Patent Description:
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, SF<NUM> gas circuit breaker of self-blast design may be used for low-current as well as high-current interruptions. The SF<NUM> gas circuit breaker of self-blast design, commercially available as Live Tank circuit breakers (LTB), may be provided with arc-assisted interrupters.

<CIT> describes a distribution class recloser comprising puffer type, compressed-gas circuit interrupters and a spring stored energy operating mechanism.

The features, aspects, and advantages of the present subject matter will be better understood with regards to the following description and accompanying figures. The use of the same reference number in different figures indicate similar or identical features and components.

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 is 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 required 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, 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 170kV, 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 closing spring, such 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 (SF<NUM>) gas, to cool and quench the arc on opening the power line. In one example, the circuit breaker may be a self-blast type SF<NUM> 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 (SF<NUM>) 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 SF<NUM> by an arc. Moreover, when the LTB operates at high rating, the valve may close due to overpressure generated in the expansion volume of SF<NUM> 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 with FIGS. <NUM>-<NUM>.

<FIG> illustrates a power system <NUM> having an intelligent electronic device <NUM>, as per an example. Although not depicted, the power system <NUM> may 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 system <NUM> is shown to have a power line <NUM>. It may be noted that the power line <NUM> may correspond to a phase, such as 'R', 'Y', or 'B' phase, or a DC power line. It may be noted that the power transmission system <NUM> may also comprise one or more neutral lines.

The power line <NUM> within the power system <NUM> may further be coupled to an electrical power source <NUM> and a load <NUM>. The power line <NUM> may further be provided with one or more circuit breaker(s), namely circuit breakers <NUM>-<NUM> and <NUM>-<NUM> (collectively referred to as circuit breaker(s) <NUM>). The power system <NUM> includes two power busses <NUM> and <NUM> that serves as electrical junctions, and the power line <NUM> may be used for transmission of electric power from the power sources <NUM> to the load <NUM>.

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

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

<FIG> illustrates a circuit breaker <NUM>, as per an example. The circuit breaker <NUM> is a switching device that may be operated manually and/or automatically for controlling and protecting an electrical power system (such as the power system <NUM>). In an example, the circuit breaker 200includes fixed contacts and moving contacts (not shown in <FIG>). 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 <NUM> kilovolts (kV) to <NUM> kV.

The circuit breaker <NUM> may include breaker chambers <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> (collectively referred to as breaker chambers <NUM>). The breaker chambers <NUM> may 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 chamber <NUM> to increase dielectric strength between the moving and the fixed contacts. In an example, the arc quenching medium used in the circuit breaker <NUM> may be sulphur hexafluoride (SF<NUM>).

The circuit breaker <NUM> further includes insulators <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>. The insulators <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> (collectively referred to as insulators <NUM>) may be hollow electrical insulators that provide insulating barrier between live electrical conductor (or power line) and metallic conducting body of the circuit breaker <NUM> that may at ground potential. The insulators <NUM> allow the electrical conductor to pass safely through a conducting barrier.

Under normal operating condition of the power system <NUM>, 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 line <NUM>). 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 line <NUM>, an IED (such as the IED <NUM>) may send opening signal to the circuit breaker <NUM>. In particular, the circuit breaker <NUM> may be operated using an operating mechanism <NUM>. On receiving the opening signal, the operating mechanism <NUM> of the circuit breaker <NUM> may be triggered to release potential energy. The potential energy may be stored in the circuit breaker <NUM> by way of, for example, metal spring, compressed air, or hydraulic pressure. In particular, the potential energy for the circuit breaker <NUM> may be stored within an opening spring system (not shown in <FIG>) and a closing spring system (not shown in <FIG>). Further, the release of the potential energy of the opening sprig system causes sliding of the moving contacts of the circuit breaker <NUM> in a speedy manner. Subsequently, the moving contacts loses physical contact with the fixed contact and the power line <NUM> may 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 breaker chambers <NUM>.

Once the electrical fault is cleared, the circuit breaker <NUM> is to be closed for bringing the power system <NUM> to normal working condition. During a closing operation of the circuit breaker <NUM>, the moving contacts and the fixed contacts are brought back in contact to resume normal operation of the power system <NUM>. 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 breaker <NUM>.

