Separable blade for wind turbine

To provide a light and economical separable blade for a wind turbine that is also equipped with a lightning rod function. A separable blade for a wind turbine wherein the blade as a whole is assembled by connecting two electrically non-conductive part blades 1T and 1R in the lateral direction, comprising metal fasteners 4, 5, 6, and 7 for fastening together the two adjacent part blades, and lightning discharge conductive wires 8 and 9, provided in an inner blade portion. The fastener 4 is exposed on the blade surface of the part blade 1T, and is connected to the lightning discharge conductive wire 9 through the other fasteners 5, 6, and 7, or a lightning discharge conductive wire 8. The lightning discharge conductive wire 9 extends to the blade root.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119 based upon Japanese Patent Application Serial No. 2007-012504, filed on Jan. 23, 2007. The entire disclosure of the aforesaid application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the fastening of separable blades for wind turbines, and the lightning protection structures thereof.

BACKGROUND OF THE INVENTION

It is well known that so-called horizontal axis wind turbines are widely used in wind power generation systems. An ordinary horizontal axis wind turbine is comprised by a rotor whereon at least two or more blades are radially attached from a hub, a nacelle that is connected to the hub and axially supports this rotor through a main shaft that is extended in an approximate horizontal direction, and a tower that is installed in an approximate vertical direction and supports the nacelle in a yaw rotatable state.

Recently progress has been made in increasing the size of horizontal axis wind turbines in order to improve the electrical generation capabilities. Lightweight and strong, FRP (fiber-reinforced plastics) have been the choice for the materials for blades.

Moreover, in order to facilitate ease of transport, separable blades have been proposed wherein part blades, which are partitioned in the longitudinal direction, are connected in series to form the whole. There is, for example, the technology such as described in Japanese Unexamined Patent Application Publication 2004-11616, wherein a connecting member is provided in the vicinity of a connecting section between part blades that are connected in series together, where the part blades and the connecting member are secured together with bolts.

In this case, a connecting member is required when the part blades are connected together, which is undesirable not only because of the precision required in the machining thereof, but because of the additional cost and weight.

Furthermore, there is another technology wherein bolts and straps are used to connect together the part blades such as described in Japanese Examined Patent Application Publication 2003-518586. Connecting in this way forms a large number of protruding parts on the surface of the blade, causing problems in terms of aerodynamic performance and noise. Additionally, this ties to increased weight and cost, the same as with the technology described in Japanese Unexamined Patent Application Publication 2004-11616.

Additionally, when the connecting members between part blades are secured by a metal frame, as described in Japanese Unexamined Patent Application Publication 2003-214322, this not only leads to increased weight and cost, but also to concerns about problems such as resonant frequencies and abrupt changes in stiffness (concentration of stresses).

On the other hand, for wind-power generation, horizontal axis wind turbines are installed in wide open spaces, and the blades thereof are located in environments prone to lightning strikes.

Hereupon, blades comprising a non-conductive material such as FRP differ from metallic blades and if struck by lightning, there is danger that the lightning bolt current will not be able to dissipate to ground resulting in damage. Recently, the increasing sizes of wind turbines which use FRP has resulted in increasing occurrences of damage due to lightning. Because of this, a conductive material is attached to an FRP blade body as a countermeasure against lightning damage in a conventional wind power generation system that uses FRP blades.

In consideration of the various problems described above, in the technology described in Japanese Unexamined Patent Application Publication 2005-220805, two part blades that are connected together, namely an inner blade part (on the blade root side) and an outer blade part (on the blade tip side) are connected together by a connecting member (a barrel nut and a tension bolt) with a metal plate interposed there between. The periphery of this metal plate is exposed at the surface of the blade, and when a lightning strikes, the electrical current from the lightning that is conducted in the metal plate is carried to the outside of the part blade through lightning discharge conductors within the blade, to escape to ground. Although this metal plate functions as a lightning receptor, there is still the problem of the provision of the metal plate leading to increased cost and weight.

The present invention was the result of contemplation on the problems with the prior art described above, and the object thereof is to provide a light and economical separable blade for a wind turbine that is also equipped with a lightning protection function.

SUMMARY OF THE INVENTION

In order to solve the problems described above, a first aspect of the present invention is a separable blade for a wind turbine wherein non-conductive part blades are connected in series in the longitudinal direction to assemble the blade as a whole, having:a fastener for fastening together two adjacent part blades, disposed in an inner blade portion; anda lightning discharge conductive wire that extends to a blade root, disposed in the inner blade portion;wherein a portion of the fastener is exposed on the blade surface of at least one of the two part blades, and at least the portion of the fastener exposed at the blade surface has an electrically conductive material, and is connected electrically to the lightning discharge conductive wire.

