Patent Publication Number: US-2021190604-A1

Title: Continuously transposed cable with an integrated sensing device

Description:
BACKGROUND 
     Technical Field 
     The present invention relates to an electrical cable, particularly to a continuously transposed cable (CTC), with an integrated sensing device, in particular for measuring temperature and/or vibrations. The conductor according to the invention is in particular destined to be used for forming a winding of an electromagnetic induction device, such as a transformer. 
     Description of the Related Art 
     Electromagnetic induction devices, such as transformers, are used in power systems for voltage level control. In particular, a transformer is an electromagnetic induction device used to step up and step down voltage in electric power systems in order to generate, transmit and utilize electrical power. In general, a transformer comprises a core, made of e.g. laminated iron, and windings. 
     In electromagnetic induction devices the temperature of the windings should be monitored in order to find possible problems, to plan maintenance or to determine if some components are getting old. This can be done for example using indirectly temperature measuring of the cooling fluids where the winding is immersed or incorporated. Another option is to monitor the winding temperature by manually inserting optical fibers in specific and limited numbers of positions of the windings. This operation is extremely long and risky because the fiber optics can be damaged during the winding handling or during the normal assembly and setup of the electromagnetic induction device itself. In addition, it is difficult or substantially impossible to measure the temperature inside the conductors forming the windings or in the internal parts of the windings. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is therefore to provide a conductor with an integrated sensing device, particularly but not exclusively for measuring temperature, which when used in conditions similar to those disclosed above, for example when used for forming windings of a transformer, allows a precise measurement of the quantity of interest, while at the same time being easy to be installed. 
     This and other objects are achieved by a continuously transposed cable (CTC) in accordance with claim  1 . 
     Dependent claims define possible advantageous embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages of the CTC cable according to the invention will be more apparent from the following description of preferred embodiments given as a way of an example with reference to the enclosed drawings in which: 
         FIG. 1  shows a perspective view of a CTC cable according to a possible embodiment; 
         FIG. 2  shows a schematic sectional view along a longitudinal development direction of the CTC cable according to a possible embodiment; 
         FIG. 3  shows a schematic sectional view along a longitudinal development direction of the CTC cable according to a further possible embodiment; 
         FIG. 4  shows a schematic sectional view along a longitudinal development direction of the CTC cable according to a further possible embodiment; 
         FIG. 5  shows a schematic sectional view along a longitudinal development direction of the CTC cable according to a further possible embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The inventive concept will be described hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. 
     With reference to the annexed Figures, a continuously transposed cable (CTC) is indicated with reference number  1 . The CTC cable  1  extends according to a longitudinal development direction L and comprises two opposite longitudinal ends  2 ,  3 . 
     The CTC cable  1  comprises a plurality of single strands  4 , each preferably in the form of a ribbon, i.e. having a transversal section substantially rectangular with a first dimension greater than the second dimension. Preferably, the strands  4  are externally at least in part electrically insulated, for example by one or more layers of electrical insulating enamel. 
     The strands  4  are arranged so to form a first  5  and a second  6  adjacent stacks, each extending along the longitudinal development direction L. Each stack  5 ,  6  comprises a plurality of strands  4 , which are overlapped in each stack  5 ,  6  according to an overlapping direction I. Furthermore, said strands  4  are preferably arranged such that at least a portion of each of them alternate in the two adjacent stacks  5 ,  6 . Still more preferably, the strands  4  are arranged such that each of them, successively along the longitudinal development direction L, takes on each possible position within a cross section of the CTC cable  1 , i.e. each position along the overlapping direction I in each of the stacks  5 ,  6 . Preferably, in case of strands having rectangular section, the smallest dimension thereof is parallel to the overlapping direction I, and the biggest dimension thereof is parallel to a lateral development direction W of the CTC cable  1 , which is perpendicular to a plane formed by the longitudinal development direction L and the overlapping direction I. 
     The stacks  5 ,  6  form a longitudinal interface  16  therebetween. 
