Wind turbine rotor blade with a lightning protection system

There is provided a wind turbine rotor blade comprising a rotor blade casing, and a lightning protection system having at least one lightning protection cable and a lighting protection cable holder. The lighting protection cable holder is fixed in or to the inside of the rotor blade casing. The lighting protection conductor holder has a first part and a second part. The first part is fixed to an inside of the rotor blade casing and has a receiving portion for receiving the lighting protection cable. The second part is in the form of a cover or covering means and is placed over the receiving portion. The first and second parts each have a radar-absorbing core or a radar-absorbing layer and an electrically insulating material which surrounds the radar-absorbing core or the radar-absorbing layer.

BACKGROUND

Technical Field

The present invention concerns a wind turbine rotor blade and a method of producing a wind turbine rotor blade as well as a lightning protection cable holder for a wind turbine rotor blade.

Description of the Related Art

Particularly in the case of wind turbines erected in the proximity of airfields, radar reflections, which are not constant, can occur by virtue of the moving rotor blades. Those non-constant rotor reflections can interfere with the radar systems of the airports or airfields.

Therefore the radar reflections generated by a wind turbine have to be reduced to be able to ensure that wind farms comprising a large number of wind turbines can be authorized in the proximity of airports or airfields or radar stations.

On the German patent application from which priority is claimed the German Patent and Trade Mark Office searched the following documents: EP 3 173 619 A1 and GB 2 488 561 A.

BRIEF SUMMARY

Provided is a wind turbine having reduced radar reflection. In particular, provided are wind turbine rotor blades which permit a reduction in radar reflections.

Thus a wind turbine rotor blade has a rotor blade casing and a lightning protection system. The lightning protection system has at least one lightning protection cable and a holder for the lightning protection cable. The holder can be fixed internally to the rotor blade casing. In particular the holder can be glued internally to the rotor blade casing. The holder has a first portion for fixing to the rotor blade casing and for receiving the lightning protection cable and a second portion which is fixed on the portion for completely enclosing the first portion and the lightning protection cable disposed therein. The first and/or second holding portion has a radar-absorbing portion and an electrically insulating material.

The electrically insulating material disposed in particular between the rotor blade casing and the lightning protection cable makes it possible to ensure that, in the event of a lightning strike, no damage is done to the material of the rotor blade casing. The radar-absorbing material can ensure that the radar reflections of the wind turbine rotor blade are considerably reduced.

According to an aspect of the present invention the radar-absorbing portion is in the form of a core of the first and/or second portion and is made from a radar-absorbing material. The electrically insulating material then surrounds the radar-absorbing core as a casing.

According to an aspect of the present invention the holder has a first part fixed on the rotor blade casing. The first part has a recess for receiving the lightning protection cable. The holder has a second part which is in the form of a cover or covering means and is fixed over or on the first part.

According to a further aspect of the present invention the first part of the holder has a straight adhesive portion, in particular consisting of the electrically insulating material. The first part of the holder also has a substantially U-shaped holding portion for receiving the lightning protection cable. A cover (as the second part) is placed over the first part and then together with the first portion completely covers over the lightning protection cable. The first and second parts each comprise an electrically insulating material with a radar-absorbing material as the core or as an inner layer.

According to a further aspect of the present invention the radar-absorbing material is in the form of a Salisbury screen or a Dallenbach layer.

The electrically insulating material can be made from TPU.

Also provided is a method of producing a wind turbine rotor blade. A rotor blade casing is provided for that purpose. Then a holder for a lightning protection cable is fixed on the inside of the rotor blade casing, in particular by adhesive. In that case in particular a first part of the holder comprising an electrically insulating material is fixed to the inside of the rotor blade casing. A radar-absorbing material is further provided in the first part. Then the lightning protection cable is placed in the first part and a second part, for example in the form of a cover or a covering means, is placed over the first part so that the lightning protection cable is completely surrounded by the first and second parts. The second part also comprises an electrically insulating material with a radar-absorbing material. In that way the lightning protection cable is completely surrounded by an electrically insulating material and a radar-absorbing material. In that arrangement the first and second parts can overlap each other so that both the electrically insulating material and also the radar-absorbing material of the first and second parts cover each other over.

Also provided is a lightning protection cable holder for a wind turbine, with a first part which can be fixed to a rotor blade internal surface with its first side and which has a recess for receiving a lightning protection cable, and a cover or a covering means which is placed as a second part on the first part so that the first and second parts overlap. The first and/or the second part each have an electrically insulating material and a radar-absorbing material.

According to an aspect of the present invention there is provided a wind turbine rotor blade having a rotor blade casing and a lightning protection system with at least one lightning protection cable. The lightning protection cable has a metallic electrical conductor, an insulating portion and radar-absorbing material. The insulating portion surrounds the metallic conductor. The radar-absorbing material can be provided in particle form in the insulating material. As an alternative thereto the radar-absorbing material can be provided as a jacket around the electrical conductor. As an alternative thereto the radar-absorbing material can be provided between the electrical conductor and the insulation portion.

Further configurations of the invention are recited in the appendant claims.

