CA2834724A1

CA2834724A1 - A flow power plant and a method for its operation

Info

Publication number: CA2834724A1
Application number: CA2834724A
Authority: CA
Inventors: Raphael Arlitt; Frank Biskup; Norman Perner
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2011-05-12
Filing date: 2012-03-30
Publication date: 2012-11-15
Also published as: WO2012152356A1; EP2707597A1; KR20150006330A; DE102011101368A1; EP2707597B1

Abstract

The invention relates to a method for operating a fluid power plant comprising a rotor with which a horizontal rotational axis, a vertical axis, and a horizontal transverse axis are associated, these being perpendicular to one another, and said rotor being driven by an inflow and generating a drive torque about the rotational axis, a thrust force in the direction of the rotational axis, and a pitching moment about the transverse axis. The power plant also comprises an electric generator that is at least indirectly connected to the rotor such that during operation, said generator produces a generator torque that brakes the rotor. The invention is characterised in that when a thrust force threshold-value is reached for the thrust force, and/or a pitching moment threshold-value for the pitching moment, an adjustment of the generator torque brings the rotor into a load-limited operation for which said rotor rotates with a tip-speed ratio that is greater than an optimum-power tip-speed ratio, and greater than a limited-power tip-speed ratio.

Description

A flow power plant and a method for its operation The invention relates to a flow power plant and a method for its operation, especially a tidal power plant which stands freely in a marine current and an operating method for such a system.
In addition to the tidal power plants which will be discussed below, further flow power plants will be used for implementing the invention, especially hydroelectric river power plants or wind power plants. Free-standing systems, i.e. such that are installed outside of a barrier structure, have been proposed for utilizing tidal currents. The flow can either freely flow around the rotor of such a tidal power plant or be arranged in a Venturi housing for accelerating the flow. A
propeller-shaped rotor is assumed for the discussions below, to which a horizontal rotational axis is assigned. Furthermore, the rotor is associated with a horizontal transverse axis and a vertical axis. The rotational axis, the transverse axis and the vertical axis form an orthogonal tripod.
The rotor of the tidal power plant usually drives an electric generator for power generation. There can be a torsion-proof connection between the rotor and the electric generator, so that the generator torque produced by the electric generator will act in a directly braking manner on the rotor during operation. An alternative configuration can be considered, for which the drive connection from the rotor to the electric generator occurs indirectly. Instead of a torsion-proof connection, a hydrodynamic circuit such as a hydrodynamic coupling or a hydrodynamic converter can be interposed in the drive train. A configuration can further be considered for which the rotor power is transmitted by means of hydrostatic components onto the electric generator.
Irrespective of the concrete configuration of the drive train, a system is assumed below in which the electric generator acts in normal operation in a braking manner , .
. ,

2 on the rotor by means of the generator torque and a specific rotational speed occurs in the rotor depending on the provided inflow and the applied generator torque. Operation can occur along a system curve on the basis of a measurement of the flow field on the rotor. The supporting generator torque will be set in power-optimal operation in such a way that a speed is obtained in the rotor which maximizes the power coefficient. As an alternative to operation at characteristic curve, the power-optimal operating point can be determined from the power data by means of an MPP controller.
Once the flow power plant reaches nominal power, power downregulation usually occurs. As a result, the system departs from power-optimal operation and power-limited operation will commence, for which the power take-up of the rotor is limited for protecting the power-electronic components used for connection to the grid. The pitch angles of the rotor blades are typically adjusted for this purpose for wind power plants, or power downregulation occurs by flow separation on the rotor. As a result of the difficult accessability of the systems for maintenance work, a simplified design without a blade angle adjusting apparatus is preferred for tidal power plants, so that the first variant of power downregulation cannot be performed in such a system. The second variant is disadvantageous because high thrust forces act on the rotor blades upon occurrence of flow separation. It is proposed as a solution by DE 10 2008 053 732 to transfer the system to the high-speed range for power downregulation. With increasing tip-speed ratio the power coefficient of the rotor decreases, so that power-limited operation can be carried out.
High loads occur in tidal power plants in power-limited operation for rotors with rigidly linked rotor blades and buoyancy rotor design. The relevant aspect is that the thrust force of the rotor in the direction of the rotational axis and the tilting moment of the rotor. The tilting moment is obtained from a vertical flow profile on the rotor, i.e. the inflow velocity via the area covered by the rotor depends on the , .
. ,

