OPERATING MECHANISM FOR CIRCUIT BREAKERS

Examples of an operating mechanism of a circuit breaker are described. The operating mechanism includes a housing, a cam element installed on a mechanically driven first shaft, a transmission lever installed on a second shaft parallel to the first shaft, and a support assembly. The transmission lever is provided with a first roller element. The support assembly includes a fork joint that is to support a second roller element and a damper element coupled to the fork joint. During a closing operation of the circuit breaker, the cam element rotates to interact with the first roller element to cause rotation of the transmission lever to close the circuit breaker and rotates further to engage with the second roller element on the fork joint to initiate a closing damper stroke.

TECHNICAL FIELD

The present subject matter relates, in general, to power systems. More specifically, the present subject matter relates to an operating mechanism of circuit breakers in the power systems.

BACKGROUND

Electrical fault occurring in a power line of an electrical power system may be caused due to a number of factors, which include equipment failures, overload, short circuit, or environmental conditions. The electrical fault may be hazardous and, in some cases, life-threatening. Therefore, clearing of electrical fault is critical to ensure safe operation of the electrical power system. Protection systems, for example, an Intelligent Electronic Device (IED), logic circuit(s), sensor(s), relay(s) and circuit breaker(s), may be utilized to provide protection to the electrical power system against the electrical fault.

During the electrical fault, a circuit breaker may interrupt power flow in the power line, hence preventing further damage to the power line and/or equipment associated with the power line. Further, for clearing short circuit electrical faults and for out-of-phase switching operations, SF6 gas circuit breaker of self-blast design may be used for low-current as well as high-current interruptions. The SF6 gas circuit breaker of self-blast design, commercially available as Live Tank circuit breakers (LTB), may be provided with arc-assisted interrupters.

DETAILED DESCRIPTION

Protection systems that include logic circuits, sensors, relays, circuit breakers, fuses, isolators, instrument transformers, and other protection devices, are provided in the power systems to control, protect and isolate electrical equipment of the electrical power systems during any electrical fault. An electrical fault may correspond to an abnormal condition in an electrical power system which may damage electrical equipment and disturb normal flow of electric current in the electrical power system. The electrical fault may occur in one or more of the three phases or a power line of the power system.

During an electrical fault, an Intelligent Electronic Device (IED) provided in the electrical power system may sense occurrence of an electrical fault. Thereafter, the IED may cause operation of a circuit breaker to protect an electrical circuit from damage that may be caused due to the electrical fault. For example, the electrical fault may occur due to an overload or a short circuit in a power line in the power system. In response to detection of the electrical fault by the IED, the circuit breaker may interrupt current flow in the power line. Once the electrical fault is cleared, the circuit breaker may be reset or closed to resume normal operation of the power line and the power system, either manually or automatically. To this end, sufficient mechanical power may be required during an opening operation and a closing operation of the circuit breaker to move a moving contact with respect to a fixed contact. Moreover, dielectric medium may be ejected between the contacts to neutralize arcing.

In one example, the circuit breaker may be a SF6 type circuit breaker having self-blast design, referred to as Live Tank Breaker (LTB). Moreover, mechanical energy for moving the moving contact for opening and closing the LTB may be provided by an operating mechanism, such as a spring operating mechanism. The spring operating mechanism may have potential energy mechanically stored in springs, in particular, opening spring and closing spring. The opening spring and the closing spring may initiate the opening operation and the closing operation, respectively, in the LTB. For example, different spring operating mechanisms, such as BLK, BLG, MSD, and FSA, may be used based on a rating of the power line to be isolated or a rating of the LTB.

During the closing operation, the closing spring may be released to engage the moving contact with the fixed contact. When the closing spring is released, it charges the opening spring, wherein an opening latch holds the opening spring in compressed position until an opening signal releases the opening latch during a next opening operation of the circuit breaker. In addition, the closing spring is then immediately mechanically charged and is held in its compressed position by a closing latch, until next operation. To this end, potential energy stored in the closing spring may be converted to kinetic energy during the release of the closing spring. This kinetic energy moves or rotates the moving contact to close the circuit breaker.

During the release of the closing spring, the closing spring may bounce resulting in repulsive forces. Although, a closing spring associated with LTB operating at low rating, such as below 170 kV, may operate with low speed and at low energy. Therefore, such closing spring may bear small repulsive force that may be overcome by the closing spring itself in order to bring the closing spring to rest.

