EP4014292A1

EP4014292A1 - Marine power supply system and distribution buoy

Info

Publication number: EP4014292A1
Application number: EP20855468.3A
Authority: EP
Inventors: Emil CHRISTIANSEN; Ulf LINDELÖF
Original assignee: Sub Connected AB
Current assignee: Sub Connected AB
Priority date: 2019-08-16
Filing date: 2020-08-12
Publication date: 2022-06-22
Also published as: EP4014292A4; WO2021034248A1

Abstract

The invention relates to a power supply system for supplying at least electrical power to at least one moored, floating marine structure (101) and a buoy for use in this system. The system comprises an onshore sub-station (102) supplying electrical power to a power consumer on the floating marine structure (101), and a power distributing buoy (110; 210; 310) arranged to electrically connect the onshore sub-station (102) and the at least one marine structure (101), wherein the power distributing buoy (110; 210; 310) is a surface piercing buoy comprising an upper buoy portion (111; 311) above the surface and a lower buoy portion (112; 312) forming a submerged spar anchored at a fixed depth by an at least one anchoring means on the seabed. The onshore sub-station (102) is connected to the power distributing buoy (110; 210; 310) via a first cable section (121; 221a; 221b; 221c) extending from the seabed into the buoy, The power distributing buoy (110; 210; 310) is connected to the at least one marine structure (101) by a second cable section (122) extending from the buoy to the marine structure (101) remote from the seabed, wherein the second cable section (122) comprises a dynamic cable. The first and second cable sections (121; 122) are electrically connected on the power distributing buoy (110; 210; 310) and arranged to transfer electric power to the marine structure (101).

Description

MARINE POWER SUPPLY SYSTEM AND DISTRIBUTION BUOY

TECHNICAL FIELD

The invention relates to a power supply system for supplying at least electrical power to at least one moored, floating marine structure and a power distributing buoy arranged to electrically connect the onshore sub-station and the at least one marine structure.

BACKGROUND OF THE INVENTION

Floating marine structures such as moored fish farms or vessels requiring electric power will usually resort to using diesel generators or on-board engines for power generation. This creates a constant source of exhaust gas emission, which is undesirable from a climate point of view, and a constant source of noise pollution, which is undesirable from the point of local inhabitants and wildlife in the vicinity of the structure.

Electrical power transfer to or from a floating marine structure is complicated by the relative movement of the marine structure relative to the seabed. A conventional sea cable is not suited for connecting to a floating marine structure, as it is relatively inflexible and will experience a seriously shortened fatigue lift caused by the constant flexing of the sea cable. US2016/301198, relating to power transfer from an off-shore wind turbine to shore, suggests a solution to this problem. The solution involves combining a sea cable on the seabed and a dynamic cable connected to the wind turbine. A problem with this arrangement is that it requires a connector for the two cables placed on the seabed. In addition, a separate submerged buoy is required between the connector and the wind turbine to avoid contact between the dynamic cable and the seabed. Once the cables are installed inside the connector, servicing or cable replacement becomes a serious problem, as the connector can only be accessed by a diver. Even if the connector is accessed by a diver, the dynamic cable is suspended from a moored, submerged buoy, making handling of the dynamic cable near the connector difficult, if not dangerous. Finally, as the connector is submerged, joining the cables underwater presents a major problem.

The object of the invention is to provide an improved power supply system that solves the above problems.

INVENTION

The above problems have been solved by a power supply system and a power distributing buoy as claimed in the appended claims. In the subsequent text, the term “floating marine structure” is intended to describe moored structures that are anchored in a way that allows the structure to move vertically with the tide and the wave. The structures can also move horizontally within a predetermined distance under the influence of winds and water currents. A non-exhaustive list of such structures includes aquatic culture installations, such as fish farms, floating exploration platforms and long-term or temporarily anchored vessels, such as oil tankers or cruise ships.

The term “off-shore power generating structure” is used to denote an optional source of electrical power that can be connected to the power supply system in addition to the shore based power supply. Additional power generating structures of this type can be used as a back-up for a shore based power supply in response to a power cut or depending on available power, pricing and/or seasonal variations. Examples of off-shore power generating structures suitable for this purpose are wave converters, wind power generators and hydrokinetic power generating structures. The latter example uses ocean or tidal currents for power generation. The off-shore power generating structures can be anchored or fixed structures depending on the type of structure and the design used.

The text refers to a first cable section comprising a static cable, which is used for connecting a power distributing buoy to land or to another power distributing buoy. The first cable section is described as being static as it is at least partially arranged stationary on the seabed. From its location on the seabed the first cable section is directed substantially vertically towards a power distributing buoy. This arrangement allows any suitable type of cable comprising an outer impermeable layer or sheath forming an enclosure for the internal electrical conductors.

Conventional static cables are sometimes referred to as sea or undersea cables and are commonly laid out on the seabed for transferring electrical power between two fixed points. Sea cables can have an outer waterproof sheath comprising a lead sheath, a metal tape or a suitable resin material that provides excellent impermeability and resistance to wear. The impermeable layer can enclose multiple twisted conductors surrounded by an insulating layer and layers comprising resin and armouring wires. Additional metal layers can be used for improving mechanical strength caused by hydrostatic pressure. This construction makes the cable very durable but also relatively stiff and inflexible. Sea cables are usually laid out stationary on the seabed and are not suitable for connecting a fixed structure and a moving structure. However, the invention provides a solution that allows the use of any suitable impermeable cable for the first cable section, including conventional sea cables and dynamic cables (see definition below), The text further refers to a second cable section comprising a dynamic cable, which is used for connecting a power distributing buoy to a floating marine structure. Dynamic cables can have an outer waterproof layer made of, for instance, multiple layers of tape-shaped components made from a suitable resin material, Kevlar © and/or metal tape, placed in alternating layers enclosing the internal electrical conductors. This construction provides a reduced level of impermeability and resistance to wear, as compared to a sea cable. However, dynamic cables will have an excellent flexibility and an improved fatigue resistance to bending. Dynamic cables are particularly suitable for connecting a fixed structure and a moving structure or two moving structures.

In the text, the term “water line” is used to denote the level of the surface of the sea on the power distributing buoy. As the power distributing buoy is moored at a fixed distance from the seabed the position of the water line will vary with the tide. When it is stated that an upper portion of the buoy is located above the water line, this implies that this portion will be above the surface of the sea under calm conditions. For a buoy according to the invention, it is desirable that the top surface of the buoy should be located at a height that allows for a safe working environment during servicing under calm conditions at the moored location. Tidal variations can also be considered for this purpose. The height of the buoy above sea level is less relevant during normal operation, as the waterproof design of the upper portion of the buoy allows it to be washed over by waves.

According to a first aspect of the invention, the invention relates to a power distributing buoy. The power distributing buoy is suitable for use in a power supply system as described below. The power distributing buoy is a surface piercing buoy comprising an upper buoy portion located above the surface and a lower buoy portion forming a submerged spar anchored at a fixed depth by at least one anchoring means on the seabed.

