[0000] CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of US provisional patent application no. 63/157,863, filed March 8, 2021, and of NO patent application no. 20210468, filed April 15, 2021, each of which is incorporated by reference herein.

BACKGROUND

1. Technical Field

[0001] The present invention relates generally to wind farms comprising wind turbines, and more particularly to arrays of offshore wind turbines.

2. Description of Related Art

[0002] Increased demand for renewable energy has resulted in the increasing development of offshore wind power. Offshore wind farms typically comprise an array of wind turbine generators that output power at a nominal turbine output voltage that is below 66kV (e.g., 11- 33kV). Each turbine requires an on-tower transformer to step up the generator voltage (e.g., 1-6 kV) to the turbine output voltage (e.g., 11 or 33kV).

[0003] The turbines are electrically connected via inter-turbine cables to form an electrical collection system which typically operates at the turbine output voltage. For large farms (e.g., >400 MW) situated far offshore (e.g., > 30km), the collection system typically connects the turbines to an offshore substation that steps up the turbine voltage for transmission to shore at a nominal export voltage that is below 220kV. An export cable coupling the offshore substation to shore operates at the export voltage. The export cable is typically coupled to an onshore substation, which additionally steps up the voltage to grid voltage (e.g., to 420 kV).

[0004] Such systems face a variety of challenges as farm size, water depth, and distance from shore increase. The size of present electrical collection systems is limited. The inter-turbine distance, the number of turbines connected in a chain, the maximum distance from turbine to substation, the total collection system length, and the farm area are limited by transmission losses in moving power from the turbines to the offshore substation. These losses at least partially result from the relatively low voltages of the turbines, collection system, and export cable. As such, the available area addressable by an array of prior turbines is limited. To implement a very large farm (e.g., over 1 GW, including over 5 GW, over 200 turbines, including over 400 turbines, and/or over 400 square km, including over 1000 square km), prior collection systems would require multiple offshore substations, substantially increasing cost. [0005] To minimize collection system losses (from turbines to offshore substation), the offshore substation must be located as close to the turbines as possible. Typically, the distance from an offshore substation to the nearest turbine is below 2x, and typically less than lx the distance between nearest neighbor turbines. To minimize transmission losses from the turbines to the substation, an offshore substation is located within the lease area, and typically among the turbines. For a lease area requiring floating turbines, such a substation is concomitantly floating. [0006] As the substation is located very close to the turbines, the export cable (carrying power to shore) must reach the entire distance from the lease area to shore. For long distances from offshore substation to shore (e.g., over 30 km, including over 60 km, including over 100 km), it would be desirable to use an export cable operating at higher voltage to reduce losses. Higher voltages may require a combination of three separate cables (as opposed to a single cable with three conductors within), which may be expensive.

[0007] The technical requirements particular to a floating installation also add significant cost. Floaters move with wind and waves, and so equipment used in or coupled to floating installations must be capable of sustaining the dynamic loads associated with floater motion. Such requirements have proven technically challenging, especially for cables. A dynamic export cable that is specified for use with floating substations is typically limited to a maximum nominal voltage that is lower than that of a static cable that cannot be connected to a floater. As a result, transmission losses from a floating substation to an onshore substation challenge the implementation of floating installations located far from shore.

SUMMARY

[0008] Various aspects provide for a wind turbine generator comprising a propeller coupled to a hub, a generator coupled to the hub and configured to be driven by the propeller to output a generator voltage and having a nominal turbine output voltage that is greater than 66kV (including at least llOkV, including at least 132kV). The turbine may comprise a transformer coupled to the generator and configured to transform the generator voltage to the desired nominal output voltage.

[0009] A wind farm (e.g., an offshore wind farm) may comprise a plurality of turbines having a nominal output voltage that is at least (e.g., greater than) 66kV (72.5kV rated voltage), including at least lOOkV. The turbines may have a nominal output voltage that is at least 1 lOkV, including at least 132kV (145kV rated), including at least 150kV. The turbines may be coupled via an electrical collection system that operates at a collection system voltage that matches the nominal output voltage of the turbines (e.g., 66kV/132kV/150kV). The turbines and collection system may operate using A/C power transmission.

[0010] An offshore substation may be electrically coupled to the turbines via the collection system. The offshore substation may be configured to receive power from the turbines at the collection system voltage and transform the power for export at a nominal export voltage (typically greater than the collection system voltage). An export cable may couple the offshore substation to the grid and/or other onshore location (including an onshore substation), and typically operates at the export voltage. A typical nominal export voltage is at least 220kV, including above 220kV, including at least 275 kV, including at least 300kV, including at least 360kV, including at least 420 kV). The export cable may transmit A/C or D/C power.

