The present invention relates to a joint reinforcement arrangement in an electrical cable, which electrical cable includes at least one heavy gauge metallic conductor embedded in at least an insulating matrix, which matrix is able to transmit shear forces arising in said cable between the conductor and the cable surface.

According to the present invention, also a method to prepare and make a reinforcement arrangement in an electrical cable joint of the above mentioned kind is provided.

Joints in electrical cables are known to be mechanically weak spots in the completed cable, especially with regards to axial forces, as the welding of the metallic conductor creates annealed areas with reduced strength and yield. The usual methods for improving the axial strength and/or yield of joints focus on improvements in the welding technique. During development of the joint for a particular project, the limits of welding technique were reached without sufficient results for the needs of the project application. The application also required that any increase in the outer diameter of the cable after jointing be minimized to the greatest extent possible. According to the present invention, a reinforcement arrangement in an electrical cable joint of the introductory said kind is provided, which joint reinforcement arrangement is distinguished in that a braided carbon fibre sleeve of predetermined length is glued onto the external surface of the cable and extends in both directions from the centre of a cable joint splice, which braided carbon fibre sleeve is kept in tension during the gluing process until hardening thereof.

Thus it is to be understood that the solution, and subject of this patent application, was to reinforce the standard cable joint externally with a braided carbon fiber sleeve (a per se standard product sold commercially), bonded to the cable and set in a matrix with epoxy resin (also per se a standard product sold commercially, and commonly used together with carbon fiber for the construction of various objects of myriad shapes and sizes). The original cable was designed to have high shear force capacity throughout its various layers of construction, and this facilitated the functioning of the carbon fiber sleeve reinforcement. The epoxy bonds the sleeve to the cable, and due to the higher stiffness of the carbon fiber/epoxy system, axial forces introduced on either end of the cable away from the joint are taken up in part by the sleeve, reducing the strain and thus force on the welded metallic conductor. With only a very small increase (typically 3- 5%) in outer diameter, the reinforced joint becomes stronger than the original cable, eliminating the traditional weak point in the cable.

Preferably the braided carbon fibre sleeve is a weave composed of crossing threads of carbon fibre, which during tension thereof, tends to decrease the diameter of the sleeve and straighten the angle of the weave in the longitudinal direction of the cable.

The cable is normally composed of one or more of the following elements; a metallic conductor consisting of a plurality of single wires or a solid rod, an inner semi- conductive layer, an insulation matrix, an outer semi-conductive layer, a metallic screen and an outer jacket, or constitutes an element within a control or power umbilical.

The glue can be in the form of a mixture of an epoxy resin and a hardener and the glue can be applied in several layers.

Also the braided carbon fibre sleeve can be applied in several layers and embedded in the glue or the epoxy resin.

According to the present invention, a method of the introductory said kind is also provided, which method is distinguished in that firstly at least one braided carbon fibre sleeve is slid onto the cable and temporarily parked at a location a predetermined distance away from the joint, if necessary the surface of the cable is prepared to ensure grip, a mixture of epoxy and hardener is applied to said surface of the cable, the braided carbon fibre sleeve is stretched over the joint to straddle over approximately the same distance in both ends of the cable, and further said mixture is added as required to at least partly embed the braided carbon fibre sleeve in said mixture of epoxy and hardener. Preferably, the surface of the cable is prepared to ensure grip by gritting the surface thereof, cleaning said surface and optionally flame treating the surface of the section to be glued. Such sleeves may be added in several layers. Then the steps of the second section above are repeated as necessary to apply one or more additional braided carbon fibre sleeves onto the cable, which subsequent sleeves are somewhat shorter than the firstly applied sleeve. Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which is given for the purpose of description, and given in context with the appended drawings where:

Fig. 1 shows in schematic view a typical braided carbon fiber sleeve, and

Fig. 2 shows in schematic view a typical cable joint before rebuilding of insulation etc.

Reference is made to figure 1 that shows a splicing area of a cable to be reinforced to strengthen the weakened area due to the splice. At both ends, to the right and to the left in the drawing, the original cable 1 can be seen. Such cable 1 can be several kilometers long and needs to be spliced at intervals to increase the total length of the cable 1, or to make repairs in case of damage. The splicing operation will be described below together with figure 2.

