Patent Publication Number: US-2022220942-A1

Title: Method for handling a wind turbine component and associated lifting system

Description:
TECHNICAL FIELD 
     The invention relates generally to methods for handling payloads with a lifting system, and more particularly to methods for handling a wind turbine component during assembly or disassembly of a wind turbine. 
     BACKGROUND 
     Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. A horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor having a plurality of blades and supported in the nacelle by means of a shaft. The shaft couples the rotor either directly or indirectly with a generator, which is housed inside the nacelle. Consequently, as wind forces the blades to rotate, electrical energy is produced by the generator. 
     When erecting or dismantling wind turbines, it is normally necessary to use an external lifting system, such as a crane, for handling the tower sections, nacelles, hubs, wind turbine blades, etc. As the size of wind turbines increases and the components become heavier, lifting systems with greater lifting capacity are required to lift the heavy components. Lifting systems with greater lifting capacity, however, are more expensive to rent and operate and are more difficult to move to the installation site. In some cases, the cost of renting such a lifting system may even exceed the cost of manufacturing elements of a wind turbine. 
     A particular lifting system, such as a crane, has a maximum load-lifting capacity C max . In practice, lifting capacity may also depend upon the momentary crane radius in a manner which is known per se, a discussion of which is not required in the context of this disclosure. The lifting system includes a hoist cable, then end of which includes an attachment assembly, such as a hook block for example, for coupling to payloads to be lifted by the lifting system. For proper operation of the lifting system, the weight of the attachment assembly W attach  must be sufficiently high. For example, for proper operation of the lifting system, it may be important to ensure that load bearing cables are kept under appropriate levels of tension and to ensure that cables are kept in relevant guide grooves such as sheave wheel grooves. It may also be necessary to ensure that the lifting assembly has enough weight to overcome the weight of the hoisting cable and any frictional forces in the system so that, for example, the attachment assembly may drop unassisted when positioned at the highest lifting position of the lifting system. In this regard, the force required to be applied for proper operation of the lifting system may be considered in terms of a threshold weight W thres  for the lifting system. Thus, the weight of the attachment assembly W attach  must be greater than the threshold weight W thres  in order for the attachment assembly to drop unassisted from the upper-most position of the lifting system and to maintain appropriate levels of tension in the lifting cable. If the weight of the attachment assembly W attach  is not greater than the threshold weight W thres , then one or more ballast weights, such as ballast plates (sometimes referred to as cheek plates), having a ballast weight W bal  may need to be added to the attachment assembly to make the weight of the attachment assembly greater than the threshold weight W thres . When a wind turbine component with a weight W load , such as wind turbine blade, is to be lifted, a lifting tool with a weight W tool  is generally used to attach the attachment assembly of the crane to the wind turbine component. In this regard, the lifting tool essentially operates as an interface between the attachment assembly and the wind turbine component. For the lifting system to be able to successfully lift the wind turbine component, the combined weight of the attachment assembly (including any ballast weights), the lifting tool, and the wind turbine component must be less than or equal to the maximum load-lifting capacity C max  of the lifting system. 
     As wind turbine components grow larger and their weight W load  increases, the size and weight of the lifting tool W tool  will generally increase to accommodate the heavier component. This increase in the weight of the wind turbine component W load  and lifting tool W tool  means a lifting system with a greater maximum load-lifting capacity C max  may be required to lift the heavier wind turbine component. Again, lifting systems with greater lifting capacity are costly and more difficult to move to the wind turbine installation site. 
