Patent Publication Number: US-10760293-B2

Title: Lattice tower

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation under 35 U.S.C. § 120 of U.S. patent application Ser. No. 14/765,245 titled “LATTICE TOWER”, filed Jul. 31, 2015, which is a U.S. National Stage Application under 35 U.S.C. § 371 of International Application No. PCT/BR2013/000036, filed Feb. 1, 2013, each of which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION (US) 
     Technical Field 
     This invention relates to lattice tower for actuate under high load conditions, more particularly to lattice towers utilized for wind turbines and other applications. 
     Background Art 
     Vertical structures for supporting high loads such as towers or the like utilized for supporting wind turbines, power transmission lines and other applications are well known in the prior art. The structural designs, components and materials of such vertical structures vary depending upon the application. 
     One type of vertical structure that has been receiving special attention in the last decades are the vertical structures for wind turbines or other high loads. 
     Wind energy has become a very attractive source of energy, both due to an increase in efficiency of the generators and an increase in market demand for clean and renewable sources of energy. The increase of the efficiency of the wind energy generators is related to a great effort in enhancing several aspects of the technology, including many issues related to the design and manufacturing of the wind energy generator components including, among others, the rotor blades, the electrical generator, the tower and the control systems. 
     Most wind turbines used in megawatt applications, nowadays varying in the range of about 1 MW to 5 MW, have a horizontal-axis wind turbine (HAWT) configuration with a main rotor shaft and an electrical generator at the top of a tower, and the rotor axis directioned to the inflow of the wind with three-blades positioned upwind. 
     The main advantage of the upwind design is the avoidance of the wind shade and resulting turbulence behind the tower. Currently, most of large scale wind turbines adopt the upwind design; however, this design has various drawbacks such as the need of some distance between the tower and the blades due to the bending of the blades and the need of a yaw mechanism to keep the rotor facing the wind. The yaw mechanism usually has a wind sensor associated by an electronic controller to a yaw drive, which includes one or more hydraulic or electric motors and a large gearbox for increasing the torque, as well as a yaw bearing. The yaw bearing provides a rotatable connection between the tower and the nacelle of the wind turbines. The yaw mechanism usually includes additional components, such as brakes that work in cooperation with the hydraulic or electric motors in order to avoid wear and high fatigue loads on the wind turbine components due to backlash during orientation of the rotor according to the wind direction. As the wind turbine will usually have cables that carry the electric current from the electric generator down through the tower, the cable may become twisted due to the rotation of the yaw mechanism. Therefore, the wind turbine may be equipped with a cable twist counter that is associated with the yaw mechanism electronic controller in order to determine the need of untwisting the cables by the yaw mechanism. 
     The downwind design, by which the rotor is placed on the lee side from which the wind blows in tower, would in principle avoid the need of a yaw mechanism if the rotor and nacelle have a suitable design that makes the nacelle follow the wind passively, utilizing the wind force in order to naturally adjust the orientation of the wind turbine in relation to the wind. This theoretical advantage is doubtful in large megawatt wind turbines because there usually remains a need to untwist the cables if the rotor continuously turns in the same direction. In addition, there are mechanical problems such as fatigue of the components due to strong loads resultant from the sudden changes of the wind direction. Nevertheless, the downwind design still presents an important advantage in regard to the structural dynamics of the machine, allowing a better balancing of the rotor and tower. In the case of larger wind turbine rotors, which nowadays have a diameter reaching about 120 meters (about 393.6 ft) or more, obtaining more flexibility in the design of the rotor blades is essential. 
     However, the increase of diameter of the rotor usually involves heavier rotors and the increase of the height of the tower, consequently, may involve the use of additional material, for instance, steel, for manufacturing the tower. 
     Hence, as a tower usually represents about fifteen to thirty percent of the cost of the wind energy generator, there is a great need to obtain higher and more robust towers at lower costs. 
     Most large wind turbines manufactured in the last two decades with a power output higher than one megawatt adopt tubular steel towers, commonly referred to as “monopoles”, as the preferred choice. The monopoles usually taper from the base to the top or close to the top, having modules connected together with bolted flanges. A constraint related with monopoles is the road transportation limitations that restrict the diameter of the segments. For instance, tubular segments with diameters higher than about 4 meters (about 13 feet) may not be transported on roads in many countries. 
     Lattice towers usually need less material (e.g. less steel) than monopoles, but require a higher number of components and bolted connections. These bolted connections are subject to the varying fatigue loads, hence, they have the disadvantage of higher maintenance needs. 
     Disclosure Technical Problem 
     One particular technical problem regarding vertical structures such as towers or the like utilized for supporting high loads such as large wind turbine generators is the lack of balancing between the stress and strain distribution of the vertical and horizontal loads vectors along the extension of the vertical structure. Due to this lack of balancing, the tower segments are designed with significant losses of materials in some segments or with assemblies that result in complex manufacturing, transportation and installations requirements. 
     Other problems to be considered are the low natural frequencies of modes of bending and torsion, and the level of vibration and trepidation that the wind causes in the tower. 
     Likewise, regardless of the upwind or downwind design, if the rotor axis is not substantially positioned to direction of the inflow of the wind there is a so called yaw error angle, causing a lower fraction of the energy in the wind flowing through the rotor area. In general, the fraction of lost power is proportional to the cosine of yaw error angle. Moreover, the yaw error causes a larger bending torque at the portion of the rotor that is closest to the source of the wind, resulting in a tendency of the rotor to yaw against the wind and the blades bend back and forth in a flapwise (or flatwise) direction for each turn of the rotor. Therefore, on one hand adequate alignment of the wind turbine rotor in relation to the wind is essential for obtaining good wind energy extraction performance and low wind turbines components wear, while on the other hand there is a need for a low cost yaw mechanism with the advantages of the downwind design. 
     Technical Solution 
     To overcome the drawbacks and problems described above and other disadvantages not mentioned herein, in accordance with the purposes of the invention, as described henceforth, one basic aspect of the present invention is directed to a lattice tower for actuate under high load conditions. 
     Advantageous Effects 
     The present invention has several advantages over the prior art. In comparison with the vertical structures of the prior art, the present invention enables a surprising reduction in the weight of the metallic structure of about 40%, depending on the design requirements of the case. One of the reasons for such expressive reduction in the total weight of the structure is that each leg of the vertical structure has a stress and strain behavior similar to a monopole, without having the restrictions of the large diameter of the single monopole vertical structures. The reduction of the weight of the metallic structure is accompanied by an advantageous reduction of the total costs of the structure, including the costs of manufacturing, transport and installation. 
     The advantage of weight reduction is accompanied by further manufacturing, transportation and installation advantages, as well as availability of a new class of vertical structures for high and critical applications, such as wind energy turbines with a power output higher than 3 MW with towers higher than 100 meters (higher than 328 feet). 
     Furthermore, another aspect of one embodiment of the invention allows the vertical and horizontal alignment of the rotor, without constant need of full force of the yaw mechanism, while also absorbing and providing damping effect for bursts winds or extreme winds. 
