Underwater power collection system including distributed transformer configuration

Abstract

A power collection system (100) for collecting power from multiple offshore power generation units comprises a three-phase subgrid (120) and a subsea substation (130). The subgrid has multiple power input points (121) leading to the power generation units and a shared three-phase power output point (122). The substation (130) is connected to the power output point, and its secondary side (132) is configured to connect to a power consumer (170). The substation comprises three single-phase transformers (140) housed in separate housings (143), where each housing is located on the seabed and configured to be raised to the surface independently of the other housings. Each phase of the power output point is connected to a corresponding primary side (141) of the single-phase transformer.

Description

[[Technical Field]]

[0001] [

[0001] ] The present disclosure relates to the field of offshore power generation. In particular, the present invention proposes a power collection system capable of increasing output power rating thanks to a distributed transformer arrangement. [[Background Art]]

[0002] [

[0002] ] The offshore wind power market is growing. Global wind capacity is expected to increase by approximately 12 GW per year, reaching a total installed power of 150 GW by 2027. Much of the ongoing research effort is directed towards upscaling, including higher power ratings and larger installations. On one hand, wind turbines are increasing in size, and typical unit sizes are expected to reach the range of 15-20 MW. On the other hand, the transition from fixed-bottom wind turbines to floating wind turbines has begun. In fact, floating installations are less dependent on the availability of favorable seabed topography and can be located far from coastlines where the most abundant wind resources are found, so they appear to be most suitable for realizing large-scale offshore wind parks.

[0003] [

[0003] ] A power collection system refers to cables and components responsible for collecting the power generated by a park of floating wind turbines and rendering it suitable for subsequent transmission and / or use by power consumers. For example, multiple power contributions collected at an intermediate voltage (e.g., 66 kV) may be combined and stepped up (e.g., to 245 kV), and then transmitted to an onshore grid via an export cable. The power collection system may be an offshore subsea system (i.e., located on the seabed) or a floating power collection system. Subsea power collection systems operate in more stable environmental conditions, are therefore easier to maintain, and, with rare exceptions, only need to be connected by dynamic export cables. Early results suggest that power collection systems in this category are more robust than floating systems and result in more limited expenditure.

[0004]

[0004] For maintenance and repair of underwater power collection systems, a more practical option (sometimes the only available option) is to lift the relevant system units to the surface and perform the work there. Maintenance and repair of lifted system units is called topside work. The need to be able to lift power collection system units implies inherent weight limitations, such as approximately 300 tons (metric tons) per unit.

[0005]

[0005] In all submarine power technologies, electrical components must, of course, be protected from seawater leakage. This can be achieved by known techniques, including oil filling and special sealing configurations, but these become considerably costly as the volume and / or physical extent of the submarine unit increases. This requirement to minimize physical size is not always easy to combine with efficient cooling, where the surface-to-volume ratio is important. The view that is generally held at the time of this disclosure is that designing submarine transformers with approximate power ratings exceeding 200 MVA power ratings presents significant challenges.

[0006]

[0006] WO2022194667A1 discloses a power collection system suitable for collecting power from an offshore power generation unit described in the preamble of claim 1. The power collection system comprises an end transformer and an intermediate transformer located on the seabed, which are implemented as three-phase transformers.

[0007]

[0007] Therefore, one problem is to propose technologies that will enable further upscaling of underwater power collection systems. [Overview of the project]

[0008]

[0008] An object of this disclosure is to make available an underwater power collection system that can be manufactured and / or maintained by conventional underwater technology and is suitable for output powers exceeding 200 MVA. A further object is to make available an underwater power collection system having these characteristics and output powers of 400 MVA or more, for example 600 MVA, and possibly up to 900 MVA. A further object is to make available an underwater power collection system in which each unit has a simple configuration, for example, having a limited number of components. A further object is to make available an underwater power collection system in which all units requiring maintenance and repair can be lifted to the surface, i.e., they are accessible for surface work. A further object is to make available a single-output (single three-phase output) underwater power collection system having these characteristics.