     To avoid the cost and difficulty of employing a lifting system with greater lifting capability, a method is needed for lifting heavier wind turbine components without employing a lifting system with a larger maximum load-lifting capacity C max . 
     SUMMARY 
     To these and other ends, a method for handling a wind turbine component is disclosed. The method includes providing a lifting system having a hoist cable and an attachment assembly coupled to the hoist cable. The attachment assembly preferably includes one or more removable ballast weights. The method includes positioning the attachment assembly near a working surface, such as the ground, platform, or deck of a ship; removing at least some of the one or more ballast weights from the attachment assembly; and attaching a lifting tool to the attachment assembly. The combined weight of the attachment assembly, including any remaining ballast weights, and the lifting tool is sufficiently greater than a threshold weight of the lifting system. The method further includes attaching a wind turbine component to the lifting tool and moving the wind turbine component using the lifting system. 
     In one aspect of the invention, the one or more ballast weights includes a plurality of ballast plates and removing at least some of the one or more ballast weights further includes removing one or more of the plurality of ballast plates from the attachment assembly. In a further aspect, the ballast plates removed from the attachment assembly may be less than or equal to the weight of the lifting tool and, more specifically, the weight of the ballast plates removed from the attachment assembly may be substantially equal to the weight of the lifting tool. 
     As will be appreciated, attaching a wind turbine component to the lifting tool may include attaching one of a nacelle, a hub, a wind turbine rotor, a wind turbine blade, or a wind turbine powertrain or sub-elements thereof to the lifting tool. The lifting tool may be specifically tailored to interface with such wind turbine components. As will also be appreciated, moving the wind turbine component may further include moving the wind turbine component from adjacent the working surface to a position adjacent an upper section of a wind turbine tower during assembly of a wind turbine. Similarly, moving the wind turbine component may further included moving the wind turbine component from adjacent an upper section of a wind turbine tower to a position adjacent the working surface during disassembly of a wind turbine. Thus, the method may be used in both the assembly and disassembly of a wind turbine. 
     In another embodiment, the method may include additional steps implemented subsequent to moving the wind turbine component using the lifting system. For example, the method may also include positioning the attachment assembly and the lifting tool adjacent the working surface; removing the lifting tool from the attachment assembly; and reattaching the removed ballast weights (e.g., the ballast plates) to the attachment assembly. The lifting system may then be used in a conventional sense. 
     In a further embodiment, a lifting system for handling a wind turbine component is disclosed. The lifting system includes a hoist cable, an attachment assembly coupled to the hoist cable, and a lifting tool attached to the attachment assembly. The combined weight of the attachment assembly and the lifting tool is sufficiently greater than a threshold weight of the lifting system. In this regard, the weight of the attachment assembly may be less than the threshold weight of the lifting system and it is by combining the attachment assembly with the lifting tool that the combined weight is sufficiently greater than the threshold weight. In an exemplary embodiment, the attachment assembly may include one or more selectively removable ballast weights, which in one embodiment may include a plurality of ballast plates. In various embodiments, the lifting tool may be configured to interface with a nacelle, a hub, a wind turbine rotor, a wind turbine blade, or a wind turbine powertrain or sub-elements thereof. The lifting system may include a crane in an exemplar embodiment. 
    
