Patent Application
20110020126
1. Field of the Invention
This invention relates to electric power-generating devices, such as wind turbines and ocean current turbines, and more particularly to a modular rotor blade for a power generating turbine, which has one or more detachable blade sections, which can be detached for shipment and assembled on-site. The invention relates further to a method for assembling a power generating turbine with modular rotor blades.
2. Description of the Prior Art
Conventional wind turbine rotors utilize blades manufactured as one piece-fixed length blades, joined at a rotating hub. These blades may be of variable pitch (selectively rotatable about their longitudinal axes) in order to alter the angle of attack relative to the incoming fluid flow, principally for power shedding in high-flow velocities.
Alternatively, these blades may be fixed pitch or stall-regulated, wherein blade lift and therefore power capture falls off dramatically as wind speeds exceed some nominal value. Both variable pitch and stall regulated rotor blades with fixed diameters are well known in the art. U.S. Pat. No. 6,726,439 B2, describes a wind or water flow energy converter comprising a wind or water flow actuated rotor assembly. The rotor of U.S. Pat. No. 6,726,439 B2 comprises a plurality of blades, wherein the blades are variable in length to provide a variable diameter rotor. The rotor diameter is controlled to fully extend the rotor at low flow velocity and to retract the rotor, as flow velocities increases such that the loads delivered by or exerted upon the rotor do not exceed set limits.
A wind power-generating device includes an electric generator housed in a turbine nacelle, which is mounted atop a tall tower structure anchored to the ground. The turbine is free to rotate in the horizontal plane such that it tends to remain in the path of prevailing wind current. The turbine has a rotor with variable pitch blades, which rotate in response to wind current. Each of the blades has a blade base section referred to as a root blade attached to a rotor hub and a blade extension referred to as an extender blade that is variable in length to provide a variable diameter rotor. The rotor diameter is controlled to fully extend the rotor at low flow velocity and to retract the rotor as flow velocity increases such that the loads delivered by or exerted upon the rotor do not exceed set limits. The power-generating device is held by the tower structure in the path of the wind current such that the power-generating device is held in place horizontally in alignment with the wind current. An electric generator is driven by the turbine to produce electricity and is connected to power carrying cables inter-connecting the generator to other units and/or to a power grid.
Wind turbine blades greater than 50 m in length cannot be transported over land using conventional equipment and technology. US Patent Application US 2007/0253824 A1 discloses a modular rotor blade for a wind turbine, wherein the rotor blade comprises at least a first rotor blade section and a second rotor blade section. The first and second rotor blade sections are rigidly fixed together to provide the complete rotor blade after the sections have been transported to the site for the wind turbine. The rotor blade sections of this prior art modular rotor blade are fixed together rigidly, i.e. once connected the rotor blade sections cannot be detached again. In case of a malfunction of or damage to, for example, the outer rotor blade section of one rotor blade, the complete rotor blade must be replaced.
Therefore, it is an object of the present invention to provide a modular rotor blade for a power generating turbine that allows simple replacement of individual rotor blade sections in case of damage to or malfunction of a section. It is a further object of the present invention to provide a method for assembling a power generating turbine with such modular rotor blades.
The first object of the invention is solved by a modular rotor blade for a power generating turbine, comprising at least two rotor blade sections, wherein each rotor blade section comprises at least one connecting part having at least one conical opening, the connecting parts of adjacent rotor blade sections rest against each other such that the conical openings of the connecting parts are aligned with each other and form a continuous conical connecting opening.
It should be noted that the expression “opening” is a generic term for the expression of a through hole referring to a hole that is reamed, drilled, milled etc., completely through the substrate, and a recess referring to hole which does not go all the way through the substrate (which is reamed, drilled, or milled to a specified depth).
One of the connecting parts can be formed, for example, as a beam or box beam protruding from the end face of one of the adjacent rotor blade sections, and the connecting part of the other rotor blade section can be formed as a receptacle, wherein the (box) beam is adapted to fit into the receptacle according to the type of a fork-tongue-joint. Alternatively, each connecting part of two adjacent rotor blade sections can also be provided as a simple connecting rod, wherein one connecting rod protrudes from the end face of a first rotor blade section and the other connecting rod of a second rotor blade section adjacent to the first rotor blade section is arranged within the other rotor blade section. Typically, the form of the connecting parts can be adjusted to the application area of the rotor blade and no specific form is predetermined. However, it is essential that the connecting parts comprise at least one conical opening and that the connecting parts of adjacent rotor blade sections rest against each other such that the conical openings of the connecting parts are aligned with each other and form a continuous conical connecting opening.
The modular rotor blade according to the present invention further comprises receiving means for receiving tensioning means, wherein the receiving means are arranged at the smaller diameter end of the continuous conical connecting opening, wherein the continuous conical connecting opening is provided by the aligned conical openings of the connecting parts. A conical bolt corresponding to the conical connecting opening is arranged within the continuous conical connecting opening, and at least one tensioning means passes through the conical bolt and tensions the conical bolt against the receiving means.
