WO2023160763A1

WO2023160763A1 - A wind turbine

Info

Publication number: WO2023160763A1
Application number: PCT/DK2023/050026
Authority: WO
Inventors: Erik GARDE; Fabian SCHWACK
Original assignee: Vestas Wind Systems A/S
Priority date: 2022-02-25
Filing date: 2023-02-16
Publication date: 2023-08-31

Abstract

The invention relates to a wind turbine (10) with a pitch system (22), the pitch system (22) comprising a drive assembly (42), wherein said drive assembly (42) is a hydraulic actuator comprising a hydraulic oil, wherein at least a part of said hydraulic oil comprises a repair additive for restoration of worn-out metal surfaces. The invention furthermore relates to a method of repairing a drive assembly (42) comprising a hydraulic actuator.

Description

A WIND TURBINE

TECHNICAL FIELD

The invention relates to a wind turbine, more particularly a pitch system comprising a hydraulic actuator comprising a hydraulic oil, wherein at least a part of said hydraulic oil comprises a repair additive for restoration of worn-out metal surfaces.

BACKGROUND

Wind turbines typically include a rotor with large blades driven by the wind. The blades convert the kinetic energy of the wind into rotational mechanical energy. The mechanical energy is typically transferred via the drive train to a generator, which then converts the energy into electrical power.

Wind turbines may control power output by rotating each blade around its longitudinal axis, also referred to as its pitch axis, thereby ‘pitching’ the blades relative to the wind.

Accordingly, each blade may be mounted to a hub by a blade bearing that allows relative movement between the blade and the hub. The blades are rotated about their longitudinal axis by a pitch system that includes one or more pitch drives or actuators. Typically pitch systems include one or more pitch drives for each blade to provide the capability to pitch the blades in a controlled way in a combination of collective and cyclic pitch angle adjustments.

Pitch drives are elements which are typically in use for several years, and over time the pitch drives will be worn out and replacement is required.

It is within the scope of embodiments of the present invention to prolong the lifetime of pitch drives in wind turbines.

SUMMARY

In accordance with the invention, there is provided a wind turbine comprising a hub; a blade having a pitch axis; and a pitch system for rotating said blade of said wind turbine relative to the hub. The pitch system comprises a blade bearing for positioning between the blade and the hub; and a drive assembly, wherein the drive member is coupled to the blade bearing via a piston rod such that movement of the drive member causes rotation of the blade bearing. The drive assembly is a hydraulic actuator comprising a stator comprising a cylindrical body; a drive member positioned at least partially within the cylindrical body and movable along an axis thereof; a plunger of the drive member dividing the cylindrical body into first and second chambers; wherein said drive assembly comprises a repair additive for restoration of worn- out metal surfaces.

Elements of the actuator, for instance the piston rod and the end caps, may be formed from stainless steel or other suitable material as is known from the art, and it is known that over the lifetime of a wind turbine (typically at least 20 years), the contact surfaces between these may be worn. Typically, problems start with a change of microgeometry and later a change of macrogeometry. Those changes lead i.a. to higher friction, higher pressure and local temperature changes. At a certain time, replacement of the actuator may be required.

With the present invention it has been realized that the lifetime of actuators may be prolonged by adding a repair additive for restoration of such surfaces to the hydraulic oil in the pitch system.

The repair additive is preferably a particle-based additive comprising micro-particles showing a tribo-chemical reaction at increased friction and temperature. Such reaction leads to a bond between the metallic surface and the micro-particles, resulting in what resembles an entirely new surface. The worn surfaces in the actuator can thereby be repaired, prolonging the actuator lifetime. The repair additives can be used from the beginning or when first signs of wear occur in the actuator.

One spot in particular inside the actuator subject to wear has been seen to be underneath the seal lip of the piston rod seals. As the pitch angle of a wind turbine is most of the wind turbine lifetime kept within a very narrow window, the pitch seals work with short strokes, and as a result of this, the lubrication effect from the hydraulic oil of the actuator right underneath the seal lip of the piston rod seals is reduced compared to the rest of the surface of the piston rod.

This issue is currently dealt with in using seal compounds with low friction like PTFE and fillers that enhance the properties of the PTFE. However, local wear is still observed. The seal in a pitch application seems to have a guessed lifetime of around 1,000 km where an application with longer strokes (i.e. better lubrication) can last something like 10,000km. Applying the present repair additive to the hydraulic oil of the pitch cylinder can help for a longer lifetime and improved performance, as wear marks can be repaired.

