Patent Publication Number: US-2023137592-A1

Title: Turner gear assembly for wind turbines and method of using same

Description:
TECHNICAL FIELD 
     The invention relates generally to wind turbines, and more particularly to a turner gear assembly for use while installing wind turbine blades on a wind turbine, and to methods of using such a turner gear assembly especially during wind turbine blade installation. 
     BACKGROUND 
     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 are typically assembled on the site where the wind turbine will operate. For example, at the site the tower is erected and an energy generating unit, is place at the top of the tower. Then, the individual blades may be attached one at a time to blade bearings circumferentially spaced about the central hub on the energy generating unit. In one specific method to attach the first blade, the central hub is rotated so that a first blade bearing on the central hub is rotated to generally the three o&#39;clock position, for example, (or alternatively the six o&#39;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&#39;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&#39;clock position and the third blade is lifted up and attached to the third blade bearing. To facilitate rotating the central hub to orient the blade bearings on the central hub, a turner gear is typically used. The turner gear is configured to drive the rotor mainshaft in rotation, especially when the wind turbine is decommissioned or prior to its commissioning. The turner gear is not normally an integral part of the drivetrain of a wind turbine but may be installed and operated solely to assist with rotating a hub or rotor, for example during installation of blades to the rotor hub. Thus, after the blades are installed on the hub, the turner gear may be removed from the wind turbine. The turner gear may be powered by electric power or sometimes by hydraulic power. In the case of a hydraulically powered turner gear, hydraulic drive elements of the turner gear are typically coupled to a hydraulic pump. Such a pump may be portable along with the turner gear, and may therefore be installed to or removed from the wind turbine respectively before or after use. Typically, the turner gear may be coupled, directly or indirectly, to the main shaft to which the rotor hub is connected. During the blade mounting process, an operator may command the turner gear to turn the main shaft e.g. clockwise or counterclockwise so as to orient the hub for attachment of successive blades. 
     When the hub has only one or two blades attached, the rotor is considered to be in an unbalanced condition. The torque needed to turn the rotor, when it is unbalanced is higher than when the rotor is in a balanced condition, i.e., when all its blades are installed. Furthermore, a rotor comprising larger, heavier blades will require higher turning torques than with smaller, lighter blades. Also, if the wind turbine site experiences high winds during installation, this may increase the torque needed to rotate the unbalanced rotor. Thus, a turner gear must be capable of generating enough torque to rotate the rotor in an unbalanced condition. An unbalanced rotor may typically comprise a hub with only a single attached blade, or with only two attached blades. 
     A turner gear may comprise one or more torque motors. As mentioned, these may be electrically or hydraulically driven. Torque motors may be attached to drive, directly or indirectly, the main shaft of the wind turbine. In some cases, torque motors of a turner gear may be installed at or near a gearbox of a drivetrain, thereby to drive a gearbox shaft in rotation, which may thereby turn the rotor hub to the desired position for blade attachment. In general, when a gearbox is present in a wind turbine powertrain, the rotor is coupled to the low speed shaft of the gearbox, sometimes known as an input shaft. A turner gear may be installed to drive a high speed shaft of a gearbox, to thereby use the gearbox to increase the applied torque. A high speed gearbox shaft may also be known as an output shaft thereof. 
     When one or more hydraulic motors are used in a turner gear, then these are driven using a hydraulic fluid pump. By way of example, a plurality of hydraulic motors may be connected in parallel to a hydraulic pump such that each motor receives the same fluid flow and pressure, which is delivered by the hydraulic pump. The hydraulic motors are thereby run in parallel so that if one of the hydraulic motors fails, the others will remain operational to at least put the hub in a safe condition until the failed hydraulic motor is fixed. Operating the hydraulic motors in parallel allows the hydraulic motors to generate maximum torque but may limit how fast they can each turn when driven by a hydraulic pump with a fixed fluid flow rate. 
     A wind turbine manufacturer may connect a turner gear to a pre-installed hydraulic pump in the wind turbine, e.g. in the nacelle. A pre-installed hydraulic pump may for example be used to power other systems in the wind turbine, such as e.g. blade pitch drive elements. Alternatively, a turner gear may be associated with or may comprise one or more dedicated hydraulic pump, which may be temporarily installed in the nacelle for the sole purpose of operating the turner gear. That installed hydraulic pump may be sized to provide a fixed fluid flow rate based on the needs of a particular wind turbine. For example, a wind turbine with large, heavy wind turbine blades will require a hydraulic pump sized to generate a greater fluid flow rate compared to a wind turbine with smaller, lighter blades, which will require a smaller hydraulic pump which generates a lower fluid flow rate. 
     The speed at which the turner gear can turn the hub or rotor is directly related to the fluid flow rate generated by the hydraulic pump. Thus, a turner gear coupled to a hydraulic pump with one fluid flow rate may rotate the rotor 120 degrees in 40 minutes, whereas the same turner gear may take 80 minutes to turn a rotor 120 degrees when coupled to a hydraulic pump generating half the fluid flow rate. This reduced rotational rate can impact the time it takes to install all of the blades. This situation may occur if the same turner gear is utilized in association with both large or small rotors. For example, a turner gear may be used with a large wind turbine where the “installed” hydraulic pump can generate a large fluid flow rate such that the turner gear may generate a large amount of torque at a given rotation speed. That same turner gear may then be removed and thereafter used during the assembly of a rotor at a smaller wind turbine whose installed hydraulic pump may generate a fluid flow rate that is appreciably less than that of the installed hydraulic pump on the larger wind turbine. As such, that same turner gear may turn at a correspondingly lower rotational speed, even while it is otherwise capable of generating more torque than required to rotate the smaller rotor on the smaller wind turbine. Consequently, that blade assembly process may take appreciably longer, even while the turner gear is capable of generating a higher torque than is needed for turning the smaller rotor. This means that more time is taken for turning a rotor than is strictly necessary when considering the power envelope of the turner gear. 