According to the invention, it is desirable to provide a buoy having a relatively slim cross- sectional shape to minimize drag from wind, waves and water currents. A slim cross- sectional shape combined with sufficient buoyancy allows the buoy to be maintained in an upright, substantially vertical position in extreme conditions, even when the wave height reaches its maximum value. In order to minimize air and water flow resistance from any direction, a substantially cylindrical buoy with circular or near circular cross-section is suitable. A slim cross-sectional shape can be achieved by selecting a relatively large value for the relationship between the total vertical extension, or length L and the average diameter D of the submerged portion. The relationship L:D is at least 6:1. The exact dimensions are determined by factors such as the mooring depth, maximum wave height, water current velocity, tidal variation and required buoyancy for the buoy in each specific mooring location. According to one non-limiting example, a power distributing buoy can have a vertical extension of 12 m and a diameter of 1 m along a major part of its submerged portion. Such a buoy is suitable for a location where the maximum wave height is 4 m at a depth of 75 m and where water current and tidal variations are assumed to be negligible.

The power distributing buoy is connectable to at least one first cable section extending from the seabed upwards into the buoy. A primary first cable section is connected to a shore based sub-station supplying electrical power, while further first cable sections can be connected to one or more additional power distributing buoys. The power distributing buoy is further connectable to a fixed secondary off-shore power generating structure by such a first cable section. The first cable section comprises a static sea cable wherein a substantially vertical portion of the first cable section extends from the seabed into the buoy. In order to support this vertical portion of the first cable section it can be connected to at least one buoy anchoring means on the seabed. This arrangement assists in reducing flexing of the cable induced by any angular movement of the power distributing buoy. The power distributing buoy is further connectable to a moored secondary off-shore power generating structure by such a second cable section. The second cable section comprises a dynamic cable as described above. The upper buoy portion comprises a junction box in which the first cable section and the second cable section are connected to or disconnected from each other.

The power distributing buoy comprises a cable bend limiter for each second cable section. Cable bend limiters usually comprise a number of interlocking elements which articulate when subjected to an external load and lock together to form a smooth curved "locking" radius. This radius is chosen to be equal to or greater than the minimum bend radius of the dynamic cable that it encloses. Once the elements have locked together, the bending moment present is transferred into the interlocking elements and back through a specially designed steel interface structure into a rigid connection on the power distributing buoy. This arrangement protects the second cable sections from potentially damaging loads. If required, a cable bend limiter can also be provided on the respective floating marine structure. The power distributing buoy also can comprise a cable bend limiter for each first cable section, at least at the transition from the seabed to the vertical extension towards the buoy. Although the first cable section is not intended to move relative to the buoy during normal operation, a bend limiter can be required during a mounting operation for attaching the first cable section to the buoy.

Typically, a cable bend limiter does not allow longitudinal extension or compression. The cable bend limiter provides smooth, low friction, continuous directional bending of the cable up to a set radius. The inner diameter of the cable bend limiter is not constricted by bending. Torsional rotation can be allowed if desired. The minimum bend radius can be adjustable via a single or combination of simple dimensional changes and the bend limiter assembly can be cascaded to any arch length. Cable bend limiters can comprise materials such as polyurethane and steel and be made to fit any flexible dynamic cable. Manufacturing specifications are based on the minimum bend radius, permissible static and dynamic loads and the outer diameter of the enclosed cable. The first and second cable portions are attached to the power distribution buoy or the marine structure via a fixture for example a console or pipe. In addition to this, the cable ends are equipped with dead-end spirals. The latter can be used both for relieving loads on the cables as well as for drawing the cables into the power distribution buoy during a mounting operation.

The junction box comprises first connecting means for at least one first cable section connectable to an electric power supply. By providing separate first connecting means for each first cable section, any one of the at least one first cable sections can be connected or disconnected without disturbing any other cables. Further first cable sections are connectable to supply power at least one further power distributing buoy, in order to expand the supply of power to further floating marine structures. Similarly, the junction box comprises second connecting means for at least one second cable section connectable to a power consumer on each floating marine structure adjacent the power distributing buoy. The provision of separate second connecting means for each second cable section, any one of the at least one second cable sections can be connected or disconnected without disturbing other cables and without interrupting the power supply to adjacent floating marine structures.

Optionally, the upper buoy portion comprises a second junction box for optical fibers. Optical fibers for digital communication can be integrated in the first and the second cable sections. The second junction box comprises connecting means for receiving an optical fiber extending from a shore based fiber network through a primary first cable section connected to the on shore sub-station. From the second junction box, the optical fiber can be connected to a corresponding optical fiber in each second cable section supplying power to one or more floating marine structures adjacent the power distributing buoy. Alternatively, or in addition, the optical fiber can be connected to a corresponding optical fiber in each further first cable section supplying power to one or more power distributing buoys.

The at least one junction box is arranged in a water-proof or weather sealed and drained compartment in the upper buoy portion. In order to provide access to the waterproof compartment, the upper buoy portion comprises a hatch or door in the outer surface of the upper buoy portion. This arrangement allows service personnel to access and enter the compartment, close the hatch, and perform the required maintenance in dry conditions. Accordingly, the service personnel can work protected from waves or gusts of wind and without running the risk of water spray entering an opened junction box during servicing. As an added precaution, the at least one junction box can itself comprise a water tight enclosure containing the connecting means for the first and second cable sections, or the optical fibers, respectively. Further, prior to servicing, a removable safety platform can be lowered onto the power distributing buoy, from a supply vessel or a helicopter, for attachment to the upper buoy portion. The removable platform comprises a floor and hand rails which provides additional safety for service personnel during servicing the buoy.

The power distributing buoy is anchored at a fixed depth and has sufficient buoyancy to maintain the upper buoy portion above the surface under all but very extreme wave conditions. The submerged spar can be assembled from multiple sections, wherein the number of sections is selected to achieve a predetermined buoyancy. The predetermined buoyancy is dependent on factors such as maximum wave height, tidal variations, magnitude of underwater currents and water depth in each buoy location. By anchoring the power distributing buoy at a fixed depth it will not move in the vertical direction to induce movement of the first cable section extending to the seabed. The buoyancy of the power distributing buoy will strive to maintain the submerged spar of the lower buoy portion upright, preferably in or near a vertical position, and aimed towards the anchoring means. If a single anchoring means is used, then the longitudinal axis of the power distributing buoy could be angled a few degrees off vertical under the influence of currents or large waves. The flexing of the static cable caused by this angular movement is negligible and will have little effect on the fatigue life of the static cable. The angular movement of the power distributing buoy can be reduced by using additional anchoring means if desired. Additional anchoring means can also be provided to prevent the power distributing buoy from twisting about its longitudinal axis. This would avoid twisting loads on the static, first cable section.

The submerged spar making up the lower buoy portion can comprise attachment means for at least one first cable section extending from the seabed to a lower portion of the submerged spar and into the upper buoy portion. The at least one first cable section can be attached directly onto an outer surface of the submerged spar by the attachment means.