     Furthermore, another aspect of one embodiment of the invention provides a large platform in relation to the size of a standard nacelle permitting the use of alternative tower design with low shadow wind and turbulence for downwind application, resulting in significant flexibility in the design of blades, substantially reducing the costs and improving performance. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and other exemplary aspects and/or advantages will become more apparent by describing in detail exemplary embodiments with reference to the accompanying drawings, which are not necessarily drawn on scale. In the drawings, some identical or nearly identical components that are illustrated in various figures can be represented by a corresponding numeral. 
       For purposes of clarity, not every component can be labeled in every drawing. 
         FIG. 1  shows a perspective view of one exemplary of a lattice tower for supporting loads according to one embodiment of this invention. 
         FIG. 2A  is a side view of one exemplary of a lattice tower according to one embodiment of this invention. 
         FIG. 2B  is a partial detailed view of the inclination at ( 31  and ( 32  angles of the bracing members in relation to the central axis of each one of the lattice tower legs, according to one embodiment of this invention. 
         FIG. 3A  is a top view of the lattice tower, according to one embodiment of this invention. 
         FIG. 3B  is a bottom view of the lattice tower, according to one embodiment of this invention. 
         FIG. 4  is a partial schematic exaggerated view of the inclination between the central longitudinal axes, the vertical axis of the tower and the leg&#39;s conicity, according to one embodiment of this invention. 
         FIG. 5A  is a side view of one exemplary of a lattice tower according to one embodiment of this invention, serving as reference to show the different configurations of the cross-sections of the tower legs along its height. 
         FIG. 5B  is a cross-section view of the legs along the third portion length of the lattice tower (with the inclination and conicity exaggerated, as well as not in scale), according to one embodiment of this invention. 
         FIG. 5C  is a partial schematic view of the leg along the third portion length of the lattice tower (with the inclination and conicity enlarged exaggerated, as well as not in scale), according to one embodiment of this invention. 
         FIG. 5D  is a cross-section view of the legs along the second portion length of the lattice tower (with the inclination and conicity enlarged as well as not in scale), according to one embodiment of this invention. 
         FIG. 5E  is a partial schematic view of the leg along the second portion length of the lattice tower (with the inclination and conicity exaggerated, as well as not in scale), according to one embodiment of this invention. 
         FIG. 5F  is a cross-section of the legs along the first portion length of the lattice tower (with the inclination and conicity enlarged as well as not in scale), according to one embodiment of this invention. 
         FIG. 5G  is a partial schematic view of the leg along the first portion length of the lattice tower (with the inclination and conicity exaggerated, as well as not in scale), according to one embodiment of this invention. 
         FIG. 6A  is a view of one exemplary polygonal cross-sectional shape according to one embodiment of this invention. 
         FIG. 6B  is a view of one exemplary reduced web profile cross-sectional shape and fairing according to one embodiment of this invention. 
         FIG. 7  is a detailed view of one exemplary connection of the modules of the lattice tower length, according to one embodiment of this invention. 
         FIG. 8  is perspective view of the support platform with inner tubular interface to perform similar function as the current technique for elongated nacelles, according to one embodiment of this invention. 
         FIG. 9  is a lateral view of the support platform with inner tubular interface, according to one embodiment of this invention. 
         FIG. 10  is a frontal view of the support platform with inner tubular interface, according to one embodiment of this invention. 
         FIG. 11  is a posterior view of the support platform with inner tubular interface, according to one embodiment of this invention. 
         FIG. 12  is a plan view of the support platform with an inner tubular interface for passageway for cables according to one embodiment of this invention. 
         FIG. 13A  is a perspective view of one exemplary of a lattice tower with support platform with inner tubular interface related to a wind energy turbine, according to one embodiment of this invention. 
         FIG. 13B  is also a perspective view of the solid model of one exemplary of a lattice tower with support platform with inner tubular interface related to a wind energy turbine, according to one embodiment of this invention. 
         FIG. 14  is a frontal view of one exemplary of a lattice tower with support platform with inner tubular interface related to a wind energy turbine, according to one embodiment of this invention. 
         FIG. 15A  is a lateral view of one exemplary of one embodiment of this invention wherein the load is an upwind turbine assembly with elongated nacelle. 
         FIG. 15B  is a lateral view of one exemplary of one embodiment of this invention wherein the load is an downwind turbine assembly with elongated nacelle. 
         FIG. 16A  is a lateral view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle. 
         FIG. 16B  is a lateral view of one exemplary of one embodiment of this invention wherein the load is a downwind turbine assembly with elongated nacelle. 
         FIG. 17A  is a top view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle. 
         FIG. 17B  is a top view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle, rotated by 90° with respect to the configuration of  FIG. 17A . 
         FIG. 17C  is a top view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle, rotated by 180° with respect to the configuration of  FIG. 17A . 
         FIG. 18A  is a top view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle. 
         FIG. 18B  is a top view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle, rotated by 90° with respect to the configuration of  FIG. 18A . 
         FIG. 18C  is a top view of one exemplary of one embodiment of this invention wherein the load is a upwind turbine assembly with elongated nacelle, rotated by 180° with respect to the configuration of  FIG. 18A . 
         FIGS. 19A and 19B  show the Table I corresponding to the dimensioning spreadsheet of a tower in steel only according to one embodiment of the present invention. 
         FIGS. 20A and 20B  show the Table II corresponding to the dimensioning spreadsheet of a tower in steel reinforced with concrete according to one embodiment of the present invention. 
         FIG. 21  shows in the Table III the summary of the comparison between three towers: the monotubular tower, the lattice tower in steel, and the lattice tower in steel reinforced with concrete. 
         FIG. 22  is a frontal view of another exemplary of a support platform represented as a yaw support structure according to one embodiment of this invention. 
         FIG. 23  is a perspective view of another exemplary of a support platform represented as a yaw support structure according to one embodiment of this invention. 
         FIG. 24  is a plan view of another exemplary of a support platform represented as a yaw support structure according to one embodiment of this invention. 
         FIG. 25  is a detailed superior view of another exemplary of a support platform represented as a yaw support structure according to one embodiment of this invention. 
         FIG. 26  is a lateral view of another exemplary of a support platform represented as a yaw support structure according to one embodiment of this invention. 
         FIG. 27  is a perspective view of another exemplary of a support platform represented as a yaw support structure with two interfaces according to one embodiment of this invention. 
         FIG. 28  is a plan view of another exemplary of a support platform represented as a yaw support structure with two interfaces according to one embodiment of this invention. 
         FIG. 29  is a plan view of another exemplary of a support platform represented as a yaw support structure with two interfaces according to one embodiment of this invention. 
         FIG. 30  is a lateral view of another exemplary of a support platform represented as a yaw support structure with two interfaces according to one embodiment of this invention. 
         FIG. 31  is a perspective view of another exemplary of a support platform represented as a structure with two interfaces according to one embodiment of this invention. 
         FIG. 32  is a plan view of one exemplary of a support platform showing the connection of the yaw support platform in the top of the lattice tower by bracing members. 
     
