Abstract:
One or more infrared transmitting ports are placed in the insulating housing of standard switchgear components to allow far infrared viewing of internal conductive components permitting earlier and more precise location of possible thermal failure through thermographic monitoring.

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 electrical switchgear allowing improved thermographic monitoring. 
     Preventive and predictive maintenance techniques provide for the monitoring of equipment to avoid costly repair and lost production associated with unexpected equipment failures. Preventive 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 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. A thermographic image can encompass multiple equipment components allowing rapid monitoring of many potential failure points. 
     Electrical switchgear, such as contactors and the like, is typically encased in a housing of electrically insulating, fire retardant material intended to protect users from electrical arcing and high voltages, as well as to protect internal components of the switchgear from external contamination. The materials from which such housings are constructed must meet a demanding set of requirements including: high temperature resistance, high tensile strength, high flexural modulus, low warpage, good dimensional stability, and low moisture absorption. The need to encase the electrical components of the switchgear in such materials can limit the effectiveness of thermographic monitoring of switchgear, requiring substantial rise in the temperature of the housing before a thermographic image can be obtained. 
     SUMMARY OF THE INVENTION 
     The present inventors have recognized that the competing goals of switchgear housing design and thermographic imaging may be reconciled by the placement of infrared ports within the housing, for example, in the form of one or more light pipes aligned with critical components of the switchgear and passing through the housing. By limiting the size of the ports, infrared transmission may be optimized without compromising the mechanical strength or protective qualities of the switchgear housing. 
     Specifically then, the present invention provides an electrical switchgear component having an electrically insulating and flame retardant housing holding at least one electrical conducting element for conducting electrical currents therethrough. The housing provides at least one electrically insulating optical element substantially transparent to infrared energy in the range of 3-15 μm, the optical element having a first end within the housing receiving infrared light from heating of the electrical conducting element and a second end passing through the housing to be visible from outside of the housing. 
     It is thus an object of the invention to provide an improved switchgear housing amenable to thermographic monitoring. 
     The optical element may be a thermoplastic material. 
     It is thus another object of the invention to provide a housing constructed of materials that may be readily fabricated in parallel with the other elements of the switchgear. 
     The housing may be generally rectangular having a first surface for mounting against a cabinet wall and wherein the optical element passes through a second surface opposite the first surface. 
     It is thus an object of the invention to transmit important thermographic information on a single readily viewable face of the switchgear. 
     The housing may include a second electrically insulating optical element transmitting infrared energy in the range of 3-15 μm having a first end within the housing receiving infrared light from heating of the electrical conducting element and having a second end passing through a second surface perpendicular to the first surface. 
     It is thus an object of the invention to permit switchgear to be mounted on the rear or side panel of a conventional metal cabinet. 
     The optical element may be constructed of two separate light conductive channels of different materials having different infrared energy transmission characteristics. 
     It is thus an object of the invention to provide for a broad-spectrum infrared port using commonly available thermoplastic materials. 
     The optical element is curved to conduct infrared energy by means of internal reflections. 
     It is thus an object of the invention to provide for light pipes allowing convenient transmission of infrared energy to observation points. 
     The electrical conducting element is a conductive metal bar or alternatively an electrical coil forming part of an electromechanical relay. 
     It is thus an object of the invention to allow improved monitoring of critical switch elements. 
     The first end of the optical element includes a lens focusing light from the electrical conducting element. The lens may be a Fresnel lens. 
     It is thus an object of the invention to provide light collecting capabilities improving the sensitivity of the thermographic monitoring process. 
     The second end of the optical element provides a diffuser. 
     It is thus another object of the invention to provide improved imaging acquisition angles for the infrared energy. 
     The switchgear may further include an infrared mirror positioned between the optical element and the electrical conducting element. 
     It is thus another object of the invention to permit substantial optical path lengths with minimal infrared attenuation. 
     The switchgear may comprise: circuit breakers, disconnects, contactors, overload relays, switches and motor starters. 
     It is thus an object of the invention to provide a technique suitable for common power devices where thermographic monitoring would prove useful. 