In an embodiment of the invention, said drive assembly comprises a third chamber between a primary and a secondary piston rod seal, said third chamber having a volume of less than 10%, preferably less than 1%, of the combined volume of said first and second chambers, said third chamber comprising hydraulic oil comprising said repair additive for restoration of worn-out metal surfaces.

In an embodiment of the invention, said third chamber is further bordered by an end cap and said piston rod.

In an embodiment of the invention, said drive assembly comprises a separate oil inlet situated axially between a primary and a secondary piston rod seal.

In a preferred embodiment of the invention, the repair additive is used very locally where it is most needed to repair locally damaged surfaces. In this embodiment, said drive assembly comprises a separate oil inlet situated axially between a primary and a secondary piston rod seal enabling said repair additive to be introduced directly into said third chamber. This is advantageous as opposed to just adding it to the complete volume of pitch system hydraulic oil since it is believed that the repair additive may be useful throughout the drive assembly, but that it is mostly useful to resist wear of the piston rod and thereby enhance the local lubrication in the positions where the piston rod seals make only short movements along the piston rod (the most common pitch angle for production), and thus increase the seal life and ultimately increase the lifetime of the hydraulic actuator.

The volume of the third chamber is much smaller than the full volume of the first and second chambers, in some embodiments said third chamber has a volume of less than 0.5%, such as less than 0.1%, of the combined volume of said first and second chambers. Adding the repair additive here as opposed to adding to the complete volume of pitch system hydraulic oil is advantageous since the repair additive may be a much more costly component than the hydraulic oil.

In an embodiment of the invention, said at least part of said hydraulic oil comprises said repair additive in an amount of 0.1-20%, such as 1-10% of the total volume. The indicated ranges here apply regardless of whether the repair additive is added to the full volume of hydraulic oil or only to the third chamber.

In an embodiment of the invention, said repair additive is based on a silicate, such as three- layer silicates. In an embodiment of the invention, said ingredient has particle sizes less than 20 pm, preferably less than 10 pm or less than 3 pm. In an embodiment of the invention, said drive assembly comprises a third chamber between a primary and a secondary piston rod seal, wherein the amount of said repair additive in hydraulic oil (Vol%) in said third chamber is higher than the amount of said repair additive in hydraulic oil (Vol%) in said first and second chambers. Needless to say, this also includes when the amount of repair additive is zero in the first and/or second chambers.

The invention further relates to a method of repairing a drive assembly comprising a hydraulic actuator, wherein said method comprises the step of adding a repair additive for restoration of worn-out metal surfaces to the hydraulic oil of said drive assembly.

In an embodiment of the invention, the method further comprises the step of adding said repair additive via a separate oil inlet situated axially between a primary and a secondary piston rod seal.

In some wind turbines comprising a primary and secondary piston rod seals as described herein, in between these seals a drain channel is present in order to drain any hydraulic oil passing the primary piston rod seal, which especially may occur once the piston rod starts to wear. For such wind turbines, adding the repair additive locally as described herein is facilitated as a retrofit solution, as the drain channel may be used as the separate oil inlet instead (allowing the drainage to occur via a potential second drain channel or via the piston rod seals).

All in all, it should be clear that the present invention provides benefits both from the start up of a new turbine and as a retrofit for existing wind turbines which start to wear.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a wind turbine;

Figure 2 is a detailed view of the hub of the wind turbine of Figure 1 with a single blade attached to show the pitch system;

Figure 3 is a sectional top view of the hub showing a top view of one of the pitch systems;

Figure 4 is a simplified schematic and section view of the actuator of the pitch system; and

Figure 5 is a close-up view of part of figure 4. DETAILED DESCRIPTION

Figure 1 shows a wind turbine 10 for generating electricity by wind power. The wind turbine 10 includes a tower 12, a nacelle 14 disposed on top of the tower, a rotor hub 16 disposed on the nacelle 14 so as to be rotatable about a substantially horizontal axis, a plurality of wind turbine rotor blades 18 attached to the hub 16 and extending radially from the horizontal axis A, and electricity-generating equipment (not shown) within the nacelle 14 that generates electricity as the hub 16 rotates. The illustrated embodiment includes three wind turbine rotor blades 18. However, it will be appreciated that the invention is not limited as such and could be applied to wind turbines having two blades or more than three blades.

