Abstract:
A system for detecting arcing between two electrical conductors includes an image capture arrangement including a plurality of image capture devices configured to be arranged in spaced relationship relative to one another and to a contact region between the electrical conductors so as to provide depth information. A processor is responsive to the image capture arrangement for computing a depth range of the contact region between the electrical conductors relative to a first image capture device of the image capture arrangement and determining if an arcing candidate appears within the computed depth range for the first image capture device of the image capture arrangement and at least one further image capture device of the image capture arrangement and, if it does, flagging the candidate as arcing at the contact region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from Australian Provisional Patent Application No 2014903670 filed on 15 Sep. 2014, the contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    This disclosure relates, generally, to the field of arcing detection and, more particularly, to a method of, and a system for, detecting arcing between two electrical conductors such as a power supply line and a conductive follower in electrical contact with the line. The disclosure has particular, but not necessarily exclusive, application to electric transportation vehicles powered via an overhead power line. 
       BACKGROUND 
       [0003]    In monitoring an electrical system comprising an overhead power supply line and an electrically conductive follower, an image capture device may detect multiple arcing candidates. Some of these arcing candidates may be false positives arising from incident light on the system, ghosting, etc. In other words, some of the candidates are not arcs but artefacts arising due to other causes. 
         [0004]    To filter out these false positives, a secondary image capture device can be employed using depth information. However, the computational cost is very high to compute a depth map from stereo images. In addition, where un-synchronised dual image capture devices are used rather than synchronised stereo image capture devices, traditional depth/disparity map computational algorithms will not work in scenarios where the detected arcing candidate is moving. In the particular application for which this system has been developed, the position of an arcing candidate can change in a very short space of time. 
         [0005]    Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application. 
       SUMMARY 
       [0006]    In a first aspect, a method of detecting arcing between two electrical conductors includes 
         [0007]    computing a depth range of a contact region between the electrical conductors relative to a first image capture device of an image capture arrangement, the image capture arrangement comprising a plurality of image capture devices in spaced relationship relative to one another and to the contact region between the electrical conductors, the image capture devices being so arranged as to provide depth information; and 
         [0008]    determining if an arcing candidate appears within the computed depth range for a first image capture device of the image capture arrangement and at least one further image capture device of the image capture arrangement and, if it does, flagging the candidate as arcing at the contact region. 
         [0009]    The image capture arrangement may comprise two unsynchronised image capture devices and the method may include arranging the image capture devices relative to the contact region in an epipolar manner. 
         [0010]    The method may include bounding the electrical conductor in a virtual polyhedron, typically a rectangular cuboid, to determine the depth range of the contact region relative to the first image capture device. The method may include, knowing the depth range, computing possible locations of each arcing candidate on an image of the at least one further image capture device and, if any arcing candidate falls outside the computed depth range with respect to the at least one further image capture device, flagging only the, or each, remaining arcing candidate as an arcing incident. 
         [0011]    In a second aspect, a system for detecting arcing between two electrical conductors includes 
         [0012]    an image capture arrangement comprising a plurality of image capture devices configured to be arranged in spaced relationship relative to one another and to a contact region between the electrical conductors so as to provide depth information; and 
         [0013]    a processor responsive to the image capture arrangement for computing a depth range of the contact region between the electrical conductors relative to a first image capture device of the image capture arrangement and determining if an arcing candidate appears within the computed depth range for the first image capture device of the image capture arrangement and at least one further image capture device of the image capture arrangement and, if it does, flagging the candidate as arcing at the contact region. 
         [0014]    The image capture arrangement may comprise a plurality of unsynchronised image capture devices. The image capture arrangement may comprise a pair of image capture devices arranged, in use, in an epipolar manner relative to the contact region. 
         [0015]    The system may include a data storage device for storing data from the processor for further analysis. 
         [0016]    The disclosure extends also to an electric vehicle which includes an image capture arrangement mounted to the vehicle, the image capture arrangement comprising a plurality of image capture devices configured to be arranged in spaced relationship relative to one another and to a contact region between electrical conductors of a power supply system for providing power to the vehicle. 
         [0017]    The image capture devices of the image capture arrangement may be arranged on the vehicle in an epipolar manner relative to the contact region. 