3 water depth, so that the balance of the thrust forces between the upper half of the rotor circle and the bottom half shows an imbalance.
In order to implement power-optimal and power-limited system management, the drive train of a generic flow power plant must be designed in the entire operating range for supporting the introduced thrust forces and tilting moments. This leads to drive trains which are complex in respect of their construction and large in respect of their design. In addition, massive constructions are necessary for the arrangement of a support structure and for the foundation. Furthermore, the inflow condition can vary to such a high extent within a tidal power plant park with several systems that different system configurations would be advantageous. A
location-specific adjustment of the flow power plants to the expected rotor loads is complex, so that typically uniform installations with a sufficiently dimensioned safety reserve are used.
The invention is based on the object of overcoming the aforementioned disadvantages of the state of the art and to provide a flow power plant, especially for obtaining power from tides, which reduces the forces and the torques in the drive train which are obtained from the thrust loads on the rotor.
Furthermore, an operating method is provided which relieves the drive train during strong inflow. It shall be possible to perform the operating method in a robust and simple way.
Furthermore, maritime growth shall influence the installation and the operating method to the lowest possible extent. Furthermore, a possibility for the simplest possible location-specific adaptation of generic flow power plants shall be provided.
The object on which the invention is based is achieved by the features of the independent claims. Advantageous embodiments are provided in the sub-claims.

4 The inventors have recognized that the thrust force of the rotor in the direction of the rotational axis and the tilting moment about a transverse axis of the rotor which is perpendicular to the vertical axis of the system and the rotational axis needs to be monitored during operation. If the thrust force reaches a thrust-force threshold value or accordingly the tilting moment reaches a tilting-moment threshold value, the currently provided power-optimal or power-limited operation is left and instead a load-limited operation is introduced. For this purpose, the braking torque applied by the electric generator to the rotor will be reduced, so that the rotor will accelerate up to a new operating point which lies at a higher rotor speed and therefore a higher tip speed ratio. As a result, the thrust force and the tilting moment are kept beneath the respectively predetermined threshold value. It is accepted in this case that in the range of higher speed ratios the power coefficient will drop, so that the system will take up less power during the phase of strong inflow. This can be compensated in the annual average by the improved rotor configuration which is enabled by the load-limited operation.
Furthermore, the entire system can be streamlined.
The tilting moment of the rotor reaches a predetermined tilting-moment threshold value when a distinct vertical flow profile is present. This is the case when there is a strong flow close to the surface which is caused by meteorological influences such as winds. The load can vary strongly under the influence of wind and waves, so that load surges in particular need to be compensated. Apart from this, the case of an excessive thrust force in the direction of the rotation axis will be discussed, wherein a characteristic curve for the thrust coefficient or for the dependence of the tilting moment on the tip speed ratio for system management will be used depending on the type of the current limit load. The rotor speed is increased in both cases to such an extent that a tip speed ratio is obtained for which the loads lie beneath the chosen threshold values.

The power-limited operation will be performed in such a way that a setpoint value for the thrust force and/or for the tilting moment is predetermined, wherein these setpoint values lie beneath the respective threshold values of the thrust force and the tilting moment. If one of the loads, i.e. the thrust force or the tilting moment,

5 can be identified as a limiting load, a temporal mean value is formed for this load and it is kept constant depending on the load setpoint value.
The increase in the rotor speed in load-limited operation for reducing the thrust force and the tilting moment can be performed up to the runaway speed. In this case, the braking torque of the electric generator will cease completely and the revolving unit with the rotor merely needs to overcome the bearing losses. The runaway speed occurring for free running represents the upper limit of load-limited operation.
A load detection device is used in a generic flow power plant for performing the operating method in accordance with the invention, which load detection device determines the thrust force and/or the tilting moment of the rotor and transmits the same to a control device. The control device comprises an open-loop or closed-loop control for the generator torque, which is capable, in addition to the measured data for the inflow velocity, to process the values of the thrust force and/or the tilting moment. In this case, characteristics-based methods are considered by additionally considering load characteristics for the thrust force and for the tilting moment. Alternatively, a closed-loop control can occur for a predetermined load that is averaged over time. For the purpose of determining the thrust force and the tilting moment, either the flow field present in the rotor circle is measured and the load is determined from a system model, or the loads are derived from load measuring apparatuses. They can be strain gauges on sections of the rotor blade or pressure sensors in the bearings for example.
Sensors which operate according to the ADCP principle are preferably used for determining the flow field on the rotor.

