Abstract:
Thermographic imaging equipment is incorporated directly into cabinets housing electrical switchgear to provide for dedicated, nearly continuous monitoring of the contained equipment. A mechanical scanning technique may allow low-cost sensors to provide essentially continuous thermographic monitoring. Dedicated thermal imaging equipment allows automatic analysis through predefined temperature threshold maps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to thermographic monitoring of electrical equipment and, in particular, to a system allowing automatic in-cabinet thermographic monitoring. 
     Preventive and predictive maintenance strategies monitor equipment to avoid costly repair and lost production associated with unexpected equipment failures. Preventative maintenance institutes regularly scheduled monitoring of electrical equipment, component replacement, and minor repairs. Predictive maintenance uses monitored data to more accurately assess maintenance scheduling and equipment replacement. 
     Thermographic monitoring can be used with preventive and predictive maintenance and employs cameras that are sensitive in the far infrared region (typically 3-15 μm) to provide non-contact thermal measurement of surface temperatures of equipment. Particularly for electronic equipment, such thermographic images may provide advanced warning of equipment failure that would not otherwise be apparent. High temperatures may indicate, for example, high resistance electrical junctions, overvoltage or overcurrent, damaged insulation or damaged conductors that may ultimately lead to catastrophic failure. A thermographic image can be taken while the equipment is in operation with minimal operator risk. Further, a thermographic image can simultaneously measure multiple components allowing rapid monitoring of many potential failure points. 
     There are a number of limitations to thermographic imaging. First, the equipment is relatively expensive and requires a trained operator to perform inspections and analyze the images. Second, although the inspections do not require contact with equipment, they can expose the operator to the risks attendant to being near operating equipment, e.g. arc flash and explosions. These risks can be minimized to some extent by the provision of infrared transparent ports or openable shutters in the equipment cabinets allowing the operator to perform the inspection without opening the equipment housings. Finally, the thermographic monitoring is necessarily periodic and may miss rapidly developing equipment failures. 
     One method of providing substantially continuous monitoring of electrical equipment is the attachment of thermal sensors (such as thermocouples or solid-state devices) directly to various portions of the equipment to provide for real time thermal monitoring. Such instrumentation of equipment can be complex and expensive if multiple points are to be monitored and is generally impractical for custom installations. The wiring attendant to such monitoring presents additional risk of short-circuits within the cabinet. 
     SUMMARY OF THE INVENTION 
     The present invention provides a low-cost, multipoint thermal monitoring system that avoids some of the disadvantages of conventional thermal monitoring by using thermographic cameras permanently installed in equipment cabinets. This is made practical, as a cost matter, through the use of a scanning camera system that may be relatively slow, and yet practical for an in-cabinet system that does not require the attendance of a human operator. The use of dedicated thermal cameras permits sophisticated automatic monitoring systems that isolate different components and track thermal conditions as a function of a state of an ancillary control process. 
     Specifically then, the present invention provides an electrical component cabinet including a housing providing fire resistant walls enclosing a housing volume and providing at least one internal component mounting panel within the housing volume for the attachment of electrical components thereto. A thermographic camera is attached to a housing wall opposite the mounting panel for imaging the electrical components, the thermographic camera being sensitive in the region of 3-15 μm. A remote monitoring station is provided communicating with the thermographic camera via an electrical connection to receive thermographic images of components attached to the internal component-mounting panel. 
     It is thus one object of the invention to provide automated multipoint thermal monitoring. 
     The thermographic camera may provide a mechanically scanned thermally sensing element. 
     It is thus an object of the invention to provide an extremely cost-effective thermographic camera taking advantage of the fact that relatively slow imaging is acceptable in a stationary camera system. 
     The mechanical scanning may use a mirror system scanning the mounting panel. 
     It is thus an object of the invention to provide for a compact thermographic camera. 
     Alternatively, the mechanical scanning may use a track for moving the thermally sensing element. 