         [0018]    The disclosure extends still further to software that, when installed in a computer, causes the computer to carry out the method described above. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    An embodiment of the disclosure is now described by way of example only with reference to the accompanying drawings in which: 
           [0020]      FIG. 1  shows a schematic, perspective view of an embodiment of a system for detecting arcing between two electrical conductors; 
           [0021]      FIG. 2  shows a schematic plan view of a part of the system of  FIG. 1 ; 
           [0022]      FIG. 3  shows a schematic, side view of the part of the system of  FIG. 1 ; 
           [0023]      FIG. 4  shows an image coordinate system used by the system; 
           [0024]      FIG. 5  shows a graphic representation of an embodiment of a method of detecting arcing between two electrical conductors; 
           [0025]      FIG. 6  shows a schematic representation of an image of two arcing candidates detected by a first image capture device of the image capture arrangement of the system; 
           [0026]      FIG. 7  shows a schematic representation of an image of the arcing candidates detected by a second image capture device of the image capture arrangement; and 
           [0027]      FIG. 8  shows a flow chart setting out the computational steps involved in the method of detecting arcing between two electrical conductors. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0028]    In the drawings, reference numeral  10  generally designates an embodiment of a system for detecting arcing between two electrical conductors. The system  10  includes an image capture arrangement  12  comprising a plurality of image capture devices, or cameras,  14 ,  16 . The cameras  14 ,  16  are digital video recorders (DVRs). 
         [0029]    In one application, the system  10  is intended for detecting arcing between electrical conductors of a power supply  18  for an electric vehicle (not shown) of the type supplied with power via an overhead power supply line, indicated schematically at  20  in  FIG. 1  of the drawings. Examples of such vehicles include trains, trams, or the like, which have a conductor  22  mounted on a follower, such as a pantograph  24 , which follows a catenary of the power supply line  20 . The conductor  22  is, for example, a carbon strip carried on the pantograph  24  and extends transversely relative to the power supply line  20  to accommodate relative lateral movement between the vehicle and the power supply line  20 . 
         [0030]    Where the conductor  22  makes contact with power supply line  20 , a contact region  26  is defined. 
         [0031]    The cameras  14  and  16  of the image capture arrangement  12  are arranged in an epipolar manner relative to the contact region  26  to obtain depth information as will be described in greater detail below. The camera  14  is a first, or main, camera and the camera  16  is a second, or secondary, camera. 
         [0032]    The system  10  includes a processor, illustrated schematically as a computer  28  in  FIG. 1  of the drawings. The processor  28  is responsive to the image capture arrangement  12  for computing a depth range  30  of the contact region  26  between the electrical conductors  20 ,  22  relative to the main camera  14  of the image capture arrangement  12 . The depth range  30  is implemented as a virtual polyhedron, typically a rectangular cuboid. 
         [0033]    The processor  28  is further configured to determine if an arcing candidate appears within the computed depth range  30  for the main camera  14  of the image capture arrangement  12  and the secondary camera  16  of the image capture arrangement  12 . 
         [0034]    The system  10  includes a receiver module  32  for receiving data from the cameras  14 ,  16  of the image capture arrangement  12  and for feeding the data to the processor  28 . While the components  14 ,  16 ,  30  and  32  are illustrated in  FIG. 1  as being hardwired, this is for illustrative purposes only. It will be appreciated that some of the components could communicate wirelessly with each other. For example, the cameras  14 ,  16  could communicate wirelessly with the receiver module  32  with the receiver module  32  being hardwired to the processor  28 . Instead, the receiver module  32  could communicate wirelessly with the processor  28  as well. 
         [0035]    Various other connectivity combinations will be readily apparent to a person of ordinary skill in the art. In other embodiments, the receiver module  32  could be an on-board, removable memory device associated with each of the cameras  14 ,  16 . The cameras  14 ,  16  may store their information on board via the removable memory devices and the memory devices could be removed for later analysis of the data. 
         [0036]    The system  10  also includes a data storage device  34  in which data output by the processor  28  are stored for analysis. 
         [0037]    In use, initially, arcing candidates P and Q ( FIG. 6 ) are detected by the cameras  14 ,  16  as shown at step  36  in  FIG. 8  of the drawings. 
         [0038]    The virtual polyhedron representative of the depth range  30  is generated about the conductor  22 . The polyhedron  30  is generated by knowing the position in three-dimensional (3D) space of the conductor  22  relative to the power supply line  20 . Also, arcing to be detected will only occur where the conductor  22  makes contact with the power supply line  20 . Based on this, the depth range between the contact region  26  and the main camera  14  is generated as the polyhedron  30 . X min , Y min , and Z min  ( FIG. 1 ) represent the closest point in 3D space of the polyhedron  30  relative to the main camera  14  and, conversely, X max , Y max  and Z max  represent the furthest point in 3D space of the polyhedron  30  relative to the main camera  14 . This is shown at step  38  in  FIG. 8  of the drawings. 
