Inter-array cables for floating platforms

Abstract

An inter-array cable (IAC) assembly, system, and method are disclosed in which a conductive cable is suspended below sea level and above the seabed between two floating platforms, e.g., floating wind turbine platforms. The cable includes one or more floating sections, reducing the weight of the suspended cable, thereby reducing static tension at the floating platform connections, and providing geometric flexibility, allowing the IAC to respond to platform motions.

Description

[Technical Field]

[0001] Cross-references to related cases This application claims priority to U.S. Provisional Patent Application No. 63 / 068,486, filed August 21, 2020, entitled "Inter-Array Cable For Floating Platforms," ​​which is incorporated herein by reference.

[0002] This application is related to U.S. patent application Ser. No. 14 / 924,448, filed October 27, 2015, entitled "Connection System For Array Cables Of Disconnectable Offshore Energy Devices," now U.S. Patent No. 10,421,524; PCT application Ser. No. PCT / US15 / 57636, filed October 27, 2015, entitled "Connection System For Array Cables Of Disconnectable Offshore Energy Devices," and U.S. patent application Ser. No. 16 / 568,798, filed September 12, 2019, entitled "Floating Electrical Connection System For Offshore Energy Devices," now U.S. Patent No. 10,858,075, each of which is incorporated herein by reference. [Background technology]

[0003] FIELD OF THE INVENTION The present application relates to offshore energy conversion units. In particular, the technology disclosed herein provides electrical connections between individual offshore energy conversion units of an offshore energy facility.

[0004] A floating offshore energy facility, such as a floating wind turbine platform (FWTP), may contain 100 individual FWTPs, each thousands of meters away from the next. The power generated by a single FWTP can be 10 MW or more, and such power often needs to be transmitted to shore via cables that carry the power of multiple FWTPs. A factor in selecting an FWTP on a platform fixed to the seabed is the ocean depth. Because FWTPs are typically selected for deep water, the cables between FWTPs that reach the seabed can be very long. Furthermore, each FWTP experiences dynamic motion due to changing sea conditions, increasing the required cable length and the stresses the cables must withstand. Furthermore, the intended lifespan of an FWTP energy facility can reach several decades.

[0005] Therefore, there is a need for a cable for electrically connecting floating platforms that addresses the particular problems.

[0006] These embodiments are illustrated by way of example, and not by way of limitation, in the accompanying drawings. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 2] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 3] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 4] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 5] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 6]FIG. 1 is a schematic diagram illustrating a side view of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 7] 7 is a schematic diagram showing a more detailed embodiment of the section shown in FIG. 6. FIG. [Figure 8] 1 is a partial perspective view illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. FIG. [Figure 9] 7 is a diagram showing the section shown in FIG. 6 in more detail. [Figure 10] 1 is a diagram illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 11] 1 is a diagram illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 12] 1 is a diagram illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 13] 1 is a diagram illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 14] 1 is a diagram illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. [Figure 15] 1 is a diagram illustrating aspects of one embodiment of an inter-array cable (IAC) for a floating platform. DETAILED DESCRIPTION OF THE INVENTION

[0008] Offshore energy facilities may include floating platforms of over 100 a, such as FWTPs, each equipped with an energy generating source such as a 10 MW wind turbine, giving the entire facility a total power capacity of 1 GW. Such facilities can be located in open ocean waters at depths exceeding 800 m.

[0009] An inter-array cable (IAC) is a cable that electrically connects two FWTPs. In deep water, avoiding the IAC touching the seabed between the FWTPs ("touchdown") offers significant advantages. First, the cable length is significantly reduced, as it no longer needs to be laid on the seabed between the two platforms. Second, the static tension in the cable at the FWTP connection increases with increasing water depth due to the longer suspended cable length and weight.

[0010] Configurations where the IAC is suspended between the FWTPs are not driven by this phenomenon as they are uncorrelated with the bathymetry. This also means that seabed irregularities do not need to be taken into account in suspended IAC configurations and the spacing of the FWTP units is the main design factor and can therefore be more standardised across the wind farm.

[0011] In one embodiment, the IAC assembly and system is based on a suspended configuration where the cable never touches the seabed. Buoyancy elements are clamped onto six different sections along the length of the cable. The additional net buoyancy added to specific sections of the cable has two main advantages: first, it reduces the weight of the suspended cable, thereby reducing static tension at the FWTP connections; and second, it provides geometric flexibility, allowing the IAC to accommodate large FWTP motions. This configuration is a type of "floating lazy wave" where multiple "lazy waves" exist.

[0012] System Overview In an embodiment, the cable assembly uses IACs to facilitate electrical connections between FWTPs, and these IACs are mated with accessories and incorporate some or all of the following features: subsea floating of the IAC between FWTPs; position control of the IAC using a dedicated mooring system for the IAC (called a tether, including anchors); compliance with platform motion during turbine operation and changing weather and ocean conditions; IAC installation sequence disconnection to allow for installation of the IAC both before or after FWTP installation, potentially for installation in front of the FWTP to facilitate location of the cable end using a surface buoy or floating I-tube (FIT), or to allow the cable end to be suspended in a surface column; and controlled release and station retention of the IAC in the event of planned disconnection of the FWTP or failure of the FWTP's station retention system (SKS), which typically includes an anchor attached by a tether.

[0013] When this disclosure refers to multiple LazyWave installations, it refers to design studies.

[0014] Overview of the operating system FIG. 1 is a schematic diagram showing a side view of one embodiment of an inter-array cable (IAC) for a floating platform. In FIG. 1, an IAC assembly 100a is in operation and connected between a FWTP 30 and a FTWP 40. The FWTPs 30, 40 are maintained in place by SKSs 50, 60, respectively. The IAC assembly is shown submerged and suspended between a tidal level 10 and the seabed 20. In FIG. 1, the IAC assembly 100a is shown to include an SKS for an insulated conductive cable 110, a levitation assembly 120, and a tether 130 having an anchor 140. For ease of explanation, cable sections 110a...110g refer to individual sections of the cable 110, levitation assemblies 120a...120f refer to the particular levitation assembly 120, tethers 130a, 130b refer to the particular tether 130, and anchors 140a, 140b refer to the particular anchor 140. This pattern is used throughout to refer to general elements or specific elements. Disclosure relating to a general element applies to each specific instance of that element, and disclosure relating to a specific element applies to the general population of that element unless otherwise stated. While six floatation assemblies 120 are shown in FIG. 1, embodiments of the IAC assembly 100a may include more or fewer floatation assemblies 120, as shown in FIGS. 4 and 5.