The wind turbine 10 of Figure 1 may form part of a plurality of identical or of similar wind turbine generators belonging to a wind farm that serves as a power generating plant connected by transmission lines with a power grid, such as a three-phase alternating current (AC) power grid. Such a power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities. The electrical power is supplied from the generator to the power grid in any manner known to a person skilled in the art.

In order to optimise energy production and improve wind farm safety, each blade 18 of the wind turbine 10 is coupled to the rotor hub 16 in a manner that allows it to rotate relative to the hub, i.e. ‘pitch’, about a longitudinal axis P of the blade. This is achieved by coupling the root end 20 of the blade 18 to the hub 16 via a pitch bearing and providing a pitch system 22 including a drive assembly, as discussed in further detail below, to control the rotation of the blade 18 according to various inputs or conditions.

Figure 2 shows a detailed view of the hub 16 of the wind turbine 10 of Figure 1. The hub 16 is shown with only one of the three blades 18 attached to it in order to show the pitch system 22 associated with that blade 18. It will be appreciated that a fully assembled wind turbine 10 will include three such wind turbine blades 18 attached to the hub 16 each with a respective pitch system 22 as described below. It should also be appreciated at this point that the arrangement of the hub and its associated components shown in Figure 2 and described below is provided here to provide context to the inventive concept, and that other hub arrangements are generally known. The hub 16 may also include a cover, for example a glass fibre cover, as shown in Figure 1 but omitted from Figure 2 for clarity. The hub 16 comprises a housing or shell 24 forming a hollow body. The shell 24 comprises three blade flanges 26 to which a respective rotor blade 18 may be mounted and a main shaft flange 28 to which a rotor lock for the main shaft of the turbine (not shown) may be mounted. The rotor blade 18 is mounted to the blade flange 26 of the hub via a blade bearing 30. The blade bearing 30 comprises an inner ring 32, an outer ring 34 and rolling elements (such as balls or rollers, not shown) positioned between the inner and outer rings 32, 34. In some embodiments, the blade bearing 30 comprises at least two rows of rollers between the inner and outer rings 32, 34.

The outer ring 34 of the blade bearing 30 is mounted to the blade flange 26, for example via bolts inserted through bolt holes 36 formed in the blade flange 26. The inner ring 32 of the blade bearing 30 is attached to a root portion 20 of the blade 18. In other embodiments, the outer ring 34 may be mounted to the blade 18 and the inner ring 32 may be mounted to the blade flange 26. A bearing plate 38 is attached to the inner ring 32 of the blade bearing 30 and may provide stiffness and strength and improve other mechanical properties of the bearing 30. The bearing plate 38 includes an aperture 40 to allow access to the inside of the blade 18 from the hub 16.

A drive assembly 42 is functionally attached to the rotor blade 18 and hub 16. The hub 16, blade 18 and drive assembly 42 together form a pitch system configured to change the pitch angle of the rotor blade 18 by applying a force to the rotor blade 18 which causes it to rotate about its pitch axis P. Note that a control system for controlling the pitch system 22 is not shown here, so as not to overly complicate the disclosure.

Figure 3 is a sectional view of the hub 16 and pitch system 22, showing the relationship between the components in more detail. The drive assembly 42 includes a linear actuator 44 coupled with both the hub 16 and the blade 18 via a mounting arrangement 46, 48 such that linear extension of the actuator 44 causes rotational movement of the blade 18 about its pitch axis P. More particularly, the pitch system 22 includes a hub mounting arrangement 46 and a blade mounting arrangement 48 that allows a degree of rotation of the actuator 44 relative to both the hub 16 and blade 18.

Figure 4 shows a simplified sectional view of the actuator 44. In the illustrated embodiment, the actuator 44 is a hydraulic actuator having a stator in the form of a cylinder 50 mounted to the hub 16 and a piston rod 52 coupled to the blade 18. As shown in Figure 3, the piston rod 52 forms part of a piston 54 or drive member that slides relative to the cylinder 50. A plunger each end by first and second end caps 62, 64.

