Abstract:
A method for detecting a high pressure condition within an interrupter includes measuring the intensity of light emitted from an arc created by contacts within the interrupter, comparing the measured intensity with a predetermined value, and providing an indication when the measured intensity exceeds the predetermined value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to detection of failure conditions in high power electrical switching devices, particularly to the detection of high pressure conditions in a vacuum interrupter. 
     2. Description of the Related Art 
     The reliability of the North American power grid has come under critical scrutiny in the past few years, particularly as demand for electrical power by consumers and industry has increased. Failure of a single component in the grid can cause catastrophic power outages that cascade throughout the system. One of the essential components utilized in the power grid are the mechanical switches used to turn on and off the flow of high current, high voltage AC power. Although semiconductor devices are making some progress in this application, the combination of very high voltages and currents still make the mechanical switch the preferred device for this application. 
     There are basically two configurations for these high power mechanical switches; oil filled and vacuum. The oil filled switch utilizes contacts immersed in a hydrocarbon based fluid having a high dielectric strength. This high dielectric strength is required to withstand the arcing potential at the switching contacts as they open to interrupt the circuit. Due to the high voltage service conditions, periodic replacement of the oil is required to avoid explosive gas formation that occurs during breakdown of the oil. The periodic service requires that the circuits be shut down, which can be inconvenient and expensive. The hydrocarbon oils can be toxic and can create serious environmental hazards if they are spilled into the environment. The other configuration utilizes a vacuum environment around the switching contacts. Arcing and damage to the switching contacts can be avoided if the pressure surrounding the switching contacts is low enough. Loss of vacuum in this type of interrupter will create serious arcing between the contacts as they switch the load, destroying the switch. In some applications, the vacuum interrupters are stationed on standby for long periods of time. A loss of vacuum may not be detected until they are placed into service, which results in immediate failure of the switch at a time when its most needed. It therefore would be of interest to know in advance if the vacuum within the interrupter is degrading, before a switch failure due to contact arcing occurs. Currently, these devices are packaged in a manner that makes inspection difficult and expensive. Inspection may require that power be removed from the circuit connected to the device, which may not be possible. It would be desirable to remotely measure the status of the pressure within the switch, so that no direct inspection is required. It would also be desirable to periodically monitor the pressure within the switch while the switch is in service and at operating potential. 
     It might seem that the simple measurement of pressure within the vacuum envelope of these interrupter devices would be adequately covered by devices of the prior art, but in reality, this is not the case. A main factor is that the switch is used for switching high AC voltages, with potentials between 7 and 100 kilovolts above ground. This makes application of prior art pressure measuring devices very difficult and expensive. Due to cost and safety constraints, complex high voltage isolation techniques of the prior art are not suitable. What is needed is a method and apparatus to safely and inexpensively measure a high pressure condition in a high voltage interrupter, preferably remote from the switch, and preferably while the switch is at operating potential. 
       FIG. 1  is a cross sectional view  100  of a first example of a vacuum interrupter of the prior art. This particular unit is manufactured by Jennings Technology of San Jose, Calif. Contacts  102  and  104  are responsible for the switching function. A vacuum, usually below 10 −4  torr, is present near the contacts in region  114  and within the envelope enclosed by cap  108 , cap  110 , bellows  112 , and insulator sleeve  106 . Bellows  112  allows movement of contact  104  relative to stationary contact  102 , to make or break the electrical connection. 
       FIG. 2  is a cross sectional view  200  of a second example of a vacuum interrupter of the prior art. This unit is also manufactured by Jennings Technology of San Jose, Calif. In this embodiment of the prior art, contacts  202  and  204  perform the switching function. A vacuum, usually below 10 −4  torr, is present near the contacts in region  214  and within the envelope enclosed by cap  208 , cap  210 , bellows  212 , and insulator sleeve  206 . Bellows  112  allows movement of contact  202  relative to stationary contact  204 , to make or break the electrical connection. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for detecting a high pressure condition within an interrupter, including measuring an intensity of at least a portion of light emitted from an arc created by contacts within the interrupter, comparing the measured intensity with a predetermined value, and providing a first indication when the measured intensity exceeds the predetermined value. 
     It is another object of the present invention to provide a method for detecting a high pressure condition within an interrupter, including transmitting a beam of light through a window placed within an exterior wall of the interrupter, reflecting the beam of light off a reflective surface, the reflective surface residing within the interior volume of the interrupter, measuring an intensity of at least a portion of the reflected beam of light, comparing the measured intensity with a predetermined value, and providing an indication when the measured intensity is less than the predetermined value. 
