WO2025008034A1

WO2025008034A1 - Wind turbine blade shell with heating element

Info

Publication number: WO2025008034A1
Application number: PCT/DK2024/050155
Authority: WO
Inventors: Stephen Jude BUGGY; Edward Noel FINN; Toby Collard; Mohamed Hashim ARIYUR; Nathan A BRILLIANT; Jesper HØRUP
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2023-07-05
Filing date: 2024-07-01
Publication date: 2025-01-09
Anticipated expiration: 2026-01-05

Abstract

A wind turbine blade shell comprising: an inner shell portion comprising a fibre reinforced composite material; an outer shell portion; an electro-thermal heating element embedded within the blade shell; and a metallic power line which is connected to the electro-thermal heating element at a terminal. The metallic power line is configured to carry electrical power to the electro-thermal heating element via the terminal. The metallic power line is sandwiched between the inner and outer shell portions.

Description

WIND TURBINE BLADE SHELL WITH HEATING ELEMENT

FIELD OF THE INVENTION

The present invention relates to a wind turbine blade shell comprising; an electrothermal heating element; and a power line which is connected to the electro-thermal heating element.

BACKGROUND OF THE INVENTION

US6145787 discloses heatable wind energy turbine blades and a method of heating and deicing the turbine blades using conductive fabrics to displace and/or cease the buildup of ice on the turbine blades by electrothermal fabric heater disposed or integrated on the turbines for effectively deicing the blades. The fabric heater element is connected by wire and/or conductive ribbon to a suitable electric source, which provides the electrical power to heat the surface of the turbine blade.

A de-icing arrangement of a wind turbine rotor blade is described in US2014/0199170. The de-icing arrangement includes an electrically conductive mat, an electrically conductive band for distributing an electric current along a first edge of the mat, and a current supply connector for connecting the band to a current supply, wherein at least the electrically conductive mat is sandwiched in the body of the rotor blade. Current supply leads are arranged in the interior of the blade. These can be flat bands of a conductive material, for example a woven copper strip.

US2020/0149513 discloses an Electro-Thermal Heating (ETH) element for a wind turbine blade. The ETH elements is sandwiched within the blade structure between laminate layers of the blade structure. The ETH element is formed from a lightweight layer of conductive material, with busbars positioned at opposite sides or ends of the ETH element, to provide the connection for the supply of electrical power. If the laminate layers of the blade are damaged and require a repair then the standard repair procedure is to grind away the laminate layers that are damaged, or to grind down to the damaged area, and the damaged laminate layers replaced with new materials.

US2022/0243703 discloses a method of inspecting a wind turbine blade. The wind turbine blade comprises an electro-thermal heating element and a surface protection layer. The wind turbine blade may further comprise an insulating layer between the electro-thermal heating element and the surface protection layer. A test point of the electro-thermal heating element may be exposed by removing blade material, such as a part of the insulating layer and a part of the surface protection layer. The parts of the insulating layer and the surface protection layer may be removed by grinding. The wind turbine blade may be repaired by replacing the removed parts of the insulating layer and the surface protection layer with repair patches.

A problem with LIS6145787 and US2014/0199170 is that a repair method as disclosed in US2020/0149513 or US2022/0243703 cannot be used to repair the wire, conductive ribbon or current supply leads, because they are within the interior of the blade and hence too far from the outer surface to be reached by grinding.

WO2011/096851 discloses a de-icing/anti-icing system comprising at least two conductive structures sandwiched in a wind turbine blade, which includes an outer surface being designed as an aerodynamic surface, at least one of the conductive is arranged adjacent the outer surface, a control unit is adapted to control the energy supply to the conductive structures for generating heat to the outer surface. One conductive structure comprises a first conductive nano structure, the conductive structure's conductive property differs from the conductive property of the other conductive structure comprising a second conductive nano structure. The first and second conductive structures are preferably compatible regarding the thermal elongation with both glass fibre reinforced plastics (GFRP) and carbon fibre reinforced plastic (CFRP) structures. According to WO2011/096851 , a common conductive structure for ice protection is made of metal, which is less compatible with GFRP and CFRP due to a higher thermal expansion which may cause debonding, failure in the electrical path etc.