However, a closing spring associated with LTB operating at high rating, may operate with high speed and at high energy. Due to high operating speed and owing to quick operations of the closing spring, such a closing spring may be subjected to high mechanical stress. Consequently, the closing spring may fail to overcome repulsive forces effectively. As a result, the closing spring may operate at high working torque that may affect mechanical endurance of the closing spring. Due to this, a number of operations or performance of the closing spring may reduce. Therefore, number of maintenance cycles for the circuit breaker may increase and reliability of the circuit breaker may decrease.

Approaches for providing an operating mechanism for a circuit breaker are described. Circuit breakers may be provided on power lines in a power system. In an example, the circuit breakers may be controlled or operated by a logic circuit or an Intelligent Electronic Device (IED). For example, an IED may trigger a circuit breaker for operation, upon sensing an electrical fault in the power system. When the electrical fault occurs in one or more phase (referred as, faulty power line) of the power system, the circuit breaker may be operated to isolate the faulty power line. The circuit breakers may isolate the faulty power line until the clearance of the electrical fault. Once the electrical fault is cleared, the circuit breaker may be closed for continuing normal operation of the power system.

As would be understood, an arc may be generated during an opening operation of the circuit breaker. Subsequently, the circuit breaker may employ an extinguishing medium, such as oil, air, vacuum, or sulphur hexafluoride (SF6) gas, to cool and quench the arc on opening the power line. In one example, the circuit breaker may be a self-blast type SF6 circuit breaker (referred to as, Live Tank Breaker (LTB)). In such a case, the LTB may have self-blast chambers for expansion volume and compression volume of extinguishing medium (SF6) separated by a valve. As would be understood, when the LTB operates at low rating, the valve may open due to overpressure generated in the compression volume of SF6 by an arc. Moreover, when the LTB operates at high rating, the valve may close due to overpressure generated in the expansion volume of SF6 by an arc.

The operating mechanism of a circuit breaker may include a housing. The housing may form an enclosure for components of the circuit breaker. Further, the operating mechanism of the circuit breaker may include a mechanically driven first shaft. For example, the first shaft may be a longitudinal tubular rotating element. The first shaft may be inserted within the housing, such as along an axial axis of the housing. The first shaft may be connected to a closing spring system of the circuit breaker.

The operating mechanism may include a cam element positioned within the housing. The cam element may be installed on the first shaft. The cam element may form a movable mechanical linkage. In an example, the cam element may have a flat body extending perpendicular to a longitudinal axis of the first shaft. In particular, a first end of the cam element may be connected to the first shaft, whereas a second end of the cam element may be connectable to other component of the circuit breaker.

Continuing further, the operating mechanism may include a transmission lever. The transmission lever may be installed on a second shaft within the housing. In an example, the second shaft may be positioned along an axial axis of the housing, parallel to the first shaft and within same axial plane as the first shaft. Moreover, the transmission lever may be provided with a first roller element. In an example, the first roller element may be a ball bearing.

The operating mechanism further includes a support assembly coupled to an inner surface of a vertical wall of the housing. The support assembly includes a fork joint having a moveable end and a pivoted end. The pivoted end of the fork joint is rigidly attached to the inner surface of the vertical wall of the housing. The movable end of the fork joint may include three prongs forming a first slot and a second slot. Moreover, the first slot of the fork joint is to rotatably secure a second roller element. In an example, the second roller element is a ball bearing.

The support assembly further includes a damper element. The damper element has a first end and a second end opposite to the first end. The first end of the damper element is rigidly pivoted on an upper horizontal surface of the housing of the circuit breaker. Moreover, the second end of the damper element is coupled to the moveable end of the fork joint. In an example, the damper element is a damper cylinder. For example, the first end may be rigidly pivoted to the upper horizontal surface of the housing via a damper spring. Further, the second end of the damper element may be movably secured within the second slot of the fork joint.

During a closing operation of the circuit breaker, a closing spring system of the circuit breaker may be released to initiate the closing operation of the circuit breaker. The closing spring may drive the cam element such that the cam element may engage with the first roller element on the transmission lever. The transmission lever is attached to the second shaft, which in turn is attached to the moving contact of the circuit breaker. The cam element may then apply mechanical force on the transmission lever to close the circuit breaker. In this manner, the transmission lever is rotated or pushed thereby closing the circuit breaker. In one example, the transmission lever may be held in closed position by a trip latch.

