Conversion kit for a vibration damper of a wind turbine and method of using same

Abstract

A conversion kit (54) temporarily attachable to a vibration damper (24) mounted in a wind turbine (10) is disclosed. The vibration damper (24) includes a mass (26, 32), and a support means (30, 36) for movably supporting the mass (26, 32). The conversion kit (54) includes a sensor arrangement (60) for measuring vibrations of the wind turbine (10), and a control system (62) configured to be operatively connectable to a movement means (58) and to the sensor arrangement (60) to direct the movement means (58) to move the mass (26, 32) in response to measurements from the sensor arrangement (60). The combination of the vibration damper (24) and the conversion kit (54) defines an augmented vibration damper (56) for the wind turbine (10) having damping characteristics different from the damping characteristics of the vibration damper (24). The movement means (58) may be part of the wind turbine (10) or be part of the conversion kit (54). A method of using the conversion kit (54) to dampen vibrations in the wind turbine (10) is also disclosed.

Description

[0001] CONVERSION KIT FOR A VIBRATION DAMPER OF A WIND TURBINE AND METHOD OF USING SAME

[0002] Technical Field

[0003] The invention relates generally to wind turbines, and more particularly to a conversion kit for converting a vibration damper in the wind turbine from a passive operating mode, used during normal operation of the wind turbine, to an active operating mode, used during a non-operational state of the wind turbine (e.g., construction, maintenance, or decommission of the wind turbine). The invention also relates to a method of using the conversion kit to convert a wind turbine vibration damper from a passive operating mode to an active operating mode.

[0004] Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into electrical power. A horizontal-axis wind turbine includes a tower and an energy generating unit positioned atop of the tower. The energy generating unit typically includes a nacelle to house mechanical and electrical components, such as a generator, and a rotor operatively coupled to the components in the nacelle through a main shaft extending from the nacelle. The rotor, in turn, includes a central hub and a plurality of blades extending radially therefrom and configured to interact with the wind to cause rotation of the rotor. The rotor is supported on the main shaft, which is either directly or indirectly operatively coupled with the generator which is housed inside the nacelle. Consequently, as wind forces the blades to rotate, electrical energy is produced by the generator. Wind turbines may be constructed onshore or offshore at locations with significant wind.

[0005] To be economical, wind turbines must be capable of sustaining continuous vibration-induced forces over long periods. Vibrations may be induced from internal or external forces and include oscillatory or repeating displacements in transverse, longitudinal, and / or torsional directions of nearly any amplitude and frequency depending on the vibration source. Typically, sources of vibrations can include any single one or a combination of wind acting on the tower (i.e., vortex generation), blades rotating past the tower, rotor rotation, nacelle yaw motion, nacelle imbalances, and imbalances in gearboxes and / or generators, to name a few. Offshore and near-shore installations present an additional vibration source - wave loads on, for example, the foundation of the wind turbine. Whether the wind turbine is floating or on a foundation structure (e.g., a monopile) directly secured to the ocean floor, wave loads are an additional source of vibrations. To make the conditions more difficult, there is often significant misalignment between the wind and the waves. This can cause large loads on the tower in a side-to-side direction, which is generally not present in onshore installations. The forces from any vibration can cause fatigue damage to the wind turbine, and substantial fatigue damage, more than that anticipated in the design, may lead to reduced operational lifetime of the wind turbine tower and / or one or more of its components. Additionally, vibrations may present safety issues and may be a limiting factor for allowing personnel to perform services on the wind turbine (e.g., sea sickness).

[0006] Vibrations at specific frequencies can cause resonance of one or more portions of the wind turbine, particularly in the wind turbine tower. Resonance, where vibrations match a natural frequency of the wind turbine, is a potentially catastrophic event in that vibration-induced forces can exceed structural integrity of the wind turbine. Wind turbine designers therefore consider vibrations, and are particularly aware of resonant frequencies, during the design process. Designers may modify wind turbine structural design to avoid resonance during operation of the wind turbine. As an example, tower wall thickness may be changed to modify the natural frequency of the wind turbine tower. Designers may alternatively or in conjunction with structural modification include devices specifically designed to damp vibrations. These devices, referred to as tuned mass dampers, are generally active, semiactive, or passive in their vibration damping. Active tuned mass dampers apply counter forces to the structure that are out of phase with the vibrations (thereby providing destructive interference with the vibration) through a control system. Passive tuned mass dampers are tuned to react to vibrations and absorb the wind turbine vibrations of specific frequencies, and semi-active tuned mass dampers combine features of active and passive dampers. Vibration dampers, such as tuned mass dampers, are often used during the construction of the wind turbine. For example, when wind turbine towers are installed at the installation site but the nacelles and rotors are not yet assembled on the towers, tuned mass dampers may be used to limit oscillations of towers due to vortex shedding. After construction of wind turbines, tuned mass dampers are installed in the wind turbines to address operational vibrations. In many cases, passive tuned mass dampers are used to reduce fatigue loads during the operational state of the wind turbine. Passive tuned mass dampers are selected for the operational state of wind turbines because such dampers require no or little power, require no or little maintenance, and are capable of reliably operating over long periods of time. Tuned mass dampers may also be used during the decommission of a wind turbine.

[0007] During the lifetime of a wind turbine, it is sometimes necessary to repair or replace one or more significant wind turbine components. For example, it may be necessary to replace one or more of the wind turbine blades, gearbox, generator, bearing housing, etc. During these maintenance processes, it can be important that the wind turbine have very little oscillations so that the components may be removed from the wind turbine and a replacement component may be assembled to the wind turbine without damage to the components and while providing a safe environment for personnel during the change out. In many cases, the passive tuned mass dampers that are already installed in the wind turbine to reduce fatigue loads during the operational state of the wind turbine are unable to adequately dampen the vibrations (i.e., reduce the amplitude of the vibration to an acceptable level) experienced by the wind turbine during such maintenance processes. Consequently, the environmental conditions (e.g., wind, waves, etc.) must be “just right” in order for the maintenance process to be initiated and completed. In many cases, the large cranes, personnel, ships, and other equipment used for the maintenance process remain one site but are idle waiting for the right conditions. Such equipment is very expensive and the cost of waiting for just the right conditions to perform maintenance on the wind turbine can be significant. Thus, there is a need in the wind turbine industry to dampen vibrations not just during operation of the wind turbine but also during non-operational states of the wind turbine. This will, in turn, increase the conditions under which construction, maintenance, or decommission processes may be initiated and completed. Thus, the amount of waiting for the right conditions and the cost of the equipment used to perform processes while in the non-operational state may be decreased.

