WO2022053124A1

WO2022053124A1 - Submarine cable

Info

Publication number: WO2022053124A1
Application number: PCT/EP2020/075023
Authority: WO
Inventors: Nicholas Wood
Original assignee: Rwe Renewables Gmbh
Priority date: 2020-09-08
Filing date: 2020-09-08
Publication date: 2022-03-17
Also published as: EP4211706A1

Abstract

The application relates to a submarine cable (100, 200, 400, 500, 700), in particular, an energy submarine cable (100, 200, 400, 500, 700), comprising at least one conductor (102, 202, 502), at least one outer sheath (104, 204, 404, 504) surrounding the at least one conductor (102, 202, 502), wherein the outer sheath (104, 204, 404, 504) has an outer sheath surface (106, 206, 406, 506), wherein a plurality of outwardly extending flexible fibres (108, 208, 308, 408, 508) is arranged on the outer sheath surface (106, 206, 406, 506).

Description

Submarine cable

The application relates to a submarine cable, in particular, an energy submarine cable, for an offshore structure, comprising at least one conductor and at least one outer sheath surrounding the at least one conductor. Furthermore, the application relates to an offshore system, a method and a use of a submarine cable.

For the purpose of transmission of electrical energy and/or data between offshore structures and/or onshore structures, it is necessary to lay extensive lengths of submarine cables on the seafloor and seabed, respectively, between the respective connection points of said structures. Such a submarine cable comprises at least one conductor for transmitting electrical energy and/or data. For instance, the at least one conductor can be made of a metal, such as copper or aluminium, or glass fibre.

In particular, submarine cables can take the form of a number of internal conductive elements protected, for instance, by a hardened armour layer and an outer (protective) sheath. The outer sheath can be a wound or moulded polymer sheath. One intention of the application of such a sheath to a submarine cable base body having said at least one conductor is to prevent minor damage, e.g. during transport and installation of said cable.

According to the prior art, this outer sheath has a smooth, continuous outer sheath surface. In other words, according to prior art, the outer sheath surface is completely free of any protrusions, structures or the like.

A non-exhaustive example, in which submarine cables are used, is the internal electrical cable network of an offshore wind farm. The internal cable network of an offshore wind farm can be formed by a plurality of submarine cables. In particular, a submarine cable in an offshore wind farm is used for power transmission (and/or data transmissions).

For example, a submarine cable can connect an offshore wind turbine and an offshore substation in order to transmit the electrical energy generated by the offshore wind turbine from the kinetic energy of the wind to the offshore substation. In turn, an offshore substation may be connected to an onshore substation of the offshore wind farm by at least one further submarine cable to transmit electrical energy to said substation and, for example, to enable the electrical energy to be fed into a public (not part of the internal cable network) electricity grid. In other variants, there can also be a direct connection between an offshore substation and an electricity grid.

Given the high frequency of marine activity in areas around offshore structures, ports and/or in littoral waters, a submarine cable laid on the seabed presents a concern and hazard to mariners, both recreational and commercial. Equally the owners and operators of the submarine cable desire mariners and other operators to stay clear of the submarine cable with anchors, fishing equipment and any subsequent cable or pipeline installations.

It is for these reasons that all submarine cable positions should be reported to at least one agency and their locations are reported, by said agency, in the public domain. It is essential that once this information is published the submarine cable remains in its reported location and does not move or alter its position on the seabed.

Furthermore, an exposed (i.e. unburied) or free spanning (i.e. unsupported over an extended length) submarine cable laid on the seabed is subject to loads and forces exerted by oceanic waves and tides and, in particular, the changes these can have on the surface of the seafloor. At low frequencies of movement the submarine cable can be moved over time to an angle in excess of its designed curve radius putting the internal conductive components, such as the at least one conductor, of the submarine cable at risk of breaking. Alternatively, if free spanning over a wide trench or between the crest of two sand waves occur, the mass of the submarine cable can cause it to be damaged and fail. At high frequencies of mechanical movement in both vertical and horizontal directions, the submarine cable can experience failure of internal connections and the at least one conductor, resulting in loss of efficiency of transmission or total failure of the submarine cable.

Therefore, according to prior art, submarine cables are typically buried in the seafloor, which serves several purposes. By fixing the submarine cable in place on the seabed lateral movement can be prevented and, in particular, a drift from its reported position can be prevented. Further, the submarine cable can be protected from external interference from other marine users and the submarine cables can be protected from damaging themselves either due to horizontal or vertical movement in excess of their mechanical design.

Prior art burial techniques for the submarine cables assume the submarine cable needs to be buried below the seabed level and surface, respectively, to depths of circa 1.5 m to 2 m, to protect it from seabed changes that can expose the cable.

According to the prior art, the typical installation sequence for the submarine cable is for it to be lowered to the seabed from a vessel. Then the submarine cable is ploughed, trenched and/or jetted into the seabed. The final method used can be selected according to seabed sediment type and/or the length of cable to be protected.

However, in all cases burial equipment is dragged or driven across the seabed to open and/or disturb the seabed sediments allowing the submarine cable to slide into and then be covered by sediment.

A burial of the submarine cable has, however, several disadvantages: The disturbance of the seafloor required to bury the cables has negative impacts on the benthic ecology. Submarine cable routes must be surveyed and adjusted to ensure they avoid sensitive areas but this is subject to the interpretation and preferences of the consenting or licencing agency. In addition, sediment disturbed by the prior art installation techniques can drift down current potentially settling on the sensitive areas that have been avoided.

Furthermore, areas of shallow geology (e.g. near surface bedrock), steep gradients and/or high levels of mobility (e.g. sandbanks and/or seabed sand waves) are generally unsuitable for present techniques resulting in a requirement to “pre-sweep” and/or dredge the seabed to reduce the gradients to those acceptable for the installation equipment. Removal and later deposition of the material is again an environmental risk managed by stringent licencing regimes.

