U.S. patent application number 12/398251 was filed with the patent office on 2009-10-15 for foundation for a wind turbine.
This patent application is currently assigned to GAMESA INNOVATION & TECHNOLOGY, S.L.. Invention is credited to CARLOS LEON PERFECTO.
Application Number | 20090255200 12/398251 |
Document ID | / |
Family ID | 40473929 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090255200 |
Kind Code |
A1 |
LEON PERFECTO; CARLOS |
October 15, 2009 |
FOUNDATION FOR A WIND TURBINE
Abstract
This invention comprises a wind turbine foundation with a hollow
central body in the shape of a truncated cone which has an upper
flange or a pedestal to connect with the tower (not shown), and a
lower slab in the shape of a plane ring. In the preferred
embodiment, the foundation leans the interior surface of the cone
and the lower slab on earth from the local terrain, which takes on
the role of permanent formwork; in an alternative embodiment, the
interior of the foundation is left hollow and accommodates
components of the wind turbine within it; and in a final
alternative embodiment, the foundation is placed over the surface
of the terrain which supports only the base of the lower slab, the
central body not being buried.
Inventors: |
LEON PERFECTO; CARLOS;
(Sarriguren (Navarra), ES) |
Correspondence
Address: |
LADAS & PARRY LLP
26 WEST 61ST STREET
NEW YORK
NY
10023
US
|
Assignee: |
GAMESA INNOVATION & TECHNOLOGY,
S.L.
|
Family ID: |
40473929 |
Appl. No.: |
12/398251 |
Filed: |
March 5, 2009 |
Current U.S.
Class: |
52/298 ;
405/229 |
Current CPC
Class: |
E02D 27/42 20130101 |
Class at
Publication: |
52/298 ;
405/229 |
International
Class: |
E02D 27/42 20060101
E02D027/42 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2008 |
ES |
P200800777 |
Claims
1. Wind turbine foundation with means of attachment to the tower at
its upper part characterized because it consists of a solid of
revolution in the shape of a hollow cone (1) whose interior surface
is seated upon permanent formwork of non-excavated earth in the
shape of a cone, and which has a second solid of revolution in the
shape of a ring (2) at its lower base.
2. Wind turbine foundation in accordance with claim 1 characterized
because the generatrix of the cone (1) is a surface in the shape of
a rhomboid, with two short sides parallel to the horizontal and the
other two longer sides formed preferably by straight lines which
are angled relative to horizontal between 20 and 60.degree.
degrees, and are separated by a distance (e) of 0.25-1.2 m between
them.
3. Wind turbine foundation in accordance with claim 1 characterized
because the lower ring (2) has a radius (R) between 8 and 14 m, a
width (L) between 2.5 and 5 m and a height (c) between 0.25 and 0.6
m.
4. Wind turbine foundation in accordance with claim 1 characterized
because the upper mouth of the cone has a diameter (Dp) between 4
and 12 m.
5. Wind turbine foundation in accordance with claim 1 characterized
because the total height (H) is between 2.5 and 4.5 m.
6. Wind turbine foundation in accordance with claim 1 characterized
because either the two long sides of the generatrix are curves, or
alternatively they are formed by the combination of one long
straight side and one long curved side.
7. Wind turbine foundation in accordance with claim 1 characterized
because alternatively the thickness (e) of the wall of the cone (1)
varies with depth in the direction of the base (2).
8. Wind turbine foundation in accordance with claim 1 characterized
because either the upper and/or lower surface of the ring has an
inclination relative to the horizontal between 0 and 45.degree.,
and/or because alternatively the central body (1) connects with the
interior radius of the ring (2) so that there is no projection into
the interior of the cone (1).
9. Wind turbine foundation in accordance with claim 1 characterized
because alternatively the earth in the hollow interior of the cone
(2) is evacuated and used to house components of the wind turbine
in the resulting free space.
10. Wind turbine foundation in accordance with claim 1
characterized because alternatively the lower plane ring (3) lays
down directly on the surface of the ground.