A second aspect of the present invention is a separable blade for a wind turbine having:a non-conductive first part blade;a non-conductive second part blade wherein the blade tip side end surface thereof is connected to the blade root side end surface of the first part blade;a fastener for fastening the first part blade and the second part blade; anda lightning discharge conductive wire that extends to a blade root, disposed in an inner blade portion;wherein a first hole part that is open on the blade surface and a second hole part that is communicated with the first hole part and that is open on the blade root side end surface of the first part blade are formed in a blade root side end portion of the first part blade; anda third hole part that is open on the blade surface and a fourth hole part that is communicated with the third hole part and that is open on the blade tip side end surface of the second part blade and continuously communicates with the second hole part are formed in a blade tip side end portion of the second part blade; wherein the fastener has:a first fastener that is disposed within the first hole part and locked by the first hole part;a second fastener that is disposed within the third hole part and locked by the third hole part; anda third fastener, which passes through the second hole part and the fourth hole part, which continuously communicate each other, for connecting the first fastener to the second fastener, to fasten tensely the first part blade to the second part blade; wherein at least one of the first fastener and the second fastener is made from an electrically conductive material and one end surface thereof is exposed at the blade surface through the hole part (that is, the first hole part for the first fastener or the third hole part for the second fastener), and is connected electrically to the lightning discharge conductive wire.

A third aspect of the present invention is a separable blade for a wind turbine as set forth in the second aspect wherein a cover member is provided for covering an opening that opens at the blade surface of either the first hole part or the third hole part, and the fastener of the other hole part (that is, the first fastener for the first hole part or the second fastener for the third hole part) is exposed at the blade surface.

A fourth aspect of the present invention is a separable blade for a wind turbine as set forth in the second or third aspect, wherein the third fastener is a rod member having an external threaded portion on a tip portion thereof, wherein the fastener comprises a nut that threads onto the external threaded portion and that is housed within either the first hole part or the third hole part, and a jack bolt that screws onto the peripheral part of the nut to jack up the nut, wherein the lightning discharge conductive wire is connected to the jack bolt.

A fifth aspect of the present invention is a separable blade for a wind turbine as set forth in the fourth aspect, wherein the cover member is provided for covering the opening of the hole part that opens at the blade surface, the hole part being either the first hole part or the third hole part that houses the nut.

A sixth aspect of the present invention is a separable blade for a wind turbine as set forth in any of the first through fifth aspects, further comprising a lightning receptor part on a blade tip part.

A seventh aspect of the present invention is a separable blade for a wind turbine as set forth in any of the first through sixth aspects, wherein the lightning discharge conductive wire is connected to a plurality of the fasteners that are provided.

In the present invention, a portion of the fastener is exposed at the blade surface as a lightning receptor part, and is connected to a lightning discharge conductive wire in a blade inner portion. The present invention was the result of contemplation on the problems with the prior art described above, and the object thereof is to provide a light and economical separable blade for a wind turbine that is also equipped with a lightning rod function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below in accordance with accompanying drawing. The below is one embodiment of the present invention, and not intended to limit the present invention.

FIG. 1(a) is an overall view of a separable blade as set forth in one embodiment of the present invention.FIG. 1(b) is a detail view of part A;FIG. 1(c) is a detail view of part B; andFIG. 1(d) is an expanded view of the exposed surface of the first fastener.FIG. 2is a cross-sectional diagram along section C-C shown inFIG. 1(b).FIG. 3is a plan view schematic diagram of the connector part, andFIG. 4is a cross-sectional diagram along section D-D.

As a shown inFIG. 1andFIG. 2, the separable blade1of the present embodiment is structured from a first part blade1T on the blade tip side, and a second part blade1R on the blade root side. The part blades1T and1R are made from a non-electrically conductive material such as FRP, and, as shown inFIG. 2, have a structure wherein top and bottom outer planes are held in a front beam2and a back beam3. The detailed connecting structure in the second part blade1R on the blade root side is shown inFIG. 5, and the detailed connecting structure in the first part blade1T on the blade tip side is shown inFIG. 6.

In the outer panel parts of the part blades1R and1T, a hole that passes through in the direction of thickness of the panels, another hole that is communicated with the other hole and opens at the connecting surface are formed. Specifically, as is shown inFIG. 6, a first hole part21that is open on the blade surface and a second hole part22that is communicated with first hole part21and that is open on the blade root side end surface25of the first part blade1T are formed in the blade root side end portion of the first part blade1T.

Additionally, as is shown inFIG. 5, a third hole part23that is open on the blade surface and a fourth hole part24that is communicated with the third hole part23and that is open on the blade tip side end surface26of the second part blade1R and that continuously communicates with the second hole part22are formed in the blade tip side end portion of the second part blade1R.