    
     
       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 perspective view of a wind turbine assembled according to an aspect of the invention. 
         FIG. 2  is a perspective view showing crane lifting a wind turbine blade to a partially assembled wind turbine. 
         FIG. 3  is a perspective view of an attachment assembly with the ballast plates removed. 
         FIG. 4  is a side view of a crane with the attachment assembly at the upper-most position of the crane. 
         FIG. 5  is a side view of the crane of the  FIG. 4  with the attachment assembly in a lower position with the ballast plates removed and lifting tool to be attached to the attachment assembly. 
         FIG. 6  is a side view of the crane of  FIG. 4  with a lifting tool attached to the attachment assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , 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 (not shown) housed inside the nacelle  14 . In addition to the generator, the nacelle  14  houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine  10 . The tower  12  supports the load presented by the nacelle  14 , the rotor  16 , and other components of the wind turbine  10  that are housed inside the nacelle  14  and also 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 faster moving air currents of lower turbulence are typically found. 
     The rotor  16  of the wind turbine  10 , which is represented as a horizontal-axis wind turbine, serves as the prime mover for the electromechanical system. Wind exceeding a minimum level will activate the rotor  16  and cause rotation in a plane substantially perpendicular to the wind direction. The rotor  16  of the wind turbine  10  includes a central rotor hub  18  and a plurality of blades  20  that project outwardly from the central hub  18  at locations circumferentially distributed thereabout in equal intervals. In the representative embodiment, the rotor  16  includes first, second, and third blades  20 , but the number may vary. The blades  20  are configured to interact with the passing air flow to produce lift that causes the rotor hub to spin about a longitudinal axis defined thereby. As shown, the tower  12  includes a foundation or base  22  for supporting the wind turbine  10 . It should be recognized that the wind turbine  10  may be an on-shore or an off-shore wind turbine. 
     The wind turbine  10  may be included among a collection of similar wind turbines belonging to a wind farm or wind park that serves as a power generating plant connected by transmission lines with a power grid, such as a three-phase alternating current (AC) power grid. The power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities. Under normal circumstances, the electrical power is supplied from the generator to the power grid as known to a person having ordinary skill in the art. 
     In accordance with an aspect of the invention, a main component of the wind turbine  10 , such as the nacelle  14 , hub  18  or a wind turbine blade  20 , may be hoisted to or from a position proximate the top of the tower  12 . With reference to  FIG. 2 , and as set forth in further detail below, an exemplary lifting system  30  for installing and/or dismantling the main components of wind turbine  10  includes a crane  32 , a lifting tool  34  for coupling to a wind turbine component, a hoist cable  36  operatively coupled to the crane  32 , and an attachment assembly  38  ( FIG. 3 ) operatively coupled to the hoist cable  36 . In one embodiment, the attachment assembly  38  may be referred to as a hook block, which may include a lifting hook. As illustrated in  FIG. 2 , the crane  32  and the lifting tool  34  are hoisting a wind turbine blade  20  to be suspended proximate the nacelle  14  so the blade  20  may be attached to the hub  18 . The exemplary lifting tool  34  may include a plurality of slings  40 , a yoke  42 , and a pair of cradles  44  suspended from the yoke  42  via one or more cables  46 . It will be appreciated that lifting tools with different configurations may be used to accommodate different wind turbine components, such as a nacelle, a hub, a wind turbine rotor, a wind turbine blade, or a wind turbine powertrain or sub-elements thereof, such as a generator, a main shaft, and a gearbox. For example, the lifting tool for the nacelle  14  will generally be different from the lifting tool for a wind turbine blade  20 , which will each be different from the lifting tool for the hub  16 . Such lifting tools for the various wind turbine components are generally known in the wind turbine industry and will not be further described herein. 