[0009]

[0009] At least some of these objectives are achieved by the present invention as defined by claim 1. The independent claims relate to advantageous embodiments.

[0010]

[0010] More precisely, a power collection system is proposed for collecting power from multiple offshore power generation units. The power collection system comprises a three-phase subgrid and a subsea substation. The subgrid has multiple power input points toward the power generation units and a three-phase power output point shared by the power input points. (The power output points of the subgrid may correspond to connectors, interfaces, or other physical features of the subgrid, or may be purely conceptual points on cables within the subgrid.) The substation is connected to the power output point, where the secondary side of the substation is configured to connect to the power consumers. According to this disclosure, the substation comprises three single-phase transformers housed in separate housings, where each housing is located on the seabed and configured to be raised to the surface separately from the other housings (i.e., after cutting cables to the other housings as needed), and each phase of the power output point is connected to the corresponding primary side of one of the single-phase transformers.

[0011]

[0011] By deploying three single-phase submarine transformers in separate housings, rather than a single three-phase submarine transformer, weight and size issues are overcome, and further upscaling becomes possible. More precisely, each single-phase transformer can be designed to be within the weight range that can be lifted using conventional offshore technology, and with a power rating that does not require a special cooling configuration. Furthermore, because the configuration of single-phase transformers is relatively simple, the lower total life cycle cost of three single-phase transformers does not need to exceed the total life cycle cost of a monolithic three-phase transformer with the same power rating. These advantages are not achieved at the expense of the power consumption side (downstream), as is the case when the power collection system is amplified by the use of multiple parallel three-phase transformers, each requiring one transmission cable, but rather all of the output power of the power collection system can be consumed at a single three-phase connection point, i.e., on the secondary side of the substation.

[0012]

[0012] Preferably, the underwater power substation is suitable for deployment at a first depth and can be lifted to the surface at the first depth separately from the other housings. The first depth may be 100m or more, e.g., 200m or more, e.g., 300m or more, e.g., 500m or more, e.g., 1000m or more. The ability to lift the transformer housings separately can be achieved in a number of alternative ways, namely, the three housings are not permanently joined to form a rigid unit, and / or any joining elements joining a pair of housings are long enough to allow separation by a distance sufficient to lift the housings (e.g., above the first depth), or are nondestructively releaseable, and / or any locking configuration joining a pair of housings can be nondestructively released.

[0013]

[0013] In some embodiments, the wind turbine array is arranged sequentially on each three-phase cable (array cable) within a subgrid, and these three-phase cables are connected to three single-phase transformers. The same phases from different array cables are connected inside each submarine transformer. This advantageously avoids the current capacity limitations of submarine wet mating connectors.

[0014]

[0014] In some embodiments, the transformer windings of three single-phase transformers, when considered together, are star-connected on the primary side and delta-connected on the secondary side. In the case of delta windings, power jumpers across the three transformers may optionally be provided. In alternative terminology, the star connection is sometimes called a Y connection.

[0015]

[0015] In some embodiments, the transformer windings are star-connected on the primary side and star-connected on the secondary side. Optionally, an unloaded delta-connected tertiary winding can be provided to suppress higher harmonics.

[0016]

[0016] In this disclosure, the term “power consumer” is used in an abstract (or black box) sense from the perspective of an underwater substation. Thus, it includes not only devices that consume power themselves, but also devices that convert power, including transmission cables (or export cables), onshore substations, offshore or onshore energy storage devices, offshore or onshore hydrogen converters, etc.

[0017]

[0017] In general, all terms used in the claims should be interpreted according to their ordinary meanings in the art unless otherwise expressly defined herein. All references to “a / an / the [element, apparatus, component, means, step, etc.]” ​​should be openly interpreted as referring to at least one instance of such element, apparatus, component, means, step, etc. unless otherwise expressly specified. No step of any method disclosed herein has to be performed in the exact order disclosed unless expressly specified otherwise. [Brief explanation of the drawing]

[0018]

