Wind turbine lightning protection system

1. A wind turbine blade comprising:

a root end and a tip end, a spanwise dimension extending between the root and tip ends, and an inboard portion extending up to 50% of the spanwise dimension from the root end towards a midpoint between the root and tip ends;

at least one electrically conductive component disposed in the inboard portion;

at least two shear webs, each shear web of the at least two shear webs having a pair of discrete spar caps; and

a lightning protection system comprising:

a down conductor cable portion disposed inside the inboard portion of the blade; and

a supporting component,

wherein the down conductor cable portion is secured in free space by the supporting component in a position near or on a camber line of a blade aerofoil section of the wind turbine blade and spaced away from the at least one electrically conductive component, and

wherein the down conductor cable portion is secured in the free space between the at least two shear webs by the supporting component and spaced away from the at least two shear webs.

2. The wind turbine blade of claim 1 , wherein the at least one electrically conductive component is a structural component comprising a spar cap, wherein the spar cap comprises carbon fibres, and wherein the carbon fibres are pultruded carbon fibres.

3. The wind turbine blade of claim 1 , wherein the blade comprises two shell halves, each of the two shell halves having an electrically conductive component, and wherein the down conductor cable portion is spaced substantially equally from both electrically conductive components.

4. The wind turbine blade of claim 1 , wherein the supporting component is one or more of: a foam piece; a foam sack; a bracket; and a straight beam.

5. The wind turbine blade of claim 4 , wherein the supporting component is an X-shaped bracket.

6. The wind turbine blade of claim 4 , wherein the supporting component is a C-shaped bracket.

7. The wind turbine blade of claim 4 , wherein the supporting component is a Y-shaped bracket.

8. The wind turbine blade of claim 1 , wherein the down conductor cable portion at least partly overlaps with the at least one electrically conductive component in the spanwise dimension.

9. The wind turbine blade of claim 1 , wherein the lightning protection system further comprises:

a down conductor;

a diverging electrical junction disposed in the inboard portion; and

a plurality of inboard down conductor cables arranged electrically in parallel to one another and disposed in the inboard portion;

wherein the lightning protection system is configured so as to conduct electricity through the down conductor, through the diverging electrical junction, through the plurality of inboard down conductor cables, towards the root end of the blade.

10. The wind turbine blade of claim 1 , wherein the lightning protection system further comprises:

a down conductor cable having the down conductor cable portion;

wherein the down conductor cable further comprises a cable first portion and a cable second portion, the cable first portion being closer to the root end of the blade than the cable second portion, each of the cable first portion and the cable second portion comprising insulation which has a respective electrical breakdown voltage, wherein the cable first portion insulation electrical breakdown voltage is higher than the cable second portion insulation electrical breakdown voltage.

11. The wind turbine blade of claim 10 , wherein the down conductor cable portion comprises the cable first portion and/or the cable second portion.

12. The wind turbine blade of claim 1 , wherein the down conductor cable portion is spaced apart from an electrically conductive portion of one or more of: a sensor system; a de-icing system, an anti-icing system; a lighting system; and a load control system.

13. The wind turbine blade of claim 1 , wherein the inboard portion extends up to 40% of the spanwise dimension from the root end towards the tip end.

14. The wind turbine blade of claim 1 , wherein the inboard portion extends up to 30% of the spanwise dimension from the root end towards the tip end.

15. The wind turbine blade of claim 1 , wherein the down conductor cable portion is disposed substantially centrally between the at least two shear webs.

16. The wind turbine blade of claim 1 , wherein the supporting component is attached to at least one of the at least two shear webs.

17. The wind turbine blade of claim 16 , wherein the supporting component is attached to the at least one of the at least two shear webs at at least two locations.

18. The wind turbine blade of claim 16 , wherein the supporting component is attached to more than one of the at least two shear webs.

19. The wind turbine blade of claim 18 , wherein the down conductor cable portion is disposed substantially centrally between a pair of the at least two shear webs.