Patent Application
20080116049
The present invention relates to electric switchgear and, more particularly, relates to an electric power switch, which is suitable for use as a capacitor switch at distribution and sub-transmission voltages, including a bi-directional toggle mechanism and linearly opposing opening and closing spring latches.
Switching of capacitor banks is a common occurrence in electric power systems. The inductive reactance of motors in home and industrial use cause less than unity power factors, which if uncorrected can increase system losses and cause voltage levels delivered to end-use customers to drop to unacceptable levels. Capacitor banks are typically switched into the electric power circuits during high levels of inductive loading, typically during the daylight and early evening hours when most people are awake and using electric power, to correct the power factor, reduce delivery losses, and boost the voltage to the end-use customers. Once the high level inductive loading subside, typically at night, the capacitor banks are switched out of the electric power circuit. Daily cyclical use of capacitors is therefore a common practice to balance the capacitive reactance with inductive loads, and thus minimizing the stated problem, as electric loads increase and decrease on a daily basis.
Because inductive residential loads typically increase and decrease on a daily cycle, capacitor switching in response to residential loads typically occurs on a daily basis. Capacitor switching can also occur multiple times daily, for example when residential loads are combined with industrial or municipal loads that occur at night or multiple times per day. Coal mining equipment, aluminum smelters, manufacturing assembly lines, municipal water pumps, and electric transportation loads, to name but a few examples, can place large, cyclical or intermittent inductive loads on an electric power system. As a result, capacitor switches often experience several hundred to several thousand operations per year. Circuit breakers that are designed to operate in response to overload and other emergency conditions, by comparison, typically operate much less frequently, on the order of only a few isolated operations up to a couple of dozen times per year.
Nevertheless, electric utilities have often utilized the same circuit switching technology used in circuit breakers for capacitor switching applications, despite the fact that the circuit breaker technology is not designed to operate nearly as frequently as capacitor switches typically experience. For example, circuit breakers are typically designed for an industry standard of 2,000 to 10,000 operations, which is intended to cover the entire lifetime of the circuit breaker. While this standard is robust and appropriate for a circuit breaker that can be expected to operate only a couple of dozen times per year, it is inadequate for a capacitor switch that can be expected to operate several hundred to several thousand operations per year. Conventional circuit breaker technology can therefore be expected to wear out too quickly when put into operation for capacitor switching applications. Circuit breakers are also designed to switch under very high short-circuit emergency current conditions, which capacitor switches are not expected to experience in normal daily operation. It is therefore inefficient and to utilize circuit breaker technology for capacitor switching applications.
As a result, capacitor switches have been designed to withstand tens of thousands of cycles. Commonly owned U.S. Pat. Nos. 7,115,828; 7,078,643; 6,583,978; 6,483,679; 6,316,742 and 6,236,010 are good examples of electric power switching technology designed specifically for the capacitor switching application. For these capacitor switches, the spring mechanism that accelerates the electrical contactor is a critical component. Because a capacitor switch normally operates to switch the capacitor bank into or out of an energized power circuit on both the opening and the closing stroke, the electrical contactor must be accelerated to an appropriate speed on both the opening and the closing strokes. In addition, because the capacitor switch is designed to cycle on at least a daily basis, the capacitor switch is preferably motorized so that it can be operated from a remote control center or automatically in response to monitored line conditions. When the capacitor switches are well designed and cost effective, an electric utility typically finds it economically feasible to install capacitor banks in many locations throughout the electric power sub-transmissions and distribution system, resulting in a dozens or hundreds of economical capacitor switch installations for a particular electric utility, and thousands of economical capacitor switch installations across the greater power grid. Considerable effort therefore goes into designing capacitor switches that have advantageous size, cost, operating and reliability characteristics.
One prior capacitor switch design in described in U.S. Pat. No. 4,636,602, which discloses a capacitor switch with a bi-directional toggle mechanism and nested opening and closing springs. However, the toggle mechanism in this design relies on expanding and contracting latch rings on a piston inside a cylinder to charge and release the opening and closing springs. Although this design is functional, the latch and trip mechanisms for the expanding and contracting latch rings are complex and can cause undesirable binding in the slide mechanism. The piston and cylinder arrangement is also a relatively large, bulky and heavy design. Placing the trip and latch components within a closed cylinder also makes it difficult to inspect and service these components, requiring disassembly of the drive unit and removal of the piston and cylinder latch mechanism.