     An insight underlying the present disclosure resides in the recognition that there may be needed a turner gear that can generate sufficient torque and rotational speed in one wind turbine and then be reconfigured to generate a different torque and rotational speed in a different wind turbine. In this way, a wind turbine requiring less torque may use the same turner gear at lower torque output but rotate at an increased speed, thereby saving time during installation. 
     SUMMARY 
     To these and other ends, a turner gear assembly for turning an unbalanced rotor of a wind turbine having a drivetrain is disclosed. The turner gear assembly includes a turner gear configured to couple to the drivetrain and having at least two motors, and a valve block operatively connectable to the turner gear and including a first flow control valve configured to be in fluid communication with a pump and with the at least two motors of the turner gear. The first flow control valve is selectively moveable between a first fluid control position and a second fluid control position. When the first flow control valve is in the first fluid control position, the at least two motors are configured to operate in parallel. When the first flow control valve is in the second fluid control position, the at least two motors are configured to operate in series. The ability to configure the valve block to operate the at least two motors in parallel, in series, or not at all (e.g., in the case of three of more motors) allows the turner gear assembly to be configured to the specific torque and rotational speed needs across a wide range of wind turbine sizes. The at least two motors may include two or more motors. Where more than two motors are provided, there may preferably be a first, and a second flow control valve. Where more than three motors are provided, there may be a first, and a second and a third flow control valve or more. 
     In one embodiment, the turner gear may have first, second, and third turner gear motors. In this arrangement, the first flow control valve may be configured to be in fluid communication with a pump and with first and second turner gear motors and the valve block may further include a second flow control valve configured to be in fluid communication with the pump and with the second and third turner gear motors. The second flow control valve may be selectively moveable between a first fluid control position and a second fluid control position. The first and second fluid control positions of the respective first flow control valve and the second flow control valve may be selectively configured such that the first, second, and third motors operate in parallel, operate in series, or operate in a combination of parallel and series. In one exemplary arrangement, when the first flow control valve is in its first fluid control position and the second flow control valve is in its first fluid control position, the first, second and third motors may operate in parallel. In another exemplary arrangement, when the first flow control valve is in its second fluid control position and the second flow control valve is in its second fluid control position, the first, second, and third motors may operate in series. In yet another arrangement, when the first flow control valve is in its second fluid control position and the second flow control valve is in its first fluid control position, the first and second motors may operate in series and the third motor may operate in parallel to the combination of the first and second motors. The turner gear assembly may include a control unit configured to selectively move the first flow control valve between its first and second positions, and when the turner gear assembly includes a second flow control valve, the control unit may be configured to selectively move both the first and second flow control valves between their respective first and second positions. 
     In another embodiment, the turner gear may have first, second, third, and fourth turner gear motors. In this arrangement, the first flow control valve is configured to be in fluid communication with the first and second motors, and the valve block includes a second flow control valve configured to be in fluid communication with the pump and with the second and third motors. The second flow control valve may be selectively moveable between a first fluid control position and a second fluid control position. The valve block may additionally include a third flow control valve configured to be in fluid communication with the pump and with the third and fourth motors. The third flow control valve may be selectively moveable between a first fluid control position and a second fluid control position. In this embodiment, the first and second fluid control positions of the respective first, second, and third flow control valves may be selectively configured such that the first, second, third, and fourth motors operate in parallel, operate in series, or operate in a combination of parallel and series. In one exemplary arrangement, when the first flow control valve is in its second fluid control position, the second flow control valve is in its first fluid control position, and the third flow control valve is in its second fluid control position, the first and second motors operate in series with each other and the third and fourth motors operate in series with each other. Still further, the turner gear may have more than four turner gear motors. In such arrangements, and in any case, it is preferred for the turner gear motors to be connected to pressurised hydraulic fluid supply via an array of flow control valves in said valve block in such a way that the turner gear motors can be driven in either a series or parallel fluid flow connection relative to other motors, preferably also in a mixed configuration of series and parallel operating turner gear motors. 
     The valve block may include a flow direction valve operatively connected to the pump The flow direction valve may be selectively movable between first and second positions, where the first position is configured to allow the fluid flowing from the pump to move in a first fluid flow direction through the turner gear motors, and the second position configured to allow the fluid from the pump to move in a second fluid flow direction through the turner gear motors. Accordingly, the turner gear motors are preferably configured to be bi-directional motors. 
     A drivetrain of a wind turbine may comprise elements including a rotor mainshaft, a mainshaft housing and a gearbox, the gearbox being drivingly coupled to the rotor mainshaft. The gearbox may comprise a low speed input shaft and a high speed output shaft. The input shaft may be operatively coupled to the rotor mainshaft. A generator may be coupled to the gearbox high speed shaft. In particular a generator may comprise a stator and a generator rotor, rotatable in relation to the stator on a generator rotor shaft. The generator rotor shaft may be coupled to the gearbox output shaft, i.e. the gearbox output shaft and the generator rotor shaft may be regarded as a high speed shaft of the drivetrain. The turner gear may be coupled to a drivetrain element of the wind turbine. In embodiments, the turner gear may be drivingly connected to a high speed shaft of the drivetrain. More particularly, the turner gear may be drivingly connected to a rotor shaft of the generator. Alternatively, the turner gear may be drivingly connected to a gearbox shaft which may preferably be a gearbox output shaft. Alternatively, in embodiments, the turner gear may be drivingly coupled to a low speed, input shaft of the gearbox, or to the blade rotor mainshaft. 