As would be understood, the operating mechanism <NUM> of the circuit breaker <NUM> may 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 mechanism <NUM> of the present subject matter is explained in detail with the following figures.

<FIG> illustrates an operating mechanism <NUM> of a circuit breaker, as per an example. The operating mechanism <NUM> of the circuit breaker (such as the circuit breaker <NUM>) may open the circuit breaker <NUM> to isolate a faulty electrical circuit (such as the faulty power line <NUM>) during an electrical fault. Thereafter, upon the clearance of the electrical fault, the operating mechanism <NUM> may close the circuit breaker <NUM> to resume normal operation of the power line <NUM> in a power system <NUM>.

The operating mechanism <NUM> includes a support assembly <NUM> for providing damping mechanism provided within a housing <NUM>. The housing <NUM> may provide protective enclosures to the components of the operating mechanism <NUM>. The operating mechanism includes a first shaft <NUM>. The first shaft <NUM> may be tubular splined shaft extending longitudinally along an axial plane of the housing <NUM>. The first shaft <NUM> may be coupled to a closing spring system near a first end of the first shaft <NUM>. The closing spring system <NUM> may 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 shaft <NUM>.

The operating mechanism <NUM> includes a cam element <NUM> positioned within the housing <NUM>. The cam element <NUM> may be installed on the first shaft <NUM>. For example, the cam element <NUM> may be provided at a central vertical axis of the first shaft <NUM>. The cam element <NUM> may have a flat body extending perpendicular to a longitudinal axis of the first shaft <NUM>. The cam element <NUM> may have a first end and a second end opposite to the first end. In particular, the first end of the cam element <NUM> may enclose a portion of the first shaft <NUM> while the second end of the cam element <NUM> may have an arc-shaped cam profile that is to engage with other components of the operating mechanism <NUM>.

Further, the operating mechanism <NUM> includes a transmission lever <NUM>. The transmission lever <NUM> is provided with a first roller element <NUM>. In an example, the first roller element <NUM> is a bearing. The transmission lever <NUM> may be installed on a second shaft <NUM> that extends parallel to the first shaft <NUM>. The second shaft <NUM> may be a tubular splined shaft extending longitudinally along an axial plane of the housing <NUM>, within a same axial plane as the first shaft <NUM>. The second shaft <NUM> may be mechanically driven to open or close of the circuit breaker <NUM>. In particular, the second shaft <NUM> may be coupled to a moving contact (not shown in <FIG>) of the circuit breaker <NUM>, that when rotated may physically separate or interact with a fixed contact (not shown in <FIG>) of the circuit breaker <NUM>.

It may be noted that the second shaft <NUM> may also be coupled to an opening spring system (not shown in <FIG>) near a first end of the second shaft <NUM>. The opening spring system may include a plurality of opening springs arranged in parallel to each other. The first end of the second shaft <NUM> may be substantially opposite to the first end of the first shaft <NUM>.

Continuing further, the operating mechanism <NUM> includes a support assembly <NUM>. The support assembly <NUM> includes a fork joint <NUM> and a damper element <NUM>. The support assembly <NUM> may provide additional damping force to the circuit breaker <NUM> by absorbing excess energy released during the operation of the circuit breaker <NUM>.

The fork joint <NUM> has a moveable end <NUM> and a pivoted end <NUM>. The pivoted end <NUM> may be coupled to an inner surface of a vertical wall <NUM> of the housing <NUM>. For example, the closing spring system may be provided external to the vertical wall <NUM>. As would be understood, the opening spring system may be provided at external to a vertical wall (not shown in <FIG>) that is opposite to the vertical wall <NUM>. The moveable end <NUM> of the fork joint <NUM> may 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 end <NUM> of the fork joint <NUM> may have a fork-shape.

In addition, each of the three prongs of the moveable end <NUM> may be provided with an opening. In particular, the opening on each of the three prongs may be along same axis. Moreover, a fork pin <NUM> may be inserted through the openings on the three prongs. Specifically, the moveable end <NUM> of the fork joint <NUM> is to support a second roller element (not shown in <FIG>). In this regard, the second roller element may be supported by the fork pin <NUM> such that the second roller element is rotatably secured within the first slot of the moveable end <NUM>. In an example, the second roller element may enclose a portion of the fork pin <NUM> that extends within the first slot of the moveable end <NUM> of the fork joint <NUM>.

