U.S. patent application number 10/587301 was filed with the patent office on 2007-12-27 for tower for a wind turbine, prefabricated metal wall part for use in a tower for a wind turbine and method for constructing a tower for a wind turbine.
This patent application is currently assigned to Corus Staal BV. Invention is credited to Heiko Sportel.
Application Number | 20070294955 10/587301 |
Document ID | / |
Family ID | 34833677 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070294955 |
Kind Code |
A1 |
Sportel; Heiko |
December 27, 2007 |
Tower for a Wind Turbine, Prefabricated Metal Wall Part for Use in
a Tower for a Wind Turbine and Method for Constructing a Tower for
a Wind Turbine
Abstract
A tower for a wind turbine. The tower has an exterior side and
an interior side. The tower is at least partly composed of
prefabricated metal wall parts. Each wall part includes an
essentially quadrangular portion having an outwardly facing surface
in the direction of the exterior of the tower and an inwardly
facing surface in the direction of the interior of the tower. The
portion having a top edge, a bottom edge, a first side edge and a
second side edge. The first side edge is provided with a first
flange along at least part of the length of the first side edge and
the second side edge is provided with a second flange along at
least part of the length of the second side edge. A method for
constructing a tower for a wind turbine.
Inventors: |
Sportel; Heiko; (CE
Uitgeest, NL) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Corus Staal BV
P.O. BOX 10000
Ijmuiden
NL
NL-1970 CA
|
Family ID: |
34833677 |
Appl. No.: |
10/587301 |
Filed: |
January 14, 2005 |
PCT Filed: |
January 14, 2005 |
PCT NO: |
PCT/EP05/00550 |
371 Date: |
June 29, 2007 |
Current U.S.
Class: |
52/40 |
Current CPC
Class: |
F03D 13/10 20160501;
E04H 12/085 20130101; Y02E 10/728 20130101; F05B 2230/60 20130101;
F05B 2240/912 20130101; Y02E 10/72 20130101; Y02P 70/50
20151101 |
Class at
Publication: |
052/040 |
International
Class: |
E04H 12/08 20060101
E04H012/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2004 |
EP |
04075337.8 |
Claims
1. Tower for a wind turbine having an exterior side and an interior
sides, the tower at least partly comprising prefabricated metal
wall parts, wherein each wall part comprises an essentially
quadrangular portion having an outwardly facing surface in the
direction of the exterior of the tower and an inwardly facing
surface in the direction of the interior of the tower, said portion
having a top edge, a bottom edge, a first side edge and a second
side edge, wherein the first side edge is provided with a first
flange along at least part of the length of the first side edges,
and wherein the second side edge is provided with a second flange
along at least part of the length of the second side edge.
2. Tower for the wind turbine according to claim 1, wherein the
first flanges and the second flanges of the prefabricated metal
wall parts extend towards the interior side of the tower.
3. Tower for the wind turbine according to claim wherein each of
the prefabricated metal wall parts have a height and a width, and
wherein at least two of the prefabricated metal wall parts have a
height which is at least about 2.5 times larger than the width of
the bottom edge.
4. Tower for the wind turbine according to claim 1, wherein the
first flange of a said prefabricated metal wall part is attached to
the second flange of an adjacent said prefabricated metal wall part
by fastening means.
5. Tower for the wind turbine according to claim 1, wherein the
essentially quadrangular portion of the prefabricated metal wall
parts is essentially rectangular wherein the length of the first
side edge is approximately equal to the length of the second side
edge and wherein the bottom edge is approximately equal to the
length of the top edge, or wherein the essentially quadrangular
portion of the prefabricated metal wall parts is essentially
trapezial wherein the length of the first side edge is
approximately equal to the length of the second side edge and
wherein the bottom edge is longer than the top edge.
6. Tower for the wind turbine according to claim 1 wherein the
tower has an essentially annular, horizontal cross-section.
7. Tower for the wind turbine according to claim 1, wherein the
essentially quadrangular portion of the respective prefabricated
metal wall parts are curved.
8. Tower for the wind turbine according to claim 1, wherein the
essentially quadrangular portion of the respective prefabricated
metal wall part is essentially flat.
9. Tower for the wind turbine according to claim 1, wherein the
first flange is provided with an additional first flange and/or
wherein the second flange is provided with an additional second
flange.