     The pump may in particular be a hydraulic pump or a group of hydraulic pumps. In embodiments the pump may be a part of the wind turbine. For example, the pump may be part of a blade pitch control system of the wind turbine. Alternatively, a turner gear assembly may include a pump, in particular a pump which may be temporarily installed and removed along with the turner gear, successively at one or more wind turbines. 
     In yet another embodiment, there is disclosed a method of operating the turner gear assembly as described above for turning an unbalanced rotor of a wind turbine. The method includes installing a turner gear at a wind turbine drivetrain by coupling the turner gear to a relevant drivetrain element, and thereafter selecting between the first fluid control position and the second fluid control position of the first flow control valve, such that when the first fluid control position is selected, the at least two motors run in parallel, and when the second fluid control position is selected, the at least two motors run in series, and operating the turner gear assembly with the first fluid control valve in the selected fluid control position. 
     For example, in one embodiment of the method, the turner gear may have first, second, and third motors and the first flow control valve in fluid communication with the first and second motors. A valve block of the turner gear assembly may further include a second flow control valve in fluid communication with the pump and with the second and third motors, the second flow control valve being selectively moveable between a first fluid control position and a second fluid control position. The method may further include selecting between the first fluid control position and the second fluid control position of the second flow control valve, such that the first, second, and third motors operate in parallel, operate in series, or operate in a combination of parallel and series. 
     In still a further embodiment, a method of turning an unbalanced rotor of a wind turbine using a turner gear assembly is disclosed. The method includes providing a first wind turbine having a central hub with a plurality of blade attachment sites, the first wind turbine further having a drivetrain operatively coupled to the central hub; providing a turner gear assembly as described above; attaching the turner gear to the drivetrain of the first wind turbine and operatively connecting the valve block to the turner gear; configuring the valve block to operate the at least two turner gear motors in a first operational mode; operating a pump of the turner gear assembly to actuate the at least two motors and turn the central hub until one of the plurality of blade sites is in a blade handling position; attaching/removing a wind turbine blade to/from the blade site at the blade handling position; and repeating the operating and attaching steps until the first wind turbine has all of its wind turbine blades attached/removed to/from a respective one of the plurality of blade sites. 
     The method may further include removing the turner gear assembly from the first wind turbine; providing the turner gear assembly to a second wind turbine having a central hub with a plurality of blade sites; attaching the turner gear to a drivetrain of the second wind turbine and operatively connecting the valve block to the turner gear; configuring the valve block to operate in a second operational mode different from the first operational mode; operating a pump of the turner gear assembly to actuate the at least two motors and turn the central hub until one of the plurality of blade sites is in a blade handling position; attaching/removing a wind turbine blade to/from the blade site at the blade handling position; and repeating the operating and attaching steps until the second wind turbine has all of its wind turbine blades attached/removed to/from a respective one of the plurality of blade sites. 
     In one embodiment, operating the pump further comprises coupling the turner gear to a hydraulic system of the wind turbine having a pump and operating the pump of the wind turbine hydraulic system to drive the turner gear motors. The hydraulic system may be the pitch control system of the wind turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG.  1    is a perspective view of a wind turbine having a tower and an energy generating unit; 
         FIG.  2    is an enlarged partial perspective view of the wind turbine of  FIG.  1    illustrating wind turbine components in the nacelle; 
         FIG.  3    is a perspective view showing a crane lifting a wind turbine blade to a partially assembled wind turbine; 
         FIG.  4   . is a perspective view of one side of a turner gear; 
         FIG.  5   . is a perspective view of the other side of the turner gear of  FIG.  4   ; 
         FIG.  6    is an exploded perspective view of the turner gear of  FIG.  4    being mounted to a generator of an energy generating unit of a wind turbine; 
         FIG.  7    is a schematic representation of a hydraulic circuit of a turner gear assembly showing with the three hydraulic motors operating in parallel; 
         FIG.  8    is a schematic representation similar to  FIG.  7   , showing the three hydraulic motors operating in series; and 
         FIG.  9    is a schematic representation similar to  FIGS.  7  and  8    showing four hydraulic motors operating in parallel. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 , also known as a blade rotor  16 , may include a central hub  22 , otherwise known or referred to herein as a rotor hub  22  or hub  22 . The blade rotor  16  may include 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 rotor  16 , including its hub  22 , to spin about its rotational axis. The rotational axis of the hub  22  and rotor  16  may in particular correspond to the longitudinal axis of the rotor mainshaft  26 . 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 if wind velocity exceeds design limitations. 
     The rotor  16  may be coupled to the gearbox  20  directly or, as shown, indirectly via a mainshaft  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 , or mainshaft housing  28 , which supports the weight of the rotor  16  and transfers the rotor  16  loads on to the tower  12 , possibly via a nacelle bedframe. A gearbox  20  transfers the rotation of the rotor  16  to a generator  18 . This transfer of rotational motion between a gearbox  20  and a generator  18  may take place via a coupling between a gearbox output shaft and a generator rotor shaft of 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 rotor mainshaft  26  and thereby also to the input shaft of the gearbox  20 , which in turn applies a torque to the generator rotor 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. 
