Low cost rail-transportable wind turbine tower

Abstract

A wind turbine tower is provided that will accommodate rail transport of wind turbine sections. The wind turbine tower includes a plurality of axial tubular sections, wherein the sections including an outer diameter no greater than a designated maximum diameter; a main structural element for each of the axial tubular sections, with the structural element being of a generally cylindrical shape; and corner reinforcements for the main structural elements. The corner reinforcements are provided generally equidistant around the circumference of the main structural element about 90 degrees apart. Corner supports may further be provided to support the corner reinforcements from a foundation of the wind turbine tower. With the corner reinforcements attached to the main structural elements, the combination falls within a space envelope that may be accommodated for rail transport.

Description

BACKGROUND OF THE INVENTION

The invention relates generally to wind turbine tower construction and more specifically to a wind tower and its method of construction that permits low cost rail transport of sections for large towers. Additionally, it permits upgrade of existing towers to be able to handle larger turbines.

For many years it has been common practice to build steel wind tower sections separately in a workshop facility and then to move each complete section to the site, where the wind turbine tower installation was performed. The tower sections would typically have a cylindrical or slightly tapered shape, and each of the sections could in turn be divided along axial lines into an adequate number of shells.

Due to the ever-increasing demand for larger capacity towers and consequently larger dimensions of all parts needed to build such towers, a physical limit has been imposed by the infrastructure, e.g. the clearance beneath a bridge or in a tunnel, is reached.

The wind load increases as the square of the wind speed and consequently, the higher the turbine towers are, the stronger should the structure be dimensioned, which in turn means that either the wall thickness should be increased or the diameter extended. It may be advantageous to increase tower diameter than the thickness of the steel plate or other wall material. Increased thickness would mean higher material costs and a requirement for heavier transportation vehicles, whether trucks, trains, ships, or helicopters, while diameters need to be small enough to limit vehicle heights in order to pass under bridges and though tunnels. Also, thicker steel stock is harder to form and fabricate.

In order to permit transport of larger diameters sections to support taller towers with larger top loads, it has been proposed that tower sections be split along vertical lines forming two half-cylindrical shells (WO 2004/083633 by Jensen). Size of the half-cylindrical shells is consistent with maximum dimensions for transportation. Bolted flanges are provided along the axial direction of the half-cylindrical shells, allowing assembly in the field after transport. However, it is desirable to limit assembly in the field due to hostile terrain and severe environmental conditions. Further, the creation of additional joints potentially subjects the tower to additional modes of failure.

FIGS. 1A and 1B, respectively, illustrate maximum space envelopes available for truck and rail transport within the United States. Rail transport is the least expensive mode of transport for large tower sections. An exemplary 80-meter tower comprises 3 tower sections of varying diameter and thickness. The present base and mid-tower sections have a 14.11 ft. maximum diameter. The present top section has an 11.5 ft maximum diameter. The space envelope 10 for transport by truck is about 14+ ft., thus allowing a tubular section 20 of approximately that diameter to fit within the space envelope. The space envelope 40 for transport by rail is up to about 11 ft. to 13 ft. on a side, thus allowing a tubular section 50 of up to that approximate that diameter to fit within the space envelope. The present top section is thus transportable by rail. The present base and mid-tower sections exceed the rail envelope. The base and mid-tower sections must be transported by truck and generally are sized within the truck-shipping envelope of about 14+ ft. Truck and rail transport outside the United States also are constrained by similar considerations of space envelope but with sizes specific to the locale.

Consequently with the lower cost of rail transport, the cost for transporting the top section is about 50% of the cost for transporting the base and mid-tower sections.

Accordingly, there is a need to provide for construction of all tower sections for large wind turbines towers where the section diameters fall within the maximum rail transport diameter, but which yet are strong enough to withstand the loads imposed on the sections.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to an apparatus and method for allowing sections of large wind turbine towers to be transported to a windfarm site by rail transport by construction of the tower sections to fall within an allowable space envelope for rail transport. Additionally, it permits upgrade of existing towers to be able to handle larger turbines.