Another drawback is that seabed features, such as sensitive archaeology and/or unexploded ordnance, are disturbed by these techniques requiring extensive surveying and mitigation before works can begin.

In addition, installation via the prior art burial techniques is often unable to achieve the desired burial depth, resulting in multiple passes to achieve full burial and often substantial remedial work using concrete mattresses, rock dumping and reburial are required, incurring additional planning permission, environmental impact, financial outlay and time delays. In summary, burial is always very costly.

However, even if successfully buried during installation, over time the natural movement of the seabed due to wave action and currents conspire to erode the material that covers the cable exposing it and undermining the cables. In addition, extreme weather events, e.g. storms or high water flows due to rainfall, can dramatically change the hydrographic conditions in proximity to cables particularly in shallow water areas. These types of events have in the past resulted in dramatic increases in scour beyond those anticipated by the cable installers and designers, leaving cables exposed even when buried successfully to target depth.

Therefore, it is an object of the present application to provide a submarine cable which at least reduces the described problems of the prior art and which, in particular, reduces the risk of damage of a laid submarine cable and allows to reduce the effort needed for installing submarine cables.

The object is solved, according to a first aspect of the application, by a submarine cable, in particular, an energy submarine cable, according to claim 1. The submarine cable comprises at least one conductor. The submarine cable comprises at least one outer sheath surrounding the at least one conductor. The outer sheath has an outer sheath surface. A plurality of outwardly extending flexible fibres is arranged on the outer sheath surface.

In contrast to the prior art, according to the application, a submarine cable is provided which at least reduces the problems of the prior art and which, in particular, reduces the risk of damage of a laid submarine cables and allows to reduce the effort for installing submarine cables, by having a plurality of flexible fibres attached to the outer sheath surface.

While the described prior art represent an intention to resist or anticipate the natural processes that occur on the seabed resulting in the exposure of a submarine cable and through expensive hard engineering techniques overcome the natural processes, the present application proposes a solution, instead of resisting the natural processes at work on the seafloor around the submarine cable, to instead encourage them to both sufficiently fix the submarine cable to the seabed and to build a protective berm for the submarine cable out of the seabed sediments.

More particularly, according to the present application, it has been recognized that seabed sediments are either eroded or deposited due to wave action and water currents. Typically erosion can occur in areas of high current flows, unconsolidated sediments without a binding agent and low frictional coefficients (smooth surfaces), with initially fine sediments eroded at low current velocities and larger sediments and quantities being eroded as current velocity increases.

Deposition typically occurs where a surface has high levels of frictional coefficients (i.e. a rough or disturbed surface), stable sediments with high cohesion (roots or vegetation to bind sediments together) and low current flows. Although the naturally occurring ocean currents cannot be slowed, it has been found by the present application that their velocity and behaviour can be altered when passing around an exposed cable, by creating areas of drag or high friction on the outer sheath surface to slow the water speeds and trap sediments.

The submarine cable according to the present application is configured to be laid onto the seabed (and not to be buried by a machine/equipment or the like into the seabed).

The submarine cable, according to the present application, is preferably a submarine energy cable. A submarine energy cable is configured to transmit electrical energy. According to an embodiment of a submarine cable according to the application, the submarine cable can be a medium voltage submarine energy cable (e.g. at least 10 kV) or a high voltage submarine energy cable (e.g. at least 60 kV).

The power capacity of the submarine energy cable is, in particular, between 3 MW and 2.5 GW.

Alternatively or additionally, the submarine cable may be a submarine data cable configured to transmit data. For instance, the submarine cable can be configured to transmit data and electrical energy.

The submarine cable comprises at least one conductor. The at least one conductor is configured to transmit electrical energy and/or data. The at least one conductor may be an electrically conductive conductor, in particular, a phase conductor (e.g. made of copper or aluminium). It shall be understood that a submarine cable can comprise two or more phase conductors.

In a preferred embodiment, (exactly) three phase conductors can be provided. This optimizes, in particular, the energy transmission via the submarine cable. An electrically conductive phase conductor can comprise one or more electrically conductive element(s).

In other variants of the application, the at least one conductor may be an optical fibre conductor, in particular, configured to transmit data. It shall be understood that a submarine cable can comprise both at least one described phase conductor and/or at least one optical fibre conductor.

In addition to the at least one conductor, a submarine cable, according to the present application, comprises an outer sheath. It shall be understood that a submarine cable can, preferably, comprise further cable elements, as explained in the further course of the present description.

The outer sheath surrounds the at least one conductor, in particular, indirectly. This means, in particular, that at least one further layer can be arranged between the outer sheath and the at least one conductor.

The outer sheath according to the application serves, in particular, to protect the (inner) submarine cable elements. The outer sheath has an outer sheath surface and, in particular, an inner sheath surface. The outer sheath surface faces outwards and, when the submarine cable is installed, contacts in particular the environment (e.g. water and/or the seabed). The inner sheath surface is turned towards the at least one conductor and contacts, in particular, an inner layer of the submarine cable. According to the present application, the outer sheath surface is provided with a plurality of fibres and “fronds”, respectively. A fibre (or fringe or frond or both) comprises two ends, a root end connected to and arranged at the outer sheath surface and an open end. A fibre is a longitudinally extended body running from the root end to the open end.

The fibres of the present submarine cable are formed as flexible fibres. This means, in particular, that the fibres are movable attached to the outer sheath surface and in particular, are bendable (upon an exertion of a force onto a fibre, e.g. caused by a water current).

By providing a plurality of such fibres, preferably distributed over the whole (relevant) outer sheath surface, sediments and the like particles can be collected and trapped, respectively, by the fibres. The sediments can deposit - little by little - at and/or between the fibres at the submarine cable laid on the seabed. After some time a berm and (sediment) cover, respectively, is formed above the submarine cable - similar to a sand dune. In particular, the created berm completely covers, and thus, protects the submarine cable.

