Patent Document

BACKGROUND OF THE INVENTION 
     The invention relates generally to wind turbines and more specifically to a method for removing and replacing equipment in a wind turbine tower. 
     A wind turbine tower (WTT) is a large structure, sometimes extending to significant heights to accommodate large wind turbine rotor blades and to strategically place the rotor blades within a wind path. For example, a typical tower may have a height as high as about 100 meters (m). Such a tower may include multiple sections, often a bottom, a middle and a top section. The length and number of individual sections may vary according to the application and height of the structure. At various heights of the wind turbine tower, landings are provided. The landings include openings for ladders to allow operators and maintenance personnel to climb between landings. The landings may also include openings above each other to allow small components, tools and equipment to be lifted from a base of the wind turbine tower to a top landing of the tower. 
     Mounted on top of the support tower for wind turbines is a nacelle. The nacelle houses, or encloses, the equipment and components of the wind turbine and includes hubs for the wind turbine blades and the power train including the bearing, gearbox and electrical generator for the wind turbine. 
       FIG. 1  illustrates an exemplary wind turbine tower. Nacelle  102  is mounted atop a tall tower  104 , only a portion of which is shown in  FIG. 1 . Wind turbine  100  also comprises a rotor  106  that includes one or more rotor blades  108  attached to a rotating hub  110 . Although the wind turbine  100 , as illustrated includes three rotor blades  108 , there are no specific limits on the number of rotor blades. 
       FIG. 2  illustrates an exemplary internal arrangement for various components housed in nacelle  102 . In some configurations, one or more microcontrollers within control panel  112  comprise a control system used for overall system monitoring and control. In some configurations, a variable blade pitch drive  114  is provided to control the pitch of blades  108  (not shown in  FIG. 2 ) that drive hub  110  as a result of wind. In some configurations, the pitch angles of blades  108  are individually controlled by blade pitch drive  114 . Hub  110  and blades  108  together comprise wind turbine rotor  106 . 
     The drive train of the wind turbine includes a main rotor shaft  116  connected to hub  110  via main bearing  130 . Gearbox  118  drives a high-speed shaft of generator  120 . In other configurations, main rotor shaft  116  is coupled directly to generator  120 . The high-speed shaft (not identified in  FIG. 2 ) is used to drive generator  120 , which is mounted on mainframe  132 . In some configurations, rotor torque is transmitted via coupling  122 . A meteorological boom  128  provides information for a turbine control system, which may include wind direction and/or wind speed. 
     Yaw drive  124  and yaw deck  126  provide a yaw orientation system for wind turbine  100 . In some configurations, the yaw system is mounted on a flange provided atop tower  104 . 
     Typically, a yaw bearing is mounted to the top section of the tower. A bedplate supporting the weight of the power train rotates on the yaw bearing, allowing wind turbine controls to rotate the nacelle to better position the blades wind respect to the wind direction for optimizing performance. A center access is provided above the topmost landing of the WTT into the nacelle. 
     The electrical controls for a yaw drive system may include multiple electric drive motors  136 . Each electric drive motor  136  may be mounted on a yaw drive  124 , which includes an internal gear train connecting the electric drive motor to a pinion gear.  FIG. 2  illustrates two yaw drives with view of two additional yaw drives blocked by the main bearing  118  and main shaft  116 . The pinion gear of the yaw drive engages the yaw gear, allowing for rotation of the yaw bearing and the nacelle. In certain embodiments, four yaw drives may be provided for the yaw gear. Operation of the electric drive motors  136  and thus positioning of the nacelle and the wind turbine blades relative to the wind is provided by a wind turbine control system. 
     Failure of one or more yaw drives may prevent the nacelle and hence the wind turbine blades from being correctly positioned with respect to the wind by the wind turbine control system. 
     A yaw drive may weigh about 1100 lbs, which makes it too heavy for manual movement in the nacelle and also an overload for the light-load installed permanent tower winch that are available in some wind towers. Conventional practice is to remove a yaw drive through a top hatch  139  of the nacelle  102  or through a larger opening, a nacelle lid  140 , depending on the size of the yaw drive. The lift may be performed by a large site crane, capable of reaching above the top of the wind turbine tower from the ground. Use of the site crane is expensive and results in delays with crane availability. An alternate practice is to provide a crane (not shown) that may be mounted within the nacelle  102 , but which extends outside a top of the nacelle and is capable of lifting the yaw drive. An access port  141  on top of the nacelle is opened to allow the erection of the crane. The hatch  139  on top of the nacelle is opened to provide a lifting path for removal of the yaw drive. A second crane may be required within the nacelle to lift the yaw drive off its foundation and move to a location for a vertical lift through the hatch  139 . Once the yaw drive has cleared the top of the nacelle, the crane arm may move the yaw drive outside the envelope of the wind tower and lower the yaw drive to the ground. 