     It is thus an object of the invention to provide a camera system having an extremely large field of view. 
     The housing may include an access door and the track may include two vertical rails flanking the door and a horizontally extending carriage moving along the vertical rails and supporting the thermally sensing element for movement therealong. The system may include a camera parking system for moving the carriage to an extreme point on the tracks when the door is opened. 
     It is thus an object of the invention to provide a front view of the electrical components that does not interfere with access to the components through the cabinet door. 
     The thermally sensing element may be a pyroelectric element. 
     Is thus an object of the invention to provide an extremely low-cost thermal imaging element. 
     The mounting panel may be on a wall of the housing opposite a door providing access to the housing and the thermographic camera may be attached to an inner surface of the door. 
     It is thus an object of the invention to provide a mounting that provides a good view of multiple electrical components without interference with those components. 
     The electrical connection may be a network connection. 
     It is thus an object of the invention to allow multiple cabinets to be readily monitored. 
     The electrical connection may be a radio transceiver system. 
     It is thus an object of the invention to eliminate the need for direct electrical connection between the remote station and the camera, simplifying installation. 
     The remote monitoring may evaluate received thermographic images on a predetermined schedule to provide an alarm if a predetermined temperature threshold is exceeded. 
     It is thus an object of the invention to provide more nearly continuous monitoring than can be obtained using a human operator and a thermographic camera. 
     The remote monitoring station may provide at least one mask corresponding to a thermographic image from the thermographic camera; the mask may provide temperature thresholds for different mask regions. The remote monitoring station may automatically compare temperatures of the thermographic image within the different mask regions to the temperature thresholds associated with the masked regions to generate an alarm when the temperature thresholds are exceeded for a given mask region. 
     It is thus an object of the invention to provide for custom multipoint monitoring allowing different temperature thresholds for different components. 
     The remote monitoring station may communicate with a controller activating electrical components mounted to the mounting panel in a series of control states and the remote monitoring station may select among different masks corresponding to different control states for the generation of the alarm. 
     It is thus an object of the invention provide a monitoring that may be dynamically adjusted according to component operating state. 
     The remote monitoring station may monitor successive thermographic images to detect degradation associated with dirt accumulating on optics of the thermographic camera to generate an alarm when the degradation exceeds a predetermined threshold. For example, the detected degradation may be a decrease in thermographic contrast. 
     It is thus an object of the invention to accommodate contamination problems incident to permanent installation of thermographic cameras in electrical cabinets. 
     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view, in phantom, of a standard electrical cabinet holding switchgear components, the cabinet having an infrared port for thermographic monitoring of the switchgear components; 
         FIG. 2  is a cross-section along the horizontal plane through a cabinet similar to that of  FIG. 1  showing a first embodiment of the invention mounting a dedicated thermographic camera on a front wall of the cabinet for monitoring of components inside the cabinet; 
         FIG. 3  is a block diagram of a camera system of  FIG. 2  providing for a mechanical scanning using a mirror and a wireless connection to a remote station in communication with an industrial controller; 
         FIG. 4  is a perspective view in phantom of the cabinet of  FIG. 1  employing a thermographic camera providing for mechanical scanning using a track assembly; 
         FIG. 5  is a figure similar to that of  FIG. 2  showing the use of two cameras to provide for more complete component coverage; 
         FIG. 6  is a simplified representation of image masks used by the remote station for establishing different temperature thresholds for different portions of the thermographic image; 
         FIG. 7  is a portion of a flowchart implemented by the remote station for providing control state awareness in the thermographic monitoring; and 
         FIG. 8  is a one-dimensional representation of two successive thermographic images showing processing for determination of optical degradation caused, for example, by contamination of the thermographic camera. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a switchgear cabinet  10  may have a rear vertical wall providing a mounting panel  12  surrounded by forwardly extending sidewalls  14 , top wall  16  and bottom wall  18  to provide a protected volume enclosed by front door  20  opposite the mounting panel  12 . Typically the cabinet  10  is constructed of steel panels to provide a strong and fire resistant housing. 
