Method of lifting a wind turbine nacelle

This invention relates to a method of lifting a wind turbine nacelle (1), the method comprising: arranging a first and second anchoring point (2,3) on each of two opposing sides of the nacelle (1), the first point (2) of each side being arranged below the center of gravity (4) of the nacelle (1) and the second point (3) of each side being arranged above the center of gravity (4), wherein one of said first and second anchoring point (2,3) of each side is immovably arranged, and wherein the other one of said first and second anchoring point (2,3) of each side is movably arranged; interconnecting said first and second anchoring point (2,3) on respective side of the nacelle (1) by means of one connecting element (5) per each of the two sides; connecting each of said connecting elements (5) to a hoisting means (11); adjusting the position of each of the movable anchoring points such that each of the connecting elements (5) is vertically aligned when lifting the nacelle (1) by the hoisting means (11).

TECHNICAL FIELD

The present invention generally relates to a method of lifting a wind turbine nacelle by means of a crane.

BACKGROUND OF THE INVENTION

When lifting a wind turbine nacelle in order to place it on top of a wind turbine tower, a crane with a yoke and wires is normally used. The nacelle is transported to the site of the tower, after which the yoke is attached to the nacelle at four points, substantially one point at each corner of the nacelle, via wires, and the nacelle is lifted by the crane.

The yoke comprises a complex arrangement of hydraulics to be able to adjust the position of the nacelle during the lift, such that the nacelle is in the correct, horizontal, position when placed on the tower. The hydraulics of the yoke is also needed to attach the yoke to the four corners of the nacelle since the nacelle is often transported in a non-horizontal, inclining, position to save space. The yoke thus needs to be hydraulically tilted to reach the lower end of the inclined nacelle, after which the yoke is tilted back to give the nacelle a horizontal attitude.

The yoke described above is rather large and complex, and thus expensive.

SUMMARY OF THE INVENTION

In view of the above, an objective of the invention is to provide a method which simplifies and reduces the cost of lifting a wind turbine nacelle onto a wind turbine tower.

According to a first aspect, the present invention relates to a method of lifting a wind turbine nacelle, the method comprising: arranging a first and second anchoring point on each of two opposing sides of the nacelle, the first point of each side being arranged below the centre of gravity of the nacelle and the second point of each side being arranged above the centre of gravity, wherein one of said first and second anchoring point of each side is immovably arranged, and wherein the other one of said first and second anchoring point of each side is movably arranged; interconnecting said first and second anchoring point on respective side of the nacelle by means of one connecting element per each of the two sides; connecting each of said connecting elements to a hoisting means; adjusting the position of each of the movable anchoring points such that each of the connecting elements is vertically aligned when lifting the nacelle by the hoisting means.

By one of the two anchoring points of each of the two opposing sides being movable, and by one point being positioned above and the other one below the centre of gravity, each of the connecting elements may be positioned in relation to the centre of gravity of the nacelle such that the nacelle may be lifted at only two points, i.e. via the connecting element of each of the two opposing sides of the nacelle, instead of the traditional four points, without rotating when it is lifted. Thus, the means for connecting the nacelle to a hoisting means may be significantly simplified. There is e.g. no longer a need for a large four point yoke to be used. In fact, a yoke is no longer needed at all, since the connecting means may be connected directly to the hoisting means via converging wires. Also, there is no longer a need for any hydraulics in order to connect an inclining nacelle to the hoisting means since the hoisting means is only connected at one point per nacelle side.

It may, however, be convenient to connect the connecting elements to the hoisting means via a yoke. This yoke may be a simple two-point yoke with no hydraulics.

The connecting elements may be connected to the yoke via e.g. wires or chains, one per connecting element, i.e. one per opposing side of the nacelle, but it may be convenient to connect the connecting elements directly to the yoke, reducing the number of wires, or such, that need to be guided to avoid entanglement. Also, the less gap there is between the yoke and the nacelle, the higher a specific hoisting means may lift the nacelle, since the yoke may be lifted to the same height regardless of the gap to the nacelle below.

The movable anchoring points may be slidably arranged along a structure of the nacelle. By being slidable, the movable anchoring points may be slided to a convenient position in relation to the immovable anchoring points and the nacelle centre of gravity in accordance with the inventive method. The anchoring points may be continuously, i.e. steplessly, slidably adjustable to allow very precise positioning of the connecting elements in relation to the centre of gravity of the nacelle, or they may be step-wise slidable. The movable anchoring points may e.g. only be locked in specific, not stepless, positions, which may simplify the anchoring point design.