     It is another object of the present invention to provide a method for detecting a high pressure condition within an interrupter, including placing a diaphragm within an outer wall of the interrupter, wherein the diaphragm is in a collapsed position for internal pressures below a first predetermined value, and the diaphragm is in an expanded condition for internal pressures above a second predetermined value. The method further includes directing a beam of light at an outer surface of the diaphragm, detecting a reflected beam of light from the outer surface when the diaphragm is in the collapsed position, producing a non-detectable reflected beam of light when the outer surface of the diaphragm is in the expanded position, and producing a high pressure indication when the beam of light is no longer detected. 
     It is another object of the present invention to provide a method for detecting a high pressure condition within an interrupter, including placing a diaphragm within an outer wall of the interrupter, wherein the diaphragm is in a collapsed position for internal pressures below a first predetermined value, and the diaphragm is in an expanded position for internal pressures above a second predetermined value. The method further includes directing a beam of light at an outer surface of the diaphragm, detecting a reflected beam of light from the outer surface when the diaphragm is in the expanded position, producing a non-detectable reflected beam of light when the outer surface of the diaphragm is in the collapsed position and, producing a high pressure indication when the beam of light is detected. 
     It is another object of the present invention to provide method for detecting a high pressure condition within an interrupter, including placing a pressure transducer within an enclosed volume of the interrupter, placing a window within an external wall of the interrupter, converting pressure measurements made by the pressure transducer to an optical signal, and directing the optical signal through the window. 
     It is another object of the present invention to provide method for detecting a high pressure condition within an interrupter, including placing a pressure transducer within an enclosed volume of the interrupter, converting pressure measurements made by the pressure transducer to an RF signal, and transmitting the RF signal to a receiver located outside the interrupter. 
     It is another object of the present invention to provide an apparatus for detecting high pressure within an interrupter, including a collapsible device, enclosed within an interrupter, having a first surface and a second surface, the first surface fixed relative to the interrupter; a shaft, having a first end and a second end, the first end attached to the second surface of the collapsible device; and, a means for detecting a position of the second end of the shaft. 
     It is another object of the present invention to provide an apparatus for detecting high pressure within an interrupter including a cylinder having a piston, a first volume, and a second volume, the piston dividing the first volume from the second volume, the first volume fluidically coupled to an interior volume of the interrupter; a shaft, attached to the piston and extending out of the cylinder; and, a means for detecting a position of the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein: 
         FIG. 1  is a cross sectional view of a first example of a vacuum interrupter of the prior art; 
         FIG. 2  is a cross sectional view of a second example of a vacuum interrupter of the prior art; 
         FIG. 3  is a partial cross sectional view of a device for detecting arcing contacts according to an embodiment of the present invention; 
         FIG. 4  is a partial cross sectional view of a cylinder actuated optical pressure switch in the low pressure state, according to an embodiment of the present invention; 
         FIG. 5  is a partial cross sectional view of a cylinder actuated optical pressure switch in the high pressure state, according to an embodiment of the present invention; 
         FIG. 6  is a partial cross sectional view of a bellows actuated optical pressure switch in the low pressure state, according to an embodiment of the present invention; 
         FIG. 7  is a partial cross sectional view of a bellows actuated optical pressure switch in the high pressure state, according to an embodiment of the present invention; 
         FIG. 8  is a partial cross sectional view of an optical device for detecting sputtered debris from the electrical contacts, according to an embodiment of the present invention; 
         FIG. 9  is a partial cross sectional view of a self powered, optical transmission microcircuit, according to an embodiment of the present invention; 
         FIG. 10  is a partial cross sectional view of a self powered, RF transmission microcircuit, according to an embodiment of the present invention; 
         FIG. 11  is a schematic view of a diaphragm actuated optical pressure switch in the low pressure state, according to an embodiment of the present invention; and, 
         FIG. 12  is a schematic view of a diaphragm actuated optical pressure switch in the high pressure state, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is directed toward providing methods and apparatus for the measurement of pressure within a high voltage, vacuum interrupter. As an example, various embodiments described subsequently are employed with or within the interrupter shown in  FIG. 1 . This by no means implies that the inventive embodiments are limited in application to this interrupter configuration only, as the illustrated embodiments of the present invention are equally applicable to the device shown in  FIG. 2  or any similar device. 
