Patent Abstract:
A partially self-erecting wind turbine tower and a method for carrying out the assembly thereof. A central extendable pylon is provided. This is placed in an upright position, with its base on a temporary foundation. A plurality of legs is then attached to the extendable pylon. The upper extreme of each of the plurality of legs is temporarily attached to the upper extreme of the extendable pylon. With the pylon and legs thus secured, a nacelle is attached to the upper extreme of the extendable pylon. A hub with attached blades is then affixed to the nacelle. The extendable pylon is then forced upward through the collar to extend the height of the assembly.

Full Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of wind energy production. More specifically the invention comprises a partially self-erecting wind turbine tower which significantly reduces the lift height required for assembly of the components. 
     2. Description of the Related Art 
       FIG. 1  depicts a prior art wind turbine  10 . Pylon  14 —which may include two or more joined segments—is affixed via base  24  to foundation  12 . Nacelle  16  houses a revolving horizontal shaft to which hub  18  and blades  20  are attached. The nacelle typically also contains a gearbox for stepping up the rotational speed of hub  18 , a generator for converting the rotating shaft energy to electrical energy, control electronics, and a braking mechanism (which may be mechanical, electrical, or a combination of the two). 
     Nacelle  16  is attached to the top of pylon  14  via yaw joint  22 . Drive mechanisms revolve the nacelle with respect to pylon  14  in order to point hub  18  into the wind.  FIG. 1  depicts a prior art device in which the rotating blades are located upwind of the pylon, which is true for most wind turbines currently in production. There are many variations on this design. There are also prior art wind turbines in which the rotating blades are located downwind of the pylon. The present invention may be adapted for use with many different types of prior art turbines. 
     The use of a single pylon in the prior art requires the diameter “D” of foundation  12  to be quite large. The mass of the foundation is required to counteract the large overturning forces placed on the base. The foundation is generally cast from concrete, and the use of such a large structure adds to the overall cost of the wind turbine installation. 
     The components of a prior art wind turbines are typically installed using a crane.  FIG. 2  shows crane  26  lifting nacelle  16  onto the top of the pylon. Boom  28  holds a cable to which hook  30  is attached. The height of the unitary pylon and nacelle will determine the “hook height.” “Hook height” is a term of art in the rigging industry. It simply means the height above the ground for the engagement portion of a lifting hook. Boom  28  must of course extend above the hook height in order to allow some vertical space for the cable and pulley assemblies. The reader will thereby easily discern that the required hook height determines the size of crane needed for a particular wind turbine installation. 
     Prior art wind turbines are quite large. Blade lengths vary between 20 meters (66 feet) and 60 meters (197 feet). The largest wind turbines have overall heights of about 200 meters (656 feet with overall blade diameters of 125 meters (400 feet). A very large wind turbine will have a pylon height of about 100 meters (328 feet). Thus, a crane having a hook height of about 120 meters (394 feet) is needed to install the largest examples of prior art wind turbines. Such wind turbines are typically installed in remote locations, where access for large machinery is limited. Transporting extremely large cranes to such sites represents a substantial portion of the total cost of installing a wind turbine. Thus, a wind turbine tower design that could be erected using a smaller crane would be advantageous. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention comprises a partially self-erecting wind turbine tower and a method for carrying out the assembly thereof. A central extendable pylon is provided. This is placed in an upright position, with its base on a temporary foundation. A plurality of legs is they attached to the extendable pylon. The upper extreme of each of the plurality of legs are preferably attached to a collar surrounding the upper extreme of the extendable pylon. 
     With the pylon and legs this temporarily secured, a nacelle is attached to the upper extreme of the extendable pylon. A hub with attached blades is affixed to the nacelle. The extendable pylon is then forced upward through the collar to extend the height of the assembly. The extendable pylon is raised to its operational position with its lower extreme being affixed to the collar. By raising the extendable pylon, the nacelle and attached huh and blades are positioned an appropriate distance above the ground. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an elevation view, showing a prior art wind turbine. 
         FIG. 2  is an elevation view, showing the use of a crane to assemble a prior art wind turbine. 
         FIG. 3  is a perspective view, showing a wind turbine constructed according to the present invention. 
         FIG. 4  is an elevation view, showing the use of a crane to erect a pylon according to the present invention. 
         FIG. 5  is a perspective view, showing a leg assembly. 
         FIG. 6  is a perspective view, showing a crane attaching a leg to a pylon. 
         FIG. 7  is a perspective view, showing a crane attaching additional legs to a pylon. 
         FIG. 8  is an elevation view, showing a crane attaching a nacelle to a pylon. 
         FIG. 9A  is an elevation view, showing a crane attaching a hub and blades to a nacelle. 
         FIG. 9B  is an elevation view, showing a hub and blades attached to a nacelle. 
         FIG. 10  is an elevation view, showing the extension of an extendable pylon. 
         FIG. 11  is a detailed elevation view, showing one possible drive mechanism for an extendable pylon. 
         FIG. 12  is a detailed elevation view, showing another possible drive mechanism for an extendable pylon. 
         FIG. 13  is a perspective view, showing an alternate embodiment for the present invention 
         FIG. 14  is an elevation view, showing another drive mechanism for the extendable pylon. 
     