10. Tower for the wind turbine according to claim 1, wherein the
first flanges and/or the second flanges are at least partly folded
back towards the inwardly facing surface of the essentially
quadrangular portion of the prefabricated metal wall part for at
least partly doubling the thickness of the first flanges and/or
second flanges.
11. Tower for the wind turbine according to claim 1, wherein the
prefabricated metal wall parts are steel parts.
12. Tower for the wind turbine according to claim 1, wherein the
first flange of at least one said prefabricated metal wall part is
vertically staggeredly attached to the second flange of an adjacent
said prefabricated metal wall part by fastening means.
13. Tower for the wind turbine according to claim 1, wherein the
circumference of the tower consists of n adjacently positioned
prefabricated metal wall parts, wherein the angle between the first
flange and the second flange is 360/n.
14. Tower for the wind turbine according to claim 1, wherein the
tower is provided with stiffening means.
15. Prefabricated metal wall parts for use in a tower for a wind
turbine at least partly composed of a plurality of said
prefabricated metal wall parts, comprising: an essentially
quadrangular portion having an outwardly facing surface and an
inwardly facing surface, said portion having a top edge, a bottom
edge, a first side edge and a second side edge, wherein the first
side edge is provided with a first flange along at least part of
the length of the first side edge, and wherein the second side edge
is provided with a second flange along at least part of the length
of the second side edge.
16. Method for constructing a tower for a wind turbine according to
claim 1 at least partly composed of said prefabricated metal wall
parts, comprising attaching one said prefabricated metal wall part
to an adjacent said prefabricated wall part.
17. Tower for the wind turbine according to claim 1, wherein each
of the prefabricated metal wall parts have a height and a width,
and wherein at least two of the prefabricated metal wall parts have
a height which is more than five times larger than the width of the
bottom edge.
18. Tower for the wind turbine according to claim 1, wherein each
of the prefabricated metal wall parts have a height and a width,
and wherein at least two of the prefabricated metal wall parts have
a height which is more than ten times larger than the width of the
bottom edge.
19. Tower for the wind turbine according to claim 1, wherein the
first flange of a said prefabricated metal wall part is attached to
the second flange of an said adjacent prefabricated metal wall part
by fastening means comprising nuts and bolts.
20. Tower for the wind turbine according to claim 1, wherein the
tower has an essentially circular horizontal cross-section.
21. Tower for the wind turbine according to claim 1, wherein the
essentially quadrangular portion of the respective prefabricated
metal wall part is essentially flat, and wherein the essentially
quadrangular portion of the respective prefabricated metal wall
part also comprises at least one kink essentially in the direction
between the bottom edge and the top edge of the prefabricated metal
wall part.
22. Tower for the wind turbine according to claim 1, wherein the
prefabricated metal wall parts are high strength steel parts.
23. Tower for the wind turbine according to claim 1, wherein the
first flange of at least one said prefabricated metal wall part is
vertically staggeredly attached to the second flange of an adjacent
said prefabricated metal wall part by fastening means, wherein more
than half of the adjacently positioned prefabricated metal wall
parts are attached vertically staggeredly.
24. Tower for the wind turbine according to claim 1, wherein the
tower is provided with stiffening means comprising one or more
stiffening rings.
25. Tower for the wind turbine according to claim 1, wherein the
tower is provided with stiffening means comprising one or more
substantially horizontal stiffening rings.
Description
[0001] This invention relates to a tower for a wind turbine which
has an exterior side and an interior side and which tower is at
least partly composed of prefabricated metal wall parts. The
invention also relates to a prefabricated metal wall part for use
in a tower for a wind turbine. The invention further relates to a
method for constructing a tower for a wind turbine which has an
exterior side and an interior side and wherein the tower is at
least partly composed of prefabricated metal wall parts.
[0002] An ongoing trend in the wind turbine market is the
increasing power of the wind turbine in conjunction with increasing
tower heights. Larger wind turbines imply an increase in size,
weight and loads acting on the tower of the wind turbine. This
requires the towers to be stronger and stiffer, and consequently
lead to bigger tower dimensions.
