Abstract:
The present invention provides a method for making a power cable that comprises the steps of extruding a power cable that has a jacket and co-extruding a hollow longitudinal duct with the extrusion of the jacket of the power cable such that the longitudinal duct is coupled to an outer surface of the jacket and an outer diameter of the longitudinal duct is substantially smaller than an outer diameter of the jacket of the power cable.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to and is a divisional of pending U.S. patent application Ser. No. 12/967,107, filed Dec. 14, 2010, the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to a method of making a power cable having microduct incorporated therewith for accommodating optical fiber cables. 
       BACKGROUND OF THE INVENTION 
       [0003]    The conventional method for distributed temperature sensing (DTS) in electrical circuits is to use optical fiber cable to function as a linear sensor. Once optical fiber is installed alongside of an electrical power cable circuit, the optical fibers generate a continuous temperature profile along the length of the electrical circuit providing real time temperature data to safely maximize the distribution capability. This method also provides detection of “hot spots” and identifies potential weak areas of an installed power cable system. These hot spots can then be proactively addressed to prevent damage and premature aging of electrical power cable systems. 
         [0004]    Currently, however, there is no easy way to install such optical fiber cables for the purpose of DTS on distribution cables. Because of the fragile nature of optical fiber cables, the fibers often get damaged using conventional installation methods. That is because a utility is required to pull in the fiber cables after the power cable installation. Therefore, a need exists for providing DTS optical fiber cable either during or after power cable installation without causing damage to the optical fiber cables. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, the present invention provides a method for making a power cable that comprises the steps of extruding a power cable that has a jacket and co-extruding a hollow longitudinal duct with the extrusion of the jacket of the power cable such that the longitudinal duct is coupled to an outer surface of the jacket and an outer diameter of the longitudinal duct is substantially smaller than an outer diameter of the jacket of the power cable. In a preferred embodiment, optical fiber is blown into the longitudinal duct. 
         [0006]    Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0008]      FIG. 1A  is a cross-sectional view of a power cable according to a first exemplary embodiment of the present invention, showing a microduct coupled thereto by a web; 
           [0009]      FIG. 1B  is a cross-sectional view of a power cable assembly having at least one power cable according to the first exemplary embodiment illustrated in  FIG. 1A ; 
           [0010]      FIG. 2A  is a cross-sectional view of a power cable according to a second exemplary embodiment of the present invention, showing a microduct embedded in an outer surface of the cable; 
           [0011]      FIG. 2B  is a cross-sectional view of a power cable assembly having at least one power cable according to the second exemplary embodiment illustrated in  FIG. 2A ; 
           [0012]      FIG. 3A  is a cross-sectional view of a power cable according to a third exemplary embodiment of the present invention, showing a microduct embedded in an outer surface of the cable; 
           [0013]      FIG. 3B  is a cross-sectional view of a power cable assembly having at least one power cable according to the third exemplary embodiment illustrated in  FIG. 3A ; 
           [0014]      FIG. 4A  is a cross-sectional view of a power cable according to a fourth exemplary embodiment of the present invention, showing a microduct coupled thereto by a channel; 
           [0015]      FIG. 4B  is a cross-sectional view of a power cable assembly having at least one power cable according to the fourth exemplary embodiment illustrated in  FIG. 4A ; 
           [0016]      FIG. 5  is a cross-sectional view of a power cable assembly according to a fifth exemplary embodiment of the present invention, showing a microduct extending through the center of the cable assembly; 
           [0017]      FIG. 6  is a cross-sectional view of a power cable assembly according to a sixth exemplary embodiment of the present invention, showing a microduct extending through the center of the cable assembly; and 
           [0018]      FIG. 7  is a cross-sectional view of a power cable assembly according to a seventh exemplary embodiment of the present invention, showing a microduct extending through the center of the cable assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring to the figures, the present invention generally provides a microduct incorporated with a power cable or a power cable assembly that is designed to allow optical fiber cabling to be installed either during or after the power cable installation. For example, the optical fiber may be blown into the hollow microduct either during or after the power cable is installed, thereby avoiding damage to the optical fiber. Utilizing a power cable or a multiple power cable assembly with a microduct, as taught by the present invention, allows conventional power cable installation and accessory (splicing and terminating) methods and processes to be employed while providing DTS to the power cabling. 