[0018] The aspects and embodiments will be described by reference to the accompanying drawings. [Figure 1] Figure 1 shows a power collection system positioned between multiple offshore power generation units and power consumers. [Figure 2] Figure 2 shows details of the power collection system and multiple connected offshore power generation units. [Figure 3] Figure 3 illustrates a first arrangement of optional switches between the single-phase transformer and the three-phase subgrid of the power collection system. [Figure 4] Figure 4 illustrates a second arrangement of optional switches between the single-phase transformer and the three-phase subgrid of the power collection system. [Figure 5] Figure 5 shows underwater power expansion modules connected in series, through which offshore power generation units can be connected to a subgrid. [Figure 6A] Figure 6A illustrates the arrangement of optional switches in front of the power output point of a three-phase subgrid to which the power generation unit is connected via a power expansion module. [Figure 6B] Figure 6B shows an alternative embodiment of the power expansion module. [Figure 7] Figure 7 shows an embodiment in which the windings of a single-phase transformer are star-connected on the primary side and star-connected on the secondary side. [Figure 8] Figure 8 shows an embodiment in which the windings of a single-phase transformer are delta-connected on the primary side and star-connected on the secondary side. [Figure 9] Figure 9 is a simplified perspective view of an underwater power collection system positioned between multiple floating wind turbines and power transmission cables. [Modes for carrying out the invention]

[0019]

[0019] Aspects of the present disclosure are fully described below with reference to the accompanying drawings, in which embodiments of the present disclosure are shown. However, these aspects may be embodied in many different forms and should not be construed as limited; rather, these embodiments are provided by way of example so that the present disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Like terms refer to like elements throughout the description.

[0020]

[0020] FIG. 1 is a schematic diagram of a power collection system 100 arranged between a plurality of offshore power generation units 110 and a power consumer 170. A similar power collection system 100 is depicted in FIG. 9.

[0021]

[0021] The power collection system 100 includes a three-phase sub-grid 120 having a plurality of power input points 121 leading to the power generation units 110, and a three-phase power output point 122. The offshore power generation units 110 may include floating or fixed support devices such as one or more (floating) wind turbines, (floating) solar cell devices, (floating) wave energy converters, or a combination of one or more of these. Fixed support devices may alternatively be described as bottom-fixed devices. The power generation units 110 may be configured to generate three-phase power such that each power generation unit 110 is connected to all three phases of the sub-grid 120. Alternatively, the power generation units 110 may be configured to generate single-phase power, wherein three subgroups of the power generation units 110 may be connected to the three phases in a substantially balanced manner. Under the first option, the power input points 121 are three-phase power input points. The power generation units 110 may include units having a rated output power on the order of 1 MW or more, for example, output power in the range of 15-20 MW or more. The power generation units 110 may be of a uniform type having equal power ratings, or may have different power ratings. In the case of large-scale floating wind turbines, the mutual spacing between the power generation units 110 may be on the order of 1 km, such as 2 km or more.

[0022]

[0022] The power output point 122 is shared by the power input points 121 in the sense that a combined current representing all power supplied to the power input points 121 is available by establishing a connection at the power output point 122, and / or in the sense that a device connected to the power output point 122 does not have a way to select a specific power input point 121 and receive power only therefrom. It should be noted that the power input points 121 and the power output point 122 may correspond to physical components or other structural features of the subgrid 120, but such correspondence does not necessarily exist. Rather, one or more of the power input points 121 and the power output point 122 may be purely conceptual. For example, in Fig. 1, whether the "power output point" is identified by reference numeral 122 or at another position between the four-way branch point on the left and the three-way branch point on the right does not produce a technical difference. As shown in Fig. 1, furthermore, the power input point 121 may be constituted by a common connection point for two or more power generation units 110.