[0011] A typical farm may be configured to provide over 100 MW of power to shore, with the collection system, substation and export cable specified accordingly. An export cable may have a power capacity that is at least 200 MW, including at least 300 MW, including at least 400 MW, including at least 450MW, including at least 500 MW. An exemplary export cable may convey at least 300 MW of power at a nominal voltage that is at least 200 kV. For a larger installation that is especially far from shore, an exemplary export cable may convey at least 420 MW of power at a nominal export voltage that is at least 420 kV. A high-voltage export cable may enable low-loss power transmission from a distant offshore substation. This flexibility in location of the substation may enable its situation in a relatively lower cost area (e.g., shallow water or on an island).

[0012] An offshore substation may be floating or disposed in a “remote onshore” configuration (e.g., on an island) and/or on a bottom fixed platform. An offshore substation may be located outside of the lease area of the farm within which the turbines are located (e.g., if an island or shallow water exists outside the lease area). A first lease area may comprise a region within which the turbines are located, and a second lease area may comprise the location of the offshore substation, which may be located relatively far from the first lease area (e.g., at least 10 km, including at least 30 km, including at least 50 km, including at least 80 km).

[0013] A nearest-neighbor distance may be defined as the distance between two turbines 112, and 113 in the array that are closest to each other (the “nearest-neighbor” turbines in the farm).

A typical nearest-neighbor distance may be from about 1 to 3 km, including from about 1.3 to 2.5 km, including from about 1.5 to 2.2 km. A distance from the offshore substation to the lease area boundary and/or the turbine (of the plurality) that is nearest the offshore substation may be at least 2x, particularly at least 3x the distance between the two turbines that are closest to each other. The distance from the offshore substation to the closest turbine and/or closest lease area boundary may be at least 5x, including at least lOx, including at least 20x, including at least 50x the distance between nearest-neighbor turbines. A distance from the offshore substation to the nearest turbine and/or lease area boundary may be at least 7 km, including at least 10 km, including at least 15 km, including at least 30 km. For large distances from turbines to substation, the use of higher turbine output voltage may reduce transmission losses to the substation, yielding flexibility with respect to the location of the substation. This flexibility may enable a lower-cost or otherwise higher performing substation location.

[0014] In an embodiment, the wind turbines are disposed on floating platforms and the offshore substation is disposed on a bottom-fixed platform or on an island (e.g., relatively far from the turbines). As such, the export cable may comprise a cable specified for static installations. Such an implementation may provide for the use of high voltage export cables (i.e., higher than would be available for a floating substation) without requiring expensive multiple cables. The advantages offered by the higher-performance export cable may offset the increased cost of higher turbine voltages, yielding increased overall performance. With the higher voltage export cable, power from a very distant floating farm may be cost-effectively brought to shore with low transmission losses. An exemplary export cable may operate at a nominal export voltage that is at least 275kV and have a power capacity that is at least 500 MW.

BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 is a schematic illustration of a high voltage offshore wind farm, per an embodiment.

DETAILED DESCRIPTION

[0016] For very large offshore wind farms, the location of the farm itself plays an important role in total system cost. Often, attractive wind conditions are located far from shore and/or in deep water. Transmission losses may limit the maximum distance from shore at which a farm may be economically viable. Floating installations impose a range of additional costs associated with the dynamic motion of floaters and equipment coupled to floaters.

[0017] Various aspects provide for wind turbines having relatively high nominal output voltages (e.g., over 66kV, corresponding to 72.5kV rated voltage). A nominal turbine output voltage may be above 100 kV, including at least 130 kV, such as 132kV (145kV rated), including at least 143 kV, including at least 150 kV, including at least 165kV, including at least 198kV. By increasing the corresponding voltage of the collection system, the substation (e.g., offshore) may be located relatively far away from the turbines themselves without incurring excess transmission losses.

In some cases, such a location enables a significant reduction the cost of other components, such that an increased cost of the turbines (e.g., higher voltage transformers) is offset by a reduced cost of other components (e.g., cables, offshore platform). Locating an offshore substation in shallow water (e.g., on a bottom fixed platform) or on an island may significantly reduce the cost of the substation itself, and the corresponding export cable (not needing to be dynamic) may be substantially less expensive. If this location is far from the turbine field, the transmission losses that might otherwise make such a location impractical may be mitigated by using high voltage turbines that yield lower transmission losses.