Since the bolt and the continuous conical connecting opening comprise a mating conical or tapered shape, tensioning of the conical bolt against the receiving means fastens the connecting parts of adjacent rotor blade sections to each other, and thereby adjacent rotor blade sections of the modular rotor blade are fastened to each other in a detachable manner. The length of the conical bolt must not match the depth of the conical connecting opening, but the bolt must abut against a sufficient part of the conical openings of each of the connecting parts of adjacent rotor blade sections. Further, the tensioning means can be provided, for example, as a screw, which is passed through the conical bolt. In order to tension the conical bolt against the receiving means the tensioning means must be attached to the receiving means. Such attachment can be achieved by providing at least one female threat within the receiving means and a male thread at the screw so that the male thread can engage the female thread thereby tensioning the bolt against the receiving means. Alternatively, such attachment can be achieved by passing a screw through the receiving means, wherein the screw comprises a male thread at the protruding part, wherein the male thread can be received by an appropriate nut. The number of tensioning means passed through the conical bolt depends on the dimensions of the conical bolt and therefore the dimensions of the modular rotor blade. For example, the number of tensioning means can be four or six.
In other words, the invention relates to a rotor blade with two or more sections, including a first rotor blade section and a second rotor blade section. The first and second rotor blade sections have provisions for attaching the second rotor blade section to the first rotor blade section in a detachable manner. The advantage of such a joint including a conical bolt received and tightened in a corresponding continuous conical connecting opening is that forces and moments are not borne by a commonly used threaded joint connection but substantially absorbed by the conical joint according to the present invention. Accordingly, the loads acting on the tensioning means are reduced and minimized thereby improving the fatigue durability of the connection between the adjacent rotor blade sections. Advantageously, the inclination of the continuous conical connecting opening as well as the inclination of the conical bolt is in the range of 1.5° to 3.5°, wherein an inclination angle for both the continuous conical connecting opening and the conical bolt of less than 3° is preferred.
During operation of the power generating turbine, the loads acting upon the conical bolts and the corresponding continuous conical connecting opening are enormous and cause play or looseness of the connection of adjacent rotor blade sections. For example, the continuous conical connecting opening is slightly widened and/or the conical bolt is deformed. Therefore, the connection between adjacent rotor blade sections must be serviced after a predetermined operation time. For that purpose a present conical bolt can be removed and replaced by a new one. However, since the level of widening of the continuous connecting opening is not known and the levels of widening are not identical if more than one continuous opening is provided, an adaption of a new conical bolt to a widened continuous opening is very difficult, time consuming and cost-intensive.
Accordingly, a preferred embodiment of the modular rotor blade of the present invention comprises a gap defined between the receiving means and the end face of the conical bolt having the smaller diameter. In this regard, the smallest outer diameter of the conical bolt is larger than the smallest inner diameter of the continuous conical connecting opening. In case of play or looseness of the connection between adjacent rotor blade sections, the tensioning means is simply retightened, whereby the conical bolt is moved further and “deeper” into the continuous conical connecting opening thereby eliminating the play and looseness of the connection between adjacent rotor blade sections. The retightening of the tensioning means can be carried out during maintenance of the power-generating turbine, so that, after maintenance, the connection between adjacent rotor blade sections equates to the initial connection with respect to fixedness, with the only difference being the penetration depth of the conical bolt into the continuous conical connecting openings. By providing the gap, maintenance regarding the above-mentioned tolerance can be facilitated and accelerated. Furthermore, the maintenance costs can be lowered since no new conical bolts have to be used.
According to another aspect of the present invention, the receiving means is integrally formed with the relevant connecting part. Such an integral design or formation of the receiving means reduces the number of parts to be lifted and assembled on site and, thus, reduces installation costs. Furthermore, the integral formation of the receiving means facilitates the usage of a (box) beam as a connecting part of one of the adjacent rotor blade sections. When using this kind of formation, an access to the interior of the (box) beam is needless and redundant.
The connecting parts have at least one conical opening. The conicity or tapering of the openings can be provided by the connecting parts itself. In this case the durability of the surface of the conical opening is determined by the material of the connecting parts, or at least determined by the material in the area of the opening. Therefore, it is preferred that each of the conical openings is provided with a (metallic) bushing arranged in a respective opening in a corresponding connecting part. By providing a conical bushing the durability of the surface of the conical openings is determined by the material of the bushings, and not by the material of the connecting part. It is therefore possible to choose a very hard and/or strong material for the bushings which is not suitable for the connecting parts itself.