A problem with WO2011/096851 is that a repair method as disclosed in US2020/0149513 or US2022/0243703 cannot be used to repair the conductive nano structures, because the grinding may release nano structures as dust into the environment, which is hazardous to health. SUMMARY OF THE INVENTION

A first aspect of the invention provides a wind turbine blade shell comprising: an inner shell portion comprising a fibre-reinforced composite material; an outer shell portion; an electro-thermal heating element embedded within the blade shell; and a metallic power line which is connected to the electro-thermal heating element at a terminal and configured to carry electrical power to the electro-thermal heating element via the terminal, wherein the metallic power line is sandwiched between the inner and outer shell portions.

Optionally the wind turbine blade shell extends from a root to a tip, and a transmission part of the metallic power line extends away from the electro-thermal heating element towards the root of the wind turbine blade shell and is sandwiched between the inner and outer shell portions.

Optionally the metallic power line has a connection part which overlaps the heating element at the terminal, and the connection part is electrically connected to the heating element via a direct contact with the heating element.

Optionally the heating element comprises a heating mat, and the connection part of the metallic power line comprises a strip which extends across a major part of a width of the heating mat.

Optionally the heating element comprises a heating mat, and a busbar which is electrically connected to the metallic power line at the terminal, wherein the busbar comprises a conductive strip which extends across a major part of a width of the heating mat.

Optionally the outer shell portion comprises a metallic surface protection layer (SPL).

Optionally the metallic SPL and/or the metallic power line comprise a porous structure (such as an expanded foil, a grid, a mesh, a woven fabric or a non-woven veil).

Optionally the metallic SPL and/or the metallic power line comprise an expanded foil, a grid, a mesh, a woven fabric or a non-woven veil. Optionally the metallic SPL and/or the metallic power line comprise an expanded foil.

Optionally the metallic SPL and/or the metallic power line comprise aluminium or copper

Optionally the metallic power line comprises a porous structure (such as an expanded foil, a grid, a mesh, a woven fabric or a non-woven veil) which is sandwiched between the inner and outer shell portions.

Optionally the metallic power line comprises an expanded foil, a grid, a mesh, a woven fabric or a non-woven veil which is sandwiched between the inner and outer shell portions.

Optionally metallic power line comprises an expanded foil which is sandwiched between the inner and outer shell portions.

Optionally the wind turbine blade shell further comprises one or more insulating layers between the metallic power line and the electro-thermal heating element.

Optionally the terminal comprises a connector which connects the metallic power line to the electro-thermal heating element, and the connector passes through the one or more insulating layers.

Optionally the wind turbine blade shell further comprises a surge protection device configured to prevent surge currents from flowing into the heating element, wherein the surge protection device is electrically coupled to the metallic power line via the connector, and the metallic power line is electrically coupled to the heating element and the surge protection device in parallel.

Optionally the metallic power line comprises a strip which is sandwiched between the inner and outer shell portions.

Optionally the metallic power line is impregnated by polymeric material. Optionally the metallic power line is sandwiched between, and optionally in direct contact with, a pair of plies of fibre-reinforced composite material (for instance glassfibre composite plies or any other type of fibre-reinforced composite material).

Optionally the metallic power line and the inner and/or outer shell section are impregnated by the same polymeric material.

Optionally the inner shell portion forms a major part of a thickness of the shell.

Optionally the outer shell portion comprises a fibre-reinforced composite material (for instance glass-fibre composite plies or any other type of fibre-reinforced composite material).

Optionally the fibre-reinforced composite material of the inner shell portion and/or the fibre-reinforced composite material of the outer shell portion comprises a glass-fibre composite material.

Optionally the inner or outer shell portion comprises a laminar stack, the laminar stack comprising two or more plies of fibre-reinforced composite material (for instance glassfibre composite plies or any other type of fibre-reinforced composite material).