     With reference to  FIG.  3   , the wind turbine  10  is shown with two blades  24  attached to the hub  22 . A lifting device  40 , such as a crane, is shown lifting the third blade  24  so a root end  42  of the blade  24  may be attached to a blade site  44 , such as a blade pitch-bearing on the central hub  22 . As shown in  FIG.  3   , the central hub  22  has been rotated after the second blade  24  was attached so that the blade pitch-bearing  44  is generally at the nine o&#39;clock position (as viewed facing the central hub  22 ). The blade pitch-bearing  44  at the nine o&#39;clock position (or alternatively in the 3 o&#39;clock position) may be considered a blade handling position where the blade  24  may be either attached to or removed from the central hub  22 . With the blade pitch-bearing  44  in that position, the lift device  40  may lift the blade  24  in a generally horizontal orientation to facilitate attaching it to the blade pitch-bearing  44 . Alternatively, the central hub  22  may be rotated so that the blade pitch-bearing  44  is generally at the six o&#39;clock position. The six o&#39;clock position may also be considered another blade handling position where the blade  24  may be either attached to or removed from the central hub  22 . In that orientation, the lifting device  40  may lift the blade  24  in a generally vertical orientation. 
     While  FIG.  3    illustrates the third blade  24  arranged to be attached to the blade pitch-bearing  44 , the first and second blades  24  may be attached in a similar fashion. To attach the first blade  24 , for example, a turner gear  50  ( FIG.  6   ), which may be coupled to a drivetrain, is operated to rotate the main shaft  26  and thereby also the central hub  22 . The turner gear  50  rotates the rotor hub  22  until the blade pitch-bearing  44  is in the desired position (three, six, or nine o&#39;clock position) depending the orientation of the blade  24  when lifted. After the first blade  24  is attached, the turner gear  50  is operated to turn the rotor hub  22  until the next blade pitch-bearing  44  is in the desired position. This process is repeated until all the blades  24  are attached to the central hub  22 , making up a blade rotor  16 . While the wind turbine  10  in  FIGS.  1 - 3    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  30  in  FIG.  2   , may include one or more of a rotor main shaft, a gearbox, and a generator. A drivetrain may also comprise a rotor mainshaft bearing and a rotor mainshaft housing  28 . A drivetrain which comprises a generator may sometimes be referred to as a powertrain. In this specification, the term “drivetrain” is used to denote a drivetrain with or without a generator, although a drivetrain  30  shown in the drawings includes a generator  18 , which may be preferred in the present context. The rotor mainshaft is considered a “low-speed shaft” that turns an input shaft of the gearbox. The gearbox has an output shaft, considered a “high-speed shaft”, that drives the generator. As such, the turner gear  50  may be coupled on the one hand to the rotor mainshaft or the low-speed, input shaft of the gearbox, or on the other hand, the turner gear  50  may be coupled to the high-speed, output shaft of the gearbox, or to the rotor shaft of the generator, which may be considered a continuation of the high-speed shaft of the gearbox. 
     When one blade  24  is attached to a central hub  22 , the rotor  16  is considered to be “unbalanced”, in particular when considered relative to the rotation axis of the central hub  22 . In that unbalanced condition, the turner gear  50  must generate more torque to turn the central hub  22  compared to when all the blades  24  are attached to the central hub  22 , which is considered a “balanced” condition of the blade rotor  16 . 
     An exemplary turner gear  50  is illustrated in  FIGS.  4 ,  5  and  6   . The turner gear  50  has turner gear motors  58  in the form of torque motors, provided for rotationally driving a nacelle drivetrain. In the illustrated embodiment, the turner gear has three torque motors  58  (see numerals  58   a ,  58   b ,  58   c ), such as hydraulically driven motors, and each with a corresponding pinion gear  60  (see numerals  60   a ,  60   b ,  60   c ). The torque motors  58  may be attached to a motor frame  62 , which may hold the motors  58  in spaced, fixed relation to each other. A motor frame  62  may simplify the task of attaching a batch or cluster of torque motors  58  to a drivetrain element. A motor frame  62  may preferably include torque supports  64  that are used to secure the turner gear  50  to the drivetrain  30  using appropriate fasteners (not shown). The motor frame  62  may be attached to a main frame  66  of the turner gear  50  by appropriate fasteners (not shown). The illustrated main frame  66  is shown including a ring gear  68  which is a primary component of an output drive of the turner gear  50 . The ring gear  68  is driven by the torque motor pinions  60 . One or more spacing blocks  70  may help to accurately position the turner gear  50  at a drivetrain  30 . Preferably spacer blocks  70  may locate the motor frame  62  at a desired distance from a drivetrain element, to ensure engagement between the turner gear output drive and the drivetrain element to which the turner gear  50  is drivingly coupled. The pinion gears  60   a ,  60   b ,  60   c  rotatingly engage the ring gear  68  such that when the motors  58   a ,  58   b ,  58   c  operate they rotate the pinion gears  60   a ,  60   b ,  60   c  which rotates the ring gear  68 . A ring flange  72  may be mounted to the ring gear  68 . The ring flange  72  may also form a part of the turner gear output drive. The ring flange  72  may have a first and a second side. A first side thereof may be mounted to the ring gear  68 . A second side of the ring flange  72  may be drivingly connectable to an element of the drivetrain  30 . As illustrated in the example, the ring flange  72  may comprise one or more torque pins  74 . The torque pins may engage with an element of the drivetrain  30  to transmit torque from the turner gear  50  to the drivetrain  30 . In the illustrated example, the second side of the flange  72  may mount to the generator  18  such that when ring gear  68  rotates, the generator rotor rotates, which in turn causes the gearbox output shaft, the gearbox input shaft and the mainshaft  26  to rotate, thereby also rotating the rotor hub  22 . 