       FIG. 3  is a partial cross sectional view  300  of a device for detecting arcing contacts according to an embodiment of the present invention. As the pressure in region  114  rises, arcing between contacts  104  and  102  will occur, due to the ionization of the gasses creating the increased pressure. An electrically isolated photo detector  310  is employed to observe the emitted light  304  generated in gap  306  as contacts  104  and  102  separate. Photo detector  310  may be a solid state photo diode or photo transistor type detector, or may be a photo-multiplier tube type detector. Due to cost considerations, a solid state device is preferred. The photo detector  310  is coupled to control and interface circuitry  312 , which contains the necessary components (including computer processors, memory, analog amplifiers, analog to digital converters, or other required circuitry) needed to convert the signals from photo detector  310  to useful information. Photo detector  310  is optically coupled to a transparent window  302  by means of a fiber optic cable  308 . Cable  308  provides the required physical and electrical isolation from the high operating voltage of the interrupter. Generally, cable  308  is comprised of an optically transparent glass, plastic or ceramic material, and is non-conductive. Window  302  is mounted in the enclosure for the interrupter, preferably in the insulator sleeve  106 . Window  302  may also be mounted in the caps (for example  108 ) if convenient or required. Window  302  is made from an optically transparent material, including, but not limited to glass, quartz, plastics, or ceramics. Although not illustrated, it may be desirable to couple multiple cables  308  into a single photo detector  310  to monitor, for example, the status of any of three interrupters in a three phase contactor. Likewise, it may also be desirable to couple three photo detectors  310 , each having a separate cable  308 , into a single control unit  312 . One advantage of the present embodiment, is that both the control unit  312  and/or photo detector  310  may be remotely located from the interrupter. This allows convenient monitoring of the interrupter without having to remove power from the circuit. It should be noted that elements  308 ,  310 , and  312  are not to scale relative to the other elements in the figure. 
     Although the measurement of light  304  produced by the arcing of contacts  102 ,  104  is an indirect measurement of pressure in region  114 , it is nonetheless a direct observation of the mechanism that produces failure within the interrupter. At sufficiently low pressure, no significant contact arcing will be observed because the background partial pressure will not support ionization of the residual gas. As the pressure rises, light generation from arcing will increase. Photo detector  310  may observe the intensity, frequency (color), and/or duration of the light emitted from the arcing contacts. Correlation between data generated by contact arcing under known pressure conditions can be used to develop a “trigger level” or alarm condition. Observed data generated by photo detector  310  may be compared to reference data stored in controller  312  to generate the alarm condition. Each of the characteristics of light intensity, light color, waveform shape, and duration may be used, alone or in combination, to indicate a fault condition. Alternatively, data generated from first principles of plasma physics may also be used as reference data. 
       FIG. 4  is a partial cross sectional view  400  of a cylinder actuated optical pressure switch  404  in the low pressure state, according to an embodiment of the present invention.  FIG. 5  is a partial cross sectional view  500  of a cylinder actuated optical pressure switch  404  in the high pressure state, according to an embodiment of the present invention. In these embodiments, a pressure sensing cylinder device  404  comprises a piston  406  coupled to spring  410 . Chamber  408  is fluidically coupled to the interior of interrupter  402  for sensing the pressure in region  416 . A shaft  412  is attached to piston  406 . Attached to shaft  412  is a reflective device  414 , which may any surface suitable for returning at least a portion of the light beam emitted from optic cable  418  to optic cable  420 . At low pressure, shaft  412  is retracted within cylinder  404 , tensioning spring  410 , as is shown in  FIG. 4 . Fiber optic cables  418  and  420 , in concert with photo emitter  422 , photo detector  424 , and control unit  426 , detect the position of shaft  412 . At high pressure, spring  410  extends shaft  412  to a position where reflective device  414  intercepts a light beam originating from fiber optic cable  418  (via photo emitter  422 ), sending a reflected beam back to photo detector  424  via cable  420 . An alarm condition is generated when photo detector  424  receives a signal, indicating a high pressure condition in interrupter  402 . The pressure at which shaft  412  is extended to intercept the light beam is determined by the cross sectional area of piston  406  relative to the spring constant of spring  410 . A stiffer spring will create an alarm condition at a lower pressure. Fiber optic cables  418  and  420  provide the necessary electrical isolation for the circuitry in devices  422 – 426 . While the previous embodiments have shown the fiber optic cables transmitting and detecting a reflected beam, it should be evident that a similar arrangement can be utilized whereby the ends of each optical cable  418  and  420  oppose each other. In this case, the end of shaft  412  is inserted between the two cables, blocking the beam, when in the extended position. An alarm condition is generated when the beam is blocked. 