Furthermore, during the closing operation, the cam element on the first shaft may disengage from the first roller element on the transmission lever. Once the cam element loses contact with the first roller element, it may be rotated further to engage with the second roller element on the fork joint to initiate a closing damper stroke. In this regard, a total energy to be absorbed by the support assembly to provide damper is dependent on a stroke length of the closing spring. As may be understood, the stroke length is a distance between a compressed and an extended length of the closing spring. In particular, the stroke length is based on distance from resting position in one state (e.g., compressed) to the resting position in the other state (e.g., expanded).

Pursuant to the present subject matter, the support assembly provides damping force to the circuit breaker. In particular, as the cam element interacts with the second roller element on the fork joint, the damper element is brought in contact with the fork joint. In operation, the damper element may absorb the energy released when the cam element loses contact or disengages with the first roller element and cause restricted flow of a damping fluid during the closing damper stroke. Due to the absorption of the energy by the support assembly, the closing spring may not have to undergo high working torque to provide damping to the circuit breaker.

The operating mechanism described in the present subject matter improves the robustness of the circuit breaker, when operating at high speed and in case of high energy application. The operating mechanism, specifically, the support assembly, fits within constricted conventional housing of the circuit breaker. Therefore, robustness of the circuit breaker is improved without increasing an overall size of the circuit breaker. The support assembly operates to provide damping to the cam element. To this end, no physical contact is present between the cam element and the second roller element of the support assembly. It may be understood that the operating mechanism described herein provides higher order kinematics at the contacts between the cam element and the second roller element. This also ensures that less space is occupied by the support assembly for providing damping action.

In addition, the second roller element of the support assembly is brought in contact with the cam element after the cam element loses contact with the first transmission lever. This prevents any effect of the operation of the support assembly on the speed or travel characteristics of the circuit breaker or the cam element. Moreover, the support assembly provides damping to the circuit breaker and brings the closing spring slowly to rest. In particular, the support assembly absorbs energy or excess repulsive force released by the closing spring so as to prevent any interference to closing travel characteristics of the cam element. The slow deceleration of the closing spring results in low stress on the closing spring due to the high energy for moving the cam element. To this end, potential energy of the closing spring may not need to be increased for high speed operation of the circuit breaker. The present subject matter is now described in conjunction withFIGS.1-7.

FIG.1illustrates a power system100having an intelligent electronic device102, as per an example. Although not depicted, the power system100may further include additional electrical components such as lightning arrestors, step-up transformers, converters, step-down transformers, measuring equipment (for example, sensors, current transformers and potential transformers), insulators, switching stations, sub-transmission substations, distribution substations, and constructional structures (for example, poles and towers). The power system100is shown to have a power line104. It may be noted that the power line104may correspond to a phase, such as ‘R’, ‘Y’, or ‘B’ phase, or a DC power line. It may be noted that the power transmission system100may also comprise one or more neutral lines.

The power line104within the power system100may further be coupled to an electrical power source106and a load108. The power line104may further be provided with one or more circuit breaker(s), namely circuit breakers110-1and110-2(collectively referred to as circuit breaker(s)110). The power system100includes two power busses112and114that serves as electrical junctions, and the power line104may be used for transmission of electric power from the power sources106to the load108.

The IED102associated with the power line104may be in electrical communication with the power line104and the circuit breaker, either directly or through other connecting means. In one example, the IED102may be provided at local terminal of the power line104. In another example, the IED102may be located at a remote location and may further be connected with measuring equipment at local terminals of the power line104. The IED102may include a fault detection mechanism to detect fault in the power line104. In one example, the IED may detect the fault based on current and voltage measurements of the power line104.

On detecting a fault in the power line104, the IED may trigger the circuit breaker(s)110. The circuit breaker(s)110operates to, for example, control opening and/or closing of a circuit (specifically, the power line104) to control flow of current through the circuit. As would be understood, the circuit breaker(s)110may be provided at terminals of the power line104for de-energization of faulty circuit or the faulty power line104.

FIG.2illustrates an example of a circuit breaker200. The circuit breaker200is a switching device that may be operated manually and/or automatically for controlling and protecting an electrical power system (such as the power system100). In an example, the circuit breaker200includes fixed contacts and moving contacts (not shown inFIG.2). In an example, the circuit breaker may be a self-blast type SF6 breaker (LTB). Moreover, a rating of the LTB may be in a range of about 72 kilovolts (kV) to 800 kV.

