ELECTRICAL CABLE WITH A TUBE FOR AN OPTICAL CABLE

TECHNICAL FIELD

The present invention relates to an electrical cable with a tube for an optical cable.

BACKGROUND

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.

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.

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 .

SUMIy[ARY

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.

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.

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.

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.

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.

The invention will now be more closely described with the aid of embodiments and with reference to enclosed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cross section of an electrical cable of well known type;

Figure 2 shows a view over suspension equipment;

Figure 3 shows a view over a strapping device;

Figure 4 shows a cross section of an electrical cable with a tube for an optical cable;

Figure 5 shows a cross section of an electrical cable with a tube for an optical cable according to the invention;

Figure 6 shows a cross section of a part of the cable in figure 5;

Figure 7 shows a cross section of a part of the cable in figure 5 acted on by a strapping device;

Figure 8 shows a cross section of an alternative embodiment of an inventive cable with a tube;

Figure 9 shows a cross section of still an alternative embodiment of an inventive cable with tubes; and

Figure 10 shows a cross section of the cable in figure 5 but equipped with extra layers.

DETAILED DESCRIPTION

Figure 1 shows an electrical cable Cl 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 .

The electrical cable Cl can be suspended between poles using suspension equipment Hl as shown in figure 2. The suspension equipment has a holder 21 with clamps 22 tightened by bolts 23 for retaining the cable Cl. The holder also has a wheel 24 on which the cable can roll when it is mounted. Figure 3 shows a strapping device Sl with resilient threads 31 turning spirally around the cable and fastened to a loop 32. An end of the cable Cl 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 Sl.

Figure 4 shows a cross section of an electrical cable C4 similar to the electrical cable Cl. It has three insulated conductors 41, 42 and 43, each with an electrical conductor 44 and an insulating layer 45. The cable C4 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 L4 which is the circumference of a circle with a radius R4. The radius is defined by the diameter of the insulated

conductors 41, 42 and 43. The threads 31 of the strapping device Sl surround the cable C4.

When the cable C4 is handled in different situations, e.g. suspended by the suspension equipment Hl or stretched by the strapping device Sl, it will be subjected to radial forces F4. 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 Sl. Although the tube 48 is embedded in the strip 47 the forces F4 from e.g. the threads 31 of the strapping device Sl 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 .

In figure 5 is shown a cross section of an electrical cable C5 which has tree insulated conductors 51, 52 and 53, each with an electrical conductor 54 and an insulating layer 55. The cable C5 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 C5 in a region between the insulating layers 55 and the inner side of the jacket 56. Different from the electrical cable C4 in figure 4 the outward side of the strip 57 in the cable C5 diverges from a continuous outwardly bending curved line L5 when the strip is not deformed. Instead the outward side of the strip 57 has an interval 15 in proximity to the plastic tube 58 that stretches inside the curved line L5. In the embodiment the outward side of the strip 57 is flat within the interval 15.

Figure 6 shows more in detail a part of the cross section of the cable C5 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 Sl. The cable is shown in a position when the strapping device is unloaded. The strip 57 is thus not deformed and in the interval 15 the strip has its flat shape.

Figure 7 shows the part of the cable cross section in figure 6 with the difference that the strapping device Sl is loaded. The strapping device is no longer fully circular, as it is shown in figure 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 L6 defining deformation zones Z7. The pressure on the tube 58 is shown by force arrows F71-F78 indicating forces on the tube 58.

The form of the strip 57 with the flat interval 15 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 Z7 of the strip 57 at the ends of the interval 15 will take up a bigger part of the load and a smaller part will influence the strip over the tube 58. The radial force F71 on the tube is therefore smaller than the force F4 shown in figure 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 F73 and F77 and also the forces F72, F74, F76 and F78. 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 C5 to be flexible, the tube 58 retains its form during the handling of the electrical cable.

Figure 8 shows an electrical cable C8 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 Sl is shown. In an interval 18 nearest to the tube 58 the outward side of the strip cross section stretches inside a continuous outwardly bending line L8. Different from the embodiment in figure 6 the cross section outward side in the interval 18 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.

In figure 9 is shown an electrical cable C9 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 figure 6.

Figure 5 shows the electrical cable C5 with three insulated conductors and the strip with the tube. Figure 9 shows the electrical cable C9 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.

In connection with figure 7 is shown how the cable C5 and its elastic strip 57 is deformed by the threads 31 of the strapping device Sl. The cables C8 and C9 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 Hl 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 figure 7.

Electrical cables often have a number of layers for different purposes e.g. as appears from figure 1. The figures 4 to 9 are simplified and do not show such layers. In figure 10 on the other hand is shown an electrical cable ClO similar to the cable C5 of figure 5. The cable ClO 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 51a, 52a and 53a around the respective insulated conductor. An electrically conductive layer 56a 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 ClO 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 58a, e.g. a smooth band. The layer 58a facilitates a movement between the tube and the surrounding strip 57, which contributes to that the tube will not be deformed when the cable ClO is bended. The layer 58a 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 58a. The strip is then placed between the conductors 51 and 53, the electrically conductive layer 56a is applied and the jacket 56 is extruded around it all.