[0003] Conventional tubular steel towers for wind turbines of 2 MW
and above require very large tower diameters and/or large wall
thickness to take the large static and fatigue loads which are
exerted on the wind turbine. These large towers are usually
constructed by prefabricating a number of tower sections from metal
plate by welding curved plates together, often referred to as
"cans", and transporting these sections to the site where the tower
is to be erected. These sections or cans are bolted to the
foundation of the tower and to each other using curved L-type
flanges requiring a large number of large bolts. The increasing
power of the wind turbines also require the flanges to be produced
with an increasing accuracy as to flatness. For land transport, the
diameter of the tower section is the main restriction. A diameter
of about 4.3 m is usually the upper limit that can be transported
to most locations in view of fly-overs etc., and the weight of the
section imposes its limits as well.
[0004] In use, the forces exerted on the top of the tower by the
rotor-turbine assembly determine the load, i.e. the bending moments
at all essentially horizontal flange connections and welds. The
ultimate strength is determined by the yield strength of the bolts
and by the buckling strength of the tubular metal wall. For the
fatigue strength the welds are critical. During service, it is very
difficult to inspect the quality of a weld. Also, on-site repairs
are awkward.
[0005] Apart from the strength, the dynamic behaviour of the tower
is another determining factor. The turbine would be severely
damaged if it were to operate at its natural resonance frequency.
CONFIRMATION COPY
[0006] It is known to increase natural frequency and/or the
strength and/or stiffness of a wind turbine by increasing the
thickness of the metal plate and/or the diameter of the tower.
However, transport problems due to size and weight of the tower
sections make this solution impractical. Also lattice towers have
been used to increase the stiffness of towers for wind turbines.
However, lattice towers require a very large number (>2000) of
individual parts, significant amounts of maintenance and are
considered visually unattractive. Moreover, the dynamic behaviour
of such towers is not adequate for large towers. Guyed towers have
also been used for wind turbines. These towers are guyed with steel
cables at about half the height of the tower. Obviously, this poses
a design problem as the cables may not come into contact with the
rotor of the wind turbine. Moreover, the costs of the foundations
for the cables and the cables itself (with diameters of about 100
mm) are high. Also the cables need to have high fatigue
strength.
[0007] Hybrid towers, such as towers with concrete walls, poured
between an inner and outer steel shell have also been proposed. The
problem is to assure the quality of the wall, once it has been
poured. When constructing a tower for a wind turbine using
prefabricated concrete elements, tension means are required to keep
the concrete wall under compressive forces. Moreover, concrete
towers are not an economical solution.
[0008] It is the object of this invention to provide a tower for a
wind turbine which provides a large stiffness. It is another object
of this invention to provide a tower for a wind turbine which
provides sufficient strength to enable application of high power
generators on top of the tower. It is still another object of this
invention to provide a tower for a wind turbine which does not
cause the aforementioned transport problems, even for very large
towers and/or towers with a wide base.
[0009] According to a first aspect of the invention, one or more of
these objects can be reached by a tower for a wind turbine wherein
the tower has an exterior side and an interior side and wherein the
tower is at least partly composed of prefabricated metal wall parts
wherein each wall part comprises an essentially quadrangular
portion having an outwardly facing surface in the direction of the
exterior of the tower and an inwardly facing surface in the
direction of the interior of the tower, said portion having a top
edge, a bottom edge, a first side edge and a second side edge,
wherein the first side edge is provided with a first flange along
at least part of the length of the first side edge and wherein the
second side edge is provided with a second flange along at least
part of the length of the second side edge. By using the
prefabricated metal wall parts according to the invention, the
stiffness of the construction is increased by the presence of the
flanges of the prefabricated metal wall parts, which act as a rib.
