Technical field of the invention

The present invention relates to a connection arrangement comprising a pulling head and an end part of an electric cable, and a method for connecting a pulling head to an end part of an electric cable. The invention mainly relates to applications within the technical field of sub- sea electric power cables. Background

When laying out electric cables, the end of the cable is provided with some kind of attachment arrangement by means of which it can be connected to the suitable machinery used for laying out cabling. This attachment arrangement is often called a pull in head or a pulling head, since the cable may then be pulled by means of this arrangement, once it has been connected to the end of the cable. The pulling head and its connection to the cable must be able to withstand the pulling forces to which they are subjected during pulling. Usually the connection between the pulling head and the electric cable is made such that the pulling forces are transferred from the pulling head to the armour layer of the electric cable. This armour layer is generally made of metal wires that are twined to form the armour.

Further, it is common to use a pipe arrangement to surround the pulling head in order to protect it during pulling of the cable. The pipe arrangement is for example buried in the ground and extends from the bottom of the sea and up to a land installation above ground. The dimensions of this pipe arrangement must be adapted to be able to receive the pulling head.

In the technical field of sub-sea electric power cables, for which the shorter wording sea cables will be used in the following, there are also other issues to consider concerning the pulling head and the connection to the cable end. One such issue is the capability to withstand water, fresh water or salt water, which puts special demands on the pulling head and the connection to the cable end.

Further, it is fairly common to use a sea cable not only for electric power cabling but also for carrying other types of cabling. For example it may include one or more opto fibre cables running alongside the electric conductor cores and also other types of cablings or hoses that may be used in what is usually called umbilical members or cabling, of which may be mentioned gas pipelines, telephone cables and similar. An opto fibre cable may e.g. be used to measure temperatures. The pulling head usually comprises a hollow sheath having an open end into which an end of the cable is inserted, and having an opposite closed end at which an attachment device is provided by means of which it is attached to the pulling machinery. According to prior art, the usual way to connect the pulling head to the end of the electric cable is to connect the armour of the cable to the sheath of the pulling head. This is done by means of a special compound that is applied between the sheath and the armour and moulded in situ. The use of this moulded compound is required in an amount that results in a connection between the pulling head and the cable end that is in the order of twice the size of the cable, and consequently the sheath must have nearly twice the diameter of the cable. The pipes used to protect the pulling head and the connection to the cable when pulling the cable, must therefore have an even larger inner diameter. Another known alternative is to attach the armour to the pulling head by means of clamping the armour between flanges in a flange arrangement. This type of arrangement also requires extra space for the flanges and the pipes must have a large diameter to also accommodate the flanges.

Summary of the invention

An object of the present invention is to provide a method for connecting a pulling head to an end part of an electric cable that is simplified and less time and space demanding, and a connection arrangement that is less space demanding and easier to use.

This object is achieved, in accordance with the present invention, by a connection arrangement comprising a pulling head and an end part of an electric cable, the electric cable comprising one or more electric conductor cores surrounded by one or more external layers comprising an armour layer of metal, the pulling head comprising a metal sheath with a first open end adapted to receive said end part of the electric cable, and a second end provided with an attachment device for attachment to a pulling device, characterized in that the end part of the electric cable is connected to the pulling head by means of a weld connecting the armour layer of the end part of the electric cable to the metal sheath of the pulling head.

The object is further achieved, in accordance with the present invention, by a method for connecting a pulling head to an end part of an electric cable, the electric cable comprising one or more electric conductor cores surrounded by one or more external layers comprising an armour layer of metal, the pulling head comprising a metal sheath with a first open end adapted to receive an end part of said electric cable, and a second end provided with an attachment device for attachment to a pulling device, characterized by connecting the end part of the electric cable to the pulling head by means of welding the armour layer of the electric cable to the metal sheath of the pulling head. By using welding to connect the armour layer to the sheath, and thus to connect the cable to the pulling head, is obtained the advantages of a simplified and quicker connection method. The welding can be performed in a shorter time than the previous moulding of the special compound. Further, the weld itself does not require a lot of space, with the result that the sheath can be made with an outer diameter that is only slightly bigger than the diameter of the electric cable. Consequently, there is an advantage of a smaller outer diameter of the pulling head and therefore also a smaller inner diameter of the pipe arrangement inside which the pulling head and the cable is pulled during the pulling of the cable to e.g. a land installation.

