Lightning protection system for a wind turbine blade
The invention relates to a lightning protection system for a wind turbine blade, where the blade is a shell body made of a composite material and comprises a root area and a tip end. The lightning protection system comprises at least one lightning receptor arranged freely accessible in or on the shell unit surface on or in the immediate vicinity of the tip of the blade, and a lightning conductor made of electrically conductive material extending within the shell body along substantially the entire longitudinal direction of the blade. The lightning receptor and the lightning conductor are electrically connected by means of a connection area. The lightning conductor in its entire longitudinal direction as well as the connection area between the lightning conductor and the lightning receptor are electrically insulated in order to prevent lightning striking through the surface of the blade.
1. A wind turbine blade with a lightning protection system ( 1 , 101 , 201 ), wherein the blade ( 1 , 101 , 201 ) is a shell body made of a composite material and comprises a root area and a tip end, and wherein the lightning protection system comprises:
at least one lightning receptor ( 3 , 103 , 203 ) arranged freely accessible in or on the shell unit surface at or in the immediate vicinity of the tip of the blade ( 1 , 101 , 201 ), and
a lightning conductor ( 2 , 102 , 202 ) made of electrically conductive material extending within the shell body along substantially the entire longitudinal direction of the blade ( 1 , 101 , 201 ), and wherein
the lightning receptor ( 3 , 103 , 203 ) and the lightning conductor ( 2 , 102 , 202 ) are electrically connected by means of a connection area,
characterized in that
the lightning conductor ( 2 , 102 , 202 ) in its entire longitudinal direction as well as the connection area between the lightning conductor ( 2 , 102 , 202 ) and the lightning receptor ( 3 , 103 , 203 ) is electrically insulated in order to prevent the built-up of streamers and/or leaders.
2. A wind turbine blade according to claim 1 , characterized in that the lightning conductor ( 2 , 102 , 202 ) and/or lightning receptor ( 3 , 103 , 203 ) are electrically insulated at least up to the shell body of the blade ( 1 , 101 , 201 ) and preferably at least partially through the shell body.
3. A wind turbine blade according to claim 1 , characterized in that the lightning conductor ( 2 , 102 , 202 ) comprises an inner conductor ( 21 ) made of electrically conductive material, such as copper or aluminium, and a bedding insulation ( 22 ) made of polyethylene, preferably HDPE.
4. A wind turbine blade according to claim 3 , characterized in that the inner conductor ( 21 ) has a diameter in the range of 3-30 mm, 5-15 mm or 7.5-12 mm and the bedding insulation ( 22 ) has a thickness of 2-15 mm, 3-10 mm or 4-7 mm.
5. A wind turbine blade according to claim 3 , characterized in that a layer of semiconducting material ( 23 ) is provided between the inner conductor ( 21 ) and the bedding insulation ( 22 ).
6. A wind turbine blade according to claim 3 , characterized in that the lightning receptor ( 3 , 103 , 203 ) and the connection area between the lightning receptor ( 3 , 103 , 203 ) and the lightning conductor ( 2 , 102 , 202 ) are insulated by means of an insulating material, which is separate from the bedding material.
7. A wind turbine blade according to claim 3 , characterized in that the tip ( 105 , 205 ) of the blade ( 1 , 101 , 201 ) is formed as a substantially solid body of insulating material.
8. A wind turbine blade according to claim 7 , characterized in that the insulating material is a plastic material, such as PVC, fibre-reinforced polymer or polyurethane (PUR), e.g. foam PUR.
9. A wind turbine blade according to claim 1 , characterized in that the lightning conductor ( 2 , 102 , 202 ) is provided with a connection means, e.g. a thread, at its outer end to connect said conductor to a corresponding means on the lightning receptor.
10. A wind turbine blade according to claim 1 , characterized in that additionally, at least one drain hole ( 4 , 104 , 204 ) is arranged at or in the immediate vicinity of the tip of the blade ( 1 , 101 , 201 ), and optionally, that a diverter extending substantially between the location of the drain hole ( 4 , 104 , 204 ) and the location of the lightning receptor ( 3 , 103 , 203 ) is positioned on the surface of the blade ( 1 , 101 , 201 ).
11. A wind turbine blade according to claim 1 , characterized in that the lightning receptor ( 3 , 103 , 203 ) has the form of a Franklin rod or is substantially shaped like an egg.
12. A wind turbine blade according to claim 1 , characterized in that a part of the tip ( 205 ) of the blade ( 201 ) is adapted to be the lightning receptor ( 203 ) made of e.g. tungsten, copper or brass.