Blade for a wind turbine

Abstract

A blade for a wind turbine, comprising a trailing edge and a leading edge extending longitudinally from a tip of the blade to a root of the blade, a lightning protection system having at least one lightning receptor at the tip of the blade for receiving lightning and at least one lightning down conductor for conducting lightning current received by the lightning receptor to the root of the blade, and a de-icing system having an electrically conductive layer arranged along the leading edge, the electrically conductive layer having a first end oriented to the tip of the blade and a second end oriented to the root of the blade, and a first connection terminal on the first end and a second connection terminal on the second end for connecting the layer with a power supply unit, the first connection terminal being connected with the lightning down conductor, wherein the first connection terminal partially contacts the layer and has a rear section connected to the layer and a front section extending longitudinally towards the tip of the blade.

Description

TECHNICAL FIELD

[0001] The present invention relates to a blade for a wind turbine, in particular to a blade comprising an anti-icing system and a lightning protection system. BACKGROUND

[0002] Blades for wind turbines having an anti-icing system and a lightning protection system are known in the art. Given that wind turbines and in particular the blades of these turbines have a high probability of being hit by lightning, it is necessary to equip the blades with a lightning protection system in order to minimize the effects of lightning in the blade, in particular in the electrical components contained in the blade and / or in the wind turbine.

[0003] On the other hand, blades are known comprising an electrically conductive layer integrated into the shell structure of the blade, in particular into the leading edge of the blade, for preventing the formation of ice which adversely affects the efficiency of the wind turbine.

[0004] The presence of an anti-icing system in the blade can also affect the efficiency of the lightning protection system. Moreover, the electrically conductive layer can attract lightning and thus damage the blade, in particular on the blade tip region comprising approximately the last five meters of the blade, and mainly on the end of the electrically conductive layer closer to the blade tip. Damage to the electrically conductive layer can cause the performance of the anti-icing system to be limited or completely disabled. Solutions to reduce the damage to the electrically conductive layer due to lightning strikes are known in the art, for example WO2018 / 095649A1.

[0005] WO2018 / 095649A1 describes a blade for a wind turbine comprising a trailing edge and a leading edge extending longitudinally from a blade tip to a blade root, a lightning protection system having a lightning receptor arranged on the blade tip for receiving lightning and a lightning down conductor for conducting the lightning current received by the lightning receptor to the blade root, and an anti-icing system having an electrically conductive layer arranged along the leading edge, the electrically conductive layer having a first end oriented to the blade tip and a second end oriented to the blade root, and a first connection terminal placed on the first end of the electrically conductive layer and a second connection terminal placed on the second end of the electrically conductive layer for electrically connecting the electrically conductive layer with a power supply unit and thus heating the electrically conductive layer in order to prevent icing. The first connection terminal of the electrically conductive layer is electrically connected with the lightning down conductor so that their potentials are equalized, thus minimizing the damage from lightning strikes. The blade has several lightning receptors arranged on the blade tip region for attracting lightning and protecting the electrically conductive layer of the anti-icing system. SUMMARY

[0006] It is an object of the present invention to provide a blade for a wind turbine as defined in the claims.

[0007] One aspect of the present invention relates to a blade for a wind turbine, the blade comprising: a trailing edge and a leading edge extending longitudinally from a blade tip to a blade root; a lightning protection system having at least one lightning receptor arranged at the blade tip for receiving lightning and at least one lightning down conductor for conducting lightning current received by the lightning receptor to the blade root; and a de-icing system having an electrically conductive layer arranged along the leading edge, the electrically conductive layer having a first end oriented to the blade tip and a second end oriented to the blade root, and a first connection terminal placed on the first end of the electrically conductive layer and a second connection terminal placed on the second end of the electrically conductive layer for electrically connecting the electrically conductive layer with a power supply unit, the first connection terminal of the electrically conductive layer being electrically connected with the lightning down conductor, wherein the first connection terminal partially contacts the electrically conductive layer and has a rear section connected to the electrically conductive layer and a front section extending longitudinally towards the blade tip.

[0008] Thus, the first connection terminal of the electrically conductive layer is dimensioned towards the blade tip to attract lightning and thus prevent it from striking directly onto the electrically conductive layer, thereby avoiding damage of the electrically conductive layer. Furthermore, the dimensioned first connection terminal is arranged at the blade tip area and allows to reduce the number of lightning receptors that need to be arranged at the blade tip area for attracting lightning and protecting the electrically conductive layer of the de-icing system. The dimensioned first connection terminal is cheaper and requires less complex manufacturing process compared to placing lightning receptors at the blade tip area.

