Patent Application
20130171002
This disclosure relates to mechanical systems for enhancing operations of wind turbines. More particularly, the disclosure relates to a hybrid wind turbine tower that includes a dual vertical bearing system adapted to permit at least a portion of the tower structure to physically rotate for optimizing wind turbine tower performance.
The rotor blades of a utility scale wind turbine are ideally pitched toward or “yawed” into the wind. This orientation optimizes the amount of wind energy captured by the rotor, and in turn maximizes torque produced on a main shaft of the wind turbine to drive associated electric generators, for example.
Accordingly, the traditional wind turbine tower structure incorporates a rotor, a rotor shaft and bearings, collectively referred to as a turbine, along with a nacelle to support such structure. All are generally situated atop of a fixed tower, and are designed to rotate on the fixed tower structure for the purpose of maintaining the rotor in a position to always directly face the wind.
The typical tower has traditionally been constructed as a nonrotating vertically upstanding structure having a circular cross-section and generally adapted to accommodate wind forces in any given azimuthal direction. As such, traditional tower construction has tended to be relatively robust, requiring more materials than towers that could otherwise employ, for example, aerodynamic configurations that might include an airfoil and other asymmetric cross-sections adapted to rotate or yaw with the rotors and nacelle to face the wind. Such structures might require less robust configurations, utilizing reduced cross-sections to save construction material costs. Construction of such towers might require less strength/thickness in those circumferential tower portions or areas normal to the wind and/or otherwise not subject to direct wind forces.
A major limitation with respect to use of aerodynamic tower structures may have historically been related to difficulties of designing bearings adapted to accommodate the relatively high bending moments typically present near the bottoms or bases of tower structures.
This disclosure proposes a wind turbine tower that incorporates a dual bearing system below the rotor swept portion of the tower, rather than providing the traditional single yaw bearing situated atop of the tower.
In one aspect of the disclosure, the dual bearing system accommodates rotation of an upper portion of the tower, along with the turbine and the nacelle.
Another aspect of the disclosure is the provision of a hybrid tower structure, with an upper rotatable tower portion thereof having a relatively smaller cross-section in a direction normal to wind forces than that of a traditional tower.
In yet another aspect of the disclosure, a dual yaw bearing system incorporates a pair of axially spaced ring bearings having preloaded angular contact rollers.
In yet a further aspect of the disclosure, a dual yaw bearing system permits an asymmetric upper rotatable portion of the tower to yaw in response to wind forces, while providing a lower circular cross-sectioned tower portion that remains fixed to a base or a ground-secured foundation.
In a still further aspect of the disclosure, an upper portion of the tower at least coincident with the rotor swept area may be rotatably yawed into the wind, with the base portion of the tower remaining fixed.
Referring initially to
The blades 16, 18, 20 (only three of which are depicted in this example; there may be more or less) may be rotated by wind energy, such that the rotor 14 may transfer that energy via a main shaft (not shown) to one or more generators (not shown). Those skilled in the art will appreciate that such wind-power driven generators may produce commercial electric power for transmission to an electric grid (not shown). Those skilled in the art will also appreciate that a plurality of such wind turbines may be effectively employed on a so-called wind turbine farm to generate significant amounts of electric power. Although the disclosed embodiment focuses on wind only, this disclosure is pertinent to fluids generally, including other gases and even liquids such as water, which may be used to drive similar turbine structures.
The tower 12 of this disclosure may be described as a hybrid tower in that it includes two distinct portions: an upper tower portion 22 that may be rotatably yawed into the wind and a lower stationary base portion 24 adapted to be secured to the ground 30. The base portion 24 is adapted to support the upper rotatable tower portion 22 at an interface 28 situated below the rotor swept area. The rotor swept area of the tower 12 is herein defined as that tower area most adjacent to, and spaced immediately behind, the spinning rotor 14.
Referring now also to
The upper tower portion 22 may be of either a hollow or a solid cross-sectioned structure. A hollow structure may be easier to fabricate, while a solid structure may present an opportunity for use of an even smaller cross-section. Either approach may, in any event, be considered to be within the scope of this disclosure.
In
Upper and lower ring bearings 42, 44 are vertically spaced apart along the tower axis “a-a” to secure a spindle 50 of the rotatable upper tower portion 22. It will be appreciated by those skilled in the art that the spindle portion 50 extends downwardly from, and is integral to, the bottom of the upper tower portion 22. The spindle 50 is rotatably secured within the circular interior of the respective inner races 56 and 60 of upper and lower ring bearings 42 and 44, and for this purpose the upper and lower inner races 56 and 60 are adapted to rotate with the spindle 50.
Those skilled in the art may appreciate that the spindle could, with some design modifications, alternatively extend upwardly from the lower base tower portion 22. Also, as may have been earlier implied with respect to the upper tower portion 22, the spindle 50 may alternatively be either a hollow or a solid member, which may or may not depend on whether the actual tower portion 22 is hollow or solid.
The ring bearings 42 and 44 include outer races 58 and 62, respectively, which are fixedly secured within a vertically oriented cup shaped portion 25 of the fixed tower base portion 24. Between the inner and outer races of both upper and lower bearings are situated a plurality of circumferentially spaced contact rollers 54, each mounted on a single spindle (not shown), each preloaded in an angular orientation with respect to the tower axis a-a for optimizing stability.
As depicted, the angular orientation of the contact rollers 54 in the upper bearing ring 42 is inverse to the angular orientation of the rollers 54 in the lower bearing ring 44. The inverse angular orientation of the respective sets of rollers 54 presents a design believed to offer a robust, laterally stable bearing system that may be adapted to accommodate significant asymmetrical wind forces against the yawing upper tower portion 22. Those skilled in the art may appreciate that the respective angular orientations of the sets of rollers 54 may alternatively be reversed; i.e. with the roller orientation as displayed in bearing ring 42 being utilized in place of that of the ring 44, and vice versa.
An optional annular bearing spacer (not shown) may be placed within the annular space 46 between the upper and lower ring bearings 42, 44 to reinforce the anchoring and securement of the bearing rings within the tower base portion 24. In addition, optional vertical load support bearings 52 may also be employed at the bottom of the fixed tower base portion to offer an enhanced axial support for the spindle.
Finally, although only the application of roller bearings has been described in reference to the disclosed structure, other bearing types and configurations may fall within the spirit and scope of this disclosure.
The present disclosure generally sets forth a mechanical system that may enhance the utility of wind towers by making them more cost efficient. A reduction in capital costs, due to reduction in raw material usage as required to fabricate upper sections of a wind turbine tower, may be achieved by designing the rotor swept portion of the tower to be rotatable, and to incorporate an aerodynamic or otherwise asymmetric tower cross-section that requires less materials than would a standard traditional circular cross-section.
The disclosure offers a wind turbine tower that incorporates a dual ring bearing and spindle shaft arrangement positioned below the rotor swept portion of the tower, rather than incorporating a single unitary tower structure having a single yawed bearing at the top of the tower. Replacement of the traditional single yaw bearing in this manner, and supporting rotation of the upper portion of the tower structure, permits both the wind turbine and the nacelle structures to rotate with the upper tower portion. As such, wind alignment of the tower with nacelle and turbine structures can be assured, permitting the tower to be constructed with smaller cross-sections in directions normal to the wind forces.