In order to save material costs and to reduce the weight of the entire rotor blade, it is preferred that the conical bolt is hollow. However, to transmit loads from one end face of the bolt to the other end face of the bolt, which is required for tensioning the bolt against the receiving means, the bolt can comprise webs or partition walls, particularly around the tensioning means passing through the bolt.
To facilitate the maintenance and the assembly of the modular rotor blade, an access door is provided in at least one of adjacent rotor blade sections. The access door must be dimensioned to allow access to the continuous connecting opening and must allow the insertion of the conical bolt. Without such an access door, access to the above-mentioned parts of adjacent rotor blade sections must be carried out from within the rotor blade. This is time consuming and simply not possible for outer, and therefore thinner blade sections.
To facilitate the alignment of adjacent rotor blade sections when assembling the rotor blade, in one preferred embodiment of the modular rotor blade according to the present invention, guiding means are arranged at the end faces of adjacent rotor blade sections. The guiding means can comprise at least one bolt at one end face of adjacent rotor blade sections and at least one corresponding recess in the end face of the other rotor blade section, wherein at least the tip of the bolt is tapered to facilitate alignment. The non-tapered portion of the bolt and a portion of the recess can comprise a female thread and a male thread, respectively. To support the connection of the adjacent rotor blade sections the threads can engage each other.
The first object of the present invention is alternatively solved by a modular rotor blade for a power generating turbine, comprising at least two rotor blade sections, wherein each rotor blade section comprises at least one connecting part, one connecting part enclosing the connecting part of an adjacent rotor blade section. The enclosing connecting part comprises at least two conical through holes and the enclosed connecting part comprises at least one through hole, wherein the through holes are arranged on the same longitudinal axis.
If the enclosed connecting part is formed without an inner space, i.e. the enclosed connecting part is not hollow, the at least one through hole is formed as a double conical through hole, wherein the openings with the greater diameter open up to the outer surfaces of the enclosed connecting part. In other words, the at least one through hole has a form comparable with an hourglass or is in the shape of a venturi nozzle.
Alternatively, the enclosed connecting part can also be formed with an inner space. In this case one of the connecting parts may be provided, for example, as a (box) beam which is enclosed by the other (enclosing) connecting part. Independent of the exact form or cross section of such an enclosed connecting part with inner space, it must comprise at least two through holes arranged on the same longitudinal axis.
As already mentioned above, the through hole(s) must be provided in such a manner that the opening with the greater diameter opens up towards the outer surfaces of the connecting parts. In this respect, the connecting parts of adjacent rotor blade sections rest against each other such that the conical through holes of the enclosing connecting part are aligned with the at least one through hole of the enclosed connecting part, thereby defining at least one conical connecting through hole. At least two conical bolts are arranged within the through holes of the enclosing part extending into the at least one through hole of the enclosed connecting part, and at least one tensioning means passes through the at least two conical bolts and tensions the conical bolts.
Since the through holes of the enclosed and the enclosing connecting parts are arranged on the same longitudinal axis and the through holes are formed as mentioned above, no receiving means for tensioning the bolts is necessary in order to connect the connecting parts of adjacent rotor blade sections in a detachable manner. Accordingly, such a design without the usage of receiving means reduces the number of parts to be lifted and assembled on site and, thus, reduces the installation costs.
One preferred embodiment of the modular rotor blade according to the second solution comprises a gap between opposing end faces of the conical bolts. Due to the gap, maintenance of the modular rotor blade is simplified as pointed out in detail above. In this respect, further embodiments of the modular rotor blade according to the second solution are set forth in the accompanying claims, wherein the advantages of these embodiments correspond to the relevant embodiments of the first solution.
With respect to a method for assembling a power generating turbine with modular rotor blades, the method comprises: the steps of manufacturing rotor blades in at least two rotor blade sections, wherein adjacent rotor blade sections have connecting parts for mounting said adjacent blade sections together; transporting said blade sections to a site; providing, at said site, a turbine on a structure that is held stationary with reference to said fluid flow, said turbine including a rotor hub and a rotor having provisions to mount first rotor blade sections to said rotor hub; connecting said first blade sections to said rotor hub; and attaching second rotor blade sections to first blade sections by mounting the connecting parts of adjacent rotor blade sections together by means of at least one conical bolt being tensioned by at least one tensioning means passing through the conical bolt. This method allows large wind turbine blades to be manufactured and transported in multiple pieces and, thus, has the advantage of reduced transportation costs for large wind turbine blades.
As a further aspect of the method according to the present invention, the second rotor blade sections are lifted by a hoist within a nacelle before attaching the second rotor blade sections to the first rotor blade sections. For example in the case of a wind turbine, this aspect has the advantage that no tower crane or helicopter is needed in order to assemble the modular rotor blades thereby reducing the costs for installation of the wind turbine.
According to a further step of the method of the present invention, the method comprises the step of attaching a blade tip to said second blade section. Due to this feature, large wind turbines can be manufactured and transported in multiple pieces thereby reducing the costs for transportation.