[0009] This and other advantages and features of the present invention will become apparent from the drawings and detailed description of the invention. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 A blade for a wind turbine comprising a lightning protection system and a de-icing system according to the prior art is shown.

[0011] Figure 2 A blade for a wind turbine comprising a lightning protection system and a de-icing system according to the present invention is shown.

[0012] Figure 3 An enlarged view of the blade tip area of the blade of Figure 2

[0013] An enlarged view of further embodiments of the blade is shown. Figures 4 to 7

[0014] An enlarged view of the blade tip area of the blade of Figure 8 DETAILED DESCRIPTION

[0015] Figure 1 ​A blade 1 for a wind turbine, according to the prior art, is shown. The blade 1 includes a lightning protection system 10 and an anti-icing system 20. The blade 1 has a trailing edge 2 and a leading edge 3 extending longitudinally from the blade tip 4 to the blade root 5. Dashed lines represent the outline of the blade 1.

[0016] The lightning protection system 10 includes a lightning receiver 11 disposed on the blade tip 4 for receiving lightning and a lightning down conductor 12 for conducting the lightning current received by the lightning receiver 11 to the blade root 5. The lightning current is conducted from the blade root 5 through the hub (not shown) to the grounding terminal.

[0017] The anti-icing system 20 includes a conductive layer 21 disposed along the leading edge 3 and having a first end 22 oriented toward the blade tip 4 and a second end 23 oriented toward the blade root 5. The anti-icing system 20 also includes a first connection terminal 24 disposed on the first end 22 of the conductive layer 21 and a second connection terminal 25 disposed on the second end 23 of the conductive layer 21 for connecting the conductive layer 21 to a power supply unit (…). Figure 1 (Not shown in the image) Electrically connected and used to heat the conductive layer 21.

[0018] The conductive layer 21 is a heating pad containing conductive material (e.g., carbon fiber) for de-icing ice formed on the blade 1. The conductive layer 21 attracts lightning strikes that could damage the blade 1; therefore, the first connection terminal 24 of the conductive layer 21 is electrically connected to the lightning down conductor 12, thereby ensuring equipotentiality between the anti-icing system 20 and the lightning protection system 10. The blade 1 also includes additional lightning receivers 13 arranged on the trailing edge 2 of the blade 1 to prevent lightning strikes on the conductive layer 21. However, most lightning strikes occur at the first end 22 of the conductive layer 21 closer to the blade tip 4 due to the enhanced electric field at that point, and the lightning receivers 11 at the blade tip 4 and the other lightning receivers 13 at the trailing edge 2 do not adequately prevent lightning from occurring at that point. To protect the conductive layer 21, several lightning receivers need to be placed in the blade tip region, which increases the cost of the blade and complicates the manufacturing process.

[0019] Figure 2 A blade 1 for a wind turbine according to the present invention is shown. Blade 1 is connected to the blade on the upper surface... Figure 1 The blade 1 described herein is the same, but has a first connection terminal 24 which is oversized toward the blade tip 4 to attract lightning and thus prevent it from striking the first end 22 of the conductive layer 21 directly.

[0020] like Figure 3As shown in detail, the first connection terminal 24 partially contacts the conductive layer 21 and has a rear section 241 connected to the conductive layer 21 and a front section 242 extending longitudinally towards the blade tip 4. The front section 242 forms a conductive block close to the blade tip 4 where lightning can directly hit, preventing it from striking the first end 22 of the conductive layer 21. As explained above, the first connection terminal 24 is electrically connected to the lightning down conductor 12, thus the first connection terminal 24 acts as a lightning receptor. The first connection terminal 24 is electrically connected to the lightning down conductor 12 through the conductor 28.

[0021] Figure 4 Another embodiment of the blade is shown in Figure 2 and Figure 3 . Preferably, the blade 1 further comprises another lightning receptor 14 arranged in parallel to the first connection terminal 24 on the trailing edge 2 of the blade 1. As explained above, the first connection terminal 24 acts as a lightning receptor on the leading edge 3, preventing lightning from striking the conductive layer 21, but lightning can hit on the trailing edge 2 on a portion opposite to the position where the first end 22 of the conductive layer 21 is placed, thus another lightning receptor 14 is placed on said area of the trailing edge 2.