Further, the damper element <NUM> may include a piston or a valve for regulating flow of fluid. The damper element <NUM> may have a first end <NUM> that is rigidly pivoted on an upper horizontal surface of the housing <NUM> of the circuit breaker <NUM>, via a damper spring <NUM>. Moreover, a second end <NUM> of the damper element <NUM> is coupled to the moveable end <NUM> of the fork joint <NUM>. In particular, the second end <NUM> of the damper element <NUM> may be supported by the fork pin <NUM> such that the second end <NUM> is movably secured within the second slot of the moveable end <NUM>. The damper element <NUM> is explained in detail with regard to <FIG>.

<FIG> illustrates a damper element <NUM>, as per an example. The damper element <NUM> may be a cylindrical structure having a perforated tube <NUM>. The damper element <NUM> may have metallic body. Moreover, the damper element <NUM> may include a longitudinally displaceable piston <NUM>. The piston <NUM> may be provided within the perforated tube <NUM> and may move inside the perforated tube <NUM>. Moreover, the damper element <NUM> may be filled with a damping fluid or an arc quenching medium, for example, oil, air, or sulphur hexafluoride. In particular, movement of the piston <NUM> is to cause restricted flow of the damping fluid during closing of the circuit breaker <NUM>.

The damper element <NUM> is provided with a first guide ring <NUM> and a second guide ring <NUM>. The first and the second guide ring <NUM> and <NUM> may act as a guide for the piston <NUM> and prevent direct metallic contact of the piston <NUM> with the cylinder body of the damper element <NUM>. The first and the second guide ring <NUM> and <NUM> may be kept in place using a circlip. Further, the first and the second guide ring <NUM> and <NUM> may be provided with internal and external sealing to prevent leakage of the retarding fluid. The first guide ring <NUM> may also support a lower end of a damper spring, such as the damper spring <NUM>.

The movement of the piston <NUM> within the perforated tube <NUM> may cause restricted flow of the damping fluid through holes on the perforated tube <NUM>. Moreover, the piston <NUM> may operate in reverse direction to prevent spill over of the retarding fluid. The first and the second guide ring <NUM> and <NUM> may optimize position of the piston <NUM> such as to prevent the piston <NUM> from hitting dead centre position, for example, at first end or second end.

Returning to <FIG>, the operating mechanism <NUM> may be triggered for an opening operation on occurrence of an electrical fault on the power line <NUM>. During the opening operation of the circuit breaker <NUM>, the opening spring system coupled to the second shaft <NUM> may be released. Due to the release of the opening springs of the opening spring system, the second shaft <NUM> may be rotated, thereby physically separating the moving contact from the fixed contact of the circuit breaker <NUM>.

When the electrical fault on the power line <NUM> is cleared, a closing operation of the circuit breaker <NUM> may be initiated. During the closing operation, the closing springs may be released. Due to the release of the closing springs, the first shaft <NUM> may be rotated thereby engaging the cam element <NUM> on the first shaft <NUM> with the first roller element <NUM> on the transmission lever <NUM>. In particular, the cam profile of the cam element <NUM> may engage with the first roller element <NUM> to push the transmission lever <NUM>. As a result, the second shaft <NUM> may move the moving contact to interact with the fixed contact thereby closing the circuit breaker <NUM>.

Pursuant to present subject matter, during the closing operation of the circuit breaker <NUM>, the support assembly <NUM> is to initiate closing damper stroke. In particular, the cam element <NUM> is rotated further to cause the cam element <NUM> to move away from the first roller element <NUM> and to engage with the second roller element on the fork joint <NUM> to initiate the closing damper stroke. As the cam profile of the cam element <NUM> engages with the second roller element, the cam element <NUM> may exert force on the damper element <NUM> to result in contraction of the damper element <NUM>. This may move the damper element <NUM> in a plane which is laterally offset from a plane of rotation of the cam element <NUM>. Moreover, as the damper element <NUM> moves, the piston <NUM> of the damper element <NUM> may also move to cause flow of the damping fluid during the closing operation of the circuit breaker <NUM>. The damper element <NUM> is brought in contact with the second roller element for starting the closing damper stroke when the cam element <NUM> is to rotate, for engaging with the first roller element <NUM>, without any interference with the damper element <NUM>.

