Relating to structural components for wind turbine blades

1. A wind turbine blade comprising an outer shell incorporating a metallic foil component, a conductive blade component in-board of the metallic foil component, and a fabric sheet assembly positioned between the metallic foil component and the conductive blade component, the fabric sheet assembly comprising:

one or more non-conductive fabric sheets which define first and second outer surfaces of the fabric sheet assembly; and

at least one conductive thread stitch penetrating a depth of the one or more fabric sheets and being exposed at the outer surfaces; thereby to enable equipotential bonding between the conductive blade component and the metallic foil component.

2. The wind turbine blade of claim 1 , wherein the at least one conductive thread stitch is arranged to contact the conductive blade component at the first outer surface, and to contact the metallic foil component at the second outer surface.

3. The wind turbine blade of claim 1 , wherein the conductive blade component comprises a conductive spar cap.

4. The wind turbine blade of claim 1 , wherein each of the fabric sheets comprises at least one of: a woven fabric sheet or a non-woven fabric sheet.

5. The wind turbine blade of claim 1 , wherein each of the fabric sheets comprises unidirectional fibres, biaxially-oriented woven fibres, or triaxially-oriented woven fibres.

6. The wind turbine blade of claim 4 , wherein the non-woven fabric sheet comprises randomly-oriented fibres.

7. The wind turbine blade of claim 1 , wherein the fabric sheet assembly comprises a plurality of non-conductive fabric sheets.

8. The wind turbine blade of claim 1 , wherein the at least one conductive thread stitch comprises a metallic thread.

9. The wind turbine blade of claim 1 , wherein the at least one conductive thread stitch comprises a non-metallic thread.

10. The wind turbine blade of claim 9 , wherein the non-metallic thread comprises a carbon fibre thread.

11. The wind turbine blade of claim 1 , wherein the at least one conductive thread stitch comprises a plurality of stitches arranged in a rectilinear pattern.

12. The wind turbine blade of claim 1 , wherein the at least one conductive thread stitch includes discrete groups comprising a plurality of stitches.

13. The wind turbine blade of claim 12 , wherein the discrete groups of stiches define at least one stitch-ring.

14. A method of assembling a wind turbine blade in a blade mould, the method comprising:

laying a metallic foil component in the blade mould;

providing a fabric sheet assembly on the metallic foil component;

laying a conductive blade component in the blade mould so that it overlays at least a portion of the fabric sheet assembly,

wherein the fabric sheet assembly comprises:

one or more non-conductive fabric sheets which define first and second outer surfaces; and

at least one conductive thread stitch penetrating a depth of the one or more fabric sheets and being exposed at the outer surfaces thereby to permit equipotential bonding between the conductive blade component and the metallic foil component via the fabric sheet assembly.

15. The method of claim 14 , wherein the at least one conductive thread stitch is arranged to contact the conductive blade component at the first outer surface, and to contact the metallic foil component at the second outer surface.

16. The method of claim 14 , further comprising laying at least one non-conductive fibre reinforced plastic structural layer in the blade mould so as to at least partially overlap the fibre reinforced plastic structural layer with the fabric sheet assembly.

17. A method of making a fabric sheet assembly for a structural component of a wind turbine blade, the method comprising:

providing one or more non-conductive fabric sheets defining first and second outer surfaces;

inserting at least one conductive thread stitch into the one or more non-conductive fabric sheets, the at least one conductive thread stitch penetrating a depth of the one or more fabric sheets and being exposed at the outer surfaces, thereby to permit electrical conduction between the first and second outer surfaces.