The movable anchoring points may be arranged in any part of the nacelle sides, but it may be convenient to arrange them in respective parts of a frame of the nacelle. If, for instance, the movable anchoring points are arranged in a casing material, the material may not have the structural strength necessary and may be torn. Depending on whether the movable anchoring points are intended to carry some, or even all, of the nacelle weight during lifting, it may be convenient to arrange them in a bearing structure of the nacelle.

The immovable anchoring points may be arranged in any part of the nacelle sides, but it may be convenient to arrange them in respective parts of the frame of the nacelle. If, for instance, the immovable anchoring points are arranged in a casing material, the material may not have the structural strength necessary and may be torn. Depending on whether the immovable anchoring points are intended to carry some, or even all, of the nacelle weight during lifting, it may be convenient to arrange them in a bearing structure of the nacelle.

The immovable anchoring points may thus be arranged in a bearing structure of the nacelle, allowing these anchoring points to carry most of the weight of the nacelle as the nacelle is lifted. The nacelle will thus not risk breaking from its own considerable weight. The bearing structure may be a part of the frame of the nacelle.

The bearing structure in which the immovable anchoring points may be arranged might be a cast iron structure, since such a structure may be strong enough to carry the weight of the nacelle. The cast iron structure may form an integral part of the frame of the nacelle, or may be joined to other parts of the nacelle frame.

In a specific embodiment, the immovable anchoring points may be arranged in a cast iron housing for a gear box of the wind turbine.

The connecting elements of the present invention may be any structural element able to connect the first and second anchoring points on each of the opposing sides of the nacelle. A connecting element may e.g. be a wire, a chain, a rod or a bar connecting the first anchoring point of a side of the nacelle with the second anchoring point of the same side of the nacelle. An advantage with using wires as connecting elements may be that wires are more easily handled, stored and transported since they may be flexible.

The anchoring points may be any means that allows a connecting element to be connected thereto. A simple and easy to use type of anchoring point is a lifting eye. Thus, it may be convenient that at least one of the anchoring points is a lifting eye. Especially, it may be convenient that the immovable anchoring points are lifting eyes.

The first anchoring points may be those anchoring points which are immovably arranged. The movably arranged anchoring points will in that case be the second anchoring points, arranged above the centre of gravity of the nacelle.

Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached claims as well as from the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With the term “nacelle” is generally meant a housing intended to be placed on a wind turbine tower. The nacelle may include e.g. a frame to define a machine housing volume and/or provide a bearing structure of the nacelle, a casing to provide closed external surfaces of the nacelle, a gear box, a transmission and a generator, and a wind turbine rotor may be connected to the nacelle.

As used in this description, a “side” of a nacelle is any external plane of the nacelle and defined by the extension of the nacelle. The side may be flat, if e.g. the nacelle is a rectangular solid, or curved, as is often the case to make the nacelle more streamlined. “Opposing sides” of the nacelle are two sides, between which the centre of gravity of the nacelle is positioned.

The hoisting means may be any type of hoisting means able to lift a wind turbine nacelle, such as a winch or crane. The hoisting means may be separate from the wind turbine, e.g. standing on the ground, or on a boat if the wind turbine is off-shore, beside the wind turbine tower, or it may be an on-board hoisting means such as a winch or crane attached to the top of the tower.

FIG. 1illustrates a nacelle1being lifted in accordance with a new method, which method is, however, not according to the present invention.

A first and a second anchoring point2and3are arranged on each of two opposing sides of the nacelle, wherein, prior to the lift, the first anchoring points2are arranged below the centre of gravity4, marked with an “x” in the figure, and the second anchoring points3are arranged above the centre of gravity4. The first and second anchoring points2and3of each side are interconnected by connecting elements5, one connection element5per side of the two opposing sides of the nacelle1such that one connecting element5connects the first anchoring point2of one of the sides with the second anchoring point3of that same side and one other connecting element5connects the first anchoring point2of the other of the sides with the second anchoring point3of that other side.

The connecting elements5are connected, at the respective second anchoring points3, to a hoisting means11via two wires6and a yoke10, one wire6being connected to the connecting element5of one of the two opposing sides and the other wire6being connected to the connecting element5of the other one of the two opposing sides. The nacelle1may then be lifted by the hoisting means11in two points, i.e. in a two-point lift, via the two wires6.