[0023]

[0023] The power collection system 100 further comprises an underwater power substation 130 including three single-phase transformers 140. Each single-phase transformer 140 is housed in its own housing 143 (or tank), the housings being positioned to rest on the seabed 102 (see Figure 9), and having a configuration that allows the housing 143 containing the transformers 140 to be lifted to the sea surface 101 (see Figure 9) independently of the other housings. In principle, the ability to lift them independently can be achieved in two main ways: any joining elements between the housings 143 are long enough to allow them to be lifted to the surface at a local depth, or any locking configurations between the housings 143 can be released non-destructively. The ability of each housing 143 to be lifted independently means that the three housings 140 are not permanently joined to form a rigid unit. In such embodiments, where a pair of housings 140 are joined by mechanical wires, electrical connections, and other movable joining elements, these joining elements should be long enough to allow the two housings 140 to be separated by a distance sufficient to lift them (i.e., at least the depth of the sea at the deployment site), or the joining elements should be able to be released non-destructively. Similarly, if the housings 140 are joined by a locking configuration, the locking configuration can be released non-destructively. The weight of the housings 140 having a single-phase transformer 140 inside is preferably less than 300 t, for example less than 200 t, for example less than 100 t.

[0024]

[0024] Preferably, the housing 143 is designed to be watertight under seabed conditions, i.e., it has a seal that can withstand hydrostatic pressure at seabed level and is manufactured from a material suitable for long-term use in seawater. Typical depths may be 100m or more, e.g., 200m or more, e.g., 300m or more, e.g., 500m or more, e.g., 1000m or more. The housing 143 may be specified for operation at maximum depths on the order of 1500m.

[0025]

[0025] Each of the transformers 140 has a primary side 141 corresponding to the primary winding and a secondary side 142 corresponding to the secondary winding. In steady-state operation, net power generally flows from the primary side 141 to the secondary side winding 142. The orientation of the primary side 141 and secondary side 142 of the transformer 140 defines the primary side 131 and secondary side 132 of the substation 130. The primary side 131 of the substation 130 interfaces with the power output point 122 of the subgrid 120, and the secondary side 132 is connected to the power consumer 170.

[0026]

[0026] Each single-phase transformer 140 may be configured for a secondary voltage of 200kV or more, for example, 245kV. The primary voltage, which is equal to the phase voltage of the subgrid 120, may be, for example, 60kV or 66kV. The power rating of the power collection system 100 corresponding to the combined power rating of the transformers 140 may be 400MVA or more, for example, 600MVA, and possibly up to 900MVA.

[0027]

[0027] As described above, the unit designated as the power consumer 170 functions as a consumer from the perspective of the underwater substation 130. That is, the power consumer 170 may perform the energy conversion itself or may facilitate the energy conversion in further downstream entities. Therefore, the power consumer 170 may be, for example, a static or dynamic transmission cable (or export cable), a land substation, an offshore or land energy storage device (e.g., a battery), an offshore or land hydrogen converter, etc. The power consumer 170 is configured to be supplied with three-phase power. In some embodiments, the outputs of the three secondary windings 142 are connected directly to the power consumer 170. Alternatively, the outputs of the three secondary windings 142 are coupled to a three-phase interface, for example by mechanically coupling three single-phase cables to a three-phase cable or connector, and then connected to the power consumer 170.

[0028]

[0028] As illustrated in Figure 9, the type of underwater power collection system 100 under consideration may comprise a plurality of floating power generation units 110 (shown as floating wind turbines in Figure 9) located near the sea surface 101, and several underwater components located on the seabed or at least partially submerged. In the illustrated power collection system 100, the cables constituting the subgrid 120 are mostly static sea cables suitable for placement on the seabed. Each of the floating wind turbines 110 is connected to the subgrid 120 via a dynamic sea cable 111, followed by a power input point 121, which here comprises a connection box (or interface) between the dynamic sea cable 111 and the static sea cable within the subgrid 120. In accordance with common terminology in the art, a dynamic sea cable is a cable designed for repeated deformation and / or mechanical loading and unloading. Generally, dynamic sea cables differ from comparable static sea cables by having better resistance to material fatigue caused by deformation. The power output point 122 may consist, as part of it, of two input subgrid cables from subgrid 120 and three output phases following housings 143a, 143b, and 143c containing their respective single-phase transformers (not shown) within substation 130. The outputs of the transformers constituting the output phases of substation 130 leave housings 143a, 143b, and 143c and are joined to a three-phase transmission cable (or export cable) 170 at connection box 171. All cables from connection boxes 121, 122, and 171, housings 143a, 143b, and 143c, and subgrid 120 are arranged to be on the seabed. This may include appropriate technical means to achieve chemical compatibility and / or watertightness with seawater. However, because the seabed environment is relatively stable, the seabed-located units of the power collection system 100 do not necessarily possess the verified resistance to repetitive motion throughout their lifecycle that is typically required from floating generators exposed to waves, dynamic cables that deform to follow ocean swells, and other similar systems.