The circuit breaker200may include breaker chambers204-1,204-2,204-3(collectively referred to as breaker chambers204). The breaker chambers204may include a medium for quenching formation of an electric arc. Typically, due to high fault current, electric arc may be formed between the moving contacts and the fixed contacts at a contact point when the contacts separate. To this end, arc quenching medium such as oil, vacuum, air, arc chute, magnetic coil, or sulphur hexafluoride, may be provided within the breaker chamber204to increase dielectric strength between the moving and the fixed contacts. In an example, the arc quenching medium used in the circuit breaker200may be sulphur hexafluoride (SF6).

The circuit breaker200further includes insulators206-1,206-2,206-3. The insulators206-1,206-2,206-3(collectively referred to as insulators206) may be hollow electrical insulators that provide insulating barrier between live electrical conductor (or power line) and metallic conducting body of the circuit breaker200that may at ground potential. The insulators206allow the electrical conductor to pass safely through a conducting barrier.

Under normal operating condition of the power system100, the fixed contacts and the moving contacts may be physically connected to each other due to applied mechanical pressure on the moving contacts. During a fault, high fault current may flow through a faulty power line (such as the power line104). In an example, a protection device, such as a relay, an instrument transformer, or a sensor, may detect the high fault current. For example, the fault may be a short circuit fault, an overcurrent fault, an overvoltage fault, or an electrical cable fault.

On detecting high fault current in the power line104, an IED (such as the IED102) may send an opening signal to the circuit breaker200. In particular, the circuit breaker200may be operated using an operating mechanism202. On receiving the opening signal, the operating mechanism202of the circuit breaker200may be triggered to release potential energy. The potential energy may be stored in the circuit breaker200by way of, for example, a metal spring, compressed air, or hydraulic pressure. In particular, the potential energy for the circuit breaker200may be stored within an opening spring system (not shown inFIG.2) and a closing spring system (not shown inFIG.2). Further, the release of the potential energy of the opening spring system causes sliding of the moving contacts of the circuit breaker200in a speedy manner Subsequently, the moving contacts loses physical contact with the fixed contact and the power line104may be isolated. During the opening operation, an electrical arc may be formed between the moving contacts and the fixed contacts, that may be quenched by the quenching medium in the breaker chambers204.

Once the electrical fault is cleared, the circuit breaker200is to be closed for bringing the power system100to normal working condition. During a closing operation of the circuit breaker200, the moving contacts and the fixed contacts are brought back in contact to resume normal operation of the power system100. For this, potential energy stored in the closing spring system may be released to move the moving contacts to engage with the fixed contact. Moreover, potential energy of the opening spring system may be restored during the closing operation of the circuit breaker200.

As would be understood, the operating mechanism202of the circuit breaker200may include other components. Examples of such components include, but are not limited to, motor, worm gear, auxiliary contacts, counter, position indicator, spring charge indicator, manual closing operation lever, manual opening operation lever, trip coil, closing coil, latches and electrical wirings. Such components are not described in detail for the sake of brevity. The operating mechanism202of the present subject matter is explained in detail with the following figures.

FIG.3illustrates an exemplary operating mechanism202of a circuit breaker. The operating mechanism202of the circuit breaker (such as the circuit breaker200) may open the circuit breaker200to isolate a faulty electrical circuit (such as the faulty power line104) during an electrical fault. Thereafter, upon the clearance of the electrical fault, the operating mechanism202may close the circuit breaker200to resume normal operation of the power line104in a power system100.

The operating mechanism202includes a support assembly300for providing damping mechanism provided within a housing302. The housing302may provide protective enclosures to the components of the operating mechanism202. The operating mechanism includes a first shaft304. The first shaft304may be a tubular splined shaft extending longitudinally along an axial plane of the housing302. The first shaft304may be coupled to a closing spring system near a first end of the first shaft304. The closing spring system302may include a plurality of closing springs arranged in parallel to each other. In an example, an intermediate fitting link may mechanically couple the closing spring system to the first shaft304.

The operating mechanism202includes a cam element306positioned within the housing302. The cam element306may be installed on the first shaft304. For example, the cam element306may be provided at a central vertical axis of the first shaft304. The cam element306may have a flat body extending perpendicular to a longitudinal axis of the first shaft304. The cam element306may have a first end and a second end opposite to the first end. In particular, the first end of the cam element306may enclose a portion of the first shaft304while the second end of the cam element306may have an arc-shaped cam profile that is to engage with other components of the operating mechanism202.