According to a first alternative example, the first cable section can be arranged in a protective casing along an outer surface of the submerged spar, at least along a major portion of its vertical extension. In a preferred example, the first cable section can extend along the entire length of the lower buoy portion and up to or into the upper buoy portion. The upper end of the first cable section can be provided with a waterproof cable grommet and be passed through a suitable opening into the water-proof compartment provided in the upper buoy portion. The opening can be located at a position above the water line of the upper buoy portion. The cable grommet can be made from natural or synthetic rubber, or a similar suitable material. The cable grommet is preferably salt water and UV-resistant. The lower end of the casing can extend to or a predetermined distance past the lower end of the lower buoy portion. The casing along an outer surface of the submerged spar protects against chafing against the submerged spar and external action caused by ice, floating debris or accidental contact with supply vessels. In order to provide desired protection, the casing can extend to a position above the water line of the upper buoy portion.

According to a further alternative example, the first cable section is arranged within the submerged spar. In this example, the first cable section can extend up to the upper buoy portion through a tubular protective casing arranged along the central longitudinal axis of the submerged spar. Alternatively, if more than one first cable section is used, the protective casing can be arranged along an internal surface of the submerged spar. The protective casing can be terminated inside the waterproof compartment. The at least one first cable section can be provided with a waterproof cable grommet at the upper and lower ends of the tubular protective casing, in order to prevent ingress of water. This arrangement will protect the cable from external action in the same way as the above example.

According to a further example, the second cable section can also be arranged in a protective casing along an outer surface of the submerged spar, at least along an upper portion of its vertical extension. In this example, the casing for the second cable section can extend from a position up to half way down the vertical extension of the lower buoy portion and up to or into the upper buoy portion. The vertical extension of the casing for the second cable section can be determined by the maximum wave height and ice conditions at a particular location. The upper end of the second cable section can be provided with a waterproof cable grommet and be passed through a suitable opening into the water-proof compartment provided in the upper buoy portion. The opening can be located at a position above the water line of the upper buoy portion. The cable grommet can be made from natural or synthetic rubber, or a similar suitable material. The cable grommet is preferably saltwater and UV-resistant. The casing along an outer surface of the submerged spar protects against external action caused by ice, floating debris or accidental contact with supply vessels. In order to provide desired protection, the casing can extend to a position above the water line of the upper buoy portion.

In order to provide additional protection for the dynamic cable making up the second cable section, the upper buoy portion can comprise a cable bend limiter for each second cable section. Optionally, a cable bend limiter can also be provided for each first cable section. The at least one cable bend limiter is attached to the power distributing buoy at the position where the second cable section leaves to buoy. When a protective casing is used, the cable bend limiter is attached to or adjacent the end of the protective casing to surround an initial section of the cable. Cable bend limiters can comprise a number of interlocking elements which articulate when subjected to an external load and lock together to form a smooth curved "locking" radius to prevent excessive bending of the enclosed cable. A cable bend limiter can also be provided on each floating marine structure receiving a second cable section. Cable bend limiters have been described in detail above.

According to a second aspect of the invention, the invention relates to a power supply system for supplying at least electrical power to at least one moored, floating marine structure. The subsequent text is mainly directed to the supply of electrical power, but the cables used in this context can also be provided with means for communication and data transmission, such as fiber optic cables. The power supply system comprises at least an onshore sub-station supplying electrical power to a power consumer on the floating marine structure and a power distributing buoy arranged to electrically connect the onshore sub station and the at least one marine structure. The power distributing buoy can additionally be supplied with electrical power from an off-shore power generating structure. Examples of off shore power generating structures suitable for this purpose are wave, wind and hydrokinetic (ocean/tidal current) power generating structures. Additional or secondary power generating structures of this type can be used as a back-up for a shore based power supply in response to a power cut or depending on available power, pricing and/or seasonal variations. For instance, during the summer the available power from the grid is usually plentiful, while the output from wind and wave power generating structures can be limited. During the autumn and winter the general power demand on the grid can be substantial, while the output from wind and wave power generating structures can be relatively large. Hence, an off-shore power generating structures can be used as a back-up or to supplement a shore based power supply.

The sub-station can comprise a transformer to transform the power supplied from the grid to a desired voltage. Similarly, the floating marine structure can comprise a further transformer to transform the power supplied from the sub-station to a desired voltage. Preferably, the transferred electrical power has a voltage intermediate the high tension voltage form the grid and the consumer voltage used on-board the floating marine structure. The power distributing buoy is a surface piercing buoy comprising an upper buoy portion above the surface and a lower buoy portion forming a submerged spar anchored at a fixed depth by at least one anchoring means on the seabed. A list of non-limiting examples of suitable anchor means include gravity anchor blocks, suction anchors and rock bolts. Anchoring means of this type are well known in the art and will not be described in further detail. The type of anchoring means is selected depending on the seabed conditions at each mooring location.

The onshore sub-station is connected to the power distributing buoy via a first cable section extending from the seabed into the buoy, wherein the first cable section comprises a static cable. The static cable can be any type of impermeable cable suitable for this purpose. The power distributing buoy is connected to the at least one marine structure by a second cable section extending from the buoy to the marine structure in a catenary remote from the seabed, wherein the second cable section comprises a dynamic cable. Preferably, the length of the dynamic second cable sections is adapted to ensure that the cables do not contact the seabed at any time, irrespective of waves and tidal conditions. With an adapted cable length the cable extends in a catenary between the power distributing buoy and the marine structure. However, should a second cable section having relatively a longer extension be required, then one or more cable supporting buoys can be used to ensure that the cable does not contact the seabed. Cable supporting buoys can be anchored at a fixed depth to minimize movement of the supported cable, although floating buoys may also be employed.

The first and second cable sections are arranged to transfer electric power to the marine structure at the voltage supplied by the sub-station. In this way electrical power can be transferred directly to the floating marine structure with a minimum of transmission losses. The use of high voltage is a requirement for power transmission over distances longer than 1-2 km. In this context, high voltage is defined as a voltage above 1 kV. The power transmission can use direct current or alternating current. For longer distances, direct current is preferred in order to maintain low transmission losses. The transferred electrical power can be converted to a desired voltage on-board the floating marine structure.

When designing the power distributing buoy, the prevailing local conditions such as the mooring depth, wave heights, water currents and expected weather conditions can decide the vertical extension of the buoy and the distance from the top of the buoy to the average sea level under calm conditions.

It is desirable to provide a buoy having a relatively slim cross-sectional shape to minimize drag from wind, waves and water currents. A slim cross-sectional shape combined with sufficient buoyancy and anchoring at a fixed depth allows the buoy to be maintained in an upright, substantially vertical position in extreme conditions, even when the wave height reaches its maximum value. In order to minimize air and water flow resistance from any direction, a substantially cylindrical buoy with circular or near circular cross-section is suitable. A slim cross-sectional shape can be achieved by selecting a relatively large value for the relationship between the total vertical extension, or length L of the buoy and the average diameter D of the lower buoy portion. The relationship L:D is at least 6:1. The exact dimensions are determined by factors such as the mooring depth, maximum wave height, water current velocity, tidal variation and required buoyancy for the buoy in each specific mooring location. For instance, the vertical extension of the buoy below the surface must exceed the maximum wave height at all times, even at low tide. This minimum submerged extension is at least equal to the maximum wave height and is measured from the position of a wave trough at low tide under maximum wave height conditions.