[0008] To address these and other drawbacks, and in a first aspect of the invention, a conversion kit temporarily attachable to a vibration damper mounted in a wind turbine is disclosed. The vibration damper includes a mass and a support means connected to the wind turbine and to the mass for movably supporting the mass. The conversion kit includes a sensor arrangement for measuring vibrations of the wind turbine and a control system configured to be operatively connectable to a movement means and to the sensor arrangement to direct the movement means to move the mass in response to measurements from the sensor arrangement. The combination of the vibration damper and the conversion kit defines an augmented vibration damper for the wind turbine having damping characteristics different from the damping characteristics of the vibration damper without the conversion kit.

[0009] In one embodiment, the movement means may be pre-attached to the wind turbine and configured to be connectable to the conversion kit. For example, the movement means may be part of the manufacture process for the wind turbine tower or the nacelle, and thus be part of the wind turbine. In another embodiment, however, the movement means may be part of the conversion kit and configured to be temporarily connectable to the wind turbine. In one embodiment, when the movement means of the conversion kit is used for a first time, the movement means may be left in the wind turbine for future use with a conversion kit that does not include the movement means.

[0010] In one embodiment, the movement means may include at least one winch connectable the wind turbine and at least one cable connectable to the at least one winch and connectable to the vibration damper. Activation of the at least one winch, as directed by the control system, causes movement of the mass. In one embodiment, the movement means may include a plurality of winches and the at least one cable. In a further embodiment, the movement means may further include a plurality of pulleys connectable to the wind turbine and / or to the vibration damper to guide the at least one cable when the at least one winch is activated. In one embodiment, the movement means may include a plurality of cables.

[0011] In another embodiment, the movement means may include a plurality of actuators each being connectable to the wind turbine and to the vibration damper. Activation of the plurality of actuators, as directed by the control system, causes movement of the mass. In one embodiment, the plurality of actuators may be selected from hydraulic actuators and / or pneumatic actuators. In one embodiment, the plurality of actuators may be arranged to move the mass in multiple directions and axes.

[0012] In one embodiment, the sensor arrangement may include at least one first sensor connectable to the wind turbine at , for example, a predetermined measuring location for determining vibration data of the wind turbine. For example, the at least one first sensor may measure a frequency and / or an amplitude of the vibration at the predetermined measuring location. The at least one sensor may include, for example, an accelerometer. In one embodiment, the sensor arrangement may further include at least one second sensor connectable to the vibration damper for measuring positional and dynamic data of the mass. For example, the at least one second sensor may measure location, direction, speed, and acceleration of the mass of the augmented vibration damper.

[0013] In one embodiment, the control system may include a controller configured to be in communication with the movement means and the sensor arrangement. The controller may include one or more processors, and a memory coupled to the one or more processors and including program code that, when executed by the one or more processors, causes the controller to direct the movement means to move the mass in response to measurements from the sensor arrangement. In one embodiment, the vibration damper has a passive operating mode, and the conversion kit is configured such that the augmented vibration damper has an active operating mode. In one embodiment, the vibration damper (e.g., in the passive operating mode) is configured to dampen vibrations and reduce fatigue loads in the wind turbine during an operational state of the wind turbine and the augmented vibration damper (e.g., in the active operating mode) is configured to dampen vibrations in the wind turbine during a non-operational state of the wind turbine, such as a construction state, maintenance state, or decommission state of the wind turbine. For example, during a blade replacement process or other large component replacement (e.g., generator, gearbox, bearing assembly, etc.) conducted in the maintenance state, the conversion kit may be temporarily brought in to modify the vibration damper that already exists in the wind turbine. In this regard, the vibration damper mounted in the tower may not be able to sufficiently dampen the vibrations in the wind turbine (e.g., to sufficiently small amplitudes) during large component replacement processes. However, the augmented vibration damper, i.e., the combination of the vibration damper and the conversion kit, may be configured to adequately dampen the vibrations in the wind turbine (e.g., so as to have relatively small amplitudes) during the replacement process.

[0014] In a second aspect of the invention, a system for damping vibrations in a wind turbine is disclosed. The system includes a vibration damper mounted to the wind turbine. The vibration damper includes a mass and a support means connectable to the wind turbine and to the mass for movably supporting the mass. The system also includes the conversion kit according to the first aspect of the invention described above temporarily attached to the vibration damper. The combination of the vibration damper and the conversion kit defines an augmented vibration damper for the wind turbine having damping characteristics different from the damping characteristics of the vibration damper without the conversion kit.

[0015] In one embodiment, for example, the conversion kit may be configured to change the mode of operation of the vibration damper. More particularly, the conversion kit may be configured to change the mode of operation of the vibration damper from a passive mode to an active mode by operatively coupling the conversion kit to the vibration damper. In one embodiment, adding the conversion kit to the vibration damper may change the damping capacity of the vibration damper. For example, the vibration damper may be sufficient at damping vibrations during an operational state of the wind turbine. However, during a non-operational state of the wind turbine, the vibration damper may be insufficient to dampen the vibrations in the wind turbine. By adding the conversion kit to the vibration damper during the non- operational state of the wind turbine, the augmented vibration damper may be capable of adequately damping the vibrations in the wind turbine (e.g., by counteracting the vibrations). In one embodiment, for example, adding the conversion kit to the vibration damper may change the frequency range and / or amplitude range over which vibrations in the wind turbine may be sufficiently damped. In an exemplary embodiment, the augmented vibration damper is configured to dampen the vibrations so as to have a relatively small amplitude.

[0016] In a third aspect of the invention, a method of altering damping characteristic of a vibration damper mounted in a wind turbine is disclosed. The method includes providing the conversion kit of the first aspect of the invention described above, and operatively connecting the conversion kit to the vibration damper. When so connected, the combination of the vibration damper and the conversion kit defines an augmented vibration damper for the wind turbine having damping characteristics different from damping characteristics of the vibration damper without the conversion kit.

[0017] In one embodiment, the vibration damper may be configured to operate in a passive operating mode and the augmented vibration damper may be configured to operate in an active operating mode. In one embodiment, the augmented vibration damper may be configured to dampen vibrations in the wind turbine within a frequency range different from the frequency range in which the vibration damper is configured to dampen vibrations in the wind turbine. Furthermore, in one embodiment, the augmented vibration damper may be configured to dampen vibrations in the wind turbine within an amplitude range different from the amplitude range in which the vibration damper is configured to dampen vibrations in the wind turbine. In one exemplary embodiment, for example, the augmented vibration damper is configured to dampen the vibrations so as to have a relatively small amplitude.

