This invention relates generally to the servicing of apparatus in elevated locations. The methods and apparatus are particularly useful for servicing wind turbine generators, and more particularly to methods and apparatus that assist in the removal replacement of gearboxes in wind turbine generators without requiring the removal of blades from the wind turbine generator. However, the methods and apparatus described herein are not limited to servicing of wind turbines, and can be used to replace various types of objects on horizontal shafts in elevated locations.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted within a housing or nacelle positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators. In many wind turbine configurations, these generators are rotationally coupled to the rotor through a gearbox. The gearbox is or can be used to step up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy. The electrical energy so produced is fed into a utility grid.
Although they are built to be quite reliable, gearboxes are mechanical devices that experience wear while in use. Also, even though gearboxes are mounted in a housing or nacelle and thus are protected from direct exposure to the elements, gearboxes can indirectly experience stress from extreme environmental conditions because of their coupling to large rotors. Thus, it will come as no surprise that gearboxes in wind turbines require occasional replacement.
In at least one known method for replacing a gearbox in a wind turbine, a crane is required to lift the gearbox out of an open nacelle. However, removing the gearbox also removes the object holding the end of the main shaft in place. In a typical wind turbine in a wind farm, a large rotor is fastened to the other end of the main shaft. This rotor has several long, heavy blades attached to a hub, so to prevent the main shaft from bending or the rotor from becoming tilted, the blades have to be removed from the rotor before the gearbox is removed. The sheer size of the wind turbines makes servicing difficult and expensive, as at the 65 to 80 meter height of some wind turbines used in generator farms, a large crane is required. Two cranes are required in some cases, because the entire rotor set must be removed in some cases and brought to the ground. A second crane is used to grab the bottom blade of the rotor and to “tail it out,” i.e., make it flat in the air so that it can be set on the ground.
In some present wind turbine designs, the secondary bearing is the gearbox. A rotor having a mass of 76,000 pounds (34,466 Kg) produces an upward lift of about 56,000 pounds (25,400 Kg) at the gearbox.
Thus, known methods of replacement or servicing of a gearbox in a wind turbine are expensive and labor-intensive.