     Preferably, the strands  4  are held together by suitable connecting devices, such as, for example, one or more ribbons or wires  14 . According to a possible embodiment, the connecting devices are electrically insulating. Therefore, for example, the ribbons or wires  14  can be made of paper, or plastic, or other suitable electrically insulating material, such as Nomex®. In some applications, alternatively, the connecting devices  14  do not perform the function of electrical isolation but only a mechanical function to hold the strands  4  together. 
     Preferably, the strands  4  are electrically connected in parallel at the longitudinal ends  2 ,  3  of the CTC cable  1 . 
     According to an embodiment, at the interface  16  between the first  5  and the second  6  stacks the CTC cable  1  comprises an insulating separator  7 , which can extend in length along the longitudinal development direction L and in width along the overlapping direction I. The insulating separator is made of an electrically insulating material, such as for example paper, up-grade paper, pressboard, Nomex® or the like. Alternatively, the insulating separator  7  can be missing. 
     The so formed CTC cable  1  comprises, in addition to the already cited longitudinal ends  2 ,  3 , a first side face  8 , a second side face  9 , an upper face  10  and a lower face  11 . The first side face  8  is the external face of the first stack  5  opposite to the interface  16  with the second stack  6 . The second side face  8  is the external face of the second stack  6  opposite to the interface  16  with the first stack  5 . The upper  10  and lower  11  faces are the remaining faces of the CTC cable  1  and correspond respectively to the upper and lower portions of the couple of first  5  and second  6  adjacent stacks. 
     The CTC cable  1  comprises one or more optical fibers  12  positioned at the interface  16  between the first  5  and the second  6  stacks. 
     The optical fibers  12  preferably extend parallel to the cable longitudinal development direction L. In accordance with an embodiment, the optical fibers  12  are positioned on or inserted inside the insulating separator  7  (in this case the insulating separator  7  can comprise for example two opposite portions and the optical fibers can be positioned therebetween. Alternatively, the insulating separator can comprise one or more tubular elements where the optical fibers can be inserted). This reduces the risk of damaging the optical fibers  12 , for example during the forming of a winding by the CTC cable  1  according to the invention. 
     According to a possible embodiment (as shown for example in  FIG. 2 ), the optical fibers  12  comprise a first portion  15  outside the CTC cable  1 , for example near the first  2  or the second  3  longitudinal end thereof, and a second portion  17  extending inside the CTC cable  1  in correspondence of the interface  16  between the stacks  5 ,  6 . The second portion  15  ends with a tip  13 , positioned inside the cable  1  in a specific position along the interface  16 , where the measurement by the optical fiber takes place. For example, the first portion  15  can be connected to a measuring apparatus (not shown in the Figures) suitable do detect a quantity, in particular the temperature, in correspondence of the tip  13  of the optical fiber. The principles underlying the measurement of the temperature at the tip of an optical fiber are known and will be not described here in detail. According to another embodiment, it is possible to measure the temperature along the second portion  17  up to the tip  13 . Again, the principles underlying the measurement of the temperature along an optical fiber are known and will be not described here in detail. 
     The so configured CTC cable can be used for forming a windings of an electromagnetic induction device, such as a transformer. For example, the free portion  15  can be positioned near the first longitudinal end  2 , which in turn can correspond to the winding top exit. Preferably, the free portion  15  does not exit the CTC cable exactly at the longitudinal end  2  or  3  but before such that optical fibers does not interfere with the connection of the winding with the electromagnetic induction device. The tip  13  can be positioned in the most suitable intermediate position between the first longitudinal end  2  and the second longitudinal end  3 , which in turn can correspond to the winding bottom exit. With this arrangement, it is possible to check the temperature in a specific position of the winding formed with the CTC cable  1 . 
       FIGS. 2-4  show further possible alternative embodiments of a CTC cable  1  usable for forming a transformer winding. In general, the CTC cable  1  can comprise a plurality of optical fibers  12  each having the tip  13  in a different position along the longitudinal development direction L and the free portions  15  positioned near the first and/or the second longitudinal ends  2 ,  3 . In this manner, it is possible to take measures in different positions, in particular when the CTC cable  1  is used for forming a winding. 
