Wind turbines for converting wind energy to electrical power have been known and applied for many years, but have found a dramatically increased application as an alternative energy source during the last couple of decades. With this renewed interest in wind power, wind turbine designs have seen significant advancements that, in turn, have allowed wind turbines to significantly increase in size and weight. By way of example, modern wind turbines may have rotors approaching 100 to 150 meters in diameter. Additionally, the weight of, for example, three wind turbine blades may be as high as 40 to 50 tons. Consequently, the assembly of wind turbines has presented some challenges for manufacturers. These challenges are not only due to the increased size and weight of the wind turbine components, but also due to shifting from traditional mounting locations to more extreme, difficult-to-access areas, such as mountainous areas and offshore sites.
One conventional technique for assembling a wind turbine includes transporting the different components to the construction site; assembling the tower sections that collectively form the tower; lifting the nacelle with a crane and mounting the nacelle on top of the tower; assembling the wind turbine rotor on the ground; and lifting the wind turbine rotor with the crane and mounting the rotor to the low-speed shaft extending from the nacelle. Depending on the particular size of the wind turbine, particular location, or other factors, the assembly process may be suitably modified. For example, the rotor hub may be coupled to the nacelle prior to mounting the nacelle on the tower, and the blades individually lifted with the crane and mounted to the hub. Those of ordinary skill in the art may recognize alternative combinations for assembling the wind turbine.
No matter which of the multiple conventional techniques utilized to assemble the wind turbine, aspects of the assembly process typically include lifting relatively large, heavy components with a crane to a height that is a significant distance off the ground, such as adjacent the top of the tower. One consideration with such an assembly step is directed to adequately and safely controlling the component during the lift. For example, during assembly, it may be important to control the orientation of the component so as to be able to mount the component to the wind turbine (e.g., nacelle, rotor hub, blade, etc.). Additionally, it may be desirable to control the component to prevent or minimize damage thereto during the lift, such as might occur by contacting the tower, the crane, or other nearby objects.
In this regard, conventional approaches for controlling the component during the lift include coupling a number of tag lines (e.g., long ropes) to the component. More particularly, one end of each tag line is coupled to the component being lifted by the crane. The length of the tag lines is such so as to position another end thereof adjacent the ground or other support surface, such as, for example, a boat or platform for offshore installations. Assembly workers on the ground or support surface then grab the tag lines and manually manipulate or control the movements of the components during the lift and installation of the component. Depending on the particular size of the wind turbine, there may be several such tag lines for controlling the various components during assembly.
The increasing size of wind turbines has made the use of manually-operated tag lines to control the orientation of wind turbine components more challenging. First, even with multiple tag lines, the orientation of the component being lifted by the crane is difficult to control. One reason is that when the component is lifted so as to be adjacent the top of the tower, the tag lines may be nearly perpendicular to the horizontal plane in which rotational control of the component is desired. As the inclination angle between the horizontal plane of the component being lifted by a crane and the tag line increases, the ability to control the orientation of the component within that horizontal plane generally decreases.
Moreover, when the wind turbine component is adjacent the top of the tower, the control point for the tag line, such as the point on the ground, boat, platform, etc. on which the assembly worker stands to grab the tag line, is at its maximum distance from the component. When using tag lines to control the component being lifted by a crane, control of the load is generally inversely proportional to the distance between the control point and the load. Thus, when using tag lines, control of the wind turbine component is generally minimized when the need to control the component is generally at its maximum (e.g., when the component is near the top of the tower).
The limited ability of manually-controlled tag lines to control the wind turbine component during lift results in a need that nearly ideal weather conditions have to be present for assembly to occur. Thus, for example, as it currently stands with the conventional tag line technique, assembly will only be attempted when wind speeds do not exceed a certain threshold, such as, for example, 12 m/s. In some environments, the number of days having such conditions may be limited, and the occurrence of these ideal-condition days is often unpredictable. The inability to assemble wind turbines in a wider range of environmental conditions presents logistical issues related to the scheduling of personnel and equipment necessary for the installation.
In addition to the above, conventional tag line techniques typically require a relatively large number of personnel on the ground to facilitate control of the wind turbine component during a crane lift. Additionally, conventional tag line techniques often result in control of the component being dispersed among several different people, (e.g., crane operator, tag line personnel) all needing the ability to effectively communicate to successfully achieve assembly. Such decentralized control may result in increased assembly time and assembly costs.
Thus, while conventional tag line control techniques are generally successful for their intended purpose, there remains a need for improved apparatus and methodologies for enhancing the control of wind turbine components during assembly thereof.