Description
FIELD OF THE INVENTION
[0001] This invention relates in general terms to a wind turbine
foundation in the shape of a cone, and more particularly a
foundation which comprises a central body in the shape of a
truncated cone over which is found an upper flange or a pedestal
for connecting with the tower and a lower slab in the shape of a
flat ring.
BACKGROUND
[0002] The power generated in a wind turbine is proportional to the
size of the rotor. Therefore, to generate more power, the size of
the blades is increased, and as a consequence there is an increase
in the size of the power train, of the turbine and the height of
the tower. It follows that there must also be an increase in
dimensions of the foundation upon which the wind turbine is
supported, up to the point where a reduction in the material used
in the foundation leads to a considerable reduction in the cost of
the wind turbine unit. To this end the above technique offers a
number of foundation options to meet ever more challenging
requirements and in turn reduce the material used and/or facilitate
installation:
[0003] Publication WO2004101898A2 shows two alternatives for a
circular foundation with prefabricated triangular sections which is
buried, using the earth from the excavation, once installed. The
first design involves 12 prefabricated pieces which are joined
together to form the foundation, and the second variant involves
the union of 10 circular segments, spaced out from each other to
save on material, and a central body.
[0004] Publication DK200100030 considers a star-shaped foundation
with 12 prefabricated triangular sections which are supported on a
base and buried using the earth from the excavation.
[0005] Publication NL1024581 defines a circular variable depth
foundation with radial and tangential reinforcements which are
symmetrical with respect to the central axis.
[0006] Publication EP1074663 is an example of a star-shaped
foundation with three stabilisers placed symmetrically around a
central support, made up of a set of rods in its peripheral
sections.
[0007] Publication U.S. Pat. No. 6,672,023 concerns a foundation
which comprises a cylindrical wall over which rests a circular base
and a pedestal with means of attachment to the tower.
[0008] The wind power industry is ever demanding foundations
optimised for the loads required to support wind turbines, and this
invention is intended to meet that demand.
SUMMARY OF THE INVENTION
[0009] Currently the most commonly used designs for wind turbine
foundations are foundation slabs of various sections (square,
circular, hexagonal, octagonal). More particularly, in the majority
of cases for wind turbines with a power rating below 1 MW square
section foundation slabs have been used since this is a very well
known solution, easy to design and calculate, and further its
simplicity makes formwork and construction easier. However as the
power of wind turbines has increased, the following disadvantages
of this type of square slab foundation have started to manifest
themselves and take on more importance: [0010] The weight is
contributed by the mass of the concrete, in other words, by one of
the most costly parts of the foundation. [0011] Inertia does not
play an important part, since we are concerned with a continuous
section. [0012] A large volume of earth fill is generated which has
to be evacuated, giving rise to an environmental and economic
problem. [0013] It is a solution with low structural efficiency,
which is not well suited to the distribution of stresses. Stresses
in the sections of the foundation reduce with distance from the
centre of the foundation, therefore a smaller section is needed at
the extremities of the foundation.
[0014] As the power of wind turbines increases, typically we see a
scaling up of solutions along with which some alternatives appear
which are not optimal for multimegawatt wind turbines of the type
considered state of the art. Specifically, for wind turbines with
power ratings greater than 2 MW, the foundation designs commonly in
use start to become uncompetitive in comparison with other more
structurally appropriate designs.
[0015] The table below sets out estimates of the foreseeable
progression of the total cost of a square section slab foundation
with increasing wind turbine power, as well as an estimate of the
cost/kW.
TABLE-US-00001 Power Total Cost Cost (MW) ( ) ( /KW) 0.85 25,189
29.6 2 60,173 30.1 4 167,783 41.9 6 259,116 43.2 8 441,960 55.2 10
874,952 87.5
[0016] As it can be seen from the table, the cost of a solid square
footing increases exponentially as higher powered wind turbines are
installed. At the same time the cost/KW of the above-mentioned
footing also increases exponentially, although not as sharply, with
increases in wind turbine power. The trends in this table are easy
to extrapolate to other well-known solutions, which shows that
other designs can be more competitive than the current ones in
relation to multimegawatt wind turbines.