     According to the embodiment shown in  FIG. 3 , the CTC cable  1  comprises three optical fibers  12 ′,  12 ″, 12 ′″, each having a respective free portion  15 ′,  15 ″,  15 ′″ and a tip  13 ′,  13 ″,  13 ′″. The free portions  15 ′,  15 ″,  15 ′″, as mentioned above, are outside the CTC cable  1  and can be connected to a measurement device. Preferably, the free portions  15 ′,  15 ″,  15 ′″ are positioned near the top exit of the winding. The tips  13 ′,  13 ″,  13 ′″ can be respectively positioned near the first longitudinal end  2  (which in turn will correspond to the winding top exit), in an intermediate position (which in turn will correspond to a middle position of the winding), and near the second longitudinal end  3  (which in turn will correspond to the winding bottom exit). With this arrangement, it is possible to check the temperature in three different position of the winding, namely at the top exit, in the middle, and at the bottom exit. 
     With reference to the embodiment shown in  FIG. 4 , the CTC cable  1  shown therein differs from the one shown in  FIG. 3  in that it comprises three groups  12 I,  12 II,  12 III of optical fibers arranged similarly to the three single optical fibers  12 ′,  12 ″,  12 ′″ of the embodiment in  FIG. 2 . Each group in turn comprises a plurality (three in the example shown) of optical fibers  12 I′,  12 I″,  12 I′″, . . . having respective tips  13 I′,  13 I″,  13 I′″; . . . and free portions positioned near the first longitudinal end  2 . 
     With reference to the embodiment shown in  FIG. 5 , the CTC cable  1  still comprises three groups  12 I,  12 II,  12 III of optical fibers each having respective tips  13 I′,  13 I″,  13 I′″; . . . arranged similarly to the three groups  12 I,  12 II,  12 III with respective tips  13 I′,  13 I″,  13 I′″; . . . of optical fibers of the embodiment in  FIG. 4 . However, in this embodiment, the free portions of the optical fibers of the first and of the second groups are positioned near the first longitudinal end  2  of the CTC cable, whereas the free portions of the optical fibers of the third group are positioned near the second longitudinal end  3  of the CTC cable. Again, the first  2  and the second  3  longitudinal ends of the CTC cable  1  can respectively correspond to the winding top exit and to the winding bottom exit, or vice versa. In this manner, it is not necessary to use too long optical fibers. 
     It is to be noted that the optical fibers  12  of the CTC cable  1  can be also used for obtaining a continuous temperature map along the cable (therefore, for example along the winding formed with the cable) instead of/in addition to the temperature at the tip  13 . According to another option, it is possible to measure the distance of the point with maximum temperature from an end of the optical fiber, as well as the temperature in this point with maximum temperature. This allows the identification of the hot-spot in a winding formed with the CTC cable  1  according to the invention. This type of measurement can be obtained for example by using a particularly treated optical fiber known as Fiber Bragg Grating (FBG), or the like. Using optical fibers of this type or of similar types, in addition, allows the measurement of vibrations. 
     The FBG is a device that exploits the wavelength of light. It behaves essentially like a strain gauge and allows to realize sensors for localized measures of deformation (bending, traction, compression, torsion) and vibration. Taking advantage of the characteristics of the host material, in particular of elastomers, it is possible to measure weight, pressure and acceleration. Its characteristics also allow temperature measurements. 
     From the above description, the skilled person will appreciate how the CTC cable according to the invention allows the construction of windings of devices, such as transformers, having an incorporated sensing device (particularly for sensing temperature and/or vibrations). Therefore, it is no longer necessary to apply the optical fibers to already formed windings. This results in a much easier and more reliable process for forming the winding. 
     Furthermore, the CTC cable allows a flexible measurement, i.e. it is possible to determine multiple points or sketches where the quantity of interest is to be measured. 
     To the above-mentioned embodiments of the CTC cable according to the invention, the skilled person, in order to meet specific current needs, can make several additions, modifications, or substitutions of elements with other operatively equivalent elements, without however departing from the scope of the appended claims.