[0029]

[0029] Figure 2 shows details of the power collection system 100 and several connected offshore power generation units 110. In some embodiments, a subgrid 120 is constructed around N array cables 123a, 123b, 123c extending radially from a power output point 122, where a power input point 121 is located along array cable 123. Figure 2 shows such a power collection system 100 in which power generation units 110a.1, 100a.2, ..., 110a.5 are connected to the power input point 121 along a first array cable 123a, power generation units 110b.1, 110b.2, ..., 110b.5 are connected to the power input point 121 along a second array cable 123b, and power generation units 110c.1, 110c.2, ..., 110c.5 are connected to the power input point 121 along a third array cable 123c. The array cable 123 in Figure 2 has an equal number of connected power generation units 110, but it can also have a different number of connected power generation units 110. The subgrid includes a number of branch switches 164 that allow individual power generation units 110 to be disconnected from their respective array cable 123. The subgrid further includes a number of trunk switches 165 that allow the outer portion of each array cable 123 to be disconnected from the subgrid. It is not necessary to have trunk switches 165 outside the outermost power input points 121, but this may result from implementing the power collection system 100 as a combination of pre-designed building blocks.

[0030]

[0030] The subgrid in Figure 2 has N=3 array cables 123, each of which is a three-phase cable and is not in a one-to-one relationship with the three single-phase transformers 140. Between the power output point 122 and each array cable 123, each phase is separated from the other phases of that array cable 123 so as to be joined with an identical phase from another N-1 array cable and directed to the corresponding one of the single-phase transformers 140. In the alternative implementation, the joined N identical phases from the array cables are connected (electrically connected) at a point inside the housing 143 containing the corresponding one of the single-phase transformers 140. The connection point inside the housing 143 may also be a busbar, and a conventional 200 MVA transformer has enough space to accommodate multiple high-voltage power feedthroughs. Thanks to the fact that the joined N identical phases from the array cables 123 are connected inside the housing 143, away from seawater, the current capacity limitations of wet coupling connectors in the sea can be avoided.

[0031]

[0031] Figures 3 and 4 illustrate possible arrangements of switches 150 between the single-phase transformers and three-phase subgrids of the power collection system. Switches 150, which can be used to isolate faults, are located between the primary side 141 of each single-phase transformer 140 and the power output point 122. In other words, the switches 150 are located on the inputs to the single-phase transformers 140 corresponding to the respective phases u, v, and w of the subsea power plant 130. In the embodiment of Figure 3, the switches are implemented as separate, dedicated switch units 150 from the housing 143. In Figure 4, the switches 150 are located inside each housing 143.

[0032]

[0032] A possible schematic diagram of a single-phase switch 150 for this purpose is shown in the upper right corner of Figure 3. The single-phase switch consists of two sub-switches 151, 152 positioned between two feedthroughs 153, 154, which allow input to the single-phase transformer 140 to enter and exit the housing of the switch unit 150. The second sub-switch 152 can be set to the grounded position or the closed position. In normal operation, both sub-switches 151, 152 are closed. When one or both of the sub-switches 151, 152 are open, the corresponding single-phase transformer 140 is disconnected from the subgrid and the single-phase transformer 140 is optionally grounded.

[0033]

[0033] A simpler implementation of the single-phase switch 150 may include a single sub-switch.