6 The load downregulation provided in accordance with the invention for limiting the thrust force of the rotor and the rotor tilting moment allows arranging the drive train to the predetermined thrust-force and tilting-moment threshold values.
This especially relates to the bearing of the revolving unit and the attached holding structures for load dissipation into the machine nacelle. This allows a modularization of the system, wherein a uniform drive train is assumed and the rotor characteristics are adjusted specific to the location. In the simplest of cases the rotor diameter is varied. Further deviations in the rotor characteristics are obtained by setting a depth distribution of the profile and/or the progression of the torsion. As a result of such a measure, differently configured systems can be used for a flow power plant park, in that only the rotor is adjusted to the respectively provided power histogram and the expected tilting moments, and standard components are used for the drive train. A uniform threshold value for the load will be determined for all systems, from which the load-limited operation will be initiated.
The invention will be explained below in closer detail by reference to embodiments shown in the drawings, wherein said drawings show the following in detail:
Fig. 1 shows the curve of the thrust force against the inflow velocity on the rotor for operation of a flow power plant in accordance with the invention.
Fig. 2 shows the power taken up by the rotor for system management according to Fig. 1.
Fig. 3 shows an example for the temporal progression of the thrust force with a transition in accordance with the invention to thrust-force-limited operation.

. .
. .

7 Fig. 4 shows a frequency curve for the power of a flow power plant in accordance with the invention.
Fig. 5 shows the progression of the tilting moment in relation to the inflow velocity on the rotor for load-limited operation in accordance with the invention with a tilting-moment-limited operating range and a thrust-force-limited operating range.
Fig. 6 shows the progression of the thrust force and the power taken up by the rotor the system management according to Fig. 5.
Fig. 7 shows a flow power plant in accordance with the invention in a partly sectional view.
Fig. 8 shows a flow power plant park with two flow power plants with identical drive trains and rotors with different rotor characteristics.
Fig. 9 shows the progression of the power coefficient, thrust coefficient and an exemplary coefficient for the tilting moment against tip speed ratio.
Fig. 7 shows a flow power plant 1 in accordance with the invention which is used for generating power from tides. The flow power plant 1 comprises a rotor 3 whose rotor blades are fixed in a rotationally rigid fashion to a hub. The rotor 3 is part of a revolving unit 2, which further comprises a cover 4 and a drive shaft 25.
The drive shaft 25 is coupled in a torsion-proof manner with a generator rotor 6.2 of an electric generator 6.
Radial bearings 11.1, 11.2 and an axial bearing 12 are used for bearing the revolving unit 2. They are partly arranged in a machine nacelle 14, which additionally accommodates the electric generator 6. The machine nacelle 14 is

8 positioned on a support structure 7. Said support structure 7 is carried on its part by a foundation part 8 which is arranged as a gravity foundation. Further foundation variants can be considered, e.g. the support structure 7 can be arranged as a tower which is inserted into a drilling foundation on the ground