In particular, the plurality of fibres are formed and arranged such that they slow the water currents passing around the submarine cable to a level at which transported sediments, particles and the like will be deposited onto the seabed around the submarine cable.

Said fibres can then act as a binding mesh into which the seabed sediments, particles and the like are trapped. Overtime the sediments, particles and the like can consolidate in the fibres becoming more stable and encouraging further deposition, to the extent where the submarine cable is completely covered in a protective berm.

Besides the fact that the installation effort of such a cable can be significantly reduced since any active burying action and equipment can be omitted, the submarine cable is laid in a secure way and can be operated with a high reliability level over the total life time due to the formed protective berm.

It is noted that the relevant outer sheath surface is the part of the outer sheath surface which is at least potentially in contact with the seabed when laid. For instance, the ends of a submarine cable (at the point of connection to the offshore wind turbine and/or substation) might be free of fibres.

According to a further embodiment of the submarine cable according to the application, a fibre (of the plurality of fibres) can be made of a material which is more flexible than the material of which the outer sheath is made. Preferably, all of the plurality of fibres can be made of a (same) material which is more flexible than the material of which the outer sheath is made. In other variants, a same or similar material can be used for a fibre and the outer sheath.

Furthermore, according to a further embodiment of the submarine cable according to the application, in an unloaded condition of a fibre (of the plurality of fibres) (i.e. in an extended position and, in particular, force-free condition), an angle included by the fibre and the outer sheath surface can be between 5° and 90°, in particular between 45° and 90°, particularly preferred between 70° and 85°. An unloaded condition means, in particular, that the cable is in a fluid (water and gas) without an exertion of a force. In other words, the fibre is in a natural position and, in particular, natural condition.

Preferably, all of the plurality of fibres can each have an included angle to the outer sheath surface which is between 5° and 90°, in particular between 45° and 90°, particularly preferred between 70° and 85°, when the respective fibre is in the unloaded condition.

In other words, the shape of the fibres and fronds, respectively, encourage them to naturally stand erect of the outer sheath surface of the submarine cable. This increases the likelihood that particles deposit between the fibres, and thus, accelerate the process of forming a berm.

According to a further embodiment of the submarine cable according to the application, in a loaded condition of the fibre (of the plurality of fibres) (e.g. when the fibres are pressed by the submarine cable), an angle included by the fibre and the outer sheath surface can be between 0° and 5°, preferably substantially 0°. Preferably, all of the plurality of fibres can each have an included angle to the outer sheath surface which is between 0° and 5°, preferably substantially 0°, when the respective fibre is in the loaded condition.

In other words, the described flexible nature of the fibres may allow them to lie flat, e.g. whilst lying on vessels deck in the cable transport reel, taking up minimal additional space on the reel. However, e.g. when removed from the reel and in free space or a fluid (like the water) the fibres can (automatically) return to their extended position and unloaded condition, respectively.

In order to optimize the deposition process, it has been further found that the fibres and/or the submarine cable should have specific parameter values and properties, respectively.

According to a preferred embodiment of the submarine cable according to the application, a ratio d_s/lf of the outer diameter d_s of the outer sheath surface and the length If of a fibre (of the plurality of fibres) can be between 0.13 and 3, preferably between 0.2 and 2. Preferably, the (average) ratio d_s/lf,a of the outer diameter d_s of the outer sheath surface and the (average) length lf,_a of all of the plurality of fibres can be between 0.12 and 3, preferably between 0.2 and 2.

Alternatively or additionally, the length If of a fibre (of the plurality of fibres) can be between 10cm and 80 cm, preferably between 20 cm and 50 cm. Preferably, the (average) length lf,_a of all of the plurality of fibres can be between 10 cm and 80 cm, preferably between 20 cm and 50cm. Such length ranges are particular advantageous in order to allow deposition between the fibres and at the submarine cable.

As already described, the fibres are flexible fibres, in particular, made of a flexible material. According to a preferred embodiment of the submarine cable according to the application, a fibre (of the plurality of fibres) can be made of a material selected from the group, comprising: plastics, in particular Neoprene (Poly chloroprene), Etylene Propylene Elastomers, Low density Polyethylene, High Density Polyethylene; rubbers, in particular Butyl Rubbers, Styrene Butadiene Rubber, Acrylonitrile Butadiene Rubber, Polysiloxane (Silicone Rubbers); elastomers, in particular Ethylene Propylene Elastomers, Polyurethane Elastomers, Thermoplastic Polyester Elastomers.

Preferably, all fibres are made of the same material. However, it is also possible that different materials can be used for at least two different fibres of the plurality of fibres.

According to a particular preferred embodiment of the submarine cable according to the application, the Young modulus of a fibre (of the plurality of fibres) can be between0.5 N/mm² and 1200 N/mm², preferably between 1 N/mm² and 1000 N /mm². Preferably, the (average) Young modulus of all fibres can be between 1 N /mm² and 1000 N /mm², preferably between 0.5 N /mm² and 1200 N /mm². Fibres with such a Young modulus have optimized flexibility properties. In other words, a fibre is, in particular, a flexible fibre if the Young modulus of a fibre is within said modulus range. For instance, a material, as described above, can be used to produce a fibre with such a preferred Young modulus.

Furthermore, according to a further embodiment of the submarine fibre according to the application, a cross-sectional area of a fibre (of the plurality of fibres) can be between 0.01 cm² and 25 cm², preferably between 0.1 cm² and 5 cm². Preferably, the (average) cross-sectional area of all fibres (of the plurality of fibres) can be between 0.01 cm² and 25 cm², preferably between 0.1 cm² and 5 cm².