Briefly in accordance with one aspect of the present invention, a wind turbine tower is provided that will accommodate rail transport of wind turbine sections. The wind turbine tower includes a plurality of axial tubular sections, wherein the sections including an outer diameter no greater than a designated maximum diameter; a main structural element for each of the axial sections, with the structural element being of a generally cylindrical shape; and corner reinforcements for the main structural elements. The corner reinforcements are provided generally equidistant around the circumference of the main structural element and separated by about 90 degrees.

In accordance with another aspect of the present invention, a support system is provided for a previously constructed wind turbine tower including a plurality of axial tubular sections with a main structural element for each of the axial sections, the structural element being of a generally cylindrical shape. The support system includes corner reinforcements for the main structural elements of at least one of the plurality of axial tubular sections. The corner reinforcements are provided generally equidistant around the circumference of the main structural element on the inside surface or the outside surface of the main structural element and the corner reinforcements further may be included within an envelope of a maximum dimension on a side that may be accommodated for rail transport. However, the corner reinforcements for repair, retrofitting or upgrade on existing towers need not be limited in size considerations of fitting into open space in the corners of the shipping envelope, since they are mostly assembled on site.

A method for providing structural support to wind turbine towers to permit the tower sections to fit within a designated space envelope for rail transport is provided. The method includes supplying a plurality of axial tubular sections with the sections including an outer diameter no greater than a designated maximum diameter; shaping a main structural element for each of the plurality of axial tubular sections to be of a generally cylindrical shape; forming corner reinforcements for attachment to the main structural elements for at least one of the plurality of axial tubular section to establish a space envelope for the combination no greater than a specified dimension on a side that may be accommodated for rail transport; and attaching the corner reinforcements for at least one of the main structural elements. The corner reinforcements are attached equidistant around the circumference of the main structural element at each corner. Further, the method includes connecting adjoining ends of corner reinforcements when the corner reinforcements extend to the adjoining The corner reinforcements can be either on the outside, or on the inside of the main structural elements. The corner reinforcements for repair, retrofitting or upgrade on existing towers need not be limited in size considerations of fitting into open space in the corners of the shipping envelope, since they are mostly assembled on site ends of the tubular axial sections.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIGS. 1A and 1B illustrate maximum available space envelopes for transport within the United States;

FIG. 2 illustrates an exemplary inventive wind turbine tower;

FIGS. 3A and 3B illustrate exemplary tower sections with corner reinforcement in the corners;

FIG. 4A illustrates an exemplary arrangement for internal reinforcement of a wind turbine tower;

FIG. 4B illustrates an exemplary arrangement for external reinforcement of a wind turbine tower, during repair, retrofit or upgrade, which need not be restricted to the space envelope for rail transport;

FIG. 5 illustrates an exemplary arrangement for corner supports of a wind turbine tower; and

FIG. 6 illustrates rail transport for tower main structural element of equal length.

DETAILED DESCRIPTION OF THE INVENTION

The following embodiments of the present invention have many advantages, including permitting wind turbine tower sections that have previously required large diameters for structural integrity to incorporate reduced diameters that fall within allowable space envelopes for rail transport. Structural integrity for the axial tubular sections may be provided by corner reinforcements, fitting into available space around the tubular sections, but within the space envelope for rail transport. Further support for the tower structure may be provided by corner supports, attached at one end to the corner reinforcements and at an opposing end to a foundation. Structural integrity for an existing wind turbine tower may also be enhanced by adding corner reinforcements and corner supports, as a repair, upgrade or retrofit.

FIG. 2 illustrates an exemplary inventive wind turbine tower. An wind turbine tower 100 incorporating the invention may include a plurality of axial tubular sections. In the exemplary wind turbine tower three axial tubular sections: a top section 110, a mid-tower section 120 and a base section 130, although the invention may be applied to wind turbine towers with a fewer or a greater number of sections. Such towers may be of a generally cylindrical shape, although a slight taper may be incorporated. The outer diameter 160 of the tower section may be no greater than a designated maximum diameter, that being defined by the maximum space envelope for rail transport. However, in a preferred embodiment of the present invention, each axial tubular section may include a main structural element 135 with a generally cylindrical shape, including a uniform cross-section. The main structural element 135 for each of the axial tubular sections may also include a uniform wall thickness 140. To further enhance transportability, the tower sections may be of equal axial length 145.

