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Title:
DAMPING OF WIND TURBINE
Document Type and Number:
WIPO Patent Application WO/2006/062390
Kind Code:
A1
Abstract:
This invention relates to a windmill, consisting of a nacelle, a rotor, a tower, which windmill is provided with a liquid-column damper which prevents vibrations resulting from normal operational loads. The invention also relates to a damper for a windmill and to a process for using a windmill provided with a damper, wherein vibrations resulting from the normal operating loads are damped utilizing the damper.

Inventors:
Van Duijvendijk, Marcel (Nico van Suchtelenstraat 6, HP Hengelo, NL-7552, NL)
Wilmink, Engbert (Giststraat 16, PT Delft, NL-2611, NL)
De Roest, Anton Herrius (Schubertlaan 16, JR Enschede, NL-7522, NL)
Application Number:
PCT/NL2005/000789
Publication Date:
June 15, 2006
Filing Date:
November 10, 2005
Export Citation:
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Assignee:
Mecal B.V. (Capitool 64, PL Enschede, NL-7521, NL)
Van Duijvendijk, Marcel (Nico van Suchtelenstraat 6, HP Hengelo, NL-7552, NL)
Wilmink, Engbert (Giststraat 16, PT Delft, NL-2611, NL)
De Roest, Anton Herrius (Schubertlaan 16, JR Enschede, NL-7522, NL)
International Classes:
F03D11/00
Domestic Patent References:
WO2002084114A12002-10-24
Foreign References:
US6695588B12004-02-24
US6626642B12003-09-30
US6672837B12004-01-06
Attorney, Agent or Firm:
Winckels J. H. F. (Johan de Wittlaan 7, NL-DEN HAAG 2517 JR, NL)
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Claims:
Claims
1. A windmill comprising a tower, a nacelle with rotor placed on the tower, further comprising a damper, wherein the damper comprises at least one tube or pipe which can be wholly or partly filled with a liquid and/or gas.
2. A windmill according to claim 1, wherein said tube or pipe comprises a substantially horizontal tube part and two vertical tube parts, so that the tube is substantially Ushaped.
3. A windmill according to any one of the preceding claims, wherein said damper is mounted in the top of the tower or mast of the windmill.
4. A windmill according to any one of the preceding claims, wherein said damper is mounted in the wall of the tower or mast of the windmill.
5. A windmill according to any one of the preceding claims, wherein said damper is mounted on the outside of the windmill.
6. A windmill according to any one of the preceding claims, wherein said damper is mounted in the nacelle of the windmill.
7. A windmill according to any one of the preceding claims, wherein two or more said dampers are used.
8. A windmill according to any one of the preceding claims, wherein horizontal tube parts of said dampers are placed in different radial directions relative to the vertical axis of the mast (or tower).
9. A windmill according to any one of the preceding claims, wherein said vertical tube parts of said damper are connected at the top side.
10. A windmill according to any one of the preceding claims, wherein the vertical tube parts of the dampers are uniformly distributed over the circumference of the wall of the mast (or tower).
11. A windmill according to any one of the preceding claims, wherein the horizontal tube part of said damper runs through the center of the mast (or tower).
12. A windmill according to claims 1 — 10, wherein the horizontal tube part of said damper runs along the wall of the mast (or tower).
13. A windmill according to claims 1 11, wherein the horizontal tube parts of the damper are interconnected in the center of the mast (or tower) to form one whole.
14. A windmill according to any one of the preceding claims, wherein, in the horizontal tube part and the vertical tube parts, said tube has different dimensions along the line of action.
15. A windmill according to any one of the preceding claims, wherein, in the horizontal tube part, said tube has a greater surface of the cross section than the vertical tube parts.
16. A windmill according to any one of the preceding claims, wherein the surface of the crosssection of the horizontal tube part is at least 1.5 (one and a half) times as great as the surface of the crosssection of the vertical tube parts.
17. A windmill according to any one of the preceding claims, wherein in a damper at least one energy dissipater is placed.
18. A windmill according to claim 17, characterized in that said energy dissipater comprises an orifice.
19. A windmill according to claim 17, wherein said energy dissipater comprises a mesh structure.
20. A windmill according to claim 17, wherein said energy dissipater comprises a moving element such as a rotor or a wheel or hinge.
21. A windmill according to any one of the preceding claims, wherein said liquid in the damper(s) under operational conditions has a viscosity which is comparable to water and a density of at least 1000 [kg/m3].
22. A windmill according to any one of the preceding claims, wherein a damper is provided with at least one sealable opening for filling up and/or discharging said liquid or gas.
23. A windmill according to any one of the preceding claims, wherein the damper comprises control means which can control the liquid level in a dynamic manner.
24. A windmill according to any one of the preceding claims, wherein said energy dissipater can be controlled through manual or automatic setting.
25. A windmill according to any one of the preceding claims, wherein this is provided with an antileakage system.
26. A windmill according to any one of the preceding claims, wherein vertical tube parts of said damper form, partly, a compressible gas column, provided with pressure valve.
27. A windmill according to any one of the preceding claims, wherein said tube parts consist, at least partly, of a flexible material.
28. A windmill according to any one of the preceding claims, wherein said damper has an Eigenfrequency which corresponds to the frequency to be damped.
29. A windmill according to any one of the preceding claims, wherein the frequency characteristic of the damper is settable.
30. A windmill according to any one of the preceding claims, wherein the frequency characteristic of the damper is settable by constructing the geometry of the damper to be adjustable.
31. A windmill according to any one of the preceding claims, wherein the frequency characteristic of the damper is settable by providing the condition of the liquid and/or the gas in the damper such that it can be influenced.
32. A windmill according to any one of the preceding claims, wherein the damper is provided with a cooling system.
33. A damper for a windmill according to claim 1, wherein the damper comprises at least one tube or pipe, which can be wholly or partly filled with a liquid or gas.
34. A process for the use of a windmill, wherein kinetic energy from vibrations in an excitation frequency resulting from a regular operating load of the wind mill is transmitted to liquid and/or gas which moves in a tube or pipe of a damper, wherein the kinetic energy of the liquid and/or the gas is dissipated in the damper by means of an energy dissipater, while the Eigenfrequency of the damper substantially corresponds to the excitation frequency.
Description:
Title: DAMPING OF WIND TURBINE

