IE20090378A1

IE20090378A1 - A mast for a wind turbine

Info

Publication number: IE20090378A1
Application number: IE20090378A
Authority: IE
Inventors: John Gerard Flaherty; John Leslie Jefferson
Original assignee: C & F Tooling Ltd
Priority date: 2009-05-15
Filing date: 2009-05-15
Publication date: 2011-01-05

Abstract

A mast (10) for a wind turbine comprising a hollow elongate member (11), the elongate member (11) being divided into sections (12) along the longitudinal axis thereof, each section (12) being divided into a plurality of elongate subunits (13), with the subunits (13) of each section (12) being arranged about the longitudinal axis of the elongate member (11) and being secured together to form the section (12) and the sections (12)being secured together to form the elongate member (11) such that the fundamental frequency of the mast is less than that of an equivalent one-piece mast. The mast (10) improves the performance of the wind turbine by maintaining a stable support and extends the lifespan of the turbine structure. Possible resonance between the fundamental mast frequency and the frequency of the blades, as they pass in front of the mast (10), is eliminated due to the lowered fundamental frequency of the mast (10) resulting from its segmented construction.

Description

This invention relates to a mast for wind turbines mid, in particular, to a wind turbine mast with improved stability.

Wind turbines are devices which convert the kinetic energy in wind into electricity. They can be separated into two types based on the axis about which the turbine rotates, namely, vertical and horizontal-axis wind turbines.

Vertical-axis wind turbines have the main rotor shaft arranged vertically. The vertical arrangement means that the turbine does not need to be pointed into the wind to be effective. This is an advantage on locations where the wind direction is highly variable and a turbine that can utilise winds from varying directions is required. However, verticalaxis wind turbines have reduced energy efficiency relative to horizontalaxis wind turbines, due to the additional drag as their blades rotate into the wind.

Horizontal-axis wind turbines have the main rotor shaft and electrical generator at the top of a tower or mast, and must be pointed into the wind. Small turbines are positioned by a wind vane, while larger turbines generally use a wind sensor coupled with a servo motor.

Wind turbine masts are known to produces turbulence, thus, the . Turbine blades are made 0903 7g of rigid material to prevent the blades from being bent into the mast by high winds.

Conventional horizontal axis turbines can be divided into three components, namely, the rotor component, the generator component and the structural support mast.

Current wind turbine masts typically are hollow, tubular, one piece structures, which exhibit a natural or fundamental frequency between 1.5 and 3Hz which is in the range of a frequency generated by the turbine.

One problem with current wind turbine masts is the occurrence of a mast “shadow”. This occurs when the wind characteristics on each blade change as it aligns with the mast during rotor rotation. This creates an unbalance which causes vibrations or oscillations that are damaging to bearings, the rotor and generator components.

Such oscillations can result in dangerously high stress and strains on the mast structure if the oscillation frequency matches the fundamental frequency on the mast. If the two frequencies resonate there could be a harmonic excitation / amplification of forces. This can lead to fatigue, crack formation, lifetime reduction and in extreme cases complete structural failure.

Current methods to overcome mast turbulence-associated problems include adding or subtracting mast mass, changing the IE Ο 9 ο 3 7 8 diameter of the masts or changing the degree of tapering of the mast. However, all of these methods have failed to produce satisfactory results.

It is an object of the present invention to overcome the disadvantages of the wind turbine masts hereinbefore described.

Accordingly, the invention provides a mast for a wind turbine comprising a hollow elongate member, the elongate member being divided into sections along the longitudinal axis thereof, each section being divided into a plurality of elongate subunits, with the subunits of each section being arranged about the longitudinal axis of the elongate member and being secured together to form the section, and the sections being secured together to form the elongate member, such that the fundamental frequency of the mast is less than that of an equivalent onepiece mast.

An advantage of the mast according to the invention is that it improves the performance of the wind turbine by maintaining a stable support and extends the lifespan of the turbine structure.