[0022] Figures 5 to 7 Other embodiments of the first connection terminal 24, the conductive layer 21 and the electrical connection to the lightning down conductor 12 are shown. Said embodiments show another lightning receptor 14 arranged on the trailing edge 2 of the blade; however, said lightning receptor 14 is not necessary to prevent lightning from striking the conductive layer 21 on the leading edge 3, as explained in Figure 3 .

[0023] As shown in the embodiments of Figure 3 and Figure 4 , the first connection terminal 24 is electrically connected to the lightning down conductor 12 and the second connection terminal 25 is electrically connected to the power supply line 27, the lightning down conductor 12 and the power supply line 27 being connected to a power supply unit. In said case, the lightning down conductor 12 acts as a power supply line for heating the conductive layer 21.

[0024] Alternatively, as shown in the embodiments of Figure 5 , the first connection terminal 24 is electrically connected to a first power supply line 26 and the second connection terminal 25 is electrically connected to a second power supply line 27, the power supply lines 26 and 27 being connected to a power supply unit, and the first power supply line 26 is connected to the lightning down conductor 12 through a surge protection device 15. In this case, the lightning down conductor 12 does not act as a power supply line for heating the conductive layer 21 and the conductive layer 21 has an independent power supply line for heating the layer 21. The surge protection device 15 protects the de-icing system 20 from surges occurring due to lightning strikes, thus reducing the current through the power supply lines 26 and 27.

[0025] The surge protection device 15 acts as a switch that is closed during the short time of a surge, i.e. when a certain voltage is not exceeded, it acts as an open switch, thereby preventing a current from passing, and when the certain voltage is exceeded, it acts as a closed switch. When the specified voltage is exceeded, an overvoltage current can flow to ground via the lightning down conductor 12 or via the supply lines 26 and 27. The circuit only lasts for the duration of the surge, typically a few microseconds up to a few milliseconds. The surge protection device 15 can be based on spark gap technology or on a voltage-dependent resistor technology (MOV) or any other known suitable device for limiting the voltage difference between conductors.

[0026] Figure 6 and Figure 7 The embodiments of Figs. 1-4 are equivalent to the above described Figure 5 but show the electrically conductive layer 21 comprising a first piece 211 arranged in parallel with a second piece 212, each piece 211 and 212 being arranged at one side of the leading edge 3.

[0027] Generally, a blade 1 for a wind turbine is manufactured in two pieces. The blade comprises an upper shell and a lower shell, which are built independently during a vacuum infusion process, and thereafter they are assembled to obtain the blade 1. Thus, in order to simplify the manufacturing process, the first piece 211 is arranged on the upper shell of the blade 1 and the second piece 212 is provided on the lower shell of the blade 1.

[0028] Figure 6 and Figure 7 The embodiments of Figs. 1-4 are equivalent to the above described Figure 5 but show the electrically conductive layer 21 comprising a first piece 211 arranged in parallel with a second piece 212, each piece 211 and 212 being arranged at one side of the leading edge 3.

[0029] The first conductor 281 and the second conductor 282 are electrically connected with the first supply line 26 and the lightning down conductor 12 is electrically connected with the first supply line 26 through the surge protection device 15. The first conductor 281 and the second conductor 282 can be extensions of the supply line 26.

[0030] Having the electrically conductive layer 21 with two pieces 211 and 212 can change a lightning strike onto the connection terminal 24 and thus, the first conductor 281 and the second conductor 282 allow a balanced current injection on the lightning down conductor 12, thereby avoiding an electric arc.

[0031] Figure 6 An embodiment shows a first connection terminal 24, which is a one-piece terminal having a first portion 243 and a second portion 244, while Figure 7 An embodiment shows a first connection terminal 24, which is a two-piece terminal having a first portion 243 and a second portion 244. This latter solution simplifies the manufacturing of the blade 1, which is manufactured in two parts, typically an upper housing and a lower housing.

[0032] The conductive layer 21 is a heating pad comprising biaxial carbon fiber fabric and is integrated into the shell of the blade 1 or placed on the shell (on both sides of the upper and lower shells separated by the leading edge 3). For example, the conductive layer 21 is a composite plate with carbon biaxial fibers having a density of 100-600 g / m². 2 The density. The conductive layer 21 can be obtained during the manufacture of the housing and is therefore part of the housing, or it can be placed on the surface of the housing after the housing is obtained.