[0015] In the embodiment of FIG. 1 , the wave shape of the IAC assembly 100a is achieved by having the levitation assembly 120 fitted over the cable 110a and providing buoyancy over several sections of the cable 110a (the number of sections varies depending on the location; here, there are six sections in FIG. 1 ). This “lazy wave” shape provides mechanical compliance to the system, allowing relative movement of the FWTPs 30, 40. In one embodiment, the IAC assembly 100a can be located at a depth below the wave action zone and within a range that minimizes current loads. The tether 130 limits lateral movement of the IAC due to current or wind. The tether 130 also helps control the position of the IAC assembly 100a when at least one end is not connected to the FWTP (see the following section). The tether 130 can also be used to provide vertical restraint in the event that the levitation module is configured to cause a net uplift on the cable. In one embodiment, the contact points with the FWTP structure can be made using a concept known as the Floating I-Tube (FIT), disclosed in cross-referenced U.S. Pat. No. 10,421,524, which is incorporated by reference.

[0016] In embodiments, the cable 110 can include any suitable conductor, but generally, two types of cables are considered: one with an aluminum (Al) wire core and a steel wire armor layer, and the other with a copper (Cu) wire core and a steel wire armor layer. Due to its lighter weight underwater, aluminum requires less buoyancy than cables based on copper conductors. Copper cores are the industry's most common choice for dynamic power cables due to their superior fatigue resistance and electrical properties. The main drawbacks of copper are the high cost and weight characteristics of such elements.

[0017] In one embodiment, one or both cables may be of dry design and insulated with XLPE. The sheathing required to withstand such loads may be stronger than that typically selected for standard shallow-water applications. Steel wire sheathing may be preferred over more advanced solutions such as carbon fiber sheathing due to the maturity of such technology. Due to the larger inner diameter of aluminum core wires, the design of such cables may be based on only fewer armor layers (e.g., four layers instead of five). These layers were selected to give the two cables similar mechanical strength.

[0018] In one embodiment, both cables can be of wet design, as the water-blocking materials required for dry designs generally have low fatigue strength and wet designs are recommended for dynamic environments.

[0019] In one embodiment, the properties of both cables can be selected to withstand a common expected safe design tension, e.g., 300 kN, based on the load at their connection to the floating platform. As a result, the aluminum cable may have an area of ​​800 mm^2, a diameter of 0.172 m, a linear weight in air of 55.2 kg / m, and a linear weight in water of 31.4 kg / m, and the copper cable may have an area of ​​630 mm^2, a diameter of 0.166 m, a linear weight in air of 57.8 kg / m, and a linear weight in water of 35.6 kg / m.

[0020] It is important to note that since cables are project specific, there are no standardized cables and cable manufacturers typically tailor subsea power cables to the application at hand. Therefore, the cable parameters for a particular installation are determined based on the design, operational, and environmental parameters of the installation.

[0021] For offshore wind farms with long platform-to-platform distances (more than 1 nautical mile) and in deep water environments (e.g., more than 1000 m), the safe working load at the required tension on the cables was set at 300 kN. This value was selected prior to design screening based on the dynamic loads that the cables were expected to be able to withstand in the worst case for both touchdown and suspension configurations.

[0022] In one embodiment, with 2580 m of aluminum cable 110 (800 mm^2) connected between the floating wind turbine platforms, the flotation assemblies 120 of the flotation modules 700 (FIG. 7) distributed over 100 m of cable 110 were located at 240 m, 640 m, 1040 m, 1440 m, 1840 m, and 2240 m along the cable, reaching a maximum depth of 541 m. In one embodiment, with 2570 m of copper cable 110 (630 mm^2) connected between the floating wind turbine platforms, the flotation assemblies 120 of the flotation modules 700 (FIG. 7) distributed over 115 m were located at 240 m, 635 m, 1030 m, 1425 m, 1820 m, and 2215 m along the cable, reaching a maximum depth of 518 m.

[0023] With respect to embodiments of cable 110, the cable's internal components (e.g., armor layers) were not modeled in the simulations discussed with respect to Tables 2 and 3. These simulations were based on the cable's overall properties, including, for example, overall diameter, weight, and stiffness. Thus, if one simulation assumes that these overall properties are likely to be achieved with (X) number of armor layers and a first inner wire diameter, and a second simulation assumes that these same properties are likely to be achieved with (Y) number of armor layers and a second inner wire diameter, both simulations will show similar results. In other words, the discussion of several armor layers is an indication of how the cross section of the cable will appear, but does not affect the simulations. Thus, embodiments of cable 110 can have a different number of armor layers, for example, from 1 to 6, without departing from the teachings herein.

[0024] Pre-Installation Overview FIG. 2 is a schematic diagram showing a side view of one embodiment of an IAC assembly 100a for a floating platform. FIG. 2 illustrates aspects of the IAC assembly 100a before installation of the FWTPs 30, 40 or after their removal. Instead of the FWTPs 30, 40, the SKSs 50, 60 are connected to pickup aids 250, 260, which may be simple floating modules, to prevent the ends of the tethers from sinking. In this embodiment, the pickup aids 250, 260 are shown suspended below the sea surface 10, for example, to prevent potential collisions. FIG. 2 shows pickup aids 210a, 210b attached to the end of cable 110a. In an embodiment, pickup aid 210 may include a simple surface buoy or FIT. In an embodiment, the pickup aids 210 maintain the end of the cable 110 at the surface 10 to facilitate retrieval and are themselves anchored to the seabed 20 by tethers 212 (212a, 212b) that include anchors 214 (214a, 214b), maintaining the position of the cable end near the location of the associated FWTP. The pickup aids 210 are shown floating on the surface 10 because they are positioned relatively close to the appropriate location of the FWTP and it is generally preferable to keep the end of the cable 110 dry. FIG. 2 illustrates that the IAC assembly 110 and SKSs 50, 60 can be laid before the FWTPs 30, 40 are installed. After the IAC assembly 100a is connected to the FWTPs 30, 40, the anchors can be temporarily removed to allow the end of the IAC assembly 100a to move freely with the movement of the FWTP.