         [0020]      FIG. 1A  illustrates a first exemplary embodiment of a power cable  100  of the present invention. The power cable  100  includes an insulated cable core  120  and a jacket  104  surrounding the cable core. The cable core  120  consists of a stranded or solid metal conductor  102  surrounded by an insulation system which may include a semi-conducting conductor shield layer  108 , an insulation layer  103 , and a semi-conducting insulation shield layer  105 . The cable core  120  may optionally include a metallic shield surrounding the insulation system. The metal conductor  102  may be formed from copper or aluminum, for example. 
         [0021]    A microduct  110  extends adjacent the jacket  104  and may be coupled to the outer surface  106  thereof by a web  112 . The microduct  110  is preferably co-extruded with the cable jacket  104  such that the microduct  110  is encapsulated in the same compound as the cable jacket and is held in place by the web  112 . The web  112  is a small amount of compound joining the power cable jacket  104  and the microduct  110 . The microduct  110  extends longitudinally along the length of the cable  100 . The co-extruded jacket  104  and microduct  110  may be made of a thermoplastic or a thermoset polymeric material, for example, such as a thermoset crosslinked polyethylene, a thermoplastic linear low density polyethylene, a thermoplastic polypropylene, or the like. The jacket  104  and microduct  110  may be either semi-conductive or non-conductive. Alternatively, the microduct  110  may be formed separately from the cable  100  and subsequently attached to the outer surface  106  of the jacket  104 . 
         [0022]    The microduct  110  is preferably substantially smaller than the power cable  100 . For example, the outer diameter of the cable jacket  104  may be about 2 inches where the outer diameter of the microduct is significantly less at about 10 mm. The inner diameter of the microduct  110  may be about 2-12 mm. 
         [0023]    As seen in  FIG. 1B , the power cable  100  may be incorporated into a power cable assembly  150 . The cable assembly includes a plurality of powers cables that may be twisted together. At least one of the plurality of cables is the power cable  100  having the microduct  110 . The remaining cables  152  and  154 , as illustrated in  FIG. 1B , do not include a microduct. Alternatively, one or more of the remaining cables  152  and  154  may include a microduct similar to the microduct  110 . Although  FIG. 1B  shows three cables, any number of cables may be included in the power cable assembly  150 . 
         [0024]      FIG. 2A  illustrates a second exemplary embodiment of a power cable  200  according to the present invention. The power cable  200  is similar to the power cable  100  of the first embodiment, except that the microduct  210  is partially embedded in the outer surface  206  of the cable jacket  204 . More specifically, a longitudinal recess  220  is formed in the jacket&#39;s outer surface  204  that is sized to receive at least a portion of the microduct  210 . The microduct  210  is preferably held in place in the recess  220  with an adhesive, such as a double-sided tape, a hot melt adhesive, glue or the like. Alternatively, the recess  220  can be eliminated and the microduct  210  bonded to the outer surface  206  of the cable jacket  204 . 
         [0025]    Similar to the first embodiment, the power cable  200  may be incorporated into a power cable assembly  250 , as seen in  FIG. 2B . The power cable assembly  250  includes a plurality of cables where at least one of the cables is the power cable  200  having the microduct  210 . As with power cable assembly  150 , the assembly  250  may include multiple cables having a microduct like microduct  210  of the power cable  200 . And the power cable assembly  250  may include any number of power cables. 
         [0026]      FIG. 3A  illustrates a third exemplary embodiment of a power cable  300  according to the present invention. The power cable  300  adds longitudinal ribs  330  to the longitudinal recess of the power cable  200  of the second embodiment to provide additional support to the microduct  310 . The support of the ribs  330  helps to keep the microduct  310  in place and to provide protection to the microduct, such as crush resistance. In particular, the ribs  330  may extend along the outer surface  306  of the jacket  304  on either side of the longitudinal recess  320 . The ribs  330  preferably extend from the jacket&#39;s outer surface  306  such that the ribs  330  extend about 75% of the outer diameter of the microduct  310 , as seen in  FIG. 3A . Alternatively, the ribs  330  may be taller than the microduct  310  such that the ribs  330  extend past the outer diameter of the microduct  310 . The ribs  330  may also be shorter, that is less than 75% of the outer diameter of the microduct  310 . Like in the second embodiment, the microduct  310  may be held in place in the recess  320  with an adhesive. The ribs  330  are preferably integrally with the cable&#39;s jacket  304 ; however, the ribs  330  may be formed separately and attached to the jacket&#39;s outer surface  306 . 