By using prefabricated metal wall parts, the transport of complete
tower sections is no longer required, thus solving the transport
problem. The prefabricated metal wall parts are easy to transport
with ordinary transport means such as trucks. Also, by using the
prefabricated parts, the size of the tower at the foundation is no
longer limited by the transport restrictions and a wider base can
be used. It also allows construction of higher towers because the
size of the base is no longer an issue. The wider base results in a
lower local pressure on the foundation, thus enabling to use a
simpler foundation. The wider base also contributes to the
stiffness of the tower, thereby enabling to use high power
generators on top of the tower. In an embodiment of the invention
the tower is substantially composed of prefabricated metal wall
parts. The tower according to this embodiment relies on
prefabricated metal wall parts as the load bearing elements, and
are readily distinguishable from concrete towers, where a wall part
serves as a mould for the concrete to be poured in and where, after
setting, the concrete serves as the main load bearing material. It
should be noted that the tower according to the invention does not
comprise concrete as a load bearing material at the location of the
prefabricated metal wall parts. It should also be noted that it is
possible to construct a tower according to the invention on top of
a concrete foundation or base wherein the concrete base extends
upwardly, the base forming the lower part of the tower, and a tower
according to the invention forming the upper part of the tower.
[0010] In an embodiment of the invention the first flanges and the
second flanges of the prefabricated metal wall parts extend towards
the interior side of the tower This enables to produce a tower
where the rib, formed by the adjacent flanges, is located on the
inside of the tower, leaving a smooth exterior appearance. A smooth
exterior leads to a reduced impact of wind force on the tower and a
smooth exterior is considered to be visually more attractive.
[0011] In an embodiment of the invention, the prefabricated metal
wall parts having a height and a width, at least two of the
prefabricated metal wall parts have a height which is about 2.5
times larger than the width of the bottom edge, preferably more
than five times larger, more preferably more than 10 times larger.
It should be noted that the height of the prefabricated metal wall
parts is to be understood to be the distance between the bottom
edge and the top edge of the prefabricated metal wall parts when
present in the tower. It should be understood that the length
direction is defined in the direction of the height of the tower.
This means that the tower comprises prefabricated metal wall parts
which are considerably higher than wide, thus resulting in long
side edges of the essentially quadrangular portion of the
prefabricated metal wall parts and thereby enabling long flanges
being provided at least partly on the side edge thereof. These long
flanges enable a large stiffening potential of the tower.
[0012] In an embodiment of the invention the first flange of a
prefabricated metal wall part is attached to the second flange of
an adjacent second prefabricated metal wall part by fastening
means. The flanges are now fixedly connected, thereby increasing
the stiffening potential because of the double thickness of the
rib. Fastening means comprise for instance a weld or a rivet. In a
preferred embodiment of the invention, the fastening means comprise
nuts and bolts. This enables to fasten quickly the first and second
flange of two adjacent panels to each other. The holes required for
the bolts to be inserted into may already be present in the
prefabricated metal wall parts or may be drilled at the site where
the connection between the adjacent panels is made. The use of nuts
and bolts also enables to temporarily undo the connection, for
instance to remove a prefabricated metal wall part from the
construction, or to replace a prefabricated metal wall part. It
also allows easy on-site and/or off-site inspection.
[0013] In an embodiment of the invention the essentially
quadrangular portion of the prefabricated metal wall parts is
preferably orthogonal or trapezial wherein the length of the first
side edge is approximately equal to the length of the second side
edge and wherein the bottom edge is longer than the top edge. In
case of constructing an essentially cylindrical tower, the use of
orthogonal prefabricated metal wall parts is called for, in case of
constructing a conical tower, trapezial prefabricated metal wall
parts are called for. Conical towers enable to construct a tower
with a large base and become slimmer with increasing height of the
tower. Tapering can be over the entire height of the tower or over
part of the length of the tower. The latter can also be achieved by
using prefabricated metal wall parts to form essentially
cylindrical tower sections and by using prefabricated metal wall
parts to form essentially conical tower sections and combine these
tower sections into one tower.
[0014] Kinked prefabricated metal wall parts may be used in the
upper levels of a conically tapered tower or tower section for a
wind turbine wherein the lower levels are made using prefabricated
metal wall parts with an essentially flat quadrangular portion,
thus reducing the number of prefabricated metal wall parts required
for a full ring. One prefabricated metal wall part with one kink in
the essentially quadrangular portion in a given upper level ring
will link up with two prefabricated metal wall parts which have an
essentially flat quadrangular portion in the ring immediately below
the upper level ring. In case the kinked prefabricated metal wall
parts contains more kinks, it may link up with a corresponding
number of prefabricated metal wall parts with an essentially flat
quadrangular portion. It will be clear that kinked prefabricated
metal wall parts in a lower level can also be combined with kinked
prefabricated metal wall parts in the upper level.