The piston rod 52 extends from the plunger 56, through the first chamber 58 and out of the cylinder 50. Hydraulic oil is provided in each of the first and second chambers 58, 60 via ports 66 extending through the end caps 62, 64. When the first and second chambers 62, 64 are pressurised such that the forces acting on the piston are in equilibrium, the piston 54 does not move relative to the cylinder 50. Pressurisation of either one of the chambers 58, 60 to cause unequal forces being applied to the respective sides of the plunger 56 causes the plunger 54 to move and thereby change the pitch angle of a connected wind turbine blade. Pressurisation of the chambers 58, 60 may be controlled by a hydraulic circuit (including a hydraulic pressure unit for supplying pressurized oil, not shown) in communication with one or both of the first and second chambers 58, 60.

In a first embodiment of the present invention, the repair additive is added to the hydraulic oil any suitable place in the system, such that it directly enters the pitch cylinder together with the hydraulic oil via the ports 66 when the piston rod 52 moves back and forth.

In a second embodiment of the present invention, the repair additive is mixed with hydraulic oil separately and the resulting mixture is added directly into a third chamber 103 where it is needed the most, for instance as shown in fig. 5 (close up of part of fig. 4), where a primary piston rod seal 100 and a secondary piston rod seal 101 is shown. In between these seals is shown a mixture inlet 102 through which the repair additive can be led directly to where it is most needed. The reason for stating that the third chamber is where the repair additive is needed the most was touched upon above (very narrow window of pitch angles most of the time). However, furthermore this is the place where there is contact with the exterior, i.e. the piston rod 52 is moving between the oil-filled chamber 58 and the exterior. Therefore, there will be more wear in this area compared to for instance the contact between the plunger 56 and the cylinder 50, which is a contact always filled with oil in use.

Furthermore, this will also be where there is a risk of leakages of oil to the external, for which reason it is more important to have good sealing, which is also a reason why two piston rod seals 100 and 101 are used. Piston rod seal 100 is here labelled the primary piston rod seal, whereas piston rod seal 101 is labelled the secondary piston rod seal. This is intended solely to be able to distinguish the two, as they may be identical. However, in some embodiments, the primary piston rod seal 100 is adapted to provide a stronger sealing than the secondary piston rod seal 101 , as any leakage of oil/repair additive in the third chamber 103 should preferably leak towards the first chamber 58 and not to the exterior.

In other embodiments a tertiary piston rod seal (not shown) could be introduced between the primary piston rod seal 100 and the exterior, in order to establish more certainty against leakage.

In some embodiments, the third chamber 103 is being filled with the oil/repair additive mixture during service and only replenished during another service. In other embodiments, there is a constant slow inflow of new mixture or intermittent pulses of new mixture. Theoretically, only what deposits on the piston rod 52 should disappear from the third chamber, but in reality there may be an advantage in allowing slight amount of leakage into the first chamber 58 or having a separate drain channel (not shown) between the primary piston rod seal 100 and the secondary piston rod seal 101 to establish some exchange of the mixture in the third chamber.

Referring back to Figures 2 and 3, the actuator 44 extends in a direction parallel to a plane defined by the blade bearing 30 and bearing plate 38. In the illustrated embodiment, the actuator 44 extends outside of the hollow cavity of the hub 16 and is connected to the hub 16 at a point outside the cavity. It will be appreciated that other configurations in which the actuator 44 is positioned entirely within the hub 16 are also possible.

In more detail, the actuator 44 is pivotally connected to the hub shell 24 via a mounting pin 70 that is oriented substantially perpendicular to the direction in which the piston rod 52 extends and perpendicular to the plane defined by the blade bearing 30 to allows a degree of lateral movement of the actuator 44 parallel to the plane in the direction of the arrows 72 in Figure 3.

The hub 16 includes a pitch aperture 74 through which the actuator 44 extends. The pitch aperture 74 has a width that is substantially greater than the width of the actuator cylinder 50 to allow some lateral movement of the cylinder 50 as described above. Two arms 76 extend from the hub 16 either side of the pitch aperture 74. Two mounting plates 78 are attached to the arms 76 either side of the actuator 44 (only one of the plates is shown in Figure 3). The mounting plates 78 extend between the arms 76 and are secured to them by bolts 80 or other fastening means. The piston rod 52 is coupled to the blade by an axle 84. The axle 84 is fixed to the bearing plate 38 at one end and received in a bearing 86 of the piston rod 52 at another end. In the illustrated embodiment, the axle 84 extends from the bearing plate 38 which itself is coupled with the blade 18 such that a force exerted on the bearing plate 38 by the actuator 44 is transferred to the blade 18. However, in other embodiments the axle 84 may extend directly from a part of the blade 18. The axle 84 is parallel to and offset from the blade pitch axis P such that linear extension or retraction of the piston rod 52 creates a tangential force inducing a torque on the blade 18. Note that this arrangement represents one way in which the piston rod may be coupled to a blade, although the skilled person would appreciate that other arrangements would be possible.