         [0027]    The power cable  300  may also be incorporated into a power cable assembly  350 , as seen in  FIG. 3B . Like the power cable assemblies  150  and  250 , the power cable assembly  350  includes a plurality of cables where at least one of the cables is the power cable  300  having the microduct  310 . The power cable assembly  350  may include multiple cables having a microduct like microduct  310  of the power cable  300 . And the power cable assembly  350  may include any number of power cables. 
         [0028]      FIG. 4A  illustrates a fourth exemplary embodiment of a power cable  400  of the present invention. The power cable  400  includes first and second shaped extensions  440  extending from an outer surface  406  of the cable&#39;s jacket  404 . The shaped extensions  440  preferably extend longitudinally along the length of the cable and form a longitudinal channel  442  therebetween that is configured to receive the microduct  410 . The shaped extensions  440  are preferably integral with the cable jacket  404 ; however, they can be formed separately and attached to the outer surface  406  of the jacket  404 . The channel  442  provides protection to the microduct  410  and can support the microduct  410  without a bonding agent, such as adhesive. Between the radial ends of the shaped extensions  440  there is a longitudinal gap  444  such that the channel  442  is not entirely enclosed. Preferably the gap  444  between the shaped ends  440  is less than 50% of the outer diameter of the microduct  410 . Alternatively, the radial ends of the shaped extensions  440  may be configured to contact one another, thereby completely enclosing the channel  442 . The shaped extensions  440  preferably have a generally triangular cross-sectional shape, as seen in  FIG. 4A ; however, the shaped extensions  440  may have any shape as long as the channel  442  therebetween can accommodate the microduct  410 . 
         [0029]    As seen in  FIG. 4B , the power cable  400  may also be incorporated into a power cable assembly  450 , as seen in  FIG. 4B . Like the power cable assemblies  150 ,  250 , and  350 , the power cable assembly  450  includes a plurality of cables where at least one of the cables is the power cable  400  having the microduct  310 . The power cable assembly  450  may include multiple cables having a microduct like microduct  410  of the power cable  400 . And the power cable assembly  450  may include any number of power cables. 
         [0030]      FIG. 5  illustrates a fifth exemplary embodiment of the present invention of a power cable assembly  500  that may include multiple power cables arranged to support a microduct  510  therebetween. More specifically, first, second, and third cables  502 ,  504  and  506  are arranged together in an assembly defining a central longitudinal axis and a longitudinal area  520  therebetween configured to receive the microduct  510 . The microduct  510  generally extends along the central longitudinal axis of the cable assembly. Although the power cable assembly  500  is shown with three cables, the assembly  500  may include any number of cables as long as the longitudinal area accommodates the microduct  510 . 
         [0031]      FIG. 6  illustrates a sixth exemplary embodiment of the present invention of a power cable assembly  600  similar to the power cable assembly  500  of the fifth embodiment, except that a foam portion  650  is provided in the longitudinal area  620  between the first, second, and third power cables  602 ,  604  and  606 . The foam portion  650  may have first, second and third arms  652 ,  654 , and  656  extending to first, second, and third cables  602 ,  604 , and  606 , respectively. The foam portion  650  provides additional protection, e.g. crush resistance, to the microduct  610  between the cables. The foam material of the foam portion  650  preferably has a low thermal resistivity, such as foam containing thermally conductive ceramic particles or graphite. 
         [0032]      FIG. 7  illustrates a seventh exemplary embodiment of the present invention of a power cable assembly  700  similar to the power cable assemblies  500  and  600 , except that the foam portion  750  is wrapped around the microduct  710  like a longitudinal tape sealed around the microduct  710 . The foam portion  750  provides support and crush resistance to the microduct  710 . 
         [0033]    While particular embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.