Turner drive system for a wind turbine and method of operating same

Abstract

A turner drive system (34) and method of operating same for correcting a stuck rotor lock (38) is disclosed. The turner drive system (34) includes a turner gear assembly (36) for rotating a rotor (16) of a wind turbine (10) having a rotor lock (38). Operation the turner drive system (34) includes detecting a stuck rotor lock condition and operating the turner gear assembly (36) to complete a first torque cycle. The first torque cycle includes setting a first torque level of the turner gear assembly (36), applying torque to the rotor (16) of the wind turbine (10) in a first rotational direction for a first time interval, and applying torque to the rotor (16) of the wind turbine (10) in a second rotational direction for a second time interval. If the stuck rotor lock condition remains, operating the turner gear assembly (36) to complete a second torque cycle at a second torque level.

Description

[0001] TURNER DRIVE SYSTEM FOR A WIND TURBINE AND METHOD OF OPERATING SAME

[0002] Technical Field

[0003] The invention relates generally to wind turbines, and more particularly to a turner drive system and method of operating the turner drive system to rotate the central hub of a wind turbine to correct a stuck rotor lock.

[0004] Background

[0005] 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.

[0006] During the assembly and disassembly of the wind turbine at the wind turbine site, the individual blades are attached or detached one at a time to blade bearings circumferentially spaced about the central hub on the energy generating unit. For example, to attach a first blade, the central hub is rotated so that a first blade bearing on the central hub is rotated to generally the three o’clock position (or alternatively the six o’clock position). In this orientation, a generally horizontally oriented blade is lifted via a lifting device, such as a crane, and then attached to the first blade bearing. After the first blade is attached to the central hub, the central hub and the first blade are rotated until a second blade bearing is generally in the three o’clock position and the second blade is lifted and attached to the second blade bearing. Again, the central hub and the first and second blades are rotated until a third blade bearing is generally in the three o’clock position and the third blade is lifted up and attached to the third blade bearing. These steps may generally be performed backwards to remove blades from the central hub of the wind turbine.

[0007] To facilitate rotating the rotor and thus the central hub during such operations as described above, a turner gear is often used. The turner gear may be part of the drivetrain of the wind turbine to assist with rotating the central hub while the wind turbine is not being used to generate power, such as to install or remove blades. After the blades are installed to or removed from the central hub, the turner gear may be removed from the wind turbine. The turner gear is typically coupled to a hydraulic pump of a hydraulic system of the wind turbine. The turner gear is typically coupled, directly or indirectly, to the main shaft to which the central hub is connected. During the blade mounting or removal process, an operator operates the turner gear to turn the main shaft either clockwise or counterclockwise so as to position a particular blade bearing where needed to attach a blade.

[0008] During the installation or removal of wind turbine blades, especially when the central hub is stopped at each rotational position to install or remove a blade, it may be necessary to lock the wind turbine rotor in position using a rotor lock. This prevents the central hub from inadvertently rotating. Any inadvertent or unexpected movement of the central hub during such operations can result in serious harm to personnel and equipment. However, when only some of the blades are attached to the central hub, the rotor is highly unbalanced. Consequently, a high torque may be applied to the rotor lock as it maintains the rotational position of the central hub. To that end, components of the rotor lock may become stuck, preventing the rotor lock from releasing to allow the central hub to be rotated by the turner gear to a different rotational position.

[0009] In a stuck rotor lock condition, an operator must determine which direction torque is being applied to the rotor lock components and operate the turner gear to rotate the central hub in the opposite direction (or the same direction) so that the rotor lock may be released. However, this process is subject to human error, and in some cases, the turner gear is operated to apply too much rotational force in the direction of the torque force, resulting in the destruction of at least the rotor lock components. Similarly, operating the turner gear to apply too much rotational force in the opposite direction of the torque force can also damage the rotor lock among other components. Either case can lead to harm to personnel working on the wind turbine.

[0010] Wind turbine manufacturers need a turner drive system and a method of operating same to release a stuck rotor lock safely in a way that eliminates the human error potential and the risk of applying excessive torque to the central hub in any direction.

[0011] Summary

[0012] To these and other ends, in one aspect of the invention, a method of operating a wind turbine to correct a stuck rotor lock condition is disclosed. The method includes providing a turner drive system that includes a turner gear assembly operatively connected to a rotor of the wind turbine for rotating a central hub of the wind turbine and a rotor lock of the wind turbine. The turner gear assembly is operatively connected to a hydraulic system such that the turner gear assembly and the rotor lock may share a hydraulic pressure source, for example. The method includes detecting a stuck rotor lock condition and operating the turner gear assembly to complete a first torque cycle. The first torque cycle includes setting a first torque level of the turner gear assembly, applying torque to the rotor of the wind turbine in a first rotational direction for a first time interval, and applying torque to the rotor of the wind turbine in a second rotational direction for a second time interval. If it is determined that the stuck rotor lock condition remains, the method includes operating the turner gear assembly to complete a second torque cycle at a second torque level. The second torque level may be greater than the first torque level.

[0013] In one embodiment, the method further includes determining if the stuck rotor lock condition remains after the second torque cycle and, if the stuck rotor lock condition remains, operating the turner gear assembly to complete a third torque cycle at a third torque level. The third torque level may be greater than the second torque level.

