NO347790B1

NO347790B1 - Offshore Array of High Voltage Turbines

Info

Publication number: NO347790B1
Application number: NO20210468A
Authority: NO
Inventors: Hans Petter Øvrevik; Knut Vassbotn
Original assignee: Deep Wind Offshore As
Priority date: 2021-03-08
Filing date: 2021-04-15
Publication date: 2024-03-25
Also published as: NO20210468A1

Description

OFFSHORE ARRAY OF HIGH VOLTAGE TURBINES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of US provisional patent application no. 63/157,863, filed March 8, 2021, which is incorporated by reference herein.

BACKGROUND

1. Technical Field

[0002] The present invention relates generally to wind turbines, and more particularly to arrays of offshore wind turbines.

2. Description of Related Art

[0003] 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 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).

[0004] 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., >500MW) 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 an export voltage that is higher than the turbine voltage (e.g., up to 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).

[0005] 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 voltage of the collection system. 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.

[0006] 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 1x the distance between nearest neighbor turbines. An offshore substation is located within the lease area, and typically among the turbines, in an effort to minimize transmission losses from the turbines to the substation. As the substation is located very close to the turbines, the export cable (carrying power to shore) must reach virtually the entire distance from the lease area to shore.

[0007] 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, but at this time, commercially available 3-phase bundled export cables are limited to 220kV specified voltage (e.g., 240kV maximum voltage, with tolerance providing for safe 220kV operation). Higher voltages would require a combination of three separate cables (as opposed to a single cable with three conductors within), which is typically prohibitively expensive.

[0008] 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. At this time, commercially available export cables that are specified for use with floating substations are limited to a maximum voltage of 66kV. As a result, transmission losses from a floating substation to an onshore substation prohibit the implementation of floating installations located far from shore. PCT patent application no. PCT/NL2011/050265 describes an offshore substation for a wind farm. (Title) PCT patent application no. PCT/EP2017/071780 describes a converter arrangement for connecting wind energy installations to an energy supply system. (Title) EP patent application no.13184177.7 describes a wind turbine transformer arrangement. (Title) PCT patent application no. PCT/DK2021/050396 describes a wind turbine transformer. (Title)

SUMMARY

[0009] 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 turbine output voltage that is greater than 66kV (e.g., above 100kV, including at least 132kV, including at least 143 kV, including at least 165kV, including at least 198kV). The turbine may comprise a transformer coupled to the generator and configured to transform the generator voltage to the desired output voltage.

[0010] A wind farm (e.g., an offshore wind farm) may comprise a plurality of turbines having an output voltage greater than 66kV, including at least 100kV, including at least 132kV. The turbines may be coupled via an electrical collection system that operates at a collection system voltage that matches the output voltage of the turbines (e.g., above 66kV). 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 export the power at an export voltage, which may be 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 export voltage is at least 220kV, including above 220kV, including at least 300kV, including at least 360kV, including at least 420 kV).

[0011] 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 30km, including at least 50km, including at least 80km).

[0012] A distance from the offshore substation to the turbine (of the plurality) that is nearest the offshore substation may be at least 2x the distance between the two turbines that are closest to each other (the “nearest-neighbor” turbines in the farm). The distance from the nearest turbine to the offshore substation may be at least 5x, including at least 10x, including at least 20x, including at least 50x the distance between nearest-neighbor turbines.

[0013] 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. 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. With the higher voltage export cable, power from a very distant floating farm may be cost-effectively brought to shore with low transmission losses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG.1 is a schematic illustration of a high voltage offshore wind farm, per an embodiment.

DETAILED DESCRIPTION

[0015] 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.

[0016] Various aspects provide for wind turbines having relatively high output voltages (e.g., over 66kV, including at least 100kV, including at least 130 kV, such as 132kV). 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 substation). 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.

[0017] Locating an offshore substation on a bottom-fixed platform or on an island may eliminate the need for a dynamic export cable. Thus, a high 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 at low loss) and the high-voltage export cable (enabled by a static offshore substation, and itself 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.

[0018] 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 an output voltage 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 voltage is greater than 66kV.

[0019] 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 greater 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 30 km, including at least 60km, including at least 100km). The substation 130 may be located 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).

[0020] Power may be exported from the substation 130 via an export cable 140 chosen to economically transport power at a voltage that is typically at least as large as the turbine output voltage. A substation may step up the turbine output voltage to an export voltage which is at least 220kV, including greater than 220kV, including at least 300 kV, including at least 400kV, such as about 420kV. 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., 420kV). For some substations, power is exported from the offshore power station at grid voltage, which may eliminate the need for an onshore substation. 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).

[0021] 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, or even >100 km away). 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 10x, including at least 50x, including at least 100x the distance between two adjacent turbines. 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.

[0022] With the available increased distance of substation to turbines, a wider range of substation location options may be available. Whereas a deep water 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 or an “remote onshore” apparatus, 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. Thus, an increased cost associated with the high voltage turbines may be reduced by lower substation costs and/or cabling costs. By locating the substation on an island, the technical construction challenges (manifest as increased cost) may be reduced even further. 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.

[0023] 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. Presently, there is no commercially available export cable that operates at a voltage greater than 66kV that is also specified for operation with a floating offshore substation. 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.

[0024] 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.

[0025] 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.

Claims

1. An offshore wind farm (100) comprising:

a plurality of offshore wind turbines (110) having an output voltage that is at least 132kV; an electrical collection system (120) electrically coupled to the turbines and configured to operate at a collection system voltage that matches the output voltage of the turbines; an offshore substation (130) electrically coupled to the wind turbines (110) via the collection system (120) and configured to receive power at the collection system voltage and export the power at an export voltage that is at least 220kV; and an export cable (140) electrically coupled to the offshore substation (130) and configured to transmit power from the substation to an onshore location at the export voltage; characterized in that:

the wind turbines (110) are disposed on floating platforms;

the offshore substation is located a first distance (131) from a nearest turbine (111) of the plurality that is at least 2x a second distance between the two turbines (112, 113) in the farm that are closest to each other;

the offshore substation (130) is disposed on a bottom fixed platform (135) or an island;

and

the export cable (140) comprises a cable specified for static installations.

2. The wind farm of claim 1, wherein the substation (130) is configured to convert the collection system voltage to an export voltage that is greater than 220kV.

3. The wind farm of claim 2, wherein the substation (130) is configured to convert the collection system voltage to an export voltage that is at least 300 kV.

4. The wind farm of claim 3, wherein the export voltage is at least 360kV.

5. The wind farm of any of claims 1-4, wherein the first distance (131) from the offshore substation (130) to the nearest turbine (111) of the plurality is at least 5x the second distance between the first turbine (112) and the nearest neighbor turbine (113) to the first turbine.

6. The wind farm of any of claims 1-5, wherein the offshore substation (130) is further configured to export the power at a grid voltage.

7. The wind farm of any of claims 1-6, wherein the offshore substation (130) is located several kilometers from the turbines.

8. The wind farm of any of claims 1-7, wherein the offshore substation (130) is located tens of kilometers from the turbines.

9. The wind farm of any of claims 1-8, wherein the offshore substation is disposed on the island.

10. The wind farm of any of claims 1-8, wherein the offshore substation is disposed on the bottom-fixed platform (135).