U.S. patent application number 12/826988 was filed with the patent office on 2011-06-16 for tower with tensioning cables.
This patent application is currently assigned to General Electric Company. Invention is credited to Bharat Sampathkumaran Bagepalli, Colwyn Mark Oscar Sayers.
Application Number | 20110138704 12/826988 |
Document ID | / |
Family ID | 44141350 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110138704 |
Kind Code |
A1 |
Bagepalli; Bharat Sampathkumaran ;
et al. |
June 16, 2011 |
TOWER WITH TENSIONING CABLES
Abstract
A tower, which may be used for a wind turbine, is provided. The
tower includes at least one concrete tower section having a
plurality of tensioning cables. The tensioning cables are
configured to induce a compressive force on the concrete tower
section. The tensioning cables are spaced from an exterior surface
of the concrete tower section by a substantially uniform
distance.
Inventors: |
Bagepalli; Bharat
Sampathkumaran; (Niskayuna, NY) ; Sayers; Colwyn Mark
Oscar; (Greenville, SC) |
Assignee: |
General Electric Company
|
Family ID: |
44141350 |
Appl. No.: |
12/826988 |
Filed: |
June 30, 2010 |
Current U.S.
Class: |
52/147 ;
52/151 |
Current CPC
Class: |
E04H 12/12 20130101;
Y02E 10/728 20130101; Y02E 10/72 20130101; E04H 12/16 20130101 |
Class at
Publication: |
52/147 ;
52/151 |
International
Class: |
E04H 12/20 20060101
E04H012/20 |
Claims
1. A tower comprising: at least one concrete tower section having a
plurality of tensioning cables, the plurality of tensioning cables
configured to induce a compressive force on the at least one
concrete tower section; wherein each of the plurality of tensioning
cables are spaced from an exterior surface of the at least one
concrete tower section by a substantially uniform distance.
2. The tower of claim 1, further comprising: at least one anchor
plate attached to a top portion of the at least one concrete tower
section; wherein each of the plurality of tensioning cables are
attached to the at least one anchor plate.
3. The tower of claim 2, wherein each of the plurality of
tensioning cables are attached to a foundation of the tower.
4. The tower of claim 1, further comprising: one or more upper
tower sections; an adapter section located between the at least one
concrete tower section and the one or more upper tower sections; at
least one anchor plate attached to at least one of the one or more
upper tower sections; wherein each of the plurality of tensioning
cables are attached to the at least one anchor plate.
5. The tower of claim 4, wherein each of the plurality of
tensioning cables are attached to a foundation of the tower.
6. The tower of claim 1, further comprising: at least one upper
tower section attached to the at least one concrete tower
section.
7. The tower of claim 6, wherein the at least one upper tower
section is comprised of rolled steel.
8. The tower of claim 1, the at least one concrete tower section
further comprising: a plurality of grooves disposed in an exterior
surface of the at least one concrete tower section; wherein each of
the plurality of tensioning cables are contained substantially
within each of the plurality of grooves.
9. The tower of claim 8, further comprising: at least one cover
configured to be attached to the tower; wherein the plurality of
tensioning cables within the plurality of grooves are substantially
covered by the at least one cover.
10. The tower of claim 1, wherein each of the plurality of
tensioning cables are configured to be closer to a top exterior
surface of the at least one concrete tower section than to a bottom
exterior surface of the at least one concrete tower section.
11. A wind turbine tower, comprising: at least one concrete tower
section having a plurality of tensioning cables, the plurality of
tensioning cables configured to induce a compressive force on the
at least one concrete tower section; wherein each of the plurality
of tensioning cables are spaced from an exterior surface of the at
least one concrete tower section by a substantially uniform
distance.
12. The wind turbine tower of claim 11, further comprising: at
least one anchor plate attached to a top portion of the at least
one concrete tower section; wherein each of the plurality of
tensioning cables are attached to the at least one anchor
plate.
13. The wind turbine tower of claim 12, wherein each of the
plurality of tensioning cables are also attached to a foundation of
the wind turbine tower.
14. The wind turbine tower of claim 11, further comprising: one or
more upper tower sections; an adapter section located between the
at least one concrete tower section and the one or more upper tower
sections; at least one anchor plate attached to at least one of the
one or more upper tower sections; wherein each of the plurality of
tensioning cables are attached to the at least one anchor
plate.
15. The wind turbine tower of claim 14, wherein each of the
plurality of tensioning cables are attached to a foundation of the
wind turbine tower.
16. The wind turbine tower of claim 11, further comprising: at
least one upper tower section attached to the at least one concrete
tower section.
17. The wind turbine tower of claim 16, wherein at least one upper
tower section is comprised of rolled steel.
18. The wind turbine tower of claim 11, the at least one concrete
tower section further comprising: a plurality of grooves disposed
in an exterior surface of the at least one concrete tower section;
wherein each of the plurality of tensioning cables are contained
substantially within the plurality of grooves.