[0018] In one embodiment, the wind turbine has an operational state and a non-operational state, and the providing and connecting steps according to the method may be performed when the wind turbine is at or near the non-operational state. The wind turbine may be placed in the non-operational state, for example, when one of the major components of the wind turbine, including a blade, generator, gearbox, bearing housing, etc., is being replaced. Furthermore, the wind turbine may be in the non-operational state during construction or decommissioning the wind turbine. In one embodiment, the method may further include operatively disconnecting the conversion kit from the vibration damper prior to the wind turbine being placed back in the operational state (or back in the operational state for a maintenance process). Thus, the conversion kit is only temporarily used during the non-operational state of the wind turbine. Once the conversion kit is used (e.g., such as during a maintenance process), at least some of the components of the conversion kit may be removed, and the wind turbine returned to its operational state, where the vibration damper (not the augmented vibration damper) is sufficient to dampen vibrations in the wind turbine.

[0019] Brief Description of the Drawings

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.

[0021] Fig. 1 is a perspective view of a wind turbine having a vibration damper disposed therein.

[0022] Fig. 2 is a schematic front view of a passive roller-type of vibration damper mounted in the wind turbine shown in Fig. 1 . Fig. 3 is a schematic front view of a passive pendulum-type of vibration damper mounted in the wind turbine shown in Fig. 1 .

[0023] Fig. 4 is a schematic perspective view of the wind turbine of Fig. 1 in a non- operational state (i.e. , maintenance state) for a blade replacement process.

[0024] Figs. 5 and 6 are schematic illustrations of an add-on conversion kit according to one embodiment of the invention.

[0025] Fig. 7 is a diagrammatic view of a control system that may be used to implement the control system of Fig. 6.

[0026] Fig. 8 is a cross-sectional view of an augmented vibration damper according to one embodiment of the invention.

[0027] Fig. 9 is a cross-sectional view of an augmented vibration damper according to another embodiment of the invention.

[0028] Fig. 10 is a cross-sectional view of an augmented vibration damper according to another embodiment of the invention.

[0029] Fig. 11 is a flowchart of a method for controlling vibrations in a wind turbine during a maintenance process on the wind turbine.

[0030] Detailed Description

[0031] With reference generally to the figures, aspects of the present invention relate to a conversion or add-on kit for modifying a vibration damper of an existing wind turbine. For example, during normal operation of the wind turbine, referred to as the operational state, the vibration damper is sufficient to dampen vibrations and fatigue loads experienced by the wind turbine. In many situations, the vibration damper for the operational state of the wind turbine is configured as a passive vibration damper, due to its little to no power requirement and its little to no maintenance during the lifetime of the wind turbine. However, there are other periods of the wind turbine where the vibration damper may be insufficient to dampen the vibrations experienced by the wind turbine. For example, during maintenance processes on the wind turbine, referred to as the maintenance state, the vibration damper may be inadequate to sufficiently dampen the vibrations experienced by the wind turbine to conduct the maintenance process. Such maintenance states may include, for example, when large, heavy wind turbine components, such as blades, generators, gearboxes, main bearings, etc., are being replaced. The inability to dampen vibrations experienced by the wind turbine (e.g., so as to have small amplitude vibrations) during these replacement processes results in lost time for equipment and personnel waiting for the right conditions that allow the maintenance process to be conducted.

[0032] To address this problem in the industry, aspects of the invention include a conversion kit that is temporarily “added on” to the existing vibration damper in the wind turbine to define an augmented vibration damper. The augmented vibration damper is configured to dampen vibrations experienced by the wind turbine during, for example, maintenance states of the wind turbine. The augmented vibration damper has different damping characteristics, as compared to the damping characteristics of the vibration damper, that make it more suitable for damping vibrations during the maintenance state. By way of example, the conversion kit may convert the vibration damper from a passive-type of vibration damper to an activetype of vibration damper. The conversion kit may change the damping capacity of the vibration damper so that the augmented vibration damper is capable of sufficiently damping vibrations experienced by the wind turbine at frequencies and / or amplitudes different from the damping capacity of the vibration damper. In any event, the conversion kit is only temporarily added to the existing vibration damper mounted in the wind turbine. When, for example, the maintenance process is completed, the conversion kit, in whole or in part, may be removed from the vibration damper and the wind turbine may be placed back in its operational state. Other advantages and benefits to the conversion kit are described herein.

[0033] To those and other ends and with reference to Fig. 1 , an exemplary wind turbine 10 is shown which includes a tower 12, a nacelle 14 disposed at the apex of the tower 12, and a rotor 16 operatively coupled to a generator (not shown) housed inside the nacelle 14, and a gearbox (not shown) housed inside the nacelle 14. In addition to the generator and gearbox, the nacelle 14 may house various components needed to convert wind energy into electrical energy and to operate and optimize the performance of the wind turbine 10. The tower 12 supports the load presented by the nacelle 14, rotor 16, and other wind turbine components housed inside or external to the nacelle 14. The tower 12 operates to elevate the nacelle 14 and the rotor 16 to a height above ground level or sea level, as may be the case, where air currents with lower turbulence and higher velocity are typically found.

[0034] The rotor 16 includes a central hub 18 and a plurality of wind turbine blades 20 (“blades”) attached to the central hub 18 at locations distributed about the circumference of the central hub 18. In the representative embodiment, the rotor 16 includes three blades 20, however the number of blades 20 may vary. The blades 20, which project radially outward from the central hub 18, are configured to interact with passing air currents to produce rotational forces that cause the central hub 18 to spin about its longitudinal axis 22. The design, construction, and operation of the blades 20 are familiar to a person having ordinary skill in the art of wind turbine design and may include additional functional aspects to optimize performance.

[0035] The rotor 16 may be coupled to the gearbox directly or indirectly by a drive shaft (not shown) to form a rotor assembly. Either way, the gearbox transfers the rotation of the rotor 16 through a coupling (not shown) to the generator. Wind exceeding a minimum speed may activate the rotor 16, causing the rotor 16 to rotate in a direction substantially perpendicular to the wind, and applying torque to the input shaft of the generator. The electrical power produced by the generator may be supplied to a power grid (not shown) or an energy storage system (not shown) for later release to the grid as understood by a person having ordinary skill in the art. In this way, the kinetic energy of the wind may be harnessed by the wind turbine 10 for power generation.

[0036] A vibration damper 24 is installed at a position as high as possible inside the wind turbine tower 12, such as in an upper-most portion of tower 12. For example, the vibration damper 24 may be located as close to an antinode of a first vibration mode in the wind turbine 10 as possible. The antinode of the first vibration mode is typically at / near highest level of the tower 12. In one embodiment, the vibration damper 24 may be located within ±15% of the height of the tower 12 to the selected antinode. By way of further example, the convertible vibration damper 24 may be located within ±10% of the height of the tower 12 to the selected antinode, and preferably within ±5% of the height of the tower 12 to the selected antinode. In one embodiment, installation of the convertible vibration damper 24 may be within an upper 30% of the wind turbine tower 12 so as to provide efficient damping of wind turbine vibrations. By placing the vibration damper 24 as high as possible in the wind turbine tower 18, the vibrations may be more efficiently dampened using smaller masses in the vibration damper 24. While Fig. 1 illustrates the vibration damper 24 as being in the tower 12, it should be understood that the vibration damper 24 may be located in other parts of the wind turbine 10, such as in the nacelle 14.