The shape of the cross-sectional area can be generally formed arbitrarily. In addition the shape can be selected to adjust and/or alter the behaviour of the fibre in terms of its flexibility and suitability for certain seabed sediment types/water speeds. For instance, the shape can be an essentially circular form, an essentially rectangular form or an essentially star form. Further, the shape can have a solid or hollow centre

In order to support the deposition of particles, sediments and the like, according to a preferred embodiment of the submarine cable of the application, the plurality of fibres can be arranged substantially over the entire outer sheath surface, preferably substantially evenly distributed. In particular, a first plurality of fibres of the total plurality of fibres can be arranged on a circular line along the circumference of the outer sheath surface, wherein a plurality of the circular lines can be arranged (parallel to each other) on the outer sheath surface.

According to a further embodiment of the submarine cable according to the application, the (average) number of fibres per 100 cm² area of the outer sheath surface can be between 1 and 50, preferably between 5 and 20 Such fibre density values are particular advantageous in order to allow deposition between the fibres and at the submarine cable. In particular, such a density is adapted to the average and, in particular, usual diameter of the sediment particles.

As already described, the submarine cable can be, preferably, a medium voltage offshore submarine energy cable or a high voltage offshore submarine energy cable, wherein the power capacity of the submarine cable can be, in particular, between 3 MW and 2.5 GW.

According to a further embodiment of the submarine cable according to the application, the at least one conductor formed as an electrically conductive phase conductor may comprise (at least) an electrically conductive (phase) core (made of one or more core element/s) and an (electrical) insulating layer (directly or indirectly) surrounding the electrically conductive core.

The at least one electrically conductive phase conductor may comprise, in particular, a conductor screen layer arranged between the electrically conductive core and the insulating layer.

Alternatively and preferably additionally, the at least one electrically conductive phase conductor may comprise, in particular, an insulation screen layer (directly or indirectly) surrounding the insulating layer and a core protection layer (directly or indirectly) surrounding the insulation screen layer (wherein a metallic shielding layer can be preferably arranged between the core protection layer and the insulating layer).

If the submarine cable has an optional cooling flow path system, configured to cool the cable, the outer layer of the electrically conductive phase conductor may be formed by the core protection layer which may be at least partly in direct contact with the at least one cooling flow path system.

Preferably, a submarine cable can be constructed as follows:

Conductor (made of Aluminium or Copper), Conductor Screen (conducting or semi conducting polymer), Insulation (polymer material, typically XLPE or EPR), Insulation Screen (conducting or semi conducting polymer), Screen / Sheath (typically copper tapes or wires or a lead sheath), Outer Sheath (typically polymeric material).

There may also be a water blocking tape or powder in or around the at least one conductor and under the sheath. The submarine cable may comprise at least one armour layer surrounding the at least one conductor. The at least one armour layer can be, in particular, configured to protect the cable elements surrounded by the armour layer. Preferably, the armour layer can be made of a plurality of (twisted) ropes or (twisted) cables. An armour layer can be made of steel (ropes). Steel might be preferred due to its density of approximately 7,8 g/cm³ at 20°C.

According to further embodiments, the at least one armour layer may be made at least partly of at least one fibre reinforced composite. The use of fibre reinforced composites leads to an offshore submarine energy cable having good vibration and damping properties, high energy absorption and good fatigue strength under dynamic stress.

Preferably, at least 80 % of the at least one armour layer can be made of a fibre reinforced composite material. For instance, at least one rope of the plurality of ropes of the at least one armour layer may be made of a fibre reinforced composite material. Preferably all ropes can be made of a fibre reinforced composite material. In other embodiments, it may also be provided that at least one rope is made of a metal (e.g. steel) and at least one rope is made of a fibre reinforced composite material.

Preferably, at least one armour layer may be at least partially made of glass fibre. Glass fibre is particularly preferred as a fibre reinforced composite material. The reason for this is the good electrical insulation properties of glass fibres.

According to another preferred embodiment, at least one armour layer can be formed at least partially from carbon fibre. Carbon fibre can preferably be used to provide a particularly resistant submarine cable.

It goes without saying that other fibre reinforced composite materials can also be used in other variants, such as aramid fibre or the like. According to a further embodiment of the submarine cable according to the application, the submarine cable may comprise at least one bedding layer. The at least one bedding layer may be arranged between two armour layers.

Alternatively or additionally, the at least one bedding layer may be arranged between the at least one (electrically conductive phase) conductor and the at least one armour layer. A bedding layer can be arranged between two armour layers and/or an armour layer and the (previously described) elements arranged inside the submarine cable, in particular, to provide a protective layer between said layers and/or said internal cable elements.

According to a further embodiment of the submarine cable according to the application, the offshore submarine cable may (as an alternative to the described conductor or, preferably, in addition to said at least one conductor) comprise at least one fibre optical cable. Said fibre optical cable may be configured to transmit data (as a communication channel) and/or may be configured to monitor the temperature of the submarine cable (location-dependent).

Preferably, the monitored temperature values can be provided to a controller of an optional cooling flow path system, e.g. a controller of a cooling device connected to the cooling flow path system. The controller may be configured to adapt at least one cooling parameter of the cooling flow path system depending on the provided temperature of the submarine cable. For instance, if the temperature of the submarine cable increases (a preset temperature limit) the controller can be configured to reduce the temperature of the cooling fluid and/or to increase the pressure of the cooling fluid according to at least one preset rule.

According to a further embodiment of the submarine cable according to the application, the submarine cable may comprise a filler material. In particular, voids in the submarine cable may be filled with a filler material to provide a circular cross- sectional shape of the submarine cable. According to a further embodiment of the submarine cable according to the application, the submarine cable may comprise at least one (common) outer cover (also called outer serving) surrounding the at least one armour layer.