     Lifting operations for equipment from the nacelle and external to the tower expose the operators and the equipment inside the nacelle to environmental conditions. High winds make these external lifts dangerous for personnel and for equipment. Safety requirements strictly limit wind velocity allowable during the outside lifts. Since windfarms are generally selected based on availability of wind for driving the blades, significant delays can be encountered while waiting for acceptable conditions. Such delays result in a waste of manpower and lost operating time for the wind turbine resulting in added expense and loss of electrical power revenues. 
     Accordingly, there is a need to provide a safe, simple, timely, and cost-effective method for replacing articles of wind turbine equipment in the nacelle. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention relates to a method for removing an article of wind turbine equipment from a nacelle of a wind turbine tower (WTT), such as a drive or a yaw drive, through an internal path in the WTT. Briefly in accordance with one aspect of the present invention, a method is provided for removing an article of wind turbine equipment from a nacelle wind turbine tower (WTT). The method includes installing a load-rated winch internal to the wind turbine tower, adapted to lowering and raising the article between a base of the WTT and the nacelle of the WTT. The method also installs an internal support crane within the nacelle, adapted to transferring the article from its mounting to the load-rated winch. The article is disassembled from its foundation. The method translates the article from its foundation to the load-rated winch internal to the WTT with the internal support crane. Once the load-rated winch supports the article, the article is lowered to the base of the wind WTT. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  illustrates an exemplary wind turbine tower; 
         FIG. 2  illustrates an exemplary arrangement of components within a nacelle for a wind turbine tower; 
         FIG. 3  illustrates an exemplary support crane arrangement; 
         FIG. 4  illustrates the support crane lifting the yaw drive; 
         FIG. 5  illustrates the yaw drive being lowered by the load-rated winch; 
         FIG. 6  illustrates the yaw drive being removed through a door at the base of the wind turbine tower; and 
         FIG. 7  illustrates a flow chart for the procedure for removing a yaw drive from a wind turbine tower through an internal path. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following embodiments of the present invention have many advantages, including removing and replacing one or more articles of equipment from the nacelle through an internal path within the WTT. Use of an internal path avoids the need to breach the nacelle and lift articles of wind turbine equipment from the nacelle external to the wind turbine tower at extremely elevated heights. With internal movement of articles of wind turbine equipment such as a yaw drive, the danger of the elevated heights and extreme environmental conditions may be avoided. Delays encountered in external lifts associated with high winds and other environmental conditions that result in loss of productivity and prolonged outage of the electric power production may also be avoided. 
       FIG. 3  illustrates an exemplary support crane arrangement. The support crane may include other suitable configurations and mountings. The support crane  200  may include a vertical pillar  205 , a pivot assembly  210 , a jib arm  215 , a hydraulic cylinder  220 , an end clasp  225  and a mounting fixture  230 . The pivot assembly  210  permits rotation of the jib arm  215  about the pillar  205 . The hydraulic cylinder  220  allows extension and retraction of the jib arm  215 . The combined rotation and extension of the jib arm  215  allows access to a wide range of locations about its point of mounting. The mounting fixture  230  may include counterplates  240 , connected by thread bars  230 . The pillar  205  is mounted and locked with locking pin  230  into base frame  240 . The mounting fixture  230  engages with receiving mounts  340  ( FIG. 4 ) within the nacelle in proximity to the yaw drives. The support crane may be mounted in proximity to the yaw drive. The support crane may be utilized to lift the drive motor off the yaw drive and then to lift and translate the yaw drive close in proximity to a winch sized for the load (load-rated winch), which may be a heavy-duty winch. 
       FIG. 4  illustrates the internal support crane lifting the yaw drive. The support crane  200  is erected on receiving mount  340  in proximity to the yaw drive  300 . The end clasp  225  of the jib arm  215  may be rigged with a chain fall  310  and hook  315 . The yaw drive  300  may be rigged with a sling  320  and two shackles  325  (second shackle not shown). The jib arm  215  positions chain fall  310  and hook  315  over the top of the yaw drive  300 . The hook  315  is attached to one shackle  325  of the yaw drive. Using the chainfall  310 , the yaw drive  300  after unbolting, may be lifted up from its foundation. The jib arm  215  may then be rotated and extended to translate the yaw drive  300  and the chainfall  310  may be let out to lower the yaw drive  300  in proximity to a hook (not shown) from the load-rated winch. The hook of the load-rated winch ( FIG. 5 ) may be engaged with second shackle of the sling  320  for the yaw drive  300 . The engagement of the hook from the load-rated winch and the sling  320  on the yaw drive  300  will take place below the main shaft  116  and above the top deck of the WTT. In the customary rigging fashion, the yaw drive load will be transferred from the hook of the chainfall  310  to the hook of the load-rated winch ( FIG. 5 ). 