[0037] As noted above, during operation of the wind turbine 10, the wind turbine 10 is subjected to a number of time varying forcing functions that produce vibrations in the wind turbine 10. The vibrations experienced by the wind turbine 10 may be due to aerodynamic vibrations and mechanical vibrations. For example, the time varying nature of the wind, turbulence, vortex formation, etc. may result in aerodynamic vibrations on the wind turbine 10. Additionally, the operation of the gearbox, generator, yaw system, and other mechanical actions (e.g., rotating shafts, etc.) may result in mechanical vibrations on the wind turbine 10. For offshore installations, vibrations experienced by the wind turbine 10 may also be due to wave loads impacting, for example, the foundation of the offshore wind turbine. To reduce fatigue loads in the wind turbine during an operational state of the wind turbine (e.g., a state of producing power), the wind turbine 10 often includes the vibration damper 24. In many cases, the vibration damper mounted in the wind turbine 10 during the operational state of the wind turbine 10 takes the form of a passive tuned mass damper (referred to hereafter as a passive vibration damper). A passive vibration damper is appealing during the operational state of the wind turbine 10 not only because it is effective in reducing fatigue loads experienced by the wind turbine during this state, but the passive vibration damper also requires little to no power for operation of the vibration damper. Additionally, passive vibration dampers are robust and require little to no maintenance during the lifetime of the wind turbine 10.

[0038] Fig. 2 is a schematic diagram of a vibration damper 24 arranged as a passive vibration damper useful during the operational state of the wind turbine 10. In the embodiment of Fig. 2, the vibration damper 24 is configured as a passive roller-type of vibration damper (sometimes referred to as a virtual pendulum damper). Fig. 3 illustrates another embodiment of a passive vibration damper 24 configured as a passive pendulum-type of vibration damper. Passive vibration dampers include two main components: i) a mass; and ii) a support means connected to the mass to allow the mass to move. In some designs, the passive vibration damper may include an additional component: iii) a damper means for damping the movement of the mass. In the embodiment shown in Fig. 2, for example, the mass takes the form of a sled or carriage 26 having a plurality of rollers 28. The support means includes a rail system having one or more curved rails 30 engaged by the rollers 28 of the carriage 26 and along which the carriage 26 is configured to move. The optional damper means may include restoring elements 31 , such as spring elements, viscous dashpots, etc. for resisting movement away from the carriage’s base position (e.g., the vertex of the curved rail 30). The damper means, when present, may additionally or alternatively include various friction elements that resist movement of the carriage 26 along the rail system. For example, the damper means may include a braking system (e.g., an eddy-current braking system) associated with the rollers 28. In the embodiment shown in Fig. 3, the mass takes the form of a pendulum 32. The support means takes the form of cables 34 configured as a suspension arrangement 36 for suspending the pendulum 32 within the wind turbine 10. The optional damper means may include restoring elements 38, such as spring elements, viscous dashpots, rubber or foam elements, friction elements (e.g., friction plates), etc. for resisting movement away from the pendulum’s base position.

[0039] As discussed above, the vibration damper 24 is configured to reduce fatigue loads experienced by the wind turbine 10 during a normal operating state of the wind turbine 10, e.g., when the wind turbine 10 is producing power or when the wind turbine is idle (e.g., with the wind turbine blades slowly rotating). However, in some instances, the wind turbine 10 will have a state where the vibration damper 24 may be insufficient to adequately dampen vibrations being experienced by the wind turbine 10, such as from an amplitude and / or safety standpoint. By way of example, and without limitation, the wind turbine 10 includes a non-operational state where aspects of the present invention may be used. For example, aspects of the present invention may be used in a construction state where the wind turbine is being constructed. Aspects of the present invention may also be used during a maintenance state where maintenance processes are being performed on the wind turbine. Moreover, aspects of the present invention may be used during a decommission state where the wind turbine is being dismantled. During a maintenance state, for example, wind turbine components may be replaced. Fig. 4 illustrates a wind turbine 10 in the maintenance state where a wind turbine blade 20 is being replaced. As illustrated in this figure, a blade replacement process includes bringing a large crane 42 to the installation site 44, disconnecting the damaged wind turbine blade 20 from the hub 18 of the rotor 16, and lowering the blade 20 to the ground using the crane 42. The crane 42 is then attached to a new or refurbished wind turbine blade 20 and raised to the top of the tower 12 with the root end 46 of the blade 20 facing toward the hub 18. The crane 42 is then manoeuvred so that the root end 46 is immediately adjacent the blade interface 48 on the hub 18. The root end 46 of the blade 20 includes a plurality of stud bolts (not shown) that have to be received within corresponding bores in the bearing (not shown) of the blade interface 48. Thus, precise alignment between the root end 46 of the blade 20 and the blade interface 48 is typically required to attach the new or refurbished blade 20 to the wind turbine 10. While Fig. 4 illustrates an onshore wind turbine installation, it should be recognized that offshore installations suffer from similar issues. Offshore installations, for example, often require a specialized ship having a large crane for performing replacement processes.

[0040] If the vibrations occurring at the blade interface 48 of the wind turbine are too severe (e.g., too large of an amplitude), it will be very difficult to attach the new or refurbished wind turbine blade 20 to the hub 18. While the vibration damper 24 mounted in the wind turbine 10 is capable of reducing fatigue during the operational state of the wind turbine 10, the vibration damper 24 is often not able to adequately dampen the vibrations occurring at the blade interface 48 to allow the attachment of the root end 46 of the blade 20 to the blade interface 48. For example, it is common that blade attachment may be attempted when calm weather conditions exist at the wind turbine site (e.g., small amplitude vibrations). Thus, depending on the weather conditions, equipment, such as the crane 42, and personnel may have to stand down until weather conditions improve. This delay can be costly for wind turbine operators. The delay in performing maintenance processes due to poor weather conditions may exist with other replacement projects. For example, similar delays can exist in the replacement of other major components of the wind turbine 10, including the generator, gearbox, and main bearing assembly, for example. Thus, aspects of the present invention should not be limited to only blade replacement processes.