[0014] In another embodiment, the turner drive system may include a valve housing with a first fluid control valve. The turner gear assembly may be operatively connected to the valve housing and include at least two motors. The first flow control valve may be operable to operate the at least two motors in parallel or in series. The method may further include operating the first flow control valve to operate the at least two motors in parallel.

[0015] In yet another embodiment, the turner drive system may include a pressure relief valve that is configured to throttle a fluid pressure of a fluid supplied to the turner gear assembly by the hydraulic pressure source. The method may include operating the pressure relief valve to reduce the fluid pressure supplied to the turner gear assembly by the hydraulic pressure source to achieve the first torque level. In one embodiment, the method may further include operating the pressure relief valve to increase the fluid pressure supplied to the turner gear assembly by the hydraulic pressure source to achieve the second torque level.

[0016] In one embodiment, the method may include activating hydraulic power supply to the rotor lock during each torque cycle. Furthermore, the first rotational direction may be opposite the second rotational direction for each torque cycle. The method may further include delaying the second torque cycle by a predetermined delay period. In that regard, the method may also include activating hydraulic power supply to the rotor lock during the predetermined delay period.

[0017] According to another aspect of the invention, a turner drive system of a wind turbine is disclosed. The turner drive system includes a rotor lock of the wind turbine and a turner gear assembly operatively connected to a rotor of the wind turbine for rotating a central hub of the wind turbine. The turner gear assembly is operatively connected to a hydraulic system of the wind turbine such that the turner gear assembly and the rotor lock may share a hydraulic pressure source, for example. The turner drive system also includes a controller operatively coupled to components of the turner drive system, such as the turner drive assembly and the rotor lock. The controller is configured to operate the turner drive system as follows: detecting a stuck rotor lock condition and operating the turner gear assembly to complete a first torque cycle. The first torque cycle includes setting a first torque level of the turner gear assembly, applying torque to the rotor of the wind turbine in a first rotational direction for a first time interval, and applying torque to the rotor of the wind turbine in a second rotational direction for a second time interval. After the torque cycle is complete, the controller proceeds to operate the turner drive system as follows: determining if the stuck rotor lock condition remains and, if the stuck rotor lock condition remains, operating the turner gear assembly to complete a second torque cycle at a second torque level. The second torque level may be greater than the first torque level and the first rotational direction may be opposite the second rotational direction.

[0018] In one embodiment, the controller is configured to operate the turner drive system as follows: determining if the stuck rotor lock condition remains after the second torque cycle and, if the stuck rotor lock condition remains, operating the turner gear assembly to complete a third torque cycle at a third torque level. The third torque level may be greater than the second torque level.

[0019] In yet another embodiment, the turner drive system may include a valve housing with a first fluid control valve. The turner gear assembly may be operatively connected to the valve housing and include at least two motors. The first flow control valve may be operable to operate the at least two motors in parallel or in series. The controller may be configured to operate the turner drive system as follows: operating the first flow control valve to operate the at least two motors in parallel.

[0020] In one embodiment, the turner drive system may include a pressure relief valve that is configured to throttle a fluid pressure of a fluid supplied to the turner gear assembly by the hydraulic pressure source. The controller may be configured to operate the turner drive system as follows: operating the pressure relief valve to reduce the fluid pressure supplied to the turner gear assembly by the hydraulic pressure source to achieve the first torque level. In another embodiment, the controller may be configured to operate the turner drive system as follows: operating the pressure relief valve to increase the fluid pressure supplied to the turner gear assembly by the hydraulic pressure source to achieve the second torque level. In yet another embodiment, the controller may be configured to operate the turner drive system as follows: activating hydraulic power supply to the rotor lock during each torque cycle.

[0021] Brief Description of the Drawings

[0022] 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.

[0023] Fig. 1 is a perspective view of a wind turbine having a tower and an energy generating unit.

[0024] Fig. 2 is an enlarged partial perspective view of the wind turbine of Fig. 1 , illustrating wind turbine components in the nacelle.

[0025] Fig. 3 is a partial schematic side view of the wind turbine of Figs. 1 and 2, illustrating a rotor lock system in a disengaged position to allow the central hub to be rotated.

[0026] Fig. 4 is a view similar to Fig. 3, illustrating the rotor lock system in an engaged position to prevent rotation of the central hub.

[0027] Fig. 5 is a schematic representation of a hydraulic circuit of a turner drive system with the three hydraulic motors of the turner gear operating in parallel.

[0028] Fig. 6 is a schematic flowchart illustrating an operational sequence of a controller associated with the turner drive system.

[0029] Fig. 7 is a schematic representation of a hydraulic circuit of a turner drive system with the four hydraulic motors of the turner gear operating in parallel.