[0025] It is notable that FWTPs 30, 40 are absent in FIG. 2 . Pickup aids 210 (e.g., FITs or surface buoys) await installation of the FWTP. Accordingly, embodiments provide for IAC assembly 100a to be installed before or after the moorings or FWTPs are installed. In other words, IAC assembly 100a can be installed in a sequence separate from both the mooring installation and the platform installation. As shown in FIG. 2 , IAC assembly 100a can be temporarily abandoned and allowed to float using surface module assembly 120 and pickup aids 210, but may be connected to the seabed using permanent tether 130 and temporary tether 212.

[0026] Temporary system placement FIG. 3 is a schematic diagram showing a side view of one embodiment of an IAC assembly 100a for a floating platform. FIG. 3 shows IAC assemblies 100a, 100b in operation with the FWTP 30 temporarily disconnected. IAC assembly 100b is identical to IAC assembly 100a and includes cable 112 identical to cable 110, floatation assembly 122 identical to floatation assembly 120, and tether identical to tether 130. IAC assembly 100b is connected to the FWTP 35 using an SKS70. The arrangement of FIG. 3 allows the FWTP 30 to be disconnected while maintaining electrical continuity across the rest of the wind farm by connecting cables 110a, 110b within a FIT version pickup aid 210a (FIT 210a). For example, the FWTP 30 can be towed to a shipyard for repair, and electrical continuity can be maintained by connecting cables 110a, 110b within FIT 210a. When the FWTP 30 returns, the FWTP may be reconnected to the SKS 50, the FIT 210a may be loaded and reconnected to the turbine of the FWTP 30, and the temporary tether of the FIT 210a may be cut and stowed (or a pick-up aid may be equipped).

[0027] System fail-safe function Figure 3 illustrates the fail-safe function of the system provided by tether 130 associated with cable 110 and the tether associated with FIT 210a. As shown in Figure 3, an electrical connection is made inside the FIT between IAC assembly 100a from FWTP1 and IAC assembly 100a from FWTP3. Because the tether remains in place, the FIT remains positioned for the return of FWTP2.

[0028] FIG. 4 is a schematic diagram showing a side view of one embodiment of an IAC assembly 400 for a floating platform. The descriptions of IAC assembly 100a and flotation assembly 120 apply to IAC assembly 400 and flotation assembly 420, except for the number of flotation assemblies. FIG. 4 shows that IAC assembly 400 includes only one flotation assembly 420, which divides cable 110 into larger sections 410a, 410b. Flotation assembly 420 is relatively larger than each flotation assembly 120 because assembly 420 is optimized to support cable 110 above the seabed and below the ocean surface. As seen in Tables 2 and 3, flotation assembly 420 provides less total buoyancy than the collection of flotation assemblies 120.

[0029] FIG. 5 is a schematic diagram showing a side view of one embodiment of an IAC assembly 500 for a floating platform. The descriptions of IAC assembly 100a and flotation assembly 120 apply to IAC assembly 500 and flotation assembly 520, except for the number of flotation assemblies. FIG. 5 shows that IAC assembly 500 can include two flotation assemblies 520a, 520b that divide cable 110 into larger sections 510a, 510b, 510c. Each flotation assembly 520 is relatively larger than each flotation assembly 120 because assembly 520 is optimized to support cable 110 above the seabed and below the ocean surface. As seen in Tables 2 and 3, flotation assembly 520 provides less total buoyancy than the collection of flotation assemblies 120.

[0030] FIG. 6 is a schematic diagram illustrating a side view of one embodiment of an IAC assembly 100a for a floating platform. In FIG. 6, an exemplary spacing 602 is 2,000 m, an exemplary maximum depth 604 is 500 m, and an exemplary wave action depth 606 is 75 m. Comparing FIG. 6 with FIGS. 1-3 shows that with the IAC assembly 100a installed, individual flotation assemblies 120 can float at different depths. The different depths can be due to several factors, including, for example, the distance of the cable 100a supported by a given flotation assembly 120, the different buoyancies of the different flotation assemblies 120, tension at the connections from the cable sections 110a, 110b to the FWTPs 30, 40, and the effects of biological colonization (marine growth) on the cable sections. Thus, Figure 1 shows that the IAC assembly 100a is assumed to have a relatively straight shape because the floating modules 120a...120f of the IAC assembly 100a are at a relatively uniform depth in the sea, Figure 2 shows that the IAC assembly 100a is assumed to have a bow shape because the floating modules 120a...120f are at different depths, and Figure 6 shows that the IAC assembly 100a is assumed to have a reverse bow shape because the floating assemblies 120a...120f are at different depths.

[0031] 1, 2, and 6 all share a common feature: they have an arcuate shape that is convex toward the sea surface side of the IAC assembly 100. As a result, each flotation assembly 120 and the unsupported sections on either side of the cable 110 impart a slight wave (a "lazy wave") to the IAC 100. Each lazy wave provides an element of slack in the IAC assembly 100, allowing it to adapt to the intended movement of the FWTP 30, 40 without being subjected to excessive tension.

[0032] 6 further illustrates that the flotation sections 120a...120f are distributed along the cable 110, with each section being buoyant such that it is below a wave action zone 606. The wave action zone 606 will vary depending on the particular environmental and geographical features at a particular location. Configuring the flotation assembly 120 with buoyancy that causes it to float in the ocean below the wave action zone 606 may reduce fatigue in the cable 110 by reducing movement of the flotation assembly 120 due to currents caused by wave action.