The main structural element 135 may be reinforced at the corners with corner reinforcements 150. The corner reinforcements may be provided generally equidistant around the circumference of the main structural element centered about 90 degrees apart. The corner reinforcements may be members preferentially of standard rolled or stamped steel plate sections, but may also include other materials providing support of equivalent strength. Typically, the corner reinforcement 150 is to be attached to the main structural element 135 by welding or other suitable attachment technique at the fabrication plant to avoid welding or additional work at the erection site where weather and terrain creates difficulties. The corner reinforcements 150 may extend axially, either fully or partially along the length of at least one of the plurality of axial tubular sections. Here the corner reinforcements 150 are shown fully extending along the length 145 of the main structural elements 135. If the corner reinforcements 150 are applied to the main structural elements 135 for adjoining axial tubular sections (e.g. base section 130 and mid-tower section 120) and generally axially further extend to meet at adjoining ends 165 of axial tubular sections, the corner reinforcements 150 are structurally connected at the adjoining ends 165. The corner reinforcements 150 may be joined by a bolted connecting piece 155 or by other assembly techniques known in the art. Further, when the corner reinforcements 150 are provided for at least a base section 130, the bottom end 170 of the corner reinforcement 150 for the base section may be attached to a foundation 175 to provide additional strength to the structure. The exemplary corner reinforcement 150 of FIG. 2 is shown with a generally uniform cross-section 198 along its length. However, a tapered corner reinforcement 150 may alternatively be provided (not shown), wherein the cross section or thickness of the corner reinforcement 150 is greater at the bottom than at the top of the reinforcement or for a base section than for a mid-tower section.

Referring again to FIG. 1A, when a structural element 20 of cylindrical shape with an outside diameter equal in length to the side of the square space envelope 10 occupies the space, about 21.5% of the space envelope 10 is unused in the corners 30 and therefore is wasted.

FIGS. 3A and 3B illustrate exemplary designs for the corner reinforcements utilizing available “corner spaces” in a space envelope for rail shipping. Various configurations of the corner reinforcements may be applied to stiffen the structure. The corner reinforcement must be sized to fit within the corner space 320. Among the configurations, V-shaped corner reinforcements 330 or H-shaped corner reinforcements 340 may be provided at each of the corner areas 320 for strengthening. Other cross-sectional shapes are possible (other than V or H). Whatever the shape, the main structural element 350 with the corner reinforcements (320, 330) installed should occupy a space envelope no greater than a specified maximum dimension on a side 365. Further, the space envelope 360 no greater than a maximum dimension on each side must be small enough to be accommodated in rail transport. For the U.S., the maximum dimension that can be accommodated for rail transport is approximately 11 ft. to 13 ft. on a side. For international rail transport, the maximum dimensional side that can be accommodated in rail transport may vary from region to region. Further, the allowable space envelope for both the U.S. and international regions may vary in the future. The scope of this invention may address all such regional variations in maximum side dimension and modifications and changes in such dimensions that may occur in the future.

The V-shapes and the H-shapes and other configurations described above for the corner reinforcements when attached along the axial length of the main structural elements may define an enclosed or semi-enclosed cavity or space 370, 380 that may extend the full length of individual tower sections or may even extend to the highest point of the top section. These cavities may be employed for running electrical, hydraulic and service lines up the tower, as far as up to the nacelle.

The corner reinforcements 150 may be provided by attaching to an outer surface 180 or an inner surface 185 of the main structural element 135. It is preferable to attach the corner reinforcements 150 to the outer surface 180 of the main structural element 135, because such placement maximizes the moment of inertia for the tower. A further advantage provided by the corner reinforcements 150 being placed on the outside surface of the main structural element 135 is to minimize the rigging and packaging when shipping. The large main structural elements 135 standing alone are cylindrical and have a tendency to roll. The corner reinforcements serve as anti-roll devices and would allow for easy anchoring of a tower section with this feature to the rail bed.