[0041] To allow various processes to be performed in a non-operational state over a greater range of weather conditions, aspects of the present invention are directed to temporarily modifying the vibration damper 24 such that the modified vibration damper, referred to hereafter as the “augmented vibration damper”, is capable of sufficiently damping vibrations in the wind turbine 10 over a greater range of vibration conditions at or adjacent the replacement site on the wind turbine 10. Thus, processes, such as maintenance processes, may be performed over a greater number of days throughout the year, and the delays due to poor weather conditions at the wind turbine site 44 may be reduced. Thus, downtime in equipment and personnel may be reduced, potentially saving wind turbine operators significant time and expense.

[0042] In this regard, Fig. 5 schematically illustrates an add-on conversion kit 54 configured to be temporarily used in combination with the vibration damper 24 (already mounted in the wind turbine 10) to define an augmented vibration damper 56. The augmented vibration damper 56 is configured to have vibration damping characteristics that are different from the vibration damping characteristics of the vibration damper 24 mounted in the wind turbine 10. The damping characteristics of the augmented vibration damper 56 are configured to adequately dampen the vibrations in the wind turbine 10 during, for example, a non-operational state and under a wider range of weather conditions at the wind turbine site 44.

[0043] By way of example and without limitation, and as described in more detail below, the augmented vibration damper 56 may operate in an operational mode different than the operational mode of the vibration damper 24. In this regard, and as discussed above, the vibration damper 24 may be configured as a passive vibration damper. However, the augmented vibration damper 54 may be configured as an active vibration damper. Thus, the conversion kit 54 may be configured to change the mode of vibration damping from a passive mode to an active mode. Additionally, the vibration damper 24 may have a frequency range and an amplitude range over which the vibration damper 24 is configured to operate (i.e. , sufficient to effectively dampen the vibration to acceptable levels). When the conversion kit 54 is added to the vibration damper 24, the frequency range and / or the amplitude range over which the augmented vibration damper 56 is configured to operate may be different than those for the vibration damper 24. Thus, the augmented vibration damper 56 is capable of effectively dampening vibrations in the wind turbine 10 to acceptable levels under different frequency and / or amplitude ranges. For example, the augmented vibration damper 56 may be capable of dampening vibrations in the wind turbine 10 to have small amplitudes and thereby allow for component replacement during a maintenance state.

[0044] Fig. 6 schematically illustrates a conversion kit 54 in accordance with an embodiment of the invention configured to be temporarily connected to the vibration damper 24. In one embodiment, the conversion kit 54 includes three main components: i) a movement means 58; ii) a sensor arrangement 60; and iii) a control system 62. The movement means 58 is configured to cause movement of the mass of the vibration damper 24. Thus, depending on the embodiment of the vibration damper 24, the movement means 58 may be configured to cause movement of the carriage 26 or the pendulum 34, for example. The movement means 58 is configured to be connectable directly or indirectly to the wind turbine 10, i.e., the movement means 58 is configured to be connectable to the wind turbine 10 or an object that is fixed to the wind turbine 10. For example, the movement means 58 may be configured to be connectable to a portion of the vibration damper 24 that is fixed relative to the wind turbine 10. In addition, the movement means 58 is configured to be connectable to the vibration damper 24. In one embodiment, for example, the movement means 58 may be configured to be connectable to the mass of the vibration damper 24 (e.g., the carriage 26 or the pendulum 32). In another embodiment, the movement means 58 may be configured to be indirectly connectable to the mass of the vibration damper 24 but capable of causing movement of the mass.

[0045] While the conversion kit 54 is described above as including the movement means 58, in another embodiment, the movement means 58 may be pre-installed in the wind turbine 10, such as during the manufacturing of the wind turbine tower or nacelle (depending on the location of the vibration damper 24). In this embodiment, the conversion kit 54 may only include the sensor arrangement 60 and the control system 62. In any event, the movement means 58 may include a power source, such as a battery, generator, etc. for providing power to the movement means 58 during use of the movement means 58.

[0046] The sensor arrangement 60 is configured to measure vibrations at a predetermined measuring location of the wind turbine 10. The predetermined measuring location may be determined by the particular process being performed on the wind turbine 10. For example, in a blade replacement process, the sensor arrangement 60 may be configured to measure vibrations at or near the blade interface 48 on the hub 18 of the wind turbine 10. This measuring location will give the most accurate data on the movements of the wind turbine 10 to determine whether the blade replacement may proceed. In one embodiment, the sensor arrangement 60 may include at least one first sensor 64 configured to be connectable to the wind turbine 10. The at least one first sensor 64 may include any type of vibration sensor capable of measuring vibration data, such as the frequency and amplitude of the vibration. By way of example, the at least one first sensor 64 may include an accelerometer.

[0047] In one embodiment, the sensor arrangement 60 may also be configured to measure data associated with the vibration damper 24, and more particularly the mass of the vibration damper 24. By way of example, the sensor arrangement 60 may be configured to measure position, direction, speed, and / or acceleration of the mass of the vibration damper 24, e.g., the carriage 26 or the pendulum 32. In one embodiment, the sensor arrangement 60 may include at least one second sensor 66 configured to be connectable to the vibration damper 24. The at least one second sensor 66 may include any type of vibration sensor capable of measuring positional and / or dynamic movement data. By way of example, the at least one second sensor 66 may include an accelerometer. The at least one second sensor 66 may be optional.

[0048] In one embodiment, the control system 62 is configured to direct the movement means 58 to move the mass of the vibration damper 24 in response to measurements from the sensor arrangement 60 to actively dampen the vibrations experienced at the predetermined measuring location of the wind turbine 10. The control system 62 is configured to be operatively connectable to the movement means 58 and operatively connectable to the sensor arrangement 60. Thereby the control system 62 may receive sensor readings from the sensor arrangement 60 and send signals to the movement means 58 to move the mass of the vibration damper 24 in a manner that reduces the vibrations occurring in the wind turbine 10.

[0049] As illustrated in Fig. 7, the control system 62 may include a controller 68 that may be used to direct the movement means 58 in response to measurements from the sensor arrangement 60. The controller 68 may include one or more processors 70, memory 72, and an input / output (I / O) interface 74. The processor 68 may include one or more devices that perform operations on data based on internal logic or operational instructions that are stored in memory 72. Memory 72 may include a single memory device or a plurality of memory devices capable of storing data. Computer program code embodied as one or more computer software applications, such as an application 76 residing in memory 72, may have instructions executed by the processor 70. One or more data structures 78 may also reside in memory 72 and may be used by the processor 70 or application 76 to store or manipulate data. The I / O interface 74 may provide a machine interface that operatively couples the processor 70 to other devices and systems, such as movement means 58 and / or the sensor arrangement 60. The application 76 may thereby work cooperatively with the external devices and systems by communicating via the I / O interface 74 to provide the various features, functions, applications, processes, or modules comprising embodiments of the invention.