In the present example, a damping force provided by the support assembly <NUM> at a start of the closing damping stroke may be less than a peak damping force. Once the contact between the cam element <NUM> and the first roller element <NUM> is 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 element <NUM> remains in closed state. Moreover, while the closing springs are charged, the second roller element on the fork joint <NUM> gets disengaged from the cam element <NUM>. In addition, the damper spring <NUM> attached to the damper element <NUM> retracts the damper element <NUM> and the fork joint <NUM> to an initial state and ready for next operation. The support assembly <NUM> including the fork joint <NUM> and the damper element <NUM> provides damper to the closing springs during the closing operation of the circuit breaker <NUM> thereby 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 is required from the closing springs.

It may be noted that the damper element <NUM> may be spaced apart from the cam element <NUM>. Moreover, the damper element <NUM> is brought into action such as to avoid impact on the closing operation or the rotation of the cam element <NUM> when engaging with the first roller element <NUM>. Moreover, the support assembly <NUM> is accommodated to fit within the compact housing <NUM> to enhance the closing operation and improve the reliability of the circuit breaker <NUM>. Furthermore, with the addition of the support assembly <NUM>, impact between spring coils in the closing springs is prevented, resulting in higher endurance performance of the closing springs.

<FIG> illustrates closing spring system <NUM> of an operating mechanism <NUM>, as per an example. The operating mechanism <NUM> may include a housing <NUM>. The housing <NUM> may form an enclosure for the components of the operating mechanism <NUM>. The housing <NUM> may be a metallic cuboidal structure. In an example, the housing <NUM> may be made of aluminium. Moreover, the housing <NUM> may be painted to avoid corrosion. The housing <NUM> may have a door, for example, at a longitudinal side of the housing. The door may include door-stops, door handles, and padlock on door handles.

The operating mechanism <NUM> includes the closing spring system <NUM>. In particular, the closing spring system <NUM> includes a plurality of closing springs (depicted as closing springs <NUM>-<NUM> and <NUM>-<NUM>). The closing springs <NUM>-<NUM> and <NUM>-<NUM> are located external to the housing <NUM>, for example, on a vertical wall (such as the vertical wall <NUM>) adjacent to the door. The closing springs <NUM>-<NUM> and <NUM>-<NUM> are arranged in parallel to each other. It may be noted that the closing springs system <NUM> to include two closing springs <NUM>-<NUM> and <NUM>-<NUM> is only illustrative and should not be construed as limiting. In other examples of the present subject matter, the closing spring system <NUM> may include a single closing spring or more than two closing springs arranged in parallel to each other.

Each of the closing springs <NUM>-<NUM> and <NUM>-<NUM> of the closing spring system <NUM> may have a first end and a second end. At the first end of the closing springs <NUM>-<NUM> and <NUM>-<NUM>, first end fittings <NUM>-<NUM> and <NUM>-<NUM>, respectively, are provided. In addition, at the second end of the closing springs <NUM>-<NUM> and <NUM>-<NUM>, second end fittings <NUM>-<NUM> and <NUM>-<NUM>, respectively, are provided. The first end fitting <NUM>-<NUM> and <NUM>-<NUM>, and the second end fittings <NUM>-<NUM> and <NUM>-<NUM> may mechanically couple the first ends and the second end, respectively, to the housing <NUM>. In certain cases, the first end fitting <NUM>-<NUM> and <NUM>-<NUM>, and the second end fittings <NUM>-<NUM> and <NUM>-<NUM> may mechanically couple the first ends and the second end, respectively, to other components of the operating mechanism <NUM> or a circuit breaker <NUM>.