Further, the operating mechanism202includes a transmission lever308. The transmission lever308is provided with a first roller element310. In an example, the first roller element310is a bearing. The transmission lever308may be installed on a second shaft312that extends parallel to the first shaft304. The second shaft312may be a tubular splined shaft extending longitudinally along an axial plane of the housing302, within a same axial plane as the first shaft304. The second shaft312may be mechanically driven to open or close the circuit breaker200. In particular, the second shaft312may be coupled to a moving contact (not shown inFIG.3) of the circuit breaker200, that when rotated, may physically separate or interact with a fixed contact (not shown inFIG.3) of the circuit breaker200.

It may be noted that the second shaft312may also be coupled to an opening spring system (not shown inFIG.3) near a first end of the second shaft312. The opening spring system may include a plurality of opening springs arranged in parallel to each other. The first end of the second shaft312may be substantially opposite to the first end of the first shaft304.

Continuing further, the operating mechanism202includes a support assembly300. The support assembly300includes a fork joint314and a damper element316. The support assembly300may provide additional damping force to the circuit breaker200by absorbing excess energy released during the operation of the circuit breaker200.

The fork joint314has a moveable end318and a pivoted end320. The pivoted end320may be coupled to an inner surface of a vertical wall322of the housing302. For example, the closing spring system may be provided external to the vertical wall322. As would be understood, the opening spring system may be provided external to a vertical wall (not shown inFIG.3) that is opposite to the vertical wall322. The moveable end318of the fork joint314may have three prongs, wherein respective first side of the three prongs may be connected. The three prongs may diverge from the first side to form a first slot and a second slot. To this end, the moveable end318of the fork joint314may have a fork-shape.

In addition, each of the three prongs of the moveable end318may be provided with an opening. In particular, the opening on each of the three prongs may be along same axis. Moreover, a fork pin324may be inserted through the openings on the three prongs. Specifically, the moveable end318of the fork joint314is to support a second roller element (not shown inFIG.3). In this regard, the second roller element may be supported by the fork pin324such that the second roller element is rotatably secured within the first slot of the moveable end318. In an example, the second roller element may enclose a portion of the fork pin324that extends within the first slot of the moveable end318of the fork joint314.

Further, the damper element316may include a piston or a valve for regulating flow of fluid. The damper element316may have a first end326that is rigidly pivoted on an upper horizontal surface of the housing302of the circuit breaker200, via a damper spring328. Moreover, a second end330of the damper element316is coupled to the moveable end318of the fork joint314. In particular, the second end330of the damper element316may be supported by the fork pin324such that the second end330is movably secured within the second slot of the moveable end318. The damper element316is explained in detail with regard toFIG.4.

FIG.4illustrates an exemplary damper element316. The damper element316may be a cylindrical structure having a perforated tube402. The damper element316may have a metallic body. Moreover, the damper element316may include a longitudinally displaceable piston404. The piston404may be provided within the perforated tube402and may move inside the perforated tube402. Moreover, the damper element316may be filled with a damping fluid or an arc quenching medium, for example, oil, air, or sulphur hexafluoride. In particular, movement of the piston404is to cause restricted flow of the damping fluid during closing of the circuit breaker200.

The damper element316is provided with a first guide ring406and a second guide ring408. The first guide ring406and the second guide ring408may act as a guide for the piston404and prevent direct metallic contact of the piston404with the cylinder body of the damper element316. The first guide ring406and the second guide ring408may be kept in place using a circlip. Further, the first guide ring406and the second guide ring408may be provided with internal and external sealing to prevent leakage of the retarding fluid. The first guide ring406may also support a lower end of a damper spring, such as the damper spring328.

The movement of the piston404within the perforated tube402may cause restricted flow of the damping fluid through holes on the perforated tube402. Moreover, the piston404may operate in reverse direction to prevent spill over of the retarding fluid. The first and the second guide ring406and408may optimize position of the piston404such as to prevent the piston404from hitting dead center position, for example, at first end or second end.

Returning toFIG.3, the operating mechanism202may be triggered for an opening operation on occurrence of an electrical fault on the power line104. During the opening operation of the circuit breaker200, the opening spring system coupled to the second shaft312may be released. Due to the release of the opening springs of the opening spring system, the second shaft312may be rotated, thereby physically separating the moving contact from the fixed contact of the circuit breaker200.