FIG. 4A illustrates an arrangement for internal reinforcement of the tower structure. Such placement of the corner reinforcements 150 on the internal surface 185 of the main structural element 135 may be made when other considerations make it undesirable or impossible to place on the outer surface 180. For example, attachment of the corner reinforcements 150 to the exterior of the tower may degrade the graceful smooth shape and aesthetic appearance that could be attributed to a wind turbine tower, possibly making it more difficult to gain public acceptance for site locations. Also (Refer to FIG. 2), for the top section 110 and mid-tower section 120, external corner reinforcements 150 could potentially interfere with wind turbine blade rotation. For these reasons, among others, it may be necessary to employ corner reinforcements internal to the main structural elements.

To provide further support for the tower, in addition to the stiffening provided by the corner reinforcement, corner supports may be provided. The corner supports may include rolled or stamped members. The rolled or stamped members may be constructed from plate steel or other material of equivalent strength. Again Referring to FIG. 2, the corner supports 190 may be attached to the corner reinforcements 150 at a connecting end 191 by bolting or other means known in the art. The base section 130 is subjected to the largest load forces, so it is usually preferable to further support the tower with corner supports 190 for the base section 130. The support end 192 of the corner support 190 may be fixed to the foundation 175. However, it is possible to apply corner supports to more than one axial tubular section of the tower (not shown) when corner reinforcements are provided to the higher sections.

FIG. 5 illustrates the corner support structure for a wind turbine tower. Here, corner reinforcements 151 are provided for the base section 130 and the mid-tower section reinforcements 152 are provided for the mid-tower section 120. Corner supports 190 may be provided for each corner reinforcement for the base section 130. The connecting end 191 of corner supports 190 are attached at the upper end of the corner reinforcements. 151 for the base section 130. The support end 192 of the corner supports 190 are anchored to a foundation 175 for the tower structure. The foundation 175 for anchoring may either be newly installed foundation 193 such as a pile foundations or an existing foundation such as the main foundation 194 for the tower.

A support system may further be provided for an upgrade, repair or retrofit of a previously constructed wind turbine tower where the wind turbine tower includes multiple axial tubular section with a main structural element for the each of the axial tubular sections. Here the structural element may be of a generally cylindrical shape, again recognizing that the structural element may include a taper. The support system may be desired to provide additional structural integrity or to address additional weight from upsizing the wind turbine and nacelle mounted atop the tower.

The support system may include corner reinforcements for the main structural element of at least one of the plurality of axial tubular sections. Refer to FIGS. 2, 3, 4 and 5. The corner reinforcements 150 may be provided generally equidistant around the circumference of the main structural element 135. The corner reinforcements 150 may be attached on either the inner surface 185 or the outer surface 180 of the main structural elements 135. For this retrofit, the corner reinforcements 150 would be installed by welding, bolting or other means known in the art that would take place on site and not in the fabricating facility. Similar to the initial installation application, the corner reinforcements may be applied to one or more of the tower sections (e.g., base 130, mid-tower 120 and top 110) and may extend partially or fully along the length of the main structural element 135. When the corner reinforcements 150 meet at adjoining ends 165 of an axial tubular section, the corner reinforcements 150 for adjoining section (e.g., base 130 and mid-tower 120) may be connected for further stiffening. The support end 192 of corner supports 190 for the base section 130 may be further stiffened by attachment to an existing or newly erected foundation 175. When the wind turbine tower already erected on site such as for a repair, retrofit or upgrade, the main structural elements 135 do not need to be transported. The requirement for transportability in this case is that the corner reinforcements themselves fit within the rail transport space envelope.

Connection for elements of the support system (corner reinforcements to main structural elements, corner reinforcements to corner reinforcements, corner supports to corner reinforcements) may be by bolting, welding or other suitable means, known in the art, for installation in the field.