Optionally the laminar stack comprises a core sandwiched between plies of fibre- reinforced composite material (for instance glass-fibre composite plies or any other type of fibre-reinforced composite material). Optionally the core comprises a foam.

The heating element is embedded within the blade shell, optionally sandwiched between a structural portion of the blade shell and a cover portion of the blade shell.

According to a further aspect of the invention, there is provided a wind turbine blade comprising a wind turbine blade shell according to the preceding aspect.

According to a further aspect of the invention, there is provided a wind turbine comprising a wind turbine blade according to the preceding aspect, and an electrical power supply coupled to the metallic power line. According to a further aspect of the invention, there is provided a method for manufacturing a wind turbine blade shell comprising: forming an outer shell portion, forming an inner shell portion comprising one or more layers of glass-fibre plies, arranging a metallic power line so that the metallic power line is sandwiched between the inner and outer shell portions, embedding an electro-thermal heating element within the blade shell so that a portion of the electro-thermal heating element is arranged adjacent to a portion of the metallic power line, and providing an electrical connection between the metallic power line and the electro-thermal heating element.

The different steps of the method may be performed in any order.

The wind turbine blade shell may be subsequently infused with resin or another polymeric matrix material. Alternatively, the fibre plies may be wet or semi-dry fibre plies, requiring no or only partial infusion of resin.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a wind turbine;

Figure 2 is a cross-sectional view of a blade shell of the wind turbine of Figure 1 ;

Figure 3 is a planform view of the blade shell of Figure 2;

Figure 4 is a planform view of a heating element and its power lines;

Figure 5A is a schematic cross-sectional view taken along a line A-A shown in Figure 4;

Figure 5B is a schematic cross-sectional view taken along a line B-B shown in Figure 4;

Figure 6A is a schematic cross-sectional view taken along a line A-A shown in Figure 4, according to a second embodiment;

Figure 6B is an alternative schematic cross-sectional view taken along a line B-B shown in Figure 4, according to the second embodiment;

Figure 7 is a planform view of an alternative heating element with straight power lines; Figure 8 is a planform view of a heating element and its power lines;

Figure 9A is a schematic cross-sectional view taken along a line A-A shown in Figure 8;

Figure 9B is a schematic cross-sectional view taken along a line B-B shown in Figure 8;

Figure 10 is a planform view of a heating element and its power lines;

Figure 11 A is a schematic cross-sectional view taken along a line A-A shown in Figure 10;

Figure 11 B is a schematic cross-sectional view taken along a line B-B shown in Figure 10;

Figure 12 shows a surge protection device (SPD) connection arrangement; and Figure 13 is a schematic cross-sectional view showing the SPD mounted in the interior of a blade shell.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Figure 1 shows a wind turbine 1 including a tower mounted on a foundation and a nacelle disposed at the apex of the tower. The wind turbine 1 depicted here is an onshore wind turbine such that the foundation is embedded in the ground, but the wind turbine 1 could be an offshore installation in which case the foundation would be provided by a suitable marine platform.

A rotor is operatively coupled via a gearbox to a generator (not shown) housed inside the nacelle. The rotor includes a central hub and a plurality of rotor blades 2, which project outwardly from the central hub. It will be noted that the wind turbine 1 is the common type of horizontal axis wind turbine (HAWT) such that the rotor is mounted at the nacelle to rotate about a substantially horizontal axis defined at the centre at the hub. While the example shown in Figure 1 has three blades, it will be realised by the skilled person that other numbers of blades are possible.

When wind blows against the wind turbine 1 , the blades 2 generate a lift force which causes the rotor to rotate, which in turn causes the generator within the nacelle to generate electrical energy.

Figures 2 and 3 illustrate one of the wind turbine blades 2 for use in such a wind turbine. Each of the blades 2 has a root end 6 proximal to the hub and a tip end 7 distal from the hub. A leading edge 5a and a trailing edge 5b extend between the root end 6 and tip end 7, and each of the blades 2 has a respective aerodynamic high pressure surface (i.e. the pressure surface) and an aerodynamic low pressure surface (i.e. the suction surface) extending between the leading and trailing edges of the blade 2. The pressure surface is on a pressure side of the blade and the suction surface is on a suction side of the blade. A chord-line 40 is shown in Figure 2, extending between the leading and trailing edges 5a, 5b.