When the electrical fault on the power line104is cleared, a closing operation of the circuit breaker200may be initiated. During the closing operation, the closing springs may be released. Due to the release of the closing springs, the first shaft304may be rotated thereby engaging the cam element306on the first shaft304with the first roller element310on the transmission lever308. In particular, the cam profile of the cam element306may engage with the first roller element310to push the transmission lever308. As a result, the second shaft312may move the moving contact to interact with the fixed contact thereby closing the circuit breaker200.

Pursuant to present subject matter, during the closing operation of the circuit breaker200, the support assembly300initiates a closing damper stroke. In particular, the cam element306is rotated further to cause the cam element306to move away from the first roller element310and to engage with the second roller element on the fork joint314to initiate the closing damper stroke. As the cam profile of the cam element306engages with the second roller element, the cam element306may exert force on the damper element316to result in contraction of the damper element316. This may move the damper element316in a plane which is laterally offset from a plane of rotation of the cam element306. Moreover, as the damper element316moves, the piston404of the damper element316may also move to cause flow of the damping fluid during the closing operation of the circuit breaker200. The damper element316is brought in contact with the second roller element for starting the closing damper stroke when the cam element306is to rotate, for engaging with the first roller element310, without any interference with the damper element316.

In the present example, a damping force provided by the support assembly300at a start of the closing damping stroke may be less than a peak damping force. Once the contact between the cam element306and the first roller element310is disengaged, full damping starts to provide the peak damping force and brings the closing springs slowly to rest. The slow deceleration of the closing springs results in the low stress on the closing springs. This improves the robustness of the closing springs.

At an end of the closing damper stroke, the damper element316remains in the closed state. Moreover, while the closing springs are charged, the second roller element on the fork joint314gets disengaged from the cam element306. In addition, the damper spring328attached to the damper element316retracts the damper element316and the fork joint314to an initial state and ready for the next operation. The support assembly300including the fork joint314and the damper element316provides damper to the closing springs during the closing operation of the circuit breaker200thereby enabling smooth operation of the closing springs and thus the circuit breaker. Due to less stress on the closing springs, the closing springs having less elasticity may be used. In addition, performance of the closing springs is enhanced as less restoring torque may be required from the closing springs.

It may be noted that the damper element316may be spaced apart from the cam element306. Moreover, the damper element316is brought into action such as to avoid impact on the closing operation or the rotation of the cam element306when engaging with the first roller element310. Moreover, the support assembly300is accommodated to fit within the compact housing302to enhance the closing operation and improve the reliability of the circuit breaker200. Furthermore, with the addition of the support assembly300, impact between spring coils in the closing springs is prevented, resulting in higher endurance performance of the closing springs.

FIG.5illustrates an exemplary closing spring system502of an operating mechanism202. The operating mechanism202may include a housing302. The housing302may form an enclosure for the components of the operating mechanism202. The housing302may be a metallic cuboidal structure. In an example, the housing302may be made of aluminium. Moreover, the housing302may be painted to avoid corrosion. The housing302may have a door, for example, at a longitudinal side of the housing. The door may include doorstops, door handles, and padlock on door handles.

The operating mechanism202includes the closing spring system502. In particular, the closing spring system502includes a plurality of closing springs (depicted as closing springs504-1and504-2). The closing springs504-1and504-2are located external to the housing302, for example, on a vertical wall (such as the vertical wall322) adjacent to the door. The closing springs504-1and504-2are arranged in parallel to each other. It may be noted that the closing springs system502to include two closing springs504-1and504-2is only illustrative and should not be construed as limiting. In other examples of the present subject matter, the closing spring system502may include a single closing spring or more than two closing springs arranged in parallel to each other.

Each of the closing springs504-1and504-2of the closing spring system502may have a first end and a second end. At the first end of the closing springs504-1and504-2, first end fittings506-1and506-2, respectively, are provided. In addition, at the second end of the closing springs504-1and504-2, second end fittings508-1and508-2, respectively, are provided. The first end fitting506-1and506-2, and the second end fittings508-1and508-2may mechanically couple the first ends and the second end, respectively, to the housing302. In certain cases, the first end fitting506-1and506-2, and the second end fittings508-1and508-2may mechanically couple the first ends and the second end, respectively, to other components of the operating mechanism202or a circuit breaker200.

