A WIND TURBINE ROTOR BLADE WITH A HEATING ELEMENT

Abstract

Wind turbine rotor blade comprising - a wind turbine rotor blade housing structure comprising a fiber-reinforced composite material; - an electric heating element disposed on an outer surface of the wind turbine rotor blade housing structure, the electric heating element having an electric heating conductor with an end section; - an electrical supply line running along a longitudinal direction of the wind turbine rotor blade; and - a connector that electrically connects the end section of the heating conductor to the power supply line, wherein the connector comprises an external thread screwed directly into the fiber-reinforced composite material and into the power supply line.

Description

A WIND TURBINE ROTOR BLADE WITH A HEATING ELEMENT The invention relates to a wind turbine rotor blade with an electric heating element. WO 2022 / 263596 A1 shows a wind turbine rotor blade with an electrical heating mat arranged on an inner side of the blade housing. Electrical contact is made between the heating mat and a conductor cable arranged inside the blade housing via metal patches. A disc-shaped metal block is in contact with the metal patch and connects to a termination block of the conductor cable by drilling a hole from the outside of the blade housing through the heating mat, the metal patch, the disc-shaped metal block, and into the termination block, and inserting a metal connecting element into the hole. EP 2526292 B1 shows a wind turbine rotor blade with an electrical heating mat. The heating mat is wrapped in copper mesh and arranged on an outer surface of the wind turbine rotor blade. A cable located inside the wind turbine rotor blade is connected to the heating mat by a bolt. The bolt is guided through a copper block located on an outer side of the heating mat and is locked by a nut located inside the wind turbine rotor blade, so that a tightening force is applied. EP 2843228 A1 discloses a wind turbine rotor blade with an electric heating system comprising a plurality of electric heating elements arranged on an outer surface of the wind turbine rotor blade. Each heating element has a carrier layer and a heating conductor arranged on the carrier layer between two opposite edges of the heating element in a serpentine pattern. The end sections of the heating conductor are connected to electrical supply lines arranged on the pressure side and the suction side of the wind turbine rotor blade. EP 2754891 B1 shows a wind turbine rotor blade with an electrical heating mat disposed on an outer side of a blade housing connected to a power supply cable disposed inside the wind turbine rotor blade. A conductive strip is placed over the heating mat. A bolt has a shank that passes through the conductive strip, the conductive mat, and the blade housing and is secured in a threaded nut inside the blade. The power supply cable is pressed between the blade housing and the nut, so as to create an electrical path for current through the nut and bolt and to the mat and conductive strip. This corresponds to the features of the preamble of claim 1. Based on this, one objective of the invention is to provide a wind turbine rotor blade with an electrical heating element that can be produced more easily and cost-effectively, and a corresponding manufacturing method. This objective is achieved with the wind turbine rotor blade with the characteristics of claim 1. Aspects of the invention are provided in the dependent claims. The wind turbine rotor blade comprises • a wind turbine rotor blade housing structure comprising a fiber-reinforced composite material; • an electric heating element disposed on an outer surface of the wind turbine rotor blade housing structure, the electric heating element having an electric heating conductor with an end section; • an electrical supply line running along a longitudinal direction of the wind turbine rotor blade; and • a connector that electrically connects the end section of the heating conductor to the power supply line; where • The connector comprises an external thread screwed into the fiber-reinforced composite material and the power supply line. The wind turbine rotor blade casing structure has an outer surface that corresponds to an aerodynamic surface of the wind turbine rotor blade. For example, the wind turbine rotor blade casing structure may be a wind turbine rotor blade half-shell, such as a pressure-side half-shell or a suction-side half-shell, or a longitudinal segment of such a half-shell. An inner surface of the wind turbine rotor blade casing structure typically faces a hollow interior space of the wind turbine rotor blade. The wind turbine rotor blade casing structure comprises a fiber-reinforced composite material comprising reinforcing fibers, such as glass fibers and / or carbon fibers, and a polymer in which the reinforcing fibers are embedded. The fiber-reinforced composite material may also be referred to as a laminate.Additionally, the wind turbine rotor blade housing structure may include additional components, such as a core material, for example, polymer foam or balsa wood, and prefabricated parts. These additional materials can be integrated into the wind turbine rotor blade housing structure, for example, through a vacuum infusion process, so that all the aforementioned components are embedded in a common polymer matrix. The electric heating element has at least one heating conductor to which a heating electric current is supplied, so that the outer surface of the wind turbine rotor blade covered by the electric heating element can be heated to prevent ice formation (anti-icing) or to remove ice already formed (de-icing) on ​​the outer surface of the wind turbine rotor blade. To guide the heating electric