[0017] From the structural point of view, analysing the typology of
the loads at the base of the tower which the wind turbine
foundations have to support, they can be summarised as a bending
moment, which is critical to the calculation, and an axial force in
the direction of the longitudinal axis of the tower. To counteract
these loads there are two alternatives which can be pursued: [0018]
Foundations based on gravity, where it is necessary to use weight,
looking to achieve volume (gravity foundations such as foundation
slabs of various cross sections). [0019] Foundations based on
inertia, where it is necessary to include components which provide
inertia by involving radii or sides (star-shaped foundations,
etc.).
[0020] After analysing the various possible foundation designs for
large wind turbines it has been possible to conclude that the
application of inertia foundation designs could be ideal for
high-power wind turbines (>4 MW) in comparison with scaling up
the gravity foundation solutions in current use.
[0021] The aim of this invention is to provide a wind turbine
foundation with a central body in the shape of a truncated cone
which is formed in concrete over the earth of the terrain, and
which has a lower slab in the shape of a plane ring.
[0022] Another aim of an alternative embodiment of this invention
is to have a wind turbine foundation with a central body in the
shape of a truncated cone whose interior houses the electrical
installations of the wind turbine or other components of the
latter, and which has a lower slab in the shape of a plane
ring.
[0023] And another aim of an alternative embodiment of this
invention is a wind turbine foundation with a central body in the
shape of a truncated cone which has a lower slab in the shape of a
plane ring which sits directly on the surface of a terrain with
great load-bearing capacity, without needing to bury the central
body, in whose interior there can also be housed a series of wind
turbine components.
[0024] One of the advantages of the preferred embodiment of this
invention is the optimisation of the total foundation cost for wind
turbines rated at 2 MW and above in comparison with the state of
the art, due principally to the saving in materials (concrete,
reinforcing steel) relative to conventional foundation designs; the
reduction in the volume of excavation, which reduces the cost of
excavation in addition to achieving a significant reduction in cost
of transport to the waste dump (economical and environmentally
friendly solution); and the reduction and simplification of the
formwork since the local earth itself is used, rather than
evacuated from the central body, as permanent formwork during the
forming in situ of the foundation concrete.
[0025] It must also be highlighted that with the preferred
embodiment there is an increase in the safety margin and the
rigidity of the foundation due to the action of the terrain which
has not been excavated and which remains housed in the hollow of
the cone, absorbing part of the load on the wall of the cone, and
because the earth which is used to bury the cone from the outside
provides increased stability to the structure of the
foundation.
[0026] The following table sets out an estimate of the progression
of the total cost and cost/kW of the hollow cone foundation for
various power ranges. It illustrates a clear reduction in the cost
of foundation with the wind turbines of the order of 2-10 MW
compared with the conventional alternatives mentioned above:
TABLE-US-00002 Power Total Cost Cost (MW) ( ) ( /KW) 0.85 32,693
38.5 2 60,431 30.2 4 131,342 32.8 6 171,137 28.5 8 268,544 33.6 10
457,214 45.7
[0027] Another advantage of this invention is the increase in
stability due to the inertia provided by the diameter of the base
of the cone, compared with the corresponding stability provided by
state of the art foundations having the same mass. Further it
improves the capacity to absorb wind turbine loads since the flow
of stresses is dispersed throughout the length of the walls of the
cone as they travel downwards through the foundation in a smooth
and uniform manner, independently of the orientation of the nacelle
and the directions of the above-mentioned loads: As the nacelle
changes its orientation to match the direction of the wind in order
to optimise the production of energy, the direction of the forces
changes with the rotation of the nacelle.