[0030] Detailed Description

[0031] With reference to Figs. 1 and 2, a wind turbine 10 includes a tower 12, a nacelle 14 disposed at the apex of the tower 12, and a rotor 16 operatively coupled to a generator 18 via a gearbox 20 housed inside the nacelle 14. In addition to the generator 18 and gearbox 20, 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 the nacelle 14 and operates to elevate the nacelle 14 and rotor 16 to a height above ground level or sea level, as may be the case, at which air currents having lower turbulence and higher velocity are typically found. The rotor 16 may include a central hub 22 and a plurality of blades 24 attached to the central hub 22 at locations distributed about the circumference of the central hub 22. In the representative embodiment, the rotor 16 includes three blades 24, however the number may vary. The blades 24, which project radially outward from the central hub 22, are configured to interact with passing air currents to produce rotational forces that cause the central hub 22 to spin about its longitudinal axis A1 . The design, construction, and operation of the blades 24 are familiar to a person having ordinary skill in the art of wind turbine design and may include additional functional aspects to optimize performance. For example, pitch angle control of the blades 24 may be implemented by a pitch control mechanism (not shown) responsive to wind velocity to optimize power production in low wind conditions, and to feather the blades 24 if wind velocity exceeds design limitations.

[0032] The rotor 16 may be coupled to the gearbox 20 directly or, as shown in Fig. 2, indirectly via a main shaft 26 extending between the hub 22 and the gearbox 20. The main shaft 26 rotates with the rotor 16 and is supported within the nacelle 14 by a main bearing support 28 which supports the weight of the rotor 16 and transfers the loads on the rotor 16 to the tower 12. The gearbox 20 transfers the rotation of the rotor 16 through a coupling to the generator 18. Wind exceeding a minimum level may activate the rotor 16, causing the rotor 16 to rotate in a direction substantially perpendicular to the wind, applying torque to the input shaft of the generator 18. The electrical power produced by the generator 18 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.

[0033] During the assembly, disassembly, or maintenance of the wind turbine 10, blades 24 may need to be removed from or attached to the central hub 22. In this context, a lifting device, such as a crane, may be used to lift and lower each blade 24 to or from the central hub 22. For such blade handling operations, the central hub 22 is selectively rotated to position a desired blade pitch-bearing 30 (and blade 24 if already attached to the central hub 22) generally horizontally, typically at the nine o’clock position (or alternatively, the three o’clock position). This rotational position of a pitch-bearing 30 and the central hub 22 is considered a blade handling position, where the blade 24 can be either attached to or removed from the desired pitchbearing 30 of the central hub 22. With the blade pitch-bearing 30 in the desired blade handling position, the lifting device may lift or lower the blade 24, in a generally horizontal orientation, to facilitate attaching it to or removing it from the blade pitchbearing 30. The six o’clock position may be considered another blade handling position where the blade 24 may be either be attached to or removed from a respective blade pitch-bearing 30 while in a generally vertical orientation.

[0034] While the wind turbine 10 is shown with three blades 24, other wind turbines 10 may have more or less than three blades 24. As used herein, the term “drivetrain,” schematically illustrated at 32 in Fig. 2, may include one or more of a rotor main shaft, a gearbox, and a generator. The rotor main shaft 26 is considered a “low- speed shaft” that turns an input shaft of the gearbox 20. The gearbox 20 has an output shaft, considered a “high-speed shaft”, that drives the generator 18. As such, the turner gear of the turner drive system may be coupled to the rotor main shaft 26, the high-speed shaft of the generator 18, or the rotor of the generator 18, which may be considered a continuation of the high-speed shaft of the generator 18. In this regard, the drawings are not intended to be limiting.

[0035] Rotating the central hub 22 to a blade handling position while the wind turbine 10 is not being used to generate power may be carried out using a turner drive system 34, illustrated schematically in Fig. 5. In accordance with embodiments of the present invention, the turner drive system 34 includes at least a turner gear assembly 36 and a rotor lock 38 of the wind turbine 10. In that regard, the central hub 22 is rotated using the turner gear assembly 36, which operates to rotate the main shaft 26 of the wind turbine 10 and, ultimately, the central hub 22. The wind turbine rotor 16 is then locked in the desired blade handling position using the rotor lock 38. The rotor lock 38 prevents inadvertent rotational movement of the central hub 22, particularly during blade handling operations. As will be described in further detail below, the turner gear assembly 36 and the rotor lock 38 of the turner drive system 34 are connected to the same hydraulic system and thus share a common hydraulic pressure source. Alternatively, the turner gear assembly 36 and the rotor lock 38 of the turner drive system 34 may receive fluid from separate hydraulic systems. An exemplary turner gear assembly 36 is illustrated in Fig. 2. The turner gear assembly 36, otherwise referred to as a turner gear 36, is configured to be coupled to the rotor 16 of the wind turbine 10 to apply a torque to the rotor 16 via the driveshaft 26 and / or gearbox 20, in order to rotate the rotor 16 and thus the central hub 22 to a desired blade handling position. The turner gear 36 may be permanently installed within the nacelle 14 or it may be temporarily installed during periods of construction, disassembly, and / or maintenance of the nacelle 14, for example. In the embodiment shown, the turner gear 36 includes three torque motors 40a, 40b, 40c, such as hydraulically driven motors, with corresponding pinion gears (not shown). The turner gear 36 mounts to the generator 18, as shown, so that the motors 40a, 40b, and 40c may operatively engage components of the generator 18, resulting in rotation of the central hub 22. Additional details of a turner gear are described in EP Application No. 4127462, owned by the Assignee of the present disclosure, the contents of which are herein incorporated in their entirety.