    
    
     EXPLANATIONS OF LETTERS AND NUMERALS 
     
       
         
           
               
               
             
               
                   
               
               
                 Numerals 
                 Explanation of numerals 
               
               
                   
               
             
            
               
                 10 
                 Lattice tower 
               
               
                 11 
                 Metallic legs 
               
               
                 12 
                 Vertical axis of the tower 
               
               
                 13 
                 Bracing members 
               
               
                 13a 
                 Auxiliary bracing members 
               
               
                 14 
                 Support platform 
               
               
                 16 
                 Central longitudinal axis 
               
               
                 17a 
                 Top portion (of lattice tower assembled) 
               
               
                 17b 
                 Base portion (of lattice tower assembled) 
               
               
                 18 
                 Flange of linkage 
               
               
                 20 
                 Module 
               
               
                 21a 
                 First portion 
               
               
                 21b 
                 First legs 
               
               
                 22a 
                 Second portion 
               
               
                 22b 
                 Second legs 
               
               
                 23a 
                 Third portion 
               
               
                 23b 
                 Third legs 
               
               
                 24 
                 Clearance upwind distance 
               
               
                 25 
                 Clearance downwind distance 
               
               
                 26 
                 Channel with reduced web 
               
               
                 27 
                 Oblong aerodynamic profile 
               
               
                 30a 
                 A frusto-conical cross-section first leg 
               
               
                 30b 
                 Bottom portion of first leg 
               
               
                 30c 
                 Top portion of first leg 
               
               
                 31a 
                 A frusto-conical cross-section third leg 
               
               
                 31b 
                 Top portion of third leg 
               
               
                 31c 
                 Bottom portion of third leg 
               
               
                 40 
                 Support platform with inner tubular interface 
               
               
                 41 
                 Platform leg 
               
               
                 42 
                 Inner tubular interface 
               
               
                 43 
                 Yaw mechanism support structure 
               
               
                 44 
                 Rotor blades 
               
               
                 45 
                 Electric generator 
               
               
                 46 
                 Body 
               
               
                 47 
                 Upper surface 
               
               
                 48 
                 Lower surface 
               
               
                 49 
                 Circular track 
               
               
                 50 
                 Yaw rotating mechanism 
               
               
                 51 
                 First axis that is perpendicular to the upper surface  
               
               
                   