[0028] Another advantage of this invention is the suitability of
the foundation for different ranges of wind turbine loads and the
different kinds of terrain upon which they can be installed since
the following design elements are easy to modify: [0029] The slope
of the conical surface can be changed to transmit stresses to the
terrain in a different manner. On occasions it may be necessary to
increase the diameter of the base of the cone to reduce the
stresses occurring in the wall of the conical surface. [0030] The
upper part of the conical surface can be used to house different
types of interface with the tower (embedded section of foundation,
post-tensioned bolts, etc.), which on its lower part could be
tubular steel or concrete.
[0031] Another advantage of this invention is the greater
structural efficiency at 80000 KNm and above at the base of the
tower. That is a better relationship between the diameter, the
material and the geometry or the structural configuration, in
comparison with the state of the art as currently published.
[0032] Another advantage of an alternative embodiment, is the
saving in the excavation itself for those terrains whose capacity
for support and properties are such that it is not necessary to
bury the conical foundation considered in this invention so that it
can be used as a base for the tower without the need for additional
foundation. Both this solution and the alternative embodiment,
where the foundation is buried evacuating the earth from the
interior of the cone, enable the foundation to be implemented in a
modular fashion with prefabricated pieces which facilitate
transport and assembly. Once installed, the above-mentioned space
can be used to house the wind turbine's electrical installations or
other components thereby optimising the interior space in the tower
and nacelle.
[0033] Other features and advantages of this invention can be seen
from the following detailed description of an illustrative
implementation which is not limitative in so far as the
accompanying FIGURES are concerned
BRIEF DESCRIPTION OF FIGURES
[0034] FIG. 1 shows a cross section of the foundation as per this
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] With this invention the conical foundation is based on a
conical shape with a lower slab (2) which receives the stresses
from the walls of the cone (1) and transmits them to the ground.
Sometimes a pedestal which is not shown can be used to connect the
foundation to the tower, at the upper part of the cone, or a
concentric ring in the form of a flange to allow access to the
hollow interior of the foundation in the case of other
embodiments.
[0036] In a similar way to inertia foundations, in this case the
inertia is supplied by the radius of the cone at its base, and the
transfer of stresses from the lower part of the tower to the
supporting ground can be achieved smoothly, on being transmitted by
the conical surface.
[0037] There are 2 main variants and one secondary variant of this
design: [0038] The filled conical foundation considered in the
preferred embodiment of this invention. As the earth is not
extracted from the interior, the walls of the conical surface (1)
are supported on the above-mentioned earth, so that smaller
stresses are produced in the walls, since local bending is avoided.
Therefore, the thickness of these walls is optimised and further an
additional saving is achieved in the transport and movement of the
surplus fill earth. [0039] And the hollow conical foundation, where
the fill earth is extracted from the interior of the cone (1). The
walls of the conical surface take greater stresses due to local
bending, so the thickness is increased. The empty space resulting
from the extraction of earth can be used to house electrical
enclosures, transformers and other types of devices or
installations (eg: lifting machinery, etc.). [0040] Additionally we
also consider an embodiment of a wind turbine base with the same
design for use in terrains with a great supporting capacity, in
which the lower slab (2) supports its base directly on the ground
with no need for any excavation. Similarly to the previous case,
the walls of the conical surface are thicker and the radius of the
lower slab (2) is also greater than under the previous
alternatives.
[0041] The main new feature and advance under the preferred
embodiment of this invention lies within the design of a conical
foundation which takes advantage moreover of the earth which is not
extracted for use as permanent formwork while the concrete is
poured in situ. This fact allows the design of the foundation to be
optimised, reducing the quantity of material used and lowering the
cost of foundations, in addition to the advantages referred to in
the preceding section.
[0042] In any instance where the preferred embodiment is not ruled
out, the foundation is made up of a plane ring (2) for the base and
a truncated cone shaped body in the central part (1) which is
formed in concrete on the unexcavated terrain.