    
    
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERALS  
               
               
                 IN THE DRAWINGS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 wind turbine 
               
               
                 12 
                 foundation 
               
               
                 14 
                 pylon 
               
               
                 16 
                 nacelle 
               
               
                 18 
                 hub 
               
               
                 20 
                 blade 
               
               
                 22 
                 yaw joint 
               
               
                 24 
                 base 
               
               
                 26 
                 crane 
               
               
                 28 
                 boom 
               
               
                 30 
                 hook 
               
               
                 32 
                 extending pylon 
               
               
                 34 
                 collar 
               
               
                 36 
                 leg 
               
               
                 38 
                 split foundation 
               
               
                 40 
                 ground 
               
               
                 42 
                 rigging 
               
               
                 44 
                 base 
               
               
                 46 
                 temporary foundation 
               
               
                 49 
                 nacelle mount 
               
               
                 50 
                 column structure 
               
               
                 52 
                 collar sub-portion 
               
               
                 54 
                 rack 
               
               
                 56 
                 worm drive 
               
               
                 58 
                 reduction gearbox 
               
               
                 60 
                 motor 
               
               
                 62 
                 cable anchor 
               
               
                 64 
                 pulley 
               
               
                 66 
                 cable 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows an embodiment of a wind turbine constructed according to the present invention. The support structure includes extendable pylon  32 , which is supported by a plurality of legs  36 . Rather than having a single unified foundation, a split foundation  38  is furnished for the base of each leg  36 . 
     The upper portion of each leg  36  is preferably attached to a collar  34 , which surrounds extendable pylon  32 . The collar may formed by uniting portions of the legs themselves, or it may be a separate structure to which the legs are attached. Whatever form it takes, the collar provides a sliding attachment between the legs and extendable pylon  32 , so that the extendable pylon can move up and down with respect to the legs. 
     The upper portions of the assembly shown are the same as those found in the prior art. Nacelle  16  is attached to the upper portion of the extendable pylon by yaw joint  22 . Rub  18  is attached to the nacelle. Blades  20  are attached to the hub. 
     The assembly of the components depicted in  FIG. 3  will now be described. The reader should bear in mind that the order of the steps could be altered, as will be apparent to those skilled in the art. 
       FIG. 4  shows the first step in the process. Crane  26  is attached to extendable pylon  32  using rigging  42 . The crane lifts the extendable pylon into a vertical orientation as shown. A temporary foundation is preferably provided beneath the base of extendable pylon  32  in order to provide stability. The extendable pylon is preferably secured to the temporary foundation. 
       FIG. 5  shows one embodiment of leg  36  in more detail. Column structure  50  is attached to split foundation  38  at its lower extreme and collar sub-portion  52  at its upper extreme. In this version, the collar surrounding the extendable pylon is formed by uniting portions of the legs themselves. Thus, collar sub-portion  52  is provided as part of the leg assembly. The collar sub portion is one-third of a ring structure which will encircle the extendable pylon when all the legs are assembled. 
     The reader should understand that all the components are depicted in a “top level” fashion. As one example—pad  48  would typically include a number of through-holes to allow threaded studs embedded in the foundation to pass through the pad when it is placed in the proper position. Nuts would then be placed on these threaded shafts to lock the pad in places. 
     Likewise each collar sub-portion would typically include connecting flanges so that bolts or other devices can be used to secure each collar sub-portion to its neighbors. As these detailed components are well understood to those skilled in the art, they have been omitted in order to promote visual clarity. 