This invention relates to a windmill comprising a nacelle, a rotor and a tower, which windmill is provided with a liquid column damper which prevents vibrations as a result of normal operating loads. The invention also relates to a damper for a windmill, and to a process for using a windmill provided with a damper, wherein vibrations as a result of normal operating loads are damped utilizing the damper.

Dampers are generally known for damping undesired vibrations. This is desirable in particular around the IP and 3P frequencies of the windmill, in which the passing rotor blades effect a load. The IP frequency is the frequency with which the rotor makes one revolution. The 3P frequency is therefore the frequency with which one blade of a windmill with three blades passes the tower. Damping these vibrations contributes to the reduction of the loads that occur in the parts of the windmill, so that these parts can be of lighter construction. This results in considerable savings in costs. As current windmills become larger, vibrations that occur form an increasing problem, to which the current techniques offer insufficient solutions. For windmills with dampers, presently, four common methods are known: a pendulum attached in the top of the tower or mast (EP 1008747; a large moving mass with spring and damper in the windmill (WO99/63219, JP20205108); a container with a liquid in the windmill (WO00/77394); guy ropes at the exterior of the windmill provided with dampers (US4261441).

A windmill provided with a pendulum in the tower has a number of important drawbacks. For instance, the pendulum can only travel a small distance due to the limited space in the tower. As a result, a considerable mass needs to be present to achieve the desired result. The large required mass leads to an undesired downwardly directed load. More important still is the

influence of this additional mass on the Eigenfrequency of the windmill, which consequently may approach the IP or 3P frequency. Further, an additional damper needs to be attached to the pendulum for damping out the vibration. Finally, the pendulum occupies a large part of the space on the inside of the mast (or tower) so that little space is left for other parts such as an elevator, platforms and cables.