The blade may be split in the spanwise direction to form a segmented blade comprising a plurality of blade portions each having a root and a tip, alternatively the blade may be continuous from the root end 6 to the tip end 7 forming one blade portion.

As shown in Figure 2, the wind turbine blade 2 includes an outer blade shell defining a hollow interior space 41 with a shear web (not shown) extending internally between upper and lower parts of the blade shell. The blade shell may comprise two half-shells 3, 4 which are separately moulded before being joined together (at the leading edge 5a and the trailing edge 5b) to form the blade 2. It will be appreciated that the blade shell need not be formed as two half-shells which are subsequently joined together but may be formed as a unitary shell structure, together with the shear web, in a "one shot" single shell process.

It will be understood that the term “wind turbine blade shell” is used herein to refer to either a unitary shell structure, or to a portion of a complete blade shell (such as a halfshell or a blade portion of a segmented blade).

The blade shell has a blade heating system comprising a set of electro-thermal heating elements positioned at the leading edge 5a. Figure 3 shows an exemplary pair of such heating elements 8, 9 in the blade shell 3 on the suction side of the blade. Further similar heating elements (not shown) may be arranged along the span of the leading edge 5a. As shown in Figure 3, the heating element 8,9 are positioned towards the tip 7 of the blade, where the interior of the blade may not be easily accessible.

Similar heating elements may also be provided in the blade shell 4 on the pressure side of the blade. One of such heating elements 8a is shown in Figure 2. The heating elements 8, 9 may be used for either or both of anti-icing (preventing ice accumulating) or de-icing (removing accumulated ice) of the blade 2.

Each heating element 8, 9 may be coupled to an electrical power supply 32 by a respective pair of power lines: one power line connected to a high voltage terminal of the power supply 32, the other power line being a return line. Other power connection architectures than illustrated may be used. For example, two or more heating elements 8, 9 may be powered by a pair of power lines, i.e. one high voltage supply line and one return line. Thus, two or more heating elements in the blade 2, such as two or more heating elements arranged in one of the shells 3, 4 may be connected in parallel or in series to a pair of power lines.

Figure 4 is a planform view of an exemplary one of the heating elements 8. The heating element 8 comprises a heating mat 12 with a busbar 16 at each end. The heating mat 12 may comprise a sheet of conductive resistive material, such as a carbon fibre veil, a carbon/glass fibre veil, or a metallic mesh, for example. As currents flow through the heating mat 12 between the busbars 16, the resistance in the material causes heat to be generated by resistive heating, Joule heating or Ohmic heating.

Each busbar 16 comprises a conductive strip (for instance copper) which extends across a major part of a width of the heating mat 12 and is in direct contact with the heating mat 12. The purpose of the busbars 16 is to ensure that current flow, and hence heating flux, is distributed uniformly across a width of the heating mat 12. The term “width” is used here to refer to the lateral dimension of the heating mat 12 at right angles to the flow of current.

Each busbar 16 is electrically connected to a respective metallic power line at a respective terminal. Figures 5 and 6 show two different terminal arrangements, with the same reference numbers used to indicate equivalent components.

Referring first to Figure 5A: the wind turbine blade shell comprises: glass-fibre plies 10a-10g; a foam core 11 sandwiched between glass fibres plies 10b, 10c; the heating mat 12 and busbar 16; a surface protection layer (SPL) 13; and surface layers such as a gel layer 14 and one or more paint layers 15. The outer surface of the paint layer 15 forms the external aerodynamic surface of the blade shell, and the inner surface of the glass fibre ply 10a forms an internal surface of the blade shell. The SPL 13 may be made of a metallic material such as aluminium or copper. The purpose of the SPL 13 is to protect the heating elements and the blade laminate if the blade is struck by lightning. In the event of a lightning strike, the surface protection layer 13 conducts electrical currents to ground via other sub-components of the electrically grounded network. Thus, the SPL 13 may act as a lightning-strike protection layer. The SPL 13 typically comprises a perforated foil, an expanded foil, a grid or a mesh. In one example the SPL 13 comprises an aluminium expanded foil.

