DEVICE AND METHOD FOR DEICING A ROTOR BLADE OF A WIND TURBINE

Technical Field of the Invention

The present invention relates to a device and a method for deicing a rotor blade of a wind turbine.

Prior Art

When ice is formed on rotor blades of a wind turbine the aerodynamic of the blade is affected and the output power decreases rapidly. When the aerodynamic losses have increased to a certain level the wind turbine must be put in an out of operation state.

A commercially available system for deicing is based on the principle of having fans inside the rotor blades, said fans distributing heated air in a duct system along the forward edge of the rotor blades. This system functions when the icing is moderate. However, if there is heavy icing on the rotor blades the system will not produce sufficient heat to perform a proper deicing. A system for deicing that has been developed in Finland has a reached a limited commercial success. The system is based on a thin heat conducting carbon fibre film that is attached to the surface of the rotor blade, said film being covered by a top-coat layer. By this arrangement the rotor blades are sensitive for strokes of lightening. Also the system demands a lot of electrical power.

A system for deicing that originally was developed for the aerospace industry has been transferred to the wind power industry. The system is based on thin heat conducting elements of graphite that are placed on the surface of the rotor blades. The material in the graphite elements bring about a rapid heating of the blade surface but a lot of effect is needed. Also modifications in the design of the wind turbines are needed to adapt to this deicing system.

Objects and Features of the Invention

A primary object of the present invention is to present a device and a method as defined above, the invention being easily applicable upon existing wind turbines.

A further object of the present invention is to protect the rotor blade during deicing, thereby fastening the deicing process .

Still a further object of the present invention is to make the device displaceable along the tower of the wind turbine.

At least the primary object of the present _. invention is fulfilled by the device and method as defined in the appending independent claims. Preferred embodiments of the invention are defined in the dependent claims .

Brief Description of the Drawings

Below preferred embodiments of the present invention will be described, reference being made to the enclosed drawings, where:

Fig. 1 shows a side view of a wind turbine that is equipped with a first embodiment of a device for deicing according to the present invention, the device being in active position; Fig. 2 shows in enlarged scale the rotor blade of the wind turbine of Fig. 1 and the device in active position; Fig. 3 shows the device according to Figures 1 and 2 in folded position;

Fig. 4 shows a section through a rotor blade and a cap that is part of the device according to the present invention; Fig. 5 shows a side view of a wind turbine that is equipped with a alternative, second embodiment of a device for deicing according to the present invention, the device being in active position; Fig. 6 shows a side view of a still alternative, third embodiment of the device according to the present invention, the device being in active position with a cap of the device in an upper position;

Fig. 7 shows a side view of the embodiment of the device according to Figure 6, the device being in active position with a cap of the device in a lower position; and

Fig. 8 shows a section through a rotor blade and a cap that is part of the device according to the embodiment of Figures 6 and 7.

Detailed Description of Preferred Embodiments of the Invention

In Figures 1 and 2 it is disclosed how the device according to the present invention is mounted on an existing wind turbine W. The device according to the present invention includes a base rail 1 that is fixed to the tower T of the wind turbine, the base rail 1 extending in the longitudinal direction of the tower T. The fastening of the base rail 1 to the tower T could for instance be effected by means of welding or bolting.

The device according to the present invention also includes a cap 3 that in active position is intended to be located adjacent a rotor blade B of the wind turbine W. The cap 3 is hingedly connected to the base rail 1 by means of a number of bars 5A, 5B, 5C, 5D, 5E that extend between the base rail 1 and the cap 3. The bars 5A, 5B, 5C, 5D, 5E are pivotally connected at both ends, i.e. at one end to the base rail 1 and at the other end to the cap 3. The connection of the bars 5B, 5C, 5D, 5E to the base rail 1 is effected via elements 6B, 6C, 6D, 6E that are displaceable relative to the base rail 1, in the longitudinal direction of the base rail 1. When for instance the cap 3 is transferred from the active position of Figure 2 to the inactive position of Figure 3 the elements 6B, 6C, 6D, 6E are displaced upwards along the base rail 1.

The device according to the present invention also includes two actuator means 7 that each comprises a first electric motor 9 that is displaceable in the longitudinal direction of the base rail 1. According to a preferred embodiment the first electric motors 9 are displaceable by means of a gear rack (not visible) that is located inside the base rail 1. Such an arrangement will be described more in detail below. The actuator means 7 also comprises struts 10 that extend between the electric motors 9 and an adherent bar 5A, 5E. The struts 10 are pivotally connected both to the electric motor 9 and to the bar 5A, 5E. By displacement of the

electric motors 9 along the base rail 1 the cap 3 will be transferred between an active position, see Fig. 1 and 2, and an inactive position, see Fig. 3. In the active position according to Figures 1 and 2 the cap 3 is located adjacent an adherent rotor blade B. In the inactive position the cap 3 is displaced from the adherent rotor blade B and takes a folded position close to the tower T.

In Figure 4 the active position of the cap 3 in relation to a blade B is shown. As is learnt from Figure 4 the cap 3 has a general U-shape in cross-section. Normally, the shape of the cap 3 is adapted to the shape of the blade B, i.e. the distance between the blade B and the cap 3 should be as constant as possible.