DETAILED DESCRIPTION

FIG. 1shows a wind turbine100comprising a tower102and a nacelle104. Arranged on the nacelle104is a rotor106having three rotor blades200and a spinner110. The rotor106is caused to rotate by the wind in operation and thereby drives a generator in the nacelle104. The rotor blade200is made from two half-shell portions230which are then secured together by adhesive. The rotor blade has a rotor blade tip210and a rotor blade root220.

FIG. 2shows a diagrammatic view of a wind turbine rotor blade. The rotor blade200has a rotor blade tip210and a rotor blade root220. The rotor blade further has a rotor blade casing230which for example comprises two half-shell portions which are secured together by adhesive.

In addition the rotor blade200has a lightning protection system300. A lightning receptor301can be provided in the region of the rotor blade tip210. The lightning protection system300further has a lightning protection cable310and a holder320for the lightning protection cable310. The lightning protection cable310can for example extend from the lightning receptor301into the region of the rotor blade root220. From there the lightning protection cable can be passed downwardly through a hub, the nacelle and the tower of the wind turbine and connected to ground.

The lightning protection cable320is fixed to the rotor blade casing230and the lightning protection cable320is placed in the holder310.

FIG. 3shows a diagrammatic cross-section of the lightning protection cable holder320. The holder320has a first part321which can be fixed to the rotor blade casing320of the rotor blade. For that purpose in particular a first straight end321acan be glued on or to the material of the rotor blade casing230. The first part321further has a receiving portion321bwhich for example is of a substantially U-shaped configuration and has an opening through which the lightning protection cable320can be placed in the first part321of the holder320.

The holder320further has a covering means or a cover322which can be placed over the receiving portion321bof the first part. The receiving portion321bhas a core or a layer of radar-absorbing material323and an electrically insulating material321bsurrounding the radar-absorbing material323.

The second part322of the holder can be of a substantially U-shaped or C-shaped configuration and can be placed over the first part321of the holder320to close an opening in the first part321. The second part322of the holder320has a radar-absorbing core323or a radar-absorbing layer324as well as an electrically insulating material surrounding the layer.

When the lightning protection cable310is placed in the receiving portion321band the covering means322is placed on the receiving portion321bthen the lightning protection cable310is completely enclosed by an electrically insulating material and a radar-absorbing material. In that case the receiving portion321band the second part322can overlap.

The receiving portion321bcan in particular have two arms which each have a radar-absorbing material and an electrically insulating material surrounding same. The second part322can also have two arms which can surround the arms of the first part in order thereby to completely enclose the lightning protection cable and thus permit optimum radar absorption.

By virtue of the fact that the radar-absorbing core or the radar-absorbing layer is completely surrounded by an electrically insulating material on the one hand this ensures effective lightning protection while on the other hand the radar absorption effects can be effectively reduced. That affords an effective way of reducing the complication and expenditure in terms of installing a lightning protection system with radar-absorbing properties in rotor blade manufacture.

The electrically insulating material can be made from a thermoplastic polyurethane TPU.

FIGS. 4A to 4Feach show a diagrammatic cross-section through a lightning protection cable according to a further aspect of the invention. The lightning protection cable according to the further aspect of the present invention can be used in the wind turbine ofFIG. 1and in the rotor blade ofFIG. 2. InFIGS. 4A and 4Bthe arrangement respectively has a lightning protection cable having a metallic conductor311, an insulator313and radar-absorbing material312, for example in the form of particles which are distributed within the electrical insulation313. While an outer jacket315is provided in the cable inFIG. 4Athat jacket is not present in the lightning protection cable shown inFIG. 4B.

FIGS. 4C and 4Dshow a further lightning protection cable having an electrical conductor311, an insulating portion313surrounding the conductor, a radar-absorbing material312, a further insulating portion314and, inFIG. 4C, an outer jacket315. The jacket315is not provided in the lightning protection cable shown inFIG. 4D.

Accordingly the radar-absorbing material312is illustrated as solid material surrounding the insulating portion313in the lightning protection cables shown inFIGS. 4C and 4D.

FIGS. 4E and 4Falso show a cross-section through a lightning protection cable. The lightning protection cable has a metallic conductor311as a core, a radar-absorbing solid material312which surrounds the core and an insulating portion313surrounding the radar-absorbing material312. Optionally—as shown inFIG. 4E—an outer jacket315can be provided. That jacket315is not provided in the lightning protection cable shown inFIG. 4F.

In a further embodiment of the invention therefore there is provided a fully insulated lightning protection system having a lightning protection conductor or cable which permits low radar reflection.

According to a further aspect of the invention there is provided a lightning protection cable or a lightning protection cable harness which in the interior has a metallic conductor and an electrical insulation around the conductor. The radar-absorbing material serves to reduce radar reflection. The radar-absorbing material312can be provided between the electrical conductor and the electrical insulation. As an alternative thereto the radar-absorbing material can also be provided around the electrical insulation.

The radar-absorbing material can represent a Salisbury screen, a magnetic absorber or a Dallenbach layer. Adequate electrical insulation can be provided between the radar-absorbing absorber and the surrounding environment. That is achieved by the electrical insulation of the electrical conductor.

The lightning protection cable shown inFIGS. 4A to 4Fcan be provided in a lightning protection conductor holder320as shown inFIG. 3, in which case it is possible to dispense with the radar-absorbing layer323.