9 of the water body.
The rotor 3 determines a horizontal rotational axis 21. A vertical axis 22 extends perpendicularly thereto. A transverse axis 23 is disposed perpendicularly to the rotational axis 21 and the vertical axis 22, said rotational axis 23 extending in the present illustration perpendicularly to plane of the paper.
Buoyancy and resistance forces which can be broken down into tangential and thrust forces are generated for a rotor 3 arranged as a buoyancy rotor as a consequence of the inflow. The entirety of the forces on the rotor 3 in the direction of the rotational axis 21 form the thrust force F. Furthermore, there is an imbalance of the thrust forces in the upper semicircle of the area covered by the rotor 3 in comparison with the bottom semicircle in the case of a vertical flow profile for the illustrated inflow 24. This leads to a torque about the transverse axis 23 which is designated in the present case as the tilting moment M.
The flow power plant 1 in accordance with the invention comprises a load detection device 26 which is associated with load measuring apparatuses 13.1, 13.2, 13.3. A load measuring apparatuses 13.1 is provided by way of example in the region of the axial bearing 12. It measures the thrust force F and the tilting moment M on the basis of the bearing forces. A further load measuring apparatus 13.2 is attached to the support structure 7. Furthermore, thrust forces on the rotor 3 are measured by means of a strain gauge which is accommodated in a rotor blade. It forms a third load measuring apparatus 13.3. The individual load measuring apparatuses 13.1 to 13.3 can be wired to the load detection device or a data exchange is provided via a radio-based system.

The load detection device 26 is connected to a control device 15 or is accommodated therein. The control device 15 comprises a feedback control apparatus 5, which is designed in such a way that the generator torque controls or adjusts the generator torque upon reaching a thrust-force threshold value FL
for the thrust force F and/or upon reaching a tilting-moment threshold value ML
for the tilting moment 10 in such a way that the rotor 3 is guided in load-limited operation BL. For this purpose, a generator torque GM is set by the frequency converter 16 which is used for connecting the electric generator 6 to an interconnected grid 20. The frequency converter 16 comprises a rectifier 17 on the generator side, an intermediate DC circuit 19 and a power inverter 18 on the grid side. The management of the generator torque GM occurs via the rectifier 17 on the generator side, which predetermines a load current by means of an open-loop or closed-loop control unit to the generator stator 6.1 of the electric generator 6 in order to adjust the stator voltage components (d, q). The load-limited operation BL
is provided by this predetermination for the generator torque GM, which is transferred by the present torsion-proof coupling with the rotor 3.
Fig. 9 schematically shows the power coefficient cp against the tip speed ratio X.
The tip speed ratio A, indicates the ratio between the blade tip speed of the rotor 3 and the inflow velocity v. The inflow velocity v represents an averaging of the flow field over the area 3 covered by the rotor 3.
The power coefficient cp is calculated from the power taken up by the rotor, the density p of the flow medium, the inflow velocity v and the rotor radius r as follows:

--p .Tt= r Cp =

The power coefficient cp has a maximum for a power-optimal tip speed ratio opt.
As a result, a generic flow power plant 1 is operated with the power-optimal tip speed ratio opt in power-optimal operation. The flow field can be measured on the rotor 3 for system management. A flow measuring apparatus 8 is shown by way 5 of example in Fig. 7, which can be arranged as an ADCP (Acoustic Doppler Current Profiler).
Fig. 9 further shows the thrust coefficient CF against the tip speed ratio = =
= =The thrust coefficient CF is determined from the thrust force F, the density p of the

10 flow medium, the inflow velocity v and the rotor radius r as follows:
1.p.v2 .7r. r2 CF =-Fig. 9 further shows the tilting moment coefficient CK for a predetermined flow profile, wherein CK can be assumed in a first approximation as being proportional to the product of CF and the rotor radius r.
As is shown in Fig. 1, the flow power plant 1 is managed with a power-optimal tip speed ratio -opt in power-optimal operation Bl for inflow velocities of v smaller than vo. For this purpose, the generator torque GM is set depending on the measured inflow velocity, or the system is controlled on the basis of a known characteristic curve, so that a flow measuring apparatus 28 can be avoided.
The nominal power Pr of the flow power plant is reached at an inflow velocity vo, and the power-limited operation B2 follows for higher inflow velocities up to v1, for which such a generator torque GM is predetermined, leading to a power-limited tip speed ratio =r which limits the absorbed power P on average to the nominal power Pr. The power-limited tip speed ratio =r is higher than the power-optimal tip speed ratio =opt.

. .

