Abstract:
A temperature monitor for monitoring plural locations on an electrical bus structure. The temperature monitor includes an infrared sensor for receiving infrared energy from a plurality of discrete predetermined locations on the bus structure, a first member defining a stationary first mask, a second member defining a rotating second mask, and a drive member driving the second member in rotation relative to the first member. Rotation of the second member relative to the first member defines an aperture translated across the first mask member to provide a moving line-of-sight that extends from the sensor and that scans to each of the discrete predetermined locations on the bus structure.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to temperature monitor and, more particularly, to a temperature monitor for providing temperature measurements taken at predetermined locations across a flexible connection of an isolated phase electrical bus conductor. 
       BACKGROUND OF THE INVENTION 
       [0002]    Large industrial electromagnet machines, such as large electrical generators used in power plants operate at extremely high energy levels. For example, large steam powered generators may operate at voltages on the order of 20,000 VAC and currents on the order of 20,000 Amps AC. The electrical power from the generator is typically carried to high potential step-up transformers by a power conductor structure comprising three large copper bus structures that are isolated from each other and are commonly known as isolated phase, or isophase, bus structures. Each isophase bus structure includes flexible connections, formed by flexible copper straps, located at spaced intervals along the bus structure. For example, there may be a flexible strap connection located every six to twenty feet along the bus structure. The flexible connections typically comprise multiple heavy flexible copper straps having opposing ends that are bolted into place on adjacently located sections of the bus structure. The flexible copper straps accommodate thermally induced expansion of the bus structures that can result from the high current transported through these structures. Large steam powered units may have up to forty flexible copper straps per flexible connection between the adjacent sections of the bus structure. 
         [0003]    Temperature changes along the isophase bus structure, such as may result from changes in the power conducted through the bus structure, can cause the bolts at either end of the flexible straps to loosen as the bus structures expand and contract. A loose connection at the interface between the flexible straps and the adjacent sections of the bus structure will result in decreased current flow in the loosened strap, causing an increase in the temperature of the remaining properly attached straps as they carry the current of the loosened strap, potentially resulting in further loosening of the bolts connecting the flexible straps. 
         [0004]    The flexible strap connections are enclosed in an isophase bus shell that surrounds the bus structure and is typically 30 to 60 inches in diameter. Accordingly, observation of the flexible connections is obstructed by the bus shell, making it difficult to monitor the condition of the flexible connections. A final failure of the bus structure generally occurs suddenly, with little or no warning since operation with only a few of the flexible straps securely in place may be sufficient to avoid or minimize a voltage drop across the flexible connection until the failure of the bus structure occurs. In particular, if a failure of the straps progresses to the end, there may be a big electrical arc that blows out the section of the isophase bus structure at the location of the strap failure. The resulting ground fault will trip the generator. However, current will continue to flow through the bus, providing energy to support the arc, until the large amount of energy in the generator rotor field has decayed and been converted to heat. Replacement parts to repair such a failure are often difficult to obtain quickly, such that a bus failure may result in an extended unplanned outage. 
         [0005]    It is known to provide an infrared monitoring device for measuring the temperature of a flexible connection on an isophase bus. For example, such an infrared monitoring device comprised an open aperture sensor, such as a thermopile, where the geometry of the aperture provided a wide field of view. Only a small portion of the field of view for the aperture included the flexible straps, and a relatively large portion of the field of view included the inner surface of the bus shell. Accordingly, changes in the temperature of the inner surface of the shell, which have a substantially higher energy output than the flexible straps, produce a greater effect on the readings of the monitoring device than even large changes in the temperature of the flexible straps. 
         [0006]    In an alternative implementation of the above-described monitoring technique, an infrared lens is positioned at the aperture to narrow the field of view seen by the sensor, and thus limit the field of view to the area of the flexible straps. Although addition of the infrared lens has been effective to narrow the field of view to monitor the flexible straps, there are still negative factors associated with this technique including the cost of the infrared lenses significantly increasing the expense of the system. In addition, infrared lenses generally have a wavelength band where they do not pass infrared radiation, and the lens provides an exposed optical surface that may collect dirt and/or dust to cause an erroneous low temperature measurement due to a reduction in the energy transmitted through the lens to the sensor. Further, even with the addition of the infrared lens, the monitoring device still only provides an average temperature measurement made across all of the straps located in the field of view of the lens, rather than enabling temperature measurements of the individual straps in the connection. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with one aspect of the invention, a temperature monitor is provided for monitoring plural locations on a structure. The temperature monitor comprises a sensor for receiving energy indicative of a temperature of a plurality of locations spaced from the sensor, a first member located between the sensor and the plurality of locations, the first member defining a first aperture, and a second member located between the sensor and the plurality of locations, the second member defining a second aperture. At least one of the first and second members is movable relative to the other of the first and second members to produce relative movement between the first and second apertures. The relative movement between the first and second apertures provides an unobstructed first line-of-sight between the sensor and at least a first location of the plurality of locations, permitting the sensor to receive energy indicative of a temperature of the first location. 