19. The wind turbine tower of claim 18, further comprising: at
least one cover configured to be attached to the wind turbine
tower; wherein the plurality of tensioning cables within the
plurality of grooves are covered by the at least one cover.
20. The wind turbine tower of claim 11, wherein each of the
plurality of tensioning cables are configured to be closer to a top
exterior surface of the at least one concrete tower section than to
a bottom exterior surface of the at least one concrete tower
section.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to towers. In particular,
but not limited thereto, the present invention relates to wind
turbine towers having tensioning cables.
[0002] 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.
[0003] 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.
[0004] Several technical installations require a tower or a mast to
which the installation is mounted. Non-limiting examples of such
installations are wind turbines, antenna towers used in
broadcasting or mobile telecommunication, pylons used in bridge
work, or power poles. Typically, the tower is made of steel and
must be connected to a foundation made of reinforced concrete. In
these cases, the typical technical solution is to provide a large,
solid reinforced concrete foundation at the bottom of the tower. In
typical applications the tower foundation extends about 12 meters
below the ground level, and can be about 18 meters or more in
diameter.
[0005] In larger utility grade wind turbines (e.g., 2.5 MW or more)
it is often desired to have towers with heights of 80 meters or
more. The higher hub heights provided by larger towers enable the
wind turbine's rotor to exist in higher mean wind speed areas, and
this results in increased energy production. Increases in tower
height invariably have lead to corresponding increases in the mass,
length and diameter of the tower. However, it becomes difficult to
construct and transport large wind turbine towers as the local
transportation infrastructure (e.g., roads, bridges, vehicles,
etc.) often impose limits on the length, weight and diameter of
tower components.
BRIEF DESCRIPTION OF THE INVENTION
[0006] According to one aspect of the present invention, a tower is
provided. The tower includes at least one concrete tower section
having a plurality of tensioning cables. The tensioning cables are
configured to induce a compressive force on the concrete tower
section. The tensioning cables are spaced from an exterior surface
of the concrete tower section by a substantially uniform
distance.
[0007] According to another aspect of the present invention, a wind
turbine tower is provided. The tower includes at least one concrete
tower section having a plurality of tensioning cables. The
tensioning cables are configured to induce a compressive force on
the concrete tower section. The tensioning cables are spaced from
an exterior surface of the concrete tower section by a
substantially uniform distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 illustrates a wind turbine to which the aspects of
the present invention can be applied;
[0009] FIG. 2 illustrates a side view of a wind turbine and wind
turbine tower, according to an aspect of the present invention;
[0010] FIG. 3 illustrates a side view of a concrete tower section,
according to an aspect of the present invention;
[0011] FIG. 4 illustrates a cut-away, perspective view of a portion
of a wind turbine tower, according to an aspect of the present
invention;
[0012] FIG. 5 illustrates a side view of a wind turbine tower,
according to an aspect of the present invention;
[0013] FIG. 6 illustrates a side view of a concrete tower section
incorporating grooves in the outer wall thereof, according to an
aspect of the present invention;
[0014] FIG. 7 illustrates a top view of a concrete tower section,
according to an aspect of the present invention;
[0015] FIG. 8 illustrates a top view of a concrete tower section
having a cover, according to an aspect of the present
invention;
[0016] FIG. 9 illustrates a partial perspective view of a portion
of a concrete tower section with the cover as shown in FIG. 8,
according to an aspect of the present invention
DETAILED DESCRIPTION OF THE INVENTION
[0017] Reference will now be made in detail to the various aspects
of the invention, one or more examples of which are illustrated in
the figures. Each example is provided by way of explanation of the
invention, and is not meant as a limitation of the invention. For
example, features illustrated or described as part of one aspect
can be used on or in conjunction with other aspects to yield yet a
further aspect. It is intended that the present invention includes
such modifications and variations.
[0018] FIG. 1 shows a wind turbine to which the aspects of the
present invention can be advantageously applied. However, it should
be understood that the present invention is not limited or
restricted to wind turbines but can also be applied to tower
structures used in other technical fields. In particular, the
various aspects of the present invention may also be applied to
antenna towers used in broadcasting or mobile telecommunication or
to pylons used in bridge work. Therefore, although the aspects of
the invention will be exemplified with reference to a wind turbine,
the scope of the present invention shall not be limited
thereto.
[0019] The wind turbine 100 shown in FIG. 1 comprises a tower 110
bearing a nacelle 120 on its top end. A rotor including a rotor hub
130 and rotor blades 140 is attached to one side of the nacelle
120. The tower 110 is mounted on a foundation 150. The tower may be
formed of rolled steel and have multiple stacked sections 112
(e.g., about three or four main sections). Alternatively, the tower
120 may be formed of a truss-like structure and/or may have a
cylindrical or tapered profile. Typically, the tower foundation 150
is made of a solid mass of reinforced concrete.