       FIG. 6  is a partial cross sectional view  600  of a bellows actuated optical pressure switch in the low pressure state, according to an embodiment of the present invention.  FIG. 7  is a partial cross sectional view of a bellows actuated optical pressure switch in the high pressure state, according to an embodiment of the present invention. Bellows  602  is mounted within interrupter  402 , and is sealed against the inside wall of the interrupter such that a vacuum seal for the interior of the interrupter  402  is maintained. The inside volume  604  of the bellows is in fluid communication with the atmospheric pressure outside the interrupter. This can be accomplished by providing a large clearance around shaft  606  or an additional passage from the interior of the bellows  602  through the exterior wall of the interrupter (not shown). Bellows  602  is fabricated in such a manner as to be in the collapsed position shown in  FIG. 7  when the pressure inside the bellows is equal to the pressure outside the bellows. When a vacuum is drawn outside the bellows, the bellows is extended toward the interior of region  416  of interrupter  420 . At the alarm (high) pressure condition shown in  FIG. 7 , shaft  606  is extended, placing reflective device  608  in a position to intercept a light beam from cable  418 , and reflect a least a portion of the beam back through cable  420  to detector  424 . The “stiffness” of the bellows relative to its diameter, determine the alarm pressure level. A stiffer bellows material will result in a lower alarm pressure level. Fiber optic cables  418  and  420  provide the necessary electrical isolation for the circuitry in devices  422 – 426 . While the previous embodiments have shown the fiber optic cables transmitting and detecting a reflected beam, it should be evident that a similar arrangement can be utilized whereby the ends of each optical cable  418  and  420  oppose each other. In this case, the end of shaft  606  is inserted between the two cables, blocking the beam, when in the extended position. An alarm condition is generated when the beam is blocked. 
       FIG. 8  is a partial cross sectional view  800  of an optical device for detecting sputtered debris from the electrical contacts, according to an embodiment of the present invention. As the pressure increases inside the interrupter, arcing will occur in gap  306  between contacts  102  and  104 . The arcing will “sputter” material from the contact surfaces, depositing this material on various interior surfaces. In particular, sputter debris will be deposited on surface  802 , and on window  302  interior surface  808 . A light beam emitted from optic cable  418  is transmitted through window  302  to reflective surface  802 . Reflective surface  802  returns a portion of the beam to optic cable  420 . The amount of sputtered debris on window surface  808  will determine the degree of attenuation of the light beam  806 . If the beam is attenuated below a certain amount, an alarm is generated by control unit  426 . Additionally, sputter debris may also cloud reflective surface  802 , resulting in further beam attenuation. Ports  804  are placed in the vicinity of window  302 , to aid in transporting any sputtered material to the window surface. This embodiment has the capability of providing a continuous monitoring function for detecting slow degradation of the vacuum inside the interrupter. Beam intensity can be continuously monitored and reported via controller  426 , in order to schedule preventative maintenance as vacuum conditions inside the interrupter worsen. 
       FIG. 9  is a partial cross sectional view  900  of a self powered, optical transmission microcircuit  902 , according to an embodiment of the present invention. Microcircuit  902  contains a substrate  904 , a photo transmission device  906 , a pressure measurement component  908 , amplifier and logic circuitry  910 , and an inductive power supply  912 . Microcircuit  902  can be a monolithic silicon integrated circuit; a hybrid integrated circuit having a ceramic substrate and a plurality of silicon integrated circuits, discrete components, and interconnects thereon; or a printed circuit board based device. The pressure within the interrupter in regions  114  and  114 ′ are measured by a monolithic pressure transducer  908 , interconnected to the circuitry on substrate  904 . Amplifier and logic circuitry  910  convert signal information from the pressure transducer  908  for transmission by optical emitter device  906 . The optical transmission from device  906  is delivered through window  302  to control unit  426  via optical cable  420 , situated outside the interrupter. The optical transmission can be either analog or digital, preferably digital. Microcircuit  902  can deliver continuous pressure information, high pressure alarm information, or both. The inductive power supply  912  obtains its power from the oscillating magnetic fields within the interrupter. This is accomplished by placing a conductor loop (not shown) on substrate  904 , then rectifying and filtering the induced AC voltage obtained from the conductor loop. Photo transmission device  906  can be a light emitting diode or laser diode, as is known to those skilled in the art. Construction of the components on substrate  904  can be monolithic or hybrid in nature. Since none of the circuitry in device  902  is referenced to ground, high voltage isolation is not required. High voltage isolation for devices  424 ,  426  is provided by optical cable  420 , as described in previous embodiments of the present invention. 
