Abstract:
A vacuum-type electrical switching apparatus ( 10 ) for high voltage electrical power. A vacuum pressure condition in a vacuum pressure space ( 21 ) surrounding electrical contact points ( 18 ) is monitored and movement of the contact points between open and closed positions is automatically prevented when the pressure exceeds a predetermined threshold in order to avoid destructive arcing between the points. A sensor ( 32 ) provides a vacuum signal ( 34 ) responsive to the vacuum pressure condition. A controller ( 36 ) automatically inhibits movements of the contact points when the vacuum signal indicates that the vacuum has degraded. A contactor ( 38 ) may be placed in series with power supply ( 28 ) and a solenoid ( 24 ) used to move the contact points, with the contactor being automatically opened by the controller in response to the degraded vacuum condition. An electromechanical opening inhibitor ( 74 ) may be energized by the controller to mechanically prevent the contact points from being moved in response to the degraded vacuum condition.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to the field of vacuum-type electrical switching devices for high voltage, high power applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various devices are used to control the flow of high voltage electrical power (for example greater than 1,000 VAC) in the electric utility and industrial applications. Such devices include circuit breakers, reclosers, capacitor switches, automatic and non-automatic sectionalizers and air-switch attachments, and they are referred to herein with the general terms switch or switching apparatus. While semiconductor switches have been developed, mechanical switches are still preferred for most high voltage applications. Such devices incorporate mating electrical contact points that are separated from each other to block the flow of current and that are joined together to allow current to flow through the switch. In order to interrupt the electrical circuit when opened, the contacts are typically immersed in oil having a high dielectric strength, or they are contained in an insulating gas such as SF 6  or in a vacuum pressure space. Loss of vacuum in a vacuum-type device will allow significant arcing to occur when the contacts are opened or will allow over-heating to occur when the contacts are closed, thereby causing damage to the contacts and creating the potential for injury to persons located near the switch.  
         [0003]     Devices are known for monitoring the pressure in the vacuum pressure space of vacuum-type switches. United States Patent Application Publication No. US 2005/0258342 A1 and U.S. Pat. Nos. 4,103,291 and 4,484,818, each incorporated by reference herein, describe examples of such devices. These monitoring devices are used to provide an indication of when the vacuum conditions surrounding the contact points have degraded. In spite of the existence of such devices for monitoring of the vacuum conditions, vacuum-type switches are often damaged due to the operation of the switch with a degraded vacuum condition surrounding the electrical contact points. An improved electrical switching apparatus that avoids such damage is needed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     The invention is explained in following description in view of the drawings that show:  
         [0005]      FIG. 1  is a schematic illustration of an improved vacuum-type electrical switching apparatus.  
         [0006]      FIG. 2  is a schematic illustration of one embodiment of a lockout apparatus as may be used with the vacuum-type electrical switching apparatus of  FIG. 1 .  
         [0007]      FIG. 3  is a logic diagram associated with the lockout apparatus of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]     Switching apparatus  10  of  FIG. 1  includes a vacuum interrupter  12 , a drive mechanism  14  for selectively switching the interrupter  12  between open and closed positions, and a lockout apparatus  16  for preventing the switching of the interrupter  12  under conditions that could cause damage to the equipment or injury to persons. The vacuum interrupter  12  includes mating electrical contact points  18  (illustrated as a stationary contact  18   s  and a moveable contact  18   m ) arranged for relative movement between a closed position, in which the contact points are in engagement for a flow of electrical current through the switching apparatus  10  as part of high voltage circuit  20 , and an open position in which the contact points are spaced apart (such as with moveable contact  18   m  displaced as illustrated in phantom) to block the flow of electrical current through the switch  10 . The contact points  18  are surrounded by a pressure boundary  22  defining a vacuum pressure space  21  within the pressure boundary  22 . The vacuum pressure condition minimizes arcing between the contact points  18  when they are moved between the open and closed positions at high voltage potential.  
         [0009]     The drive mechanism  14  may include a solenoid  24  connected to the moveable contact point  18   m  via an electrically insulating rod  26  of a suitable dielectric material such as fiberglass. The solenoid  24  may be selectively energized by a power supply  28 , which is responsive to a control signal  29  generated in response to operator input via a remote control  30 . The remote control  30  may be located in the general vicinity of the vacuum interrupter  12  or it may be distantly remote. Under normal operating conditions when the vacuum pressure within the pressure boundary  22  is acceptably low, the operator input via the remote control  30  is effective to connect the power supply  28  with the solenoid  24  to selectively move the contact points  18  between the open and closed positions.  