                 of the platform 
               
               
                 52 
                 Longeron of turbine support platform 
               
               
                 53 
                 First end turbine support platform frame 
               
               
                 54 
                 Second end turbine support platform frame 
               
               
                 55 
                 Second axis that is perpendicular to the first axis 
               
               
                 56 
                 Wind energy turbine with elongated nacelle 
               
               
                 57 
                 Yaw actuator 
               
               
                 58 
                 Wheels 
               
               
                 58a 
                 Dampener element 
               
               
                 60 
                 Wind direction 
               
               
                 61 
                 Interface 
               
               
                 61a 
                 Second Interface 
               
               
                 63 
                 Gearbox 
               
               
                 64 
                 Passageway for cables 
               
               
                 65 
                 Shaft 
               
               
                 66 
                 Furling mechanism 
               
               
                   
               
            
           
         
       
     
     MODES FOR INVENTION 
     Hereinafter, exemplary embodiments will be described with reference to the attached drawings. Like reference numerals in the drawings denote like elements. While exemplary embodiments are described herein, they should not be construed as being limited to the specific descriptions set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete. In the drawings, the sizes of components may be exaggerated or made smaller for purposes of clarity. 
     The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising”, “having”, “containing” or “involving”, and variations thereof used in this description, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The dimensions as recited herein are merely exemplary and other dimensions may be used in conjunction with the exemplary embodiments as would be understood by one of skill in the art. 
       FIG. 1 , which is on an approximate scale, shows a perspective view of an exemplary lattice tower  10 , higher than 60 meters (about 197 ft), according to one embodiment of the present invention. The lattice tower  10  is formed by three metallic legs  11 , configurated in metallic shells, which have their central longitudinal axis  16  inclined in relation to the vertical axis  12  of the lattice tower  10 . At the foundation, in base portion  17   b , the three legs  11  are arranged in an equilateral triangular configuration around the vertical axis  12  of the tower, in a distance greater than 4 meters measured between the centers  16  of each leg of the lattice tower  10 . The metallic legs  11  have a substantially circular and closed cross-section and are connected to each other along the lattice tower  10  structure height by a plurality of bracing members  13  and auxiliary bracing members  13   a  which are arranged diagonally and horizontally, respectively. A support platform  14  is disposed at the top portion  17   a  of the lattice tower  10  serving as an interface for supporting loads like wind turbine, electric power transmission lines, telecommunications systems, and other applications. 
       FIG. 2A  is a side view of one exemplary embodiment of the invention showing the silhouette (the vertical profile) of the lattice tower  10  wherein its metallic legs  11  are divided in three portions: a first portion  21   a , a second portion  22   a  and a third portion  23   a . The first portion  21   a  and the third portion  23   a  have two inverted right circular truncated conical shape which are interconnected, at their narrow end, by the second portion  22   a  which has cylindrical shape of smaller diameter. All portions are aligned through its central longitudinal axis  16 . 
       FIG. 2A  shows also a plurality of bracing members  13  and auxiliary bracing members  13   a , arranged diagonally and horizontally, respectively, and attached to the metallic legs  11  of the lattice tower  10  at regular intervals along the length of the metallic legs  11 , having the function of providing resistance to lateral and/or rotational displacement to stiffen the lattice tower  10 . The construction of said bracing members  13 , especially the diagonal ones which are constructed in the interior of the lattice tower  10  in a X-shaped format, are made up in a configuration inclined in a β1 and β2 angle in relation to the central longitudinal axis  16  of each metallic leg  11 , as depicted in  FIG. 2B . Although the angles β1 and β2 are not necessarily identicals and may vary according to the position of the bracing member  13  along the height of the lattice tower  10 , said angles have values between about 30 and 60 degrees, preferably around 45 degrees. The side view shown in  FIG. 2A , illustrates also the three metallic legs  11  of the lattice tower  10  wherein the metallic legs are divided in three portions along its length, each portion formed preferentially by at least one module or module  20 . This division is according to the assembly of the tower considering its inverted truncated conical portions and cylindrical portion, as well as is intended to provide a better understanding of its design function, as previously described. 
     The first portion  21   a  is formed by three first legs  21   b , the second portion  22   a  which is formed by second legs  22   b , each second leg  22   b , preferentially, is linearly aligned with and coupled to a corresponding first leg  21   b  of the first portion  21   a . A third portion  23   a  includes three third legs  23   b , each third leg  23   b , preferentially, is linearly aligned with and coupled to a corresponding second leg  22   b  of the second portion  22   a.    
     The  FIG. 3A  is a top view of the lattice tower, according to one embodiment of this invention, which helps to understand the three metallic legs  11  shape having two inverted right circular truncated conical shape which are interconnected, at their narrow end. 