[0034]

[0034] Figure 5 shows details of a power collection system 100 in which series-connected underwater power expansion modules 160 are used to connect offshore power generation units 110 to array cables 123 of a subgrid 120. The power expansion modules 160 can be understood as a modular system that provides the branch switches 164 and trunk switches 165 introduced above with reference to Figure 2. In one embodiment, the power expansion module 160 comprises a switchable input terminal 162 arranged to connect to a power generation unit and at least two interconnection terminals 163 suitable for connecting the power expansion module 160 in series to an adjacent power expansion module. The power expansion module 160 may further comprise a connection to a data network 128, and the power expansion module 160 may exchange protection and control-related information with other components of the power collection system 100. The data network 128 may be a digital packet-switched network such as an Ethernet® network. The power expansion module 160 has a housing 161 that is arranged to be placed on the seabed 102 and is therefore designed to be watertight in seabed conditions.

[0035]

[0035] In the applicant's previous disclosure EP4063646A1, several implementations of a power expansion module 160 suitable for use with the teachings herein are described.

[0036]

[0036] The input terminal 162 of the power expansion module 160 connected to the power generation unit 110 is switchable by a switching circuit constituting a branch switch 164, thereby allowing the power generation unit 110 to be isolated as desired. In some embodiments, including that shown in Figure 5, the interconnection terminal 163 is also switchable by a switching circuit constituting a trunk switch 165, which allows for the isolation of adjacent power expansion modules. In an alternative configuration shown in Figure 6B, the power expansion module 160 includes two trunk switches 165a and 165b, one on each side of the branch switch 164. The availability of two trunk switches 165a and 165b that can be switched independently of each other allows for fault isolation at a finer granularity.

[0037]

[0037] Figure 6A shows how power expansion modules 160 are arranged in series on the array cable 123 of the subgrid. The array cable has a ring topology, and as a result each power generation unit 110 is located on a loop with two paths to the power output point 122, which allows for many options for fault isolation. In the embodiment of Figure 6A, the subgrid further includes switches 150 between the power output point 122 and each array cable 123. More precisely, there are independent switches 150 between each end of the loop-shaped array cable 123 and the power output point 122. Note that Figure 6A includes several examples of reference numeral 122, which refers to galvanic connection points of the power collection system 110 that can be collectively identified as the power output points of the subgrid.

[0038]

[0038] As described above, Figure 6B shows an alternative configuration of the power expansion module 160 that can replace one or more of the power expansion modules 160 shown in Figure 6A.

[0039]

[0039] Figure 7 shows an embodiment of an underwater substation 130 in which the windings 144 of a single-phase transformer 140 are star-connected on the primary side 131 and on the secondary side 132. It is understood that the two windings 144 inside each of the three housings 140 are magnetically coupled. This embodiment is relatively simple and inexpensive to manufacture and install. The neutral points 146 on both the primary and secondary sides can be firmly grounded inside the housing 143. To attenuate third and higher harmonics, an unloaded delta-connected tertiary winding can be added to the circuit shown in Figure 7.

[0040]

[0040] Figure 8 shows an embodiment in which the windings 144 of a single-phase transformer are delta-connected on the primary side and star-connected on the secondary side. Power jumpers 145 are provided to complete the delta connection, each of which is an electrical connection provided between a pair of single-phase transformers 140. At least one segment of each power jumper 145 is provided as a sea cable. In some embodiments, each power jumper 145 is permanently connected to one single-phase transformer 140 and is arranged to connect to a further single-phase transformer 140 when two transformers 140 are deployed (pigtail configuration). Preferably, the connection to the further single-phase transformers 140 is disconnectable, i.e., can be returned non-destructively, in order to allow the transformers 140 to be lifted separately for maintenance and repair. In the case of high-current installations, each pair of single-phase transformers 140 may be connected in parallel by a plurality of power jumpers 145.

[0041]

[0041] The aspects of the present disclosure have been described above primarily with reference to several embodiments. However, as will be readily apparent to those skilled in the art, embodiments other than those disclosed above are equally possible within the scope of the present invention, as defined by the appended claims.