current through the heating conductor, an end section of the heating conductor is connected to an electric supply line that runs along the longitudinal axis of the wind turbine rotor blade. The electric supply line is typically directed toward one end of the root of the wind turbine rotor blade, where it connects to a power source.Typically, both ends of the electric heating element have an end section connected to an electrical supply line. The electrical connection between the power supply line and the heating conductor end section is made via a connector comprising an external thread directly engaged in the fiber-reinforced composite material and the power supply line. This means that the external thread of the connector engages with an inner surface of an opening in the fiber-reinforced material, as well as with an inner surface of an opening in the power supply line. The openings in both materials are filled with a portion of the connector that has the external thread. The inner surfaces of the fiber-reinforced composite material and the power supply line comprise sections that have an internal thread or a comparable surface structure that is in direct engagement with the external thread of the connector.As a result, the connector cannot move in its longitudinal direction without damaging the inner surface structure of the adjacent fiber-reinforced composite material or the inner surface structure of the power supply line, respectively. To insert the connector into the fiber-reinforced composite material and the power supply line, the connector has been screwed in. Therefore, to remove the connector without damaging the inner surface of the fiber-reinforced composite material and the inner surface of the power supply line, the connector must be unscrewed. The resulting threaded connection differs from a threaded bolt, which simply passes through the corresponding openings and is secured with a nut on the opposite side. The external thread of the connector is in direct contact with the surrounding fiber-reinforced composite material and the electrical supply line, and is therefore anchored directly to the fiber-reinforced composite material and the electrical supply line. The electrical contact between the connector and the power supply line is provided by the direct coupling of the outer thread of the connector and the adjacent inner surface of a corresponding opening in the power supply line. When making an electrical connection between a threaded connector and a power supply line, the person skilled in the art typically prepares two contact surfaces, each as large as possible, and brings them into immediate contact by applying a pressing force, specifically by tightening the two elements together using a fastener and nut on the external thread. The prior art document EP 2754891 B1, discussed in the introductory portion, follows this approach. The inventors realized that, in the specific application of an end section of an electrical heating element arranged on an outer surface of a wind turbine rotor blade, an end section that must be connected to a power supply line of the wind turbine rotor blade, good electrical contact can also be achieved on the threaded section of the connector when it is screwed directly onto the power supply line.In this case, it is not necessary to attach a nut to the connector, which is, if possible, at the very least difficult within the narrow interior space of a wind turbine rotor blade. The inventors also realized that when the connector is screwed directly into the fiber-reinforced composite material, sufficient, if not better, mechanical anchoring of the connector to the wind turbine rotor blade housing structure is achieved. Overall, the proposed solution provides good electrical contact and is easy to manufacture, and is therefore superior from an economic point of view. In one respect, the connector's external thread is self-cutting. This means that it is not necessary to provide the fiber-reinforced composite material and the power supply line with an internal thread before screwing on the connector. Instead, the connector can simply be screwed onto the fiber-reinforced composite material and the power supply line, preferably after creating a cylindrical opening in these materials by drilling a hole with a diameter smaller than the external thread diameter. The external thread will then cut a corresponding, closely fitting internal thread into the fiber-reinforced composite material and the power supply line as the connector is screwed on.This makes inserting the connector particularly easy and automatically results in good electrical contact between the external thread and the power supply line and a strong anchoring of the external thread in the fiber-reinforced material. In one respect, the connector is electrically connected to the power supply line exclusively through its external threads. This means there is no additional contact between the connector and the power supply line, except between the external threads and the adjacent surface structure of the power supply line. A nut is not required for the connector. Furthermore, no tightening force is required between the connector and the power supply line. Additionally, no indirect electrical contact is necessary, for example, between a section of the connector head and the power supply line, such as by placing a conductive sleeve between them. In one aspect, the connector comprises a head section that abuts the end section of the heating conductor. As a result, good electrical contact is formed between the connector and the end section of the heating conductor. The required clamping force between a lower face of the head section and the end section of the heating conductor can be achieved by threading the connector