     As depicted in the  FIG. 3B , the three metallic legs  11  are arranged symmetrically at equal angles around a vertical axis of the tower  12  and with equal distances “d” between each other, in a triangular configuration, preferably in an equilateral configuration. Eventually, small variations due to the geometric dimensioning and tolerances that may be considered for the assembly, for instance due manufacturing or land and foundation limitations. The distance “d” between the central longitudinal axes  16  of each leg in the bottom portion  17   b  of the lattice tower base when fixed to the ground, is greater than 4 meters (about 13.12 ft). 
       FIG. 4  is a partial schematic view of the inclination between the central longitudinal axis and the vertical axis of the tower, according to one embodiment of this invention. The scale of this view has been exaggerated for clarity. In the example, the central longitudinal axis  16  of each metallic leg  11  can be inclined until an angle (θ) of 1.7 degree in relation to the vertical axis of the lattice tower  10  and around the central longitudinal axis  16  in accordance to the characteristics of load it is intended for, like wind turbine, electric power transmission lines, and other applications. 
     Additionally, the lattice tower  10  is configured to provide a general aspect of the vertical profile (silhouette) wherein in an exaggerated scale the tower would have an hourglass-shape that defines the lower portion of the tower relatively broad at its lower end (distance “Ab” in the base portion  17   b ) and relatively narrow at its upper end (distance “At” in the top portion  17   b ), as depicted in  FIG. 4 , but in fact in a true scale the general aspect of the vertical profile (silhouette) would appear to be linearly vertical at right angles. Furthermore, as depicted from  FIG. 04 , the distance “At” is, preferentially, lower than the distance “Ab”. 
     The tower configuration shown in  FIG. 4 , is suitable to ensure a proper distribution of the efforts that are caused by loading the lattice tower  10  once this type of silhouette allows reinforcing the top portion  23   a  of the metallic legs  11  with diameters and thicknesses larger than normally found in prior art. Also, this configuration allows a double effect in terms of structure once that increases the strength and the natural frequency of the tower and at the same time reduces its manufacturing, transport and installation costs. In addition, the portions  22   a  and  23   a , as depicted in  FIG. 2A , are especially suitable to reduce the aerodynamic turbulence in the region where the rotor blades passes, allowing the use of a downwind configuration as shown in  FIG. 16B . The downwind design, as shown in  FIG. 16B , is very advantageous because the clearance  24  is not a problem while the blade  44  bends deviating from the lattice tower  10  in this wind condition. 
     In the case of the upwind design, as shown in  FIG. 15A , as the tower is much stronger than conventional towers, it is possible to increase the clearance upwind distance  24  reducing the chance of a rotor blade striking the tower. 
     The design of the lattice tower  10  is made to support dynamic loads on the support platform  14  at the top portion of the tower  17   a  that cause reaction forces and moments in a base portion  17   b  of the lattice tower  10 , that be above than 10 (ten) times greater that reaction forces and moments caused by wind loads on the lattice tower itself. 
     For reference and as an example of a load, a large scale wind turbine available commercially with nominal output of 7.58 MW has an approximate weight of the foundation of the turbine tower about 2,500 ton, the tower itself 2,800 ton, the machine housing 128 ton, the generator 220 ton, and the rotor (including the blade) 364 ton. Accordingly, the dynamics loads on the support platform caused by the generator and the rotor are much higher than maximum wind loads imposed specifically in the tower itself. Usually, a tower for supporting only standard telecommunication antennas would be subject to completely different loads, because in this case the wind loads in the tower are usually higher than the loads caused by the telecommunication antennas in the top of the tower. 
     The metallic legs  11  are designed in truncated conical portions in the first portion  21   a  and in the second portion  23   a , and in cylindrical portion in the second portion  22   a  so that the diameter variation remains smooth throughout the metallic legs  11  length avoiding discontinuities that can cause areas of stress concentration which can also cause air bubbles during concreting, in case of adopting combinations of different materials in the metallic legs  11  construction. 
     Additionally, the conicity of the column axle envelope of the lattice tower  10  is preferably constant and can also be adjusted in order to compensate the variable conicity of the metallic legs  11 , resulting in bracing members  13  that are identical, with the same length, diameter and thickness over the entire height of the lattice tower  10 . This possibility allows standardizing the length of such bracing members, reducing the cost of their production and facilitating the assembly at site once, among others advantages, it will not be need to numbering them. 
       FIG. 5A  is a side view of one exemplary of a lattice tower  10  according to one embodiment of this invention, serving as reference for showing in a schematic way the different configurations of the cross-sections of the tower legs along its height H. In the exemplary embodiment the outside diameter “D” to thickness “t” and ratio (D/t) of each metallic leg  11  is greater than 30. 
       FIGS. 5B, 5D and 5F  are views of cross-section of the legs along the portions length of the lattice tower  10 , said cross-sections are closed sections, according to one embodiment of this invention. 
     As shown in  FIGS. 5B and 5C , schematically adapted, preferentially one of the third legs  23   b  has also a frusto-conical cross-section  31   a  and a top portion  31   b  at least one third leg  23   b  has a larger diameter than the bottom portion  31   c  of the at least one third leg  23   b.    
     The second portion  22   a  is formed by second legs  22   b  having a cylindrical structure, as depicted schematically in  FIGS. 5D and 5E . Thus, the diameter of each respective third leg  23   b  of the third portion  23   a  is larger than the diameter of each respective second leg  22   b  in the second portion  22   a.    