     Reference will now be made to exemplary embodiments shown in  FIGS.  7 - 9   . Multiple torque motors  58  of the turner gear  50  are connectable via hydraulic fluid lines to a pressurised hydraulic fluid source including a pump  80 . The illustrated torque motors  58   a - d  are hydraulic motors. In a most basic mode, hydraulic fluid flows from the pump  80 , via a valve block  78  to and from the hydraulic motors  58  and then back to the pump  80 . Hydraulic fluid flow between the pump  80  and the motors  58  may be adjusted by means of flow control valves  106 ,  108 ,  110  in the valve block  78 . The valve block  78  may comprise pump interface ports channeling hydraulic fluid between the pump  80  and the bock  78 . The valve block  78  may comprise torque motor interface ports  94   a - d ,  104   a - d , channeling hydraulic fluid between the block  78  and each of the motors  58   a - d . The pump interface ports and the motor interface ports  94 ,  104  are connected by a network of hydraulic fluid lines within the valve block  78 . Flow control valves  106 ,  108 ,  110  in the hydraulic fluid line network in the valve block  78  adjust the fluid flow path through the valve block  78  between the pump interface ports and the motor interface ports  94 ,  104 . Thereby, the flow control valves  106 ,  108 ,  110  in the hydraulic fluid line network in the valve block  78  adjust the fluid flow path between the pump  80  and the respective motors  58   a - d . Each flow control valve  106 ,  108 ,  110  may be linked with hydraulic fluid lines to and from pump  80  interface ports in the valve block  78 . In addition, each fluid control valve  106 ,  108 ,  110  may be linked with motor interface ports  94 ,  104  to and from more than one motor  58 . Each flow control valve  106 ,  108 ,  110  can be selectively adjusted between two fluid control positions, a first, parallel flow position ( 106   b ,  108   b ,  110   b ) or a second, series flow position ( 106   a ,  108   a ,  110   a ). As such a flow control valve  106 ,  108 ,  110  can be controlled to selectively place associated hydraulic motors  58  in a series flow connection or in a parallel flow connection. 
     The hydraulic pump  80  may be configured to run at a constant speed to generate a predetermined, fixed fluid flow rate, i.e. measurable in e.g. gallons per minute (gpm) or litres per minute (Ipm). In other words, after the hydraulic pump  80  is installed and adjusted, the hydraulic pump  80  may preferably deliver a fixed fluid flow rate at a fixed pressure level when it runs under normal conditions. If the pump  80  were connected exclusively with a single motor  58 , then the motor  58  would exhibit a speed and a level of torque corresponding to respectively to the pump&#39;s full fluid flow output flow rate and to the pumped fluid pressure. Consequently, the effect of placing e.g. two similar motors  58  in a parallel fluid flow connection, would be to apply half the fluid flowing from the pump  80  to each motor  58 , at essentially the full pumped fluid pressure (ignoring minor losses e.g. due to fluid friction in the flow lines). This would generate a level of torque at each driven motor  58  corresponding to a full pressure amount of the fluid passing through it from the pump  80 . The halved fluid flow rate due to the reduced, i.e. halved, fluid flow through each motor  58  reduces the motor speed by half, when compared to the speed at which a single motor  58  would run, if all the pumped fluid were carried to and from the one motor  58 . Conversely, the effect of placing e.g. two similar motors  58  in a series fluid flow connection, would be to apply the full fluid flow rate from the pump  80  to each motor  58 , at essentially half the pumped fluid pressure. This would result in a level of torque at each driven motor  58  corresponding to half the full pressure amount of the fluid passing through it from the pump  80 . The full fluid flow rate through each motor  58  would maintain the motor speed at the speed at which a single motor  58  would run, if it were connected exclusively to the pump  80 . Similarly, with three motors  58   a - c , as illustrated in  FIGS.  7  and  8   , the flow control valves  106 ,  108 ,  110  can be set such that there are either in parallel (see flow positions  106   b ,  108   b ,  110   b  shown in  FIG.  7   ) or in series (see flow positions  106   a ,  108   a ,  110   a  shown in  FIG.  8   ). Hence analogously, with three motors  58   a - c  placed in parallel fluid flow connection with a pump  80  as per the example of  FIG.  7   , and with the pump  80  operating at a constant rate, each motor  58   a,b,c  may run at the same, full torque level as a single connected motor  58  would, even while only at one third of the speed. And with three motors  58   a - c  placed in series fluid flow connection with a pump  80  as per the example of  FIG.  8   , and with the pump  80  operating at a constant rate, each motor  58   a,b,c  may run at the same, full speed as a single connected motor  58  would, even while only delivering one third of the torque. An alternative arrangement, not shown, might see any two motors e.g.  58   a ,  58   b  placed in parallel, and a remaining motor  58   c  placed in series with the two which are in parallel. This would deliver a level of speed lower than the full speed of a single motor  58  and higher than the one-third speed level of three motors  58  placed in parallel. In other words, it would deliver an intermediate level of performance in respect of both speed and torque, between a complete parallel arrangement and a complete series arrangement of the motors  58 . 
