The invention concerns wind power plants. More specifically, the invention concerns a wind power plant designed as a semi-submersible trimaran, as set out by the preamble of claim 1.

Background of the invention

The prior art includes WO 2019/172773 Al, which describes a wind power plant comprising a frame on a floating pontoon wherein the frame is constructed as a lattice rig upright on the pontoon, forming a plurality of rectangular or square openings in the rig for receiving respective interchangeable wind turbine generators with associated drive propellers driven by incoming wind. Each wind turbine generator is arranged to travel up the rear of the rig and through the openings towards the front of the rig. Each turbine generator comprises one or more pairs of propeller blades forming a propeller set having a blade diameter defining the turbine rotational plane, each propeller set being arranged at a distance from the front side of the rig, to be rotated by the incoming wind towards the rig

The prior art also includes WO 2016/122327 Al, which describes a wind power plant comprising a platform having a deck and a frame. The frame comprises a plurality of generator stations, each configured for receiving and supporting a respective removable wind turbine generator. Generator conveyance means are configured and arranged for moving a wind turbine generator between the deck and a generator station. The wind turbine generator comprises a housing in which a turbine is rotatably arranged. The turbine comprising a plurality of blades interconnected by a peripheral rim; and the rim comprises a plurality of magnets. The housing comprises a plurality of coils arranged in close proximity to the peripheral rim. The platform may be a floating platform, supported by at least a main hull and connectable to a seabed via turret mooring, whereby the power plant is allowed to weathervane.

The object of this invention is to provide certain improvements to the prior art, such as but not limited to, design of the trimaran hull, structural design of the matrix sail, design of the elevator system, integration of the matrix sail on the trimaran hull, and installation of electrical cables between transformer stations and turbines.

Summary of the invention

The invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention.

It is thus provided a floating wind power plant designed as a semi-submersible trimaran characterized by

- an elongated hull arranged to be submerged in a body ow water, wherein the hull comprises a two buoyant structures and one of the buoyant structures comprises a turret whereby the hull may be moored to a seabed;

- wherein a deck structure is arranged on the other buoyant structure and extending transversely to the hull and being supported by first and second lateral buoyant structures,

- wherein the entire plant may rotate around the turret. In one embodiment, the wind power plant comprises a matrix sail arranged on and supported by the deck structure, comprising a plurality of forward towers that are perpendicular to the deck structure and a plurality of rear towers that are inclined towards the forward towers, whereby the matrix sail is stable without the need for inclined bracing struts behind the matrix sail. In one embodiment, the forward towers are connected by inclined elements, such that the entire forward row of towers comprise a truss structure, and wherein wind turbines are connected to the inclined elements.

In one embodiment, the wind power plant further comprises a turbine elevator comprising an elevator platform with two arms being movably connected to and supported by respective towers, and an opening is formed between the elevator platform and the towers and the inclined elements.

In one embodiment, a rail arrangement is arranged on the elevator platform and a smaller platform on which a wind turbine may be placed with its two rotor blades in a horizontal position, and wherein the wind turbine may be moved sideways such that the rotor blades may be rotated about its axis without touching the matrix sail members, and where the one rotor blade is located in an opening between the elevator platform and a tower truss bracing when the elevator platform has a greater height above the platform deck than the rotor radius.

In one embodiment, the matrix sail is assembled in a horizontal position and where the rear row of towers are connected to the platform deck with a hinge device and then lifted or pulled into a vertical position before it is attached to the platform deck.

In one embodiment, the matrix sail is assembled on the trimaran deck, commencing with assembling the top section and then jacking it sufficiently high in order to insert new tower sections and bracings, and then repeating the cycle until the entire the matrix sail is completed and permanently connected to the platform deck.

In one embodiment, all cables between the wind turbines in the matrix sail and an electrical conversion system, is arranged in the forward row of towers, in that attachment devices are established inside the towers and the cables are connected to these points and individual guides which prevent the cables from moving and keep them at a correct distance from each other.