According to one alternative, the upper and lower portion can have substantially the same cross-sectional shape and dimensions along the entire extension of the buoy. According to a further alternative, the cross-sectional shape and dimensions of the upper portion of the buoy can be enlarged in order to provide sufficient space for a maintenance crew inside the upper portion.

The power distributing buoy is anchored at a fixed depth and has a lower portion comprising a submerged spar providing sufficient buoyancy to maintain the upper buoy portion upright even under extreme wave conditions. As a result the power distributing buoy will not move in the vertical direction to induce movement of the first cable section extending to the seabed. The buoyancy of the power distributing buoy will strive to maintain the submerged spar of the lower buoy portion upright and aimed towards the anchoring means. If one anchoring means is used, then the longitudinal axis of the power distributing buoy could be angled a few degrees off vertical relative to the anchoring point under the influence of currents or large waves. The flexing of the static cable caused by this movement is negligible adjacent the seabed and will have little or no effect on the fatigue life of the static cable. The angular displacement of the power distributing buoy can be reduced by using additional anchoring means if desired. Additional anchoring means can also be provided to prevent the power distributing buoy from twisting about its longitudinal axis. This would avoid twisting loads on the static, first cable section.

According to the invention, the power distributing buoy comprises a junction box in which the first and second cable sections are electrically connected or disconnected. The first cable section extends from the seabed to a lower portion of the submerged spar and into the upper buoy portion. The junction box can be arranged in a water-proof compartment in the upper buoy portion, which compartment can be accessed through a hatch or door from the outside of the upper buoy portion. This arrangement allows service personnel to access and enter the compartment, close the hatch, and perform the required maintenance in dry conditions. Accordingly, the service personnel can work protected from waves or gusts of wind and without running the risk of water spray entering an opened junction box during servicing. Further, prior to servicing, a removable safety platform can be lowered onto the power distributing buoy, from a supply vessel or a helicopter, for attachment to the upper buoy portion. The removable platform provides additional safety for service personnel servicing the buoy.

According to one example, the first cable section can be arranged in a protective casing along an outer surface of the submerged spar, at least along a major portion of its vertical extension. In this example, the casing for the first cable section can extend from the lower end of the submerged spar up to the upper buoy portion. At least the upper end of the first cable section can be provided with a waterproof cable grommet and be passed from the casing through a suitable opening into the water-proof compartment provided in the upper buoy portion. The opening can be located at a position above the water line of the upper buoy portion. The cable grommet can be made from natural or synthetic rubber, or a similar suitable material. The cable grommet is preferably salt water and UV-resistant. The casing along an outer surface of the submerged spar protects against external action caused by ice, floating debris or accidental contact with supply vessels. In order to provide desired protection, the casing can extend to a position above the water line of the upper buoy portion.

According to a further example, the first cable section is arranged within the submerged spar. In this example, the first cable section can extend up to the upper buoy portion through a tubular protective casing arranged along the central longitudinal axis of the submerged spar. Alternatively, if more than one first cable section is used, the protective casing can be arranged along an internal surface of the submerged spar. The protective casing can be terminated inside the waterproof compartment. The at least one first cable section can be provided with a waterproof cable grommet at the upper and lower ends of the tubular protective casing, in order to prevent ingress of water. This arrangement will protect the cable from external action in the same way as the above example.

As described above, the first cable section comprises a static sea cable wherein a substantially vertical portion of the first cable section extends from the seabed into the buoy. In order to support this vertical portion of the first cable section it can be connected to one of the at least one buoy anchoring means on the seabed. This arrangement can assist in reducing flexing of the cable induced by an angular movement of the power distributing buoy, which movement is described above. According to a further example, the second cable section can also be arranged in a protective casing along an outer surface of the submerged spar, at least along an upper portion of its vertical extension. In this example, the casing for the second cable section can extend from a position up to half way down the vertical extension of the submerged spar and up to the upper buoy portion. The upper end of the second cable section can be provided with a waterproof cable grommet and be passed through a suitable opening into the water proof compartment provided in the upper buoy portion. The opening can be located at a position above the water line of the upper buoy portion. The cable grommet can be made from natural or synthetic rubber, or a similar suitable material. The cable grommet is preferably salt water and UV-resistant. The casing along an outer surface of the submerged spar protects against external action caused by ice, floating debris or accidental contact with supply vessels. In order to provide desired protection, the casing can extend to a position above the water line of the upper buoy portion.

The above example describes one floating marine structure connected to an on-shore substation via a power distributing buoy. However, the system according to the invention can be expanded to comprise multiple floating marine structures supplied by a power distributing buoy, or multiple power distributing buoys each supplying one or more floating marine structures. According to a first example, a first power distributing buoy is connected to at least one further power distributing buoy by a further first cable section extending from the first power distributing buoy to the seabed, along the seabed towards the at least one further power distributing buoy, and then up into the further power distributing buoy. The further first cable section is a static cable, such as a sea cable, and can be extended to and from the seabed from each power distributing buoy in the same way as described above. According to a further example, the first power distributing buoy and each further power distributing buoy can be connected to at least one further marine structure by a further second cable section extending from the respective buoy or buoys. Each second cable section extending in a catenary between a buoy and a floating marine structure is arranged remote from the seabed as described above.

An advantage of the system is that it can be expanded or reduced in size according to a current need for electrical power on-board one or more floating marine structures. A power distributing buoy according to the invention allows for simple connection or disconnection of additional floating marine structures or to extend to power supply to further power distributing buoys and one or more associated floating marine structures.

According to one example, the first and second cable sections are arranged to transfer electric power to the marine structure at the voltage supplied by the sub-station. The transferred electric power from the sub-station can have a voltage greater than 1 kV, preferably 3 kV or higher.

An advantage of the invention is that it provides a system for supplying electrical power to moored marine structures that are anchored in a way that allows the structure to move vertically with the tide and the wave, as well as horizontally within a predetermined distance under the influence of winds and currents. A non-exhaustive list of such structures includes aquatic culture installations, such as fish farms, floating exploration platforms and long-term or temporarily anchored vessels, such as oil tankers or cruise ships. The system provides a means for electrification of aquatic culture installations, eliminating the need for continuously operated diesel generators. The system further provides a means for supplying electric power to vessels anchored off-shore in or near inhabited or ecologically sensitive areas, eliminating the need for operating the on-board engines while connected to a power distributing buoy. A further advantage is that the system allows the use of high voltage cables, which reduces transmission losses and allows transmission over longer distances.