[0015] In an embodiment of the invention the tower has an
essentially annular, preferably essentially circular horizontal
cross-section. An essentially annular horizontal cross section is
also obtained if a polygonal horizontal cross section is taken with
a large number of facets such as a pentagon or hexagon.
[0016] In an embodiment of the invention the essentially
quadrangular portion of the prefabricated metal wall parts are
curved with a radius corresponding to the radius of the tower at
the position of the location of the prefabricated metal wall part.
This allows constructing a tower with a smooth curvature, and in
case the first and second flanges extend towards the interior side
of the tower, the exterior of the tower will be smooth. In another
embodiment of the invention the quadrangular portion of the first
prefabricated metal wall parts is essentially flat. The use of an
essentially flat quadrangular portion has the advantage that there
is no need for a locally dependent curvature in the quadrangular
portion and is therefore easier to produce. It is also more
convenient during transport of the prefabricated metal wall parts.
The application of such prefabricated metal wall parts causes the
exterior of the tower to be polygonal. In still another embodiment
the essentially flat quadrangular prefabricated metal wall parts
also comprises at least one kink essentially in the direction
between the bottom edge and the top edge of the prefabricated metal
wall part. The kink (or kinks) therefore runs in the direction of
the height of the tower. With the kink (or kinks) a higher buckling
stiffness of the prefabricated metal wall part is obtained. It may
also increases the number of facets of the polygonal thereby
achieving a smoother exterior of the tower.
[0017] The invention is also embodied in a tower for a wind turbine
as described hereinabove wherein the first flange is provided with
an additional first flange along at least part of the length of the
first flange and/or wherein the second flange is provided with an
additional second flange along at least part of the length of the
second flange. This is advantageous for instance for a further
increase in stiffening the tower, particularly when the first
flange and second flange are both provided with an additional
flange, wherein the first flange with its respective additional
flange preferably essentially forms an L-shape and/or wherein the
second flange with its respective additional flange preferably
essentially forms an L-shape. For the purpose of this application,
these additional flanges on the first and/or second flanges may be
used to attach objects thereto such as stairs, or internal
floors.
[0018] The invention is also embodied in a tower for a wind turbine
as described hereinabove wherein the first and/or second flanges
are at least partly folded back towards the inwardly facing surface
of the essentially quadrangular portion of the prefabricated metal
wall part, thereby effectively doubling the thickness of the
flanges. This doubling of the flanges causes an additional
stiffening of the construction. It will be clear to the skilled
person that the flange could also be folded back twice or more
contributing to the stiffening effect.
[0019] In an embodiment of the invention the prefabricated metal
wall parts are steel parts, preferably high strength steel parts,
for instance having a yield strength of about 355 MPa or higher.
The use of steel enables to use prefabricated metal wall parts of a
small thickness, which reduces the weight of the tower. The use of
high strength steel prefabricated metal wall parts enables a
further reduction in weight of the tower. As a result, the
foundation of the tower can be constructed more efficient.
[0020] In an embodiment of the invention the first flange of a
first prefabricated metal wall part is vertically staggeredly
attached to the second flange of an adjacent second prefabricated
metal wall part by fastening means. This application of
prefabricated metal wall parts by a stretching bond type connection
of the flanges of two adjacent prefabricated metal wall parts also
requires the application of prefabricated metal wall parts of
different lengths, at least in the first and last ring of the tower
or tower section. The application of this staggered connection has
the advantage over constructing the tower from rings of connected
non-staggeredly connected prefabricated metal wall parts that the
forces are lead through the construction without having to be led
through horizontal flanges which connect the aforementioned rings.
The overlap at the edges between the staggeredly connected
prefabricated metal wall parts is between 1:2 and 1:4, preferably
about 1:3, meaning that about 1/2 to 3/4, preferably about 2/3 of
the respective side edges of adjacent prefabricated metal wall
parts overlap.
[0021] In another embodiment of the invention the circumference of
the tower consists of n adjacently positioned prefabricated metal
wall parts, wherein the angle between the first flange and the
second flange is 360/n.