The connection arrangement according to the present invention may comprise a heat protection device mounted around the one or more conductor cores at the end part of the electric cable. This device provides the advantage of protecting the conductor cores and other elements of the electric cable from the heat generated from the welding. The heat protection device may have an annular shape that will surround the conductor core or the group of conductor cores.

According to one feature, the first open end of the metal sheath is located over the heat protection device and externally thereof, and an end portion of a freed armour layer part of the armour layer, which is detached from the one or more conductor cores at the end part of the electric cable, is located over the metal sheath at its first open end and in contact with the metal sheath. This is made in order to facilitate the welding and to provide good contact between the sheath and the armour layer that are to be welded together. This also has the advantage of making it possible to have electric contact between the sheath of the pulling head and the armour layer, which is useful in some cases.

According to another feature of the connection arrangement, the metal sheath may have a first external annular recessed portion, at its first open end, adapted to accommodate the end portion of the freed armour layer part. This will contribute to providing good contact between the sheath and the armour and facilitate the welding operation. It will also have the advantage of making it possible to avoid having a larger diameter in the weld region, where the free end of the armour layer lies on top of the sheath.

According to another feature, the heat protection device is also a centering device for the one or more electric conductor cores. It is preferably an annular device surrounding the conductor core/cores and will keep them firmly in place even when the armour layer has been detached from the conductor cores at the end of the cable. As yet another feature, the connection arrangement may comprise a support device for supporting the freed armour layer part. This support device is located externally of the freed armour layer part.

Further, the connection arrangement may comprise a weld protection member mounted over the area of the weld. This protection member may be e.g. a shrink hose, a tape or a suitable film adapted to protect the weld from corrosion and also prevent other damage to the weld and the weld area. According to another feature, the metal sheath may have a second external annular recessed portion, which is adapted to accommodate the weld protection member. This has the advantages of providing an area where the weld protection member may be securely fitted and without adding to the outer diameter of the sheath.

Additionally, the electric cable may further comprise one or more fibre optic cables surrounded by said armour layer.

According to an embodiment of the connection arrangement, the electric cable may be a 3-phase medium or high voltage cable comprising three electric conductor cores.

According to the invention, the method may further comprise, prior to welding, detaching the armour layer from the one or more conductor cores at the end part of the electric cable in order to obtain a freed armour layer part, separated from the one or more electric conductor cores at the end part of the electric cable. This will make the armour more easily accessible for the welding operation.

Further, the method may comprise, prior to welding, mounting a heat protection device around the one or more conductor cores at the end part of the electric cable. As an additional step, the method comprises, prior to welding, placing the first open end of the metal sheath of the pulling head over the heat protection device and externally thereof, and placing an end portion of the freed armour layer part over the metal sheath at its first open end such that it is in contact with the metal sheath. The advantages of this have already been described.

The method may also comprise mounting a support device externally of the freed armour layer part. This will prevent that the freed armour layer is detached further from the conductor cores during pulling of the cable.

Additionally, the method may also comprise mounting a protection member over the area of the weld, after welding.

The present invention may be used for a sea cable that is pulled out of the water in order to be connected to a land installation, which should also be interpreted to include oil platforms, wind power plants at sea and similar. The invention is also suitable to be used for a cable being pulled out of the water or laid into the water not only from the shore but also from a vessel. However, the present invention is not limited to the technical field of sea cables, but may also be used for land cables.

Further, the present invention is not limited to electric power cables comprising only electric conductors, but the cables may also include e.g. fibre optic cabling and even other types of cablings or hoses that may be used in what is usually called umbilical members or cabling, as previously mentioned.

The electric cables may be e.g. medium or high voltage cables of 10kV - 400 kV or even higher. They may be AC or DC cables, 3-phase or single-phase cables.

Further, the invention may be used for electric cables with one or multiple layers of armour, and the armour may be of different materials, e.g. steel, galvanized or stainless steel, copper, aluminium. The electric cable may also comprise other additional layers, as known per se.