A further aspect of the application is an offshore system. The offshore system comprises at least one offshore structure. The offshore system comprises at least one previously described submarine cable connected to the offshore structure. The offshore system may be preferably an offshore wind farm.

The offshore wind farm may comprise at least one first offshore structure (e.g. offshore wind turbine, offshore substation etc.) and at least one further structure (such as an onshore substation or another offshore structure, e.g. an offshore wind turbine, offshore substation, etc.). The first offshore structure and the further structure can be connected by a submarine cable described above.

An offshore wind turbine may have a generator that converts the kinetic energy of the wind into electrical energy.

It shall be understood that also other structures can be connected to a submarine cable described above.

A further aspect of the application is a method for producing/manufacturing a submarine cable, in particular, a previously described submarine cable. The method comprises: providing a cable base body containing at least one conductor, and applying an outer sheath having an outer sheath surface to the cable base body, wherein a plurality of outwardly extending flexible fibres is arranged on the outer sheath surface. In particular, at least a cable base body can be provided which includes all cable elements of a submarine cable (except the outer sheath). An outer sheath can then be applied to at least a section of the cable base body, for instance, by an extrusion process.

According to a preferred embodiment of the method according to the application, the plurality of fibres can be affixed to the outer sheath surface of the submarine cable during the manufacturing process, either as a strip with the fibres attached which could be wound or wrapped around the outer sheath surface, and/or as a jacket or additional sheath that could be fitted around the outer sheath surface. The fibres can also be fitted as a part of the installation sequence. Furthermore, it can also be retrofitted during a cable repair to encourage reburial of a cable repair bight or re-laid cable length.

A still further aspect of the application is a use of a previously described submarine cable for laying the submarine cable on a seabed surface.

According to the present application, the outer sheath surface of submarine cables is, in particular, fitted with flexible fibres and structures for the purpose of fixing it to the seabed. The flexible structures fixed to a submarine cable can lie flat when resting against another surface but assume an extended position when in a fluid (water and gas), e.g. in the unloaded condition.

The present submarine cable with the plurality of fibres is configured, in particular, to encourage the deposition of materials, inert and organic, for the purposes of anchoring the submarine cable in place and construction of a protective berm above said cable.

Due to the described submarine cable, a new installation process is possible where the submarine cable can be lowered from the vessel to the seafloor without additional burial equipment being required. This increases speed of installation and reduces cost and complexity significantly.

A further advantage of the submarine cable of the present application is that it does not disturb the seabed sediments during installation, therefore having minimal impact on the benthic ecology.

In addition, the submarine cable of the present application can be laid across areas that normally present problems for traditional installation techniques such as steep slopes, near seabed surface bedrock and/or high frequency sandwaves with minimal need for preparatory works.

Seabed features, such as shallow geology, archaeological features and unexploded ordnance, can be crossed by a submarine cable without disturbance, reducing installation risks and mitigation requirements.

By using submarine cables according to the present application, there is a substantial reduction in the cost and time required for cable installation, and remedial works and additional anchoring technologies would be unnecessary.

Little or no post installation maintenance might be required for the submarine cable according to the present application, as any disturbance to the protective sediments due to extreme weather events or third party activity will be repaired by the natural processes encouraged by the specific design of the submarine cable according to the present application.

In particular, due to the special design a self-burying submarine cable can be provided according to the present application.

The features of the submarine cables, offshore systems, methods and uses can be freely combined with one another. In particular, features of the description and/or the dependent claims, even when the features of the dependent claims are completely or partially avoided, may be independently inventive in isolation or freely combinable with one another.

These and other aspects of the present patent application become apparent from and will be elucidated with reference to the following figures. The features of the present application and of its exemplary embodiments, as presented above, are understood to be disclosed also in all possible combinations with each other.

In the figures show:

Fig. 1 a schematic view of an embodiment of a submarine cable according to the application,

Fig. 2 a schematic sectional view of a further embodiment of a submarine cable according to the application,

Fig. 3 a schematic view of different cross section shapes of fibres attachable to an outer sheath surface of an embodiment of a submarine cable according to the application,

Fig. 4a a schematic view (side and cross-section view) of a further embodiment of a submarine cable according to the application in a first state,

Fig. 4b a schematic view (side and cross-section view) of the embodiment according to Fig. 4a in a further state,

Fig. 4c a schematic view (side and cross-section view) of the embodiment according to Fig. 4a in a further state, Fig. 4d a schematic view (side and cross-section view) of the embodiment according to Fig. 4a in a further state,

Fig. 4e a schematic view (side and cross-section view) of the embodiment according to Fig. 4a in a further state,

Fig. 5 a perspective view of a further embodiment of the submarine cable according to the application,

Fig. 6 a diagram of an embodiment of a method according to the application, and

Fig. 7 a schematic view of an embodiment of an offshore system according to the application.

Like reference signs in different figures indicate like elements.

Figure 1 shows a schematic (part) view, in particular, a sectional side view, of an embodiment of a submarine cable 100 according to the present application. The submarine cable 100 is configured to be laid on the seabed surface.

The submarine cable 100 comprises at least one conductor 102. The at least one conductor is configured to transmit electrical energy and/or data. The conductor 102 can be made of copper, aluminium or another metal. In other variants, the conductor 102 can be an optical fibre conductor.

The submarine cable 100 comprises at least one outer sheath 104 surrounding the at least one conductor 102. It shall be understood that a submarine cable may comprise further (not shown) cable elements as will be described in subsequent embodiments. The outer sheath 104 has an (circumferential) outer sheath surface 106. According to the present application, a plurality of outwardly (in radial direction of the longitudinal axis 107) extending flexible fibres 108.1, 108.2 is arranged on the outer sheath surface 106.

