Lightning protection device in modular blade

Abstract

The invention relates to a lightning protection device in a modular blade, which connects an outer module (2) at a lightning stroke to an inner module (3) through which the lightning is conducted to the hub, comprising a lightning down-conducting electrical cable (9). According to the invention, the device (7) is an elastic element having a greater electrical conductivity than an adhesive (12) for fixing the insert (11) in a hole previously drilled inside the carbon fibers (6), which device forms the metal joint (4) of the modular blade (100). The device (7) is an elastomer having a preferably annular shape, surrounding each metal element (4) constituting the blade joint, and covering a gap formed between the carbon fibers (6) of the cover (5) and the aforementioned metal elements (4). The use of other shapes and other conductive materials that allow its geometry to be resilient is also an option.

Description

Technical Field

[0001] The invention relates to a lightning protection device for a metal connection of a modular blade comprising two parts: a tip region or outboard module, where lightning strikes and is conducted to a blade joint, and a root region or inboard module, where lightning is conducted from the joint to a hub of a wind turbine. Background Art

[0002] In order for the lightning protection system on wind turbine blades to be effective, all conductive elements must be electrically connected to the lightning transmission cable with equipotential bonding. Both the carbon fiber, which is a conductive material, and the metal connector, which is also conductive, must be equipotentialized. When the conductive elements remain isolated, there will be several problems, such as the generation of very high potential differences between them due to induction phenomena caused by the lightning when it passes through the lightning rod system, or the lightning being eliminated in the case of striking a conductive element that is not connected to the down conductor.

[0003] The parts of the blade to be connected are made of composite material, inside which is housed an insert glued into a hole previously machined in the composite laminate. The joining is completed by one or more intermediate metal elements anchored to the insert by one or more bolts.

[0004] When the composite material that houses the metal insert is glass fiber, lightning transmission is simple, because glass fiber is non-conductive. But when the composite material is carbon fiber, lightning transmission is complicated, because the carbon fiber is conductive and is only separated from the insert by a thin layer of adhesive (non-conductive) used to glue it. Although the blade has multiple connections between the carbon fiber laminate and the down conductor, there is a risk that some of the lightning current transmitted by the carbon laminate will pass through the thin layer of adhesive and be conducted to the metal insert. This can occur because the waveform of the lightning current has a first phase in which the current grows at a high speed, so it tries to conduct itself, not along the path of least resistance (the connection between the carbon and the cable), but along the path of least inductance (the connection between the laminate and the insert once the dielectric strength of the adhesive is broken). The adhesive can cause its temperature to rise and affect its properties. Once the peak of the waveform is reached, the current decreases at a slower rate, so it will preferentially pass through the path of least resistance (the connection between the carbon and the wire).

[0005] Patent WO2022042809A1 relates to electrically connecting a metal insert and a blade laminate, which is electrically conductive. By forming an electrical path between the metal insert and the conductive material on the hole surface, a clear path for the current is created, which prevents uncontrolled passage through the adhesive.

[0006] Another novel way to maintain the integrity of the joint is by using a device that prevents the degradation of the adhesive used to bond the insert. The device is placed between the conductive laminate of the inner module and the intermediate metal element and between the intermediate metal element and the conductive laminate of the outer module. The device is present in both the upper and lower shells of the blade. Summary of the invention

[0007] The invention completes a lightning protection system for a blade having a conductive laminate connected at multiple points to a downconductor cable, the lightning protection system having a device that conducts a small percentage of the current transmitted by the conductive laminate of the blade, which current is not diverted to the cable during the high intensity peak reached at the beginning of an impact and continues through the carbon fibers and through the metal joints.

[0008] The object of the present invention is that the claimed device is an elastic element having a greater electrical conductivity than the adhesive used to glue the insert to the carbon fibers of the modular blade.

[0009] Another object of the invention is that the device is arranged in the gap formed between the conductive laminate of the blade and the intermediate element of the metal joint, so as to surround the insert by virtue of its annular shape.

[0010] According to the above, the following advantages arise: avoiding damage to the adhesive and the carbon fibers housing the threaded insert, using a system that is easy to arrange in the blade assembly process, and the elasticity of the device ensures contact during assembly and operation of the blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Below is given a brief description of a series of drawings which serve for a better understanding of the invention and which relate specifically to an embodiment of said invention which is provided as a non-limiting example of the invention.

[0012] Figure 1 Represents the outline of a modular blade with two parts (outer and inner) to be connected.

[0013] Figure 2 Details of the joining of modular blades are shown.

[0014] Figure 3 A cross-sectional view of one of the metal elements forming the joint is shown, along with the lightning protection cable and its intermediate connection point.

[0015] Figure 4 is a cross-sectional view of the preceding figure with details of a practical embodiment of the device of the invention on a specific metal joint.

[0016] Figure 5 and Figure 6Two possible cross-sectional views of the device according to the invention using different materials are shown. DETAILED DESCRIPTION

[0017] like Figure 1 As shown, the modular blade 100 comprises a connection area 1 which divides the blade into two parts: the tip or outboard module 2 of the blade and the root or inboard module 3 of the blade. The modularity of the blade is applied to large blades, where the transportation of the entire blade becomes very complicated or practically impossible. On the contrary, the connection area 1 is very small so as not to make the modular blade 100 have a greater weight than desired. The blade has an internal structure formed by two covers and one or two composite webs, which constitute an internal beam on which the upper shell and the lower shell are arranged.