In an example, the closing spring system502may include a moveable arm510. In particular, the second end of the closing springs504-1and504-2may be coupled to the moveable arm510, wherein the moveable arm510is further installed on the housing302. The closing spring system502may also include a retainer plate (not shown inFIG.5) to prevent movement of the moveable arm510in an outward direction. In particular, the retainer plate may extend from a base of the housing302, parallel to the moveable arm510. For example, due to the moveable arm510, the release of the closing springs504-1and504-2may not be limited along a longitudinal direction. The movable arm510may cause oscillation of the closing springs504-1and504-2between corresponding extreme left and extreme right position, depicted inFIG.5as dotted lines. This may provide greater surface area for release of the closing springs504-1and504-2.

Moreover, the first end of the closing springs may be coupled to the housing302by way of an intermediate fitting link512. In an example, the intermediate fitting link512may be coupled to a first shaft (such as the first shaft304) of the operating mechanism202. The first shaft304may also be coupled to an opening spring system (not shown inFIG.5), wherein the first shaft304may be rotated for closing the circuit breaker200. It may be noted that a number of fastening means may be used for installing the closing springs504-1and504-2and the moveable arm510on the housing302. Examples of the fastening means include, but are not limited to, studs, pins, bolts, bearings, and screws. For example, bolt connections may be used for installing or rigidly coupling a component within the housing302or on the housing302, instead of weld connection that may introduce possible distortions due to weld lines.

The operating mechanism202further includes an opening spring system (not shown inFIG.3). The opening spring system may include a plurality of opening springs provided external to the housing302, for example, on a vertical wall adjacent to the door and opposite to the vertical wall322with the closing spring system502. During an opening operation of the circuit breaker200, the plurality of opening springs may be released to isolate the faulty power line104.

During a closing operation of the circuit breaker200, the closing springs504-1and504-2may be released. For example, the circuit breaker may operate at high rated voltage, such as above 170 kV. In such a case, the closing springs504-1and504-2may be released with high energy and high speed. The closing springs504-1and504-2are separated and may operate independently for closing the circuit breaker200. Since the working torque for closing of the circuit breaker is provided by the plurality of closing springs, i.e., the closing springs504-1and504-2, stress on a single spring is reduced.

Although, the plurality of closing springs in parallel may eliminate high stress on single spring, however, the closing springs may still be subjected to high stress during the closing operation of high energy breakers or high rating LTB. In particular, in circuit breakers used in high voltage application, such as at 170 kV or higher, the plurality of closing springs may fail to effectively provide adequate damping force. During operation in high energy environment, travel characteristics and endurance of the plurality of closing springs may be affected. This may reduce a number of operations or M2+ characteristic that may be required from the plurality of closing springs.

To this end, a support assembly (such as the support assembly300) within the operating mechanism202is provided for the circuit breaker200that provides adequate damping force, improves reliability of the circuit breaker, and reduces redundancy of closing springs of the circuit breaker. The support assembly300may provide damper to the closing springs504-1and504-2. In this regard, the support assembly300may cause the closing springs504-1and504-2to decelerate thereby slowly bringing the closing springs504-1and504-2to rest. This may further decrease the stress on the closing springs504-1and504-2. Therefore, use of plurality of closing springs504-1and504-2and the support assembly300may eliminate frequent redundancy of the closing springs504-1and504-2. This may further improve robustness of the circuit breaker to 200 to satisfy IEC standard for M2 performance, to perform more than 10000 operations, of the closing springs504-1and504-2. Moreover, the moveable arm510may introduce one or more degree of freedom by enabling rocking or oscillatory motion of the closing springs504-1and504-2. This may further reduce stress on the closing springs504-1and504-2.

FIG.6illustrates a graph600depicting an operating characteristic of a circuit breaker, as per an example. In particular, the graph600is a time-travel characteristic graph for an operating mechanism202of the circuit breaker200. As would be understood, the time-travel characteristic graph600may depict operating characteristics or performance of the circuit breaker200. In particular, the time-travel characteristic graph600illustrates an effect of the support assembly300on operating characteristics during a closing operation of the circuit breaker200.