         [0008]    In accordance with another aspect of the invention, a temperature monitor is provided for monitoring plural locations on an electrical bus structure. The temperature monitor comprises an infrared sensor for receiving infrared energy from a plurality of discrete predetermined locations on a bus structure, a first member comprising a stationary first mask, a second member comprising a rotating second mask, and a drive member driving the second member in rotation relative to the first member. Rotation of the second member relative to the first member defines an aperture translated across the first mask member to provide a moving line-of-sight that extends from the sensor and that scans to each of the discrete predetermined locations on the bus structure. 
         [0009]    In accordance with a further aspect of the invention, a method of monitoring temperature at plural locations on an electrical bus structure is provided. The method comprises the steps of providing a temperature sensor at a location in spaced relation to an electrical conductor, providing a mask structure between the electrical conductor and the sensor, the mask structure comprising a first mask and a second mask, defining a plurality of lines of sight from the sensor to the electrical conductor by moving the second mask relative to the first mask, and determining a temperature at each of a plurality of laterally spaced locations on the electrical conductor, where each of the locations corresponds to a distinct angle defined by a line-of-sight extending from the sensor and passing through the mask structure to the electrical conductor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
           [0011]      FIG. 1  is a partially cut away perspective view of an isophase bus structure including a temperature monitor in accordance the present invention; 
           [0012]      FIG. 2  is an exploded view of a temperature monitor illustrating the present invention; 
           [0013]      FIG. 3  is a diagrammatic illustration of cooperating mask structures for the temperature monitor of  FIG. 2 ; 
           [0014]      FIG. 4  is a diagrammatic side elevation view illustrating a position sensor for the temperature monitor of  FIG. 2 ; and 
           [0015]      FIGS. 5A-5D  are diagrammatic illustrations of the operation of the temperature sensor sequentially obtaining a temperature reading from a series of adjacent locations on an electrical conductor of the isophase bus structure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
         [0017]    Referring to  FIG. 1 , an isophase bus structure  10  is illustrated including an electrical bus conductor  12  supported within an enclosure or shell  14  by a plurality of insulator assemblies  16   a,    16   b,    16   c,    16   d.  In the illustrated bus structure  10 , the electrical conductor  12  is configured with a square cross-section and is supported by four insulator assemblies  16   a,    16   b,    16   c,    16   d,  however, the present invention is not limited to this particular configuration for the electrical conductor  12  and other configurations, such as conductors having a circular configuration, may be incorporated in accordance with the principles of the invention described herein. 
         [0018]    The electrical conductor  12  is typically formed with one or more flexible connections  18 , illustrated herein by a set of straps  20  comprising four laterally spaced straps  20   a,    20   b,    20   c,    20   d  extending along each side of the electrical conductor  12  between longitudinally spaced conductor sections  12   a,    12   b  of the electrical conductor  12 . Each strap  20   a,    20   b,    20   c,    20   d  preferably comprises a flexible copper strap and includes opposing ends  22 ,  24  attached to the respective conductor sections  12   a,    12   b.  The ends  22 ,  24  are generally fastened in position on the conductor sections  12   a,    12   b  by bolts  26 . The flexible connection  18  accommodates thermally induced movements between the conductor sections  12   a,    12   b,  where the sets of straps  20  will flex as the gap between the conductor sections  12   a,    12   b  increases and decreases. 
         [0019]    In the event that the bolted connections at the ends  22 ,  24  of one or more of the straps  20   a,    20   b,    20   c,    20   d  become loose, a loss of current may occur across the connection of the loosened strap with an associated decrease in temperature, and a proportional increase in the temperature of the remaining straps  20   a,    20   b,    20   c,    20   d  at the flexible connection  18 . In order to detect such temperature changes, indicative of a current drop in the loosened strap  20   a,    20   b,    20   c,    20   d,  each of the sets of straps  20  may be monitored by a temperature monitor unit  28  mounted on the shell  14 . Specifically, a temperature monitor unit  28  (only two shown) may be mounted opposite each set of straps  20  located on each side of the electrical conduit  12  at the flexible connection  18 . 