Due to the limited space, a windmill provided with a moving mass also has as a drawback that the mass needs to be very large to provide the desired damping. This leads, in turn, to an undesired increase in the weight, which will adversely affect the Eigenfrequency of the windmill. With this type of damper too, an additional damper needs to be added to damp out the movements of the mass. Additionally, the risk is present that the damper becomes defective and the mass can move unguidedly in the windmill so that damage can occur. A container with liquid has as a drawback that the liquid slowly evaporates. As a result, the mass can change and with it, the Eigenfrequency of the damper and possibly the windmill as a whole can undesirably change. Also, a large mass of liquid is required to provide the desired damping. This, once more, occupies much of the limited space and also leads to an increase of the vertical load and an undesired change of the Eigenfrequency.

The greatest drawback of guy cables is that they occupy much space on the outside of the windmill. In addition, with large windmills, guy cables cannot be practically used, as to this end, very many or very thick cables provided with dampers are required. These guy cables further form an obstruction for the blades.

So-called liquid column dampers are known for use in buildings as a protection against earthquakes.

The object of the invention is to provide a windmill which is provided with a damper for the purpose of damping out undesired vibrations as a result of regular operating loads, and wherein the above-mentioned drawbacks are

avoided, while maintaining the advantages. In particular, the object of the invention is to provide a windmill with damper wherein a net weight savings is realized.

To this end, at least one damper is placed on or in the windmill, while this damper comprises at least one tube or pipe which can be wholly or partly filled with a liquid and/or gas.

This has as an advantage that kinetic energy of vibrations in an excitation frequency, resulting from the regular operating load, is transmitted to the liquid and/or the gas in the damper. As a consequence, the liquid and/or the gas begins to move in the tube or pipe, however, due to its inertia, the liquid and/or the gas does not move in phase with the vibrations of the windmill. The movement of the liquid and/or the gas then causes friction, as a result of which kinetic energy is dissipated. In this manner, the amplitude of the vibrations of the windmill is damped and the occurring loads are reduced. Preferably, this tube consists of a horizontal tube part and two vertical tube parts, so that it is substantially U-shaped. The advantage achieved herewith is that the path the liquid and/or the gas can travel is lengthened. As a result, less mass of liquid and/or gas is required while a good damping is achieved. Also, the required space is proportionally smaller. Preferably, the damper is placed in or at the top part of the windmill, where the amplitude of the windmill is the most extreme. This has as an advantage that the damper can absorb more kinetic energy than when it is placed at a lower lever. As a result, a better operation is realized. Depending on the design of the windmill, it can be advantageous to choose a more specific positioning in the windmill. When the damper is mounted in the tower or mast of the windmill, this is not to the expense of the already limited space in the nacelle. Optionally, the choice can be made to arrange the damper in the wall of the tower so that it does not take up space in the tower either. Another option is to mount the damper on the outside of the wind turbine. When, conversely, provision of the damper in the nacelle is opted for, this has as an

advantage that it moves along with the rotor and therefore always has the same position relative to the wind direction and the passing blades. The nacelle is also the highest point so that more energy can be absorbed. It must be noted that these examples do not exclude other variants. It is possible to vary the Eigenfrequency of a damper within a specific bandwidth by controlling the amount of liquid mass present in the damper. By selecting the Eigenfrequency of a damper to be such or, optionally, by setting it dynamically such that it corresponds wholly or partly to the frequency range that needs to be damped, an effective damping can be realized. Usually, this corresponds to the IP and/or 3P frequency of the windmill in which this is excited by the rotor blades. Generally, these are low frequencies, of less than 1 Hz. When furthermore two or more dampers are provided in the windmill, it is possible to damp several frequency ranges.

It is noted that by means of the damper according to the invention, energy is dissipated which is obtained by excitation of the windmill. As a rule, the excited energy comprises a spectrum in which nP frequencies are included, wherein n represents the number of blades of the rotor and P is the frequency of revolution of the rotor.

By manually and/or dynamically controlling the frequency characteristic of the damper, the functionality of the damper can be optimized for different windmill systems as well as for different situations, such as different excitation frequencies.