As shown in Figure 4, the metallic power line comprises a transmission part 18 which extends in a spanwise direction away from the electro-thermal heating element 8 towards the root 6 of the wind turbine blade shell; and a connection part 17 which extends in a chordwise direction away from the electro-thermal heating element 8 towards the trailing edge 5b of the wind turbine blade shell. The connection part 17 is connected to the busbar 16 by a connector 20-24 shown in Figure 5A.

The connector comprises a bolt with a head 20, a threaded shaft 21 , a nut 22, a washer 23 and a spacer 24. All parts 20-24 of the connector are made of a conductive material such as a metal.

In the example of Figure 5A, the connection part 17 of the metallic power line is sandwiched between the core 11 and the glass-fibre ply 10c.

The nut 22 may be fitted into a bore (not shown) in the core 11 and the glass-fibre plies 10a, 10b. Similarly the spacer 24 may be fitted into a bore (not shown) in the glassfibre plies 10d, 10c. The head 20 is relatively thin so no bore may be needed in the glass fibre plies 10e, 10f. Alternatively the head 20 may be fitted into a bore (not shown) in one or both of the glass-fibre plies 10e, 10f.

In the example of Figure 6A, the connection part 17 of the metallic power line is sandwiched between the glass-fibre plies 10a, 10b. The spacer 24 may be fitted into a bore (not shown) in the glass-fibre plies 10b, 10c, 10d and the core 11. The washer 23 may be fitted into a bore (not shown) in the glass-fibre ply 10a.

In both Figure 5A and Figure 6A, when the nut 22 is tightened, the parts 17, 24, 12, 16 are clamped between the washer 23 and the head 20 of the bolt, forming a secure pressure connection between them and ensuring that electrical current can flow unimpeded from the metallic power line 17 into the busbar 16 via the shaft 21 and the head 20 of the bolt.

The glass-fibre plies 10c, 10d provide an insulating layer between the metallic power line 17 and the electro-thermal heating element 12, 16. The shaft 21 of the connector passes through this insulating layer 10c, 10d, the shaft 21 extending in the thickness direction of the laminate (i.e. the vertical direction of Figures 5A and 6A).

Figure 7 is a planform view of an alternative power line arrangement, with the same reference numbers used to indicate equivalent components as in Figure 4. In the case of Figure 7, each metallic power line comprises a transmission part 18 which extends in a spanwise direction away from the electro-thermal heating element 8 towards the root 6 of the wind turbine blade shell, and a small connection part. A portion of the electro-thermal heating element is arranged adjacent to the connection part of the metallic power line. The connection part is connected to the busbar 16 by a connector 20-24 shown in Figure 5A or Figure 6A. Unlike the previous embodiments, the connection part does not extend in the chordwise direction, but instead the metallic power line lies entirely in a straight line (at least in the part of the blade shell shown in Figure 7).

Figures 8 and 9A show a different terminal arrangement, again with the same reference numbers used to indicate equivalent components to the previously described terminal arrangements.

In the example of Figures 8 and 9A, the connection part 17 of the metallic power line has an overlapping portion which overlaps the outer face of the busbar 16 of the heating element 8 at the terminal, and this overlapping portion is electrically connected to the heating element via a direct contact with the outer face of the busbar 16.

As shown in Figure 9A, the overlapping portion of the connection part 17 of the metallic power line is sandwiched between the busbar 16 and the glass-fibre ply 10e.

Unlike in the previous embodiments, there is no connector passing through the thickness of the laminate stack between the busbar 16 and the connection part 17 of the metallic power line. Instead, the metallic power line is electrically connected to the heating element via a direct contact with the busbar 16.

Figures 10 and 11A show a different terminal arrangement, again with the same reference numbers used to indicate equivalent components to the previously described terminal arrangements.