On the inner side of the cap 3 a number of heating elements 11 are provided, said heating elements 11 comprising a base 12 that is attached to the inner side of the cap 3. Each heating element 11 also comprises a infrared heater 13 that is pivotally attached to the base 12. The pivotal attachment of the infrared heaters 13 makes it possible to adjust the infrared heaters 13 relative to the shape of the rotor blade B. Feeding of electrical power to the infrared heaters 13 could either be effected from the generator or from the transformer of the wind turbine W. During the deicing phase the infrared heaters 13 melts the ice that has been formed on the blade B. When the ice has been melt the infrared heaters 13 are switched off and the cap 3 assumes the folded position according to Figure 3. This deicing procedure is repeated for all of the rotor blades B. When deicing is completed the wind turbine W is again put into operation. In Figure 5 an alternative embodiment of the device according to the present invention is disclosed. The main difference, compared to the embodiment described above, is the design of the base rail. As is evident from Figure 5 the base rail 101 extends all the way from the top of the tower T to the ground level. At the lower end of the base rail 101 supporting means 102 are provided, said supporting means 102 resting on the ground. Thus the base rail 101 is supported by the ground. In order to stabilize the base rail 101 sidewards a number of straps 104 are provided on the upper half of the

tower T. These straps 104 force the base rail 101 against the tower T. The device according to Figure 5 also comprises a cap 3 and the folding mechanism as described above, i.e. bars 5A- 5E and actuator means 7. In Figure 5 the device according to the present invention is shown in active position.

In Figure 6 a still further embodiment of the invention is shown, said embodiment being equipped with a rack and pinion drive arrangement. The base rail 201 is equipped with rack means along at least an upper portion of the base rail 201. The base rail 201 comprises a first sub-rail 215 that is fixed to the tower T, e.g. by means of welding or bolting. The first sub-rail 215 is preferably U-shaped in cross-section and teeth 216 are provided at the free ends of the parallel walls of the first sub-rail 215, said teeth 216 being distributed in the longitudinal direction of the first sub-rail 215. The length of the first sub-rail 215 may vary. However, it is preferred that the first sub-rail 215 extends downwards such far that the second sub-rail 217, including the cap 203, may be displaced to the area of the ground level, this facilitating maintenance work on the device according to the present invention.

The base rail 201 also comprises a second sub-rail 217 that is received in the first sub-rail 215, the second sub- rail 217 being displaceable relative to the first sub-rail 215, in the longitudinal direction of the sub-rails 215, 217. It is preferred that the first sub-rail 215 is U-shaped in cross-section since there will be a lateral guidance of the second sub-rail 217.

The embodiment according to Figure 6 is equipped with second electric motors 218 in order to make it possible to displace the second sub-rail 217 relative to the first sub- rail 215. The second electric motors 218 are fastened to the second sub-rail 217, in the area of the ends of the second sub-rail 217. The second electric motors 218 comprises pinion means (not shown) and the second electric motors 218 are designed to cooperate with the tooth 216 of the rack means of the first sub-rail 215 and hence displacement of the second sub-rail 217 relative to the first sub-rail 215 is effected.

The cap 203 is via bars 5A-5C connected to the second sub-rail 217, the bars 5A-5C being hingedly/pivotally connected both to the second sub-rail 217 and to the cap 203. The connection of the bars 5B and 5C to the second sub-rail 217 is effected via elements 6B and 6C, said elements 6B and 6C being displaceable relative to the second sub-rail 217, in the longitudinal direction of the second sub-rail 217. Thus, the cap 203 may assume an active position, as shown in Figure 6, or an inactive, folded position similar to the position shown in Figure 3 of another embodiment. The transfer of the cap 203 from the inactive position to the active position, or vice versa, is effected with actuator means similar to the actuator means 7 that are described above in connection with another embodiment. Since the cap 203 is connected to the second sub-rail 217 it means that also the cap 203 is displaceable in the longitudinal direction of the first sub- rail 215 and also in the longitudinal direction of the tower T.

In this connection it should be pointed out that in the embodiment according to Figure 6 the cap 203 has a shorter length that the length of a blade B. This is possible due to the fact that the cap 203 is displaceable along the blade B. This is illustrated in Figures 6 and 7, where the cap 203 assumes an upper position in Figure 6 and a lower position in Figure 7.

In Figure 8 a cross-section through the cap 203 is shown and also a cross-section through the blade B that will be subjected to deicing by the cap 203. As is evident from Figure 8 the cap 203 comprises a front portion 220 and two side portions 221 that are connected to the front portion 220 by means of hinges 222 that extend in the longitudinal direction of the cap 203, i.e. in a direction perpendicular to the paper in Figure 8. The hinges 222 are spring-loaded, i.e. the side portions 221 are urged towards the blade B. By this arrangement it is possible to adjust the cross-sectional shape of the cap 203 to the shape of the blade B, this being especially important when the cap is displaced along the blade B. To effect such adjustment the cap 203 is equipped with a number of spacing rods 223 that at one end is fixed to the

inner side of the side portions 221, said spacing rods 223 at the other end carrying a rotatable roller 224. Due to the spring-loaded hinge arrangement it is possible to adjust the cross-sectional shape of the cap 203 to the cross-sectional blade B that is subjected to deicing. Thus, the rotatable rollers 224 will normally be urged towards the exterior of the blade B, and hence the shape of the cap 203 will adapt to the shape of the blade B. In this connection it should be pointed out that the cross-sectional shape of the blade B varies along the longitudinal direction of the blade B.

The cap 203 is equipped with heating elements 11 that in principle could be identical to the heating elements 11 of the cap 3.

Feasible Modifications of the Invention

In the embodiments described above the displacement of the cap 3; 203 between active and inactive position, or vice versa, is effected by actuator means 7 that comprises first electric motors 9 that are displaceable along the base rail 1 by means of a gear rack. However, within the scope of the present invention it is feasible that the actuator means comprises other components for effecting the transfer between an active position or an inactive position of the cap 3; 203. In exemplifying and non-restricting purpose pressure medium cylinders or wire arrangements are mentioned.

In the embodiments described above infrared heaters 13 are mounted on the inner side of the cap 3; 203. However, within the scope of the present invention it is feasible to use other heating means, e.g. other types of electrical heating elements.