[0050] Fig. 8 illustrates an augmented vibration damper 56 in accordance with one embodiment of the invention. In this embodiment, the vibration damper 24 takes the form of a roller-type of passive vibration damper 24 as shown in Fig. 3. The movement means 58 of the conversion kit 54 may include at least one winch 82 and at least one cable 84. The at least one winch 82 may be temporarily attached to the wind turbine 10 to support the at least one winch 82. For example, and without limitation, the at least one winch 82 may be connected to a bracket (not shown) that is mounted to the wind turbine 10. In one embodiment, the bracket may, for example, be welded to the wind turbine 10 and form a permanent part of the wind turbine 10. In another embodiment, the bracket may be temporarily attached to the wind turbine 10. For example, the bracket may be temporarily magnetically attached to the wind turbine 10. Furthermore, the bracket may be temporarily attached to the wind turbine using various fasteners, such as bolts, clamps, screws, etc. In one embodiment, such as that shown in Figs. 8 and 9, the movement means 58 may include a plurality of winches 82 configured to be temporarily attached to the wind turbine 10 adjacent the vibration damper 24, and more particularly, the mass thereof.

[0051] The at least one cable 84 is connected to or connectable to the at least one winch 82 and capable of withstanding tension forces sufficient to cause movement of the mass, such as the carriage 26 or pendulum 32 of the vibration damper 24, when the at least one winch 82 is activated. The at least one cable 84 is configured to be connected to the vibration damper 24 to cause movement of the mass of the vibration damper 24. In a preferred embodiment, the at least one cable 84 is configured to be connectable to the mass of the vibration damper 24. Thus, as shown in Figs. 8 and 9, in one embodiment, the at least one cable 84 is configured to be connectable to the carriage 26 of the vibration damper 24. More particularly, because the at least one cable 84 is capable of transmitting only tension forces, in one embodiment, the at least one cable 84 is configured to be connectable to the carriage 26 at two connection points 86, 88. The two connection points 86, 88 on the carriage 26 are selected to move the mass in opposed directions along the rail 30 of the rail system that supports the carriage 26 in the wind turbine 10. For example, the two connection points 86, 88 may be on opposed sides of the carriage 26. The at least one winch 82, such as the pair of winches 82 illustrated in Figs. 8 and 9, are configured to cooperate with each other to apply a tension force in the at least one cable 84 on one side of the carriage 26 or the other when the winches 82 are activated. The portion of the at least one cable 84 having the tension is then the direction that the carriage 26 will move. Thus, the carriage 26 is able to move back and forth along the rail 30 of the rail system, upon the direction of the control system 62, upon activation of the at least one winch 82. Moreover, the coupling of the movement means 58, such as the at least one winch 82 and the at least one cable 84, converts the passive roller-type vibration damper 24 into the augmented vibration damper 56 having an active mode of operation.

[0052] As further shown in Fig. 8, the augmented vibration damper 56 may further include one or more guides 90 for guiding the at least one cable 84 from the at least one winch 82 to the vibration damper 24, such as the mass of the vibration damper 24. For example, the one or more guides 90 may include one or more pulleys for guiding the at least one cable 84. In one embodiment, the pulleys 90 may be temporarily connectable to the wind turbine 10. Similar to above, the one or more guides 90 may be connected to a bracket (not shown) that is mounted to the wind turbine 10. In one embodiment, the bracket may, for example, be welded to the wind turbine 10 and form a permanent part of the wind turbine 10. In another embodiment, the bracket may be temporarily attached to the wind turbine 10. For example, the bracket may be temporarily magnetically attached to the wind turbine 10. Furthermore, the bracket may be temporarily attached to the wind turbine using various fasteners, such as bolts, clamps, screws, etc. While the one or more guides are illustrated as pulleys, it should be appreciated that the guides may take other forms, including various hooks, eyelets, etc. that allow a cable to be redirected, for example. Figs. 8 and 9 also schematically illustrate the other components of the conversion kit 54 in forming the augmented vibration damper 56. As discussed above, the sensor arrangement 60 includes at least one first sensor 64 (one shown) connected to the wind turbine 10 and optionally at least one second sensor 66 (one shown) connected to the vibration damper 24, and more particularly to the mass thereof, which in Figs. 8 and 9 take the form of carriage 26. The at least one first sensor 64 and the at least one second sensor 66 are operatively coupled to the control system 62. In one embodiment, the first and second sensors 64, 66 may be connected to the wind turbine 10 and the carriage 26, respectively, by a wired connection. In another embodiment, however, the first and second sensors 64, 66 may be wirelessly connected to the wind turbine 10 and the carriage 56, respectively.

[0053] While Figs. 8 and 9 illustrate the at least one first sensor 64 being connected to the wind turbine tower 12, this is merely exemplary. As explained above, the at least one first sensor 64 may be positioned at a predetermined measuring location on the wind turbine 10. The predetermined measuring location may depend on the particular construction, maintenance, or decommission process being performed on the wind turbine 10. For a blade replacement process, for example, the at least one first sensor 64 may be located in the nacelle 14 of the wind turbine 10, the hub 18 of the wind turbine 10, and / or at or adjacent the blade interface 48, where the root end 46 of the replacement blade 20 is configured to attach. Other locations are also possible. For other maintenance processes, the predetermined measuring location may be appropriately selected to provide an understanding of the vibrations that may impact the replacement process. Thus, aspects of the invention should not be limited to the predetermined measuring location being at any particular location.

[0054] The controller 68 of the control system 62 is configured to receive signals from the sensor arrangement 60. Those signals from the sensor arrangement 60 are analyzed according to a control algorithm that is stored in the controller 68. Active vibration dampers are known in the wind turbine industry and control algorithms for generating movements of a mass for “actively” counteracting vibrations in a wind turbine are also well known in the wind turbine industry. Thus, the details of the control algorithm that directs movement of the mass based on measurements from the sensor arrangement 60 will not be discussed in further detail. Based on such control algorithms, however, the controller 68 of the control system 62 generates signals that direct the movement means 58 to move the mass in accordance with the control algorithm. In one embodiment, the controller 68 may be connected to the movement means 58, such as the at least one winch 82, by a wired connection. In another embodiment, however, the movement means 58 may be wirelessly connected to the controller 68.