     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 perspective view of a switchgear component such as may be installed in the cabinet of  FIG. 1  showing the addition of infrared ports for monitoring internal temperatures; 
         FIG. 3  is a cross-sectional view along lines  3 - 3  of  FIG. 2  showing placement of infrared ports for monitoring internal conductors; 
         FIG. 4  is a fragmentary view similar to that of  FIG. 3  showing a port for monitoring a solenoid coil in a contactor; 
         FIG. 5  is a perspective fragmentary view of a corner of the switchgear component of  FIG. 2  showing the use of light pipes allowing thermographic monitoring from a front and side surface of the switchgear component; 
         FIG. 6  is a perspective view of a light pipe and a window formed from multiple materials to optimize infrared transmission range, the light pipe further providing a lens surface and diffuser surface; 
         FIG. 7  is a fragmentary view similar to that of  FIG. 3  showing the use of an infrared mirror and Fresnel lens for optimizing infrared transmission; and 
         FIG. 8  is a fragmentary perspective view of an alternative embodiment of the invention with a terminal block cover constructed of infrared transparent material. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a switchgear cabinet  10  may provide a rear vertical wall  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 rear vertical wall  12 . Typically the cabinet  10  is constructed of steel panels to provide a strong and fire resistant enclosure. 
     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 and which may be connected to an electrical interlock or the like. 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 (not shown) while providing maximum protection to the camera operator. 
     The cabinet  10  may include multiple switchgear components including, for example: circuit breakers  24 , disconnect  26 , contactors  28 , over-load relays  30 , motor starters  32 , and switches  34 . While such switchgear is typically electromechanical, the present invention also contemplates switchgear providing the same functionality using solid-state, semiconducting, elements such as silicon-controlled rectifiers (SCRs). The switchgear components 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 switchgear components  24 - 34  may be mounted on the rear vertical wall  12  or on the sidewalls  14  to be, ideally, within an inspection cone defined by the port  23 . 
     Referring now to  FIG. 2 , an example switchgear component of contactor  28  provides for a mounting flange  36  having mounting holes  38  for mounting the flange  36  against the rear vertical wall  12  or sidewalls of the cabinet  10 . The flange  36  may form part of a contactor housing  39 , the housing being generally rectangular. The contactor  28  may provide for multiple internal contact sets  40  each presenting screw terminals  42  to receive wiring through the top and bottom surfaces  15  of the contactor  28 , with the screw terminals accessible for tightening through apertures  44  in a front surface  17  of the contactor  28 . The apertures  44  are constructed to minimize the possibility of contamination entering into the housing  39 . 
     A central window  46  in the front surface  17  of the contactor  28  passing light in the visible spectrum may be used to reveal the position of a contact bar  50  associated with an internal solenoid  52  (both shown in  FIG. 3 ). 
     Generally, the present invention adds a series of infrared transmitting infrared ports  48  to the housing  39  to permit the optical transmission of far infrared (3-15 μm) radiation from inside the housing  39  to one or more points visible outside the housing  39 . The infrared ports  48  thus preserve the integrity of the housing  39  in preventing the ingress of contamination (in contrast to a hole). The infrared ports  48  may be exposed through a front surface  17  of the housing  39  opposite the flange  36  or through one or both side surfaces  19  perpendicular to the flange  36  allowing for the mounting of the contactor  28  on either the rear vertical wall  12  or sidewalls  14  while still allowing the portions of the infrared ports  48  exposed through the housing  39  to be visible through the port  23  on door  20  of the switchgear cabinet  10 . The infrared ports  48  may provide a wider viewing angle than a simple aperture, for example, by having a properly shaped outer surface to redirect the thermal energy over a wider viewing angle by prismatic or diffusing elements. 
     Referring now to  FIG. 3 , each contact set  40  may have a movable contact bar  50  attached to a solenoid  52  to move toward and away (and thus to connect with and disconnect from) internal stationary contacts  54   a  and  54   b . The internal stationary contacts  54   a  and  54   b  in turn may connect through conductor  56  with corresponding screw terminals  42 . As noted above, typically the screw terminals  42 , will receive wiring through apertures  58  in the top or bottom surfaces  15  of the housing  39 . Generally, the apertures  58  are sized so that they are largely filled by the wiring received by terminals  42  preventing the ingress of dirt or environmental contamination. 