[0018] Locating an offshore substation on a bottom-fixed platform or on an island may eliminate the need for a dynamic export cable. A higher voltage static cable may be used to export power to shore, as opposed to a lower voltage export cable (yielding higher transmission losses) or an expensive, complicated system of multiple export cables. The high-voltage turbines (enabling a distant, static, offshore substation) and the high-voltage export cable (enabling low-loss transmission to shore) may combine to yield a substantially more efficient offshore wind farm. This efficiency may be especially important when a very high wind-power lease area is located very far from shore. Various aspects may be implemented onshore.

[0019] FIG. 1 is a schematic illustration of a high voltage (in this case offshore) wind farm, per an embodiment. A wind farm 100 may comprise a plurality of wind turbines 110, typically disposed within a lease area 102, which may be offshore. A wind turbine may have a nominal output voltage that is at least (e.g., greater than) 66kV (e.g., at least 132 kV). An electrical collection system 120 may couple the wind turbines to a substation (typically an offshore substation) 130. The collection system 120 operates at a collection system voltage that is chosen to match the output voltage of the turbines. A typical collection system nominal voltage is greater than 66 kV (e.g., 110 kV). The collection system voltage may be at least 132kV, including at least 150kV.

[0020] The substation 130 is configured to receive incoming power from the collection system 120 (at the collection system voltage) and export the power at an export voltage that is typically higher than the collection system voltage. Substation 130 may be located a distance 131 that is relatively far from the nearest turbine 111 (e.g., at least 10 km, including at least 30 km, including at least 60km, including at least 100km). The substation 130 may be located far outside of the lease area 102 within which the turbines 110 are disposed. With the relatively high output voltage of the turbines and collection system, transmission losses may be low, despite the substation being located far from the turbines themselves. An offshore substation may be located on a bottom-fixed platform 135, which is often disposed in a shallow water region 132 (as show in FIG. 1). An offshore substation may be disposed on island (not shown), which may substantially reduce construction and maintenance costs.

[0021] Power may be exported from the substation 130 via an export cable 140 chosen to economically transport power at the nominal export voltage. A substation (e.g., having a transformer, choke, rectifier, circuit breaker, switches, and the like) may step up the turbine output voltage to a nominal export voltage which is at least 220kV, including greater than 220kV, including at least 275kV, including at least 300 kV, including at least 400kV, such as at least 420kV. The export cable 140 may have a power capacity that is over 200MW, including at least 300MW, including at least 400MW, including at least 500MW.

[0022] An export cable may comprise a bundled 3-phase cable. An export cable may comprise several (e.g., three) single-phase cables. The choice of cable typically requires a comparison of (at least) the manufacturing cost vs. the installation cost. For very large power capacities, the size and mass of the conductor itself may present manufacturing challenges, especially for a bundled cable. While single-conductor cables may be easier to manufacture, they are typically more expensive to install. According to a particular exploitation plan, the additional installation cost associated with using discrete single-phase cables may be compared to the marginal manufacturing cost difference (bundled vs. discrete cables) to select an optimal export cable. [0023] An export cable may comprise a static cable specified only for fixed installations. An export cable may comprise a dynamic portion specified for dynamic (e.g., floating) installations, such as a floating substation. In an embodiment, a system comprises a hybrid cable having a dynamic portion (e.g., proximate to a floating substation) and a static portion (e.g., proximate to shore). Such a cable may be advantageous with for a highly attractive lease area that is not near any shallow water or island upon which the offshore substation could be situated (e.g., a floating array and floating substation located especially far from shore).

[0024] For an offshore substation, the export cable may transmit power from the substation to shore (e.g., to an onshore substation or to the grid). For an export cable operating below grid voltage, power to shore may be additionally stepped up to grid voltage (e.g., 420k V). For some substations, the nominal export voltage may match the grid voltage, such that power is exported from the offshore substation to an onshore location at grid voltage. Such a configuration may eliminate the need for an onshore substation, which may substantially reduce cost. In the example shown in FIG. 1, the export cable 140 is coupled to an onshore substation 150 configured to convert the inbound power from the export cable voltage to grid voltage (e.g., 300- 420 kV).