[0036] As briefly described above, once the central hub 22 is rotated to the desired blade handling position (or another desired rotational position) using the turner gear 36, the wind turbine rotor 16 may be locked in place using the rotor lock 38 to thereby prevent inadvertent or undesired rotational movement of the central hub 22. With reference to Figs. 3 and 4, the rotor lock 38 includes one or more engagement elements 50 that are movable between a disengaged or unlocked position (Fig. 3) and an engaged or locked position (Fig. 4). When in the unlocked position, as illustrated schematically in Fig. 3, the engagement elements 50 are withdrawn from the central hub 22 or otherwise disengaged from the rotor 16. This allows the main shaft 26 to be rotated by the turner gear 36, for example, to rotate the central hub 22 about its longitudinal axis A1 . Fig. 4 schematically illustrates the rotor lock 38, and in particular the engagement elements 50 moved into the locked position to prevent rotation of the central hub 22 about its longitudinal axis A1 . The rotor lock 38 may include one or more sensors associated with each engagement element 50 to detect its position to determine if the engagement element 50 is in the locked or unlocked position. These sensors may be used to determine a stuck condition of the rotor lock 38. The engagement elements 50 may be in the form of pins, bolts, gears, or similar mechanisms capable of physically restraining rotational movement of the central hub 22.

[0037] When only some of the blades 24 are attached to the central hub 22, as shown in Figs. 2, the central hub 22 is considered to be “unbalanced” relative to the rotation of the central hub 22. Additionally or alternatively, uneven wind loads on the blades 24, independent of the number of blades 24 attached to the wind turbine 10, may also create an unbalanced state of the central hub 22. In either case, if the rotor 16 is locked in position with the rotor lock 38, the unbalanced state may cause the rotor 16 to move slightly, resulting in the engagement elements 50 of the rotor lock 38 becoming frictionally engaged with components of the rotor 16. In certain cases, this engagement prevents actuators intended to unlock the rotor lock 38 (i.e., actuators configured to withdraw the engagement elements 50 from an engagement with the rotor 16) from moving the engagement elements 50 to the unlocked position. Conventionally, to free the engagement elements 50 so that they may be moved to the unlocked position, an operator manually operates the turner gear 36 to rotate the rotor 16 to free the engagement elements 50. However, there is a risk that the operator may inadvertently apply torque in the wrong direction and / or too much torque force, increasing the binding force on the engagement elements 50 of the rotor lock 38 instead of decreasing it, for example. This can lead to damage to parts of the wind turbine 10, such as cracking of the bearings, especially considering the forces involved, particularly during an unbalanced condition of the wind turbine 10.

[0038] Considering the issues described above, the present invention provides the turner drive system 34 and methods of operating same that ensure the torque applied by the turner gear 36 to the rotor 16 to free a stuck rotor lock 38 is applied progressively and in a controlled manner to avoid causing damage, such as plastic deformation, to one or more of the engagement elements 50 or other components of the wind turbine 10. As will be described in further detail below, a method according to one embodiment includes operating the turner gear 36 to apply torque progressively and in both clockwise and counterclockwise rotational directions to free the stuck engagement elements 50, while simultaneously operating the rotor lock 38 in an attempt to release the engagement elements 50. Operating the turner gear 36 to rotationally “rock” the rotor 16 is more effective than simply applying torque in one rotational direction, as it addresses the possibility that the engagement elements 50 may be stuck due to forces acting in either rotational direction as well as being subjected to different force loads about the circumference of the main shaft 26 and central hub 22. Additionally, the rocking movement caused by alternating between clockwise and counterclockwise rotations helps prevent the application of excessive torque in a single direction, which could potentially damage the engagement elements 50 or other components of the wind turbine 10.

[0039] Fig. 5 schematically illustrates an exemplary embodiment of the turner drive system 34 for carrying out methods of operating the wind turbine 10 in accordance with one embodiment of the present invention. As shown, the turner drive system 34 includes the turner gear 36, the rotor lock 38, and a valve block or housing 52. In particular, the turner gear 36 and the rotor lock 38 are each operatively connected to common pressure source, being a hydraulic pump 54 and a tank 56 of a hydraulic system in the nacelle 14. In another embodiment, the turner gear 36 and the rotor lock 38 may receive fluid from separate hydraulic sources. For example, the hydraulic source for the turner gear 36 may be portable and brought to the wind turbine 10 to operate the turner gear 36. In the embodiment shown, the pump 54 and tank 56 are installed in the nacelle 14 and may power other hydraulic systems driving components of the wind turbine 10, such as the blade pitch control system, for example. In another embodiment, a hydraulic pump may be temporarily installed in the nacelle 14 to power the motors 40a, 40b, 40c. In the embodiment shown, the three motors 40a, 40b, 40c of the turner gear 36 are operatively connected to the valve housing 52 which is in turn operatively connected to the hydraulic pump 54 and the tank 56.