     Additionally, as shown schematically in the  FIGS. 5F and 5G  preferentially at least one of the first legs  21   b  has a frusto-conical cross-section  30   a  and a bottom portion  30   b  of the at least one first leg  21   b  has a larger diameter than a top portion  31   b  of the at least one first leg  21   b.    
     Preferentially, the metallic legs  11  have a circular closed cross-section as shown in the  FIGS. 5B, 5D and 5F . Alternatively, the metallic legs  11  can also be designed in a shape having, for example, a polygonal cross-sectional shape provided that an aerodynamic fairing, provided that the frusto-conical shape is kept, as depicted in  FIG. 6A . 
     The polygonal cross-sectional shape is shown in  FIG. 6A  as being, preferentially at least a dodecagon, but it is understood that it could be formed into other polygonal shapes, such as a tridecagon, tetradecagon, and so on, according to the suitable construction. 
     The  FIG. 6B  illustrates another example of cross-sectional shape embodiments, preferably used as a profile for the bracing members  13  and auxiliary bracing members  13   a , wherein a channel section with reduced web  26  is covered by a fairing with an oblong aerodynamic profile  27 . The function of the fairing is to cover the channel section, so that the said section profile remains closed, enhancing the aerodynamic behavior of the metallic section with a low cost material of easy formation, such as polymers, composite materials or other materials, as depicted in  FIG. 6B . The fairing is intended to minimize turbulence caused by the wind and can be designed, alternatively, as example, into another aerodynamic suitable shapes, which may also include dimples or waves (not shown in the  FIG. 6B ) on the surface to generate tiny eddy currents over which air can flow smoothly, reducing turbulence and improving aerodynamic performance. 
     Beyond the metallic material applied for the construction of said metallic legs  11 , for instance steel, they can also be constructed with metallic materials associated with composite materials, or composite material with reinforced concrete, or composite material with pre-stressed concrete, or combinations thereof; for example, the metallic legs  11  can be filled with reinforced concrete for reinforcement of the structure. As the vertical structures for the preferred applications, such as wind energy generators, are usually very high, for instance higher than 60 meters, each metallic leg  11  will usually be fabricated in separated segments that are joined together during installation on the site. This means a combination of materials along the length of the lattice tower  10  like, for example and not limited to: the first portion  21   a  manufactured together with pre-stressed concrete, the second portion  22   a  manufactured together with concrete material with reinforced concrete and the third portion  23   a  manufactured together with composite materials, or other suitable materials combinations. 
     As example of one embodiment of this invention, the coupling between portions  21   a ,  22   a  and  23   a  as well as between modules  20  of every respective portion is done by using flange  18  coupling, as depicted in  FIG. 7 . 
     The bracing members  13  and the auxiliary bracing members  13   a  are preferentially cylindrical shaped, or channel sections (U) with an oblong fairing, and with substantially similar or equal length along the entire height of the lattice tower  10 , because with the largest amount of equal parts reduces manufacturing costs and facilitates assembly. 
     Although the skilled in the art usually adopt for the bracing diagonal members and horizontal bars the standard sections commonly used for the purpose of constructing lattice towers, they can be advantageously substituted by bracing members  13  and auxiliary bracing members  13   a  having at least one channel section wherein the length of the channel web is smaller than the length of the channel legs as the ones describes in the WO 2010/076606A1, which specification is incorporated herein by reference. 
     Accordingly the bracing members  13  or auxiliary bracing members  13   a  can be constructed with a closed cross section, or by using a composite material, or by using a metallic bracing member reinforced with a composite material, or metallic bracing member with closed cross section filled with concrete, or other suitable combinations thereof. 
     The exemplary embodiment shown in  FIGS. 8 to 12  illustrate how the load, in the case of a wind energy turbine, can be supported atop the said lattice tower  10  through a support platform with an inner tubular interface  40  that is, in turn, coupled to the lattice tower structure  10  by each platform leg  41  with each respective third leg  23   b  of the third portion  23   a.    
     The support platform with inner tubular interface  40  is formed by three platform legs  41 , each platform leg coupled to a respective third leg  23   b  of the third portion  23   a  and an inner tubular interface  42  coupled to the three platform legs  41 , as depicted in  FIGS. 8 to 12 . In the case of supporting a wind turbine, the inner tubular interface is formed by a steel tube and is fixed on the support to allow connection with the nacelle, using the state of the art in terms of nacelle fixation. 
     In the exemplary embodiment shown in  FIGS. 13A and 13B , a wind energy turbine with elongated nacelle  56  is coupled to the lattice tower  10 , at its top. Thus, as the lattice tower gives less wind shade than a tubular steel tower (monopole), the said lattice tower can be arranged to an upwind or downwind design, in accordance with the wind direction  60  and depending upon the suitable application or construction, as depicted respectively in  FIGS. 14 to 18B . 
     For illustrative and exemplificative purposes, not limiting the present invention, the  FIGS. 19A and 19B  show the Table I which is a dimensioning spreadsheet of an exemplary embodiment of the lattice tower  10  with 138 meters high (about 453 ft), using only metallic legs and bracing members without a composite material reinforcement. The dimensioning spreadsheet shows up the essential dimensions of the structure of the exemplary lattice tower  10  starting from the quantity of modules  20  as well as their height wherein the modules  20  are connected together form the lattice tower  10  high. 