As shown in Figures 10 and 11 A, the connection part 17 of the metallic power line has an overlapping portion which overlaps the heating mat 12 at the terminal, and this overlapping portion is electrically connected to the heating element via a direct contact with the outer face of the heating mat 12. As shown in Figure 11A, the overlapping portion of the connection part 17 of the metallic power line is sandwiched between the busbar 16 and the glass-fibre ply 10e.

The embodiment of Figure 10 and 11A is similar to the embodiment of Figure 8 and 9A, except that the heating element 8 consists of a heating mat 12 with no busbars. Rather, the overlapping portion of the connection part 17 of the metallic power line is lengthened (compared with the connection part 17 of Figure 8) to form an elongate strip which extends across a full width of the heating mat 12, or at least across a major portion of the width. This elongate strip performs the same function as the busbar 16 in the previous embodiments.

Each blade shell 3, 4 may be laid up in a mould as a stack of plies. The stack may include fibre plies, metal plies (such as the SPL 13, heating elements 8, 9, and power lines 17, 18) and the connectors 20-24. Some of the plies may include a plurality of plies stitched or otherwise attached together as a kit.

The plies may be pre-cut to fit the shape of the mould such that the stacks of plies readily conform to the shape of the mould and a number of plies may be laid up in the mould easily and in a short time, preferably without the need for any cutting or detailed shaping of the plies once in the mould. Alternatively the plies may be cut in the mould. The stacks of plies may include dry fibres to be subsequently infused with resin or alternatively the fibre plies may be wet or semi-dry fibre plies, requiring no or only partial infusion of resin prior to consolidation and cure within the mould. The stack of plies may alternatively be laid up ply-by-ply in the mould. The stacks of plies may be prepared out of the mould on a flat or near flat surface outside the mould such that the stack of plies assume their form or shape upon being laid up in the mould. Alternatively the stack of plies may be laid up on a suitably shaped surface outside the mould such that the stack of plies assume their (near final) form or shape outside the mould before being laid up in the mould.

The resin (or other polymeric matrix material) is indicated by reference 19 in the drawings. The resin 19 may impregnate the porous elements of the blade shell, including the glass-fibre plies 10-e, the heating mats 12, and the porous mesh material of the SPL 13 and the power line 17, 18.

Note that the drawings are schematic, and not to scale. Resin-rich regions are shown between the various layers in the cross-sectional views, but such resin-rich regions may be thinner, or not present, and certain elements of the stack (for instance the heating mat 12 and the busbars 16) may be in direct contact (without any resin between them) to ensure a good electrical connection.

In all of the embodiments described above, the heating elements 8, 9 are embedded within the blade shell, sandwiched between a structural portion of the blade shell (which may include a core 11 and glass-fibre plies 10a-10d) and a cover portion of the blade shell (which may include glass-fibre plies 10e-g, the SPL 13 and the surface layers 14, 15).

Typically the cover portion of the shell is laid up first, then the heating elements 8, 9 are arranged on the cover portion. Alternatively the structural portion may be laid up first, then the heating elements 8, 9 are arranged on the structural portion.

The transmission part 18 of the metallic power line is embedded within the blade shell, sandwiched between an inner shell portion and an outer shell portion, as shown by way of example in Figures 5B, 6B, 9B and 11 B.

In the case of Figure 5B, the inner shell portion comprises the core 11 and glass-fibre plies 10a, 10b; and the outer shell portion comprises the glass-fibre plies 10c-g, the SPL 13 and the surface layers 14, 15. In the case of Figure 6B, the inner shell portion comprises a single glass-fibre ply 10a; and the outer shell portion comprises the glass-fibre plies 10b-g, the core 11 , the SPL 13 and the surface layers 14, 15.

In the case of Figures 9B and 11 B, the inner shell portion comprises the core 11 and glass-fibre plies 10a-d; and the outer shell portion comprises the glass-fibre plies 10e- g, the SPL 13 and the surface layers 14, 15.