[0022] According to a second aspect of the invention, the
prefabricated metal wall part for use in a tower for a wind turbine
as described hereinabove is characterised in that the prefabricated
metal wall part comprises an essentially quadrangular portion
having an outwardly facing surface and an inwardly facing surface,
said portion having a top edge, a bottom edge, a first side edge
and a second side edge, wherein the first side edge is provided
with a first flange along at least part of the length of the first
side edge and wherein the second side edge is provided with a
second flange along at least part of the length of the second side
edge.
[0023] According to a third aspect of the invention, a method is
provided for constructing a tower for a wind turbine as described
hereinabove, wherein the tower is at least partly composed of
prefabricated metal wall parts as described hereinabove.
[0024] When constructing a tower according to the invention, there
is no need for a high capacity crane to lift the tower sections on
top of each other at the site where the tower is constructed. A
relatively small building crane will be adequate to lift one
prefabricated metal wall parts at a time, except in the case tower
complete tower sections are built from the prefabricated metal wall
parts which are then hoisted upon the foundation or the tower
section already present. In that case a more powerful crane is
required.
[0025] The absence of horizontal welds in the towers according to
the invention eliminates a known source of fatigue failure, thereby
allowing to relieve design restrictions for instance by allowing to
use thinner gauge metal plate. The locations where a bottom edge of
a first prefabricated metal wall part touches a top edge of a
prefabricated metal wall part which is located immediately below
the first prefabricated metal wall part can be sealed by using
sealing means, for instance a sealant. This prevents the outside
atmosphere to enter the structure and prevents corrosion. The
locations where the first flange of a prefabricated metal wall part
is connected to the second flange of the adjacent prefabricated
metal wall part can, if so desired, also be sealed using sealing
means, such as a sealant.
[0026] In an embodiment of the invention the tower is provided with
stiffening means, such as one or more preferably substantially
horizontal stiffening rings. These stiffening means are preferably
provided in the interior of the tower to absorb the horizontal
forces exerted on the tower. These stiffening means may be provided
at different heights of the tower. The prefabricated metal wall
parts are connected to the ring, thereby obtaining an increased
stiffness of the tower. Additional connecting struts may be used to
connect the prefabricated metal wall parts to the ring. The
stiffening means may also be formed by internal floors, or the
stiffening means, such as a stiffening ring along internal
circumference of the tower, may provide the base for the internal
floor or floors. The stiffening means may also contribute to the
even distribution of forces and loads over the entire circumference
of the tower.
[0027] The prefabricated metal wall parts can be produced for
example from hot-rolled metal using commonly known technology. The
hot-rolled metal may be plate material or coiled material. This
material, after optional leveling can be cut to the desired
dimensions and shape, and the flanges can be formed on the edges of
the essentially quadrangular portion of the prefabricated metal
wall parts using conventional bending techniques. The optional
curvature of the essentially quadrangular portion of the
prefabricated metal wall parts or the kink or kinks can likewise be
easily introduced. The prefabricated metal wall parts may be coated
prior to use in the tower e.g. with zinc and/or an organic coating
to extend the service life and to reduce maintenance.
[0028] The prefabricated metal wall parts may also comprise
additional built-in functionality such as a door for entering the
interior of the tower. Internal structures like stairs and floors
can be easily installed.
[0029] The present invention will now be further explained by the
following non-limitative drawings and examples.
[0030] In these drawings:
[0031] FIG. 1 is a schematic representation of a wind turbine;
[0032] FIG. 2 is a schematic representation of a tower for a wind
turbine according to the state of the art (not to scale);
[0033] FIG. 3 is a schematic representation of towers for a wind
turbine according to the invention (not to scale);
[0034] FIG. 4 is a schematic representation of a prefabricated
metal wall parts according to the invention (not to scale);
[0035] FIG. 5 is a schematic cross-section of the first ring of a
tower for a wind turbine also highlighting a schematic
representation of the bolted connection;
[0036] FIG. 6 is a schematic representation of an L-shaped
flange.
[0037] FIG. 7 is a schematic representation of the tower
construction at the location of a stiffening ring.
[0038] In FIG. 1 a schematic representation of a wind turbine 1 is
shown. The wind turbine 1 comprises a generator 2, a rotor 3 and a
tower 4 onto which the combination of the generator and the rotor
is mounted. The tower 4 has an exterior surface which forms the
outside of the tower 4 and an interior surface which forms the
inside of the tower. The tower consists of four tower sections
4a-4d. The wind turbine is placed on a foundation 19.