Accordingly, there is an ongoing need for a cost effective electric power switch suitable for use as a capacitor switch. There is a further need for a capacitor switch that includes an improved bi-directional toggle mechanism that does not rely on expanding and contracting latch rings located on a piston inside a cylinder to charge and release the opening and closing springs.
The present invention meets the needs described above in an electric power switch for introducing and removing an electric service component from an electric power system. In particular, the switch is suitable for use as a capacitor switch for introducing and removing a capacitor bank from an electric power circuit. The capacitor switch includes a drive unit having a bi-directional toggle mechanism and linearly opposing opening and closing spring latches. The opening and closing spring latches are located on opposing sides of the toggle mechanism, which includes an open-cage spring mechanism with coaxial, nested opening and closing springs operated by a rotating, motor-driven charging cam. When the capacitor bank is disconnected from the electric power circuit, the drive unit maintains the circuit interrupter in an open configuration with the opening and closing springs discharged. To introduce the capacitor bank into the electric power circuit, the motor rotates the charging cam through one complete rotation, which charges the opening and closing springs and trips the closing spring latch to release the closing spring to close the circuit interrupter and thereby introduce the capacitor bank into the electric power circuit. The drive unit then maintains the circuit interrupter in a closed configuration with the opening spring charged, ready to remove the capacitor bank from the electric power circuit. When it is time to open the circuit interrupter, the opening spring latch is tripped to release the opening spring and thereby remove the capacitor bank from the electric power circuit. This returns the drive unit and circuit interrupter to their original configurations, in which the drive unit maintains the circuit interrupter in the open configuration with the opening and closing springs discharged.
The capacitor switch includes a number of additional advantageous features. In particular, the circuit interrupter includes a removable lid that provides access to a removable insertion resistor. This allows the insertion resistor to be changed out without having to remove or disassemble the circuit interrupter. In addition, the linkage in the drive unit includes dual slot links to prevent binding in the toggle action. The drive unit also includes in-line bumper rings to cushion the deceleration of the open and close plungers to reduce jarring and wear in the drive unit. The open-cage configuration of the spring mechanism allows easy access to these components for inspection and maintenance. The linear layout of the drive unit, with the opening and closing spring latches positioned on opposing sides of the toggle mechanism, is also amenable to easy access to these components for inspection and maintenance.
Generally described, the invention may be as an interrupter drive unit in or for an electric power switch for switching an electric service device, such as a capacitor bank into and out of electric communication with an electric power circuit. In each configuration, the advantages of invention are accomplished by the interrupter drive unit, which is specifically designed to operate an electric power switch for an alternating current electric power system operating at a system frequency, typically about fifty or sixty Hertz depending on the local system operating standard. The electric power switch typically includes a circuit interrupter with an electric contactor for introducing and removing the electric service component from an electric power circuit. The interrupter drive unit is typically connected to the circuit interrupter by way of an interrupter linkage that moves the electric contactor between a closed position in which the electric service component is electrically connected to the electric power circuit and an open position in which the electric service component is electrically removed from the electric power circuit.
The interrupter drive unit includes an opening spring that is operative for moving the interrupter linkage through an opening stroke to move the electric contactor from the closed position to the open position while preventing a current restrike at the system frequency. The opening spring is regulated by an opening spring latch that is movable to a latched position for maintaining the opening spring in a charged configuration, and movable to a tripped position in response to an open trip action to release the opening spring to move the interrupter linkage through the opening stroke. An opening stroke triggering device imparts the open trip action to the opening spring latch
The interrupter drive unit includes a closing spring that is operative for moving the interrupter linkage through a closing stroke to move the electric contactor from the open position to the closed position while conducting a current arc during less than one-half of a current cycle at the system frequency. The opening spring is regulated by a closing spring latch that is movable to a latched position for maintaining the closing spring in a charged configuration and releasing the closing spring in response to a close trip action to move the interrupter linkage through the closing stroke. A closing stroke triggering device imparts the close trip action to the closing spring latch;
In addition, the interrupter drive unit includes a bi-directional toggle mechanism that is operative for moving the opening spring latch to its latched position, moving the opening spring to its charged configuration, moving the closing spring latch to its latched position, and moving the closing spring to its charged configuration. The opening spring latch, the closing spring latch and the toggle mechanism are positioned in a linear configuration with the toggle mechanism located linearly between the opening spring latch and the closing spring latch.