The invention provides a system that allows power transfer to floating off-shore locations using a combination of a wear resistant and extremely impermeable, but inflexible sea cable and a flexible dynamic cable. The system comprises a power distributing buoy that facilitates simple access for connecting, disconnecting, servicing or replacing the cables or parts thereof. This is a particular advantage for the dynamic cables used in the system, as such cables are most susceptible to wear and fatigue due to the constant movement of floating marine structures. The further system allows for rapid expansion of the power supply system, simply by adding further power distributing buoys. Additional power distributing buoys can be connected to an existing buoy and/or to each other or to further floating structures without having to access cables placed on the seabed. Underwater operations requiring divers or advanced ROV (Remotely Operated underwater Vehicle) equipment can therefore be dispensed with, saving both time and cost.

FIGURES

In the following text, the invention will be described in detail with reference to the attached drawings. These schematic drawings are used for illustration only and do not in any way limit the scope of the invention. In the drawings:

Figure 1A shows a schematic basic power supply system according to the invention;

Figure 1B shows a schematic anchoring means for the system in Fig.lA;

Figure 2A shows a schematic layout of an alternative system according to the invention;

Figure 2B shows a schematic layout of an expanded system according to the invention;

Figure 2C shows a schematic layout of an alternative system according to the invention;

Figure 3A shows a schematic first side view of a power distributing buoy according to the invention;

Figure 3B shows a schematic second side view of the buoy in Fig.3A;

Figure 3C shows a schematic plan view cross-section of the buoy in Fig.3B;

Figure 3D shows a schematic plan view of the buoy in Fig.3C;

Figure 4 shows a schematic cross-section of a compartment in an upper portion of a buoy according to the invention; and

Figure 5 shows a schematic perspective view of a power distributing buoy according to the invention.

DETAILED DESCRIPTION

Figure 1A shows a schematic basic power supply system 100 according to the invention. The power supply system 100 is arranged to supply at least electrical power to at least one moored, floating marine structure 101. The power supply system comprises an onshore sub station 102 supplying electrical power to a power consumer 103 on the floating marine structure. A power distributing buoy 110 is arranged to electrically connect the onshore sub station 102 and the at least one marine structure 101. The sub-station 102 comprises a transformer (not shown) to transform the power supplied from the grid 104 to a desired voltage. Similarly, the floating marine structure 101 comprises a further transformer 105 to transform the power supplied from the sub-station 102 to a desired voltage. Preferably, the transferred electrical power has a voltage intermediate the high tension voltage form the grid 104 and the consumer voltage used on-board the floating marine structure 101. The power distributing buoy 110 is a surface piercing buoy comprising an upper buoy portion 111 above the water surface W and a lower buoy portion 112 forming a submerged spar anchored at a fixed depth by an anchoring means 113 on the seabed B. A list of non-limiting examples of suitable anchor means include gravity anchor blocks, suction anchors and rock bolts. The anchoring means is selected depending on the seabed conditions at each mooring location. In the example shown a gravity anchor block 114 is used, which is connected to the lower end of the power distributing buoy 110 by at least one anchoring wire 115.

The onshore sub-station 102 is connected to the power distributing buoy 110 via a first cable section 121 in the form of a static cable placed on the seabed. Adjacent the anchoring means 113 the first cable section 121 extends in a curve from the seabed B and in a substantially vertical direction up towards the buoy 110 and into the upper buoy portion 111. The first cable section 121 is provided with a bend limiter (not shown) at least at the transition from the seabed to the vertical extension towards the buoy 110. A further bend limiter can be required at the lower end of the buoy during a mounting operation for attaching the first cable section to the buoy. A suitable bend limiter can be a CPS Bend stiffener as manufactured by Seaproof Solutions ™ .

In this example the first cable section 121 comprises a conventional sea cable, which is made possible by the power distributing buoy 110 described below and its anchoring arrangement. The flexing of the first cable section 121 using the power distributing buoy 110 according to the invention will be negligible and has little effect on the fatigue life of the cable. The power distributing buoy 110 is connected to the marine structure 101 by a second cable section 122 extending from the upper buoy portion 111 of the buoy 110 to the marine structure 101 remote from the seabed. The second cable section 122 comprises a suitable dynamic cable. Dynamic cables have an excellent flexibility and an improved fatigue resistance to bending and are particularly suitable for connecting a fixed structure and a moving structure or two moving structures. The first and second cable sections 121, 122 are arranged to transfer electric power to the marine structure 101 at the voltage supplied by the sub-station 102. In this way electrical power can be transferred directly to the floating marine structure 101 with a minimum of transmission losses. Figure 1B shows a schematic anchoring means 113 for the system in Figure 1A. Figure 1B shows an anchoring means 113 comprising a concrete gravity anchor block 114 placed on the seabed B, which gravity anchor block 114 is connected to the lower end of the power distributing buoy (see Fig.lA) by an anchoring wire 115. An optional, second anchoring wire 116 can be provided as a back-up if required. The second anchoring wire 116 can be provided to prevent the power distributing buoy from twisting about its longitudinal axis. This would avoid twisting loads on the static, first cable section 121. The gravity anchor block 114 is provided with metal lifting loops 117 to allow it to be lowered into position on or re positioned on the seabed. A first cable section 121 in the form of a static cable extends along the seabed B from an onshore sub-station (see Fig.lA) towards the anchoring means 113. Adjacent the anchoring means 113 the first cable section 121 extends in a curve 123 from the seabed B and in a substantially vertical direction up towards the power distributing buoy. A suitable attachment means 124, such as a metal or plastic fastening strap, is used to maintain the first cable section 121 in a fixed position relative to the anchoring means 113. In this example, the attachment means 124 is attached to a lifting loop. The power distributing buoy can comprise an optional cable bend limiter 125 (indicated in dashed lines) for the first cable section 121 at the transition from the seabed to the vertical extension towards the buoy. Although the first cable section 121 is not intended to move relative to the buoy or the anchoring means during normal operation, a bend limiter can be required during a mounting operation for attaching the first cable section to the buoy.

Figure 2A shows a schematic layout of an alternative power supply system according to Figure 1A. Occasionally it may be necessary to move a marine structure 101 as shown in Figure 1A to a new mooring position. As indicated in Figure 2A, this can be achieved by deploying a second power distributing buoy 210 at the new position. The mooring of a power distributing buoy according to the invention is indicated in Figures 1A and 1B. A further first cable 221 is then laid on the seabed between the initial power distributing buoy 110 and the second power distributing buoy 210 at the new mooring position. The ends of the further first cable 221 extends from the seabed to the initial power distributing buoy 110 and the second power distributing buoy 210, respectively, in the same way as the initial first cable 121 (see Fig.lA). Subsequently, the marine structure 101 and its dynamic second cable section 122 is disconnected from the initial power distributing buoy 110 and towed to the new mooring position. When the marine structure 101 has been moored its dynamic second cable section 122 is connected to the second power distributing buoy 210. All cable connections are located in the upper portion of the respective power distributing buoys, as will be described below. As the upper portion of each power distributing buoy is above the surface of the water there is no need for divers and/or sub-sea operations. Optionally the initial first cable can be replaced by a longer cable section extending to the new mooring position of the marine structure.

