Abstract:
An electrical cable with three insulated conductors, a tube for an optical cable, a strip of elastic material embedding the tube, and a jacket. When the cable is handled, e.g. suspended between poles or dredged into the ground, the tube can be deformed by external forces. This makes it impossible to blow or float the optical cable into the tube. The tube is protected by the strip, and especially by the strip having a flat interval in proximity to the tube. External forces will mainly deform the strip at the ends of the interval and less of the forces will hit the tube. The deformation sets up an interior pressure in the strip that acts in sideward direction on the tube and contributes to keep it round and non deformed.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electrical cable with a tube for an optical cable. 
         [0002]    BACKGROUND 
         [0003]    According to existing technology an electrical cable for power transmission can be combined with an optical cable into one and the same electrical cable. The combination can be performed in different ways and in a frequently used design the electrical cable is equipped with a tube of plastic. The tube can be arranged in a region between the insulated electrical conductors and the cable jacket. The optical cable is blown into the tube with air or floated into it with water when the electrical cable is already installed. 
         [0004]    In the international application WO 97/40504 is described a self-supporting electrical cable with shield bands around the insulated electrical conductors, which bands efficiently protect the cable when it is suspended from fixed points. The cable could have been equipped with a tube in the mentioned region. The international application WO 2004/006272 describes an electrical cable with a shielding strip of partially electrically conducting material running along the cable in the region between the insulated electrical conductors and the cable jacket. An electrically conducting wire runs in the strip along its entire length and forms an efficient protection to switch off a cable voltage when the cable is penetrated by an electrically conducting object. Also in this cable a tube could have been arranged. 
         [0005]    Cables of the above described type are well fitted for their purpose, but a problem arises if they are equipped with the tube for an optical cable. The tube can be deformed when the cable is manufactured or handled and the deformation makes it impossible to install the optical fiber. The deformation can take place e.g. when the cable is suspended by suspension equipment along the cable or is retained by strapping devices at the cable ends. A cable dredged into the ground can be deformed by stones and even a cable laid on the bottom of the sea can be subjected to forces deforming the tube. The tube can be made very strong so that it withstands the deforming forces. This has the drawback that the tube will be very stiff and all the cable will be rigid and very difficult to handle. 
       SUMMARY 
       [0006]    The invention is concerned with a problem that a tube for an optical cable or fiber integrated in an electrical cable can easily be deformed. The tube must be flexible so that the electrical cable will be easy to handle. 
         [0007]    An object with the invention is thus to form an electrical cable with an integrated tube or tubes for an optical cable. The electrical cable is to be easy to handle and with still the tube/tubes is protected against deformation. 
         [0008]    The problem is solved by an insulated electrical cable with one or more tubes intended for optical cables. The electrical cable has at least two electrical conductors of metal, each surrounded by an electrically insulating layer and a jacket surrounding the electrical conductors and their electrically insulating layers. At least one strip of elastic material arranged in a region between the insulating layers of the electrical conductors and the inner side of the jacket. The tube is arranged in the strip and is surrounded by the elastic material. In a non deformed state the strip has a cross section with an outward side, facing the inner side of the jacket, which outward side follows a continuous outwardly bending curved line except for in an interval in proximity to the tube. In this interval the cross section outward side lies inside said curved line. 
         [0009]    Optionally, in the interval the cross section outward side is flat and a further option is that the cross section outward side has an indentation. An option is also that the outwardly bending curved line is the circumference of a circle. 
         [0010]    The electrical cable has the advantage that it is flexible and easy to handle and the tube for the optical cable is well protected against deformation. The electrical cable can be manufactured using standard equipment and the optical cable can easily be floated or blown into the tube when the electrical cable is already installed. 
         [0011]    The invention will now be more closely described with the aid of embodiments and with reference to enclosed drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a cross section of an electrical cable of well known type; 
           [0013]      FIG. 2  shows a view over suspension equipment; 
           [0014]      FIG. 3  shows a view over a strapping device; 
           [0015]      FIG. 4  shows a cross section of an electrical cable with a tube for an optical cable; 
           [0016]      FIG. 5  shows a cross section of an electrical cable with a tube for an optical cable according to the invention; 
           [0017]      FIG. 6  shows a cross section of a part of the cable in  FIG. 5 ; 
           [0018]      FIG. 7  shows a cross section of a part of the cable in  FIG. 5  acted on by a strapping device; 
           [0019]      FIG. 8  shows a cross section of an alternative embodiment of an inventive cable with a tube; 
           [0020]      FIG. 9  shows a cross section of still an alternative embodiment of an inventive cable with tubes; and 
           [0021]      FIG. 10  shows a cross section of the cable in  FIG. 5  but equipped with extra layers. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows an electrical cable C 1  of well known type. The cable has three insulated conductors  1 ,  2  and  3  each including a conductor  4  and an insulating layer  5 . The cable is surrounded by a jacket  6  and has shield bands  7  on each of the insulated conductors between the insulating layer and the jacket. 
