, a spacer wheel 234, and an auxiliary disengaging flange 236.

The auxiliary driving assembly 212 is configured for driving the auxiliary shaft 208 in the first direction based on rotation of the main shaft 206. In addition, the auxiliary driving assembly 212 is configured for permitting rotation of the auxiliary shaft 208 in a second direction (II) , the second direction (II) being opposite to the first direction (I), as depicted in the adjoining figures.

It should be noted that the rotation of auxiliary shaft 208 in the second direction (II) is independent of the rotation of main shaft 206. In various exemplary embodiments of the present invention, the main shaft 206 rotates only in the first direction (I) while the auxiliary shaft 208 rotates in a back-and- forth manner along the first direction (I) and the second direction (II) . The auxiliary cam wheel 226 is fixedly mounted on the

auxiliary shaft 208 substantially near the first end 208a. Similarly, the auxiliary driving wheel 228 is fixedly mounted on the main shaft 206 substantially near the second end 206b. The auxiliary controlling means 230 are configured for selectively engaging/disengaging the auxiliary driving wheel 228 to/from the auxiliary cam wheel 226 based on respective angular positions in a longitudinal plane (Y-Z) perpendicular to the axial direction (X) . The auxiliary controlling means 230 are similar in

construction as the main controlling means 218. As mentioned earlier, the auxiliary controlling means 230 include the auxiliary engaging lever 232 and the auxiliary disengaging flange 236. The auxiliary engaging lever 232 is arranged in a fixed spaced relationship relative to the auxiliary driving wheel 228. This is achieved using the spacer wheel 234. The auxiliary engaging lever 232 is biased towards an engaging position permitting the auxiliary engaging lever 232 to engage to the auxiliary cam wheel 226. As in case of main driving assembly 210, the required biasing of the auxiliary engaging lever 232 may be achieved using a spring. The auxiliary disengaging flange 236 is configured for displacing the auxiliary engaging lever 232 towards a disengaging position permitting the auxiliary engaging lever 232 to disengage from the auxiliary controlling means 230.

In an exemplary embodiment of the present invention, an operating lever 238 is fixedly mounted on the auxiliary shaft 208 substantially near the second end 208b. In this

embodiment, the auxiliary shaft 208 is coupled to the opening spring assembly 204 through the operating lever 238. As shown in the adjoining figures, the closing spring

assembly 202 is connected to the main shaft 206, in

particular the crank-end thereof, using a connection rod 244. Similarly, the opening spring assembly 204 is connected to the auxiliary shaft 208, and in particular the operating lever 238, using a connection rod 246.

In an exemplary embodiment of the present invention, the operating lever is further connected to a contact assembly (not shown) within the circuit breaker such that the charged and discharged states of the opening spring assembly 204 correspond to the closed and the open states respectively of the circuit breaker. In this embodiment, the operating lever 238 is coupled to a damping assembly 248 such that

oscillations in the opening spring assembly 204 subsequent to opening the circuit breaker are damped.

In various other embodiments of the present invention, the foregoing correspondence between the states of the opening spring assembly 204 and the circuit breaker may be achieved using alternative designs, as will be apparent to one

ordinarily skilled in the art.

In addition to the foregoing, the drive mechanism 200 further includes a closing latch 240 and a tripping latch 242. Each latch 240, 242 are operable in an activated and a deactivated state . In an activated state, the closing latch 240 maintains the closing spring assembly 202 in the charged state, while in the deactivated state, the closing latch 240 permits

transition of the closing spring assembly 202 from the charged state to the discharged state. As mentioned earlier, the drive mechanism 200 is configured such that when the closing spring assembly 202 transfers from the charged state to the discharged state, the circuit breaker transitions from the open state to the closed state.

Similarly, in an activated state, the tripping latch 242 maintains the opening spring assembly 204 in the charged state, while in the deactivated state, the tripping latch 242 permits transition of the opening spring assembly 204 from the charged state to the discharged state. As mentioned earlier, the drive mechanism 200 is configured such that when the opening spring assembly 204 transfers from the charged state to the discharged state, the circuit breaker

transitions from the closed state to the open state.

As can further be seen from FIG 2, the opening spring

assembly 204 is coupled to a contact assembly 252 through a connection rod 250. The contact assembly 252 is similar to the one described previously in conjunction with FIG 1A through IB. It should be noted that in FIG 2, only one contact assembly 252 is shown which corresponds to a single- phase circuit breaker. However, in various exemplary

embodiments of the present invention, the contact assembly 252 may correspond to a three-phase circuit breaker. In this example, the connection rod 252 is configured to operate all movable contacts in individual phases to achieve open and/or close state thereof.

The operation of the circuit breaker in relation to the closing spring assembly 202 and the opening spring assembly 204 will be further explained in conjunction with FIGS 4 through 7. The operation of the drive mechanism 200 along with further constructional details will now be explained in the following description. It should be noted that a specific exemplary embodiment of the present invention will be described

hereinafter, and for clarity of understanding relative positions of various components is explained in terms of specific angular positions in degrees. However, it should be understood that the specific values of degrees for angular positions are only exemplary in nature and should not be construed to limit the invention in any manner whatsoever.

Referring to FIG 4, a schematic view of a drive mechanism 200 during a discharged-discharged state is depicted in

accordance with an embodiment of the present invention.

While explaining further constructional details and operation of the drive mechanism 200 in the following description, reference shall be made to a 'reference angular position' in a longitudinal plane (YZ) perpendicular to the axial

direction (X) . This reference angular position is indicated by Line reference angular position L0.