[0018] Figure 2 An intermediate metal element 4 is shown, which constitutes the bond of the modular blade 100. Said intermediate metal element 4 is arranged in an upper cover 5 and a lower cover (not visible in the figure). The material used for the cover laminate in the connection area 1 is carbon fiber 6, a highly resistive and electrically conductive composite material.

[0019] The modular blade has a cable to transmit lightning, but part of its current is also transmitted through the laminate of the carbon fiber cover, which is connected to the cable at multiple points. The part of this current transmitted by the laminate of the carbon fiber cover can pass through the metal joint.

[0020] Figure 3 A cross-section of a blade joint connection is shown. The metal joint consists of a metal element 4 comprising one or more bolts 10 threadedly connected to their respective inserts 11 which are in turn glued to the carbon fibers 6 of the connection area 1 by means of a non-conductive adhesive 12. To prevent degradation of the adhesive 12, for each connection element there is a spark gap 7 between the carbon fibers 6 on the inside and the metal element 4 and another spark gap 7 between the metal element 4 and the carbon fibers 6 on the outside. These spark gaps 7 are arranged during assembly of the metal joint and are mounted on the upper cover 5 and the lower cover.

[0021] The conductive laminate of the cover 5 has a plurality of connection points 8 allowing them to be connected to a lightning transmission cable 9. The cable 9 is responsible for receiving a lightning strike on the outer side 2, through a receiver at the blade tip, and transmitting it to an outlet to the hub through the inner side 3. The cable 9 can also be connected to the metal element 4, through another connection point 8', for equipotentialization.

[0022] Figure 4The cross-section is produced on a particular metal joint. Using a single bolt 10', which is threaded between the insert 11 of the outer module 2 and the insert 11 of the inner module 3, a metal wedge element is added to the gap formed between the blade modules, acting as a simple prestressing machine. Said element consists of lateral washers 13 and a central wedge 14, which are traversed by their corresponding transverse screws (not shown in the figure), the tightening of which realizes the prestressing. Washers 13 and central wedge 14 both have their oppositely inclined faces.

[0023] like Figure 4 As shown in detail, the insert 11 has a threaded area 15 in which the single bolt 10 ′ is screwed and fixed after slightly widening its diameter. The insert 11 protrudes from the carbon fiber 6 that accommodates it, so that a small gap is formed between the cover 5 and the washer 13, in which the spark gap 7 is arranged. The smooth face of the washer 13 contacts the spark gap 7, and the inclined face contacts the central wedge 14.

[0024] The spark gap 7 is an elastomer having an annular shape, which is conductive and is assembled during the assembly process of the blade so as to surround each element forming the metal joint. The spark gap 7 can be made of a conductive elastomer material made by doping a small amount of conductive material, or alternatively, made of a metal material having a geometry that allows it to obtain elasticity.

[0025] The section of the spark gap 7 preferably has an annular shape. Figure 5 and 6 As shown, it can have other sections and other materials that improve the contact with the composite material and with the metal part of the joint.

[0026] The first figure shows a double ring 7 ′ of elastomeric material with an inclined step between two levels. The ring with the largest diameter is the thinnest and is arranged in contact with the carbon fibers 6 of the cover 5 , the inner ring with a smaller diameter is arranged in contact with the gasket 13 of the metal joint 4 .

[0027] The second figure shows an alternative solution using a metal material formed by two facing and overlapping C-shaped rings, with an internal spring 7" providing the required elasticity.

Claims

1. A device for lightning protection in a modular blade (100), wherein: Metal connection elements are arranged in the upper cover (5) and in the lower cover both on the side of the outer module (2) and on the side of the inner module (3), the metal connection elements (4) each comprising one or more prestressed bolts (10) threaded into inserts (11) glued by adhesive (12) into previously drilled holes in the interior of the carbon fiber composite material part (6), characterised in that the device for lightning protection in a modular blade comprises: a spark gap (7), which is an elastic element having a greater conductivity than the adhesive (12) used to glue the drilled insert (11) to the interior of the carbon fiber composite material part (6), - a spark gap (7) is arranged between the cover (5) and an element of the metal joint, - The spark gap (7) is elastic, which ensures contact with the cover (5) and the metal connection element during assembly and operation of the blade.

2. The device for lightning protection in a modular blade according to claim 1, wherein: Each spark gap (7) has an annular shape and surrounds each of the elements forming the metal joint.

3. Arrangement for lightning protection in a modular blade according to the preceding claims, wherein: The spark gap (7) is a conductive elastomer and has raised sections to improve contact with the carbon fiber composite material part and with the metal parts of the joint.

4. Arrangement for lightning protection in a modular blade according to the preceding claims, wherein: The spark gap (7) is formed from a metallic material having a geometry that allows it to be resilient.

5. Arrangement for lightning protection in a modular blade according to the preceding claims, wherein: A single bolt (10') is screwed into the insert (11) of the outer module (2) and the inner module (3) by means of a metal wedge element consisting of a washer (13) and a central wedge (14) traversed by their respective transverse screws, the tightening of which achieves the prestressing, the spark gap (7) being arranged between the smooth surface of the bushing (13) and the carbon fiber composite material part (6).

6. Arrangement for lightning protection in a modular blade according to the preceding claim, wherein: The elastic body is provided with double rings and an inclined step (7') between the double rings, wherein the ring with the largest diameter is the thinnest and is arranged to contact the carbon fiber composite material part (6), and the inner ring with a smaller diameter is arranged to contact the gasket (13).

7. Arrangement for lightning protection in a modular blade according to the preceding claims, wherein: It has a metal material formed by two facing and overlapping C-shaped rings, with an internal spring (7") providing the required elasticity, arranged between carbon fibers (6) and a washer (13).

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