Further, the damper can be designed for dissipating the energy simultaneously in different directions. The frequency characteristic of the damper can for instance be set by constructing the geometry of the damper to be settable.

For instance, by designing at least a number of parts of the damper to be flexible, the distance between vertical parts of the damper can be adjusted. Further, thø damper can comprise a plural number of horizontal and/or vertical tubes and/or pipes which are mutually adjustably connected. In a

specific embodiment, the damper comprises, for instance, a plural number of conduits which can interconnect particular tubes. For instance, the damper can comprise two or more annular conduits adjacent a side wall of the tower, on which a plural number of vertical tubes is mounted. Conduits and/or tubes can be closed off, at least partly, by means of control means such as taps. In such a manner, mutual dimensions and/or flow velocities can be adjusted. Such adjustments influence, as desired, the frequency characteristic of the damper. Further, the condition of the liquid and/or the gas can be influenced. For instance, the liquid level can be adjusted by connecting a cylinder to a tube and/or conduit, while in the cylinder, a movable piston is provided forming a separation from the liquid and/or the gas. By moving the piston, the liquid level and hence the characteristic of the damper can be adjusted. In addition, the gas pressure in a tube and/or conduit can be set, so that the liquid level of the liquid adjusts itself. Here too, a piston can be used, optionally under spring action or by means of a different mechanical and/or hydraulic construction. The frequency characteristic resulting from liquid and/or gas variations can also be set differently, for instance by placing pressure elements in solid form, such as cylinders, on a piston or in a tube and/or duct, preferably in vertical subsystems. The damper according to the invention can further be designed such that each or virtually each vertical segment of the damper comprises an energy dissipater, so that an effective damping can be obtained, also when only one horizontal segment is provided. Incidentally, it is preferred that the space in which the damper is arranged is provided with an active or passive cooling system, such as heat transmissive walls and/or cooling ribs and/or fans. The cooling system can further be coupled to the cooling system of the wind turbine. Through the provision of a cooling system, the dissipated energy can be discharged in the form of heat, thereby preventing significant temperature increase.

The invention will be further elucidated with reference to exemplary embodiments which, are represented in the drawings. In the drawing:

Fig. 1 shows two embodiments of a U-shaped damper;

Fig. 2 shows two dampers which are positioned at right angles to each other;

Fig. 3 shows a damper wherein the vertical tube parts are also interconnected via the top side;

Fig. 4 shows a cross-section of the mast, wherein several dampers are positioned along the wall; Fig. 5 shows a cross-section of the mast, wherein several dampers are contiguously interconnected in the center of the horizontal tube part;

Fig. 6 shows a damper wherein the surface of the cross-section of the horizontal tube part is larger than of the vertical tube parts;

Fig. 7A shows a damper provided with an energy dissipater in the form of an orifice;

Fig. 7B shows a damper provided with an energy dissipater in the form of a mesh structure;

Fig. 7 C shows a damper provided with an energy dissipater in the form of a rotor; Fig. 8 shows a damper provided with an anti-leakage system, feed and discharge opening, and controllable energy dissipater; and

Fig. 9 shows a part of a damper, provided with a valve in vertical tube parts.

The Figures are only schematic representations of preferred embodiments of the invention. In the Figures, corresponding parts are indicated with identical reference numerals.

Fig. 1 shows the basic design of a damper 1 according to the invention. The horizontal tube part 2 and the vertical tube parts 3 form a structure which can be wholly or partly filled with a liquid and/or a gas. Preferably, under operating conditions, the liquid used has a viscosity comparable to that of