         [0039]    With the depth information provided by the polyhedron  30 , the 3D positions of arcing candidates P and Q are available to the main camera  14 . The arcing candidates P and Q project to p′ and q′ in an image  40  ( FIG. 6 ) of the main camera  14  and to p″ and q″ on an image  42  ( FIG. 7 ) of the secondary camera  16 . 
         [0040]    Having the first camera image  40  and the expected depth range  30 , the possible locations of each of the arcing candidates P and Q on the image  42  of the secondary camera  16  can be computed using epipolar geometry. The expected projection of each arcing candidate P and Q appears as a line segment  44  (represented by the rectangle with diagonal hatching) and  46  (represented by the rectangle with vertical hatching) in an epipolar line (not shown) in the image  42 , respectively. 
         [0041]    In the illustrated example, the projection q″ of the arcing candidate Q falls outside its projected, expected depth range as represented by the line segment  46  in the image  42 . As such, it is determined that arcing candidate Q is not arcing but is, instead, a false positive arising from, for example, incident light artefacts, or the like. 
         [0042]    In greater detail, for each camera  14 ,  16 , the projection of a 3D point in the world coordinate system can be computed as: 
         [0000]    
       
         
           
             
               
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         [0043]    Given an image point, its 3D position can be obtained if the depth (“z” in world coordinate system) is specified by: 
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         [0044]    For each arcing candidate located at p left (u L ,v L ) on the main image, with expected depth ranging between [Z min , Z max ], and expected inter-frame movement [Δx, Δy], the following process is effected to determine if it is a false positive. 
         [0045]    The eight corner points (M 1 , M 2 , . . . , M 8 ) of the expected 3D region (i.e. the virtual polyhedron representative of the depth range  30 ) can be obtained as: 
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         [0046]    As shown at step  48  in  FIG. 8  of the drawings, the corner points of the virtual polyhedron representative of the depth range  30  are projected on to the image  42  of the secondary camera  16 . Projecting these eight corner points to the secondary camera  16  obtains eight image points (step  50  in  FIG. 8 ): 
         [0000]        p   right,i   =PM   i ( i= 1, 2, . . . , 8) 
         [0047]    In step  52 , the convex hull bounding the points p right,1 , p right,2 , . . . , p right,8  is computed. 
         [0048]    The processor  28  determines if there are any possible arcing candidates within the image region enclosed by the convex hull at step  54 . As indicated above, in the illustrated embodiment, the processor  28  has computed that the projection q″ of the arcing candidate Q falls outside the depth range as represented by the line segment  46  in the image  42  of the secondary camera  16 . As a result, the processor  28  flags the arcing candidate Q as a false positive as shown at step  56  in  FIG. 8   
         [0049]    Conversely, the projection p″ of the arcing candidate P falls within its projected depth range as represented by the line segment  44  in the image  42  of the secondary camera  16 . The processor  28  therefore flags the arcing candidate P as an arcing incident as shown at step  58  in  FIG. 8 . 
         [0050]    As described above, an application of the system  10  is its use in monitoring the overhead power supply line  20  and the conductor  22  carried on the pantograph  24  of the vehicle to detect arcing. Arcing can occur due to numerous factors, for example, incorrect or inadequate tensioning of the overhead power supply line  20 , inadequate maintenance of the conductor  22 , or the like. The system  10  enables arcing to be detected and monitored to enable remedial action to be taken. 
         [0051]    In other systems requiring depth information of which the Applicant is familiar, stereo images are used. However, the computational cost to compute a depth map from stereo images is very high. With the system  10  of the present disclosure, it is not necessary to do block/feature matching between the main image  40  and the secondary image  42 . For each arcing candidate in the main image  40 , it is only necessary to compute eight corner 3D points which enclose the region in which arcing could possibly occur and project those eight corner points on to the secondary image  42 . This simply involves direct matrix multiplication resulting in far lower computational costs and data bandwidths. 
         [0052]    It is a further advantage of the described disclosure that a system  10  is provided which is robust and relatively low cost. Unsynchronised dual cameras  14 ,  16  are used rather than synchronised, stereo cameras. However, the use of separate, unsynchronised cameras means that traditional depth/disparity map computation algorithms cannot be used if the object being monitored is moving which can occur, in the case of overhead power supply line/pantograph mounted conductor assemblies in a very short space of time. 
         [0053]    It is therefore yet a further advantage of the described system  10  that it is possible to relax the 3D region slightly to accommodate frame rates, vehicle speeds, etc. The only effect of this is to enlarge the search region (the line segments  44  and  46 ) slightly on the secondary image  42  without significantly impacting on computational costs. 
         [0054]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.