       FIGS. 20A and 20B  show the Table II which is also a dimensioning spreadsheet of an exemplary embodiment of the lattice tower  10  which is 138 meters high (about 453 ft), wherein the legs and bracing members include reinforced concrete. 
     In the embodiments of described in the Tables I and II in the  FIGS. 19A, 19B, 20A and 20B  the central longitudinal axes  16  of the metallic legs  11  are inclined with less than 0.35 degrees in relation to the vertical axis of the tower  12 . The metallic legs  11  have variable conicity, wherein their diameter starts with 1,000 mm (about 3.281 ft) at the base decreasing to 510 mm (about 1.673 ft) at 84 meters high (about 275.5 ft) (relating to the first portion  21   a  already shown in  FIG. 2A ); keeps up the diameter with 510 mm (about 1.673 ft) up to 120 meter high (about 393.6 ft) (relating to the cylindrical second portion  22   a  already shown in  FIG. 2A ). Thereafter the conicity of the metallic legs  11  has the same value as the first portion  21   a , but in a reversed way, and the diameter of the metallic legs  11  increases to 598 mm (about 1.960 ft) at the top of lattice tower  10  in 138 meters high (about 452.6 ft). 
     The thicknesses of the legs modules  20  are those normally available in the market standards. The thickness of the bracing member  13  and the auxiliary bracing members  13   a  was calculated to withstand stresses on the base portion  17   b  of the lattice tower  10 . The connections systems of the bracing members  13  and of auxiliary bracing members  13   a  with the metallic legs  11  of the lattice tower  10  as well as among themselves, are made of steel and weight about 9.7 tons. 
     In the exemplary embodiment shown in  FIG. 13A , the lattice tower  10  has about 0.19 degrees of conicity to compensate the variable conicity of the metallic legs  11 . The conicity of the lattice tower  10  is constant along its vertical axis  12 , and the longitudinal central legs axis  16  is linear and concentric to the axle of the portions  21   a ,  22   a  and  23   a , for not generating points of stress concentration. 
     Therefore, due to the shape of the lattice tower  10  as well as the structural performance and behavior it is obtained a surprising reduction in the total cost of the structure, beside the increase of frequency if comparing with a standard monopole tower, normally used for loading wind turbine, as depicted bellow in the Table III. Costs were estimated on a relative currency, covering the costs of materials, manufacturing, logistics and manpower, not considering the cost of special transportation required by components with large dimensions or weights. Metallic legs  11 , bracing members  13  and auxiliary bracing members  13   a  may be fabricated by any suitable metallic material, for instance, steel. A high strength low-alloy structural steel is preferred, and for the comparison shown, the properties of the steel preferably used are the following: yield strength (fy) is about 3,806 kgf/cm 2 ; young&#39;s modulus (E) is about 2,100,000 kgf/cm 2  and density is about 7,850 kgf/m 3 . Concrete used has about the following properties: strength (fck) is 510 kgf/cm 2 ; young&#39;s modulus (E) is 343,219 kgf/cm 2  and density is 2,300 kgf/m 3 . The embedded steel bars of the reinforced concrete have about the following properties: yield strength (fy) is 5,000 kgf/cm 2 ; young&#39;s modulus (E) is 2,100,000 kgf/cm 2  and density is 7,850 kgf/m 3 . 
     The  FIG. 21  shows the Table III corresponding to the lattice tower  10  in steel only, taking as reference for the comparison and named here as TA1, for wind turbines installed in a high greater than 60 meters (about 196.8 ft), is lower cost, of simpler logistics and better spectrum of natural frequencies than a monopole, also in steel and named here as TM1, considering an equivalent resistance. The manufacturing cost of the lattice tower  10  is reduced to ⅓ of the cost of the monopole. Considering a lattice tower  10  wherein is used a combination of materials, like steel and reinforced concrete named here as TAC1, the cost is reduced to ⅕ of the monopole TM1, as also depicted in the Table III. 
     The frequency of the first mode increases from 0.151 Hz, for the monopole tower TM1, to 0.297 Hz, for the TA1. The frequency of 0.297 Hz is out of the frequency range of the rotor blades of a wind turbine. For the lattice tower TAC1 wherein is used a combination of materials in the legs and bracing members, the frequency rises to 0.381 Hz. It also shows that by changing steel by mixed materials of the same resistance, for example, reinforced concrete, the cost of the TAC1 decreases even more at the same time the frequency spectrum is improved. For TAC1, the frequency of the first mode increases to 0.381 Hz and the cost is reduced approximately 40% in relation to the cost of the TA1. 
     The Table III summarizes the comparison between the three technologies studied. The lattice tower TAC1 in steel and reinforced concrete has the following advantages: 
     1) Lower Cost: it costs about 20% of monopole TM1 and about 61% a lattice tower TA1 in steel only; 
     2) It has natural frequency of 0.387 Hz, about 28% higher than the lattice tower TA1 in steel and about 152% higher than the monopole TM1; 
     3) Transport is simpler and lower cost: The concrete is of lower cost transport and can be obtained easily nearby of the most sites of installations, thus the more expensive cost for transporting is for the steel. The tower TAC1 used 99.2 tons of steel, considering the steel used in the shells of the legs as well as for reinforcing the concrete and for the flanges. This value is 59% of a TA1 tower which has 167.0 tons and is 25% the mass of the monopole tower TM1, with 402.5 tons. For the monopole tower TM1 the cost is even higher, because it is necessary special transporting system for tubes of 4 meters diameter (13.123 ft) with 12 or 24 meters of length (about 39.4 or 78.7 ft of length). 
     The lattice tower also presents an equivalent diameter from 1.6 to 1.8 meters (about 5.245 to 5.905 ft) with indices of exposed area ranging from 13.5% to 15.5%, in the tower height achieved by the length of the rotor blades. As also the metallic legs  11  of the tower are distributed along a distance of 12 meters (about 39.4 ft) between their central longitudinal axes  16 , the turbulence caused by the tower is small, which allows its use also to downwind configurations. This setting is more critical in the tower like monopoles in steel or concrete. 