Accordingly, the present invention provides a design of an easily re- and post-tensioning joint of modular rotor blades.
This design prevents all movements within the joint and prevents the structural fatigue that would be caused by such movements. The invention has the advantage that it lowers the transportation costs of current wind turbine blades exceeding 50 meters or more in length, and allows larger wind turbine blades to be transported on existing air, land and water travel routes. The invention has the further advantage that the joint of adjacent rotor blade sections allows large wind turbine blades to be manufactured and transported in multiple pieces without associated maintenance costs for re-tensioning of joints. Further, the invention has the advantage of reduced transportation costs for large wind turbine blades. Furthermore, the invention has the advantage of allowing outboard blades severely damaged due to a lightening strike to be replaced without replacing the whole blade. Finally, the invention has the advantage of not requiring annual maintenance.
The invention will be described in detail with reference to the drawings in which:
In these figures, the same numerals refer to similar elements in the drawings. It should be understood that the sizes of the different components in the figures may not be to scale, or in exact proportion, and are shown for visual clarity and for the purpose of explanation.
Referring to
With respect to
In this embodiment the connecting part 14 of the second rotor blade section 11, the second connecting part 14, is formed as a beam with two side walls, and upper and lower sides (connecting part 14 can also be referred to as a “tongue”), and the connecting part 16 of the first rotor blade section 10, the first connecting part 16, is formed as a receptacle (and can also be referred to as a “fork”). The first connecting part 16 is adapted to receive the second connecting part 14, and the cross section of the second connecting part 14 is adjusted to the cross section of the first connecting part 16 so that the upper and lower surfaces of the second connecting part 14 support overlapping portions of the first rotor blade section 10.
In alternative embodiments, the cross section of the second connecting part can comprise a rectangular cross section (including a square cross section) or an elliptical cross section (including a circular cross section).
The modular rotor blade shown in
At the end faces of each rotor blade section 10, 11 guiding means 29a, 29b are provided, wherein the second section guiding means 29a are formed as at least partially conical bolts and the first section guiding means are provided as corresponding openings in the end face. During the assembly of the modular rotor blade the guiding means support the alignment of the relevant rotor blade section. Furthermore, in case the bolts and the openings are provided with male and female threads, the guiding means can be used to support the connection between adjacent sections.
Each connecting part 14, 16 comprises four conical openings 41, 42, wherein at the shown embodiment the conical openings extend through the overall depth of the side walls, i.e. the openings define through holes.
The conical or tapered bolts 30, according to the type of shear bolts can be tensioned by means of tensioning 28 means in the shape of four or six smaller sized bolts. This design allows the bolts 28 to be easily re-tensioned in the field via a small removable access door 32 in the first rotor blade section 10 and/or the second rotor blade section 11. This design of the joint also prevents all movement within the joint and prevents structural fatigue, which would be caused by this movement. A similar access door and fork-and-tongue joint elements wholly contained within the blade structure are provided for the blade tip 1, but are not shown in
With respect to
Between the receiving means 18 and the smaller diameter end face of the conical bolt 30 (the left end face in
As mentioned above, the conical bolt 30 is substantially hollow. However, to bear forces acting on the bolt 30, webs 21 are formed within the conical bolt 30, which encloses the tensioning means 28.
According to the shown embodiment the tensioning means 28 are provided as screws with a male thread at one end, wherein the male head engages with the female thread of the receiving means 18 for tensioning the conical bolt 30. In an alternative embodiment, the receiving means 18 may comprise through holes passed by the tensioning means 28 which are clamped against the receiving means 18 by counter nuts.
With respect to
The embodiment shown in
The third embodiment utilizes an enclosing connecting part 16 and an enclosed connecting part 14. In contrast to the second embodiment the enclosed connecting part 14 is solid, i.e. no separate side walls and therefore no space within the connecting part is provided. Accordingly, the enclosed connecting part 14 is not hollow. The enclosing connecting part 16 comprises two conical through holes and the enclosed connecting part 14 comprises one through hole, wherein the through holes are, in the assembled state of the modular rotor blade, arranged on the same longitudinal axis. The through hole of the enclosed connecting part 14 is formed as a double conical through hole, wherein the openings with the greater diameter open up to the outer surfaces of the enclosed connecting part. The conical through holes of the enclosing connecting part are aligned with the at least one through hole of the enclosed connecting part, thereby defining one double conical through hole. Within these conical connecting recesses two bolts 30 are arranged enclosing a gap 26 between their opposing end faces. A number of tensioning means 28 in the shape of screws are passed through the bolts 30 and tensions the bolts 30 against each other. The tensioning mechanism is the same as that shown in
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the scope of the invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2009/000052 | 1/14/2009 | WO | 00 | 10/11/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61011189 | Jan 2008 | US |