[0033] As shown in the figure, the conductive layer 21 is a single heating pad extending from the blade tip 4 to the blade root 5 along the leading edge 3 of the blade 1, and for example, occupies approximately 2 / 3 of the leading edge 3. Alternatively, the conductive layer 21 may have two or more heating pads extending along the leading edge 3 of the blade 1; in this case, each heating pad has a connection terminal at its end for receiving power, but according to the invention, only the first connection terminal 24 of the first heating pad arranged in the blade tip region needs to be enlarged.

[0034] As shown in the figure, terminals 24 and 25 are placed at the ends 22 and 23 of the conductive layer 21, but they can also be placed close to the ends 22 and 23. For example, although according to the present invention, the first terminal 24 needs to be arranged on the first end 22 as close as possible to the blade tip 4, the second terminal 25 does not need to be placed exactly on the second end 23, and can be placed close to the second end 23.

[0035] As shown in the figure, the connecting terminals 24 and 25 have a shape similar to that of the conductive layer 21. Both the connecting terminals 24 and 25 and the conductive layer 21 have a rectangular shape. Preferably, the connecting terminals 24 and 25 are flat connecting terminals. More preferably, the connecting terminals 24 and 25 are flat metal sheets.

[0036] Power supply lines 26 and 27 are standard low-voltage lines used to transmit power from the blade root 5 to the connection terminals 24 and 25. Other flat or mesh metal conductors can be used instead of wires. Connector 28, as well as the first conductor 281 and the second conductor 282, are preferably standard low-voltage lines.

[0037] The drawing shows a single lightning down conductor 12, however, a plurality of lightning down conductors can also be used, in which case each lightning down conductor is electrically connected to the electrically conductive layer 21 as described above.

[0038] The supply lines 26 and 27 and the lightning down conductor 12 are arranged within the casing of the blade 1. The lines 26 and 27 and the conductor (down conductor) 12 are arranged onto the inner surface of the casing or within the casing, for example onto the shear web. On the other hand, the terminals 24 and 25 of the electrically conductive layer 21 are placed within the casing or onto the outer surface of the casing, thus the electrically conductive element 29 is arranged on the rear section 241 of the first connection terminal 24 to transmit the electric current from the terminal 24 to the lightning down conductor 12 or to the first supply line 26 and the lightning down conductor 12. The second connection terminal 25 also has another electrically conductive element 29 to transmit the electric current from the terminal 25 to the second supply line 27 (see Figure 8 ). The electrically conductive elements are preferably made of copper, brass or aluminium.

[0039] The skilled person will note that the longer the front section 242 of the first connection terminal 24, the closer to the blade tip 4 it will be and the better it will attract lightning, but in order to reduce costs, the applicant has verified by experiment that the first connection terminal 24 attracts lightning appropriately when a specific measure of the first connection terminal 24 is used. See Figure 8 .

[0040] The front section 242 of the first connection terminal 24 extends longitudinally from the first end 22 of the electrically conductive layer 21 by a length "a" comprised between 200-1500 mm. This length allows lightning to strike onto the connection terminal 24 far from the first end 22 of the electrically conductive layer 21. The rear section 241 of the first connection terminal 24 connecting the electrically conductive layer 21 has a length "d" of at least 30 mm. This minimum length "d" of overlap of the layer 21 with the terminal 24 guarantees an appropriate electrical transmission between the first connection terminal 24 and the electrically conductive layer 21.

[0041] More preferably, the first connection terminal 24 has a width "b" equal to or greater than the width "c" of the electrically conductive layer 21. Making the width "b" of the first connection terminal 24 greater than the width "c" of the electrically conductive layer 21 allows the first connection terminal 24 to protrude laterally from the electrically conductive layer 21, thus the electrically conductive element 29 is placed on the rear section 241 of the first connection terminal 24 for electrically connecting the first end 22 of the electrically conductive layer 21 with the lightning down conductor 12 or the first supply line 26 through the conductor 28. The relationship b / c>1 also allows better performance of the connection terminal 24 to attach lightning strikes.

[0042] It is undesirable to make the width "b" of the first connection terminal 24 smaller than the width "c" of the conductive layer 21 because current injection problems can occur between the terminal 24 and the conductive layer 21. In any case, the width "b" of the first connection terminal 24 can be reduced by increasing the length "a" of the front section 242 of the first connection terminal 24.

[0043] The lengths "a" and "d" of the first connection terminal 24 are parallel to a longitudinal axis of the blade 1 that extends longitudinally from the blade tip 4 to the blade root 5. The length "a" extends from the first end 22 of the conductive layer 21 towards the blade tip 4 to a front end of the connection terminal 24. The length "d" extends from the first end 22 of the conductive layer 21 towards the blade root 5 to a rear end of the connection terminal 24, so that the conductive layer 21 overlaps with the rear section 241 of the first connection terminal 24.