Figure 2B shows a schematic layout of an expanded power supply system according to the invention. The system in Figure 2B comprises an initial power supply system 100 as described in Figure 1A. As described above, the power supply system is supplied with electric power from an on-shore sub-station 102 connected to the grid 104. The sub-station 102 is connected to an initial power distributing buoy 110 via a first cable section 121, wherein the first cable section 121 comprises a sea cable. The initial power distributing buoy 110 is in turn connected to an associated floating marine structure 101 by a second cable section 122 extending from the initial power distributing buoy 110 to the marine structure 101 remote from the seabed, wherein the second cable section 122 comprises a dynamic cable. The first and second cable sections 121, 122 are arranged to transfer electric power to the marine structure 101 at the voltage supplied by the sub-station 102. Note that the cable sections are only schematically indicated in Figure 2B.

The expanded power supply system comprises a further three power supply system 200a, 200b, 200c, which are supplied with electric power via the initial power supply system 100. The initial power distributing buoy 110 is electrically connected to a first further power distributing buoy 210a via a further first cable section 221a laid along the seabed. The initial power distributing buoy 110 is also connected to a second further power distributing buoy 210b via a further first cable section 221b laid along the seabed. The second power distributing buoy 210b is in turn connected to a third further power distributing buoy 210c via a further first cable section 221c laid along the seabed. Each marine structure 201a, 200b, 200c is connected to its respective power distributing buoy 210a, 210b, 210c by further dynamic second cable sections 222a, 222b, 222c suspended remote from the seabed.

In Figure 2B, the on-shore sub-station 102 is a primary source of electrical power to the power supply system. Optionally, the power supply system can be provided with an additional, or secondary, source of electrical power in the form of an off-shore power generating structure 230. The off-shore power generating structure 230 is connected to a power distributing buoy 210b via a static first cable section 231 laid along the seabed. Alternatively, if the off-shore power generating structure is moored near a power distributing buoy it is possible to use a dynamic cable section in a catenary remote from the seabed. Examples of off-shore power generating structures suitable for this purpose are wave, wind and hydrokinetic (ocean/tidal current) power generating structures. The schematically indicated optional off-shore power generating structure 230 in Figure 2B is a wave power converter. Figure 2B only shows one possible example of an expanded power supply system according to the invention. Such a system can comprise further power distributing buoys, each connected to one or more further power distributing buoy. Each power distributing buoy can in turn supply one or more floating marine structures. The possible expansion of the system is limited by the available power from the on-shore sub-station, and to some extent by the distance between the sub-station and remote floating marine structures.

Figure 2C shows a schematic layout of an alternative system according to the invention.

The system in Figure 2C comprises an initial power supply system 100 as described in Figure 2B. As described above, the power supply system is supplied with electric power from an on-shore sub-station 102 connected to the grid 104. The sub-station 102 is connected to an initial power distributing buoy 110 via a first cable section 121, wherein the first cable section 121 comprises a sea cable. The initial power distributing buoy 110 is in turn connected to an associated floating marine structure 101 by a second cable section 122 extending from the initial power distributing buoy 110 to the marine structure 101 remote from the seabed, wherein the second cable section 122 comprises a dynamic cable. The first and second cable sections 121, 122 are arranged to transfer electric power to the marine structure 101 at the voltage supplied by the sub-station 102. Note that the cable sections are only schematically indicated in Figure 2B.

The alternative power supply system comprises a further three power supply system 200a, 200b, 200c, which are supplied with electric power via the initial power supply system 100. The initial power distributing buoy 110 is electrically connected to a first further power distributing buoy 210a via a further first cable section 221a laid along the seabed. The initial power distributing buoy 110 is also connected to a second further power distributing buoy 210d via a further first cable section 221d laid along the seabed.

The second power distributing buoy 21 Od is in turn connected to a secondary, source of electrical power in the form of an off-shore power generating structure 230. The off-shore power generating structure 230 is moored near second further power distributing buoy 21 Od and is connected to the buoy 210d via a dynamic second cable section 231 in a catenary remote from the seabed. In this example, this first off-shore power generating structure 230 is a wave converter has a mooring that allows a limited displacement relative to its anchoring means. The relative movement between the second power distributing buoy 21 Od and the first off-shore power generating structure 230 requires the use of a dynamic cable 231 , in the same way as the marine structures 101, 201a described above. Depending on the distance to the moving power generating structure 230, the second cable section 231 can require one or more cable supporting buoys to ensure that the second cable section 231 does not contact the seabed. Cable supporting buoys can be anchored at a fixed depth to minimize movement of the supported cable, although floating buoys may also be employed.

The second power distributing buoy 210d can also be connected to a further secondary, source of electrical power in the form of a second off-shore power generating structure 240. The second off-shore power generating structure 240 is a fixed structure located remote from the buoy 210d and is connected to the power distributing buoy 210d via a static first cable section 241 laid along the seabed. In this example, this first off-shore power generating structure 230 is a wind turbine that is either moored or built at a fixed position on the seabed. As there is no relative movement between the second power distributing buoy 21 Od and the second off-shore power generating structure 240 it is possible to use a static first cable section 241. The connection of the second off-shore power generating structure 240 can be made in the same way as the connection between two power distributing buoys 110, 21 Od as described above.

In Figure 2C, the on-shore sub-station 102 is a primary source of electrical power to the power supply system. As described above, the power supply system can be provided with at least one secondary source of electrical power. Secondary power generating structures of this type can be used as a back-up for a shore based power supply in response to a power cut or depending on available power, pricing and/or seasonal variations. For instance, during the summer the available power from the grid is usually plentiful, while the output from wind and wave power generating structures can be limited. During the autumn and winter the general power demand on the grid can be substantial, while the output from wind and wave power generating structures can be relatively large. Hence, an off-shore power generating structures can be used as a back-up or to supplement a shore based power supply. Surplus power not utilised by the power supply system can be fed to the on-shore sub-station and the grid via intermediate power distributing buoys. Examples of secondary sources of electrical power suitable for this purpose are wave, wind and hydrokinetic (ocean/tidal current) power generating structures.

Figure 3A and 3B show schematic first and second side views of a power distributing buoy 310 according to the invention. The buoy 310 in this example comprises an upper buoy portion 311 located above the water line W and a lower buoy portion 312 submerged below the water line W. The vertical extension L1 of the upper buoy portion 311 is selected to maintain this portion above sea level in calm conditions and at low tide. Under calm conditions the upper portion 311 is not washed over by waves and a service platform (see Fig.4) can be attached to the top of the buoy in order to allow maintenance to be performed. The lower end of the submerged buoy portion 312 is provided with an attachment portion 313 to which an anchoring wire (not shown; see Fig.1A-B; “115”) is attached. As the power distributing buoy 310 is anchored at a fixed depth, the position of the waterline W in the figure will vary with the tide and intermittently with varying wave heights. The position shown indicates the water level in calm conditions, during which maintenance can be performed.