Brief description of the drawings

These and other characteristics of the invention will become clear from the following descriptions of an embodiment of the invention, given as non-restrictive example, with reference to the attached schematic drawings, wherein:

Figure l is a perspective view of an embodiment of the wind power plant according to the invention;

Figure 2 is perspective view of an elevator device according to the invention, in a position for retrieving a wind turbine from its position in a matrix structure;

Figure 3 is a perspective view of the elevator device supporting a wind turbine; Figures 4 and 5 are perspective views of steps of installing of removing a wind turbine by means of the invented elevator device;

Figure 6 is a perspective view of a wind turbine supported by the invented elevator device and arranged behind the forward row of towers; Figure 7 is a perspective view of a cable installation configuration; and

Figure 8 is a perspective view of a fastener plate comprising a plurality of cable guides

Detailed description of embodiments of the invention

The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ’’upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

Design of the trimaran hull (see figure 1) Figure 1 illustrates an embodiment of the wind power plant according to the invention floating in a body of water W. The power plant comprises a semi-submersible trimaran hull 1 having a central pontoon 2 and first and second lateral pontoons 3,4 arranged on opposite sides of the central pontoon. The pontoons 2,3,4 may be vertical cylinders, but the invention shall not be limited to such design. The pontoons 2, 3, 4 are interconnected via a deck structure 5, which also serves as a foundation for a matrix structure 6, hereinafter referred to as a matrix sail 6. The matrix sail 6 comprises a plurality of columns (preferably steel columns) 7a, 8a that are interconnected by bracings 9, 10. The columns 7a, 8a form a forward row of towers 7, and a rear row of towers 10. In one embodiment, the matrix sail 6 may have dimensions of 300 meters tall and 300 meters wide. This requires a trimaran design that ensures lateral stability, but the trimaran must also have a considerable length. The entire concept must be designed to withstand 100-year waves. The challenge is thus that the trimaran natural frequency will be very close to the frequency of the largest waves. This could easily induce large pitching movements on the trimaran, and the acceleration at the top of the matrix sail may become too large to handle. Designing the matrix sail (i.e. the vertical towers) such that the towers can withstand the large acceleration is possible but not very efficient. According to the invention it is thus necessary to change the trimaran design, compared to disclosures in earlier patent applications, such that also its natural frequency is changed.

This is achieved as follows: Instead of using three parallel hulls, as in the prior art, pontoons (here: vertical cylinders) 2,3,4 are used. The central pontoon 2 is arranged approximately directly below the matrix sail 6, and a forward structure 23 where the turret and the electric swivel (not shown) for mooring are placed. Such turret and swivel mooring is well known in the art, and need therefore not be described in detail. The central pontoon 2 and the forward structure 23 are interconnected via a hull lb below the water surface. This sub-surface hull has a flat surface. The first and second lateral pontoons 3,4 (e.g. two vertical cylinders) provide buoyancy and stability. These pontoons are connected to the platform deck 5, which supports the matrix sail. Calculations show that designing the concept in this fashion reduces hull movements - laterally and in the longitudinal direction (i.e. pitch) - to an absolute minimum and well inside all requirements regarding safety and functionality for the sensitive electric equipment. The design criterion has been 1000-year waves and wind speed.

Structural design of the matrix sail (figures k 2)

The lateral bracing of the concept is designed to obtain sufficient lateral strength in the matrix sail 6 and to avoid large sail areas and structures exposed to the wind, that are used solely for bracing and not for generation of electricity. According to the invention, this is solved by establishing truss bracings in the forward vertical towers 7 as an integrated part of the construction. The wind turbines 11 are also mounted on these truss bracings. The rear row of towers 8 also comprise truss bracing.

As a non-limiting example, the following design dimensions may be relevant: A total of 13 columns laterally and nine columns vertically upwards. This accommodates 13 wind turbines 11 laterally and nine wind turbines 11 vertically. Each tower between the columns has a height of approximately 300 meters and a diameter of 1.2 meter. The wind turbines with propeller blades 12 are mounted such that the propeller blades extend outside of the forward towers (see figure 2). Inclined pipes (truss bracings) 10 with a diameter of 1 meter extend between each of these towers. These inclined pipes act as a truss and provide the sail with the required lateral bracing without generating any particular drag. In addition to the forward row of towers 7, the matrix sail 6 comprises a rearward, inclined, row of towers 8. In the present example, the distance between the two rows of towers is 45 meters at the foundation (i.e. at the deck 5) and 15 meters at the top. A number of bracings (trusses) are used between the two rows of towers and between the rearward towers. Designing the matrix sail in this manner removes the requirement for inclined bracings behind the sail, as the sail - by virtue of its design - has sufficient intrinsic strength and stability. This sail design will also exhibit very good lateral bracing and will be virtually self-supporting.