At the time of assembly, first the first fastener4is inserted into the first hole part21. The first fastener4is a cylindrical metal component, and a horizontal hole4a, wherein internal threads are cut, is open in the center of the periphery thereof. The first hole part21has a diameter of a size that is able to essentially accommodate the first fastener4without a gap. The first hole part21may be an opening wherein there is a gap with the first fastener4on the blade tip end side, but because there will be the need to fill the gap later, preferably the design is such that, if possible, there will be no gap.

Next, one end of the third fastener5, having an external threaded portion5bis inserted from the second hole part22and screwed into the horizontal hole4a, and the first fastener4and the third fastener5are screwed together. The first fastener4is held by the first hole part21, so the third fastener5cannot be withdrawn without unscrewing from the first fastener4. The third fastener5is a metal bolt having external threaded portions5aand5bon both ends thereof.

After the operations described above have been completed for all sets of first fasteners4and third fasteners5, In order to insert the end of parts of the third fasteners5having the external threaded portions5a, protruding from the blade root side end surfaces25of the first part blades1T, into the fourth hole parts24, and the blade root side end surfaces25of the first part blades1T and the blade tip side end surfaces26of the second part blades1R are aligned. At this time, the lightning discharge conductive wire9that extends from the tip lightning receiver part10is passed into the second part blade1R. Additionally, the second fastener6is disposed within the third hole part23, and the end part of the third fastener5having the external threaded portion5ais inserted into the horizontal hole6aof the second fastener6. When the blade root side end surface25of the first part blade1T and the blade tip side end surface26of the second part blade1R are brought somewhat together, the external threaded portion5awill protrude to the blade root side from the horizontal hole6a, as shown inFIG. 5. The third fastener5is passed through the second hole part22and the fourth opening port24.

The third hole part23is a long hole, having a cylindrical inner surface, in the end part on the blade tip end side. The second fastener6is a cylindrical metal component, and a horizontal hole6ais open in the center of the periphery thereof. Note that a portion of the periphery of the second fastener6is formed as a flat surface so as to ensure a seat for the fastener7.

Next, the nut7aof the fastener7is screwed onto the external threaded portion5a. The fastener7each comprise a nut7a, a jack bolt7b, and a washer7c, all made of metal, and can use off-the-shelf products.

The jack bolt7bscrews onto the periphery of the nut7ato jack up relative to the watcher7c. The washer7clays against the flat surface that is formed in a portion of the periphery of the second fastener6.

Here, before passing to the next process, a lightning discharge conductive wire8is attached to the jack bolt7bof each of the fasteners7, and the various fasteners7are connected by the lightning discharge conductive wires8, as shown inFIG. 3. Similarly, as shown inFIG. 4, the upper and the lower fasteners7and7are connected by the lightning discharge conductive wire13aby installing the lightning discharge conductive wire13to at least one jack bolt7bon each side. Additionally, the lightning discharge conductive wire9that extends from the tip lightning receiver part10is connected to at least one of the jack bolt7b. The end portion of the lightning discharge conductive wire9extends toward the blade root and comes out the opening at the blade root.

Next, the jack bolt7bis screwed in to jack up the nut7arelative to the washer7c. That is, a wrench is inserted into the third hole part23to fit onto the head of the jack bolt7b, rotate the jack bolt7bin the screw-in direction. This causes the first fastener4and the second fastener6to be tightened in the direction of mutually approaching each other. The first fastener4interlocks with the first hole part21, and the second fastener6interlocks with the third hole part23. Consequently, a tensile force is produced on the third fastener5, and the third fastener5fastens tensely the first part blade1T and the second part blade1T. The lightning discharge conductive wires8,9, and13, which are attached to the jack bolt7b, are pinched between the head of the jack bolt7band the nut7a, to be connected securely.

After the operations described above have been completed for all sets of fasteners, then, as shown inFIG. 1(b) andFIG. 2, a cover member11, for covering the opening that opens at the blade surface of the third hole part23, is attached to the blade surface of the second part blade1R. The cover member11is secured to the outer panel of the second part blade1R by a tapping thread12.

As is shown inFIGS. 1(b), (c), and (d), the periphery of the cover member11, the partition parts of the first part blade1T and the second part blade1R, and the periphery of the exposed part of the first fastener4are caulked with a sealant S made from epoxy or silicone. A non-electrically-conductive material such as resin or FRP, or the like, may be used for the material for the cover member11; an electrically conductive material is not suitable.

The separable blade1as set forth in the present example embodiment is structured as described above, and is attached to the hub of the horizontal axis wind turbine.

The lightning discharge conductive wire9is grounded via the hub, the nacelle, and the tower. The lightning discharge conductive wire9may extend to the ground, or may be grounded through the use of metal components in the hub, the nacelle, and the tower.