         [0020]    Referring to  FIG. 2 , an exploded view of a temperature monitor unit  28  is shown and includes a housing  30  having an inner wall  32 . The inner wall  32  may be formed to define a first mask member  33  comprising a circular area. A plurality of elongated support members  34  are attached to the inner wall  32  and provide a mount for supporting a circuit board  36  in spaced relation to the inner wall  32 . The circuit board  36  defines a stationary base for supporting a drive member, such as a motor  38 , on an outer side  40  thereof. A rotatable motor shaft  42  is driven by the motor  38  and passes through a hole  44  in the circuit board  36  to support a rotatable disk member  46 , defining a second mask member  48 . The first and second mask members  33 ,  48  are located in close association with each other to define a mask structure. The motor shaft  42  extends along a rotation axis  50  that extends centrally through the first mask member  33  to support the disk member  46  for rotation concentrically with the first mask member  33 . 
         [0021]    The first mask member  33  includes a first elongated aperture  52  extending through the inner wall  32 . The first aperture  52  is configured as an elongated straight slot extending along a line  54  ( FIG. 3 ) that is spaced from the rotation axis  50  and is generally parallel to a tangent of the first mask member  33 . The line  54  defining the extension of the first aperture  52  is generally perpendicular to a longitudinal axis  56  ( FIG. 1 ) of the electrical conductor  12  when the monitor unit  28  is located in an operable position on the shell  14 , as illustrated in  FIG. 1 . 
         [0022]    As seen in  FIG. 3 , the second mask member  48  includes a second aperture  58  that is configured as an elongated straight slot extending transversely to the first aperture  52  along a line  60  radially outwardly from the rotation axis  50 . The relative locations of the first aperture  52  and the second aperture  58  are such that the second aperture  58  intersects the first aperture  52  as the disk member  46  rotates to define a quadrangular line-of-sight aperture  62 . The line-of-sight aperture  62  moves along the line  54  within the length of the first aperture  52  as the second aperture  58  sweeps across the first aperture  52  to provide a moving line-of-sight extending from a sensor  64  to the straps  20   a,    20   b,    20   c,    20   d  of the flexible connection  18 . The sensor  64  may comprise a thermopile or equivalent infrared sensor for sensing infrared energy received from the straps  20   a,    20   b,    20   c,    20   d.    
         [0023]    Referring to  FIG. 4 , the position of the line-of-sight aperture  62  may be determined by a position sensor unit  66 . The position sensor unit  66  may comprise an encoder wheel  68  (see also  FIG. 2 ) mounted to the shaft  42  and including at least one position aperture  70 , a light source  72  mounted to one side of the encoder wheel  68 , such as mounted to an inner side  74  of the circuit board  36 , and a support member  76  holding an optical sensor  78  in position adjacent a side of the encoder wheel  68  opposite the light source  72 . As the disk member  46  is rotated by the shaft  42 , the encoder wheel  68  rotates and causes the position aperture  70  to pass between the light source  72  and the optical sensor  78  to cause the sensor  78  to trigger as an indication of the rotational position of the shaft  42 . The circuit board  36  may include circuitry to monitor the position of the shaft  42  in order to provide the corresponding location of the line-of-sight aperture  62 . 
         [0024]    It should be noted that the light source  72  may be an LED or any equivalent light source. Further, it should be understood that the present invention is not limited to the described encoder structure and that other rotational position sensing structures may be incorporated in the structure described herein. 
         [0025]    Referring to  FIGS. 5A-5D , the successive movement of the line-of-sight from the temperature monitor unit  28  to different locations on a respective set of straps  20  is illustrated diagrammatically with reference to the plurality of straps  20   a,    20   b,    20   c,    20   d  arranged perpendicular to a line  79  extending perpendicular to the longitudinal axis  56 . The line  79  may comprise a line that is substantially collinear with the rotation axis  50  of the shaft  42 .  FIGS. 5A-5D  illustrate distinct angles φ of a line-of-sight from the sensor  64  to each of the locations of the straps  20   a,    20   b,    20   c,    20   d.    