As described above, the power distributing buoy 310 is arranged to receive a first cable section from an on-shore sub-station (see Fig.lA) and/or from a second power distributing buoy (see Fig.2B). As indicated in Figures 1A and 1B, such first cable sections will extend in a substantially vertical direction from the seabed. A tubular component such as a pipe or tube 314 with an internal cross-section adapted to receive a first cable section is mounted along the outer surface of the submerged lower buoy portion 312. The tube 314 extends vertically upwards from a position adjacent the lower end of the submerged lower buoy portion 312 to a position where it meets and enters inside the upper portion 311. This tube 314 supports the first cable section in a fixed position relative to the power distributing buoy 310 and provides a protective casing protecting it from chafing and external actions. The power distributing buoy 310 can be provided with at least one further tube 316 for connecting a further first cable section to a second power distributing buoy. Figure 3B shows a power distributing buoy 310 provided with two tubes 314, 316 mounted in parallel on opposite sides of the submerged lower buoy portion 312.

According to an alternative example, one or more vertically extending tubes can be arranged within the submerged buoy portion 312

The power distributing buoy 310 is also arranged to receive a second cable section from a floating marine structure to be supplied with electrical power. As indicated in Figures 1A and 1B, such second cable sections will extend between a power distributing buoy and an adjacent marine structure in a catenary remote from the seabed. Preferably, the length of the dynamic second cable sections is adapted to ensure that the cables do not contact the seabed at any time. Should a second cable section having relatively a longer extension be required, then one or more cable supporting buoys can be used to ensure that the cable does not contact the seabed. Cable supporting buoys can be anchored at a fixed depth to minimize movement of the supported cable, although floating buoys may also be employed.

A further tubular component such as a pipe or tube 315 with an internal cross-section adapted to receive a second cable section is mounted along an upper part of the outer surface of the submerged buoy portion 312. The tube 315 extends vertically upwards from a position less than half way down the lower end of the submerged buoy portion 312 to a position where it meets and enters inside the upper portion 311. The lower end of the tube 315 is provided with a curved section 317 to provide a gradual transition to the catenary of the second cable section. Optionally, a bend limiter can be provided at the end of the curved section 317 to provide further protection of the cable caused by movement induced by the marine structure. This tube 315 supports the first cable section in a fixed position relative to the power distributing buoy 310 and provides a protective casing protecting it from chafing and external actions. The power distributing buoy 310 can be provided with at least one further tube (not shown) for connecting a further second cable section to a second marine structure.

The lower portion 312 comprises a submerged spar providing sufficient buoyancy to maintain the power distributing buoy 310 upright even under extreme wave conditions. As a result the power distributing buoy 310 will not move in the vertical direction to induce movement of the first cable section extending to the seabed. The buoyancy of the power distributing buoy will strive to maintain the submerged spar of the lower buoy portion upright and aimed towards the anchoring means. The vertical extension L1 of the upper portion 311 above sea level W during calm conditions is determined by the anchoring depth, and to some extent by local tidal conditions. The buoyancy of the power distributing buoy is determined by the displacement, which is dependent on the average diameter D and the vertical extension L2 of the submerged lower portion 312, and the weight of the power distributing buoy. In this example, the average diameter is used, as the diameter of the buoy can vary along its length. If the lower buoy portion is made up of multiple cylindrical sections, then the diameter of these sections can be used. The relationship between the total vertical extension (L1 + L2) of the buoy (110; 210; 310) and the average diameter D of the lower buoy portion 112; 312 is selected to be at least 6:1. The vertical extension L2 of the buoy below the surface must exceed the maximum wave height at all times, even at low tide. This minimum submerged extension is at least equal to the maximum wave height and is measured from the position of a wave trough at low tide under maximum wave height conditions.

According to the example shown in Figures 3A and 3B, the cross-sectional shape and dimensions of the upper portion 311 of the buoy is larger than the diameter D of the lower portion 312. In this example, the upper portion 311 is enlarged in order to provide a compartment 320 for a maintenance crew inside the upper portion 312. Alternatively, the upper and lower portion can have substantially the same cross-sectional shape and dimensions along the entire extension of the buoy, as long as there is sufficient space for a maintenance compartment in the upper portion. Figure 3C shows a schematic cross-section of the power distributing buoy 310 in Figure 3B. This figure indicates the location of the maintenance compartment 320 in the upper portion 311 of the buoy. The maintenance compartment 320 comprises a junction box 323 wherein the cables entering and leaving the upper portion 311 can be connected. Figure 3C further shows that the lower portion 312 of the power distributing buoy 310 can be assembled from multiple hollow, tubular sections 312a-312e. When assembling a power distributing buoy according to the invention, the number of tubular sections can be selected depending on the buoyancy and vertical extension required for the maximum wave height and tidal conditions for each mooring location.

Figure 3D shows a schematic plan view of the power distributing buoy 310 in Fig.3A-3C. This figure provides a view into the maintenance compartment 320 in the upper portion 311 of the buoy. The locations for the tubes 314, 316 supporting a respective first cable section 321a and 321b are indicated by arrows. A further arrow indicates the location for the tube 315 supporting a second cable section 322. From the locations where the tubes 314, 316 for the first cable section 321a, 321b and the tube 315 for the second cable section 422 enters the upper portion 311, each cable section 321a, 321b, 322 is arranged to follow the internal wall of the maintenance compartment 320 to a junction box 323. The junction box 323 is waterproof and comprises electrical connectors to allow the cables to be connected according to the current configuration of the power distributing buoy 310.

Figure 4 shows a schematic perspective view of the maintenance compartment 320 in the upper portion 311 of the power distributing buoy in Figures 3C and 3D. An upper surface 401 along the edge of the upper portion 311 is arranged to support a cover (see Fig.5) with a hatch allowing access to the maintenance compartment 320. The upper surface 401 is provided with multiple holes 402 for screws attaching cover to the upper portion 311. The cover is sealed against the upper portion 311, making the maintenance compartment 320 waterproof. Figure 4 shows two cable sections 321b, 322 fixed to the internal wall of the maintenance compartment 320 by means of brackets 403, allowing the cables to follow the internal wall to a junction box 323. The junction box 323 in this example comprises a first junction box 404 for connecting electrical cables and a second junction box 405 for optical fibers for communication and data transmission.

The first junction box comprises first and second connecting means 406. First connecting means are provided for at least one first cable section connectable to an electric power supply or to at least one further first cable section. By providing separate first connecting means for each first cable section, any one of the at least one first cable sections can be connected or disconnected without disturbing any other electrical cables. Further first cable sections are connectable to supply power at least one further power distributing buoy, in order to expand the supply of power to further floating marine structures. Similarly, second connecting means are provided for at least one second cable section connectable to a power consumer on each floating marine structure adjacent the power distributing buoy. The provision of separate second connecting means for each second cable section allows each second cable section to be be connected or disconnected without disturbing other electrical cables and without interrupting the power supply to adjacent floating marine structures.