     A control unit  116  associated with the valve block  78  may allow automated control of the flow control valves  106 ,  108 ,  110  in the valve block  78 . For example, a user interface associated with the control unit  116  may be operable by an operator to select the settings of the flow control valves  106 ,  108 ,  110 . Alternatively, the control unit may be associated with a computer or wireless network allowing software interaction with the flow control valves  106 ,  108 ,  110  and thereby of the motor output characteristics of the turner gear assembly  52 . 
     In embodiments, a flow control body  76  (see numerals  76   a ,  76   b ,  76   c ) may optionally be coupled, respectively, to each motor  58   a - c . A flow control body  76 , described further below, allows hydraulic fluid lines to be connected to a motor  58  to supply pressurized hydraulic fluid thereto. A flow control body  76  may further include fluid flow management elements described further below, for managing hydraulic fluid to and away from a motor  58 . A flow control body  76  may in particular comprise a hydraulic fluid inflow and outflow connection for allowing hydraulic fluid flow connection to and from a hydraulic fluid pumping arrangement. When installing a turner gear assembly  52  at a drivetrain of a nacelle, it may be preferred to first operatively connect the turner gear  50  to a drivetrain element, as mentioned above, and subsequently to connect a hydraulic fluid pumping arrangement of the turner gear assembly  52  to the turner gear  50 , e.g. via pipes or hoses, as described below. 
       FIGS.  7 - 9    schematically illustrate exemplary embodiments of a turner gear assembly  52  which collectively includes the turner gear  50  and a hydraulic fluid pumping arrangement in the form of a valve block or housing  78 , associated with a pump  80  and a control unit  116 . The turner gear  50  comprises motors  58  (see numerals  58   a,b,c,d ), each of which may be associated with an optional flow control body  76 . The turner gear  50  is operatively connectable to a hydraulic fluid pumping arrangement including a valve block  78 , which is in turn operatively connected to a hydraulic pump  80  associated with a hydraulic fluid tank  84 . A pump motor  82  drives the hydraulic pump  80  so the hydraulic pump  80  may send hydraulic fluid (not shown) from the tank  84 , through the valve block  78 , and to the turner gear  50  and back again in a fluid flow circuit. The term “pump” may be used herein to refer collectively to a pump and a pump motor. Each turner gear motor  58  may be connectable to a valve block  78  via motor interface ports  94 ,  104 . Optionally, each turner gear motor  58  may be associated with a respective flow control body  76  (see numerals  76   a - d ) which in turn is connectable in hydraulic fluid flow connection with the valve block  78  which controls hydraulic fluid flow to the motors  58  (see numerals  58   a - d ). The hydraulic fluid flow connection between a motor  58   a - d  and a said valve block  78  may comprise an inflow and an outflow port  94 ,  104 . Inflow and outflow may be interchangeable in the context of reversing fluid flow direction  90 ,  92  and thereby reversing the drive direction of the turner gear motors  58 . For example, a flow control body  76   a - d  associated with a respective motor  58   a - d  may be removably connectable to a valve block  78  associated with a pump  80  via inflow and outflow motor interface ports  94 ,  104 . In particular, a respective motor  58   a - d  may be removably connectable to a valve block  78  via one or more quick-disconnect couplings  96 ,  102  on fluid lines in communication with said motor interface ports  94 ,  104 . There may be provided a pair of quick-disconnect couplings  102   a ,  96   a ;  102   b ,  96   b ;  102   c ,  96   c ;  102   d ,  96   d  for respective pairs of motor interface ports  94 ,  104  (see numerals  94   a - d ,  104   a - d ) to and from a motor  58 . For ease of connection and disconnection between a valve block  78  and a motor  58 , fluid inflow and outflow lines to and from the motor interface ports  94 ,  104  at the valve block  78  may include lengths of flexible hose. An inflow and outflow line in the form of a flexible hose combined with a quick disconnect coupling  96 ,  102  may facilitate or speed up the temporary installation or removal of a turner gear assembly  52  at a nacelle drivetrain. 
     The valve block  78  preferably includes one or more fluid flow control valves  106 ,  108 ,  110  for selectably controlling fluid flow between the pump  80  and the motors  58 . In particular, each, any or all of fluid flow control valves  106   a - d ,  108   a - d ,  110   a - d  in the valve block  78  associated with a pump  80  may be switched to selectably place associated turner gear motors  58   a - d  in parallel or in series fluid-flow relation relative to the pump  80 . Optionally, all the motors  58   a - d  may thereby be placed in parallel connection such as in  FIG.  7  or  9   , or all the motors  58   a - d  may be placed in series connection such as in  FIG.  8   , or some of the motors  58  may be placed in series connection even while others are placed in parallel connection. Additionally, the valve block  78  may comprise a flow-direction valve  88  interposed between pump ports at the valve block  78  and the flow control valves  106 ,  108 ,  110 . Optionally, a fluid filter  86  may be provided on the fluid line between the pump  80  and the valve block  78 , preferably along a portion of said line which is a fluid outflow line in relation to the pump  80 . The flow direction valve  88  may be actuated so the fluid exits the valve block  78  and circulates to the motors  58  in an outbound first fluid flow direction, as represented by arrow  90 . After passing through the motors  58 , the fluid flow returns into the valve block  78  and through the flow direction valve  88  as in a return fluid flow direction, represented by arrow  92 . Thereafter, it exits the valve block  78 , and returns to the tank  84 . The flow direction valve  88  may have two operational positions,  88   a ,  88   c , each of which corresponds to a respective forward or reverse direction of the turner gear motors  58   a - d . The flow-direction valve  88  may be a three-position flow-direction valve  88 , as illustrated. Accordingly, the flow-direction valve may optionally also include a third position  88   b , described below. In  FIG.  7   , the fluid is shown flowing through a first direction fluid flow position  88   c  of the flow-direction valve  88 . The fluid flow  90  then flows towards the motors  58   a - d  as represented by arrows  90   a ,  90   b ,  90   c ,  90   d . The fluid to and from the motors  58  may flow through fluid connection lines  94 ,  104  (see numerals  94   a ,  94   b ,  94   c ,  94   d ), which may be a flexible hose, to a respective fluid control body  76   a - d  of a respective motor  58   a - d.    