[0040] An electric motor 58 provides power to the hydraulic pump 54 so that the hydraulic pump 54 may send hydraulic fluid (not shown) from the tank 56 to the motors 40a, 40b, 40c of the turner gear 36 and the rotor lock 38. In one embodiment, the hydraulic pump 54 may run at a constant speed to generate a predetermined, fixed fluid flow rate, i.e., gallons per minute (gpm) or litres per minute (Ipm) to each connected consumer. In other words, the hydraulic pump 54 will deliver a fixed fluid flow rate to at least the turner gear 36 and the rotor lock 38 when the hydraulic pump 54 runs under normal conditions.

[0041] With respect to the rotor lock 38, when the hydraulic pump 54 is running, hydraulic fluid exits the pump 54 and flows to the rotor lock 38, as indicated by directional arrows 60, to drive movement of the engagement elements 50 via hydraulically powered actuators (or motors) 62, for example. Fluid then exits the rotor lock 38 and returns to the tank 56. The flow of fluid to the rotor lock 38 may not flow through the valve block 52, as shown, or it may be supplied to the rotor lock 38 from the valve block 52 in an alternative embodiment. In either case, when the hydraulic pump 54 is running, fluid is pumped to both the rotor lock 38 and the turner gear 36. The fluid pumped to both the rotor lock 38 and the turner gear 36 may be supplied at different working pressures and flows. In the embodiment shown, the fluid flow split between the rotor lock 38 and the turner gear 36 is generally 30% of the fluid flow being directed to the turner gear 36 and 70% of the fluid flow being directed to the rotor lock 38. However, this ratio is merely exemplary, and it will be understood that other ratios of fluid flow are possible, such as a 20 / 80 ratio (rotor lock 38 / turner gear 36), a 60 / 40 ratio (rotor lock 38 / turner gear 36) or a 50 / 50 split, for example. However, neither the turner gear 36 nor the rotor lock 38 will receive zero flow, even at high pressures that may be required to free a stuck rotor lock 38.

[0042] With respect to the turner gear 36, when the hydraulic pump 54 is running, hydraulic fluid exits the hydraulic pump 54, enters into the valve housing 52 and may pass to a three-position flow direction valve 64. The three-position flow direction valve 64 is actuatable so that the fluid may exit the valve housing 52 and circulate to the motors 40a, 40b, 40c. After passing through the motors 40a, 40b, 40c, the fluid flows back into the valve housing 52 and through the three-position flow direction valve 64, exits the valve housing 52, and returns to the tank 56. The three-position flow direction valve 64 may have three operational positions. The three-position flow direction valve 64 may be a type of servo-valve relying on feedback control to regulate the flow of fluid. Further, the turner drive system 34 may include more than one three- position flow direction valve 64, if required.

[0043] As shown in Fig. 5, the valve housing 52 may include one or more flow control valves 72, 74. The two-position flow control valves 72, 74 provide the turner gear 36 with additional control over the speed at which the turner gear 36 rotates the rotor 16 as well as the torque applied by the turner gear 36 to rotate the rotor 16. In that regard, with the two-position flow control valves 72, 74 may be set in a parallel, series, or combination operating configuration to vary the speed at which the turner gear 36 rotates the rotor 16 as well as the torque applied by the turner gear 36 to rotate the rotor 16.

[0044] A control unit 76 may be operatively coupled to the various components of the turner drive system 34, such as the pump 54, components of the valve housing 52 such as the three-position flow direction valve 64 and the two-position valves 72, 74, and the rotor lock 38 to control operation of the turner drive system 34. In that regard, the turner drive system 34 may include certain sensors to facilitate control of the turner drive system 34, such as a pressure gauge 78 and a temperature gauge 80 used to monitor the pressure and temperature of the hydraulic fluid exiting the pump 54, each of which being operatively connected to the control unit 76. The turner drive system 34 may also include a torque sensor 82 and a speed sensor 84 used to monitor the torque output and speed output of the turner gear 36 on the rotor 16, each of which is operatively connected to the control unit 76.

[0045] The turner drive system 34, and in particular the valve housing 52 further includes a pressure release valve 86 operatively connected to the control unit 76. The pressure release valve 86 may be utilized to allow the fluid exiting the pump 54 to return to the tank 56 should the fluid experience downstream pressure over a predetermined high pressure threshold. In the embodiment shown, the pressure release valve 86 is in the form of an autocompensated valve or servo valve configured to adjust its positioning to maintain a constant pressure drop across the valve to thereby ensure that a consistent, steady fluid pressure downstream of the valve to the motors 40a, 40b, 40c. In response to pressure measurements by the pressure sensor 78, for example, the pressure release valve 86 may open more or less (i.e., throttle) to regulate the flow of fluid, thereby controlling the pressure of the fluid being delivered to the motors 40a, 40b, 40c. In the embodiment shown, the pressure release valve 86 regulates the pressure and flow of fluid to the turner gear 36. Thus, an additional advantage of the pressure release valve 86 is that it enables steady and precise control of the torque output from the turner gear 36, as will be described in further detail below.