     The front door  20  may be opened and closed for access to the enclosed volume in the cabinet  10  by means of a handle  22  which may turn to lock the cabinet  10  and which may be connected to an electrical interlock (not shown) or the like to disconnect power from the cabinet  10  when the door  20  is opened. The door  20  may support a port  23  providing either an infrared transparent window or an openable shutter allowing viewing of internal components by a thermographic camera  21  by a human operator while providing maximum protection to the operator. 
     The cabinet  10  may include multiple electrical components  24 , for example: circuit breakers, disconnects, contactors, over-load relays, motor starters, and switches. The electrical components  24  are characterized by having internal conductors rated for handling powers in excess of 100 volt-amperes such as present a potential of destructive electrical overheating. The electrical components  24  may be mounted on the mounting panel  12  to be, ideally, within an inspection cone  27  defined by the port  23  and the optics of the camera  21 . 
     Referring now to  FIG. 2 , in the present invention a port  23  may be eliminated and a thermographic camera  26  may be mounted on the inner surface of the door  20  to provide an inspection cone  27  also subtending the electrical components  24 . 
     Referring also to  FIG. 3 , in the first embodiment, the camera  26  may include a single infrared sensitive element  28  whose optical axis  30  may be scanned in a raster pattern  32  within the inspection cone  27  by means of a gimbaled mirror  34  tipping about an x and y axis under the control of servomotors  36  controlled by a camera acquisition unit  38 . Infrared transmissive optics (not shown), either in the form of a front surface focusing mirror or a Fresnel lens may be used to provide a spot field of view suitable for scanning. Alternatively collimation type systems, for example a tube or the like, may be used. 
     The optical axis  30  may be chopped by a mechanical blade system  39  as is known in the art to permit absolute temperature assessments and to eliminate problems of thermal drift. A signal  40  obtained from the infrared sensitive element  28  may be received by an image reconstructor  42  which maps values of the signal  40  to points in the raster pattern  32  to produce a thermographic image  60  in much the same manner as a photograph. The thermographic image  60  may be provided to a transmitter  44  having any antenna  50  outside of the cabinet  10  for transmitting the thermographic image  60  to a remote station  52 . 
     Power for the acquisition unit  38  may be obtained by a current transformer or tap  47  that may be attached to power wiring elsewhere in the cabinet  10  for simple installation. Because the inside of the door  20  is typically free from circuitry and has a good vantage point of the electrical components  24 , retrofit installations may be readily had. 
     Referring now to  FIG. 4 , in an alternative embodiment, the thermographic camera  26 ′ may provide for an infrared sensitive element  28  that is scanned in a raster pattern matching the raster pattern  32 . In this case, the infrared sensitive element  28 , for example, may be held on a horizontal track  51  to be moved therealong under computer control, for example, from the acquisition unit  38 , the latter driving a stepper motor and belt system in the horizontal track  51  of a type known in the art. Horizontal track  51  may in turn be suspended by its ends on vertical tracks  53  preferably flanking the opening of the door  20  to be out of the way of the door  20 . The attachment between the horizontal track  51  and the vertical tracks  53  allows movement of the horizontal track  51  vertically also under control of the acquisition unit  38  using stepper motors and belt systems in the vertical tracks  53  of a type known in the art. 
     This version of the camera  26 ′ may provide for an extremely large acquisition cone  27 , being effectively the area of the raster  32 , and simplified optics without the need for focusing lenses or the like, which however may be used if desired. 
     A signal from the door handle  22 , which typically also provides for an electrical interlock to the internal components  24 , may be provided to the acquisition unit  38  to move the horizontal track  51  to a park position at either fully up or fully down limits to allow ready access to the interior of the cabinet  10  through the door  20 . 