[0033] FIG. 7 is a schematic diagram showing more detailed aspects of the section shown in FIG. 6. FIG. 7 illustrates that levitation assembly 120 may include individual levitation modules 700 connected to cable 110. While FIG. 7 shows three levitation modules 700a...700c connected to cable 110, in embodiments, the number may vary depending on the buoyancy provided by the particular levitation modules and the total buoyancy required. For example, FIG. 7 shows that each levitation assembly 120 may have 11 levitation modules. FIG. 6 shows that levitation modules 700 have a diameter 702, a length 704, and a pitch 706. In one embodiment, better results were achieved when the pitch exceeded 5 m, and the same buoyancy was distributed over larger sections.

[0034] Figure 8 is a drawing showing a portion of one embodiment of levitation module 700. In Figure 8, levitation module 700 is shown without the rear half of body 810. Levitation module 700 includes lift holes 802, securing straps 804, internal clamps 806, and two tensioning assemblies 808. The missing rear half of body 810 mirrors the half shown in tensioning assemblies 808 that house cables 110 and clamps 806.

[0035] In one embodiment, an exemplary levitation module 700 may have an outer diameter 702 of 1.3 m, a length 704 of 1.2 m, a density of 350 kg / m^3, a pitch 706 of 10 m, and a displacement of approximately 1600 kg (copper cable is slightly heavier than aluminum).

[0036] In one embodiment, the flotation modules 700 may be cylindrical polyethylene structures (typically in a lazy wave configuration) filled with a buoyant material and distributed along a section of cable 110. Depending on the water depth, different chemicals and / or ratios may be used to fill the modules. Each flotation module 700 provides an upward thrust to the cable, reducing tension, particularly during hang-off. The requirements of the selected IAC configuration establish the amount of net buoyancy required for a particular cable section. Based on these requirements, optimization can be performed to select the most cost-effective and technically performant module design. In embodiments, other types of flotation modules may be used; for example, buoys may be attached to the cable 110 in a similar distribution arrangement to the flotation modules 700 within the flotation assembly 120.

[0037] Additionally, in embodiments, sections of cable 110 may be made buoyant by adding a buoyant coating to the cable or by making the sections buoyant in other ways.

[0038] FIG. 9 is a diagram illustrating in more detail the sections shown in FIG. 6. FIG. 9 shows that, for example, after FWTP 30 has been returned to its position between FWTPs 34, 40 (see FIG. 3), a FIT 900 (the same FIT described with reference to pickup aid 210) can be used to connect cable 110 to FWTP 30 and cable 112 to FWTP 30. In FIG. 9, FWTP 30 is shown to include cross members 32, 34. FIT 900 is attached to cross members 32, 34 with brackets. Cable section 110a enters FIT 900 through bend stabiliser 910a, which is connected to bend stabiliser receptacle 908a. Cable 110a extends within splash band (or FIT body) 906 of FIT 900 to a hang-off and connector housing, within which cable 110a is connected to cabling 902 from an energy generating device, such as a wind turbine generator. Cable section 112g is similarly routed and connected to cabling 902.

[0039] As shown in Figure 9, the FIT900 is rigidly attached to the FWTP30 during normal operation. To disconnect the FIT900 from the FWTP30, it is lowered to the floating draft, detached from the bracket, and towed away from the FWTP30 by a small support vessel. This is only necessary while the FWTP30's station support system is disconnected. The FIT900 is designed to support two or more electrical cables, and the FWTP30 is onshore for operational and maintenance activities. Prior to deployment, the FIT900's enclosed bay can be pressurized to ensure the necessary buoyancy. After major operational and maintenance operations, the FWTP30 can be moved into its installed position and connected to the SKS70. The disconnection process is then reversed, and the FIT900 is pushed back onto the platform by a small vessel. Fenders located at the bottom of the FWTP30 guide the FIT900 in place and restrict its movement. A winch mounted on the FWTP30 can be used to lift the FIT900. Winch tension varies depending on water depth and IAC assembly.

[0040] 10 is a diagram illustrating an embodiment of FIT 900 in which cable section 110 enters bend stiffener 910 and extends through latch mechanism 908 connected to inner tube 1002, which itself extends into splash zone 906. Section 1000 indicates the relative location of the bottom of the column of FWTP 30, for example, where a water seal plate may be located.

[0041] 11 shows a cable section 110 passing through a bend sinter 910. In one embodiment, the bend sinter 910 is a conical / tapered element, typically made from polyurethane. The bend sinter 910 is used to locally transition the stiffness applied to the cable 110 and maintain curvature and bending stresses within acceptable limits, preventing fatigue and overbending failure. The bend sinter 910 is suitable for dynamic loading. A bend sinter 910 is typically required when the cable enters the FIT.

[0042] FIG. 12 is a diagram illustrating aspects of one embodiment of the IAC assembly 100. In FIG. 12, a pull head 1200 is shown attached to the end of the cable 110. The pull head 1200 is a temporary addition to the IAC assembly 100 and is used to pull the top end of the cable to the required position on the platform. The pull head 1200 is designed to withstand the installation loads and subsea environment and to be able to pull the cable 110 through the bend stiffener 910, stiffener receptacle 908, and tube 1002 without causing any damage to the cable or any of its components. Two pull heads are required per IAC assembly 100 to perform the first and second end pull operations. Once the pull head 1200 is removed, the cable section 110a can be electrically connected to the cabling 902.

[0043] In one embodiment, the pick-up aid 210 may include a buoy or one or more flotation modules 700 in place of the FIT 900. Such an arrangement may be used, for example, when the IAC assembly 100 is deployed in front of the FWTP 30. The pick-up aid 210 thus keeps the retraction head 1200 at the surface and accessible for use in pulling the cable 110 through the FIT 900.

[0044] FIG. 13 is a diagram illustrating an embodiment of FIT 900. FIG. 13 shows a hang-off device 1300 through which cable section 110 exits and connects to cabling 902. Hang-off device 1300 is located on top of inner tubing 1002 within hang-off and connector housing 904. Hang-off device 1300 is an assembly that, once connected to the top of tubing 1002 via a flange, supports cable 110 at a suspension point on FWTP 30 before cable 110 reaches electrical connection 1506 (FIG. 15) on cabling 902.