The interrupter drive unit may also include a charging cam operative to rotate through an operational cycle. During the operational cycle, the cam sets the opening spring latch to maintain the opening spring to its charged position, moves the opening spring to its charged position, sets the closing spring latch to maintain the closing spring to its charged position, moves the closing spring to its charged position, and trips the closing spring latch. In this configuration, the interrupter drive unit may also include an electric motor operative for rotating the charging cam through its operational cycle.
In its normal operating mode, when the electric service device is connected to the electric circuit, the interrupter drive unit may be configured to maintain the circuit interrupter in the closed configuration with the opening spring charged, ready to remove the electric service component from the electric power circuit, while the electric service component is electrically connected to the electric power circuit. In addition, when the electric service device is removed from the electric circuit, the interrupter drive unit may be configured to maintain the circuit interrupter in the open position with the opening and closing springs discharged when the electric service component is electrically disconnected from the electric power circuit.
With respect to more detailed design features, the opening stroke triggering device may be an electric solenoid, and the closing stroke triggering device may be a mechanical trigger actuated by the bi-directional toggle mechanism. The opening spring and the closed spring may also be arranged in a coaxial nested arrangement, and the toggle mechanism may include first and second slot links to prevent binding in the toggle action.
In view of the foregoing, it will be appreciated that the present invention provides a cost effective electric power switch suitable for use as a capacitor switch. In particular, the configuration of the device when deployed as a capacitor switch gives it a number of advantages over conventional capacitor switches, including the provision of a switch that is less expensive, less complex, and more reliable than conventional designs.
The present invention may be embodied in a drive unit in or for an electric power switch, such as a capacitor switch, for connecting and disconnecting an electric service component to an electric power circuit. The specific electric power switch described below with minor modifications to adapt to the specific operating voltage is suitable for use as a capacitor switch at distribution and sub-transmission voltages up to about 72.5 kV. With appropriate modifications to provide adequate lengths and acceleration for the opening and closing strokes, the same basic switch design can be use to implement switches for transmission voltages up to about 245 kV. The drive unit is designed to operate three suitable circuit interrupters to create a three-phase electric power switch. An illustrative circuit interrupter is described in commonly-owned U.S. Pat. No. 7,078,643, and the present invention may be implemented as an improvement to this device as a retrofit or as part of new system equipment. The invention may also be deployed in connection with one or more of the electric power switch features disclosed in commonly-owned U.S. Pat. Nos. 7,115,828, 6,583,978; 6,483,679; 6,316,742 and 6,236,010. All of these patents are incorporated herein by reference.
The improved interrupter drive unit, with a linearly arranged drive train including open and close latches on either side of a bi-directional toggle mechanism, allows for this device to achieve a nominal designed rating of at least twenty thousand (20,000) operations, which represents a significant improvement over prior capacitor switching mechanisms. The drive unit is also less expensive, more reliable, more compact, and easier to maintain that prior capacitor switching mechanisms. These improvement results primarily from the linear arrangement of the drive train, which provides for an improved latch design and an open cage spring mechanism. Other features and advantages of the invention and its illustrative embodiments are described below with reference to the figures.
Turning now to the figures, in which like numerals refer to similar elements throughout the several figures,
More specifically, the control unit 20 accelerates the penetrating contactor, which includes two contactors that move into and out of electrical communication and physical contact during the opening and closing strokes, while forcing the dielectric gas to flow into the gap between the contactors to extinguish the spark that forms in the gap between the contactors as the contactors move into and out of electric connection under high voltage. A capacitor bank for an electric power circuit stores a large electric charge, which discharges (at least in part) across the spark gap between the contactors during the opening stroke. The contactor also conducts an arc on the closing stroke as the contactors physically approach each other. The drive unit for a capacitor switch should therefore be designed to accelerate the contactor sufficiently to extinguish the arcs that occur in the spark gap of the contactor on the opening and closing strokes. For a capacitor switch, the opening stroke is usually more critical than the closing stroke because there is typically less time and travel distance for the contactors to accelerate from the closed position during the opening stroke.