[0046] When the two-position flow control valves 72, 74 are operated to place the turner gear 36 in a parallel operating configuration, also referred to as “turtle mode,” each motor 40a, 40b, 40c receives one-third of the fluid flow rate that is directed to the turner gear by the pump 54. This distribution ensures that each motor 40a, 40b, 40c generates approximately the same amount of output torque to turn the central hub 22. Since each motor 40a, 40b, 40c only receives one-third of the fluid flow in the parallel configuration, the motors 40a, 40b, 40c rotate the rotor 16 and the central hub 22 at a slower rate or speed compared to if they were receiving the full flow rate of fluid available from the pump 54. In this way, torque may be controlled to a lower level. For example, in the parallel or turtle mode configuration, the motors 40a, 40b, 40c may rotate the rotor 16 at only 50% of the turner gear’s 36 maximum rotational speed capability. However, there is no pressure loss of the fluid supplied to each motor 40a, 40b, 40c in the parallel or turtle mode configuration, allowing for 100% of the maximum torque capability of the turner gear 36 to be available. Finally, should one of the motors 40a, 40b, 40c fail or otherwise become inoperable, the other two unaffected motors may continue to function to at least place the central hub 22 in a safe position.

[0047] The pressure relief valve 86 allows for the throttling of the fluid pressure supplied to each motor 40a, 40b, 40c in the parallel or turtle mode configuration. This provides for a full range of torque capabilities from 0% to 100% of the maximum torque of the turner gear 36 to be available. The active feedback from the autocompensated pressure relief valve 86 allows for precise control of the fluid pressure supplied to each motor 40a, 40b, 40c, and thus precise control of the torque applied by the turner gear 36 to the rotor 16. Consequently, the torque applied by the turner gear 36 to the rotor 16 may be precisely controlled and, based on active feedback, may be incrementally increased to free a stuck rotor lock 38, as described below. This operational configuration of the turner drive system may be referred to as “Gentle Mode.”

[0048] When the two-position flow control valves 72, 74 are operated to place the turner gear 36 in the series operating configuration, each motor 40a, 40b, 40c experiences the same fluid flow rate from the pump 54 but at a lower pressure. In particular, each motor 40a, 40b, 40c receives the full flow rate of fluid available from the pump 54. As a result, each motor 40a, 40b, 40c may rotate the rotor at 100% of the turner gear’s 36 maximum rotational speed capability when in the series configuration. However, the lower pressure of the fluid delivered to each motor 40a, 40b, 40c in the series configuration only allows for 50% of the maximum torque capability of the turner gear 36 to be available, for example. Like the parallel configuration described above, the pressure relief valve 86 may be operated to throttle the fluid pressure supplied to each motor 40a, 40b, 40c providing for a range of torque capabilities from 0% to 50% of the maximum torque of the turner gear to be available in the series configuration.

[0049] With reference to Fig. 6, an exemplary method 100 of operating the turner drive system 34 to release a stuck rotor lock 38 will now be described. In that regard, Fig. 6 is a schematic flowchart illustrating an operational sequence 100 of the turner drive system 34, some or all of which may be carried out by the controller 76. As shown, in a first step 102, a rotor lock (RL) stuck condition is detected. The rotor lock stuck condition may be determined by an operator and / or detected when one or more engagement elements 50 fail to move to the unlocked position after being commanded to do so. If it is determined that the rotor lock 38 is stuck, the Gentle Mode procedure may be initiated in step 104. Once the Gentle Mode procedure has been initiated, hydraulic power supply to the rotor lock 38 is activated, as indicate by block 106. In that regard, during the Gentle Mode procedure, the rotor lock actuator(s) 62 receive a full hydraulic power supply that would otherwise move the engagement elements 50 to the unlocked position if not in the stuck condition. This allows the engagement elements 50 to be immediately moved to the unlocked position once the engagement elements 50 become unstuck or disengaged as a result of the Gentle Mode procedure.

[0050] With continued reference to Fig. 6, the turner gear 36 is placed in Turtle Mode, as indicated by block 108. To place the turner gear 36 in Gentle Mode, the turner gear 36 may first be operated to a parallel, series, or combination configuration, as described above. That is, Turtle Mode may be carried out with the motors 40a, 40b, 40c of the turner gear 36 operating in a parallel, series, or combination configuration. In the exemplary embodiment described and shown in Fig. 6, the turner gear 36 is first operated to a parallel configuration in block 108. In that regard, the flow control valves 72, 74 are operated to place the motors 40a, 40b, 40c in a parallel operating configuration. Once in the parallel configuration, the turner gear 36 may then operate in Gentle Mode as the pressure relief valve 86 is operated to provide up to 100% of the maximum torque capability of the turner gear 36. While in Gentle Mode, the turner gear 36 may rotate the rotor 16 at 50% of the turner gear’s 36 maximum rotational speed capability. Once in Gentle Mode, an initial torque level (i.e. , torque level 1 ) is set for the turner gear 36, as indicated by block 110. The initial torque level is low, such as between about 5% to about 25% of the maximum torque capability of the turner gear 36. In the embodiment shown, the initial torque level may be about 20% of the maximum torque capability of the turner gear 36. The low torque level is achieved using the pressure relief valve 86, as described above.

