Abstract:
A wind generator having removable change-out bearings includes a rotor and a stator, locking bolts configured to lock the rotor and stator, a removable bearing sub-assembly having at least one shrunk-on bearing installed, and removable mounting bolts configured to engage the bearing sub-assembly and to allow the removable bearing sub-assembly to be removed when the removable mounting bolts are removed.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &amp; DEVELOPMENT 
   The U.S. Government has certain rights in this invention as provided for by the terms of NREL Subcontract No. NREL-ZAM-4-31235-05, Prime Contract DE-AC36-99GO10337 awarded by the Department of Energy. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to generators, and more particularly to wind turbine generators having replaceable bearings. 
   Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient. 
   Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is 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 that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid. 
   Wind turbines including direct drive generators eliminate the gearbox, and reliability problems associated with the gearboxes. However, in at least some known geared wind turbines, both the generator and main bearings may prematurely fail. Because the direct drive generator bearings also function as the main bearings of the wind turbine, a means to readily replace the bearings is needed. To facilitate replacement of such bearings, at least one known direct drive wind turbine utilizes a single large-diameter bearing with a bolt-on flange. However, the combination of the large diameter and bolt-on flange causes the bearing to be expensive in comparison to other known bearing arrangements. 
   To facilitate reducing costs while optimizing turbine availability, bearing replacement should be performed rapidly at the wind turbine site with a minimal infrastructure and skill set required. However, known shrunk-on bearings used in direct drive wind turbines generally require change-out at the factory. 
   BRIEF DESCRIPTION OF THE INVENTION 
   One aspect of the present invention therefore provides a wind generator having removable change-out bearings. The generator includes a rotor and a stator, locking bolts configured to lock the rotor and stator, a removable bearing sub-assembly having at least one shrunk-on bearing installed, and removable mounting bolts configured to engage the bearing sub-assembly and to allow the removable bearing sub-assembly to be removed when the removable mounting bolts are removed. 
   Another aspect of the present invention provides a method for changing bearings in a direct-drive wind generator. The method includes locking a rotor and a stator of the generator, and while the generator is in place on a tower on which it is installed, dismounting a bearing sub-assembly from the generator. The method further includes either replacing or repairing the bearing sub-assembly, or both, and, while the generator is still in place on the tower, assembling the replaced or repaired bearing sub-assembly in the generator. 
   It will thus be observed that configurations of the present invention provide wind turbines with bearings that are easy to remove without having to disassemble the entire wind turbine generator, hub, and blades. Moreover, some configurations of the present invention will also be observed to provide other advantages, such as light weight construction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a drawing of an exemplary configuration of a wind turbine. 
       FIG. 2  is a cut-away perspective view of a nacelle of the exemplary wind turbine configuration shown in  FIG. 1  and including a known geared drivetrain. 
       FIG. 3  is a side cut-away view of a configuration of an exemplary direct drive generator configuration including removable change-out bearings installed. 
       FIG. 4  is a side cut-away view of the configuration shown in  FIG. 3  with its bearing assembly pulled out. 
       FIG. 5  is a side cut-away view of an alternative embodiment of a direct drive generator configuration including removable change-out bearings installed. 
       FIG. 6  is a side cut-away view of the configuration shown in  FIG. 5  with its bearing assembly pulled out. 
       FIG. 7  is a side cut-away schematic view of the configuration shown in  FIG. 6 , showing examples of suitable locations for a removal door or hatch. 
       FIG. 8  is a side cut-away view of an exemplary configuration of a direct drive generator configuration including removable change-out bearings in which a stator sub-assembly or rotor sub-assembly, or both, comprise carbon fiber and/or composite material. 
       FIG. 9  is a side cut-away view of an exemplary configuration of a two-bearing wind generator using carbon fiber and/or composite material. 
       FIG. 10  is a side cut-away view of an exemplary configuration of a single-bearing generator using carbon fiber and/or composite material. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In some configurations and referring to  FIG. 1 , a wind turbine  100  comprises a nacelle  102  housing a generator (not shown in  FIG. 1 ). Nacelle  102  is mounted atop a tall tower  104 , only a portion of which is shown in  FIG. 1 . Wind turbine  100  also comprises a rotor  106  that includes one or more rotor blades  108  attached to a rotating hub  110 . Although wind turbine  100  illustrated in  FIG. 1  includes three rotor blades  108 , there are no specific limits on the number of rotor blades  108  required by the present invention. 
   In some configurations and referring to  FIG. 2 , various components are housed in nacelle  102  atop tower  104  of wind turbine  100 . The height of tower  104  is selected based upon factors and conditions known in the art. In some configurations, one or more microcontrollers within control panel  112  comprise a control system used for overall system monitoring and control. Alternative distributed or centralized control architectures are used in some configurations. 