In all cases the inner shell portion comprises a fibre-reinforced composite material. This fibre-reinforced composite material may comprise glass, carbon, or any other type of fibre, impregnated with a matrix material (such as a resin or other polymer). The inner shell portion may consist of a single ply of fibre-reinforced composite material (for example glass fibre ply 10a) or it may comprise a laminar stack with multiple plies of fibre-reinforced composite material (for example glass fibre plies 10a, 10b).

Typically the outer shell portion is laid up first, then the metallic power line is arranged on the outer shell portion. Alternatively, the inner shell portion may be laid up first, then the metallic power line is arranged on the inner shell portion.

The connection part 17 of the metallic power line may also be embedded within the blade shell, sandwiched between the inner and outer shell portions mentioned above.

Embedding or sandwiching the metallic power line 17, 18 within the blade shell may provide a number of technical advantages.

A first advantage is that the metallic power line 17, 18 is closer to the exterior of the blade shell, and hence easier to repair, for instance by a repair method as disclosed in US2020/0149513 or US2022/0243703. This is particularly useful for parts of the metallic power line which are positioned towards the blade tip end 7 which is more difficult to access from the hollow interior space 41.

This repair advantage is most particularly achieved by the embodiments of Figures 5A, 9A and 11A because in these embodiments the metallic power line 17, 18 is closer to the exterior of the blade shell. In these embodiments the inner shell portion forms a major part of a thickness of the shell, including for instance a laminar stack comprising two or more plies 10a-d of fibre-reinforced composite material, and/or a core 11 sandwiched between plies 10a-10d of fibre-reinforced composite material.

A second advantage of sandwiching the metallic power line 17, 18 within the blade shell is that the manufacturing process can be simpler. For example, the metallic power line 17, 18 can be laid up in the mould along with the other plies in the stack. Also, the metallic power line 17, 18 may be supplied as a “kit” in combination with one or more fibre plies. By way of example, in the embodiment of Figure 6B the metallic power line 17, 18 may be sandwiched between, and optionally in direct contact with, the glassfibre plies 10a, 10b, which enables the three layers stitched together and rolled up to form a “kit”. Alternatively, the metallic power line 17, 18 of Figure 6B may be laid up on a single glass-fibre ply 10a, and the two layers rolled up to form a similar “kit”.

The metallic SPL 13 may also be provided in a similar “kit” form, potentially in combination with the metallic power line 17, 18. Note that the SPL 13 may cover all or most of the metallic power lines 17, 18 to protect them from lightning strike.

The metallic SPL 13 and/or the metallic power line 17, 18 typically comprise a porous structure (such as an expanded foil, a grid, a mesh, a woven fabric or a non-woven veil). Such a porous structure is advantageous because it saves weight and enables the structure to be impregnated by the polymeric matrix material 19.

Any portion of the metallic power line 17, 18 may be made from of a single piece of material such as single piece metallic porous structure or a monolithic porous structure. Thus, a metallic power line 17, 18 extending from the power supply 32 to the heating element 8 may be made from of a single piece of material as defined above. It is understood that the metallic power line 17, 18, such as a power line 18 extending from the power supply 32 to the heating element 8, may comprise a plurality of portions of the metallic power line 17, 18 which are electrically connected to form the metallic power line 17, 18 or any section thereof.

Advantageously the metallic SPL 13 and the metallic power line 17, 18 are made from the same material, for example an aluminium or copper expanded foil. Further, the metallic SPL 13 and the metallic power line 17, 18 may originate from the same source structure (for instance a single roll of material). In this way the manufacturing is simplified since the same product is used both for the SPL layer and the metallic power lines 17, 18.

Optionally a surge protection device (SPD) 30 shown in Figures 12 and 13 may be provided. The SPD is configured to prevent surge currents from flowing into the heating element 8 or the power supply 32.

The SPD 30 may be electrically coupled to the power line 17, 18 via the connector 20- 24, so that the power line 17, 18 is electrically coupled to the heating element 8 and the SPD 30 in parallel as shown in Figure 12.