     As illustrated in  FIG. 3 , an exemplary attachment assembly  38  may include a base  50  defined by, for example, base members  50   a ,  50   b  and a lifting hook  54  coupled to the base  50  and configured to attach to a payload for handling by the crane  32 . In one embodiment, the attachment assembly  38  may further include one or more selectively removable ballast weights  48 , such as a plurality of ballast plates (which in one embodiment may be referred to as cheek plates), for increasing the weight of the attachment assembly  38 . The ballast plates  48  may be selectively, removably attached to the side of base members  50   a ,  50   b , which form part of the attachment assembly  38 . For example, fasteners  52 , such as bolts and nuts, may be used to secure the ballast plates  48  to the base members  50   a ,  50   b . Each ballast plate  48  has a known weight and collectively the ballast plates  48  attached to the base members  50   a ,  50   b  have a known ballast weight W bal . Other devices, such as straps, clevis fastener, etc. besides hook  54  may be incorporated into the attachment assembly  38  to provide a way to attach the lifting tool  34  to the attachment assembly  38 . Other types of ballast weights besides ballast plates may also be used, such as a so-called “headache ball.” In one embodiment, the lifting hook  54  may be removed from the attachment assembly  38  in addition to removing the ballast plates  48 . This option may be used, for example, when the lifting tool  34  may be operatively connectable to the attachment assembly  38  without requiring the use of the lifting hook  54 . Advantageously, removing the lifting hook  54  may further decrease the weight of the attachment assembly  38  prior to attaching the lifting tool  34 , and thereby increase the weight of the payload that may be lifted by the crane  32 . 
       FIG. 4  shows the crane  32  with the attachment assembly  38  in an upper-most position. The attachment assembly  38  may be coupled to the hoist cable  36  during the initial assembly of the crane  32 . Here, the upper-most position may refer to a configuration where the main boom of the crane  32  is rotated as close to vertical as possible and the attachment assembly  38  is positioned (raised) to essentially its highest point possible, i.e., close to the top pulley as possible. In the upper-most position, the weight of the attachment assembly W attach  must be sufficient to ensure the load bearing cables are kept under appropriate levels of tension, to ensure the cables are kept in relevant guide grooves, such as sheave wheel grooves, and to overcome the combined weight of the hoist cable  36  and the frictional forces, such as in pulleys (not shown), so that the attachment assembly  38  drops in an unassisted manner. The weight to achieve these operational criteria with the attachment assembly  38  at the upper-most position may be considered in terms of a threshold weight W thres  of the crane  32 . Thus, in the normal course of crane operation the weight W attach  of the attachment assembly  38  must be sufficiently greater than the threshold weight W thres  to allow the attachment assembly  38  to drop unassisted from the upper-most position to near a working surface that supports the crane  32  (e.g., the ground, platform, deck of a ship, etc.). 
     As used herein, sufficiently greater means no more than about 10% greater than the threshold weight W thres , preferably no more than about 5% greater than the threshold weight W thres , and even more preferably no more than about 2% greater than the threshold weight W thres . In many lifting scenarios, the weight W attach  of the attachment assembly  38  alone may not be great enough to achieve the operational criteria at the upper-most position, such as, overcoming the combined weight of the hoist cable  36  and the frictional forces in the crane  32 . Thus, when the weight W attach  of the attachment assembly  38  is less than the threshold weight W thres , additional weight W bal  in the form of ballast weight  48 , e.g., ballast plates, must be added to the attachment assembly  38  so that the weight W attach  of the attachment assembly  38  including the ballast weight W bal  is sufficiently greater than the threshold weight W thres . In this way, the attachment assembly  38  (with the included ballast weight  48 ) may drop down unassisted from the upper-most position of the crane  32  to near the working surface. The arrangement of the attachment assembly  38 , including the one or more ballast weights  48 , to be sufficiently greater than the threshold weight W thres  required for proper operation of the crane  32  is in the normal course of assembling the crane  32  for operation. 
     In order for a lifting system  30  to successfully complete a lift operation of a wind turbine component, the combined weight of the attachment assembly W attach , including any ballast weight W bal , the lifting tool W tool , and the wind turbine component W load  must be equal to or less than the maximum load-lifting capacity C max  of the lifting system  30 . In other words, and in mathematical terms, 
     