[0039] In FIG. 2 a tower 4 for a wind turbine according to the
state of the art is shown. Tower segments 4a, 4b, 4c and 4d are
mounted on top of each other. These tower segments are made
off-site and connected through horizontal flanges and large bolts
and nuts. These flanges are indicated schematically by the thick
horizontal lines between the tower sections. The tower segments are
made from curved plates which are welded together horizontally and
vertically. These welds, indicated with the dashed lines, are known
to be a possible source of fatigue failure, particularly the
horizontal welds. For a tower of about 80 m high, a base of about
4.3 m and a top diameter of about 2.3 m is commonly used. The
dimension of the base is limited by transport limitations.
[0040] In FIG. 3a a tower 4 for a wind turbine according to the
invention is shown, wherein the staggered prefabricated metal wall
parts each stagger over about half the length of the neighbouring
prefabricated metal wall part and FIG. 3b shows a tower wherein the
staggered prefabricated metal wall parts each stagger over about a
third of the length of the neighbouring prefabricated metal wall
part. The base of the tower is about 6.5 m in diameter whereas the
top of the tower has a diameter of about 2.3 m. The 6.5 m base
diameter poses no transport problems because it can be transported
to the building site in pieces. The increase in width of the base
of the tower increases the stiffness of the tower. It also enables
to construct higher towers width adequate stiffness to install high
power wind turbines.
[0041] FIG. 4a shows an embodiment of a prefabricated metal wall
part 5 according to the invention for use in a tower 4 for a wind
turbine 1 as described hereinabove. The prefabricated metal wall
part 5 is characterised in that the wall part comprises an
essentially quadrangular portion 6 having an outwardly facing
surface 7 facing the exterior of the tower and an inwardly facing
surface 8 facing the interior of the tower, said portion having a
top edge 9, a bottom edge 10, a first side edge 11 and a second
side edge 12, wherein the first side edge 11 is provided with a
first flange 13 along at least part of the length of the first side
edge 11 and wherein the second side edge 12 is provided with a
second flange 14 along at least part of the length of the second
side edge 12. The first flange 13 is provided with an additional
first flange 15 which essentially forms an L-shape with the first
flange 13 and the second flange 14 is provided with an additional
second flange 16 which essentially forms an L-shape with the second
flange 14. The prefabricated metal wall parts are not drawn to
scale. The cross section A-A is shown in FIG. 4b. Typical
dimensions for such a prefabricated metal wall parts for the lower
ring of a conical tower or tower segment would be a width at the
top edge 9 of between about 0.60 and 1.00 m, for example about 0.86
m, a width at the bottom edge 10 of between about 1.30 and 0.70 m,
for example about 1.04 m, a height of between about 10 and 20
meters, for example 20 meters, and a height of the extending first
flange 13 and second flange 14 of between 0.10 and 0.20 m, for
example about 0.15 m. A typical thickness of the prefabricated
metal wall parts would be between 8 and 16 mm, for example about 12
mm.
[0042] In FIG. 5a a schematic cross section of the first ring of a
tower for a wind turbine is shown. The essentially circular
cross-section of the tower in this example is composed of eighteen
prefabricated metal wall parts 5. The exterior of the tower is
indicated by 4', the interior of the tower is indicated by 4''. In
this embodiment of the invention, the first flange of each
prefabricated metal wall parts is attached to the second flange of
the adjacent prefabricated metal wall parts by bolts and nuts which
are passed through holes in the first and second flange. FIG. 5b
shows a part of the first ring with the prefabricated metal wall
parts 5 and the nuts and bolts 17.
[0043] In FIG. 6 a schematic representation is shown of the
L-shaped flange 18 which can be used to attach prefabricated metal
wall parts of the first ring to the foundation 19 of the tower, or
to the top ring on which the generator is attached.