[0044] The width "b" of the first connection terminal 24 and the width "c" of the conductive layer 21 are transverse to the longitudinal axis of the blade 1.

[0045] The connection terminal 24 has a thickness of between 100 pm and 1000 pm.

[0046] According to one preferred embodiment, the first connection terminal 24 is a rectangular metal sheet having a length "a" of 500 mm, a width "b" of 700 mm, a length "d" of 50 mm and a thickness of 0.15 mm. The conductive layer 21 is a rectangular heating mat having a width "c" of 600 mm and a thickness of 0.3 mm.

Claims

1. A blade for a wind turbine, comprising: From the trailing edge (2) and the leading edge (3) longitudinally extending from the blade tip (4) to the blade root (5); a lightning protection system (10) having at least one lightning receptor (11) arranged on the blade tip (4) for receiving lightning and at least one lightning down conductor (12) for conducting lightning currents received by the lightning receptor (11) to the blade root (5); and a de-icing system (20) having an electrically conductive layer (21) arranged along the leading edge (3), the electrically conductive layer (21) having a first end (22) directed to the blade tip (4) and a second end (23) directed to the blade root (5), and a first connection terminal (24) placed on the first end (22) of the electrically conductive layer (21) and a second connection terminal (25) placed on the second end (23) of the electrically conductive layer (21) for electrically connecting the electrically conductive layer (21) with a power supply unit, the first connection terminal (24) of the electrically conductive layer (21) being electrically connected with the lightning down conductor (12), characterized in that the first connection terminal (24) partly contacts the electrically conductive layer (21) and has a rear section (241) connected to the electrically conductive layer (21) and a front section (242) longitudinally extending towards the blade tip (4), wherein the first connection terminal (24) has a width (b) equal to or greater than a width (c) of the electrically conductive layer (21).

2. The vane of claim 1, wherein, The front section (242) of the first connection terminal (24) longitudinally extends from the first end (22) of the electrically conductive layer (21) a length (a) between 200-1500 mm.

3. The vane of claim 2, wherein, The rear section (241) of the first connection terminal (24) connecting the electrically conductive layer (21) with the first connection terminal (24) has a length (d) of at least 30 mm.

4. Blade according to any of claims 1-3, further comprising a further lightning receptor (14) arranged in parallel with the first connection terminal (24) on the trailing edge (2) of the blade (1).

5. The blade of any one of claims 1-3, wherein, The first connection terminal (24) is electrically connected with the lightning down conductor (12) and the second connection terminal (25) is electrically connected with a power supply line (27), the lightning down conductor (12) and the power supply line (27) being connected to the power supply unit.

6. The blade of any one of claims 1-3, wherein, The first connection terminal (24) is electrically connected with a first power supply line (26) and the second connection terminal (25) is electrically connected with a second power supply line (27), the power supply lines (26, 27) being connected to the power supply unit and the first power supply line (26) being connected to the lightning down conductor (12) through a surge protection device (15).

7. The vane of claim 6, wherein, The electrically conductive layer (21) comprises a first piece (211) arranged in parallel with a second piece (212), each piece (211, 212) being arranged at one side of the leading edge (3).

8. The vane of claim 7, wherein, The first connection terminal (24) comprises a first portion (243) arranged at one side of the front edge (3) and partially contacting the first piece (211), and a second portion (244) arranged at the other side of the front edge (3) and partially contacting the second piece (212), the first portion (243) being electrically connected with the lightning down conductor (12) by a first conductor (281), and the second portion (244) being electrically connected with the lightning down conductor (12) by a second conductor (282).

9. The vane of claim 8, wherein, The first conductor (281) and the second conductor (282) are electrically connected with the first power supply line (26), and the lightning down conductor (12) is electrically connected with the first power supply line (26) by the surge protection device (15).

10. The vane of claim 8 or 9, wherein, The first connection terminal (24) is a single-piece terminal having the first portion (243) and the second portion (244).

11. The blade of claim 8 or 9, wherein, The first connection terminal (24) is a two-piece terminal having the first portion (243) and the second portion (244).

12. The blade according to any of claims 1-3 and 7-9, further comprising an electrically conductive element (29) arranged on the rear section (241) of the first connection terminal (24) to transmit electric current from the first connection terminal (24) to the lightning down conductor (12).

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