     The fluid exits motors  58  and returns to the valve block  78  via a fluid connection line and an interface port  94 ,  104 , depending on the momentary fluid flow direction i.e. depending on which direction the motors  58  are turning in. In  FIG.  7   , fluid returns in a direction  92  from a motor  58  to a valve block  78  via fluid connection line  104  and quick disconnect coupling  102 . Additional optional elements in a turner gear assembly may include a hose rupture valve  100   a ,  100   b ,  100   c , (inside a flow control body  76 ). This feature, along with associated check valves  98   a - c , 100   a - c  may automatically disable a fluid connection to the motor interface ports  94 ,  104  at a valve block  78 , in case fluid flow lines between the motor  58  and the valve block are breached, e.g. in case a hydraulic fluid connection hose or quick-disconnector  96 ,  102  between the valve block  78  and a motor  58  is or becomes unseated or is breached in some way. The fluid from motors  58   a - d  may pass through flow control valves  106 ,  108 ,  110  having positions  106   a ,  106   b ,  108   a ,  108   b , or  110   a ,  110   b  respectively. As illustrated in  FIG.  7   , the flow control valves  106 ,  108  aretwo-position flow control valves and are in positions  106   b ,  108   b , respectively. The fluid from motor  58   c  flows directly back to flow direction valve  88 . 
     The quick disconnect couplings  96   a - d  and quick disconnect couplings  102   a - d  permit the valve block  78  to be readily connected to and disconnected from the motors  58 , and thus the turner gear  50 . It will be appreciated that the valve block  78  may also be readily connected to and disconnected from the pump  80  and tank  84 . As such, both the turner gear  50  and the valve block  78  may be temporarily installed in one wind turbine during the blade installation process and then removed and temporarily installed in a different wind turbine for another blade installation process. 
     With the flow control valves  106 ,  108  set in parallel connection positions  106   b ,  108   b  as illustrated in  FIG.  7   , the three motors  58   ac  are considered to be operating in parallel. When all motors  58   a - d  operate in parallel that may be called a “straight” mode of operation. Another “straight” mode of operation is when all three motors  58   a - d  operate in series, which will be discussed in more detail below. When some (but not all) of the motors  58  operate in parallel or series, then that may be called a “mixed” mode of operation. For example, looking at the arrangement of  FIG.  7   , in the straight parallel configuration, each motor  58   a - c  receives one-third of the fluid flow rate generated by the pump  80  so that each motor  58   a - c  generates approximately the same amount of output torque which may be used to turn the central hub  22 . Should one of the motors  58   a - c  fail or if a corresponding hose fails and cannot deliver fluid to one of the motors  58   a - c , then the other two unaffected motors  58  may continue to function or at least put the central hub  22  in a safe position. The fluid flow rate to each motor  58   a  will be one third the fluid flow rate from the pump  80  and thereby the motor speed will correspond to one third the maximum speed of the motors  58  were placed in series. 
       FIG.  7    illustrates the fluid flow circulating in a first fluid flow direction as illustrated by the direction of arrows  90 ,  92 . To change (reverse) the fluid flow to a second fluid flow direction, the flow direction valve  88  may be moved to second fluid flow direction position  88   a . With the flow direction valve  88  in its second position  88   a , the outbound fluid flow travels to the opposite side of the motors  58   a - c  so that they turn in the opposite direction. Alternatively, and still as illustrated, if the flow direction valve  88  has an optional third position  88   b , called an open center, then with the flow direction valve in its third position, the fluid from the pump  80  returns to the tank  84  and does not flow to the motors  58 , so they do not turn. Third position  88   b  thereby allows the pump  80  to remain operational, but without sending fluid to any of the motors  58 . 
     Control unit  116  may be operatively coupled to the various components illustrated in  FIGS.  7 - 9   , such as pump  80 , flow direction valve  88 , and flow control valves  106 ,  108 ,  110  so that an operator may change their respective operations or positions as necessitated by the blade assembly process. A pressure gauge  118  and a temperature gauge  120  may be used to monitor the pressure and temperature of the hydraulic fluid exiting the pump  80 . A pressure release valve  122  may be utilized to allow the fluid exiting the pump  80  to return to the tank  84  should the fluid experience downstream pressure over a predetermined high pressure threshold. A filter  86  may be positioned on a hydraulic fluid line in the valve block  78 , in particular between a pump interface port and a flow direction valve  88 . An additional fluid filter  124  with a bypass check valve  126  may be used to filter the fluid returning to the tank  84 . A check valve maybe positioned just prior to the tank  84  to prevent fluid in the various lines from draining back into the tank  84  when the pump  80  is shut off. 