The conceptual change also necessitates a design change of the wind turbine propellers (rotors). A change from four-bladed rotors to rotors with only two blades is necessary. This will retain the possibility of lifting up the generator with a two-bladed rotor on the rear side of the forward row of towers 7 and push the wind turbine generator forward, such that the propeller blades 12 are arranged in front of the forward row of towers 7 (see figure 2). Design of the elevator system (figures 2-6)

Due to the changes made to the matrix sail 6, with the inclined truss braces between the forward towers and the change to rotors with only two blades, a completely new elevator system design is also required. The requirement for the elevator system is that turbines may easily be placed in - removed from - the matrix sail. The invented elevator is very compact and requires little assembly work at heights above the trimaran deck 5. As the design on the forward and rear towers does not allow access stairs or ladders inside the towers, a separate rescue system in connection with the elevator system must be established, that allows for safe evacuation from an elevator with technical problems and which has become immobilized high up in the matrix sail. The elevator 13 comprises an elevator platform 13a with wheels (not shown) underneath, such that is may be moved sideways down onto the deck/platform behind the forward row of towers 7. In one embodiment, two fixed arms 14 are arranged on the elevator platform 13a, and two small guide wheels (not shown) are mounted on the arms. The guide wheels run in guide rails (not shown) integrated in the forward towers 7. A winch system (not shown), in which one or more winches are placed on the platform 5 below the matrix sail, is configured to move the elevator 13 up and down along the matrix sail columns. It shall be understood that the elevator may be supported by the towers and moved with respect to the towers by other, technically similar, support and movement devices.

By virtue of the design of the two arms 14, there will be an open area - typically e.g. 2 meters between the elevator platform 13a and the towers and the inclined bracings.

An important aspect is that the propeller diameter is greater than the distance between the towers in the forward -most row of towers 7. Therefore, when the generator with its propeller is to be pushed through the matrix opening, the propeller angle with the horizontal axis may have a certain angle. But because the propeller diameter is greater than the matrix opening, the propeller - when rotated - with the propeller wing which is turned downwards will abut against one of the arms on the elevator platform. This is solved as follows. The elevator with the turbine on top, is first run upwards approximately 10 meters. Referring to figure 2, a rail arrangement is established on the elevator platform 13a, comprising a first railway 16 whereby the wind turbine generator 11 may be moved back and forth towards and away from the columns 7a, and a second railway 16 whereby the wind turbine generator 11 may be moved back and forth sideways, generally perpendicularly to the first railway. It shall be understood that the wind turbine generator may be supported by the platform 13a and moved with respect to the platform 13a by other, technically similar, support and movement devices.

A small carriage (not shown) with wheels or similar (not shown) sits on this rail arrangement, and the wind turbine 11 with its propellers 12 is fastened on top of this platform. This carriage may be pushed sideways, and when it has been moved far enough, the propeller may be rotated down without colliding with one of the arms. The other propeller blade, which will move upwards, may also move freely without touching the bracings between the rear and forward towers. When the propeller has achieved an angle of about 50 degrees to the vertical plane, the elevator 13 may be moved upwards without colliding with any of the towers or the inclined truss bracings. When the elevator has reached the desired matrix opening, a small bridge (not shown) is established between the elevator platform 13a and the wind turbine mount (not shown) on the inclined truss bracing, and the turbine with its propellers is pushed into position and electrical cables are connected to the turbine.

When a turbine 11 is to be removed, e.g. for service or repair, the cycle is executed in reverse. That is, the turbine elevator 13 is moved up to the appropriate matrix opening, the bridge is established and the propeller is arranged in a position such that it does not collide with the inclined truss bracing. It is then pulled in onto the turbine elevator- platform. The turbine elevator is lowered, until it is about 10 meters above the platform deck and the turbine is run sideways on the elevator platform such that the propeller may rotate in horizontal position before the turbine elevator is lowered completely down onto the platform deck and run further to the service station for possible repair.