[0055] Fig. 10 illustrates an augmented vibration damper 56 in accordance with one embodiment of the invention. In this embodiment, the vibration damper 24 takes the form of a pendulum-type of passive vibration damper 24 as shown in Fig. 3. The movement means 58 of the conversion kit 54 may include at least one actuator 94. The at least one actuator 94 may be temporarily attached to the wind turbine 10 to support the at least one actuator 94. For example, and without limitation, the at least one actuator 94 may be connected to a bracket (not shown) that is mounted to the wind turbine 10. In one embodiment, the bracket may, for example, be welded to the wind turbine 10 and form a permanent part of the wind turbine 10. In another embodiment, the bracket may be temporarily attached to the wind turbine 10. For example, the bracket may be temporarily magnetically attached to the wind turbine 10. Futhermore, the bracket may be temporarily attached to the wind turbine using various fasteners, such as bolts, clamps, screws, etc. In one embodiment, such as that shown in Fig. 10, the movement means 58 may include a plurality of actuators 94 configured to be temporarily attached to the wind turbine 10 adjacent the vibration damper 24, and more particularly, the mass thereof. In one embodiment, the at least one actuator 94 may include a hydraulic actuator. In another embodiment, the at least one actuator 94 may include a pneumatic actuator. In still a further embodiment, the at least one actuator 94 may include an electric actuator having a drive motor, for example. Other actuators may be possible and remain within the scope of the present invention.

[0056] The at least one actuator 94 is also configured to be connected to the vibration damper 24 to cause movement of the mass of the vibration damper 24. In a preferred embodiment, the at least one actuator 94 is configured to be connectable to the mass of the vibration damper 24. Thus, as shown in Fig. 10, in one embodiment, the at least one actuator 94 is configured to be connectable to the pendulum 32 of the vibration damper 24. The at least one actuator 94 is capable of generating forces sufficient to cause movement of the mass of the vibration damper 24 when the at least one actuator 94 is activated. Although the at least one actuator 94 is capable of pushing and pulling the pendulum 32, in one embodiment, the at least one actuator 94 includes a plurality of actuators 94 configured to be connectable to the pendulum at multiple connection points 96, 98. The two connection points 96, 98 on the pendulum 32 may be selected to move the mass in opposed directions in the wind turbine 10. For example, the two connection points 96, 98 may be on opposed sides of the pendulum 32. The at least one actuator 94, such as the pair of actuators 94 illustrated in Fig. 10, is configured to cooperate with each other to apply forces to the pendulum 32 when the actuators 94 are activated. Thus, the pendulum 32 is able to move back and forth, upon the direction of the control system 62, upon activation of the at least one actuator 94. Similar to the above, the coupling of the movement means 58, to the vibration damper 24 converts the passive pendulum-type vibration damper 24 into an augmented vibration damper 56 having an active mode of operation.

[0057] In one embodiment, pairs of opposed actuators 94 may be distributed about the perimeter of the pendulum 32 of the vibration damper 24 (shown in phantom). In this way, the pendulum 32 may be moved back and forth in multiple directions along movement axes. The movement axes may be, for example, orthogonal to each other.

[0058] Fig. 10 also schematically illustrates the other components of the conversion kit 54 in forming the augmented vibration damper 56. As discussed above, the sensor arrangement 60 includes at least one first sensor 64 (one shown) connected to the wind turbine 10 and optionally at least one second sensor 66 (one shown) connected to the vibration damper 24, and more particularly to the mass thereof, which in Fig. 10 takes the form of the pendulum 32. The at least one first sensor 64 and the at least one second sensor 66 are operatively coupled to the control system 62. In one embodiment, the first and second sensors 64, 66 may be connected to the wind turbine 10 and the pendulum 32, respectively, by a wired connection. In another embodiment, however, the first and second sensors 64, 66 may be wirelessly connected to the wind turbine 10 and the carriage 56, respectively.

[0059] While Fig. 10 illustrates the at least one first sensor 64 being connected to the wind turbine tower 12, this is merely exemplary. As explained above, the at least one first sensor 64 may be positioned at a predetermined measuring location on the wind turbine 10. The predetermined measuring location may depend on the particular maintenance process being performed on the wind turbine 10. For a blade replacement process, for example, the at least one first sensor 64 may be located in the nacelle 14 of the wind turbine 10, in the hub 18 of the wind turbine 10, and / or at or adjacent the blade interface 48, where the root end 46 of the replacement blade 20 is configured to attach to the hub 18. Other locations are also possible. For other maintenance processes, the predetermined measuring location may be appropriately selected to provide an understanding of the vibrations that may impact the replacement process. Thus, aspects of the invention should not be limited to the predetermined measuring location being at any particular location.

[0060] The controller 68 of the control system 62 is configured to receive signals from the sensor arrangement 60. Those signals from the sensor arrangement 60 are analyzed according to a control algorithm that is stored in the controller. Active vibration dampers are known in the wind turbine industry and control algorithms for generating movements of a mass for “actively” counteracting vibrations in a wind turbine are also well known in the wind turbine industry. Thus, the details of the control algorithm that directs movement of the mass based on measurements from the sensor arrangement 60 will not be discussed in further detail. Based on such control algorithms, however, the controller 68 of the control system 62 generates signals that direct the movement means 58 to move the mass in accordance with the control algorithm. In one embodiment, the controller 68 may be connected to the movement means 58, such as the at least one actuator 94, by a wired connection. In another embodiment, however, the movement means 58 may be wirelessly connected to the controller 68. While the above illustrates the at least one winch 82 / at least one cable 84 arrangement in combination with the roller-type of vibration damper 24 and the at least one actuator 94 arrangement in combination with the pendulum-type of vibration damper 24, it should be recognized that the least one winch 82 / at least one cable 84 arrangement may be used in combination with the pendulum-type of vibration damper 24 and the at least one actuator 94 arrangement may be used in combination with the roller-type of vibration damper 24.

[0061] Fig. 11 illustrates a method 100 of damping vibrations in a wind turbine using the conversion kit 54 discussed above. In a first step 102, the wind turbine 10 may be taken out of its operational state and moved to its non-operational state in anticipation of a process, such as a component replacement process being performed on the wind turbine 10. In a next step 104, the conversion kit 54 may be temporarily and operatively connected to the vibration damper 24 that is mounted in the wind turbine 10. This defines the augmented vibration damper 56 in the wind turbine 10. Thus, for example, the movement means 58 may be connected to the wind turbine 10 and the vibration damper 24 (such as the mass thereof), the sensor arrangement 60 may be connected to the wind turbine 10 and the vibration damper 24, and the control system 62 may be connected to the movement means 58 and the sensor means 60. The augmented vibration damper 56 has damping characteristics that are different from the damping characteristics of the (unmodified) vibration damper 24. In this regard, the augmented vibration damper 56 may be configured to have damping characteristics particularly suited to the maintenance process being performed on the wind turbine 10. By way of example, and without limitation, the damping characteristics of the augmented vibration damper 56 may be particularly suited for a blade replacement process. This may include, for example, damping vibrations so as to have relatively low amplitudes.