[0045] Figure 14 is a diagram illustrating aspects of one embodiment of the FIT. Shown in Figure 14 is a latch mechanism 908 connecting the bend stiffener 910 to the inner tube 1002. The latch mechanism 908 uses a rigid connection to lock the bend stiffener 910 to the tube 1002, which transfers bending shear and bending moment loads from the cable 110 to the FIT 900. In one embodiment, the bend stiffener may be connected directly to the inner tube 1002.

[0046] FIG. 15 is a diagram illustrating aspects of one embodiment of a FIT. In FIG. 15, FIT 900 is shown connected to FWTP 30 using a clamping system 1502. Hang-off device 1300 is exposed by removing hang-off and connector housing 904. Cable section 110a is connected to electrical connection 1506, to which cabling 902 can be connected. A joint box cover 1504 can be lowered over connection 1506 to enclose FIT 900 and provide buoyancy. Cable 112 (not shown for clarity) is provided with its own hang-off device 1300 and connection 1506. Both cable 110 and cable 112 are covered by joint box cover 1504.

[0047] FIT900 provides for quick connection and reconnection of cables 110, 112, for example, in the case of major maintenance operations. Connection 1506 may be a high voltage T-connector (e.g., as described in the Nexans or NKT catalog). In an embodiment, two or more cables 110 may be routed within FIT900 and connected to cabling 902, as shown by cable 110. When the FWTP 30 needs to be removed from the wind farm, cabling 902 may be disconnected from connection 1506, and joint box cover 1504 may be sealed to FIT900, preparing the FIT900 for deployment at sea.

[0048] System fail-safe function In the event of a failure of the FWTP SKS, e.g., SKS60, the IAC assembly 100 can be released from the FWTP undergoing a large position change. The buoyancy of the FIT 900 and flotation assembly 120 then moves the IAC assembly 100a away from the seabed, and the tethers 130 and 212 ensure that the FIT 900 remains within a small offset from its original FWTP position without drifting towards other assets. The multiple tethers 130, 140 ensure that the failure of one tether will not cause the IAC assembly to drift at the wind farm.

[0049] In one embodiment, to allow for emergency release of the cable, a link mating to the connection assembly can be weakened, such as by hang-off device 1300. In the event of an incident that increases the tension in the cable beyond a safe acceptable limit of tension (such as a fisherman's net or mooring line breakage scenario), the weak link can be released and the cable 110 can be freed before damage occurs to the FIT900 or SKS60.

[0050] In embodiments, tethers 130, 140 connected to the IAC assembly 100 control the position of the IAC assembly 100, particularly when the FWTP is removed. The use of tethers helps keep the IAC assembly 100 away from the FWTP mooring lines. In the upper section, the tethers 130, 140 may include connectors for attaching the tether to the IAC assembly 100. The majority of the tether may be synthetic rope, and the lower section of the tether includes an anchor, e.g., a weight of over 10 tons. Additionally, the use of bend stiffeners or bend restrictors at the tether points and at the transition from the floating section to the free end is optional.

[0051] Advantages of the embodiment Advantages of the concepts discussed herein include a reduced overall IAC length for the entire facility compared to an arrangement where either IAC is laid on the seabed between connected FWTPs; reduced loads on the IAC connections at the FWTP compared to an arrangement where the hang-off supports the weight of the entire suspended length of the IAC cable in a surface column; reduced hydrostatic pressure rating of the IAC assembly 100 compared to an arrangement where the IAC is laid on the seabed between connected assets (this advantage increases with increasing water depth at the FWTP location); a flexible installation procedure compared to techniques where the cable is laid after FWTP connection to the SKS (installation of the IAC assembly 100a can be detached and performed before or after the SKS and / or FWTP); and a temporary termination compared to installation methods that require the cable end to be temporarily left on the seabed before connecting to the FWTP. These include reduced hydrostatic ratings (such as the retraction head 1200); reduced buoyancy requirements for the FIT compared to the arrangement required by the FIT to support the full weight of the suspended IAC against the seabed; simplified equipment and installation procedures compared to current techniques that attempt to reduce touchdown point forces on the riser or umbilical by using midwater arches or deep water rated flotation modules or coatings; drier IAC terminations (the installation procedure does not require the IAC to be left in deep water, and the terminations can be kept dry inside the FIT); continuity (electrical continuity can be maintained if one FWTP unit is removed from the facility); and redundancy (in the event of an SKS failure, IAC connection failure, or IAC tether failure, the tethered floating IAC remains in place and will not drift on the field).

[0052] As described above, embodiments of the IAC can be used in a variety of ways, including a method in which the length of cable required to connect two FWTPs can be reduced by using an IAC assembly to float the cable between the two FWTPs, rather than lowering the cable from one FWTP to the seabed, running it along the seabed, and then raising it to the second FWTP. In one embodiment of the method, the IAC assembly is designed so that the main flotation and tether sections, e.g., the sections of cable 110 bounded by the first and last flotation assemblies 120, are positioned within the surface column below the wave action zone and at a depth where current loads and weights possibly caused by marine growth are reduced.

[0053] The method reduces the weight associated with the attachment of the cable to the FWTP by using an IAC assembly to suspend the cable between two FWTPs rather than lowering the cable from the FWTP to the seabed. This weight reduction is used in this method to reduce the load-bearing requirements of the connectors from the IAC assembly to the FWTPs compared to the load-bearing requirements of the connectors that would be required if the cable were suspended from the FWTP to the seabed.

[0054] The method reduces the buoyancy required for the pick-up aid (such as a buoy or FIT) by using an IAC assembly to float the cable between two FWTPs, rather than lowering the cable from the FWTP to the seabed.

[0055] The method reduces the degree of environmental protection (sealing) required for the cable between the FWTPs by using an IAC assembly to float the cable between two FWTPs, rather than lowering the cable from the FWTP to the seabed.

[0056] In the method, in a first step, the IAC assembly can be installed between a first location and a second location, the first location and the second location being designated for the FWTP. In a second step, the first FWTP and the second FWTP can be installed in the first location and the second location. In this method, the order of the first and second steps may be reversed.

[0057] In the method, in one step, an IAC assembly can be installed between a first location and a second location, the first location and the second location being designated for a FWTP. In a second step, an SKS can be installed in each of the first location and the second location. In a third step, a first FWTP and a second FWTP can be installed in the first location and the second location. In this method, the first step can be performed before or after any other step.