As can be seen from figure 1, a fibre 108.1, 108.2 and frond 108.1, 108.2, respectively, is a longitudinally extended body 101 with two ends 103, 105, i.e. a root end 103 connected to and arranged at the outer sheath surface 106 and an open end 105. The distance If between said ends 103, 105 represents the length of a fibre 108.1, 108.2. Preferably, all fibres 108.1, 108.2 can have (almost) the same length If.

A fibre 108.1, 108.2 is, in particular, rod-shaped. Due to the flexible design of the fibres 108.1, 108.2, the fibres 108.1, 108.2 can be moved, as indicated by the arrows 109, for instance, caused by a (natural) water current.

Preferably, outer sheath 104 and fibres 108.1, 108.2 can be made of different materials. In particular, a fibre 108.1, 108.2, preferably all fibresl08.1, 108.2, can be made of a material, which is more flexible than the material of which the outer sheath 104 is made. Preferred materials of the fibres 108.1, 108.2 include Neoprene (Polychloroprene), Butyl Rubbers, Ethylene Propylene Elastomers, Low Density Polyethylene , High Density Polyethylene , Polyurethane Elastomers, Styrene Butadiene Rubber, Acrylonitrile Butadiene Rubber, Polysiloxane (Silicone Rubbers) and Thermoplastic Polyester Elastomers.

The material (together with the shape of a fibre 108.1, 108.2) is, in particular, selected such that the fibres 108.1, 108.2 have a specific Young modulus in order to provide a specific flexibility. Preferably, the (average) Young modulus of all fibres 108.1, 108.2 can be between 0.5 N /mm² and 1200 N /mm², preferably between 1 N /mm² and lOOON/mm². In particular, the material and the shape of a fibre 108.1, 108.2 (of the plurality of fibres 108.1, 108.2) is such that in an unloaded condition of a fibre 108.1, 108.2 (i.e. in an extended position without an exertion of a force onto the fibre 108.1, 108.2), an angle 110 included by the fibre 108.1, 108.2 and the outer sheath surface 106 is between 25° and 90°, in particular between 45° and 90°, particularly preferred between (the shown) 70° and 85°.

In an loaded condition of the fibre (e.g. when a force presses the fibre 108.1, 108.2 in the direction to the outer sheath surface), an angle 110 included by the fibre 108.1,

108.2 and the outer sheath surface 106 is between 0° and 5°, preferably substantially 0°. In other words, the fibres 108.1, 108.2 can lay flat against the outer sheath surface 106.

As can be further seen from figure, preferably, all included angles 110 of all fibres

108.1. 108.2 can be oriented in the same direction, in particular, a direction parallel to the longitudinal axis 107

Furthermore, the fibres 108.1, 108.2 can cover the whole relevant outer sheath surface 106 of the submarine cable 100. The (average) number of fibres per 100 cm² area of the outer sheath surface can be between 1 and 50, preferably between 5 and 20.

In particular, the distance dn (in the direction of the longitudinal axis 107) between two (directly) adjacent fibres 108.1, 108.2 can be between 1 and 60cm. The ratio dfi/ds of the distance dn to the outer diameter d_s of the outer sheath 104 can be, preferably, between 0.03 and 6.

In addition, a ratio d_s /If of the outer diameter d_s of the outer sheath surface 104 and the length If of a fibre 108.1, 108.2 is preferably between 0.12 and 3. The length If of a fibre 108.1, 108.2 can be, preferably, between 10 cm and 80 cm. Figure 2 shows a schematic (cross) sectional view of a further embodiment of a submarine cable 200 according to the application. In order to avoid repetitions, in the following only the differences between the embodiment of figure 1 and the embodiment of figure 2 are essentially described. With regard to the other components of the submarine cable 200 it is referred to the above example.

The depicted submarine cable 200 is, in particular, a medium voltage cable or a high voltage cable. The submarine (energy) cable 200 may preferably have a power capacity between 3 MW and 2.5 GW.

In particular, the submarine cable 200 may be a MV (medium voltage) submarine cable 200 comprising a power capacity between 3 MW and 70 MW, preferably between 9 MW and 60 MW, or a HV (high voltage) submarine cable 200 comprising a power capacity between 70 MW and 2.5 GW, preferably between 360 MW and 1500 MW.

The illustrated submarine cable 200 has three conductors 202.1 to 202.3 in form of phase conductors 202.1 to 202.3 to transmit electrical energy (or power or current). A phase conductor 202.1 to 202.3 can be formed in one piece, but also in several pieces. A phase conductor 202.1 to 202.3 can be round or sector-shaped and/or be formed as a single or multiple wire.

Around each phase conductor 202.1 to 202.3, it is advantageous to first form a (inner conductive) layer 212.1 to 212.3 (non-metallic, conductive sheath) (e.g. as a conductor screen layer), then an insulating layer 220.1 to 220.3 (e.g. 220.1 to 220.3 (e.g. singlelayer extruded) (also known as an insulation screen) and then an (outer conductive) layer 214.1 to 214.3 (consisting of a non-metallic sheath in combination with a metallic part) as, for example, core protection layer 214.1 to 214.3 (also known as a core protection layer). Between core protection layer 214.1 to 214.3 and insulation layer 220.1 to 220.3 an additional (not shown) metallic shielding may be provided. An optional optical conductor cable 222 can also be provided as a further conductor 222. The optical conductor cable 222 can be coupled with a (not shown) temperature detection device to monitor the temperature in the submarine cable. It can (alternatively or additionally) be used for data transmission.

In order to obtain an essentially circular cable cross-section for the submarine cable 200, the submarine cable 200 usually has a filler material 216 (also called fillers).

A so-called bedding layer 224 can be arranged between the at least one armour layer 218 and the previously described cable elements (phase conductor, optical phase conductor cable etc.) arranged inside the submarine cable 200, in order to provide, in particular, a protective layer 224 between the at least one armour layer 218 and the cable elements in the inside.