   In some configurations, a variable blade pitch drive  114  is provided to control the pitch of blades  108  (not shown in  FIG. 2 ) that drive hub  110  as a result of wind. In some configurations, the pitches of blades  108  are individually controlled by blade pitch drive  114 . Hub  110  and blades  108  together comprise wind turbine rotor  106 . 
   The drive train of the wind turbine includes a main rotor shaft  116  (also referred to as a “low speed shaft”) connected to hub  110  via main bearing  130  and (in some configurations), at an opposite end of shaft  116  to a gear box  118 . Gear box  118  drives a high speed shaft of generator  120 . In other configurations, main rotor shaft  116  is coupled directly to generator  120 . The high speed shaft (not identified in  FIG. 2 ) is used to drive generator  120 , which is mounted on main frame  132 . In some configurations, rotor torque is transmitted via coupling  122 . In configurations of the present invention, generator  120  is a direct drive permanent magnet generator. 
   Yaw drive  124  and yaw deck  126  provide a yaw orientation system for wind turbine  100 . A meterological boom  128  provides information for turbine control system  300 , which may include wind direction and/or wind speed. In some configurations, the yaw system is mounted on a flange provided atop tower  104 . 
   In some configurations of the present invention and referring to  FIG. 3 , generator  120  (shown only in part in  FIG. 3  and subsequent figures) is a direct drive generator with permanent magnets  302 . Generator  120  is provided with removable (change-out) bearings  304  installed on a removable bearing sub-assembly  306 . (Configurations can use at least one up to any number of bearings  304 , even though  FIG. 3  shows a configuration using exactly two bearings.) To change or upgrade a bearing  304 , rotor  106  and stator  308  of generator  120  are locked using locking bolts  310  to ensure that stator  308  and rotor  106  remain in place up-tower where generator  120  is installed. Hub  312  and blades  108  are then disassembled on locked generator  120 . Bearing sub-assembly  306  is then dismounted by, for example and referring to  FIG. 4 , removing mounting bolts  314  along two flanges  314 . Alternatively, the entire generator  120  may be lowered to the ground, locking bolts  310  installed, and bearing sub-assembly  306  replaced. 
   In yet other configurations of the present invention and referring to  FIG. 5 , a two-bearing generator  520  is provided with removable bearings  304 . Generator  520  configurations can generally be substituted for, but are otherwise distinguished from generator  120  configurations in that generator  520  configurations do not require removal of hub  312 . (Configurations of generator  520  can use at least one up to any number of bearings  304 , even though  FIG. 5  shows a configuration using exactly two bearings.) Shrunk-on bearings  304  are installed on a removable bearing sub-assembly  506 . To change or upgrade a bearing  304 , rotor  106  and stator  508  are locked using, for example, locking bolts  310 , to ensure that stator  508  and rotor  106  will remain in place up-tower where generator  520  is installed. Bearing subassembly  506  is then dismounted by removing mounting bolts  314  along two flanges  314 . Bearing subassembly  506  can be removed within the tower cabin or nacelle  102  as shown in  FIG. 6  and later lowered to the ground via an exit hatch or door  710 , which are provided, for example, at the top or rear of generator housing  512 , as shown in  FIG. 7 . In some configurations, to ensure that hub  312  and blades  108  are held stably, several turn-buckle locks  514  are inserted either before disengaging bearing subassembly  506 , or simultaneously or shortly thereafter. Turn-buckle locks  514  can be inserted before disengaging bearing subassembly  506  using access ports  516  shown in  FIG. 5 . The use of turn-buckle locks  514  ensures direct load-path from hub  312  and blades  108  into generator housing  512  and tower  104  with bearings  304  removed. Alternatively, the entire generator  520  may be lowered to the ground, locking bolts  310  installed, and bearing sub-assembly  506  replaced. 
   In some configurations of the present invention and referring to an example configuration shown in  FIG. 8 , either stator sub-assembly  800  or rotor sub-assembly  802 , or both, may comprise carbon fiber and/or another suitable composite material. The use of such material or materials results in a low weight wind generator modular unit. Another example of a two-bearing wind generator using carbon fiber and/or composite material is shown in  FIG. 9 , and an example of a single-bearing generator using such material is shown in  FIG. 10 . 
   Further, in some configurations of the present invention and referring again to  FIG. 3 , damping inserts  316  can be provided that isolate hub and blade dynamics and noise from the generator and the tower. 
   Exemplary embodiments of maintenance/assembly methods and apparatus are described above in detail. The methods and the apparatus are not limited to the specific embodiments described herein nor to the specific components being replaced or assembled, but rather, the maintenance/assembly methods described herein may be utilized independently and separately from other methods described herein or to replace other components not described herein. For example, other turbine components can also be replaced using the methods described herein. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.