into the fiber-reinforced composite material to press the head section against the end section of the heating conductor arranged on the outer surface of the wind turbine rotor blade housing structure. In one respect, the connector is a screw with an external thread. An electrical contact between the connector and the end section of the heating conductor can then be formed directly between the upper end / head section of the screw. In one aspect, the connector comprises a threaded insert with both an external and an internal thread. This is a particularly useful solution when a relatively large diameter external thread is desired to maximize the contact surface along the external thread. The internal thread can then be used to connect the end section of the electric heating element via an additional element of the connector. In one aspect, the connector comprises a screw with an external thread that engages with the internal thread of the threaded insert. This screw may have a contact section with the end section of the electrical heating element. An electrical connection is automatically formed between the screw and the threaded insert through the threaded connection between them. In one aspect, the electrical supply line comprises a plurality of braided copper wires. These copper wires can have relatively fine dimensions, such as a diameter ranging from 0.2 mm to 1.5 mm. Braiding these copper wires results in a flexible supply line with a total cross-sectional area of, for example, 50 mm². The electrical supply line can have a rectangular cross-section with a width ranging from 20 mm to 40 mm and a thickness ranging from 1.0 mm to 3.0 mm. Sufficient electrical contact is achieved by threading the external thread of the connector onto the braided copper wires. In one aspect, the power supply line is arranged on an inner side of the rotor blade housing structure. The power supply line can then be attached to the rotor blade housing structure, for example, while the rotor blade housing structure is still in a manufacturing mold and / or has not yet been assembled with other housing structures to form the complete wind turbine rotor blade. In one respect, the power supply line is integrated into the rotor blade housing structure. This can be achieved, for example, during the manufacturing of the wind turbine rotor blade housing structure by placing the power supply line, along with other components, in a manufacturing mold, for instance, using a vacuum infusion process. This results in a secure integration of the power supply line, preferably on an inner side of the rotor blade housing structure, allowing for easy connection to the power supply line from the outer side of the wind turbine rotor blade housing structure by screwing the connector onto the structure. In one respect, the end section of the heating conductor comprises a cable terminal. The cable terminal is electrically and mechanically connected to the heating conductor, for example, by crimping. The cable terminal provides a reliable means of establishing electrical contact with the power supply line via the connector. In one aspect, the heating conductor comprises either a metallic heating wire or a bundle of carbon fibers. In both cases, the electrical resistance of the heating conductor can be selected according to requirements, for example, by choosing the number and / or thickness of the carbon fibers. The objective indicated above is also achieved by the method with the features of claim 14. Preferred aspects are provided in the dependent claim. The method is for manufacturing a wind turbine rotor blade and comprises the following stages: • provide a wind turbine rotor blade comprising - a wind turbine rotor blade housing structure comprising a fiber-reinforced composite material, - an electric heating element disposed on an outer surface of the wind turbine rotor blade housing structure, the electric heating element having an electric heating conductor with an end section, - an electrical supply line running along a longitudinal direction of the wind turbine rotor blade, and • Connect the power supply line to the end section of the electric heating conductor by screwing a connector comprising an external thread directly into the fiber-reinforced composite material and into the power supply line. With regard to the characteristics and advantages of the method, the previous explanations concerning the related wind turbine rotor blade apply accordingly. In particular, the connection between the power supply line and the end section of a heating conductor is made simply by screwing an externally threaded connector directly into the fiber-reinforced composite material and the power supply line. In one respect, the stage of connecting the power supply line to the end section of the electric heating conductor includes • drill a hole in the wind turbine rotor blade housing structure from an outside side; and • Screw the connector into the hole. The hole drilled in the wind turbine rotor blade housing has a diameter smaller than the outer diameter of the external thread, so the connector is secured to the housing by direct coupling between the external thread and the fiber-reinforced composite material. Even if the hole is also drilled in the power supply line, the connector's external thread will still engage with the power supply line. In particular, when using a self-cutting external thread, it may be sufficient to drill the hole only in the fiber-reinforced material. When the connector is screwed in, the screw will also penetrate the power supply line, especially if it is located beneath the fiber-reinforced composite material and / or is made of braided copper wires. The invention is explained in more detail below, based on the drawings. The drawings