     The use of rotor downwind brings numerous advantages to the turbine. In this condition the drag and centrifugal force helps reduce the moment at the blade root by approximately 50%, thereby reducing by 50% the weight of the blades and the hub. Thus it is less weight to be balanced in the nacelle. By having a lower moment of inertia, the azimuth control system is lighter and lower cost. These and other advantages lead to reduced final weight atop the tower in 30 to 40%. Less weight on top implies higher natural frequencies, further improving the performance of tower in steel and reinforced concrete. Consequently, by these surprising effects, a significantly more economical tower is obtained, as it is summarized in the TABLE III, as depicted in  FIG. 21 . 
     Further, in another exemplary embodiment as shown from  FIGS. 23 to 31 , the support platform with inner tubular interface  40  is alternatively substituted or complemented with a yaw mechanism support structure  43  which is also provided to support a wind energy turbine with elongated nacelle  56 , which have a plurality of rotor blades  44  operatively coupled to gearbox  63  and the electric generator  45  by a shaft  65 . 
     The yaw mechanism support structure  43  is formed by a body  46 , an upper surface  47 , a lower surface  48  and a preferentially circular track  49 , defined, also preferentially, close to the perimeter of the upper surface  47  of the yaw mechanism support structure  43 . 
     Additionally, as depicted in  FIG. 23 , a yaw rotating mechanism  50  is coupled to the support platform at a position, preferentially centered within the circular track  49  and extending above the upper surface  47  of the support platform. Thus, the yaw rotating mechanism  50  is configured to rotate about a first axis  51  that is, preferentially, perpendicular to the upper surface of the support platform. Further, the yaw rotation mechanism  50  is coupled to longeron of turbine support platform  52  by mean of a furling mechanism  66 . In addition, a passageway for cables  64  (shown in  FIG. 24 ), for example, power cable, is defined in the yaw rotating mechanism  50 . By keeping cables internal to the axis of yaw rotating mechanism  50  is avoided to get the cables pinched in other parts of the mechanism, thereby avoiding wear on the cables. 
       FIG. 24  shows the longeron of turbine support platform  52  having a first end  53  and a second end  54  spaced apart from the first end by a distance of at least one radius of the circular track  49 , the longeron of turbine support platform  52  being pivotally coupled to the yaw rotating mechanism  50  to allow the longeron of turbine support platform  52  to pivot about a first axis  51  that is substantially perpendicular to the second axis  55  and substantially parallel to the upper surface  47  of the support platform, the longeron of turbine support platform  52  being configured to support at least the weight of the plurality of rotor blades  44  and the electric generator  45  of the wind energy turbine with elongated nacelle  56  mounted thereto. 
       FIGS. 24 to 26  show the interface  61  disposed proximate the second end  54  of the longeron of turbine support platform  52  and between the longeron of turbine support platform  52  and the substantially circular track  49 , the interface  61  being configured to provide for the second end  54  of the longeron of turbine support platform  52  to move along the substantially circular track  49  to provide adequate yaw to the wind direction  60 . Additionally, the interface  61  is provided with a yaw actuator  57  wherein a yaw locking mechanism (not shown) is incorporated. 
     The interface  61  is represented by at least two wheels  58 , preferentially six to transfer turbine loads to the track  49  while the wind turbine is pivoting around the yaw rotating mechanism  50 , according to one embodiment of this invention. Alternatively, the interface  61  may be provided with, for example, a pinion gear and a toothed track. Additionally, the wheels  58  are covered by a dampener element  58   a  provided for absorption of vibration which may be caused the wind  60 . The dampener element  58   a , incorporated into the wheels  58  of the said interface  61 , is, for example, based on an elastomeric material. 
     A second interface  61   a  is provided at the first end  53  of the turbine support platform frame  52 . The second interface  61   a  has the same function and elements of the interface  61  and is symmetrically positioned in relation to the yaw mechanism rotating support  50  to ensure suitable loading distribution of the wind energy turbine elements along the platform as well as to reduce furling rotation which may be caused by the wind force. 
     This design allows ensuring the wind energy turbine  56  with elongated nacelle is producing the maximal amount of electric energy at all times, by keeping the rotor blades  44  in an optimal positioning into the wind as the wind direction changes. Further, the yaw mechanism support structure  43  provides better weight distribution of the load along its second axis  55 , thus reducing an asymmetric load along the structure of the yaw mechanism support structure  43  and the lattice tower  10  which may be caused by the multidirectional flowing of wind. 
       FIGS. 27 to 31  illustrate another exemplary embodiment wherein the shaft  65  is shorter than the exemplary embodiment shown in  FIGS. 22 to 26 . 
       FIG. 31  is a perspective view of one exemplary of a support platform wherein the yaw rotation mechanism  50  is directly coupled to longeron of turbine support platform  52  without using a furling mechanism  66 . 
       FIG. 32  is a plan view of one exemplary of a support platform, representing, for example as the one described in  FIG. 23 or 26 , showing the connection of the yaw support platform atop the lattice tower  10  by bracing members, preferentially, by six bracing members, symmetrically arranged below the lower surface  48  of the yaw support structure  43 . 
     While exemplary embodiments have been particularly shown and described, various changes in form and details may be made therein by a person skilled in the art. Such changes and other equivalents are also intended to be encompassed by the following claims.