         [0010]     The lockout apparatus  16  prevents the relative movement (opening or closing) of the contact points  18  when the pressure within the pressure boundary  22  is above a predetermined threshold value. The threshold value may be selected to avoid damage to equipment and danger to nearby persons due to arcing between the contact points  18 , and may be approximately 10-2 torr to 10-4 torr in various embodiments, for example. The lockout apparatus  16  includes a sensor  32  associated with the vacuum interrupter  12  for generating a vacuum signal  34  responsive to the vacuum pressure condition within the pressure boundary  22 . Examples of such sensors  32  are described in the aforementioned United States Patent Application Publication No. 2005/0258342 A1. Vacuum signal  34  is used to control the state of a controller  36  and a contactor  38  disposed in series with the solenoid  24  and power supply  28 . When sensor  32  detects a degraded (raised) pressure condition within the pressure boundary  22 , controller  36  receives the corresponding vacuum signal  34  and, in turn, opens contactor  38  to prevent the energizing of solenoid  24 , thereby preventing the movement of contacts  18 . Thus the drive mechanism  14  and lockout apparatus  16  function together as a control element  17  responsive to both the control signal  29  and vacuum signal  34  to control the movement of the contact points  18  when the vacuum pressure is acceptable and automatically to prevent the movement of the contact points  18  when the vacuum pressure is degraded. Since nearly all operations of vacuum-type switches are controlled electrically from either a local or remote control, the present invention will be effective in preventing changes of state of such switches when the protective vacuum has degraded. By preventing operations with a loss of vacuum condition, the potential for catastrophic failures and personal injury will be minimized.  
         [0011]     Controller  36  may also generate an indication signal  40  for an indicator  42  to signal the degraded/raised pressure condition. The indicator  42  may be a light or other visual or audible device and it may be part of an operator control display. The indicator  42  may be disposed proximate the remote control  30  or at a related site, such as at a centralized maintenance or service center for alerting appropriate maintenance personnel to the need for servicing of the vacuum interrupter  12 . Indication signal  40  and/or control signal  29  may be transmitted via a network, such as the Internet or wireless communication network.  
         [0012]     Vacuum-type switches may develop small leaks that result in a very slow loss of vacuum conditions, for example over a period of months or even years. A history of the pressure values measured by sensor  32  may be stored in a database  44 . The history may be a time history, and/or the data may be recorded historically against another count variable, such as number of cycles of contact point movement. Controller  36  or another processor may be used to access the database  44  to develop trending information from the history of pressure information, thereby providing a predictive capability for use in making maintenance decisions. The trending information may be an extrapolation of sensed pressures to forecast when the pressure is expected to reach a threshold value, with repair/replacement of the vacuum interrupter  12  being scheduled prior to the pressure degrading to the point of causing damage to the equipment when the contacts  18  are moved. The trending information and any forecast data may be displayed remotely via remote indicator  42 , such as at a maintenance/repair facility.  
         [0013]      FIG. 1  also illustrates a second sensor  46  providing an environment signal  48  responsive to a parameter of the environment of the pressure boundary  22 . Such environmental parameters may include temperature, voltage, mechanical shock, lightning detection, breaker position, or other parameter affecting the switching apparatus  10  and specifically the integrity of the pressure boundary  22 . The database  44  may be used to correlate the history of the vacuum signal  34  and a corresponding history of the environmental signal  48 . Such information may be useful in diagnosing a cause of loss of vacuum within the vacuum pressure space  21 . For example, if the pressure begins to increase shortly after a voltage excursion in circuit  20 , one may conclude that the voltage excursion caused some mechanical failure of the pressure boundary  22 . Such correlations may be useful for determining the root cause of a switching apparatus pressure loss condition, and subsequently in assessing economic responsibility for the repair of the degraded condition.  