[0058] Preliminary Considerations In developing the features of the present disclosure, several cable configurations were considered using computer simulations. These included:

[0059] In the touchdown configuration, the central section of the cable (between the two floating platforms) is laid to the seabed. From one platform to the next, the cable is lowered from the platform's connection point to the seabed, laid on the seabed for some distance, and finally raised again to the next platform's connection point. The first touchdown configuration is the catenary curve. With the catenary curve configuration, the cable is laid freely in the water and on the seabed between the platforms, without any subsea equipment other than the top bend stabiliser. It can be the most economical in shallow waters, both in terms of hardware and installation costs, but not in deep waters. The catenary curve configuration is not preferred for deepwater applications due to the high loads induced by the length of cable suspended from the platform connection to the seabed and the movement of the platform, which remains connected to the cable, within the touchdown zone on the seabed. The second is catenary curve flotation. In the catenary curve flotation configuration, the cable is laid in the same manner as the catenary curve configuration, but flotation modules are evenly distributed along the cable to reduce the line's equivalent subsea weight. As a result, the cable partially lifts off the seabed but does not induce lazy waves. The third is touchdown lazy wave, in which a section of cable from a single "lazy wave" to this configuration is fitted into the surface column by a flotation assembly. The advantage of this solution is that it provides compliance with platform motion in all directions. Disadvantages include the possibility of cable compression in the touchdown area and the possibility of the cable bending on the seabed if the platform motion is too large for the water depth. This solution may be preferred for riser and umbilical applications in shallow waters due to its robustness, simplicity, and relatively low overall cost.

[0060] Non-touchdown configurations include: The U-shape is the simplest of the suspension configurations and therefore the most economical in terms of cable accessories. The U-shape cable is suspended from hang-off to hang-off without any additional subsea equipment other than the top bend stabiliser. Similar to the U-shape, but with flotation modules evenly distributed along the entire length of the cable, reducing the line's equivalent subsea weight, U-shape flotation reduces cable tension levels but does not induce lazy waves. In a single-floating lazy wave, a flotation assembly is placed at a mid-point on the cable, providing the suspension solution with the geometric rigidity of a wave configuration and reducing cable tension. In a multiple-floating lazy wave, multiple flotation assemblies are attached to the cable with unsupported sections of cable between them. For multiple-floating lazy waves, the number and characteristics of flotation assemblies must be optimized to enhance overall cable loads and motions. With a sufficient number of flotation assemblies, multiple-floating lazy waves benefit from both the U-shape and touchdown lazy wave solutions. Table 1 summarizes the configuration and preliminary considerations.

[0061] [Table 1]

[0062] Static Screening The first step in the screening focused on static considerations using further computer simulations, where seven configurations were compared under the same conditions, which will not be described.

[0063] Table 2 shows the results of the static screening for each of the seven configurations. Two configurations, the U-shape and the catenary curve, were rejected at this stage because they were unable to achieve a solution with a maximum cable tension below 300 kN, which was the criterion selected for safe allowable working loads.

[0064] Furthermore, the single floating lazy wave solution was rejected because the maximum tension is close to the design limit in statics and is expected to increase when moving to dynamic simulations.

[0065] As a result, in the screening process, the solutions selected to proceed to the next dynamic step were: U-shaped flotation (lowest tension, resulting in shortest cable length and intermediate buoyancy requirements), multiple flotation lazy wave (low tension, resulting in short cable length and intermediate buoyancy requirements), catenary curve flotation (low tension, resulting in long cable length and highest buoyancy requirements), and touchdown lazy wave (intermediate tension, resulting in longest cable length and lowest buoyancy requirements).

[0066] [Table 2]

[0067] Dynamic Screening The second step of the analysis consisted of selected dynamic cases of the remaining configurations. This dynamic screening could be used to distinguish between the remaining configurations. A key dynamic case was run on the four remaining configurations from the previous step to evaluate the dynamic behavior of the solutions. Screening was also performed on cable lengths and repartitioning of the floating assemblies on the cables to optimize the four configurations for their respective dynamic behavior. The floating wave solutions were divided into sub-solutions of 3, 4, 5, and 6 sections (called "waves"), with floating assemblies applied in between. The results are presented in Table 3.

[0068] From this step, both the U-shaped flotation solution and the catenary curve flotation solution were rejected due to excessive maximum tension. From the various sub-solutions within the multiple lazy waves, the six-floating lazy wave configuration showed the best overall results, achieving best or near-best results. As a result, the preferred solution at the end of this step during the screening process was the six-floating lazy wave (lowest cable load, short cable length, and intermediate buoyancy requirements).

[0069] [Table 3]

[0070] Note that in general, a multiple floating lazy wave solution will have only slightly higher buoyancy requirements and will have 1000 m less cable than a touchdown lazy wave. In the above embodiment, the optimal number of floating assemblies was determined to be six, but the optimal number may be more or less than six depending on various technical and economic factors.

[0071] The following paragraphs include enumerated embodiments.

[0072] Embodiment 1. A cable assembly for conducting power from a first floating platform to a second floating platform while maintaining the cable assembly off the seabed and reducing tension at the cable-to-platform connection, the cable assembly comprising: a cable; and a first floating section joined to the cable, the first floating section configured such that when the cable is connected to the first and second floating platforms, the first floating section sinks below the sea surface and provides buoyancy to prevent the cable from contacting the seabed.

[0073] Embodiment 2. The cable assembly of embodiment 1, wherein the first floating platform comprises a first floating wind turbine platform, and the cable comprises an insulated conductive cable sized to conduct electrical power generated at least by the first floating wind turbine platform.

[0074] Embodiment 3. The cable assembly of embodiment 1, wherein the first floating section is configured to provide buoyancy so that when the cable is connected to the first floating platform and the second floating platform, the cable does not contact the seabed and the first floating section floats in the sea so that it is convex toward the sea surface.

[0075] Embodiment 4. A cable assembly as described in embodiment 3, wherein the first levitation section includes a plurality of first levitation modules, each module connected to the cable, and the plurality of first levitation modules are distributed along the first section of the cable.