Another advantage of the mast according to the invention is that each section has an individual fundamental frequency which contributes to the overall assembly fundamental frequency. The resultant effect of segmenting the mast is a dampening and reduction of the overall fundamental frequency of the mast.

According to one embodiment of the invention, the fundamental frequency of the mast is below about 1Hz. /£ 0 9 03 78 An advantage of the mast according to the invention is that it has a fundamental frequency lower than a one-piece mast of similar dimensions which would have a fundamental frequency in the range of 1.5-3 Hz.

Another advantage of this aspect of the mast according to the invention is that once the mast is constructed, the overall fundamental frequency of the mast is maintained at a lower frequency than the frequency of the rotating blades of the turbine, which helps to reduce the likelihood of resonance between the fundamental frequency of the mast and the frequency of the rotating blades of the turbine as a blade passes the mast during rotation of the turbine rotor.

The sections of the mast can be secured together by any appropriate means, such as by bolts. Hereinafter such securing means will be referred to collectively as bolts.

According to a further embodiment of the invention, the elongate member has a generally circular cross section, the elongate member tapers from the base end to the upper end thereof, and each subunit has an arcuate shape.

An advantage of this aspect of the mast according to the invention is that a large circular base provides stability for the mast and helps to support the weight of the mast and wind turbine.

Another advantage of this aspect of the mast according to the invention is that the arcuate shape of each subunit allows the formation of a generally circular cross section elongate member which is aerodynamic.

IE Ο 9 Ο 3 7 8 According to a further embodiment of the invention, the subunits of one section align with the subunits of the neighbouring section.

An advantage of the mast according to the invention is that the subunits can be assembled easily.

Another advantage of the mast according to the invention is that if any section is damaged, the damaged subunit can be replaced.

A further advantage of the mast according to the invention is that by constructing the mast from subunits the overall weight of the mast is reduced by up to 50% relative to a mast constructed as a single unit.

According to a further embodiment of the invention, each subunit has an upstanding flange along each longitudinal edge thereof, the flange facing out from the elongate member, with the flanges of one subunit aligning with the flanges of the neighbouring subunit and the flanges being bolted together.

An advantage of this aspect of the mast according to die invention is that the flanges enable the subunits to be secured to one another providing structural support and forming a rigid structure.

According to a further embodiment of the invention the bolted flanges of the subunits of each section align with the bolted flanges of the neighbouring sections to form upstanding ribs along the length of the elongate member.

IE Ο 9 Ο 3 7 8 An advantage of this aspect of the mast according to the invention is that the flanges provide structural support and aid in lowering the fundamental frequency of the mast According to a further embodiment of the invention, the flanges 5 on the subunits of the section forming the base of the mast widen outwards towards the base to provide buttresses for the mast.

Additional buttresses may be added to the base to provide support and reinforce the mast structure.

An advantage of this aspect of the mast according to the 10 invention is that the buttresses provide stability and strength to the base of the mast.

The base can be secured and pivoted on one side of a solid platform such as a concrete platform. The pivot allows the mast to be lowered for maintenance work to be carried out on the turbine.

Preferably, the subunits are made of pressed steel.

According to a further embodiment of the invention a resilient material is sandwiched between neighbouring subunits and neighbouring sections where they are bolted together.

, An advantage of this aspect of the mast according to the invention is that the resilient material dampens the oscillations resulting from any turbulence which reduces the movement of the mast and prevents damage. ΙΕ ο 9 Ο 3 7 8 Ί Preferably, the resilient material is selected from the group consisting of fluoropolymer, latex, polyethylene, polyurethane, polyvinyl chloride (PVC), rubber, silicone and thermoplastic rubber (TPR).

The invention will be further illustrated by the following 5 description of an embodiment thereof, given by way of example only with reference to the accompanying figures in which: Fig, 1 is a perspective view of a mast in accordance with the invention; and Fig. 2 is an exploded view of the mast of Fig. 1.