show: Figure 1 is a schematic of a wind turbine rotor blade, in a perspective view. Figure 2 a heating element in a schematic view, Figure 3 a cross-section through the wind turbine rotor blade of Figure 1, Figures 4 to 6 are schematic cross-sectional views illustrating three manufacturing stages, using a connector comprising a screw. Figures 7 to 9 are three schematic cross-sectional views illustrating the manufacturing stages using a connector comprising a threaded insert. The wind turbine rotor blade 10 of Figure 1 has a blade root 12, a blade tip 14, a leading edge 16, a trailing edge 18, and a longitudinal direction extending from the blade root 12 to the blade tip 14. A heating system 20 comprises a plurality of electric heating elements 22 arranged on an outer surface of the wind turbine rotor blade. The wind turbine rotor blade comprises two wind turbine rotor blade halves, one on a pressure side and one on a suction side, bonded together along the leading edge 16 and along the trailing edge 18. Each of the wind turbine rotor blade halves is a wind turbine rotor blade shell structure. An electrical supply line runs along the longitudinal direction of the wind turbine rotor blade 10, from the blade root 12 towards one of the outermost electrical heating elements 22. Figure 2 shows an electric heating element 22 comprising an electric heating conductor 26 arranged in a serpentine pattern on a base material 28. The electric heating conductor 26 has two end sections 30, each provided with a wire terminal 32. Figure 3 shows the wind turbine rotor blade 10 of Figure 1 in cross-section in a longitudinal position, including one of the electric heating elements 22. The base material 28 with the serpentine section of the electric heating conductor 26 extends over the leading edge 16. Two electrical supply lines are also shown. A first electrical supply line 34 is arranged on a pressure side of the wind turbine rotor blade 10, and a second electrical supply line 36 is arranged on the suction side of the wind turbine rotor blade 10. A first end section 30 of the electric heating conductor 26 extends to the first electrical supply line 34, and a second end section 30 of the electric heating conductor 26 extends to the second electrical supply line 36. Figure 4 shows an enlarged section of the cross-section in Figure 3, including the first electrical supply line 34. The wind turbine rotor blade housing structure includes a fiber-reinforced composite material 38, such as a laminate with a thickness ranging from 2 mm to 50 mm, forming an outer surface 40 of the wind turbine rotor blade housing structure. On the other side of the fiber-reinforced composite material 38, the first electrical supply line 34 is arranged. It is surrounded by a core material 42 that is connected to an inner side of the fiber-reinforced composite material 38. Figure 4 shows the configuration before mounting the end section of the electrical heating element 22. Figure 5 shows the same elements described with reference to Figure 4 after a cylindrical hole 44 has been drilled through the fiber-reinforced composite material 38 and the first power supply line 34. The diameter of this hole 44 is smaller than the diameter of an external thread 48 of the connector 46 (see Figure 6). In Figure 6, the end section 30 of the electrical heating conductor 26, with the wire terminal 32 and a washer 58 underneath, has been placed on the outer surface 40 of the wind turbine rotor blade housing structure, and a connector 46 having an external thread 48 has been screwed into the hole, directly into the fiber-reinforced composite material 38 and into the first electrical supply line 34. As illustrated by the zigzag lines, the external thread 48 of the connector 46 is directly engaged with the adjacent inner surface of the fiber-reinforced composite material 38, as well as with the adjacent inner surface of the first electrical supply line 34. In this way, the connector 46 is mechanically anchored in the fiber-reinforced composite material 38 and electrically connected to the first electrical supply line 34 directly through the external thread 48.Connector 46 also comprises a head section 50 that abuts the cable terminal 32. In the example illustrated in Figures 7 to 9, the situation in Figure 7 is identical to that described with reference to Figure 4. Figure 8 differs from Figure 5 in that a larger diameter hole 44 has been drilled through the fiber-reinforced composite material 38 and the first power supply line 34. Figure 9 shows that the connector 46 comprises, in this case, a threaded insert 52 having an internal thread 56 and an external thread 48 having a larger diameter than the external thread 48 of the screw-shaped connector 46 of Figure 6. This threaded insert 52 has been screwed directly into the hole 44 shown in Figure 8. Again, the external thread 48 provides mechanical anchoring of the connector 46 in the fiber-reinforced composite material 38 and an electrical connection to the first power supply line 34. In contrast to Figure 6, Figure 9 shows a connector 46 comprising an additional screw 54 that is threaded into the internal thread 56 of the threaded insert 52 and is used to fix and electrically connect the wire terminal 32 to the threaded insert 52. List of reference numbers 10 wind turbine rotor blade 12 shovel root 14 shovel tip 16 leading edge 18 trailing edge 20 heating system 22 electric heating element 24 power supply line 26 electric heating conductor 28 base material 30 end section 32 cable terminal 34 first power supply line 36 second power supply line 38 fiber-reinforced composite material 40 exterior surface 42 core material 44 hole 46 connector 48 external thread 50 head section 52 threaded insert 54 screw 56 internal thread 58 washer