A bedding layer (not shown) can also be arranged between two adjacent armour layers and between an armour layer and the outer sheath 204.

An armour layer 218 can be formed by several ropes 218.1, 218.2. For example, one rope 218.1 may be made of metal (e.g. steel) and/or a composite material (e.g. carbon fibre, glass fibre etc.) and at least one other rope 218.2 may be made of metal (e.g. steel) and/or a composite material (e.g. carbon fibre, glass fibre etc.).

All the layers described above (except the outer sheath 204) may form the cable body 230 as described in the application. As already described, this body may have more, less and/or other layers. On the outer sheath 204, a plurality of flexible fibres 208 are arranged.

In particular, the distance drc (in the peripheral direction) between two (directly) adjacent fibres 108.1, 108.2 can be between 0 cm and 20 cm. The ratio ds/ds of the distance drc to the outer diameter d_s of the outer sheath 104 can be, preferably, between 0 and 2. Figure 3 shows a schematic view of different cross section shapes of fibres 300a to 300d attachable to an outer sheath surface of an embodiment of a submarine cable according to the application. In order to avoid repetitions, in the following only the differences between the embodiment of figure 3 and the embodiments of the former figures are essentially described.

As can be seen from figure 3, a first exemplified fibre 308a has a circular-shaped cross section, a second exemplified fibre 308b has a rectangular-shaped cross section, a third exemplified fibre 308c has an elliptical-shaped cross section, a fourth exemplified fibre 308d has a star-shaped cross section, a fifth exemplified fibre 308e has a half elliptical-shaped cross section, a sixth exemplified fibre 308f has an arcshaped cross section, and a seventh exemplified fibre 308g has a cross section with a hollow centre. It shall be understood that different cross sections can be combined with each other. For example, a circular-shaped cross section can also have a hollow centre. Preferably, all fibres of a submarine cable can comprise the same cross section form. It shall be understood that the fibres of a submarine cable can also comprise different cross section forms.

The figures 4a to 4e shows schematic views of an embodiment of a submarine cable 400 in different (life time) states. In order to avoid repetitions, in the following the merely differences between the embodiment of figures 4a to 4e and the embodiments of the former figures are essentially described.

In figure 4a, the submarine cable 400 is shown in e.g. a transport state. The flexible nature of the fibres 408 allow them to lie flat whilst lying on e.g. the vessels deck in the cable transport reel, taking up minimal additional space on the reel.

When removed from the reel and in free space or a fluid the fibres 408 will return to their extended position (figure 4b). In particular, figure 4b shows the fibres 408 in an unloaded condition. Figure 4c shows the submarine cable 400 (just) laid on the seabed surface 442 of the seabed 440. When laid on the seabed surface 442 the fibres 408 nearest the seabed 440 will be compressed (but may overtime and with some mobility of the seabed sediments recover their erect shape). The fibres 408 on the non-seabed side would be freestanding in the current flow.

Little by little, particles 446, sediments 446 and the like are trapped by the fibres 408 of the submarine cable (see figure 4d). The fibres 408 may slow the water currents passing around the submarine cable 400 to a level at which transported sediments 446 will be deposited onto the seabed around the submarine cable 400. The fibres 408 are designed such that the fibres 408 act as a binding mesh into which the seabed sediments 446 are trapped.

Overtime the sediments 446 will consolidate in the fibres 408 becoming more stable and encouraging further deposition, to the extent where the submarine cable 400 is completely covered in a protective berm 444 (see figure 4e).

Figure 5 shows a perspective view of a further embodiment of the submarine cable 500 according to the present application. In order to avoid repetitions, in the following merely the differences between the embodiment of figure 5 and the embodiments of the former figures are essentially described.

As can be seen from figure 5, the whole outer sheath surface 506 of the submarine cable 500 has a plurality of flexible fibres 508, which generally extend in a radial direction. The flexible fibres 508 are, preferably, evenly distributed over the total surface 506.

Figure 6 shows a diagram of a method, in accordance with the present application, for manufacturing or producing a submarine cable, in particular, a submarine cable according to one of the previous embodiments. In a first step 601, a basic cable body (e.g. according to figure 2) is provided, containing at least one conductor (preferably three phase conductors).

In a further step 602, an outer sheath with an outer sheath surface is applied to the cable base body, e.g. by an extrusion process, wherein a plurality of outwardly extending flexible fibres is arranged on the outer sheath surface. The fibres can be attached or fixed to the outer sheath surface in different ways, e.g. by an adhesion process.

Preferably, the fibres may be affixed to the outer sheath surface of the cable during the manufacturing process, either as a strip with the fibres attached which can be wound or wrapped around the cable or as a jacket or additional sheath that can be fitted around the cable. The fibres can also be fitted as part of the installation sequence. Furthermore, it can also be retrofitted during a cable repair to encourage reburial of a cable repair bight or re-laid cable length.

Figure 7 shows a schematic view of an embodiment of an offshore system 760 according to the application. In order to avoid repetitions, in the following merely the differences between the embodiment of figure 7 and the embodiments of the former figures are essentially described.

In the present example, the offshore system 760 is an offshore wind farm 760. In other examples, the offshore system can also be another system, like a gas or oil (exploration) system and platform, respectively, or the like.

Two offshore wind turbines 762 are shown as examples of offshore structures 762. It shall be understood that an offshore wind farm may have a large number of offshore wind turbines and at least one (not shown) offshore substation. For example, a plurality of offshore wind turbines may be electrically interconnected to form several strings, each string being electrically connected to an offshore substation. The offshore substation may in turn be electrically connected to another offshore substation or an onshore substation of the offshore wind farm.

An offshore wind turbine762 is presently installed via a foundation structure in the seabed 740. In other variants of the application, an offshore structure may also be a floating offshore structure with a floating foundation structure.