In an example, the closing spring system <NUM> may include a moveable arm <NUM>. In particular, the second end of the closing springs <NUM>-<NUM> and <NUM> may be coupled to the moveable arm <NUM>, wherein the moveable arm <NUM> is further installed on the housing <NUM>. The closing spring system <NUM> may also include a retainer plate (not shown in <FIG>) to prevent movement of the moveable arm <NUM> in outward direction. In particular, the retainer plate may extend from a base of the housing <NUM>, parallel to the moveable arm <NUM>. For example, due to the moveable arm <NUM>, the release of the closing springs <NUM>-<NUM> and <NUM>-<NUM> may not be limited along a longitudinal direction. The movable arm <NUM> may cause oscillation of the closing springs <NUM>-<NUM> and <NUM>-<NUM> between corresponding extreme left and extreme right position, depicted as dotted lines. This may provide greater surface area for release of the closing springs <NUM>-<NUM> and <NUM>-<NUM>.

Moreover, the first end of the closing springs may be coupled to the housing <NUM> by way of an intermediate fitting link <NUM>. In an example, the intermediate fitting link <NUM> may be coupled to a first shaft (such as the first shaft <NUM>) of the operating mechanism <NUM>. The first shaft <NUM> may also be coupled to an opening spring system (not shown in <FIG>), wherein the first shaft <NUM> may be rotated for closing the circuit breaker <NUM>. It may be noted that a number of fastening means may be used for installing the closing springs <NUM>-<NUM> and <NUM>-<NUM> and the moveable arm <NUM> on the housing <NUM>. 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 housing <NUM> or on the housing <NUM>, instead of weld connection that may introduce possible distortions due to weld lines.

The operating mechanism <NUM> further includes an opening spring system (not shown in <FIG>). The opening spring system may include a plurality of opening springs provided external to the housing <NUM>, for example, on a vertical wall adjacent to the door and opposite to the vertical wall <NUM> with the closing spring system <NUM>. During an opening operation of the circuit breaker <NUM>, the plurality of opening springs may be released to isolate the faulty power line <NUM>.

During a closing operation of the circuit breaker <NUM>, the closing springs <NUM>-<NUM> and <NUM>-<NUM> may be released. For example, the circuit breaker may operate at high rated voltage, such as above <NUM> kV. In such a case, the closing springs <NUM>-<NUM> and <NUM>-<NUM> may be released with high energy and high speed. The closing springs <NUM>-<NUM> and <NUM>-<NUM> are separated and may operate independently for closing the circuit breaker <NUM>. Since the working torque required for closing of the circuit breaker is provided by the plurality of closing springs, i.e. the closing springs <NUM>-<NUM> and <NUM>-<NUM>, 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 170kV 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 required from the plurality of closing springs.

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

<FIG> illustrates a graph <NUM> depicting an operating characteristic of a circuit breaker, as per an example. In particular, the graph <NUM> is a time-travel characteristic graph for an operating mechanism <NUM> of the circuit breaker <NUM>. As would be understood, the time-travel characteristic graph <NUM> may depict operating characteristics or performance of the circuit breaker <NUM>. In particular, the time-travel characteristic graph <NUM> illustrates an effect of the support assembly <NUM> on operating characteristics during a closing operation of the circuit breaker <NUM>.

The graph <NUM> is a plot of time, along X-axis, against travel, along Y-axis. In an example, a transducer may be connected to the circuit breaker <NUM> to determine travel of contacts, i.e., moving contact and fixed contact, of the circuit breaker <NUM> with 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 breaker <NUM>, the graph <NUM> may be plotted.