[0025] By utilizing a relatively high collection system voltage, transmission losses from the turbines 110 to the substation 130 may be reduced without requiring the increased cost associated with larger gauge cabling in the collection system itself. With reduced losses, the substation may be located relatively far from the turbines themselves (e.g., several kilometers, including tens of kilometers). An offshore substation (130) may be located outside the area defined by the perimeter of the turbine array and/or outside the lease area 102 within which the turbines are situated.

[0026] As compared to the distance between two nearest-neighbor turbines, a distance from the substation 130 to the nearest turbine 110 may be at least 2x the distance between the two nearest-neighbor turbines. The distance from nearest turbine to substation may be at least 5x, including at least lOx, including at least 50x, including at least lOOx the distance between two adjacent turbines.

[0027] Higher turbine/collection system voltages may allow the collection system to “reach” on otherwise inaccessible offshore substation location (e.g., island or shallow water). With the available increased distance between the substation and the turbines, a wider range of substation location options may be available. Whereas a deepwater region proximate to floating turbines might require a floating substation, a distal shallow water region (or even an island) may allow for implementation using a bottom fixed platform, which may technically easier and less expensive. By locating the substation on a bottom-fixed platform, the construction challenges may be greatly reduced as compared to a floating offshore substation. By situating an offshore substation on an island, construction and operation costs may be even lower (closer to onshore costs), yielding a “remote onshore” location for the offshore substation. Thus, an increased cost associated with the high voltage turbines may be reduced by lower substation costs and/or cabling costs. In exemplary FIG. 1, a shallow water region 132 is located a distance from the turbines that would be prohibitive using lower voltage collection systems, but technically feasible using the turbines 110 and collection system 120 described herein. Having reached location 132 (shallow water or island), the system may use an export cable specified for static installations, which may have a higher voltage and/or power capacity than an export cable specified for dynamic installations. The combination of these features may yield an overall increase in performance that justifies their increased cost. A marginally increased capital cost may be offset by marginally increased operating revenue over the lifetime of the farm.

[0028] In some cases, additional technical barriers may be overcome by a preferred offshore substation location. A substation disposed on a floater requires the use of dynamic cables and connections that are specified to tolerate the movements of the floater on the waves. Anchoring costs, access costs, and other costs also typically higher for floating installations. The location of an offshore substation on a bottom fixed platform in shallow water (FIG. 1) or on an island (enabling even lower cost couplings and cables) may eliminate the need for floater-compatible components (e.g., cabling and couplings). As such, various embodiments address a long-felt market need. Higher voltage cables may be specified for static installations, but not the dynamic installations characteristic of floaters. The use of high voltage turbines and collection system may provide for a substation location on a bottom-fixed platform or island, which subsequently eliminates the requirement of dynamic export cables that are constrained to operate at low voltages.

[0029] For long distances 133 from substation to shore (e.g., over 30km, including at least 50km, including at least 100km, including at least 200km), locating the substation on a bottom- fixed platform or island may provide for the use of a high voltage export cable (e.g., at least 200kV, including at least 300kV, including at least 400kV). Such high voltage export cables 140 enable increased distances from substation to shore without substantially increased transmission losses or correspondingly higher cable gauges. As such, system cost may be additionally reduced. In the case of floating turbines (where prior offshore substations would also need to float near the turbines), various embodiments may overcome the technical limitations on the voltage of dynamic export cables. In an embodiment, distance 131 from the substation to the closest turbine is at least 3x, including at least 5x the nearest-neighbor turbine distance, and the distance 133 from the substation to shore is at least 5x, including at least lOx the distance 131 from the substation to the turbines. A distance 131 from an offshore substation to the nearest turbine 111 may be at least 7 km, including at least 10 km. A distance 133 from the offshore substation to shore may be at least 30 km, including at least 50 km, including at least 100 km.

[0030] Various aspects may comprise a coupling 114 that receives power from several turbines in parallel and outputs a single line to the collection system (e.g., at least a 2-into-l coupling as shown in FIG. 1, including 3-into-l, including at least 4-into-l, including at least 6-into-l). A coupling 114 may comprise a separate transformer that steps up the turbine output nominal voltage for transmission to the substation. The collection system may operate at the stepped-up voltage or an even higher collection system voltage. The stepped-up voltage may be between the turbine output voltage and the export voltage, particularly not exceeding the collection system voltage.

[0031] Various features described herein may be implemented independently and/or in combination with each other. An explicit combination of features in an embodiment does not preclude the omission of any of these features from other embodiments. Features described in separate embodiments may be combined, notwithstanding that their combination is not explicitly recited as such. The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.