liquid water and a density of at least 1000 kg/m 3 . It is in particular preferred to use tap water provided with at least 20% of anti-freeze to prevent freezing while in the remaining part, air is present. Additional advantages of the use of anti-freeze are the high specific weight and the relatively low cost price of it. Upon excitations of the windmill, the mass inertia of the liquid in the substantially horizontal tube part 2 of the damper provides a displacement of the liquid relative to the tube. The vertical tube parts 3 then provide a lengthening of the path the mass can travel. Additionally, the liquid level in the vertical tube parts will change too, which provides a potential difference between the two columns, effecting a swinging movement of the liquid which, due to its corresponding Eigenfrequency, will have a much larger amplitude than the windmill as a whole. A part of the kinetic energy of the windmill, caused by the vibrations, is absorbed in the damper in this manner, so that excitations of the windmill as a whole are reduced. The friction occurring as a result of the movements of the liquid through the tube provides for dissipation of the kinetic energy, which consequently damps out. Preferably, tube parts 3 are partly closed off to prevent evaporation, this is however not necessary. In Fig. 1 a tube with a round as well as one with a square cross-section are shown. However, other forms are not excluded. It is not necessary either that the tube parts are completely straight or arranged perpendicular relative to each other. Optionally, the tube parts mentioned can consist wholly or partly of flexible material so that they can be easily guided along the desired path.

Fig. 2 shows two dampers 1, also indicated with A and B, which, in this case, are positioned approximately at right angles to each other. In this preferred embodiment, the middle of the two horizontal tube parts 2 is, approximately, in the center of the vertical axis 4 of the tower of the windmill. The upper damper A has its line of action substantially in the direction of the axis 6, while damper B has its line of action substantially in the direction of the axis 5. In this manner, the dampers are placed in different radial directions relative to the vertical axis of the tower. As movements of the tower

deviate more from a direction of, for instance, axis 5, the damper B will damp less, but damper A will effect more damping. Thus, the advantage is achieved that movement in different radial directions relative to the vertical axis 4 is damped to a greater or lesser extent. By optionally positioning several dampers in an analogous manner at approximately equal angles relative to each other, movements in varying radial directions can be damped in a relatively better manner.

Fig. 3 shows a variant of a damper, with the vertical tube parts 3 coupled at the top side via an additional tube 7. This has as an advantage that in case of open tube parts 3, the liquid cannot escape via one extremity, but, in the event of violent movements, will flow back via tube 7. In this manner the liquid is also prevented from being abruptly stopped in its movement, when tube parts 3 are entirely or partly closed off, causing new, undesired forces to occur. Finally, a coupling via the top side also offers the possibility of filling this with a gas.

The preferred embodiment which is shown in Fig. 4 by means of a schematic cross -section, demonstrates how the dampers 1 are uniformly distributed over the circumference of the wall and along the inside wall 8 of the tower. In this manner too, it can be realized that movements in all radial directions relative to the axis of the tower are damped. This also has as an advantage that the dampers occupy relatively little space in the center of the tower so that sufficient space is available for, for instance, a ladder, elevator, optional cables or other provisions or space. The thickness of the tower wall 8 is not represented in this Figure, as this is not relevant to this embodiment. In this embodiment, vertical tube parts 3 are positioned against wall 8 while horizontal tube parts 2 are located farther from the wall. However, also variants hereon are conceivable which hardly, if at all, influence the functionality. An option may for instance also be to place the vertical tube parts 2 somewhat farther away from the wall, by means of connecting pieces, so that for instance more space is available for filling up, attaching, or for

cables that are to run behind this. Further, the horizontal tube parts may be designed to be curved so that they lie closer to the wall of the tower.

In Fig. 5, an embodiment is shown in which the dampers 1, each acting in a different direction and also located at the same height, are interconnected in intersection 9, approximately in the middle of the tower to form a whole via the horizontal tube parts 2. Vertical tube parts 3 of the dampers are uniformly distributed over the circumference of the tower wall. Intersection 9 allows the dampers 1 to mutually exchange liquid. This offers the advantage that damping in the then desired direction can take place better, as the mass of the liquid that flows in the direction to be damped is relatively greater than when the dampers do not communicate. For the working principle, it is not required that coupling 9 is located exactly in the middle of the dampers. It is, for instance, also possible to provide an annular tube with which the dampers are interconnected to each other. Also other variants with which the dampers, located at approximately the same height, are interconnected are not excluded.