The mounting pin 70 forms a pivot about which the actuator 44 can rotate to allow some lateral movement of the piston rod 52, in a direction or plane that is generally perpendicular to the longitudinal direction of the piston rod 52 along the major axis 6. The pivotal mounting of the actuator 44 at each end allows the rod end 90 to follow an arc 92 of the bearing plate 38 (shown in Figure 3) as it extends from the cylinder 50.

The actuator 44 may further include a position sensor 68 such as a linear position sensor associated with the piston 54 and in communication with a control module (not shown) of the pitch system (not shown). The control module may operate the hydraulic circuit to position the actuator 44 by any means known in the art.

The invention has been exemplified above with reference to specific embodiments. However, it should be understood that the invention is not limited to the particular examples described above but may be designed and altered in a multitude of varieties within the scope of the invention as specified in the claims.

Claims

1. A wind turbine (10) comprising: a hub (16); a blade (18) having a pitch axis (P); and a pitch system (22) for rotating said blade (18) of said wind turbine (10) relative to said hub (16), the pitch system (22) comprising: a blade bearing (30) for positioning between the blade (18) and the hub (16); and a drive assembly (42), wherein the drive member (54) is coupled to the blade bearing (30) via a piston rod (52) such that movement of the drive member (54) causes rotation of the blade bearing (30), wherein said drive assembly (42) is a hydraulic actuator comprising: a stator comprising a cylindrical body (50); a drive member (54) positioned at least partially within the cylindrical body (50) and movable along an axis thereof; a plunger (56) of the drive member (54) dividing the cylindrical body (50) into first and second chambers (58, 60); wherein said drive assembly (42) comprise a hydraulic oil; characterized in that at least a part of said hydraulic oil comprises a repair additive for restoration of worn-out metal surfaces.

2. A wind turbine according to claim 1, wherein said drive assembly (42) comprises a third chamber (103) between a primary (100) and a secondary (101) piston rod seal, said third chamber (103) having a volume of less than 10%, preferably less than 1%, of the combined volume of said first and second chambers, said third chamber (103) comprising hydraulic oil comprising said repair additive for restoration of worn-out metal surfaces.

3. A wind turbine according to claim 2, wherein said third chamber (103) is further bordered by an end cap (62) and said piston rod (52).

4. A wind turbine according to any of the preceding claims, wherein said drive assembly (42) comprises a separate oil inlet (102) situated axially between a primary (100) and a secondary (101) piston rod seal.

5. A wind turbine according to any of the preceding claims, wherein said at least part of said hydraulic oil comprises said repair additive in an amount of 0.1-20%, such as 1-10% of the total volume.

6. A wind turbine according to any of the preceding claims, wherein said repair additive is based on a silicate.

7. A wind turbine according to any of the preceding claims, wherein said repair additive comprises at least one ingredient chosen from the group of three-layer silicates.

8. A wind turbine according to any of the preceding claims, wherein said ingredient has particle sizes less than 20 pm, preferably less than 10 pm or less than 3 pm.

9. A wind turbine according to any of the preceding claims, wherein said drive assembly (42) comprises a third chamber (103) between a primary (100) and a secondary (101) piston rod seal, wherein the amount of said repair additive in hydraulic oil (Vol%) in said third chamber is higher than the amount of said repair additive in hydraulic oil (Vol%) in said first and second chambers (58, 60).

10. Method of repairing a drive assembly (42) comprising a hydraulic actuator according to any of the preceding claims, wherein said method comprises the step of adding a repair additive for restoration of worn-out metal surfaces to the hydraulic oil of said drive assembly (42).

11. Method according to claim 10, further comprising the step of adding said repair additive via a separate oil inlet (102) situated axially between a primary (100) and a secondary (101) piston rod seal.

12. Method according to claim 11, further comprising the step of retrofitting an existing drain channel into said separate oil inlet (102).