Figure 5 shows a schematic perspective view of a power distributing buoy 310 according to Figures 3A-3D and Figure 4. As described above, a junction box can be arranged in a water proof maintenance compartment 320 in the upper portion 311 of the buoy, which compartment can be accessed for maintenance or connection/disconnection of cables when necessary. Prior to maintenance, a removable safety platform 501 can be lowered onto the upper portion 311 of the power distributing buoy 320, from a supply vessel or a helicopter, for temporary attachment to the upper portion 311. The removable platform 501 comprises a floor 502 and hand rails 503 which provides additional safety for service personnel during servicing the buoy. The floor 502 of the safety platform 501 has an opening providing access to a cover 504 at upper surface of the upper portion 311. Access to the maintenance compartment 320 is provided through a hatch 505 in the cover 504 at the top of the upper portion 311 of the buoy. This arrangement allows service personnel to access and enter the compartment, close the hatch, and perform the required maintenance in dry conditions. Accordingly, the service personnel can work protected from waves or gusts of wind and without running the risk of water spray entering an opened junction box during servicing. When the maintenance is completed, the hatch 505 is sealed and the removable safety platform 501 is released from the power distributing buoy 310, The entire platform 501 can then be lifted off (see arrow A) by a supply vessel or a helicopter.

The invention should not be deemed to be limited to the embodiments described above, but rather a number of further variants and modifications are conceivable within the scope of the following patent claims.

Claims

1. A power distributing buoy (110; 210; 310) comprising a surface piercing buoy having an upper buoy portion (111; 311) above the surface, and a lower buoy portion (112; 312) comprising a submerged spar anchored at a fixed depth by at least one anchoring means (113) on the seabed characterized in that

- the power distributing buoy (110; 210; 310) is connectable to at least one first cable section (121; 221a; 221b; 221c) extending from the seabed into the buoy,

- the power distributing buoy (110; 210; 310) is connectable to at least one marine structure (101; 201a; 201b; 201c) by a second cable section (122; 222a; 222b; 222c) extending from the buoy to the marine structure (101; 201a; 201b; 201c) remote from the seabed, and that

- the upper buoy portion (111 ; 311) comprises a junction box (323), in which junction box the at least one first cable section (121; 221a; 221b; 221c) and the at least one second cable section (122; 222a; 222b; 222c) are arranged to be connected or disconnected.

2. Power distributing buoy (110; 210; 310) according to claim 1, character ized in that the at least one first cable section (121; 221a; 221b; 221c) is a static cable and that the second cable section (122; 222a; 222b; 222c) is a dynamic cable.

3. Power distributing buoy (110; 210; 310) according to claim 1 or 2, character ized in that the upper buoy portion (111; 311) comprises a second junction box (405) for optical fibres.

4. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-3, characterized in that the junction box (323) is arranged in a water-proof compartment (320) comprising a hatch (505) for access to the junction box (323).

5. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-4, characterized in that a removable safety platform (501) is attachable to the upper buoy portion (111; 311).

6. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-5, characterized in that the submerged spar comprises multiple assembled sections (312a-312e), wherein the number of sections is selected to achieve a predetermined buoyancy.

7. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-6, characterized in that the submerged spar comprises a protective casing (314, 316) for each first cable section (121; 221a; 221b; 221c) extending along the entire lower buoy portion (112; 312) to the upper buoy portion (111; 311).

8. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-7, characterized in that the submerged spar comprises a protective casing (315) for each first cable section (122; 222a; 222b; 222c) extending from a position up to half way down the vertical extension of the lower buoy portion (112; 312) to the upper buoy portion (111; 311).

9. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-8, characterized in that the at least one first cable section (121; 221a; 221b; 221c) extends vertically from the anchoring means (113) into the buoy,

10. Power distributing buoy (110; 210; 310) according to any one of the above claims 1-9, characterized in that the relationship between the total vertical extension (L) of the buoy (110; 210; 310) and the average diameter (D) of the lower buoy portion (112; 312) is at least 6:1.

11. A power supply system for supplying at least electrical power to at least one moored, floating marine structure (101), the system comprising:

- a primary supply of electrical power comprising an onshore sub-station (102),

- a power distributing buoy (110; 210; 310) arranged to electrically connect the onshore sub station (102) and the at least one marine structure (101); wherein the power distributing buoy (110; 210; 310) is a surface piercing buoy comprising an upper buoy portion (111 ; 311) above the surface and a lower buoy portion (112; 312) forming a submerged spar anchored at a fixed depth by an at least one anchoring means on the seabed, characterized in that

- the onshore sub-station (102) is connected to the power distributing buoy (110; 210; 310) via a first cable section (121; 221a; 221b; 221c) extending from the seabed into the buoy,

- the power distributing buoy (110; 210; 310) is connected to the at least one marine structure (101) by a second cable section (122) extending from the buoy to the marine structure (101) remote from the seabed, wherein the second cable section (122) comprises a dynamic cable, and the first and second cable sections (121; 122) are electrically connected on the power distributing buoy (110; 210; 310) and arranged to transfer electric power to the marine structure (101).

12. System according to claim 11, characterized in that the power distributing buoy (110; 210; 310) comprises a junction box (323) in which selected cable sections (121; 122) are electrically connected or disconnected.

13. System according to claim 11 or 12, characterized in that the first cable section (121; 221a; 221b; 221c) extends vertically from the seabed towards a lower portion of the submerged spar and upwards into the upper buoy portion (111; 311).

14. System according to any one of claims 11-13, characterized in that the first cable section (121) is arranged in a protective casing along an outer surface of the lower buoy portion (112; 312).

15. System according to any one of claims 11-15, characterized in that the first cable section (121; 221a; 221b; 221c) is connected to a buoy anchoring means (113) for the power distributing buoy on the seabed.

16. System according to any one of claims 11-15, characterized in that the power distributing buoy (110; 210; 310) is connected to at least one further power distributing buoy (210a; 210b; 210c) by a further first cable section (221a; 221b; 221c) extending from the power distributing buoy (110; 210; 310) to the seabed towards the at least one further power distributing buoy (210a; 210b; 210c).

17. System according to any one of claim3 11-16, characterized in that each further power distributing buoy (210a; 210b; 210c) is connected to at least one further marine structure (201a; 201b; 201c) by a further second cable section (222a; 222b; 222c) extending from the buoy remote from the seabed.

18. System according to any one of claims 11-17, characterized in that the power distributing buoy (110, 210d) is electrically connected to a secondary supply of electrical power comprising at least one offshore power generating structure (230, 240).

19. System according to any one of claims 11-18, characterized in that the first and second cable sections (121; 221a; 221b; 221c ; 122; 222a; 222b; 222c) are arranged to transfer electric power to the marine structure (101) at the voltage supplied by the sub-station (102).

20. System according any one of claims 11-19, characterized in that the first and second cable sections (121, 122) comprise a fiber optic cable.