METHOD FOR INFLUENCING THE DISTRIBUTION OF LIGHTNING CURRENT IN ELECTRICAL SYSTEMS INTEGRATED INTO ROTOR BLADES OF WIND TURBINES

Description

[0001] The invention relates to a method for influencing the lightning current distribution in electrical systems which are integrated into rotor blades of wind turbines, wherein at least one lightning current receptor is located in the respective rotor blade in order to conduct lightning currents via a discharge device from the rotor blade tip to the rotor blade root and further to earth, according to patent claim 1.

[0002] DE 10 2007 050 009 A1 discloses a rotor blade for a wind turbine, wherein the rotor blade contains a lightning protection system. The rotor blade body has a collector, i.e., a receptor, which is designed as a location for the impact of a lightning strike. Furthermore, an insulated arrester element is present within the rotor blade body, wherein the insulated arrester and the at least one receptor are connected to one another. Furthermore, a dielectric layer is present, which covers the arrester as insulation. The arrester is connected to an earth connection.

[0003] A wind turbine with a lightning protection system is already known from DE 100 22 128 C1. The corresponding lightning protection system is capable of absorbing a high lightning current and diverting it via a spark gap into the tower and then into the ground to a grounding connection. The lightning protection system there ensures that the lightning current does not flow via the rotor bearings or existing main bearings, which would require multiple spark gaps. It has been shown that in such lightning protection systems, the galvanically isolated lightning protection devices are subject to static charging by the rotor blades. The electrostatic charging of the rotor blade is caused by the air friction of the rotating rotor blades of the wind turbine. The static charging continues until the flashover voltage of the air gap is reached. As a result, a flashover occurs.However, the arcing generates electromagnetic waves with a high bandwidth that can interfere with the electronic components of the wind turbine.

[0004] US2015 / 204311A1 is another relevant prior art document.

[0005] To prevent this charging of the rotor blades, a continuous discharge is proposed. A continuous discharge path is designed with such low resistance that static charging of the rotor blades is avoided, while also being capable of withstanding surge voltages of 30 kV and more. A discharge circuit consisting of a series connection of an ohmic resistor and an inductor is provided.

[0006] The prior art teaching therefore addresses the problem of electrostatic charging of rotor blades and lightning protection. The prior art device for continuously discharging rotor blades, with a discharge circuit and inductance, is not functional during static discharge because the discharge currents represent a low-amplitude direct current. In the event of a lightning strike, the voltage across the spark gap increases. The magnitude of the voltage depends, among other things, on the distance, the radius of curvature of the contact tips, and the humidity. The inductance present limits the increase in the lightning current flowing through the static arrester. This provides passive protection for the discharge resistance. A potentially useful lightning current distribution is not addressed in the prior art teaching.

[0007] It is well known that wind turbines are subject to a high probability of being struck by lightning due to increasing heights and their exposed locations. The rotor blades of a wind turbine are particularly frequently hit by direct lightning strikes. As described above, it is therefore common practice to equip rotor blades with a device for collecting lightning strikes and a device for diverting lightning currents from the rotor blade tip to the rotor blade root. Such devices are commonly referred to as receptors and are integral parts of the corresponding rotor blade.

[0008] Furthermore, rotor blades containing electrical or electronic systems are increasingly being used. These electrical or electronic systems are used, for example, to control warning lights in the rotor blade tips, adjust the angle of attack of the rotor blades, provide rotor blade heating, and for other purposes.

[0009] In principle, it is necessary to include these electrical or electronic systems in the lightning protection equipotential bonding. However, this carries the risk that the relevant electrical branch of the additional electrical system will be exposed to excessive partial lightning current, potentially resulting in damage or destruction to the electrical components in the respective system.

[0010] Based on the foregoing, the object of the invention is therefore to provide a method for influencing the lightning current distribution in electrical systems integrated into the rotor blades of wind turbines. At least one lightning current receptor is located in the respective rotor blade to conduct lightning currents via a discharge device from the rotor blade tip to the rotor blade root and further to ground. The object is to ensure that, in addition to the necessary integration of additional electrical systems within the rotor blade into the lightning protection equipotential bonding, these systems are protected from excessive partial lightning currents.

[0011] The object of the invention is achieved by a teaching according to claim 1, wherein the subclaims comprise at least expedient embodiments and further developments.

[0012] The methodology is based on the basic idea of ​​arranging at least one, preferably several, surge arresters between the respective electrical system located in the rotor blade and the part of the discharge device located in the rotor blade.

[0013] By adding an additional impedance in the overvoltage or equipotential bonding path, the partial current flowing through the electrical system in the case of a lightning strike is reduced.

[0014] According to the invention, the additional impedance is designed such that the resulting potential difference between the electrical system and the arrester in the event of lightning is matched to the dielectric strength of the respective electrical system and the required separation distance between the respective electrical system and the arrester.

[0015] This results in an intentional, targeted increase in impedance in the surge arrester path between the electrical system and the actual arrester device, with the result that the lightning current distribution is influenced in such a way that a reduction in the partial lightning currents in the electrical or electronic system to be protected and the corresponding circuits is achieved.

[0016] The coordination of the design of the additional impedance with the dielectric strength of the respective electrical systems, and the associated design of the separation distance between the separate systems, i.e., the actual electrical system and the arrester device, required for the inventive implementation, can be realized particularly advantageously in rotor blades of wind turbines that contain corresponding electrical systems. In rotor blades of wind turbines, the required separation distance is not easily realized under all circumstances and conditions. It is necessary to check along the entire length of the rotor blade whether the separation distance between the integrated or existing electrical system and the lightning current arrester, which is required due to the geometric structure of the rotor blade, is sufficient.If the voltage between both systems exceeds the respective dielectric strength, additional potential equalization must be provided in accordance with the invention.