         [0026]      FIG. 5A  illustrates a first position of the line-of-sight aperture, indicated by  62   a,  defining a straight line-of-sight  80   a  between the sensor  64  and the strap  20   a.  Further, the field-of-view provided to the sensor  64  comprises essentially only the strap  20   a,  and the surrounding background areas are substantially blocked out. As the disk member  46  rotates, the line-of-sight aperture moves to a second position, indicated by  62   b,  where a straight line-of-sight  80   b  is defined between the sensor and the strap  20   b.  It should be noted that as the disk member  46  rotates to the second aperture position  62   b,  energy from the first strap  20   a  is blocked out, as well as energy from substantially all other background areas surrounding the strap  20   b,  to essentially provide a limited field-of-view centered on the strap  20   b  from which energy is received. 
         [0027]    Similarly, further rotation of the disk member  46  causes the line-of-sight to pass through two subsequent defined aperture positions  62   c  and  62   d  corresponding to straight lines-of-sight  82   c  and  82   d  extending from the sensor  64  to the straps  20   c  and  20   d,  respectively. It should be understood that the motor  38  drives the shaft  42  at a slow enough speed to permit the sensor  64  to respond to the energy emitted by the particular strap  20   a,    20   b,    20   c,    20   d  located within the line-of-sight defined through the aperture  62  to the sensor  64 . 
         [0028]    The signal generated by the position sensor unit  66  may be used to trigger the temperature sensing operation at a predetermined point in the rotation of the shaft  42 , such as at a location where the first position of the aperture  62   a  is formed by the intersection of the first and second apertures  52 ,  58 . The motor  38  may comprise a stepper motor or other motor for providing a controlled rotation of the shaft  42 . In addition, the encoder wheel  68  for the position sensor unit  66  may include a plurality of position apertures  70  where, for example, each position aperture  70  may be indicative of a line-of-sight aperture position  62   a,    62   b,    62   c,    62   d.  By providing a temperature measurement associated with each one of a plurality of locations on the flexible connection  18 , it is possible to identify a particular overheated strap  20   a,    20   b,    20   c,    20   d,  and additionally enables a trending analysis of the temperature of each of the straps  20   a,    20   b,    20   c,    20   d,  to provide an indication of a degrading condition within the flexible connection  18 . 
         [0029]    Additional line-of-sight aperture positions may be provided if, for example, the set of straps  20  includes additional straps, or to provide a temperature measurement for locations other than the straps  20   a,    20   b,    20   c,    20   d  on the flexible connection  18 . Specifically, it may be desirable to obtain at least one temperature measurement from the interior surface of the shell  14  in order for temperature changes of the straps  20   a,    20   b,    20   c,    20   d  to be adjusted with reference to the environmental or background temperature of the enclosed area of the isophase bus structure  10 . In order to obtain the background temperature, a further line-of-sight aperture position may be provided extending to the side of either of the edge straps  20   a  or  20   d  in order for the line-of-sight to extend past the flexible connection  18  of the electrical conductor  12  to the interior wall surface of the shell  14 . The interior surface temperature obtained from the shell  14  may be subtracted from the measured strap temperatures to provide adjusted strap temperature measurements. 
         [0030]    It should be noted that the shape of the first and second masks  33 ,  48  and first and second apertures  52 ,  58  is provided for convenience in the present explanation, and alternative shapes or configurations of these components may be provided within the scope of the present invention. For example, the apertures  52 ,  58  may be provided with shapes that vary across their length dimensions configured such that the area of the line-of-sight aperture  62  at any given temperature measurement location is equivalent to the area at every other location. Alternatively, a microprocessor may be provided to process the signal from the sensor  64  and compensate for the known variations in the aperture size, where the known position of the line-of-sight aperture  62  as it moves along the line  54  may be used in combination with a look-up table to adjust the measured temperature readings with reference to the particular known dimensional characteristics of the aperture  62  for any given position. It should be understood that the apertures  52 ,  58  could be any aperture configuration capable of cooperating to provide a limited field-of-view from the sensor  64  to spatially distinct locations. 
         [0031]    In a further modification of the invention, the disk member  46  may be provided with a plurality of the apertures  58  located at predetermined circumferentially spaced locations around the disk member  46 . In such a construction, a temperature measurement of the straps  20   a,    20   b,    20   c,    20   d  may be obtained each time one of the plurality of the apertures  58  sweeps across the aperture  52 . 
         [0032]    The temperature monitor unit  28  may be formed as a completely contained module that may include the above-described temperature detection structure as well as a motor controller, an infrared detection circuit, process logic, and alarm logic to provide an alert corresponding to an overheat condition. The units  28  may be mounted as independent monitors at selected locations on the shell  14  and may be connected in any selected configuration to a common display box to provide a temperature monitor system for the isophase bus structure  10 . 
         [0033]    While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.