The support system for an existing tower may further include corner supports for each of the corner reinforcements for at least one of the plurality of axial tubular sections. The corner supports may be connected to the corner reinforcements at one end and to a new or existing foundation for the tower at an opposing end. Further, when providing corner reinforcements for a previously installed wind tower and transport of the tower sections is not of concern, then the utilization of four corner reinforcements centered about 90 degrees around the outer surface is not limiting, so additional corner reinforcements may be provided at other circumferential locations.

FIG. 4B illustrates corner reinforcements in field upgrades, retrofits and repairs of existing wind turbine towers. The corner reinforcements may be external corner reinforcements 410 or internal corner reinforcements 420. The external reinforcements 410 or the internal reinforcements 420 are not transported with the tower sections for an existing tower. Therefore, the requirements for rail transport sizing in repair, upgrade, after-market and retrofit applications is that only the corner reinforcements themselves need be limited within the space envelope 430 for rail transportability. The combination of the main structural element 135 and the corner reinforcement 410 may exceed the space envelope 430.

FIG. 6 illustrates rail transport for tower main structural elements of an exemplary 3 section wind tower. A locomotive 610 with at least 3 railcars 620, 630 and 640 carry tower sections. In the exemplary tower with 3 sections, one section is allocated to each of the railcars. The top section 110, for this example, has a main structural element 650 does not utilize corner reinforcements and satisfies space requirements for rail transport. The main structural element 660 for the mid-tower section 120 and base section 130 are provided with corner reinforcements 150 that in combination fall within the space envelope 670 for rail transport. Each tower section is of substantially equal length 680 that can be accommodated by the length of the railcars 620, 630 and 640. Corner supports 190 may be stored inside one or more of the sections. Further, for U.S. transport, the length of railcar is limited to about 89 feet. Rail transport outside the U.S. also are constrained by similar considerations of length, but with sizes specific to the locale.

The invention further includes a method for providing structural support to wind turbine towers to permit the tower sections to fit within a designated space envelope for rail transport. The method includes supplying a plurality of axial tubular sections, with the sections having an outer diameter no greater than a designated maximum diameter. A main structural element for each of the plurality of axial tubular sections is shaped to be of a generally cylindrical shape. Corner reinforcements are formed for attachment to the main structural elements for at least one of the plurality of axial tubular section to establish a space envelope for the combination no greater than a specified dimension on a side that may be accommodated for rail transport. The corner reinforcement may extend either partially or fully along the length of the axial tubular section. The corner reinforcements are attached for at least one of the main structural elements, the corner reinforcements being equidistant around the circumference of the main structural element at each corner.

The method further includes attaching the corner reinforcements when the corner reinforcement is supplied for at least a base section to a foundation for the wind tower. Corner supports are provided for each corner reinforcement of at least the base section when the corner reinforcements are provided for at least the base section. Then the method provides for attaching one end of the corner support to the corner reinforcement. The opposing end of the corner support is attached to at least one of a new foundation and an existing foundation for the tower.

Attaching corner reinforcements and corner supports on the outside surface of the main cylindrical element provides greater support for the tower by increasing the moment of inertia. However, outside reinforcement may interfere with aesthetic appearance of the tower, thus providing some incentive to provide reinforcement attached to the inner surface of the main structural element. Interference of the top section and the mid-tower section with rotation of a turbine blade may also require that corner reinforcements be provided inside the main structural element, although such support will be less effective than outside reinforcement.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

1. A wind turbine tower comprising: a plurality of axial tubular sections, the sections including an outer diameter no greater than a designated maximum diameter;a main structural element for each of the axial sections, the structural element being of a generally cylindrical shape; andcorner reinforcements for the main structural elements, the corner reinforcements provided generally equidistant around the circumference of the main structural element and separated by about 90 degrees.

2. The wind turbine tower according to claim 1, wherein the corner reinforcements extend generally axially at least one of partially or fully along a length of at least one of the plurality of axial tubular sections.