[0017] In a preferred embodiment, the additional impedance and its electrical connection are designed to be low-inductive in order to keep the voltage drop across the additional impedance and the potential difference between the respective electrical system and the discharge device low in the case of high lightning current gradients.

[0018] In one embodiment of the invention, in order to limit the voltage drop, the necessary total additional impedance can be realized by distributing several low individual impedances over the relevant current path.

[0019] The additional impedance can be achieved by using a material with a higher conductivity or by using a semiconducting material. According to the invention, stainless steel or rust-proof steel is used instead of copper in the system component that should be exposed to partial lightning currents as little as possible.

[0020] The desired additional impedance can also be achieved by deliberately increasing the impedance in the respective surge arrester. For example, a varistor with an increased rated voltage or a spark gap with an increased arc voltage can be used as a surge arrester. However, it is also possible to use standard surge arresters, such as varistors or spark gaps, which are equipped with an additional externally arranged additional impedance.

[0021] The invention will be explained in more detail below using an embodiment and with the aid of figures.

[0022] Here we show: Fig. 1 shows a schematic diagram of a rotor blade of a wind turbine with, for example, two receptors connected to an earth wire as a discharge device, as well as an electrical system arranged in the rotor blade, which may be a rotor blade heating system, and Fig. 2 shows a diagram similar to that according to Fig. 1 , but with an overvoltage protection device and additional impedance provided between the electrical system and the earth wire or the discharge device within the rotor blade.

[0023] In the representations according to Fig. 1 and 2 is assumed to be a rotor blade 5 of a wind turbine.

[0024] For example, two receptors 1 are configured as lightning arresting elements in the rotor blade 5. Between the receptors 1, a ground wire is located as a discharge device capable of conducting lightning currents to ground. An electrical system, in particular an electrical load 3 for a rotor blade heater, is connected to an external power source 6 via power supply lines 7.

[0025] The actual separation distance between the power supply lines 7 and the earth line 2 or discharge device is ≤ 1 m, as symbolically shown in the Fig. 1 is shown.

[0026] The actual required separation distance according to EN 62305-3 s is as follows: s = k i ⋅ k c / k m ⋅ l with k 1 = 0.08 for LPL1 km = 1.0 for air kc = 1.0 for n=1 (number of downstream lines) l = 50 m.

[0027] The separation distance s would therefore have to be 4 m. From the illustration according to Fig. 1 It is evident that the actual separation distance is much smaller than the required separation distance. Without integration into a lightning protection equipotential bonding system, a lightning strike to the receptors 1 would result in a flashover, completely destroying the electrical load 3 and the power supply lines 7.

[0028] When displaying according to Fig. 2 an arrangement of, in the example, three overvoltage protection devices 4 with additional impedance is specifically formed between the electrical consumer 3, ie the power supply lines 7, and the earth line 2.

[0029] This arrangement enables the electrical consumer 3 with its power supply lines 7 to be integrated into the potential equalization via the earth line 2 to the symbolically represented earth.

[0030] The voltage drop across the surge protection device with additional impedance 4 is equal to the potential difference between the ground wire 2 and the power supply line 7 and is, for example, 200 kV. At 200 kV, the separation distance is ≥ 800 mm. This means that the actual separation distance of approximately 1 m is entirely sufficient to prevent flashovers. At the same time, the design of a surge protection device with additional impedance prevents excessive partial lightning currents from flowing through the electrical load 3 or the power supply lines 7.

[0031] The solution presented not only makes it possible to integrate additional electrical systems present in wind turbine rotor blades into a potential equalization system, but also ensures that the relevant branch of the additional electrical system is not unnecessarily exposed to partial lightning current. The main lightning current continues to flow via the lightning protection system designed for this purpose in the rotor blade, comprising receptors and a ground wire or discharge device.

Claims

1. A method for influencing the lightning current distribution in electrical or electronic systems which are integrated in rotor blades of wind turbines, wherein at least one lightning current receptor is located in the respective rotor blade in order to conduct lightning currents via a discharge device from the rotor blade tip to the rotor blade root and onwards to earth, wherein at least one overvoltage arrester for forming an overvoltage discharge path is arranged between the respective electrical or electronic system positioned in the rotor blade and the part of the discharge device which is positioned in the rotor blade, characterized in that the partial current flowing through the electrical or electronic system in the event of lightning is reduced by a respective additional impedance in the overvoltage discharge path, wherein the additional impedance is designed such that, in the event of lightning, the resulting potential difference between the electrical or electronic system and the discharge device is matched with the dielectric strength of the respective electrical or electronic system and the required separation distance between the respective electrical or electronic system and the discharge device, the additional impedance and the electrical interconnection thereof are in this respect formed to be low-inductance so as to keep the voltage drop across the additional impedance and the potential difference between the respective electrical or electronic system and the discharge device low in case of high lightning current gradients, wherein the necessary entire additional impedance is realized by distributing several low individual impedances across the current path concerned for limiting the voltage drop, and the additional impedance is realized by stainless steel or corrosion-resistant steel or by using a semiconducting material.

2. The method according to claim 1, characterized in that the separation distance can be varied by the additional impedance.

3. The method according to either of the preceding claims, characterized in that the desired additional impedance is realized by a targeted impedance increase in the respective overvoltage arrester.