       FIG. 10  is a partial cross sectional view  1000  of a self powered, RF transmission microcircuit  1002 , according to an embodiment of the present invention. Microcircuit  1002  contains a substrate  1004 ; a pressure measurement component  1006 ; amplifier, logic, and RF transmission circuitry  1008 ; and an inductive power supply  1010 . Microcircuit  1002  can be a monolithic silicon integrated circuit; a hybrid integrated circuit having a ceramic substrate and a plurality of silicon integrated circuits, discrete components, and interconnects thereon; or a printed circuit board based device. The pressure within the interrupter in regions  114  and  114 ′ are measured by a monolithic pressure transducer  1006 , interconnected to the circuitry on substrate  1004 . Amplifier and logic circuitry convert signal information from the pressure transducer  1006  for transmission by an RF transmitter integrated within circuitry  1008 . The RF transmission from device  906  is delivered through insulator  106  to receiver unit  1014 , situated outside the interrupter. Various protocols and methods are suitable for RF transmission from integrated circuitry, as are well known to those skilled in the art. For purposes of this disclosure, RF transmission includes microwave and millimeter wave transmission. Receiver unit  1014  may be located at any convenient distance from the interrupter, within range of the transmitter contained within microcircuit  1002 . Receiver unit may set up to monitor the transmissions from one or a plurality of microcircuits resident in multiple interrupter devices. Unit  1014  contains the necessary processors, memory, analog circuitry, an interface circuitry to monitor transmissions and issues alarms and other information as required. The inductive power supply  1010  obtains its power from the oscillating magnetic fields within the interrupter. This is accomplished by placing a conductor loop (not shown) on substrate  1004 , then rectifying and filtering the induced AC voltage obtained from the conductor loop. 
       FIG. 11  is a schematic view  1100  of a diaphragm actuated optical pressure switch in the low pressure state, according to an embodiment of the present invention.  FIG. 12  is a schematic view  1200  of a diaphragm actuated optical pressure switch in the high pressure state, according to an embodiment of the present invention. A low cost alternative embodiment for detecting high pressures within the interrupter can be obtained through use of a diaphragm  1101 . Diaphragm  1101  is fixed to structure  1104 , which is generally hollow and tubular in shape. Structure  1104  is in turn fastened to a portion of interrupter segment  1106 . Alternatively, diaphragm  1101  could be attached directly to a an outer surface of the interrupter, if convenient. Due to the fragile nature of the thin dome material, structure  1104  acts as a weld or braze interface to the thicker metal structure of the interrupter. Possibly, structure  1104  could be brazed to a port in the insulator section (for example, ref  106  in prior figures) as well. At low pressures inside the interrupter, dome  1101  would reside in the collapsed position, as shown in  FIG. 11 . At high pressure, dome  1101  would be in the extended position of  FIG. 12 . The pressures at which the dome transitions from the collapsed position to the extended position would be within the range of 2 to 14.7 psia, preferably between 2 and 7 psia. The dome position is detected by components  418 – 426 . In the low pressure state, the collapsed dome produces a relatively flat surface  1102 . A light beam generated by emitter device  422  is transmitted to surface  1102  via optical cable  418 . A reflected beam is returned from surface  1102  to optical detector device  424  via optical cable  420 . At a high pressure condition, the dome snaps into an approximately hemispherical expanded shape, having significant curvature in its surface  1202 . This curvature deflects the light beam emitted from the end of optical cable  418  away from the receiving end of cable  420 , causing a loss of signal at detector  424 , and generating an alarm condition within the circuitry of device  426 . It is also be possible to reverse the logic by using optical cables  418  and  420  to detect the near proximity of the dome in its extended position, creating a loss of signal when its pulled down into an approximately flat position. Alternatively, the position of the dome may be detected by a mechanical shaft (not shown) placed in contact with the dome&#39;s outer surface, the opposite end of the shaft intercepting and optical beam as is shown in the embodiments of  FIGS. 4–7 .