In the separable blade1as set forth in the present embodiment, the exposed parts of the first fastener4in the vicinity of the partition part of the blade1serve as lightning receptor parts along with the Tip lightning receptor member10. The lightning electrical current that strikes the Tip lightning receptor member10escapes to the ground through the lightning discharge conductive wire9. The lightning electrical current that strikes the first fastener4escapes to the ground through the fasteners5,6,7and the lightning discharge conductive wires8,9,13.

In the separable blade1as set forth in the present example embodiment, no special member for discharging the lightning is provided in the partition part, and thus the separable blade1is light and economical. Because there are no operations for building in a special member to discharge the lightning, the assembly operations are easy, and assembly can be performed in a short time. It possible to design the fasteners that are disposed within the blades so as to have adequate thickness, not only making it possible to ensure adequate fastening strength, but also making it possible to have desirable aerodynamic properties with little effect on the external shape of the blades.

The end portion (the exposed portion) of the first fastener4that is exposed on the blade surface of the first part blade1T may protrude slightly from the blade surface of the first part blade1T, or may be flush with the blade surface of the first part blade1T. Even though having the first fastener4protrude from the blade surface will increase the lightning strike rate, doing so will have a negative impact on the aerodynamic properties. The height of protrusion of the first fastener4from the blade surface should be designed taking this into consideration.

Note that while in the present embodiment, of all of the fasteners, only the first fastener4was exposed at the blade surface to be a lightning receptor part, the second fastener6may also be exposed at the blade surface to be a lightning receptor part as well. In such a case, the height of the protrusion of the second fastener6from the cover member11(including the case where in the height of protrusion is zero) can be designed as appropriate, and this height can be achieved easily by forming, in the cover member11, a hole or notch to expose the second fastener6. Both the first fastener4and the second fastener6may be exposed so as to be lightning receptor parts, or, instead, only one or the other may be exposed to be a lightning receptor part.

Furthermore, in the reverse of the embodiment described above, the first hole part21, the second hole part22, and the first fastener4may be provided in the second part blade1R and the third hole part23, the fourth hole part24, the second fastener6, and the fastener7may be provided in the first part blade1T.

Additionally, while the embodiment described above was one of a separable blade wherein the blade as a whole was assembled by connecting two part blades1T and1R in the lateral direction, instead the separable blade may be structured such that the blade as a whole is assembled by connecting, in the lateral direction, three or more part blades. When there are two or more partition parts as the result of having three or more part blades, the connecting structure with the lightning receptor part as set forth in the present invention may be applied to all of the partition parts, or the connecting structure with the lightning receptor part as set forth in the present invention may be applied to only a portion of the partition parts.

Additionally, while in the embodiment described above, all of the fasteners4,5,6, and7were made from an electrically conductive material, at least the parts of the fasteners that are exposed at the blade surface, and the portions of the parts that are exposed at the blade surface, may be made from an electrically conductive material, and these may be connected within the blade to the lightning discharge conductive wire. If there are adequately strong non-conductive bolts, nuts, or other fasteners, these may be used as desired outside of the lightning discharge path.

While in the example embodiment described above, the lightning discharge conductive wire was connected to the jack bolt7bof the fastener7, the lightning discharge conductive wire may be connected to any part of any fastener insofar as there is electrical conductivity with the portion of the fastener that is exposed at the blade surface. The following embodiment is useful if the jack bolt7bis not used, and in other cases.

Another embodiment pertaining to the connecting structure between the lightning discharge conductive wire and the fastener is, as shown inFIG. 7throughFIG. 9, a structure wherein the lightning discharge conductive wires8,9, and13are connected to the lightning receptor part that is the first fastener4. The connection may be made using a bolt, by welding, or the like. If the connection is made using a bolt, then, as shown inFIG. 9, for example, a bolt15is fastened by screwing into a screw hole4bthat is provided on the inner end of the first fastener4, through crimp-type terminals14that are provided on the lightning discharge conductive wires8,9, and13, to cause the crimp-type terminals14to be pressed onto the first fastener4. Each of the first fasteners4,4,4. . . above and below are provided with screw holes4b, and the respective lightning discharge conductive wires8,9, and13can be connected using bolts15.

When the second fastener6is exposed on the blade surface as the lightning receptor part instead of, or in addition to, the first fastener4, preferably the lightning discharge conductive wires are connected to the second fastener6. In this case as well, a screw hole is provided in the second fastener6to connect the lightning discharge conductive wire to the second fastener6using a bolt, or the connection is made through welding or through the use of some other method.

The connections between the lightning discharge conductive wires and the fasteners of the part blades may use bolt connections, welding, or other connecting methods, but preferably the method is one which, as far as is possible, does not reduce the strength with which the part blade is secured, and regardless of the method used, the connection should be designed so that there will be no problems in terms of strength.