[0076] Embodiment 5. The cable assembly of embodiment 3, further comprising a second flotation section joined to the cable at a second section of the cable between the first flotation assembly and the second flotation assembly, wherein the second flotation section is configured to provide buoyancy so that when the cable is connected to the first floating platform and the second floating platform, both the first flotation section and the second flotation section float in the sea and prevent the cable from contacting the seabed, and the second flotation section floats in the sea so that it is convex toward the sea surface.

[0077] Embodiment 6. The cable assembly of embodiment 5, further comprising a first anchor connected to the cable within the second section of the cable.

[0078] Embodiment 7. The cable assembly of embodiment 5, further comprising a terminal flotation module, the terminal flotation module being connected to a first end of the cable in a third section of the cable between the terminal flotation module and the first flotation section, the terminal module being configured to provide buoyancy such that when the first end of the cable is not connected to the first floating platform, the terminal module floats on the sea surface, the first flotation assembly and the second flotation assembly are submerged, and the cable does not contact the seabed.

[0079] Embodiment 8. The cable assembly of embodiment 7, further comprising a second anchor connected to the cable between the second flotation section and a second end of the cable.

[0080] Embodiment 9. A system comprising a first floating platform, a second floating platform, and a cable assembly connectable between the first floating platform and the second floating platform, wherein the cable assembly comprises a cable and a first floating section joined to the cable, and the first floating section is configured to provide buoyancy such that when the cable is connected to the first floating platform and the second floating platform, the first floating section is submerged in water and the cable does not contact the seabed.

[0081] Embodiment 10. The system of embodiment 9, wherein the first floating platform comprises a first floating wind turbine platform, the second floating platform comprises a second floating wind turbine platform, and the cable comprises an insulated conductive cable sized to conduct electrical power generated by at least the first floating wind turbine platform.

[0082] Embodiment 11. The system described in embodiment 9, wherein the first floating section is configured to provide buoyancy so that when the cable is connected to the first floating platform and the second floating platform, the cable does not contact the seabed and the first floating section floats in the sea so that it is convex toward the sea surface.

[0083] Embodiment 12. The system described in embodiment 11, wherein the first levitation section includes a plurality of first levitation modules, each module connected to the cable, and the plurality of first levitation modules are distributed along the first section of the cable.

[0084] Embodiment 13. The system of embodiment 11, further comprising a second buoyancy section joined to the cable at a second section of the cable between the first buoyancy assembly and the second buoyancy assembly, wherein the second buoyancy section is configured to provide buoyancy so that when the cable is connected to the first floating platform and the second floating platform, both the first buoyancy section and the second buoyancy section float in the sea and prevent the cable from contacting the seabed, and the second buoyancy section floats in the sea so that it is convex toward the sea surface.

[0085] Embodiment 14. The system of embodiment 13, further comprising a first anchor connected to the cable within the second section of the cable.

[0086] Embodiment 15. The system described in embodiment 14, further comprising a terminal flotation module, the terminal flotation module being connected to a first end of the cable in a third section of the cable between the terminal flotation module and the first flotation section, the terminal module being configured to provide buoyancy so that when the first end of the cable is not connected to the first floating platform, the terminal module floats on the sea surface, the first flotation assembly and the second flotation assembly are submerged, and the cable does not contact the seabed.

[0087] Embodiment 16. The system of embodiment 15, further comprising a second anchor connected to the cable between the second levitation section and a second end of the cable.

[0088] Embodiment 17. A method for providing an electrical connection between a first floating platform and a second floating platform, comprising: providing a cable assembly connectable between the first floating platform and the second floating platform, the cable assembly including a cable and a first floating section joined to the cable, the first floating section configured to provide buoyancy so that when the cable is connected to the first floating platform and the second floating platform, the first floating section is submerged in water and prevents the cable from contacting the seabed; and connecting the cable assembly to electrical connections on the first floating platform and the second floating platform.

[0089] Embodiment 18. The method of embodiment 17, wherein the first floating section is configured to provide buoyancy such that when the cable is connected to the first floating platform and the second floating platform, the cable does not contact the seabed and the first floating section floats in the sea such that the first floating section is convex toward the sea surface.

[0090] Embodiment 19. The method of embodiment 18, wherein the first levitation section includes a plurality of first levitation modules, each module connected to the cable, and the plurality of first levitation modules are distributed along the first section of the cable.

[0091] Embodiment 20. The method of embodiment 18, further comprising providing a second buoyancy section joined to the cable in a second section of the cable between the first buoyancy assembly and the second buoyancy assembly, the second buoyancy section being configured such that when the cable is connected to the first floating platform and the second floating platform, both the first buoyancy section and the second buoyancy section are submerged in the sea, providing buoyancy so that the cable does not contact the seabed, and the second buoyancy section floats in the sea so that it is convex toward the sea surface.

[0092] Embodiment 22. The method of embodiment 21, further comprising: providing a first anchor connected to the cable within the second section of the cable; and providing a first terminal flotation module connected to a first end of the cable in a third section of the cable between the terminal flotation module and the first flotation section, the first terminal module being configured to provide buoyancy such that when the first end of the cable is not connected to the first floating platform, the first terminal module floats on the sea surface, the first flotation assembly and the second flotation assembly are submerged, and the cable does not contact the seabed; and disconnecting the first end of the cable from the first floating platform, allowing the first terminal module to float on the sea surface.

[0093] Embodiment 23. The method of embodiment 22, further comprising: providing a second anchor connected to the cable between the second flotation section and a second end of the cable; providing a second terminal flotation module connected to the second end of the cable in a fifth section of the cable between a second terminal flotation module and the second flotation section, the second terminal module being configured to provide buoyancy such that when the second end of the cable is not connected to the second floating platform, the second terminal module floats on the sea surface, the first flotation assembly and the second flotation assembly are submerged, and the cable does not contact the seabed; and disconnecting the second end of the cable from the second floating platform, allowing the second terminal module to float on the sea surface.

[0094] The preceding description is provided to enable those skilled in the art to practice the various aspects described herein. In embodiments, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects.