       FIG. 6  is a perspective view showing crane  26  lifting leg  36  into position. Base  44  of extendable pylon  32  has been placed on temporary foundation  46 . In this particular embodiment, the base is secured to the temporary foundation so that leg  36  can be leaned against the top of extendable pylon  32 . The lower portion of the leg is then attached to the split foundation and the upper portion is attached to the extendable pylon (This is preferably a temporary attachment while the rest of the legs are placed in position). 
       FIG. 7  shows the assembly at a later stage, after all three legs  36  have been placed in position. The three collar sub-portions present in this embodiment have been united to form a collar around extendable pylon  32 . Nacelle mount  49  is located on the top of the extendable pylon. Those skilled in the art will realize that once the structure is united as shown, it is very stable and crane  26  can be detached from the structure. 
     One of the present invention&#39;s key advantages is the fact that the nacelle, hub, and blades can be attached before the pylon assembly is raised to its full height.  FIGS. 8 ,  9 A, and  9 B show these steps of the assembly process. 
     In  FIG. 8 , crane  26  has lifted nacelle  16  into position above extendable pylon  32 . Once the nacelle is in this position the hub and blades can be attached. The blades are typically attached to the hub while the hub is lying on the ground. The hub with its attached blades is then lifted as an assembly.  FIG. 9A  shows the crane being used to lift hub  18  and its attached blades into position so that it can be connected to nacelle  16 . The hub is attached to the nacelle as in the prior art.  FIG. 9B  shows the hub after it has been attached to the nacelle. 
     The reader will observe how the hook height above the ground is substantially reduced in comparison to the prior art process shown at  FIG. 2 . The step shown in  FIG. 8  is typically the highest lift that must be made during the assembly process. Thus, the height of the nacelle at that point will dictate the size of the crane needed for the assembly. Since the nacelle is considerably lower than for the prior art devices, a smaller crane can be used. 
     it is not necessary in the configuration shown in  FIG. 98  to provide a free rotation path for all the blades—as the design is not intended to be operated in this configuration. The extendable pylon must be raised to place the nacelle in the proper position for operation. 
       FIG. 10  shows the assembly of  FIG. 9A  with extendable pylon  32  raised to its operational position. Collar  34  preferably provides a sliding mount for the extendable pylon so that it can be slowly raised and then locked in position. Once in the position shown in  FIG. 10  the tower assembly functions as a conventional prior art wind turbine tower. There are some notable structural differences, however. Returning briefly to  FIG. 1 , the reader will observe how base  24  of prior art pylon  14  attaches to foundation  12 . Even moderate wind forces place a very large bending moment on the interface between the base and the foundation. As a result, the attachment features must be made very strong. In addition, the foundation must resist the resulting overturning forces using only its mass (It is typically a steel reinforced concrete pad). The foundation must be made very large and—with the escalating cost of concrete and steel—this contributes substantially to the overall expense. 
     Returning now to  FIG. 3 , the reader will observe how the bases of the three legs  36  shown are widely separated. If the outward angle of each leg is configured appropriately, the forces placed on split foundation  38  will be primarily axial loads with little to no bending moment. Thus, even though there are three separate foundations in the embodiment shown, the volume of concrete required is substantially less than for the single large foundation shown in  FIG. 1 . 
     Having received the information that the extendable pylon is raised to its operational position after the nacelle is installed, the reader may wish to know some examples of the types of mechanisms that could be used to perform the raising. The present invention is in no way dependent upon the type of raising mechanism actually selected, so the following examples should properly be viewed as two examples among many other possibilities. 
     There are two basic approaches to raising the extendable pylon. These shall be referred to as “internal” lifting mechanisms and “external” lifting mechanisms. In the internal approach, the lifting mechanism remains part of the tower assembly itself. In the external approach, the actual driving force for the lifting mechanism is external to the tower assembly. This latter approach is likely more cost-effective since once the tower is raised, it is likely to remain raised for extended periods. Thus, a single external lifting device could easily service several dozen wind turbine structures. 