       FIG.  8    shows the same schematic layout shown in  FIG.  7   , but the flow control valves  106 ,  108  are placed in series connection positions  106   a ,  108   a , respectively. In this configuration, the motors  58   a ,  58   b ,  58   c  are considered to be operating in series. As such, each motor  58   a ,  58   b ,  58   c  experiences the same fluid flow rate from the pump  80  but at a lower pressure. Compared to the configuration in  FIG.  7   , the motors  58   a ,  58   b ,  58   c  will rotate three times faster, but their torque output will be decreased to one-third each. With the two-position flow control valves  106 ,  108  in positions  106   a ,  108   a , the fluid leaving motor  58   a  is redirected by two-position flow control valve  106  so that it flows next to motor  58   b  as represented by arrow  134 . Similarly, the fluid leaving motor  58   b  is redirected by two-position valve  108  so that it flows next to motor  58   c  as represented by arrow  136 . Thus, a single stream of fluid flows through the three motors  58   a ,  58   b ,  58   c  before that fluid returns to the tank  84  as represented by arrow  138 . Similar to the above, the direction of the fluid flow may be changed (reversed) by moving the three-position flow direction valve  88  from position  88   c  to position  88   a.    
     If the blade assembly process requires additional torque beyond what the configuration in  FIG.  8    can generate, two-position valve  108  may for example be switched to parallel position  108   b  so that only motors  58   a ,  58   b  operate in series. In this configuration the fluid flow generated by the pump  80  is divided equally between motors  58   a ,  58   b  and motor  58   c  such that motors  58   a ,  58   b  generate less torque than motor  58   c , but they each operate at the same speed. In this configuration, the overall torque output is greater than the configuration in  FIG.  8    (all motors in series), but the rotational speed is less. In yet another configuration, motor  58   c  could be disconnected altogether, such as by disconnecting the quick disconnect  96   c  so that no fluid flows to motor  58   c  and only motors  58   a ,  58   b  operate in series. Thus, an operator may configure the different two-way flow control valves  106 ,  108  and/or disconnect a particular motor  58   a - 58   c  to achieve a required output torque or a desired rotational speed, depending of the requirements of the particular blade assembly. Alternatively, one or more shutoff valves (not shown) may be used to specifically control the fluid flow to the individual motors  58   a ,  58   b ,  58   c  so that each motor  58   a ,  58   b ,  58   c  may be selectively shutoff (or turned on) to meet the torque requirements during the blade installation process. 
       FIG.  9    schematically illustrates a similar layout shown in  FIG.  7   , but with an additional motor  58   d  with corresponding components of flow control body  76   d , quick disconnect couplings  96   d ,  102   d , check valves  98   d ,  112   d , hose rupture valve  100   d ,  114   d . The motor  58   d  is connected to motor interface ports  94   d ,  104   d  at the valve block  78 . To accommodate operatively connecting the motor  58   d  to the pump  80 , the valve block  78  may include an additional flow control valve  110  which may be a two-position valve with a respective positions  110   a  for a series connection and a position  110   b  for a parallel connection. By manipulating the flow control valve  110 , the motors  58   c ,  58   d  may thereby 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  50  to increase the torque output of the turner gear as torque requirements increase. Similarly, a corresponding flow control valve may be added to the valve block  78  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  50 . In  FIG.  9   , the flow control valves  106 ,  108 ,  110  may be switched between series connection and parallel connection positions  106   a ,  106   b ,  108   a ,  108   b ,  110   a ,  110   b  to put some or all of the motors  58   a - 58   d  in series so that varying amounts of output torque may be produced by the turner gear  50 . Again, just like in the three-motor configuration of  FIGS.  7  and  8   , an operator may configure the different flow control valves  106 ,  108 ,  110  via controller  116  and/or disconnect a particular motor  58   a - 58   d  to achieve a required output torque or a desired rotational speed, depending of the torque requirements of the particular blade assembly. 
     In one advantageous aspect of the invention, a “standardized” turner gear assembly may be used on different wind turbines having different sizes and different torque requirements. By design, the standardized turner gear may be used during the blade installation process on respective large, medium, and small wind turbines, despite the possibility that the torque requirements may vary widely for each installation. In addition, by using a standardized turner gear assembly, the installer does not have to be concerned with using a turner gear that is not compatible with either the structure (e.g., the gearbox or generator) or the torque requirements of the wind turbine. By manipulating the various valves in the valve block, the installer may configure the turner gear  50  to achieve a sufficient amount of torque without sacrificing rotational speed. 
     The flexibility of the turner gear assembly as disclosed herein also allows the installer to configure the turner gear to compensate for wind conditions at the work site. In this regard, wind conditions during the wind blade installation process may increase the torque requirements placed upon the turner gear e.g. by adding increased wind resistance against a turning motion of a blade rotor. To address the wind loading, the turner gear may be designed to produce not only the torque required to turn the unbalanced rotor, but also the torque required to overcome wind loading at the work site. Thus, where low wind conditions are present during the blade installation process, the turner gear assembly may be configured to generate a lower amount of torque, which may allow the turner gear to turn faster. In contrast, if moderate to high wind conditions are present at the work site, the turner gear assembly may be configured to produce additional torque, but at a slower rotational speed. Thus, a single turner gear assembly may be adapted for use on a wide range of wind turbines during a wide range of wind conditions. By adjusting the settings of the turner gear assembly for the specific wind turbine and installation (and conditions), a balance between torque requirements and rotational speed of the central hub may be achieved. A valve block at a turner gear assembly may be integral with the turner gear motors or separably connectable thereto. 
     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 is not limited to the specific embodiments or details or illustrative examples shown and described herein.