[0051] After the initial torque level is set, the turner gear 36 is operated to apply torque to rotate the rotor 16 and the central hub 22 in a first clockwise or counterclockwise direction for a first predetermined time interval, as indicated by block 112. For example, the turner gear 36 may be operated to apply torque to rotate the rotor 16 and the central hub 22 in a clockwise direction for approximately 30 seconds. However, the time interval may be longer or shorter. Following the application of torque to the rotor 16 in a first direction by the turner gear 36, the turner gear 36 is operated to apply torque to rotate the rotor 16 and the central hub 22 in an opposite direction for a second time interval, as indicated by block 114. Continuing the example above, the turner gear 36 may be operated to apply torque to rotate the rotor 16 and the central hub 22 in a counterclockwise direction for approximately 30 seconds. However, the time interval may be longer or shorter. Furthermore, rotating the rotor 16 in a single direction (i.e., only step 112 or step 114) may be all that is required to free the stuck rotor lock 38. Steps 112 and 114 define a torque cycle in which the turner gear 36 rotationally rocks the rotor 16 and central hub 22. This short rocking motion facilitates loosening of the stuck engagement elements 50 without risking damage to them or other components of the wind turbine 10.

[0052] If the engagement elements 50 are released and moved to the unlocked position at any point during the Gentle Mode procedure, and in particular steps 112 and 114 described above, the Gentle Mode procedure and operational sequence 100 is terminated, as indicated by block 116. Upon the termination of the Gentle Mode procedure, hydraulic power supply to the rotor lock 38 is also stopped. However, at the completion of step 114, if one or more engagement elements 50 of the rotor lock 38 are still determined to be stuck, as indicated by step 118, then the torque level of the turner gear 36 is increased, as indicated by block 120. That is, the torque level of the turner gear 36 is increased to a second torque level. The increase in the torque level of the turner gear 36 to a second torque level (i.e., torque level 2) may be incremental, such as a 15% or less increase in the torque level from torque level 1. For example, torque level two may be about 27% of the maximum torque capability of the turner gear 36. This incremental increase in torque is achieved through operation of the pressure relief valve 86. The torque level may be precisely maintained though operation of the pressure relief valve 86 based on active feedback from one or more sensors, such as the pressure sensor 78 and / or the torque sensor 82, for example. Once the torque level is increased, the method proceeds back to block 112 to begin the rocking process of the torque cycle again. There may be a built in delay period between the completion of one torque cycle (i.e., steps 112 and 114 at torque level 1 ) and the start of the next torque cycle (i.e., steps 112 and 114 at torque level 2). During the delay period, hydraulic power supply to the rotor lock 38 may be activated. The predetermined delay period may be 30 seconds, for example.

[0053] If the engagement elements 50 are not able to be released after the completion of the second torque cycle, the method may proceed to again increase the torque level of the turner gear 36 for a third torque cycle. The increase in the torque level of the turner gear 36 to a third torque level (i.e., torque level 3) may again be incremental, such as a 15% or less increase in the torque level. For example, torque level three may be about 36% of the maximum torque capability of the turner gear 36. Once the torque level is increased, the method proceeds back to block 112 to begin the rocking process of the torque cycle again.

[0054] If the engagement elements 50 are not able to be released after the completion of the third torque cycle, the method may proceed to again increase the torque level of the turner gear 36 for a fourth torque cycle. The increase in the torque level of the turner gear 36 to a fourth torque level (i.e., torque level 4) may again be incremental, such as a 15% or less increase in the torque level. For example, torque level three may be about 43% of the maximum torque capability of the turner gear 36. Once the torque level is increased, the method proceeds back to block 112 to begin rocking process of the torque cycle again.

[0055] The Gentle Mode procedure may be aborted at any point manually. Further, the method may have more than four torque cycles, if necessary. However, it is believed that the engagement elements 50 will typically be released after two or three torque cycles. In either case, the method provides at least the following benefits: it prevents the over-torquing of gearbox bearings as the result of a stuck rotor lock; it prevents the plastic deformation of components of the rotor lock system; and it prevents cracking of the main bearing arrangement as the result of a stuck rotor lock.

[0056] Fig. 7 schematically illustrates a similar layout of the turner drive system 34 shown in Fig. 5, but with an additional motor 40d. To accommodate operatively connecting the motor 40d to the pump 54, the valve housing 52 may include an additional two- position flow control valve 90. By controlling the two-position flow control valves 72, 74, 90, the motors 40a, 40b, 40c, 40d may be run in parallel or series as dictated by the blade assembly process. It will be appreciated that additional motors may be added to the turner gear 36 to increase the torque output of the turner gear 36 as torque requirements increase. Similarly, a corresponding two-position valve may be added to the valve housing 52 for each additional motor so that each additional motor may be run in parallel or in series with the other motors in the turner gear 36.

[0057] While the invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable 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. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the Applicant’s general inventive concept.

Claims

CLAIMS1 . A method of operating a wind turbine (10), comprising: providing a turner drive system (34) including a turner gear assembly (36) operatively connected to a rotor (16) of the wind turbine (10) for rotating a central hub (22) of the wind turbine (10) and a rotor lock (38) of the wind turbine (10), the turner gear assembly (36) being operatively connected to a hydraulic system of the wind turbine (10); detecting a stuck rotor lock condition; operating the turner gear assembly (36) to complete a first torque cycle, comprising: setting a first torque level of the turner gear assembly (36); applying torque to the rotor (16) of the wind turbine (10) in a first rotational direction for a first time interval; and applying torque to the rotor (16) of the wind turbine (10) in a second rotational direction for a second time interval; determining if the stuck rotor lock condition remains; and if the stuck rotor lock condition remains, operating the turner gear assembly (36) to complete a second torque cycle at a second torque level.