[0095] The use of terms such as "aspects" does not imply that such aspects are essential to the subject technology or that such aspects apply to all configurations of the subject technology. Disclosure of an aspect may apply to all configurations, or to one or more configurations. A term such as aspect may refer to one or more aspects, and vice versa. The use of terms such as "configuration" does not imply that such aspects are essential to the subject technology or that such aspects apply to all configurations of the subject technology. Disclosure of a configuration may apply to all configurations, or to one or more configurations. A term such as configuration may refer to one or more configurations, and vice versa.

[0096] All structural and functional equivalents of the elements of the various embodiments described throughout this disclosure that are known or that later become known by those skilled in the art are expressly incorporated herein by reference.

Claims

1. 1. A cable assembly comprising: a cable having a plurality of cable sections, a first cable end, and a second cable end; a first levitation section joined to the cable at a first cable section; a second levitation section joined to the cable at a second cable section and a third cable section, the third cable section extending between the first and second levitation sections; a terminal levitation module connected to the first cable end and a fourth cable section, the fourth cable section extending between the terminal levitation module and the first levitation section; A cable assembly comprising: the first and second flotation sections are configured to provide buoyancy to the cable such that, when the cable is connected between the first and second floating platforms, the first and second cable sections are convex toward the sea surface and float in the water below the sea surface so that the cable does not contact the seabed; The cable assembly is configured such that, when the first cable section is not connected to the first floating platform, the terminal flotation module floats on the sea surface, the first flotation section and the second flotation section float in the sea, and the cable provides buoyancy so that it does not contact the seabed.

2. the first floating platform comprises a first floating wind turbine platform; the cable comprises an insulated conductive cable sized to conduct electrical power generated by at least the first floating wind turbine platform. The cable assembly of claim 1 .

3. 2. The cable assembly of claim 1, wherein the first levitation section includes a plurality of first levitation modules, each first levitation module being connected to the cable, and the plurality of first levitation modules being distributed along the first cable section.

4. The cable assembly of claim 1 , further comprising a first anchor connected to the cable within the third cable section.

5. 10. The cable assembly of claim 1, further comprising a second anchor connected to the cable at the second cable end or between the second levitation section and the second cable end.

6. A cable assembly, a cable having a plurality of cable sections, a first cable end, and a second cable end; a first levitation section joined to the cable at a first cable section; a second levitation section joined to the cable at a second cable section and a third cable section, the third cable section extending between the first and second levitation sections; A cable assembly comprising: the first and second flotation sections are configured to provide buoyancy to the cable such that, when the cable is connected between the first and second floating platforms, the first and second cable sections are convex toward the sea surface and float in the water below the sea surface so that the cable does not contact the seabed; A cable assembly wherein the first cable end is suspended within a surface column when the first cable end is not connected to the first floating platform.

7. 1. A system comprising: a first floating platform; a second floating platform; and 1. A cable assembly comprising: a cable having a plurality of cable sections, a first cable end, and a second cable end; a first levitation section joined to the cable at a first cable section; a second levitation section joined to the cable at a second cable section and a third cable section, the third cable section extending between the first and second levitation sections; a terminal levitation module connected to the first cable end and a fourth cable section, the fourth cable section extending between the terminal levitation module and the first levitation section; a cable assembly including: A system comprising: the first and second buoyancy sections are configured to provide buoyancy to the cable such that, when the cable is connected between the first and second floating platforms, the first and second cable sections are convex toward the sea surface and float in the water below the sea surface so that the cable does not contact the seabed; The system is configured such that, when the first cable section is not connected to the first floating platform, the terminal flotation module floats on the sea surface, the first flotation section and the second flotation section float in the sea, and the terminal flotation module provides buoyancy so that the cable does not contact the seabed.

8. the first floating platform comprises a first floating wind turbine platform; the second floating platform comprises a second floating wind turbine platform; the cable comprises an insulated conductive cable sized to conduct electrical power generated by at least the first floating wind turbine platform. The system of claim 7.

9. 8. The system of claim 7, wherein the first levitation section includes a plurality of first levitation modules, each first levitation module connected to the cable, and the plurality of first levitation modules are distributed along the first cable section.

10. The system of claim 7 , further comprising a first anchor connected to the cable within the third cable section.

11. 11. The system of claim 10, further comprising a second anchor connected to the cable at the second cable end or between the second levitation section and the second cable end.

12. 1. A method for providing an electrical connection between a first floating platform and a second floating platform, the method comprising: providing a cable assembly connectable between the first floating platform and the second floating platform, the cable assembly comprising: a cable having a plurality of cable sections, a first cable end, and a second cable end; a first levitation section joined to the cable at a first cable section; a second levitation section joined to the cable at a second cable section and a third cable section, the third cable section extending between the first and second levitation sections; a first termination levitation module connected to the first cable end and a fourth cable section, the fourth cable section extending between the first termination levitation module and the first levitation section; Including, The first and second buoyant sections are configured to provide buoyancy to the cable such that, when the cable is connected between the first and second floating platforms, the first and second cable sections are convex toward the sea surface and float in the water below the sea surface such that the cable does not contact the seabed. And, connecting the cable assembly to electrical connections on the first floating platform and the second floating platform; A method comprising:

13. 13. The method of claim 12, wherein the first levitation section includes a plurality of first levitation modules, each first levitation module connected to the cable, and the plurality of first levitation modules are distributed along the first cable section.

14. providing a first anchor connected to the cable within the third cable section; disconnecting the first cable end from the first floating platform to allow the first terminal flotation module to float on the sea surface; The method of claim 12 further comprising:

15. providing a second anchor connected to the cable at the second cable end or between the second levitation section and the second cable end; providing a second terminal flotation module, the second terminal flotation module connected to the second cable end, the second terminal flotation module configured to provide buoyancy to the cable such that, when the second cable end is not connected to the second floating platform, the second terminal flotation module floats on the sea surface, the first and second flotation sections float in the sea, and the cable does not contact the seabed; disconnecting the second cable end from the second floating platform to allow the second terminal flotation module to float on the sea surface; and The method of claim 14 further comprising:

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