11 As is shown in Fig. 1, the thrust force F increases with rising inflow velocity v in power-limited operation B2 until the thrust-force threshold value FL is reached.
System management will then leave the power-limited operation B2 and will enter load-limited operation BL. This is shown in the temporal progression for the thrust force F as illustrated in Fig. 3. The thrust force exceeds the thrust-force threshold value FL for an averaged inflow velocity v above vo. As a result of this event, the load-limited operation BL commences, which in the present case is the thrust-limited operation B3.
The load-limited operation BL is preferably carried out as characteristic operation, for which not only the averaged inflow velocity v on the rotor but also the thrust force and/or the tilting moment acting on the rotor will be considered. A
thrust-force setpoint value Fs beneath the thrust-force threshold value FL will be predetermined for the present embodiment in an especially preferred way in order to ensure that the fluctuations caused by system inertia and control deviation are kept beneath the predetermined thrust-force threshold value FL. The feedback control can be arranged adaptively in order to enable reaction to the present velocity fluctuations in the inflow.
In the simplified diagram of Fig. 1, the load-limited operation BL is shown in the range between the averaged inflow velocities v1 and v2. The load to be limited in the present case is the thrust force F, so that a thrust-limited operation B3 is assigned a thrust-limited tip speed ratio XF as a load-limited operation BL.
The illustration shows that the rotor 3 of the flow power plant 1 is further guided into the tip speed range, and the load-limited tip speed ratio XL lies above the power-limited speed ratio Xr in the load-limited operation BL. This leads to the power drop in the load-limited operation BL as shown in Fig. 2.

12 The load-limited operation BL can merely be performed up to a limit speed for the inflow at v2, for which a tip speed ratio Xci is reached which is associated with the runaway speed. A further increase in the tip speed ratio = is no longer possible with rising inflow velocity v, so that the loads on the drive train will increase again.
A renewed increase in the thrust force F is shown by way of example for the operation at the runaway speed B4 in Fig. 1. The system configuration must be designed in such a way that the operation at runaway speed B4 lies outside of the power spectrum predicted for the present location of the plant.
Fig. 4 illustrates the system management in accordance with the invention on the basis of a frequency curve. The hours of operation are shown on the abscissa and the power P absorbed by the rotor is shown on the ordinate. The frequency curve represents the operation duration, for which a predetermined system power is exceeded. It is shown that the system is guided in power-limited operation B2 for an operation duration Tr ¨ T2 and the nominal power Pr is achieved. If the power present in the flow increases further as illustrated by the dashed part of the frequency curve, the load-limited operation BL occurs in accordance with the invention, so that the system power lies beneath the nominal power Pr for a short operating period T2 as a result of load limitation at especially high flow velocities.
Despite this reduction in power during a few hours of operation with highest load of the system, the total power yield of a flow power plant in accordance with the invention is still increased, because the rotor can be arranged with a large dimension due to the load limitation and the power yield in the medium-range of the power spectrum is thus increased.
Fig. 5 illustrates a further embodiment for the load-limited operation BL in accordance with the invention, wherein the tilting moment M applied against the tip speed ratio = leads to the consequence that the tilting-moment threshold value ML is reached at the inflow velocity vo. This leads to the transition to the load-limited operation BL, which in the present case is the tilting-moment-limited

13 operation B5. For this purpose, a load-limited tip speed ratio =L is set which is higher in relation to the power-optimal tip speed ratio =opt. In the present case, the progression of the tip speed ratios = between the averaged inflow velocities vo and v1 in tilting-moment-limited operation B5 follows the tilting-moment-limited power coefficient =fri. This leads to the drop in the power P absorbed by the rotor 3 in tilting-moment-limited operation B5 which is shown in Fig. 6. It is assumed for the present embodiment that the thrust force F absorbed by the rotor will rise further as shown in Fig. 6 in this operating range with increasing inflow velocity v until the thrust-force threshold value FL for an inflow velocity v1 is reached. The load-limited operation BL is continued from this averaged inflow velocity v1 as a thrust-limited operation B3. As is shown in Fig. 5, the tip speed ratio =
follows the thrust-limited tip speed ratio =F for this purpose. Consequently, the thrust force F
remains substantially constant and the tilting moment M decreases with increasing inflow velocity v. The embodiment explained in connection with Figs. 5 and 6 is merely provided by way of example. A load-limited operation BL which is arranged as a tilting-moment-limited operation B5 can also be considered.
Load limitation with a predetermined value for the thrust-force threshold value FL
and the tilting-moment threshold value ML allows a simplification of the system modularization. Fig. 8 shows a flow power plant park with a first flow power plant 1.1 and a second flow power plant 1.2 for illustration purposes. Inflows 24.1, 24.2 with a different flow profile are present for the flow power plants 1.1 and 1.2. For the adjustment of the system, a similarly arranged drive train 27 is assumed for the first power plant 1.1 and the second power plant 1.2. This relates especially to the bearing components like the radial bearings 11.1, 11.2 as shown in Fig. 7 and the axial bearing 12 and the drive shaft 25. Furthermore, the machine nacelle