In this concept there is no access, i.e. stairs or elevator device, inside the vertical towers. An external rescue system must therefore be established, such that personnel are able to get from the turbine elevator and down onto the platform deck in a safe and reliable manner, should the turbine elevator malfunction while high up in the matrix sail. According to the invention, this is solved as follows: A small rescue capsule (not shown) is arranged on the turbine elevator platform 13a, and can accommodate e.g. 3-4 persons. If the turbine elevator malfunctions, the personnel can walk into the rescue capsule. A guide wheel (not shown) is then manually connected to one of the guide rails which is connected to one of the vertical towers used by the turbine elevator. A winch drum is arranged inside the rescue capsule, and the wire from this drum is connected to the turbine elevator platform. Personnel may now manually lower themselves down to the platform deck in a safe and reliable manner, completely independent of electrical installations. Integrating the matrix sail on the trimaran hull:

According to the invention, in this concept the matrix sail 6 is integrated with the trimaran platform deck 5. In a non-limiting example, the matrix sail 6 is approximately 300 meters wide and 300 meters tall. According to the invention, two alternative methods remain for building and integrating the sail in this concept.

Alternative 1 : A suitable area on dry land is designated, in practice a quay with a length of at least 300 meters (corresponding to the sail width) and an area on the quay having a width of 60 to 100 meters. The depth at the edge of the quay must be minimum 10 meters (the trimaran draft). Construction of the matrix sail is then commenced on the quay, and it is pushed from the edge of the quay and onto barges as it is being built. In this manner, the entire sail is built horizontally with the rearmost row of towers down towards the quay. The trimaran is then positioned such that the lowermost towers are in the correct position, where they are to be connected to the platform deck. A hinge device is arranged here and the towers are physically connected to the trimaran platform deck. The top of the sail, which is lying horizontally on the quay, is now being lifted up by large jacks or is being pulled across large wheels on the quay edge, where the wheels have a height which is greater than the height of the hinge points. The top of the sail will now be elevated as the structure is pulled towards the edge of the quay. In addition, at least two large crane vessels are arranged adjacent to the platform front side. These crane [now] barges lift the sail up, together with the jacks on land (or the other system as described) and the matrix sail is finally erected to a vertical position on top of the trimaran platform deck, and all towers may be welded to the platform deck.

Alternative 2: Another method of sail integration will be to build the sail on the platform deck, where the process is commenced by building the sail top section in its full width, and jacking sections in the entire width of the sail upwards by one or more hydraulic jacks, and inserting new tower elements along in the process. All bracings and the inclined truss bracings are installed as the sail is jacked upwards. In our concept, the sail has a width at the lowermost position (between the forward-most and rear-most row of towers) of 45 meters and a width at the top of 15 meters. This makes the sail relatively stable, but external bracings, in the form of additional support struts or wires, will nonetheless be necessary during the construction period. The jacks with bidirectional cylinders could also function as additional support points in an emergency situation.

Installation of electrical cables between omformer stations and turbines (figures 7. 8) The matrix sail 6 according to the present invention may comprise several tens of turbines, in for example 117. The uppermost turbines 11 are located almost 300 meters above the platform deck 5. Relatively thick, insulated electrical power cables 19 are routed down to and below the platform deck 5, where they are connected to an electrical converter system (not shown). The cables can be inspected and easily replaced if cable failures should occur. The cables 19 are installed in the forward towers. In one embodiment, these have an internal diameter of 110 cm. Holes have been arranged in the platform deck below each of the forward towers, where all cables to a vertical row of turbines are arranged. The cables are pulled upwards inside the towers, each to the correct position in relation to the turbine to which it is to be connected. In order to achieve this, small hatches 21 are provided in the forward tower wall 18 where the inclined truss bracings lower parts are connected to the vertical towers. The cables are pulled further through the inclined truss bracings, up to the turbine attachment and there through a small hole and up to the turbine. In order to prevent the cables 19 from moving back and forth inside the vertical towers when the concept is moving in large waves, fastener plates 20 comprising a plurality of cable guides 22 are arranged at certain intervals inside the towers, whereby the cables are immobilized and not damaged. If cable is damaged, it will easily be disconnected from the turbine, lowered down, and a new cable may be pulled up.