[0020] It would be advantageous to increase tower height in order
to capture more energy due to higher mean wind speeds. An aspect of
the present invention provides a tower or tower section fabricated
from concrete. A concrete base section can be used to elevate a
conventional rolled-steel tower, or the entire tower can be formed
of concrete. Concrete is defined as a mixture of aggregates and
binder or any suitable masonry support. As one non-limiting example
only, the aggregates may be sand and gravel or crushed stone, and
the binder may be water and cement.
[0021] While concrete is strong in compression, it is weak in
tension. Steel is strong under forces of tension, so combining the
two elements results in the creation of very strong concrete
components. In conventional reinforced concrete, the high tensile
strength of steel is combined with concrete's great compressive
strength to form a structural material that is strong in both
compression and tension. The principle behind prestressed concrete
is that compressive stresses induced by high-strength steel tendons
in a concrete member before loads are applied will balance the
tensile stresses imposed in the member during service.
[0022] Compressive stresses can be induced in prestressed concrete
either by pretensioning or post-tensioning the steel reinforcement.
In pretensioning, the steel is stretched before the concrete is
placed. High-strength steel tendons or cables are placed between
two abutments and stretched to a portion of their ultimate
strength. Concrete is poured into molds around the tendons/cables
and allowed to cure. Once the concrete reaches the required
strength, the stretching forces are released. As the steel reacts
to regain its original length, the tensile stresses are translated
into a compressive stress in the concrete.
[0023] In post-tensioning, the steel or cable is stretched after
the concrete hardens. Concrete is cast in the desired shape first.
Once the concrete has hardened to the required strength, the steel
tendons or cables are attached and stretched against the ends of
the unit and anchored off externally, placing the concrete into
compression. According to an aspect of the present invention,
post-tensioned concrete is used for wind turbine towers or wind
turbine tower sections.
[0024] FIG. 2 illustrates a wind turbine tower, in a partially
exploded view, according to an aspect of the present invention. The
wind turbine 200 includes a tower 210 which may include one or more
sections 112. The tower sections 112 may be formed of rolled steel.
A concrete tower section 215 is located at the bottom of the tower
and supports the upper sections 112. The concrete tower section 215
includes concrete walls 260 which may be formed in one or more
sections and have a tapered (as shown) or cylindrical shape.
Alternatively, the tower sections 210 and/or 215 can have any
desired cross-section, such as but not limited to, oval,
rectangular, polygonal, etc. One or more anchor plates 270 are
secured to the top of the concrete walls 260. The anchor plates 270
can extend radially outward past the upper outer edge of walls 260.
A plurality of tensioning cables 280 are secured at one end to the
anchor plates 270, and at the other end to foundation 250.
[0025] The tensioning cables 280 are located circumferentially
around and external to the concrete walls 260, and are positioned
close to and at a substantially uniform distance from an outer or
exterior surface of concrete walls 260. The term "substantially
uniform" can be defined as having approximately the same, or having
a slightly varying distance (e.g., a slight taper). In other words,
the tensioning cables 280 can be parallel to or nearly parallel to
the outer surface of concrete walls 260. As one non-limiting
example only, the tensioning cables 280 may be spaced from an
exterior surface of a top portion of concrete wall 260 by about two
inches, whereas the cables 280 may be spaced from an exterior
surface of a bottom portion of concrete wall 260 by about six
inches. The cables 280 can be of the post-tensioned type, and they
apply a compressive force to concrete walls 260. The use of
external cables results in a larger moment arm and lower cable
forces, and eventually, smaller cables would be required when
compared to using the cables internal to the concrete segments. In
other aspects of the invention, the tensioning cables 280 are
positioned close to an exterior surface of concrete walls 260, but
may be configured to have a slightly increasing or slightly
decreasing distance from the exterior surface of concrete walls
260.
[0026] During operation of the wind turbine 200, wind flows in the
direction indicated by arrow 202. The force of the wind creates a
load on the wind turbine and tower. The up-wind side of the tower
(i.e., the left side of the tower as shown in FIG. 2) would be
under tension, while the down-wind side of the tower (i.e., the
right side of the tower as shown in FIG. 2) would be under
compression. As discussed previously, concrete performs very well
under compression. However, concrete does not perform as well under
tension. The tensioning cables 280 help to counteract the wind
caused forces of tension on the tower section 215.
[0027] One advantage provided by the present invention is the
reduction of the effective moment-arm on tower section 215. By
positioning the tensioning cables 280 close to and external to the
exterior surface of concrete walls 280 the tower 210, 215 reduces
its effective moment-arm to provide resistance to wind loads. This
invention moves the cables outside, but in close proximity to the
tower walls. For example, a very small diameter tower having
internal cables would need thicker walls and thicker cables to
counteract the forces applied by the wind, when compared to a
larger diameter tower having external cables. The larger diameter
tower could be made with thinner concrete walls and have smaller
diameter cables when compared to the very small diameter tower.