Claims

1. A power collection system (100) for collecting electricity from multiple offshore power generation units (110), A three-phase subgrid (120) having multiple power input points (121) directed toward a power generation unit and a three-phase power output point (122) shared by the power input points, and Suitable for deployment at a first depth of sea, it comprises an underwater substation (130) connected to a power output point, where the secondary side (132) of the substation is arranged to be connected to a power consumer (170), The substation comprises three single-phase transformers (140) housed in separate housings (143), each of which is positioned to be placed on the seabed (102) and positioned to be lifted to the sea surface (101) at the first sea depth separately from the other housings. A power collection system (100) characterized in that each phase of the power output point is connected to a corresponding primary side (141) of the single-phase transformer.

2. The subgrid (120) further comprises a three-phase array cable (123) with N≧2 that extends radially from the power output point (122) and along which the power input point (121) is arranged in series. Between the power output point and each array cable, each phase is separated from the other phases of that array cable so as to be joined with the same phase from another array cable of N-1. The power collection system (100) according to claim 1, wherein the N identically joined phases from the array cable are connected at a point inside the housing (143) which includes one of the single-phase transformers (140).

3. The power collection system (100) according to claim 1 or 2, further comprising a switch (150) between the power output point (122) and each array cable (123) of the subgrid (120).

4. A power collection system (100) according to any one of claims 1 to 3, further comprising a switch (150) between the primary side (141) of each single-phase transformer (140) and the power output point (122).

5. The power collection system (100) according to any one of claims 1 to 4, wherein the single-phase transformer (140) comprises a magnetic coupling winding (144) that is delta-connected on the primary side (131) of the substation (130) and star-connected on the secondary side (132) of the substation.

6. The power collection system (100) according to claim 5, further comprising a power jumper (145) provided between a pair of single-phase transformers (140) to establish the delta connection of their windings (144).

7. The power collection system (100) according to claim 6, wherein each power jumper (145) is permanently connected to one single-phase transformer (140) and is arranged to connect to further single-phase transformers when deployed.

8. The power collection system (100) according to any one of claims 1 to 4, wherein the single-phase transformer (140) comprises a magnetic coupling winding (144) that is star-connected on the primary side (131) of the substation (130) and star-connected on the secondary side (132) of the substation.

9. The power collection system (100) according to claim 8, wherein at least one of the single-phase transformers (140) further comprises an unloaded delta-connected tertiary winding configured to attenuate harmonics.

10. The power collection system (100) according to any one of claims 5 to 9, wherein the star-connected winding is grounded at the neutral point (146) inside the housing (143).

11. The power collection system (100) according to any one of claims 1 to 10, further comprising an underwater power expansion module (160), each comprising a switchable input terminal (162) arranged to be connected to a power generation unit and at least two interconnection terminals (163) suitable for connecting the power expansion module in series with an adjacent power expansion module.

12. At least one power expansion module (160) is provided with a switchable interconnect terminal (163) that allows for the disconnection of adjacent power expansion modules. Herein, the power expansion module preferably includes an interconnect terminal that can be switched independently of other interconnect terminals on the power expansion module, the power collection system (100) according to claim 11.

13. The power collection system (100) according to any one of claims 1 to 12, wherein the power input point (121) is a three-phase power input point.

14. The power collection system (100) according to any one of claims 1 to 13, wherein the housing (143) of the single-phase transformer (140) is designed to be watertight under seabed conditions.

15. The power collection system (100) according to any one of claims 1 to 14, wherein the power consumer (170) is a three-phase power consumer connected to the secondary side (142) of each of the three single-phase transformers (140).

16. The power collection system (100) according to any one of claims 1 to 15, wherein the substation (130) is configured for a secondary phase voltage of at least 200 kV.

17. A power collection system (100) according to any one of claims 1 to 16, configured for output power of at least 400 MVA.

18. The offshore power generation unit (110) comprises at least one floating wind turbine, at least one floating solar cell configuration, and / or at least one floating wave energy converter, the power collection system (100) according to any one of claims 1 to 17.

19. At least one of the following is true: The three housings (143) are not permanently joined to form a rigid unit. Any joining element connecting a pair of housings (143) is either long enough to allow the housings to be separated by a distance sufficient to lift them, or is nondestructively detachable. A power collection system (100) according to any one of claims 1 to 18, wherein any locking configuration joining a pair of housings (143) can be released non-destructively.

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