       FIG. 1   i  shows one embodiment of an internal lifting mechanism. Extendable pylon has a rack  54  a linear gear) attached adjacent to each leg. Thus, for a version having three legs there would be three racks, A worm drive  56  engages each rack. Motor  60  drives worm drive  56  through reduction gearbox  58 . The motor can be any type of motor, such as an electric motor or a hydraulic motor. The motor and worm drive are located in a suitable position, such as inside the top of each leg. With this arrangement, the motor assemblies in each of the three legs operate simultaneously to slowly raise extendable pylon  32 . While feasible, the use of the worm gear and racks is not preferred because of the cost of fabricating such structures. 
       FIG. 12  shows an example of an embodiment using an external lifting device, in this embodiment each leg  36  features a pulley  64 . A cable  66  is run through the hollow center of the leg, over pulley  64 , and attached to cable anchor  62  on extendable pylon  32 . An external winch is then used to apply tension to cable  66 , thereby lifting the extendable pylon. 
     The advantage of this second approach is that the pulleys and cables are relatively inexpensive, and they are the only things which remain in the tower assembly. Thus, a single winch vehicle could service many different wind turbines. 
       FIG. 14  shows another type of lifting mechanism which can be made internal or external. The drawing shows an elevation view. Extendable pylon is equipped with a plurality of cables  66 . These are anchored to the pylon by cable anchors  62  (which are placed in suitable locations). The cables pass up to the vicinity of collar  34 . In this embodiment, the cables actually pass through the collar. 
     A prestressing jack  68  is placed on an upper surface of the collar. Those skilled in the art will know that prestressing jacks are used to prestress cables in steel-reinforced concrete assemblies. They have a center passage through which the cable is passed. The cable is then secured to an extendable piston. In the embodiment of  FIG. 14 , several prestressing jacks are supplied. Hydraulic pressure is applied (from an internal or external source) and the prestressing jacks raise the cables—thereby lifting the telescoping pylon. 
     As those skilled in the art will know, prestressing jacks can be configured to pull a cable for the length of a piston stroke, then reset the attachment between the piston and the cable at a lower position so that a new pull can be made. The cycle is then repeated for as many repetitions as are needed. Of course, other devices for holding the pylon in position while the jacks are reset can be employed. 
     Prestressing jacks could be used in an internal or external lifting configuration. They are relatively light and could be lifted into position as needed. Thus, a single set of jacks could serve many wind towers. Of course, they are also relatively inexpensive. Thus, in some applications, it would make sense to place a set of lifting jacks on each wind turbine. 
     Of course, the present invention provides operational options which simply were not present in the prior art. When high wind conditions are present in the prior art, the only option is to brake the spinning hub to a stop and feather the blades. Using the present invention, it is possible to lower the height of the nacelle to roughly half its operational height. If the leg design is modified to provide clearance this feature could make it possible to continue generating electricity even in high winds. Those skilled in the art will know that wind speed tapers significantly at lower altitude. The operational advantage of providing internal raising and lowering drives for the extendable pylon—thereby providing relatively rapid movement of the extendable pylon—may be sufficient in some circumstances to warrant the additional cost of such systems (though in many applications this may not be true). 
     Those skilled in the art will also realize that the ability to lower the height of the nacelle, hub, and blades will greatly facilitate maintenance operations. This is true regardless of whether the internal or external lifting approach is selected. 
     The number of legs selected for the assembly will depend upon many conditions and the invention is by no means limited to using only three legs.  FIG. 13  shows an embodiment using four legs  36  and four split foundations  38 . Five, six, or even more legs might be used to suit particular conditions. Those skilled in the art will also realize that the legs should ideally have a tubular cross section to minimize weight and cost. However, any sufficiently strong cross section could be used. 
     The preceding description contains significant detail regarding the novel aspects of the present invention. It should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As one example, the unitary structures depicted for the extendable pylon and the legs could be made as multi-piece assemblies that are unified during the construction of the tower. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.

Technology Classification (CPC): 5