[0028] FIG. 3 illustrates a side view of concrete tower section
215. Tensioning cables 280 are affixed at one end to anchor
plate(s) 270, and at the other end to foundation 250. The anchor
plate 270 is attached (e.g., by bolts or fasteners) to the top of
the concrete tower 260, and a portion of the anchor plate 270
protrudes outboard beyond the outer diameter of the top of concrete
tower 260. The tensioning cables 280 are attached to the anchor
plate 270 at the overhanging portion of the anchor plate. The
anchor plate 270 can be made in multiple segments (e.g., three or
four sections) that substantially cover the top of concrete walls
260. The anchor plate 270 may also have holes (not shown) through
which the flange attachment bolts are embedded into the concrete
wall 260. These can be used to attach the upper potion of the
concrete wall 260 to conventional steel tube tower sections 112. At
the bottom end, the cables are secured/attached into the
foundation.
[0029] FIG. 4 illustrates a partial perspective view of a portion
of a wind turbine tower according to an aspect of the present
invention. An optional adapter section 405 may be used between a
concrete tower section 260 and an upper tower section 112. In one
example, the adapter section could be formed of concrete and/or
steel, and the upper tower section 112 may be formed of rolled
steel. The anchor plate 270 acts as an attachment point for
tensioning cables 280 and the flange 113 of upper tower section
112. The flange can be attached to the anchor plate 270 with any
suitable fastening arrangement (e.g., a nut, washer and bolt
system). The tensioning cables 280 may also be attached to the
anchor plate in a similar fashion and may have threaded ends
designed to accept a washer and nut.
[0030] FIG. 5 illustrates a side view of a wind turbine tower 500
having multiple concrete tower sections 260, 361, 362. The second
concrete tower section 361 is attached via anchor plate 270 or via
a flange (not shown) to bottom section 260. Tensioning cables 381
are placed circumferentially around the exterior surface of
concrete tower section 361, and are attached to anchor plates 270
and 371. The third concrete tower section 362 is attached via
anchor plate 371 or via a flange (not shown) to second concrete
tower section 361. Tensioning cables 382 are placed
circumferentially around the exterior surface of concrete tower
section 362, and are attached to anchor plate 371 and anchor plate
372. Alternatively, the individual tensioning cables 280, 381, 382
may be replaced by ling individual cables running from the
foundation 250 to the top anchor plate 372. As discussed
previously, upper concrete tower sections 361 and 362 could be
replaced with one or more steel tower sections. The upper steel
tower sections would not require the tensioning cables 381 and
382.
[0031] In another aspect of the present invention, FIG. 6
illustrates a side view of a concrete tower section 615 having
external grooves 690 in which the tensioning cables 680 can reside.
This configuration helps to center the cable loads in the body of
the concrete wall 660, thus ensuring a more uniform compressive
load in the concrete wall 660. This configuration may also reduce
the occurrence of tensile loads in the concrete wall 660.
[0032] FIG. 7 illustrates a view from the top down of concrete
tower section 615. The concrete wall 660 and the grooves 690 formed
therein are shown in phantom. The anchor plate 670 can be
configured to overhang the outer portions of concrete wall 660 or
the anchor plate 670 may have its outer diameter aligned (as shown)
or approximately flush with the outer diameter of wall 660. The
anchor plate 670 can be attached to concrete wall 660 via bolts 672
or any other suitable fastener or fastener arrangement.
[0033] FIG. 8 illustrates a top down view of another aspect of the
present invention. A removable, non-structural or semi-structural
cover 810 can be incorporated on the outside of the concrete tower
section 615, covering both the tensioning cables 680 and the
concrete wall 660. The cover 810 can be made of plastic, composite,
sheet metal or any other suitable fabric or material. The cover 810
may be comprised of one or more sections, and may have one or more
seams. The seams could be arranged vertically, horizontally and/or
any direction therebetween. The cover 810 can also provide
protection (e.g., from the weather, vandalism, etc.) for the
tensioning cables 680 and or the concrete wall 660. FIG. 9
illustrates a partial perspective view of the concrete tower
section 615 during installation of cover 810.
[0034] The grooves 690 in concrete wall 660 provide several
advantages, a few of which are, (1) protecting the external
tensioning cables 680 (even more so with cover 810), (2) keeps the
cables 680 away from view (i.e., reduces visual impact), (3) allows
for easy maintenance of the cables 680 by facilitating external
access, and (4) centers the compressive load on the concrete (due
to the post-tensioned cables 680) in the body of the concrete wall
660.
[0035] 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.
* * * * *