14 and the load-bearing structures between the drive train 27 and the respective support structure 7.1, 7.2 of the first flow power plant 1.1 and the second flow power plant 1.2 correspond to one another. The rotor characteristics are adjusted to the location of the plant. A first rotor 3.1 with a rotor radius r1 is shown, which . .
. .

exceeds the rotor radius r2 of the second rotor 3.2. Furthermore, the length of the support structure 7.1 of the first flow power plant 1.1, which is arranged as a tower, in comparison with the length of the support structure 7.2 of the second flow power plant is adjusted in such a way that the apex of the first rotor 3.1 is situated at the same immersion depth as the apex of the second rotor 3.2. An adjustment to the length of the support structure 7.1, 7.2 can be provided for the foundation 8.1, 8.2. A uniform foundation 8.1, 8.2 is used for a simpler configuration however.
Further embodiments of the invention can be provided within the scope of the following claims. For example, the frequency with which the thrust-force threshold value FL and the tilting-moment threshold value ML is reached can be detected and stored in order to determine the necessity for a maintenance measure.

List of reference numerals 1 Flow power plant 1.1 First flow power plant 5 1.2 Second flow power plant 2 Revolving unit 3 Rotor 3.1 First rotor 3.2 Second rotor 10 4 Cover 5 Feedback control apparatus 6 Electric generator 6.1 Generator stator 6.2 Generator rotor

15 7, 7.1, 7.2 Support structure 8, 8.1, 8.2 Foundation 9 Ground of water body 10 Water surface 11.1, 11.2 Radial bearing 12 Axial bearing 13.1, 13.2 Load measuring apparatus 14 Machine nacelle 15 Control device

16 Frequency converter

17 Rectifier on the generator side

18 Inverter on the grid side

19 Intermediate DC circuit

20 Interconnected grid

21 Rotational axis

22 Vertical axis

23 Transverse axis

24, 24.1, 24.2 Inflow

25 Drive shaft

26 Load detection device

27 Drive train

28 How measuring apparatus X Tip speed ratio Xd Tip speed ratio assigned to runaway speed Xopt Power-optimal tip speed ratio Xr Power-limited tip speed ratio XL Load-limited tip speed ratio XF Thrust-limited tip speed ratio Xm Tilting-moment-limited tip speed ratio Power Thrust force Fr Nominal thrust force FL Thrust-force threshold value Fs Thrust-force setpoint value Pr Nominal power v, VO, V11 V2 Averaged inflow velocity vn Nominal inflow velocity B1 Power-optimal operation B2 Power-limited operation B3 Thrust-limited operation B4 Operation at runaway speed 85 Tilting-moment-limited operation BL Load-limited operation vma, Maximum velocity cp Power coefficient CF Thrust coefficient cK Tilting moment coefficient nd Runaway speed M Tilting moment ML Tilting-moment threshold value r, r1, r2 Rotor radius GM Generator torque T Operating duration

Claims

CLAIMS:

1. A method for operating a flow power plant (1), comprising 1.1 a rotor (3), to which a horizontal rotational axis (21), a vertical axis (22) and a horizontal transverse axis (23) are assigned, which stand perpendicularly to each other, wherein the rotor (3), driven by an inflow (24), generates a driving torque about the rotational axis (21), a thrust force (F) in the direction of the rotational axis (21) and a tilting moment (M) about the transverse axis (23);
1.2 an electric generator (6) which is connected at least indirectly to the rotor (3), so that the electric generator (6) produces a generator torque (GM) during operation which brakes the rotor (3);
characterized in that 1.3 upon reaching a thrust-force threshold value (F L) for the thrust force (F) and/or a tilting-moment threshold value (M L) for the tilting moment (M) the rotor (3) is guided to load-limited operation (B L) by setting the generator torque (GM), for which the rotor (3) revolves at a tip speed ratio (.lambda.) that is larger than a power-optimal tip speed ratio (.lambda.opt) and larger than a power-limited tip speed ratio (.lambda.R).