2. The method according to claim 1 , wherein the second torque level is greater than the first torque level.

3. The method according to claim 1 or 2, further comprising: determining if the stuck rotor lock condition remains after the second torque cycle; and if the stuck rotor lock condition remains, operating the turner gear assembly (36) to complete a third torque cycle at a third torque level.

4. The method according to claim 3, wherein the third torque level is greater than the second torque level.

5. The method according to any one of the previous claims, wherein the turner drive system (34) further comprises a valve housing (52) including a first fluid controlvalve (72), the turner gear assembly (36) being operatively connected to the valve housing (52) and including at least two motors (40a, 40b), wherein the first fluid control valve (72) is operable to operate the at least two motors (40a, 40b) in parallel or in series, the method further comprising: operating the first flow control valve (72) to operate the least two motors (40a, 40b) in parallel.

6. The method according to any one of the previous claims, wherein the turner drive system (34) further comprises a pressure relief valve (86) that is configured to throttle a fluid pressure of a fluid supplied to the turner gear assembly (36) by the hydraulic pressure source (54), the method further comprising; operating the pressure relief valve (54) to reduce the fluid pressure supplied to the turner gear assembly (36) by the hydraulic pressure source (54) to achieve the first torque level.

7. The method according to claim 6, further comprising: operating the pressure relief valve (86) to increase the fluid pressure supplied to the turner gear assembly (36) by the hydraulic pressure source (54) to achieve the second torque level.

8. The method according to any one of the previous claims, further comprising: activating hydraulic power supply to the rotor lock (38) during each torque cycle.

9. The method according to any one of the previous claims, wherein the first rotational direction is opposite the second rotational direction.

10. The method according to any one of the previous claims, further comprising: delaying the second torque cycle by a predetermined delay period.11 . The method according to claim 10, further comprising: activating hydraulic power supply to the rotor lock (38) during the predetermined delay period.

12. A turner drive system (34) of a wind turbine (10), comprising: a rotor lock (38) of the wind turbine (10); a turner gear assembly (36) operatively connected to a rotor (16) of the wind turbine (10) for rotating a central hub (22) of the wind turbine (10), the turner gear assembly (36) being operatively connected to a hydraulic system of the wind turbine (10); and a controller (76) operatively coupled to the turner drive system (34), the controller (76) being configured to operate the turner drive system (34) as follows: detecting a stuck rotor lock condition; operating the turner gear assembly (36) to complete a first torque cycle, comprising: setting a first torque level of the turner gear assembly (36); applying torque to the rotor (16) of the wind turbine (10) in a first rotational direction for a first time interval; and applying torque to the rotor (16) of the wind turbine (10) in a second rotational direction for a second time interval; determining if the stuck rotor lock condition remains; and if the stuck rotor lock condition remains, operating the turner gear assembly (36) to complete a second torque cycle at a second torque level.

13. The turner drive system (34) of claim 12, wherein the second torque level is greater than the first torque level.

14. The turner drive system (34) according to claim 12 or 13, wherein the controller (76) is configured to operate the turner drive system (34) as follows: determining if the stuck rotor lock condition remains after the second torque cycle; and if the stuck rotor lock condition remains, operating the turner gear assembly (36) to complete a third torque cycle at a third torque level.

15. The turner drive system (34) of claim 14, wherein the third torque level is greater than the second torque level.

16. The turner drive system (34) of any one of the previous claims, further comprising a valve housing (52) including a first fluid control valve (72), the turner gear assembly (36) being operatively connected to the valve housing (52) and including at least two motors (40a, 40b), wherein the first fluid control valve (72) is operable to operate the at least two motors (40a, 40b) in parallel or in series, wherein the controller (76) is configured to operate the turner drive system (34) as follows: operating the first flow control valve (72) to operate the at least two motors (40a, 40b) in parallel.

17. The turner drive system (36) according to any one of the previous claims, further comprising a pressure relief valve (86) that is configured to throttle a fluid pressure of a fluid supplied to the turner gear assembly (36) by the hydraulic pressure source (54), wherein the controller (76) is configured to operate the turner drive system (34) as follows: operating the pressure relief valve (86) to reduce the fluid pressure supplied to the turner gear assembly (36) by the hydraulic pressure source (54) to achieve the first torque level.

18. The turner drive system of claim 17, wherein the controller (76) is configured to operate the turner drive system (34) as follows: operating the pressure relief valve (86) to increase the fluid pressure supplied to the turner gear assembly (36) by the hydraulic pressure source (54) to achieve the second torque level.

19. The turner drive system (34) of any one of the previous claims, wherein the controller (76) is configured to operate the turner drive system (34) as follows: activating hydraulic power supply to the rotor lock (38) during each torque cycle.

20. The turner drive system (34) of any one of the previous claims, wherein the first rotational direction is opposite the second rotational direction.