The main disengaging flange 224 is arranged at an offset of about 0 degrees relative to the reference angular position L0. The auxiliary disengaging flange 236 is arranged at an offset relative to the reference angular position L0, wherein the offset ranges from about 200 degrees to 280 degree, more particularly, from about 220 degrees to about 260 degrees, and still more particularly is about 240 degrees. It should be noted that the main disengaging flange 224 and the

auxiliary disengaging flange 236 are fixedly mounted to a housing/enclosure of the drive mechanism 200 and/or the circuit breaker and remain stationary through the operation of the drive mechanism 200.

The relative positions of various constituent elements within the main driving assembly 210 and the auxiliary driving assembly 212 as shown in FIG 4 corresponds to a discharged- discharged state of the drive mechanism 200.

As will be explained later on in the present description, drive mechanism 200 is in such state only prior to first use, after a reset operation, or after a fault condition in the drive mechanism 200.

During the discharged-discharged state of the drive mechanism 200, both the closing spring assembly 202 and the opening spring assembly 204 are in discharged state. The main

engaging lever 220 and the auxiliary engaging lever 232 are arranged at about 60 degrees offset relative to the reference angular position L0. Similarly, the main cam wheel 214 and the auxiliary cam wheel 226 are arranged at about 240 degrees offset relative to the reference angular position L0.

The drive mechanism 200 is operated to change the state thereof from the discharged-discharged state to charged- discharged state.

While charging the closing spring assembly 202, the main driving wheel 216 is rotated about 180 degrees before the main engaging lever 220 engages the main cam wheel 214 and further rotates about 180 degrees along with the main cam wheel 214 whereby the closing spring assembly 202 transitions to the charged state. Towards the end of charging of the closing spring assembly 202, the main disengaging flange 224 displaces the main engaging lever 220 such that main driving wheel 216 is disengaged from the main cam wheel 214.

During the charging of the closing spring assembly 202, as the main cam wheel 214 rotates about 180 degrees in the first direction (I) , the main shaft 206 and along with the main shaft 206, the auxiliary driving wheel 228, also rotates about 180 degrees to reach an offset of about 240 degrees relative to the reference angular position L0. At the end of charging of the closing spring assembly 202, the auxiliary engaging lever 232 is engaged to the auxiliary cam wheel 226.

As explained earlier, at the end of charging of the closing spring assembly 202, the closing latch 240 is activated to maintain the closing spring assembly 202 in the charged state .

Referring to FIG 5, a schematic view of a drive mechanism 200 during a charged-discharged state is depicted in accordance with an embodiment of the present invention.

During this state of the drive mechanism 200, the circuit breaker is still in the open state. When a signal to close the circuit breaker is received, the closing latch 240 is deactivated, thus the closing spring assembly 202 discharges such that the potential energy stored in the closing spring assembly 202 is used to charge the opening spring assembly 204 and at the same time, transition the circuit breaker to the closed state.

As the closing spring assembly 202 discharges, the main shaft 206 rotates about 180 degrees in the first direction (I) . As the main shaft 206 rotates, the auxiliary driving wheel 228 drives the auxiliary cam wheel 226 through the auxiliary engaging lever 232. The auxiliary cam wheel 226 and hence, the auxiliary shaft 208 rotate about 60 degrees along the first direction (I) . At this position, the auxiliary

disengaging flange 236 disengages the auxiliary engaging lever 232 from the auxiliary cam wheel 226. The auxiliary driving wheel 228 continues to rotate further and reach a position of about 60 degrees offset relative to the reference angular position L0. During the rotation of the auxiliary shaft 208, the opening spring assembly 204 transitions to the charged state. At the same time, the circuit breaker

transitions to the closed state. The tripping latch is activated to maintain the opening spring assembly 204 in the charged state. Referring now to FIG 6, a schematic view of a drive mechanism 200 in a discharged-charged state is depicted in accordance with an embodiment of the present invention.

The drive mechanism 200 is configured such that the closing spring assembly 202 is charged immediately after the closing spring assembly 202 is discharged during closing the circuit breaker .

In the discharged-charged state, the drive mechanism 200 is operated further in a manner described in conjunction with FIG 4 to charge the closing spring assembly 202. The

auxiliary driving wheel 228 rotates about 180 degrees in the first direction (I) to reach the position shown in the adjoining figure. The drive mechanism 200 now achieves a charged-charged state, as depicted in FIG 7.

Referring now to FIG 7, a schematic view of a drive mechanism in a charged-charged state is illustrated in accordance with an embodiment of the present invention.

In the charged-charged state, the circuit breaker is closed. The closing spring assembly 202 and the opening spring assembly 204 are in the charged state. The closing latch 240 and the tripping latch 242 are activated to maintain the closing spring assembly 202 and the opening spring assembly 204 respectively in the charged states. When a signal to open the circuit breaker is received, the tripping latch 242 is deactivated. The auxiliary shaft 208 and the auxiliary cam wheel 226 rotate in the second

direction (II) such that the auxiliary engaging lever 232 engages the auxiliary cam wheel 226. At the end of opening of the circuit breaker, the drive mechanism 200 reaches a charged-discharged state as shown in FIG 5. Thus, during regular use of the circuit breaker, the drive mechanism 200 continues to transition between the charged- discharged state, the discharged-charged state, and the charged-charged state.

The present invention, thus, provides a drive mechanism suitable for use in electrical switchgear, and in particular, a circuit breaker, which is simple and robust, compact, easy to maintain, and cost effective.

While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those

embodiments. In view of the present disclosure, many

modifications and variations would present themselves, to those of skill in the art without departing from the scope of various embodiments of the present invention, as described herein. The scope of the present invention is, therefore, indicated by the following claims rather than by the

foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.