Further features and advantages of the invention will also become apparent from the following detailed description of embodiments.

Brief description of the drawings

A detailed description of the present invention and embodiments thereof, given as examples only, will now be made with reference to the accompanying schematic drawings, in which:

Fig. 1 shows a perspective view of a connection arrangement according to the present invention;

Fig. 2 is a side view, partly in cross section, of an embodiment of the connection arrangement according to the present invention;

Fig. 3 is a side view, partly in cross section, of a variant of the connection arrangement according to the present invention;

Fig. 4 is a cross section along A-A of the embodiment shown in Fig. 2;

Fig. 5 is a cross section along B-B of the embodiment shown in Fig. 2; and

Fig. 6 is an enlarged view of the embodiment shown in Fig. 2 of the connection arrangement according to the present invention, partly in cross section.

In the drawings, the same elements or corresponding elements in the different embodiments have been given the same reference number.

Detailed description

In Fig. 1 is shown a connection arrangement 1 comprising a pulling head 2 and an end part 4 of an electric cable 6. In Fig. 2 is shown an embodiment of the connection arrangement where parts of the pulling head and cable end have been removed in order to show the interior thereof. The pulling head 2 comprises a metal sheath 8 having a first open end 10 adapted to receive an end part 4 of an electric cable 6, and a second opposite closed end 12 provided with an attachment device 14. The attachment device 14 is illustrated as a shackle but it may have any other appropriate design suitable for attachment of the pulling head to a pulling device (not shown). When the attachment device 14 is attached to a pulling device, the cable may be pulled and moved as has been explained previously when describing the background of the invention.

The electric cable in the embodiment in Fig. 2 is a 3-phase electric cable having three electric conductor cores 16, of which only two are visible in Fig. 2, and the electric cable may be any type of such a cable. A cross section of this cable taken along A-A in Fig. 2 can also be seen in Fig. 4. The three conductor cores 16 of the cable are grouped together and surrounded by an armour layer 18. Externally of the armour layer there is a yarn layer 20 to protect the armour layer from mechanical damage or corrosion. In this embodiment there are also filling profiles 22 located between the conductor cores and the armour layer, in order to support the conductor cores and keep them in stable positions within the armour layer. These filling profiles 22 may be designed to have channels 24 adapted to receive and support one or more fibre optic cables 26, or possibly other types of cables or hoses. In the embodiment of Figs. 2, 4 and 5 there is one fibre optic cable illustrated. However, it is not unusual to have two or three fibre optic fibre cables together with the conductor cores in the electric cable. It should be noted though, that in some applications there will be no fibre optic cables at all.

The armour layer 18 and the sheath 8 are made of a metal that is suitable for welding. The armour layer is usually made of armour wires of for example steel, galvanized or stainless steel, copper, aluminium. It is also possible to have multiple armour layers. Instead of the filling profile, other kinds of filling may be used, e.g. yarn filling, in order to support and stabilise the conductor cores.

Reference is now primarily made to Fig. 6 showing the connection arrangement 1 in an enlargement of part of Fig. 2 showing a cross section along B-B in Fig. 2. In Fig. 6 is shown that the armour layer 18, at the end part 4 of the electric cable 6, has been detached from the conductor cores 16 so that there is a freed armour layer part 32 that is free from the conductor cores and thereby allowing it to be spaced apart from the conductor cores. The end part 4 of the electric cable is inserted into a first open end 10 of the pulling head sheath 8. The sheath 8 is provided with a first annular recessed portion 28 externally at its first open end. This annular recessed portion is adapted to receive and accommodate an end portion 30 of the freed armour layer part 32, externally on the sheath. The freed armour layer part 32 is connected to the sheath 8 by means of a weld 34 in the region of the recessed portion 28 where the end portion 30 of the freed armour layer part contacts the sheath 8.

There is also an annular heat protection device 34 mounted externally of the conductor cores 16 at the end part 4 of the electric cable, between the sheath 8 and the conductor cores in the region where the freed armour layer 32 is mounted on the sheath and where the welding is to be performed. In the illustrated embodiment, this heat protection device is also a centering device for the conductor cores. The purpose of this protection and centering device is to protect the ends of the conductor cores from the heat produced during the welding operation and to hold them together when inserted into the first open end of the sheath 8.