[0044] In FIG. 7 a schematic representation of part of the tower
construction at the location of a stiffening ring is shown. The
adjacent, staggeredly connected prefabricated metal wall parts are
connected using an overlap at the edges (i.e. in a stretcher-bond
type connection) of 1:3 and are also connected to the stiffening
ring 20 using connecting struts 21. As shown, these connecting
struts 21 are connected to the flanges 13, 14 (see FIG. 4) of the
prefabricated metal wall parts on one side, and to the stiffening
ring 20 on the other side. In FIG. 7 four prefabricated metal wall
parts are shown which are indicated with A, B, C and D. The lower
edge of part A and the upper edge of part B are adjacent. The first
side edge of part A is adjacent and connected to the second side
edge of part C by their adjacent flanges and fastening means (not
shown). The connecting struts 21 extend above and below the
stiffening ring 20, thereby enabling fixedly connecting the side
edges of upper p art A to the side edges of lower part B. Due to
the 1:3 overlap in this example only about 1/3 of the circumference
of the tower has a horizontal seam at or near the location of the
stiffening ring. In the example of FIG. 8 the horizontal seam
between part A and B is located near the stiffening ring 20.
[0045] To construct a tower for a wind turbine according to the
invention it is possible to first form a full ring of the tower by
attaching at least two adjacent prefabricated metal wall parts
along their adjacent flanges. This first full ring can be connected
to an essentially flat and essentially horizontal foundation for
the tower. Of course, the same result is obtained when starting
with a first prefabricated metal wall part which is attached to the
foundation after which a second prefabricated metal wall part is
attached to the first prefabricated metal wall part and the
foundation. Similarly, the following full ring can be constructed
upon the ring already present by first building the entire ring and
subsequently lifting is on top of the ring already present, or by
connecting prefabricated metal wall parts to the ring already
present and to each other one by one, the former procedure
requiring a larger capacity crane than the latter procedure. Rings
are added to the rings already present until the desired height of
the tower is obtained.
[0046] The connection between the first full ring and the
foundation may be achieved by using a flange that is connected to
the foundation. In case of using prefabricated metal wall parts
with an essentially flat or kinked quadrangular portion, the
flanges may be simple L-shaped flanges. In case of using
prefabricated metal wall parts with a curved quadrangular portion,
the flanges should have a corresponding curvature.
[0047] To construct a tower for a wind turbine according to the
invention it is possible to first form a full ring of the tower by
attaching at least two adjacent prefabricated metal wall parts
along their adjacent flanges vertically staggeredly. This implies
the use of prefabricated metal wall parts of different lengths. In
the example of FIG. 3a, full length prefabricated metal wall parts
are combined with prefabricated metal wall parts of half that
length whereas in the example of FIG. 3b, full length prefabricated
metal wall parts are combined with prefabricated metal wall parts
of 2/3 and 1/3 of that length (i.e. an overlap of 1:3). Off course,
it is also possible to stagger the prefabricated metal wall parts
differently than those mentioned in FIG. 3. These embodiments are
also considered to be part of the invention. After the first full
ring has been completed and connected to the foundation, the
remainder of the tower is constructed using essentially full length
prefabricated metal wall parts. In the last full ring prefabricated
metal wall parts of different lengths have to be used to make the
top edge of the last ring level. Of course it is also possible to
use prefabricated metal wall parts of non-full length elsewhere in
the tower if so desired. This staggeredly attaching the
prefabricated metal wall parts provides in a large stiffness of the
tower, without introducing horizontal fully annular or circular
flanges to connect tower sections.
[0048] When constructing a tower according to the invention, the
tower may be constructed top down by starting to construct the top
of the tower whilst being suspended onto a yoke construction, the
yoke construction being provided with lifting means, such as a
hydraulic jack. By first completing a full ring of the tower,
preferably by connecting the prefabricated metal wall parts
staggeredly, only just above ground level, and subsequently lifting
the ring using the yoke and jacks, the following parts can also be
mounted just above ground level. This way, there is no need for
very high cranes during the construction of the tower, and the
construction can be largely performed just above ground level,
where wind forces are usually more moderate than high in the air.
Also, correction of any misalignment is easier to perform. Another
advantage of this top-down or push-up method is that it is more
practical to fit a stiffening ring from below in a tapered
construction and simultaneously using it to align the prefabricated
metal wall parts and to optionally correct any misalignment.
[0049] It is of course to be understood that the present invention
is not in any way limited to the described embodiments and examples
described above, but encompasses any and all embodiments within the
scope of the description and the following claims.
* * * * *