According toFIG. 1, the positions of the anchoring points2and3have not been correlated to the centre of gravity4of the nacelle1, why the nacelle1will tip, or rotate, as illustrated by the arrow inFIG. 1, when the nacelle1is lifted by the hoisting means11. The nacelle1will thus, according to the method not of the invention illustrated inFIG. 1, be two-point lifted to e.g. a wind turbine tower in a far from horizontal position, rendering mounting the nacelle on the tower much more difficult, or impossible. Due to the anchoring points2and3not being correctly correlated to the nacelle1centre of gravity4, the connecting means5will not be vertically aligned during lifting of the nacelle1by the hoisting means11. Rather, the connecting means5will be at an angle alfa (“α”) to a vertical axis during lifting.

Thus, the method ofFIG. 1alleviates problems with the prior art by allowing use of a simpler two-point lifting method, removing the need for the large and complex yoke of prior art, but the method ofFIG. 1is not functional for the purpose of lifting a nacelle1to the top of a wind turbine tower since the nacelle1is rotated to a substantially non-horizontal, or even almost vertical, position during lifting.

FIG. 2illustrates a nacelle1being lifted in accordance with the present invention.

A first and a second anchoring point2and3are arranged on each of two opposing sides of the nacelle1, wherein the first anchoring points2are arranged below the centre of gravity4, marked with an “x” in the figure, and the second anchoring points3are arranged above the centre of gravity4. The first and second anchoring points2and3of each side are interconnected by connecting elements5, one connection element5per side of the two opposing sides of the nacelle1such that one connecting element5connects the first anchoring point2of one of the sides with the second anchoring point3of that same side and one other connecting element5connects the first anchoring point2of the other of the two sides with the second anchoring point3of that other side.

According to this specific embodiment of the present invention, the first anchoring points2are immovably arranged in a bearing structure of the nacelle1. The second anchoring points3are movably arranged in the nacelle1such that they may be moved sideways, i.e. in a longitudinal direction of the nacelle illustrated by the double headed arrow inFIG. 2, thus allowing adjustment of the positions of the second anchoring points3in view of the respective positions of the first, immovable, anchoring points2and the nacelle1centre of gravity4such that the nacelle1will not rotate during lifting.

The connecting elements5are connected, at the respective second anchoring points3, to a hoisting means11via two wires6and a yoke10, one wire6being connected to the connecting element5of one of the two opposing sides and the other wire6being connected to the connecting element5of the other one of the two opposing sides. The nacelle1may then be lifted by the hoisting means11in two points, i.e. a two-point lift, via the two wires6.

Since the movably arranged anchoring points3have been positioned with due consideration to the centre of gravity4of the nacelle1, the nacelle1will not start to rotate as it is lifted. Instead, the nacelle1will be lifted in balance in a highly controlled fashion and in a substantially horizontal position. Specifically, the connecting elements5will be vertically aligned during the lift. Depending on how much the movably arranged anchoring points3need to be horizontally moved in respect of the respective immovably arranged anchoring point2of each side, the nacelle1might not be perfectly horizontal during the lift, but the connecting elements5will still be vertical.

Since the first, immovable, anchoring points2of this embodiment of the invention are arranged in a bearing structure of the nacelle1, these first anchoring points2may be allowed to carry most, or all, of the weight of the nacelle1during the lift.

FIG. 3illustrates a side of a wind turbine nacelle1. A frame of the nacelle1, which frame is a bearing structure of the nacelle1, comprises a cast iron housing7for a gear box as well as a plurality of metal beams8. A first anchoring point2is immovably arranged in the frame at the cast iron housing7, and a second anchoring point3is movably arranged in the frame at a beam8. A connecting element5, here in the form of a looped, or doubled, wire, interconnects the first anchoring point2and the second anchoring point3.

The first, immovable, anchoring point2is arranged to carry most of the weight of the nacelle1.

With reference toFIG. 4, the second, movable, anchoring point3is arranged slidable along the essentially horizontal beam8and may by means of e.g. a pin9and holes in the beam8be indexed to different horizontal positions longitudinally along the beam8. The skilled man will appreciate that the pin9and/or the holes in the beam8may be substituted for any other indexation means.

The connecting element5of the embodiment of the invention disclosed inFIGS. 3 and 4extend above the second anchoring point3and there forms a loop, or eye, to which e.g. a wire6or a yoke10may be connected for lifting the nacelle1by means of a hoisting means11.