3. The wind turbine tower according to claim 2, wherein when the corner reinforcements extending generally axially further extend to meet at adjoining ends of axial tubular sections, the corner reinforcements being structurally connected at the adjoining ends.

4. The wind turbine tower according to claim 2, wherein when at least one of the plurality of axial tubular sections comprise a base section, then the corner reinforcements for the base section further extend into a foundation for the tower.

5. The wind turbine tower according to claim 2, wherein the corner reinforcements are fixed to at least one of an inner surface and an outer surface of the main structural element.

6. The wind turbine tower according to claim 5, the wind turbine tower further comprising: corner supports including a connecting end and a support end, wherein when the corner reinforcements are attached to the main structural element for at least one of the plurality of axial tubular sections then the connecting ends of the corner supports are attached to the corner reinforcements for at least one of the plurality of axial tubular sections.

7. The wind turbine tower according to claim 6, the wind turbine tower further comprising: a foundation wherein when the corner supports are provided to the corner reinforcements for at least one of the plurality of axial tubular sections, the corner supports are anchored at the support end to a foundation for the tower.

8. The wind turbine tower according to claim 7, wherein the foundation for the corner supports comprises: at least one of an existing foundation for the tower and non-existing newly-installed pile foundations.

9. The wind turbine tower according to claim 6, wherein when the corner reinforcements are fixed to an outer surface of the main structural element, then the main structural element with the corner reinforcements installed comprises: a space envelope no greater than a specified maximum dimension on a side.

10. The wind turbine tower according to claim 9, wherein the space envelope no greater than a specified maximum dimension on a side comprises: a space envelope that may be accommodated by rail transport.

11. The wind turbine tower according to claim 6, the corner supports comprise: at least one of rolled members and stamped members.

12. The wind turbine tower according to claim 6, a cavity within the corner reinforcement further comprises: at least one of electrical lines, hydraulic lines and service lines running up the tower.

13. The wind turbine tower according to claim 6, wherein the corner reinforcements further comprise additions to a previously constructed tower following installation.

14. The wind turbine tower according to claim 1, the corner reinforcements comprising: at least one of rolled and stamped members.

15. The wind turbine tower according to claim 1, the sections further comprising: a uniform cylindrical cross-section; anda uniform wall thickness.

16. The wind turbine tower according to claim 1, the axial tubular sections further comprising: equal axial lengths.

17. A support system for a previously constructed wind turbine tower including a plurality of axial tubular sections with a main structural element for each of the axial sections, the structural element being of a generally cylindrical shape; the support system comprising: corner reinforcements for the main structural elements of at least one of the plurality of axial tubular sections, the corner reinforcements provided generally equidistant around the circumference of the main structural element on the inside surface or the outside surface of the main structural element and the corner reinforcements further being included within an envelope of a maximum dimension on a side that may be accommodated for rail transport.

18. The support system for a previously constructed wind turbine tower according to claim 16, further comprising: corner supports for each of the corner reinforcements for at least one of the plurality of axial tubular sections.

19. A method for providing structural support to wind turbine towers to permit the tower sections to fit within a designated space envelope for rail transport, the method comprising: supplying a plurality of axial tubular sections, the sections including an outer diameter no greater than a designated maximum diameter;shaping a main structural element for each of the plurality of axial tubular sections to be of a generally cylindrical shape;forming corner reinforcements for attachment to the main structural element for at least one of the plurality of axial tubular section to establish a space envelope for the combination no greater than a specified dimension on a side that may be accommodated for rail transport; andattaching the corner reinforcements for at least one of the main structural elements, the corner reinforcements being equidistant around the circumference of the main structural element at each corner.

20. The method for providing structural support to wind turbine towers to permit the tower sections to fit within a designated space envelope for rail transport of claim 19, the method further comprising: supplying a corner support for each corner reinforcement when the corner reinforcement is provided for at least one of the plurality of axial tubular sections;attaching a connecting end of the corner support to each corner reinforcement; andattaching a support end of the corner support to at least one of a new foundation and an existing foundation for the tower.