         [0023]    The electrical cable C 1  can be suspended between poles using suspension equipment H 1  as shown in  FIG. 2 . The suspension equipment has a holder  21  with clamps  22  tightened by bolts  23  for retaining the cable C 1 . The holder also has a wheel  24  on which the cable can roll when it is mounted.  FIG. 3  shows a strapping device S 1  with resilient threads  31  turning spirally around the cable and fastened to a loop  32 . An end of the cable C 1  can be held by the strapping device and the cable can be stretched by pulling the loop  32 . The threads then strap up around the cable and prevent it from sliding out of the strapping device S 1 . 
         [0024]      FIG. 4  shows a cross section of an electrical cable C 4  similar to the electrical cable C 1 . It has three insulated conductors  41 ,  42  and  43 , each with an electrical conductor  44  and an insulating layer  45 . The cable C 4  has a surrounding jacket  46  and has also a plastic tube or duct  48  intended for an optical cable or equally an optical fiber. The tube is embedded in a strip  47  of elastic material, which strip runs along the cable in a region between the insulating layers  45  and the inner side of the jacket  46 . When the electrical cable is uninfluenced from external forces the outward side of the strip  47  follows a continuous outwardly bending curved line L 4  which is the circumference of a circle with a radius R 4 . The radius is defined by the diameter of the insulated conductors  41 ,  42  and  43 . The threads  31  of the strapping device S 1  surround the cable C 4 . 
         [0025]    When the cable C 4  is handled in different situations, e.g. suspended by the suspension equipment H 1  or stretched by the strapping device S 1 , it will be subjected to radial forces F 4 . The forces can arise e.g. when the cable rolls over the wheel  24 , the bolts  23  for the clamps  22  are tightened or when the cable is stretched by the strapping device S 1 . Although the tube  48  is embedded in the strip  47  the forces F 4  from e.g. the threads  31  of the strapping device S 1  can be big enough to deform the strip  47  and the tube  48  such that it will be impossible to blow or float an optical cable into the tube. 
         [0026]    In  FIG. 5  is shown a cross section of an electrical cable C 5  which has tree insulated conductors  51 ,  52  and  53 , each with an electrical conductor  54  and an insulating layer  55 . The cable C 5  has a surrounding jacket  56  and has also a plastic tube  58  intended for an optical cable. The tube is embedded in a strip  57  of elastic material, which strip runs along the cable C 5  in a region between the insulating layers  55  and the inner side of the jacket  56 . Different from the electrical cable C 4  in  FIG. 4  the outward side of the strip in the cable C 5  diverges from a continuous outwardly bending curved line L 5  when the strip is not deformed. Instead the outward side of the strip  57  has an interval I 5  in proximity to the plastic tube  58  that stretches inside the curved line L 5 . In the embodiment the outward side of the strip  57  is flat within the interval I 5 . 
         [0027]      FIG. 6  shows more in detail a part of the cross section of the cable C 5  with the insulated conductors  51  and  53 , the strip  57 , the jacket  56  and the tube  58 . The figure also shows the threads  31  of the strapping device S 1 . The cable is shown in a position when the strapping device is unloaded. The strip  57  is thus not deformed and in the interval I 5  the strip has its flat shape. 
         [0028]      FIG. 7  shows the part of the cable cross section in  FIG. 6  with the difference that the strapping device S 1  is loaded. The strapping device is no longer fully circular, as it is shown in  FIG. 6  and the strip  57  is deformed by the threads  31  of the strapping device. The position of the strip when not deformed is shown by a dashed line L 6  defining deformation zones Z 7 . The pressure on the tube  58  is shown by force arrows F 71 -F 78  indicating forces on the tube  58 . 