Time-travel characteristics of the circuit breaker <NUM> without the support assembly <NUM> is depicted using non-dotted line <NUM> while time-travel characteristics of the circuit breaker <NUM> provided with the support assembly <NUM> is depicted using dotted line <NUM>. In particular, a damper element (such as damper element <NUM>) of the support assembly <NUM> operates to cause damping of the cam element (such as the cam element <NUM>) of the circuit breaker <NUM>. To this end, the damper element <NUM> initiates closing damper stroke to provide damping to the cam element <NUM> after the cam element <NUM> disengages completely with a transmission lever (such as transmission lever <NUM>) 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 graph <NUM>, travel measurements of the circuit breaker <NUM> without the support assembly <NUM> is higher as compared to travel measurements of the circuit breaker <NUM> using the support assembly <NUM>. It may further be concluded that impact or stress experienced by closing springs <NUM>-<NUM> and <NUM>-<NUM> of the circuit breaker <NUM> without the support assembly <NUM> is for higher duration as compared to impact or stress experienced by closing springs <NUM>-<NUM> and <NUM>-<NUM> of the circuit breaker <NUM> with the support assembly <NUM>. Therefore, it may be concluded that the support assembly <NUM>, including the fork joint <NUM> and the damper element <NUM>, may considerably improve the endurance of the closing springs <NUM>-<NUM> and <NUM>-<NUM>. As a result, early failure of the closing springs, for example, before <NUM> 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 breaker <NUM>). In particular, the method for performing the closing operation of the circuit breaker <NUM> is implemented by an operating mechanism <NUM> of the circuit breaker <NUM>. In an example, the circuit breaker <NUM> may 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 breaker <NUM> and the operating mechanism <NUM>. 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 breaker <NUM> comprises 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 element <NUM> and the transmission lever <NUM> are positioned within a housing <NUM> of the operating mechanism <NUM>. The cam element <NUM> is installed on a mechanically driven first shaft <NUM> of the operating mechanism <NUM>. Moreover, the transmission lever <NUM> is installed on a second shaft <NUM> of the operating mechanism <NUM> that is parallel to the first shaft <NUM>. The transmission lever <NUM> is provided with the first roller element <NUM>. In an example, the first shaft <NUM> may further be coupled to a closing spring system <NUM> while the second shaft <NUM> may further be coupled to an opening spring system or tripping spring system. To such an end, the rotation of the cam element <NUM> causes the cam element <NUM> to engage with the first roller element <NUM> of the transmission lever <NUM> to close the circuit breaker <NUM>.

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 mechanism <NUM> further comprises a support assembly <NUM> that may be coupled to an inner surface of a vertical wall <NUM> of the housing <NUM>. The support assembly <NUM> comprises the fork joint <NUM> and a damper element <NUM>. The fork joint <NUM> may have a moveable end <NUM> and a pivoted end <NUM>. The moveable end <NUM> may have at least three progs that may form a first slot and a second slot, such as a fork-shape. Moreover, the moveable end <NUM> may support the second roller element, such as within the first slot. Furthermore, the damper element <NUM> may have a first end <NUM> that is rigidly pivoted on an upper horizontal surface of the housing <NUM>, and a second end <NUM> that is coupled to the moveable end <NUM> of the fork joint <NUM>, such as within the second slot of the movable end <NUM>.

To such an end, the cam element <NUM>, when rotated further, may engage with the second roller element on the fork joint <NUM> to provide damping to the cam element <NUM> during the closing operation of the circuit breaker <NUM>. It may be noted that the damping element <NUM> operates to provide damping after the cam element <NUM> disengages completely with the first roller element <NUM> of the transmission lever <NUM>. In this manner, travel characteristics of the cam element <NUM> is not affected by the operation of the damper element <NUM>.

Claim 1:
An operating mechanism (<NUM>) of a circuit breaker (<NUM>, <NUM>) comprising:
a housing (<NUM>);
a cam element (<NUM>) positioned within the housing (<NUM>), wherein the cam element (<NUM>) is installed on a mechanically driven first shaft (<NUM>);
a transmission lever (<NUM>) provided with a first roller element (<NUM>), wherein the transmission lever (<NUM>) is installed on a second shaft (<NUM>) such that the second shaft (<NUM>) is parallel to the first shaft (<NUM>); and
a support assembly (<NUM>) coupled to an inner surface of a vertical wall (<NUM>) of the housing (<NUM>), wherein the support assembly (<NUM>) comprises:
a fork joint (<NUM>) having a moveable end (<NUM>) and a pivoted end (<NUM>), wherein the moveable end (<NUM>) is adapted to support a second roller element;
and
a damper element (<NUM>) having a first end (<NUM>) and a second end (<NUM>), characterised in that the first end (<NUM>) of the damper element (<NUM>) is rigidly pivoted on an upper horizontal surface of the housing (<NUM>) of the circuit breaker (<NUM>, <NUM>), and the second end (<NUM>) of the damper element (<NUM>) is coupled to the moveable end (<NUM>) of the fork joint (<NUM>),