The preferred embodiment schematically represented in Fig. 6 shows a damper with different dimensions along the line of action 12 in the horizontal tube part 10 and the vertical tube parts 11. In particular, in this preferred embodiment, the surface of the cross-section of the horizontal tube part 10 is greater than that of the vertical tube parts 11. Preferably, the surface of the cross-section of the horizontal tube is at least one and a half times as great as the vertical tube part. The advantage hereof is that the liquid mass in the horizontal tube part, through which kinetic energy of the windmill is absorbed, is relatively greater while the total required mass remains limited. The proportionally greater surface of the vertical tube parts and the higher flow- through velocity also provide more dissipation of kinetic energy while the possible build-up of a potential difference between the two vertical tube parts 11 remains the same.

Fig. 7 shows three embodiments of dampers in which is placed at least one energy dissipater. It is also possible to place several energy dissipaters in

both the horizontal and the vertical tube parts. This is, however, not shown in the Figures. Fig. 7A shows an embodiment wherein the damper is provided with an orifice 13. In this embodiment, orifice 13 comprises a ring 14 which is attached contiguously to the wall of the horizontal tube part 2, thereby forming a constricted passage 15. With this, the advantage is achieved that the constricted passage 15 provides for a turbulence and additional friction so that more kinetic energy is dissipated in the form of heat. The form of the ring 14 of orifice 13 can be selected in different manners, depending on the liquid used and desired friction. In Fig. 7B, the energy dissipater mentioned comprises a mesh structure 16. By means of this mesh structure 16 too, it is achieved that a turbulence and friction are formed so that kinetic energy is dissipated. The energy dissipater in Fig. 7C comprises rotor 17. Adding an energy dissipater in the form of a moving element such as a rotor, a wheel or a hinge has as an advantage that with it, an energy dissipating friction is provided which is settable by means of the friction on a moving element. If desired, the possibility exists to actively control the moving element and thus influence the liquid flow so that this is equal to the excitation frequency of the tower. Optionally, it would be possible to convert kinetic energy, via such an energy dissipater, into electric energy. Fig. 8 shows an embodiment of damper 1 provided with at least one closable opening 18, consisting of coupling 19 and controllable closure 20 for filling and/or discharging the liquid or gas mentioned. It is then preferred to couple opening 18 to the underside of horizontal tube part 2, or at least at the lowest point of the damper so that a good discharge of a liquid is possible. The advantage of these provisions is that, in a simple manner, the damper can be filled to the correct level with the liquid mentioned by, for instance, a feed hose. In this embodiment, closable opening 21, consisting of coupling 22 and adjustable closure 23 are represented too. If desired, in this manner, the supply can take place independently of the discharge. In particular it can be advantageous that damper 1 comprises control means which can control the

liquid level in a dynamic manner. The advantage thereof is that the Eigenfrequency of a damper 1 can be automatically adjusted depending on the occurring operating conditions and the desired damping. It must be noted that the control means can also comprise a level indicator for continuously determining the liquid level. In other cases too it can be advantageous that a damper comprises a level indicator so that the Eigenfrequency of the damper can be derived in a simple manner. The embodiment in Fig. 8 is also provided with an anti-leakage system, consisting, in this case, of anti-leakage tray 24 which is placed under damper 1 by means of attachment means 25. This has as an advantage that in case of leakage, the liquid is not released in the windmill where it may do damage. In addition, the design in Fig. 8 is provided with an energy dissipater in the form of an orifice 13 which is controllable through manual or automatic setting via regulator 26. What is achieved in this manner is that the occurring resistance for the liquid in the tube can be adjusted so that it can be geared, in situ, to the operating conditions of the windmill, via a control system or manual setting. It is also possible to vary other energy dissipaters by means of control means.

The part shown of the damper in Fig. 9 comprises, in the vertical tube parts 3 a compressible gas column 27 which is provided with valve 28. With swinging movements of the liquid as a result of vibrations in the tower, when the liquid level decreases in vertical tube part 3, gas is drawn into the gas column 27 from outside valve 28. When the liquid level in tube part 3 rises, the gas in gas column 27 is compressed whereupon, at a predetermined pressure, it can escape via valve 28. As a result, the compressible gas column functions as a traditional air damper. As the gas experiences resistance from valve 28, kinetic energy in the damper is converted into heat.