Method for sensing lightning-current parameters at installations having one or more capturing devices and lightning-current diversion paths

Abstract

The invention relates to a method for sensing lightning-current parameters at installations comprising a plurality of capturing devices and lightning-current diversion paths, in particular for exposed and/or tall buildings, including wind turbines, by using a plurality of sensors on the lightning-current diversion paths to identify a lightning-current event, and comprising subsequent evaluation of the lightning-current event and the effect of the lightning-current event on the particular installation. According to the invention, a lightning-current detection sensor is formed on each of the capturing devices or each lightning-current diversion path, which lightning-current detection sensor provides a yes/no statement concerning a lightning-current event with respect to the particular capturing device or the particular lightning-current diversion path. Furthermore, at least one lightning-current measurement sensor is provided at a central point of the merging of the lightning-current diversion paths toward the ground, which at least one lightning-current measurement sensor detects both surge currents having a duration of less than 5 ms and long-term currents having a duration of more than 5 ms, wherein furthermore the magnitude of the charge of the particular long-term current that has occurred is determined and is used to determine possible effects on the installation.

Claims

1. Method for sensing lightning-current parameters at installations comprising a plurality of capturing devices and lightning-current diversion paths, in particular for exposed and/or tall buildings, including wind turbines, by using a plurality of sensors on the lightning-current diversion paths to identify a lightning-current event, and comprising subsequent evaluation of the lightning-current event and the effect of the lightning-current event on the particular installation, characterized in that a lightning-current detection sensor is arranged at each of the capturing devices or at each lightning-current diversion path, which lightning-current detection sensor provides a yes/no statement concerning a lightning-current event in relation to the respective capturing device of the respective lightning-current diversion path, wherein at least one lightning-current measurement sensor is provided at a central point of the merging of the lightning-current diversion paths toward the ground, which lightning-current measurement sensor detects both surge currents having a duration of less than 5 ms and long-term currents having a duration of more than 5 ms, wherein furthermore the magnitude of the charge of the particular long-term current that has occurred is determined and used to determine possible effects on the installation, wherein the installation is a wind turbine having rotor blades, a rotor shaft and a hub, and wherein the at least one lightning-current measurement sensor is provided at the rotor shaft.

2. Method according to claim 1, characterized in that when possible effects of lightning currents are determined, the obtained lightning-current parameters are allocated to the respective lightning-current diversion path, and the spatial allocation of the lightning-current detection sensors to the parts of the installation is referred to for this purpose.

3. Method according to claim 1, characterized in that the obtained charge values due to the lightning current are used to analyze the expected lifetime of in particular mechanical, energized components of the installation.

4. Method according to claim 1, characterized in that the at least one lightning-current measurement sensor comprises two Rogowski coils, wherein a first Rogowski coil detects single pulses of a high current level with up to about 200 kA and a short pulse duration of up to 5 ms, and a further Rogowski coil detects long-term current of lower currents at a pulse duration of up to 1 s.

5. Method according to claim 1, characterized by the lightning-current detection sensors are provided at a respective connection point between at least one rotor blade of the rotor blades and the hub.

6. Method according to claim 5, characterized in that the signal transmission for the yes/no decision is performed in a wireless manner between the lightning-current detection sensors and an evaluating unit.

7. Method according to claim 6, characterized in that the electrical operating power required for operating the lightning-current detection sensors is obtained from the kinetic energy of the rotor blades.

Description

(1) According to the invention, in addition to detecting short-term pulses and current peak values, an identification of the charge caused by long-term currents is performed along with determining the specific energy in this respect over the complete long-term current flow duration so that damages due to high charge values are reliably assessable. By way of the inventive measures, charge values and W/R of short-term and long-term components of a lightning stroke are thus identified. This makes it possible to also consider that case in the evaluation in which only a long-term current having low superimposed pulses occurs which cannot be recorded in known measuring devices.

(2) The teaching according to the invention moreover enables long-term currents without superimposed pulse currents to be detected and evaluated. Such long-term currents represent about 50% of the lightning discharges at installations having a tall operating height.

(3) Detecting long-term currents is in particular of great importance at high buildings or exposed buildings or installations as is the case in particular in wind energy plants. The implementation of the inventive method creates a solution satisfying all of the requirements of relevant standards in terms of operation and lightning protection in wind turbines.

(4) In the method for sensing lightning-current parameters at installations comprising a plurality of capturing devices and lightning-current diversion paths, in particular for exposed and/or tall buildings such as wind turbines, according to the invention, a lightning-current detection sensor is arranged at each of the capturing devices or at each lightning-current diversion path, which lightning-current detection sensor exclusively provides a yes/no statement concerning a lightning-current event in relation to the respective capturing device of the respective lightning-current diversion path. These lightning-current detection sensors may be of a very simple configuration. They only serve to detect at which capturing device or in which lightning-current diversion path a strike has actually occurred. The lightning-current detection sensors are configured according to the invention so as to supply data to a central evaluating unit without any additional measuring line, and in fact especially give notice of a lightning current having flown in the diversion path concerned.

(5) At least one lightning-current measurement sensor is provided at a central point of the merging of the lightning-current diversion paths toward the ground, which lightning-current measurement sensor detects both surge currents having a duration of less than 5 ms and long-term currents having a duration of more than 5 ms, wherein furthermore the magnitude of the charge of the particular long-term current that has occurred is determined and used to determine possible effects on the installation.