Claims

1. A wind turbine rotor blade (10) comprising: • a wind turbine rotor blade housing structure comprising a fiber-reinforced composite material (38); • an electrical heating element (22) disposed on an outer surface (40) of the wind turbine rotor blade housing structure,having the electrical heating element (22) an electrical heating conductor (26) with an end section (30); • an electrical supply line (24) running along a longitudinal direction of the wind turbine rotor blade (10); and • a connector (46) electrically connecting the end section (30) of the electrical heating conductor (26) to the electrical supply line (24); characterized in that the connector (46) comprises an external thread (48) directly threaded into the fiber-reinforced composite material (38) and into the electrical supply line (24).

2. The wind turbine rotor blade (10) of claim 1, wherein the external thread (48) is self-cutting.

3. The wind turbine rotor blade (10) of claim 1 or 2,wherein the connector (46) is electrically connected to the power supply line (24) exclusively through the external thread (48).

4. The wind turbine rotor blade (10) of any of claims 1 to 3, wherein the connector (46) comprises a head section (52) that abuts the end section (30) of the heating conductor (26).

5. The wind turbine rotor blade (10) of any of claims 1 to 4, wherein the connector (46) is a screw having the external thread (48).

6. The wind turbine rotor blade (10) of any of claims 1 to 4, wherein the connector (46) comprises a threaded insert (52) having the external thread (48) and an internal thread (56).

7. The wind turbine rotor blade (10) of claim 6,wherein the connector (46) comprises a screw (54) having an external thread engaged with the internal thread (56) of the threaded insert (52).

8. The wind turbine rotor blade (10) of any of claims 1 to 7, wherein the power supply line (24) includes a plurality of braided copper wires.

9. The wind turbine rotor blade (10) of any of claims 1 to 8, wherein the power supply line (24) is arranged on an inner side of the rotor blade housing structure.

10. The wind turbine rotor blade (10) of any of claims 1 to 9, wherein the power supply line (24) is integrated into the rotor blade housing structure.

11. The wind turbine rotor blade (10) of claim 10,wherein the power supply line (24) is integrated into the rotor blade housing structure by a vacuum infusion process.

12. The wind turbine rotor blade (10) of any of claims 1 to 11, wherein the end section (30) of the heating conductor (26) comprises a cable terminal (32).

13. The wind turbine rotor blade (10) of any of claims 1 to 12, wherein the heating conductor (26) comprises a metallic heating wire or a carbon fiber bundle.

14. A method for manufacturing a wind turbine rotor blade (10), the method comprising the following steps: • providing a wind turbine rotor blade (10) comprising - a wind turbine rotor blade housing structure comprising a fiber-reinforced composite material (38),- an electric heating element (22) disposed on an outer surface (40) of the wind turbine rotor blade housing structure, the electric heating element (22) having an electric heating conductor (26) with an end section (30), - an electric supply line (24) running along a longitudinal direction of the wind turbine rotor blade (10), • connecting the electric supply line (24) to the end section (30) of the electric heating conductor (26) by screwing a connector (46) comprising an external thread (48) directly into the fiber-reinforced composite material (38) and into the electric supply line (24).

15. The method of claim 14,wherein the step of connecting the electrical supply line (24) to the end section (30) of the electrical heating conductor (26) includes • drilling a hole (44) in the wind turbine rotor blade housing structure from an outside side; and • screwing the connector (46) into the hole (44).

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