In addition, because the voltage is alternating, the current inherently extinguishes periodically at each current zero crossing and the voltage periodically builds to its peak magnitude each half cycle, the voltage tends to cause a restrike as the voltage approaches its maximum magnitude each half cycle. Each time the current restrikes as the spark gap widens on the opening stroke the restrike occurs as a higher voltage. A restrike occurring across a relatively high voltage across a relatively wide contactor gap, for example a first or second restrike during an opening stroke can damage the contactor and cause an undesirable disturbance on the electric power circuit. For this reason, the basic design criterion of the drive unit 30 is to accelerate the contactors of the circuit interrupter 10 sufficiently to prevent a restrike from occurring during the opening stroke. On the closing stroke, the contactor is designed conduct an arc for at most one-half of the power cycle, which is 50 Hertz or 60 Hertz depending on the location. The drive unit 30 for the 38 kV switch shown in
The circuit interrupter 10 is designed to be operated as part of an electric power system forming a large number of electric power circuits, which are represented schematically in
As noted above, the interrupter control unit 20 includes an interrupter drive unit 30 and a mechanical interrupter linkage 40 that transmits motion of the drive unit to the circuit interrupter 10. The drive unit 30 includes a linear arrangement with a bi-directional toggle mechanism located between a close latch 36 (also referred to as the closing latch) and an open latch 38 (also referred to as the closing latch). The toggle mechanism is typically operated by a motor 34, which can be controlled locally, remotely or automatically. The linear configuration of the drive unit, with the latches spaced apart from the toggle mechanism, produces significant advantages for the drive unit. These advantages generally include a simpler, less expensive and more reliable electric power switch that is designed to achieve a higher number of switching operations than prior switch configurations designed for the similar applications. The specific toggle and latch mechanisms, and an illustrative operating sequence, are described in greater detail with reference to
The drive unit 30 is shown in
As shown in
Referring to the drive unit in the state shown in
The push rod 64 is also connected to an open release rod 70, which mechanically couples the push rod to the open latch 38. Moving the push rod 64 to its left lateral position causes the open latch 38 to move to a latched position, as shown in
Referring again to
A typical operating sequence of the drive unit 30 will now be described with
Activating the solenoid 72 to trip the open latch 38 transitions the drive unit from the state shown in
From the state shown in
From the state shown in
The electric power switch 8 may be implemented as a standard unit that can be employed, with minor modification to adapt to the selected operating voltage, at different standard system voltages, such as 15.5 kV, 25.8 kV, 38 kV, 48.3 kV and 72.5 kV. The illustrative capacitor switch show substantially to scale in
The interrupter control unit 20, or portions of the control unit, are shown substantially to scale in
The skilled engineer will be readily able to implement design alternatives for the specific features of the preferred embodiments described above. In particular, the drive unit may be configured in different sizes with appropriate springs and other components to meet the contactor acceleration requirements for electric power switches operating at different voltages. Specific drive unit can therefore be designed for standard distribution, sub-transmission and transmission voltages operated by various electric utilities up to about 245 kV. As another design choice, the close latch may be tripped by a solenoid rather than a mechanical linkage driven by the charging cam, and both tripping devices may be replaced by other suitable design choices. The open and close springs could be arranged in a lateral series rather than a nested configuration. The drive unit could be operated manually or by an actuator other than an electric motor. The motor may be operated locally or remotely automatically or under supervisory control. Many other design choices may be altered within the teaching of the present invention. Nevertheless, it should also be appreciated that the specific design features shown in the figures and described above are considered appropriate to provide desirable cost, size, reliability and lifetime operation characteristics.
In view of the foregoing, it will be appreciated that present invention provides significant improvements in capacitor switches for electric power distribution and sub-transmission applications. It should be understood that the foregoing relates only to the exemplary embodiments of the present invention, and that numerous changes may be made therein without departing from the spirit and scope of the invention as defined by the following claims.
This application claims priority to commonly-owned U.S. Provisional Patent Application No. 60/860,307, which is incorporated herein by reference. This application incorporates by reference the disclosures of commonly-owned U.S. Pat. Nos. 7,115,828; 7,078,643; 6,583,978; 6,483,679; 6,316,742 and 6,236,010.
| Number | Date | Country | |
|---|---|---|---|
| 60860307 | Nov 2006 | US |