[0043] The cross section of the plane ring (2) is preferably
rectangular, but additionally the upper and/or lower side could
have a slight slope between 0 and 45.degree. relative to the
horizontal. The dimensions of the above-mentioned ring can have,
depending on the load and dimensions of the wind turbine, a radius
(R) of up to 18 m, a thickness (L) of up to 6 m, and a height (c)
of up to 1 m. In a preferred embodiment but not ruled out under
this invention, and other than as shown in FIG. 1, the lower ring
(2) is joined to the central conical body (1) in the interior area
of the ring (2) so as not to leave a projection into the interior,
with the aim of facilitating excavation work, formwork and the
pouring of concrete.
[0044] The section of the conical body (1) of the preferred
embodiment, is produced via a generatrix in the form of a rhomboid
with the two short sides parallel to the horizontal at its upper
and lower extremes and the two long sides parallel at an
inclination falling preferably between 20 and 60.degree. with
respect to the horizontal. The thickness (e) defined by the
distance between the above-mentioned long sides of the generatrix
is preferably constant and depending on requirements reaches values
up to 1.4 m. Alternatively, the thickness of the cone can increase
(1) as we approach the lower ring (2). In an alternative to the
preferred embodiment, additionally the above-mentioned long sides
of the generatrix are formed from complex curves with a large
radius of curvature, which produces a foundation in the shape of a
cone with pseudo-spherical walls.
[0045] The total height of the foundation (H) reaches values up to
6 m, and the diameter (Dp) of the upper mouth of the central body
reaches dimensions up to 15 m in diameter depending on the diameter
of the tower and the load from the wind turbine.
[0046] The dimensions of the foundation will vary depending on the
load bearing capacity of the earth and also on the load from the
wind turbine. However, by way of example, for a wind turbine of the
order of 2 to 4 MW the ranges of the principal dimensions are:
[0047] H: between 2.5 and 4.5 m preferably [0048] R: between 8 and
14 m preferably [0049] Dp: between 4 and 12 m preferably [0050] L:
between 2.5 and 5 m preferably [0051] c: between 0.25 and 0.6
preferably [0052] e: between 0.25 and 1.2 m preferably
[0053] Initially the conical foundation design is intended to be
executed in situ with conventional concrete having characteristic
strength between 25 and 35 MPa.
[0054] Alternatively, this design can be carried out using
high-strength concrete, special concrete, fibre reinforced
concrete. Another alternative is provided by prefabricated concrete
components with different qualities of concrete for the different
components (conical surface, lower slab, etc.).
[0055] Within the process of pouring concrete in situ, in the case
of the preferred embodiment with the hollow filled with earth, the
excavation must be carried out taking account of the final volume
of the conical foundation. Once the excavation is carried out, a
layer of mud slab is placed on the ground, and upon that the
previously pre-mounted reinforcements, for subsequent pouring of
concrete. Depending on the slope of the conical surface, it may be
necessary to use formwork.
[0056] In the case where prefabricated components are used we open
up a wider range of shapes for the foundation, since the rhomboid
which characterises the generatrix of the hollow cone (1) can
easily change its long sides to produce pseudo-spherical surfaces
in the walls of the cone (1), or alternatively to combine straight
lines with curves in the two long sides of the generatrix. In this
case, it is also necessary to use cables to pre-tension or
post-tension the above-mentioned prefabricated components in the
axial and/or radial directions of the foundation.
[0057] In the alternative embodiment of the hollow variant, the
concrete pouring for the conical surface (1) requires the use of
interior formwork, which must be suitably underpinned and held
together, either that or make use of prefabricated components for
ease of transport and assembly as described above.
[0058] The calculations for the dimensions and costs of the
foundation as set out above are based on the study of modelling by
finite elements, the quantity of reinforcements and tensile
strength required for the case of the preferred embodiment where
concrete is poured in situ being deduced from a study of the
distribution of stresses in the most unfavorable section nodes in
each model of the wind turbine. In the comparative study between
the various designs, there has also been an analysis of the main
components of cost (blinding concrete, structural concrete,
reinforcements, formwork, earth fill and compaction, excavation and
transport to the waste dump, etc.) to produce the tables shown
above.
* * * * *