In order to protect the connection area of the sheath 8 and the armour layer 18, and the weld, there may be provided a protection member 38 over this area. This protection member may for example comprise a shrink hose. In order to support and accommodate the protection member, the sheath may be provided with a second external annular recessed portion 40 close to its first open end 10. This second recessed portion is located further in from the end of the sheath than the first recessed portion 28.

In Fig. 6 is also illustrated a support device 42 for the armour wire of the freed armour layer part 32, which is mounted externally of the armour layer. The support device preferably has an annular form with an internal shape of truncated cone. The truncated shape will support the freed armour layer from the outside so that it is not bent outwards more than necessary for its end part 30 to fit over the sheath 8. At the truncated end the support device will fit closely around the not detached armour layer of the cable, in order to prevent that more than the desired freed armour layer part 32 gets detached from the cable when it is subjected to pulling forces during pulling of the cable by means of the pulling head. The protection member 38 may be extended to also cover this support device 42.

In Fig. 3 is illustrated a connection arrangement where the electric cable is a single phase power cable 6 with one conductor core 16. Nonetheless, the details of the connection arrangement are the same as for the embodiment shown in Fig. 2 and Fig. 6. In this type of electric cable, the electric cable may also comprise an opto fibre cable, e.g. running in a metallic tube alongside the single conductor core 16. This metallic tube may be located where some wires of the armour have been removed.

Generally, the pulling head 2 may be made of two separable parts so that a top part with the attachment device may be detachable in order to get access to the cable end with the conductor cores inside the sheath.

The conductor cores and the opto fibre cables may have any type of end sealings as known per se. The method of connecting the pulling head to the end part of an electric cable comprises the following steps, though the order of these steps may sometimes be changed:

In preparation, the armour layer 18 at the end part 4 of the electric cable 6 is detached from the one or more conductor cores 16 at the end part 4 of the cable. If there is a yarn layer 20 or other layer externally of the armour layer, such external layers must be removed first. If there are several armour layers, usually all of the armour layers are detached from the cable at the end part. This will make it possible to get access to the conductor cores 16 in order to make it possible to install end sealing devices on the conductors, as known per se. If there are fibre optic cables 26, these will also be provided with end sealings, as known per se. It may also be practical to pre-mount e.g. the support device 42 and the protection member 38 on the cable such that they later on can easily be moved to their proper location.

The next step comprises installing the heat protection and centering device 36 around the one or more conductor cores 16 at the end part of the electric cable. After this, the first open end 10 of the metal sheath 8 of the pulling head is mounted over the protection and centering device 36 and externally thereof, and the end portion 30 of the freed armour layer part 32 is placed on the first recessed portion 28 of the sheath at its first open end such that it is in contact with the metal sheath. During this, the top part of the pulling head comprising the attachment device may be in detached state if such a type of pulling head is used. Then the end part 4 of the electric cable is connected to the pulling head by means of welding the end portion 30 of the freed armour layer part 32 to the metal sheath 8, where they are in contact.

After the welding has been completed, a support device 42 for the armour wire may be mounted, if required, externally of the freed armour layer part 32 and preferably extending over the freed armour layer part and continuing also over a portion of the conductor cores where the armour layer has not been detached. This will keep the freed armour layer part firmly in place and protect it during pulling of the cable. It will also prevent that the armour layer 18 further down the cable 6 becomes detached due to the pulling forces. Then a protection member 38 may suitably be mounted over the area of the weld 34. This protection member will suitably also extend onto the cable and as far as to where the armour layer is firmly attached to the conductor cores. If there is a support device 42 for the armour wire, this should preferably be covered by the protection member. The protection member may also suitably extend past the weld 34 onto part of the sheath, as has been described above in connection with description of the second recessed portion 28 of the sheath 8. The protection member may e.g. comprise a shrink hose. Finally, if the pulling head has a detachable top part, this part is mounted. The connection is thus complete and the pulling head 2 is connected to the electric cable 6. The invention shall not be considered limited to the illustrated embodiments, but can be modified and altered in many ways, as realised by a person skilled in the art, without departing from the scope defined in the appended claims.