[0062] In a next step 106, the maintenance process may be performed on the wind turbine 10 with the augmented vibration damper 56 dampening vibrations in the wind turbine 10 during the maintenance process. Once the maintenance process is completed, the conversion kit 54 may be disconnected from the vibration damper 24. Additionally, at least some of the components of the conversion kit 54 may be removed from the wind turbine 10. Thus, for example, the movement means 58 may be disconnected from the wind turbine 10 and the vibration damper 24, the sensor arrangement 60 may be disconnected from the wind turbine 10 and the vibration damper 24, and the control system 62 may be disconnected from the movement means 58 and the sensor means 60. Thus, in one embodiment, all of the components of the conversion kit 54 may be removed from the wind turbine 10. In another embodiment, the mechanical components of the conversion kit 54 may remain with the wind turbine 10. For example, the sensor arrangement 60 and the control system 62 may be removed from the wind turbine 10 while aspects of the movement means 58 may stay with the wind turbine 10. The components of the conversion kit 54 that stay behind, however, are operatively disconnected from the vibration damper 24. In a final step of the method 100, the wind turbine 10 may be taken out of its non-operational state and returned to its operational state with the vibration damper 24 dampening vibrations experienced by the wind turbine 10 during operation.

[0063] While the above describes using the conversion kit 54 during a maintenance state of the wind turbine 10, it should be recognized that benefits may also be gained by using the conversion kit 54 during other states of the wind turbine 10, such as during a construction state of the wind turbine 10 and / or a decommission state of the wind turbine 10.

[0064] While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the various features of the invention may be used alone or in any combination depending on the needs and preferences of the user.

Claims

CLAIMS1. A conversion kit (54) temporarily attachable to a vibration damper (24) mounted in a wind turbine (10), the vibration damper (24) comprising: a mass (26, 32); and a support means (30, 36) connected to the wind turbine (10) and to the mass (26, 32) for movably supporting the mass (26, 32), the conversion kit (54), comprising: a sensor arrangement (60) for measuring vibrations of the wind turbine (10); and a control system (62) configured to be operatively connectable to a movement means (58) for causing movement of the mass (26, 32) and to the sensor arrangement (60) to direct the movement means (58) to move the mass (26, 32) in response to measurements from the sensor arrangement (60), wherein the combination of the vibration damper (24) and the conversion kit (54) defines an augmented vibration damper (56) for the wind turbine (10) having damping characteristics different from the damping characteristics of the vibration damper (24).

2. The conversion kit (54) of claim 1 , wherein the movement means (58) is: i) pre-attached to the wind turbine (10) and configured to be connectable to the conversion kit (54); or ii) the movement means (58) is part of the conversion kit (54) and is configured to be temporarily connectable to the wind turbine (10).

3. The conversion kit (54) of claim 1 or 2, wherein the movement means (58) comprises: at least one winch connectable the wind turbine (10); and at least one cable (84) connectable to the at least one winch (82) and connectable to the vibration damper, wherein activation of the at least one winch (82), as directed by the control system (62), causes movement of the mass (26, 32).

4. The conversion kit (54) of claim 3, wherein the movement means (58) includes a plurality of winches (82) and the at least one cable (84).

5. The conversion kit (54) of claim 3 or 4, wherein the movement means (58) further comprises a plurality of pulleys (90) connectable to the wind turbine (10) and / or the vibration damper (24) to guide the at least one cable (84) when the at least one winch (82) is activated.6 The conversion kit (54) of claim 1 or 2, wherein the movement means (58) comprises: a plurality of actuators (94) each being connectable to the wind turbine (10) and to the vibration damper, wherein activation of the plurality of actuators (94), as directed by the control system (62), causes movement of the mass (26, 32).

7. The conversion kit (54) of claim 6, wherein the plurality of actuators (94) may be selected from hydraulic actuators and / or pneumatic actuators.

8. The conversion kit (54) of any of the preceding claims, wherein the sensor arrangement (60) comprises: at least one first sensor (64) connectable to the wind turbine (10) for determining a frequency and / or amplitude of the vibration experienced by the wind turbine (10).

9. The conversion kit (54) of any of claim 8, wherein the sensor arrangement (60) further comprises: at least one second sensor (66) connectable to the vibration damper (24) for measuring movements of the mass (26, 32).

10. The conversion kit (54) of any of the preceding claims, wherein the control system (62) comprises: a controller (68) configured to be in communication with the movement means (58) and the sensor arrangement (60), the controller (66) comprising:one or more processors (70); and a memory (72) coupled to the one or more processors (70) and including program code that, when executed by the one or more processors (70), causes the controller (68) to direct the movement means (58) to move the mass (26, 32) in response to measurements from the sensor arrangement (60).11 . The conversion kit (54) of any of the preceding claims, wherein the vibration damper (24) has a passive operating mode, and wherein the conversion kit (54) is configured such that the augmented vibration damper (56) has an active operating mode.

12. A system for damping vibrations in a wind turbine (10), the system comprising: a vibration damper (24) mounted to the wind turbine (10), the vibration damper (24) comprising: a mass (26, 32); and a support means (30, 36) connectable to the wind turbine (10) and to the mass (26, 32) for movably supporting the mass (26, 32), and the conversion kit (54) of any of claims 1-11 temporarily attached to the vibration damper (24), wherein the combination of the vibration damper (24) and the conversion kit (54) defines an augmented vibration damper (56) for the wind turbine (10) having damping characteristics different from the damping characteristics of the vibration damper (24).

13. A method of altering damping characteristic of a vibration damper (24) mounted in a wind turbine (10), comprising: providing the conversion kit (54) of any of claims 1-11 ; operatively connecting the conversion kit (54) to the vibration damper (24), wherein the combination of the vibration damper (24) and the conversion kit (54) defines an augmented vibration damper (56) for the wind turbine (10) having damping characteristics different from damping characteristics of the vibration damper (24).

14. The method of claim 13, wherein the vibration damper (24) is configured to operate in a passive operating mode and the augmented vibration damper (56) is configured to operate in an active operating mode.

15. The method of claim 13 or 14, wherein the augmented vibration damper (56) is configured to dampen vibrations in the wind turbine (10) within a frequency range different from the frequency range in which the vibration damper (24) is configured to dampen vibrations in the wind turbine (10).

16. The method of any of claims 13-15, wherein the augmented vibration damper (56) is configured to dampen vibrations in the wind turbine (10) within an amplitude range different from the amplitude range in which the vibration damper (24) is configured to dampen vibrations in the wind turbine (10).

17. The method of any of claims 13-16, wherein the wind turbine (10) has an operational state and a non-operational state, and wherein the providing and connecting steps are performed when the wind turbine (10) is at or near the non- operational state.

18. The method of claim 17, further comprising: operatively disconnecting the conversion kit (54) from the vibration damper (24); and placing the wind turbine (10) in the operational state.

19. The method of claim 18, further comprising removing at least some of the components of the conversion kit (54) from the wind turbine (10).

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