(6) Accordingly, it is only necessary to form a high-grade lightning-current measurement sensor at a central point of the merging of the lightning-current diversion paths which is capable of determining the relevant lightning-current parameters at high accuracy.

(7) Due to the wireless connection of the lightning-current detection sensors to the central unit, problems otherwise given in wired data transmission, in particular with respect to the necessary separating distance, will not be generated.

(8) Since the lightning-current detection sensors only provide and are required to forward the mentioned yes/no statement with respect to a lightning current and a measuring in the classical sense is not performed, the sensors may be constructed in a simple manner and may be realized at low cost. Moreover, such sensors have a very low energy consumption so that expensive external power supply devices may be omitted. The necessary energy for the lightning-current detection sensor may be obtained, for instance, from the electromagnetic field of the actual lightning current. There is likewise the option in lightning-current detection sensors provided in movable lightning conductors, e.g. rotor blades of wind turbines, to obtain the necessary energy from the kinetic energy of the rotor blades, e.g. while utilizing piezo elements.

(9) In a further development of the invention, when possible effects of lightning currents are determined, the obtained lightning-current parameters are allocated to the respective lightning-current diversion path, wherein the spatial allocation of the lightning-current detection sensors to the corresponding parts of the installation is referred to for this purpose. In this respect, the respective lightning-current detection sensor, when forwarding a yes statement related to a lightning-current event, will also transmit an address indicating the spatial allocation of the respective lightning-current sensor.

(10) The charge values due to the lightning current are used to analyze the expected lifetime of mechanical, energized components of the installation, wherein a tabular assignment of empirical values from long-term studies may be referred to in this respect.

(11) In a design of the invention, the at least one lightning-current measurement sensor comprises two Rogowski coils. A first Rogowski coil detects single pulses of a high current level with up to 200 kA and a short pulse duration of up to 5 ms.

(12) A second Rogowski coil is used for long-term current detection of lower currents at a pulse duration of up to 1 s.

(13) The method according to the invention is in particular intended for being used in wind turbines, wherein the lightning-current detection sensors are provided at the respective connection point between the respective wind power rotor blade and the hub, and the at least one lightning-current sensor is provided at or in proximity of the rotor shaft, preferentially in the area of the transition of the hub to the nacelle.

(14) Preferably, in this inventive use as well, the signal transmission for the yes/no decision is performed in a wireless manner between the lightning-current detection sensors and an evaluating unit.

(15) The electrical operating power required for operating the lightning-current detection sensors is obtained, in a further development according to the invention, from the kinetic energy of the rotor blades.

(16) The invention will be explained below in more detail on the basis of an exemplary embodiment of the preferred use in wind turbines.

(17) Due to the higher requirements that wind turbines have to meet with respect to performance and the involved investment costs, assurances and wind farm operators demand a reliable measuring system for identifying lightning currents. This not only applies to new installations but also to retrofits of already existing wind turbines.

(18) The standard DIN EN 61400-24, wind turbinespart 24: lightning protection, regulates among other things how the lightning-current discharging system and the connecting components thereof must be realized. Connections to the discharging system must be fixed and permanent and ensure that the overall system is able to withstand the combined effect of electrical, thermal and electrodynamic influences of the lightning current.

(19) Proofs must be presented that the lightning protection system is able to withstand the mechanical load in the rotor blades. All of the connecting components need to be certified. Internal parts of the discharging system and the connecting components must be realized such that the risk of internal discharges which might originate from these parts, is kept as low as possible. Externally mounted discharging means are defined as capturing devices. The manufacturers of such devices and installations are required to fix a method for a regular inspection of all of the parts of the discharging system and its connecting parts which wear out due to environmental conditions, so that the conditions and the estimated design value of the lifetime and the maintenance intervals of the corresponding parts are verifiable.

(20) Due to the height and exposed position of the rotor blades of wind turbines, the entire rotor blade construction is often subjected to strong electrical fields during its operating lifetime. Thunderclouds generate strong static and transient electrical fields which act upon the rotor blade construction by electricity and deteriorate the insulating properties of composite materials over time.

(21) The inventive method in its preferred application in wind turbines serves to detect all relevant lightning-current parameters, and this both of short-term pulses and long-term components and the charge values thereof, so that a very reliable assessment of damages can be performed and maintenance intervals fixed in a reasonable manner.

(22) When wireless lightning-current detection sensors are used, the advantage as compared to wired lightning-current sensors is that the measuring signal can be transmitted over rotating components. The central data acquisition with respect to the yes/no values delivered by the lightning-current detection sensors is performed by means of a unit which is expediently accommodated in the nacelle of the wind turbine. The hub or shaft leading to the actual electrodynamic generator via a gear, forms the central point of the merging of the lightning-current diversion paths toward the ground. There, a lightning-current measurement sensor will be provided which is composed, for instance, of two specifically modified Rogowski coils. The Rogowski coils are designed such that single pulses are detected from the current level, on the one hand, and yet a long-term current detection of lower currents of up to a pulse duration of 1 s can be realized, on the other.

(23) The data obtained and collected in the evaluating unit of the respective wind turbine can be checked for relevance and transmitted to the plant operator in terms of an alarm function upon detecting abnormal disturbance variables. In order to guarantee an alarm data transmission even when the entire wind turbine is failing, a UMTS or GSM telecommunication connection backed by emergency power may be referred to.