As shown in Figure 13, the SPD 30 may be mounted within the interior of the blade and electrically coupled to the connecter 20-24 by a wire 33. The SPD 30 may also be connected to the SPL 13, which in turn is connected to a down conductor 31.

When energised by the power supply 32, the metallic power line 17, 18 is at 577V and during normal operation the SPD 30 is closed. When lightning strikes the metallic power line 17, 18, its voltage increases above a threshold (for example 1500V) which causes the SPD 30 to trip and open, causing the currents caused by the lightning strike to flow into the SPL 13 then to ground via the down conductor 31.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims

Claims

1. A wind turbine blade shell (3) comprising: an inner shell portion (10a) comprising a fibre-reinforced composite material; an outer shell portion (10e- g, 13-15); an electro-thermal heating element (8) embedded within the blade shell; and a metallic power line (17,18) which is connected to the electrothermal heating element at a terminal and configured to carry electrical power to the electro-thermal heating element via the terminal, wherein the metallic power line is sandwiched between the inner and outer shell portions.

2. A wind turbine blade shell according to claim 1 , wherein the metallic power line comprises a connection part (17) which overlaps the heating element at the terminal, and the connection part (17) is electrically connected to the heating element via a direct contact with the heating element (8).

3. A wind turbine blade shell according to claim 2, wherein the heating element (8) comprises a heating mat (12), and the connection part (17) of the metallic power line comprises a strip which extends across a major part of a width of the heating mat (12).

4. A wind turbine blade shell according to any preceding claim, wherein the metallic power line comprises a porous structure which is sandwiched between the inner and outer shell portions.

5. A wind turbine blade shell according to any preceding claim, wherein the metallic power line (17,18) comprises an expanded foil, a grid, a mesh, a woven fabric or a non-woven veil which is sandwiched between the inner and outer shell portions.

6. A wind turbine blade shell according to any preceding claim, wherein the wind turbine blade shell further comprises one or more insulating layers (11) between the metallic power line and the electro-thermal heating element; the terminal comprises a connector (20-24) which connects the metallic power line to the electro-thermal heating element; and the connector passes through the one or more insulating layers.

7. A wind turbine blade shell according to any preceding claim, wherein the wind turbine blade shell further comprises a surge protection device (30) configured to prevent surge currents from flowing into the heating element (8), wherein the surge protection device (30) is electrically coupled to the metallic power line via the connector, and the metallic power line is electrically coupled to the heating element and the surge protection device in parallel.

8. A wind turbine blade shell according to any preceding claim, wherein the metallic power line (17,18) is impregnated by polymeric material.

9. A wind turbine blade shell according to any preceding claim, wherein the metallic power line is sandwiched between a pair of plies (10a, 10b) of fibre- reinforced composite material.

10. A wind turbine blade shell according to any preceding claim, wherein the inner shell portion (10a, 10b, 11) forms a major part of a thickness of the shell.

11. A wind turbine blade shell according to any preceding claim, wherein the outer shell portion comprises a fibre-reinforced composite material (10e,10f).

12. A wind turbine blade shell according to any preceding claim, wherein the inner or outer shell portion comprises a laminar stack, the laminar stack comprising two or more plies of fibre-reinforced composite material.

13. A wind turbine blade shell according to any preceding claim, wherein the inner shell portion comprises a core (11) sandwiched between plies (10a, 10b) of fibre-reinforced composite material.

14. A wind turbine blade (2) comprising a wind turbine blade shell according to any preceding claim.

15. A wind turbine (1) comprising a wind turbine blade (2) according to claim 14, and an electrical power supply (32) coupled to the metallic power line.

16. A method for manufacturing a wind turbine blade shell comprising: forming an outer shell portion (13-15), forming an inner shell portion comprising one or more layers of glass-fibre plies (10a), arranging a metallic power line (17, 18) so that the metallic power line is sandwiched between the inner and outer shell portions, - embedding an electro-thermal heating element (12) within the blade shell so that a portion of the electro-thermal heating element is arranged adjacent to a portion of the metallic power line, and providing an electrical connection between the metallic power line and the electro-thermal heating element (12).