         [0029]    The form of the strip  57  with the flat interval I 5  protects the tube  58  from being deformed in two different ways. Firstly the force from the threads  31  is more uniformly distributed over a wider range of the strip. The deformation zones Z 7  of the strip  57  at the ends of the interval I 5  will take up a bigger part of the load and a smaller part will influence the strip over the tube  58 . The radial force F 71  on the tube is therefore smaller than the force F 4  shown in  FIG. 4 . Secondly the compression of the strip  57  in the deformation zones causes a pressure in the strip that gives rise to tangential forces, mainly the forces F 73  and F 77  and also the forces F 72 , F 74 , F 76  and F 78 . The tangential forces stabilize the tube  58  and contribute to prevent it from collapsing. Thus, although the tube  58  is somewhat weak and flexible enough to let also the electrical cable C 5  to be flexible, the tube  58  retains its form during the handling of the electrical cable. 
         [0030]      FIG. 8  shows an electrical cable C 8  with the insulated conductors  51  and  53 . It has a jacket  81  and a strip  82  of elastic material, which runs along the cable in a region between the insulated layers of the insulated conductors and the inner side of the jacket. The tube  58  is embedded in the strip as in previous embodiments and also the thread  31  of the strapping device S 1  is shown. In an interval I 8  nearest to the tube  58  the outward side of the strip cross section stretches inside a continuous outwardly bending line L 8 . Different from the embodiment in  FIG. 6  the cross section outward side in the interval I 8  has an indentation. By adjusting the cross section of the strip it is possible to adjust the distribution of the forces on the tube  58 . An optical cable (or fiber)  83  is shown in the tube  58 . 
         [0031]    In  FIG. 9  is shown an electrical cable C 9  with two insulated conductors  91 ,  92  surrounded by a jacket  93 . The cable has two tubes (or ducts)  94 ,  95  for optical cables (or fibers). The tubes are embedded in each an elastic strip  96 ,  97  running along the electrical cable in regions between the insulated conductors and the inner side of the jacket. In intervals nearest to the tubes the outward side on each of the strips is flat in the same manner as is shown in  FIG. 6 . 
         [0032]      FIG. 5  shows the electrical cable C 5  with three insulated conductors and the strip with the tube.  FIG. 9  shows the electrical cable C 9  with two strips having each an embedded tube. Also electrical cables having four and even more insulated conductors and a plurality of strips with tubes are covered by the invention. 
         [0033]    In connection with  FIG. 7  is shown how the cable C 5  and its elastic strip  57  is deformed by the threads  31  of the strapping device S 1 . The cables C 8  and C 9  can be deformed by the strapping device in a corresponding manner and the tubes  58 ,  94  and  95  are then protected by the respective elastic strip. The cables can as mentioned be subjected to deforming forces in other ways e.g. from the suspension equipment H 1  or when the cable is dredged into the ground. The tubes are then protected from deformation in a way similar to what is described in connection with  FIG. 7 . 
         [0034]    Electrical cables often have a number of layers for different purposes e.g. as appears from  FIG. 1 . The  FIGS. 4 to 9  are simplified and do not show such layers. In  FIG. 10  on the other hand is shown an electrical cable C 10  similar to the cable C 5  of  FIG. 5 . The cable C 10  has the insulated conductors  51 ,  52  and  53 , the strip  57  with the tube  58  and the jacket  56 . It also has electrically conducting layers  51   a,    52   a  and  53   a  around the respective insulated conductor. An electrically conductive layer  56   a  surrounds the insulated conductors  51 ,  52  and  53  and the strip  57  and is in close contact with the inside of the jacket  56 . If an electrically conducting object penetrates the cable C 10  and comes into contact with the electrical conductors  54  a shortcut will arise and the voltage to the cable can be switched off. This effect is improved by making also the strip  57  of electrically conductive material. The tube  58  is surrounded by a sliding layer  58   a,  e.g. a smooth band. The layer  58   a  facilitates a movement between the tube and the surrounding strip  57 , which contributes to that the tube will not be deformed when the cable C 10  is bended. The layer  58   a  facilitates the removing of the strip from the tube  58  with less risk for damages on the tube. The cable is manufactured by traditional means, e.g. the strip  57  is extruded on the tube  58  with its sliding layer  58   a.  The strip is then placed between the conductors  51  and  53 , the electrically conductive layer  56   a  is applied and the jacket  56  is extruded around it all.