     Portions of the conductors  56  are aligned beneath infrared ports  48  on the front surface  17  of the housing  39  allowing infrared energy  60  in the far infrared region to pass therethrough. Monitoring the temperature of the conductors  56  provides a measure of the temperature both of the screw terminals  42  and the contacts  54  by means of high thermal conduction through the conductors  56 . Alternatively, but not shown, infrared ports  48  may be aligned directly with the contacts  54  or screw terminals  42 . 
     The infrared ports  48  may be constructed of a thermoplastic that provides for a high degree of transmission in the far infrared region. Generally such plastics do not meet the requirements of the material of the housing  39 , but their limited area permits them to be included in the housing  39  without significantly compromising the structural characteristics of that housing  39 . Plastic material suitable for use in this application, for example, may be commercially available from Fresnel Technologies Inc. of Fort Worth, Tex. under the trade names of Poly IR. In certain applications other materials providing far infrared transmission may also be used, including for example synthetic sapphire (Al2O3) or quartz (SiO2). The infrared ports  48  may be snapped into place in a completed housing  39 , co-molded with the housing  39 , glued in place, or held under an installed flange according to techniques well known in the art. 
     Referring now to  FIG. 4 , in an optional embodiment, an infrared light pipe  62  may be provided in the front surface  17  having a canted end  64  allowing the infrared light pipe  62  to be laterally displaced from its target (in this case internal solenoid  52 ) while providing for the collection of infrared energy  60  from the internal solenoid  52  itself. In this way, the collection of infrared energy may be had without interference with the central window  46 , previously described, providing a view of the contact bar  50  in the visible spectrum. 
     Referring now to  FIG. 5 , infrared ports  48  exposed at the front surface  17  of the contactor  28  may be supplemented with light pipes  66  laterally conducting far infrared light, for example, from conductors  56  to a side surface  19 . The light pipes  66  may employ internal reflection to conduct light to an arbitrary location on the side surface  19  over a curved optical path. 
     Referring now to  FIG. 6 , conveniently, the optical elements comprising the infrared ports  48  and infrared light pipes  62  and  66  may be constructed of multiple different polymer materials to pass a broad transmission spectrum. For example the infrared optical elements of infrared ports  48  and infrared light pipes  62  and  66  may have a portion constructed of a first polymer  70  having a spectrum  72  providing, for example, substantial transparency in a range of 7-12 μm and a second polymer  74  having substantial transparency beyond 12 μm as indicated by spectrum  76 . In this way, the optical elements of infrared ports  48 , and infrared light pipes  62  and  66  may be manufactured using common manufacturing techniques while still providing for broad spectral transmission useful for optical thermography. 
     The optical elements of infrared ports  48  and infrared light pipes  62  and  66  may have an outer roughened surface  78  providing a diffuser facing out of the housing  39  to allow for a range of viewing angles of the exposed ends of the infrared ports  48  and infrared light pipes  62  and  66  and an inner lens  80  designed to provide for improved acquisition of infrared energy from a target inside the housing. 
     Referring now to  FIG. 7 , the high attenuation of polymer materials in the infrared range may be accommodated for a long optical path through the use of a front surface infrared mirror  82 , for example being metallized plastic, providing for free space transmission of infrared energy  60 . The infrared mirror  82  may be a planar mirror positioned on an inner surface of the front surface  17  to reflect light at an angle from the conductors  56  to an infrared port  48  on the side surface  19 . The optical port may include a Fresnel lens  49  focused through an infrared mirror  82  on conductor  56  to reject infrared light from other surfaces and thus to provide for selectivity. Alternatively, the infrared mirror  82  may be a concave mirror positioned beneath the conductor  56  to focus light on an opposed infrared port  48 . 
     Referring now to  FIG. 8 , the present invention contemplates that the optical elements may also be implemented as protective covers  90  composed entirely or predominantly of infrared transparent material and that may fit over, for example, terminal blocks  92  associated with switchgear and the like. 
     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.