An offshore wind turbine 762 is configured to convert the kinetic energy of the wind into electrical energy. To transmit the generated electrical energy to a further offshore wind turbine 762 and then, for example, to an onshore substation, the offshore wind farm has an internal cabling network in the form of submarine cable 700. A submarine cable 700 may, for example, be formed like a submarine cable described in relation to figures 1 to 5.

In particular, a submarine cable 700 may preferably be divided into at least two, in particular (exactly) three, sections 700.1 to 700.3. A first and a third section 700.1, 700.3 can each run from an electrical connection 764 of an offshore structure 762 to (approximately) the seabed surface 742. The second section 700.2 (representing the relevant part of the cable 700) runs from one end of the first section 700.1 to one end of the third section 700.3.

In other words, the first and third sections 700.1, 700.3 are essentially surrounded exclusively by water in the installed condition of submarine cable 700 shown, while the second section 700.2 rests on the bottom of seabed surface 742 (and will after some time be covered by a (not shown) berm).

Alternatively the first and third sections 700.1, 700.3 are routed down the inner foundation leg(s) of the offshore wind turbine 762 either externally or internally.

The first and the third section 700.1, 700.3 can preferably have an outer sheath surfaces without fibres, i.e. with a smooth, profile-free surface. The outer sheath surface of the second section 700.2 comprises the plurality of fibres, as described above. In addition, the first and third sections 700.1, 700.3 can have a substantially oval cross-sectional area and the second section 700.2 can have a substantially circular basic cross-sectional area. In other words, the first and third sections 700.1, 700.3 are optimized for a course through water and the second section 700.2 is optimized for a laying on a seabed surface 742.

Additionally, the first and third sections 700.1, 700.3 can have a substantially circular basic cross-sectional area.

Claims

C l a i m s A submarine cable (100, 200, 400, 500, 700), in particular, an energy submarine cable (100, 200, 400, 500, 700), comprising: at least one conductor (102, 202, 502), at least one outer sheath (104, 204, 404, 504) surrounding the at least one conductor (102, 202, 502), wherein the outer sheath (104, 204, 404, 504) has an outer sheath surface (106, 206, 406, 506), characterized in that a plurality of outwardly extending flexible fibres (108, 208, 308, 408, 508) is arranged on the outer sheath surface (106, 206, 406, 506). The submarine cable (100, 200, 400, 500, 700) according to claim 1, characterized in that a fibre (108, 208, 308, 408, 508) is made of a material which is more flexible than the material of which the outer sheath (104, 204, 404, 504) is made. The submarine cable (100, 200, 400, 500, 700) according to claim 1 or 2, characterized in that in an unloaded condition of a fibre (108, 208, 308, 408, 508), an angle included by the fibre (108, 208, 308, 408, 508) and the outer sheath surface (106, 206, 406, 506) is between 5° and 90°, in particular between 45° and 90°, particularly preferred between 70° and 85°. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that in an loaded condition of the fibre (108, 208, 308, 408, 508), an angle included by the fibre (108, 208, 308, 408, 508) and the outer sheath surface (106, 206, 406, 506) is between 0° and 5°, preferably substantially 0°.

5. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that a ratio d_s/lf of the outer diameter d_s of the outer sheath surface (106, 206, 406, 506) and the length If of a fibre (108, 208, 308, 408, 508) is between 0.12 and 3, preferably between 0.2 and 2.

6. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that the length If of a fibre (108, 208, 308, 408, 508) is between 10 cm and 80 cm, preferably between 20 cm and 50 cm.

7. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that a fibre (108, 208, 308, 408, 508) is made of a material selected from the group, comprising: plastics, in particular Neoprene, Etylene Propylene Elastomers, Low density Polyethylene, High Density Polyethylene; rubbers, in particular Butyl Rubbers, Styrene Butadiene Rubber, Acrylonitrile Butadiene Rubber, Polysiloxane.

8. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that the Young modulus of a fibre (108, 208, 308, 408, 508) is between 0.5 N /mm² and 1200 N /mm², preferably between 1 N /mm² and 1000 N /mm².

9. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that a cross-sectional area of a fibre (108, 208, 308, 408, 508) is between 0.01 cm² and 25 cm², preferably between 0.1 cm² and 5 cm². The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that the plurality of fibres (108, 208, 308, 408, 508) are arranged substantially over the entire outer sheath surface (106, 206, 406, 506), preferably substantially evenly distributed. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that the number of fibres (108, 208, 308, 408, 508) per 100 cm² area of the outer sheath surface (106, 206, 406, 506) is between 1 and 50, preferably between 5 and 20. The submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims, characterized in that the submarine cable (100, 200, 400, 500, 700) is a medium voltage offshore submarine energy cable (100, 200, 400, 500, 700) or a high voltage offshore submarine energy cable (100, 200, 400, 500, 700). The submarine cable (100, 200, 400, 500, 700) according to claim 12, characterized in that the power capacity of the submarine cable (100, 200, 400, 500, 700) is between 3 MW and 2,5 GW. An offshore system (760), comprising: at least one offshore structure (762), and at least one submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims connected to the offshore structure (762). A method for producing a submarine cable (100, 200, 400, 500, 700), in particular, a submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims 1 to 13, comprising providing a cable base body (230) containing at least one conductor (102, 202, 502), and applying an outer sheath (104, 204, 404, 504) having an outer sheath surface (106, 206, 406, 506) to the cable base body (230), wherein a plurality of outwardly extending flexible fibres (108, 208, 308, 408, 508) is arranged on the outer sheath surface (106, 206, 406, 506). A use of a submarine cable (100, 200, 400, 500, 700) according to any of the preceding claims 1 to 13 for laying the submarine cable (100, 200, 400, 500, 700) on a seabed surface (442, 742).