Lighting receptor for a wind turbine blade

1. A wind turbine blade ( 10 ) comprising a lightning receptor arrangement ( 11 , 12 ) comprising at least an external metallic receptor element configured and arranged in one side of the wind turbine blade ( 10 ) in an operative position for receiving a lightning strike, an internal element joined at least to an internal side of a shell ( 17 ) of the wind turbine blade ( 10 ), and a down conductor ( 18 ) of a grounding arrangement connected to the internal element, wherein:

the external metallic receptor element is a self-threading screw ( 21 ) having a head ( 23 ) and a threaded shaft ( 25 );

the internal element comprises an electrically conductive block ( 20 ) configured with at least one initially unthreaded hole ( 41 ) opening in a surface of the block for cooperating with said threaded shaft ( 25 ), wherein the internal element also comprises an insulating coating ( 27 ) for the electrically conductive block ( 20 ), and wherein the surface of the block abuts and is in direct contact with the insulating coating ( 27 );

a material of the self-threading screw ( 21 ) has higher hardness and lower ductility than a material of the electrically conductive block ( 20 ), and the threaded shaft ( 25 ) and the at least one unthreaded hole ( 41 ) are dimensioned so that the self-threading screw is capable of achieving a threaded connection with the conductive block by a process of threading the self-threading screw ( 21 ) into the at least one unthreaded hole ( 41 ) of the conductive block ( 20 ) with formation of threads in the at least one unthreaded hole, wherein the self-threading screw is secured in the block in the operative position with a top of the head of the screw aligned with an external side of the shell and with an empty space between a bottom of the head of the screw and the insulating coating ( 27 ), and with the threaded connection transmitting to the block all lightning currents received by the self-threading screw ( 21 ); and

the internal element is joined to the shell ( 17 ) with an adhesive force capable of withstanding a torque applied to the head ( 23 ) of the self-threading screw ( 21 ) for threading it to the at least one unthreaded hole ( 41 ).

2. The wind turbine blade according to claim 1 , wherein the at least one unthreaded hole extends into the electrically conductive block a depth such that, with the self-threading screw in threaded connection with the at least one unthreaded hole and secured in the block with the empty space between the head of the screw and the surface of the block, a void exists between a bottom of the self-threading screw and a bottom of the at least one unthreaded hole.

3. A wind turbine blade ( 10 ) comprising a lightning receptor arrangement ( 11 , 12 ) comprising at least an external metallic receptor element configured and arranged in one side of the wind turbine blade ( 10 ) in an operative position for receiving a lightning strike, an internal element joined at least to an internal side of a shell ( 17 ) of the wind turbine blade ( 10 ), and a down conductor ( 18 ) of a grounding arrangement connected to the internal element, wherein:

the external metallic receptor element is a self-threading screw ( 21 ) having a head ( 23 ) and a threaded shaft ( 25 );

the internal element comprises an electrically conductive block ( 20 ) configured with at least one initially unthreaded hole ( 41 ) opening in a surface of the block for cooperating with said threaded shaft ( 25 ), wherein the surface of the block abuts and is in direct contact with the internal side of the shell;

a material of the self-threading screw ( 21 ) has higher hardness and lower ductility than a material of the electrically conductive block ( 20 ), and the threaded shaft ( 25 ) and the at least one unthreaded hole ( 41 ) are dimensioned so that the self-threading screw is capable of achieving a threaded connection with the conductive block by a process of threading the self-threading screw ( 21 ) into the at least one unthreaded hole ( 41 ) of the conductive block ( 20 ) with formation of threads in the at least one unthreaded hole, wherein the self-threading screw is secured in the block in the operative position with a top of the head of the screw aligned with an external side of the shell and with an empty space between a bottom of the head of the screw and the surface of the block, and with the threaded connection transmitting to the block all lightning currents received by the self-threading screw ( 21 ), and

the internal element is joined to the shell ( 17 ) with an adhesive force capable of withstanding a torque applied to the head ( 23 ) of the self-threading screw ( 21 ) for threading it to the at least one unthreaded hole ( 41 ).

4. The wind turbine blade ( 10 ) according to claim 3 , wherein each of the threaded shaft ( 25 ) and the at least one unthreaded hole ( 41 ) has a cylindrical shape, wherein a ratio between a diameter (D 1 ) of a base of the cylindrical shape of the threaded shaft ( 25 ) and a diameter (D 2 ) of a base of the cylindrical shape of the at least one hole ( 41 ) ranges from 1.03 to 1.60.

5. The wind turbine blade ( 10 ) according to claim 3 , wherein:

the self-threading screw ( 21 ) is made of steel, stainless steel or tungsten;

the electrically conductive block ( 20 ) is made of aluminium, copper or brass.

6. The wind turbine blade ( 10 ) according to claim 3 , further comprising an additional self-threading screw ( 22 ) as a metallic receptor element in an opposite side of the wind turbine blade ( 10 ) for receiving a lightning strike having a head ( 24 ) and a threaded shaft ( 26 ) wherein:

the electrically conductive block ( 20 ) is also configured with an additional initially unthreaded hole ( 42 ) in an opposite surface for cooperating with the threaded shaft ( 26 ) of the additional self-threading screw ( 22 );

the additional self-threading screw has a head and a threaded shaft;

a material of the additional self-threading screw ( 22 ) has higher hardness and lower ductility than the material of the electrically conductive block ( 20 ), and the threaded shaft ( 26 ) of the additional self-threading screw ( 22 ) and the additional unthreaded hole ( 42 ) are dimensioned so that the additional self-threading screw is capable of achieving a threaded connection with the additional unthreaded hole, wherein the additional self-threading screw is configured and dimensioned such that the additional self-threading screw can be secured in the block notwithstanding an empty space between the head of the additional self-threading screw and the opposite surface of the block, and the threaded connection can transmit all lightning currents received by the additional self-threading screw ( 22 ).

7. The wind turbine blade ( 10 ) according to claim 6 , wherein the threaded shaft ( 26 ) of the additional self-threading screw ( 22 ) and the additional unthreaded hole ( 42 ) are also dimensioned so that the threaded connection between them has a length that enables an alignment of the head ( 24 ) of the additional self-threading screw ( 22 ) with a second outer surface of the shell ( 19 ) of the wind turbine blade ( 10 ) for aerodynamic continuity purposes.

8. The wind turbine blade ( 10 ) according to claim 6 , wherein each of the threaded shaft ( 26 ) of the additional self-threading screw ( 22 ) and the additional unthreaded hole ( 42 ) has a cylindrical shape, wherein a ratio between a diameter (D 1 ) of a base of the cylindrical shape of the threaded shaft ( 25 ) and a diameter (D 2 ) of a base of the cylindrical shape of the additional unthreaded hole ( 41 ) ranges from 1.03 to 1.60.

9. The wind turbine blade ( 10 ) according to claim 6 , wherein the additional self-threading screw ( 22 ) is made of steel, stainless steel or tungsten.

10. The wind turbine blade according to claim 3 , wherein the at least one unthreaded hole extends into the electrically conductive block a depth such that, with the self-threading screw in threaded connection with the at least one unthreaded hole and secured in the block with the empty space between the head of the screw and the surface of the block, a void exists between a bottom of the self-threading screw and a bottom of the at least one unthreaded hole.