After such splicing operation, the cable surface is similar to the original cable. In order to ensure at least the original strength in the splicing area, a first braided carbon fiber sleeve of approximately 3 meters length is bonded to the outer surface of the cable and set in a matrix of epoxy resin and hardener coated on, or applied, to the cable surface. Then a second braided carbon fiber sleeve of approximately 2 meters length is bonded to the outer surface of the first sleeve and set in another layer of epoxy resin and hardener applied to the outer surface of the first sleeve. Still more epoxy resin mixed with hardener can be applied to the surface of the second sleeve to more or less embed the sleeve into the epoxy resin. Additional layers can be added in the same fashion. A still more detailed procedure of the preparation and method step by step will follow below.

Reference is now made to figure 2 that shows a typical cable splice where the central metallic conductor 2, typically copper or aluminum, is spliced by welding. The cable 1 is ready to be rebuilt in respective layers of insulation and screens starting with the innermost layer 3 of inner semi conductive material. Next layer 4 is an insulation material rebuilt onto the layer 3. Then a layer 5 of outer semi conductive material is applied onto the layer 4. A metallic screen 6 is applied around the layer 5 and spliced by welding to the screen of both cable ends. Finally an outer jacket 7 is applied around the screen 6 and thus completes the cable 1, though a weak spot is present in the splice.

Next procedure will be to continue as described in connection with figure 1 and outlined in detail below.

Below a detailed description of the materials, storage and the procedure how to apply a first and a second sleeve at site will follow. This is only one example of one

embodiment of the invention and shall not be considered as a limitation of the invention to this particular embodiment.

1. Introduction

1.1. This procedure describes the method in which the medium voltage electrical cables for power umbilicals are to be reinforced in the spliced section using two layers of carbon fibre sleeve and epoxy resin. This procedure is intended for verification testing on short samples.

2. Safety All relevant personnel shall review the material safety datasheets for the materials involved, as well as the following documents:

• http://www.westsvstem.com/ss/how-to-prevent-overexposure-to- epoxy/

• http://www.westsystem.com/ss/other-epoxy-related-hazards/

• http://www.westsystem.com/ss/environmental-concerns/

• http://www.westsystem.com/ss/epoxy-chemistry/

• http://www.westsystem.com/ss/di spensing-mixing/

The work area shall be adequately ventilated, and all necessary personal protective equipment as described in the documents above shall be worn by all relevant personnel.

Materials and Storage

• Carbon Fibre Braided Sleeve

o (Siltex part number 050.12040243-C)

o 50mm nominal outer diameter at 45 degree lay angle

o Weight: 3K (3000 filaments per yarn)

o To be stored in a clean area to avoid contamination

• West System Epoxy 105

o Storage requirements are listed in the MSDS.

• West System Hardener 205

o Storage requirements are listed in the MSDS.

• West System calibrated measuring pumps (#300, Mini Pump Set (for Group Size A, B or C))

• Mixing containers

• Cleaner/solvent appropriate for PE (ethanol)

• 80-grit sand paper

• Propane torch

• Tape

• Work benches with clamping and tensioning capabilities

• Screw Clamps

• Personal protective equipment: disposable gloves, eye protection, protective clothing covering arms

Prepare the cable sample

4.1. Note: the work shall be performed in a clean, covered location at normal room temperature, away from dust and debris.

4.2. Grip one end of the cable with the workbench approximately 3 meters away from the middle of the cable splice.

4.3. Prepare carbon fibre braid

4.3.1. Check the braiding for damages/defects:

• Broken fibres

• Inconsistent braiding pattern

• Presence of dust or debris

• Discard length if any damage is found

4.3.2. Measure and cut the carbon fibre sleeves. 4.3.2.1. Each reinforced cable section shall have a 3000mm base layer and 2000mm top layer, centered on the conductor weld in the spliced cable (or weakened point for preliminary testing).

4.3.2.2. Cut one 2500mm length and one 1700mm length. Maintain a 45 degree lay angle of the carbon fibre braiding during measuring. These lengths will stretch to 3000mm and 2000mm when applied to the cable at approximately 30 degrees lay angle.

4.3.3. Slide the two carbon sleeves onto the cable, beginning with the shorter length. Working with one length at a time, bunch up the sleeves so that they are both stored away from the 3 meter area to be reinforced.