2. A method according to claim 1, wherein the thrust force (F) or the tilting moment (M) is kept constant in load-limited operation (B L) for temporal averaging in a predetermined time interval.

3. A method according to one of the claims 1 or 2, wherein the load-limited operation (B L) is carried out up to a tip speed ratio (.lambda.) which corresponds to a tip speed ratio (.lambda.d) assigned to the runaway speed.

4. A method according to one of the preceding claims, wherein the thrust force (F) and/or the tilting moment (M) are measured on a component of a revolving unit (2) comprising the rotor (3) an/or a component of the bearing of the revolving unit (2) and/or a component of the support structure (7) and/or a component of the foundation (8) of the flow power plant (1).

5. A method according to one of the preceding claims, wherein the thrust force (F) and/or the tilting moment (M) are determined by a measurement of the inflow (24) which drives the rotor (3).

6. A method according to one of the preceding claims, wherein the reaching of the thrust-force threshold value (F L) and/or the tilting-moment threshold value (M L) is detected and recorded in a control device (15).

7. A method according to one of the preceding claims, wherein the generator torque (GM) is transmitted by torsion-proof coupling between the rotor (3) and a generator rotor (6.1) of the electric generator (6).

8. A flow power plant, comprising 8.1 a rotor (3), to which a horizontal rotational axis (21), a vertical axis (22) and a horizontal transverse axis (23) are assigned, which stand perpendicularly to each other;
8.2 an electric generator (6) which is connected to the rotor (3) at least indirectly, so that the electric generator (6) produces a generator torque (GM) during operation which brakes the rotor (3);
8.3 a load detection device (26) for determining the thrust force (F) of the rotor (3) in the direction of the rotational axis (21) and/or the tilting moment (M) of the rotor (3) about the transverse axis (23), which is connected to a control device (15) with an open-loop or closed-loop control for the generator torque (GM), wherein the control device (15) is arranged in such a way that upon reaching a thrust-force threshold value (F L) for the thrust force (F) and/or a tilting-moment threshold value (M L) for the tilting moment (M) the rotor (3) is guided by the setting of the generator torque (GM) to load-limited operation (B L), for which the rotor (3) revolves at a tip speed ratio (.lambda.) which is higher than a power-optimal tip speed ratio (.lambda.opt) and higher than a power-limited tip speed ratio (.lambda.R).

9. A flow power plant according to claim 8, wherein the load-limited operation (B L) reaches up to a tip speed ratio (.lambda.) which corresponds to a tip speed ratio (.lambda.d) assigned to the runaway speed.

10. A flow power plant according to one of the claims 8 or 9, wherein the electric generator (6) is a synchronous machine and the control device (15) for the open-loop or closed-loop control of the load current in the electric generator (6) is formed by adjusting the stator voltage components (d, q).

11. A flow power plant park, comprising at least two flow power plants (1.1, 1.2) according to one of the claims 8 to 10, wherein the drive train (27) of the flow power plants (1.1, 1.2) is identical, and the first rotor (3.1) of the first flow power plant (1.1) has deviating rotor characteristics in relation to the second rotor (3.2) of the second flow power plant (1.2).

12. A flow power plant park according to claim 11, wherein the deviation of the rotor characteristics is set by different rotor radii (r1, r2) and/or different profile properties and/or differences in the depth distribution of the profile and/or the progression of the torsion for the first rotor (3.1) and the second rotor (3.2).

13. A flow power plant park according to one of the claims 11 or 12, wherein the drive train (27) is configured for a predetermined thrust-force threshold value (F L) and/or a predetermined tilting-moment threshold value (M L).