Referring to Fig. 1 there is indicated, generally at 10, a mast for a wind turbine, in accordance with the invention. The mast 10 comprises a hollow elongate member 11, the elongate member 11 being divided into four sections 12 along the longitudinal axis thereof, each section 12 being divided into four elongate subunits 13 made of pressed steel, with the subunits 13 of each section 12 being arranged about the longitudinal axis of the elongate member 11 and being bolted together to form the section 12, and the sections 12 being bolted together to form the elongate member 11.

On construction, the elongate member 11 has a circular cross section, the elongate member 11 tapers from base end 14 to upper end 15 thereof, and each subunit 13 has an arcuate shape.

Referring to Fig. 2 the subunits 13 of one section 12 align with the subunits 13 of the neighbouring section 12. Each subunit 13 has an upstanding flange 16 along each longitudinal edge thereof, the flanges 16 k ’ r IE facing out from the elongate member 11, with the flanges 16 of one section 12 aligning with the flanges 16 of the neighbouring section 12.

The flanges have pre-drilled holes 17 that allow the flanges 16 to be bolted to one another. The base end 14 of the mast 10 has pre5 drilled holes 18 that allow the base end 14 of the mast 10 to be bolted to a solid concrete base (not shown). The wind turbine (not shown) is bolted to a platform 19 on the upper end 15 of the mast 10.

The flanges 16 on the subunits at the base end 14 widen outwards towards the base to provide buttresses 20 for the mast.

Additional smaller buttresses 21 reinforce the mast structure. The base end 14 of the mast 10 has a pivot 22 on one side. The pivot allows the mast to be lowered for maintenance work to be carried out on the turbine.

The formation of the mast 10 from the sections 12 results in a mast with a low overall fundamental frequency than an equivalent onepiece mast. The low mast frequency prevents resonance occurring between the frequency with which the rotor blades (not shown) shadow the mast 10 and the rotation of the rotor blades (not shown) on the wind turbine (not shown). This prevents crack formation, turbine lifetime reduction and structural fatigue.

Claims

1. Claims: 1. A mast for a wind turbine comprising a hollow elongate member, the elongate member being divided into sections along the longitudinal axis thereof, each section being divided into a plurality of 5 elongate subunits, with the subunits of each section being arranged about the longitudinal axis of the elongate member and being secured together to form the section, and the sections being secured together to form the elongate member, such that the fundamental frequency of the mast is less than that of an equivalent one-piece mast. 10

2. A mast according to Claim 1, wherein the fundamental frequency of the mast is below about 1Hz.

3. A mast according to Claim 1 or 2, wherein the elongate member has a generally circular cross section, the elongate member tapers from the base end to the upper end thereof, and each subunit has 15 an arcuate shape.

4. A mast according to any one of Claims 1-3, wherein the subunits of one section align with the subunits of the neighbouring section.

5. A mast according to Claim 4, wherein each subunit has an 20 upstanding flange along each longitudinal edge thereof, the flange facing out from the elongate member, with the flanges of one subunit aligning with the flanges of the neighbouring subunit and the flanges being bolted together. IE 0 9 03 78

6. A mast according to Claim 5, wherein the bolted flanges of the subunits of each section align with the bolted flanges of the neighbouring sections to form upstanding ribs along the length ofthe elongate member. 5

7. A mast according to Claim 5 or 6, wherein the flanges on the subunits of the section forming the base of the mast widen outwards towards the base to provide buttresses for the mast.

8. A mast according to any preceding claim, wherein tiie subunits are made of pressed steel.

9. 10 9. A mast according to any preceding claim, wherein a resilient material is sandwiched between neighbouring subunits and neighbouring sections where they are bolted together. 10. A mast according to Claim 9, wherein the resilient material is selected from the group consisting of fluoropolymer, latex, 15 polyethylene, polyurethane, polyvinyl chloride (PVC), rubber, silicone and thermoplastic rubber (TPR).

10.

11. A mast according to Claim 1 for a wind turbine, substantially as hereinbefore described with particular reference to and as illustrated in the accompanying drawings.