4.3.4. Fasten the other end of the cable 2 meters away from the centre of the splice and secure it to another fixing point or workbench.

4.3.5. Using the workbench tensioning device, tighten the cable until it is as straight as possible (lift the cable in the middle during tightening)

4.3.6. Mark the floor below the cable with the location of the centre of the splice, and with marks for 1500mm and 1000mm away from the centre on each side.

4.3.7. Using 80-grit sandpaper, thoroughly abrade (with minimal loss of

material) the surface of the cable in the 3 meter section centred on the weld that will be reinforced.

4.3.8. Clean the surface of the section of cable to be reinforced with an ethanol cleaner/solvent.

4.3.9. Flame-treat the 3 meter section by passing a propane torch (or similar) over the surface of the cable. Ensure that no melting of the outer jacket occurs.

Apply the 1 ^st sleeve

• All activities in this section must be completed within 10 minutes of mixing the epoxy

5.1. Prepare the epoxy

5.1.1. Prepare the pumps. The #300 mini pump set is designed to dispense epoxy and hardener in a 5:1 ratio with a single depression of each pump. Select the correct tube lengths from the kit for the pumps and screw the pumps onto the epoxy and hardener containers. Prime the pumps by pressing each several times into a container to remove any air. Discard any dispensed material.

5.1.2. Mix the epoxy and hardener. In an appropriate mixing container, add an equal number of pumps of the epoxy and hardener and stir them together. Note that once the elements are combined, the pot life is approximately 10 minutes for lOOg at room temperature. Work with small quantities. Apply the epoxy to the 3 meter section of cable to be reinforced. This can be done by hand.

Work the 2500mm braid over the cable until one end is aligned with the edge of the glued section.

5.2. Wrap tape around the aligned end of the sleeve and apply a screw clamp over it.

Care must be taken not to damage the outer sheath of the cable (the tape is for protection only).

5.3. Work the free end of the sleeve over the glued area and pull it as tight as

possible by hand, ensuring that all the fibers are in close contact with the cable. Clamp the free end as described above.

6. Apply the 2 ^nd sleeve

• All activities in this section must be completed with 10 minutes of completing the final activity in the previous section.

6.1. Prepare a new batch of epoxy as described above

6.2. Apply the epoxy by hand over the 1 ^st sleeve. Ensure that the carbon braid is thoroughly saturated.

6.3. Work the 1700mm braid over the first sleeve until one end is 1 meter from the center of the reinforced area.

6.4. Tape and clamp the end of the braid as described above.

6.5. Work the rest of the sleeve over the cable until fully stretched with close

contact with the 1 ^st sleeve.

7. Finalize the sleeve

• All activities in this section must be completed with 10 minutes of completing the final activity in the previous section.

7.1. Prepare a new batch of epoxy as described above.

7.2. Apply the epoxy by hand over the 1 ^st sleeve. Ensure that the carbon braid is thoroughly saturated, and that no drips are allowed to harden.

7.3. Allow the epoxy to cure for 6-8 hours before handling. A similar existing application of braided carbon fiber sleeves with epoxy resin are lightweight tubes made of the material, formed around pipe that is removed after curing of the epoxy. Typical variations would be in the length of the sleeve used, the number of layers used, the weight of the carbon fibers, etc, resulting in more or less reinforcement against axial forces, and more or less increase in outer diameter. The development was made on medium voltage power cables, but this could apply to low voltage or high voltage cables as well, or any cable with sufficient shear force capacity throughout its layers.

Other materials may be potentially used for this application, including prepregnated unidirectional carbon fiber tape or other carbon fiber material that can be applied externally after jointing (as opposed to in advance as the sleeve must be). Any other material of suitable stiffness and strength, such as glass fiber, aramid fiber, etc could also potentially be used, as could wire mesh if it could be successfully bonded to the surface in question.

Other common techniques for the application of epoxy resin to carbon fibre material, such as vacuum bag moulding and heat application to decrease curing time could be alternative application methods or could be incorporated to the embodiment described above.

Typical test results:

40,00

35.00

30,00

25,00

20,00

15,00

10,00

5,00

0,00

0,8 1 1

Elongation (%)