         [0014]      FIG. 2  illustrates one embodiment of a lockout apparatus  50  as may be used with the vacuum-type electrical switching apparatus  10  of  FIG. 1 . In this embodiment, the vacuum pressure sensor  32  includes a flag  52 , which is an element that moves in response to changes in the pressure within the vacuum pressure space  21 .  FIG. 2  illustrates the flag  52  in solid lines in a normal operation position, and in dashed lines in a switch failure position (high pressure in the vacuum pressure space  21 ). The flag  52  functions selectively to block or to pass light energy that is produced by a light emitting diode (LED)  54  or other light source in response to the pressure condition within the switch pressure boundary  22 . This type of sensor is more fully described in the aforementioned United States Patent Application Publication No. US 2005/0258342 A1. The lockout apparatus  50  incorporates three light sensitive diodes (LSD)  56 ,  58 ,  60  or other light detecting devices. The first light sensitive diode  56  is positioned to receive light from the LED  54  regardless of the switch operability, and to generate a current signal R 1  in response to such received light. Signal R 1  is fed into controller  36  along with current signal C 1  responsive to current being supplied by the power source  62  and current signal S 1  responsive to a current being supplied to LED  54 . Second light sensitive diode  58  is positioned to receive light from LED  54  only when the flag  52  is in its normal operating position (i.e. when a proper level of vacuum exists in the vacuum pressure space  21 ). A current sensor associated with LSD  58  provides signal R 2  to controller  36  responsive to the light received by LSD  58 . Third LSD  60  is positioned to receive light from LED  54  only when the flag  52  is in its switch failure position (i.e. when a degraded level of vacuum exists in the vacuum pressure space  21 ). A current sensor associated with LSD  60  provides signal R 3  to controller  36  responsive to the light received by LSD  58 . An auto-compensation loop  61  monitors the light output of LED  54  and automatically adjusts the output of power source  62  to maintain the light output within a predetermined range.  
         [0015]     Upon sensing a degraded vacuum condition, controller  36  is programmed to provide appropriate output signal(s)  64 ,  66 ,  68 . Error indication signal  64  may be used to energize an indicator  70 , such as a signal light or screen display indication associated with the switch control system. Opening circuit inhibitor signal  66  may be used to activate an opening circuit inhibitor  72 , such as the contactor  38  discussed with respect to  FIG. 1 , for automatically preventing the electrical movement of the switch contact points  18 . Electrometrical inhibitor signal  66  may be used to activate an electromechanical opening inhibitor  74 , such as a solenoid driven mechanical latch that prevents the manual movement of the switch contact points  18 .  
         [0016]      FIG. 3  is a logic diagram of one embodiment of the logic  80  that may be implemented by controller  36  for the lockout apparatus of  FIG. 2 . When power relay  82  first provides power to the circuit, the logic  80  initiates an auto-check at step  84  to confirm that the values of each of the current signals C 1 , S 1 , R 1 , R 2  and R 3  are within defined ranges of acceptability. If all of the signals are within acceptable ranges, the switching apparatus is declared to be operable; if not, the switching apparatus is declared to be degraded. A count circuit  86  may be used to require multiple checks prior to taking action, such as a 3-times counter requiring three findings of an unacceptable current prior to declaring the switch as degraded, or a timing circuit to require a finding of an operable switch within a defined time period prior to a default finding of a degraded switch. Upon passing of the count circuit  86  gate, the power to the system is turned off at step  88  or timed-out at step  90 , and one or more automatic lockout steps  92 ,  94 ,  96  are taken, corresponding to the automatic lockout elements  70 ,  72 ,  74  of  FIG. 2 . If the switch is declared operable at step  84 , all such automatic lockout elements are deactivated at respective steps  98 ,  100 ,  102 .  
         [0017]     The built-in redundancy of the light paths and current measurements described in  FIGS. 2 and 3  provides a high level of assurance that false indications of degraded vacuum are minimized. For example, if only a single LSD were used to receive light from the LED, a low current value on that single LSD may be misdiagnosed as a degraded vacuum condition even if the low current value were due to a failed power supply, a failed LED, or a mis-positioned flag. In the embodiment of  FIGS. 2 and 3 , a degraded vacuum condition may be defined as the occurrence of a low current value for R 2  together with the simultaneous occurrence of a high current value for R 3 . Such embodiment would not require LSD  56  or signals C 1 , S 1  or R 1 . However, for a more thorough diagnosis of the sensor performance, all of the signals C 1 , S 1 , R 1 , R 2  and R 3  may be analyzed together to diagnose various types of failures, such as a loss of power (low C 1  value), a failed LED (low R 1  value), a failure of any of the LSD&#39;s (inappropriate combination of current values S 1 , R 1 , R 2  and R 3 ), etc.  
         [0018]     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.