The graph600is a plot of time, along X-axis, against travel, along Y-axis. In an example, a transducer may be connected to the circuit breaker200to determine travel of contacts, i.e., moving contact and fixed contact, of the circuit breaker200with respect to time. In particular, the transducer may detect a stroke which is defined as the total travel distance of contacts, from resting position in one state (e.g., opened) to the resting position in the other state (e.g., closed). By observing closing time along with travel measurement, other parameters, such as penetration, overtravel, and rebound may be determined. Based on the stroke, penetration, overtravel and rebound of the circuit breaker200, the graph600may be plotted.

Time-travel characteristics of the circuit breaker200without the support assembly300is depicted using non-dotted line602while time-travel characteristics of the circuit breaker200provided with the support assembly300is depicted using dotted line604. In particular, a damper element (such as damper element316) of the support assembly300operates to cause damping of the cam element (such as the cam element306) of the circuit breaker200. To this end, the damper element316initiates closing damper stroke to provide damping to the cam element306after the cam element306disengages completely with a transmission lever (such as transmission lever308) of the circuit breaker. In this manner, the damper element or the support assembly does not affect the travel characteristics of the cam element.

As may be concluded from the graph600, travel measurements of the circuit breaker200without the support assembly300is higher as compared to travel measurements of the circuit breaker200using the support assembly300. It may further be concluded that impact or stress experienced by closing springs504-1and504-2of the circuit breaker200without the support assembly300is for higher duration as compared to impact or stress experienced by closing springs504-1and504-2of the circuit breaker200with the support assembly300. Therefore, it may be concluded that the support assembly300, including the fork joint314and the damper element316, may considerably improve the endurance of the closing springs504-1and504-2. As a result, early failure of the closing springs, for example, before 10000 operations, may be prevented thereby enhancing reliability of the circuit breaker. This may reduce a number of maintenance cycles of the circuit breaker, thus making is cost-effective. Moreover, strong closing springs may not be required, thus further reducing costs associated with the circuit breaker. As the support assembly can be accommodated within compact housing of existing operating mechanism, an overall size of the operating mechanism is not affected.

In an example, the present subject matter also provides a method for performing a closing operation of a circuit breaker (such as the circuit breaker200). In particular, the method for performing the closing operation of the circuit breaker200is implemented by an operating mechanism202of the circuit breaker200. In an example, the circuit breaker200may be a SF6 type circuit breaker having self-blast design, referred to as Live Tank Breaker (LTB). In the present example, the method is described with respect to the circuit breaker200and the operating mechanism202. However, such implementation of the method should not be construed as limiting in any way. In other examples, the method may be implemented by different operating mechanism of another type of circuit breakers.

The method for performing the closing operation of the circuit breaker200comprises rotating a cam element to interact with a first roller element to cause rotation of a transmission lever to close the circuit breaker. In particular, the cam element306and the transmission lever308are positioned within a housing302of the operating mechanism202. The cam element306is installed on a mechanically driven first shaft304of the operating mechanism202. Moreover, the transmission lever308is installed on a second shaft312of the operating mechanism202that is parallel to the first shaft304. The transmission lever308is provided with the first roller element310. In an example, the first shaft304may further be coupled to a closing spring system502while the second shaft312may further be coupled to an opening spring system or tripping spring system. To such an end, the rotation of the cam element306causes the cam element306to engage with the first roller element310of the transmission lever308to close the circuit breaker200.

The method further comprises rotating the cam element further to cause the cam element to move away from the first roller element and to engage with a second roller element on a fork joint of a support assembly to initiate a closing damper stroke. As described previously, the operating mechanism202further comprises a support assembly300that may be coupled to an inner surface of a vertical wall322of the housing302. The support assembly300comprises the fork joint314and a damper element316. The fork joint314may have a moveable end318and a pivoted end320. The moveable end318may have at least three progs that may form a first slot and a second slot, such as a fork-shape. Moreover, the moveable end318may support the second roller element, such as within the first slot. Furthermore, the damper element316may have a first end326that is rigidly pivoted on an upper horizontal surface of the housing302, and a second end330that is coupled to the moveable end318of the fork joint314, such as within the second slot of the movable end318.

To such an end, the cam element306, when rotated further, may engage with the second roller element on the fork joint314to provide damping to the cam element306during the closing operation of the circuit breaker200. It may be noted that the damping element316operates to provide damping after the cam element306disengages completely with the first roller element310of the transmission lever308. In this manner, travel characteristics of the cam element306is not affected by the operation of the damper element316.

Although implementations of present subject matter have been described in language specific to structural features and/or methods, it is to be noted that the present subject matter is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained in the context of a few implementations for the present subject matter.