       FIG. 5  illustrates the yaw drive being lowered by the load-rated winch. The load-rated winch  510  may be attached with a lifting strap  515  to a main shaft  116  of the wind turbine. Alternatively, the load-rated winch  510  may be supported by lifting pads or other appropriate supports within the nacelle  102 . The load-rated winch may be powered from a local electric power supply within the WTT. A chain hook  520  on the load-rated winch  510  attaches to the shackle  330  of the sling  320  for the yaw drive  300 . The yaw drive  300  is lowered through the landing hatch  540  of the top deck  550  and through the landing hatches of the other decks (not shown) within the WTT until the base is reached. 
       FIG. 6  illustrates the yaw drive being removed through a door at the base of the wind turbine tower. A truck  600  with a boom  610  may be positioned in proximity to a tower door  620  of the wind turbine tower. The tower door  620  is opened and the boom  610  may extend to engage the yaw drive  300  with a hook  630 . Alternatively, a fork truck or similar device may be used to remove the yaw drive from the base of the tower. 
     The method of removal of the yaw drive from the WTT may be reversed to hoist the a replacement yaw drive up the tower, translate the yaw drive to its foundation and mount the yaw on its foundation within the nacelle. 
       FIG. 7  illustrates a flow chart for an embodiment of a procedure for removing an article of wind turbine equipment from the nacelle of the WTT through an internal path. In this exemplary embodiment, the article of wind turbine equipment is a yaw drive. 
     In a first step  710  the wind tower is prepared for the removal of the yaw drive by shutting down the wind turbine system, locking the nacelle from rotation and deenergizing the yaw drive. Deenergizing may also require removing power from any interferences that need to be removed during the procedure. 
     In step  720 , an internal support crane is installed. The internal support crane may be is mounted in proximity to the yaw drive. Step  730  includes installing a load-rated winch internal to the WTT where the load-rated winch is adapted to lowering and hoisting the yaw drive between the nacelle and the base of the WTT. Installing the load-rated winch may include lifting the load-rated winch up the WTT with a permanent tower winch. The load-rated winch may be shifted to a mounting position by transferring the load-rated crane to the internal support crane with a come-along. Once carried by the internal support crane, the load-rated winch may be positioned under the main shaft. The load-rated winch may then be mounted to the main shaft with a lifting strap. Alternatively, the load-rated winch may be mounted to other convenient locations such as lifting pads or mounts. 
     Step  740  includes disassembling the yaw drive from its foundation. Interferences may be removed such as catwalks and other components restricting the disassembly of the yaw drive. The electric motor may be removed from the yaw drive if useful in moving the yaw drive. Scribe marks are made on the foundation to indicate the orientation of the yaw drive with respect to the foundation for use in the subsequent replacement of the yaw drive. The yaw drive is disconnected from the foundation by unbolting. The yaw drive is removed from the foundation using lift provided by a chain fall on the internal support crane. 
     In step  750 , the yaw drive is translated from its foundation to the load-rated winch. Interferences may be removed to facilitate transfer of the yaw drive to the internal crane. The yaw drive is lifted with the chain fall, swung by the jib arm around the pivot assembly, and lowered with the chain fall to move the yaw drive around various obstructions and down under the main shaft, in proximity to the hook of the load-rated winch. The hook of the load-rated winch may be attached to a second shackle on the yaw drive sling. Then the yaw drive load may be shifted to the load-rated winch. Step  760  includes lowering the yaw drive to the base for removal from the WTT. Once at the base, the yaw drive may be removed through the tower door using a truck hoist, winch or forklift. 
     In step  770 , a replacement yaw drive is restored to operation, which may include hoisting a replacement yaw drive to above the top deck with the load-rated winch. The internal support crane is positioned in proximity to the yaw drive and the replacement yaw drive is transferred to the support crane. The support crane translates the replacement yaw drive to a position above its mounting. The replacement yaw drive is lowered with the chain fall onto its foundation, orienting the replacement yaw drive in accordance with the marking before removal. The yaw drive is bolted in place. The electric drive motor is restored, if previously removed. Removed interferences are restored. The load-rated winch is removed and the tower winch is replaced. The internal support crane is removed. The replacement yaw drive is operationally tested and the wind turbine tower and wind control system are restored to operating condition. 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.

Technology Category: 2