       
         
           
             
               
                 
                   
                     C 
                     max 
                   
                   ≥ 
                   
                     
                       W 
                       attach 
                     
                     + 
                     
                       W 
                       bal 
                     
                     + 
                     
                       W 
                       tool 
                     
                     + 
                     
                       W 
                       load 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In accordance with an aspect of the invention, the combined weight of the attachment assembly W attach  (including any ballast weight W bal ) and lifting tool W tool  may be minimized so that the weight of the wind turbine component W load  may be maximized. Consequently, a heavier load may be lifted by the lifting system  30  without having to use another lifting system with a greater maximum load-lifting capacity C max . Thus, as illustrated in  FIG. 4 , the method for hoisting a wind turbine component includes initially providing the lifting system  30  with the attachment assembly  38  and one or more ballast weights  48  where the combined weight of the attachment assembly  38  and the ballast weights  48  (e.g., ballast plates) is sufficiently greater than a threshold weight W thres  for that lifting system  30 . 
     Subsequently and as illustrated in  FIG. 5 , the attachment assembly  38  may be positioned near the working surface (e.g., ground, platform, deck of a ship, etc.) and at least some of the one or more ballast weights  48  may then be removed from the attachment assembly  38 . Next, the lifting tool  34  may then be coupled to attachment assembly  38 , as illustrated in  FIG. 6 . In an advantageous aspect, the combined weight of the attachment assembly  38  (including any remaining ballast weights  48 ) and the lifting tool  34  may be configured to be sufficiently greater than the threshold weight W thres  of the lifting system  30 . In other words, the role of the ballast weights  48  on the attachment assembly  38  in order to reach the threshold weight W thres  now being provided by the lifting tool  34 . In one embodiment, for example, the weight W tool  of the lifting tool  34  should be greater than and preferably substantially equal to the weight W bal  of the ballast weights  48  removed from attachment assembly  38 . It should be appreciated that in some embodiments, only some of the ballast weights  48  may be removed before the lifting tool  34  is attached to the attachment assembly  38 . In other embodiments, however, all of the ballast weights  48  may be removed before the lifting tool  34  is attached to the attachment assembly  38 . Minimizing the combined weight of the attachment assembly  38 , including the ballast weights  48 , and the lifting tool  34  to be sufficiently greater than the threshold weight W thres  of the lifting system (or as close as possible should the weight W tool  of the lifting tool  34  be greater than the weight W bal  of the ballast weights  48 ) allows the weight of the wind turbine component W load  being handled by the crane  32  to be maximized. 
     As illustrated in  FIG. 2 , with the lifting tool  34  connected to the attachment assembly  38 , the wind turbine component, such as a wind turbine blade  20 , may be coupled to the lifting tool  34  and then lifted to an upper section of the wind turbine  10  during, for example, assembly of the wind turbine  10 . After the wind turbine blade  20  (or other wind turbine component) is installed, the attachment assembly  38  and the lifting tool  34  may be lowered to the surface so that another wind turbine component may be affixed to the same or different lifting tool  34  and hoisted to an upper section of the wind turbine. This process may be repeated until all wind turbine components are hoisted to an upper section of the wind turbine  10  and installed. The operations may be reversed when disassembling the wind turbine  10 . 
     When the lifting tool(s)  34  is/are no longer needed, the lifting tool  34  may be removed from the attachment assembly  38  and the one or more ballast weights  48 , e.g., the ballast plates, may be reinstalled on the attachment assembly  38 . Again, the combined weight of the attachment assembly  38  and the one or more ballast weights  48  may be sufficiently greater than the threshold weight W thres  for that lifting system. In this way, the lifting system may be used in a conventional sense for handling other aspects of wind turbine installation. If the ballast weights  48  are not reinstalled on the attachment assembly  38  and the attachment assembly  38  is lifted to the upper-most position, the attachment assembly  38  may be unable to drop unassisted from the upper-most position. Thus, it is important to reattach the ballast weights  48  to the attachment assembly  38  after removing the lifting tool  34 . 
     Moving up in crane size to perform a wind turbine installation results in a significant increase in costs associated with the rental, operation and transport of the crane. Aspects of the present invention are directed to using a lifting system, such as a crane, in a particular way that maximizes the payload that is able to be hoisted by the lifting system when taking into account the weight of operational equipment, such as the attachment assembly (e.g., hook block) and lifting tool, necessary to achieve a particular lift. More particularly, aspects of the invention are directed to using the combined weight of the attachment assembly and the lifting tool to be sufficiently greater than the threshold weight required for proper operation of the lifting system. This may be achieved by selectively removing one or more ballast weights associated with the attachment assembly. By configuring the attachment assembly (including any remaining ballast weights) and the lifting tool to be just sufficiently greater than the threshold weight of the lifting system (as opposed to just the attachment assembly, including ballast weights, being slightly greater than the threshold weight of the lifting system, as in convention crane arrangements), the weight of the payload hoisted by the lifting system may be maximized. This in turn may allow a smaller crane to lift larger wind turbine components during assembly or disassembly of a wind turbine, and thereby avoid the increased costs associated with a larger crane. 
     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&#39;s general inventive concept.