     Referring now to  FIG. 5 , in yet an alternative embodiment, two cameras  26   a  and  26   b  may be mounted opposite the mounting panel  12  on sidewalls  14  to provide overlapping inspection cones  27   a  and  27   b  providing improved visibility of components throughout the cabinet  10  including when mounted on the sidewalls  14 . Because the cameras  26   b  and  26   a  need not be mounted on the door  20 , in-cabinet wiring may be simplified. 
     Referring still to  FIGS. 3 and 6 , the remote station  52  may receive the thermographic images  60  on a regular schedule, for example, using a polling system implemented by software program  54  held in the remote station  52 . In the polling system, the remote station  52  requests image data from the acquisition units  38  of one or more cabinets  10  using a periodic polling message. Alternatively a data “push” system may be used allowing the acquisition units  38  to transmit on periodic schedule, for example, at different times on the same channel or on different channels. 
     Upon receipt of the thermographic images  60 , the remote station  52  matches each incoming thermographic image  60  to a mask  62  for that particular cabinet  10 . The mask  62  defines multiple regions  64   a ,  64   b , and  64   c  within the image  60  that are in turn mapped to predetermined temperature thresholds  66   a ,  66   b , and  66   c . The regions  64  may circumscribe particular component images  65  to identify pixels within the image  60  associated with a particular component  24  and thus the temperature of the component  24  isolated from other components  24 . In this way, the thermographic images  60  may be automatically analyzed, and if the temperature in a particular mask region  64  exceeds its corresponding temperature threshold  66  an alarm may be sounded. By defining multiple regions  64   a ,  64   b , and  64   c  within each image  60 , components  24  (or elements of components  24 ) that are normally hotter may be given thresholds that are higher than elements that normally run cooler. 
     The remote station  52  may communicate with data entry devices  61  for the entry of custom temperature thresholds and for defining the masks (for example by drawing on thermographic images  60 ) presented on an attached display  63 . 
     Referring again to  FIG. 3 , preferably the remote station  52  may communicate with a programmable logic controller  70  of the type known in the art, for example, as manufactured by Rockwell Automation Inc. of Milwaukee, Wis., executing a control program  72  for the control of industrial machines and processes implemented, in part, through the electrical components  24 . In particular, the programmable logic controller  70  may communicate through one or more I/O modules  74  directly with the electrical components  24  or with elements that control the electrical components  24 . In this way, the remote station  52  may have state knowledge of the control process and may select different masks  62  depending on the state of the machine and thus the state of the electrical components  24 . 
     Thus, referring to  FIG. 7 , at each machine state  80  determined from the programmable logic controller  70 , an appropriate mask  62  may be selected and the temperature distribution may be evaluated at decision block  82  according to that mask  62 . In this way, for example, when the electrical components  24  are in an idle state, a mask  62  having low temperature thresholds  66  may be used to detect aberrant operating conditions providing improved sensitivity. If the temperature for that state  80  is exceeded, an alarm may be sounded as indicated by process block  86 . In contrast, when the electrical components  24  are being exercised by control of the process, a mask  62  having higher temperature thresholds  66  may be used to decrease false alarms. 
     The temperatures at each state  80  may be recorded per process block  86  and those temperatures used, for example, in comparison with temperatures at other states  80 ′ to help establish an alarm threshold  66  as indicated by process block  88 . Thus, for example, idle temperatures may be used to establish a baseline for operating temperatures. 
     Referring now to  FIG. 8 , successive images  60   a  and  60   b  (here depicted as a single image line) may be statistically analyzed to detect the degradation of the optics of the camera  26 , for example dirt on the lens or mirror system. One particular algorithm for detecting dirt may consider the range  90  or variance of the new data of the thermographic image  60  being computed according to standard statistical techniques. A decrease in variance may, for example, indicate that the lens is dirty and thus trigger maintenance by a human operator. 
     The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.